Calretinin as a marker of specific neuronal subsets in primate substantia nigra and subthalamic nucleus

Neurotransmitter and receptor systems in the subthalamic nucleus

The Subthalamic Nucleus (STh) is a lens-shaped subcortical structure located ventrally to the thalamus, that despite being embryologically derived from the diencephalon, is functionally implicated in the basal ganglia circuits. Because of this strict structural and functional relationship with the circuits of the basal ganglia, the STh is a current target for deep brain stimulation, a neurosurgical procedure employed to alleviate symptoms in movement disorders, such as Parkinson's disease and dystonia. However, despite the great relevance of this structure for both basal ganglia physiology and pathology, the neurochemical and molecular anatomy of the STh remains largely unknown. Few studies have specifically addressed the detection of neurotransmitter systems and their receptors within the structure, and even fewer have investigated their topographical distribution. Here, we have reviewed the scientific literature on neurotransmitters relevant in the STh function of rodents, non-human primates and humans including glutamate, GABA, dopamine, serotonin, noradrenaline with particular focus on their subcellular, cellular and topographical distribution. Inter-species differences were highlighted to provide a framework for further research priorities, particularly in humans.

Release of 6-nitrodopamine from human popliteal artery and vein

6-Nitrodopamine (6-ND) is a novel catecholamine that is released from human umbilical cord vessels, and it causes vascular relaxation by acting as a dopamine D₂-receptor antagonist. Here it was investigated whether human peripheral vessels obtained from patients who have undergone surgery for leg amputation release 6-ND, and its action in these tissues. Popliteal artery and vein strips present basal release of 6-ND, as measure by liquid chromatography coupled to tandem mass spectrometry. The release was significantly reduced when the tissues were pre-treated with the nitric oxide synthase inhibitor L-NAME (100 μM), or when the endothelium was mechanically removed. In U-46619 (3 nM) pre-contracted rings, 6-ND induced concentration-dependent relaxations (pEC50 8.18 ± 0.05 and 8.40 ± 0.08, in artery and vein rings, respectively). The concentration-dependent relaxations induced by 6-ND were unaffected in tissues pre-treated with L-NAME, but significantly reduced in tissues where the endothelium has been mechanically removed. In U-46619 (3 nM) pre-contracted rings, the selective dopamine D₂ receptor antagonist L-741,626 also caused concentration-dependent relaxations (pEC₅₀ 8.92 ± 0.22 and 8.79 ± 0.19, in artery and vein rings, respectively). The concentration-dependent relaxations induced by L-741,626 were unaffected in tissues pre-treated with L-NAME, but significantly reduced in tissues where the endothelium has been mechanically removed. This is the first demonstration that 6-nitrodopamine is released from human peripheral artery and vein rings. The results also indicate that endothelium-derived dopamine is a major contractile agent in the popliteal artery and vein, and that selective dopamine D₂-receptor antagonists such as 6-ND, may have therapeutic potential in the treatment of human peripheral vascular diseases.

Calcium-binding proteins typify the dopaminergic neuronal subtypes in the ventral tegmental area of zebra finch, Taeniopygia guttata

Calcium-binding proteins (CBPs) regulate neuronal function in midbrain dopamine (DA)-ergic neurons in mammals by buffering and sensing the intracellular Ca²⁺ , and vesicular release. In birds, the equivalent set of neurons are important in song learning, directed singing, courtship, and energy balance, yet the status of CBPs in these neurons is unknown. Herein, for the first time, we probe the nature of CBPs, namely, Calbindin-, Calretinin-, Parvalbumin-, and Secretagogin-expressing DA neurons in the ventral tegmental area (VTA) and substantia nigra (SN) in the midbrain of zebra finch, Taeniopygia guttata. qRT-PCR analysis of ventral midbrain tissue fragment revealed higher Calbindin- and Calretinin-mRNA levels compared to Parvalbumin and Secretagogin. Application of immunofluorescence showed CBP-immunoreactive (-i) neurons in VTA (anterior [VTAa], mid [VTAm], caudal [VTAc]), SN (compacta [SNc], and reticulata [SNr]). Compared to VTAa, higher Calbindin- and Parvalbumin-immunoreactivity (-ir), and lower Calretinin-ir were observed in VTAm and VTAc. Secretagogin-ir was highly localized to VTAa. In SN, Calbindin- and Calretinin-ir were higher in SNc, SNr was Parvalbumin enriched, and Secretagogin-ir was not detected. Weak, moderate, and intense tyrosine hydroxylase (TH)-i VTA neurons were demarcated as subtypes 1, 2, and 3, respectively. While subtype 1 TH-i neurons were neither Calbindin- nor Calretinin-i, ∼80 and ∼65% subtype 2 and ∼30 and ∼45% subtype 3 TH-i neurons co-expressed Calbindin and Calretinin, respectively. All TH-i neuronal subtypes co-expressed Parvalbumin with reciprocal relationship with TH-ir. We suggest that the CBPs may determine VTA DA neuronal heterogeneity and differentially regulate their activity in T. guttata.

