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.

Differential distribution of GABAA receptor subunits in soma and processes of cerebellar granule cells: effects of maturation and a GABA agonist.

Quantitative analysis of the density of alpha 1 and beta 2/3 GABAA receptor subunits was performed at the electron microscope level after indirect pre-embedding immunogold labeling with subunit-specific antibodies of rat cerebellar granule cell cultures grown for 4 or 8 days and in the presence or absence of the GABAA receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4c]pyridin-3-ol (THIP). THIP (150 microM) induced a 2-fold increase in the number of alpha 1 and beta 2/3 subunits in both cell bodies and processes in 4-day-old cultures. Extending the culture period to 8 days led to a polarization of the receptor expression, since the increase in the number of subunits selectively was observed in the processes.

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.

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.

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.

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).

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.

Immunobiochemical characterization of the NMDA-receptor subunit NR1 in the developing and adult rat brain.

To investigate the developmental and regional expression of the NR1-subunit of the NMDA-receptor on the protein level, two polyclonal antisera [NR1(N) and NR1(C)] were raised against fusion proteins derived from the N- and C-terminal domain of the NR1-subunit, respectively. In Western blots of rat brain membranes, both antisera specifically recognized a single protein band with an apparent molecular size of 115 kDa. The regional distribution of the NR1-subunit immunoreactivity was analyzed in the developing and adult rat brain using sections blotted onto nitrocellulose membranes for immunostaining.

GABAA receptor alpha 1 subunit, an early marker for area specification in developing rat cerebral cortex.

Changes in the expression of neurotransmitter receptors in developing cerebral cortex may be related to the functional maturation of distinct areas. In the present study, we have tested whether GABAA receptor expression in neonatal rats reflects the differentiation of cortical areas. Specifically, the alpha 1 subunit, one of the most prevalent GABAA receptor subunits in adult cerebral cortex, is up-regulated postnatally, suggesting a link with the establishment of inhibitory circuits.

Distribution, prevalence, and drug binding profile of gamma-aminobutyric acid type A receptor subtypes differing in the beta-subunit variant.

Native gamma-aminobutyric acid type A (GABAA) receptors containing different beta-subunit variants were identified immunobiochemically with antisera recognizing selectively the beta 1-, beta 2-, or beta 3-subunit. As determined by immunoprecipitation, the beta 2-subunit was present in 55-60% of GABAA receptors, while only minor receptor populations contained the beta 1-subunit (16-18%) or the beta 3-subunit (19-25%). Since the sum of these values amounts to about 100%, it is concluded that GABAA receptors largely contain only a single type of beta-subunit.

Switch in the expression of rat GABAA-receptor subtypes during postnatal development: an immunohistochemical study.

The involvement of GABA in neuronal differentiation and maturation precedes its role as inhibitory neurotransmitter in the brain. It was therefore investigated whether GABAA receptors mediating the actions of GABA in neonatal and adult brain can be distinguished by their molecular structure and cellular location. Immunohistochemistry with subunit-specific antibodies was employed to analyze changes in the distribution of GABAA-receptor subunits during postnatal development.

Biphasic differential changes of GABAA receptor subunit mRNA levels in dentate gyrus granule cells following recurrent kindling-induced seizures.

GABAA receptor alpha 1, beta 3 and gamma 2 subunit mRNA levels have been measured in hippocampus using in situ hybridization, following 1, 10 and 40 seizures produced by rapid kindling stimulations. Major alterations of gene expression were largely confined to the dentate gyrus. One stimulus-induced seizure reduced gamma 2 mRNA levels in the dentate gyrus by 30%.

Developmental regulation of voltage-gated K+ channel and GABAA receptor expression in Bergmann glial cells.

Bergmann glial cells are closely associated with neurons: during development they provide guiding structures for migrating granule cells and in the adult cerebellum they display intimate interactions with Purkinje cells. In this study, we have addressed the question of whether such changes in neuronal-glial interactions during development are accompanied by variations in the membrane properties of Bergmann glial cells. We used a mouse cerebellum slice preparation to study membrane currents of the Bergmann glial cells at various stages of development in situ using the patch-clamp technique.

Selective allocation of GABAA receptors containing the alpha 1 subunit to neurochemically distinct subpopulations of rat hippocampal interneurons.

The identification of a large variety of GABAA receptor subunits by molecular cloning suggests the existence of multiple receptor subtypes differing in localization and functional properties. In the present study we analysed immunohistochemically the cellular distribution of GABAA receptors containing the alpha 1 subunit in the rat hippocampus with a subunit-specific antiserum. Prominent staining of numerous interneurons was evident in Ammon's horn and the dentate gyrus, which contrasted with moderate and diffuse immunoreactivity in the dendritic layers of pyramidal and granule cells.

Inhibitory neurotransmission in rat spinal cord: co-localization of glycine- and GABAA-receptors at GABAergic synaptic contacts demonstrated by triple immunofluorescence staining.

