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PubMed1996

Developmental expression and functional characterization of the potassium-channel subunit Kv3.1b in parvalbumin-containing interneurons of the rat hippocampus.

The expression of the voltage-gated K(+)-channel subunit Kv3.1b in the developing hippocampus was determined by immunoblot and immunohistochemical techniques. Kv3.1b protein was detected first at postnatal day (P) 8. The Kv3.1b-immunopositive cell number per tissue section reached a maximum at P14 and was maintained through P40. In contrast, the Kv3.1b protein content of isolated membrane vesicles in immunoblots progressively increased through P40, suggesting an increase in Kv3.1b content per cell throughout this time period. Kv3.1b protein was expressed selectively in the somata, proximal dendrites, and axons of cells lying within or near the pyramidal cell layer, consistent with their being GABAergic inhibitory interneurons. Kv3.1b was present in approximately 80% of parvalbumin-positive interneurons. The developmental onset of Kv3.1b and parvalbumin immunoreactivity was identical. In contrast, Kv3.1b was mostly absent from the subset of somatostatin-positive inhibitory interneurons. Electrophysiological recordings were made from stratum pyramidale interneurons in which morphology and Kv3.1b-positive immunoreactivity were confirmed post hoc. Outward currents had voltage-dependent and biophysical properties resembling those of channels formed by Kv3.1b. The current blocked by low concentrations of 4-aminopyridine (4-AP) showed marked inactivation, suggesting that Kv3.1b may coassemble with other members of the Kv3 subfamily. In current-clamp recordings, concentrations of 4-AP that blocked the current through Kv3.1b channels allowed us tentatively to assign a role to Kv3.1b-containing channels in action-potential repolarization. These data demonstrate that Kv3.1b is regulated developmentally in a specific subpopulation of hippocampal interneurons and that channels containing this subunit may be a major determinant in imparting "fast-spiking" characteristics to these and other cells throughout the central nervous system containing the Kv3.1b subunit.

Action Potentials↗
PubMed1996

Parvalbumin-immunoreactive neurons make inhibitory synapses on pyramidal cells in the human amygdala: a light and electron microscopic study.

In the present study we investigate the inhibitory circuitries that regulate the neuronal activity in the lateral and basal nuclei, which are the main sensory input regions of the amygdala. Axon terminals immunoreactive for parvalbumin, a calcium-binding protein known to colocalize with GABA, were examined in these regions with electron microscopy, and their postsynaptic targets were identified and characterized. In the lateral nucleus, parvalbumin-immunoreactive (PV-ir) axons formed terminal rows which made symmetric synaptic contacts on the axon initial segments of the pyramidal cells. In the basal nucleus, pericellular baskets of PV-ir fibers established symmetric synapses on pyramidal cell somata and proximal dendrites. Our data suggest that PV-ir neurons play a crucial inhibitory role in the control of pyramidal cell activity in the human amygdala.

Adult↗
PubMed1997

Effects of prenatal ethanol exposure on parvalbumin-expressing GABAergic neurons in the adult rat medial septum.

Exposure of human fetuses to ethanol often results in the fetal alcohol syndrome. Animal models of fetal alcohol syndrome have been developed and used to examine the consequences of prenatal ethanol exposure on the central nervous system. The objective of this study was to determine the long-term effects of prenatal ethanol exposure on parvalbumin-expressing (PA+) GABAergic neurons of the rat medial septum. Pregnant Long-Evans rats were maintained on 1 of 3 diets from gestational day 0 to 21: an ethanol-containing liquid diet in which ethanol accounted for 35% of the total calories, a similar diet with the isocaloric substitution of sucrose for ethanol, or a lab chow control diet. Offspring were killed on postnatal day 60, and their brains were prepared for parvalbumin immunocytochemistry. Female rats exposed to the ethanol-containing diet during gestation had 42% fewer PA+ neurons in the medial septum and reduced PA+ cell density when compared with female rats exposed to the sucrose diet. Ethanol females also had fewer PA+ neurons per unit volume than sucrose females. Male rats exposed to ethanol did not display a similar reduction in PA+ neurons or density. No effect of prenatal diet was found on the area or volume of the medial septum, nor were cell diameters affected. As such, prenatal exposure to ethanol seems to reduce permanently the number of PA+ neurons in the female rat medical septum without affecting area, volume, or neuronal size. Functional implications and possible relations to the fetal alcohol syndrome are discussed.

