Immunocytochemical studies of GABAergic neurons in rat basal ganglia and their relations to other neuronal systems

The pars reticulata of the substantia nigra: a window to basal ganglia output

Together with the internal segment of the globus pallidus (GP(i)), the pars reticulata of the substantia nigra (SNr) provides a main output nucleus of the basal ganglia (BG) where the final stage of information processing within this system takes place. In the last decade, progress on the anatomical organization and functional properties of BG output neurons have shed some light on the mechanisms of integration taking place in these nuclei and leading to normal and pathological BG outflow. In this review focused on the SNr, after describing how the anatomical arrangement of nigral cells and their afferents determines specific input-output registers, we examine how the basic electrophysiological properties of the cells and their interaction with synaptic inputs contribute to the spatio-temporal shaping of BG output. The reported data show that the intrinsic membrane properties of the neurons subserves a tonic discharge allowing BG to gate the transmission of information to motor and cognitive systems thereby contributing to appropriate selection of behavior.

Hypolocomotion in rats with chronic liver failure is due to increased glutamate and activation of metabotropic glutamate receptors in substantia nigra

BACKGROUND/AIMS

Patients with hepatic encephalopathy show altered motor function, psychomotor slowing and hypokinesia. The underlying mechanisms remain unclear. This work's aims were: (1) to analyse in rats with chronic liver failure due to portacaval shunt (PCS) the neurochemical alterations in the basal ganglia-thalamus-cortex circuits; (2) to correlate these alterations with those in motor function and (3) to normalize motor activity of PCS rats by pharmacological means.

METHODS

Extracellular neurotransmitters levels were analysed by in vivo brain microdialysis. Motor activity was determined by counting crossings in open field.

RESULTS

Extracellular glutamate is increased in substantia nigra pars reticulata (SNr) of PCS rats. Blocking metabotropic receptor 1 (mGluR1) in SNr normalizes motor activity in PCS rats. In ventro-medial thalamus of PCS rats GABA is increased and it is normalized by blocking mGluR1 in SNr. Blocking mGluR1 in SNr increases and mGluR1 activation reduces glutamate in motor cortex and motor activity.

CONCLUSIONS

Increased extracellular glutamate and activation of mGluR1 in SNr are responsible for reduced motor activity in rats with chronic liver failure. Blocking mGluR1 in SNr normalizes motor activity in PCS rats, suggesting that, under appropriate conditions, similar treatments could be useful to treat the psychomotor slowing and hypokinesia in patients with hepatic encephalopathy.

Subthalamic stimulation evokes complex EPSCs in the rat substantia nigra pars reticulata in vitro

The subthalamic nucleus (STN) plays an important role in movement control by exerting its excitatory influence on the substantia nigra pars reticulata (SNR), a major output structure of the basal ganglia. Moreover, excessive burst firing of SNR neurons seen in Parkinson's disease has been attributed to excessive transmission in the subthalamonigral pathway. Using the 'blind' whole-cell patch clamp recording technique in rat brain slices, we found that focal electrical stimulation of the STN evoked complex, long-duration excitatory postsynaptic currents (EPSCs) in SNR neurons. Complex EPSCs lasted 200-500 ms and consisted of an initial monosynaptic EPSC followed by a series of late EPSCs superimposed on a slow inward shift in holding current. Focal stimulation of regions outside the STN failed to evoke complex EPSCs. The late component of complex EPSCs was markedly reduced by ionotropic glutamate receptor antagonists (2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitro-quinoxalone) and by a GABAA receptor agonist (isoguvacine) when these agents were applied directly to the STN using a fast-flow microapplicator. Moreover, the complex EPSC was greatly enhanced by bath application of the GABAA receptor antagonists picrotoxin or bicuculline. These data suggest that recurrent glutamate synapses in the STN generate polysynaptic, complex EPSCs that are under tonic inhibition by GABA. Because complex EPSCs are expected to generate bursts of action potentials in SNR neurons, we suggest that complex EPSCs may contribute to the pathological burst firing that is associated with the symptoms of Parkinson's disease.

Neurochemical characterization of dopaminergic neurons in human striatum

We examined the neurochemical phenotype of striatal neurons expressing tyrosine hydroxylase (TH) mRNA to determine if they form a distinct class of neurons within the human striatum. Double in situ hybridization (ISH) and immunohistochemical (IHC) procedures were used to know if TH mRNA-positive striatal neurons express molecular markers of mature neurons (MAP2 and NeuN), dopaminergic neurons (DAT and Nurr1) or immature neurons (TuJ1). All TH mRNA-labeled neurons were found to express NeuN, DAT and Nurr1, whereas about 80% of them exhibited MAP2, confirming their neuronal and dopaminergic nature. Only about 30% of TH mRNA-labeled neurons expressed TuJ1, suggesting that this ectopic dopaminergic neuronal population is principally composed of mature neurons. The same double ISH/IHC approach was then used to know if these dopamine neurons display markers of well-established classes of striatal projection neurons (GAD65 and calbindin) or local circuit neurons (GAD65, calretinin, somatostatin and parvalbumin). Virtually all TH-labeled neurons expressed GAD65 mRNA, about 30% of them exhibited calretinin, but none stained for the other striatal neuron markers. These results suggest that the majority of TH-positive neurons intrinsic to the human striatum belong to a distinct subpopulation of striatal interneurons characterized by their ability to produce dopamine and GABA.

Different function of pedunculopontine GABA and glutamate receptors in nucleus accumbens dopamine, pedunculopontine glutamate and operant discriminative behavior

The nucleus accumbens, as the main input structure of the ventral basal ganglia loop, is described as a limbic-motor interface. Dopamine input to nucleus accumbens modulates processing of concurrent glutamate input from limbic structures carrying motor and motivational information. There is evidence that these dopamine/glutamate interactions are fundamentally involved in response selection processes. However, the pedunculopontine tegmental nucleus (PPTg) in the brainstem is connected with limbic structures as well as dopaminergic midbrain areas, which also project to the nucleus accumbens. Furthermore, behavioral studies implicate the PPTg in complex, motivated behavior. Thus, the PPTg might be involved in motivated behavior by influencing response selection processes in the nucleus accumbens. In this study we used in vivo microdialysis in freely moving rats in order to inhibit (100, 200, 300 and 400 microm baclofen) or stimulate [5, 12.5, 25 or 50 micromalpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA)] the PPTg in animals that are performing an operant discrimination task for food reward. The behavioral consequences were correlated with dopamine and glutamate levels in nucleus accumbens and PPTg, respectively. PPTg inhibition by local GABAB receptors impaired the response rate and accuracy of performance in the operant discrimination task. PPTg stimulation by local AMPA receptors exclusively impaired the response rate. Both treatments blocked the performance-driven dopamine signal in nucleus accumbens, whereas glutamate in PPTg was enhanced after AMPA administration only. The data indicate that the PPTg functionally participates in a network of subcortical and cortical structures, which is responsible for the execution of motivated behavior and response selection processes.

GABAergic interneurons in human subthalamic nucleus

The subthalamic nucleus (STN) is considered a homogeneous structure composed essentially of projection neurons that exert a profound glutamate-mediated excitatory influence upon the main output structures of the basal ganglia. It is currently the most efficient target for deep brain stimulations designed to alleviate symptoms of Parkinson's disease. STN neurons were analyzed by applying stereological methods and single/double-immunostaining procedures to postmortem material obtained from normal individuals. Besides a multitude of closely packed projection neurons ( approximately 24.7 mum in diameter), the human STN (mean volume, 174.5 +/- 20.4 mm3; total neuronal density, 239.5 +/- 31.9 x 10(3)) contained smaller neurons (approximately 12.2 microm), which displayed glutamic acid decarboxylase (GAD)(65/67) immunoreactivity and shared the morphological features of interneurons described in Golgi studies of primate STN. These putative gamma-aminobutyric acid (GABA)ergic interneurons accounted for 7.5% of the total neuronal population of the STN. Although present throughout the nucleus, they were significantly more numerous in its posterior-ventral-medial sector, which belongs to the limbic/associative functional territory. Many projection neurons located dorsolaterally in the STN showed parvalbumin immunoreactivity and others lying ventromedially displayed calretinin immunostaining, but none of the GAD-positive interneurons expressed these calcium-binding proteins. Although less abundant than projection neurons, GABAergic interneurons might play a important role in the intrinsic organization of the STN. The morphological and chemical heterogeneity of the human STN reported here might have important implications in the functional organization of the basal ganglia.

Single-axon tracing and three-dimensional reconstruction of centre median-parafascicular thalamic neurons in primates

The axonal projections from the centre median (CM)/parafascicular (Pf) thalamic complex in squirrel monkeys were studied after microiontophoretic injections of biotinylated dextran amine under electrophysiological guidance. A total of 29 axons connected to their parent cell body were entirely reconstructed from serial sections with a camera lucida. Our investigation shows that the CM and Pf nuclei in primates comprise three types of projection neurons: (1) neurons that innervate densely and focally the striatum; (2) neurons that arborize diffusely in the cerebral cortex; and (3) neurons that innervate both striatum and cerebral cortex. Striatal innervation of CM origin consists of dense clusters of axon terminals exhibiting pedunculated varicosities and forming oblique bands in the dorsolateral sector of putamen (sensorimotor striatal territory). The same type of striatal innervation occurs in the head of caudate nucleus (associative striatal territory) in cases of Pf-labeled neurons. The CM neurons that target cerebral cortex arborize principally in motor and premotor areas, whereas Pf neurons innervate chiefly prefrontal areas. Cortical innervation from both nuclei is much more profuse in layers V and VI than in layer I. Our three-dimensional reconstruction studies show that dendritic and axonal arborizations of CM neurons extend essentially along the sagittal plane. These results revealed that, in contrast to rodents where virtually all Pf neurons project to both striatum and cortex, the primate CM/Pf complex harbors several types of highly patterned projection neurons. As such, this complex might be considered as an integral part of the widely distributed basal ganglia neuronal system.

