Striatal Compartments Research Articles

Cellular Localization of Huntingtin in Striatal and Cortical Neurons in Rats: Lack of Correlation with Neuronal Vulnerability in Huntington’s Disease

Immunohistochemistry and single-cell RT-PCR were used to characterize the localization of huntingtin and/or its mRNA in the major types of striatal neurons and in corticostriatal projection neurons in rats. Single-label immunohistochemical studies revealed that striatum contains scattered large neurons rich in huntingtin and more numerous medium-sized neurons moderate in huntingtin. Double-label immunohistochemical studies showed that the large huntingtin-rich striatal neurons include nearly all cholinergic interneurons and some parvalbuminergic interneurons. Somatostatinergic striatal interneurons, which are medium in size, rarely contained huntingtin. Calbindin immunolabeling showed that the vast majority of the medium-sized striatal neurons that contain huntingtin are projection neurons, but only approximately 65% of calbindin-labeled projection neurons (localized to the matrix compartment of striatum) were labeled for huntingtin. Calbindin-containing projection neurons of the matrix compartment and calbindin-negative projection neurons of the striatal patch compartment contained huntingtin with comparable frequency. Single-cell RT-PCR confirmed that striatal cholinergic interneurons contain huntingtin, but only approximately 65% of projection neurons contained detectable huntingtin message. The finding that huntingtin is not consistently found in striatal projection neurons [which die in Huntington's disease (HD)] but is abundant in striatal cholinergic interneurons (which survive in Huntington's disease) suggests that the mutation in huntingtin that causes HD may not directly kill neurons. In contrast to the heterogeneous expression of huntingtin in the different striatal neuron types, we found all corticostriatal neurons to be rich in huntingtin protein and mRNA. One possibility raised by our findings is that the HD mutation may render corticostriatal neurons destructive rather than render striatal neurons vulnerable.

Role of arachidonic acid in the regulation of the NMDA-evoked release of acetylcholine in striatal compartments.

The role of endogenously released arachidonic acid in the control of the NMDA (50 microM)-evoked release of [3H]-acetylcholine previously formed from [3H]-choline was investigated in striosome-enriched areas and in the matrix of the rat striatum using a microsuperfusion procedure in vitro. Experiments were performed with either mepacrine (0.2 microM) or bovine serum albumin (BSA, 0.02%) which inhibits phospholipase A2 activity or binds endogenously released arachidonic acid, respectively. Both treatments similarly reduce the NMDA-evoked release of [3H]-acetylcholine, this effect being more pronounced in striosomes than in the matrix. These reductions result from a facilitation of dopamine release, since they were not observed in the presence of (-)sulpiride, the D2 dopamine receptor antagonist. Moreover, the superfusion with BSA was shown to enhance the release of [3H]-dopamine (formed from [3H]-tyrosine), this effect being of larger amplitude in striosomes than in the matrix. In control conditions, due to the blockade of the presynaptic inhibitory effect of GABA on dopamine release, bicuculline (GABA(A) receptor antagonist) reduces the NMDA-evoked release of [3H]-acetylcholine in both striatal compartments. Bicuculline was no longer effective following superfusions with either mepacrine or BSA, suggesting that these treatments eliminate the GABAergic presynaptic inhibitory control on dopamine transmission and thus lead to the dopamine-mediated inhibition of [3H]-acetylcholine release. These results indicate that arachidonic acid endogenously formed under weak stimulation of NMDA receptors contributes to the regulation of the evoked release of [3H]-acetylcholine by facilitating GABAergic transmission and that this process is more important in striosomes than in the matrix.