The Stereological Analysis and Spatial Distribution of Neurons in the Human Subthalamic Nucleus

The subthalamic nucleus (STN) is a small, ovoid structure, and an important site of deep brain stimulation (DBS) for the treatment of Parkinson’s disease. Although the STN is a clinically important structure, there are many unresolved issues with regard to it. These issues are especially related to the anatomical subdivision, neuronal phenotype, neuronal composition, and spatial distribution. In this study, we have examined the expression pattern of 8 neuronal markers [nNOS, NeuN, parvalbumin (PV), calbindin (CB), calretinin (CR), FOXP2, NKX2.1, and PAX6] in the adult human STN. All of the examined markers, except CB, were present in the STN. To determine the neuronal density, we have performed stereological analysis on Nissl-stained and immunohistochemical slides of positive markers. The stereology data were also used to develop a three-dimensional map of the spatial distribution of neurons within the STN. The nNOS population exhibited the largest neuronal density. The estimated total number of nNOS STN neurons is 281,308 ± 38,967 (± 13.85%). The STN neuronal subpopulations can be divided into two groups: one with a neuronal density of approximately 3,300 neurons/mm³ and the other with a neuronal density of approximately 2,200 neurons/mm³. The largest density of STN neurons was observed along the ventromedial border of the STN and the density gradually decreased toward the dorsolateral border. In this study, we have demonstrated the presence of 7 neuronal markers in the STN, three of which were not previously described in the human STN. The human STN is a collection of diverse, intermixed neuronal subpopulations, and our data, as far as the cytoarchitectonics is concerned, did not support the tripartite STN subdivision.

Selective Knockout of the Vesicular Monoamine Transporter 2 (Vmat2) Gene in Calbindin2/Calretinin-Positive Neurons Results in Profound Changes in Behavior and Response to Drugs of Abuse

The vesicular monoamine transporter 2 (VMAT2) has a range of functions in the central nervous system, from sequestering toxins to providing conditions for the quantal release of monoaminergic neurotransmitters. Monoamine signaling regulates diverse functions from arousal to mood, movement, and motivation, and dysregulation of VMAT2 function is implicated in various neuropsychiatric diseases. While all monoamine-releasing neurons express the Vmat2 gene, only a subset is positive for the calcium-binding protein Calbindin 2 (Calb2; aka Calretinin, 29 kDa Calbindin). We recently showed that about half of the dopamine neurons in the mouse midbrain are positive for Calb2 and that Calb2 is an early developmental marker of midbrain dopamine cells. Calb2-positive neurons have also been identified in other monoaminergic areas, yet the role of Calb2-positive monoaminergic neurons is poorly understood. To selectively address the impact of Calb2-positive monoaminergic neurons in behavioral regulation, we took advantage of the Cre-LoxP system to create a new conditional knockout (cKO) mouse line in which Vmat2 expression is deleted selectively in Calb2-Cre-positive neurons. In this Vmat2^{lox/lox;Calb2−Cre} cKO mouse line, gene targeting of Vmat2 was observed in several distinct monoaminergic areas. By comparing control and cKO mice in a series of behavioral tests, specific dissimilarities were identified. In particular, cKO mice were smaller than control mice and showed heightened sensitivity to the stereotypy-inducing effects of amphetamine and slight reductions in preference toward sucrose and ethanol, as well as a blunted response in the elevated plus maze test. These data uncover new knowledge about the role of genetically defined subtypes of neurons in the brain’s monoaminergic systems.

