Cholinergic synaptic input to different parts of spiny striatonigral neurons in 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.

Synaptic relationships of enkephalinergic and cholinergic neurons in the nucleus accumbens of the rat

Leucine5-enkephalin- and choline acetyltransferase-containing, presumably cholinergic, neurons revealed by dual label immunocytochemistry were found in the shell and core of the rat nucleus accumbens. The perikarya, dendrites and boutons of cholinergic neurons were labeled with the diaminobenzidine precipitate, whereas those of the enkephalinergic neurons were labeled with silver-intensified colloidal gold. Ultrastructural examination revealed that both the enkephalinergic and the cholinergic boutons generally formed symmetric synapses with unlabeled dendrites and, occasionally, with unlabeled dendritic spines. Enkephalin-immunoreactive terminals which were much larger than cholinergic boutons, seldom apposed or formed synapses with cholinergic structures in the nucleus. In the core, cholinergic terminals were frequently found apposed to enkephalin-immunoreactive dendrites and perikarya and were often seen in synaptic contact with enkephalinergic dendrites, whereas in the shell, cholinergic boutons seldom apposed or contacted enkephalinergic targets. These findings show that enkephalinergic and cholinergic neurons differ in their synaptic arrangements within the nucleus accumbens and provide further evidence for differentially organized intrinsic connections of shell and core territories.

Dopaminergic and muscarinic regulation of striatal enkephalin and substance P messenger RNAs following striatal dopamine denervation: effects of systemic and central administration of quinpirole and scopolamine

Striatal dopamine depletion produces an increase in enkephalin and a decrease in substance P messenger RNAs. Subsequent systemic administration of either the D2 dopamine agonist, quinpirole, or the muscarinic antagonist, scopolamine, results in the reduction of the lesion-induced elevation in striatal enkephalin messenger RNA. These changes in enkephalin messenger RNA levels may be mediated solely within the striatum or through trans-synaptic circuits involving the striatum. To dissociate these possibilities, we have compared the effects of systemic and central administration of quinpirole and scopolamine on striatal enkephalin and substance P messenger RNAs using in situ hybridization histochemistry. Systemic administration of both quinpirole and scopolamine blocked the elevation of striatal enkephalin messenger RNA normally observed in 6-hydroxydopamine-lesioned rats. In addition, high doses of systemic scopolamine (25 and 50 mg/kg per day) prevented the lesion-induced decrease in striatal substance P messenger RNA levels. In order to determine whether the effects of these drugs are mediated directly within the striatum, central administration of quinpirole and scopolamine were compared. In contrast to systemic administration, intraventricular and intrastriatal infusion of quinpirole but not scopolamine prevented the lesion-induced change in striatal enkephalin messenger RNA. However, neither quinpirole nor scopolamine administered centrally affected the level of substance P messenger RNA in the striatum of 6-hydroxydopamine-induced lesioned animals. Together, these data suggest that changes in D2 receptor activation directly in the striatum are responsible for the effects of quinpirole on enkephalin messenger RNA. In contrast, the effect of systemic scopolamine on striatal enkephalin and substance P messenger RNAs may not be mediated within the striatum.

The neostriatum and nucleus accumbens in parkinsonism-dementia complex of Guam: a pathological comparison with Alzheimer's disease and progressive supranuclear palsy

The neostriatum, nucleus accumbens and basal nucleus of Meynert (bnM) in the parkinsonism-dementia complex of Guam (Guam PDC) were examined immunohistologically, ultrastructurally, quantitatively and topographically, and the results were compared with those in Alzheimer's disease (AD) and progressive supranuclear palsy (PSP). Compared to neurologically normal controls, the number of large neurons in Guam PDC was reduced by approximately 70% in the caudate nucleus and putamen and by more than 90% in the nucleus accumbens. The decreased number of large neurons in the neostriatum was significantly correlated to that in the bnM. The remaining large neurons and many of the medium-sized neurons in the neostriatum and nucleus accumbens were immunopositive for tau protein and contained varying amounts of 21- to 25-nm-wide paired helical filaments (PHFs) admixed with straight tubules. Curly fibers and circularly arranged reactive astrocytes were seen in the nucleus accumbens of many PDC patients. Collectively, these findings, which are similar in part to those of AD and differ from those of PSP, suggest that the large neurons in the neostriatum and nucleus accumbens in Guam PDC degenerate through PHF formation, and that extremely severe loss of large neurons in the nucleus accumbens may be linked to marked degeneration of the limbic and ventral tegmental areas and nucleus dorsal raphe.

Light and electron microscopic characterization of cholinergic and dopaminergic structures in the striatal complex and the dorsal ventricular ridge of the lizard Gekko gecko

The purpose of the present study was to visualize the morphological substrate underlying acetylcholine-dopamine interactions in the striatal complex of the lizard Gekko gecko and to compare the results with data obtained by others in mammals. The results are also discussed in the light of data obtained previously by us on neurochemical aspects of acetylcholine-dopamine interactions in Gekko and in rats. The study is part of a large research program in which the cholinergic and dopaminergic elements of the striatum of rats and reptiles are studied at morphological and neurochemical levels. We employed light microscopic immunocytochemistry, using single-label staining with antibodies against choline acetyltransferase (ChAT) and dopamine (DA) and double-staining with antibodies against ChAT and tyrosine hydroxylase (TH). A detailed analysis of ultrastructural characteristics of ChAT- and DA-immunolabeled striatal tissue was undertaken. The morphology and synaptic relations of the ChAT-immunopositive neurons in the basal forebrain of the lizard Gekko gecko are very similar to those of the cholinergic cells in the striatum of mammals. Probably, the cholinergic cells are in both mammals and reptiles interneurons that receive inputs of intrinsic or extrinsic origin and project upon output neurons. The location of ChAT-immunopositive somata outside the patches of high TH- or DA-immunoreactivity is at odds with the situation in the striatum of mammals and suggests the possibility of axoaxonal or axodendritic contacts at the level of these patches. We found no essential differences between the synaptic relations of the dopaminergic fibers in the striatal complex of Gekko and the conditions described for rats. In conclusion, we found little evidence for the presence of synaptic interaction between the cholinergic and dopaminergic systems in the striatum of this reptile. The possibility of nonsynaptic interaction, however, remains open.

Modulatory functions of neurotransmitters in the striatum: ACh/dopamine/NMDA interactions

The striatum is viewed as a structure performing fast neurotransmitter-mediated operations through somatotopically organized projections to medium-size spiny neurons. This view is contrasted with another view that depicts the striatum as a site of diffuse modulatory influences mediated by cholinergic interneurons and by dopamine and N-methyl-D-aspartate receptors. These two operational and organizational modes both contribute, through their mutual interaction, to the function of basal ganglia. Detailed knowledge of the neural mechanisms by which such interactions take place and are expressed into behaviour, can provide new insight into the physiopathology and new clues for therapy of disorders of basal ganglia.