Animals↗
PubMed1997

Tonotopic organization of auditory cortical fields delineated by parvalbumin immunoreactivity in macaque monkeys.

Tonotopic maps, obtained from single and multi-unit recordings in the primary and surrounding areas of the auditory cortex, were related to chemoarchitecture of the supratemporal plane, as delineated by immunoreactivity for parvalbumin. Neurons in the central core were sharply tuned and formed two complete tonotopic representations corresponding to the primary auditory area (AI) and the rostral (R) area. High frequencies were represented posteriorly in AI and anteriorly in R, the representation reversing in the anterior part of the core. Neurons in regions of less dense immunostaining previously described as lateral (L) and posteromedial (P-m) fields, showed broader frequency tuning. Two tonotopic representations were found in L: in an anterolateral (AL) field, corresponding to a field previously reported by others, high frequencies were represented anteriorly and low frequencies posteriorly; in a posterolateral field (PL) the trend reversed. There was a further reversal on entering P-m from the high frequency representation in PL and progressively lower frequencies tended to be represented more medially in P-m, but P-m may contain two representations reported by others. Neurons in the previously described anteromedial (A-m) and medial (M) fields of weaker immunostaining, were even more broadly tuned. A tonotopic progression from low frequency representation posteriorly to high frequency representation anteriorly was observed in the medial field. Frequency representation in A-m remains uncertain. No tonotopic representation could be demonstrated with the stimuli used in the zones of very weak parvalbumin immunostaining outside AL, PL, P-m, A-m, and M. The properties of neurons in the core and surrounding zones are likely to reflect inputs from the ventral and dorsal medial geniculate nuclei, respectively. The fields outside the core seem to be the starting points for separate streams of auditory corticocortical connections passing into association cortex.

Acoustic Stimulation↗
PubMed1997

Correlation of mATPase, parvalbumin, and cytochrome c oxidase in rat skeletal muscle fibres.

Muscle fibre typing is conventionally performed on unfixed frozen sections. Within the particular classes of fibre types mATPase correlates well with the type of myosin heavy chain (MHC). However, investigation of other properties, e.g., parvalbumin (PV) level, cannot be determined on unfixed frozen sections. Determination of PV, which correlates with the relaxation time, is performed immunohistochemically on fixed tissue. By that method a comparison of mATPase activity and the amount of PV within the same muscle fibre is difficult. The present method, combining histochemistry of mATPase and cytochrome c oxidase with parvalbumin immunohistochemistry on consecutive sections, allows the distinction of six fibre types: I, IB, IIA, IIB, IIAB, IIX, and a C fibre population without division into IC and IIC fibres. The advantages and disadvantages of the present method are discussed.

Animals↗
PubMed1975

Conformational studies on parvalbumins by circular dichroism.

Structural variations of two parvalbumins, Whiting III and Pike III, in various denaturing conditions, have been studied by circular dichroism. CD signals are depressed from 4 urea. For Pike III, acidic pH, sodium dodecyl sulfate or complete removal of Ca2+ show little effect in the far ultraviolet region but rather strong effects in the near ultraviolet. For Whiting III similar results are obtained at acidic pH. Carboxymethylated Whiting III (0.15 Ca2+/mol) shows, on the contrary, decreased CD signals in the far and in the near ultraviolet spectra. Addition of Ca2+ fully restores the native CD spectra in both proteins. Ca2+ binding produces structural modifications which are found to vary according to parvalbumin and which seem in any case different from those described for troponin C.

Animals↗
PubMed1975

Investigation of some physico-chemical properties of muscular parvalbumins by means of the luminescence of their phenylalanyl residues.

