The organization of the projection from the cerebral cortex to the striatum in the rat

Fenfluramine-induced activation of the immediate-early gene c-fos in the striatum: possible interaction between serotonin and dopamine

DL-Fenfluramine, a serotonin (5-HT) releasing agent, induces rapid expression of Fos-like immunoreactivity (Fos-LI) in the striatum as well as in other brain structures receiving a dense 5-HT innervation. Fenfluramine-induced Fos-LI expression in the striatum may result directly from the activation of 5-HT receptors or may be the result of interactions between dopamine (DA) and 5-HT neurotransmitter systems. To discriminate between these two possibilities, various groups of rats were pretreated with different 5-HT antagonists or a DA D1 antagonist, 20 min before fenfluramine administration. Animals were killed 60 min later. In the striatum, fenfluramine-induced expression of Fos-LI was almost completely blocked by SCH 23390, methysergide and S(-)-propranolol. The immediate-early gene response to fenfluramine was only slightly affected by pretreatment with the 5-HT2A/2C antagonist ritanserin. Fenfluramine was also administered to sham-operated and to unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. In the 6-OHDA-lesioned rats, fen-fluramine-induced Fos-LI was decreased by 60% on the DA denervated side compared to the intact side and to sham-operated rats. To further probe the possibility of a direct activation of Fos-LI by 5-HT receptor subtypes, we evaluated the expression of Fos-LI after the administration of different 5-HT agonists. Our results demonstrate that neither 8-OH-DPAT, CGS-12066B, RU 24969 nor phenyl-biguanide was able to reproduce the effects of fenfluramine. Only a high dose of DOI (8.5 mg/kg) produced a moderate expression of Fos-LI in the dorsomedial part of the striatum. This contrasted with the Fos-LI expression in other brain areas where 8-OH-DPAT and DOI (2.5 and 8.5 mg/kg) reproduced the effects of the 5-HT releasing agent. Our results suggest that the release of 5-HT by fenfluramine induced Fos-LI expression predominantly in a striatal region related to associative functions and, that this c-fos response may be under the control of both 5-HT and DA. Moreover, the mechanism by which fenfluramine induces c-fos expression in the striatum differs from other brain regions.

Total number of neurons in the neostriatal, pallidal, subthalamic, and substantia nigral nuclei of the rat basal ganglia: a stereological study using the cavalieri and optical disector methods

The total number of neurons within six subdivisions of the rat basal ganglia was estimated using unbiased stereological counting methods and systematic random sampling techniques. Six young adult rats were perfuse-fixed, their right cerebral hemispheres were embedded in glycolmethacrylate, and a complete set of serial 40-mu m sections was cut through each hemisphere. After a random start, a systematic subset (e.g., every tenth) of these sections was used to estimate the total volume of each subdivision using Cavalieri's method. The same set of sampled sections was used to estimate the number of neurons in a known subvolume (i.e., the Nv) by the optical disector method. The product of the total volume and the Nv by these methods yields an unbiased estimate of the total number of neurons. It was found that the right basal ganglia consisted, on average, of 2.79 million neostriatal or caudate-putamen neurons (with a coefficient of variation of 0.07), 46,000 external globus pallidus neurons (0.11), 3,200 entopeduncular/internal globus pallidus neurons (0.10), 13,600 subthalamic neurons (0.10), 7,200 substantial nigra pars compacta neurons (0.15), and 26,300 substantia nigra pars reticulata neurons (0.07).

Projections of the medial and lateral prefrontal cortices to the amygdala: a Phaseolus vulgaris leucoagglutinin study in the rat

The projections of different subfields of the medial and lateral prefrontal cortices to the amygdala were studied in the rat using the sensitive Phaseolus vulgaris leucoagglutinin anterograde tract tracing technique. Injections into the infralimbic cortex produced anterograde labeling in the lateral capsular subdivision of the central nucleus, superficial (corticomedial) amygdaloid nuclei, lateral and accessory basal nuclei, and the anterior amygdaloid area. Injections into the caudal portion of the infralimbic cortex produced additional labeling in the intermediate subdivision of the central nucleus. The prelimbic cortex had projections to the medial portion of the magnocellular basal nucleus and adjacent portions of the lateral nucleus and lateral capsular subdivision of the central nucleus. The medial precentral cortex had projections to the rostromedial part of the magnocellular basal nucleus and adjacent portions of the lateral capsular subdivision of the central nucleus. Injections into the lateral orbital and ventral agranular insular cortices produced labeled fibers in the rostral part of the superficial amygdala, lateral capsular subdivision of the central nucleus, and the lateral and accessory basal nuclei. The dorsal agranular insular area had projections to several different subdivisions of the central nucleus as well as to the rostrolateral magnocellular basal nucleus; the latter projections were complementary to those originating in the prelimbic area. The present study indicates that each portion of the prefrontal cortex has a distinctive projection to the amygdala. The ventral areas of the lateral and medial prefrontal cortices, which receive olfactory projections, are the only prefrontal cortical areas with projections to the olfactory-related superficial amygdaloid nuclei. The more dorsally situated prefrontal areas, the dorsal agranular insular area and prelimbic cortex, have complementary projections to the basal nucleus, suggesting that they modulate separate prefrontal cortico-striatal-pallid circuits. The specificity of prefrontal cortico-amygdaloid projections is indicative of their involvement in discrete functions.

Prefrontal cortex inputs of the nucleus accumbens-nigro-thalamic circuit

The functional organization of the cortico-nucleus accumbens-substantia nigra pars reticulata circuit was investigated in the rat using combined anatomical and electrophysiological approaches. The nucleus accumbens neurons which project to the substantia nigra pars reticulata are located in a circumscribed region of the core immediately adjacent and extending dorsally to the anterior commissure. As shown by retrograde and anterograde transports of wheatgerm agglutinin conjugated to horseradish peroxidase, the region of the nucleus accumbens related to the substantia nigra was found to receive bilateral inputs from restricted areas of the medial and lateral prefrontal cortex, i.e., prelimbic/medial orbital and dorsal agranular insular areas. The electrical stimulation of these medial and lateral prefrontal cortical areas induced excitatory responses in nucleus accumbens neurons projecting to the dorsomedial substantia nigra pars reticulata. Interestingly, an important proportion (61%) of the nucleus accumbens-nigral cells responding to the stimulation of the lateral prefrontal cortex were also excited by the stimulation of the medial prefrontal cortex, demonstrating the existence of a convergent influence of these cortical areas on single nucleus accumbens cells. Furthermore, the present data also show that the stimulation of the medial prefrontal cortex results in a powerful inhibition of the tonic firing of the substantia nigra pars reticulata neurons. In conclusion, this study reveals the existence of a functional link between the prefrontal cortex (prelimbic/medial orbital and agranular insular areas) and the nucleus accumbens neurons which innervate the dorsomedial region of the substantia nigra pars reticulata. Since the dorsomedial region of substantia nigra pars reticulata is known to project to subfields of the mediodorsal and ventromedial thalamic nuclei related to the prefrontal cortex, the present data further demonstrate the existence of a prefrontal-nucleus accumbens-thalamo-cortical circuit involving the substantia nigra pars reticulata.

Corticostriatal projections from layer V cells in rat are collaterals of long-range corticofugal axons

Corticostriatal projections arising from the infragranular layers of the motor and second somatosensory cortices were studied in rats after labeling small pools of neurons with biocytin. Camera lucida reconstruction of 263 fibers arising from laminae V and VI revealed that all corticostriatal projections derive from collaterals of lamina V cells whose main axons descend into the cerebral peduncle. In contrast, lamina VI cells do not branch upon the striatum, but upon the thalamus. Together with the results obtained in previous tracing studies, the present data raise the possibility that no neuron is exclusively corticostriatal. We therefore propose that all corticostriatal projections are collaterals given off by the axons of two types of neurons: layer V cells whose main axon project to the brainstem and/or spinal cord, and layer III cells that project to the contralateral hemisphere.

Neural dynamics in cortex-striatum co-cultures--II. Spatiotemporal characteristics of neuronal activity

Neural dynamics in organotypic cortex-striatum co-cultures grown for three to six weeks under conditions of dopamine deficiency are described. Single neuron activities were recorded intra- and extracellularly, and spatiotemporal spreading of population activity was mapped using voltage-sensitive dyes. The temporal properties of spike firing were characterized by interspike interval histograms, autocorrelation and crosscorrelation. Cortical pyramidal neurons (n = 40) showed irregular firing with a weak tendency to burst or to oscillate. Crosscorrelations revealed strong near-coincident firing and synaptic interactions. Disinhibition was a notable feature in a strongly firing cortical interneuron. Cortical activity spread in the co-culture, thus inducing an overall, homogeneous depolarization in the striatal part. Striatal cells were divided into principal cells and type I and II secondary cells. Principal cells (n = 40) were similar to those reported previously in vivo. Spiking activity ranged from irregular spiking at very low rates to episodic bursting, with an average burst duration of 1 s. Interspike intervals were single-peaked. Intracellular recordings revealed characteristic, long-lasting subthreshold depolarizations ("enabled state") that were shortened by local muscarinic receptor blockade. During prolonged time periods in the "enabled state", locally applied bicuculline induced strong firing in most principal neurons. Striatal secondary type I neurons (n = 25) showed high spiking rates, single- and double-peaked interval histograms and low-threshold, short-lasting stereotyped bursting activity and occasional rhythmic bursting. The firing of these neurons was increased by bicuculline. Crosscorrelations showed synchronization of these cells with principal cell activity. Secondary type II neurons (n = 15) revealed tonic, irregular firing patterns similar to cortical neurons, except with occasional firing in doublet spikes. We conclude that under conditions of dopamine deficiency in corticostriatal co-cultures (i) the cortex induces the "enabled" state and typical bursting mode in striatal principal neurons; (ii) principal neurons are strongly inhibited during the "enabled" state; (iii) muscarinic activity, presumably from tonically active striatal cholinergic interneurons, stabilizes the "enabled" state; (iv) striatal GABAergic interneurons receives synaptic inhibition and take part in synchronized activity among striatal principal cells. Our results favor the view of the striatum as a lateral inhibition network.

