Charles, Kelly Jane; (2003) Characterisation of γ-aminobutyric acid B receptor subunits and related proteins in the rat central nervous system. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

Since its identification as the major inhibitory neurotransmitter in the central nervous system, γ-aminobutyric acid (GABA) and its receptors have been extensively studied. Thus far two distinct classes of GABA receptors have been identified. lonotropic GABAA/C receptors are ligand gated ion channels and metabotropic GABAB receptors are G-protein coupled. Functional GABAB receptors are composed of two obligate receptor subunits, GABAB1 and GABAB2. Several splice variants of GABAB1 have been indentified (GABAB1a-f), though none of the thus far identified splice variants exhibit unique pharmacologies. Subunit specific and splice variant specific antisera have been generated to probe the biochemistry and protein distribution of these receptor subunits. In this thesis I have utilised such antisera to study the comparative localisation of each receptor subunit throughout the rat central nervous system. These studies revealed that both obligate receptor subunits are expressed in the same regions in the brain, spinal cord and dorsal root ganglia. Co-localisation studies, using confocal microscopy, confirmed that the same neurons within the CA1 subregion of the hippocampus express both GABAB1 and GABAB2 receptor subunits. At the ultrastructural level I have demonstrated that both receptor subunits are expressed in both pre- and post-synaptic membranes in the CA1 subregion of the hippocampus. I have also used these antisera to study the expression of these GABAB receptor subunits in non-neuronal cells. Co-localisation studies revealed that both obligate subunits are expressed in native and cultured astrocytes, as well as in activated microglia in culture. GABAB receptor subunits were, however, absent from myelin forming cells in the white matter of the rat spinal cord. A novel putative GABAB receptor-like protein (GABABL) was recently identified by our group at GlaxoSmithKline. Using immunohistochemistry to map the distribution of GABABL in the rat central nervous system I have developed antisera to GABABL and shown that this protein is widely distributed in a manner similar to that of GABAB1/2. GABABL is also expressed in parvalbumin, calbinidin and calretinin positive interneurons within the hippocampus but was absent from astrocytes in this region.

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