Regional differences in the sensitivity of cholinergic neurons to dopaminergic drugs and quipazine in the rat striatum

Mu opioid control of the N-methyl-D-aspartate-evoked release of [3H]-acetylcholine in the limbic territory of the rat striatum in vitro: diurnal variations and implication of a dopamine link

Using an in vitro microsuperfusion procedure, the release of newly synthesized [(3)H]-acetylcholine (ACh), evoked by N-methyl-D-aspartate (NMDA) receptor stimulation, was investigated in striosome-enriched areas and matrix of the rat striatum. The role of micro-opioid receptors, activated by endogenously released enkephalin, on the NMDA-evoked release of ACh was studied using the selective micro-opioid receptor antagonist, beta-funaltrexamine. Experiments were performed 2 (morning) or 8 (afternoon) h after light onset, in either the presence or absence (alpha-methyl-p-tyrosine, an inhibitor of dopamine synthesis) of dopaminergic transmission. As expected, based on the presence of micro-opioid receptors in striosomes, beta-funaltrexamine (0.1 nM, 10 nM and 1 microM) enhanced the NMDA (1 mM+10 microM D-serine)-evoked release of ACh in striosome-enriched areas but not in the matrix. Interestingly, these responses were significantly more pronounced in afternoon than in morning experiments. In the presence of alpha-methyl-p-tyrosine, the NMDA-evoked release of ACh was increased with similar amplitude in morning and afternoon experiments. However, in this condition (without dopamine transmission), the facilitatory effects of beta-funaltrexamine on the NMDA-evoked release of ACh were suppressed totally in the morning and only partially in the afternoon. The selective micro-opiate agonist, [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (1 microM, coapplied with NMDA), was without effect on the NMDA-evoked release of ACh but abolished both dopamine-dependent (morning) and dopamine-independent (afternoon) responses of beta-funaltrexamine (10 nM and 1 microM).Therefore, in the limbic territory of the striatum enriched in striosomes, the micro-opioid-inhibitory regulation of ACh release follows diurnal rhythms. While dopamine is required for this regulation in the morning and the afternoon, an additional dopamine-independent process is present only in the afternoon.

N-methyl-D-aspartate-evoked release of [3H]acetylcholine in striatal compartments of the rat: regulatory roles of dopamine and GABA

The N-methyl-D-aspartate-evoked release of [3H]acetylcholine previously formed from [3H]choline was estimated in striosome- (identified by [3H]naloxone binding) or matrix-enriched areas of the rat striatum using an in vitro microsuperfusion procedure. Experiments were performed in either the absence or the presence of dopaminergic and/or GABAergic receptor antagonists. Although the cell bodies of the cholinergic interneurons were mainly found in the matrix, in the absence of magnesium, N-methyl-D-aspartate (50 microM) stimulated the release of [3H]acetylcholine in both striatal compartments. These responses were blocked by either magnesium, dizocilpine maleate, 7-chlorokynurenate or tetrodotoxin. N-Methyl-D-aspartate responses were concentration-dependent, but the 1 mM N-methyl-D-aspartate response was higher in striosomes than in the matrix. The co-application of D-serine (10 microM) enhanced the 10 microM N-methyl-D-aspartate response in both compartments, but reduced those induced by 1 mM N-methyl-D-aspartate, this reduction being higher in striosomes. The blockade of dopaminergic transmission with the D2 and D1 dopaminergic receptor antagonists, (-)-sulpiride (1 microM) and SCH23390 (1 microM), was without effect on the 50 microM N-methyl-D-aspartate-evoked release of [3H]acetylcholine, but markedly enhanced the 1 mM N-methyl-D-aspartate+D-serine-evoked response in striosomes and to a lesser extent in the matrix. Disinhibitory responses of similar amplitude were observed not only in striosomes but also in the matrix when (-)-sulpiride was used alone, while SCH23390 alone enhanced the 1 mM N-methyl-D-aspartate+D-serine response only in striosomes and to a lower extent than (-)-sulpiride. These results indicate that D2 receptors are mainly involved in the inhibitory effect of dopamine on the 1 mM N-methyl-D-aspartate+D-serine-evoked release of [3H]acetylcholine. They also show that the stimulation of D1 receptors can either reduce (striosomes) or enhance (matrix) this response, since in the latter case the effect induced by the combined application of the D1 and D2 receptor antagonists was smaller than that observed with the D2 receptor antagonist alone. Indicating that released GABA facilitates N-methyl-D-aspartate responses, the blockade of GABAA receptors with bicuculline (5 microM) reduced the 50 microM N-methyl-D-aspartate-evoked release of [3H]acetylcholine in both striatal compartments and the 1 mM N-methyl-D-aspartate+D-serine response in the matrix. These effects result from an inhibition by GABA of the evoked release of dopamine, since the reducing effects of bicuculline on N-methyl-D-aspartate responses were not observed under the complete blockade of dopaminergic transmission by the D1 and D2 receptor antagonists. Further demonstrating a facilitatory role of GABA in the control of N-methyl-D-aspartate-evoked release of [3H]acetylcholine, in the presence of bicuculline, (-)-sulpiride and SCH23390 alone or in combination enhanced, in both compartments, the responses induced not only by 1 mM N-methyl-D-aspartate+D-serine, but also by 50 microM N-methyl-D-aspartate.

Cholinergic innervation in the human striatum: a three-compartment model

The mammalian striatum is divided into compartments that are anatomically and neurochemically distinct. The dorsal striatum has been described as containing two compartments, striosomes and matrix, while the ventral striatum is thought to have a more complex, multi-compartmental organization. In this study, we sought to characterize the compartmentalization of the dorsal and ventral portions of the human striatum using choline acetyltransferase as a marker. Image analysis was used to assess relative densities of immunostaining, and three distinct, choline acetyltransferase-immunostained compartments were demonstrated: intensely immunostained, moderately immunostained and weakly immunostained areas. The dorsomedial portion of the striatum was made up of moderately immunostained regions embedded within a densely immunostained background, thus manifesting the characteristic striosome/ matrix organization of the dorsal striatum. However, the ventral and lateral two-thirds of the striatum were made up of a mixture of densely immunostained, moderately immunostained and weakly immunostained areas, with the moderately immunostained region forming the bulk of the background tissue, and smaller, densely immunostained and weakly immunostained regions embedded within it. These compartments were compared to regions defined by distinct levels of acetylcholinesterase immunostaining in adjacent sections; the staining patterns produced by the two cholinergic markers were found to be identical except in some portions of the nucleus accumbens, where acetylcholinesterase immunostaining was found to be more intense than choline acetyltransferase immunostaining. The immunoreactive somata were mapped within sections stained for choline acetyltransferase taken from different rostrocaudal levels of the striatum, and the distributions and densities of immunoreactive somata within these three cholinergic compartments were determined. In general, the densities of cholinergic somata roughly correlated with immunostaining intensity of regions, e.g. the most intensely immunostained compartment also had the highest densities of cholinergic somata. However, in the rostroventral striatum, the densities of cholinergic somata in the weakly immunostained compartment roughly equalled the densities of cholinergic somata in the moderately immunostained compartment, suggesting that local axonal arborizations of cholinergic cells may differ in density or orientation between the two compartments, or, alternatively, that some of the cholinergic cells in the weakly immunostained compartment may project outside of the striatum. The large proportion of striatum displaying ventral striatal characteristics (a complex, multi-compart-mental organization) in humans relative to that observed in other mammals suggests that the role of the ventral striatum may be expanded and more highly differentiated in the human brain.

