Protein Parvalbumin Immunoreactivity Research Articles

Ultrastructural analysis of parvalbumin synapses in human dorsolateral prefrontal cortex.

Coordinated activity of neural circuitry in the primate dorsolateral prefrontal cortex (DLPFC) supports a range of cognitive functions. Altered DLPFC activation is implicated in a number of human psychiatric and neurological illnesses. Proper DLPFC activity is, in part, maintained by two populations of neurons containing the calcium-binding protein parvalbumin (PV): local inhibitory interneurons that form Type II synapses, and long-range glutamatergic inputs from the thalamus that form Type I synapses. Understanding the contributions of each PV neuronal population to human DLPFC function requires a detailed examination of their anatomical properties. Consequently, we performed an electron microscopic analysis of (1) the distribution of PV immunoreactivity within the neuropil, (2) the properties of dendritic shafts of PV-IR interneurons, (3) Type II PV-IR synapses from PV interneurons, and (4) Type I PV-IR synapses from long-range projections, within the superficial and middle laminar zones of the human DLPFC. In both laminar zones, Type II PV-IR synapses from interneurons comprised ∼60% of all PV-IR synapses, and Type I PV-IR synapses from putative thalamocortical terminals comprised the remaining ∼40% of PV-IR synapses. Thus, the present study suggests that innervation from PV-containing thalamic nuclei extends across superficial and middle layers of the human DLPFC. These findings contrast with previous ultrastructural studies in monkey DLPFC where Type I PV-IR synapses were not identified in the superficial laminar zone. The presumptive added modulation of DLPFC circuitry by the thalamus in human may contribute to species-specific, higher-order functions.

Distribution of calcium-binding proteins parvalbumin and calbindin in the pigeon telencephalic auditory center

Immunoreactivity for calcium-binding proteins parvalbumin (PV) and calbindin (CB) was studied in the pigeon (Columba livia) telencephalic auditory center. All its regions displayed overlapping distribution patterns of PV and CB immunoreactivity, although in the central (L2) vs. peripheral (L1, L3, CMM) layers they were dissimilar. L2 and the inner L1 sublayer (L1i) were distinguished by a higher immunoreactivity of neuropil for both proteins and the presence (in L2) of numerous small densely packed granular-type cells: heavily stained PV-ir and, as a rule, poorly stained CB-ir neurons. In Lli, the number of neurons and the density of neuropil immunoreactive to both proteins decreased. The outer L1 sublayer (L1e) as well as L3 and CMM were characterized by a generally lesser density and irregular distribution of immunoreactive neuropil and a heterogenous repertoire of PV-ir and CB-ir neurons referring to diverse morphological types, with an increased number of large multipolar cells. The differences in PV and CB immunoreactivity among different regions of the pigeon telencephalic auditory center revealed the similarity of the latter to the laminar auditory cortex in mammals.

Parvalbumin increases in the medial and lateral geniculate nuclei of aged rhesus macaques.

Subcortical auditory structures in the macaque auditory system increase their densities of neurons expressing the calcium binding protein parvalbumin (PV) with age. However, it is unknown whether these increases occur in the thalamic division of the auditory system, the medial geniculate nucleus (MGN). Furthermore, it is also unclear whether these age-related changes are specific to the macaque auditory system or are generalized to other sensory systems. To address these questions, the PV immunoreactivity of the medial and lateral geniculate nuclei (LGN) from seven rhesus macaques ranging in age from 15 to 35 was assessed. Densities of PV expressing neurons in the three subdivisions of the MGN and the six layers of the LGN were calculated separately using unbiased stereological sampling techniques. We found that the ventral and magnocellular subdivisions of the MGN and all six layers of the LGN increased their expressions of PV with age, although increases in the MGN were greater in magnitude than in the LGN. Together, these results suggest that the MGN shows age-related increases in PV expression as is seen throughout the macaque ascending auditory system, and that the analogous region of the visual system shows smaller increases. We conclude that, while there are some similarities between sensory systems, the age-related neurochemical changes seen throughout the macaque auditory system cannot be fully generalized to other sensory systems.