Neural dynamics in cortex-striatum co-cultures--I. anatomy and electrophysiology of neuronal cell types

An in vitro system was established to analyse corticostriatal processing. Cortical and striatal slices taken at postnatal days 0-2 were co-cultured for three to six weeks. The anatomy of the organotypic co-cultures was determined using immunohistochemistry. In the cortex parvalbumin-positive and calbindin-positive cells, which resembled those seen in vivo, had laminar distributions. In the striatum, strongly stained parvalbumin-positive cells resembling striatal GABAergic interneurons and cholinergic interneurons were scattered throughout the tissue. The soma area of these interneuron classes was larger than the average striatal soma area, thus enabling visual selection of cells by class before recording. Cortical neurons with projections to the striatum showed similar morphological features to corticostriatal projection neurons in vivo. No projections from the striatum to the cortex were found. Intracellular recordings were obtained from 94 neurons. These were first classified on the basis of electrophysiological characteristics and the morphologies of cells in each class were reconstructed. Two types of striatal secondary neurons with unique electrophysiological dynamics were identified: GABAergic interneurons (n = 17) and large aspiny, probably cholinergic, interneurons (n = 15). The electrophysiological and morphological characteristics of cortical pyramidal cells (n = 27), cortical interneurons (n = 1), as well as striatal principal neurons (n = 34), were identical to those reported for similar ages in vivo. Organotypic cortex-striatum co-cultures are therefore suitable as an in vitro system in which to analyse corticostriatal processing. The network dynamics, which developed spontaneously in that system, are examined in the companion paper.

Glutamate and Parkinson's disease

Altered glutamatergic neurotransmission and neuronal metabolic dysfunction appear to be central to the pathophysiology of Parkinson's disease (PD). The substantia nigra pars compacta--the area where the primary pathological lesion is located--is particularly exposed to oxidative stress and toxic and metabolic insults. A reduced capacity to cope with metabolic demands, possibly related to impaired mitochondrial function, may render nigral highly vulnerable to the effects of glutamate, which acts as a neurotoxin in the presence of impaired cellular energy metabolism. In this way, glutamate may participate in the pathogenesis of PD. Degeneration of dopamine nigral neurons is followed by striatal dopaminergic denervation, which causes a cascade of functional modifications in the activity of basal ganglia nuclei. As an excitatory neurotransmitter, glutamate plays a pivotal role in normal basal ganglia circuitry. With nigrostriatal dopaminergic depletion, the glutamatergic projections from subthalamic nucleus to the basal ganglia output nuclei become overactive and there are regulatory changes in glutamate receptors in these regions. There is also evidence of increased glutamatergic activity in the striatum. In animal models, blockade of glutamate receptors ameliorates the motor manifestations of PD. Therefore, it appears that abnormal patterns of glutamatergic neurotransmission are important in the symptoms of PD. The involvement of the glutamatergic system in the pathogenesis and symptomatology of PD provides potential new targets for therapeutic intervention in this neurodegenerative disorder.

Involvement of ventrolateral striatal dopamine in movement initiation and execution: a microdialysis and behavioral investigation

Previous studies have demonstrated that the ventrolateral region of the rat neostriatum is the site at which dopamine depletions produce profound motor deficits that interfere with food handling and lever pressing. In the present work, two experiments were undertaken to investigate the role of ventrolateral striatal dopamine in lever pressing. The first experiment was a detailed characterization of the motor impairments induced by injections of the neurotoxic agent 6-hydroxydopamine into the ventrolateral striatum. Behavioral output during lever pressing on a fixed ratio 5 schedule was recorded by a computerized system that measured the duration and response initiation time for each lever press. Response initiation time was defined as the time from offset of one lever press to the onset of the next one. Dopamine depletions resulting from 6-hydroxydopamine injections profoundly depressed lever pressing response rate. This deficit was largely due to a dramatic increase in the average response initiation time. Analysis of the distribution of response initiation times indicated that dopamine-depleted rats made relatively few responses with fast initiation times (e.g. 0-125 ms), and also that dopamine depletions led to a dramatic increase in the number of pauses in responding (i.e. response initiation times greater than 2.5 s). This slowing of the initiation of movement was very sensitive to the effects of dopamine depletions, and even animals with mild dopamine depletions (29.1% of control levels) showed increased initiation times. Analysis of response durations indicated that dopamine depletions resulted in a shift in the distribution of durations such that depleted rats had a modal response duration of 375-500 ms, in contrast to the control mode of 125-250 ms. There was an overall increase in average response duration among animals with more severe dopamine depletions, although rats with moderate depletions showed no change in average response duration. In the second experiment, in vivo dialysis methods were used to study the dynamic activity of ventrolateral striatal dopamine during lever pressing. During the performance of a 30-min fixed ratio 5 lever pressing session, there was a small but significant increase (20.9% above baseline) in dopamine release. There was not a linear or curvilinear correlation between lever pressing rate and increases in dopamine release. The relatively modest increase in ventrolateral striatal dopamine release during lever pressing and the lack of relation between dopamine release and behavioral output may indicate that dopamine in the ventrolateral striatum plays mainly a permissive role in lever pressing. These results suggest that ventrolateral striatal dopamine depletions in rats produce deficits in skilled motor control that are similar to the motor deficits observed in patients with Parkinson's disease.

Ventral striatopallidothalamic projection: IV. Relative involvements of neurochemically distinct subterritories in the ventral pallidum and adjacent parts of the rostroventral forebrain

Retrograde and anterograde tract-tracing studies were carried out to determine whether the capacity of the nucleus accumbens to influence the thalamic mediodorsal nucleus via ventral striatopallidothalamic connections disproportionately favors the shell over the core subterritory. After injections of Fluoro-Gold into the mediodorsal thalamic nucleus, retrogradely labeled neurons were detected in sections also processed for calbindin-D 28-kD and neurotensin immunoreactivities to facilitate identification of subterritories in the ventral pallidum. Fluoro-Gold-labeled cells were counted in series of sections cut through the ventral pallidum, rostral globus pallidus, nucleus of the vertical limb of the diagonal band, preoptic region, lateral hypothalamus, and the sublenticular gray region, including parts of the extended amygdala. Data were expressed as cells/unit area and as percentages of all labeled forebrain cells. Mediodorsal nucleus-projecting rostroventral forebrain neurons were most numerous in the ventromedial part of the subcommissural ventral pallidum and pallidal parts of the olfactory tubercle. Few were observed in the dorsolateral part of the subcommissural ventral pallidum. In addition, following injections into the ventral pallidum, anterogradely transported biotinylated dextran amine was evaluated in sections processed for calbindin or tyrosine hydroxylase immunoreactivities. Injection into the ventromedial part of the subcommissural ventral pallidum resulted in robust anterograde labeling of the medial segment of the mediodorsal nucleus and ventral tegmental area and weak labeling of the substantia nigra and subthalamic nucleus. Conversely, after injection into the dorsolateral part of the subcommissural ventral pallidum, anterograde labeling was weak in the mediodorsal nucleus and ventral tegmental area, but robust in the substantia nigra and subthalamic nucleus. The results are consistent with a predominant accumbens shell influence on the mediodorsal nucleus and with cortico-ventral striatopallidal-thalamocortical pathways that begin and end in different parts of the frontal lobe.

The placement of a striatal ibotenic acid lesion affects skilled forelimb use and the direction of drug-induced rotation

The motor consequences of excitotoxic striatal damage have been evaluated extensively in the rat, using tests of whole body motor asymmetry and of deficits in skilled paw and limb movements. However conflicting results of both the type and extent of behavioural deficits have been reported, particularly in the direction of rotation observed in response to the dopamine receptor agonist, apomorphine. The present study investigated the effect of unilateral ibotenic acid lesions in the dorsal striatum of the adult rat, placed at either anterior, posterior, medial, or lateral loci, on rotation in response to both amphetamine and apomorphine, and in the "staircase test" of skilled forelimb use. In a 2 x 2 matrix design experiment, adult female albino rats received a double unilateral lesion of 0.5 microliter 0.06 M ibotenic acid injected at each of two sites either anterior (medial and lateral), posterior (medial and lateral), medial (anterior and posterior), or lateral (anterior and posterior). Rats that received posterior lesions showed a marked ipsilateral rotation in response to both amphetamine and apomorphine, while animals receiving anterior lesions showed little ipsilateral or a slight contralateral bias. Rats receiving lateral lesions showed a marked impairment of contralateral paw use on the "staircase test," while animals with medial lesions showed no significant difference to control unoperated animals. These results confirm the somatotopic organisation of the dorsal striatum in its control of motor functions, and indicate the need to take into account the locus of an excitotoxic lesion in the design of lesion and transplantation studies if we are to achieve reliable tests of the behavioural deficits and recovery.