The influence of pH, temperature and Ca2+-release on the phenylalanyl and tyrosyl fluorescene of muscular parvalbumins from white muscles of hake and carp has been investigated. Within the pH range from 7 to 8, Ca2+-saturated parvalbumins show a conformational change registered by fluorescence, that is associated with the release of some of the bound Ca2+. Removal of Ca2+ by means of EGTA (ethyleneglycolbis-(aminoethylether)tetra-acetic acid) considerably narrows the region of protein nativity, increases the accessibility of their chromophores to quencher ions (Cs+ and CNS-) and decreases their stability against heat denaturation. The usefulness of measurements of the phenylalanine fluorescence and of the tyrosine-phenylalanine energy transfer in the investigation of these and other proteins is discussed.

Albumins↗
PubMed1975

The amino-acid sequence of the most acidic major parvalbumin from frog muscle.

The primary structure of the most acidic (pI - 4.50) of the two major parvalbumins from frog (Rana esculenta) has been determined from a study of its trypsic peptides and of overlapping peptides generated by limited trypsic digestion, chymotrypsic digestion and N-bromosuccinimide cleavage of the protein. The amino acid sequence so obtained is considered in comparison with those known for other parvalbumins and for rabbit troponin-C.

Amino Acid Sequence↗
PubMed1998

Rostral-caudal variation in troponin T and parvalbumin correlates with differences in relaxation rates of cod axial muscle.

Relaxation rate is an important determinant of axial muscle power production during the oscillatory contractions of undulatory locomotion. Recently, significant differences have been reported in the relaxation rates of rostral versus caudal white muscle fibers of the Atlantic cod Gadus morhua L. The present study investigates the biochemical correlates of this rostral-caudal physiological variation. Using denaturing gel electrophoresis, a series of fresh muscle samples from the dorsal epaxial muscle region was analyzed and several differences were detected. First, a gradual shift occurs in the expression of two troponin T isoforms along the length of the body. Second, rostral muscles were found to contain significantly greater amounts of parvalbumin than caudal muscles. Third, two soluble Ca(2+)-binding proteins, in addition to parvalbumin, were also detected in the rostral muscle samples yet were absent from the caudal samples. This suite of rostral-caudal variations provides a strong biochemical basis for regional differences in the relaxation rates of cod white muscle.

Animals↗
PubMed1996

Distribution of the calcium-binding proteins parvalbumin and calretinin in the auditory brainstem of adult and developing rats.

Parvalbumin (PV), calretinin (CR), and calbindin (CB) are calcium-binding proteins which are presumably involved in the regulation of the intracellular calcium concentration. Within the rat auditory system, CB is transiently expressed in several nuclei during the period of synapse refinement, indicating a specific function of CB during development, yet little is known in this regard about PV and CR. In order to gather more information about calcium-binding proteins during development, we analyzed the spatiotemporal distribution of PV and CR in the rat auditory brainstem using immunocytochemistry. In the adult, PV was heavily present in somata and neuropil of all nuclei and in fibers of all tracts. CR was found in somata of the cochlear nucleus and peripheral aspects of the inferior colliculus as well as in fibers extending into the superior olivary complex and the nuclei of the lateral lemniscus. The developmental expression of PV was characterized by a relatively late appearance in somata (at postnatal day 8), followed by a rapid increase to adult levels. In contrast, CR immunoreactivity was already strong two days before birth, yet the number and intensity of labeled neurons subsequently decreased and CR disappeared almost completely in the superior olivary complex, nuclei of the lateral lemniscus, and central aspects of the inferior colliculus. These data, together with those on CB, show that CR, CB, and PV are sequentially expressed during auditory brainstem development. They also suggest that the presence of the three proteins can be correlated with definite developmental stages.

Aging↗
PubMed1998

Cat intraamygdaloid inhibitory network: ultrastructural organization of parvalbumin-immunoreactive elements.