Serotonergic modulation of cholinergic function in the central nervous system: cognitive implications

Accumulating evidence suggests that serotonin may modulate cholinergic function in several regions of the mammalian brain and that these serotonergic/cholinergic interactions influence cognition. The first part of this review is an overview of histological, electrophysiological and pharmacological (in vitro, in vivo) data indicating that, in several brain regions (e.g., hippocampus, cortex and striatum), there are neuroanatomical substrates for a serotonergic/cholinergic interaction, and that alterations in serotonergic activity may induce functional changes in cholinergic neurons. In the second part, the review focuses on experimental approaches showing or suggesting that central cholinergic and serotonergic mechanisms are cooperating in the regulation of cognitive functions. These arguments are based on lesion, intracerebral grafting and pharmacological techniques. It is concluded that not all mnesic perturbations induced by concurrent manipulations of the serotonergic and cholinergic systems can be attributed to a serotonergic modification of the cholinergic system. The cognitive faculties of an organism arise from interactions among several neurotransmitter systems within brain structures such as, for instance, the hippocampus or the cortex, but also from influences on memory of other general functions that may involve cerebral substrates different from those classically related to mnesic functions (e.g., attention, arousal, sensory accuracy, etc.).

Effects of central cholinergic blockade on striatal dopamine release measured with positron emission tomography in normal human subjects

Previously we demonstrated that positron emission tomography (PET) can be used to measure changes in the concentrations of synaptic dopamine and acetylcholine. Whether induced directly or indirectly through interactions with other neurotransmitters, these studies support the use of PET for investigating the functional responsiveness of a specific neurotransmitter to a pharmacologic challenge. In an extension of these findings to the human brain, PET studies designed to measure the responsiveness of striatal dopamine release to central cholinergic blockade were conducted in normal male volunteers using high-resolution PET and [11C]raclopride, a D2-dopamine receptor antagonist. [11C]Raclopride scans were performed prior to and 30 min after systemic administration of the potent muscarinic cholinergic antagonist, scopolamine (0.007 mg/kg). After scopolamine administration, [11C]raclopride binding decreased in the striatum (specific binding) but not in the cerebellum (nonspecific binding) resulting in a significant decrease, exceeding the test/retest variability of this ligand (5%), in the ratio of the distribution volumes of the striatum to the cerebellum (17%). Furthermore, scopolamine administration did not alter the systemic rate of [11C]raclopride metabolism or the metabolite-corrected plasma input function. These results are consistent not only with the known inhibitory influence that acetylcholine exerts on striatal dopamine release but also with our initial 18F-labeled N-methylspiroperidol and benztropine studies. Thus these data support the use of PET for measuring the functional responsiveness of an endogenous neurotransmitter to an indirect pharmacologic challenge in the living human brain.

Serotonin regulation of neostriatal tachykinins following neonatal 6-hydroxydopamine lesions

In order to determine whether dopamine mediates the effects of serotonin on tachykinin biosynthesis in the neostriatum, serotonin neurotransmission was altered following depletion of dopamine. Neonatal rats received intracisternal injections of saline or the dopamine neurotoxin 6-hydroxydopamine (6HD). This lesion caused significant reductions in the neostriatum of substance P-like immunoreactivity as well as levels of mRNA coding for preprotachykinin (PPT; the prohormone precursor to tachykinins substance P, neurokinin A and related peptides). Two months later, rats were treated for 5-6 days with saline or the serotonin-uptake inhibitor, zimelidine. Zimelidine treatment of unlesioned animals significantly increased PPT mRNA levels in the neostriatum. However, zimelidine treatment failed to increase PPT mRNA content in 6HD-treated animals. By contrast, neostriatal substance P-like immunoreactivity was restored by zimelidine treatment of 6HD-lesioned animals. These results suggest that an intact nigrostriatal pathway may be required for serotonin neurotransmission to alter PPT mRNA levels in the neostriatum. However, neostriatal tachykinins may be regulated by direct serotonin innervation.

Representation of the body by single neurons in the dorsolateral striatum of the awake, unrestrained rat

Single cell recordings in awake monkeys and cats have demonstrated that individual body parts are represented within striatal subregions receiving projections from somatic sensorimotor cortex. Literature indicating that the lateral striatum of the rat receives similar cortical inputs and subserves sensorimotor functions prompted a study of whether this subregion contains similar representations of the body. Single cell recordings were obtained from 923 neurons of 24 awake, unrestrained rats. Of 788 neurons categorized according to body part, 264 (34%) discharged in relation to active movement, passive manipulation, and/or cutaneous stimulation of a particular part of the body; the remainder were related to global, whole body movement (38%) or were unresponsive (28%). Neurons related to individual body parts were recorded throughout the entire anterior-posterior extent of the dorsolateral striatum (+1.60 to -2.12 mm A-P, from bregma), intermingled among each other in all 3 dimensions. Two topographic arrangements were observed. First, neurons that fired rhythmically, in phase with low frequency (5-6 Hz) whisking of the vibrissae were segregated in the caudal striatum (-0.2 to -2.12 mm A-P) from neurons related to other body parts, which were distributed from +1.6 to -0.8 mm A-P. Second, representations of the head and face were located ventral to those of the limbs, despite substantial overlap in their overall distributions. A prominent feature of individual electrode tracks was the clustering together of cells related to the same body part. Neurons related to body parts exhibited substantial diversity, which took several distinct forms. Some neurons fired during movement or sensory stimulation in any direction, whereas others showed selectivity for a particular direction. Certain neurons responded to sensory stimulation of a large unilateral region of the body (e.g., all vibrissae or the entire forelimb), whereas others responded to stimulation of highly restricted regions (e.g., a single vibrissa or a single forepaw digit). Finally, neurons differed in the extent to which they exhibited active and passive properties. Among vibrissae-related neurons, one group fired rhythmically during whisking but did not respond to sensory stimulation of the vibrissae; a second group responded to sensory stimulation of the vibrissae but did not fire rhythmically during whisking; a third group showed both properties. Among limb-related neurons, firing during active movement was a property of every cell; none showed sensory responsiveness without showing a relation to active movement of one limb. Of the limb-related neurons, 89% tested responded to passive manipulation of the limb to which the neuron was actively related, and 71% also responded to cutaneous stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Recombinant human nerve growth factor is biologically active and labels novel high-affinity binding sites in rat brain