Excitatory amino acid receptors mediate the orofacial stereotypy elicited by dopaminergic stimulation of the ventrolateral striatum

The present experiments examined the role of excitatory amino acid receptors in the orofacial stereotypy induced by direct amphetamine microinjection into the ventrolateral striatum. In these experiments, the influence of prior intra-ventrolateral striatum treatment with various excitatory amino acid antagonists on the expression of amphetamine-stimulated oral stereotypy was observed. In all experiments, behavioral observations were conducted in the home cage using a time-sampling procedure. In the first experiment, different groups of rats received bilateral microinfusions of either kynurenic acid, 2-amino-5-phosphonopentanoic acid, 6,7-dinitroquinoxaline or dizocilpine maleate. The excitatory amino acid antagonists were administered immediately prior to bilateral microinfusions of d-amphetamine. Both N-methyl-D-aspartate and non-N-methyl-D-aspartate antagonists dose-dependently attenuated or blocked the expression of dopamine-mediated stereotypy. 2-Amino-5-phosphonopentanoic acid was the most potent of these compounds, totally suppressing stereotypy at a dose of 0.3 micrograms (equivalent to 1.5 nmol). In the second experiment, the same compounds were tested for their ability to suppress physostigmine-induced mouth movements. Cholinergic stimulation of the ventrolateral striatum has previously been shown to elicit non-directed mouth movements, quite distinguishable from stimulus-directed, amphetamine-induced biting. Excitatory amino acid antagonists were administered in the same doses prior to bilateral infusion of physostigmine (2.5 micrograms/0.5 microliters). The expression of physostigmine-induced mouth movements was for the most part not affected by excitatory amino acid antagonists, although dizocilpine maleate slightly reduced this oral behavior. In a third experiment, behavior was observed following infusion of the antagonists alone, using the same doses as in the previous experiments. No behavioral alterations were observed with the exception of a small increase in nonspecific mouth movements induced by kynurenic acid and 2-amino-5-phosphonopentanoic acid. These findings indicate that the expression of dopamine-mediated oral stereotypy, induced by amphetamine stimulation of the ventrolateral striatal region, is highly dependent on activation of striatal excitatory amino acid receptors. In contrast, oral behavior induced by cholinergic stimulation of the ventrolateral region is not mediated by glutamate input. These results are discussed in relation to the synaptic organization of neuronal elements within the striatum. Moreover, the relevance to further understanding of orofacial dyskinesias is noted.

GABAergic modulation of striatal cholinergic interneurons: an in vivo microdialysis study

Striatal cholinergic interneurons have been shown to receive input from striatal gamma-aminobutyric acid (GABA)-containing cell elements. GABA is known to act on two different types of receptors, the GABAA and the GABAB receptor. Using in vivo microdialysis, we have studied the effect of intrastriatal application of the GABAA-selective compounds muscimol and bicuculline and the GABAB-selective compounds baclofen and 2-hydroxysaclofen, agonists and antagonists, respectively, at GABA receptors, on the output of striatal acetylcholine (ACh). Intrastriatal infusion of 1 and 10 mumol/L concentrations of the GABAA antagonist bicuculline resulted in a significant increase in striatal ACh output, whereas infusion of 1 and 10 mumol/L concentrations of the GABAA agonist muscimol significantly decreased the output of striatal ACh. Both compounds were ineffective in changing the output of striatal ACh at lower concentrations. Infusion of concentrations up to 100 mumol/L of the GABAB-selective antagonist 2-hydroxy-saclofen failed to affect striatal ACh output, whereas infusion of 10 and 100 mumol/L baclofen, but not 0.1 and 1 mumol/L baclofen, significantly decreased the output of striatal ACh. Thus, agonist-stimulation of GABAA and GABAB receptors decreases the output of striatal ACh in a dose-dependent fashion, whereas the GABAAergic system appears to inhibit tonically the output of striatal ACh via GABAA receptors, but not via GABAB receptors. We hypothesize that although GABAA mediated regulation of striatal ACh occurs via GABA receptors on the cholinergic neuron, the GABAB mediated effects may be explained by presynaptic inhibition of the glutamatergic input of the striatal cholinergic neuron.

A selective lesion of striatonigral neurons decreases presynaptic binding of [3H]hemicholinium-3 to striatal interneurons

We have used the suicide transport agent, volkensin, to produce selective lesions of striatal efferent neurons projecting to the substantia nigra in the rat. In order to evaluate potential trans-synaptic effects, we examined cholinergic interneurons intrinsic to the striatum following destruction of striatonigral projection neurons by nigral injection of volkensin. There was no change in the number of large interneurons identified either by Nissl stain or by immunocytochemistry for choline acetyltransferase, indicating that volkensin was not directly toxic to this group of neurons. However, [3H]hemicholinium-3 binding to the choline re-uptake site on the presynaptic cholinergic terminals decreased. No change in [3H]hemicholinium-3 binding was seen after destruction of dopaminergic afferents with 6-hydroxydopamine. Striatonigral afferents to the cholinergic interneurons contain substance P which has been shown to stimulate acetylcholine release. The decrease in [3H]hemicholinium-3 binding may reflect loss of this afferent input. However, striatonigral neurons are an efferent target of the cholinergic interneuron as well, and a presynaptic effect due to loss of target neurons also may contribute.

Cholinergic neurons are distributed preferentially in areas rich in substance P-like immunoreactivity in the caudate nucleus of the adult cat

The distribution of cells stained immunocytochemically for the cholinergic marker choline acetyltransferase was compared to the pattern of substance P immunoreactivity in the caudate nucleus of adult cats using a double-label immunocytochemical protocol and three-dimensional reconstructions of adjacent sections single-labeled for either substance P or choline acetyltransferase. Substance P immunoreactivity was distributed in a highly complex mosaic within the caudate nucleus of the cat. In the dorsal caudate nucleus, substance P-rich zones consisting of either clusters of substance P-positive cell bodies or fibers were seen against a lighter staining background. The density of cholinergic neurons was found to be significantly greater within these substance P-rich patches in comparison to surrounding regions. The pattern of substance P immunoreactivity within the ventral caudate nucleus differed from that in more dorsal regions. Clear substance P-rich patches were not seen in this region, but a large substance P-rich area consisting of a dense plexus of substance P-containing fibers was visible. Embedded within this substance P-rich area were fairly discrete patches of light substance P staining. As in the dorsal caudate nucleus, increased numbers of cholinergic neurons and processes were associated with substance P-rich regions in the ventral caudate nucleus. Choline acetyltransferase-positive perikarya also appeared to be concentrated in substance P-rich areas in the nucleus accumbens and olfactory tubercle. The results of this study suggest that a close relationship exists between the distribution of substance P fibers and cholinergic perikarya in the striatum of the cat.

Fos immunoreactivity after stimulation or inhibition of muscarinic receptors indicates anatomical specificity for cholinergic control of striatal efferent neurons and cortical neurons in the rat

Cholinergic neurons play a major role in the control of striatal activity via muscarinic receptors. The action of acetylcholine also appears to be dependent on the striosome-matrix compartmentalization of the striatum. This study was designed to find out whether modification of acetylcholine tone activates neurons in the striatum and forebrain of the rat. We looked for the appearance of immunoreactivity to Fos, a regulatory protein that is thought to convert synaptic signals into changes in gene expression. Pharmacological manipulation of muscarinic receptors was found to induce specific patterns of Fos immunoreactivity in distinct neuronal populations of the forebrain, including the striatum. Oxotremorine, a non-selective muscarinic agonist, induced Fos immunoreactivity in the striatum with a large predominance in striosomes (mostly in enkephalinergic neurons), in layers 4 and 6 of the cortex, and also in the piriform cortex and septum. The muscarinic agonist pilocarpine had an identical effect in the cortex, but the striosomal prevalence was less clear-cut than that observed after oxotremorine. Treatment with dopamine-depleting agents (6-hydroxydopamine or reserpine) and inhibitors of glutamate and opiate receptor (MK-801 and naloxone respectively) had no effect on the action of oxotremorine. This suggests that the induction of Fos provoked by oxotremorine does not involve dopamine, glutamate or opiates. Atropine, a non-specific muscarinic antagonist, also induced Fos immunoreactivity in the striatum but with matrix predominance (mostly in substance P neurons), as well as in the cingulate cortex, and the olfactory tubercle. Scopolamine, a muscarinic antagonist, induced Fos in both striosomal and matrix compartments in the striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural features of the choline acetyltransferase-containing neurons and relationships with nigral dopaminergic and cortical afferent pathways in the rat striatum