Projection neurons of the basolateral (BL) amygdaloid complex are regulated by an intrinsic inhibitory network. To improve our understanding of this inhibitory circuit, we studied the synaptology of parvalbumin-immunopositive (PV+) elements as this calcium-binding protein is localized in a subpopulation of gamma-aminobutyric acid (GABA)-ergic interneurons. Two populations of PV+ cells were identified on the basis of soma shape (ovoid, type A vs. polygonal, type B). In the lateral and BL nuclei, the majority of boutons in contact with PV+ cells formed asymmetric synapses (types 1-3; 94%), whereas a minority (type 4, 6%) established symmetric synaptic contacts and resembled GABAergic terminals. In both nuclei, type B PV+ perikarya were more densely innervated than were type A neurons. However, the pattern of synaptic innervation of type B PV+ neurons differed in the two nuclei: in the lateral nucleus, they were almost exclusively innervated by a population of small, presumed excitatory terminals (type 1), whereas the four categories of terminals contributed more equally to their innervation in the BL nucleus. PV+ boutons belonged to a single category of terminals that was enriched with GABA and formed symmetric synapses mostly with the proximal part of PV neurons. The proportion of axosomatic synapses was significantly higher in the lateral nucleus than in the BL nucleus (33% vs. 18%). The reverse was true for the contacts with proximal dendrites (33% in the lateral nucleus vs. 46% in the BL nucleus). The remaining terminals formed synapses with distal dendrites (23-28%) and spines (8-12%). These results indicate that PV+ interneurons receive massive excitatory inputs and that PV+ terminals are strategically located to exert a powerful inhibitory control of amygdala neurons.

Amygdala↗
PubMed1998

Dependence of parvalbumin expression on Purkinje cell input in the deep cerebellar nuclei.

A complete loss of Purkinje cell (PC) input leads to an increase in expression of the calcium-binding protein parvalbumin (Parv) in neurons of the deep cerebellar nuclei (DCN) of PC degeneration (pcd) mutants. To verify this apparent dependence of Parv expression on PC input in the DCN, the patterns of expression in five other cerebellar mutants (weaver, staggerer, leaner, nervous, and lurcher) with differing grades and chronologies of PC loss were compared. Degree and time course of PC loss and the subsequent denervation of DCN neurons were monitored by using Calbindin D-28k (Calb) immunocytochemistry. Similar to pcd mice, somatal Parv in lurcher mutants increased massively throughout the cerebellar nuclei. In nervous and leaner mutants, somatal Parv was restricted to almost completely denervated nuclear areas, whereas areas with appreciable remnants of PC input were spared. The first appearance of Parv+ somata was closely correlated with the time course of PC degeneration--postnatal day 19 in lurcher mutants and postnatal day 23 in nervous mutants. In staggerer mice, neurons immunopositive for Parv as well as for Calb were present in outer DCN areas, likely representing ectopic PCs rather than DCN neurons. No Parv+ DCN somata were found in weaver mutants at any time. In conclusion, increased expression of somatal Parv in DCN neurons is not restricted to the specific histopathology in pcd mutants but is a common mechanism that is dependent on the topography and severeness of PC-input loss. The functional significance of the Parv increase and its possible contribution to the degree of motor disability among the different mutants are discussed.

Animals↗
PubMed1998

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.

Animals↗
PubMed1999

Postnatal development of calretinin- and parvalbumin-positive interneurons in the rat neostriatum: an immunohistochemical study.

On the basis of cytochemical and morphologic differences, two classes of gamma-aminobutyric acidergic (GABAergic) interneurons expressing calcium-binding proteins have been identified in the striatum of adult animals: neurons expressing either parvalbumin (PV) or calretinin (CR). The function of these calcium-binding proteins is not clear, however, they are associated with distinct classes of inhibitory interneurons within the adult neostriatum. By using immunocytochemical techniques, we analyzed the postnatal maturation and the spatiotemporal distribution of PV- and CR-positive neurons in the rat neostriatum compared with a third class of interneurons characterized by the expression of the acetylcholine-synthesizing enzyme, choline acetyltransferase (ChAT). PV-positive cells appeared initially on postnatal day 9 in the lateral region of the striatum. During postnatal weeks 2 and 3, the numbers of PV-positive neurons increased, and this cell population spread progressively in a lateromedial direction. In contrast, CR-expressing neurons were present at birth. During the first few days after birth, the number of CR-immunoreactive cells increased, reaching a peak on postnatal day 5 before declining during the following 2 weeks. A mediolateral gradient was evident temporarily. ChAT-containing neurons were detectable at birth in the lateral striatum. During postnatal weeks 1 and 2, the neurons matured along a lateral-to-medial gradient. The results indicate that the maturation of striatal interneurons is regulated differentially during postnatal development, resulting in a distinct spatiotemporal genesis of phenotypes. The sequential expression of CR and PV suggests a stage-dependent development of subsets of inhibitory interneurons and, hence, the stage-dependent maturation of functionally distinct inhibitory circuits within the neostriatum.

