Immunohistochemical characterization of parvalbumin-containing interneurons in the monkey basolateral amygdala

Interneurons expressing the calcium-binding protein parvalbumin (PV) are a critical component of the inhibitory circuitry of the basolateral nuclear complex (BLC) of the mammalian amygdala. These neurons form interneuronal networks interconnected by chemical and electrical synapses, and provide a strong perisomatic inhibition of local pyramidal projection neurons. Immunohistochemical studies in rodents have shown that most parvalbumin-positive (PV+) cells are GABAergic interneurons that co-express the calcium-binding protein calbindin (CB), but exhibit no overlap with interneuronal subpopulations containing the calcium-binding protein calretinin (CR) or neuropeptides. Despite the importance of identifying interneuronal subpopulations for clarifying the major players in the inhibitory circuitry of the BLC, very little is known about these subpopulations in primates. Therefore, in the present investigation dual-labeling immunofluorescence histochemical techniques were used to characterize PV+ interneurons in the basal and lateral nuclei of the monkey amygdala. These studies revealed that 90–94% of PV+ neurons were GABA+, depending on the nucleus, and that these neurons constituted 29–38% of the total GABAergic population. CB+ and CR+ interneurons constituted 31–46% and 23–27%, respectively, of GABAergic neurons. Approximately one quarter of PV+ neurons contained CB, and these cells constituted one third of the CB+ interneuronal population. There was no colocalization of PV with the neuropeptides somatostatin or cholecystokinin, and virtually no colocalization with CR. These data indicate that the neurochemical characteristics of the PV+ interneuronal subpopulation in the monkey BLC are fairly similar to those seen in the rat, but there is far less colocalization of PV and CB in the monkey. These findings suggest that PV+ neurons are a discrete interneuronal subpopulation in the monkey BLC and undoubtedly play a unique functional role in the inhibitory circuitry of this brain region.     

Strain differences in the effect of rTMS on cortical expression of calcium-binding proteins in rats

Using a rat model to study the cellular effects of repetitive transcranial magnetic stimulation (rTMS) with regard to changes in cortical excitability, we previously described opposite effects of continuous and intermittent theta-burst stimulation (cTBS, iTBS) on the expression of the calcium-binding proteins (CaBP) parvalbumin (PV), calbindin (CB) and calretinin (CR) in Dark Agouti rats (DA). While iTBS significantly reduced the number of cortical PV+ cells but did not affect the CB+ cells, cTBS resulted in a decrease in CB+ cells with no effects on PV+ cells. We concluded that activity of these classes of cortical interneurons is differently modulated by iTBS and cTBS. When testing two further rat strains, Sprague–Dawley (SD) and Long Evans (LE), we obtained deviating results. In SD, iTBS reduced PV and CB expression, while cTBS only reduced PV expression. In contrast, reanalysed DA showed reduced CB expression after cTBS and reduced PV expression after iTBS, while LE shows an intermediate reaction. CR expression was unaffected in any case. Interestingly, we found significantly different basal expression patterns of the CaBPs for the strains, with DA and LE showing much higher numbers of PV+, CB+ and CR+ cells than SD, and with particularly higher number of CB+ and CR+ cells in DA compared to the other two strains. These findings demonstrate that inhibitory systems may be either differently developed in rats belonging to diverse strains or show different basal levels of activity and CaBP expression and may therefore be differently sensitive to the rTMS protocols.     

Altered expression of parvalbumin and calbindin in interneurons within the primary visual cortex of neonatal enucleated hamsters

In the present study, we tested the hypothesis that the expression of calcium binding proteins (CaBPs), parvalbumin (PV), calretinin (CR) and calbindin (CB), is dependent upon sensory experience as emphasized in visual deprivation and deafferentation studies. The expression of CaBPs was studied in interneurons within the primary and extrastriate visual cortices (V1, V2M, V2L) and auditory cortex (AC) of adult hamsters enucleated at birth. The effects of enucleation were mainly confined to area V1 where there was a significant volume reduction (26%) and changes in the laminar distribution of PV and CB immunoreactive (IR) cells. The density of PV-IR cell bodies was significantly increased in layer IV and reduced in layer V. Moreover, the density of CB-IR neurons was inferior in layer V of V1 in enucleated hamsters (EH) compared to controls. These results suggest that some features of the laminar distribution of specific CaBPs, in primary sensory cortices, are dependent upon or modulated by sensory input.     