Regional chemoarchitecture of the brain of lungfishes based on calbindin D-28K and calretinin immunohistochemistry

Lungfishes are the closest living relatives of land vertebrates, and their neuroanatomical organization is particularly relevant for deducing the neural traits that have been conserved, modified, or lost with the transition from fishes to land vertebrates. The immunohistochemical localization of calbindin (CB) and calretinin (CR) provides a powerful method for discerning segregated neuronal populations, fiber tracts, and neuropils and is here applied to the brains of Neoceratodus and Protopterus, representing the two extant orders of lungfishes. The results showed abundant cells containing these proteins in pallial and subpallial telencephalic regions, with particular distinct distribution in the basal ganglia, amygdaloid complex, and septum. Similarly, the distribution of CB and CR containing cells supports the division of the hypothalamus of lungfishes into neuromeric regions, as in tetrapods. The dense concentrations of CB and CR positive cells and fibers highlight the extent of the thalamus. As in other vertebrates, the optic tectum is characterized by numerous CB positive cells and fibers and smaller numbers of CR cells. The so-called cerebellar nucleus contains abundant CB and CR cells with long ascending axons, which raises the possibility that it could be homologized to the secondary gustatory nucleus of other vertebrates. The corpus of the cerebellum is devoid of CB and CR and cells positive for both proteins are found in the cerebellar auricles and the octavolateralis nuclei. Comparison with other vertebrates reveals that lungfishes share most of their features of calcium binding protein distribution with amphibians, particularly with salamanders.

Endogenous calcium buffering capacity of substantia nigral dopamine neurons

Dopamine (DA)-containing cells from the substantia nigra pars compacta (SNc) play a major role in the initiation of movement. Loss of these cells results in Parkinson's disease (PD). Changes in intracellular calcium ion concentration ([Ca(2+)](i)) elicit several events in DA cells, including spike afterhyperpolarizations (AHPs) and subthreshold oscillations underlying autonomous firing. Continuous Ca(2+) load due to Ca(2+)-dependent rhythmicity has been proposed to cause the death of DA cells in PD and normal aging. Because of the physiological and pathophysiological importance of [Ca(2+)](i) in DA cells, we characterized their intrinsic Ca(2+)-buffering capacity (K(S)) in brain slices. We introduced a fluorescent Ca(2+)-sensitive exogenous buffer (200 microM fura-2) and cells were tracked from break-in until steady state by stimulating with a single action potential (AP) every 30 s and measuring the Ca(2+) transient from the proximal dendrite. DA neurons filled exponentially with a tau of about 5-6 min. [Ca(2+)](i) was assumed to equilibrate between the endogenous Ca(2+) buffer and the exogenous Ca(2+) indicator buffer. Intrinsic buffering was estimated by extrapolating from the linear relationships between the amplitude or time constant of the Ca(2+) transients versus [fura-2]. Extrapolated Ca(2+)-transients in the absence of fura-2 had mean peak amplitudes of 293.7 +/- 65.3 nM and tau = 124 +/- 13 ms (postnatal day 13 [P13] to P17 animals). Intrinsic buffering increased with age in DA neurons. For cells from animals P13-P17, K(S) was estimated to be about 110 (n = 20). In older animals (P25-P32), the estimate was about 179 (n = 10). These relatively low values may reflect the need for rapid Ca(2+) signaling, e.g., to allow activation of sK channels, which shape autonomous oscillations and burst firing. Low intrinsic buffering may also make DA cells vulnerable to Ca(2+)-dependent pathology.

Phenotype, compartmental organization and differential vulnerability of nigral dopaminergic neurons

The degeneration of nigral dopaminergic (DA-) neurons is the histopathologic hallmark of Parkinson's disease (PD), but not all nigral DA-cells show the same susceptibility to degeneration. This starts in DA-cells in the ventrolateral and caudal regions of the susbtantia nigra (SN) and progresses to DA-cells in the dorsomedial and rostral regions of the SN and the ventral tegmental area, where many neurons remain intact until the final stages of the disease. This fact indicates a relationship between the topographic distribution of midbrain DA-cells and their differential vulnerability, and the possibility that this differential vulnerability is associated with phenotypic differences between different subpopulations of nigral DA-cells. Studies carried out during the last two decades have contributed to establishing the existence of different compartments of nigral DA-cells according to their neurochemical profile, and a possible relationship between the expression of some factors and the relative vulnerability or resistance of DA-cell subpopulations to degeneration. These aspects are reviewed and discussed here.

