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

Distribution of limbic system-associated membrane protein immunoreactivity in primate basal ganglia

The limbic system-associated membrane protein is a 64,000-68,000 mol.wt molecule known to be preferentially expressed by neurons in limbic structures of rats and cats. The present immunohistochemical study describes the distribution of this protein in the basal ganglia of Macaca fascicularis. The ventral striatum of the cynomolgus monkey displays a very intense immunostaining, whereas the dorsal striatum is much more weakly stained, except for some small zones scattered in the caudate nucleus and, to a lesser extent, in the putamen. These protein-rich zones are in register with striosomes, as visualized on adjacent sections immunostained for calbindin. At pallidal levels, immunostaining for the protein is observed only in the subcommissural regions, at the ventromedial tip of the internal pallidum, and in the caudoventral portion of the external pallidum. At nigral levels, the immunostaining is highly heterogeneous with a marked decreasing rostrocaudal gradient. The staining is most intense in nigral regions that receive striatal inputs and are enriched with calbindin. Nigral sectors populated by dopaminergic neurons, as visualized on adjacent sections immunostained for tyrosine hydroxylase, are largely devoid of immunoreactivity. In contrast, the immunostaining is uniformly intense in the ventral tegmental area. This study provides the first neuroanatomical evidence for teh existence of the limbic system-associated membrane protein in primate brain. It reveals that this glycoprotein is distributed in a highly heterogeneous manner in primate basal ganglia, where it preferentially labels regions that are anatomically and functionally linked to the limbic system.

Ontogeny of the striatal neurons expressing neuropeptide genes in the human fetus and neonate

The distribution patterns of neurons expressing mRNAs for four neuropeptides in the human striatum were studied during ontogeny by the use of in situ hybridization. The results of our study demonstrate that somatostatin, enkephalin, dynorphin, and substance P mRNAs are present in striatal neuronal populations from week 12 of fetal life. Each neuronal population undergoes a specific differentiation. Neurons containing somatostatin mRNA are scattered throughout the caudate-putamen up until birth. Neurons containing enkephalin, dynorphin, or substance P mRNAs evolve throughout fetal life in relation to caudate-putamen and patch-matrix compartmentalization. Neurons containing enkephalin mRNA (distinct from those containing substance P or dynorphin mRNAs) are present in the matrix from week 12 of fetal life. These neurons are preferentially distributed in the matrix and, at birth, display higher enkephalin mRNA content in the matrix than in the patches. Dynorphin mRNA is found in the caudate and putamen, preferentially in the patch neurons; nevertheless, a low level of dynorphin mRNA is also present in neurons of the caudate matrix. Substance P mRNA is initially restricted to caudate neurons. At birth, both substance P and dynorphin mRNAs are expressed at high levels in the patches. These results demonstrate that each neuropeptide gene is expressed during human fetal life in neurons with a specific topology and pace of development in relation to caudate-putamen and patch-matrix differentiation. These results also contribute evidence that neurochemical evolution of the striatal neuronal populations is not complete at birth in humans.

Reward shifts and motor responses following microinjections of opiate-specific agonists into either the core or shell of the nucleus accumbens

Differences in pharmacology, anatomical connections, and receptor densities between the "core" and "shell" of the nucleus accumbens suggest that behavioral activity normally modulated by the accumbens, such as reward and motor functions, may be differentially regulated across the mediolateral axis. This study investigated the effects of opiate receptor-specific agonists on reward and motor functions in either the accumbens core or shell, using the intracranial self-stimulation (ICSS) rate-frequency curve-shift method. Microinjections of the mu opiate receptor-specific agonist, DAMGO (vehicle, 0.03 nmol, and 0.3 nmol), or the delta opiate receptor-specific agonist DPDPE (vehicle, 0.3 nmol, 3.0 nmol), were administered bilaterally in a random dose order with a minimum of 3 days between injections. Rats were tested over three consecutive 20-min rate-frequency curves immediately following a microinjection to investigate the time course of drug effects. Both opiate agonists decreased the ICSS frequency necessary to maintain half-maximal response rates when injected into the medial and ventral shell region of the accumbens. However, DAMGO microinjections into the lateral accumbens core or the control site of the caudate increased the frequency necessary to elicit half-maximal response rates, while DPDPE microinjections into these regions had no effect. Evaluation of motor effects show that administration of DAMGO resulted in a suppression of activity in all locations. In contrast, DPDPE microinjections resulted in little or no effect on lever pressing activity at any location.

