GABAA receptor β2 and β3 subunits mRNA in the hippocampal formation of aged human brain with Alzheimer-related neuropathology (original) (raw)
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Aging-related subunit expression changes of the GABA(A) receptor in the rat hippocampus
1996
Aging-related changes in the subunit expression of some hippocampal GABA A receptors have been found. Quantitative in situ hybridization has revealed that 1 subunit messenger RNA expression was significantly increased in the hippocampus (34%) of old rats. The largest increases were observed in the dentate gyrus (76%) and in the CA1 field (30%). Quantitative immunocytochemistry also showed increased protein expression of the 1 subunit in the dentate gyrus (19%) and CA1 (14%) of old rats. The increased 1 messenger RNA and protein expression led to increased proportions of assembled GABA A receptors that contained 1 subunits, as revealed by quantitative immunoprecipitation of ( 3 H)flunitrazepam and ( 3 H)muscimol binding. In contrast, there were no significant changes in the expression of 2 , 3 and total 2 ( 2S + 2L ) subunits, although a slightly increased expression of 2L peptide was detected in the hippocampus proper (7%), but not in the dentate gyrus.
Brain Pathology
The hippocampus plays key roles in learning and memory and is a main target of Alzheimer's disease (AD), which causes progressive memory impairments. Despite numerous investigations about the processes required for the normal hippocampal functions, the neurotransmitter receptors involved in the synaptic deficits by which AD disables the hippocampus are not yet characterized. By combining histoblots, western blots, immunohistochemistry and high-resolution immunoelectron microscopic methods for GABA B receptors, this study provides a quantitative description of the expression and the subcellular localization of GABA B1 in the hippocampus in a mouse model of AD at 1, 6 and 12 months of age. Western blots and histoblots showed that the total amount of protein and the laminar expression pattern of GABA B1 were similar in APP/PS1 mice and in age-matched wild-type mice. In contrast, immunoelectron microscopic techniques showed that the subcellular localization of GABA B1 subunit did not change significantly in APP/PS1 mice at 1 month of age, was significantly reduced in the stratum lacunosum-moleculare of CA1 pyramidal cells at 6 months of age and significantly reduced at the membrane surface of CA1 pyramidal cells at 12 months of age. This reduction of plasma membrane GABA B1 was paralleled by a significant increase of the subunit at the intracellular sites. We further observed a decrease of membrane-targeted GABA B receptors in axon terminals contacting CA1 pyramidal cells. Our data demonstrate compartment-and age-dependent reduction of plasma membrane-targeted GABA B receptors in the CA1 region of the hippocampus, suggesting that this decrease might be enough to alter the GABA B-mediated synaptic transmission taking place in AD.
International Journal of Molecular Sciences
Metabotropic γ-aminobutyric acid (GABAB) receptors contribute to the control of network activity and information processing in hippocampal circuits by regulating neuronal excitability and synaptic transmission. The dysfunction in the dentate gyrus (DG) has been implicated in Alzheimer´s disease (AD). Given the involvement of GABAB receptors in AD, to determine their subcellular localisation and possible alteration in granule cells of the DG in a mouse model of AD at 12 months of age, we used high-resolution immunoelectron microscopic analysis. Immunohistochemistry at the light microscopic level showed that the regional and cellular expression pattern of GABAB1 was similar in an AD model mouse expressing mutated human amyloid precursor protein and presenilin1 (APP/PS1) and in age-matched wild type mice. High-resolution immunoelectron microscopy revealed a distance-dependent gradient of immunolabelling for GABAB receptors, increasing from proximal to distal dendrites in both wild type...
GABA A receptor subunit expression changes in the rat cerebellum and cerebral cortex during aging
Molecular Brain Research, 1997
Ž . Significant aging-related decreased expression of various GABA R subunit mRNAs a , g , b , b and d was found in both A 1 2 2 3 cerebellum and cerebral cortex using quantitative dot blot and in situ hybridization techniques. Contrary to the other subunits, the a 6 mRNA expression was significantly increased in the aged cerebellum. Parallel age-related changes in protein expression for g and b 2 2 r 3 Ž . Ž . decrease and a increase were revealed in cerebellum by quantitative immunocytochemistry. However, no significant changes in a 6 1 w 3 x protein expression nor in the number or affinity of H zolpidem binding sites were detected in cerebellum even though a mRNA 1 expression was significantly decreased in the aged rat. Age-related increased expression of a mRNA and protein in the cerebellum was 6 w 3 x accompanied by no significant changes in the number of diazepam-insensitive H Ro15-4513 binding sites. In the cerebral cortex, no Ž . changes in the protein expression of the main GABA receptor subunits a , g and b
Neuroscience, 2003
The aim of this study was to investigate the mRNA expression of the two GABA(B1) receptor isoforms and the GABA(B2) subunit, in human postmortem control hippocampal sections and in sections resected from epilepsy patients using quantitative in situ hybridisation autoradiography. Utilising human control hippocampal sections it was shown that the oligonucleotides employed were specific to the receptor. Hippocampal slices from surgical specimens obtained from patients with hippocampal sclerosis and temporal lobe epilepsy were compared with neurologically normal postmortem control subjects for neuropathology and GABA(B) mRNA expression. Neuronal loss was observed in most of the hippocampal subregions, but in the subiculum no significant difference was detected. The localisation of GABA(B1a) and GABA(B1b) isoform mRNAs in human control hippocampal sections supported and extended earlier studies using the GABA(B1) pan probe, which does not distinguish between the two GABA(B1) isoforms. Mo...