Delayed neuronal damage following focal ischemic injury in stroke-prone spontaneously hypertensive rats

We detected the delayed accumulation of 45Ca in the lateral part of the striatum 3 days after distal middle cerebral artery (MCA) occlusion in stroke-prone spontaneously hypertensive rats (SHRSP). However, the mechanism of delayed neuronal damage in the striatum, which is not supplied by the occluded MCA, remains unknown. The aim of this study was to evaluate whether the delayed damage involves alterations in the extracellular release of neurotransmitter monoamines and amino acids. Chronological changes in the distribution of neuronal damage were determined by 45Ca autoradiography. The microdialysis probes were inserted into either the medial or lateral part of the striatum. The dialysate content of monoamines, their metabolites and amino acids was determined by analytical techniques. 45Ca accumulation was detected only in the cortex and corpus callosum by 24 hours postischemia and extended to the pyramidal tract, thalamus and lateral portion of the striatum by 3 days. A 3-fold increase in glutamate content, and a 2-fold increase in dopamine content were observed only in the lateral part of the striatum following ischemia. The results suggest that excessive release of glutamate and dopamine is related to delayed neuronal damage that occurs in the lateral part of the striatum in this ischemic model.

Aromatic L-amino acid decarboxylase immunoreactive cells in the rat striatum: a possible site for the conversion of exogenous L-DOPA to dopamine

The efficacy of L-dihydroxyphenylalanine (L-DOPA) in ameliorating the symptoms of Parkinson's disease (PD) is attributed to its conversion to dopamine (DA) by the enzyme aromatic L-amino-acid decarboxylase (AADC) in the striatum. Although the site of this conversion in the DA-denervated striatum has yet to be identified, it has been proposed that L-DOPA could be converted to DA at non-dopaminergic sites containing AADC. In the present study, we used immunocytochemical techniques to examine the localization of AADC and DA in the striatum of rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal dopaminergic projection. In the DA-denervated striatum, we observed AADC-immunoreactive (-IR) cells with morphological characteristics similar to a class of small aspiny interneuron. Although usually obscured by a dense plexus of AADC-IR fibers, these cells could also occasionally be detected in the intact striatum. Acute administration of L-DOPA to DA-denervated animals elicited contralateral rotational behavior as well as a pronounced c-fos protein immunoreactivity in the striatum ipsilateral to the lesion. Following acute administration of L-DOPA, but not after acute saline, DA-IR cells were detected in the denervated striatum. These DA-IR cells are similar in morphology and were found in the same location as the AADC-IR cells. These results strongly suggest the existence of a class of AADC-containing striatal cells that can form DA from exogenous L-DOPA in the rat. In the DA deafferented striatum, DA produced by these cells from exogenous L-DOPA could be released to exert physiological effects on DA receptive tissue. It is possible that similar cells could contribute to the efficacy of L-DOPA in the treatment of Parkinson's disease.

The vestibular nuclei of the rat project to the lateral part of the thalamic parafascicular nucleus (centromedian nucleus in primates)

To clarify the vestibular projections to the centromedian-parafascicular nuclear complex, the Phaseolus vulgaris leucoagglutinin (PHA-L) and horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP), tracing studies have been done in rats. The data demonstrated that the lateral parafasicular nucleus received vestibular afferents mainly from the ventral part of medial vestibular nucleus, and the superior and inferior vestibular nuclei, with an ipsilateral predominance. These findings suggest the vestibular influence to the motor loop of the basal ganglia thalamocortical projections.

Augmentation of prefrontal cortical monoaminergic activity inhibits dopamine release in the caudate nucleus: an in vivo neurochemical assessment in the rhesus monkey

Prefrontal cortical modulation of caudate nucleus dopamine release was investigated in the rhesus monkey using the in vivo microdialysis technique. Reliable and stable basal caudate nucleus dopamine levels were quickly attained within hours following insertion of the dialysis probes. High-potassium (60 mM) or tetrodotoxin (10 microM) infusions significantly altered caudate nucleus dopamine levels in the dialysate indicating that measured dopamine levels reflected impulse-dependent release from the presynaptic pool. Pharmacological augmentation of monoaminergic transmission in the sulcus principalis region of the prefrontal cortex resulted in significant alterations in caudate nucleus dopamine levels. Increase of monoaminergic activity by infusion of either D-amphetamine (100 microM) or cocaine hydrochloride (100 microM) resulted in a gradual and prolonged decrease in caudate nucleus dopamine levels. Similar decreases were noticed in caudate nucleus dopamine metabolite levels. The present results indicate that in non-human primates modulation of dorsolateral prefrontal cortical monoaminergic transmission results in alterations in dopamine levels in subcortical structures. This observation may have clinical implications for therapeutic management of certain neuropsychiatric disorders, particularly schizophrenia.

Cortical stimulation induces Fos expression in striatal neurons via NMDA glutamate and dopamine receptors

Cortical electrical stimulation has been shown to induce dense and widespread Fos expression throughout the ipsilateral and contralateral striatum. This raises interest for studying the mechanisms underlying the regulation of striatal neuron activity by cortical afferents, and for elucidating the interactions with other systems. However, the receptors mediating cortical-stimulation-induced expression of Fos in striatal neurons have not been identified. This was studied in the work reported here by stimulating the cortex after administration of glutamate or dopamine receptor antagonists, or after 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal dopaminergic system. Pretreatment with the non-competitive N-methyl-D-aspartate (NMDA) glutamate receptor antagonist MK-801 led to a marked reduction in the stimulation-induced density of Fos-immunoreactive nuclei in both the medial (about 80% reduction) and lateral (about 50-60% reduction) striatum. Preadministration of the D1-selective dopamine antagonist SCH-23390 alone or in combination with the D2-selective dopamine antagonist eticlopride led to a reduction in the stimulation-induced density of Fos-positive nuclei of about 60-65% in the lateral striatum, but no significant change in the medial region. The effects of 6-OHDA lesion were less pronounced, and the stimulation-induced density of Fos-immunoreactive nuclei decreased by only about 25% in the lateral region. These results indicate that both dopamine and NMDA glutamate receptors are involved in the induction of Fos by cortical stimulation, and support the hypothesis that cortex-dopamine interactions in the lateral striatum may be functionally different from those in the medial striatum.

Ultrastructural localization of delta-opioid receptor and Met5-enkephalin immunoreactivity in rat insular cortex

The insular cortex has been implicated in the reinforcing properties of opiates as well as in the integration of responses to sensory-motor stimulation. Moreover, the delta-opioid receptor (DOR) and the endogenous opioid ligand, Met5-enkephalin (ENK) are known to be prominently distributed in insular limbic cortex. To examine the anatomical sites for opioid activation of DOR in rat insular cortex, we used immunoperoxidase for detection of an antiserum raised against a peptide sequence unique to the DOR alone, and in combination with immunogold-silver labeling for ENK. Light microscopy showed intense DOR-like immunoreactivity (DOR-LI) in pyramidal cells and interneurons in deep laminae, and in varicose processes in both superficial and deep layers of the insular cortex. Ultrastructural analysis of layers V and VI in insular cortex showed that the most prominent immunoperoxidase labeling for DOR was in dendrites. This labeling was associated with asymmetric excitatory-type junctions postsynaptic to unlabeled terminals. Dendritic DOR-LI was also distributed along selective portions of non-synaptic plasma membranes and subsurface organelles. In dually labeled sections, dendrites containing DOR-LI sometimes received synaptic input from ENK-labeled terminals or more infrequently colocalized with ENK. Other axon terminals were exclusively immunolabeled for DOR or more rarely contained both DOR and ENK immunoreactivity. Within labeled axon terminals, distinct segments of the plasma membrane and membranes of immediately adjacent synaptic vesicles showed the largest accumulation of the peroxidase reaction product for DOR. These results indicate that in rat insular cortex DOR is primarily heteroreceptive, but also serves an autoreceptive function on certain ENK-containing neurons. Our results also provide the first ultrastructural evidence that in rat insular cortex endogenous opioids interact through the DOR (1) to modulate the postsynaptic responses to other excitatory afferents and (2) to presynaptically regulate the release of other neurotransmitters. The modulatory actions on both ENK-containing and non-ENK-containing neurons may contribute significantly to the reinforcing properties of exogenous opiates acting on the DOR in limbic cortex.