Glutamic acid decarboxylase 67 mRNA regulation in two globus pallidus neuron populations by dopamine and the subthalamic nucleus

The globus pallidus (GP) consists of two neuron populations, distinguished according to their immunoreactivity for parvalbumin (PV). The PV-immunoreactive (PV+) neurons project preferentially to "downstream" targets such as the subthalamic and entopeduncular nuclei, whereas neurons lacking PV (PV- neurons) project preferentially to the striatum, suggesting a role for PV- cells in feedback to striatal neurons. Although dopamine D2 antagonist administration induces immediate early gene expression preferentially in PV- GP neurons, little is known about long-term regulation of PV- versus PV+ GP neurons. Nigral 6-hydroxydopamine (6-OHDA) lesions or repeated D2-class antagonist injections have been shown to increase pallidal expression of glutamate decarboxylase (GAD(67) isoform) mRNA. This increase in GAD(67) is believed to be secondary to activation of excitatory subthalamopallidal projections. The current study examined the effects of subthalamic nucleus (STN) lesion on 6-OHDA- or repeated D2 antagonist-induced changes in GP GAD(67) mRNA expression in PV+ and PV- neurons. Five or 21 d after nigral 6-OHDA injections or after 3, 7, or 21 d of D2 antagonist administration, GAD(67) mRNA increased in both the PV- and PV+ GP neurons, but the magnitude of the increase was significantly greater in PV- neurons. By contrast, STN lesion resulted in declines in GAD(67) mRNA in both cell populations, with the decreases in PV+ neurons exceeding those in PV- neurons. Furthermore, STN lesion completely blocked 6-OHDA- or D2 antagonist-induced GAD(67) mRNA increases in PV+ cells but only partly offset the GAD(67) mRNA increase in PV- pallidal neurons. Thus, the PV+ and PV- neurons are influenced in qualitatively similar ways by dopamine and the STN, but these cell types exhibit contrasting degrees of regulation by the dopaminergic and STN perturbations. This pattern of results has implications for pallidal control of striatal versus downstream basal ganglia nuclei.

Comparative cellular distribution of GABAA and GABAB receptors in the human basal ganglia: immunohistochemical colocalization of the alpha 1 subunit of the GABAA receptor, and the GABABR1 and GABABR2 receptor subunits

The GABA(B) receptor is a G-protein linked metabotropic receptor that is comprised of two major subunits, GABA(B)R1 and GABA(B)R2. In this study, the cellular distribution of the GABA(B)R1 and GABA(B)R2 subunits was investigated in the normal human basal ganglia using single and double immunohistochemical labeling techniques on fixed human brain tissue. The results showed that the GABA(B) receptor subunits GABA(B)R1 and GABA(B)R2 were both found on the same neurons and followed the same distribution patterns. In the striatum, these subunits were found on the five major types of interneurons based on morphology and neurochemical labeling (types 1, 2, 3, 5, 6) and showed weak labeling on the projection neurons (type 4). In the globus pallidus, intense GABA(B)R1 and GABA(B)R2 subunit labeling was found in large pallidal neurons, and in the substantia nigra, both pars compacta and pars reticulata neurons were labeled for both receptor subunits. Studies investigating the colocalization of the GABA(A) alpha(1) subunit and GABA(B) receptor subunits showed that the GABA(A) receptor alpha(1) subunit and the GABA(B)R1 subunit were found together on GABAergic striatal interneurons (type 1 parvalbumin, type 2 calretinin, and type 3 GAD neurons) and on neurons in the globus pallidus and substantia nigra pars reticulata. GABA(B)R1 and GABA(B)R2 were found on substantia nigra pars compacta neurons but the GABA(A) receptor alpha(1) subunit was absent from these neurons. The results of this study provide the morphological basis for GABAergic transmission within the human basal ganglia and provides evidence that GABA acts through both GABA(A) and GABA(B) receptors. That is, GABA acts through GABA(B) receptors, which are located on most of the cell types of the striatum, globus pallidus, and substantia nigra. GABA also acts through GABA(A) receptors containing the alpha(1) subunit on specific striatal GABAergic interneurons and on output neurons of the globus pallidus and substantia nigra pars reticulata.

Late degeneration of nigro-striatal neurons in ATM-/- mice

The generation of an Atm -/- mouse model of the human ataxia-telangiectasia (AT) opened new avenues toward a better understanding of the molecular and cellular basis of AT. We have recently reported that 5-month-old Atm-/- mice exhibit severe loss of tyrosine hydroxylase-positive, dopaminergic nigro-striatal neurons, down to 26% of age-matched controls. In the present study we analyzed development of the dopaminergic cell loss in the context of the nigro-striatal system. We found that dopaminergic neurons are formed normally in the Atm-/- mouse, and degenerate during the first few months of life; there was no difference between 1-month-old Atm-/- and control mice in the number of dopaminergic cells that were retrogradely labeled by an injection of fluorescent tracer into the striatum. On the other hand, a dramatic reduction in the number of labeled cells was found in 5-month-old Atm-/- mice. This cell loss was significant in areas A9 and A10 but not in area A9-I. These findings indicate that midbrain dopaminergic neurons in Atm-/- mice initially send normal axons to the striatum, only to degenerate later in life. In addition, an age-dependent as well as topographic, medial-to-lateral loss of GAD, met-enkephaline and substance-P immunopositive cells was found in the striatum of the Atm-/- mice. This phenomenon was significant only in the 5-month-old Atm-/- mice (3 months after the beginning of detectable dopaminergic cell loss). In both the striatum and the substantia nigra, the apparent cell loss was accompanied by gliosis. In addition, alpha-synuclein immunopositive bodies were observed in the cortex, striatum and substantia nigra of these mice. The present data indicate that Atm-/- mice exhibit a progressive, age-dependent, reduction in dopaminergic cells of the substantia nigra, followed by a reduction in projection neurons of the striatum. Thus, the Atm-/- mouse may model the extrapyramidal motor deficits seen in AT patients.

Information processing, dimensionality reduction and reinforcement learning in the basal ganglia

Modeling of the basal ganglia has played a major role in our understanding of this elusive group of nuclei. Models of the basal ganglia have undergone evolutionary and revolutionary changes over the last 20 years, as new research in the fields of anatomy, physiology and biochemistry of these nuclei has yielded new information. Early models dealt with a single pathway through the nuclei and focused on the nature of the processing performed within it, convergence of information versus parallel processing of information. Later, the Albin-DeLong "box-and-arrow" model characterized the inter-nuclei interaction as multiple pathways while maintaining a simplistic scalar representation of the nuclei themselves. This model made a breakthrough by providing key insights into the behavior of these nuclei in hypo- and hyper-kinetic movement disorders. The next generation of models elaborated the intra-nuclei interactions and focused on the role of the basal ganglia in action selection and sequence generation which form the most current consensus regarding basal ganglia function in both normal and pathological conditions. However, new findings challenge these models and point to a different neural network approach to information processing in the basal ganglia. Here, we take an in-depth look at the reinforcement driven dimensionality reduction (RDDR) model which postulates that the basal ganglia compress cortical information according to a reinforcement signal using optimal extraction methods. The model provides new insights and experimental predictions on the computational capacity of the basal ganglia and their role in health and disease.

When inhibition goes incognito: feedback interaction between spiny projection neurons in striatal function

Theories about basal ganglia function have always been driven by our knowledge about the spiny projection neurons of the striatum. At the core of these theories lies the question of how, precisely, spiny projection neurons process cortical inputs. Most recently, studies demonstrating the role of spiny projection neurons in local synaptic GABA transmission have provided several new avenues for exploring striatal dynamics. They have also suggested new experimental directives for examining the specific ways in which spiny projection neurons both compete and cooperate through their local axon collaterals during cortical input processing.

Differential cannabinoid-induced electrophysiological effects in rat ventral tegmentum

Cannabinoids are known to exert mainly excitatory effects on dopaminergic cells of the ventral tegmental area (VTA). We have utilized an in vivo multiple-single unit electrophysiological approach to assess different neuronal contributions that may ultimately lead to excitation in this area. Baseline neuron recordings, using low impedance microwires, showed a variety of waveforms with a wide range of durations (0.8-3.2 ms). In the first experiment systemic injection of the potent cannabinoid agonist HU210 (100 microg/kg, i.p.) led predominantly to an increase in firing rate (approximately 214%, compared to pre-drug) in slowly firing cells with broad action potentials, possibly driven by a majority of presumed dopaminergic neurons (n = 31). However, the firing rate of some units was either unaffected (<25%, n = 9) or even decreased (approximately 67%, n = 9) following cannabinoid injection concomitantly with excitation. Apomorphine (75 microg/kg, i.p.) injected following HU210 produced a marked inhibition of both responses (approximately 76%) in 39 out of 49 cells. The second group of animals was treated with the CB(1) receptor antagonist SR141716A (1 mg/kg, i.p.), which had no effect when injected alone but prevented all HU210-evoked changes in firing rate suggesting that cannabinoid receptors mediated the observed responses (n = 39). Taken together, the present results suggest that the observed actions of cannabinoids may involve complex neurotransmitter interactions leading to differential effects on dopamine release. These heterogeneous neuronal responses are likely to underly the behavioural discrepancies reported in animal models of cannabinoid reinforcement.

