BASIC ASPECTS OF GABA-TRANSMISSION IN ALCOHOLISM, WITH PARTICULAR REFERENCE TO GABA-TRANSAMINASE

Neuronal dysfunction is the neurobiological basis for alcoholic behavi our, and ethanol craving seems related to hypofunction of the GABA-erg ic activity. Gamma-aminobutyric acid (GABA) is the major inhibitory ne urotransmitter in the central nervous system (CNS). In several studies , GABA has been shown to be an important target of ethanol in the CNS, partly, as a consequence of damage to membrane-bound enzymes and rece ptors. GABA is involved in mediating pre- and post-synaptic inhibition of neuronal activity. It is speculated that the initial excitatory ef fects of ethanol may be due to inhibition of GABA-ergic activity where as the sedative effects of the higher doses may be mediated by the act ivation of this inhibitory system. In the CNS, GABA is synthesised fro m glutamic acid by the enzyme glutamate decarboxylase (GAD) and catabo lized into succinic semialdehyde by the enzyme GABA-transaminase (GABA -T), which are pyridoxal phosphate (PLP) dependent enzymes. Platelet G ABA-T was characterized as being similar to central GABA-T. Inhibition of GABA-T with certain potent and selective compounds markedly increa ses the levels of brain GABA. Experimentally, acute ethanol treatment does not alter GABA-T activity whereas chronic treatment produces an i ncrease in the activity, though, with some reservations since a bimoda l effect has been found in chronically ethanol-treated rats. Thus, as it will be discussed below, it may be suggested that GABA-T inhibitors (e.g. vigabatrin) could have a potential role in the treatment of alc oholism and in some of the problems of ethanol withdrawal and of other drugs of abuse. Related studies on metabolism and concentrations of G ABA are also promising and show a greater increase in our understandin g of the aetiology and treatment of ethanol dependence and withdrawal. In general, this article also reviews both the animal and clinical ob servations in the field of alcoholism with regard to the GABA system. (C) 1997 Elsevier Science B.V.