DISSOCIATION OF SPATIAL REFERENCE MEMORY, SPATIAL WORKING-MEMORY, ANDHIPPOCAMPAL MOSSY FIBER DISTRIBUTION IN 2 RAT STRAINS DIFFERING IN EMOTIONALITY

Rats of the inbred strains DA/Han and BDE/Han were compared on two com plex spatial learning tasks, a spatial reference memory task in a 16-u nit multiple T-maze and a spatial working memory task in an eight-arm radial-maze. In addition, sizes of hippocampal messy fiber terminal fi elds were measured. BDE rats showed marked superiority in multiple T-m aze learning whereas DA rats outperformed BDE rats on the radial-maze task. DA rats had significantly larger intra-and infrapyramidal messy fiber terminal fields (IIP-MF). This is consistent with findings from other studies suggesting that large IIP-MF are related to excellent sp atial radial-maze learning, but it also indicates that size of IIP-MF is correlated with processing of a specific type of spatial informatio n rather than with overall spatial abilities. BDE rats had more extend ed suprapyramidal messy fiber projections (SP-MF) and a larger hilus. Rats of both strains differed in exploratory behaviour and emotionalit y: DA rats revealed little freezing and had a high rearing activity, w hereas BDE rats showed frequent freezing and reared rarely. Results su ggest that IIP-MF are involved with flexible expression of memory, upd ating environmental information and parallel processing whereas SP-MF might be linked to processing of familiar information. Presumably, emo tional factors contribute to performance differences. (C) 1997 Elsevie r Science B.V.