Glutamate and GABA modulate dopamine in the pedunculopontine tegmental nucleus

The pedunculopontine tegmental nucleus (PPTg) has an important anatomical position connecting basal ganglia and limbic systems with motor execution structures in the pons and spinal cord. It receives glutamatergic and GABAergic input and has additional reciprocal connections with mesencephalic dopaminergic neurons, suggesting that the PPTg plays a key role in frontostriatal information processing. In vivo microdialysis in freely moving rats, in combination with behavioral analysis, was used in this study to investigate whether the dopaminergic input can be modulated at the level of the PPTg via N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) or GABA(B) receptors. Stimulation of the GABA(B) receptor decreased dopamine release in the PPTg while that of the AMPA and NMDA receptors increased it. A time-related comparison of the effects of NMDA (0.75 and 1 mM) and AMPA (50 and 25 microM) revealed a more long-lasting effect after AMPA stimulation than after NMDA. However, only the infusion of the GABA(B) receptor agonist baclofen (100 and 200 microM) stimulated stereotyped behavior (e.g. sniffing, digging or head movements) and contralateral circling. This study clearly demonstrates that GABAergic as well as glutamatergic terminals in the PPTg are critically involved in the modulation of the dopamine system. Moreover, a decrease in PPTg dopamine via GABA(B) receptor stimulation seems to be behaviorally relevant.

A novel technique for quantitative immunohistochemical imaging of various neurochemicals in a multiple-stained brain slice

Here we describe a novel technique for comparative analysis of the distributions of various neurochemicals visualized using multiple immunohistochemistry in the same brain slice. As an example, the distributions of tyrosine hydroxylase, substance P and glutamate decarboxylase in coronal slices of rat brains were compared. Each slice was divided into approximately 220,000-300,000 microareas at 20-microm intervals, and the immunohistochemical intensities of the three substances in each microarea were analyzed independently using a brain mapping analyzer; a microphotometry system previously developed in our laboratory (Sutoo et al., J. Neurosci. Methods, 1998; 85: 161-73). No significant differences between the distribution of each substance were observed in single- and triple-labeled slices. We believe that this method will facilitate the investigation of the functions of the central nervous system and the disorders thereof in various diseases.

Role of Dopaminergic D2 Receptors in the Regulation of Glutamic Acid Decarboxylase Messenger RNA in the Striatum of the Rat

Levels of messenger RNA (mRNA) encoding glutamic acid decarboxylase (GAD) and preproenkephalin (PPE) were measured by Northern blot and in situ hybridization analyses in the striatum of the rat, after chronic injections of two neuroleptics, sulpiride and haloperidol. The Northern blot analysis showed that the chronic injection of sulpiride at high doses (80 mg/kg, twice a day, 14 days) increased striatal GAD and PPE mRNA levels by 120% and 78% respectively, when compared to vehicle-injected rats. Haloperidol injections at relatively low doses (1 mg/kg, once a day, 14 days) produced parallel increases in GAD (40%) and PPE (52%) mRNA levels. After in situ hybridization densitometric measurements were performed on autoradiograms from rats treated with sulpiride, haloperidol or vehicle. The distribution of GAD and PPE mRNA signals in control rats was homogeneous along the rostrocaudal extension of the striatum. A similar increase was found along this axis after sulpiride (20%) and haloperidol (30%) treatments. The cellular observation of hybridization signals showed that grain density for GAD mRNA was increased in a majority of striatal cells after both treatments. By contrast, the PPE mRNA hybridization signal only increased in a subpopulation of neurons. The effects of such treatments were also analysed by measuring GAD activity in the striatum and in its output structures, the globus pallidus and the substantia nigra. After the administration of sulpiride, GAD activity was not modified in the striatum but increased in the globus pallidus (by 17%). After haloperidol treatment, GAD activity was increased in the globus pallidus (20%) and the substantia nigra (17%). It is concluded that the interruption of dopaminergic transmission, more precisely the D2 receptor blockade, promotes in striatopallidal neurons an increase in GAD mRNA accompanied by an increase in GAD activity and PPE mRNA. A possible regulation of GAD mRNA and GAD activity in striatonigral neurons is also discussed.

In vivo characterization of basal amino acid levels in subregions of the rat nucleus accumbens: effect of a dopamine D(3)/D(2) agonist

Recent evidence demonstrates that two subdivisions of the nucleus accumbens, the dorsolateral core and the ventromedial shell can be distinguished by morphological, immunohistochemical and chemoarchitectural differences. In the present study, we measured basal levels of amino acids in microdialysates from both the shell and core subterritories of the nucleus accumbens in freely moving rats using HPLC with fluorescence detection. The effect of the dopamine D(3)/D(2) receptor agonist quinelorane (30 microg/kg s.c.) was then investigated in both subregions. With the exception of glutamate, histidine, and serine, which showed similar levels in both subterritories, alanine, arginine, aspartate, gamma-aminobutyric acid, glutamine, and tyrosine were significantly higher in the shell compared with the core. In contrast, taurine levels were significantly lower in the shell than in the core. A particularly striking difference across subregions of the nucleus accumbens was observed for basal GABA levels with a shell/core ratio of 18.5. Among all the amino acids investigated in the present study, quinelorane selectively decreased dialysate GABA levels in the core subregion of the nucleus accumbens. The results of the present study point to specific profiles of both shell and core in terms of: (1) basal chemical neuroanatomical markers for amino acids; and (2) GABAergic response to the DA D(3)/D(2) agonist quinelorane.

Muscarinic m1 and m2 receptor proteins in local circuit and projection neurons of the primate striatum: anatomical evidence for cholinergic modulation of glutamatergic prefronto-striatal pathways

The cellular and subcellular localization of muscarinic receptor proteins m1 and m2 was examined in the neostriatum of macaque monkeys by using light and electron microscopic immunocytochemical techniques. Double-labeling immunocytochemistry revealed m1 receptors in calbindin-D28k--positive medium spiny projection neurons. Muscarinic m1 labeling was dramatically more intense in the striatal matrix compartment in juvenile monkeys but more intense in striosomes in the adult caudate, suggesting that m1 expression undergoes a developmental age-dependent change. Ultrastructurally, m1 receptors were predominantly localized in asymmetric synapse-forming spines, indicating that these spines receive extrastriatal excitatory afferents. The association of m1-positive spines with lesion-induced degenerating prefronto-striatal axon terminals demonstrated that these afferents originate in part from the prefrontal cortex. The synaptic localization of m1 in these spines indicates a role of m1 in the modulation of excitatory neurotransmission. To a lesser extent, m1 was present in symmetric synapses, where it may also modulate inhibitory neurotransmission originating from local striatal neurons or the substantia nigra. Conversely, m2/choline acetyltransferase (ChAT) double labeling revealed that m2-positive neurons corresponded to large aspiny cholinergic interneurons and ultrastructurally, that the majority of m2 labeled axons formed symmetric synapses. The remarkable segregation of the m1 and m2 receptor proteins to projection and local circuit neurons suggests a functional segregation of m1 and m2 mediated cholinergic actions in the striatum: m1 receptors modulate extrinsic glutamatergic and monoaminergic afferents and intrinsic GABAergic afferents onto projection neurons, whereas m2 receptors regulate acetylcholine release from axons of cholinergic interneurons.

Adenosine A(2A) receptor enhances GABA(A)-mediated IPSCs in the rat globus pallidus

1. The actions of adenosine A(2A) receptor agonists were examined on GABAergic synaptic transmission in the globus pallidus (GP) in rat brain slices using whole-cell patch-clamp recording. GP neurones were characterized into two major groups, type I and type II, according to the degree of time-dependent hyperpolarization-activated inward rectification and the size of input resistance. 2. The A(2A) receptor agonist 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamido- adenosine (CGS21680; 0.3-3 microM) enhanced IPSCs evoked by stimulation within the GP. The actions of CGS21680 were blocked by the A(2A) antagonists (E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxanthine (KF17837) and 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM241385). 3. The CGS21680-induced increase in IPSCs was associated with a reduction in paired-pulse facilitation. CGS21680 (0.3 microM) increased the frequency of miniature IPSCs (mIPSCs) without affecting mIPSC amplitude. These observations demonstrated that the enhancement of IPSCs in the GP was attributable to presynaptic, but not postsynaptic, A(2A) receptors. 4. The results suggest that A(2A) receptors in the GP serve to inhibit GP neuronal activity, thereby disinhibiting subthalamic nucleus neurone activity. Thus, the A(2A) receptor-mediated presynaptic regulation in the GP, together with the A(2A) receptor-mediated intrastriatal presynaptic control of GABAergic neurotransmission described previously, may play a crucial role in controlling the neuronal functions of basal ganglia. This A(2A) receptor-mediated presynaptic dual control in the striatopallidal pathway could also afford the mode of action of A(2A) antagonists for ameliorating the symptoms of Parkinson's disease in an animal model.

Central GABAergic mechanisms are involved in apnea induced by SLN stimulation in piglets

Stimulation of the superior laryngeal nerve (SLN) results in apnea in animals of different species, the mechanism of which is not known. We studied the effect of the GABA(A) receptor blocker bicuculline, given intravenously and intracisternally, on apnea induced by SLN stimulation. Eighteen 5- to 10-day-old piglets were studied: bicuculline was administered intravenously to nine animals and intracisternally to nine animals. The animals were anesthetized and then decerebrated, vagotomized, ventilated, and paralyzed. The phrenic nerve responses to four levels of electrical SLN stimulation were measured before and after bicuculline. SLN stimulation caused a significant decrease in phrenic nerve amplitude, phrenic nerve frequency, minute phrenic activity, and inspiratory time (P < 0.01) that was proportional to the level of electrical stimulation. Increased levels of stimulation were more likely to induce apnea during stimulation that often persisted beyond cessation of the stimulus. Bicuculline, administered intravenously or intracisternally, decreased the SLN stimulation-induced decrease in phrenic nerve amplitude, minute phrenic activity, and phrenic nerve frequency (P < 0.05). Bicuculline also reduced SLN-induced apnea and duration of poststimulation apnea (P < 0.05). We conclude that centrally mediated GABAergic pathways are involved in laryngeal stimulation-induced apnea.

