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J M Fritschy

Publications and source records attributed to J M Fritschy.

At least 91 records · Page 5Linked to original sources
PubMed1996

Differential distribution of gamma-aminobutyric acidA receptor subunit (alpha 1, alpha 2, alpha 3, alpha 5 and beta 2 + 3) immunoreactivity in the medial prefrontal cortex of the rat.

A detailed mapping of the gamma-aminobutyric acid (GABA)A receptor subunits (alpha 1, alpha 2, alpha 3, alpha 5 and beta 2 + 3) in the infralimbic/ventral prelimbic region (IL/vPL) of the rat frontal cortex was carried out using subunit-specific antibodies. The alpha 1 and beta 2 + 3 subunit antibodies immunostained all layers of the IL/vPL region. Layers II and III displayed immunostaining of cell bodies whereas I, V and VI showed predominantly neuropil staining. The size of the alpha 1-positive cell bodies corresponded to that of small interneurons (range, 20-55 microns2; mean +/- SEM, 37 +/- 5.5 microns2) as well as pyramidal cells or large interneurons (range, 87-135 microns2; mean +/- SEM, 103.4 +/- 9.7 microns2). However, beta 2 + 3 antibody immunostained only small cell bodies. Immunoreactivity for alpha 2 was restricted to layers I and II, whereas alpha 3 and alpha 5 subunit expression was seen only in layer VI. The antibody to the alpha 2 subunit immunostained small cell bodies (range, 29-63 microns2; mean +/- SEM, 32 +/- 4.5 microns2) in layer II, resembling interneurons. Conversely, both alpha 3 and alpha 5 antibodies immunostained large cell bodies (range, 94-151 microns2; mean +/- SEM, 115.7 +/- 13.4 microns2), consistent with pyramidal cell labelling in layer VI.

Animals↗
PubMed1996

Developmental profile of GABAA-receptors in the marmoset monkey: expression of distinct subtypes in pre- and postnatal brain.

Gamma aminobutyric acid (GABA)A-receptors are expressed in fetal mammalian brain before the onset of synaptic inhibition, suggesting their involvement in brain development. In this study, we have analyzed the maturation of the GABAA-receptor in the marmoset monkey forebrain to determine whether distinct receptor subtypes are expressed at particular stages of pre- and postnatal ontogeny. The distribution of the subunits alpha 1, alpha 2, and beta 2,3 was investigated immunohistochemically between embryonic day 100 (6 weeks before birth) and adulthood. Prenatally, the alpha 2- and beta 2,3-subunit-immunoreactivity (-IR) was prominent throughout the forebrain, whereas the alpha 1-subunit-IR appeared in selected regions shortly before birth. The alpha 2-subunit-IR disappeared gradually to become restricted to a few regions in adult forebrain. By contrast, the alpha 1-subunit-IR increased dramatically after birth and replaced the alpha 2-subunit in the basal forebrain, pallidum, thalamus, and most of the cerebral cortex. Staining for the beta 2,3-subunits was ubiquitous at every age examined, indicating their association with either the alpha 1- or the alpha 2-subunit in distinct receptor subtypes. In neocortex, the alpha 1 -subunit-IR was first located selectively to layers IV and VI of primary somatosensory and visual areas. Postnatally, it increased throughout the cortex, with the adult pattern being established only during the second year. The switch in expression of the alpha 1- and alpha 2- subunits indicates that the subunit composition of major GABAA-receptor subtypes changes during ontogeny. This change coincides with synaptogenesis, suggesting that the emergence of alpha 1- GABAA-receptors parallels the formation of inhibitory circuits. A similar pattern has been reported in rat, indicating that the developmental regulation of GABAA-receptors is conserved across species, possibly including man. However, the marmoset brain is more mature than the rat brain at the onset of alpha 1-subunit expression, suggesting that alpha 1-GABAA-receptors are largely dispensable in utero, but may be required for information processing after birth.

Animals↗
PubMed1996

Brain cell type specificity and gliosis-induced activation of the human cytomegalovirus immediate-early promoter in transgenic mice.

