Cellular substrate of the histochemically defined striosome/matrix system of the caudate nucleus: a combined Golgi and immunocytochemical study in cat and ferret

The human neostriatum shows compartmentalization of neuropeptide gene expression in dorsal and ventral regions: an in situ hybridization histochemical analysis

Expression of neuropeptide messenger RNAs in striatal neurons was studied in post mortem human brain tissue by the use of in situ hybridization histochemistry. Clusters of cells expressing high levels of prodynorphin messenger RNA, and less strikingly, preprotachykinin messenger RNA, were prominent in the caudate nucleus and were present but less pronounced in the putamen. Proenkephalin and prosomatostatin messenger RNA-containing cells were more homogeneously distributed throughout the striatum, though the latter were much sparser. The four neuropeptide messenger RNA patterns in the nucleus accumbens were rather homogeneous compared with the dorsal striatum. Of these, prodynorphin messenger RNA showed a higher level of expression per cell in the nucleus accumbens relative to the dorsal striatum. The relationship of neuropeptide-containing cell clusters to the striosomal organization was characterized by looking at the register of these markers with patterns of low acetylcholinesterase activity and dense mu opiate receptor binding. In the caudate and putamen, clusters of cells expressing high levels of dynorphin and preprotachykinin messenger RNAs were clearly in register with the striosomes. The accumbens was defined by high prodynorphin messenger RNA levels, both low and high levels of acetylcholinesterase staining, and very low to absent mu opiate receptor binding. The distribution of high-expressing prodynorphin messenger RNA-containing cells--to the patch compartment and throughout the entire ventral striatum/nucleus accumbens region--defines the limbic domain of the neostriatum and suggests particular relevance to human striatal organization and function, because the distribution of this opioid neuropeptide is considerably more compartmentalized in human than in non-human species.

The distribution of cholinergic perikarya with respect to enkephalin-rich patches in the caudate nucleus of the adult cat

The distribution of cholinergic interneurons with respect to enkephalin-rich patches in the caudate nucleus of the cat was examined using both computer-assisted 3-D reconstruction and immunocytochemical techniques. Examination of the 3-D distribution of perikarya staining for choline acetyltransferase (ChAT) revealed that these cells were not evenly distributed within the caudate nucleus but exhibited areas of increased and decreased density. Comparison of the 3-D distribution of cholinergic perikarya to that of the enkephalin-rich patches indicated that areas of increased ChAT+ cell density often corresponded to the positions of enkephalin-rich patches within the dorsal-lateral caudate nucleus. At more ventral regions, there was no clear correspondence between areas of increased ChAT+ cell density and enkephalin-rich patches. In agreement with these observations, a quantitative analysis of sections double-labeled for ChAT and enkephalin revealed that the density of cholinergic neurons within enkephalin-rich patches was twice that in the surrounding tissue in the dorsal region of the caudate nucleus. In contrast at more ventral levels, the difference in the density of ChAT+ cells in enkephalin-rich patches did not significantly differ from that in the surrounding striatal tissue. Both the results of the 3-D and the double-labeling analysis suggest that cholinergic neurons are not evenly distributed within the caudate nucleus of the cat but form loose clusters which are associated dorsally with the enkephalin-rich patches. These results also provide further evidence of heterogeneity within the striosomal compartment in the cat.

Localisation of parvalbumin-immunoreactive structures in primate caudate-putamen

To investigate the morphology, distribution, and connections of parvalbumin-containing neurones in the caudate-putamen of primates, perfuse-fixed sections were stained to reveal parvalbumin immunoreactivity. In agreement with previous observations, the caudate-putamen was rich in parvalbumin-positive neurones and neuropil. The neuropil staining was uneven such that the dense background staining was interspersed with zones of relatively weak staining. The distribution corresponded to the striosome/matrix system as defined by substance P or met-enkephalin immunostaining in adjacent sections. Because parvalbumin-positive neurones are present in regions known to project to the caudate-putamen and the majority of parvalbumin-positive terminals in the matrix formed asymmetric synapses, it is concluded that the uneven staining is probably due to afferents of the neostriatum. The morphology of the parvalbumin-immunoreactive neurones varied between the striosomes and matrix; those in the matrix were smaller and possessed dendritic arborisations that were relatively uniform, whereas those in the striosomes were generally more extensively stained and possessed a greater variation in their dendritic branching patterns. The dendrites frequently crossed the boundary between the striosomes and matrix. A population of giant parvalbumin-immunoreactive neurones was also observed in the putamen. Electron microscopic analysis revealed that, in addition to terminals forming asymmetric synapses, a smaller population formed symmetric synaptic specialisations and are presumed to be derived from the local parvalbumin-immunoreactive neurones. Terminals of the latter group formed synapses with medium-sized spiny neurones. Because parvalbumin-positive neurones receive input from the cortex, they may transmit cortical information to spiny neurones.

Identification and characterization of striatal cell subtypes using in vivo intracellular recording and dye-labeling in rats: III. Morphological correlates and compartmental localization

In the first two reports of this series, in vivo intracellular recording techniques were used to characterize the electrophysiological properties of two types of striatal neurons that had been identified by their distinct response patterns to stimulation of corticostriatal afferents. In this paper, we examined whether cells showing Type I or Type II response patterns also differed with respect to their morphology or compartmental localization by combining intracellular recording and Lucifer yellow staining with immunocytochemical localization of calbindin 28 kd immunoreactivity. In the majority of cases, both Type I and Type II neurons exhibited similar morphological characteristics, with 80% of the Type I cells (13/16) and all of the Type II cells (n = 40) being small or medium spiny neurons. In each case where the morphological class of the cell was different than the spiny cell class, the cell exhibited a Type I response pattern. These spiny neurons had somata that averaged 17.1 +/- 1.3 microns in diameter and gave rise to between four and eight primary dendrites. The axons typically arose from cell bodies (7/13 for Type I and 25/40 for Type II cells) and emitted extensive local axonal collaterals. However, the axons of Type I cells more frequently originated from the dorsal surface of the somata (9/13; 69%), whereas Type II axons more frequently arose from the ventral surface of the somata (25/35; 71%), which may account for their different extracellular waveforms. In coronally sectioned tissue (n = 18), the axons always projected laterally when the somata were located in the medial striatum and projected medially when the somata were in the lateral striatal region. In a subset of experiments (N = 22), Lucifer yellow-stained neurons were localized with respect to their position within the patch and matrix compartments of the striatum using subsequent staining for calbindin 28 kd immunoreactivity. Of the 20 labeled medium spiny neurons examined (Type II: N = 13; Type I: N = 7), 19 were located in the calbindin-positive matrix compartment. The only neuron localized to the patch compartment was a medium spiny cell that exhibited a Type II paired impulse response pattern. In addition, of the two aspiny neurons from this group with beaded dendrites, one was localized to the border between adjacent patch and matrix compartments, whereas the other was located completely within the matrix compartment. Therefore, despite their distinct paired impulse response patterns, the majority of both Type I and Type II neurons were medium spiny cells located in the matrix compartment of the striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Dendritic domains of medium spiny neurons in the primate striatum: relationships to striosomal borders