The aim of this study was first to specify the morphology and neuronal environment of the large cholinergic neurons, and second to determine the distribution and mode of termination of the corticostriatal and dopaminergic inputs on these neurons in the rat striatum. Immunocytochemical procedures with a monoclonal antibody against choline acetyltransferase, Golgi staining and standard electron microscopic techniques were used to specify the ultrastructural features of the putatively cholinergic classical large neurons. The large/choline acetyltransferase-positive neurons are characterized by a voluminous, eccentric, and deeply indented nucleus leaving a large cytoplasmic area, and by the presence of an abundant granular endoplasmic reticulum and of many polysomes and free ribosomes. Serial ultrathin sectioning further indicated the presence of nematosomes or nucleolus-like bodies within the nucleus and the cytoplasm of the large neurons. In addition, these neurons were found to be in direct apposition with up to four surrounding neurons showing features typical of medium-sized spiny neurons. These data support the view that the putatively cholinergic neurons may have an intense metabolic activity and may be involved in striatal clusters. When choline acetyltransferase immunostaining was coupled with the identification of degenerating corticostriatal afferents after lesion of the cerebral cortex, degenerating terminals were seen to form synapses of an asymmetrical type on distal labelled dendrites, but these contacts were very rare. On the other hand, nigrostriatal dopaminergic axons, identified by means of either the degeneration method or tyrosine hydroxylase immunostaining, were often found to run directly for long distances around the choline acetyltransferase-positive cell bodies. Occasionally, dopaminergic terminals formed possible symmetrical synapses on choline acetyltransferase-positive cell bodies or proximal dendrites. These data provide evidence that the putatively cholinergic neurons are directly contacted by corticostriatal and dopaminergic nigrostriatal afferents. The respective positions and nature of the two types of contacts further provide morphological support for the hypothesis that postsynaptic interactions may occur between the corticostriatal and dopaminergic nigrostriatal afferents at the level of the cholinergic neurons.

Cellular substrates for interactions between dynorphin terminals and dopamine dendrites in rat ventral tegmental area and substantia nigra

Dynorphin and other kappa opioid agonists are thought to elicit aversive actions and changes in motor activity through direct or indirect modulation of dopamine neurons in ventral tegmental area (VTA) and substantia nigra (SN), respectively. We comparatively examined the immunoperoxidase localization of anti-dynorphin A antiserum in sections through the VTA and SN of adult rat brain to assess whether there were common or differential distributions of this opioid peptide relative to the dopamine neurons. We also more directly examined the relationship between dynorphin terminals and dopamine neurons in VTA and SN by combining immunoperoxidase labeling of rabbit dynorphin antiserum and immunogold-silver detection of mouse antibodies against tyrosine hydroxylase (TH) in single sections through the VTA and SN. Light microscopy showed dynorphin-like immunoreactivity (DY-LI) in varicose processes. These were relatively sparse in VTA and were unevenly distributed in the SN, with little labeling in the pars compacta (pcSN) and the highest density of DY-LI in the medial and lateral pars reticulata (prSN). Electron microscopy established that the regional differences were attributed to differences in density (number/unit area) of immunoreactive profiles. The profiles containing DY-LI were designated as axon terminals based on having diameters greater than 0.1 micron, few microtubules and many synaptic vesicles. In both the VTA and SN, the dynorphin-labeled terminals contained primarily small (35-40 nm) clear vesicles. These vesicles were rimmed with peroxidase immunoreactivity and were often seen clustered above axodendritic synapses. These synaptic specializations were usually symmetric; however a few asymmetric densities also were formed by immunoreactive terminals in both VTA and SN. Additionally, most of the dynorphin-labeled terminals contained 1-2, but occasionally 7 or more intensely peroxidase positive dense core vesicles (DCVs). Approximately 60% of the DCVs were located near axolemmal surfaces. The axolemmal surfaces contacted by immunoreactive DCVs were more often apposed to dendrites in the VTA; while in the SN other axon terminals were the most commonly apposed neuronal profiles. In both regions, a substantial proportion of the plasmalemmal surface in contact with the labeled DCVs was apposed to astrocytic processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential response of striatal dopamine and muscarinic cholinergic receptor subtypes to the loss of dopamine. III. Results in Parkinson's disease cases

The distribution and number of DA uptake sites, DA receptors (D1 and D2) and cholinergic muscarinic receptors (M1 and M2) were examined by autoradiography in the striatal complex of Parkinson's and age-matched control cases. The greatest loss of DA uptake sites occurred in the dorsolateral striatum which was the only region showing an increase in D2 receptors. The number of M2 receptors was reduced in the dorsolateral striatum and M1 receptors were reduced in most regions of the striatum. The anatomical pattern of changes in DA uptake sites, D2 receptors and M2 receptors suggests a coordinated change in the dopaminergic-cholinergic interneuron synapse in Parkinson's disease.

Input from the frontal cortex and the parafascicular nucleus to cholinergic interneurons in the dorsal striatum of the rat

Evidence derived from many experimental approaches indicates that cholinergic neurons in the dorsal striatum (caudate-putamen) are responsive to excitatory amino acids. Furthermore, evidence from physiological experiments indicate that the excitatory input is derived from the cortex and/or the thalamus. The object of the present experiment was to anatomically test whether cholinergic neurons receive cortical and/or thalamic input in the dorsal striatum using a combined anteograde tracing and immunocytochemical approach at both the light- and electron-microscopic levels. Rats received injections of the anterograde tracers Phaseolus vulgaris-leucoagglutinin or biocytin at multiple sites in the frontal cortex or parafascicular nucleus of the thalamus. Sections of the striatum were stained to reveal the anterogradely transported markers and then immunostained to reveal choline acetyltransferase immunoreactivity. The striata of these animals contained dense networks of anterogradely labelled fibres that were dispersed throughout the neuropil and interspersed with the choline acetyltransferase-immunoreactive (i.e. cholinergic) perikarya and dendrites. The anterogradely labelled fibres were often closely apposed to the choline acetyltransferase-immunoreactive neurons. Examination of electron-microscopic sections failed to demonstrate cortical terminals in synaptic contact with the cholinergic neurons even when choline acetyltransferase-immunoreactive structures were examined that had first been identified in the light microscope as having cortical terminals closely apposed to them. In these cases it was often observed that the cortical terminal, although apposed to the membrane of the labelled neurone, made synaptic contact with an unlabelled spine that was in the vicinity. In contrast to the cortical input, analysis of material that was double-stained to reveal thalamostriatal terminals and choline acetyltransferase-immunoreactive structures, revealed that the thalamostriatal terminals were often in asymmetrical synaptic contact with the perikarya and dendrites of cholinergic neurons. It is concluded that the cholinergic neurons of the dorsal striatum, like those of the ventral striatum or nucleus accumbens [Meredith and Wouterlood (1990) J. comp. Neurol. 296, 204-221] receive very little or no input from the cortex but are under a prominent synaptic control by the thalamostriatal system. Those pharmacological effects of excitatory amino acids on the cholinergic systems of the striatum are therefore presumably related to the thalamostriatal and not the corticostriatal system.

