Electrophysiologic evidence that retinotectal synaptic transmission in the goldfish is nicotinic cholinergic.
A previous study identified, by conduction velocity following optic nerve shock, 3 classes of retinal fibers which project to 3 distinct laminae of the goldfish optic tectum. In the present study, the effect of various pharmacological agents on the synaptic efficacy of each of the 3 classes of retinal fibers was assessed by the use of current source-density analysis. All 3 classes of optic fibers appear to be nicotinic cholinergic. Six different nicotinic antagonists were tested. All 6 were effective in decrementing the responses of all 3 classes to a criterion level: alpha-bungarotoxin (10-8 M), alloferin (10-5 M), curare (10-4 M), metocurine (10-4 M), hexamethonium (10-4 M) and gallamine (10-3 M). Atropine, a muscarinic antagonist, had only a slight effect even at 10-3 M. Five nicotinic agonists tested also decremented synaptic responses: nicotine (10-5 M), carbamylcholine (10-4 M), acetylcholine (10-4 M), succinyl choline (10-4 M) and decamethonium (10-3 M), presumably via cellular depolarization and receptor desensitization. Two inhibitors of acetylcholinesterase prolonged the response at 10-4 M and decremented it as well at 10-3 M. Hemicholinium 3, an inhibitor of the high affinity uptake of choline, produced a gradual activity-dependent decrement in the responses. Beta-bungarotoxin, a presynaptically-acting toxin, abolished not only the postsynaptic components but also the presynaptic components at 10-6 M. In all other cases the presynaptic deflections were generally unaffected, and with the exception of the toxins, a return to at least 90% of the control value was achieved. In contrast, GABA (10-3 M) and bicuculine (10-4 M) both produced no discernible effect on the 3 classes of responses, and glutamate (10-3 M) produced only a slight decrement, which probably represents a non-specific effect.
D000818:Animals; D005071:Evoked Potentials / Q000187:drug effects; D006054:Goldfish; D009900:Optic Nerve / Q000502:physiology; D010276:Parasympatholytics / Q000494:pharmacology; D010277:Parasympathomimetics / Q000494:pharmacology; D011950:Receptors, Cholinergic / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D013477:Superior Colliculi / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects; D014795:Visual Pathways / Q000187:drug effects / Q000502:physiology
D010276:Parasympatholytics; D010277:Parasympathomimetics; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic