EFFECTS OF GAMMA-AMINOBUTYRIC-ACID (GABA) ON SYNAPTOGENESIS AND SYNAPTIC FUNCTION

The correct establishment and function of synapses depend on a variety of factors, such as guidance of pre- and postsynaptic neurons as well as receptor development and localization. gamma-Aminobutyric acid (GA BA) has a pronounced effect on these events and elicits differentiatio n of neurons; that is, GABA acts as a trophic signal. Accordingly, act ivating preexisting GABA receptors, a trophic GABA signal enhances the growth rate of neuronal processes, facilitates synapse formation, and promotes synthesis of specific proteins. Transcription and de novo sy nthesis are initiated by the GABA signal, but the intracellular link b etween GABA receptor activation and DNA transcription is largely unkno wn. GABA also controls the induction and development of functionally a nd pharmacologically different GABA(A) receptor subtypes. The induced receptors are likely to be inserted only into the synaptic membrane do main. However, this ability to target the induced GABA(A) receptors is probably coupled to the maturation of neurons and not to the action o f GABA per se. The induced GABA(A) receptors apparently mediate a pron ounced inhibition of neurotransmitter release, whereas other subtypes of GABA(A) receptors may be modulatory rather than inhibitory.