The topographic distribution of the efferents from neocortical neurons is not only dependent upon where in the neocortex the cells develop. A transplantation study within one single neocortical region

It has been proposed that the distribution of efferents developed by neocortical neurons depends upon where in the neocortex the cells develop, not where they were generated. However, the capacity of diverse isocortical areas to differentiate connectional characteristics belonging to other isocortical areas has recently been questioned in several experiments using heterotopic transplantation paradigms. The present study was designed to determine whether the principle of multipotentiality is still valid within one single isocortical region. Mediolateral bands of embryonic (E16) frontal neocortex were dissected out and grafted into the left frontal cortex of neonate hosts according to either correct or inverted mediolateral orientation. Five to six months after grafting, a retrograde tracer was injected into the dorsomedial or ventrolateral left neostriatum of the host. The mediolateral distribution of the cell labeling within the transplant was then compared to that of an equivalent frontal cortical area (ECA) in control cases. The results indicate that strips of embryonic frontal neocortex transplanted according to a correct mediolateral orientation are able to develop a projection towards the host striatum whose mediolateral topographical distribution is not significantly different from that arising from the frontal neocortex of control animals. The percentages of transplant cells labeled in the medial or lateral division of the grafts were not significantly different from those found medially or laterally in the ECA in control cases. Following inversion of the mediolateral orientation of the grafts at the time of transplantation, the percentages of cells labeled in the medial or lateral division of the grafts were nearly equal whatever the site of tracer deposit within the host neostriatum. These results indicate that even within one single neocortical region the principle of areal interchangeability is not entirely validated and that the development of neocortical efferents is not only guided by extrinsic factors.

Patterns of convergence and segregation in the medial nucleus accumbens of the rat: relationships of prefrontal cortical, midline thalamic, and basal amygdaloid afferents

In the rat, fibers from the prelimbic cortex terminate in the medial nucleus accumbens. Anterior paraventricular thalamic and parvicellular basal amygdaloid fibers reached both the prelimbic cortex and the medial nucleus accumbens. All three afferent systems have an inhomogenous distribution within the nucleus accumbens, and whether or not these projections actually reach the same areas is unknown. Our aim was to evaluate the relationships of the three afferents with respect to the shell, the core, and the cell clusters of the nucleus accumbens. Double anterograde tracing and single anterograde tracing combined with immunohistochemistry for calbindin (D28k) or Nissl stain was used. Following tracer injections in the prelimbic cortex and the anterior paraventricular thalamus, a complementary (i.e., nonoverlapping) pattern of fibers was found in the shell. Thus, afferents from the prelimbic cortex are associated with cell clusters, whereas those from the anterior paraventricular thalamus avoid these cells but are affiliated with regions exhibiting weak homogeneous calbindin immunoreactivity. In the calbindin-poor patches of the core, the situation is reversed as both sets of fibers overlap. In cases with injections in the prelimbic cortex and the parvicellular basal amygdala, a pattern of overlap was seen in the shell and core. Thus, the fibers in the shell were found together in association with cell clusters, whereas regions of weak homogeneous calbindin immunoreactivity were avoided. In the core, overlap was seen in the patch compartment. Finally, with parvicellular basal amygdala/paraventricular thalamus injections, a complementary fiber organization was present in the shell, but overlap was prominent in the patches of the core. The results demonstrate that the relationships of prelimbic cortical, paraventricular thalamic, and parvicellular basal amygdaloid afferents in the nucleus accumbens vary according to their compartmental (immunohistochemical and cellular) affiliation. Compartmentalization is therefore a possible anatomical substrate for condensation or segregation of neuronal signals passing through the nucleus accumbens.

Alterations in immediate-early gene proteins in the rat forebrain induced by acute morphine injection

Injection of morphine (10 mg/kg) induced a complex immediate-early gene response in the rat forebrain, as detected with immunocytochemistry. The c-Fos protein was induced consistently in the dorsomedial caudate-putamen, the nucleus accumbens, and in midline and intralaminar nuclei of the thalamus. In some rats induction was also seen in the parietal and insular cortex and in lateral regions of the caudate-putamen. Induction was detectable, although weak, at 30 min, was maximal at 2 h, and was undetectable 3 h after injection. JunB was induced in the same regions of the caudate-putamen as found for c-Fos, but was not induced in the nucleus accumbens or thalamus. In the caudate-putamen, JunB induction was still present 3 h after injection. A considerably smaller induction of c-Jun was noted in the dorsomedial caudate-putamen and in deep neocortex. Expression of JunD was inhibited in intralaminar and midline thalamic nuclei. Increases in numbers of cells immunoreactive for a Jun-related antigen (Jra) were found in the caudate-putamen and nucleus accumbens. These results indicate a complex immediate-early gene response to acute morphine, suggesting that morphine activates or inhibits specific neurons and circuits in the forebrain.

Effects of ibotenic acid lesions of the ventral striatum and the medial prefrontal cortex on ethanol consumption in the rat

The purpose of this study was to to assess the effect on ethanol drinking of ibotenic acid lesions in the medial prefrontal cortex and the ventral striatum of female rats with continuous access to water and a 6% ethanol solution. Ibotenic acid infusions in the prefrontal cortex did not affect ethanol intake at any time, but a significant increase in water intake was observed on the third postoperative week. Ventral striatal lesions significantly increased ethanol intake during the first 2 postoperative weeks. On the third week consumption was not significantly different from vehicle-infused controls. Apparently, then, severe excitoxic injury to the ventral striatum is compatible with normal, or increased, intake of ethanol; in contrast, similar lesions reduce the intake of other drugs of abuse such as psychostimulants and opioids.

D3 and D2 dopamine receptors: visualization of cellular expression patterns in motor and limbic structures

The distribution of the D3 and D2 dopamine receptor subtypes in forebrain regions of the basal ganglia and mesocorticolimbic system was determined. This was assessed through combined fluorescent visualization of subtype selective anti-peptide antibodies for these cloned receptors and detection of their ligand recognition sites using the D2 subfamily antagonist,N-(p-aminophenethyl) spiperone (NAPS fluoroprobe). The double-labeling technique enabled direct comparison of the cloned receptor proteins and NAPS fluoroprobe binding in vitro. The application of these two methods together produced results comparable to single-labeling paradigms. Functional D3 receptors, defined as the coincident fluorescence of the D3 receptor antisera and fluoroprobe binding, were detected in the core region of the nucleus accumbens and exhibited a laminated expression pattern in the frontal cortex. D3 receptor protein was expressed robustly in neurons of the dorsolateral striatum, but showed an intense neuropil reaction in the globus pallidus. Functional D2 receptors, defined as the coincident fluorescence of the D2 receptor antisera and fluoroprobe binding, were detected in the frontal cortex and the medial shell of the nucleus accumbens. Thus, heterogeneities occurred in the cellular expression of functional D3 and D2 receptors in forebrain dopaminoceptive areas. D3 appears more related to basal ganglia and structures involved with motoric behavior, while D2 was associated with regions associated with cognitive/affective functions.

Effects of local connectivity on striatal function: stimulation and analysis of a model

Neuronal population activity was investigated by computer simulation of a network model based on the neostriatum. Three network topologies were studied, based on different assumptions about the synaptic connectivity among medium spiny neurons. In all networks neurons were interconnected by inhibitory synapses. The connectivity was either symmetric, in which case all connections between cells were reciprocal and equal in strength; or asymmetric. Simulations showed that networks with symmetric connectivity receiving randomly distributed afferent excitation produced stationary spatial activity patterns. In contrast, asymmetric connectivity in homogeneous networks produced slow travelling-wave activity across the network. We suggest that the shape of the medium spiny neurons is an important determinant of synaptic connectivity and that changes in the shape of these neurons caused by Huntington's disease would result in asymmetric connectivity. Slow travelling-wave activity produced by asymmetric connectivity in the neostriatum could explain some aspects of the choreic movement and some electromyographic features seen in Huntington's patients.

Metabolic mapping of rat striatum: somatotopic organization of sensorimotor activity

Diseases that affect the striatum produce movement disorders, for which rats have been a useful model. To determine the organization of functional, neural activity in the rat striatum related to motor activity, we used electrical stimulation of the motor cortex and [14C]deoxyglucose autoradiography. The stimulation produced movements of each of three body regions. Both the motor and somatosensory cortex were activated. Image analysis was used to objectively localize peak activation and to provide a map for further stereotaxic and localization studies. In the anterior striatum, in the dorsolateral sector, regions of peak activation were well separated for each body region: the hindlimb peak activation was dorsomedial, the forelimb ventrolateral and vibrissae medial. Also, the activation fields were larger in anterior than in posterior striatum. Furthermore, activation ipsilateral to movement was present and the peak localization was offset from peaks contralateral to movement. In addition, there were activation regions in lateral striatum where body region representations may overlap. This is the first demonstration of a global striatal somatotopy that separates the limbs and vibrissae in rats. The functional average revealed by the deoxyglucose autoradiography showed a predominant isotropic or rod-like representation of sensorimotor activity for the limbs in striatum during movement and confirms aspects of the anatomy known for the corticostriate system in primates: metabolism was 'patchy,' and extended throughout long anteroposterior domains in striatum. These extensive and patchy arrangements suggest integrative, combinational and/or associative networks.

