AGE-RELATED-CHANGES IN PAVLOVIAN CONDITIONING - CENTRAL NERVOUS-SYSTEM CORRELATES

Two groups of New Zealand Albino rabbits, average age 6 and 40 mo. were subjected to Pavlovian conditioning in which eyeblink (EB) and heart rate (HR) responses were assessed. At the end of conditioning biogenic amine content was assessed in several brain areas; dopamine receptor binding was assessed in caudate nucleus. Older animals revealed an impairment in EB conditioning relative to the young animals; the conditioned decelerative HR response was increased in magnitude in the old animals. Significant deficits in cortical norepinephrine and serotonin were observed in the old subjects but in both old and young animals the magnitude of the bradycardia was positively correlated with forebrain norepinephrine and inversely correlated with serotonin concentration. Receptor binding experiments revealed that 3H-spiroperidol receptor density was decreased in caudate nuclei of old animals; receptor affinity was unaffected by age.