[Effects of neurotransmitters and blockers on electroretinogram c-wave and light peak of the chick]

Effects of neurotransmitters (GABA, glycine) and their antagonists (picrotoxin, strychnine) on retinal potentials were investigated in the chick. Electroretinogram (ERG) c-wave and light peak of the standing potential of the retina were recorded from the eyes of anesthetized chicks by a standard method of direct current recording after intravitreal injection of various concentrations of GABA, glycine, picrotoxin and/or strychnine. The amplitude of the c-wave was measured at 2 and 5 sec after onset of the light stimulus, using as indices the fast-rise c-wave (cF-wave) and the slow-rise c-wave (cs-wave), respectively. GABA (10(-6)M) and glycine (10(-5)M) enhanced the amplitude of the c-wave but maintained normal waveform. Picrotoxin (3mM) reversed the polarity of the cs-wave from positive to negative, whereas the cF-wave maintained normal polarity. An injection of strychnine (10mM) alone depressed the c-wave amplitude but did not change the waveform. The amplitude of the light peak of the retinal standing potential increased by administration of GABA or glycine, whereas it decreased with picrotoxin or strychnine. Post d-trough and post d-peak were enlarged by picrotoxin, while they were suppressed by strychnine. The results suggest that GABA and glycine are possibly related to generation of the c-wave and the light peak.