FIMBRIA-FORNIX VS SELECTIVE HIPPOCAMPAL-LESIONS IN RATS - EFFECTS ON LOCOMOTOR-ACTIVITY AND SPATIAL-LEARNING AND MEMORY

The behavioral effects of interrupting the axons that pass in the fimb ria and dorsal fornix were compared with the effects of selective remo val of the cells that comprise the hippocampus with ibotenic acid. Sta rting 4.5 months after surgery, lesioned and control rats were (i) tra ined in both the Morris water maze and the eight-arm radial maze using protocols that placed an emphasis on either working memory (WM) or re ference memory (RM) and (ii) tested for locomotor activity in the home cage. In comparison to sham-operated rats, the rats fi om both lesion groups were impaired in most learning/memory tasks, but there were so me interesting differences between the two lesioned groups. When compa red to rats with fimbria-fornix lesions (FIFX rats) hippocampal rats ( HIPP rats) were slower in learning to swim to a visible platform and s howed a greater impairment than FIFX rats in the radial-maze task when the testing procedure required the utilization of RM and WM in a more demanding WM task. In the test of locomotor activity, FIFX and contro l rats did not differ, but HIPP rats were more active than the rats in both other groups. The pattern of results obtained after a 4.5-month recovery period support the following general conclusions. (1) While t here are some similarities in the effects on behavior of interrupting the axons in the fimbria-fornix compared to removing the hippocampus, there are some important differences. (2) From the findings that are a vailable, a possible explanation to account for the difference between FIFX and HIPP rats is that the 4.5-month survival time permitted some recovery in the group of rats with FIFX lesions. (3) While it is well known that the Morris water maze and the radial-arm maze tasks provid e useful measures of spatial learning and memory processes, our result s suggest that the information provided by the two spatial learning ta sks may differ in important respects. (C) 1998 Academic Press.