Human cytomegalovirus (HCMV) can cause debilitating, sometimes fatal, opportunistic infections in congenitally infected infants and in immunodeficient individuals such as patients with the acquired immunodeficiency syndrome (AIDS). Molecular mechanisms that determine cell type specificity of HCMV infection and latency are poorly understood. We recently described a transgenic mouse model for analysis of HCMV major immediate-early (IE) promoter regulation and showed that sites of IE promoter activity during murine embryogenesis correlate with known target tissues of congenital HCMV infection in human fetuses (Koedood et al., 1995). Among various permissive human tissues, the brain is a site where HCMV infections can be devastating. Here, we have used immunohistochemical double-labeling analysis to identify specific cell types with HCMV-IE promoter activity in brains of transgenic mice at several postnatal stages. IE promoter activity was restricted to some endothelial cells, ependymal cells, choroid plexus epithelia, and neurons at discrete locations in the forebrain, brainstem, and cerebellum. Endothelial cells and neurons with activity were proportionately more abundant in neonatal than in adult brains. Although the IE promoter was normally silent in most astrocytes, activity was strongly induced in reactive astrocytes in response to a neocortical stab lesion. The findings support a model, consistent with clinical literature on HCMV encephalitis, whereby tissue damage and gliosis caused by HCMV infection of endothelial and ependymal cells progressively renders adjacent permissive neurons and reactive astrocytes accessible to infection. This transgenic model system should facilitate identification of factors that regulate the HCMV IE promoter with regard to infection permissivity and reactivation from latency.

Animals↗
PubMed1996

The gamma 2 subunit of the GABAA receptor is concentrated in synaptic junctions containing the alpha 1 and beta 2/3 subunits in hippocampus, cerebellum and globus pallidus.

The gamma 2 subunit is necessary for the expression of the full benzodiazepine pharmacology of GABAA receptors and is one of the major subunits in the brain. In order to determine the location of channels containing the gamma 2 subunit in relation to GABA-releasing terminals on the surface of neurons, a new polyclonal antipeptide antiserum was developed to the gamma 2 subunit and used in high resolution, postembedding, immunoelectron-microscopic procedures. Dual immunogold labelling of the same section for two subunits, and up to three sections of the same synapse reacted for different subunits, were used to characterize the subunit composition of synaptic receptors. The gamma 2 subunit was present in type 2, "symmetrical" synapses in each of the brain areas studied, with the exception of the granule cell layer of the cerebellum. The gamma 2 subunit was frequently co-localized in the same synaptic junction with the alpha 1 and beta 2/3 subunits. The immunolabelling of synapses was coincident with the junctional membrane specialization of the active zone. Immunolabelling for the receptor often occurred in multiple clusters in the synapses. In the hippocampus, the gamma 2 subunit was present in basket cell synapses on the somata and proximal dendrites and in axo-axonic cell synapses on the axon initial segment of pyramidal and granule cells. Some synapses on the dendrites of GABAergic interneurones were densely labelled for the gamma 2, alpha 1 and beta 2/3 subunits. In the cerebellum, the gamma 2 subunit was present in both distal and proximal Purkinje cell dendritic synapses established by stellate and basket cell, respectively. On the soma of Purkinje cells, basket cell synapses were only weakly labelled. Synapses on interneuron dendrites were more densely labelled for the gamma 2, alpha 1 and beta 2/3 subunits than synapses on Purkinje or granule cells. Although immunoperoxidase and immunofluorescence methods show an abundance of the gamma 2 subunit in granule cells, the labelling of Golgi synapses was much weaker with the immunogold method than that of the other cell types. In the globus pallidus, many type 2 synapses were labelled for the gamma 2 subunit together with alpha 1 and beta 2/3 subunits. The results show that gamma 2 and beta 2/3 subunits receptor channels are highly concentrated in GABAergic synapses that also contain the alpha 1 and beta 2/3 subunits. Channels containing the gamma 2 subunit are expressed in synapses on functionally distinct domains of the same neuron receiving GABA from different presynaptic sources. There are quantitative differences in the density of GABAA receptors at synapses on different cell types in the same brain area.

Animals↗
PubMed1996

Laminar compartmentalization of GABAA-receptor subtypes in the spinal cord: an immunohistochemical study.

