Taste aversion learning and aging: a comparison with the effect of dorsal hippocampal lesions in rats.

The relationship between hippocampal function and aging was explored in Wistar rats using taste aversion learning by comparing the performance of adult dorsal hippocampal lesioned and fifteen-month-old intact rats with that of adult intact rats. In experiment 1 the conditioned blocking phenomenon was absent in the hippocampal and the aging rats. Unlike the adult intact rats, the hippocampal and aging rats were not impaired in acquiring a learned aversion to a cider vinegar solution (3 %) presented as a serial compound with a previously conditioned saccharin solution (0.1 %). In experiment 2 both the hippocampal and the aging rats developed reduced aversions to a saline solution (0.5 %) followed by an i.p. injection of lithium chloride (0.15 M; 2 % b.w.) if the taste solution was previously preexposed without consequences. This latent inhibition effect was similar to that seen in intact adult rats. In both experiments, the aging rats exhibited enhanced conventional learned taste aversions. It is concluded that aging is not a unitary process but induces both hippocampal dependent and hippocampal independent complex changes in the functioning of the neural circuits, implementing taste aversion learning.