Behavioral assessment of forgetting in aged rodents and its relationship to peripheral sympathetic function

Observation of age-related memory deficits in rodents is often dependent on the behavioral task used to assess these changes, rather than being universal to all memories. A review of studies using aversively-motivated multiple trial training paradigms suggests that the apparent acquisition deficits common to older animals may instead be due to a confounding tendency of these animals to behavioral rigidity or perseveration. Data obtained using single trial training paradigms, such as the one-trial passive avoidance task, indicate that young and old rodents can learn tasks with equal facility, that retention in young and old animals is similar at short training-testing intervals, but that retention is impaired in aged animals at longer training-testing intervals. We suggest that the adrenal medulla, a peripheral source of catecholamines, secretes catecholamines that act outside the blood-brain barrier to modulate memory processes. Further, we review evidence suggesting that the ability of the adrenal medulla to respond to the stresses of footshock during aversively-motivated training are impaired in aged rodents, and that this impairment may contribute to the rapid forgetting observed in senescent animals.