猫外侧膝状体神经元HRP示踪结合Calbindin的免疫组织化学研究

目的 HRP示踪结合Calbindin双标猫外侧膝状体核(LGN)至视皮质的中继神经元.方法 在猫视皮质的17区多点微量注射30%HRP,逆行标记LGN至视皮质的中继神经元,先以金标抗HRP-抗孵育切片,用免疫金银法将HRP颗粒转化黑色银颗粒.然后用ABC法作Calbindin(CB)的免疫组化,试图双标记LGN的中继神经元.结果 HRP标记细胞与CB免疫阳性细胞清晰可辨,HRP标记细胞内为银染黑色颗粒,而CB免疫阳性细胞为染色均匀的棕色.猫LGN的A、A_1和C板层均有CB免疫阳性神经元的分布;HRP标记细胞分布于A和A_1板层.LGN内未见HRP和CB的双标记神经元.结论 LGN内含CB神经元可能不参与视觉信息的传导,而是与局部视觉信息的整合有关.     

Severe, Early and Selective Loss of a Subpopulation of GABAergic Inhibitory Neurons in Experimental Transmissible Spongiform Encephalopathies

Little is known about the pathogenetic basis of characteristic symptoms in transmissible spongiform encephalopathies (TSEs) such as myoclonus and characteristic EEG hyperactivity. We investigated the GABAergic system and its subpopulations in mice inoculated with experimental scrapie (ME7, RML, 22A strains) and Creutzfeldt-Jakob disease (CJD; Fujisaki strain), to study damage to inhibitory neurons. Since recent studies have shown electrophysiological changes in prion protein (PrP) knockout mice, we also studied mice lacking or overexpressing the PrP gene. Antibodies against glutamic acid decarboxylase (GAD), parvalbumin (PV), calbindin (CB), and calretinin (CR) were used to stain GABAergic neurons, and isolectin-B₄ to stain perineuronal nets around PV+ neurons. In scrapie infected mice, cortical PV+ neurons were severely reduced while CB+ and CR+ neurons were well preserved. In CJD inoculated mice, loss of PV+ neurons was severe and occurred very early after inoculation. PrP^-/- and tg20 mice showed normal appearance of PV, CB, CR, GAD+ neurons and their neuropil, and of isolectin-B₄+ perineuronal nets. The early, severe and selective loss of cortical PV+ neurons in experimental scrapie and CJD suggest selective loss of PV+ GABAergic neurons as important event during disease development, possibly as one basis of excitatory symptoms in TSEs.     

Parvalbumin and calbindin D-28K immunoreactive neurons in area MT of rhesus monkey

The chemical characteristics of the neurons of the motion sensitive visual area, area MT, remain to be established. We studied the distribution pattern of two calcium binding proteins, parvalbumin (PV) and calbindin D28K (CB) in this area, using specific monoclonal antibodies and the peroxidase-antiperoxidase (PAP) immunohistochemical technique. Aldehyde fixed 30-micron-thick cryostat sections from area MT of five animals were processed free floating for immunohistochemical staining. Besides studying the morphological characteristics of PV and CB positive neurons, quantitative analysis was carried out to determine their (1) perikaryal area (Pa) and diameter, (2) numerical densities (NV)/mm3 cortical tissue, (3) absolute number (NC) in a column of cortex under 1 mm2 cortical surface along with (4) layerwise absolute number (NL) under 1 mm2 cortical surface and (5) laminar percentage distribution of immunoreactive (IR) neurons. Quantitative analysis was carried out using a Leica QMC 500 image analysis system connected to a DMRE microscope. The results showed that both types of IR neurons were localized to all cortical layers except layer I. The PV +ve neurons were equidistributed between the supra- and infragranular layers, with the highest percentage being present in layer III (45%) followed by layer V (21%). The CB +ve neurons, on the other hand, were predominantly localized in supragranular layers, with the highest percentage being in layer III (54%) and the next highest percentage in layer II (18%). The average Pa and diameter of PV +ve neurons were found to be 96.90 +/- 28.43 micron 2 and 11.01 +/- 1.61 microns respectively. The CB +ve neurons were significantly smaller in size than the PV +ve neurons, with average Pa and diameter of the former being 92.23 +/- 26.18 micron 2 and 10.39 +/- 1.23 microns respectively. The NV for PV and CB +ve neurons showed ranges of 3157-3894 and 2303-2585, with means of 3347 +/- 285 (+/- SD) and 3436 +/- 100 respectively. The values for NC showed ranges of 5230-5444 and 4020-4268 with means of 5378 +/- 85 and 4167 +/- 95 for PV and CB neurons respectively. Variations in size together with the differential distribution of these neurons in the cortical layers may indicate their involvement in different functional circuitaries.     