Decortication decreases paired-pulse facilitation in the neostriatal slice of the rat

Paired-pulse facilitation, a form of short-term synaptic enhancement, occurs in the neostriatum. The present experiments were designed to determine the contributions of neostriatal afferents to the maintenance of this form of short-term facilitation. There are 3 major afferents to the neostriatum: the neocortex, the substantia nigra and the medial thalamus. Since the largest inputs into the neostriatum emanate from the neocortex and substantia nigra, the effects of unilateral decortication or unilateral dopamine depletion on paired-pulse facilitation were primarily examined. Intracellular recordings were made from neostriatal neurons in brain slices 2 weeks following unilateral decortication or dopamine-depleting lesions. Statistically significant decreases in paired-pulse facilitation of the synaptic response evoked by local stimulation occurred only after neocortical damage. In contrast, paired-pulse facilitation in neostriatal neurons ipsilateral to the dopamine depleting lesion was not significantly altered. These results indicate that the corticostriatal input is primarily responsible for neostriatal short-term synaptic facilitation.

Distribution of Fos-positive neurons in cortical and subcortical structures after picrotoxin-induced convulsions varies with seizure type

The distribution of Fos protein was mapped in rat brain following a single non-focal convulsive seizure. Single seizures were induced with intravenous picrotoxin in unhandled animals housed in isolation. Different convulsive behaviours occurred unpredictably. The least severe seizures were predominantly localised to the face, head and forelimbs, without loss of posture control (restricted seizures). The most extensive seizures affected all limbs and trunk, sometimes with falling (generalised seizures). There was a correlation between seizure behaviour and distribution of Fos induction. After restricted seizures, Fos was induced at highest levels in neocortex and piriform cortex and was prominent in entorhinal cortex, caudal-ventral caudate-putamen and amygdala. Regions of thalamus were consistently and lightly labelled, but Fos induction did not occur in hippocampus. After generalised seizures, there was Fos induction in cortex but less than after restricted seizures and, in three of four animals, also in dentate gyrus, hippocampus and subiculum. There was occasional or variable labelling of thalamus, basolateral amygdala and caudate-putamen. One animal with generalised seizures showed no hippocampal Fos induction. The findings indicate that picrotoxin induces seizures with at least two different patterns of neuronal involvement. The cortex, part of the caudate-putamen, amygdala and thalamus are involved in restricted seizures while the hippocampus, cortex and thalamus are involved in generalised seizures. The results do not support the view that generalised seizures are a progression from restricted forms. Cortical Fos involvement is entirely consistent with the participation of cortex in non-focal epilepsy. In these non-focal seizures, the dentate-hippocampus may be a source of excitation to cortex in the generalised group while the cortex appears to be the predominant site of excitation in the restricted group.

Cholinergic regulation of tachykinin- and enkephalin-gene expression in the rat striatum

Ninety-five percent of the neurons in the corpus striatum of the rat are medium spiny projection neurons, which contain tachykinins such as substance P, neurokinin A, and neurokinin B and the opiate peptides, enkephalin and dynorphin. The remaining 5% consist of interneurons, of which a small but significant proportion are cholinergic. The influence of these cholinergic interneurons on the neuropeptidergic projection systems in the striatum is poorly understood at this time. The present study explores the relationship between cholinergic receptor activation or muscarinic blockade on striatal neuropeptide gene expression. Adult male Sprague-Dawley rats were treated chronically either with a cholinergic agonist (physostigmine: 0.5 mg/kg/3 x day), a muscarinic antagonist (scopolamine HCl: 0.4 mg/kg/3 x day), or vehicle (PBS: 0.1 ml/100 g) administered for 6 days (s.c.). In situ hybridization was performed with probes directed against mRNAs for beta-preprotachykinin (a transcript containing substance P, neurokinin A, and other tachykinins), neurokinin B and preproenkephalin. Physostigmine administration resulted in a 12% decrease in the dorsolateral caudate-putamen and a 27% increase in the core of the nucleus accumbens in substance P/neurokinin A mRNA; and a 29% increase in the caudate-putamen and an 11% increase in the core of the nucleus accumbens in preproenkephalin mRNA levels. Scopolamine treatment resulted in a 28% and 48% decrease, respectively, in the caudate-putamen and in the shell of the nucleus accumbens in substance P/neurokinin A mRNA levels. Neurokinin B mRNA levels were increased by 50% in the shell of the accumbens after scopolamine. Preproenkephalin mRNA levels increased by 24% in the caudate-putamen and decreased by 20% in the core of the nucleus accumbens. From these results we tentatively conclude that cholinoceptive neuropeptidergic neurons are segregated along dorsoventral and mediolateral axes in the striatum, thus giving rise to non-homogenous responses upon cholinergic receptor activation or muscarinic blockade.

Heterogeneous and compartmental distribution of zinc in the striatum and globus pallidus of the rat

The distribution of vesicular or chelatable zinc was analysed in the dorsal and ventral subdivisions of the striatum and globus pallidus of the rat with Danscher's selenium method. Acetylcholinesterase and Calbindin-D28k were used as striatal and pallidal markers in order to analyse the possible compartmentalization of the distribution of zinc in the striatum and globus pallidus. The main findings of this study are the following: (1) The distribution of vesicular zinc in the dorsal striatum was heterogeneous. A peripheral rim of tissue heavily stained for zinc was detected in the medial, dorsal and lateral striatal areas, along most of the rostrocaudal extent of the striatum. addition, patch-like zones intensely stained for zinc were prominent in the rostral half of the caudate-putamen complex. (2) In some regions of the rostral half of the caudate-putamen complex, the staining for zinc appeared to follow the well-known striatal patches (striosomes)/matrix organization. However, in other regions of the rostral half of the striatum such a relation was not detected. (3) The ventral striatum also showed a heterogeneous staining for zinc. Thus, in the most ventral part of the caudate-putamen complex, both subdivisions of the nucleus accumbens and parts of the olfactory tubercle displayed different patterns of compartmentalized distribution of zinc. In the dorsal half of the shell of the nucleus accumbens, some patches with an intense reaction for zinc seemed to overlap with acetylcholinesterase-poor patches. (4) There was a remarkable absence of staining for zinc in the globus pallidus. This histochemical study illustrates, on the one hand, the high content of vesicular zinc in the dorsal and ventral subdivisions of the striatum, which was distributed following different patterns of chemical compartmentalization, and on the other hand, the absence of vesicular zinc in the globus pallidus of the rat.

Chronic blockade of muscarinic cholinergic receptors by systemic trihexyphenidyl (Artane) administration modulates but does not mediate the dopaminergic regulation of striatal prepropeptide messenger RNA expression

A striatal dopaminergic denervation leads to changes in the expression of messenger RNA encoding prepropeptides contained in striatal efferent neurons. Such a dopaminergic lesion also abolishes a functional equilibrium between dopaminergic and cholinergic transmissions, generally believed to operate within the neostriatum, which constitutes the theoretical basis for the clinical use of antimuscarinic drugs in extrapyramidal diseases. It is possible, therefore, that changes in prepropeptide messenger RNA expression are mediated by an alteration in cholinergic transmission. To test this hypothesis, we have examined in rats whether trihexyphenidyl, an antimuscarinic drug of wide clinical use, can counteract the changes in preproenkephalin, preprotachykinin and preprodynorphin messenger RNA expression produced by a unilateral 6-hydroxydopamine lesion of substantia nigra dopaminergic neurons. Two weeks after the lesion, trihexyphenidyl was continuously administered through an osmotic minipump (5 mg/day for 15 days) to half of the lesioned and sham-operated rats, the other half receiving the vehicle. Using quantitative in situ hybridization histochemistry, messenger RNAs were analysed at two rostrocaudal levels (anterior and central) of the neostriatum. In parallel, M1 muscarinic receptors were measured by autoradiography of [3H]pirenzepine binding sites. In sham-operated rats, trihexyphenidyl administration produced a significant increase (17-27%) in M1 binding sites. In addition, preproenkephalin messenger RNA levels were decreased (-38%) in the central part, while preprodynorphin messenger RNA levels were significantly increased (+22%) at both striatal levels. In 6-hydroxydopamine-lesioned rats, the expected changes in messenger RNAs were observed when ipsi- versus contralateral side values were compared, but changes were not always detected when comparison was established between values from the dopamine-denervated neostriatum and those from sham-operated rats. The trihexyphenidyl administration in 6-hydroxydopamine-lesioned animals was unable to reproduce the up-regulation of M1 receptors, even in the intact neostriatum. This antimuscarinic treatment further increased preproenkephalin messenger RNA levels in the denervated anterior neostriatum, amplifying the ipsi- versus contralateral difference. It also potentiated the imbalance in preprotachykinin messenger RNA expression, mainly as a result of an increase of preprotachykinin messenger RNA levels in the intact neostriatum. In contrast, trihexyphenidyl treatment by increasing preprodynorphin messenger RNA in both neostriata abolished the ipsi- versus contralateral difference observed in lesioned rats. In conclusion, with the exception of preprodynorphin messenger RNA, trihexyphenidyl treatment was unable to counteract the imbalance in prepropeptide messenger RNA expression produced by a unilateral striatal dopaminergic denervation and even amplified this effect. These results question the neostriatum as the site of action of antimuscarinic drugs in producing their therapeutic effect in extrapyramidal syndromes.