Neurochemical heterogeneity of the primate nucleus accumbens

In order to further investigate the neurochemical anatomy of the primate nucleus accumbens (NAC), the distributions of the neuropeptides leucine-enkephalin (Leu-ENK), neurotensin (NT), and substance P (SP) and of haloperidol-induced c-fos expression were investigated in the macaque monkey using immunohistochemical methods. To define the boundaries of the NAC, dopamine (DA) and tyrosine hydroxylase (TH) immunohistochemistry was performed. In addition, to formulate the distinction between subdivisions of the nucleus accumbens, immunohistochemistry for calbindin-D28 (CBD) and SP was employed. In general, the medial part of NAC, which consisted of small to medium-sized cells, was low for CBD immunoreactivity and moderate to high for SP immunoreactivities, while the dorsolateral part, which was composed of small cells, showed the opposite pattern of immunostaining for CBD and SP. Many Leu-ENK-immunoreactive perikarya were observed in the dorsal NAC at its middle and caudal levels. There were moderate densities of Leu-ENK-positive fibers throughout the medial part of the NAC. At the dorsolateral margin of the NAC, Leu-ENK-positive fibers formed patches. Most NT-positive perikarya were found in the dorsolateral subdivision. SP-positive perikarya were scarce in the NAC. Dense distribution of NT- and SP-containing fibers or puncta were observed in the mediodorsal part (medial subdivision), where a dense field of DA-immunoreactive fibers was observed. The ventral part (ventral subdivision) contained moderate numbers of NT- and SP-immunoreactive fibers. Haloperidol-induced c-fos expression was very extensive in the medial half of NAC, particularly in the mediodorsal region, which overlapped with the DA- and peptide-rich region. The present study indicates that the NAC of the primate can be subdivided into at least three subterritories, the dorsolateral, medial and ventral subdivision, by neuropeptide histochemistry as well as by the response of its constituent neurons to haloperidol.

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

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

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.

Primate cingulostriatal projection: limbic striatal versus sensorimotor striatal input

The organization of the projections from the cingulate cortex to the striatum in the monkey was studied using the retrograde tracers Lucifer Yellow conjugated to dextran amines and horseradish peroxidase conjugated to wheat germ agglutinin. These tracers were injected into the different regions of the ventral (limbic) striatum and the dorsal (sensorimotor) striatum. The shell region of the nucleus accumbens was defined using calbindin-D28K immunohistochemistry. Following injections into the ventral striatum, there are numerous retrogradely labeled neurons in the various regions of the primate cingulate cortex, most of which are derived from layer V. The cytoarchitectural subdivisions of cingulate cortex include the anterior cingulate cortex, areas 25, 24a-c, and 24a'-c', and the posterior cingulate cortex, areas 23a-c, 29, 30, and 31. There is a topographical organization of the projections from these different cingulate areas to the ventral and dorsal striatum. The medial ventral striatum receives input from the rostral part of the anterior cingulate cortex (areas 25 and 24a,b). The shell region of the nucleus accumbens receives fibers from areas 25, 24a,b, and 24a',b'. Projections to the central ventral striatum including the core of the nucleus accumbens are derived primarily from areas 25, 24a, 24b, and the medial part of area 24c. However, few labeled cells are detected in areas 24c and 24c'. The lateral ventral striatum receives input primarily from areas 24b, 24b' and 23b and medial portion of area 24c. The medial ventral striatum and the shell of the nucleus accumbens have a similar distribution of labeled cells, such that these regions derive their input almost entirely from the rostral anterior cingulate cortex. In contrast to the ventral striatum, the dorsal sensorimotor striatum receives projections from areas 24c, 24c' 23c and 31. These arise primarily from the lateral portion of lower bank and the fundus of the cingulate sulcus. Our results demonstrate that areas 24c, 24c' and 23c, the lateral portion of the lower bank and the fundus of the cingulate sulcus project to the dorsal sensorimotor striatum. The medial portion of the lower bank of the cingulate cortex projects to the ventral striatum including the core of the nucleus accumbens. Different projections to striatum from discrete subdivisions of cingulate cortex indicate that these areas are heterogeneous and have different functions such that the fundus of the cingulate sulcus is related to skeletomotor function, whereas the medial portion of the lower bank of the cingulate sulcus is associated with the limbic-related and association cortical function.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Neurochemical compartmentalization of the globus pallidus in the rat: an immunocytochemical study of calcium-binding proteins