Role of arachidonic acid in the regulation of the NMDA‐evoked release of acetylcholine in striatal compartments

Role of arachidonic acid in the regulation of the NMDA‐evoked release of acetylcholine in striatal compartments

Distinct modifications by neurokinin 1 (SR140333) and neurokinin 2 (SR48968) tachykinin receptor antagonists of the N-methyl- d-aspartate-evoked release of acetylcholine in striosomes and matrix of the rat striatum

The effects of SR140333 and SR48968 (neurokinin 1 and neurokinin, tachykinin receptor antagonists, respectively) on the N-methyl- d-aspartate-evoked release of [ 3H]acetylcholine (previously formed from [ 3H]choline) were investigated in striosome-enriched areas and in the matrix of the rat striatum using an in vitro microsuperfusion method. In both striatal compartments, SR140333 and SR48968 did not modify the 50 μM N-methyl- d-aspartate-evoked release of [ 3H]acetylcholine. However, in low concentrations, both SR140333 (0.1 μM to 1 pM) and SR48968 (0.1 μM to 0.1 nM) markedly enhanced the 1 mM N-methyl- d-aspartate (+10 μM d-serine)-evoked release of [ 3H]acetylcholine in striosome-enriched areas. These responses were dopamine-dependent since they were not observed any more following the local blockade of D 2 receptors by sulpiride or of dopamine synthesis by α-methyl-p-tyrosine. A dopamine-dependent disinhibitory effect (of lower amplitude) on the 1 mM N-methyl- d-aspartate (+10 μM d-serine)-evoked release of [ 3H]acetylcholine was also induced by SR48968 (0.1 μM to 0.1 nM) (but not by SR140333) in the matrix. In addition, in the matrix, as shown only in the presence of α-methyl-p-tyrosine, both SR140333 and SR48968 reduced the 1 mM N-methyl- d-aspartate (+10 μM d-serine)-evoked response and these non-dopamine-mediated inhibitory effects only occurred at the highest tested concentration (0.1 μM) of the antagonists. Indicating the specificity of these responses, the effects of SR140333 were reproduced by RP67580, another neurokinin, receptor antagonist and, as expected from previous binding studies, corresponding SR140333 and SR48968 enantiomers were without effect. These results suggest that under potent stimulation of N-methyl- d-aspartate receptors, endogenously released substance P and neurokinin A (or related tachykinins) regulate differently the N-methyl- d-aspartate-evoked release of [ 3H]acetylcholine in striosomes and in the matrix. The inhibitory effects of these tachykinins on the evoked release of [ 3H]acetylcholine are mediated by dopamine. On the contrary, their facilitatory responses are only observed in the matrix under blockade of dopamine transmission.

Visceral afferent pathways to the thalamus and olfactory tubercle: behavioral implications

The goal of this study was to support the hypothesis that visceral signals may integrate and influence behavior by way of direct pathways from the nucleus tractus solitarii (NTS) to the olfactory tubercle and the midline/intralaminar thalamus. An anterograde tracer, biotinylated dextran amine (BDA) was iontophoresed bilaterally into the caudal NTS to optimize terminal labeling. NTS-cortical projections traversed both limbs of the diagonal bands providing heavy innervation, and terminated lightly within layer 3 of the olfactory tubercle. NTS-thalamic projections terminated within anterior and, as previously shown, posterior divisions of nucleus paraventricularis thalami and avoided the adjoining mediodorsal thalamic nucleus. Heretofore unrecognized projections were traced to the parafascicular and reuniens thalamic nuclei, and the peripeduncular nucleus. Control experiments identified the nucleus gracilis as the principal source of ascending projections to ventroposterior lateral, posterior and intralaminar thalamic nuclei. Our data corroborate the supposition that olfactory signals may integrate with visceral stimuli in the striatal compartment of olfactory tubercle. NTS projections encompass thalamic nuclei that project topographically to the prefrontal cortex, hippocampus and ventral (limbic) striatum, regions activated by visceral stimulation. Structural data support the idea that compartments of the non-discriminative thalamus may contribute to perception and behavioral responses to visceral stimulation.

