Maternal deprivation affects behaviour from youth to senescence: amplification of individual differences in spatial learning and memory in senescent Brown Norway rats.
Previous studies have shown that deprivation of the infant rat from maternal care has pronounced effects on the stress system during ontogeny. Here we test the hypothesis that 24 h of maternal deprivation at postnatal day 3 will cause persistent changes in behaviour. Spatial learning and memory of male Brown Norway rats deprived as infants were observed in the Morris water maze at 3, 12, 24 and 30-32 months of age (young, adult, aged, senescent). Their nondeprived mother-reared littermates served as controls. (i) With increasing age, water maze performance declined in deprived and nondeprived groups. However, once the task was learned the animals maintained their good performance during retest at later ages. (ii) Maternal deprivation delayed acquisition until adulthood and caused at every age a higher degree of persistent behaviour as judged from the performance of deprived rats' free swim trials and reversal trials. (iii) At senescence the mean performance in the water maze did not differ between the groups. Instead, the individual performance was strikingly different within each group. Senescent deprived rats were either nonimpaired or impaired with only a few animals showing an intermediate performance. Thus, a large group of animals ( approximately 40%) ages successfully as they are resistant to the effect of maternal deprivation. In contrast, the majority of the control animals displayed intermediate performance. Taken together, maternal deprivation has life-long consequences for behaviour and culminates at senescence in amplification of individual differences in learning ability rather than in a generalized deterioration of cognitive functions.