Neurochemical organization of the human basal ganglia: anatomofunctional territories defined by the distributions of calcium-binding proteins and SMI-32

The distribution of the calcium-binding proteins calbindin-D28K (CB), parvalbumin (PV) and calretinin (CR), and of the nonphosphorylated neurofilament protein (with SMI-32) was investigated in the human basal ganglia to identify anatomofunctional territories. In the striatum, gradients of neuropil immunostaining define four major territories: The first (T1) includes all but the rostroventral half of the putamen and is characterized by enhanced matriceal PV and SMI-32 immunoreactivity (-ir). The second territory (T2) encompasses most part of the caudate nucleus (Cd) and rostral putamen (PuT), which show enhanced matriceal CB-ir. The third and fourth territories (T3 and T4) comprise rostroventral parts of Cd and PuT characterized by complementary patch/matrix distributions of CB- and CR-ir, and the accumbens nucleus (Acb), respectively. The latter is separated into lateral (prominently enhanced in CB-ir) and medial (prominently enhanced in CR-ir) subdivisions. In the pallidum, parallel gradients also delimit four territories, T1 in the caudal half of external (GPe) and internal (GPi) divisions, characterized by enhanced PV- and SMI-32-ir; T2 in their rostral half, characterized by enhanced CB-ir; and T3 and T4 in their rostroventral pole and in the subpallidal area, respectively, both expressing CB- and CR-ir but with different intensities. The subthalamic nucleus (STh) shows contrasting patterns of dense PV-ir (sparing only the most medial part) and low CB-ir. Expression of CR-ir is relatively low, except in the medial, low PV-ir, part of the nucleus, whereas SMI-32-ir is moderate across the whole nucleus. The substantia nigra is characterized by complementary patterns of high neuropil CB- and SMI-32-ir in pars reticulata (SNr) and high CR-ir in pars compacta (SNc) and in the ventral tegmental area (VTA). The compartmentalization of calcium-binding proteins and SMI-32 in the human basal ganglia, in particular in the striatum and pallidum, delimits anatomofunctional territories that are of significance for functional imaging studies and target selection in stereotactic neurosurgery.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Localization of calcium-binding proteins and GABA transporter (GAT-1) messenger RNA in the human subthalamic nucleus

The distribution of messenger RNA encoding the human GAT-1 (a high-affinity GABA transporter) was investigated in the subthalamic nucleus of 10 neurologically normal human post mortem cases. Further, the distribution of messenger RNA and protein encoding the three neuronally expressed calcium-binding proteins (calbindin D28k, parvalbumin and calretinin) was similarly investigated using in situ hybridization and immunohistochemical techniques. Cellular sites of calbindin D28k, parvalbumin, calretinin and GAT-1 messenger RNA expression were localized using human-specific oligonucleotide probes radiolabelled with [35S]dATP. Sites of protein localization were visualized using specific anti-calbindin D28k, anti-parvalbumin and anti-calretinin antisera. Examination of emulsion-coated tissue sections processed for in situ hybridization revealed an intense signal for GAT-1 messenger RNA within the human subthalamic nucleus, indeed the majority of Methylene Blue-counterstained cells were enriched in this transcript. Further, a marked heterogeneity was noted with regard to the expression of the messenger RNA's encoding the three calcium-binding proteins; this elliptical nucleus was highly enriched in parvalbumin messenger RNA-positive neurons and calretinin mRNA-positive cells but not calbindin messenger RNA-positive cells. Indeed, only an occasional calbindin messenger RNA-positive cell was detected within the mediolateral extent of the nucleus. In marked contrast, numerous parvalbumin messenger RNA-positive cells and calretinin messenger RNA-positive cells were detected and they were topographically distributed; parvalbumin messenger RNA-positive cells were highly enriched in the dorsal subthalamic nucleus extending mediolaterally; calretinin messenger RNA-positive cells were more enriched ventrally although some degree of overlap was apparent. Computer-assisted analysis of the average cross-sectional somatic area of parvalbumin, calretinin and GAT-1 messenger RNA-positive neurons revealed them all to be in the range of 300 microm2. The unique patterns of calcium-binding protein gene expression were similarly reflected at the protein level; an abundance of parvalbumin- and calretinin-immunopositive neurons were observed whereas only occasional intensely-labelled calbindin-immunopositive fibres were seen, no calbindin-immunopositive cells were detected. Single and double labelling studies show that parvalbumin-immunopositive neurons were mainly localized in the dorsal region of the nucleus, and calretinin-immunopositive neurons were mainly localized in the ventral region although there was overlap with double-labelled neurons located in the middle and dorsal regions. The significance of these findings, in particular the expression of GAT-1, a high-affinity GABA uptake protein, for basal ganglia signalling is discussed.