Medium spiny neurons are the projection neurons of the striatum. They receive the majority of striatal afferents, and they make up the vast majority of all neurons in the striatum. These densely spiny cells thus constitute a major substrate for input-output processing in the striatum. In the experiments described here we analyzed the dendritic fields of spiny neurons in the squirrel monkey striatum and plotted their orientations with respect to the borders between striosomes and matrix. Medium-sized spiny neurons in the caudate nucleus were filled intracellularly in a fixed-slice preparation with the fluorescent dye Lucifer Yellow. Dendritic arbors were reconstructed following immunostaining of the injected neurons with antiserum to Lucifer Yellow and counterstaining for striosome/matrix compartments. A majority of the medium spiny neurons studied had dendritic arborizations that remained within their compartment of origin. Thus the striosome/matrix subdivision not only partitions neurotransmitter molecules and extrinsic striatal connections into two domains in the primate caudate nucleus, but also constrains the dendritic arbors of many projection neurons there. Other medium spiny neurons, however, in both striosomes and matrix, had dendrites that crossed from one compartment into the other. About a quarter of the spiny neurons reconstructed had at least one such crossing dendrite. These results suggest that compartmentalization of afferent and efferent processing by projection neurons in the primate striatum is not absolute. For a subpopulation of spiny neurons in striosomes and matrix, inputs to one compartment could have a direct influence on output cells of the other.

Dendritic arbors of spiny neurons in the primate striatum are directionally polarized

Despite the relatively unfeatured cytoarchitecture of the striatum, this large subcortical region has been found to have a modular macroscopic substructure comprising the neurochemically distinct striosomes and matrix, and, within the matrix, patchy input and output arrangements called matrisomes. In the study reported here, we explored the possibility that the cellular architecture of the striatum is also more specialized than previously suspected. We injected medium spiny neurons in lightly fixed slices of the squirrel monkey caudate nucleus, reconstructed their dendritic arbors, and analyzed the orientations of these arbors with respect to the cardinal planes of the striatum. The data were unequivocal in suggesting that many spiny neurons, whether near striosomes or not, have dendritic arbors with preferred orientations along a diagonal axis running from rostral, dorsal, and medial to caudal, ventral, and lateral. This axis corresponds to the orientations of many striosomes and matrisomes in the squirrel monkey's caudate nucleus. We therefore suggest that the primate striatum is characterized not only by a macroscopic organization dividing it into striosomes and matrisomes, but also by a microscopic architecture observed by the dendritic arbors of many of its projection neurons. We obtained comparable supplementary observations for the ferret caudate nucleus, suggesting that such spatial alignment of spiny dendritic arbors may be a general feature of striatal organization. These polarized dendritic arrangements could provide a cellular framework for compartmental input-output processing within the striatum.

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.

Morphological differences between projection neurons of the core and shell in the nucleus accumbens of the rat

The somatodendritic morphology of projection neurons in the shell and core of the rat nucleus accumbens was studied. These cells were retrogradely labelled with Fast Blue from the ventral mesencephalon (substantia nigra/ventral tegmental area) and subsequently injected intracellularly with Lucifer Yellow and processed immunocytochemically. Digitized reconstructions revealed that the cell bodies of neurons located throughout the nucleus are small-to-medium in size. Neurons in the shell have significantly fewer dendritic arbours with fewer branch segments, fewer terminal segments, and lower spine densities than those in the core. Values for the same parameters are significantly greater for cells in lateral than in medial parts of the shell but the same for neurons located within and without enkephalin enriched parts of the core, with an exception of spine density being significantly greater in the enkephalin-rich compartment. Calculations based on these data reveal that neurons in the core have as much as 50% more surface area than those in the shell, which suggests that core neurons have a greater potential for collecting synaptic information than have shell cells. Furthermore, the differential distribution and action of various neurochemicals such as dopamine in the shell and core, supports the idea that different morphologies reflect the presence of distinct neuronal circuits in these two territories.

Compartmentalization of excitatory amino acid receptors in human striatum

Division of the mammalian neostriatum into two intermingled compartments called striosomes and matrix has been established by analysis of enzyme activity, neuropeptide distribution, nucleic acid hybridization, and neurotransmitter receptor binding. Striosomes and matrix are distinct with respect to afferent and efferent connections, and these regions provide the potential for modulation and integration of information flow within basal ganglia circuitry. The primary neurotransmitters of corticostriatal afferents are excitatory amino acids, but to date no correlation of excitatory amino acid receptors and striatal compartments has been described. We examined binding to the three pharmacologically distinct ionotropic excitatory amino acid receptors, N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, and kainate, in human striatum using in vitro receptor autoradiography and compared the binding to striosomes and matrix histochemically defined by acetylcholinesterase activity. Our findings reveal increased binding to N-methyl-D-aspartate receptors and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in matrix relative to striosomes and increased kainate receptor binding in striosomes relative to matrix. These results suggest that afferent input to the two striatal compartments may be mediated by pharmacologically distinct excitatory amino acid receptor subtypes.