To assess the significance of GABAA-receptor heterogeneity, which is based on a family of at least 15 subunits, the cellular localization and subunit composition of GABAA-receptor subtypes were analyzed immunohistochemically in the rat spinal cord. The distribution of subunits alpha 1, alpha 2, alpha 3, alpha 5, beta 2,3, and gamma 2 was investigated with subunit-specific antibodies, and their colocalization within individual neurons was visualized by double-immunofluorescence staining. The results reveal a widespread expression of the subunits, alpha 3, beta 2,3, and gamma 2 in the spinal cord, whereas the three other alpha subunits displayed a more restricted, lamina-specific distribution. The alpha 1 and alpha 5 subunits were most abundant in the intermediate zone, whereas the alpha 2 subunit was predominant in the superficial layers of the dorsal horn and in somatic and preganglionic motoneurons. From colocalization studies, seven subunit combinations could be identified (alpha 3/beta 2,3/gamma 2; alpha 2/beta 2,3/gamma 2; alpha 1/beta 2,3/gamma 2; alpha 5/beta 2,3/gamma 2; alpha 1/alpha 5/beta 2,3/gamma 2; alpha 2/gamma 2; alpha 2/alpha 5/gamma 2) that correspond presumably to distinct receptor subtypes. Although most neurons expressed the subunit triplet alpha x/beta 2,3/gamma 2, the beta 2,3 subunits could not be detected in motoneurons that may thus possess "atypical" receptor subtypes (alpha 2/gamma 2 and alpha 2/alpha 5/gamma 2). ON the subcellular level, aggregates of immunoreactivity, suggestive of postsynaptic GABAA receptors, typically were seen on the surface of neuronal somata and proximal dendrites. In addition, an intense diffuse staining was observed in laminae I--III for the subunits alpha 2, alpha 3, beta 2,3, and gamma 2, presumably localized on primary afferent terminals. The localization of GABAA-receptor subtypes in distinct laminar compartments of the spinal cord suggests that GABAA-receptor heterogeneity is of relevance for the modulation of sensory inputs, nociception, and motor control at segmental levels.

Animals↗
PubMed1996

Modifications of gamma-aminobutyric acidA receptor subunit expression in rat neocortex during tolerance to diazepam.

We evaluated whether tolerance to the antagonism of bicuculine-induced seizures by diazepam is associated with changes (i) in the content of mRNAs encoding for gamma-aminobutyric acidA (GABAA) receptor subunits, (ii) in the expression density of these subunits, and (iii) in the 1,4-benzodiazepine binding site characteristics in discrete neocortical structures. We found that in diazepam-tolerant rats, the content of the mRNA encoding for the alpha 1 subunit of the GABAA receptor decreased in the frontoparietal motor (FrPaM) cortex and in the hippocampus (42% and 20%, respectively) but not in the frontoparietal somatosensory (FrPaSS) cortex, striatum, olfactory bulb, and cerebellum. In the FrPaM cortex, gamma 2S and gamma 2L subunit mRNA contents were also decreased (48% and 30%, respectively), whereas that of alpha 5 was increased (30%). In the FrPaM and FrPaSS cortices as well as in cerebellum of diazepam-tolerant rats, the content of alpha 2, alpha 3, alpha 6, beta 2, and delta subunit mRNA was unchanged, as was the content of alpha 2, alpha 5, gamma 1, and gamma 2S subunit mRNA in the hippocampus. Furthermore, the reduction in alpha 1 subunit mRNA content in the FrPaM cortex and the anticonvulsant tolerance to diazepam returned to control values 72 hr after termination of the protracted diazepam treatment. Rats receiving a treatment with imidazenil in doses equipotent and with a schedule identical to that of diazepam failed to exhibit tolerance to the anticonvulsant action of this drug or cross-tolerance to diazepam. In these rats, the content of mRNA encoding for alpha 1, alpha 2, alpha 3, alpha 5, alpha 6, gamma 1, gamma 2S, gamma 2L, and delta GABAA receptor subunits failed to change in the FrPaM and FrPaSS cortices, in the hippocampus, and in the other brain areas that were studied in diazepam-tolerant rats. Although the density and affinity of [3H]flumazenil and [3H]imidazenil binding failed to change in the FrPaM and FrPaSS cortices of diazepam-tolerant rats, the expression density of alpha 1 subunit immunogold labeling decreased by 37%, whereas that of alpha 5, gamma 2L/S, and beta 2/3 increased by 158%, 50%, and 47%, respectively, in the FrPaM cortex, and the density of the alpha 5 subunit selectively increased (209%) in the FrPaSS cortex. In contrast, the immunogold labeling density of the alpha 1, alpha 5, gamma 2L/S, and beta 2/3 subunits failed to change in either the FrPaM or FrPaSS cortex of rats receiving protracted imidazenil treatment.

