In vivo effects of glycine on retinal ultrastructure and averaged electroretinogram

Glycine, when injected intravitreally, has an inhibitory action on the electroretinogram (ERG) of the rabbit resulting in a transient loss of the oscillatory potentials of the b-wave. This inhibitory action is reversible within 24 h after glycine injection. In autoradiographs, after [3H] glycine administration, the radioactive label is mainly found over the inner nuclear layer (INL) and inner plexiform layer (IPL) without predilection of specific cell types and/or synapses. Electron microscopy reveals cytopathological changes in amacrine cells, in particular their cell membranes. These changes are conspicuous especially 1-2 h after the injection and the cells become normal again within 24 h. It is concluded that glycine has an inhibitory action upon the rabbit ERG in vivo. This action, on the basis of our morphological observations under our experimental conditions, may be due to an overall somatic membrane action rather than to an action as inhibitory neurotransmitter at the synaptic level. The reversible cellular lesions of amacrine cells after glycine administration with a concomitant, transient loss of oscillatory potentials (OP) supports the hypothesis that the cellular origin of OP is situated in amacrine cells.