Topographical organization of the projections from physiologically identified areas of the motor cortex to the striatum in the rat

The present study was undertaken to determine in the rat the topography of the neostriatal projections originating from the motor cortex. For that purpose, anterograde tracers (Phaseolus vulgaris leucoagglutinin: PHA-L; wheat germ agglutinin conjugated to horseradish peroxidase: WGA-HRP) were deposited in discrete cortical sites physiologically identified by microstimulation. Five major motor areas were considered in this study: the rostral (RFL) and caudal (CFL) forelimb areas, the hindlimb (HL) area, the vibrissae motor-frontal eye field (V-FEF) region and the jaw, lips and tongue (JLT) area (according to the nomenclature of Neafsey et al.). The results indicate that functionally different regions of the motor cortex project to different sectors of the caudate putamen (CPU). All 3 distinct limb areas RFL, CFL and HL project to the dorsolateral quarter of the CPU, V-FEF area projects to the dorsomedial quarter, whereas the JLT area projects to the ventrolateral quarter. The pattern of terminal labeling is relatively consistent, whatever the cortical area in which the tracer is deposited. This pattern is characterized by the presence of two or more labeled bands which are obliquely oriented along a ventrolateral-dorsomedial axis. Control experiments were also undertaken in which a retrograde tracer (WGA-HRP) was deposited in various neostriatal loci. The results are congruent with the findings of the anterograde study and further indicate that a given neostriatal sector receives projections from cytoarchitectonically different but functionally related regions of the neocortex. The somatotopic features of both motor and somatosensory corticostriatal projections appear to be in register. In addition, the striatal distribution of motor cortical fibers was compared in 6 experimental cases to the compartmental subdivision of the striatum in patches and matrix, following immunohistochemical localization of calbindin 28 kDa. The calbindin-immunoreactivity is extremely weak in the dorsolateral sector but is higher in the central and ventrolateral parts of the CPU. In these deep striatal regions receiving fibers from V-FEF, JLT and, to a lesser extent, from the limb areas, the cortical fibers are mostly directed to the matrix. The band-like organization of the projection from the motor cortex is correlated to the patch-matrix organization. The patches correspond to the bands of low density of terminal fibers and the matrix to the bands of high terminal density. The present results provide an anatomical basis to both electrophysiological and behavioral observations suggesting that functional distinctions can be established between subregions of the striatum.

The neostriatal mosaic: multiple levels of compartmental organization

The striatum, which is the major component of the basal ganglia, displays a complex mosaic organization of neurochemical systems that are related to its neuroanatomical connections. This mosaic organization reflects multiple levels of functional compartments. The first level is determined by the segregation of two major striatal output systems, one to the globus pallidus (external segment) and the other to the entopeduncular nucleus and substantia nigra. The second level segregates the cortical outputs of sublaminae of layer V between the patch and matrix compartments of the striatum, which project to the dopaminergic and GABAergic neurons in the substantia nigra, respectively. The third level is related to the topography of cortical inputs by which regions of the striatum may be functionally defined on the basis of the cortical areas with which they are connected. Neurochemical markers display complex mosaic patterns in the striatum that, when examined in the context of the multi-level compartmental organization of the striatum, reveal the highly organized manner by which the striatum processes cortical information.

Afferent-boundary interactions in the developing neostriatal mosaic

The caudate-putamen (neostriatum) of the mammalian basal ganglia is composed of two neurochemically distinct compartments termed patch (island, striosome) and matrix that overall contribute to a mosaic organization. In the present study, the distribution of the developmentally regulated extracellular matrix molecule tenascin, as well as several other neural cell adhesion molecules, was examined in the neostriatal mosaic of the early postnatal mouse and compared with tyrosine hydroxylase distribution following partial destruction of the dopaminergic nigrostriatal projection. During normal neostriatal development, tenascin is most dense within the matrix compartment and highly concentrated in boundaries around patches. This pattern is apparent on embryonic day 18, and for the most part disappears by postnatal day 12. Tenascin immunoreactivity is altered in the neostriatum following lesions of the nigrostriatal pathway in the first postnatal week revealed by an overall reduced expression of this molecule and a marked reduction in tenascin staining of boundaries at the interface of tyrosine hydroxylase-rich patch and tyrosine hydroxylase-poor matrix compartments. When compared to tyrosine hydroxylase immunoreactivity, other cell adhesion molecules tested failed to show altered intensities and patterns of immunoreactivity within the neostriatum after similar lesions. Reduced levels of tenascin in the lesioned neostriatum, in register with altered levels of tyrosine hydroxylase immunostaining of dopaminergic inputs, suggests that axons may affect the expression of particular recognition molecules in their target structures. The fact that boundaries are malleable can be related to afferent-induced plastic events in the differentiation of cellular elements in the developing nigrostriatal system.

The neostriatal mosaic: multiple levels of compartmental organization

Although schizophrenia may result from dysfunction of the cerebral cortex the possible indirect involvement of the basal ganglia may be important as this neural system provides a major neural system through which the cortex affects behavior. Processing of cortical input occurs within the striatum, which is the main component of the basal ganglia, where excitatory cortical input is transformed to oppositely modulate the output nuclei of the basal ganglia. The details of this transformation, as well as the role of dopamine in this process, are beginning to unfold. Striatal projections to the globus pallidus, through connections with the subthalamic nucleus, modulate excitatory input to the output neurons of the basal ganglia, GABAergic neurons in the internal segment of the globus pallidus and in the substantia nigra, whereas striatal projections directly to these neurons, provide inhibitory inputs. Thus, cortically driven activity in these two striatal output pathways oppositely modulate the output neurons of the basal ganglia. Dopamine appears to play a crucial role in this transformation. D1 and D2 dopamine receptors are specifically expressed by striatonigral and striatopallidal neurons, respectively. The direct action of dopamine through these receptors appears to oppositely modulate the responsiveness of striatal output pathways to cortical input. Insights into the role of dopaminergic function within the basal ganglia may have direct relevance to the development of treatments for schizophrenia.

