Antisense studies of brain GABAA receptors

gamma-Aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the brain. The GABAA receptor complex, which is assumed to have a pentamer structure assembled from different polypeptide subunits, contains the binding sites for several clinically important compounds, e.g., the benzodiazepines and the barbiturates. A dysfunction of GABAergic inhibitory neurotransmission mediated via the GABAA receptor has been hypothesised to be a central factor in the pathogenesis of epilepsy. Antisense technology is based on the possibility of selectively inhibiting gene expression at the level of messengerRNA (mRNA). An antisense oligodeoxy nucleotide (ODN), a short synthetic single-stranded DNA molecule, is believed to inhibit the biosynthesis of a particular protein via nucleotide specific hybridisation to the mRNA encoding the protein. Antisense ODNs are used as tools for the investigation of the physiological roles played by individual proteins. The aim of the present study was to investigate the feasibility of selectively inhibiting the expression of a major subunit of the GABAA receptor complex in the rat brain in vivo by means of antisense technology. The thesis describes the changes observed following intrahippocampal administration of antisense ODN targeted to the GABAA receptor gamma 2 subunit. This subunit is a constituent of the majority of GABAA receptor complexes in the brain. Biochemical, morphological, electroencephalographic and behavioural changes induced by the antisense ODN treatment are described. The results support the notion that the primary event induced by the antisense ODN is a specific down-regulation of the gamma 2 subunit protein and that this leads to a decrease in the number of functional GABAA receptors and a state of diminished hippocampal GABAergic inhibitory neurotransmission. Antisense ODN-treated rats spontaneously develop limbic status epilepticus; prolonged antisense ODN treatment results in severe neurodegenerative changes in the hippocampus. The results of the study support the hypothesis that the GABAA receptor is critically involved in epileptogenesis. The results are viewed as a contribution to the understanding of the GABAA receptor complex and of mechanisms of epileptic phenomena and neuronal cell death. The presented animal model is suggested as a pathophysiologically relevant model of temporal lobe epilepsy and limbic status epilepticus. The results may also be of value for the general characterisation of antisense technology as a neuroscientific tool.