Neurotoxic action of kainic acid in the isolated toad and goldfish retina: I. Description of effects

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Abstract
The neurotoxic action of kainic acid (KA) was investigated by histological methods in the isolated retina of toads and goldfish. Particular attention was paid to the earliest and most sensitive response to KA in the outer plexiform layer (OPL). KA caused vacuolization of proximal and distal segments of horizontal cell dendrites in the OPL as well as perikaryal vacuolization and/or chromatin clumping in selected classes of neurons in the inner nuclear layer. Further, KA caused vacuolization and swelling in the inner plexiform layer. These effects were very similar in the retinae of goldfish and toad. The extent of vacuolization in the OPL was graded with KA concentration and with length of incubation. For 15‐minute incubations, half‐maximal vacuolization was found at 10–20 μM KA. At 25 μM KA, OPL vacuolization was evident within 1–2 minutes of application of KA. In goldfish, but not in toad, rod‐connecting dendrites were less sensitive to KA than cone‐connecting dendrites.