GABA signalling during development: new data and old questions

In addition to being the major inhibitory neurotransmitter, gamma -aminobut yric acid (GABA) is thought to play a morphogenetic role in embryonic devel opment. During the last decade, considerable progress has been made in eluc idating the molecular mechanisms involved in GABA synthesis and biological action. The present review is an attempt to summarise recent results on the ontogeny of the different components of embryonic GABA signalling with an emphasis on the synthesis of GABA by different molecular forms of glutamic acid decarboxylase (GAD).