A light and electron microscopic study of NADPH-diaphorase-, calretinin- and parvalbumin-containing neurons in the rat nucleus accumbens

The rat nucleus accumbens contains medium-sized, spiny projection neurons and intrinsic, local circuit neurons, or interneurons. Sub-classes of interneurons, revealed by calretinin (CR) or parvalbumin (PV) immunoreactivity or reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry, were compared in the nucleus accumbens core, shell and rostral pole. CR, PV and NADPH-diaphorase-containing neurons are shown to form three non-co-localising populations in these three areas. No significant differences in neuronal population densities were found between the subterritories. NADPH-diaphorase-containing neurons could be further separated morphologically into three sub-groups, but CR- and PV-immunoreactive neurons form homogeneous populations. Ultrastructurally, NADPH-diaphorase-, CR- and PV-containing neurons in the nucleus accumbens all possess nuclear indentations. These are deeper and fewer in neurons immunoreactive for PV than in CR- and NADPH-diaphorase-containing neurons. CR-immunoreactive boutons form asymmetrical and symmetrical synaptic specialisations on spines, dendrites and somata, while PV-immunoreactive boutons make only symmetrical synaptic specialisations. Both CR- and PV-immunoreactive boutons form symmetrical synaptic specialisations with medium-sized spiny neurons and contact other CR- and PV-immunoreactive somata, respectively. A novel non-carcinogenic substrate for the peroxidase reaction (Vector Slate Grey, SG) was found to be characteristically electron-dense and may be distinguishable from the diaminobenzidine reaction product. We conclude that the three markers used in this study are localised in distinct populations of nucleus accumbens interneurons. Our studies of their synaptic connections contribute to an increased understanding of the intrinsic circuitry of this area.     

Types of neurons, synaptic connections and chemical characteristics of cells immunoreactive for calbindin-D28K, parvalbumin and calretinin in the neocortex

This article provides a general account of types of neurons, synaptic connections and chemical characteristics (colocalization studies) of cells immunoreactive for the three main calcium-binding proteins found in the neocortex, namely, calbindin-D28K, parvalbumin and calretinin. The main conclusion is two-fold. First, all, or the majority, of calbindin-, parvalbumin- and calretinin-immunoreactive cells are smooth nonpyramidal neurons (interneurons) which participate in a variety of complex cortical circuits that may differ depending on the species, cortical area or layer where they are located. Second, in general, different types of nonpyramidal neurons are stained for each of these calcium-binding proteins and display different chemical characteristics regarding a variety of neurotransmitters (or related compounds), cell surface markers and receptors. However, a certain overlap exits, which also shows regional and species differences.     

