Ultrastructural localization of calbindin-D28k and GABA in the matrix compartment of the rat caudate-putamen nuclei

Morphology and morphometry of interneuron subpopulations of the marmoset monkey (Callithrix jacchus) striatum

The mammalian striatum has long been considered a homogeneous entity. However, neuroanatomical and histochemical studies reveal that the striatum is much more heterogeneous than previously suspected. The caudate (Cd) and putamen (Pu) are composed of two chemical compartments: the matrix and the striosomes. Striatal interneurons have been classified into a variety of morphological and neurochemical subtypes. In this study, we compared the distribution of multiple neurochemical markers in the striatum of marmosets and described the morphology of different types of striatum interneurons. The immunoreactivities of choline-acetyl transferase (ChAT), neuropeptide Y (NPY), nitric oxide synthase (NOS), calretinin (CR), parvalbumin (PV) were analyzed along the entire rostrocaudal extent of the marmoset striatum. Calbindin immunohistochemistry is useful in identifying medium spiny neurons (MSNs), with efficient soma staining. Based on the size of the CB-positive cells, considered medium-sized, as expected, cholinergic cells are larger in area and diameter than the other subpopulations investigated, followed by NOS, NPY, PV and CR. In adjacent CB and PV-stained sections, the matrix and striosomes were clearly distinguished. The matrix is strongly reactive to CB and PV neuropils, while the striosomes exhibit low reactivity, especially in the dorsal Cd. Therefore, we provide a detailed description morphology and distribution of striatal interneuron populations in a model as a valuable tool for studying neurodegenerative pathogenesis, progression and treatment strategies.

CYP46A1 Activation by Efavirenz Leads to Behavioral Improvement without Significant Changes in Amyloid Plaque Load in the Brain of 5XFAD Mice

Efavirenz, the FDA-approved anti-retroviral medication, is evaluated in the clinical trial in patients with mild cognitive impairment or early dementia due to Alzheimer's disease. Efavirenz is assessed for activation of cytochrome P450 46A1 (CYP46A1), a CNS-specific enzyme that converts cholesterol to 24-hydroxycholesterol. Cholesterol 24-hydroxylation is the major pathway for brain cholesterol removal, and a mechanism that controls brain cholesterol turnover. The present study tested efavirenz on 5XFAD mice (an Alzheimer's model) at a very low daily dose of 0.1 mg/kg body weight. Efavirenz treatment started from three months of age, after amyloid plague appearance, and continued for 6 months. This treatment led to CYP46A1 activation in the brain, enhancement of brain cholesterol turnover, behavioral improvements, reduction in microglia activation but increased astrocyte reactivity. The levels of the soluble and insoluble amyloid 40 and 42 peptides were unchanged while the number and area of the dense core amyloid plaques were slightly decreased. The measurements of the brain levels of several pre- and post-synaptic proteins (Munc13-1, PSD-95, gephyrin, synaptophysin, synapsin-1, and calbindin-D28k) suggested efavirenz effect at the synaptic level. Efavirenz treatment in the present work seems to represent a model of behavioral and other improvements independent of the levels of the amyloid peptides and provides insight into potential outcomes of the future clinical trial.

The key genes, phosphoproteins, processes, and pathways affected by efavirenz-activated CYP46A1 in the amyloid-decreasing paradigm of efavirenz treatment

