Effects of hippocampal x-irradiation-produced granule cell agenesis on instrumental runway performance in rats.

BRUNNER, R. L , S. J. HAGGBLOOM AND R. A. GAZZARA. Effects of hippocampal x-irradiation.produced granule-cell agenesis on instrumental runway performance in rats. PHYSIOL. BEHAV. 13(4) 485--494, 1974. Rats in which xqrradiation during early postnatal life had interfered with the acquisition of dentate granule cells ran faster than controls during extinction of a runway response acquired under a consistent food reward schedule. A training schedule of randomly rewarded and nonrewatded trials increased running speeds to an equal extent in x-irradiated and control groups during extinction. The second and third experiments showed that unlike a reported total inability of hippocampal lesioned rats to pattern their running responses appropriate to a single alternation schedule of reward and nonreward, x-irradiated rats, while impaired in acquiring response alternation, did pattern and had persistenl deficits compared to controls only when the task was made very simple by reducing the number of daily trials to two. The results are discussed in terms of an hypothesized reduction in the aversiveness of nonreward and a consequent reduction in the growth of inhibition in x-irradiated rats.