Differential expression of calcium-binding proteins in the red nucleus of the developing and adult human brain

The adult human red nucleus consists of two parts: (1) the parvocellular part, which is clearly separated from (2) the magnocellular part. The latter and its rubrospinal projection is known to be rudimentary in the adult human brain. Information concerning the fetal or neonatal features of the red nucleus is sparse. This study is aimed at providing a detailed account of the distribution of three calcium-binding proteins: calretinin (CR), calbindin (CB), and parvalbumin (PV), which are known to be expressed in distinct neuronal populations. Special attention has been paid to transient phenomena. CB was the most abundant protein in the magnocellular part in fetal and perinatal brains; immunoreactive (ir) neurons appeared numerous and densely packed. In the adult only few and widely spaced ir nerve cells were present. CR-expression largely corresponds to that of CB, except that fewer neurons were immunolabelled. In double- labellings the majority of neurons expressed both CB and CR; a moderate number of nerve cells solely expressing CR was present in the magnocellular part. PV-ir fibers and a moderate number of small cells were observed in the fetal, perinatal as well as the adult parvocellular part. A few PV-ir neurons were seen in the magnocellular part of the fetal and perinatal brains. Our results indicated that: (1) the magnocellular and parvocellular parts of the red nucleus were well-demarcated portions from fetal life onwards, thus a dominance of the parvocellular part over the magnocellular occurred during development; (2) the magnocellular part was more prominent in the fetal period than in adulthood; (3) neurons in the red nucleus were heterogeneous with respect to the immunoreactivities towards the three calcium-binding proteins examined; (4) the transient prominence of the magnocellular part might be a substrate for a specific transitory pattern of motor behaviour. Accepted: 7 September 2000     

Dynamic patterns of colocalization of calbindin, parvalbumin and GABA in subpopulations of mouse basolateral amygdalar cells during development

Calbindin cells represent a major interneuron subtype of the cortical/pallial regions, such as the basolateral amygdala, which are often analyzed in studies of tangential migration of interneurons from the subpallial ganglionic eminences to the pallium/cortex. However, previous evidence suggests that during development the calbindin cells may include more than one of the interneuron subtypes found in the adult pallium/cortex. Furthermore, in the adult basolateral amygdala, calbindin cells include a subpopulation of non-GABAergic (non-interneuron) cells. To better characterize these cells throughout development, in the present study we investigated the colocalization of calbindin, parvalbumin and GABA in cells of the mouse basolateral amygdala during late embryonic (E16.5) and several postnatal ages from birth until 4 weeks after birth (P0, P10 and P28). Our results indicate that CB, PV and GABA show a dynamic pattern of colocalization in cells of the mouse basolateral amygdalar nucleus throughout development. From E16.5 through P28, the majority of CB+ neurons and virtually all PV+ neurons are GABAergic. However, after P10, the percentage of GABAergic CB+ cells decline from 96% to 70%. Furthermore, while only 9% of CB+ neurons are PV+ at P10, this percentage raises to 42% at P28. At all postnatal ages studied, the majority of the PV+ cells are CB+, suggesting that PV+ interneurons develop postnatally mainly as a subpopulation within the CB+ cells of the basolateral amygdalar nucleus. These results are important for interpreting data from interneuron migration.     

Differential regulation of parvalbumin and calretinin interneurons in the prefrontal cortex during adolescence

Determining the normal developmental trajectory of individual GABAergic components in the prefrontal cortex (PFC) during the adolescent transition period is critical because local GABAergic interneurons are thought to play an important role in the functional maturation of cognitive control that occurs in this developmental window. Based on the expression of calcium-binding proteins, three distinctive subtypes of interneurons have been identified in the PFC: parvalbumin (PV)-, calretinin (CR)-, and calbindin (CB)-positive cells. Using biochemical and histochemical measures, we found that the protein level of PV is lowest in juveniles [postnatal days (PD) 25–35] and increases during adolescence (PD 45–55) to levels similar to those observed in adulthood (PD 65–75). In contrast, the protein expression of CR is reduced in adults compared to juvenile and adolescent animals, whereas CB levels remain mostly unchanged across the developmental window studied here. Semi-quantitative immunostaining analyses revealed that the periadolescent upregulation of PV and the loss of the CR signal appear to be attributable to changes in PV- and CR-positive innervation, which are dissociable from the trajectory of PV- and CR-positive cell number. At the synaptic level, our electrophysiological data revealed that a developmental facilitation of spontaneous glutamatergic synaptic inputs onto PV-positive/fast-spiking interneurons parallels the increase in prefrontal PV signal during the periadolescent transition. In contrast, no age-dependent changes in glutamatergic transmission were observed in PV-negative/non fast-spiking interneurons. Together, these findings emphasize that GABAergic inhibitory interneurons in the PFC undergo a dynamic, cell type-specific remodeling during adolescence and provide a developmental framework for understanding alterations in GABAergic circuits that occur in psychiatric disorders.     

