Functional transmitters at retinal ganglion cells in the cat

The effects of iontophoretically applied putative neurotransmitters and their antagonists on the responses of retinal ganglion cells were studied in the optically intact eye of anaesthetized cats. L-aspartate enhanced and a N-methyl-D-aspartate receptor blocker, 2-amino-5-phosphonovalerate, blocked visual excitations of "sustained" cells, whereas acetylcholine enhanced, and the nicotinic receptor blocker, dihydro-beta-erythroidine, blocked those of "transient" cells. GABA enhanced and bicuculline blocked inhibitions of on-centre cells, but glycine enhanced and strychnine blocked those of off-centre cells, whether the cells were "sustained" or "transient". The possibility that: (A) aspartate may be an excitatory transmitter at both "on-" and "off-sustained" cells and acetylcholine, at both "on-" and "off-transient" cells; (B) GABA may be an inhibitory transmitter for on-centre, and glycine, for off-centre cells, is discussed.