Iodinated recombinant human nerve growth factor (125I-rhNGF) stimulated neurite formation in PC12 cell cultures with a half-maximal potency of 35-49 pg/ml, compared with 39-52 pg/ml for rhNGF. In quantitative ligand autoradiography, the in vitro equilibrium binding of 125I-rhNGF to brain sections showed a 10-fold regional variation in density and was saturable, reversible, and specifically displaced by up to 74% with rhNGF or murine NGF (muNGF). At equilibrium, 125I-rhNGF bound to these sites with high affinity (Kd 52-85 pM) and low capacity (Bmax less than or equal to 13.2 fmol/mg of protein). Calculation of 125I-rhNGF binding affinity by kinetic methods gave average Kd values of 24 and 31 pM. Computer-generated maps revealed binding in brain regions not identified previously with 125I-muNGF, including hippocampus; dentate gyrus; amygdala; paraventricular thalamus; frontal, parietal, occipital, and cingulate cortices; nucleus accumbens; olfactory tubercle; subiculum; pineal gland; and medial geniculate nucleus. NGF binding sites were distributed in a 2-fold increasing medial-lateral gradient in the caudate-putamen and a 2-fold lateral-medial gradient in the nucleus accumbens. 125I-rhNGF binding sites were also found in most areas labeled by 125I-muNGF, including the interpedunucular nucleus, cerebellum, forebrain cholinergic nuclei, caudoventral caudate-putamen, and trigeminal nerve nucleus. 125I-rhNGF binding sites were absent from areas replete with low-affinity NGF binding sites, including circumventricular organs, myelinated fiber bundles, and choroid plexus. The present analysis provides an anatomical differentiation of high-affinity 125I-rhNGF binding sites and greatly expands the number of brain structures that may respond to endogenous NGF or exogenously administered rhNGF.

Minaprine improves impairment of working memory induced by scopolamine and cerebral ischemia in rats

Using a repeated acquisition procedure in a three-panel runway apparatus, the effects of minaprine on the impairment of working memory produced by scopolamine, ethylcholine aziridinium ion (AF64A) or cerebral ischemia were investigated in rats. Minaprine (3.2-32 mg/kg IP) as well as idebenone (10-100 mg/kg IP) and physostigmine (0.1-0.32 mg/kg IP) dose-dependently reduced the increase of errors (pushes made on the two incorrect panels located at each choice point) induced by 0.56 mg/kg IP scopolamine. Cerebral ischemia for 5 min caused a significant increase of errors in the runway task. Minaprine at 3.2 and 10 mg/kg administered IP immediately after blood recirculation and again 30 min before the runway test conducted 24 h after ischemia, significantly reduced increases in errors expected to occur after 5 min of ischemia. Physostigmine 0.1 mg/kg similarly attenuated the increase in errors in ischemic rats. However, minaprine at doses up to 32 mg/kg IP failed to reduce the increase of errors induced by AF64A 2.5 nmol injected into the dorsal hippocampus. These findings suggest that minaprine exerts an ameliorating effect on amnesia produced by scopolamine and cerebral ischemia, probably through mediation of its stimulant action on central cholinergic systems.

Demonstration of a medial to lateral gradient in the density of cholinergic neuropil in the rat striatum

The striatum is anatomically organized into both distinctly bounded compartments (striosomes) and gradients of neuronal markers. Biochemical markers of striatal cholinergic systems are distributed in increasing amounts laterally. We have investigated the morphologic basis of this gradient by quantitative analysis of neuronal somata and neuropil stained immunocytochemically for choline acetyltransferase (ChAT). We found in both immature and adult rats that there was no difference in the density (neurons mm2) of somata in the medial and lateral compartments. In both age groups, however, there was a clear increase in ChAT-positive neuropil laterally. This medial to lateral gradient was present in all striatal planes examined. This gradient corresponds to the distribution of some other, non-cholinergic, striatal biochemical markers, and is likely to represent an important organizational feature of striatal anatomy, with functional implications.

Inhibition of striatal acetylcholine release by endogenous serotonin

We have examined the hypothesis that endogenous serotonin (5-HT) exerts an inhibitory influence on the release of acetylcholine (ACh) in striatum. Striatal slices were prepared from adult rats, preincubated with [3H]choline, superfused, and exposed to electrical field stimulation. The stimulation-induced overflow of tritium into the superfusate was used as a measure of ACh release. We observed that fluoxetine, an inhibitor of 5-HT uptake, reduced ACh overflow in slices prepared from caudal striatum, an area of high 5-HT concentration, but not in slices from rostral striatum, an area of low 5-HT concentration. Moreover, methysergide, a 5-HT antagonist, increased ACh efflux in caudal but not rostral striatum. Finally, direct activation of 5-HT receptors with the 5-HT agonist, quipazine, inhibited stimulation-induced ACh overflow in both rostral and caudal striatum. These results suggest that endogenous 5-HT normally is capable of inhibiting striatal ACh release, and that the extent of the modulation is related to the degree of serotonergic innervation. In addition, 5-HT receptors capable of modulating ACh release are present in 5-HT-poor rostral striatum, as well as in 5-HT-rich caudal striatum.

Regionally selective manifestations of neostriatal aging

Presynaptic and postsynaptic markers of the cholinergic and dopaminergic systems have characteristic topographical distributions within the striatum. Aside from the dopaminergic afferents, several other afferent systems exhibit a heterogeneous distribution in the striatum. The net result is that each part of the striatum receives a specific and unique combination of afferents. Moreover, the intrinsic striatal systems also have unique distributions, so each part of the striatum consists of a unique combination of afferent and intrinsic neurotransmitter systems. In view of these points, one may expect that the striatum is functionally very complex, integrating information from a wide variety of brain areas. One may also assume from these facts that the striatum is a functionally heterogeneous structure. Consistent with that conclusion, behavioral and pharmacological studies show that interruption of neurotransmission in localized regions of the striatum produces very specific behavioral and physiological effects. Age-related neurochemical changes are also confined to specific striatal regions. Which regions are affected will depend on a variety of factors, including the neurochemical parameter studied and the species or strain of animal. However, we still do not know what factors make a particular striatal area vulnerable to the effects of aging or disease. Moreover, a question that remains to be answered is whether the regions that are affected by neurodegenerative diseases are the same ones affected during normal aging. If so, then this may provide a clue as to why neurodegenerative diseases of the basal ganglia increase in frequency with advancing age. Nevertheless, discrete regional neurochemical alterations may underlie specific symptoms of these diseases. Further study of this relationship may provide the basis for treatments that better target the source of the symptoms. Not only would this increase the effectiveness of the treatment, it would help reduce potential side effects. This may be particularly important, for example, with respect to the use of tissue explants in the treatment of diseases of the basal ganglia.