Animals↗
PubMed1999

Differential subcellular localization of forward and feedback interareal inputs to parvalbumin expressing GABAergic neurons in rat visual cortex.

In rat visual cortex, forward and feedback interareal pathways innervate both pyramidal and gamma-aminobutyric acid (GABA)ergic (Johnson and Burkhalter [1996] J. Comp. Neurol. 368:383-398). GABAergic neurons consist of different cell types of which the largest group expresses parvalbumin (PV; Gonchar and Burkhalter [1997] Cereb. Cortex 4:347-358). Here, we report that PV neurons in layers 2/3 are synaptic targets of forward and feedback projections between area 17 and the lateromedial area (LM) of rat visual cortex. In both forward and feedback pathways, approximately 90% of axon terminals in layer 2/3 labeled by tracing with biotinylated dextran amine formed synapses with PV-negative profiles. In both pathways, most of these profiles resembled dendritic spines. Although there were no differences in the innervation of PV-negative targets, the two pathways differed in the innervation of PV-positive neurons. In each pathway, approximately 10% of terminals formed synapses with PV-positive profiles. However, in the forward pathway, the size of the contacted PV-positive profiles was larger than in the feedback pathway. Moreover, in the forward pathway, axon terminals on PV-positive profiles were larger, contained more mitochondria and docked synaptic vesicles than feedback synapses on PV neurons. Our results show that PV neurons provide a major target for area 17 <-> LM forward and feedback pathways terminating in upper layers. In each pathway, the proportion of axons contacting PV neurons is similar. However, both pathways differ in the subcellular localization and morphology of synapses on PV neurons. These asymmetries may contribute to the inequality in the strength of disynaptic inhibition evoked by forward and feedback inputs (Shao and Burkhalter [1996] J. Neurosci. 16:7353-7365).

Afferent Pathways↗
PubMed1999

Distribution and patterns of connectivity of interneurons containing calbindin, calretinin, and parvalbumin in visual areas of the occipital and temporal lobes of the macaque monkey.

Immunocytochemical techniques were used to examine the distribution of double-bouquet cells and chandelier cells that were immunoreactive (-ir) for the calcium-binding proteins calbindin (CB), calretinin (CR), and parvalbumin (PV) in the primary visual area (V1), the second visual area (V2), and cytoarchitectonic area TE in the macaque monkey. Furthermore, the connections between CB-, CR-, and PV-ir neurons in these visual areas were investigated at the light microscope level by using a dual-immunocytochemical staining procedure. The most significant findings were three-fold. First, the number and distribution of CB-ir and CR-ir double-bouquet cells and PV-ir chandelier cells differed considerably between different visual areas. In particular, the different distribution of double-bouquet cells was illustrated dramatically at the V1/V2 border, where CB-ir double-bouquet axons were very few or lacking in V1 but were very numerous in V2. Furthermore, PV-ir chandelier cell terminals were relatively sparse in V1, more frequent in V2, and most frequent in area TE. Second, the percentage of CB-, CR-, and PV-ir neurons receiving multiple contacts on their somata and proximal dendrites from other calcium-binding protein neurons varied between 22% and 85%. The highest percentage of contacts found between immunolabelled cells and multiterminals were for the combinations CR/CB (76-85%; percent of cells immunoreactive for CB that were innervated by multiterminals immunoreactive for CR), followed by the combination PV/CR (42-48%), and then by the other combinations that had similar percentages (22-32% for CR/PV; 26-37% for CB/CR; 29-42% for CR/PV). Third, differences in the relative proportions of CB, CR, and PV terminals in contact with CB-, CR-, and PV-ir neurons were consistent between the different cortical areas studied. Thus, certain characteristics of intraareal circuits differ, whereas others remain similar, in different areas of the occipitotemporal visual pathway. The differences may represent regional specializations related to the different processing of visual stimuli, whereas the similarities may be attributed to general functional requisites for interneuronal circuitry.

