Microinjection of GABA-A agonist muscimol into the dorsal but not the ventral hippocampus impairs non-mnemonic measures of delayed non-matching-to-position performance in rats.

Anatomical studies of afferent and efferent connections suggest that the hippocampus may have more than one information processing role that varies along the septo-hippocampal axis. The present study was conducted to test whether a distinct functional specialization for the dorsal versus ventral extents of the hippocampus could be detected. The effects of a GABA-A receptor agonist, muscimol, microinjected into either the dorsal or ventral hippocampus on an operant, spatial delayed non-matching-to-position (DNMTP) task were measured. A decrease in the number of trials completed per session and disruption of several DNMTP discrimination parameters were produced by muscimol microinjection into the dorsal hippocampus but not into the ventral hippocampus. Muscimol injected into either site did not impair the measure of working memory, delayed choice accuracy. These results are consistent with the view that hippocampal function varies along the septo-temporal axis, and that the dorsal hippocampus is relatively more critical to visual discrimination performance than the ventral hippocampus. Copyright 1998 Elsevier Science B.V.