Ultrastructural examination of enkephalin and substance P input to cholinergic neurons within the rat neostriatum

Enkephalin and substance P-containing inputs to cholinergic perikarya were examined in the rat neostriatum using an ultrastructural immunocytochemical double-labeling protocol. Sections of rat neostriatum were double-labeled for either choline acetyltransferase (ChAT) and substance P or ChAT and enkephalin using silver intensified colloidal gold and peroxidase as labels. Regions containing both ChAT-positive neurons and peroxidase reaction product were identified in the light microscope prior to sectioning for electron microscopy. Substance P-containing terminals which contained round synaptic vesicles and made symmetrical synaptic contacts were commonly observed in the neostriatum. Substance P synapses onto ChAT-positive perikarya and dendrites were frequently observed: up to 5 synaptic contacts were observed onto a ChAT-positive dendrite. Enkephalin labeling was also seen in a population of axon terminals containing round synaptic vesicles and exhibiting symmetrical synaptic specializations. In contrast to substance P-containing terminals, relatively few synaptic contacts were observed onto ChAT-positive labeled perikarya and dendrites although enkephalin-labeled terminals were seen in frequent contact with perikarya and dendrites of unlabeled spiny neurons. Since enkephalin and substance P are contained within different populations of striatal spiny neurons, the results of the present study suggest that these two types of neurons differ in their intrinsic striatal connections.

Modulation of GABA release by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and N-methyl-D-aspartate receptors in matrix-enriched areas of the rat striatum

Using a new in vitro superfusion device, the release of preloaded [3H]GABA was examined in microdiscs of tissues taken from sagittal slices in matrix-enriched areas of the rat striatum. Potassium (9 mM, 15 mM) stimulated the release of [3H]GABA in a concentration- and calcium-dependent manner and the veratridine (1 microM)-evoked release of [3H]GABA was completely abolished in the presence of tetrodotoxin (1 microM). The selective glutamatergic agonist alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (1 mM) enhanced the potassium-evoked release of [3H]GABA as well as the basal outflow of [3H]GABA. This latter effect was found to be calcium-dependent, partially diminished by tetrodotoxin (1 microM), completely blocked by 6,7-dinitro-quinoxaline-2,3-dione (0.1 mM), which is generally used as an antagonist of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors, but not affected by (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK801, 10 microM), a specific antagonist of N-methyl-D-aspartate receptors. Similarly, N-methyl-D-aspartate (1 mM) enhanced both the potassium (9 mM) and the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (1 mM)-evoked release of [3H]GABA but when used alone, due to the presence of magnesium in the superfusion medium, was ineffective on the basal efflux of [3H]GABA. A stimulatory effect of N-methyl-D-aspartate (1 mM) on the basal outflow of [3H]GABA was observed, however, when magnesium was omitted from the superfusion medium. The stimulatory effect of N-methyl-D-aspartate (1 mM) observed in the presence of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate was not potentiated by glycine (1 microM, in the presence of strychnine 1 microM) and the N-methyl-D-aspartate-evoked response seen in the absence of magnesium was not enhanced by D-serine (1 mM), suggesting that endogenous glycine is already acting on N-methyl-D-aspartate receptors. In fact, in the absence of magnesium, 7-chloro-kynurenate (1 mM) completely abolished the stimulatory effect of N-methyl-D-aspartate on the release of [3H]GABA confirming that under our conditions, the glycine site of the N-methyl-D-aspartate receptor is saturated. N-methyl-D-aspartate-evoked responses were all blocked by MK801 (10 microM). Finally, the N-methyl-D-aspartate-evoked response seen in the absence of magnesium was markedly reduced in the presence of tetrodotoxin (1 microM).(ABSTRACT TRUNCATED AT 400 WORDS)

Functional heterogeneity of the matrix compartment in the cat caudate nucleus as demonstrated by the cholinergic presynaptic regulation of dopamine release

Previously, using a new in vitro microsuperfusion procedure, we have demonstrated marked differences in the cholinergic presynaptic regulation of the release of [3H]dopamine continuously synthesized from [3H]tyrosine in two close striosomal- and matrix-enriched areas of the cat caudate nucleus. A tetrodotoxin-resistant stimulatory effect of acetylcholine mediated by muscarinic receptors was observed in both compartments. However, in addition, two opposing types of tetrodotoxin-sensitive acetylcholine-evoked regulation of [3H]dopamine release were only seen in the matrix: one facilitatory, involving nicotinic receptors located on as yet unidentified neurons, and the other inhibitory, mediated by muscarinic receptors located on dynorphin-containing neurons. In the present study, using the same approach, a functional heterogeneity was demonstrated in the matrix. Indeed, in various conditions the effects of acetylcholine (50 microM) on the release of [3H]dopamine were different in a matrix-enriched area (matrix 2) distinct from that previously investigated (matrix 1); these areas being characterized by the presence or absence of islands of striatonigral cells, respectively. As in matrix 1, acetylcholine induced a short-lasting stimulation of [3H]dopamine release in matrix 2 but, in contrast to that observed in matrix 1, the acetylcholine-evoked response in matrix 2 was not modified in the presence of tetrodotoxin (1 microM). Experiments made in the presence of the tetrodotoxin and atropine (1 microM) indicated that both muscarinic and nicotinic receptors are located on dopaminergic nerve terminals in matrix 2 while muscarinic receptors are only present in matrix 1. In the absence of tetrodotoxin, the short-lasting stimulation of [3H]dopamine release was transformed into a long-lasting response in the presence of pempidine (50 microM), in matrix 2 but not in matrix 1 while prolonged responses were seen in both matrix areas in the presence of atropine. Finally, the acetylcholine short stimulatory effect on [3H]dopamine release was transformed into a long stimulatory response in the presence of bicuculline (50 microM) but not naloxone (1 microM) in matrix 2 while the reverse was observed in matrix 1. By providing further evidence for a functional heterogeneity of the matrix, our results suggest that depending on the matrix area investigated, dynorphin- or GABA-containing neurons are involved in the indirect cholinergic inhibitory control of dopamine release.

Scopolamine attenuates haloperidol-induced c-fos expression in the striatum

Haloperidol increases the expression of Fos, the protein product of the proto-oncogene c-fos, in some parts of the central nervous system. Haloperidol also produces catalepsy in rodents and extrapyramidal side effects in humans, both of which are reduced by muscarinic receptor antagonists. In order to gain insight into the neurochemical and neuroanatomical substrates of haloperidol-induced catalepsy we examined the effects of the muscarinic receptor antagonist scopolamine on haloperidol-induced Fos expression in the striatum, nucleus accumbens and lateral septal nucleus. At a dose that reduced the cataleptic effect of haloperidol, scopolamine decreased the neuroleptic-induced Fos expression in the striatum and lateral septal nucleus but not the nucleus accumbens. These results indicate that haloperidol may increase c-fos expression in medium spiny striatal neurons indirectly by enhancing striatal acetylcholine release. They are also consistent with the hypothesis that neuroleptic-induced increases in striatal c-fos expression are predictive of extrapyramidal side effects produced by these compounds.