Animals↗
PubMed1995

Distribution of NMDA receptor subunit proteins NR2A, 2B, 2C and 2D in rat brain.

The regional distribution of the NMDA receptor subunits NR2A, 2B, 2C and 2D was visualized in adult rat brain using the histo-blot technique with newly developed subunit-specific antisera. NR2A immunoreactivity was found in almost all regions of the brain, whereas NR2B staining was restricted to forebrain, and NR2D immunoreactivity to diencephalic, mesencephalic and brain stem structures. NR2C staining was confined to cerebellum, thalamus and olfactory bulb. Thus, NMDA receptors containing the NR2A subunit are likely to represent a receptor subtype predominant throughout the brain, while those containing the NR2B, NR2C or NR2D subunit represent more region-specific receptor subtypes. The regionally overlapping distribution of certain NR2 subunits points to the existence of NMDA receptors containing more than one NR2 subunit variant.

Animals↗
PubMed1995

GABAA-receptor subunit composition in the circadian timing system.

In the present study, the distribution of GABAA-receptor alpha 1-, alpha 2-, alpha 3-, alpha 5-, beta 2.3- and gamma 2-subunits were localized immunohistochemically with subunit specific antibodies in the rat circadian timing system (CTS). The areas examined include the principal circadian pacemaker, the suprachiasmatic nucleus (SCN), and areas that receive important SCN input including the intergeniculate leaflet (IGL), subparaventricular zone (SPVZ), paraventricular hypothalamic nucleus (PVH), the retrochiasmatic area (RCh) and the paraventricular nucleus of the thalamus (PVT). The SCN has an unusual pattern with immunoreactivity for the alpha 2-, alpha 3-, alpha 5-, and gamma 2-subunits but not for the commonly expressed alpha 1- and beta 2.3-subunits. In all of the areas receiving SCN efferent input (SPVZ, PVH, RCh, PVT and IGL), staining is present either for all six subunits or for the three common subunits, alpha 1-, beta 2.3-, and gamma 2. There is some evidence for a differential distribution of subunits at the cellular level. The alpha 2-, and beta 2.3-subunits are predominantly expressed in neuropil, the alpha 3-, alpha 5- and gamma 2-subunits are predominantly expressed over perikarya and the alpha 1-subunit is expressed over both neuropil and perikarya in the areas in which subunit immunoreactivity is found. The demonstration of this regional and cellular expression of GABAA-receptor subunits should contribute to our understanding of GABAergic neurotransmission in the CTS.

Animals↗
PubMed1995

Regional and cellular expression sites of the alpha 1 subunit of GABAA receptors in the rat basal forebrain: a cytochemical study with glutamic acid decarboxylase, choline acetyltransferase, calcium-binding proteins and nitric oxide synthase as second markers.

Forebrain sections of adult male Wistar rats were processed for the immunohistochemical detection of the GABAA receptor alpha 1 subunit. Alternate sections were used for double-staining with antibodies to glutamic acid decarboxylase (GAD), choline acetyltransferase (ChAT), the calcium binding proteins parvalbumin (PARV), calbindin (CALB) and calretinin (CR) as well as to nitric oxide synthase (NOS). alpha 1 receptor subunit-immunoreactive neurons were found to be inhomogeneously distributed in the rat basal forebrain. Numerous alpha 1 subunit-immunostained neurons occupied the central part of medial septum and diagonal band, the whole ventral pallidum and the globus pallidus. A moderate number was found in the lateral septum, and only very few in the striatum and nucleus accumbens. Double-immunofluorescence labelling revealed an apparently complete co-expression of GAD-immunoreactivity in alpha 1 subunit-immunoreactive cells of rat basal forebrain, but only a region-dependent proportion of GAD-immunoreactive cells showed alpha 1 subunit-immunoreactivity. Co-expression of PARV-immunoreactivity characterized the vast majority of the alpha 1 subunit-immunoreactive cells in the medial septum, diagonal band, ventral pallidum and globus pallidus. Striatal alpha 1 subunit-immunopositive neurons appeared PARV-immunonegative and did also not react with the other immunoreagents used in this study, except the GAD-antibody. CR-immunoreactivity was co-expressed in alpha 1 subunit-immunopositive cells of the ventral lateral septal nucleus and only exceptionally in the ventral pallidum, where the vast majority of CR-positive cells was monolabelled. A small minority of ChAT-immunoreactive, but in no case CALB- and NOS-immunoreactive cells were found to express the alpha 1 subunit-immunoreactivity. These findings confirm the data obtained by analyses of other brain regions suggesting a preferred co-existence of this GABAA receptor subunit with PARV and to a lesser degree with CR.