Connectivity and Convergence of Single Corticostriatal Axons

The distribution of synapses formed by corticostriatal neurons was measured to determine the average connectivity and degree of convergence of these neurons and to search for spatial inhomogeneities. Two kinds of axonal fields, focal and extended, and two striatal tissue compartments, the patch (striosome) and matrix, were analyzed separately. Electron microscopic examination revealed that both kinds of corticostriatal axons made synapses at varicosities that could be identified in the light microscope, and each varicosity made a single synapse. Thus, the distribution of varicosities was a good estimate of the spatial distribution of synapses. The distance between axonal varicosities was measured to determine the density of synaptic connections formed by one axon within the volume occupied by a striatal neuron. Intersynaptic distances were distributed exponentially, except that synapses were rarely located <4 microm apart. The mean distance between synapses was approximately 10 microm, so axons made a maximum of 40 synapses within the dendritic volume of a spiny neuron. There are approximately 2840 spiny neurons located within the volume of the dendrites of one spiny cell (Oorschot, 1996), so each axon must contact </=1.4% of all cells in its axonal arborization. Within the same volume there are approximately 30.5 million asymmetric synapses (Ingham et al., 1996), approximately half of which are cortical in origin. Thus, approximately 380,000 cortical axons innervate the volume of the dendritic tree of one spiny cell. Striatal neurons with totally overlapping dendritic volumes have few presynaptic cortical axons in common, and cortical cells with overlapping axons have few striatal target neurons in common. These results explain the absence of redundancy in the responses of neurons located near each other in the striatum.

Early Patterning of Prelimbic Cortical Axons to the Striatal Patch Compartment in the Neonatal Mouse

The striatum receives excitatory input from virtually the entire cerebral cortex. In the adult, this input is segregated into two functionally distinct compartments of the striatum, the patch (striosome) and matrix regions. This study determined whether the patterning of corticostriatal afferents from the prelimbic cortex to the striatal patch compartment develops during the early period of collateral formation or instead at the time of peak synaptogenesis. Initial formation of corticostriatal axon collaterals was observed by embryonic day (E) 19. Quantification of corticostriatal collaterals revealed a significant increase in the number and complexity of collateral branches at postnatal day 6 as compared to E19. Concomitant with the increase in collateral branching, a heterogeneous pattern of collateralization consisting of parallel rows of corticostriatal collaterals was observed in the medial striatum. In addition to the rows, clusters of corticostriatal axons occurred more laterally. These clusters colocalized with patches of dense tyrosine hydroxylase-positive fibers, a marker for the striatal patch compartment in the neonatal mouse. Together, these data indicate that corticostriatal patterning occurs during the period of early axon collateralization resulting in a segregation of corticostriatal axon collaterals from the prelimbic cortex to the striatal patch compartment.

Activity-Regulated Phosphorylation of cAMP Response Element Binding Protein in the Developing Striatum: Implications for Patterning the Neurochemical Phenotypes of Striatal Compartments

A distinct feature of the striatum is that much of the expression of neurochemicals in this forebrain structure follows a compartmental (striosome/matrix) ordering. How this pattern of neurochemical compartmentation is developed and regulated is still unknown. In the present paper we propose that a key feature of this early striatal plasticity is differential control of the activation kinetics of the cAMP response element binding protein (CREB), which in turn influences striatal expression of genes containing cAMP response elements in their promoter sequences. Specifically, we propose that activity-dependent regulation of the kinetics of CREB phosphorylation, brought about early expressed protein phosphatases and protein phosphatase inhibitors in the developing striatal compartments, helps to set up and to maintain patterning of the neurochemical prototypes characteristic of striatal compartments.

Repeated administration of cocaine, nicotine and ethanol: effects on preprodynorphin, preprotachykinin A and preproenkephalin mRNA expression in the dorsal and the ventral striatum of the rat

It is established that dopamine (DA) controls the expression of preprodynorphin (PPDYN), preprotachykinin A (PPT-A) and preproenkephalin (PPE) mRNAs in striatal structures. Since cocaine, nicotine and ethanol enhance extracellular DA concentration, we have examined whether their repeated administration produced common changes in the expression of these mRNAs. Quantitative in situ hybridization histochemistry was performed in rats 2 h after a final challenge subsequent to repeated subcutaneous injections (3× a day) of cocaine (12.5 mg/kg), nicotine (0.4 mg/kg) for 14 days and ethanol (160 mg/kg) for 7 days. In the dorsal striatum, cocaine produced simultaneous PPDYN and PPT-A mRNA increases without PPE mRNA change whereas nicotine and ethanol produced no modification. After cocaine, PPDYN mRNA was preferentially increased in striatal patch compartment. In the nucleus accumbens, the effects were more complex. In cocaine-treated rats, we measured concomitant increases of PPDYN and PPE mRNA in the rostral pole, an isolated induction of PPT-A mRNA signals in the core without any change in the two shell subregions: the cone and the ventral shell. In contrast, after nicotine and ethanol, the ventral shell was the only accumbal subregion which showed a neuropeptide mRNA alteration, nicotine leading to decreased PPDYN mRNA and ethanol to increased PPT-A mRNA contents. The neuropeptide regulation after chronic treatment with these psychostimulant drugs does not strictly conform to a general DA control scheme in the dorsal and the ventral striatum. The cocaine effects can be clearly distinguished from those of nicotine and ethanol in terms of neuropeptide regulation and striatal subregions affected.