Heterogeneity of parvalbumin expression in the avian cerebellar cortex and comparisons with zebrin II

The cerebellar cortex has a fundamental parasagittal organization that is reflected in the physiological responses of Purkinje cells, afferent and efferent connections, and the expression of several molecular markers. The most thoroughly studied of these molecular markers is zebrin II (ZII; a.k.a. aldolase C). ZII is differentially expressed in Purkinje cells, resulting in a pattern of sagittal stripes of high expression interdigitated with stripes of little or no expression. In this study, we examined the expression of the calcium binding protein parvalbumin (PV) in the cerebellum of several avian species (pigeons, hummingbirds, zebra finches) and compared it to the expression of ZII. We found that PV immunoreactivity was distributed across the cerebellar cortex such that there were sagittal stripes of PV immunopositive (PV+) Purkinje cells alternating with PV immunonegative (PV-) Purkinje cells. Although most Purkinje cells in the anterior lobe were PV+, there were several thin (i.e. only a few Purkinje cells wide) PV- stripes spanning the folia. In the posterior lobe, PV+ and PV- stripes were also apparent, but the PV- stripes were much wider than in the anterior lobe. In sections processed for both ZII and PV, the expression was generally complementary: PV+ stripes were ZII-, and vice-versa. This complementary expression was most apparent in folia II-IV and VIII-IXcd. The complementary expression was not, however, absolute; some Purkinje cells co-expressed PV and ZII whereas others lacked both. These novel findings relate to the complex neurochemical organization of the cerebellum, and are likely important to issues regarding cerebellar plasticity.

Progression of temporal lobe epilepsy in the rat is associated with immunocytochemical changes in inhibitory interneurons in specific regions of the hippocampal formation

Immunocytochemical markers of specific rat hippocampal interneuron subpopulations, including the calcium binding proteins parvalbumin (PV), and calretinin (CR) were examined in relation to the evolution of spontaneous seizures after electrically induced status epilepticus (SE). PV/CR/NeuN immunoreactive neurons were counted in the hippocampal formation at different time intervals after SE and related to spontaneous hippocampal discharge activity. Decreased PV immunoreactivity was observed within 1 day after SE in the hilus, pre- and parasubiculum, and in the entorhinal cortex layers II and V/VI. In layer III, the density of detectable PV immunoreactive neurons did not decrease significantly, whereas the number of surrounding principal neurons was extensively decreased within a week in most post-SE rats, and after 3–4.5 months in all rats that had developed a progressive evolution of seizures. CR immunoreactive neuron number decreased in all hippocampal subregions except for the stratum lacunosum-moleculare and the EC layer II, in which the density did not decrease significantly. The apparent decrease in the number of PV and CR immunoreactive hilar neurons was correlated with the duration of the SE and was most extensive in rats with a progressive form of epilepsy. The loss of CR and PV expression or the loss of CR- and PV-containing neurons in specific regions of the hippocampal formation may play a role in the progressive nature of epilepsy possibly via increasing the entorhinal–hippocampal activity.

Alterations of the neocortical GABAergic system in the pilocarpine model of temporal lobe epilepsy: Neuronal damage and immunocytochemical changes in chronic epileptic rats

A wealth of previous studies reported pathological alterations in extrahippocampal regions in mesial temporal lobe epilepsy. Previous experimental findings have also demonstrated that the entorhinal cortex and the neocortex are damaged in different animal models of acute limbic seizures. The present study was aimed at verifying possible alterations in neocortical areas, and, in particular, structural changes of GABAergic interneurons in the sensorimotor cortex, in pilocarpine-induced chronic epilepsy in the rat. Series of sections were Nissl stained and processed for immunocytochemistry using antibodies that recognize nonphosphorylated neurofilament (SMI311), glial fibrillary acidic protein (GFAP), the calcium-binding protein parvalbumin (PV) which is expressed by a subset of cortical GABAergic neurons, the GABA transporter (GAT1), and isoform 65 of glutamic acid decarboxylase (GAD65), the GABA synthetic enzyme. Epileptic rats showed decreased cortical thickness, and diffuse gliosis was observed with GFAP antibody. Neurofilament alterations were also detected in sections processed using SMI311 antiserum. In addition, a diffuse decrease of PV, GAD65, and GAT1 immunoreactivity was observed in the sensorimotor cortex. Altered expression of PV, GAD65, and GAT1 pointed out specific neocortical disturbances in GABAergic inhibition, which could play a crucial role in seizure generation and expression. Thus, the present findings indicate that damage of GABAergic interneurons could be strictly associated with neocortical hyperexcitability in temporal lobe epilepsy.