Altered neuronal distribution of parvalbumin in anterior cingulate cortex of rabbits exposed in utero to cocaine

Previous studies of rabbits exposed in utero to cocaine have revealed an increase in the number of neurons which are GABA immunoreactive in the anterior cingulate cortex (ACC), suggesting a cocaine-elicited modification in the balance of excitatory and inhibitory interactions. Of the major calcium binding proteins expressed by different subgroups of GABAergic neurons, parvalbumin has been observed in conditions involving excess excitation, and may serve to protect neurons from excitotoxicity. In the present study, we used immunocy-tochemistry to compare the effects of prenatal cocaine exposure on the postnatal development of parvalbumin immunoreactivity in interneurons of the visual cortex (VC) and ACC. We determined the number and laminar distribution of parvalbumin immunoreactive neurons, and we also assessed the distribution of parvalbumin immunoreactivity within primary, secondary and tertiary dendrites of neurons in these two cortical areas. In both ACC and VC, parvalbumin immunoreactive neurons were first observed around postnatal day 10 (P10) and their number increased rapidly from P10 to P20. At all ages studied (P10 to P60) there was no difference between cocaine-exposed and saline control animals in the number or laminar distribution of parvalbumin immunoreactive neurons in either cortical area. However, the distribution of parvalbumin immunoreactivity within dendrites revealed a significant difference between cocaine-exposed and saline control animals in ACC but not in VC. In ACC, at all ages studied, there was an increase in the number of primary, secondary and tertiary dendrites which were parvalbumin immunoreactive in cocaine-exposed animals compared with saline controls. This difference was most striking in secondary dendrites, and in laminae V and VI. The effect was observed at doses of 4 and 3 mg/kg per injection but not at 2 mg/kg per injection. In contrast to ACC, in VC there was no difference in the number of immunoreactive dendrites in cocaine-exposed animals compared with saline controls. These observations are consistent with the hypothesis that the ACC of rabbits exposed in utero to cocaine is characterized by altered excitatory/inhibitory interactions. ACC receives a dense dopaminergic input, but VC receives minimal dopaminergic innervation. Mechanisms by which the action of cocaine on the developing dopaminergic system may modify the balance of excitation and inhibition in ACC are discussed.     

Monoclonal antibody HNK-1 selectively stains a subpopulation of GABAergic neurons containing the calcium-binding protein parvalbumin in the rat cerebral cortex

Summary Monoclonal antibody HNK-1 is shown to outline selectively a subpopulation of GABAergic neurons containing a specific calcium-binding protein parvalbumin (PV) in the adult rat parietal cortex, using preand postembedding immunocytochemistry at light microscopic level. About 98% of HNK-1 stained cells in the rat parietal cortex were PV immunoreactive. About 95% of HNK-1 immunoreactive cells were also shown to be stained with a lectin, Vicia villosa agglutinin (VVA), with a specific affinity for terminal N-acetylgalactosamine, which has been previously shown to stain selectively a subpopulation of PV-containing GABAergic neurons in this region. Furthermore almost all HNK-1 immunoreactive cells were also stained with a monoclonal antibody, 3B3, which is specific for chondroitin sulfate proteoglycan. 3B3 was shown in the present study to stain selectively a subpopulation of PV-immunoreactive neurons in the adult rat parietal cortex. In addition, a direct comparison of two monoclonal antibodies HNK-1 and VC1.1 revealed that these two were identical in their staining properties and that they defined the same subset of PV-containing GABAergic neurons in the rat parietal cortex.     