[3H]vesamicol binding in brain: autoradiographic distribution, pharmacology, and effects of cholinergic lesions

An autoradiographic analysis of high-affinity binding sites for the vesicular acetylcholine transport blocker [3H]vesamicol (2-(4-phenylpiperidino) cyclohexanol; AH 5183) was conducted in rat brain. [3H]Vesamicol binding was displaced 52-99% by DPPN [( 2,3,4,8]-decahydro-3-(4-phenyl-1-piperidinyl)-2-napthalenol) (IC50 = 14 nM) and by ketanserin (500 nM), haloperidol (43 nM), and vesamicol analogs, but not by drugs selective for adenosine, adrenergic, amino acid, calcium channel, monoaminergic, opioid, PCP, sigma, or several other receptor classes. [3H]Vesamicol binding was most concentrated in the interpeduncular nucleus and fifth and seventh cranial nerve nuclei. Moderate binding was found in the lateral caudate-putamen, medial nucleus accumbens, olfactory tubercle, vertical and horizontal diagonal bands of Broca, and basolateral amygdala. The distribution of [3H]vesamicol binding was similar to distributions of acetylcholine (r = 0.88), acetylcholine esterase (r = 0.97), choline acetyltransferase (ChAT) (r = 0.97), and [3H]hemicholinium-3 binding sites (r = 0.95-0.99). Lower correlations were obtained between [3H]vesamicol and muscarinic receptor densities (r = 0.50-0.70). Few exceptions to the match between binding and cholinergic neuronal markers were found, e.g., the molecular layer of the cerebellum and the thalamus. Lesions of cholinergic neuronal projections to the neocortex or hippocampus reduced [3H]vesamicol binding in each of these regions, but to a lesser extent than reductions in ChAT. [3H]Vesamicol binding sites appear to be anatomically associated with brain cholinergic neurons, a locus that is consistent with the control by this site of vesicular acetylcholine uptake.

Quantitative autoradiography of dopamine D2 sites in rat caudate-putamen: localization to intrinsic neurons and not to neocortical afferents

Dopamine D2 receptors, labeled with [3H]spiroperidol or [3H]sulpiride, show a lateral-to-medial gradient in the caudate-putamen, with a more than two-fold greater density laterally than medially. It has been thought that D2 receptors are located on at least two neuronal elements of the caudate-putamen, neurons intrinsic to this structure and axons whose cell bodies reside in the cortex. As a first step in establishing what neuronal elements underlie this heterogeneous organization of D2 receptors, we took advantage of quantitative autoradiography to examine the association of these receptors with those elements. The present findings show that the D2 sites are almost exclusively located on neurons whose somata reside in the caudate-putamen and are not located on terminals of corticostriatal axons. A detailed comparison of the distribution of histochemically identified acetylcholinesterase neurons with that of D2 receptors in serially adjoining sections suggests a common organizational pattern. The density of [3H]spiroperidol sites in rat caudate-putamen was determined after unilateral injection of the neurotoxin quinolinic acid into this structure or after ablation of neocortical regions. Quantification of the tissue damage was achieved by acetylcholinesterase histochemistry (following diisopropylfluorophosphate treatment), as well as by thionin and luxol fast staining of sections adjacent to those used for [3H]spiroperidol autoradiography. In identically treated animals, biochemical determination of the extent of tissue damage was made utilizing assays for high-affinity [3H]choline and [3H]glutamate uptake in the caudate-putamen. In quinolinic acid-injected rats, the density of D2 sites was decreased by 90-95% at the site of complete loss of large acetylcholinesterase-positive neurons. Other animals, given ablations of specific neocortical fields (medial prefrontal, motor, somatosensory) or of the entire parietal-frontal cortex of one hemisphere, showed no loss of caudate-putamen D2 sites unless the cortical ablation caused accompanying damage of the caudate-putamen. In the caudate-putamen of all animals there was a close correspondence between the D2 sites and the striatal neurons (and processes) that show strong acetylcholinesterase reactivity. We suggest that the caudate-putamen topography of D2 sites is based largely on the internal organization of this structure and may preferentially involve acetylcholine-containing intrinsic neurons.

Quantitative autoradiography of brain binding sites for the vesicular acetylcholine transport blocker 2-(4-phenylpiperidino)cyclohexanol (AH5183)

2-(4-Phenylpiperidino)cyclohexanol (AH5183) is a noncompetitive and potent inhibitor of high-affinity acetylcholine transport into cholinergic vesicles. It is reported here that [3H]AH5183 binds specifically and saturably to slide-mounted sections of the rat forebrain (Kd = 1.1 to 2.2 X 10(-8) M; Bmax = 286 to 399 fmol/mg of protein). The association and dissociation rate constants for [3H]AH5183 binding are 8.6 X 10(6) M-1 X min-1 and 0.18 min-1, respectively. Bound [3H]AH5183 can be displaced by nonradioactive AH5183 and by the structural analog (2 alpha,3 beta,4A beta,8A alpha)-decahydro-3-(4-phenyl-1-piperidinyl)-2- naphthalenol but not by 10 microM concentrations of the cholinergic drugs acetylcholine, choline, atropine, hexamethonium, eserine, or hemicholinium-3 or by the structurally related compounds 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-phenylpyridine, (+/-)-N-allylnormetazocine (SKF 10,047), levoxadrol, or dexoxadrol. Quantitative autoradiography reveals that [3H]AH5183 binding sites are distributed heterogenously throughout the rat forebrain and are highly localized to cholinergic nerve terminal regions. At the level of the caudate nucleus-putamen, the highest concentrations of saturable [3H]AH5183 binding (713-751 fmol/mg of protein) are found in the vertical limb of the diagonal band and the olfactory tubercle, with lesser amounts (334-516 fmol/mg of protein) in the caudate-putamen, nucleus accumbens, superficial layers of the cerebral cortex, and the primary olfactory cortex. At day 7 after transsection of the left fimbria, [3H]AH5183 binding and choline acetyltransferase activity in the left hippocampus were reduced by 33 +/- 6% and 61 +/- 7%, respectively. These findings indicate that [3H]AH5183 binds to a unique recognition site in rat brain that is topographically associated with cholinergic nerve terminals.