The globus pallidus external segment forms a major target center of the mammalian striatum which is characterized by neurochemically distinct compartments. The present study was undertaken to determine if a corresponding compartmentalization exists within the globus pallidus external segment in the rat. Immunocytochemical examination of the calcium-binding proteins parvalbumin and calbindin D28kDa, which are present in neurons of the striatal matrix compartment, was employed. The results indicate three neurochemically distinct compartments within the globus pallidus external segment: 1) an area in the medial aspect of the entire length of the globus pallidus that contains dense immunoreactivity for calbindin D28kDa; 2) a narrow rim at the striatopallidal junction in the rostral two-thirds of the globus palidus that contains calbindin D28kDa immunoreactivity designated as the "border zone" of the globus pallidus; and 3) an area between these two zones showing very poor immunoreactivity for calbindin D28kDa but containing parvalbumin immunoreactive neurons. The calbindin D28kDa immunoreactive border zone corresponds to the area of the globus pallidus where striatal inputs converge extensively, whereas the rest of the nucleus is involved in segregated, topographically organized pathways. Parvalbumin-containing neurons are involved in the propagation of striatal output related to striosomal and sensorimotor aspects of basal ganglia function. The present results also indicate that calbindin D28kDa immunoreactivity is completely absent from striosomal neurons and is therefore a useful marker for striatal compartments.

Compartmental organization of the peptide network in the human caudate nucleus

The mammalian striatum may be divided into a striosomal compartment and a surrounding matrix region. We have examined the distribution of leucine enkephalin (LENK) and substance P (SP) immunoreactivity in relation to striosomes defined by calbindin-D (CABD) staining in alternate 70 microns serial sections from the human caudate nucleus. The distribution of LENK immunoreactivity showed a transition from dorsal to ventral striatum: dorsally, LENK-rich patches were present in a lightly stained matrix; mid-ventrally, annular patches of LENK staining with a lighter core were seen. These patches corresponded to striosomal regions defined by CABD-poor zones. In contrast, in the ventral caudate and nucleus accumbens, LENK-poor zones matched CABD-defined striosomes. CABD staining in the matrix was intense in the dorsal caudate, diminishing ventrally. SP-rich zones in dorsal caudate and SP-poor areas in the mid-ventral region overlapped striosomes. In the ventromedial sector, the SP staining pattern was complex and did not consistently correlate with striosomes. Computer-assisted three-dimensional reconstruction of the striosomal system in the human, based on regions of either high LENK or low CABD immunoreactivity, revealed the existence of considerable long-range order. Patches appeared aligned over several millimeters to form long, horizontal structures in the caudate nucleus, with occasional orthogonal interconnecting crossbridges. Our results are in accord with previous work in the human and in other species. These three-dimensional networks are strikingly similar across individuals and may relate to the segregation of and interactions between striatal circuits.

