Transmitters mediating inhibition of ganglion cells in the cat retina: iontophoretic studies in vivo.
The effects of iontophoretically applied gamma-aminobutyrate (GABA) and glycine and their antagonists, bicuculline and strychnine on inhibition of retinal ganglion cells were studied in the optically intact eye of anaesthetised cats. Two kinds of inhibition were studied. One is the inhibition which occurs when a spot (a white spot for on-centre and a black spot for off-centre cells) which produces a maximal response from a cell, is removed from the receptive field centre, i.e. the central post-excitatory inhibition. The other is the inhibition which occurs when an annulus (a white annulus for on-centre and a black annulus for off-centre cells) which occupies the surround region of the receptive field, is presented, i.e. the surround inhibition. GABA enhanced and bicuculline blocked the post-excitatory inhibition at the receptive field centre and surround inhibition of on-centre but not off-centre cells regardless of whether the cell was 'sustained' or 'transient' type. On the other hand, glycine enhanced and strychnine blocked the post-excitatory inhibition at the receptive field centre and surround inhibition of off-centre but not on-centre cells, regardless of whether the cell was 'sustained' or 'transient' type. Inhibition of on-centre cells, thus, appears to be mediated by GABA, whereas that of off-centre cells, by glycine regardless of whether the cells are 'sustained' or 'transient'. Possible existence of GABAergic and glycinergic amacrine cells making postsynaptic contact with on-centre and off-centre ganglion cells, respectively, is proposed. Other possible explanations are discussed.
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002415:Cats; D005998:Glycine / Q000494:pharmacology; D007478:Iontophoresis; D009433:Neural Inhibition / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000502:physiology*; D012160:Retina / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000502:physiology*; D013331:Strychnine / Q000494:pharmacology; D014794:Visual Fields / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018377:Neurotransmitter Agents; D005680:gamma-Aminobutyric Acid; D013331:Strychnine; D005998:Glycine; D001640:Bicuculline