Striatal substance P cell clusters coincide with the high density terminal zones of the discontinuous nigrostriatal dopaminergic projection system in the cat: a study by combined immunohistochemistry and autoradiographic axon-tracing

A portion of the nigrostriatal projection that originates from presumably dopaminergic neurons in the caudal pars compacta of the substantia nigra and the suprajacent pars dorsalis (retrorubral area), was shown by [3H]amino acid autoradiographic tracing to distribute nonhomogeneously in the head of the caudate nucleus, such that zones of high density termination are in register with the archipelago of substance P cell clusters revealed immunohistochemically in the same and adjacent tissue sections of the cat's brain. Axons from this same portion of the substantia nigra distribute densely at caudal levels of the putamen where again substance P-immunoreactive striatal cells are numerous. In nearby tissue sections from the same cases, tyrosine hydroxylase-like immunoreactivity suggested only subtle variations in the density of the catecholamine axon network within the striatum. Thus, whereas dopamine axons are distributed densely throughout the striatum, those originating from cells in the caudal pars compacta et dorsalis of the substantia nigra and ending in the head of the caudate nucleus appear to terminate preferentially within the substance P cell clusters. These data suggest that the striatal substance P cells, which send their axons selectively to the entopeduncular nucleus and substantia nigra, but much less so the globus pallidus, are a major target of nigrostriatal dopamine transmission. This result is discussed with respect to the anatomical, neurochemical and functional organization of the striatifugal projection system.

Effects of dopamine depletion on the spontaneous activity of type I striatal neurons: relation to local dopamine concentration and motor behavior

The relation between the electrophysiological activity of Type I striatal neurons, local dopamine (DA) concentration, and motor behavior in rats was investigated using intraventricular administration of the neurotoxin 6-hydroxydopamine (6-HDA) and extracellular single-unit recording. Results are compared with findings of past experiments in which the activity of Type II striatal neurons was examined after comparable 6-HDA-induced lesions. Several differences between the present observations and the earlier results were found. First, although large depletions (greater than 50%) of DA local to the site of the recording were required before the spontaneous firing rate of either cell type was increased, the levels necessary for this effect were found to be less for Type I cells than for Type II neurons. Second, although DA depletions of greater than 50% always were associated with increased Type I cell activity, depletions of greater than 95% resulted in spontaneous firing rates that were lower than those observed after depletions of approximately 90%. Thus, the relation between extent of dopaminergic depletion and Type I cell firing rate was biphasic, whereas that relation previously was found to be monophasic for Type II neurons. Finally, whereas increased Type I cell activity in the lateral striatum was associated with the aphagia, adipsia, and akinesia induced by large DA-depleting brain lesions, increased Type II cell activity in the medial striatum was found to be associated with these impairments. Because accumulating evidence suggests that the functioning of the lateral striatum is more critical for these behaviors, however, it is proposed that the substrate of the behavioral dysfunctions resulting from DA depletion is the Type I cell population in lateral striatum.

Differential effects of striatal injections of dopaminergic, cholinergic and GABAergic drugs upon swimming behavior of rats

The present study provides a detailed report about similarities and dissimilarities between the effects of neostriatally applied dopaminergic (apomorphine, 250-300 ng; haloperidol, 250-500 ng), cholinergic (carbachol, 50-100 ng; scopolamine, 200-500 ng), and GABAergic (muscimol, 1-2 ng; bicuculline, 5-35 ng) drugs upon swimming of rats. The used swimming test consisted of 4 parts: (a) open-field test for analyzing drug-induced changes in normal behavior; (b) 'swimming without escape' test for analyzing drug-induced changes in the ability to switch from one type of behavior to another; (c) 'swimming with escape' test for analyzing drug-induced changes in the ability to switch from ongoing swimming behavior to climbing behavior by allowing the rats to escape via a rope; and (d) 'rope' test for analyzing drug-induced changes in the kind of contact behaviors needed to switch to the latter climbing behavior. In the open-field test the drugs produced neither abnormal behavior nor motor disturbances, which prevented the display of normal behavior in the remaining tests. Both apomorphine and carbachol produced identical effects in all tests. Muscimol produced overall effects which were not only opposite to those of apomorphine and carbachol, but also comparable to those of scopolamine. All effects elicited by apomorphine, carbachol and muscimol were antagonized by their corresponding antagonists: haloperidol, scopolamine and bicuculline respectively, whereas the effects of the latter were suppressed by their corresponding agonists. These data globally show that dopamine and acetylcholine act in the same direction but opposite to that of GABA as far as it concerns the regions investigated. The finding that haloperidol injected into the GABA target area produced effects which were not only similar to those of haloperidol injected into the dopamine target area, but also dissimilar to those of muscimol and bicuculline injected into the GABA target area, shows that the effects were drug-specific rather than region-specific. Though 3 distinct cholinergic regions were investigated, cholinergic-specific effects could only be elicited from one region, suggesting that the neostriatum is heterogeneous in this respect. Finally, well-delineated dissimilarities between haloperidol-, scopolamine-, and muscimol-treated rats were found in the rope test. These data show that behavior-relevant information transmitted by GABAergic drugs surmounted that transmitted by cholinergic drugs which, in turn, surmounted behavior-relevant information transmitted by dopaminergic drugs.

Frontal decortication and adaptive changes in striatal cholinergic neurons in the rat

Interruption of the corticostriatal pathway by undercutting the cortex resulted in a reduction of glutamate uptake by 55% and in a depression of acetylcholine (ACh) synthesis by 30% in striatum after two postlesion weeks without affecting the content of ACh and choline, the specific binding of [3H]dexetimide to muscarinic receptors, the activity of choline acetyltransferase and the levels of noradrenaline, serotonin, dopamine and 3,4-dihydroxyphenylacetic acid. The influence of this excitatory pathway on striatal cholinergic neuropharmacology was investigated. It was found that the effect of a number of agonists (R-apomorphine, bromocriptine, lisuride, quinpirole, JL-14389, 2-chloroadenosine, oxotremorine and methadone), capable of depressing cholinergic activity in the striatum through receptor-mediated responses--reflected as an increase in ACh content--is operative only when the corticostriatal pathway is intact. By contrast, antagonists capable of decreasing ACh content, i.e. the typical neuroleptics pimozide, haloperidol and the atypical ones clozapine, L-sulpiride, as well as the anti-muscarinic agent scopolamine, were not influenced by the lesion. The possibility that the lesion non-specifically damaged striatal cells on which the agonists, but not the antagonists acted was excluded by results showing, firstly, that the increase in striatal ACh elicited by the ACh precursor, choline, was not blocked by decortication, and secondly, that the degeneration of the corticostriatal neurons did not prevent the ACh-increasing effect of bromocriptine, a long-acting ergot alkaloid, when sufficient time was allowed for the drug to act. It was furthermore possible to restore the inhibitory action of apomorphine on cholinergic neurons either by short-term chemical lesion of the nigrostriatal dopaminergic input or by the administration of choline.(ABSTRACT TRUNCATED AT 250 WORDS)

