Kainic acid neurotoxicity does not depend on intact retinal input in the goldfish optic tectum

Abstract

Kainic acid neurotoxicity has been studied in the optic tectum of the goldfish 4 eeks after eye enucleation. The effect of drug treatment has been tested with respect to both neurochemical and morphological parameters. The neurotransmitter-related enzymes, choline acetyltransferase, acetylcholinesterase and glutamate decar☐ylase, show about 50% decrease in the deafferentated tectum 6 days after kainic acid administration. Relevant morphological alterations of the tectal structure can also be noticed at the same stage. The neurotoxic effects of kainic acid in the deafferentated optic tectum are therefore quite similar to the effects previously noticed for the intact optic tectum of normal fish. Control experiments on the effect of optic nerve degeneration by itself on the levels of the neurotransmitter-related enzymes in the optic tectum, have shown no significant decrease in glutamate decar☐ylase, a slight decrease in acetylcholinesterase and a more marked drop in choline acetyltransferase. The findings are discussed with reference to some of the hypotheses advanced in order to explain kainic acid neurotoxicity. It is proposed that the neurotoxic effect of kainic acid after removal of specific excitatory afferents, may vary in differrent nervous centers depending on differences of the remaining extrinsic connections and of the intrinsic neural circuits.