The aim of the present study was to give insight into the mechanisms of action of ethanol on the function of retinal ON and OFF channels. In order to fulfill this aim the effects of ethanol on the electroretinographic (ERG) ON (b-wave) and OFF (d-wave) responses were investigated in intact frog eyecups and in eyecups, where the activity of proximal retinal neurons was blocked by 1 mM N-methyl-D-aspartate (NMDA). Ethanol at all concentrations tested (0.25%, 0.5% and 1%) increased the b-wave amplitude and diminished the d-wave amplitude in the intact eyecups. The time characteristics of the d-wave, but not the b-wave were slowed. Perfusion with NMDA alone also caused significant enhancement of the b-wave amplitude and diminution of the d-wave amplitude. When ethanol was applied in combination with NMDA, its effects on both the b- and d-waves were fully preserved. The results obtained indicate that ethanol effects on the amplitude and time course of the ERG b- and d-waves are due to its action in the distal frog retina. A hypothesis is presented that the opposite effects of ethanol on the b- and d-wave amplitude are due to one and the same mechanism-inhibition of the ionotropic non-NMDA glutamate receptors in retinal horizontal and OFF bipolar cells.
Keywords: Ethanol, electroretinogram, retina, NMDA