Distinct sites of functional interaction between dopamine, acetylcholine and gamma-aminobutyrate within the neostriatum: an electromyographic study in rats

In order to study the functional interaction between dopamine, acetylcholine and gamma-aminobutyrate within the rat neostriatum, we investigated the effect of intrastriatal injection of different drugs acting on these transmitter systems on muscle tone measured as tonic activity in the electromyogram of the gastrocnemius muscle. Bilateral injection of haloperidol (500 ng) into the rostral neostriatum (rostral injection: A8920-9650(46] induced tonic activity in the electromyogram, whereas injection into the intermediate part (intermediate injection; A7020-7890(46] was ineffective. Muscimol (25 ng) induced tonic activity in the electromyogram, when injected into the intermediate part and not into the rostral part, while bethanechol (1 microgram) was effective when injected into either site. Haloperidol-induced tonic activity in the electromyogram was prevented by coadministration of apomorphine (500 ng) or scopolamine (1 microgram), but not of bicuculline (300 ng). Haloperidol-induced tonic activity in the electromyogram was also reduced by subsequent intermediate injection of scopolamine or bicuculline, while apomorphine was ineffective. Tonic activity in the electromyogram induced by rostral injection of bethanechol was prevented by coadministration of scopolamine, but not of apomorphine. Intermediate injection of scopolamine or bicuculline reduced the tonic activity in the electromyogram after rostral or intermediate injection of bethanechol. Tonic activity in the electromyogram induced by intermediate injection of muscimol was prevented by coadministration of bicuculline, but not of scopolamine. Rostral injection of apomorphine or scopolamine failed to alter the tonic activity in the electromyogram induced by intermediate injection of bethanechol or muscimol. These results point to the existence of: a functional interaction between dopamine and acetylcholine in the rostral neostriatum; a functional interaction between acetylcholine and gamma-aminobutyrate in the intermediate neostriatum, and a functional flow of information from the rostral to the intermediate neostriatum.

Local cerebral glucose utilisation following indoleamine- and piperazine-containing 5-hydroxytryptamine agonists

Substances with varying structural components have been shown to have 5-hydroxytryptamine (5-HT)-like properties in the CNS. In this study, putative 5-HT agonists with indoleamine moeities--lysergic acid diethylamide (LSD) and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT)--and with piperazine moieties--quipazine (Quip) and 6-chloro-2-(1-piperazinyl)pyrazine (6-CPP) were administered to rats. Local cerebral glucose utilisation was measured using the [14C]2-deoxyglucose autoradiographic technique. It was found that in most cerebral structures, these substances produced dose-dependent reductions in glucose utilisation. However, Quip and 6-CPP increased glucose utilisation in specific areas of the diencephalon (e.g., nucleus reuniens) and produced a biphasic effect in some but not all extrapyramidal structures (e.g., ventromedial caudate nucleus). No such increases in local cerebral glucose utilisation were measured following LSD or 5-MeODMT administration. These results indicate that although similarities exist between the effects of indoleamine- and piperazine-containing 5-HT agonists on local cerebral glucose utilisation there are also significant differences in the overall patterns of response produced.

Intra-regional variations in the effect of aging on high affinity choline uptake, choline acetyltransferase and muscarinic cholinergic receptors in rat neostriatum

High affinity sodium-dependent choline uptake (HACU), choline acetyltransferase (ChAT) and quinuclidinyl benzilate binding ([3H]-QNB) are measured in synaptosomal preparations from four areas of the neostriatum of Fischer 344 rats of three different ages (6, 18 and 30 months). There is a marked regional distribution of all three markers, being higher generally in lateral as compared to medial striatal regions. In addition, in the medial neostriatum, all three measures are higher rostrally than caudally. HACU is reduced with age in the rostromedial and the caudolateral neostriatum. Small (usually less than 20%) but significant decreases in muscarinic cholinergic receptors occur in all regions of the neostriatum. There are no significant age-associated differences in ChAT activity in any region. The lack of decrease in ChAT is evidence that the reductions in HACU in striatal subregions are not simply the result of a loss of axon terminal integrity. The changes in HACU may reflect altered activity of cholinergic neurons in specific striatal subregions.

Immunocytochemical localization of choline acetyltransferase within the rat neostriatum: a correlated light and electron microscopic study of cholinergic neurons and synapses

Monoclonal antibodies to choline acetyltransferase (ChAT) were used in an immunocytochemical study to characterize putative cholinergic neurons and synaptic junctions in rat caudate-putamen. Light microscopy (LM) revealed that ChAT-positive neurons are distributed throughout the striatum. These cells have large oval or multipolar somata, and exhibit three to four primary dendrites that branch and extend long distances. Quantitative analysis of counterstained preparations indicated that ChAT-positive neurons constitute 1.7% of the total neuronal population. Electron microscopy (EM) of immunoreactive neurons initially studied by LM revealed somata characterized by deeply invaginated nuclei and by abundant amounts of organelle-rich cytoplasm. Surfaces of ChAT-positive neurons are frequently smooth, but occasional somatic protrusions and dendritic spines occur. Although infrequently observed, axons of ChAT-positive neurons branch, receive synapses, and become myelinated. Unlabeled boutons make both symmetrical and asymmetrical synapses with ChAT-positive somata and proximal dendrites, but are more numerous on distal dendrites. In addition, some unlabeled terminals form asymmetrical synapses with ChAT-positive somata and dendrites that are distinguished by prominent subsynaptic dense bodies. Light microscopy demonstrated a dense distribution of ChAT-positive fibers and punctate structures in the striatum, and these structures appear to correlate, respectively, with labeled preterminal axons and presynaptic boutons identified by EM. ChAT-positive boutons contain pleomorphic vesicles, and make symmetrical synapses primarily with unlabeled dendritic shafts. Furthermore, they establish synaptic contacts with somata, dendrites and axon initial segments of unlabeled neurons that ultrastructurally resemble medium spiny neurons. These observations, together with the results of other investigations, suggest that medium spiny GABAergic projection neurons receive a cholinergic innervation that is probably derived from ChAT-positive striatal cells. The results of this study also indicate that cholinergic neurons within caudate-putamen belong to a single population of cells that have large somata and extensive sparsely spined dendrites. Such neurons, in combination with dense concentrations of ChAT-positive fibers and terminals, are the likely basis for the large amounts of ChAT and acetylcholine detected biochemically within the neostriatum.

