Impairment of acquisition but not retention of a simple operant discrimination performance in aged Fischer 344 rats.

Although deterioration of learning and memory in aged rodents has been reported using a variety of tasks, little information is available on the effects of aging on acquisition and retention of reference memory in food-motivated tasks. In the present study, to examine reference memory, a simple operant discrimination task was used. Aged (24 month) and young (5 month) Fischer 344 rats were trained to discriminate brightness for food reward in an operant chamber. Aged rats showed significantly impaired learning compared to young rats, and the level of discrimination of aged rats was significantly lower than that of young rats. The aged rats also exhibited impaired learning in discriminating an auditory cue. Aged rats as well as young rats had good retention of brightness discrimination performance 30 days after the last training session. Scopolamine (0.3 mg/kg) did not impair discrimination learning nor affect well-trained discrimination performance in young rats. These data suggest that acquisition but not retention of reference memory is impaired in aged rats, and that the impaired acquisition observed in aged rats may not be due to dysfunction of the central cholinergic systems.