Long-term effects of repeated maternal separation on three different latent inhibition paradigms

In the present study we investigated the effect of repeated maternal separation on postnatal days 12, 14, 16, and 18 for 6 h/day on Wistar rats on three latent inhibition (LI) paradigms: two-way active avoidance, conditioned emotional response (CER), and conditioned taste aversion (CTA). In addition, hyperactivity induced by d-amphetamine and stereotypies induced by apomorphine were evaluated. In all three LI experiments, the control animals showed only marginal LI, whereas the maternally separated animals showed enhanced LI (only males in CTA). In two-way active avoidance within the nonpreexposed condition maternally separated animals showed improved acquisition of avoidance learning compared with the control animals. Sensitivity in response to amphetamine and apomorphine was not altered by the maternal separation procedure. Thus, maternal separation in this study, contrary to previous reports, but in line with results obtained following early handling before weaning, led to enhancement of the LI phenomenon as assessed in each of the three procedures. As our maternal separation procedure (6 h on days 12, 14, 16, and 18) led to behavioral outcomes that differed from those reported by Ellenbroek and Cools (24 h on day 10), it is suggested that maternal separation regimens that are dissimilar may lead to different and sometimes opposite behavioral effects.