GABA-INDUCED SYNAPTIC FACILITATION AT TYPE-B TO TYPE-A PHOTORECEPTOR CONNECTIONS IN HERMISSENDA

Gamma-aminobutyric acid (GABA) is a prevalent neurotransmitter in both vertebrate and invertebrate systems. Here we report that, in addition to its usual inhibitory actions, GABA induced synaptic facilitation a t type B to A photoreceptor connections of the marine mollusk Hermisse nda when applied transiently to the isolated nervous system. Synaptic facilitation also occurred in response to mechanical stimulation of th e GABAergic hair cells, which are normally activated by rotational unc onditioned stimuli during behavioral training of the intact animal. Th is synaptic facilitation represents a novel form of GABA-induced neuro modulation which may contribute to learning-dependent suppression of p hototaxis in Hermissenda. (C) 1997 Elsevier Science Inc.