Chemical anatomy of striatal interneurons in normal individuals and in patients with Huntington's disease

This paper reviews the major anatomical and chemical features of the various types of interneurons in the human striatum, as detected by immunostaining procedures applied to postmortem tissue from normal individuals and patients with Huntington's disease (HD). The human striatum harbors a highly pleomorphic population of aspiny interneurons that stain for either a calcium-binding protein (calretinin, parvalbumin or calbindin D-28k), choline acetyltransferase (ChAT) or NADPH-diaphorase, or various combinations thereof. Neurons that express calretinin (CR), including multitudinous medium and a smaller number of large neurons, are by far the most abundant interneurons in the human striatum. The medium CR+ neurons do not colocalize with any of the known chemical markers of striatal neurons, except perhaps GABA, and are selectively spared in HD. Most large CR+ interneurons display ChAT immunoreactivity and also express substance P receptors. The medium and large CR+ neurons are enriched with glutamate receptor subunit GluR2 and GluR4, respectively. This difference in AMPA GluR subunit expression may account for the relative resistance of medium CR+ neurons to glutamate-mediated excitotoxicity that may be involved in HD. The various striatal chemical markers display a highly heterogeneous distribution pattern in human. In addition to the classic striosomes/matrix compartmentalization, the striosomal compartment itself is composed of a core and a peripheral region, each subdivided by distinct subsets of striatal interneurons. A proper knowledge of all these features that appear unique to humans should greatly help our understanding of the organization of the human striatum in both health and disease states.

Immunohistochemical studies of the localization of neurons containing the enzyme that synthesizes dopamine, GABA, or gamma-hydroxybutyrate in the rat substantia nigra and striatum

gamma-Hydroxybutyrate (GHB) is an endogenous metabolite of gamma-aminobutyric acid (GABA), which is synthesized in the neuronal compartment of the central nervous system. This substance possesses several properties that support its role as a neurotransmitter/neuromodulator in brain. In particular, it is synthesized by a specific pathway that transforms GABA into succinic semialdehyde via GABA-T activity; then succinic semialdehyde is converted into GHB by a specific succinic semialdehyde reductase (SSR). The last enzyme is considered as a marker for neurons that synthesize GHB. This compound binds in brain to receptors whose distribution, ontogenesis, kinetics, and pharmacology are specific. Endogenous GHB, but also GHB exogenously administered to rats, participate in the regulation of dopaminergic activity of the nigrostriatal pathway. To investigate the distribution of GHB neurons in this pathway and the anatomic relationships between dopaminergic and GHB neurons, immunocytochemical identification of dopamine, GABA, and GHB neurons was carried out in the substantia nigra and striatum of the rat. The following markers for these neurons were used: anti-tyrosine hydroxylase (TH) antibodies for dopamine neurons, anti-glutamate decarboxylase (GAD) antibodies for GABA neurons, and anti-succinic semialdehyde reductase (SSR) antibodies for GHB neurons. GABA neurons were studied because GAD and SSR co-exist frequently in the same neuron, and GABA alone also exerts its own regulatory effects on dopaminergic neurons. This study reveals the co-existence of GAD/SSR and GAD/SSR/TH in numerous neurons of the substantia nigra. However, some neurons appear to be only GAD or SSR positive. In the striatum, TH-positive terminals surround many GHB neurons. GAD innervation is abundant in close contact with unlabeled neurons in the caudate-putamen, whereas distinct SSR-positive punctuates are also present. The existence of SSR-reactive synapses and neurons was confirmed in the striatum at the electron microscopic level. On the basis of these results, a clear anatomo-functional relationship between GHB and dopamine networks cannot be defined; however, we propose the modulation by GHB of striatal intrinsic neurons that could then interfere with the presynaptic control of dopaminergic activity.

Third group of neostriatofugal neurons: neurokinin B-producing neurons that send axons predominantly to the substantia innominata

Neostriatal neurons that produce neurokinin B were investigated immunocytochemically in the rat brain with an antibody against the C-terminal portion of the precursor prepropeptide of neurokinin B, preprotachykinin B (PPTB). PPTB-immunoreactive neurons were scattered throughout the neostriatum and constituted 5.1% of neostriatal neurons. They were immunopositive for projection neuron markers, such as precursor peptides of substance P, enkephalins, and dynorphins, but negative for intrinsic neuron markers, suggesting that PPTB was expressed in neostriatal projection neurons. However, PPTB-immunoreactive neurons were immunonegative for dopamine- and cyclic AMP-regulated phosphoprotein, which is known to be produced by striatopallidal and striatonigral neurons. Furthermore, almost no PPTB-immunoreactive axon terminals were observed in the substantia nigra or globus pallidus. The authors then made large kainic acid lesions in the neostriatum to reveal the target areas of PPTB-producing neurons and observed a decrease in PPTB-immunoreactive fibers in the sublenticular portion of the substantia innominata and, to much lesser extent, in the bed nucleus of the stria terminalis and central nucleus of the amygdala. After injection of wheat germ agglutinin into the substantia innominata, PPTB immunoreactivity was detected in many retrogradely labeled neostriatal neurons. In contrast, no PPTB immunoreactivity was observed in striatonigral or striatopallidal neurons after injection of retrograde tracers into the substantia nigra or globus pallidus. Thus, neurokinin B-producing neostriatal neurons were considered to send projection fibers predominantly to the substantia innominata. Furthermore, PPTB-immunoreactive axonal swellings were closely apposed to neurokinin B receptor-immunoreactive dendrites in the substantia innominata. Overall, the present results indicate that the rat brain possesses a chemically and hodologically unique neostriatofugal pathway in addition to the direct and indirect pathways.

Functional changes of the basal ganglia circuitry in Parkinson's disease

The basal ganglia circuitry processes the signals that flow from the cortex, allowing the correct execution of voluntary movements. In Parkinson's disease, the degeneration of dopaminergic neurons of the substantia nigra pars compacta triggers a cascade of functional changes affecting the whole basal ganglia network. The most relevant alterations affect the output nuclei of the circuit, the medial globus pallidus and substantia nigra pars reticulata, which become hyperactive. Such hyperactivity is sustained by the enhanced glutamatergic inputs that the output nuclei receive from the subthalamic nucleus. The mechanisms leading to the subthalamic disinhibition are still poorly understood. According to the current model of basal ganglia organization, the phenomenon is due to a decrease in the inhibitory control exerted over the subthalamic nucleus by the lateral globus pallidus. Recent data, however, suggest that additional if not alternative mechanisms may underlie subthalamic hyperactivity. In particular, given the reciprocal innervation of the substantia nigra pars compacta and the subthalamic nucleus, the dopaminergic deficit might influence the subthalamic activity, directly. In addition, the increased excitatory drive to the dopaminergic nigral neurons originating from the hyperactive subthalamic nucleus might sustain the progression of the degenerative process. The identification of the role of the subthalamic nucleus and, more in general, of the glutamatergic mechanisms in the pathophysiology of Parkinson's disease might lead to a new approach in the pharmacological treatment of the disease. Current therapeutic strategies rely on the use of L-DOPA and/or dopamine agonists to correct the dopaminergic deficit. Drugs capable of antagonizing the effects of glutamate might represent, in the next future, a valuable tool for the development of new symptomatic and neuroprotective strategies for therapy of Parkinson's disease.

Alpha(1)-adrenoceptor-mediated excitation of substantia nigra pars reticulata neurons

The effect of noradrenaline was studied in principal neurons of the substantia nigra pars reticulata in rat brain slices using patch clamp recordings. Perfusion of noradrenaline or the alpha(1)-adrenoceptor agonist phenylephrine increased the spontaneous firing activity of reticulata cells. The alpha(1)-adrenoceptor antagonist prazosin counteracted the effects of noradrenaline. In contrast, the beta-adrenoceptor agonist isoproterenol did not affect the activity of reticulata cells and the beta-adrenoceptor antagonist pindolol did not prevent noradrenaline's effect. In whole-cell recordings, at -60 mV holding potential, noradrenaline caused a tetrodotoxin-resistant inward current with a time-course similar to the increase in firing activity. Analysis of the reversal potential of this current did not give homogeneous results. The net noradrenaline current could be associated with a conductance decrease or increase, or in some cases it did not reverse over a range from -120 to -30 mV. It is suggested that noradrenaline increases the excitability of substantia nigra reticulata cells through alpha(1)-adrenoceptors. Both a reduction and an increase in membrane conductance may mediate this effect. The increase in the tonic firing of principal reticulata cells caused by noradrenaline may have significant consequences in regulating the final output of the basal ganglia and consequently in motor-related behaviours.

Striatal cells containing aromatic L-amino acid decarboxylase: an immunohistochemical comparison with other classes of striatal neurons

In a previous study, we described a population of striatal cells in the rat brain containing aromatic L-amino acid decarboxylase, the enzyme involved in the conversion of L-DOPA into dopamine. We have also presented evidence that these cells produce dopamine in the presence of exogenous L-DOPA. In this paper, we further characterize these striatal aromatic L-amino acid decarboxylase-containing cells in order to determine whether they form a subclass of one of the known categories of striatal neurons or if they represent a novel cell type. Using immunohistochemical methods, we compared the morphology and distribution of the aromatic L-amino acid decarboxylase-immunolabeled cells with those of other classes of striatal neurons. Our results show that both the morphology and distribution of aromatic L-amino acid decarboxylase-immunolabeled cells are very distinctive and do not resemble those of cells labeled for other striatal neuronal markers. Double-labeling procedures revealed that aromatic L-amino acid decarboxylase cells do not co-localize somatostatin or parvalbumin, and only a very small percentage of them co-localize calretinin. However, the population of aromatic L-amino acid decarboxylase cells label intensely for GABA.Overall, our results suggest that these aromatic L-amino acid decarboxylase-containing cells represent a class of striatal GABAergic neurons not described previously.