Patterns of muscarinic cholinergic binding in the striatum and their relation to dopamine islands and striosomes

The distribution of muscarinic cholinergic binding sites in the striatum was studied in relation to the locations of other neurochemical markers in the developing rat, cat, ferret, and human. In addition, patterns of striatal muscarinic binding were studied in the adult cat. Receptor binding autoradiography was carried out with tritiated propylbenzilylcholine mustard [( 3H]-PrBCM), an irreversible muscarinic antagonist, and subsequent serial section analyses involved comparisons among patterns of muscarinic binding, catecholamine histofluorescence, acetylcholinesterase (AChE) staining, Nissl staining, and cell labeling with [3H]-thymidine. Muscarinic binding in the immature striatum was characterized by local patchiness as well as regional density gradients in all species, with the most complex patterns appearing in the human. Patches of dense muscarinic binding were shown to lie in register with fluorescent dopamine islands (rat, cat, ferret), with AChE-positive patches (all species), and with clusters of neurons pulse-labeled by exposure to [3H]-thymidine on embryonic day 27 (ferret). At the developmental stages examined, the [3H]-PrBCM-positive patches were roughly aligned with regions of weak Nissl staining (cat, human). Striatal [3H]-PrBCM binding in the adult cat was dense, and though it usually appeared nearly homogeneous, in some sections patches of elevated binding were present. These had as counterparts, in neighboring sections, AChE-poor striosomes. We conclude that during development muscarinic cholinergic function is compartmentalized in the striatum in association with dopamine-containing afferents, and that this compartmentalization may persist to some degree in the adult.

Striatal topography of D-2 receptors correlates with indexes of cholinergic neuron localization

The topography of dopamine D-2 receptor sites determined from autoradiographs of the rat striatum was compared with previously published values for choline acetyltransferase activity and high-affinity choline uptake within subregions of the striatum. The density of D-2 sites in the caudate-putamen correlates strikingly with these indexes of cholinergic neuron distribution.

Presynaptic muscarinic modulation of nicotinic excitation in the rat neostriatum

In rat neostriatal slices, cholinergic agents were tested for their effects on endogenous ACh release and on electrical activity. ACh release was evoked by 25 mM K+ during two 5-min periods between which a slice was allowed to rest for 20 min; drugs were present during the second stimulation period. In the absence of a cholinesterase inhibitor, only Ch outflow was monitored. For the recording of electrical activity, intrastriatal stimulation evoked field potentials which were monitored in the absence and presence of drugs in the perfusate. Atropine (1-100 microM) increased endogenous ACh release by 32-91% and effective doses were 10-fold lower in the presence of a cholinesterase inhibitor. Atropine also increased the amplitudes of synaptic population spikes in the field potentials. The muscarinic agonists muscarine (100 microM) and oxotremorine (25 and 100 microM) decreased endogenous ACh release. Atropine (10 microM) blocked the depressant effect of muscarine (100 microM). Muscarine (100 microM-1 mM) and oxotremorine (10-100 microM) decreased the electrically evoked excitation in the rat neostriatal slices, and their effects were reversed by atropine. Only higher concentrations of nicotine (1 and 5 mM) decreased the synaptic population spikes, but potassium-stimulated Ch outflow was not affected. It is concluded that in the neostriatum presynaptic muscarinic receptors modulate nicotinic excitation since potassium-stimulated ACh release and intrinsically evoked synaptic excitation are influenced by muscarinic drugs in the same way.

Neurochemical effects of minaprine, a novel psychotropic drug, on the central cholinergic system of the rat

Minaprine, a novel psychotropic drug with antidepressant, anticataleptic and antiaggressive properties, produced an increase in rat brain regional acetylcholine content at a subconvulsant dose of 30 mg/kg IP. The greatest increase (60%) was produced in the striatum, whereas an increase of about 35% was obtained in the hippocampus and the rest of the cortex. A small but significant increase of 14% was also found in the midbrain-hindbrain region. Minaprine decreased choline content only in the striatum. No tolerance to acute challenge was observed after 10-day chronic treatment. In vitro, the drug had no effect on striatal choline acetyltransferase activity up to a concentration of 160 microM and only weakly displaced (3H) dexetimide from its specific muscarinic receptor binding sites in striatum (IC50, 2 X 10(-4) M). After in vivo administration the drug did not affect sodium-dependent high affinity choline uptake by a hippocampal homogenate. On the other hand, the drug inhibited both striatal and hippocampal acetylcholinesterase activity at high (40-160 microM) concentrations in vitro. In vivo the drug produced a brief (5 min), small (18%) decrease in the enzymic activity which corresponded in time to the peak drug level attained in the brain, but was not concomitant with a change in striatal acetylcholine content. By contrast, the increase in striatal acetylcholine appeared after 30 min when there was no longer inhibition of acetylcholinesterase activity and when the level of minaprine in brain was reduced by 78%. Blockade of dopamine receptors by pimozide pretreatment partially prevented the increase in striatal acetylcholine produced by minaprine, whereas interference with cholinergic or serontonergic neurotransmission was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of rat brain 5-hydroxytryptamine metabolism by sublethal doses of organophosphate agents

The early and late effects of sublethal doses of two organophosphate agents (paraoxon and soman) on 5-hydroxytryptamine (5-HT) metabolism were investigated in several rat brain areas. Parallel determinations of acetylcholinesterase (AcChE) inhibition were performed. An increase in 5-HT level was observed during the first phase of soman intoxication and a rise in 5-hydroxyindol acetic acid (5-HIAA) appeared in the early and late effects of both anticholinesterase agents with a predominant action in the striatum. These data suggested that paraoxon and soman induce a long-lasting increase in 5-HT turnover. This action cannot be related neither to the AcChE inhibition nor to the acetylcholine level.

Head turning induced by unilateral intracaudate thyrotropin-releasing hormone (TRH) injection in the cat

Unilateral intracaudate injection of TRH in cats (10 microgram) induced head turning responses similar to the responses produced by dopamine (DA) (10 microgram). Contralateral head turning responses were observed after injections in the central part of the caudate body, whereas, injections placed more laterally induced ipsilateral responses. While haloperidol (3 mg/kg i.m.) suppressed the DA-induced response, it appeared to potentiate the effects of TRH. Cyproheptadine (10 mg/kg i.p.) did not alter the TRH-induced responses. These results suggest that, although TRH induces DA-like effects on postural symmetry, the mediation of TRH effects bypasses striatal dopaminergic and serotonergic receptors. While intracaudate TRH and DA induced head turning, they did not alter the level of head motility as measured by the number of head movements. Haloperidol, but not cyproheptadine pretreatment, decreased the level of head motility providing evidence that postural symmetry is modulated within the striatum, whereas head motility is regulated by extrastriatal dopaminergic mechanisms.