The Dopamine Transporter: Comparative Ultrastructure of Dopaminergic Axons in Limbic and Motor Compartments of the Nucleus Accumbens

The dopamine transporter (DAT) regulates extracellular dopamine concentrations, transports neurotoxins, and acts as a substrate for cocaine reinforcement. These functions are known to differ in the limbic-associated shell and motor-associated core compartments of the nucleus accumbens (NAc). Previous studies have shown differential expression of DAT in the NAc shell and core but were limited in resolution to the regional level. Thus, it is not known whether there are differences in the amount, subcellular localization, or plasmalemmal targeting of DAT within individual dopaminergic axons in the two regions. We used high-resolution electron microscopic immunocytochemistry to investigate these possibilities. We show that in both the shell and core, DAT immunogold labeling is present in tyrosine hydroxylase-immunoreactive varicose axons that form symmetric synapses. Within these labeled axons, most DAT gold particles are located on extrasynaptic plasma membranes, but some are associated with intracellular membranes. Dopaminergic axons in the shell contain lower mean densities of both total DAT gold particles (per square micron) and plasmalemmal DAT gold particles (per micron) than those in the core. Within labeled axons in the NAc shell and core, however, there are no detectable differences in the subcellullar distribution of DAT or the percentage of total DAT gold particles that are located on plasma membranes. These studies are the first to examine and compare the subcellular localization of DAT in the NAc shell and core. As a result, they identify intrinsic, cell-specific differences in the expression of DAT within dopaminergic axons in these functionally distinct striatal compartments.

Ultrastructural immunocytochemical localization of μ-opioid receptors in dendritic targets of dopaminergic terminals in the rat caudate–putamen nucleus

Many motor effects of opiates acting at μ-opioid receptors are thought to reflect functional interactions with dopaminergic inputs to the caudate–putamen nucleus. We examined the cellular and subcellular bases for this interaction in the rat caudate–putamen nucleus by dual immunocytochemical labelling for μ-opioid receptors and tyrosine hydroxylase, a marker mainly for dopamine in this region. μ-Opioid receptor-like immunoreactivity showed a patchy distribution by light microscopy. Within the patches, electron microscopy revealed that immunogold labelling for μ-opioid receptors was mainly distributed along extrasynaptic plasma membranes of medium spiny neurons. In contrast, immunoperoxidase labelling for tyrosine hydroxylase was exclusively located in axons and axon terminals without detectable μ-opioid receptor-like immunoreactivity. Forty-six percent of the total μ-opioid receptor-labelled neuronal profiles ( n=1441) were in contact with tyrosine hydroxylase-immunoreactive axons and terminals. These contacts were characterized by closely apposed parallel plasma membrane segments, without well-defined synaptic junctions, or with punctate symmetric specializations. From 639 noted appositions, over 90% were between μ-opioid receptor-labelled dendrites and/or dendritic spines and tyrosine hydroxylase-containing terminals. The dendritic spines containing μ-opioid receptor-like immunoreactivity often received asymmetric synapses characteristic of excitatory inputs from unlabelled terminals. Axon terminals containing μ-opioid receptor-like immunoreactivity formed asymmetric synapses with dendritic spines, or apposed tyrosine hydroxylase-labelled terminals. Our results suggest that, in striatal patch compartments, μ-agonists and dopamine dually modulate the activity of single spiny neurons mainly through changes in their postsynaptic responses to excitatory inputs. In addition, our findings implicate μ-opioid receptors and dopamine in the presynaptic regulation of excitatory neurotransmitter release within the striatal patch compartments.