Presynaptic L-type Ca(2)+ channels on excessive dopamine release from rat caudate putamen

We investigated by means of behavioral and neurochemical studies the role of the nerve terminal L-type voltage sensitive Ca(2)+ channel on dopamine (DA) release. Microinjection of Bay K 8644 (BAYK), an L-type Ca(2)+ channel stimulant, into the rat caudate putamen increased locomotor activity and rearing behavior in a dose-dependent manner, whereas injections into the amygdala had no effect. DA receptor antagonists significantly blocked BAYK-induced hyperactivity. Significant increases of extracellular DA levels were detected by microdialysis 20 min after BAYK administration into caudate putamen and then declined. This increase was influenced by tetrodotoxin, an axonal Na(+) channel blocker. Pretreatment with nimodipine and nicardipine, but not nifedipine, which are 1, 4-dihydropyridine L-type Ca(2)+ channel antagonists, administered into the caudate putamen significantly blocked BAYK-induced hyperactivity and DA efflux. These results indicate that the extraordinary DA release in the caudate putamen was mediated by extreme stimulation of the nicardipine and nimodipine-sensitive L-type Ca(2)+ channel present in the nerve terminal of striatal DA neurons.

Regional and cellular localisation of GABA(A) receptor subunits in the human basal ganglia: An autoradiographic and immunohistochemical study

The regional and cellular localisation of gamma-aminobutyric acid(A) (GABA(A)) receptors was investigated in the human basal ganglia using receptor autoradiography and immunohistochemical staining for five GABA(A) receptor subunits (alpha(1), alpha(2), alpha(3), beta(2, 3), and gamma(2)) and other neurochemical markers. The results demonstrated that GABA(A) receptors in the striatum showed considerable subunit heterogeneity in their regional distribution and cellular localisation. High densities of GABA(A) receptors in the striosome compartment contained the alpha(2), alpha(3), beta(2, 3), and gamma(2) subunits, and lower densities of receptors in the matrix compartment contained the alpha(1), alpha(2), alpha(3), beta(2,3), and gamma(2) subunits. Also, six different types of neurons were identified in the striatum on the basis of GABA(A) receptor subunit configuration, cellular and dendritic morphology, and chemical neuroanatomy. Three types of alpha(1) subunit immunoreactive neurons were identified: type 1, the most numerous (60%), were medium-sized aspiny neurons that were immunoreactive for parvalbumin and alpha(1), beta(2,3), and gamma(2) subunits; type 2 (38%) were medium-sized to large aspiny neurons immunoreactive for calretinin and alpha(1), alpha(3), beta(2,3), and gamma(2) subunits; and type 3 (2%) were large sparsely spiny neurons immunoreactive for alpha(1), alpha(3), beta(2,3), and gamma(2) subunits. Type 4 neurons were calbindin-positive and immunoreactive for alpha(2), alpha(3), beta(2,3), and gamma(2) subunits. The remaining neurons were immunoreactive for choline acetyltransferase (ChAT) and alpha(3) subunit (type 5) or were neuropeptide Y-positive with no GABA(A) receptor subunit immunoreactivity (type 6). The globus pallidus contained three types of neurons: types 1 and 2 were large neurons and were immunoreactive for alpha(1), alpha(3), beta(2,3), and gamma(2) subunits and for parvalbumin alone (type 1) or for both parvalbumin and calretinin (type 2); type 3 neurons were medium-sized and immunoreactive for calretinin and alpha(1), beta(2, 3), and gamma(2) subunits. These results show that the subunit composition of GABA(A) receptors displays considerable regional and cellular variation in the human striatum but are more homogeneous in the globus pallidus.

Neurochemical modulation of the P13 midlatency auditory evoked potential in the rat

Previous studies have shown that the vertex-recorded P13 auditory evoked potential in the rat appears to be the rodent equivalent of the human P1 (or P50) potential. This sleep state-dependent potential appears to be generated, at least in part, by cholinergic pedunculopontine nucleus projections. The present studies used localized microinjections of neuroactive compounds into the region of the pedunculopontine nucleus in order to modulate the vertex-recorded P13 potential. Both the GABAergic agonist, muscimol, and the noradrenergic alpha2 receptor agonist, clonidine, were found to reduce the amplitude of the P13 potential in a dose-dependent manner. The suppressive effect of clonidine on P13 potential amplitude was blocked by pretreatment with the noradrenergic alpha2 receptor antagonist, yohimbine. In addition, habituation of the P13 potential, measured using a paired stimulus paradigm, was increased by micro-injection of a dose of muscimol or clonidine which did not change the amplitude of the P13 potential induced by the first stimulus of a pair. In contrast, microinjection of yohimbine decreased habituation of the P13 potential. These results show that the vertex-recorded P13 potential and its habituation can be modulated by activation of known inhibitory synapses, both GABAergic and noradrenergic, at the level of the pedunculopontine nucleus. This provides further evidence that the P13 potential is generated, at least in part, by pedunculopontine nucleus outputs.

The internal globus pallidus is affected in progressive supranuclear palsy and Parkinson's disease

Our structural studies of the substantia nigra in parkinsonian patients identified previously unsuspected changes in the pars reticulata, suggesting significant dysfunction in this basal ganglia output. There have been few similar structural studies of the other major basal ganglia output, the internal segment of the globus pallidus. This is despite significant evidence that this basal ganglia region is crucially important for generating parkinsonian symptoms. In fact current surgical interventions target this region in Parkinson's disease. The cellular anatomy of the internal globus pallidus was compared among five controls, six patients with Parkinson's disease, and five patients with progressive supranuclear palsy. Neurons and pathological structures were quantified using the unbiased fractionator method. Only cases with progressive supranuclear palsy had detectable pathology within the internal globus pallidus in the form of tau-positive neuronal and glial tangles and substantial neurodegeneration. Cases with Parkinson's disease had a significant reduction in the proportion of neurons containing parvalbumin but were without significant neurodegeneration, consistent with dysfunction of both basal ganglia output nuclei in advanced parkinsonism. Surgical ablation of the internal globus pallidus for Parkinson's disease appears at odds with the significant neurodegeneration in the similarly akinetic and rigid patients with progressive supranuclear palsy. The results are discussed in association with current hypotheses of basal ganglia function and recent experimentation in patients undergoing pallidotomy for hyperkinetic disorders.

The distribution of dynorphinergic terminals in striatal target regions in comparison to the distribution of substance P-containing and enkephalinergic terminals in monkeys and humans

Single- and double-label immunohistochemical techniques using several different highly specific antisera against dynorphin peptides were used to examine the distribution of dynorphinergic terminals in globus pallidus and substantia nigra in rhesus monkeys and humans in comparison to substance P-containing and enkephalinergic terminals in these same regions. Similar results were observed in monkey and human tissue. Dynorphinergic fibers were very abundant in the medial half of the internal pallidal segment, but scarce in the external pallidal segment and the lateral half of the internal pallidal segment. In substantia nigra, dynorphinergic fibers were present in both the pars compacta and reticulata. Labeling of adjacent sections for enkephalin or substance P showed that the dynorphinergic terminals overlapped those for substance P in the medial half of the internal pallidal segment, but showed only slight overlap with enkephalinergic terminals in the external pallidal segment. The substance P-containing fibers were moderately abundant along the borders of the external pallidal segment, and enkephalinergic fibers were moderately abundant in parts of the internal pallidal segment. Dynorphinergic and substance P-containing terminals overlapped extensively in the nigra, and both extensively overlapped enkephalinergic fibers in medial nigra. Immunofluorescence double-labeling studies revealed that dynorphin co-localized extensively with substance P in individual fibers and terminals in the medial half of the internal pallidal segment and in substantia nigra. Thus, as has been found in non-primates, dynorphin within the striatum and its projection systems appears to be extensively localized to substance P-containing striatopallidal and striatonigral projection neurons. Nonetheless, our results also raise the possibility that a population of substance P-containing neurons that projects to the internal pallidal segment and does not contain dynorphin is present in primate striatum. Our results also suggest the possible existence of populations of striatopallidal and striatonigral projection neurons in which substance P and enkephalin or dynorphin and enkephalin, or all three, are co-localized. Thus, striatal projection neurons in primates may not consist of merely two types, one containing substance P and dynorphin and the other enkephalin.

Modulation of GABA release by dopamine in the substantia nigra

The role of specific dopamine receptor subtypes in the regulation of GABA release in the substantia nigra was investigated using microdialysis in the awake rat. Both basal and potassium-stimulated changes in the extracellular concentrations of GABA were examined in response to the local perfusion of tetrodotoxin (TTX), the D1 agonist SKF 38393, or the D2 agonist LY 171555 through the microdialysis probe in the substantia nigra. Although TTX (1 microM) did not alter the basal extracellular concentrations of GABA in the substantia nigra, it attenuated the potassium-stimulated (80 mM K+) release of GABA. SKF 38393 had no effect on basal extracellular concentrations of GABA, but did potentiate K+ -stimulated release of GABA in a concentration-dependent manner. The potentiated response at the highest concentration of SKF 38393 (100 microM) was blocked by the D1 antagonist SCH 23390. In contrast to the effect of the D1 agonist, the D2 agonist LY 171555 attenuated the stimulated release of GABA. These data indicate that although basal extracellular concentrations of GABA in the substantia nigra may not be derived from neuronal pools, K+ -stimulated release of GABA is impulse-mediated and is modulated by the D1 and the D2 receptors. Local interactions between dopamine and GABA in the substantia nigra may have important implications for the direct regulation of basal ganglia efferent activity and motor behavior.

Modulation of quinolinic acid-induced depletion of striatal NADPH diaphorase and enkephalinergic neurons by inhibition of nitric oxide synthase

The present study was designed to examine the role of nitric oxide (NO) in quinolinic acid (QUIN)-induced depletion of rat striatal nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase and enkephalinergic neurons. Intrastriatal injection of QUIN produced a dose-dependent decrease in NADPH diaphorase and enkephalin positive cells, with cell loss being evident following the injection of 6 and 18 nmol QUIN, respectively. To evaluate the role of NO in QUIN-induced toxicity, animals were pretreated with the non-specific nitric oxide synthase (NOS) inhibitor, Nomega-nitro-l-arginine (l-NAME) or the selective neuronal NOS inhibitor, 7-nitro indazole (7-NI). l-NAME (2x250 mg/kg, i.p. 8 h apart) maximally inhibited striatal NOS activity by 85%, while 7-NI (50 mg/kg, i.p.) maximally inhibited striatal NOS activity by 60%. Pretreatment with l-NAME or 7-NI potentiated the loss of NADPH diaphorase neurons resulting from intrastriatal injection of low doses of QUIN (18 nmol). Neither NOS inhibitor had any effect on the loss of striatal NADPH diaphorase neurons induced by a higher dose of QUIN (24 nmol). In contrast, 7-NI partially prevented the QUIN (18 and 24 nmol)-induced loss of enkephalinergic neurons, while l-NAME had no effect. These results indicate that NO formation may play a role in QUIN-induced loss of enkephalinergic neurons, but not in the loss of NADPH diaphorase neurons.

