[Gamma-aminobutyric acid and glutamate decarboxylase].

Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the CNS, taking part in processes which are now relatively well understood but also in processes which are remarkable progress has been achieved. The most thoroughly studied field of GABA operation is its role of inhibitory neurotransmitter realized through the mediation of GABA-A and GABA-B receptors. There are at least 40 per cent of synaptic inhibitory events in the CNS in which the neurotransmitter action of GABA is involved. The action of GABA on GABA-A receptor, a Cl- channel, is influenced by benzodiazepines, barbiturates and other substances, suggesting that some neurological and psychiatric diseases are connected with the function of GABA-A receptor. In addition to synaptic inhibition, GABA has several metabolic regulatory functions. GABA is produced not only in neurons but also in beta cells of the pancreas and in tubular cells of the kidney cortex. Its role in these parenchymatous cells is not sufficiently understood. Similarly as GABA, glutamic acid decarboxylase (GAD), an enzyme catalysing GABA formation from glutamate, has also been intensively studied. GAD structure, its function in various parts of the CNS and in some parenchymatous cells, and the regulation of GAD activity are still in the focus of interest. Recently GAD has been demonstrated to act as autoantigen in the rare neurological disease "stiff man syndrome" (SMS) and in insulin-dependent diabetes mellitus (IDDM). In the presented paper a short review of GABA functions, GAD properties and of the antigenic feature of GAD are given. (Fig. 7, Ref. 41.)