SELECTIVE ACTIVITY ENHANCEMENT AND PERSISTENCE IN WEANLING RATS AFTERHIPPOCAMPAL X-IRRADIATION IN INFANCY - POSSIBLE RELEVANCE FOR ADHD

We examined the effects of focal X-irradiation of the hippocampus in i nfancy on the partial reinforcement extinction effect (FREE) in weanli ng rats in a runway and on running wheel activity at 40 days of age. O ur results show a dose-dependent X-irradiation-related reduction in gr anule cell neurogenesis. Weanling rats showed a corresponding increase in running speed in both acquisition and extinction and a dose-depend ent reduction in the PREE-an increase in persistence after CRF and a d ecrease in persistence after PRF training. The same degree of hippocam pal granule cell agenesis had no effect on running wheel activity. The se results suggest that the enhanced speeds in the runway are incentiv e-related and do not reflect simple hyperactivity but rather hyperreac tivity. The discussion of these results is in part a speculation regar ding their possible relation to some explanations of attention deficit -hyperactivity disorder in children. (C) 1994 Academic Press, Inc.