Efavirenz (EFV) is an anti-HIV drug, and cytochrome P450 46A1 (CYP46A1) is the major brain cholesterol hydroxylase. Previously, we discovered that EFV activates CYP46A1 and improves behavioral performance in 5XFAD mice, an Alzheimer's disease model. Herein, the unbiased omics and other approaches were used to study 5XFAD mice in the amyloid-decreasing paradigm of CYP46A1 activation by EFV. These approaches revealed increases in the brain levels of postsynaptic density protein 95, gephyrin, synaptophysin, synapsin, glial fibrillary acidic protein, and CYP46A1 and documented altered expression and phosphorylation of 66 genes and 77 proteins, respectively. The data obtained pointed to EFV effects at the synaptic level, plasmin-depended amyloid clearance, inflammation and microglia phenotype, oxidative stress and cellular hypoxia, autophagy and ubiquitin-proteasome systems as well as apoptosis. These effects could be realized in part via changes in the Ca²⁺-, small GTPase, and catenin signaling. A model is proposed, in which CYP46A1-dependent lipid raft rearrangement and subsequent decrease of protein phosphorylation are central in EFV effects and explain behavioral improvements in EFV-treated 5XFAD mice.-Petrov, A. M., Mast, N., Li, Y., Pikuleva, I. A. The key genes, phosphoproteins, processes, and pathways affected by efavirenz-activated CYP46A1 in the amyloid-decreasing paradigm of efavirenz treatment.

Antioxidant supplementation upregulates calbindin expression in cerebellar Purkinje cells of rat pups subjected to post natal exposure to sodium arsenite

Optimal cytoplasmic calcium (Ca²⁺) levels have been associated with adequate cell functioning and neuronal survival. Altered intracellular Ca²⁺ levels following impaired Ca²⁺ homeostasis could induce neuronal degeneration or even cell death. There are reports of arsenite induced oxidative stress and the associated disturbances in intracellular calcium homeostasis. The present study focused on determining the strategies that would modulate tissue redox status and calcium binding protein (CaBP) (Calbindin D28k-CB) expression affected adversely by sodium arsenite (NaAsO₂) exposure (postnatal) of rat pups. NaAsO₂ alone or along with antioxidants (AOXs) (alpha lipoic acid or curcumin) was administered by intraperitoneal (i.p.) route from postnatal day (PND) 1-21 (covering rapid brain growth period - RBGP) to experimental groups and animals receiving sterile water by the same route served as the controls. At the end of the experimental period, the animals were subjected to euthanasia and the cerebellar tissue obtained therefrom was processed for immunohistochemical localization and western blot analysis of CB protein. CB was diffusely expressed in cell body as well as dendritic processes of Purkinje cells (PCs) along the PC Layer (PCL) in all cerebellar folia of the control and the experimental animals. The multilayered pattern of CB +ve cells along with their downregulated expression and low packing density was significantly evident in the arsenic (iAs) alone exposed group as against the controls and AOX supplemented groups. The observations are suggestive of AOX induced restoration of CaBP expression in rat cerebellum following early postnatal exposure to NaAsO₂.

Lateral and feedforward inhibition suppress asynchronous activity in a large, biophysically-detailed computational model of the striatal network

Striatal medium spiny neurons (MSNs) receive lateral inhibitory projections from other MSNs and feedforward inhibitory projections from fast-spiking, parvalbumin-containing striatal interneurons (FSIs). The functional roles of these connections are unknown, and difficult to study in an experimental preparation. We therefore investigated the functionality of both lateral (MSN-MSN) and feedforward (FSI-MSN) inhibition using a large-scale computational model of the striatal network. The model consists of 2744 MSNs comprised of 189 compartments each and 121 FSIs comprised of 148 compartments each, with dendrites explicitly represented and almost all known ionic currents included and strictly constrained by biological data as appropriate. Our analysis of the model indicates that both lateral inhibition and feedforward inhibition function at the population level to limit non-ensemble MSN spiking while preserving ensemble MSN spiking. Specifically, lateral inhibition enables large ensembles of MSNs firing synchronously to strongly suppress non-ensemble MSNs over a short time-scale (10–30 ms). Feedforward inhibition enables FSIs to strongly inhibit weakly activated, non-ensemble MSNs while moderately inhibiting activated ensemble MSNs. Importantly, FSIs appear to more effectively inhibit MSNs when FSIs fire asynchronously. Both types of inhibition would increase the signal-to-noise ratio of responding MSN ensembles and contribute to the formation and dissolution of MSN ensembles in the striatal network.

