Journal of Neuroscience, Vol 6, 1857-1865, Copyright © 1986 by Society for Neuroscience
Factors affecting release of 3H-dopamine from perfused carp retina
P O'Connor, SJ Dorison, KJ Watling and JE Dowling
The effects of putative retinal neurotransmitters and several neuropeptides
on 3H-dopamine release from isolated perfused carp (Cyprinus carpio)
retinas were studied. Of the transmitter candidates tested, only serotonin
(5-HT) and the 5-HT agonist tryptamine released 3H-dopamine. However, the
release evoked by these agents was calcium (Ca2+) independent and not
blockable by the 5-HT antagonist methysergide. We also investigated the
antagonism of inhibitory inputs as a potential regulatory mechanism for
dopamine release and found that the GABA antagonists, bicuculline and
picrotoxin, stimulated a dose- dependent release of 3H-dopamine. The
effects of the GABA antagonists were dependent on extracellular Ca2+ and
could be inhibited by perfusion of the retina with GABA. Bicuculline and
picrotoxin also stimulated an increase in cAMP accumulation, which was
inhibited by the dopamine antagonist haloperidol. Our results support the
hypothesis that the dopaminergic interplexiform cells of the teleost retina
are under GABAergic inhibitory control.