Animals↗
PubMed1995

Cerebellar granule cells in vitro recapitulate the in vivo pattern of GABAA-receptor subunit expression.

GABAA-receptor heterogeneity is based on the combinatorial assembly of a family of 15 subunits (alpha 1-6, beta 1-3, gamma 1-3, delta, rho 1-2) into multiple receptor subtypes. The factors regulating the differential expression of GABAA-receptor subtypes in the CNS are largely unknown. In the present study, we have used primary cultures of rat cerebellar granule cells as model system to analyze to which extent the expression, subunit composition, and subcellular localization of GABAA-receptors depend on signals available in the cerebellum in vivo, in particular GABAergic input which is lost in vitro. GABAA-receptor subunits were visualized immunohistochemically with subunit-specific antibodies and their subcellular localization was investigated by confocal laser microscopy with selective markers for dendritic proteins (microtubule-associated protein 2, non-phosphorylated neurofilaments) and synaptic vesicles (synaptophysin). Triple immunofluorescence staining experiments revealed that dissociated granule cells taken from 7-day-old rats and maintained in culture for 9 days co-expressed the subunits alpha 1 alpha 6 beta 2,3 gamma 2 delta, a subunit repertoire which is identical to that seen in vivo in the adult cerebellum. GABAA-receptor subunits were localized selectively in granule cell somata and in proximal neurites immunopositive for MAP-2. No staining was detected in distal neurites immunopositive for neurofilaments. GABAA-receptor subunits frequently were aggregated in clusters closely apposed to synaptophysin-immunoreactive varicosities, suggesting a post-synaptic localization. Thus, major functional determinants of GABAA-receptors in granule cells (subunit repertoire, subcellular segregation and clustering in post-synaptic sites) develop in vitro, indicating that they are regulated to a large extent by intrinsic factors, independently of GABAergic input.

Animals↗
PubMed1995

Benzodiazepine-insensitive mice generated by targeted disruption of the gamma 2 subunit gene of gamma-aminobutyric acid type A receptors.

Vigilance, anxiety, epileptic activity, and muscle tone can be modulated by drugs acting at the benzodiazepine (BZ) site of gamma-aminobutyric acid type A (GABAA) receptors. In vivo, BZ sites are potential targets for endogenous ligands regulating the corresponding central nervous system states. To assess the physiological relevance of BZ sites, mice were generated containing GABAA receptors devoid of BZ sites. Following targeted disruption of the gamma 2 subunit gene, 94% of the BZ sites were absent in brain of neonatal mice, while the number of GABA sites was only slightly reduced. Except for the gamma 2 subunit, the level of expression and the regional and cellular distribution of the major GABAA receptor subunits were unaltered. The single channel main conductance level and the Hill coefficient were reduced to values consistent with recombinant GABAA receptors composed of alpha and beta subunits. The GABA response was potentiated by pentobarbital but not by flunitrazepam. Diazepam was inactive behaviorally. Thus, the gamma 2 subunit is dispensable for the assembly of functional GABAA receptors but is required for normal channel conductance and the formation of BZ sites in vivo. BZ sites are not essential for embryonic development, as suggested by the normal body weight and histology of newborn mice. Postnatally, however, the reduced GABAA receptor function is associated with retarded growth, sensorimotor dysfunction, and drastically reduced life-span. The lack of postnatal GABAA receptor regulation by endogenous ligands of BZ sites might contribute to this phenotype.

Animals↗
PubMed1995

GABAA-receptor heterogeneity in the adult rat brain: differential regional and cellular distribution of seven major subunits.