Modeling Huntington's disease with induced pluripotent stem cells

Huntington's disease (HD) causes severe motor dysfunction, behavioral abnormalities, cognitive impairment and death. Investigations into its molecular pathology have primarily relied on murine tissues; however, the recent discovery of induced pluripotent stem cells (iPSCs) has opened new possibilities to model neurodegenerative disease using cells derived directly from patients, and therefore may provide a human-cell-based platform for unique insights into the pathogenesis of HD. Here, we will examine the practical implementation of iPSCs to study HD, such as approaches to differentiate embryonic stem cells (ESCs) or iPSCs into medium spiny neurons, the cell type most susceptible in HD. We will explore the HD-related phenotypes identified in iPSCs and ESCs and review how brain development and neurogenesis may actually be altered early, before the onset of HD symptoms, which could inform the search for drugs that delay disease onset. Finally, we will speculate on the exciting possibility that ESCs or iPSCs might be used as therapeutics to restore or replace dying neurons in HD brains.

Quinpirole elicits differential in vivo changes in the pre- and postsynaptic distributions of dopamine D₂ receptors in mouse striatum: relation to cannabinoid-1 (CB₁) receptor targeting

RATIONALE

The nucleus accumbens (Acb) shell and caudate-putamen nucleus (CPu) are respectively implicated in the motivational and motor effects of dopamine, which are mediated in part through dopamine D₂-like receptors (D₂Rs) and modulated by activation of the cannabinoid-1 receptor (CB₁R). The dopamine D(₂/D3) receptor agonist, quinpirole elicits internalization of D₂Rs in isolated cells; however, dendritic and axonal targeting of D₂Rs may be highly influenced by circuit-dependent changes in vivo and potentially influenced by endogenous CB₁R activation.

OBJECTIVE

We sought to determine whether quinpirole alters the surface/cytoplasmic partitioning of D₂Rs in striatal neurons in vivo.

METHODS

To address this question, we examined the electron microscopic immunolabeling of D₂ and CB₁ receptors in the Acb shell and CPu of male mice at 1 h following a single subcutaneous injection of quinpirole (0.5 mg/kg) or saline, a time point when quinpirole reduced locomotor activity.

RESULTS

Many neuronal profiles throughout the striatum of both treatment groups expressed the D₂R and/or CB₁R. As compared with saline, quinpirole-injected mice showed a significant region-specific decrease in the plasmalemmal and increase in the cytoplasmic density of D₂R-immunogold particles in postsynaptic dendrites without CB₁R-immunolabeling in the Acb shell. However, quinpirole produced a significant increase in the plasmalemmal density of D₂R immunogold in CB₁R negative axons in both the Acb shell and CPu.

CONCLUSIONS

Our results provide in vivo evidence for agonist-induced D₂R trafficking that is inversely related to CB₁R distribution in postsynaptic neurons of Acb shell and in presynaptic axons in this region and in the CPu.

Dendritic SNAREs add a new twist to the old neuron theory

Dendritic exocytosis underpins a broad range of integrative and homeostatic synaptic functions. Emerging data highlight the essential role of SNAREs in trafficking and fusion of secretory organelles with release of peptides and neurotransmitters from dendrites. This Perspective analyzes recent evidence inferring axo-dendritic polarization of vesicular release machinery and pinpoints progress made with existing challenges in this rapidly progressing field of dendritic research. Interpreting the relation of new molecular data to physiological results on secretion from dendrites would greatly advance our understanding of this facet of neuronal mechanisms.

Enhanced dendritic availability of μ-opioid receptors in inhibitory neurons of the extended amygdala in mice deficient in the corticotropin-releasing factor-1 receptor