Time dependent loss of tissue GABA content and immunoreactivity in hippocampal slices
Brain Research Bulletin, 1991
BRAIN RES BULL 26(4) 559-564. 1991.-1mmunohistochemical detection of GABA was used to evaluate changes of the GABA innervation in hippocampal slices maintained in vitro. In parallel experiments the amount of GABA, glutamate and aspartate was measured with high performance liquid chromatography. The results showed that while glutamate and aspartate levels remained fairly constant, GABAergic neurons suffered remarkable alterations. During 8 hours' incubation the GABA content of the tissue and the number of GABA containing neuronal cell bodies decreased by 79.7% and 84.6%. respectively. The qualitative features of the immunoreactivity of the neuropil did not change. In conclusion, while in hippocampal slices tissue glutamate and aspartate levels are only slightly affected by the in vitro maintenance, more than half of the tissue GABA content is lost during prolonged in vitro incubation. As a consequence of the GABA loss, the ratio of endogenous inhibitory and excitatory amino acid transmitters has been altered. which could influence the viability of adult hippocampal tissue in in vitro conditions.
Neuropharmacology, 1999
Immunocytochemical and autoradiographic methods were used to localize the GABA B receptor in the normal rat hippocampus. GABA B receptor 1-like immunoreactivity (GBR1-LI) was most intense in presumed GABAergic interneurons of all hippocampal subregions. It was also present throughout the hippocampal neuropil, where it was most intense in the dendritic strata of the dentate gyrus, which are innervated by the perforant pathway and inhibitory dentate hilar cells, and in strata oriens and radiatum of area CA3. The dendritic regions of area CA1 exhibited less GBR1-LI than area CA3. GBR1-LI was detectable in the somata of CA1 pyramidal cells, but was minimal or undetectable within the somata of dentate granule cells and CA3 pyramidal cells. GBR1-LI was similarly minimal in the dentate hilar neuropil, and in stratum lucidum, the two regions that contain granule cell axons and terminals. Nor was GBR1-LI detectable in the inhibitory basket cell fiber systems that surround hippocampal principal cell somata. Fluorescence co-localization studies indicated that significant proportions of interneurons expressing somatostatin, neuropeptide Y, cholecystokinin, calbindin, or calretinin also expressed GBR1-LI constitutively. Conversely, parvalbumin-positive GABAergic basket cells of the dentate gyrus and hippocampus, which form GABA A receptor-mediated inhibitory axo-somatic synapses, rarely contained detectable GBR1-LI. High resolution autoradiography with the GABA B receptor antagonist CGP 62349 revealed a close correspondence between receptor ligand binding and GBR1-LI, with several notable exceptions. Ligand binding closely matched GBR1-LI throughout the hippocampal, cortical, thalamic, and cerebellar neuropil. However, the hippocampal interneuron somata and dendrites that exhibited the most intense GBR1-LI, and the GBR1-positive somata of CA1 pyramidal cells, did not exhibit a similar density of [ 3 H]-CGP 62349 binding. These data clarify the relationship between immunocytochemically identified receptor protein and potentially functional receptors, indicating that GBR1-LI reflects both non-functional cytoplasmic GBR1 and the ligand-bindable form of the protein, both before dimerization with GBR2 and after translocation to functional sites within cells. The staining and binding patterns further suggest that GBR1 is constitutively expressed in specific neuronal populations, and may exist in higher concentration in the axons of inhibitory hippocampal pathways that innervate dendritic zones, than in axo-somatic inhibitory terminals. Whether GBR1 is inducible in cells that contain GBR1 mRNA, but no detectable constitutive protein, remains to be determined in experimental studies.
Neuroscience Letters, 2011
A bicuculline-resistant and TPMPA-sensitive GABAergic component was identified in hippocampal neurons in culture and in acute isolated brain slices. In both preparations, total GABAergic activity showed two inactivation kinetics: fast and slow. RT-PCR, in situ hybridization (ISH) and immunohistochemistry detected expression of GABA subunits. Immunogold and electron microscopy indicated that the receptors are mostly extrasynaptic. In addition, by RT-PCR and immunofluorescence we found GABA present in amygdala and visual cortex.