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

The N-methyl- d-aspartate-evoked release of [ 3H]acetylcholine previously formed from [ 3H]choline was estimated in striosome- (identified by [ 3H]naloxone binding) or matrix-enriched areas of the rat striatum using an in vitro microsuperfusion procedure. Experiments were performed in either the absence or the presence of dopaminergic and/or GABAergic receptor antagonists. Although the cell bodies of the cholinergic interneurons were mainly found in the matrix, in the absence of magnesium, N-methyl- d-aspartate (50 μM) stimulated the release of [ 3H]acetylcholine in both striatal compartments. These responses were blocked by either magnesium, dizocilpine maleate, 7-chlorokynurenate or tetrodotoxin. N-Methyl- d-aspartate responses were concentration-dependent, but the 1 mM N-methyl- d-aspartate response was higher in striosomes than in the matrix. The co-application of d-serine (10 μM) enhanced the 10 μM N-methyl- d-aspartate response in both compartments, but reduced those induced by 1 mM N-methyl- d-aspartate, this reduction being higher in striosomes. The blockade of dopaminergic transmission with the D 2 and D 1 dopaminergic receptor antagonists, (−)-sulpiride (1 μM) and SCH23390 (1 μM), was without effect on the 50 μM N-methyl- d-aspartate-evoked release of [ 3H]acetylcholine, but markedly enhanced the 1 mM N-methyl- d-aspartate + d-serine-evoked response in striosomes and to a lesser extent in the matrix. Disinhibitory responses of similar amplitude were observed not only in striosomes but also in the matrix when (−)-sulpiride was used alone, while SCH23390 alone enhanced the 1 mM N-methyl- d-aspartate + d-serine response only in striosomes and to a lower extent than (−)-sulpiride. These results indicate that D 2 receptors are mainly involved in the inhibitory effect of dopamine on the 1 mM N-methyl- d-aspartate + d-serine-evoked release of [ 3H]acetylcholine. They also show that the stimulation of D 1 receptors can either reduce (striosomes) or enhance (matrix) this response, since in the latter case the effect induced by the combined application of the D 1 and D 2 receptor antagonists was smaller than that observed with the D 2 receptor antagonist alone. Indicating that released GABA facilitates N-methyl- d-aspartate responses, the blockade of GABA A receptors with bicuculline (5 μM) reduced the 50 μM N-methyl- d-aspartate-evoked release of [ 3H]acetylcholine in both striatal compartments and the 1 mM N-methyl- d-aspartate + d-serine response in the matrix. These effects result from an inhibition by GABA of the evoked release of dopamine, since the reducing effects of bicuculline on N-methyl- d-aspartate responses were not observed under the complete blockade of dopaminergic transmission by the D 1 and D 2 receptor antagonists. Further demonstrating a facilitatory role of GABA in the control of N-methyl- d-aspartate-evoked release of [ 3H]acetylcholine, in the presence of bicuculline, (−)-sulpiride and SCH23390 alone or in combination enhanced, in both compartments, the responses induced not only by 1 mM N-methyl- d-aspartate + d-serine, but also by 50 μM N-methyl- d-aspartate.

Concurrent cellular output from two proliferative populations in the early embryonic mouse corpus striatum

In mice, the striatal compartment of the forebrain is established by embryonic day 11 (E11, E0 = day of conception) when a lateral ganglionic eminence emerges surrounding the lateral and ventral margins of the forebrain ventricles. The inception of the striatal compartment is evidence of altered cell cycle kinetics, especially a rapid production of postmitotic cells, within a discrete portion of the telencephalic neuroepithelium. As a step toward understanding the mechanisms which contribute to the development of a cytokinetically distinct striatal compartment, we characterized the rate and pattern of cellular output in the lateral ganglionic neuroepithelium of mice on E11. The data show that the striatal compartment is distinguished by concurrent and equivalent levels of cell output from two proliferative populations: a dominant secondary proliferative population and a smaller, pseudostratified ventricular epithelium. In addition, although the ganglionic neuroepithelium is expanding on E11, 30-35% of the daughter cells produced leave the cell cycle and become postmitotic. These cytogenetic events, occurring in the lateral ganglionic progenitor population, may contribute to the development of a distinct striatal compartment within the telencephalon.

