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 materna l 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 w ill cause persistent changes in behaviour. Spatial learning and memory of m ale 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 i ncreasing age, water maze performance declined in deprived and nondeprived groups. However, once the task was learned the animals maintained their goo d performance during retest at later ages. (ii) Maternal deprivation delaye d acquisition until adulthood and caused at every age a higher degree of pe rsistent behaviour as judged from the performance of deprived rats' free sw im trials and reversal trials. (iii) At senescence the mean performance in the water maze did not differ between the groups. Instead, the individual p erformance was strikingly different within each group. Senescent deprived r ats were either nonimpaired or impaired with only a few animals showing an intermediate performance. Thus, a large group of animals (approximate to 40 %) ages successfully as they are resistant to the effect of maternal depriv ation. In contrast, the majority of the control animals displayed intermedi ate performance. Taken together, maternal deprivation has life-long consequ ences for behaviour and culminates at senescence in amplification of indivi dual differences in learning ability rather than in a generalized deteriora tion of cognitive functions.