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 grafts could ameliorate performance of rats with fimbria-fornix lesions in an operant differential reinforcement of low rates of responding (DRL) task. Although the best recovery was demonstrated by the group in which the grafts were made 10 days following the lesion surgery, this factor (lesion-graft interval) was confounded with the developmental stage of the donor tissue, and it was suggested that the age of the embryonic donor was a more significant factor than the lesion graft interval in achieving good recovery. The present study provides a better control of embryonic age of the donor tissues, and we report that cholinergic rich septal grafts implanted into the host hippocampus either immediately or 11 days following fimbria-fornix lesion yielded better recovery than when the grafts were implanted after longer (8 weeks) lesion-graft intervals. In addition, grafts implanted into the intact hippocampus were without significant effect when the host rats were subjected to a delayed fimbria-fornix lesion made 10 weeks after graft implantation. These results corroborate the hypothesis of Nieto-Sampedro, Manthorpe and colleagues that 'wound-derived neurotrophic factors' can promote the functional viability of embryonic septal grafts in the hippocampus, even if such factors are not absolutely necessary for graft survival.