Hydrolysis of substance P in the rabbit retina: I. Involvement of acetylcholine and acetylcholinesterase. An in vivo study

The laminar patterns of acetylcholinesterase (AChE) activity and substance P (SP) immunoreactivity within the inner plexiform layer (IPL) of the rabbit retina show striking similarities. Discrete bands of SP-immunoreactivity were seen at 1-7%, 40-48% and 85-95% depth of IPL. AChE activity was present throughout the entire thickness of the IPL with moderately stained bands in each sublamina (3-24% in sublamina a and 62-89% in sublamina b depth IPL). These bands were bordered on both sides by bands of even greater density (in sublamina a 0-3% and 24-34% and in sublamina b 55-62% and 89-100% depth IPL). Cell processes staining for choline acetyltransferase (ChAT) have previously been shown to ramify at 19-24% and 63-79% depth levels. Thus, SP- and ChAT-immunoreactive bands are located in both sublaminae, positioned within regions of moderate AChE activity and flanked by bands with greater AChE activity. This strong morphological correspondence and reported interactions between acetylcholine (ACh), AChE and SP in vitro provide the basis for the present study to determine whether such interactions can be demonstrated in vivo. Retinas infused with ACh showed a 60% average increase in SP-IR as compared with untreated retinas from the same animals. Treatment with diisopropylfluorophosphate (DFP) also resulted in a 56% increase in SP-IR. The ability of ACh to induce increased levels of SP was not inhibited by CoCl2, atropine or mecamylamine, ruling out the possibilities of polysynaptic transmission or involvement of muscarinic or nicotinic receptors. Infusion of ACh did not increase the levels of preprotachykinin-mRNA indicating that the increase in SP-IR is not due to de novo synthesis but rather to inhibition of the enzyme(s) responsible for SP degradation. Whether AChE functions alone or in concert with other enzymes to hydrolyze SP cannot be determined from these experiments but is addressed in a separate study.

Heterogeneous distribution of dopamine D2 receptor mRNA in the rat striatum: a quantitative analysis with in situ hybridization histochemistry

Dopamine D2 receptor mRNAs have recently been cloned and their gross distribution in the central nervous system described. Quantitative in situ hybridization histochemistry with a cRNA probe complementary to the mRNAs encoding approximately 70% of the third intracellular loop of the rat D2 receptor was performed on sections of rat brain to determine whether differences previously observed in the density of ligand binding sites in subregions of the striatum were related to differences in mRNA levels. Film autoradiographic analysis demonstrated 30% more hybridization signal in the lateral compared to the medial caudate-putamen, a distribution parallel to that of binding of ligands specific for the D2 receptor. Inspection at the cellular level using emulsion autoradiography also indicated a differential distribution of the D2 receptor mRNA. Fewer positively labelled cells, as well as fewer silver grains per cell, were seen in the medial compared to the lateral half of the striatum. This suggests that the gradient seen in autoradiographic studies of the distribution of D2 receptors is related both to regional differences in D2 mRNA levels and to the density of cells expressing the receptor. In addition, the distribution of cells expressing D2 receptor mRNA in the extrastriosomal matrix was compared to that in striosomes identified by the presence of a high density of 3H-naloxone binding sites. Labelled cells were mainly found in the matrix (3H-naloxone binding-poor) but were also seen in striosomes (3H-naloxone binding-rich). The results suggest that differences in levels of D2 binding sites in subregions of the striatum are related to differences in the level of expression of this receptor in intrinsic striatal neurons, suggesting differential regulation of dopamine D2 receptor gene expression in topographically distinct striatal neurons.

Restricted cortical termination fields of the midline and intralaminar thalamic nuclei in the rat

The projections from the midline and intralaminar thalamic nuclei to the cerebral cortex were studied in the rat by means of anterograde tracing with Phaseolus vulgaris-leucoagglutinin. The midline and intralaminar nuclear complex taken as a whole projects to widespread, predominantly frontal, cortical areas. Each of the constituent thalamic nuclei has a restricted cortical projection field that overlaps only slightly with the projection fields of adjacent midline and intralaminar nuclei. The projections of the intralaminar nuclei cover a larger cortical area than those of the midline nuclei. The laminar distributions of fibres from individual midline and intralaminar thalamic nuclei are different and include both deep and superficial cortical layers. The parataenial, paraventricular and intermediodorsal midline nuclei each project to circumscribed parts of the prefrontal cortex and the hippocampal and parahippocampal regions. In the prefrontal cortex, the projections are restricted to the medial orbital, infralimbic, ventral prelimbic and agranular insular fields, and the rostral part of the ventral anterior cingular cortex. In contrast to the other midline nuclei, the rhomboid nucleus projects to widespread cortical areas. The rostral intralaminar nuclei innervate dorsal parts of the prefrontal cortex, i.e. the dorsal parts of the prelimbic, anterior cingular and dorsal agranular insular cortical fields, the lateral and ventrolateral orbital areas, and the caudal part of the ventral anterior cingular cortex. Additional projections are aimed at the agranular fields of the motor cortex and the caudal part of the parietal cortex. The lateral part of the parafascicular nucleus sends fibres predominantly to the lateral agranular field of the motor cortex and the rostral part of the parietal cortex. The medial part of the parafascicular nucleus projects rather sparsely to the dorsal part of the prelimbic cortex, the anterior cingular cortex and the medial agranular field of the motor cortex. Individual midline and intralaminar thalamic nuclei are thus in a position to directly influence circumscribed areas of the cerebral cortex. In combination with previously reported data on the organization of the midline and intralaminar thalamostriatal projections and the prefrontal corticostriatal projections the present results suggest a high degree of differentiation in the convergence of thalamic and cortical afferent fibres in the striatum. Each of the recently described parallel basal ganglia-thalamocortical circuits can thus be expanded to include projections at both the cortical and striatal levels from a specific part of the midline and intralaminar nuclear complex. The distinctive laminar distributions of the fibres originating from the different nuclei emphasize the specificity of the midline and intralaminar thalamocortical projections.