Intrastriatal and intrasubthalamic stimulation of metabotropic glutamate receptors: a behavioral and Fos immunohistochemical study

Prior work has shown that intrastriatal injection of the metabotropic glutamate receptor agonist 1S,3R-ACPD results in pronounced contralateral rotation, and the basis for this effect is thought to be increased activity of dopaminergic nigrostriatal neurons. We tested this hypothesis by determining the expression of Fos-like immunoreactivity after intrastriatal injection of 1S,3R-ACPD. Intense Fos-like immunoreactivity was noted in the globus pallidus, entopeduncular nucleus, subthalamic nucleus and substantia nigra pars reticulata. Ablation of the subthalamic nucleus 10 days prior to intrastriatal injection of 1S,3R-ACPD abolished rotational behaviour but not Fos-like immunoreactivity in the globus pallidus, entopeduncular nucleus and substantia nigra. Intrasubthalamic injection of 1S,3R-ACPD produced marked contralateral rotation and a pattern of Fos-like immunoreactivity similar to that seen after intrastriatal 1S,3R-ACPD injection. These results suggest that stimulation of striatal metabotropic glutamate receptors inhibits striatal projection neuron activity, while stimulation of subthalamic metabotropic glutamate receptors increases subthalamic nucleus activity. Increased subthalamic nucleus activity is necessary and sufficient for the expression of rotational behavior. These results also suggest that metabotropic glutamate receptor antagonists may be useful in the treatment of Parkinson's disease.

In vivo studies of extracellular metabolites in the striatum after distal middle cerebral artery occlusion in stroke-prone spontaneously hypertensive rats

BACKGROUND AND PURPOSE

We demonstrated in a previous study that 45Ca accumulation in the lateral part of the striatum was detected 3 days after distal middle cerebral artery (MCA) occlusion using a 45Ca autoradiographic technique in stroke-prone spontaneously hypertensive rats. However, the mechanism of delayed neuronal damage that occurred in the lateral part of the striatum is unknown. We examined changes in amino acids and monoamines in the striatums of rat brains after MCA occlusion in stroke-prone spontaneously hypertensive rats using an in vivo brain microdialysis technique.

METHODS

Microdialysis probes were inserted into the lateral or medial part of the striatum 24 hours before the experiment. The dialysis probe was perfused continuously at 2 microL/min with Ringer's solution, and the dialysate samples were collected every 20 minutes. After a 3-hour period for baseline stabilization, the right MCA was occluded. The dialysate count of monoamines and amino acids was determined by high-performance liquid chromatography.

RESULTS

After MCA occlusion, a threefold transient increase in glutamate was observed in the lateral part of the striatum. The level returned to its baseline value 60 minutes after MCA occlusion. Dopamine in the lateral part increased twofold to its peak value. This release persisted for 2 hours after MCA occlusion. There were no significant changes in these components in the extracellular fluid of the medial part of the striatum.

CONCLUSIONS

Our study demonstrated that changes of neurotransmitters in the lateral part of the striatum after MCA occlusion differed from those in the medial part. These results suggest that excessive release of glutamate and dopamine is related to delayed neuronal damage that occurs in the lateral part of the striatum in this model.

Complex deficits on reaction time performance following bilateral intrastriatal 6-OHDA infusion in the rat

The present study examined the ability of rats subjected to bilateral 6-hydroxydopamine lesions of the terminal area of the nigrostriatal dopamine system to perform a prelearned reaction time task. This lesion model, the induction of a partial dopamine denervation of the striatum (74% depletion of dopamine striatal tissue content) with a retrograde degeneration of dopamine cell bodies in the substantia nigra, sparing the mesolimbic dopaminergic pathway, closely approximates the neuronal degeneration observed in human idiopathic Parkinson's disease. Rats were trained previously to release a lever, within a reaction time limit, after the presentation of a visual cue through reinforcement with food pellets. The onset of the light stimulus varied randomly after an unpredictable delay period of 0.25-1.0 s. Rats with dopaminergic lesions showed moderate to extensive performance deficits which were not compensated for the five postoperative weeks. More than half of the lesioned animals (64%) showed severe deficits, characterized by a concomitant increase in the number of anticipated (premature release of the lever before the visual cue) and delayed responses (lever release after the reaction time limit) with shortened reaction times in some cases. A smaller proportion (36%) of lesioned animals exhibited mild impairment of performance with a large increase in delayed responses and lengthening of reaction times but with no change in the number of anticipated responses. Asymmetric lesions had no effect on the reaction time performance. Examination of tyrosine hydroxylase immunostaining revealed that in the most impaired animals dopamine depletion was extensive in the medial striatum, whereas it was restricted to the dorsolateral striatum in the least impaired animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptic reorganisation in the rat striatum after dopaminergic deafferentation: an ultrastructural study using glutamate decarboxylase immunocytochemistry

The ultrastructure of GABAergic and non-GABAergic synapses in the adult rat neostriatum was examined 6-8 months after unilateral removal of the nigrostriatal dopaminergic pathway by 6-hydroxydopamine injection into the medial forebrain bundle. GABAergic profiles were identified by preembedding glutamate decarboxylase (GAD) immunocytochemistry performed on parasagittal vibratome sections. In three representative fields of the striatum, the nature and number of boutons and their postsynaptic partners were determined and the differences between the striata ipsi- and contralateral to the lesion analyzed. The percentage of GAD-immunoreactive boutons was increased from 23% on the intact side to 28% on the lesioned side. In addition, the GABAergic boutons underwent significantly more multiple contacts with several independent postsynaptic profiles, preferentially with dendritic spines. This could reflect a lesion-induced sprouting of local GABAergic axon terminals. On the other hand, although the vast majority of GABAergic boutons underwent synaptic contacts with dendrites (77% vs. 80%), the number of boutons per dendrite or per dendritic circumference remained unchanged. Thus, the higher frequency of GABAergic boutons may simply reflect the loss of the dopaminergic nerve endings, without a heterosynaptic replacement by GABAergic boutons. The deafferentation also induced structural changes of the postsynaptic profiles. Some dendritic spines had a shortened neck; others were completely integrated in the dendrite which now contained a spine apparatus and was contacted by boutons with the features of axospinous synapses. The spine retraction resulted in a quantitative decrease in the number of spines. Analysis of the synaptic curvature revealed that only spines with a flat contact zone were lost. Concurrently, the number of dendrites was increased, of the GAD-containing in particular, suggesting that the denrites of GABAergic interneurons tend to elongate and/or arborize. Taken together, the results of the present study show that the dopaminergic denervation caused a remodeling of the postsynaptic neurons. The relative increase of the number of GABAergic boutons and their synaptic contacts suggests that an altered wiring of the intrinsic GABAergic system contributes to the changes in the striatal output activity.

Neurotransmitter-related gene expression in intrastriatal striatal transplants. III. Regulation by host cortical and dopaminergic afferents

Grafted striatal neurons have previously been shown to receive innervation from both the host cerebral cortex and dopaminergic substantia nigra. In the present study, we have used quantitative in situ hybridization histochemistry for striatal neuropeptide mRNAs, to determine the extent of functional integration exhibited by these two afferent systems. DARPP-32, preproenkephalin (PPE) and preprotachykinin (PPT) mRNAs were all expressed within discrete patches of the graft (termed P-regions) which corresponded well with each other on adjacent sections. Dopamine-depleting 6-OHDA lesions resulted in a marked increase in PPE mRNA levels and a concomitant decrease in PPT mRNA expression both in the remaining host striatum and in the P-regions of the graft. In a previous report [7], we have shown that cortical and dopaminergic afferents to the striatum interact in the regulation of PPE mRNA expression, such that in the absence of functional dopaminergic inputs, intact prefrontal corticostriatal afferents are necessary in order to maintain increased PPE mRNA levels. In the present study, we observed that cortical knife cut lesions placed at the level of the foreceps minor in previously 6-OHDA-lesioned animals resulted in a normalization of PPE mRNA expression, not only in the remaining host striatum but also within the P-regions of striatal grafts. Cellular analysis showed that this normalization was most pronounced in the peripherally situated P-regions (along the graft borders), which are known to receive dense host-derived cortical input. The cortical lesions had no significant effect on the 6-OHDA-induced reduction of PPT mRNA levels neither in the remaining lost striatum nor in the striatal graft. The expression of DARPP-32 mRNA in the remaining host striatum or striatal graft was not affected by either 6-OHDA lesion or cortical transection, demonstrating the specificity of the cortical lesion effect. These results indicate that both cortical and dopaminergic afferents originating in the host, functionally regulate neuropeptide mRNA expression within the striatal grafts, and that the two afferent systems interact with each other in the regulation of enkephalin gene expression in grafted neurons. On basis of recent results [9] showing that the enkephalin-expressing neurons are identical, at least in part, to efferent graft neurons projecting to the host globus pallidus, it is proposed that the cortical-dopamine interaction demonstrated here may play an important role in the recovery of complex motor performance induced by the striatal transplants.