Calretinin-immunoreactive neurons in primate pedunculopontine and laterodorsal tegmental nuclei

Single- and double-antigen localization procedures were used to study the distribution, morphological characteristics and chemical phenotype of neurons containing the calcium-binding protein calretinin in the pedunculopontine and laterodorsal tegmental nuclei of the cynomolgus monkey (Macaca fascicularis). Calretinin was detected in neurons that belonged to a highly heteromorphic and widely distributed subpopulation of the pedunculopontine and laterodorsal tegmental nuclei in the cynomolgus monkey. Double-immunostaining experiments revealed that about 12% of these calretinin-containing neurons displayed immunoreactivity for another calcium-binding protein, Calbindin-D28k. The calretinin/Calbindin-D28k double-labeled neurons had small to medium-sized perikarya, from which emerged a bipolar or multipolar dendritic arborization. Calretinin was also present in approximately 8% of the cholinergic neurons of the pedunculopontine/laterodorsal nuclear complex, as visualized on single sections immunostained for both calretinin and choline acetyltransferase. These calretinin/choline acetyltransferase double-labeled neurons displayed markedly different sizes and shapes, and occurred preferentially in the pars compacta and dissipata of the pedunculopontine tegmental nucleus. Numerous calretinin-immunoreactive fibers were also present within and around the superior cerebellar peduncle. Some of these varicose fibers closely surrounded large non-immunoreactive neurons, as well as large neurons staining positively for choline acetyltransferase. This study provides the first evidence for the existence of calretinin-immunoreactive neurons within the primate pedunculopontine and laterodorsal tegmental nuclei. Our data suggest that calretinin may play a role in the function of the pedunculopontine/laterodorsal nuclear complex by acting either alone or in conjunction with acetylcholine or Calbindin-D28k.

Distribution of calbindin D-28k and parvalbumin neurons and fibers in the rat basal ganglia

This review deals with the distribution of immunoreactivity for calbindin D-28k (CB) and parvalbumin (PV) in the different nuclei of the rodent basal ganglia analyzed with the data available after the use of single and double antigen procedures applied to single sections. These findings reveal that CB and PV are distributed according to a highly heterogeneous pattern in the caudate putamen complex (CPu), globus pallidus (GP), entopeduncular nucleus (EP), subthalamic nucleus (STh) and substantia nigra (SN) of the rat. In each basal ganglia structure, the two calcium-binding proteins label different neuronal subsets. Therefore, the use of CB and PV immunohistochemistry may be considered as an excellent tool to define distinct chemoarchitectonic and functional domains within the complex organization of the basal ganglia. Double immunohistochemical methods are also useful to illustrate the relationships between the different chemical subdivisions of the CPu, GP, EP, STh and SN and the chemically characterized connections with each other and with other forebrain and brainstem structures. However, specific rules should be followed when combining single and double immunostaining procedures, and the results of such studies must be evaluated with caution. When they are used properly, these methods can reveal hitherto unknown principles of organization of the basal ganglia and thus shed new light on the anatomical and functional organization of this set of subcortical structures involved in the control of motor behavior.