Increase of striatal methionin enkephalin content following lesion of the nigrostriatal dopaminergic pathway in adult rats and reversal following the implantation of embryonic dopaminergic neurons: a quantitative immunohistochemical analysis

The aim of the present study was to test whether intrastriatal implants of embryonic dopaminergic neurons are able to normalize the lesion-induced dysfunction of striatal enkephalinergic neurons, one of the major output systems of the striatum. The ascending dopaminergic pathway of adult rats was unilaterally lesioned. Three weeks later a cell suspension obtained from the mesencephali of ED14 rat embryos was implanted into the denervated striatum and striatal methionin enkephalin immunostaining was quantified six months later by the use of an image analyser. Methionin enkephalin immunostaining was unevenly distributed in the striatum of control animals. Besides the classical patch/matrix pattern, a mediolateral gradient was also present and, moreover, immunostaining decreased towards caudal levels. Seven months after the lesion of the nigrostriatal dopaminergic pathway, methionin enkephalin immunostaining was found to be increased in the denervated striatum by about 50%. However, relative increases were more sustained in the areas where basal methionin enkephalin immunostaining were lowest, i.e. the lateral striatum and posterior striatal areas. This resulted in an attenuation of the global gradients seen in the normal striatum. Increased immunostaining was also found in the ipsilateral globus pallidus. The implantation, into the denervated striatum, of embryonic dopaminergic neurons led to a reversal of the lesion-induced increase of striatal and pallidal methionin enkephalin immunostaining six months later. Moreover, this reversal resulted in an overshoot, as the level of immunostaining in the graft-bearing striatum was found to be lower than the levels found in the normal striatum. It is concluded that grafts of embryonic dopaminergic neurons can normalize the function of one of the major output systems of the striatum and, through it, influence more distant targets of this structure. This suggests a physiological basis for the behavioral effects observed previously with such grafts.

The striatal mosaic in primates: patterns of neuropeptide immunoreactivity differentiate the ventral striatum from the dorsal striatum

Patterns of immunoreactivity for calcium-binding protein, tyrosine hydroxylase and four neuropeptides in the ventral striatum (nucleus accumbens, olfactory tubercle and ventromedial parts of the caudate nucleus and putamen) were compared to patterns of these markers in the dorsal striatum (the majority of the neostriatum) in rhesus monkey. The striatal mosaic was delineated by calcium-binding protein and tyrosine hydroxylase immunoreactivities. Both markers were found preferentially in the matrix of the dorsal striatum. The mosaic configurations of tyrosine hydroxylase, but not calcium-binding protein immunoreactivity, were similar in dorsal and ventral striatal regions. Substance P and leucine-enkephalin were not distributed homogeneously; distinct types and the prevalence of patches of substance P and leucine-enkephalin immunoreactivity distinguish the dorsal striatum from the ventral striatum and distinguish the caudate nucleus from the putamen. In the dorsal striatum, substance P and leucine-enkephalin patches consist of dense islands of immunoreactive neurons and puncta or clusters of immunoreactive neurons marginated by a dense rim of terminal-like puncta; the matrix was also enriched in leucine-enkephalin-immunoreactive neurons but contained less substance P-immunoreactive neurons. Patches were more prominent in the caudate nucleus than in the putamen. In the caudate, compartments low in tyrosine hydroxylase and calcium-binding protein immunoreactivities corresponded to cytologically identified cell islands and to patches enriched in substance P and leucine-enkephalin. These patches had a discrete infrastructure based on the location of substance P and leucine-enkephalin-immunoreactive neurons and terminals. In the ventral striatum, patches that showed low levels of substance P and leucine-enkephalin immunoreactivities were embedded in a matrix rich in immunoreactive cell bodies, fibers and terminals. In the accumbens, regions showing little tyrosine hydroxylase were in spatial register with patches low in substance P and leucine-enkephalin. Neurotensin- and somatostatin-immunoreactive neurons or processes were also compartmentally organized, particularly in the ventral striatum. Neurotensin-immunoreactive neurons were present predominantly in the nucleus accumbens but not in the dorsal striatum. Some regions enriched in neurotensin immunoreactivity were spatially registered with zones low in tyrosine hydroxylase, substance P and zones enriched in leucine-enkephalin. Areas enriched in somatostatin-immunoreactive processes overlapped with both tyrosine hydroxylase-rich and -poor regions in the ventral striatum. Our results show that the chemoarchitectonic topography of the striatal mosaic is different in the dorsal and ventral striatum of rhesus monkey and that the compartmental organization of some neurotransmitters/neuropeptides in the ventral striatum is variable and not as easily divisible into conventional patch and matrix regions as in the dorsal striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of the thalamostriatal projections in the rat, with special emphasis on the ventral striatum

The organization of the thalamic projections to the ventral striatum in the rat was studied by placing injections of the retrograde tracer cholera toxin subunit B in the ventral striatum and small deposits of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) in individual midline and intralaminar thalamic nuclei. In order to provide a complete map of the midline and intralaminar thalamostriatal projections, PHA-L injections were also made in those parts of the intralaminar nuclei that project to the dorsal striatum. The relationship of thalamic afferent fibres with the compartmental organization of the ventral striatum was assessed by combining PHA-L tracing and enkephalin immunohistochemistry. The various midline and intralaminar thalamic nuclei project to longitudinally oriented striatal sectors. The paraventricular thalamic nucleus sends most of its fibres to medial parts of the nucleus accumbens and the olfactory tubercle, whereas smaller contingents of fibres terminate in the lateral part of the nucleus accumbens and the most ventral, medial, and caudal parts of the caudate-putamen complex. The projections of the parataenial nucleus are directed towards central and ventral parts of the nucleus accumbens and intermediate mediolateral parts of the olfactory tubercle. The intermediodorsal nucleus projects to lateral parts of the nucleus accumbens and the olfactory tubercle and to ventral parts of the caudate-putamen. The projection of the rhomboid nucleus is restricted to the rostrolateral extreme of the striatum. A diffuse projection to the ventral striatum arises from neurons ventral and caudal to the nucleus reuniens rather than from cells inside the nucleus. Fibres from the central medial nucleus terminate centrally and dorsolaterally in the rostral part of the nucleus accumbens and medially in the caudate-putamen. Successively more lateral positions in the caudate-putamen are occupied by fibres from the paracentral and central lateral nuclei, respectively. The lateral part of the parafascicular nucleus projects to the most lateral part of the caudate-putamen, whereas projections from the medial part of this nucleus terminate in the medial part of the caudate-putamen and in the dorsolateral part of the nucleus accumbens. Furthermore, a rostral to caudal gradient in a midline or intralaminar nucleus corresponds to a dorsal to ventral and rostral to caudal gradient in the striatum. In the ventral striatum, thalamic afferent fibres in the "shell" region of the nucleus accumbens avoid areas of high cell density and weak enkephalin immunoreactivity.(ABSTRACT TRUNCATED AT 400 WORDS)

