SEPTAL GRAFTS IMPROVE ACQUISITION OF AN OPERANT TIMING TASK AFTER FIMBRIA-FORNIX LESIONS IN RATS - ROLE OF THE INTERVAL BETWEEN LESION AND TRANSPLANTATION SURGERIES

In a previous study we evaluated the conditions under which septal gra fts could ameliorate performance of rats with fimbria-fornix lesions i n an operant differential reinforcement of low rates of responding (DR L) task. Although the best recovery was demonstrated by the group in w hich the grafts were made 10 days following the lesion surgery, this f actor (lesion-graft interval) was confounded with the developmental st age of the donor tissue, and it was suggested that the age of the embr yonic donor was a more significant factor than the lesion graft interv al in achieving good recovery. The present study provides a better con trol of embryonic age of the donor tissues, and we report that choline rgic rich septal grafts implanted into the host hippocampus either imm ediately or 11 days following fimbria-fornix lesion yielded better rec overy than when the grafts were implanted after longer (8 weeks) lesio n-graft intervals. In addition, grafts implanted into the intact hippo campus were without significant effect when the host rats were subject ed to a delayed fimbria-fornix lesion made 10 weeks after graft implan tation. These results corroborate the hypothesis of Nieto-Sampedro, Ma nthorpe and colleagues that 'wound-derived neurotrophic factors' can p romote the functional viability of embryonic septal grafts in the hipp ocampus, even if such factors are not absolutely necessary for graft s urvival.