Immunohistochemical characterization of the shell and core territories of the nucleus accumbens in the rat

The nucleus accumbens in the rat has been parcelled into shell and core subdivisions. Despite accumulating evidence for such a division of the nucleus accumbens, these territories have not been delineated throughout the rostrocaudal extent of the nucleus. In the present study, an attempt has been made to delineate the shell and core using the distribution of calcium-binding protein immunoreactivity, substance P immunoreactivity and acetylcholinesterase activity in transverse and horizontal sections through the nucleus accumbens. It was found that the pattern of calcium-binding protein immunoreactivity provides the most unequivocal criterion to divide the nucleus accumbens into a ventral and medial, peripheral shell displaying low to moderate immunostaining, and a more laterally and dorsally located, strongly stained inner core. In most parts of the nucleus, borders seen in the calcium-binding protein immunoreactivity pattern can also be recognized in the distributions of substance P immunoreactivity and acetylcholinesterase activity. It is concluded that the shell occupies most of the rostral part of the nucleus accumbens, whereas rostrally the core is represented only in the most lateral part. Differences in staining intensities for all three markers indicate that both the shell and core have a heterogeneous structure. Patterns of connectivity appear to support the division of the nucleus accumbens as indicated by calcium-binding protein immunoreactivity in the present study.

Human striatum: chemoarchitecture of the caudate nucleus, putamen and ventral striatum in health and Alzheimer's disease

The morphology and distribution of perikarya positive for choline acetyltransferase, somatostatin, calcium binding protein (calbindin D28K) and nicotinamide adenine dinucleotide phosphate diaphorase were surveyed in the human striatum. Choline acetyltransferase and somatostatin antibodies labeled separate populations of large striatal interneurons. Somatostatin immunoreactivity and nicotinamide adenine dinucleotide phosphate diaphorase (nitric oxide synthase) activity were completely co-localized. Calbindin antibody identified two distinct groups of striatal neurons: (1) numerous medium-sized, lightly stained neurons, probably analogous to striatopallidal projection neurons in the rat, and (2) much less numerous, large, darkly stained neurons. Half of the latter group, but none of the former, were also nicotinamide adenine dinucleotide phosphate diaphorase-positive. Somatostatin-positive and medium-sized, calbindin-positive neurons were more numerous in the caudate nucleus than in the putamen or ventral striatum. By contrast, large calbindin-immunoreactive neurons were more frequently encountered in the putamen. Choline acetyltransferase-positive neurons were evenly distributed across striatal components. In aged control subjects, the size of large, darkly stained calbindin-positive neurons was reduced relative to young subjects. Aging had no effect on somatostatin-, medium-sized calbindin-, or choline acetyltransferase-positive neurons. However, in histologically confirmed cases of Alzheimer's disease, there was a selective, 75% loss of choline acetyltransferase-immunoreactive perikarya from the ventral striatum, but not from the dorsal striatum, compared to aged controls. Furthermore, the remaining cholinergic neurons in the ventral striatum of Alzheimer's disease cases were significantly smaller than similar neurons in controls. These results indicate that various striatal components which have been shown to differ in their anatomical connectivity and functional specialization, also differ in their neurochemical signatures. The specific and marked loss of choline acetyltransferase-positive neurons from the ventral striatum in Alzheimer's disease is consistent with the characteristic cholinergic and 'limbic' pathology in this disease.

The organization of midbrain projections to the ventral striatum in the primate

Because the dopaminergic neurons of the midbrain form a continuum, boundaries between the ventral tegmental area, substantia nigra pars compacta, and retrorubral area are difficult to distinguish in the primate. Therefore, dopaminergic neurons have been subdivided into more readily discernible dorsal and ventral tiers. The projections from these dorsal and ventral tier neurons of the ventral mesencephalon to the ventral striatum were labeled by injections of horseradish peroxidase conjugated to wheatgerm agglutinin and Lucifer Yellow conjugated to dextran amines into different regions of the nucleus accumbens, the ventral caudate nucleus, and the rostral, ventral putamen in the primate. Neurons projecting to the ventral striatum are not topographically organized in the ventral mesencephalon. Retrogradely labeled neurons are found in the medial densocellular zone of the ventral tier following injections into all regions of the ventral striatum except the ventromedial shell region of the nucleus accumbens. These medial nigral neurons have diverging projections throughout the mediolateral extent of the ventral striatum. In addition, neurons of the dorsal tier project to all ventral striatal regions examined. Notably, neurons projecting to the shell region of the nucleus accumbens are limited to the dorsal tier, throughout the rostrocaudal extent of the substantia nigra. Both dorsal and ventral tier neurons innervate the ventral striatum. Not only do neurons of the ventral tegmental area project to the ventral striatum, but also many of the pars compacta. The projections to the shell region of the nucleus accumbens are more restricted, suggesting that the dopaminergic regulation of this accumbens subterritory is distinct from the rest of the ventral striatum.