A simple ordering of neocortical areas established by the compartmental organization of their striatal projections

The compartmental organization of corticostriatal projections from the fronto-orbito-insular cortex was studied in the cat. Cortical areas in this field were found to have a highly organized projection to the striatum, selectively innervating striosomes dorsally and predominantly avoiding them ventrally within their striatal fields of termination. These observations have two important implications for striatal processing. First, some cortical areas preferentially terminate in different compartments in different parts of the striatum. Therefore, the sources of input to striosomes and matrix are not categorical but switch according to the striatal region considered. Second, three properties of the bicompartmental termination pattern--one-dimensionality, common polarization, and multiple positions at which the pattern switched from "fills" to "avoids"--allowed us to order the corticostriatal projections with respect to one another. This ordering of the striatal projections of cortical areas implies an ordering of the cortical areas themselves, one that is independent of transcortical connections. For the corticostriatal projections described in this report, the ordering is [parietal, dorsomedial prefrontal, ventrolateral prefrontal, insular, rostral temporal] cortex. Our analysis suggests that a major function of striatal compartmentalization is to segregate and then bring together inputs from cortical areas at different positions in this ordering. The ordering may also serve as a simple format for specifying corticostriatal connections in development.

Neurotransmitters and neuromodulators in the basal ganglia

The basal ganglia have become a focus for work on neurotransmitter interactions in the brain. These structures contain a remarkable diversity of neuroactive substances, organized into functional subsystems that have unique developmental histories and vulnerabilities in neurodegenerative diseases. A new view of the basal ganglia is emerging on the basis of this neurochemical heterogeneity, suggesting that dynamic regulation of transmitter expression may be a key to extrapyramidal function.

Striosomal organization of cholinergic and dopaminergic uptake sites and cholinergic M1 receptors in the adult human striatum: a quantitative receptor autoradiographic study

The distribution of cholinergic pre- and postsynaptic markers and dopaminergic presynaptic markers was analyzed in the adult human striatum, using quantitative receptor autoradiography. The distribution of the different binding sites indicates that cholinergic and dopaminergic uptake sites display a striosomal organization, with a higher binding site density in the striatal matrix. M1 muscarinic cholinergic receptor distribution parallels the distribution of cholinergic presynaptic markers. Our data show that cholinergic and dopaminergic terminals, and M1 receptors are enriched in the matrix of the adult human striatum.

Co-expression of neuropeptides in the cat's striatum: an immunohistochemical study of substance P, dynorphin B and enkephalin

The expression of tachykinin-like and opioid-like peptides was studied in medium-sized neurons of the caudate nucleus in tissue from adult cats pretreated with colchicine. Two methods, a serial thin-section peroxidase-antiperoxidase technique and a two-fluorochrome single-section technique, were applied. Quantitative estimates were made mainly with the peroxidase-antiperoxidase method. The numbers of neurons expressing substance P-like, dynorphin B-like, and enkephalin-like immunoreactivity were recorded in regions identified, respectively, as striosomes and extrastriosomal matrix. Striosomes were defined by the presence of clustered substance P-positive and dynorphin B-positive neurons and neuropil. Tests for the co-existence of enkephalin-like peptide and glutamate decarboxylase-like immunoreactivity were also made with the peroxidase-antiperoxidase method. Co-expression of substance P-like and dynorphin B-like immunoreactivities was the rule both in striosomes and in the matrix. In striosomes, substance P-like immunoreactivity was found in 96% of dynorphin B-immunoreactive neurons, and in the matrix 89% of dynorphin B-positive cells contained substance P-like immunoreactivity. Substance P/dynorphin B-positive neurons corresponded to over half (57%) of the neurons in striosomes but only 39% of the neurons in the matrix. Both in the matrix and in striosomes, about two-thirds of all neurons (63% and 65%, respectively) were identified as enkephalin-positive. Among all substance P/dynorphin B-positive medium-sized neurons, 76% also contained enkephalin-like antigen. The enkephalin-positive neurons characterized by triple peptide co-existence (enkephalin/substance P/dynorphin B) represented a mean of 63% of striosomal enkephalin-positive neurons (41% of all striosomal neurons) and 35% of matrical enkephalin-positive neurons (26% of all matrical neurons). Finally, nearly all enkephalin-positive neurons were immunoreactive for glutamate decarboxylase, and therefore probably GABAergic, but only about half the glutamate decarboxylase-positive population was enkephalin-immunoreactive. These findings suggest that neuropeptides from three distinct precursors may be co-localized in single medium-sized neurons in the striatum, and that the differential patterns of co-expression of substance P-like, dynorphin B-like, and enkephalin-like peptides may confer functional specializations upon subpopulations of GABAergic neurons giving rise to the efferent projections of the striatum. The linked expression of substance P-like and dynorphin B-like peptides in single neurons both in striosomes and matrix suggests that some regulatory mechanisms controlling peptide expression apply regardless of compartment.(ABSTRACT TRUNCATED AT 400 WORDS)

Distinct presynaptic control of dopamine release in striosomal and matrix areas of the cat caudate nucleus

By use of a sensitive in vitro microsuperfusion method, the cholinergic prsynaptic control of dopamine release was investigated in a prominent striosome (areas poor in acetylcholinesterase activity) located within the core of cat caudate nucleus and also in adjacent matrix area. The spontaneous release of [3H]dopamine continuously synthesized from [3H]tyrosine in the matrix area was found to be twice that in the striosomal area; the spontaneous and potassium-evoked releases of [3H]dopamine were calcium-dependent in both compartments. With 10(-6) M tetrodotoxin, 5 x 10(-5) M acetylcholine stimulated [3H]dopamine release in both striosomal and matrix areas, effects completely antagonized by atropine (10(-6) M), thus showing the involvement of muscarinic receptors located on dopaminergic nerve terminals. Experiments without tetrodotoxin revealed a more complex regulation of dopamine release in the matrix: (i) In contrast to results seen in the striosome, acetylcholine induced only a transient stimulatory effect on matrix dopamine release. (ii) Although 10(-6) M atropine completely abolished the cholinergic stimulatory effect on [3H]dopamine release in striosomal area, delayed and prolonged stimulation of [3H]dopamine release was seen with atropine in the matrix. The latter effect was completely abolished by the nicotinic antagonist pempidine (10(-5) M). Therefore, in the matrix, in addition to its direct (tetrodotoxin-insensitive) facilitatory action on [3H]dopamine release, acetylcholine exerts two indirect (tetrodotoxin-sensitive) opposing effects: an inhibition and a stimulation of [3H]dopamine release mediated by muscarinic and nicotinic receptors, respectively.