Morphological organization of the globus pallidus-subthalamic nucleus system studied in organotypic cultures

The morphological organization of the globus pallidus (GP), the subthalamic nucleus (STN), and the pallidosubthalamic projection was studied in organotypic cultures. Coronal slices from the GP, the STN, the striatum (CPu), and the cortex (Cx) were taken from the rat after postnatal days 0-2 and grown for 2 or 5-6 weeks. For analysis, immunocytochemistry against glutamate (GLU), parvalbumin (PV), and calretinin (CR) was combined with confocal microscopy. After 2 weeks in vitro, the STN showed a densely packed, homogeneous GLU-immunoreactive (ir) cell population. Pallidal GLU-ir neurons were heterogeneous, consisting of large-sized weakly GLU-ir neurons and small-sized intensively GLU-ir neurons. After 5-6 weeks in vitro, pallidal axons had radiated from numerous large-sized PV-ir cells and selectively innervated the STN, where they heavily ramified. Cultured STN neurons were not stained for PV; however, multipolar intensely PV-ir neurons were located at the border of the STN with their dendrites oriented towards the STN. Double labeling for PV and CR in both mature cultures and in the adult rat revealed that the culture CR-ir neurons from the GP, the Cpu, and from areas adjacent to the STN were different from cultured PV-ir neurons and their morphologies and distribution corresponded to that in vivo. These results demonstrate that 1) cultured CP and STN neurons display similar morphologies found in in vivo, 2) PV-ir pallidal neurons heavily and selectively innervate the STN; 3) there is a specific class of STN border neurons; and 4) in contrast to the in vivo situation, most cultured STN neurons are PV-negative.

Calretinin gene expression in the human thalamus

The localization and levels of expression of the calcium-binding protein calretinin (CR) in the human thalamus was studied with an in situ hybridization method applied to formalin-fixed postmortem material from normal individuals. The riboprobe used was generated from a specific fragment of human CR cDNA. As visualized on X-ray film autoradiographs, high levels of CR gene transcript occurred in several thalamic nuclei, including the reticular nucleus, mediodorsal nucleus, rostral intralaminar nuclei (paracentral, central medial and central lateral) and several midline nuclei (paraventricular, reuniens and medioventral nuclei). In the reticular nucleus, neurons expressing CR mRNA were few in number but formed dense and widely distributed clusters. In contrast, virtually all neurons in the rostral intralaminar and midline nuclei expressed very high levels of CR mRNA and formed a prominent rim around the mediodorsal nucleus, which contained scattered clusters of labeled neurons. The caudal intralaminar nuclei, principally the centromedian nucleus, displayed very few neurons expressing CR mRNA. Only the medial part of the parafascicular nucleus expressed moderate levels of CR mRNA. The nuclei of the ventral group (ventral anterior, lateral and posterior nuclei) were virtually devoid of CR gene transcript. This highly heterogeneous pattern of mRNA expression suggests that CR may be heavily involved in the function of the so-called non-specific nuclei, but not in that of the specific relay nuclei of the human thalamus. The data also demonstrate that the presence of CR gene transcript can easily be detected on formalin-fixed sections of the human brain.

Distribution of calretinin, calbindin-D28k and parvalbumin in the hypothalamus of the squirrel monkey

The immunohistochemical approach was used to study the distribution of three calcium-binding proteins of the 'EF hand' family, namely calretinin, calbindin-D28k and parvalbumin, in the preoptico-hypothalamic complex of the squirrel monkey (Saimiri sciureus). These three calcium-binding proteins were found to be heterogeneously distributed in the primate hypothalamus. Neurons expressing high levels of calretinin immunoreactivity were particularly abundant in the infundibular (arcuate) nucleus, the suprachiasmatic nucleus, the lateral area and the dorsomedial nucleus of the hypothalamus. Neurons displaying immunoreactivity for calbindin-D28k were especially numerous in the medial preoptic area and diagonal band nucleus, as well as in the magnocellular subdivision of the paraventricular nucleus, the suprachiasmatic nucleus, the supraoptic nucleus, the infundibular nucleus, the ventromedial nucleus and the mammillary bodies of the hypothalamus. Fibers displaying intense immunoreactivity for either calretinin or calbindin-D28k were very abundant in the median eminence of the hypothalamus. In contrast to calretinin- and calbindin-D28k, parvalbumin was largely absent from the primate preoptico-hypothalamic complex. Parvalbumin-immunoreactive neurons occurred in significant number only in the most lateral portion of the medial mammillary nucleus in the squirrel monkey. The results of the present study suggest that calretinin and calbindin-D28k may act, either in concert or in a complementary manner, so as to participate in some specific aspects of the multifarious role of the hypothalamus in primates. In contrast to the other two calcium-binding proteins, parvalbumin is unlikely to be involved in a significant manner in hypothalamic functions in primates.

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 parvalbumun-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.