Activation of the corticotropin-releasing factor-1 (CRF-1) receptor in the anterolateral BNST (BSTal), a key subdivision of the extended amygdala, elicits opiate-seeking behavior exacerbated by stress. However, it is unknown whether the presence of CRF-1 affects expression of the μ-opioid receptor (μ-OR) in the many GABAergic BSTal neurons implicated in the stress response. We hypothesized that deletion of the CRF-1 receptor gene would alter the density and/or subcellular distribution of μ-ORs in GABAergic neurons of the BSTal. We used electron microscopy to quantitatively examine μ-OR immunogold and γ-aminobutyric acid (GABA) immunoperoxidase labeling in the BSTal of CRFr-1 knockout (KO) compared to wild-type (WT) mice. To assess regional specificity, we examined μ-OR distribution in dorsal striatum. The μ-ORs in each region were predominantly localized in dendrites, many of which were GABA-immunoreactive. Significantly, more cytoplasmic μ-OR gold particles per dendritic area were observed selectively in GABA-containing dendrites of the BSTal, but not of the dorsal striatum, in KO compared to WT mice. In both regions, however, significantly fewer GABA-immunoreactive axon terminals were present in KO compared to WT mice. Our results suggest that the absence of CRF-1 results in enhanced expression and/or dendritic trafficking of μ-ORs in inhibitory BSTal neurons. They also suggest that the expression of CRF-1 is a critical determinant of the availability of GABA in functionally diverse brain regions. These findings underscore the complex interplay between CRF, opioid, and GABA systems in limbic and striatal regions and have implications for the role of CRF-1 in influencing the pharmacological effects of opiates active at μ-ORs.

Circadian trafficking of calbindin-ir in fibers of SCN neurons

Calbindin-D28K (CalB)-containing cells form a distinct cluster within the core of the hamster suprachiasmatic nucleus (SCN). These cells are directly retinorecipient but lack detectable rhythms in clock gene expression or electrical activity. In studies exploring SCN connectivity using double-label immunochemistry, we previously reported an absence of contacts among CalB fibers and vasopressin (VP) cells in animals sacrificed during the day. Here, we explored circadian variations in CalB-immunoreactivity (-ir) and re-examined the connections between CalB and other SCN cell types at zeitgeber times (ZT) 4 and 14. The results reveal a circadian rhythm of CalB-ir in fibers of SCN cells with high expression during the night and subjective night and low expression during the day and subjective day. This circadian difference is not seen in the other brain regions studied. Significantly more appositions were detected between CalB fibers and VP cells during the night than during the day, while circadian variation in numbers of contacts was not seen between CalB fibers and vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK), or gastrin-releasing peptide (GRP) cells. There was no detectable variation in appositions from any peptidergic fiber type onto CalB cells. The present findings suggest that CalB cells relay photic information to VP oscillator cells of the SCN shell in a temporally gated manner.

Effects of dopaminergic modulation on the integrative properties of the ventral striatal medium spiny neuron

Dopaminergic modulation produces a variety of functional changes in the principal cell of the striatum, the medium spiny neuron (MSN). Using a 189-compartment computational model of a ventral striatal MSN, we simulated whole cell D1- and D2-receptor-mediated modulation of both intrinsic (sodium, calcium, and potassium) and synaptic currents (AMPA and NMDA). Dopamine (DA) modulations in the model were based on a review of published experiments in both ventral and dorsal striatum. To objectively assess the net effects of DA modulation, we combined reported individual channel modulations into either D1- or D2-receptor modulation conditions and studied them separately. Contrary to previous suggestions, we found that D1 modulation had no effect on MSN nonlinearity and could not induce bistability. In agreement with previous suggestions, we found that dopaminergic modulation leads to changes in input filtering and neuronal excitability. Importantly, the changes in neuronal excitability agree with the classical model of basal ganglia function. We also found that DA modulation can alter the integration time window of the MSN. Interestingly, the effects of DA modulation of synaptic properties opposed the effects of DA modulation of intrinsic properties, with the synaptic modulations generally dominating the net effect. We interpret this lack of synergy to suggest that the regulation of whole cell integrative properties is not the primary functional purpose of DA. We suggest that D1 modulation might instead primarily regulate calcium influx to dendritic spines through NMDA and L-type calcium channels, by both direct and indirect mechanisms.