GABAA-receptors display an extensive structural heterogeneity based on the differential assembly of a family of at least 15 subunits (alpha 1-6, beta 1-3, gamma 1-3, delta, rho 1-2) into distinct heteromeric receptor complexes. The subunit composition of receptor subtypes is expected to determine their physiological properties and pharmacological profiles, thereby contributing to flexibility in signal transduction and allosteric modulation. In heterologous expression systems, functional receptors require a combination of alpha-, beta-, and gamma-subunit variants, the gamma 2-subunit being essential to convey a classical benzodiazepine site to the receptor. The subunit composition and stoichiometry of native GABAA-receptor subtypes remain unknown. The aim of this study was to identify immunohistochemically the main subunit combinations expressed in the adult rat brain and to allocate them to identified neurons. The regional and cellular distribution of seven major subunits (alpha 1, alpha 2, alpha 3, alpha 5, beta 2,3, gamma 2, delta) was visualized by immunoperoxidase staining with subunit-specific antibodies (the beta 2- and beta 3-subunits were covisualized with the monoclonal antibody bd-17). Putative receptor subtypes were identified on the basis of colocalization of subunits within individual neurons, as analyzed by confocal laser microscopy in double- and triple-immunofluorescence staining experiments. The results reveal an extraordinary heterogeneity in the distribution of GABAA-receptor subunits, as evidenced by abrupt changes in immunoreactivity along well-defined cytoarchitectonic boundaries and by pronounced differences in the cellular distribution of subunits among various types of neurons. Thus, functionally and morphologically diverse neurons were characterized by a distinct GABAA-receptor subunit repertoire. The multiple staining experiments identified 12 subunit combinations in defined neurons. The most prevalent combination was the triplet alpha 1/beta 2,3/gamma 2, detected in numerous cell types throughout the brain. An additional subunit (alpha 2, alpha 3, or delta) sometimes was associated with this triplet, pointing to the existence of receptors containing four subunits. The triplets alpha 2/beta 2,3/gamma 2, alpha 3/beta 2,3/gamma 2, and alpha 5/beta 2,3/gamma 2 were also identified in discrete cell populations. The prevalence of these seven combinations suggest that they represent major GABAA-receptor subtypes. Five combinations also apparently lacked the beta 2,3-subunits, including one devoid of gamma 2-subunit (alpha 1/alpha 2/gamma 2, alpha 2/gamma 2, alpha 3/gamma 2, alpha 2/alpha 3/gamma 2, alpha 2/alpha 5/delta).(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdala↗
PubMed1995

Colocalization of gephyrin and GABAA-receptor subunits in the rat retina.

Gephyrin is a protein that copurifies with the glycine receptor (GlyR) and is required for the clustering of GlyRs at postsynaptic sites. Previously, it was thought that antibody mAb 7a, directed against gephyrin, was a specific marker for GlyR. However, there is evidence that gephyrin can also be found at nonglycinergic synapses. Here, immunocytochemistry was applied to show this directly for the rat retina. Both gephyrin and different subunits of the gamma-aminobutyric acid (GABA)A receptor were localized to discrete puncta in the inner plexiform layer, and these puncta were shown by electron microscopy to represent synaptic sites. Double immunocytochemistry revealed that GABAA receptors and GlyRs are not colocalized. However, gephyrin and different subunits of GABAA receptors were found to occur at the same synapses. The amount of colocalization varied with the GABAA receptor subunit composition and was most extensive for the alpha 2 subunit, less for the alpha 3 subunit, and minimal for the alpha 1 subunit. The gephyrin present at GABAergic synapses of the retina might also be involved with clustering of receptors at the postsynaptic sites. Hence, localization of gephyrin can no longer be considered as a unique marker of glycinergic synapses.

Animals↗
PubMed1995

Co-occurrence of perineuronal nets with GABAA receptor alpha 1 subunit-immunoreactive neurones in the rat septal region.

The immunocytochemical demonstration of the GABAA receptor alpha 1 subunit was combined with the Wisteria floribunda agglutinin staining of lattice-like extracellular matrix components--known as perineuronal nets--in the rat basal forebrain. Both were found to be co-localized in the septal-diagonal band region (e.g. in the medial septum, 96%), but only exceptionally in the ventral pallidum (3-10%) and nowhere in other basal forebrain subdivisions. This co-occurrence of perineuronal nets with septo-hippocampal projection neurones--previously characterized as GABAergic--expressing the GABAA receptor alpha 1 subunit- as well as parvalbumin-immunoreactivity, suggests the involvement of these intra- and extraneuronal components in the fast spiking neuronal activity essential for the generation and maintenance of hippocampal theta rhythm.

