EVIDENCE FOR RECOVERY OF SPATIAL-LEARNING FOLLOWING ENTORHINAL CORTEXLESIONS IN MICE

The influence of entorhinal cortex lesions on behaviour and concommita nt changes in synaptophysin immunoreactivity (IR) in the denervated de ntate gyrus was assessed. Male, C57/B6 mice received either bilateral (BI), unilateral (UNI), or no lesion (SHAM) to the entorhinal cortex. At various stages post-lesion the animals were evaluated in tests to e xamine neurological and cognitive (spatial and cued learning, Morris w ater maze) function. UNI lesioned animals from 6-36 days post-lesion s howed no neurological nor marked cued learning deficit, yet a profound spatial learning deficit. However by 70 days post-lesion, spatial lea rning ability was clearly evident. In contrast, BI lesioned animals sh owed severe spatial learning deficits throughout the test period (6-70 days), cued learning was also impaired. In parallel groups of UNI les ioned mice, 6-36 days post-lesion there was a marked reduction (- 40%) in synaptophysin IR in the dentate gyrus molecular layer. However by 70 days post-lesion a clear increase in this measure was noted. Change s in the expression of the growth associated protein, GAP43, were also noted over this period. Taken together, the present results suggest s ome recovery of spatial learning following unilateral entorhinal corte x lesions in mice. This behavioural recovery of a hippocampally depend ant task may be associated with a recovery of function related to the synaptic remodelling and elevation of synapse number in the denervated hippocampus, as evidenced by changes in synaptophysin and GAP43 IR.