Increased calbindin-D28k immunoreactivity in striatal projection neurons of R6/2 Huntington's disease transgenic mice

Striatal degeneration in Huntington's disease (HD) is associated with increases in perikaryal calbindin immunolabeling in yet-surviving striatal projection neurons. Since similar increases have also been observed in surviving striatal projection neurons after intrastriatal injection of the excitotoxin quinolinic acid, the increased calbindin in HD striatum has been interpreted to suggest an excitotoxic process in HD. We used immunolabeling to assess if calbindin is elevated in striatal projection neurons of R6/2 HD transgenic mice. These mice bear exon 1 of the human huntingtin gene with 144 CAG repeats and show some of the neuropathological signs (e.g., neuronal intranuclear inclusions) and clinical traits (e.g., wasting prior to early death) of HD. We found an increased frequency of calbindin-immunoreactive neuronal perikarya in the striatum of 6- and 12-week-old R6/2 mice compared to wild-type controls. This increase was most notable in the normally calbindin-poor dorsolateral striatum. We found no significant changes in the total area of striatum occupied by the calbindin-negative striosomes and no consistent changes in striatal calbindin mRNA. The increase in calbindin in R6/2 striatal neurons was thus limited to the matrix compartment, and it may be triggered by increased Ca2+ entry due to the demonstrated heightened NMDA sensitivity of these neurons. The data further support the similarity of R6/2 mice to HD, and are consistent with the occurrence of an excitotoxic process in striatum in both.

The ultrastructural organization of the patch matrix compartments in the human striatum

The mammalian striatum is a heterogeneous structure characterized by striosomes and matrix. The synaptic organization of the striatum has been described previously in various mammalian species including human; however, potential ultrastructural differences in striosomal organization have not been well studied. Samples (n = 7) of striatal tissue were obtained from the Maryland Brain Collection (mean age, 37.7 +/- 9.4 years; and mean PMI, 5.3 +/- 1.4 hours). Tissue was prepared for calbindin immunocytochemistry to identify striosomal (patch) and extrastriosomal matrix (matrix) compartments and subsequently prepared for electron microscopy. Synaptic density was determined, using stereologic methods, for all synapses combined and for various subsets of synapses such as asymmetric, symmetric, axospinous, axodendritic, and perforated in the patch and matrix of the caudate (CP, CM) and putamen (PP, PM). An ANOVA revealed significant between-group (CP, CM, PP, PM) differences (P < 0.05) for the following types of synapses: total combined, asymmetric, axospinous, and asymmetric axospinous. Each of these four types was significantly increased in density in the CP vs the PP, whereas the matrix (CM vs PM) showed no significant differences in density in these or other synapses. In the caudate (CP vs CM), the synaptic density of the types of synapses studied did not vary significantly between the patch and the matrix. In the putamen, the matrix (PM) had higher synaptic densities than that of the patches (PP) for total synapses, symmetric dendritic, and perforated. These data show that the patch and matrix compartments are heterogeneous at the ultrastructural level, imparting another level of complexity to the striatum-a fact that should be taken into consideration when studying diseases of this brain region at the electron microscopic level.

Behavioral and morphological comparison of two nonhuman primate models of Huntington's disease

OBJECTIVE

Huntington's disease is a progressive neurodegenerative disease characterized by movement disorder, cognitive deterioration, and selective striatal degeneration. No effective treatment exists, and thus stable primate models could aid in the development of novel therapies.

METHODS

Two primate models of Huntington's disease were analyzed: bilateral stereotactic intrastriatal injections of quinolinic acid (QA), and daily systemic intramuscular administration of 3-nitropropionic acid (3-NP) for up to 8 weeks in male Cebus apella monkeys. The animals' behavior was evaluated before, during, and 3 months after administration of the neurotoxin. Magnetic resonance imaging scans of the brain were obtained before and after treatment.