Calbindin D-28k as a marker for the associative cortical territory of the striatum in macaque

An immunohistochemical study was made to investigate the topographic distribution of calbindin D-28k in relation to the associative and sensorimotor cortical territories in the macaque striatum. An intense calbindin-staining was found in the caudate nucleus and ventromedial putamen, i.e., in the associative striatum. In contrast, only a weak immunoreaction was found in the dorsolateral, sensorimotor, putamen. Calbindin immunoreactivity thus appears as a specific marker for the associative striatum.

Islands and striosomes in the neostriatum of the rhesus monkey: non-equivalent compartments

Cytoarchitectonically defined cell-dense islands and regions of low acetylcholinesterase reactivity referred to as striosomes have been regarded as equivalent markers of the non-matrix compartment in the neostriatum. We examined islands and striosomes in adjacent sections to determine the degree of correspondence between the two neostriatal compartmental markers. Islands are aggregated centrally within the caudate, whereas striosomes are located throughout the entire nucleus, including the dorsolateral and ventromedial sectors. Moreover, even within the central sector, striosomes are more prevalent than islands. The present quantitative analysis suggests that islands may be further characterized as acetylcholinesterase-poor since the vast majority of islands co-localize with striosomes. However, due to the fact that striosomes are more numerous and more widely distributed throughout the neostriatum, less than a third of all striosomes are coincident with islands in adjacent sections. Comparison of each of these compartmental markers with the patterned terminal field of the prefrontal cortical projection revealed a near one-to-one correspondence between islands and terminal-free zones in the prefrontal projection. The percentage of striosomes which are aligned with fenestrations in the prefrontal projection is also quite high; however, because more striosomes than islands are found within the prefrontal terminal domain, some striosomes that fit within terminal-free zones do not have corresponding islands. These results indicate that islands and striosomes are not entirely equivalent compartmental markers and further suggest that contemporary, two-compartment models may not adequately represent the heterogeneity of the neostriatum.

Heterogeneous distribution of D1, D2 and D5 receptor mRNAs in monkey striatum

The primate striatum has a compartmental organization reflected both in the topography of its afferent projections and in the segregation of its morphologically similar but neurochemically distinct efferent neurons. Discretely projecting mesostriatal neurons release dopamine (DA) which modulates the responses of striatal neurons to other afferent inputs. Multiple DA receptor (DAR) subtypes have been cloned and characterized and mapping their cellular expression is crucial for understanding the influence of DA on striatal function. We report the distribution of mRNAs for D1, D2 and D5 DAR subtypes (D2R, D2R and D5R) in the striatum of cynomolgus monkeys (Macaca fascicularis) studied by in situ hybridization histochemistry (ISH) using monkey-specific cRNA probes. Adjacent sections were stained for calbindin immunoreactivity to distinguish striosomal and matrix compartments for comparison with the patterns obtained with ISH. In the caudate nucleus, D1R mRNA was concentrated in calbindin-poor striosomes where dense grain clusters were seen overlying the majority of medium-sized neurons (diameter approximately 15 microns). D1R mRNA localization was relatively homogeneous in the putamen. By contrast, the distributions of D2R and D5R mRNAs showed no clear preference for the striosomal or matrix compartments of either caudate nucleus or putamen. In the ventral striatum (nucleus accumbens, olfactory tubercle and ventral portions of caudate nucleus and putamen), expression of D1R and D2R mRNA was sparse relative to dorsal striatum, while D5R mRNA expression was roughly equal in ventral and dorsal striatum. Circumscribed zones of hybridization associated with islands of tightly packed small cells occurred with all three DAR mRNA subtypes in the ventral striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Specificity in the efferent projections of the nucleus accumbens in the rat: comparison of the rostral pole projection patterns with those of the core and shell