Studies on the indirect feedback inhibition of cholinergic neurons triggered by oxotremorine in striatum

Oxotremorine produced 30-75% increases in rat striatal acetylcholine content and 10-15% decreases in choline content at the subtremorogenic doses of 0.34-1.34 mumol/kg, without affecting choline acetyltransferase and acetylcholinesterase activities and the sodium-dependent high affinity uptake of choline. The increase in acetylcholine was blocked by atropine and by reserpine indicating that oxotremorine indirectly influences the intrinsic striatal cholinergic neurons through a monoamine-mediated negative feedback loop. Experiments designed to interfere with neurotransmitter function indicated that noradrenaline and not dopamine or serotonin, mediated the response to oxotremorine.

Microtopography of tyrosine hydroxylase, glutamic acid decarboxylase, and choline acetyltransferase in the substantia nigra and ventral tegmental area of control and Parkinsonian brains

Tyrosine hydroxylase (TH), glutamic acid decarboxylase (GAD), and choline acetyl transferase (CAT) were used as markers for catecholamine, gamma-aminobutyric acid, and acetylcholine containing neurons in human mesencephalon. Their rostrocaudal, mediolateral, and dorsoventral distribution was investigated within the substantia nigra pars compacta (SNC) and pars reticulata (SNR) and in the ventral tegmental area (VTA). TH activity was highest in the caudal, medial, and ventral SNC and in the middle of VTA medio-ventrally. The enzyme activity in SNR was low and uniformly distributed. In SNC as well as SNR, GAD activity was high and greater laterally and in the middle of the rostro-caudal extent. No particular pattern of distribution was observed in VTA. an area with low GAD content. In the substantia nigra, CAT activity was low. A characteristic medio-ventral distribution with a peak of high enzyme activity in the middle of the rostrocaudal extent was observed. In VTA, enzyme levels were high and also concentrated medio-ventrally and in the middle of the area. In parkinsonian brains, the distribution of TH was uniformly affected throughout the rostro-caudal extent. In VTA the enzyme activity was not as reduced as in SNC and SNR; the CAT pattern was only disrupted in a very localized part of SNC but not in SNR and VTA. In all three areas, GAD activity was reduced to a uniformly low distribution.

Regional distribution of cholinergic parameters within the rat striatum

The topographical distribution of choline acetyltransferase, muscarinic receptor binding and high affinity choline uptake was studied in 21 separate areas of the rat striatum. The areas of the nucleus chosen represented dorsolateral, dorsomedial, ventrolateral and ventromedial regions along the rostrocaudal aspect of the striatum, such that a three-dimensional distribution of the cholinergic parameters could be obtained. Within any given rostrocaudal section, no significant dorsoventral differences were noted for any of the cholinergic parameters. On the other hand, marked differences were found in a comparison of the medial and lateral striatum. Choline acetyltransferase, muscarinic receptor binding and high affinity choline uptake were more concentrated in the lateral striatum than the medial striatum, and the magnitude of this medio-lateral disparity increased from rostral to caudal regions of the nucleus. The lateral striatum exhibited no significant rostrocaudal variations in the cholinergic parameters; however, the medial portion of the striatum did exhibit differences along its rostrocaudal extent, with the rostral-most sections being enriched relative to the more caudal sections. These results suggest that the cholinergic system in the striatum is heterogeneously distributed within this nucleus, with the lateral portion possessing a greater cholinergic innervation than the medial portion. They further suggest that future neurochemical studies of cholinergic alterations in the striatum should include a consideration of the possibility of regional effects within the nucleus rather than treating the striatum as a homogeneous tissue.

Evidence of the modulatory role of serotonin in acetylcholine release from striatal interneurons

The release of acetylcholine was studied in isolated striatal slices of the rat. The spontaneous and ouabain-stimulated release of acetylcholine was higher in those slices where serotonergic input was somehow impaired: raphe nuclei lesion or p-chlorophenylalanine pretreatment or 5, 7-dihydroxytryptamine pretreatment resulted in a higher release. L-(m-chlorophenyl)-piperazine, a pure serotonin receptor stimulant and D-fenfluramine, a serotonin releaser significantly reduced the release of acetylcholine evoked by ouabain. Serotonin antagonists (cyproheptadine, mianserine and methysergide) prevented the effect of serotonin agonists. When the serotonergic neurons were destroyed either by p-chlorophenylalanine or by 5, 7-dihydroxytryptamine pretreatment D-fenfluramine had no inhibitory action; however, the effect of L-(m-chlorophenyl)-piperazine was not affected. It is suggested that there is a link between serotonergic and cholinergic neurons in the striatum: serotonin released from raphe-striatal neurons is able to inhibit the release of acetylcholine from striatal interneurons.

Comparison of the effects of the stereoisomers of fenfluramine on the acetylcholine content of rat striatum, hippocampus and nucleus accumbens

The (+)- and (-)- isomeric forms of fenfluramine were compared for their effects on rat brain area acetylcholine (ACh) content. The drugs showed similar patterns in increasing ACh content in the accumbens and hippocampus and in being ineffective in the brainstem. The actions differed in the striatum where the (+)-form markedly increased ACh content while the (-)-form produced no change. Both isomer-induced increases in ACh in the accumbens were prevented when 5-HT synthesis was blocked by p-chlorophenylalanine, thus denoting 5-hydroxytryptaminergic mediation of these effects. In striatum, the increase in ACh induced by (+)-fenfluramine was summated with the increase in ACh induced by dopamine receptor stimulation with apomorphine and was not prevented by dopamine receptor blockade with pimozide. On the other hand, apomorphine's effect was blocked by (-)-fenfluramine while pimozide pretreatment unmasked an increase in ACh induced by (-)-fenfluramine. The results favour the notion that there is a population of cholinergic neurons intrinsic to the striatum which is under inhibitory 5-HT regulation and independent of inhibitory dopamine regulation.

Intrinsic excitation in the rat neostriatum mediated by acetylcholine

Synaptic excitation elicited by local stimulation in neostriatal slices was found to be mediated by acetylcholine (ACh). The synapses generating this excitation belong to intrinsic neurons. Thus, for the first time, direct evidence for the existence of intrinsic excitatory cholinergic neurons in the neostriatum is provided.