FUNCTIONAL CEREBRAL-ACTIVITY DURING REGENERATION FROM ENTORHINAL LESIONS IN THE RAT

The consequences of an unilateral electrolytic entorhinal lesion on th e functional activity in all major anatomically defined brain regions were evaluated in the rat. The C-14-2-deoxyglucose method served as a tool to quantify alterations of local cerebral glucose utilization (LC GU) ipsilateral and contralateral to the lesion at 4 days, 2 weeks, or 3 months after stereotaxic surgery. Apart from a few minor increases in the contralateral hemisphere, the predominant pattern consisted of reductions in the range of 10-40% in the ipsilateral hemisphere. Ipsil aterally, in extrahippocampal areas, LCGU had re gained control levels at 2 weeks postlesion in contrast to hippocampal regions, where reduc tions were more pronounced than in other brain areas and partially per sisted for up to 3 months. Interestingly, the termination zones of ent orhinal fibers in the dentate gyrus did not regain control levels with in 3 months. We conclude from the data that functional recovery of den ervated primary target areas does not occur within 3 months after ento rhinal lesions and that altered functional activity may be found beyon d the primary target areas predominantly during the acute recovery per iod after the lesion. The data suggest that sprouting fibers do not re establish a fully functional neuronal network during the recovery peri od.