The efferent connections of the rostral pole of the rat accumbens, where distinct core and shell subterritories can not be identified, were examined with the aid of the anterogradely transported plant lectin, Phaseolus vulgaris-leucoagglutinin (PHA-L), for comparison with the previously reported projection patterns of the accumbal core and shell. Injection sites and transported PHA-L were evaluated with the aid of reference to adjacent sections processed to display substance P or calbindin 28 kD immunoreactivities, i.e., markers that demonstrate the core and shell. Lateral parts of the rostral pole gave rise to a "core-like" projection system that involved the rostroventral globus pallidus, subcommissural ventral pallidum, entopeduncular nucleus and an adjacent part of the lateral hypothalamus, lateral ventral tegmental area, dorsal pars compacta, and structures in the lateral mesencephalic tegmentum and central grey. The medial part of the rostral pole gave rise to a "shell-like" innervation of the subcommissural ventral pallidum, lateral preoptic region, lateral hypothalamus, ventral tegmental area, dorsalmost pars compacta, retrorubral field, lateral midbrain tegmentum, and central grey. In contrast to the large numbers of axon varicosities observed through the entire length of lateral hypothalamus following shell injections, dense accumulations of axon collaterals and varicosities in hypothalamus were limited to the levels of origin of the stria medullaris bundle and entopeduncular nucleus and to the posterlateral region following medial injections. The medial part of the rostral pole contributed some projections to preoptic and sublenticular regions, but not to the bed nucleus of the stria terminalis. Noteworthy concentrations of calbindin immunoreactive cells observed in the lateral rostral pole correlate with the origin of the "basal ganglia-like" projection system, provoking the speculation that ventral striatal calbindin immunoreactive cells contribute principally to basal ganglia-like projections while cells lacking calbindin immunoreactivity contribute to the innervation of hypothalamus and midbrain tegmentum.

The dopamine hypothesis of schizophrenia: limbic interactions with serotonin and norepinephrine

The "dopamine hypothesis" of schizophrenia has been the predominant guiding theoretical construct for driving studies of the neurobiology of schizophrenia. There has, however, been much interest in the contributions of non-dopamine systems to the clinical symptoms of schizophrenia, in particular, norepinephrine and serotonin. However, direct evidence for altered transmission in monoamine systems has been quite limited. In part this reflects a focus on specific brain regions for different transmitters, in contrast to a "neural systems" approach. Thus, evidence for the dopamine hypothesis has been derived from studies of the basal ganglia in schizophrenic cases and infrequently from other (e.g. cortical) regions. Recent studies have suggested that disturbances in the organization or development of the temporal lobe may underlie certain aspects of the symptoms of schizophrenia In particular, the hippocampus may show cellular loss or disturbances in cell orientation. These results are supported by the work that has identified neuropsychological and in vivo brain disturbances in schizophrenia specific to the medial temporal lobe. However, not all cases show such pathology and it is likely that these disorders could, in addition, involve an important afferent and/or efferent system associated with the temporal lobe. This model is based on the currently held view that parallel cortico-striatal-pallidal-thalamo circuits form an important basis for information processing in the brain. One such circuit involves the primary efferent of the hippocampus, the subiculum, and associated cortical regions that project onto the ventral striatum. Many of the cortical regions that project directly to the ventral striatum also project to the hippocampus via the entorhinal cortex. These include the anterior cingulate, posterior cingulate, superior temporal cortex, and inferior temporal cortex. The ventral striatum, made up of the nucleus accumbens, olfactory tubercle, and ventral putamen, has as its target the ventral pallidum. The ventral pallidum projects to the medial dorsal nuclei of the thalamus, which, in turn, projects to the anterior prefrontal cortical area. This loop has been referred to as the limbic loop. The patterns of innervation and expression of monoamine receptors in the brain have been delineated for the non-human primate and are being unraveled in the human. We, and other, have described the patterns of receptor expression in the limbic circuit. However, few studies have been published to date that detail what the neurochemical counterparts of the neuronal and neuropsychological disturbances in the limbic circuit might be. We have explored the possibility that monoamine systems are altered at more than one synaptic station in this circuit.(ABSTRACT TRUNCATED AT 400 WORDS)