RESULTS

Frontal cognitive function as evaluated by object retrieval-detour task test demonstrated a marked deterioration in successful responses, with an increase in barrier reaches in both groups. No significant change in performance of fine motor tasks was observed. QA-treated animals displayed hyperactivity at night. Animals in both groups demonstrated abnormal posture, and the 3-NP-treated group showed spontaneous and apomorphine-induced dystonia and dyskinesia. The QA-treated group displayed large areas of increased signal on T2-weighted images in the caudate and putamen bilaterally. Treatment with 3-NP resulted in smaller lesions. Immunohistochemistry and morphometric analyses revealed that both groups had lesions in the striatum. A large area of neuronal loss with glial sparing was observed in the QA-treated group, including the caudate and putamen bilaterally. The 3-NP-treated group displayed smaller lesions restricted to the dorsolateral putamen.

CONCLUSION

These results suggest that both QA and 3-NP induce behavioral and morphological features that resemble the juvenile and akinetic-rigid variants of Huntington's disease, with the group with 3-NP-induced lesions displaying smaller lesions and spontaneous dyskinesia.

Behavioural correlates of striatal glial fibrillary acidic protein in the 3-nitropropionic acid rat model: disturbed walking pattern and spatial orientation

The 3-nitropropionic acid animal model is a model where excitotoxicity, mitochondrial dysfunction and oxidative stress, mechanisms common to various neurodegenerative diseases, are involved. The present study investigated whether behavioural alterations in this model were related to striatal damage. Wistar and Lewis rats were exposed to 3-nitropropionic acid and their behavioural performance (open field, walking pattern and Morris Water Maze task) was tested after the injections and after a recovery period of 3 weeks. No changes in activity were found in the open field test. Altered walking pattern was observed in the footprint analysis, although a different response was observed in the Wistar rats compared to the Lewis rats. Initially increased latency times were observed during visual discrimination learning in the Morris Water Maze task in 3-nitropropionic acid-treated Wistar rats compared to Wistar controls. During spatial discrimination learning (invisible platform) in the Morris Water Maze task the swimming velocity was decreased in both rat strains as a result of 3-nitropropionic acid treatment. Increased striatal glial fibrillary acidic protein concentration in Wistar rats correlated with several parameters of the footprint analysis and with the latency and distance in visual as well as spatial discrimination learning in the Morris Water Maze. It is concluded that measurement of walking pattern and spatial orientation performance are sensitive indicators to monitor behavioural changes in relation to striatal degeneration in the 3-nitropropionic acid animal model. In addition, Lewis rats are less sensitive towards 3-nitropropionic acid treatment than Wistar rats.

Chemical organization of the macaque monkey olfactory bulb: II. Calretinin, calbindin D-28k, parvalbumin, and neurocalcin immunoreactivity

The distribution and morphologic features of calcium-binding protein- (calbindin D-28k, calretinin, neurocalcin, and parvalbumin) immunoreactive elements were studied in the macaque monkey olfactory bulb by using specific antibodies and the avidin-biotin-immunoperoxidase method. A characteristic laminar pattern of stained elements was observed for each marker. Scarce superficial short-axon cells and superficial stellate cells demonstrated calbindin D-28k immunoreactivity in the outer layers, whereas a moderate number of calbindin D-28k-immunoreactive granule cells and scarce deep short-axon cells were observed in the inner layers. Calretinin-staining demonstrated abundant periglomerular cells and granule cells and a scarce number of other interneuronal populations. Most neurocalcin-immunopositive elements were external and medial tufted cells and periglomerular cells, although other scarcer interneuronal populations were also immunostained. A few superficial and deep short-axon cells as well as small interneurons in the external plexiform layer were the only elements immunoreactive to parvalbumin. The distribution of the immunoreactive elements in the olfactory bulb of the macaque monkey showed a high similarity to that reported in the human, whereas it demonstrated a different and simpler pattern to what has been reported in the olfactory bulb of macrosmatic animals. It suggests more homogeneous calcium-mediated cell responses after stimulation that could be correlated to the lower capability to modulate olfactory signals in microsmatic animals. In addition, these results indicate that experimental models in rodents do not provide an accurate estimation of calcium-binding protein-immunoreactive neuronal populations in the primate olfactory system.