Organization of the avian "corticostriatal" projection system: a retrograde and anterograde pathway tracing study in pigeons

Birds have well-developed basal ganglia within the telencephalon, including a striatum consisting of the medially located lobus parolfactorius (LPO) and the laterally located paleostriatum augmentatum (PA). Relatively little is known, however, about the extent and organization of the telencephalic "cortical" input to the avian basal ganglia (i.e., the avian "corticostriatal" projection system). Using retrograde and anterograde neuroanatomical pathway tracers to address this issue, we found that a large continuous expanse of the outer pallium projects to the striatum of the basal ganglia in pigeons. This expanse includes the Wulst and archistriatum as well as the entire outer rind of the pallium intervening between Wulst and archistriatum, termed by us the pallium externum (PE). In addition, the caudolateral neostriatum (NCL), pyriform cortex, and hippocampal complex also give rise to striatal projections in pigeon. A restricted number of these pallial regions (such as the "limbic" NCL, pyriform cortex, and ventral/caudal parts of the archistriatum) project to such ventral striatal structures as the olfactory tubercle (TO), nucleus accumbens (Ac), and bed nucleus of the stria terminalis (BNST). Such "limbic" pallial areas also project to medialmost LPO and lateralmost PA, while the hyperstriatum accessorium portion of the Wulst, the PE, and the dorsal parts of the archistriatum were found to project primarily to the remainder of LPO (the lateral two-thirds) and PA (the medial four-fifths). The available evidence indicates that the diverse pallial regions projecting to the striatum in birds, as in mammals, are parts of higher order sensory or motor systems. The extensive corticostriatal system in both birds and mammals appears to include two types of pallial neurons: 1) those that project to both striatum and brainstem (i.e., those in the Wulst and the archistriatum) and 2) those that project to striatum but not to brainstem (i.e., those in the PE). The lack of extensive corticostriatal projections from either type of neuron in anamniotes suggests that the anamniote-amniote evolutionary transition was marked by the emergence of the corticostriatal projection system as a prominent source of sensory and motor information for the striatum, possibly facilitating the role of the basal ganglia in movement control.

Cerebral blood flow and glucose metabolism of the ischemic rim in spontaneously hypertensive stroke-prone rats with occlusion of the middle cerebral artery

To determine acute postischemic metabolic changes of the ischemic rim under conditions of poor collateral circulation, we examined cerebral blood flow and glucose metabolism in the area of the brain around the ischemic tissue in 36 male spontaneously hypertensive stroke-prone rats (SHRSP) in the acute stage of focal ischemia. The right middle cerebral artery (MCA) was occluded dorsal to the rhinal fissure. Four hours after occlusion, local cerebral blood flow (LCBF), glucose content (LCGC), and glucose utilization (LCGU) were measured by quantitative autoradiographic techniques. The lumped constant was determined from the corresponding LCGC. LCBF showed a widespread and marked decrease in the cortex surrounding the ischemic core, in the thalamus, and in the medial portion of the striatum in the MCA-occluded hemisphere, while the lateral segment of the striatum showed an increase of 36%, compared with findings on the contralateral side. LCGC showed little regional variation, but there was an increase of 38% in the zone bordering the ischemic area. LCGU at the cortex surrounding the ischemic core and in the external capsule showed an increase of 55%. The cortex surrounding the ischemic core, the thalamus, and the lateral segment of the striatum in the MCA-occluded hemisphere showed significant decreases in LCGU. It has been speculated that a high accumulation of glucose reflects a demand for glucose for anaerobic glycolysis in the border areas and that such a demand is probably greater in cases of impaired oxygen delivery due to the presence of microcirculatory disturbances in the MCA-occluded SHRSP.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic treatment with dizocilpine maleate increases the number of striatal neurons expressing the D2 receptor gene

N-methyl-D-aspartate antagonists have been proposed as potential therapeutic agents in different neurological diseases, including Parkinson's disease. The effects of gene expression of a chronic treatment with the non-competitive N-methyl-D-aspartate antagonist, dizocilpine maleate (0.8 mg/kg day, per os for 50 days) were analysed in rat striata. Using quantitative in situ hybridization, we measured the messenger RNA expression of the genes encoding D1, D2 dopamine receptors, N-methyl-D-aspartate receptor 1 subunit of N-methyl-D-aspartate receptor, preproenkephalin A and substance P. Chronic treatment with dizocilpine maleate induced a moderate but significant increase in messenger RNA of the N-methyl-D-aspartate receptor 1 subunit in the striatum and the adjacent cortex, suggesting an action of dizocilpine maleate in these two regions. This treatment did not induce any change in D1 receptor, preproenkephalin A or substance P messenger RNA content in the striatum, whereas D2 receptor messenger RNA was increased in the striatum of treated rats. Microscopic analysis revealed that it was the number of medium-sized neurons expressing D2 receptor messenger RNA that was significantly enhanced, while the mean amount of message per cell remained unchanged. These results demonstrate that glutamate via N-methyl-D-aspartate receptors, regulates the D2 receptor gene in striatal neurons. A chronic treatment with dizocilpine maleate increases the number of striatal neurons expressing the D2 receptor gene, suggesting a recruiting phenomenon.

Quinolinic acid-induced increases in calbindin D28k immunoreactivity in rat striatal neurons in vivo and in vitro mimic the pattern seen in Huntington's disease

In Huntington's disease striatal neurons undergo marked changes in dendritic morphology and coincidently exhibit an increase in immunoreactive calbindin D28k (calbindin), a cytosolic calcium-binding protein which is highly abundant in these neurons. Previous studies in the rat striatum have shown that excitotoxic injury, which is linked to a rise in intracellular Ca2+, mimics many of the neurochemical and neuropathological characteristics of Huntington's disease. We speculated, therefore, that the apparent increase in calbindin labeling in Huntington's disease spiny neurons may signal the response to an excitotoxic process. To investigate this possibility, we compared the cellular features of calbindin immunoreactivity in grade 1-4 Huntington's disease cases with those seen in rat striatal neurons in vivo and in vitro following treatment with N-methyl-D-aspartate (NMDA) receptor agonist, quinolinic acid. In human post mortem control cases calbindin immunoreactivity was seen primarily in the somata and proximal dendrites of striatal neurons. In the Huntington's disease cases, calbindin labeling was markedly increased throughout the second and third order dendrites and in spines, and this change was more prevalent in advanced cases (grades 3-4). In the rat brain, two weeks after intrastriatal injection of quinolinic acid (6-20 ng), surviving medium-spiny neurons in the transition zone around the lesion core exhibited a marked increase in calbindin immunoreactivity similar to that seen in Huntington's disease spiny neurons. In more peripheral areas away from the lesion and on the contralateral unlesioned side, calbindin immunostaining was confirmed to somata and proximal dendrites. In situ hybridization histochemistry with an 35S-labeled oligonucleotide probe showed no change or a decrease in calbindin mRNA levels in neurons within the transition zone, suggesting that the observed increase in calbindin staining was not the result of increased transcription. In 12 day old postnatal striatal cultures, 2-6 h exposures to quinolinic acid (0.5 mM) significantly increased the length of neurites exhibiting calbindin immunoreactivity when compared to untreated controls. This effect was blocked by the selective NMDA receptor blocker (+/-)-2-amino-5-phosphonopentanoic acid (AP-5), indicating that an NMDA receptor-mediated mechanism contributed to the change in staining pattern. Results in rats suggest that the subcellular redistribution of calbindin immunoreactivity observed in Huntington's disease spiny neurons may be related to an NMDA receptor-induced excitotoxic process. An increased availability of calbindin protein at dendrites and spines may reflect a greater demand for Ca2+ buffering precipitated by an abnormal rise in in intracellular Ca2+.

D1 and D2 dopamine receptors differentially increase Fos-like immunoreactivity in accumbal projections to the ventral pallidum and midbrain

Alterations in dopaminergic neurotransmission have profound effects on neuronal expression of the putative activity marker, Fos, in both the dorsal and ventral striatum. Stimulants such as D-amphetamine and cocaine increase Fos-like immunoreactivity by enhancing the activation of D1 dopamine receptors. In contrast, neuroleptics such as haloperidol and raclopride increase Fos-like immunoreactivity by blocking striatal D2 dopamine receptors. In the dorsal striatum, D1 receptor stimulation elevates Fos-like immunoreactivity predominantly in neurons projecting to the midbrain (substantia nigra), whereas D2 receptor antagonism enhances Fos-like immunoreactivity principally in neurons projecting to the pallidum (globus pallidus). These findings are consistent with the proposal that D1 receptors are located chiefly on striatonigral neurons, whereas D2 receptors reside mainly on striatopallidal neurons. Since the nucleus accumbens (largest component of the ventral striatum) also sends projections to the midbrain (ventral tegmental area and substantia nigra) and pallidum (ventral pallidum), the present study utilized retrograde tract-tracing techniques to determine if there was a similar segregation of D1 agonist- and D2 antagonist-induced Fos-like immunoreactivity in these accumbal projections. In addition, we examined whether these relationships were the same in the core and shell regions of the nucleus accumbens. Like the dorsal striatum, D1 agonists (D-amphetamine and CY 208-243), but not D2 antagonists (haloperidol and clozapine), increased Fos-like immunoreactivity in accumbal neurons projecting to the midbrain (ventral tegmental area and substantia nigra). Also like the dorsal striatum, D2 antagonist-induced Fos-like immunoreactivity was located preferentially in accumbal neurons projecting to the pallidum (ventral pallidum). However, unlike the dorsal striatum, where the vast majority of neurons which display D1 agonist-induced Fos-like immunoreactivity project to the midbrain, nearly 50% of those neurons in the nucleus accumbens which were Fos-immunoreactive after D-amphetamine or CY 208-243 projected to the ventral pallidum. Thus, a similar number of accumbal neurons which expressed D1 agonist-induced Fos-like immunoreactivity were retrogradely labelled from the midbrain and ventral pallidum. Accumbal projections to the midbrain and ventral pallidum were retrogradely labelled with different retrograde tracers in order to determine the degree of collateralization between these pathways. Approximately 20% of retrogradely labelled neurons displayed both tracers, indicating that collateralization and damage to fibres of passage could not account for all of those cases in which D1 agonist-induced Fos-like immunoreactivity was detected in accumbal neurons projecting to the ventral pallidum.(ABSTRACT TRUNCATED AT 400 WORDS)

