THE EFFECTS OF INTRAHIPPOCAMPAL GRAFTS, TRAINING, AND POSTOPERATIVE HOUSING ON BEHAVIORAL RECOVERY AFTER SEPTOHIPPOCAMPAL DAMAGE IN THE RAT

This study examined whether the expression of behavioral effects of gr afts rich in cholinergic neurons placed into the hippocampus of rats w ith septohippocampal damage may be modulated by postoperative housing or training conditions. Among 91 Long-Evans female rats, 61 sustained a bilateral aspirative lesion of the fimbria-fornix fibers and all ove rlying tissue, while 30 were given sham operations. Ten days after sur gery, fetal septal suspension grafts were performed in the hippocampus of half the lesioned rats. Two days later, all rats were randomly ass igned to one of three housing or training conditions: standard, standa rd with daily training, and enriched. Two and 5 months later, the rats were tested for learning using a Hebb-Williams maze. At both these de lays, performance was clearly impaired in lesioned rats and was found to be ameliorated by grafts only in rats which had received daily trai ning. Cresyl violet staining and acetylcholinesterase histochemistry s howed that, irrespective of the housing or training conditions, all gr afts had survived and provided the denervated hippocampus with a subst antial cholinergic reinnervation. Our results suggest that the benefic ial behavioral effects of intrahippocampal suspension grafts of septal cells may depend on the postsurgical training or handling conditions of the graft recipients. This result might be of importance for interp reting some behavioral effects of grafts, since in most studies in whi ch grafts were found to induce beneficial behavioral effects (especial ly on learning capacity), these effects were generally observed at the end of a rather long testing period. Moreover, the present findings s how that this delay, before graft function is expressed, might be link ed not only to the time needed by grafts to establish a functional rei nnervation in the host brain, but also to the training and/or handling conditions of the graft recipient. (C) 1995 Academic Press, Inc.