Optical responses to micro-application of GABA agonists in the embryonic chick brain stem

We investigated optical responses induced by micro-application of muscimol and baclofen in the embryonic chick brain stem. Muscimol evoked biphasic op tical signals which were similar to those induced by GABA. The first compon ent was a dye-dependent absorption change that reflected membrane depolariz ation, and the second component was an intrinsic optical change coupled wit h changes in the membrane potential. On the other hand, baclofen did not el icit any optical change. The optical responses induced by muscimol persiste d in the presence of picrotoxin and 2-hydroxysaclofen, suggesting that they contain a component which is not mediated by classical GABA receptors. Neu roReport 12:95-98 (C) 2001 Lippincott Williams & Wilkins.