Compartment-specific changes in the density of choline and dopamine uptake sites and muscarinic and dopaminergic receptors during the development of the baboon striatum: a quantitative receptor autoradiographic study

In the fetal and young primate neostriatum, cholinergic and dopaminergic markers show patches of high density surrounded by a lower-density matrix. In the adult, the same markers display the opposite pattern, a lower density in striosomes, surrounded by a higher-density matrix. In order to understand the developmental sequences leading to the adult compartmental organization of the primate neostriatum, a quantitative technique was used to study the ontogeny of pre- and postsynaptic components of cholinergic and dopaminergic neurons in baboon caudate nucleus and putamen. The development of specific uptake mechanisms for choline and dopamine and receptors was studied by means of quantitative autoradiography of the specific binding of [3H]-hemicholinium-3 [( 3H]-HC3) and [3H]-mazindol [( 3H]-MAZ) to the choline and dopamine uptake systems, respectively. [3H]-pirenzepine [( 3H]-PIR) was used to label M1 muscarinic receptors and [3H]-spiroperidol [( 3H]-SPI) was used to label striatal dopamine D2 receptors. Serial sections were used for each ligand to determine the precise anatomical relationships between the binding patterns of the different markers. Our aim was to determine whether the adult striosomal distribution of the binding sites studied was due to 1) a selective decrease in patch/striosomal binding density or 2) a selective increase in matrix binding density. Our studies show that a postnatal decrease in the density of [3H]-HC3 sites in the patch/striosomes and an increase in the matrix density of [3H]-MAZ sites are the primary, but not the sole, changes in the compartmental distribution of these sites leading to the adult striosomal organization of the striatal cholinergic and dopaminergic innervation. D2 receptors follow the general developmental pattern of [3H]-MAZ and [3H]-HC3, changing their density of distribution in both compartments during the developmental period examined. In addition, M1 muscarinic receptors already display their adult pattern in the newborn baboon striatum, and therefore represent one of the first neurochemical makers to adopt its mature organization.

The functional anatomy of basal ganglia disorders

Basal ganglia disorders are a heterogeneous group of clinical syndromes with a common anatomic locus within the basal ganglia. To account for the variety of clinical manifestations associated with insults to various parts of the basal ganglia we propose a model in which specific types of basal ganglia disorders are associated with changes in the function of subpopulations of striatal projection neurons. This model is based on a synthesis of experimental animal and post-mortem human anatomic and neurochemical data. Hyperkinetic disorders, which are characterized by an excess of abnormal movements, are postulated to result from the selective impairment of striatal neurons projecting to the lateral globus pallidus. Hypokinetic disorders, such as Parkinson's disease, are hypothesized to result from a complex series of changes in the activity of striatal projection neuron subpopulations resulting in an increase in basal ganglia output. This model suggests that the activity of subpopulations of striatal projection neurons is differentially regulated by striatal afferents and that different striatal projection neuron subpopulations may mediate different aspects of motor control.

The distribution of neurotensin receptors and acetylcholinesterase in the human caudate nucleus: evidence for the existence of a third neurochemical compartment

The distribution of neurotensin receptors in the human caudate nucleus was studied using autoradiographic methods following in vitro labelling of cryostat sections with [3H]neurotensin, and the pattern of receptor labelling was compared to the distribution of acetylcholinesterase (AChE) staining in adjacent sections. A heterogeneous pattern of neurotensin receptors was found in the caudate nucleus. Patches of low receptor density aligned with the AChE-poor striosomes, regions of moderate receptor density corresponded with the AChE-rich matrix zone, and annular regions of high receptor density aligned with the AChE-negative border zone lying between the AChE-poor striosome and the AChE-rich matrix compartments. These results suggest the existence of 3 neurochemical compartments within the human caudate nucleus.

Three-dimensional organization of the striosomal compartment and patchy distribution of striatonigral projections in the matrix of the cat caudate nucleus

Acetylcholinesterase staining on successive frontal or sagittal sections was used to determine the three-dimensional organization of the striosomal and matrix compartments in the adult cat caudate nucleus. Reconstruction drawings of the acetylcholinesterase-poor zones (striosomes) indicated that the striosomal compartment is a labyrinthine network organized in the rostrocaudal and mediolateral axis which is reproducible from one animal to another. Four main anteroposterior channels converging in the mediorostral pole of the caudate nucleus were distinguished. Seven to eight diagonally oriented channels crossing the previous ones were seen also in the mediolateral axis on the central core of the caudate nucleus. The pattern of organization of the numerous and tortuous striosomal channels was more complicated medially, while the lateral part of the caudate nucleus was represented mainly by the matrix compartment. In addition, a sub-compartmentation of the matrix was demonstrated by retrograde tracing studies made by injecting either horseradish peroxidase-wheat germ agglutinin, [14C]amino acids or a mixture of horseradish peroxidase-wheat germ agglutinin and [14C]amino acids in several areas of the substantia nigra pars reticulata. Labelled patches were seen with both tracers, their topographical localization depended on the nigral injection site but reconstruction analysis indicated that the populations of cells which innervate the substantia nigra pars reticulata originate in the two third lateral parts of the caudate nucleus all along its rostrocaudal extension. Examination of horseradish peroxidase-wheat germ agglutinin labelled cells indicated that not all cells were labelled in patches suggesting a further sub-compartmentation of these patches. Finally, a comparison of the topographical distributions of labelled patches and of striosomes revealed that most patches were located in the extrastriosomal matrix.