Morphology and compartmental location of cells exhibiting DNA damage after quinolinic acid injections into rat striatum

Although excitotoxic injury is thought to play a role in many pathologic conditions, the type of cell death induced by excitotoxins in vivo and the basis for the differential vulnerability of neurons to excitotoxic injury are still poorly understood. Morphologic alterations and the presence of DNA damage were examined in adult rat striatum after an intrastriatal injection of low doses of quinolinic acid, a N-methyl-D-aspartate receptor agonist. Rats were killed 6, 8, 10, or 12 hours after quinolinate or vehicle injection. Numerous neurons with necrotic morphologies were detected in the quinolinate-injected striata. In addition, few neurons with apoptotic morphologies were found in the dorsomedial striatum. DNA strand breaks were detected in tissue sections by in situ nick translation with (35)S-radiolabeled nucleotides and emulsion autoradiography. Labeled cells were first detected outside the needle track 10 hours after quinolinate injection and, on average, 20% of neurons exhibited DNA damage by 12 hours after surgery. DNA damage was found in cells with both apoptotic and necrotic morphologies. A marked differential vulnerability to DNA damage at this time was observed in two striatal compartments, the striosomes, identified as regions of dense [(3)H]naloxone binding, and the extrastriosomal matrix: the great majority of labeled cells were found in the extrastriosomal matrix and extremely few were seen in the striosomes. This preferential distribution was not due to premature cell death in the striosomes which contained numerous unlabeled neurons. The results suggest a greater vulnerability of neurons in the matrix, versus the striosomes, to early excitotoxin-induced DNA damage in rat striatum.

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.

Calbindin D28k blocks the proapoptotic actions of mutant presenilin 1: reduced oxidative stress and preserved mitochondrial function

Mutations in the presenilin 1 (PS-1) gene account for many cases of early-onset autosomal dominant inherited forms of Alzheimer's disease. Recent findings suggest that PS-1 mutations may sensitize neurons to apoptosis induced by trophic factor withdrawal and exposure to amyloid beta-peptide (Abeta). We now report that overexpression of the calcium-binding protein calbindin D28k prevents apoptosis in cultured neural cells expressing mutant PS-1 (L286V and M146V missense mutations). Elevations of the intracellular Ca2+ concentration and generation of reactive oxygen species induced by Abeta, and potentiated by mutant PS-1, were suppressed in calbindin-overexpressing cells. Impairment of mitochondrial function by Abeta (which preceded apoptosis) was exacerbated by PS-1 mutations and was largely prevented by calbindin. These findings suggest that PS-1 mutations render neurons vulnerable to apoptosis by a mechanism involving destabilization of cellular calcium homeostasis, which leads to oxidative stress and mitochondrial dysfunction.

Ultrastructural study of nitric oxide synthase-containing striatal neurons and their relationship with parvalbumin-containing neurons in rats

Single- and double-label electron microscopic immunocytochemistry was used to examine the ultrastructure of striatal neurons containing nitric oxide synthase (NOS+) and evaluate the synaptic relationship of NOS+ striatal neurons with those containing parvalbumin (PV+). In both the single-label and double-label studies, NOS+ perikarya were observed to possess polylobulated nuclei. In the single-label studies, NOS+ terminals were seen forming synaptic contacts with dendritic shafts and dendritic spines that did not contain NOS, but not with NOS+ perikarya or dendrites. In the double-label studies (using diaminobenzidine and silver intensified immunogold as markers), nitric oxide synthase and parvalbumin immunoreactions were found in two different populations of medium-sized aspiny striatal neurons. The PV+ axon terminals were seen forming symmetric synapses on the dendritic spines of neurons devoid of PV or NOS labeling, on PV+ dendrites, and on NOS+ soma and dendrites. In contrast, NOS+ terminals were not observed to form synaptic contacts with the dendrites or soma of either PV+ or NOS+ neurons. These findings suggest that NOS+ striatal interneurons form synaptic contact with the spines and presumably the dendrites of striatal projection neurons, but not with the dendrites or soma of PV+ or NOS+ striatal interneurons. NOS+ neurons do, however, receive synaptic input from PV+ neurons.

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.