Choline acetyltransferase- and substance P-like immunoreactive elements in fetal striatal grafts in the rat: a correlated light and electron microscopic study

Fetal striatal neurons were transplanted into the ibotenic acid-lesioned rat striatum. Three months after transplantation, the graft tissue was processed for choline acetyltransferase- and substance P-like immunoreactivity and was subsequently examined at the light and electron microscopic levels. The study demonstrated that choline acetyltransferase- and substance P-like-immunoreactive neurons were homogenously present throughout fetal striatal grafts, although in decreased numbers compared with those in the normal rat striatum. The majority of the choline acetyltransferase-immunoreactive neurons had fusiform, oval, or polygonal somata with somatic diameters greater than 20 microns and contained deeply invaginated nuclei surrounded by copious cytoplasm. In addition, choline acetyltransferase-immunoreactive neurons with somatic diameters between 10 and 20 microns were also demonstrated. The grafts' substance P-like-immunoreactive neurons, which had somatic diameters between 10 and 25 microns and had oval or polygonal perikarya, could be classified into two types based on their ultrastructural characteristics. Type I neurons contained an unindented nucleus which was surrounded by a thin rim or moderate amount of cytoplasm, whereas Type II immunoreactive neurons contained an indented nucleus which was surrounded by copious cytoplasm. Choline acetyltransferase- and substance P-like-immunoreactive dendrites in the grafts' neuropil were contacted by multiple unlabeled axon terminals. In addition, choline acetyltransferase- and substance P-like-immunoreactive axon terminals forming symmetric contacts with unlabeled dendrites were present within the graft. The study demonstrated that many of the neuroanatomical features of choline acetyltransferase- and substance P-like-immunoreactive elements found in the normal rat striatum are present in mature fetal striatal grafts.

The effect of intrastriatal application of directly and indirectly acting dopamine agonists and antagonists on the in vivo release of acetylcholine measured by brain microdialysis

The effect of intrastriatal application of D-1, D-2 and indirect dopaminergic drugs on the release of striatal acetylcholine as a function of the post-implantation intervals was studied using in vivo microdialysis. The dopamine D-2 agonists LY 171555 and (-)N0437 inhibited the release of striatal acetylcholine to 40% of control values 16-24 h after implantation of the dialysis cannula. When LY 171555 was infused 40-48 h after implantation of the dialysis cannula, the response was attenuated to 20% of control values. Meanwhile, the effectiveness of infusions of the antagonists (-)sulpiride and haloperidol was augmented from a non significant effect at 16-24 h to a 150% increase 40-48 h after implantation of the cannula. Infusions of the dopamine releasing agent amphetamine or the dopamine uptake inhibitor nomifensine resulted in a dose-dependent increase in the overflow of dopamine. Not until a sevenfold increase in the level of dopamine was seen, the release of acetylcholine was significantly affected. This hyporesponsiveness of the striatal cholinergic interneurons to endogenous dopamine could not be attributed to dopamine D-1 receptor activation, since no effects on striatal acetylcholine release were found by intrastriatal infusions of the selective D-1 agonist CY 208-243 or the selective D-1 antagonist SCH 23390. The results indicate that dopamine D-2 receptors are involved in the regulation of striatal acetylcholine release and that these receptors are tonically occupied by endogenous dopamine under the present experimental conditions 40-48 h after probe implantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrastriatal dopamine-rich implants reverse the changes in dopamine D2 receptor densities caused by 6-hydroxydopamine lesion of the nigrostriatal pathway in rats: an autoradiographic study

The aim of the present study was to test whether intrastriatal implants of embryonic dopaminergic neurons are able to normalize the lesion-induced hypersensitivity of striatal dopaminergic receptors. The ascending dopaminergic pathway of adult rats was unilaterally lesioned using 6-hydroxydopamine. Three weeks later a cell suspension obtained from the mesencephali of ED 14 rat embryos was implanted into the denervated striatum. Rotational responses to dopaminergic agonists were tested five months after implantation. One month later animals were killed and striatal dopaminergic receptor densities were quantified using autoradiography, the dopaminergic reinnervation of the host striatum being visualized with [3H]GBR 12935, a ligand labelling dopamine uptake sites. The lesion induced a behavioural hypersensitivity to dopaminergic agonists and lesioned animals displayed a strong rotation contralateral to the lesion in response to a test dose of the D1 agonist compound SKF 38393 (2.5 mg/kg) or of the D2 agonist LY 171555 (0.15 mg/kg). These responses were completely abolished by the graft. The normal distribution of D1 and D2 dopaminergic receptors in the rat striatum was similar to that described previously. Seven months after the lesion of the nigrostriatal dopaminergic pathway, the density of D1 receptors was not significantly affected while the density of D2 receptors was increased by about 25-50%. The implantation of embryonic dopaminergic neurons into the denervated striatum led to a slight decrease of D1 receptor densities and to a reversal of the lesion-induced increase of striatal dopaminergic D2 receptors six months later. Moreover, this reversal concerned not only the reinnervated striatal region but also extended into non-reinnervated areas of the striatum. It is concluded that grafts of embryonic dopaminergic neurons can normalize the density of dopaminergic D2 receptors.

Cellular interactions in the striatum involving neuronal systems using ?classical? neurotransmitters: Possible functional implications

The neostriatum contains a wide variety of neuroactive substances associated with several well-defined functional neuronal systems. This structure, which is the seat of numerous neurological pathological disorders, is commonly used as a model for studying the basic mechanisms of neurotransmitter interactions in the brain and their putative involvement in striatal functions. Increasing interest has been focusing lately on the cellular interactions that may occur between the corticostriatal putatively glutamatergic system and the nigrostriatal dopaminergic input. Current evidence suggests that the activatory corticostriatal glutamatergic input may play a more crucial role in regulating striatal functions than was formerly assumed in comparison with the dopaminergic input. The key role of cholinergic interneurons in the striatum may therefore be attributable to the fact that they modulate the glutamatergic transmission to GABA striatal efferent neurons. Likewise, dopamine may actually act indirectly in the striatum by "tuning down" the cortical excitation of striatal neurons. Consequently, an impairment of the dopaminergic transmission such as that occurring in Parkinsonism may lead to an increase in the corticostriatal glutamatergic transmission, which may further contribute towards reinforcing the "imbalance" between subsets of striatal neuronal systems controlling the output of the basal ganglia.

Ultrastructural relationships between choline acetyltransferase- and neuropeptide y-containing neurons in the rat striatum

The relationships between cholinergic and neuropeptide Y-containing neuronal systems in the rat striatum were examined using a dual immunoperoxidase labelling method. These neurons were identified by their immunoreactivity to choline acetyltransferase and neuropeptide Y, respectively, and were visualized on the same sections using 3,3'-diaminobenzidine and benzidine dihydrochloride as distinct chromogens under two conditions: (i) neuropeptide Y detection by the 3,3'-diaminobenzidine diffuse brown reaction product and choline acetyltransferase detection by the benzidine dihydrochloride blue, granular reaction product; (ii) choline acetyltransferase detection by 3,3'-diaminobenzidine and neuropeptide Y detection by benzidine dihydrochloride. Although both neuropeptide Y- and choline acetyltransferase-immunoreactive cell bodies were simultaneously detected and were easily distinguishable whatever the conditions used, neuropeptide Y- and choline acetyltransferase-immunoreactive dendrites and axons could not be visualized on the same sections, since only the diaminobenzidine-labelled processes were detectable. Light microscopic observations on sections dual labelled with either method confirmed that choline acetyltransferase and neuropeptide Y immunoreactivities were localized in morphologically different populations of striatal neurons scattered throughout the striatum, choline acetyltransferase immunoreactivity being associated with large neurons and neuropeptide Y immunoreactivity with medium-sized neurons. In addition, the choline acetyltransferase-immunoreactive neurons were found to be more numerous than the neuropeptide Y-immunoreactive neurons and to be prevalent in the dorsolateral areas of the striatum, whereas neuropeptide Y-immunoreactive neurons were preferentially found in the ventromedial areas of this structure. Electron microscopic observations on sections processed under either condition revealed that choline acetyltransferase-positive terminals form synaptic contacts of the symmetrical type with neuropeptide Y-positive somata and proximal dendrites and that choline acetyltransferase-positive neurons are contacted by neuropeptide Y-positive terminals. These data show that the striatal neuropeptide Y- and choline acetyltransferase-containing neuronal systems have reciprocal synaptic interactions and provide morphological support for the hypothesis that striatal cholinergic and neuropeptide Y interneuron activities may be functionally linked.