224. Putative thalamic terminals are decreased in the prefrontal cortex in schizophrenia

Recent studies have reported decreased neuron number in the mediodorsal thalamic nucleus (MDTN), the principal source of thalamic projections to the prefrontal cortex (PFC), in subjects with schizophrenia. In thalamic relay nuclei, the calcium binding protein parvalbumin (PV) is present in the neurons that provide the major thalamic projection to the cortical layers deep 3-4. In ultrastructural studies of area 9 in monkey PFC, we found PV immunoreactivity in axon terminals forming Gray’s Type I (excitatory) synapses exclusively in layers deep 3 and 4 (Melchitzky, et al., J Comp Neurol, 1998). In order to test the hypothesis that schizophrenia is associated with altered thalamic inputs to PFC, we examined PV-immunoreactive varicosities in PFC area 9 of 20 pairs of schizophrenic and control subjects matched for age, sex, and postmortem interval. Systematic random sampling techniques were used to quantify the density of PV-immunoreactive varicosities in 1 μm thick sections. The density of PV-positive varicosities did not differ between schizophrenic and control subjects in layers 2-superficial 3, whereas a significant (p = .006) decrease (24%) was found in layers deep 3-4 of the schizophrenic subjects. PV-positive axon terminals from cortical local circuit neurons are present in both superficial and middle cortical layers. Since the reduction in PV-labeled varicosities was present only in the middle zone, these findings suggest that the PV-positive terminals from thalamic relay nuclei are decreased in schizophrenia. These data are convergent with the results of other postmortem studies demonstrating altered thalamic-prefrontal cortical connectivity in schizophrenia.

Changing pattern of expression of parvalbumin immunoreactivity during human fetal spinal cord development

Expression of the calcium binding protein parvalbumin (PV) by different classes of spinal neuron has been shown to be developmentally regulated in both rat and monkey. From postmortem studies of eight human cervical spinal cords ranging in age from 11 to 35 weeks postconceptional age, we report that parvalbumin immunoreactivity is similarly plastic in human lower cervical spinal cord development, with many changes occurring prenatally. At 11-14 weeks postconceptional age, there was prominent immunostaining of primary sensory afferents that could be seen coursing through the dorsal horn and extensively innervating the motoneuron pools. Motoneurons were also found to be clearly immunoreactive for choline acetyltransferase by this age. A few ventral horn neurons that were not motoneurons were also parvalbumin immunoreactive. By 24-27 weeks postconceptional age, sensory afferents were still immunoreactive, as were many other axons throughout the white matter. In addition, many ventral horn neurons were now immunoreactive as well as a few dorsal horn neurons. By 31-35 weeks postconceptional age, there was extensive immunostaining of neurons throughout the spinal cord, including a few moderately immunoreactive motoneurons. There were many immunopositive axons in all the white matter tracts except the corticospinal tracts; however, staining of sensory axons traversing the grey matter was less prominent by this age. In the rat, expression of PV by primary sensory neurons coincides with the onset of fetal limb movement. The onset of expression of PV in ventral horn neurons coincides with later developmental events after the arrival of corticospinal inputs, whereas widespread PV immunoreactivity in dorsal horn neurons marks the attainment of a mature pattern of PV expression. The extent to which expression of PV immunoreactivity can be taken to indicate landmarks in human development will be discussed.

Parvalbumin is expressed in a reciprocal circuit linking the medial geniculate body and auditory neocortex in the rabbit.