On the significance of subterritories in the "accumbens" part of the rat ventral striatum

Although many workers have appreciated the striking cytologic and neurochemical similarities of neostriatum, accumbens and olfactory tubercle, a compelling case for regarding these areas as territories in a striatal complex awaited the arguments made by Heimer and his colleagues based on their investigations of connections. A number of recent papers support this viewpoint and extend it with the characterization of three accumbal subterritories: core, shell and rostral pole. The case for separate classifications of systems traversing the accumbens has become more compelling with each study that demonstrates connectional, cytoarchitectural and neurochemical specificity conforming to the boundaries separating the core and its downstream targets from the shell and its projection fields. Furthermore, its apparent composite of core-like and shell-like characteristics distinguishes the rostral pole as yet another unique subterritory. Differences in compartmental organization distinguish the accumbens and neostriatum. The available data are consistent with the periventricular and rostrolateral enkephalin-rich zones being ventralmost parts of the neostriatal patch and matrix compartments, respectively. The accumbal cell cluster compartment, on the other hand, appears to be a separate entity, with connectional and neurochemical features that are dissimilar to both patch and matrix of neostriatum. Boundaries between the accumbens and caudate-putamen remain elusive, and the point of view that such boundaries do not exist but, rather, are represented by "transition zones" must to a large degree reflect the reality. Likewise, it is important to acknowledge that the boundaries between accumbal subterritories are not necessarily distinct or observed faithfully by all of the afferent systems. "Transition zones" appear to be particularly significant organizational features in rostral and lateral parts of the accumbens. Interestingly, histochemically distinct cell clusters tend to be numerous in boundary regions between adjacent territories and subterritories. The predominant organizational pattern appears to be one in which the core, shell and rostral pole engage different forebrain systems that possibly subserve entirely different functions mediated by distantly related mechanisms. In this regard, it is of paramount interest that the processing of information conveyed to the accumbens by diverse cortical and subcortical inputs occurs within distinct and perhaps very different dopaminergic environments in the core, shell and rostral pole (e.g., see Refs 24, 34, 90, 110).

Cholinergic innervation of the human striatum, globus pallidus, subthalamic nucleus, substantia nigra, and red nucleus

The anatomical organization of cholinergic markers such as acetylcholinesterase, choline acetyltransferase, and nerve growth factor receptors was investigated in the basal ganglia of the human brain. The distribution of choline acetyltransferase-immunoreactive axons and varicosities and their relationship to regional perikarya showed that the caudate, putamen, nucleus accumbens, olfactory tubercle, globus pallidus, substantia nigra, red nucleus, and subthalamic nucleus of the human brain receive widespread cholinergic innervation. Components of the striatum (i.e., the putamen, caudate, olfactory tubercle, and nucleus accumbens) displayed the highest density of cholinergic varicosities. The next highest density of cholinergic innervation was detected in the red nucleus and subthalamic nucleus. The level of cholinergic innervation was of intermediate density in the globus pallidus and the ventral tegmental area and low in the pars compacta of the substantia nigra. Immunoreactivity for nerve growth factor receptors (NGFr) was confined to the cholinergic neurons of the basal forebrain and their processes. Axonal immunoreactivity for NGFr was therefore used as a marker for cholinergic projections originating from the basal forebrain (Woolf et al., '89: Neuroscience 30:143-152). Although the vast majority of striatal cholinergic innervation was NGFr-negative and, therefore, intrinsic, the striatum also contained NGFr-positive axons, indicating the existence of an additional cholinergic input from the basal forebrain. This basal forebrain cholinergic innervation was more pronounced in the putamen than in the caudate. The distribution of NGFr-positive axons suggested that the basal forebrain may also project to the globus pallidus but probably not to the subthalamic nucleus, substantia nigra, or red nucleus. The great majority of cholinergic innervation to these latter three structures and to parts of the globus pallidus appeared to come from cholinergic neurons outside the basal forebrain, most of which are probably located in the upper brainstem. These observations indicate that cholinergic neurotransmission originating from multiple sources is likely to play an important role in the diverse motor and behavioral affiliations that have been attributed to the human basal ganglia.