Expression and colocalization patterns of calbindin-D28k,calretinin and parvalbumin in the rat hypothalamic arcuate nucleus

Calcium binding proteins (CaBPs) form a diverse group of molecules that function as signal transducers or as intracellular buffers of Ca²⁺ concentration. They have been extensively used to histochemically categorize cell types throughout the brain. One region which has not yet been characterized with regard to CaBP expression is the hypothalamic arcuate nucleus, which plays a vital role in neuroendocrine control and the central regulation of energy metabolism. Using in situ hybridization and immunofluorescence, we have investigated the cellular distribution of the three CaBPs, calbindin-D28k (CB), calretinin (CR) and parvalbumin (PV) in the rat arcuate nucleus. Both mRNA and immunoreactivity was detected in the arcuate nucleus for CB – located in the medial aspects – and CR – located ventrolaterally. No PV mRNA was detected in the arcuate nucleus. Immunofluorescence results for PV were ambiguous; while one antibody detected a group of cell somata, a different antibody failed to visualize any arcuate nucleus cell profiles. Using double-labeling, neither of the examined CaBPs were observed in cells immunoreactive for the signaling molecules agouti gene-related protein, tyrosine hydroxylase, neurotensin, growth hormone-releasing hormone, somatostatin, enkephalin, dynorphin or galanin. We did, however, observe CB- and CR-immunoreactivity, in two distinct populations of neurons immunoreactive for the melanocortin peptide α-melanocyte-stimulating hormone. These data identify distinct subpopulations of arcuate neurons defined by their expression of CaBPs and provide further support for differentiation between subpopulations of anorexigenic melanocortin neurons.     

Dopaminergic innervation of interneurons in the rat basolateral amygdala

The basolateral nuclear complex of the amygdala (BLC) receives a dense dopaminergic innervation that plays a critical role in the formation of emotional memory. Dopamine has been shown to influence the activity of BLC GABAergic interneurons, which differentially control the activity of pyramidal cells. However, little is known about how dopaminergic inputs interface with different interneuronal subpopulations in this region. To address this question, dual-labeling immunohistochemical techniques were used at the light and electron microscopic levels to examine inputs from tyrosine hydroxylase-immunoreactive (TH+) dopaminergic terminals to two different interneuronal populations in the rat basolateral nucleus labeled using antibodies to parvalbumin (PV) or calretinin (CR). The basolateral nucleus exhibited a dense innervation by TH+ axons. Partial serial section reconstruction of TH+ terminals found that at least 43-50% of these terminals formed synaptic junctions in the basolateral nucleus. All of the synapses examined were symmetrical. In both TH/PV and TH/CR preparations the main targets of TH+ terminals were spines and distal dendrites of unlabeled cells. In sections dual-labeled for TH/PV 59% of the contacts of TH+ terminals with PV+ neurons were synapses, whereas in sections dual-labeled for TH/CR only 13% of the contacts of TH+ terminals with CR+ cells were synapses. In separate preparations examined in complete serial sections for TH+ basket-like innervation of PV+ perikarya, most (76.2%) of TH+ terminal contacts with PV+ perikarya were synapses. These findings suggest that PV+ interneurons, but not CR+ interneurons, are prominent synaptic targets of dopaminergic terminals in the BLC.     

Localization of Nitric Oxide Synthase-containing Neurons in the Bat Visual Cortex and Co-localization with Calcium-binding Proteins

Microchiroptera (microbats) is a suborder of bats thought to have degenerated vision. However, many recent studies have shown that they have visual ability. In this study, we labeled neuronal nitric oxide synthase (nNOS)—the synthesizing enzyme of the gaseous non-synaptic neurotransmitter nitric oxide—and co-localized it with calbindin D28K (CB), calretinin (CR), and parvalbumin (PV) in the visual cortex of the greater horseshoe bat (Rhinolophus ferrumequinum, a species of microbats). nNOS-immunoreactive (IR) neurons were found in all layers of the visual cortex. Intensely labeled neurons were most common in layer IV, and weakly labeled neurons were most common in layer VI. Majority of the nNOS-IR neurons were round- or oval-type neurons; no pyramidal-type neurons were found. None of these neurons co-localized with CB, CR, or PV. However, the synthesis of nitric oxide in the bat visual cortex by nNOS does not depend on CB, CR, or PV.     