Antiparkinsonian dopamine agonists: a review of the pharmacokinetics and neuropharmacology in animals and humans

With the intention of compensating for the deficit of endogenous dopamine (DA) in the basal ganglia of Parkinsonian patients by substitution with agents which directly stimulate central DA receptors, synthetic DA agonists have been introduced almost 20 years ago for the symptomatic treatment of Parkinson's disease. The original expectation that DA agonists would be able to completely restore extrapyramidal motor function in Parkinsonian patients has turned out as too mechanistic and simplicative. However, undoubtedly DA agonists have improved therapeutic possibilities in Parkinson's disease. Thus, clinical evidence from controlled chronic studies in patients indicates that the therapeutic results following the early application of DA agonists in combination with L-DOPA on a long-term base are superior to the respective monotherapy. However, none of the DA agonists currently employed for antiparkinsonian treatment i.e. apomorphine and the ergoline derivatives bromocriptine, lisuride and pergolide, is optimal with respect to pharmacokinetic properties (poor oral bioavailability with considerable intra- and interindividual variation) or pharmacological profiles (low selectivity for DA receptors in case of the ergot agonists). The pathophysiology underlying Parkinson's disease which turned out more complex than initially expected might provide another explanation for the limited therapeutic potential of DA agonists. Therefore, apart from summarizing the pharmacokinetics, biotransformation, neuropharmacology and neurobiochemistry of the DA agonists employed clinically, the present article also reviews physiological aspects of (a) central dopaminergic neurotransmission including the topographical distribution of DA receptor subtypes and their functional significance, (b) the intracellular signal processing in striatal output neurons and (c) the intraneuronal mechanisms which integrate the various neurotransmitter signals converging on the striatal output neuron to a demand-adjusted effector cell response via the cross-talk between the different second messenger systems. Based on these considerations, potential pharmacological approaches for the development of improved antiparkinsonian drugs are outlined. There is a therapeutic demand for more selective and better bioavailable DA agonists. In particular, selective D-1 receptor agonists are highly desirable to provide a more specific probe than SKF 38 393 for clarifying the current controversy on the disparate findings in nonprimate species and monkeys or Parkinsonian patients, respectively, regarding the functional significance of D-1 receptors for the antiparkinsonian action of DA agonists or L-DOPA. The therapeutic importance of D-2 receptor activation is generally accepted; whether DA agonists combining a balanced affinity to both D-1 and D-2 receptors within one molecule (to some extent a property of apomorphine) might be superior to subtype-specific DA agonists remains to be tested clinically.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of dynorphin-containing neurons in the presynaptic inhibitory control of the acetylcholine-evoked release of dopamine in the striosomes and the matrix of the cat caudate nucleus

The roles of acetylcholine and dynorphin (1-13) in the presynaptic control of the release of [3H]dopamine continuously synthesized from [3H]tyrosine were examined in a prominent striosomal enriched area and in an adjacent matrix enriched area of the cat caudate nucleus. This was achieved using microsuperfusion devices applied vertically onto coronal slices of cat brain. These devices were placed in a striosomal enriched area located in the core of the structure (acetylcholinesterase-poor zone) and in an adjacent matrix enriched area (acetylcholinesterase-rich zone). [3H]Tyrosine was delivered continuously to each microsuperfusion device and [3H]dopamine released was estimated in the superfusate. As previously shown, in the presence of tetrodotoxin (1 microM), acetylcholine (50 microM) induces a prolonged stimulation of [3H]dopamine release in both compartments through an interaction with muscarinic receptors. Our present study indicates that both dynorphin 1-13 (1 microM) and the selective kappa agonist trans-3,4-dichloro-N-methyl-N[2-(1-pyrrolidinyl)cyclohexyl]benzeneace tamine (U50488) (1 microM) inhibit the tetrodotoxin-resistant acetylcholine-evoked release of [3H]dopamine, these effects being slightly more pronounced in the matrix than in the striosomal enriched area. Naloxone (1 microM) reversed the inhibitory effect of U50488 in both areas. These results suggest that dynorphin exerts an inhibitory presynaptic control of dopamine release through kappa opioid receptors located on dopamine nerve terminals in the striosome as well as in the matrix. However, the presynaptic cholinergic control of dopamine release is much more complex in the matrix than in the striosomal enriched area. Besides its tetrodotoxin-resistant stimulatory effect, acetylcholine exerts two opposing tetrodotoxin-sensitive effects on [3H]dopamine release, one facilitatory and the other inhibitory. We demonstrate here that in the superfused matrix enriched area, the indirect acetylcholine inhibitory response is mediated by dynorphin-containing neurons. Indeed, the short-lasting stimulatory effect of acetylcholine on [3H]dopamine release was converted into a long-lasting response in the presence of naloxone (1 microM), and, in this latter condition, the co-application of dynorphin 1-13 (1 microM) restored the short-lasting stimulatory effect.

The neural network of the basal ganglia as revealed by the study of synaptic connections of identified neurones

The study of synaptic connections in the electron microscope has established an 'elementary' circuit for the neostriatum which consists of a pathway from cortical areas (neocortex, hippocampus, amygdala) to medium spiny neurones of the striatum that also receive converging synaptic input from midbrain dopamine neurones. The striatal medium spiny neurones are projection neurones and they form synaptic contacts with output neurones in the globus pallidus and substantia nigra reticulata. In this way, dopaminergic afferents can directly modulate the flow of information from cortical areas through the striatum to the 'premotor' areas of the brainstem and to the thalamus. It is proposed that certain parts of the striatum can themselves control the activity of midbrain dopamine neurones and so one part of the striatum can 'gate' the flow of information through another part.

Striatal preprotachykinin and preproenkephalin mRNA levels and the levels of nigral substance P and pallidal Met5-enkephalin depend on corticostriatal axons that use the excitatory amino acid neurotransmitters aspartate and glutamate: quantitative radioimmunocytochemical and in situ hybridization evidence

Because excitatory amino acid (EAA) neurotransmission has been implicated in long-term postsynaptic events, we conducted an initial study to determine whether or not the EAA-utilizing corticostriatal projection might influence peptide biosynthesis in neurons of the rat's basal ganglia. The content of EAAs in the caudatoputamen was reduced by frontal cortical ablation or by chronic intracerebroventricular infusion of methionine sulfoximine (MS). At 7 days following cortical ablation striatal Asp and Glu were reduced by 15% and 24%, respectively, while MS infusion (24 micrograms/day) for 7 days reduced synaptosomal levels of Asp by 61% and Glu by 48%. With either treatment, quantitative radioimmunocytochemistry revealed that substance P (SP) in the substantia nigra was increased by approximately 38%, while Met5-enkephalin (ME) in the globus pallidus was not changed. In situ hybridization with oligonucleotide probes revealed changes in the rostral striatum of preprotachykinin (PPT) and preproenkephalin (PPE) mRNA levels: cortical ablation reduced PPT mRNA by 17% and PPE mRNA by 20% dorsally, while it increased PPE mRNA (but not PPT mRNA) by 23% ventrally. Likewise, the infusion of MS decreased PPT (32%) and PPE mRNA (28%) dorsally, and increased PPE mRNA (50%) ventrally. In addition to the 7 day time point, the same measurements of EAAs, peptides and mRNAs were made at 14, 21 and 28 days after cortical excisions. At 14 days, the level of striatal Asp had returned to control value, but Glu remained depressed by 21%; nigral SP remained increased by 24%, and pallidal ME decreased by 15%. PPT and PPE mRNA remained depressed dorsally by 15% and 25%, respectively, while the increase in PPE mRNA noted ventrally at 7 days had returned to control values by 14 days. With the exception of Glu, which remained depressed by 18% at 21 and 28 days, all other values had returned to control levels by 21 days. The results indicate that a large reduction in EAA neurotransmission can influence differentially the steady-state levels of neuropeptides in striatal neurons and this change is brought about, at least in part, by an alteration in gene transcription.

