Kainic acid-induced denervation supersensitivity of nicotinic, cholinergic receptors in ganglion cells of the rat retina.

The rat retina contains both nicotinic and muscarinic cholinergic receptor sites as demonstrated by specific, high affinity binding of the nicotinic ligand, [3H]-alpha-bungarotoxin, and the muscarinic ligand, [3H]-quinuclidinyl benzylate. Seven days after an intraocular injection of 5 nmol of kainic acid, nicotinic binding was increased three-fold. We suggest that nicotinic sites may be located on ganglion cells because previous studies have shown that many ganglion cells are spared after kainic acid treatment and in fact, have an increased physiological response to ACh under these conditions. The increase in nicotinic sites may reflect a supersensitivity response to the loss of acetylcholine input after the kainic acid lesion. In contrast, muscarinic binding was decreased by 70% after kainic acid treatment. These data suggest that muscarinic sites are located on amacrine cells since these cells are destroyed by kainic acid treatment and some are known to be cholino-receptive. Some of the retinal muscarinic sites may function as inhibitory autoreceptors which regulate acetylcholine release from cholinergic amacrine cells.