Concurrent cellular output from two proliferative populations in the early embryonic mouse corpus striatum

In mice, the striatal compartment of the forebrain is established by embryonic day 11 (E11, E0 = day of conception) when a lateral ganglionic eminence emerges surrounding the lateral and ventral margins of the forebrain ventricles. The inception of the striatal compartment is evidence of altered cell cycle kinetics, especially a rapid production of postmitotic cells, within a discrete portion of the telencephalic neuroepithelium. As a step toward understanding the mechanisms which contribute to the development of a cytokinetically distinct striatal compartment, we characterized the rate and pattern of cellular output in the lateral ganglionic neuroepithelium of mice on E11. The data show that the striatal compartment is distinguished by concurrent and equivalent levels of cell output from two proliferative populations: a dominant secondary proliferative population and a smaller, pseudostratified ventricular epithelium. In addition, although the ganglionic neuroepithelium is expanding on E11, 30-35% of the daughter cells produced leave the cell cycle and become postmitotic. These cytogenetic events, occurring in the lateral ganglionic progenitor population, may contribute to the development of a distinct striatal compartment within the telencephalon. J. Comp. Neurol. 383:220-230, 1997. © 1997 Wiley-Liss, Inc.

Effects of graft-derived dopaminergic innervation on the target neurons of patch and matrix compartments of the striatum

Fetal dopaminergic neurons grafted into the dopamine-depleted striatum have previously been shown to normalize neurochemical and behavioural abnormalities. However, the extent of graft-induced recovery of striatal compartments, which differ in their ontogeny, neurochemical properties and function, is still not clear. The striosome and matrix compartments of the striatum provide a segregated projection to somatostatin-containing GABAergic neurons of the rostral part of the entopeduncular nucleus and somatostatin-negative GABAergic neurons of the caudal part of the entopeduncular nucleus, respectively. In the present study, preprosomatostatin and glutamate decarboxylase messenger RNA levels in the rostral and caudal parts of the entopeduncular nucleus were determined six and 18months postgrafting in rats with complete recovery of rotational behaviour following apomorphine challenge, and in rats with unilateral 6-hydroxydopamine lesions or sham lesions and no grafts.Sections were processed for in situ hybridization using 35S-labelled cRNA probes for glutamate decarboxylase (67,000 mol. wt isoform; GAD67) and preprosomatostatin. Autoradiographs showed a marked increase in preprosomatostatin messenger RNA within the ipsilateral entopeduncular nucleus in 6-hydroxydopamine-lesioned rats, and a substantially lower increase six months postgrafting. At 18months postgrafting, the preprosomatostatin messenger RNA levels were symmetrical within the entopeduncular nucleus. Unilateral depletion of striatal dopamine resulted in a moderate increase in GAD67 messenger RNA levels within the ipsilateral entopeduncular nucleus, along with a substantial decrease in GAD67 levels within the contralateral nucleus. By six months postgrafting, the GAD67 levels had decreased considerably within the ipsilateral entopeduncular nucleus, while the messenger RNA levels had returned to normal within the contralateral nucleus. Interestingly, at 18months postgrafting, the GAD67 levels remained decreased within the ipsilateral entopeduncular nucleus and were significantly lower than the normal value.The results indicate that fetal nigral grafts placed within the dopamine-depleted striatum can restore the neurochemical alterations seen in striatal target areas such as the entopeduncular nucleus. This may form the neurochemical basis of graft-induced behavioural recovery, as the normalization of neurotransmitter messenger RNA levels in the entopeduncular nucleus reflects the restoration of overall activity in both direct and indirect striatal output pathways. The results also indicate that the graft-derived dopaminergic innervation restores the output of both striosome and matrix compartments of the striatum. The present results also showed a progressive recovery leading to over-compensation of neurotransmitter messenger RNA levels following grafting, perhaps indicating the importance of feedback regulation of grafted dopaminergic neurons by the host.

The neostriatal mosaic: basis for the changing distribution of neurokinin-1 receptor immunoreactivity during development.