Animals↗
PubMed1999

Distribution of parvalbumin immunoreactivity in the brain of the tench (Tinca tinca L., 1758).

The distribution of parvalbumin (PV) immunoreactivity in the tench brain was examined by using the avidin-biotin-peroxidase immunocytochemical method. This protein was detected in neuronal populations throughout all main divisions of the tench brain. In the telencephalic hemispheres, PV-immunopositive neurons were distributed in both the dorsal and ventral areas, being more abundant in the area ventralis telencephali, nucleus ventralis. In the diencephalon, the scarce distribution of PV-containing cells followed a rostrocaudal gradient, and the most evident staining was observed in the nucleus periventricularis tuberculi posterioris and in a few nuclei of the area praetectalis. In the mesencephalon, abundant PV-immunoreactive elements were found in the tectum opticum, torus semicircularis, and tegmentum. In the tectum opticum, PV-immunoreactivity presented a laminar distribution. Three PV-containing neuronal populations were described in the torus semicircularis, whereas in the tegmentum, the PV staining was mainly located in the nucleus tegmentalis rostralis and in the nucleus nervi oculomotorii. In the metencephalon, Purkinje cells were PV-immunopositive in the valvula cerebelli, lobus caudalis cerebelli, and in the corpus cerebelli. In the myelencephalon, PV immunoreactivity was abundant in the nucleus lateralis valvulae, in the nucleus nervi trochlearis, nucleus nervi trigemini, nucleus nervi abducentis, nucleus nervi glossopharyngei, and in the formatio reticularis. Mauthner cells were also PV immunostained. By contrast to other vertebrate groups, only a restricted population of PV-containing neurons was GABA-immunoreactive in the tench, demonstrating that this calcium-binding protein cannot be considered a marker for GABAergic elements in the teleost brain. This study demonstrates a low phylogenetic conservation of the distribution of PV comparing teleosts and tetrapods.

Animals↗
PubMed1998

Parvalbumin immunoreactive neurons in the rat septal complex have substantial glial coverage and receive few direct contacts from catecholaminergic terminals.

Our previous studies have demonstrated that septohippocampal neurons in the rat septal complex have substantial glial coverage and have a number of synaptic associations with catecholaminergic terminals. While similar ultrastructural characteristics are observed for septal cholinergic neurons, the morphology and synaptic relations of catecholaminergic terminals with septal GABAergic neurons is largely unknown. Since the GABAergic septohippocampal neurons colocalize the calcium-binding protein, parvalbumin (PVA), the present study examined the ultrastructural relations of PVA neurons with catecholaminergic terminals in the septal complex. Single sections were dually labeled with antibodies to PVA and either tyrosine hydroxylase (TH) or dopamine-beta-hydroxylase (DBH). By light microscopy, processes with TH- and DBH- (TH/DBH) immunoreactivity were near PVA-labeled neurons. By electron microscopy, PVA-labeled perikarya had an average diameter of 14.9+/-6 microm and were ovoid or elongated. PVA-labeled perikarya (n = 124) had a large amount of astrocytic coverage (75+/-14%) and a low amount of terminal coverage (15+/-12%). PVA-labeled perikarya and dendrites mostly were contacted by terminals lacking immunoreactivity for either PVA or TH/DBH (82% of 1,663). Of the TH/DBH terminals or axons near PVA somata and dendrites, few (3% of 1,663) directly contacted them while the majority abutted adjacent glial or neuronal profiles. Some TH/DBH- and PVA-labeled terminals contacted the same dendrites; a few of these contained immunoreactivity for PVA. The results demonstrate that PVA-containing GABAergic septal neurons, like cholinergic neurons, are mostly surrounded by astrocytes and have very little terminal coverage. However, in contrast to cholinergic neurons, PVA-containing neurons are contacted primarily by non-catecholaminergic terminals suggesting that any functional interactions would be indirect. These findings further support the functional diversity of subpopulations of septohippocampal neurons.

Animals↗