Noradrenergic regulation of immediate early gene expression in rat forebrain: differential effects of alpha 1- and alpha 2-adrenoceptor drugs

Noradrenergic (NAergic) transmission in the rat cerebral cortex has recently been shown to be involved in the regulation of the basal expression of NGFI-A, an immediate early gene (IEG) which encodes a zinc-finger transcription factor. The present study further investigated the role of the NAergic system in mediating cortical IEG expression and possible topographical changes in expression of NGFI-A mRNA in rat forebrain after alpha 1- and alpha 2-adrenoceptor (AR) agonist and antagonist treatment. Expression of c-fos and c-jun, which encode leucine-zipper class transcription factors, was also studied. Male Sprague-Dawley rats were injected intraperitoneally with either an alpha 1-AR agonist (methoxamine, 5 or 10 mg/kg); an alpha 1-AR antagonist (prazosin, 5 mg/kg); an alpha 2-AR agonist (clonidine, 0.5 mg/kg); or an alpha 2-AR antagonist (methoxyidazoxan, 5 mg/kg) and killed after 1 h. IEG mRNA levels were detected by quantitative in situ hybridization histochemistry using 35S-labelled oligonucleotides. High basal levels of NGFI-A mRNA were present in cortical layers IV and VI, hippocampal CA1, piriform cortex, amygdala and caudate putamen. alpha 1-AR agonist and antagonist treatment had essentially no effect on IEG mRNA, despite producing characteristic behavioral and peripheral effects at the doses used. Methoxyidazoxan significantly increased (mean%) NGFI-A mRNA in: cerebral cortex (44); caudate putamen (82); amygdala (92); and CA1 of hippocampus (48), while clonidine significantly decreased NGFI-A mRNA in the various cortical layers to a similar extent (27-37%). Basal c-fos mRNA expression was lower than that for NGFI-A in forebrain areas including cortex, caudate putamen and hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional repair of striatal systems by neural transplants: evidence for circuit reconstruction

Intrastriatal grafts of nigral and adrenal tissues have been found to be effective in alleviating many of the simple motor and sensorimotor deficits associated with lesions of the nigrostriatal dopamine system. However, the mechanisms by which such grafts exert their effects may be less specific than originally conceived, and both pharmacological and trophic actions play an essential role. Damage to intrinsic cortico-striatal circuits are unlikely to prove similarly amenable to such diffuse mechanisms of repair. Nevertheless, striatal grafts have been found to alleviate cognitive and motor deficits after excitotoxic lesions of the neostriatum. Accumulating evidence suggests that in this particular case many aspects of functional recovery may indeed be attributable to the striatal grafts providing an effective functional reconstruction of damaged neuronal circuits within the host brain.

Effect of subthalamic nucleus lesion on mitochondrial enzyme activity in rat basal ganglia

The subthalamic nucleus (STN) plays a major role in the control of basal ganglia output, and its overactivity may be central to the symptoms of Parkinson's disease. In order to elucidate the functional relationship between STN and its projection nuclei, we studied the short-term (1 week) effect of a selective lesion of STN on the activity of succinate dehydrogenase (SDH) and cytochrome oxidase (CO), two markers of neuronal activity, in the basal ganglia of rats. STN ablation induced a discrete reduction of oxidative metabolism, ipsilaterally to the lesion, in substantia nigra pars reticulata and globus pallidus, the rodent homologue of lateral globus pallidus. Such changes, ascribable to the interruption of the STN excitatory output to these nuclei, were present after 24 h and remained stable, or increased, throughout the observation period. A transitory, ipsilateral decrease was also observed in the caudate-putamen and the somato-sensory cortex, likely due to involvement of polysynaptic pathways. SDH and CO activity were always altered in the same areas, but SDH changes were more pronounced and occurred more rapidly. These results shed further light on the role played by STN in the control of basal ganglia output.

Excitotoxic lesions of the core and shell subregions of the nucleus accumbens differentially disrupt body weight regulation and motor activity in rat

The behavioral effects of bilateral N-methyl-D-aspartate (NMDA) lesions of the core and medial shell subregions of the nucleus accumbens were evaluated in rats. Body weight was monitored for 2 weeks following surgery. Locomotor activity and open field behavior were recorded 1 week after surgery. The core-lesion group had difficulty recovering from the lesion and had significantly lower weights throughout the experiment. The shell-lesion group had normal recovery and weighed significantly more than controls over the course of the experiment. In the activity cage test, the core-lesion group was hyperactive when compared to controls and to the shell-lesion group. Activity of the shell-lesion group was similar to that of their sham-controls. Three weeks postlesion, the core-lesion group was still significantly more active. In the open field test, peripheral locomotion scores were significantly higher in the core-lesion group when compared to their controls, whereas the scores of the shell-lesion group were similar to controls. In the other open field measures, both lesion groups were hyperactive; however, the scores of core-lesion group were significantly higher than those of the shell-lesion group on all measures. Histological analysis indicated small, discrete areas of damage within the core or medial shell accumbens regions. These preliminary results suggest that these two subregions can be behaviorally differentiated.

Mapping of globus pallidus and ventral pallidum lesions that produce hyperkinetic treading

The purpose of this study was to identify sites where striatopallidal lesions produce two distinct sensory-triggered hyperkinetic syndromes: (1) exaggerated forelimb treading alone to oral taste infusions and (2) sensorimotor exaggerated treading plus enhanced aversive reactions to taste infusions. The behavioral characteristics of these syndromes have been described previously (Berridge, K.C. and Cromwell, H.C., Behav. Neurosci., 104 (1990) 778-795). Bilateral excitotoxin lesions were made using quinolinic acid (10 micrograms in 1 microliter) in the caudate/putamen, nucleus accumbens, globus pallidus or ventral pallidum/substantia innominata. In order to identify the precise center, borders, severity and size of lesion sites that caused these hyperkinetic treading syndromes, neuron counts (modified fractionator technique) and glial fibrillary acidic protein immunoreactivity (GFAP-IR) densitometry were used in a stereological mapping analysis. The site of lesions that produced the hyperkinetic treading syndrome without enhanced aversion was found to be restricted to the globus pallidus (GP). Damage exceeding 60% neuron loss bilaterally within a 0.8 x 1.0 x 1.0 mm subregion of the ventromedial GP produced this syndrome. The site of lesions that produced the combined syndrome of hyperkinetic treading and aversive enhancement was ventral to the globus pallidus, within the ventral pallidum/substantia innominata (VP/SI). Damage exceeding 70% neuron loss bilaterally within a 1.0 x 0.5 x 1.0 mm diameter subregion of the ventromedial ventral pallidum/substantia innominata produced this syndrome. This subterritory was located immediately lateral to the border of the lateral hypothalamus. Bilateral lesions to the caudate/putamen or nucleus accumbens did not produce either hyperkinetic treading syndrome. These results are discussed in terms of the connectivity of the ventral pallidal/substantia innominata and globus pallidus regions and in terms of neuropathological models of hyperkinetic disorders.

Behavioural consequences of neural transplantation

Neural grafts can reverse many functional deficits associated with brain damage, whether of traumatic, toxic, neurodegenerative or genetic origin. In some model systems recovery can be partial or complete; whereas in others the grafts have limited effects or may actually cause further dysfunction. In order to devise rational and effective transplantation strategies it is necessary to understand the mechanisms by which grafts exert their functional effects. Several alternatives have been proposed, and these include non-specific consequences of surgery, acute diffuse neurotrophic and growth mechanisms, chronic diffuse release of deficient neurochemicals, bridging tissues for host regeneration, diffuse reinnervation of the host brain, and reciprocal graft-host reconnection. These alternative mechanisms are not necessarily exclusive in any particular situation, and all have been seen to apply in different model systems.

Long-term behavioral recovery in parkinsonian rats by an HSV vector expressing tyrosine hydroxylase

One therapeutic approach to treating Parkinson's disease is to convert endogenous striatal cells into levo-3,4-dihydroxyphenylalanine (L-dopa)-producing cells. A defective herpes simplex virus type 1 vector expressing human tyrosine hydroxylase was delivered into the partially denervated striatum of 6-hydroxydopamine-lesioned rats, used as a model of Parkinson's disease. Efficient behavioral and biochemical recovery was maintained for 1 year after gene transfer. Biochemical recovery included increases in both striatal tyrosine hydroxylase enzyme activity and in extracellular dopamine concentrations. Persistence of human tyrosine hydroxylase was revealed by expression of RNA and immunoreactivity.