Aging-related changes in calcium-binding proteins in rat perirhinal cortex

Dysregulation of intracellular calcium homeostasis has been linked to neuropathological symptoms observed in aging and age-related disease. Alterations in the distribution and relative frequency of calcium-binding proteins (CaBPs), which are important in regulating intracellular calcium levels, may contribute to disruption of calcium homeostasis. Here we examined the laminar distribution of three CaBPs in rat perirhinal cortex (PR) as a function of aging. Calbindin-D28k (CB), parvalbumin (PV), and calretinin (CR) were compared in adult (4 mo.), middle-aged (13 mo.) and aged (26 mo.) rats. Results show an aging-related and layer-specific decrease in the number of CB-immunoreactive (-ir) neurons, beginning in middle-aged animals. Dual labeling suggests that the age-related decrease in CB reflects a decrease in neurons that are not immunoreactive for the inhibitory neurotransmitter GABA. In contrast, no aging-related differences in PV- or CR-immunoreactivity were observed. These data suggest that selective alterations in CB-ir neurons may contribute to aging-related learning and memory deficits in tasks that depend upon PR circuitry.     

The interneuronal nature of GABAergic neurons in the lateral geniculate nucleus of the rhesus monkey: a combined HRP and GABA-immunocytochemical study

Summary Neurons immunoreactive to a GABA antibody, located in the retrogradely labeled segment of LGN of the rhesus monkey obtained after massive injections of HRP in a sector of the striate cortex, were examined for HRP label in plastic semithin (1 μm) sections of LGN. In a total of 691 GABA(+) neurons sampled from the 6 main geniculate layers none was seen to contain HRP grains. In contrast, the vast majority of GABA(-) neurons were densely labeled with HRP reaction product. It is concluded from these results that GABAergic cells in macaque LGN do not project to the striate cortex, as previous studies have shown for equivalent cells in cat LGN, and therefore reasons are given to consider these cells as interneurons in this nucleus. In addition, several GABA(-) neurons which were also unlabeled with HRP were observed isolated in the midst of populations of neurons homogeneously labeled with this enzyme. These cells were mostly located at or near the interlaminar zones and some of them were substantially larger than the neighboring geniculostriate relay cells in the parvocellular subdivision of LGN. For these characteristics, these unlabeled somata are considered to correspond to the geniculate neurons projecting to prestriate cortical visual areas in the macaque described in several studies and which, the present results suggest, do not branch collateral axons to the striate cortex. Supported by grants EY 02877 and HD 03352 from the National Institutes of Health     

Human prefrontal layer II interneurons in areas 46, 10 and 24

Background:

Prefrontal cortex (PFC) represents the highest level of integration and control of psychic and behavioral states. Several dysfunctions such as autism, hyperactivity disorders, depression, and schizophrenia have been related with alterations in the prefrontal cortex (PFC). Among the cortical layers of the PFC, layer II shows a particular vertical pattern of organization, the highest cell density and the biggest non-pyramidal/pyramidal neuronal ratio. We currently characterized the layer II cytoarchitecture in human areas 10, 24, and 46.

Objective:

We focused particularly on the inhibitory neurons taking into account that these cells are involved in sustained firing (SF) after stimuli disappearance.

Methods:

Postmortem samples from five subjects who died by causes different to central nervous system diseases were studied. Immunohistochemistry for the neuronal markers, NeuN, parvalbumin (PV), calbindin (CB), and calretinin (CR) were used. NeuN targeted the total neuronal population while the rest of the markers specifically the interneurons.

Results:

Cell density and soma size were statically different between areas 10, 46, 24 when using NeuN. Layer II of area 46 showed the highest cell density. Regarding interneurons, PV+-cells of area 46 showed the highest density and size, in accordance to the proposal of a dual origin of the cerebral cortex. Interhemispheric asymmetries were not identified between homologue areas.

Conclusion:

First, our findings suggest that layer II of area 46 exhibits the most powerful inhibitory system compared to the other prefrontal areas analyzed. This feature is not only characteristic of the PFC but also supports a particular role of layer II of area 46 in SF. Additionally, known functional asymmetries between hemispheres might not be supported by morphological asymmetries.