The pattern of neurokinin-1 receptor-like immunoreactivity (NK-1Rir) was mapped in perinatal and adult mouse striatum by using a new polyclonal antiserum. NK-1Rir was detected in the differentiating regions of the ganglionic eminences on embryonic day 12.5 (E12.5). NK-1Rir structures were enriched in the striatal patch compartment between E16.5 and approximately postnatal day 3 (P3); distributed more uniformly, within portions of both the patch and matrix compartments on P7; and enriched in the matrix compartment in the adult. Analysis of the phenotype of NK-1Rir cells on P2, P7, and in the adult suggested that cholinergic cells accounted for the majority of NK-1Rir cells early postnatally, with increasing contributions from somatostatinergic cells later postnatally. In the adult, approximately half of NK-1Rir cells were cholinergic and half were somatostatinergic. The transient enrichment of NK-1R-bearing cells and processes in the patch compartment which contains cells that express substance P (SP), a putative ligand for the NK-1R, may be a consequence of compartment formation or may be functionally important for compartment development.

Distinct regulations by septide and the neurokinin-1 tachykinin receptor agonist [pro9]substance P of the N-methyl-D-aspartate-evoked release of dopamine in striosome- and matrix-enriched areas of the rat striatum.

The effects of septide (a short substance P C-terminal analogue) and of the neurokinin-1 receptor agonist [Pro9]substance P on the N-methyl-D-aspartate (50 microM)-evoked release of [3H]dopamine (continuously synthesized from [3H]tyrosine) were investigated in the absence or the presence of the selective neurokinin-1 receptor antagonist RP 67580 in selected striosome- and matrix-enriched areas of the rat striatum. Experiments were performed in vitro using a microsuperfusion procedure described previously. At a concentration of 0.1 microM, septide and [Pro9]substance P stimulated the spontaneous release of [3H]dopamine in striosome-enriched areas similarly. However, in this compartment, these peptides induced larger and opposite effects on the N-methyl-D-aspartate (50 microM)-evoked release of [3H]dopamine (estimated in the absence of magnesium). Indeed, septide markedly enhanced the N-methyl-D-aspartate response, while [Pro9]substance P largely reduced the N-methyl-D-aspartate-evoked release of [3H]dopamine. Septide also enhanced the N-methyl-D-aspartate response in the matrix, but [Pro9]substance P was without effect. When used alone, at 0.1 or 1 microM, RP 67580 reduced by about 33% the N-methyl-D-aspartate-evoked release of [3H]dopamine in striosome-enriched areas. In contrast, in the matrix, the N-methyl-D-aspartate response was enhanced in the presence of a low concentration of the antagonist, while the higher concentration was ineffective. In striosomes, the reducing effect of [Pro9]substance P and the enhancing action of septide on the N-methyl-D-aspartate response were respectively blocked in the presence of low and high concentrations of RP 67580, while the stimulatory effect of septide on the N-methyl-D-aspartate response in the matrix was prevented with both concentrations of the neurokinin-1 receptor antagonist. Finally, the co-application of [Pro9]substance P (0.1 microM) with septide (0.1 microM) abolished the enhancing effect of septide on the N-methyl-D-aspartate-evoked release of [3H]dopamine in both striatal compartments. Altogether, these results suggest that substance P and eventually one of its metabolites, substance P(6-11) or another endogenous tachykinin released under the action of N-methyl-D-aspartate, contribute to the regulation of [3H]dopamine release in both striatal compartments. They also extend previous observations which allowed us to demonstrate that the local circuits contributing to the presynaptic regulation of [3H]dopamine release differ in striosome- and matrix-enriched areas. Furthermore, in agreement with observations made in some peripheral tissues, the present results support the existence of "septide-sensitive" tachykinin receptors in the rat striatum or alternatively of septide sensitive sites on tachykinin neurokinin-1 receptors distinct from those sensitive to neurokinin-1 receptor agonists, coupled to distinct transducing systems, and thus leading to biological responses which differ from those evoked by neurokinin-1 receptor agonists.

Patchy distribution of substance P receptor immunoreactivity in the developing rat striatum

Developmental changes of the distribution pattern of substance P receptor (SPR) were investigated immunohistochemically in the rat striatum. The SPR immunoreactivity in the striatum first emerged at postnatal day 1 and transiently showed a patchy pattern of distribution until it displayed the adult pattern of homogeneous distribution by the end of the third postnatal week. The SPR-immunoreactive patches were most marked in the medial and dorsolateral parts of the striatum, as well as in the subcallosal streak. They matched tyrosine hydroxylase-enriched areas and, conversely, avoided calbindin-enriched zones. No neurons within the SPR-immunoreactive patches contained either choline acetyltransferase or somatostatin, which is known to be contained in intrinsic neurons in the striatum. The vast majority of SPR-immunoreactive patch neurons also contained DARPP-32, a phosphoprotein that is expressed in striatal projection neurons with D 1 dopamine receptor. The results indicate that SPR-immunoreactive patches which appear transiently in the developing striatum are in register with the striatal patch compartment, and that SPR immunoreactivity within these patches may be expressed on projection neurons rather than intrinsic neurons. Such SPR immunoreactivity in projection neurons in striatal patches may fade out in adulthood.

Calcium-binding proteins in primate basal ganglia

This paper describes the distribution of the calcium-binding proteins calbindin-D28k, parvalbumin and calretinin in primate basal ganglia. The data derive from immunocytochemical studies undertaken in squirrel monkeys ( Saimiri sciureus ) and in normal human individuals. In the striatum, calbindin labels medium-sized spiny projection neurons whereas parvalbumin and calretinin mark two separate classes of aspiny interneurons. The striatal matrix compartment is markedly enriched with calbindin while striatal patches (striosomes) display a calretinin-rich neuropil. In the pallidum, virtually all neurons contain parvalbumin but none express calbindin. Calretinin occurs only in a small subpopulation of both large and small pallidal neurons. In the subthalamic nucleus, there exists a multitude of parvalbumin-positive cells and fibers but the number of calretinin and calbindin-positive neuronal elements is small. In the substantia nigra/ventral tegmental area complex, calbindin and calretinin occur principally in dopaminergic neurons of the dorsal tier of the pars compacta and in those of the ventral tegmental area. Parvalbumin is strictly confined to the GABAergic neurons of the pars reticulata and lateralis. Calbindin-rich fibers abound in the pars reticulata and lateralis, while calretinin-positive axons are confined to the pars compacta. These results indicate that calbindin and parvalbumin are distributed according to a strikingly complementary pattern in primate basal ganglia. Calretinin is less ubiquitous but occurs in all basal ganglia components where it labels distinct subsets of neurons. Such highly specific patterns of distribution indicate that calbindin, parvalbumin and calretinin may work in synergy within primate basal ganglia.

Colocalization of serotonin receptor subtypes 5-HT2A, 5-HT2C, and 5-HT6 with neuropeptides in rat striatum.

There are two primary output pathways from the striatum: a projection to the globus pallidus, and projection to the substantia nigra. Certain striatally expressed neuropeptides are differentially distributed between these two pathways. Specifically, enkephalin is expressed in striatopallidal neurons, whereas substance P and dynorphin are expressed in striatonigral neurons. Several serotonin receptors are also prominently expressed in the striatum, but little is known about how they fit into the molecular neuroanatomy described above. We used double-label in situ hybridization to determine the striatal distribution of the mRNAs of the serotonin2A (5-HT2A), serotonin2C (5-HT2C), and serotonin6 (5-HT6) receptors in relation to enkephalin, substance P, and dynorphin expressing output neurons. Rat brain sections were simultaneously hybridized with an 35S riboprobe for one of the serotonin receptors and a digoxygenin labeled riboprobe for one of the neuropeptides. Sections were examined by using brightfield microscopy, and the degree of colocalization of the two mRNAs determined. All the serotonin receptors colocalized extensively with all three of the neuropeptides examined. None of the serotonin receptors showed preferential colocalization in striatopallidal (enkephalin containing), or striatonigral (substance P or dynorphin containing) cells. The 5-HT2A and 5-HT2C mRNAs displayed a differential distribution with regard to the scattered islands of strongly dynorphin mRNA positive cells, which are thought to reside in the striatal patch compartment. Within these islands, 5-HT2C mRNA expression was much higher than in surrounding areas. 5-HT2A mRNA showed the opposite pattern with decreased expression over dynorphin rich cell clusters.