Synaptic inhibition in rat spinal cord is mediated by the amino acids gamma-aminobutyric acid (GABA) and glycine. Most spinal cord neurons respond to both neurotransmitters, suggesting co-expression of GABAA- and strychnine-sensitive glycine-receptors in individual cells. While the distribution of glycine-receptors has been extensively characterized, much less is known about the cellular localization of GABAA-receptors in spinal cord neurons.

Differential regulation of N-methyl-D-aspartate receptor subunit messenger RNAs in kindling-induced epileptogenesis.

N-methyl-D-aspartate-receptors are implicated in several neuropathological conditions including epilepsy. As a model of complex partial seizures, rapid hippocampal kindling was chosen to investigate changes in the expression of messenger RNAs encoding the N-methyl-D-aspartate-receptor subunits NR1, NR2A and NR2B both during and in the period immediately following the induction of the kindled state. The study demonstrates a cell-specific, time-dependent modulation of the N-methyl-D-aspartate-receptor subunit messenger RNAs almost entirely restricted to the granule cells of the dentate gyrus.

Neuron-specific expression of GABAA-receptor subtypes: differential association of the alpha 1- and alpha 3-subunits with serotonergic and GABAergic neurons.

GABAA-receptors in the brain display a striking structural heterogeneity, which is based on a multiplicity of diverse subunits. The allocation of GABAA-receptor subtypes to identified neurons is essential for an analysis of the functional significance of receptor heterogeneity. Among GABA-receptive neurons, well-characterized examples include the serotonergic and GABAergic neurons in the raphe nuclei.

GABAA-receptors: drug binding profile and distribution of receptors containing the alpha 2-subunit in situ.

The highest structural diversity of GABAA-receptor subunits is observed among members of the alpha-subunit class. Using subunit-specific antisera, the receptors containing the alpha 2-subunit were characterized. Western blots revealed an apparent molecular size of 52 kDa for the alpha 2-subunit.

Five subtypes of type A gamma-aminobutyric acid receptors identified in neurons by double and triple immunofluorescence staining with subunit-specific antibodies.

The extraordinary structural diversity of subunits forming type A gamma-aminobutyric acid (GABAA) receptors in the brain is expected to give rise to different modes of GABAergic synaptic inhibition and different profiles of modulatory drugs effective in anxiolytic, hypnotic, and antiepileptic therapy. To identify receptor subtypes in situ, the most prevalent subunits were visualized by double and triple immunofluorescence staining in rat brain, using polyclonal antibodies to the alpha 1, alpha 3, and gamma 2 subunits and a monoclonal antibody to locate both the beta 2 and the beta 3 subunit. At both cellular and subcellular levels five distinct patterns of subunit colocalization were identified: I, alpha 1 beta 2,3 gamma 2; II, alpha 3 beta 2,3 gamma 2; III, alpha 1 alpha 3 beta 2,3 gamma 2; IV, alpha 3 gamma 2; and V, alpha 1 alpha 3 gamma 2.

Restoration of ascending noradrenergic projections by residual locus coeruleus neurons: compensatory response to neurotoxin-induced cell death in the adult rat brain.

There is clinical and experimental evidence that monoamine neurons respond to lesions with a wide range of compensatory adaptations aimed at preserving their functional integrity. Neurotoxin-induced lesions are followed by increased synthesis and release of transmitter from residual monoamine fibers and by axonal sprouting. However, the fate of lesioned neurons after long survival periods remains largely unknown.

GABAA-receptor subtypes differing in alpha-subunit composition display unique pharmacological properties.

GABAA-receptor subtypes in rat brain were characterized using anti-peptide antisera specific for the alpha 1-, alpha 3- and alpha 5-subunits. While a high abundance of alpha 1-containing receptors was demonstrated by immunoprecipitation (80-90% of receptors), the receptors precipitated with the alpha 3- and the alpha 5-antiserum were less frequent (18-25% and 10-23%, respectively). The three receptor populations displayed unique pharmacological properties as shown by radioligand binding.

Differential effects of reserpine on brainstem catecholaminergic neurons revealed by Fos protein immunohistochemistry.

The effects of a single systemic injection of reserpine on c-fos proto-oncogene expression in catecholaminergic neurons of the rat brainstem were studied by immunohistochemistry for Fos proteins (Fos). In control rats, a few Fos immunoreactive neuronal nuclei were observed in the tectum and mesencephalic central gray. Within hours after drug injection, a substantial number of brainstem neurons stained intensely for Fos.

Experimentally-induced neuron loss in the locus coeruleus of adult rats.

Systemic administration of the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) to adult rats causes widespread degeneration of locus coeruleus (LC) axon terminals. The present study was conducted to determine the effects of DSP-4-induced LC axon lesions on LC cell bodies. Six months after DSP-4 treatment, quantitative analysis of Nissl-stained sections revealed a profound loss of LC perikarya, ranging from 20 to 73% of control.