Recent studies of the rabbit auditory forebrain have shown that antibodies directed against the calcium-binding protein parvalbumin (PV) specifically demarcate auditory neocortex and the ventral division of the medial geniculate body (MGV). The auditory cortex is characterized by two PV- immunoreactive bands: dense terminal-like labeling within layer III/IV and a prominent band of PV+ somata in the upper half of layer VI. In some cases, there are distinct patches of PV immunoreactivity within layers III/IV of auditory cortex that appear similar to the patchy termination of thalamocortical axons labeled by the injection of anterograde tracers into MGV. The presence of PV+ patches in III/IV, PV+ somata in layer VI, and the high density of PV+ neurons and terminals in the MGV suggest the existence of a reciprocal PV+ circuit linking primary auditory cortex (AI) and the MGV. In the present study, double-labeling experiments in adult rabbits were carried out to provide evidence for this circuit. Focal injections of the tracers biocytin or biotinylated dextran amine (BDA) into the MGV labeled thalamocortical afferent patches within layer III/IV and retrogradely labeled corticothalamic neurons in layer VIa of the ipsilateral auditory cortex. Adjacent sections stained with antibodies against PV revealed terminal-like PV-immunoreactive patches in III/IV and PV+ somata in VIa that were in register with those labeled by BDA injections into the MGV. Serial section reconstruction of BDA-labeled corticothalamic neurons in VIa revealed pyramidal cells with tangentially oriented basal dendrites and sparsely branched apical dendrites that ascended to layer I. Fluorescent double-labeling studies demonstrated that a subpopulation of corticothalamic neurons also express PV. PV-negative corticothalamic neurons were also found. Discrete injections of BDA into auditory cortex labeled bands of neurons in the ipsilateral MGV, whose orientation paralleled the fibrodendritic laminae characteristic of this subdivision. Retrograde double-labeling experiments showed that most MGV relay neurons also express PV. Small numbers of PV-negative relay neurons were also found. These studies provide evidence for the existence of multiple, chemically coded pathways linking primary auditory cortex and the MGV.

Parvalbumin is expressed in a reciprocal circuit linking the medial geniculate body and auditory neocortex in the rabbit

Recent studies of the rabbit auditory forebrain have shown that antibodies directed against the calcium-binding protein parvalbumin (PV) specifically demarcate auditory neocortex and the ventral division of the medial geniculate body (MGV). The auditory cortex is characterized by two PV- immunoreactive bands: dense terminal-like labeling within layer III/IV and a prominent band of PV+ somata in the upper half of layer VI. In some cases, there are distinct patches of PV immunoreactivity within layers III/IV of auditory cortex that appear similar to the patchy termination of thalamocortical axons labeled by the injection of anterograde tracers into MGV. The presence of PV+ patches in III/IV, PV+ somata in layer VI, and the high density of PV+ neurons and terminals in the MGV suggest the existence of a reciprocal PV+ circuit linking primary auditory cortex (AI) and the MGV. In the present study, double-labeling experiments in adult rabbits were carried out to provide evidence for this circuit. Focal injections of the tracers biocytin or biotinylated dextran amine (BDA) into the MGV labeled thalamocortical afferent patches within layer III/IV and retrogradely labeled corticothalamic neurons in layer VIa of the ipsilateral auditory cortex. Adjacent sections stained with antibodies against PV revealed terminal-like PV-immunoreactive patches in III/IV and PV+ somata in VIa that were in register with those labeled by BDA injections into the MGV. Serial section reconstruction of BDA-labeled corticothalamic neurons in VIa revealed pyramidal cells with tangentially oriented basal dendrites and sparsely branched apical dendrites that ascended to layer I. Fluorescent double-labeling studies demonstrated that a subpopulation of corticothalamic neurons also express PV. PV-negative corticothalamic neurons were also found. Discrete injections of BDA into auditory cortex labeled bands of neurons in the ipsilateral MGV, whose orientation paralleled the fibrodendritic laminae characteristic of this subdivision. Retrograde double-labeling experiments showed that most MGV relay neurons also express PV. Small numbers of PV-negative relay neurons were also found. These studies provide evidence for the existence of multiple, chemically coded pathways linking primary auditory cortex and the MGV. J. Comp. Neurol. 400:349–362, 1998. © 1998 Wiley-Liss, Inc.

Reduced immunoreactivity to calcium-binding proteins in Purkinje cells precedes onset of ataxia in spinocerebellar ataxia-1 transgenic mice.

