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SELECTIVE IMPAIRMENT OF REVERSAL LEARNING BY TEMPORAL DELAYS IN RATS TREATED WITH TRIMETHYLTIN
Citation:
Bushnell, P. SELECTIVE IMPAIRMENT OF REVERSAL LEARNING BY TEMPORAL DELAYS IN RATS TREATED WITH TRIMETHYLTIN. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-90/424 (NTIS PB91171793).
Description:
Recent theories of hippocampal function focus on its role in the formation of associations in the temporal domain. eversal learning paradigm based on leverpress automaintenance vas developed to vary the CS-UCS relationship along two independent dimensions, one temporal and one not: S+-UCS delay and the robability of reinforcement [P(RFT] following the CS+. ight male hooded Long-Evans rats were trained to reverse these automaintained discriminations repeatedly, until stable reversal performance was achieved. he neurotoxicant trimethyltin (TMT) was used to induce lesions in the CNS, including the CA3-4 region of Ammon's Horn in dorsal hippocampus. ollowing iv injection of 7 mg/kg TMT to half the rats, reversal performance was assessed under varying conditions of delay and P(RFT). fter recovery from the acute effects of TMT (1-2 weeks), treated rats reversed normally when no delay separated the CS+ and UCS; with delays of 2 to 4 sec, they reversed less completely within a session than did controls. Changing P(RFT) did not differentially affect the performance of the treated rats. orphological damage was quantified by measuring the length of the remaining pyramidal cell line in sections of dorsal hippocampus. he degree of behavioral impairment correlated significantly with hippocampal damage only at nonzero CS+-UCS delays. hese results indicate that TMT impaired rats' ability to integrate temporal, but not probabilistic, relationships between stimulus events, and are consistent with theories of hippocampal mediation of temporal associations.