Radial maze performance in inbred mice: Evidence for strain-dependent neural nets subserving spatial learning abilities

Abstract

C57BL/6 (C57) and DBA/2 (DBA) inbred mice perform differently on spatial tasks, with C57 mice doing better than DBA ones. Previous results have shown that hippocampal lesions impair performance in a radial eight-arm maze in both strains, while amygdaloid and frontal-cortex lesions have a deleterious effect only in the “high-learner” C57 strain. The high spatial-learning abilities of C57 mice seem, therefore, to be based upon a neural net recruiting distinct brain areas. The aim of the present study was to examine whether the genotype-dependent involvement of brain structures remains the same in radial-maze tasks with procedures that reduce or abolish interstrain performance differences. C57 and DBA mice with hippocampal, amygdaloid, or sham lesions were tested in a spatial (Experiment 1) or a visually cued (Experiment 2) version of the 4-baited-arm task using a radial 8-arm maze. No interstrain difference in baseline performance was observed in the two tasks. In the spatial discrimination task, hippocampal lesions impaired performance in both strains, while amygdaloid lesions had a selective deleterious effect on reentry into baited arms in the C57 strain only. Hippocampal but not amygdaloid lesions impaired performance on the visual discrimination task in both strains. Spatial, but not visual, discriminative learning seems, therefore, to involve a different circuitry according to the strain considered. The question of whether the areas recruited for each circuit cooperate by processing distinct but complementary memory attributes or whether they are simply vicariant may have strong implications for studies concerning functional recovery.