Earlier we have shown alterations in immunoreactivity (IR) to the calcium-binding proteins parvalbumin (PV) and calbindin D-28k (CaB) in surviving Purkinje cells of patients with spinocerebellar ataxia-1 (SCA-1). In the present study we determined PV and CaB expression (by immunohistochemical and immunoblot analyses) in Purkinje cells of transgenic mice (TM) expressing the human SCA-1 gene with an expanded (line B05) and normal (line A02) CAG tract, as well as in age-matched nontransgenic mice (nTM). Heterozygotes in the B05 line develop progressive ataxia beginning around 12 weeks of age. A02 animals are phenotypically indistinguishable from wild-type (nontransgenic) animals. In the cerebella of 8-, 9-, and 12-week-old TM-B05 there was a progressive decrease in PV IR in Purkinje cells compared with nTM and TM-A02. Parvalbumin immunostaining in interneurons was well preserved in all groups. A progressive decrease was also observed in CaB IR in Purkinje cells of 8-, 9-, and 12-week-old TM-B05. Cerebellar Purkinje cells of 6-week-old TM-B05, which exhibit no ataxia and even lack demonstrable Purkinje cell loss, also revealed reduction in PV IR. This change was matched by a significant decrease in the amount of cerebellar PV in 6-week-old TM-B05 as determined by Western blot analysis. Calbindin D-28K immunohistochemistry did not detect any marked changes in CaB IR within Purkinje cells at 4 weeks. However, at 6 weeks immunostaining and immunoblot analysis revealed a significant decrease in CaB in TM-B05 compared with controls. These data suggest that decreased levels of calcium-binding proteins in Purkinje cells in SCA-1 transgenic mice may cause alteration in Ca2+ homeostasis.

Parvalbumin in the human anterior cingulate cortex: morphological heterogeneity of inhibitory interneurons

The calcium-binding protein parvalbumin (PV) is a marker for a certain subset of GABAergic cortical interneurons. In the present study, indirect immunocytochemistry with an antibody against PV was performed on serial sections of human anterior cingulate cortex (Brodmann's area 24), an important relay centre of the limbic system. PV-positive structures are distributed in a layer- and cell type-specific manner. Based on morphological features and laminar distribution pattern, PV-immunoreactive interneurons are subdivided into eight different classes. PV immunoreactivity within the neuropil comprises dendritic and axonal processes. Area 24 contains two densely immmunolabelled neuropil bands in layers III and Vb. Axon cartridges are preferably located in layers V and VI. The results provide a 'PV immunoarchitecture' as a basis for further studies of PV immunoreactivity under pathological conditions. PV is assumed to play a role in maintaining calcium homeostasis in nerve cells, and to modulate neuronal excitability and resistance to biochemical damage. On the other hand, PV immunoreactivity has recently been shown to undergo characteristic changes during different stages of brain maturation. Therefore, examination of PV-positive structures will provide new insights into cortical circuitry in neurodegenerative as well as neurodevelopmental disorders.

Complementary expression of parvalbumin and calbindin D-28k delineates subdivisions of the rabbit medial geniculate body.

The complementary pattern of immunohistochemical staining for the calcium-binding proteins parvalbumin (PV) and calbindin D-28k (CB) was used to delineate four major subdivisions of the rabbit medial geniculate body (MGB). PV immunoreactivity predominates in the ventral and medial divisions, whereas CB-immunoreactive cells characterize the dorsal and internal divisions. The ventral nucleus is strongly PV+ due to dense neuropil labeling and moderately labeled somata. The medial nucleus contains both medium-sized and large PV+ somata, as well as thick PV+ axons and terminals. The wedge-shaped internal nucleus composed of densely labeled CB+ cells, separates the dorsal and ventral nuclei rostrally, and expands caudally to encapsulate the posterior MGV. Large multipolar CB+ neurons with radiate dendrites characterize the dorsal nucleus. The differential expression of PV and CB also distinguishes the deep dorsal and superficial dorsal subnuclei in the dorsal division and a ventrolateral component in the ventral division. A comparison with studies of MGB connectivity in a variety of species suggests that PV immunoreactivity is highest in subdivisions that receive a substantial input from the central nucleus of the inferior colliculus and that project to primary auditory cortex. In contrast, CB immunoreactivity characterizes nuclei that receive input primarily from other sources, such as the paracentral nuclei of the inferior colliculus, the lateral tegmentum, and the spinal cord, and that project to secondary auditory areas. The ability of calcium-binding protein immunohistochemistry to delineate neuronal compartments across indistinct cytoarchitectonic borders makes it a powerful tool for guiding future connectional and physiological studies of the MGB.