Hippocampal and midline thalamic fibers and terminals in relation to the choline acetyltransferase-immunoreactive neurons in nucleus accumbens of the rat: a light and electron microscopic study

The synaptic interactions between terminals of allocorticostriatal and thalamostriatal fibers and the cholinergic neurons in the nucleus accumbens were investigated using degeneration and dual labelling immunocytochemistry in Wistar rats. The presumptive cholinergic neurons were labelled with antibodies directed against choline acetyltransferase and the afferent fibers were labelled anterogradely with Phaseolus vulgaris-leucoagglutinin. Fibers from the subiculum of the hippocampal formation and from the midline and intralaminar thalamus project densely into the medial nucleus accumbens where they overlap a relatively dense population of choline acetyltransferase-immunoreactive neurons. Varicosities containing Phaseolus vulgaris-leucoagglutinin juxtapose the immunoreactive neurons. To study the possibility that the cholinergic neurons could be the synaptic targets of these incoming fibers, the subiculum, the fornix, and the midline/intralaminar thalamus were lesioned in separate animals and brain sections were immunoprocessed for choline acetyltransferase and studied with the electron microscope. In addition, dual-labelling electron microscopic immunocytochemistry was employed. In total, 164 synaptic terminals from the subiculum/hippocampus and 130 from the midline/intralaminar thalamus were examined; all formed asymmetrical synaptic specializations. No hippocampal endings were seen to contact the somata or primary dendrites of the choline acetyltransferase-immunoreactive neurons; however, three were found in synaptic contact with distal, immunolabelled dendritic shafts. Most hippocampal terminals established contacts with unlabelled spines. Fifteen percent of the thalamic endings were found to synapse on the somata and the primary and distal dendrites of the choline acetyltransferase-immunoreactive neurons. The remaining thalamic terminals established synaptic junctions with small unlabelled dendrites or spines. These findings have important implications not only for our understanding of the synaptic organization of the hippocampal and thalamic projections to the nucleus accumbens, but also for the contribution of the cholinergic neurons to the circuitry of this nucleus.

Intrastriatal grafts derived from fetal striatal primordia: II. Reconstitution of cholinergic and dopaminergic systems

Reconstitution of striatal cholinergic and dopaminergic systems was studied in intrastriatal grafts derived from embryonic day 15 rat striatal primordia and implanted into adult host rats in which unilateral ibotenic acid lesions had previously been made in the striatum. Histochemical, immunohistochemical, and ligand binding autoradiographic techniques were applied to analyze different constituents of these two systems and to study their locations relative to each other in grafts allowed to grow for 9-17 months following transplantation. For the cholinergic system, a modular organization was found in the striatal grafts with stains for choline acetyltransferase and acetylcholinesterase, respectively the synthetic and degradative enzymes for cholinergic neurons; by autoradiographic [3H]hemicholinium binding, specific for high affinity choline uptake sites associated with cholinergic terminals; and by autoradiographic [3H]pirenzepine binding, selective for M1 receptors. For the dopaminergic system, a comparable modular organization was found in the grafts by immunostaining for tyrosine hydroxylase, the catecholamine synthetic enzyme; by autoradiographic [3H]mazindol binding for dopamine uptake sites; and by [3H]SCH23390 binding for dopamine D1 receptors and [3H]sulpiride binding for dopamine D2 receptors. The results indicate that the distributions of the cholinergic and dopaminergic markers in striatal grafts are in close anatomical register. These markers for intracellular and membrane-associated components of the cholinergic and dopaminergic systems were preferentially localized in the acetylcholesterase-rich patches of the grafts in which cortical and thalamic fibers have also been found in striatal grafts, and in which output neurons projecting to the pallidum are located. This anatomical correlation suggests that the substrates for cholinergic-dopaminergic interactions typical of the normal striatum may be reinstated in the grafts both in relation to efferent neurons establishing connections with the host brain that are typical of normal striatofugal connections, and in relation to major afferent fiber systems from the host brain originating in regions known to project densely to the normal striatum. Accordingly, the cholinergic and dopaminergic systems in such grafts may regulate the functional influence of the grafts on the behavior of host animals.

Striatal dopamine in motor activation and reward-mediated learning: steps towards a unifying model

On the basis of behavioural evidence, dopamine is found to be involved in two higher-level functions of the brain: reward-mediated learning and motor activation. In these functions dopamine appears to mediate synaptic enhancement in the corticostriatal pathway. However, in electrophysiological studies, dopamine is often reported to inhibit corticostriatal transmission. These two effects of dopamine seem incompatible. The existence of separate populations of dopamine receptors, differentially modulating cholinergic and glutamatergic synapses, suggests a possible resolution to this paradox. The synaptic enhancement which occurs in reward-mediated learning may also be involved in dopamine-mediated motor activation. The logical form of reward-mediated learning imposes constraints on which mechanisms can be considered possible. Dopamine D1 receptors may mediate enhancement of corticostriatal synapses. On the other hand, dopamine D2 receptors on cholinergic terminals may mediate indirect, inhibitory effects of dopamine on striatal neurons.

Immunocytochemical localization of cholinergic terminals in the region of the nucleus basalis magnocellularis of the rat: a correlated light and electron microscopic study

The cholinergic circuitry in the nucleus basalis magnocellularis of the rat was investigated in a correlated light and electron microscopic study by using monoclonal antibodies against the acetylcholine-synthesizing enzyme, choline acetyltransferase, following the unlabelled antibody peroxidase-antiperoxidase immunocytochemical procedure. After the immunocytochemical approach, large cholinergic cells and a few immunoreactive fibres exhibiting a varicose appearance, were detected by light microscopy in portions of the nucleus basalis magnocellularis located within the anatomical limits of the globus pallidus, mostly in its ventromedial part. Cholinergic neurons and fibre-like structures were also found within the substantia innominata on the edge of globus pallidus. The same material studied by light microscopy was analysed with the electron microscope. At the ultrastructural level, the immunopositive neurons showed the same cytological characteristics and pattern of synaptic input as cholinergic basal forebrain cells. Additionally, scarce immunoreactive preterminal axons and terminal boutons were detected in the region. The immunoreactive terminals were scattered or formed occasional clusters and appeared as heavily immunostained vesicle-filled boutons making exclusively axodendritic synaptic contacts principally with immunonegative distal dendrites. Both symmetric and asymmetric synaptic contacts established between these structures were detected, although the symmetric contacts were the more numerous. The surface of postsynaptic immunonegative dendrites in asymmetric synaptic contact with immunoreactive terminals was generally covered by terminals that lacked detectable immunoreactivity. In contrast, those in symmetric synaptic contact with labelled terminals showed much sparser input from immunonegative terminals, suggesting that they may belong to interneurons. Very rarely, cholinergic terminals were detected in asymmetric synaptic contact with dendrites which also contained positive immunoreaction product. Asymmetric contacts were frequently characterized by the presence of subjunctional dense bodies. The detection of cholinergic terminals in the region of the nucleus basalis magnocellularis of the rat indicates that this region not only contains cholinergic projecting neurons, but receives a cholinergic input itself. Results of this study provide evidence of the existence of a cholinergic transmission in the basal forebrain of the rat, and also that acetylcholine might play a role in the regulation of the extrinsic cortical cholinergic innervation. The possible sources of this innervation are discussed.