Frontal syndrome as a consequence of lesions in the pedunculopontine tegmental nucleus: a short theoretical review

In this review, it is argued that the consequence of bilateral damage to the pedunculopontine tegmental nucleus (PPTg) in experimental animals is the production of a form of frontal syndrome. Frontal syndrome is a term used to describe the behavioural consequences of damage to the frontal lobes in human patients. These behavioural changes can be classified as disinhibition of behaviour (a release of behavioural control), the production of inappropriate behaviour (which in patients can be either inappropriate actions or verbal behaviour), and the production of perseverative behaviour (the maintenance of an action beyond the point at which it should have been terminated). The psychological changes which underlie these behavioural changes are thought to involve executive functions, which include such things as the prospective planning of sequences of actions, attentional shifting and working memory. In this review, I attempt to demonstrate two things: first, that there are significant anatomical connections from frontostriatal systems to the PPTg. The motor cortex projects directly to the PPTg while the prefrontal cortex contacts it via striatal circuitry, forming clear routes by which the frontal lobes can communicate with the PPTg. Second, having established the existence of connections between frontostriatal systems and the PPTg, behavioural data are described. Experimental animals bearing bilateral lesions of the PPTg have been examined in a wide variety of tasks. Animals bearing such lesions are not impaired in basic processes of feeding, drinking, locomotion, or grooming and simple observation of lesioned rats' normal behaviour reveals no obvious gross impairment in function. However, the results of more subtle tests reveal a wide variety of deficits in various tasks. The outcome of these experiments are in many ways contradictory, but in the vast majority of cases, the changes can be described as involving disinhibition of behaviour, the release of inappropriate behaviour, and the production of perseverative behaviour. Anatomical and behavioural data support the conclusion that there are functional connections between frontal systems and the PPTg. This review also discusses what psychological processes might be served by such connections.

Structural and functional evolution of the basal ganglia in vertebrates

While a basal ganglia with striatal and pallidal subdivisions is 1 clearly present in many extant anamniote species, this basal ganglia is cell sparse and receives only a relatively modest tegmental dopaminergic input and little if any cortical input. The major basal ganglia influence on motor functions in anamniotes appears to be exerted via output circuits to the tectum. In contrast, in modern mammals, birds, and reptiles (i.e., modern amniotes), the striatal and pallidal parts of the basal ganglia are very neuron-rich, both consist of the same basic populations of neurons in all amniotes, and the striatum receives abundant tegmental dopaminergic and cortical input. The functional circuitry of the basal ganglia also seems very similar in all amniotes, since the major basal ganglia influences on motor functions appear to be exerted via output circuits to both cerebral cortex and tectum in sauropsids (i.e., birds and reptiles) and mammals. The basal ganglia, output circuits to the cortex, however, appear to be considerably more developed in mammals than in birds and reptiles. The basal ganglia, thus, appears to have undergone a major elaboration during the evolutionary transition from amphibians to reptiles. This elaboration may have enabled amniotes to learn and/or execute a more sophisticated repertoire of behaviors and movements, and this ability may have been an important element of the successful adaptation of amniotes to a fully terrestrial habitat. The mammalian lineage appears, however, to have diverged somewhat from the sauropsid lineage with respect to the emergence of the cerebral cortex as the major target of the basal ganglia circuitry devoted to executing the basal ganglia-mediated control of movement.

GABA(A) receptors in the primate basal ganglia: an autoradiographic and a light and electron microscopic immunohistochemical study of the alpha1 and beta2,3 subunits in the baboon brain

The distribution of gamma-aminobutyric acid(A) (GABA(A)) receptors was investigated in the basal ganglia in the baboon brain by using receptor autoradiography and the immunohistochemical localisation of the alpha1 and beta2,3 subunits of the GABA(A) receptor by light and electron microscopy. In the caudate-putamen, the alpha1 subunit was distributed in high densities in the matrix compartment, and the beta2,3 subunits were more homogeneously distributed; the globus pallidus showed lower levels of the alpha1 and beta2,3 subunits. Four types of alpha1 subunit immunoreactive neurons were identified in the baboon striatum: the most numerous (75%) were type 1 medium-sized aspiny neurons; type 2 (2%) were large aspiny neurons with an indented nuclear membrane located in the ventral striatum; type 3 neurons were the least numerous (1%) and were comprised of large neurons in the ventromedial regions of the striatum; and type 4 (22%) neurons were medium to large aspiny neurons located in striosomes. At the ultrastructural level, alpha1 and beta2,3 subunit immunoreactivity was localised in the neuropil of the striatum in both symmetrical and asymmetrical synaptic contacts. In the globus pallidus, alpha1 and beta2,3 subunits were localised on large neurons and were found in three types of synaptic terminals: type 1 terminals were small and established symmetrical synapses; type 2 terminals were large; and type 3 terminals formed small synaptic terminals with subjunctional dense bodies. These results show that the subunit composition of GABA(A) receptors varies between the striosome and the matrix compartments in the striatum and that there is receptor subunit homogeneity in the globus pallidus.

Striatal mechanisms in Parkinson's disease: new insights from computer modeling

We review data and hypotheses concerning the functional anatomy of the striatum and the role of its corticostriatal and nigrostriatal afferents in Parkinson's disease (PD). Starting from molecular mechanisms of glutamatergic and dopaminergic actions in the striatum we have developed a compartmental model of striatal principal neurons that displays a significant degree of biological realism. Simulations of a network of striatal projection neurons under conditions likely to be found in healthy subjects as well as untreated and therapeutic situations of advanced PD provide clues concerning the dynamics of neuronal interactions and their possible effects on downstream motor structures in the generation of positive and negative motor symptoms. We present tentative biological explanations of the symptoms of rigidity and akinesia in PD leading to predictions concerning the origin of abnormal movements and the beneficial effects of dopaminergic treatment. Although these attempts are not yet sufficient to account for the complexity of clinical symptoms found in PD they can guide further empirical research and foster fruitful interactions between experimentalists, theoreticians, and clinicians in unraveling the functional anatomy of the basal ganglia.

Differentiation of the inhibitory effects of calcium antagonists on abnormal behaviors induced by methamphetamine or phencyclidine

The abnormal behaviors induced by methamphetamine (MAP: 1 mg/kg) or phencyclidine (PCP: 10 mg/kg) were measured using behavioral analysis following the microinjection of one of three calcium (Ca) antagonists (nifedipine: Nif, nicardipine: Nic and flunarizine: Flu) into the rat caudate putamen or amygdala. The intraperitoneal administration of MAP or PCP induced abnormal behaviors in a time-dependent manner; the maximum locomotor activity was measured 30-45 min after the administration of MAP or PCP. This hyperactivity was sustained for more than 2 h. Following microinjection of these Ca antagonists into the caudate putamen, each showed a different pattern of inhibition on MAP- or PCP-induced abnormal behaviors. Nic and Flu were effective at reducing these abnormal behaviors, in contrast, Nif was ineffective. In particular, the inhibitory effect of Nic was stronger than that of Flu. Microinjection of these Ca antagonists into the amygdala did not show any reductive effect on the hyperactivity induced by MAP or PCP. These results demonstrate that these Ca antagonists have different pharmacological properties and that both L- and T-type Ca2+ channels modulate the dopamine release in the rat caudate putamen. These results further lead us to suggest the presence of a subtype of L-type Ca2+ channels in the caudate putamen.

Collateral projections from striatonigral neurons to substance P receptor-expressing intrinsic neurons in the striatum of the rat

It is well known that striatonigral neurons produce substance P (SP); however, no SP receptor (SPR) has so far been found in the substantia nigra. On the other hand, a previous study in the rat striatum indicated that SPR was expressed only in cholinergic or somatostatinergic intrinsic neurons (Kaneko et al. [1993] Brain Res. 631:297-303). Thus, it was assumed that SP produced by striatonigral neurons might be released through their intrastriatal axon collaterals to act upon intrinsic neurons in the striatum. To confirm this assumption, the distribution of axon collaterals of striatonigral neurons was examined in the striatum of the rat. The experiments were performed on brain slices by combining retrograde labeling with tetramethylrhodamine-dextran amine, electrophysiological recording, intracellular staining with biocytin, and immunocytochemistry for SPR. The distribution of axons of cholinergic striatal neurons (a group of SP-negative intrinsic striatal neurons) was also examined. It was observed that 16% of varicosities of intrastriatal axon collaterals of striatonigral neurons, as well as 6% of axonal varicosities of cholinergic neurons, were in close apposition to dendrites and cell bodies of SPR-immunoreactive striatal neurons. Since SPR-immunoreactive striatal neurons constituted only 2.7% of the total population of striatal neurons (Kaneko et al. [1993] Brain Res. 631:297-303), it appeared that axonal varicosities of striatonigral neurons were preferentially apposed to SPR-immunoreactive striatal neurons and that the varicosities in close apposition to SPR-immunoreactive neurons were derived more frequently from striatonigral neurons than from cholinergic interneurons. Confocal laser scanning microscopy indicated that axonal varicosities in close apposition to SPR-immunoreactive cells showed synaptophysin immunoreactivity, a marker of synaptic vesicles. In intrastriatal axons of striatonigral neurons, it was further revealed from electron microscopy that axonal varicosities in close apposition to SPR-immunoreactive dendrites, at least a part of them, made synapses of the symmetric type. Striatonigral neurons might release SP preferentially around cholinergic or somatostatinergic intrinsic neurons to regulate them through SP-SPR interactions.