Nimodipine accelerates the postnatal development of parvalbumin and S-100β immunoreactivity in the rat brain

The effects of chronic maternal perinatal nimodipine treatment on the immunocytochemical distribution of the Ca 2+-binding proteins parvalbumin (PV) and S-100β in neocortex and hippocampus were studied at the age of postnatal day (PD) 5, 7, 10, 14 and 20. The Ca 2+ antagonist nimodipine (1000 ppm BAY e 9736 in daily food) was administered to pregnant rats starting at postconceptual day 11. The expression of PV exemplified in layer V of parietal and retrosplenial cortex and in all hippocampal layers of CA1 and CA3 was enhanced by more than two-fold in the offspring of nimodipine-treated dams at PD 10 compared with placebo-treated animals. The difference was no longer present at PD 14 and 20. Nimodipine administration also significantly increased the number of S-100β-immunopositive glial cells in upper neocortical layers I–III at PD 5 and 7. Again, the difference between nimodipine and placebo-treated animals disappeared after PD 10. The data indicate an accelerated development of PV and S-100 immunoreactivity in the postnatal forebrain as a result of perinatal blockade of the L-type Ca 2+ current.

Selective changes in the microorganization of the human epileptogenic neocortex revealed by parvalbumin immunoreactivity.

The microanatomy of the human lateral temporal cortex removed from patients with intractable temporal lobe epilepsy was studied using correlative light and electron microscopic immunocytochemical methods for the localization of the calcium-binding protein parvalbumin (PV). PV immunostaining was mainly used to label a subpopulation of powerful cortical inhibitory interneurons that have been shown to be lost at epileptic foci in certain animal models of epilepsy. In the human neocortex with normal appearance, we identified the same local neuronal circuitry as in the normal monkey cortex, but in some regions of the same cortex, a fine disorganization of neuronal circuits (loss of inhibitory neurons and presumptive thalamocortical terminals) was found. This abnormal circuitry may interfere with normal cerebral activity in epileptic patients. These results also indicate that PV immunoreactivity can be a useful tool to study normal and abnormal synaptic circuits in the human cerebral cortex.

Axons and axon terminals of cerebellar Purkinje cells and basket cells have higher levels of parvalbumin immunoreactivity than somata and dendrites: quantitative analysis by immunogold labeling

The immunointensities of calcium-binding proteins parvalbumin (PV) and calbindin D28K were quantified in different parts of Purkinje cells and interneurons (basket cells and stellate cells) of the rat cerebellum. An electron microscopic, postembedding immunogold procedure on Lowicryl K4M-embedded thin sections was applied. Neuronal profiles were identified by double-labeling immunocytochemistry using the combination of the two primary antibodies, mouse monoclonal anti-rat calbindin D28K and rabbit polyclonal anti-rat PV. The secondary antibodies were conjugated with colloidal gold of different sizes (10 and 15 nm diameter). In the cerebellar cortex, double-labeled profiles were identified as Purkinje cells and profiles labeled only with anti-PV were identified as inteneurons. The densities of gold particles were used for statistical comparison of the relative levels of PV and calbindin D28K in somata, dendrites, dendritic spines, axons and axon terminals of Purkinje cells, and interneurons. The axons and axon terminals of Purkinje cells and basket cells had significantly higher levels of PV immunoreactivity than Purkinje cell somata, primary, secondary, and tertiary dendrites, and dendritic spines, as well as interneuron somata. On the other hand, the present study could not determine conclusively whether calbindin D28K was distributed homogeneously throughout soma, dendrites, and axons of Purkinje cells or was also concentrated in Purkinje cell axons. To estimate absolute PV concentrations, we made a series of artificial standard samples which were aldehyde-fixed 10% bovine serum albumin containing given concentrations of PV (0, 12.5, 25, 50, 100, 200, and 400 microM, 1 and 2 mM), and calibration curves were deduced from quantitative immunogold analyses of these standard samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Parvalbumin immunoreactivity reveals layer IV of monkey cerebral cortex as a mosaic of microzones of thalamic afferent terminations

