It has been reported in the rat that postnatal manipulations can induce robust and persistent effects on offspring neurobiology and behavior, mediated in part via effects on maternal care. There have, however, been few studies of the effects of postnatal manipulations on maternal care. Here, we describe and compare the effects on maternal behavior on postnatal days 1-12 of two manipulations, early handling (EH, 15-min isolation per day) and early deprivation (ED, 4-hr isolation per day), relative to our normal postnatal husbandry procedure. Maternal behavior was measured at five time points across the dark phase of the reversed L:D cycle. EH yielded an increase in arched-back nursing across several time points but did not affect any other behavior. ED stimulated a bout of maternal behavior such that licking and arched-back nursing were increased at the time of dam-litter reunion, although not at any other time point. Neither EH nor ED affected weaning weight significantly. Importantly, within-treatment variation was high relative to these between-treatment effects.

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This study examined whether early isolation (EI), early handling (EH), or early nonhandling (NH) in infant rats alters (a) prepulse inhibition (PPI) of the acoustic startle response (ASR) or its disruption by apomorphine, (b) motor activity or its stimulation by amphetamine, or (c) corticosterone activity (because of its modulation of dopamine activity), in adulthood and in comparison with a normal-husbandry postnatal control environment. EI did not affect PPI, reduced PPI disruption by apomorphine in males, and increased amphetamine-stimulated activity in males. NH increased the ASR, reduced activity in the open field, and increased corticosterone reactivity in males. In all paradigms, the effects of EH were similar to those of the control environment. This study provides an important contribution to the evidence on the relationship between postnatal experience and long-term neurobehavioral development in the rat and the relevance of this approach to animal models of neuropsychiatric disorder.

Effects of manipulations of the rat pup-dam relationship on affective learning and memory in adulthood have received scant systematic investigation. The authors previously described how early handling (EH; 15 min isolation/day) and early deprivation (ED; 4 hr isolation/day) exert similar effects on spontaneous adult affect (open-field behavior, acoustic startle, endocrine stress response) relative to nonhandling (NH; C. R. Pryce, D. Bettschen, N. I. Bahr, & J. Feldon, 2001). The present study demonstrates that both EH and ED adults exhibit enhanced active avoidance relative to NH adults. Fear-conditioned context and conditioned stimulus (CS) freezing were unaffected in both EH and ED, but stress hormone responses to the CS were reduced in EH males and ED females relative to NH. In the water maze, ED adults exhibited enhanced spatial learning and memory relative to NH.

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