Preproenkephalin mRNA expression in the caudate-putamen of MPTP monkeys after chronic treatment with the D2 agonist U91356A in continuous or intermittent mode of administration: comparison with L-DOPA therapy

The effect of chronic treatment with the D2 dopamine agonist U91356A or L-DOPA therapy on the regulation of preproenkephalin (PPE) mRNA was investigated in the caudate-putamen of previously drug-naive cynomolgus monkeys Macaca fascicularis rendered parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In MPTP monkeys, pulsatile treatment with either L-DOPA or U91356A relieved parkinsonian symptoms but caused progressive sensitization to treatment and, as expected, induced choreic dyskinesias. In contrast, U91356A given in a continuous mode led to partial behavioral tolerance without appearance of dyskinesias. Using in situ hybridization histochemistry, lesioning was shown to produce elevation of PPE mRNA levels in the lateral and medial parts of the putamen and in the lateral part of the caudate nucleus compared to control animals at the three rostrocaudal regions analyzed. In general, no change of PPE mRNA levels were observed in the medial caudate after MPTP lesioning with or without L-DOPA or U91356A treatments in the three rostrocaudal regions measured except for an increase in the caudal part of L-DOPA-treated MPTP monkeys. In the putamen and lateral caudate nucleus, elevated PPE mRNA expression by MPTP generally was not corrected (or only partially corrected) by chronic L-DOPA treatment except for the rostral medial putamen where correction to control values was observed. In general, pulsatile administration of U91356A partially corrected the lesion-induced elevation of PPE mRNA levels in the putamen and lateral caudate nucleus whereas the correction was more pronounced and widespread when MPTP monkeys received the continuous administration of this drug. These results indicate that the mode of administration of a D2 dopamine receptor agonist, such as U91356A, although at a roughly equivalent dosage influences the extent of inhibition of the expression of PPE in the denervated striatum of monkeys. In addition, the general lack of correction of the MPTP-induced increase of PPE mRNA in the striatum of L-DOPA-treated monkeys compared to the decreases observed with the D2 agonist treatments suggest that the D1 agonist component of L-DOPA therapy opposes the D2 agonist activity. Hence, D1 receptor agonist activity would stimulate PPE mRNA expression whereas D2 receptor agonists inhibit the expression of this peptide. Increases in PPE expression in the striatum may be implicated in the induction of dyskinesias since both groups of treated MPTP monkeys displaying dyskinesias had elevated striatal PPE mRNA levels whereas the MPTP monkeys with the lowest striatal PPE mRNA levels developed tolerance without dyskinesias.

The morphological and chemical characteristics of striatal neurons immunoreactive for the alpha1-subunit of the GABA(A) receptor in the rat

The distribution, morphology and chemical characteristics of neurons immunoreactive for the alpha1-subunit of the GABA(A) receptor in the striatum of the basal ganglia in the rat brain were investigated at the light, confocal and electron microscope levels using single, double and triple immunohistochemical labelling techniques. The results showed that alpha1-subunit immunoreactive neurons were sparsely distributed throughout the rat striatum. Double and triple labelling results showed that all the alpha1-subunit-immunoreactive neurons were positive for glutamate decarboxylase and immunoreactive for the beta2,3 and gamma2 subunits of the GABA(A) receptor. Three types of alpha1-subunit-immunoreactive neurons were identified in the striatum on the basis of cellular morphology and chemical characteristics. The most numerous alpha1-subunit-immunoreactive neurons were medium-sized, aspiny neurons with a widely branching dendritic tree. They were parvalbumin-negative and were located mainly in the dorsolateral regions of the striatum. Electron microscopy showed that these neurons had an indented nuclear membrane, typical of striatal interneurons, and were surrounded by small numbers of axon terminals which established alpha1-subunit-immunoreactive synaptic contacts with the soma and dendrites. These cells were classified as type 1 alpha1-subunit-immunoreactive neurons and comprised 75% of the total population of alpha1-subunit-immunoreactive neurons in the striatum. The remaining alpha1-subunit-immunoreactive neurons comprised of a heterogeneous population of large-sized neurons localized in the ventral and medial regions of the striatum. The most numerous large-sized cells were parvalbumin-negative, had two to three relatively short branching dendrites and were designated type 2 alpha1-subunit-immunoreactive neurons. Electron microscopy showed that the type 2 neurons were characterized by a highly convoluted nuclear membrane and were sparsely covered with small axon terminals. The type 2 neurons comprised 20% of the total population of alpha1-subunit-immunoreactive neurons. The remaining large-sized alpha1-immunoreactive cells were designated type 3 cells; they were positive for parvalbumin and were distinguished by long branching dendrites extending dorsally for 600-800 microm into the striatum. These neurons comprised 5% of the total population of alpha1-subunit-immunoreactive neurons and were surrounded by enkephalin-immunoreactive terminals. Electron microscopy showed that the alpha1-subunit type 3 neurons had an indented nuclear membrane and were densely covered with small axon terminals which established alpha1-subunit-immunoreactive symmetrical synaptic contacts with the soma and dendrites. These results provide a detailed characterization of the distribution, morphology and chemical characteristics of the alpha1-subunit-immunoreactive neurons in the rat striatum and suggest that the type 1 and type 2 neurons comprise of separate populations of striatal interneurons while the type 3 neurons may represent the large striatonigral projection neurons described by Bolam et al. [Bolam J. P., Somogyi P., Totterdell S. and Smith A. D. (1981) Neuroscience 6, 2141-2157.].

Dopaminergic neurons intrinsic to the primate striatum

Intrinsic, striatal tyrosine hydroxylase-immunoreactive (TH-i) cells have received little consideration. In this study we have characterized these neurons and their regulatory response to nigrostriatal dopaminergic deafferentation. TH-i cells were observed in the striatum of both control and 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-treated monkeys; TH-i cell counts, however, were 3.5-fold higher in the striatum of MPTP-lesioned monkeys. To establish the dopaminergic nature of the TH-i cells, sections were double-labeled with antibodies to dopamine transporter (DAT). Immunofluorescence studies demonstrated that nearly all TH-i cells were double-labeled with DAT, suggesting that they contain the machinery to be functional dopaminergic neurons. Two types of TH-i cells were identified in the striatum: small, aspiny, bipolar cells with varicose dendrites and larger spiny, multipolar cells. The aspiny cells, which were more prevalent, corresponded morphologically to the GABAergic interneurons of the striatum. Double-label immunofluorescence studies using antibodies to TH and glutamate decarboxylase (GAD67), the synthetic enzyme for GABA, showed that 99% of the TH-i cells were GAD67-positive. Very few (<1%) of the TH-i cells, however, were immunoreactive for the calcium-binding proteins calbindin and parvalbumin. In summary, these results demonstrate that the dopaminergic cell population of the striatum responds to dopamine denervation by increasing in number, apparently to compensate for loss of extrinsic dopaminergic innervation. Moreover, this population of cells corresponds largely with the intrinsic GABAergic cells of the striatum. This study also suggests that the adult primate striatum does retain some intrinsic capacity to compensate for dopaminergic cell loss.

Glutamate decarboxylase (GAD65) gene expression is increased by dopamine receptor agonists in a subpopulation of rat striatal neurons

The mRNA levels encoding for the two isoforms of glutamate decarboxylase (GAD65 and GAD67) were measured in the adult rat striatum following systemic administration of dopamine receptor agonists. Double-labeling in situ hybridization histochemistry was used to measure GAD65 or GAD67 mRNA levels in neurons labeled or not with a preproenkephalin (PPE) cRNA probe. Chronic treatment with the D1/D2 dopamine receptor agonist apomorphine or with the D1 dopamine receptor agonist SKF-38393 induced an increase in GAD65 but not GAD67 mRNA levels in different sectors of the striatum. These effects were abolished by pre-administration of the D1 dopamine receptor antagonist SCH-23390. On double-labeled sections, GAD65 mRNA labeling was distributed in neurons labeled and unlabeled with the PPE cRNA probe. About half of all neuronal profiles labeled with the GAD65 cRNA probe were also labeled with the PPE cRNA probe. Quantification of labeling at cellular level demonstrated a significant increase of GAD65 mRNA levels in PPE-unlabeled neurons. On the other hand, no significant changes of GAD65 mRNA levels were detected in PPE-labeled neurons. Our results demonstrate a differential effect of dopamine receptor agonists on striatal GAD65 and GAD67 gene expression. In particular, we show that GAD65 mRNA levels are selectively increased in presumed striato-nigral neurons following treatments with dopamine receptor agonists. These data provide evidence that the GAD65 isoform is preferentially involved in the regulation of GABAergic neurotransmission in striato-nigral neurons.

Evidence of gamma-aminobutyric acidergic control over the catecholaminergic projection from the medulla oblongata to the central nucleus of the amygdala

It is known that the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM) project to the central nucleus of the amygdala (Ce), conveying visceral information. Conversely, the Ce sends projections to the NTS and the VLM. To understand better the role of catecholamine and gamma-aminobutyric acid (GABA) in these reciprocal connections, experiments were performed by combining lectin-conjugated horseradish peroxidase (WGA-HRP) anterograde and retrograde transport with preembedding immunocytochemistry to detect tyrosine hydroxylase (TH), and postembedding immunocytochemistry to detect GABA. The light microscopic study suggested that the majority of neurons in the NTS and the VLM projecting to the Ce were TH immunoreactive (TH-IR). Most of them were located at the level of the obex. Under the electron microscope, the GABAergic and non-GABAergic terminals were found to form synaptic contacts with the TH-(IR) or Ce-projecting or TH-IR/Ce-projecting double-labelled neurons of the NTS and VLM. The GABAergic terminals mostly formed symmetrical synaptic contacts with the postsynaptic structure in which perikarya (14-19%), dendrites (79-84%), and spines (2%) were observed. Approximately 94% of the axon terminals in the NTS and 90% of those in the VLM arising from the Ce were GABAergic and appeared not to form synaptic contacts with the TH-IR or Ce-projecting neurons in these regions. The present results demonstrated that the catecholaminergic neurons of the NTS and VLM projecting to the Ce receive an extensive GABAergic innervation and that the amygdala projection to the medulla is mostly GABAergic.