Animals↗
PubMed1995

GABAA receptor subunits have differential distributions in the rat retina: in situ hybridization and immunohistochemistry.

The distributions of nine different subunits of the gamma-aminobutyric acidA (GABAA) receptor (alpha 1, alpha 2, alpha 3, alpha 5; beta 1, beta 2, beta 3; gamma 2; delta) were investigated in the rat retina using immunocytochemistry and in situ hybridization. With the exception of the alpha 5 subunit, all subunits could be localized. Each subunit was expressed in characteristic strata within the inner plexiform layer (IPL). Some subunits (e.g., gamma 2) showed a ubiquitous distribution, while others (e.g., delta) were restricted to narrow sublayers. Double labeling experiments using different combinations of the subunit-specific antibodies revealed colocalizations of subunits within individual neurons. Additionally, GABAA receptor subunits were mapped to distinct populations of retinal neurons by coapplication of defined immunocytochemical markers and subunit-specific antibodies. Cholinergic amacrine cells were found to express the alpha 2, beta 1, beta 2/3 and delta subunits, while dopaminergic amacrine cells express the alpha 2, alpha 3 and gamma 2 subunits. Dissociated rod bipolar cells express the alpha 1 and gamma 2 subunits. In summary, this study provides evidence for the existence of multiple GABAA receptor subtypes in the retina. The distinct stratification pattern of the subunits in the IPL suggests that different functional circuits involve specific subtypes of GABAA receptors.

Animals↗
PubMed1995

Heterogeneity of GABAA-receptors: cell-specific expression, pharmacology, and regulation.

Vigilance, anxiety, memory, epileptogenic activity and muscle tension can be regulated by a modulation of GABAA-receptor function. A multitude of different GABAA-receptors exist in the brain due to the combinational assembly of various subunits encoded by at least 15 genes. The clarification of the physiological and pharmacological significance of GABAA-receptor subtypes, in combination with their cellular localization, will make it possible to identify the neuronal circuits regulating the respective CNS states and to provide strategies for the development of subtype-specific drugs for selective therapies.

Animals↗
PubMed1995

Identification of distinct GABAA-receptor subtypes in cholinergic and parvalbumin-positive neurons of the rat and marmoset medial septum-diagonal band complex.

GABAA-receptor heterogeneity is based on a multiplicity of subunits (alpha 1-6, beta 1-4, gamma 1-4, delta, rho 1-2) encoded by distinct genes. Flexibility in GABAergic signal transduction and allosteric modulation is expected to arise from the differential assembly of subunits into receptor subtypes. The aim of the present study was to investigate the potential diversity of receptor subtypes expressed by defined neuron populations, as identified by their neurotransmitter phenotype. To this end we have determined immunohistochemically the subunit repertoire of cholinergic and GABAergic neurons in the basal forebrain of rat and marmoset monkey, focusing on the medial septum-diagonal band complex. Co-localization of the GABAA-receptor subunits alpha 1, alpha 3, beta 2, beta 3, and gamma 2 with markers of cholinergic and GABAergic neurons (choline acetyltransferase and parvalbumin, respectively) was assessed by double- and triple immunofluorescence staining. The results reveal that cholinergic neurons in the rat basal forebrain are typically characterized by the subunit combination alpha 3/beta 3/gamma 2, whereas most of the parvalbumin-positive GABAergic neurons express either the subunit combination alpha 1/beta 2/gamma 2 or the combination alpha 1/alpha 3/beta 2/gamma 2. A similar pattern was observed in marmoset monkey, with GABAA-receptors containing the alpha 1-subunit being associated with parvalbumin-positive cells, but never with cholinergic neurons. Thus, the expression of distinct subunit repertoires by cholinergic and GABAergic neurons points to a functional specialization which is conserved across species. These subunit combinations are likely to correspond to different receptor subtypes, and may reflect the engagement of cholinergic and GABAergic neurons in distinct neuronal circuits in the basal forebrain.

Animals↗