Correlative light and electron microscopic immunocytochemical methods were used to study the pattern of staining for the calcium-binding protein parvalbumin (PV) in the primary visual area (area 17) and area 3b of the first somatic sensory area of the monkey cerebral cortex. A conspicuous feature of the light microscopic staining pattern is the presence of focal aggregations of immunoreactive terminal-like puncta within the major thalamic recipient layers (IV and VI). At the electron microscopic level these aggregations of puncta are found to be immunoreactive terminals most of which form asymmetric synapses, principally on dendritic pines and, to a lesser extent, on dendritic shafts. Outside the aggregations, most PV-immunoreactive terminals form symmetric synapses. Correlative observations in the present and other studies indicate that the aggregations of PV-immunoreactive terminals form asymmetric synapses arise from thalamic afferent fibers while those forming symmetric synapses arise from intrinsic γ-aminobutyric acid neurons. The aggregations of PV immunoreactivity in layers IV and VI form microzones of preferred thalamic afferent terminations which may contribute to the formation of functional columns based upon focussed thalamic inputs.

Parvalbumin immunoreactivity of the lateral geniculate nucleus in adult rhesus monkeys after monocular eye enucleation

Immunocytochemical methods with antiserum to the calcium-binding protein parvalbumin (PV) were used to examine the effects of monocular enucleation on parvalbuminergic neurons and processes in the lateral geniculate nucleus (LGN) of adult rhesus monkeys. In the LGN of normal monkeys, numerous PV-positive neurons, including the largest neurons in the nucleus, and many PV-positive processes occur in all six laminae. After monocular enucleation, PV immunoreactivity is reduced in the neuropil of the denervated laminae compared to adjacent nondenervated and to normal laminae. PV immunoreactivity of somata in denervated laminae, however, appears to be indistinguishable from that of somata in nondenervated laminae, although neurons in the denervated laminae are smaller in size. Since LGN neurons in denervated laminae have lost their visual input, the functional role of PV in this nucleus may not relate directly to visual information processing.

Parvalbumin-, calretinin- and calbindin-D28k-immunoreactivity and GABA in a forebrain region involved in auditory filial imprinting

The distribution and morphology of neurons containing the Ca-binding proteins parvalbumin (PV), calbindin-D28k (CaBP) and calretinin (CaR) are described in a rostral forebrain region (MNH) of the chick, known to be involved in auditory filial imprinting. PV immunoreactivity is chiefly a marker for numerous large to medium-sized neurons in the neostriatal part of MNH. They show patchy staining of their dendrites, but PV-positive spines are not visible. CaBP is represented in a different neuron population with on the average slightly smaller-sized somata, which carry long, spiny, CaBP-positive dendrites. In contrast to PV and CaBP, CaR immunoreactivity is a marker chiefly for neuropil in MNH but only for few stained neurons. They may be spiny and show the largest size variations. The density of CaR-immunoreactive neuropil is highest in the hyperstriatal part of MNH. Double immunostaining for PV and CaBP reveals that these proteins are expressed mostly in different neuron populations, with only few neurons containing both proteins. These neuron populations appear to form an interconnected network within MNH. A possible relationship between the expression of either Ca-binding protein and the presence of the inhibitory transmitter GABA is also examined. The GABA-antibody labels scattered, very small to medium-sized neurons and dense punctate neuropil. The comparison of the area histograms of somata reveals an overlap with all 3 Ca-binding protein containing cell populations, except for a large proportion of small GABA-positive neurons. The characteristics of immunostained neuron populations are compared to the previously described 3 Golgi-types of neurons in MNH, and possibilities of a functional implication of the proteins in MNH plasticity are examined.