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

The detailed organization of the corticostriate projection has been investigated in the brain of the rat using the technique of retrograde transport of horseradish peroxidase following the placement of small, iontophoretic injections of horseradish peroxidase conjugated to lectin throughout all major regions of the striatum (caudate-putamen, nucleus accumbens and olfactory tubercle). The results demonstrate that all major regions of the cerebral cortex project to the striatum on both sides of the brain with an ipsilateral predominance. The cells of origin of both the ipsilateral and contralateral corticostriate projections lie mainly in lamina V (especially lamina Va) with very small numbers in lamina III of the neocortex and mesocortex, and in the deep laminae of the allocortex. The results show that each striatal locus receives inputs from several cortical regions, i.e. there is extensive overlap in the corticostriate projection, and that, in general terms, each cortical region projects onto a longitudinally oriented region of the striatum. In particular, the major subdivisions of the cerebral cortex--the neocortex, mesocortex and allocortex--project onto defined but partially overlapping regions of the striatum: the neocortex projects to the caudate-putamen; the mesocortex projects mainly to the medial and ventral regions of the caudate-putamen but also to the ventral striatum (nucleus accumens and olfactory tubercle); and the allocortex projects mainly to the ventral striatum but also to the medial and ventral parts of the caudate-putamen. Within each of these major projection systems there is a further organization, with the constituent parts of each major cortical region projecting to smaller longitudinal components of the major projection fields. Each neocortical area projects to a longitudinal region of the dorsal striatum (caudate-putamen): the sensory and motor areas project topographically onto the dorsolateral striatum such that the rostral sensorimotor cortex (head areas) projects to central and ventral regions and the more caudal sensorimotor cortex (limb areas) projects to dorsal regions of the dorsolateral striatum; the visual area projects to the dorsomedial striatum; and the auditory area projects to the medial striatum. Each mesocortical area projects to a longitudinal area of the striatum: the most posteromedial mesocortex (the retrosplenial area) projects to the dorsomedial striatum; more anterior and lateral parts of the mesocortex project to more ventral parts of the striatum: and the most lateral mesocortex (the agranular insular and perirhinal areas) project to the ventrolateral striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Compartmental origins of striatal efferent projections in the cat

Injections of the retrograde tracer, wheat germ agglutinated-horseradish peroxidase were placed in the substantia nigra, in adjoining dopamine-containing cell groups A8 and A10, and in the internal and external parts of the pallidal complex of 20 cats in order to identify the compartmental origins of striatal efferent projections to the pallidum and midbrain. Patterns of retrograde cell-labeling in the caudate nucleus were analysed with respect to its striosomal architecture as detected in sections stained for acetylcholinesterase. Where possible, a similar compartmental analysis of cell-labeling in the putamen was also carried out. In 15 cats anterograde labeling in the striatum was studied in the sections stained with wheat germ agglutinated-horseradish peroxidase or in autoradiographically treated sections from cases in which [35S]methionine was mixed with the wheat germ agglutinated-horseradish peroxidase in the injection solution. Predominant labeling of projection neurons lying in striosomes (usually with some labeling of dorsomedial matrix neurons) occurred in a subset of the cases of nigral injection, including all cases (n = 9) in which the injection sites were centered in the densocellular zone of the substantia nigra pars compacta [Jiménez-Castellanos J. and Graybiel A. M. (1987) Neuroscience 23, 223-242.] Dense labeling of neurons in the extrastriosomal matrix, with at most sparse labeling of striosomal neurons, occurred in all cases of pallidal injection (n = 8) and in two cases of nigral injection in which the injection sites were lateral and anterior to the densocellular zone. Mixed labeling of striosomal and matrical neurons occurred in a third group of cases in which the injection sites were lateral to the densocellular zone but close to it. In a single case with an injection site situated in the pars lateralis of the substantia nigra, there was preferential labeling of striosomal neurons in the caudal caudate nucleus but widespread labeling of neurons in both striosomes and matrix in the putamen. A second type of compartmental ordering of projection neurons was found in the extrastriosomal matrix of the striatum. In cases of pallidal and nigral injection, there were gaps in cell labeling that did not match striosomes precisely, and often clusters of labeled cells appeared that did not correspond to acetylcholinesterase-poor striosomes but, instead, to patches of matrix. Especially prominent were clusters beside striosomes. There was a topographic ordering of striatal projection neurons both in the striosomes and in the extrastriosomal matrix according to their dorsoventral and latitudinal positions.(ABSTRACT TRUNCATED AT 400 WORDS)

The distribution and compartmental organization of the cholinergic neurons in nucleus accumbens of the rat

In this study the distribution of the cholinergic neurons was examined in relation to the compartmental organization of nucleus accumbens. This was accomplished by charting the location of the choline acetyltransferase-immunoreactive neurons and mapping their distribution in relation to cytoarchitectural features and the patterns of acetylcholinesterase activity and enkephalin immunoreactivity. Choline acetyltransferase-containing perikarya are inhomogeneously distributed in nucleus accumbens. Their density is lowest at the rostral pole and highest, caudomedially, at the septal pole. The cells form a compact, medial column and a diffuse, lateral zone and, moreover, there are distinct gradients in their distribution. The highest numbers of immunoreactive perikarya occur within the intensely immunostained zones of choline acetyltransferase-immunoreactive neuropil in ventral and ventromedial parts of the nucleus, whereas lower numbers coincide with choline acetyltransferase-poor zones in the central part of the nucleus. Zones of intensely choline acetyltransferase-immunoreactive neuropil are largely in register with regions of high acetylcholinesterase activity in middle and caudal parts of the nucleus but do not coincide rostrally. Choline acetyltransferase-rich zones correspond to moderate enkephalin immunoreactivity in the outer shell of the nucleus, but a moderately choline acetyltransferase-immunostained matrix surrounds "patches" of intense enkephalin immunoreactivity in the core. Small aggregates of cells, which feature commonly in nucleus accumbens, seem to be avoided by both choline acetyltransferase- and enkephalin-immunoreactive zones. Choline acetyltransferase-immunoreactive processes are mostly confined by the boundaries of their respective immunoreactive zones. Few choline acetyltransferase-immunoreactive neurons lie in the enkephalin-rich patches and those that lie close to the patches show little preference in the directionality of their processes such that some cross the borders, whereas others do not. Thus, our findings show that the cholinergic elements are differentially distributed within nucleus accumbens; that these elements are compartmentally ordered; and that, in light of their limited access to other compartments, they possibly play only a minor role in intercompartmental communication.