Correlative decrease of large neurons in the neostriatum and basal nucleus of Meynert in Alzheimer's disease

A quantitative investigation was performed on the large neurons in the neostriatum and basal nucleus of Meynert (bnM) in patients with Alzheimer's disease (AD) and progressive supranuclear palsy (PSP). The degree of decrease of the large neurons in the neostriatum was quite similar to that in the bnM; these decreases were significantly correlative in AD, but not in PSP. These findings indicate that the large neurons in the neostriatum and bnM, which are considered to be cholinergic and to exclusively possess nerve growth factor receptors in the cerebrum, degenerate simultaneously in an equal ratio in AD.

Localization of striatal dopamine receptor function by central injection of an irreversible receptor antagonist

The stereotypic head-down sniffing response to systemically administered apomorphine (0.65 mumol/kg) was assessed in rats 48 h after the bilateral injection of 0.2-0.5 microliters of the irreversible receptor antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (60 micrograms/microliters) into the caudate-putamen and nucleus accumbens. This response was significantly attenuated in animals that had received injections of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline into the anterior/ventral part of the caudate-putamen but not in those that received injections into regions more dorsal/posterior. Animals were killed after apomorphine challenge and the region of dopamine D1 or D2 receptor reduction due to N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline mapped and quantified. This analysis revealed that the dopamine receptors involved in the apomorphine-induced stereotyped head-down sniffing response were located in a discrete region of the ventrolateral caudate-putamen and the dorsolateral nucleus accumbens. Animals that were pretreated with the selective dopamine D2 receptor antagonist raclopride (0 20 mumol/kg, i.p.) 20 min prior to central injection of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline into this area showed a dose-dependent protection of the stereotyped sniffing response to systemic apomorphine 48 h later. This combination of techniques constitutes a novel way to investigate striatal function and the results obtained support the concept of a functional subdivision of both the caudate-putamen and the nucleus accumbens.

Cholinergic stimulation of the ventrolateral striatum elicits mouth movements in rats: pharmacological and regional specificity

Cholinomimetic drugs are known to induce changes in perioral behavior in rodents, characterized primarily by "purposeless" chewing movements, but little is known about their central sites of action. Using observational methods, the effects of direct microinfusion of a mixture of physostigmine and acetylcholine (PS/Ach, 0, 0.5, 2.5, 5.0 micrograms of each in 0.5 microliter saline) into the ventrolateral striatum (VLS) were assessed. Cholinergic stimulation of this region produced a dose-dependent induction of mouth movements, characterized by chewing movements, jaw opening and closing, tongue protrusions and jaw tremors. These movements were not directed toward any stimulus. In some rats, cholinergic stimulation of the VLS also induced stereotyped self-biting, although this effect was less prominent and of shorter duration. Induction of mouth movements by cholinergic stimulation of the VLS was blocked by prior administration of atropine, either systemically (50 mg/kg) or directly into the VLS (10 micrograms). Systemic administration of methylatropine (50 mg/kg) did not block the mouth movements. Pretreatment with haloperidol (2.5 micrograms into VLS) had no effect on PS/Ach-induced mouth movements. Infusion of PS/Ach (0, 2.5, 5.0 micrograms) into the dorsolateral or ventromedial striatum did not produce significant changes in oral behavior, although the level of mouth movements was somewhat higher at the medial site. The three sites studied were also differentiated with respect to spontaneous motor behaviors (locomotion and rearing) following direct cholinergic stimulation. These findings are considered as further evidence for the role of the ventrolateral striatum in oral motor behavior.

Ontogeny of M1 and M2 muscarinic binding sites in the striatum of the cat: relationships to one another and to striatal compartmentalization

The ontogeny of striatal M1 and M2 muscarinic cholinergic binding sites was studied autoradiographically in cats ranging in age from embryonic day 40 to postnatal day six. Direct labeling with [3H]pirenzepine revealed M1 sites, and M2 sites were labeled with [3H]N-methylscopolamine in the presence of pirenzepine. In serial tissue sections, distributions of striatal M1 and M2 sites were compared to one another and to patterns of acetylcholinesterase staining and tyrosine hydroxylase-like immunoreactivity. The younger fetal material demonstrated heterogeneous distributions for both subtypes of muscarinic binding sites, with patches of dense binding corresponding to islands of dopaminergic nigrostriatal innervation. For both M1 and M2 binding, lateral to medial and caudal to rostral density gradients were present in the patches and in the surrounding matrix. During fetal development and into the perinatal period, overall muscarinic binding increased, but more so in the matrix than in the patches. By postnatal day six striatal M2 binding appeared nearly homogeneous. M1 binding, however, was slightly more concentrated in patches than in matrix. The patches of elevated M1 binding were still present at maturity, and corresponded to striosomes. These findings suggest that the ontogenetic regulation of muscarinic binding sites is influenced by location relative to striatal compartments, and that expression of M1 and M2 binding site subtypes is differentially regulated.

Differential sparing of somatostatin-neuropeptide Y and cholinergic neurons following striatal excitotoxin lesions

We previously found that quinolinic acid striatal excitotoxin lesions result in a relative sparing of somatostatin and neuropeptide Y neurons. In the present study we examined dose-response effects of excitotoxins acting at the three subtypes of glutamate receptors: N-methyl-D-aspartate (AA1), quisqualate (AA2), and kainic acid (AA3). Concentrations of both somatostatin-like immunoreactivity (SLI) and neuropeptide a Y-like immunoreactivity (NPYLI) were compared with those of substance P-like immunoreactivity (SPLI) and GABA. Kainic acid (AA3), quisqualic acid (AA2), and AMPA (AA2) resulted in dose-dependent reductions in all four neurochemical markers examined, while N-methyl-D,L-aspartate (AA1) and quinolinic acid (AA1) resulted in relative sparing of SLI and NPYLI. At doses of each excitotoxin which resulted in comparable 50% reductions in both GABA and SPLI only N-methyl-D,L-aspartate and quinolinic acid had no significant effect on concentrations of SLI and NPYLI. The relative sparing of somatostatin-neuropeptide Y neurons was confirmed histologically by using histochemical staining for NADPH-diaphorase neurons combined with either Nissl stains, or immunohistochemical staining for enkephalin. Lesions with N-methyl-D-aspartate agonists resulted in preferential sparing of NADPH-diaphorase neurons while these neurons were more vulnerable than other neurons to kainic acid or AMPA. Choline acetyltransferase neurons were relatively spared, as compared with other neurons, by agents acting at all three glutamate receptor subtypes. N-methyl-D,L-aspartate lesions were blocked with MK-801, while there was no effect on quisqualic acid or kainic acid lesions. The relative sparing of somatostatin-neuropeptide Y neurons following striatal excitotoxin lesions with N-methyl-D-aspartate (AA1) agonists probably reflects a paucity of AA1 receptors on these neurons. Since these neurons are also spared in Huntington's disease, excitotoxins acting at the N-methyl-D-aspartate (AA1) site provide an improved neurochemical model of this illness.