Influence of dopamine on GABA release in striatum: evidence for D1-D2 interactions and non-synaptic influences

Striatal slices from the rat were preincubated with [3H]GABA and superfused in the presence of nipecotic acid and aminooxyacetic acid, inhibitors of high-affinity GABA transport and GABA aminotransferase, respectively. GABA efflux was estimated by monitoring tritium efflux, 98% of which was in the form of [3H]GABA. The following three major observations were made: (1) The overflow of GABA evoked by electrical field stimulation (8 Hz) was increased two-fold by SKF-38393 (10 microM), an agonist at the D1 family of dopamine receptors. This increase was completely blocked by the D1 receptor antagonist SCH-23390 (10 microM). However, SCH-23390 had no effect on GABA overflow when given alone. Thus, dopamine agonists appear to exert an excitatory influence on GABA release; however, this effect was not elicited by endogenous dopamine under the conditions of this experiment. (2) Electrically evoked GABA overflow was reduced 50% by quinpirole (10 microM), an agonist at the D2 family of dopamine receptors, and this effect was blocked by the D2 antagonist sulpiride (10 microM). Moreover, exposure to sulpiride alone caused a 60% increase in GABA overflow, and this effect was abolished by 3-iodotyrosine (2 mM), a dopamine synthesis inhibitor. Thus, D2 agonists appear to exert an inhibitory influence on dopamine release, an effect that can be exerted by endogenous stores of dopamine. (3) The stimulatory effect of SKF-38393 was attenuated by quinpirole, whereas the sulpiride-induced increase in GABA efflux was attenuated by SCH-23390. Sulpiride also increased [3H]GABA efflux during KCl-induced depolarization, an effect that was antagonized by SCH-23390 as in the case of electrical stimulation. However, although tetrodotoxin did not alter the stimulatory effect of sulpiride, it did block the ability of SCH-23390 to antagonize the sulpiride-induced increase in GABA overflow. These latter results suggest that there is an interaction between D1 and D2 receptors whereby the effects of dopamine mediated via D1 sites are inhibited by an action on D2 sites. In conclusion, our results suggest that (i) dopamine agonists can exert an excitatory influence on depolarization-induced GABA release within neostriatum via D1 receptors and an inhibitory influence via D2 receptors; (ii) under the conditions of these experiments, endogenous dopamine fails to act on D1 sites but does exert an inhibitory influence via D2 sites; and (iii) there is an interaction between D1 and D2 receptors such that the actions of dopamine mediated via D1 sites are inhibited as a result of the concomitant actions exerted via D2 sites.

Ultrastructural immunocytochemical localization of the dopamine D2 receptor within GABAergic neurons of the rat striatum

Classical antipsychotics, which block dopamine (DA) D2 receptors, showing intrastriatal variation in their effectiveness in modulating GABAergic function. To determine the cellular basis for such differences, we examined the electron microscopic immunocytochemical labeling of D2 receptors and GABA in the dorsolateral caudate-putamen (CPn) and the nucleus accumbens (Acb) shell. In both regions, peroxidase reaction product and gold-silver deposits representing D2 receptor immunoreactivity (D2-IR) and GABA immunoreactivity (GABA-IR), respectively, were detected in dendrites and perikarya having characteristics of either spiny projection neurons or aspiny interneurons. Some perikarya in both regions are dually labeled with D2-IR and GABA-IR. Neurons axon terminals in each region also contained one or both markers. However, there were notable regional differences in the immunolabeling patterns. In the CPn, D2-IR was more commonly seen in dendrites/spines than in axon terminals, and proportionally more dendrites were dually labeled than in the Acb. In the Acb shell, D2-IR was detected with similar frequency in terminals and dendrites/spines, but more terminals co-localized D2-IR and GABA-IR in this region compared with the CPn. These results provide the first ultrastructural evidence for direct D2-mediated effects of DA on striatal GABAergic neurons. They further suggest that modulation of GABAergic neurons by DA acting at D2 receptors may be relatively more postsynaptic in the CPn, but more presynaptic in the Acb shell.

Ketamine modulation of the temporal pattern of discharges and spike train interactions in the rat substantia nigra pars reticulata

This study compares the temporal pattern of discharges of extracellularly recorded substantia nigra pars reticulata (SNr) single units in two experimental conditions: Equithesin- and ketamine-induced anesthesia. The analysis of the statistical properties of the spike trains recorded in the Equithesin group of animals showed that this experimental condition could be considered as a control condition with respect to previous data reported in the literature. We investigated the glutamatergic modulation of SNr activity at spike train level in a steady-state condition by using the anesthetic agent ketamine, which is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) glutamatergic receptors. The most relevant effect of ketamine at single unit level was to induce burst discharges, with an intraburst frequency rate near 50 Hz, specifically in units characterized by an initial long refractoriness in the Equithesin condition. The other classes of single units tended to discharge at a higher rate without any significant change in their temporal pattern of firing. Simultaneous recording of the spike trains of 108 SNr pairs (46 and 62 during Equithesin and ketamine condition, respectively) were equally distributed between pairs of units simultaneously recorded from the same electrode and from distinct electrodes at a distance up to 400 microm in the same hemisphere. Ketamine induced a significant increase in the number of pairs with synchronous firing (from 4 to 49%), which was strongly, but not exclusively, associated with an increased tendency to fire in bursts. Neighboring cells tended to fire with a similar pattern in either condition of recording, whereas synchronous firing between distant cells was observed only during ketamine condition.

Effects of secretogranin II-derived peptides on the release of neurotransmitters monitored in the basal ganglia of the rat with in vivo microdialysis

In vivo microdialysis was used to study the effect of secretogranin II-derived peptides on dynorphin B (Dyn B), dopamine, gamma-aminobutyric acid (GABA), glutamate and aspartate release in the substantia nigra and neostriatum of halothane-anaesthesized rats. In the substantia nigra, local infusion of secretoneurin (secretogranin II 154-186) (1-50 microM) increased, in a concentration-dependent manner, extracellular aspartate, glutamate, Dyn B, dopamine and GABA levels. The effect was particularly prominent on aspartate and glutamate levels which, following 50 microM of secretoneurin, were increased by > 20 and > 10 fold, respectively. However, the effect of secretoneurin on Dyn B release appeared to be more specific, since a significant increase (> 20 fold) was already observed following 1 microM of secretoneurin. In the neostriatum, Dyn B, glutamate, aspartate and GABA levels were also increased by local secretoneurin infusion, but the effect was less prominent than in the substantia nigra. In the substantia nigra, only Dyn B levels were significantly increased following infusion of 10 microM of the secretoneurin-C terminal (secretoneurin-15C), whereas Dyn B and GABA levels were increased by the same concentration of the secretogranin II C terminus (YM). Only glutamate and aspartate levels were increased by local infusion of 10 microM of secretogranin II 133-151 (LF), a peptide adjacent to secretoneurin in the primary amino acid sequence. In the neostriatum, Dyn B and GABA levels were increased by 10 microM of secretoneurin-15C. Dyn B levels were also increased by 10 microM of YM, and glutamate and aspartate levels were increased by 10 microM of both YM and LF. Thus secretogranin II-derived peptides affect extracellular levels of several putative neurotransmitter systems monitored in the basal ganglia of the rat with in vivo microdialysis. The effect of Dyn B appears to be specific and related to a physiological role of secretoneurin, since (i) it occurs in an area where secretoneurin-immunocytochemistry has been observed, (ii) is exerted at comparatively low concentrations, and (iii) is mimicked by secretoneurin-15C. The increases in excitatory amino acid levels produced by high concentrations of secretoneurin and other secretogranin II-derived peptides reflect, perhaps, a potential neurotoxicity produced by abnormal accumulation of these peptides.

Glutamate decarboxylase-67 messenger RNA expression in normal human basal ganglia and in Parkinson's disease

Expression of glutamate decarboxylase-67 messenger RNA was examined in the basal ganglia of normal controls and of cases of Parkinson's disease using in situ hybridization histochemistry in human post mortem material. In controls glutamate decarboxylase-67 messenger RNA expression was detected in all large neurons in both segments of the globus pallidus and in three neuronal subpopulations in the striatum as well as in substantia nigra reticulata neurons and in a small sub-population of subthalamic neurons. In Parkinson's disease, there was a statistically significant decrease of 50.7% in glutamate decarboxylase-67 messenger RNA expression per neuron in the lateral segment of the globus pallidus (controls: mean 72.8 microns2 +/- S.E.M. 8.7 of silver grain/neuron, n = 12; Parkinson's disease: mean 35.9 microns2 +/- S.E.M. 9.7 of silver grain/neuron, n = 9, P = 0.01, Student's t-test). In the medial segment of the globus pallidus, there was a small, but non-significant decrease of glutamate decarboxylase-67 messenger RNA expression in Parkinson's disease (controls: mean 100.6 microns2 +/- S.E.M. 7.2 of silver grain/neuron, n = 11; Parkinson's disease: mean 84.8 microns2 +/- S.E.M. 13.0 of silver grain/neuron, n = 7, P = 0.1, Student's t-test). No significant differences in glutamate decarboxylase-67 messenger RNA were detected in striatal neuronal sub-populations between Parkinson's disease cases and controls. These results are the first direct evidence in humans that there is increased inhibitory drive to the lateral segment of the globus pallidus in Parkinson's disease, as suggested by data from animal models. We therefore provide theoretical support for current experimental neurosurgical approaches to Parkinson's disease.