SEX-DIFFERENCES IN MATERNAL BEHAVIORS OF IMMATURE RATS - THE ROLE OF EMOTIONALITY

Immature rats are able to give maternal care to pups and may increase their inclusive fitness by helping newborn siblings. Immature males ar e generally reported to be more maternal than females. In this researc h we studied sex differences and the extent to which they may be due t o a different emotional response to novelty. We studied maternal respo nse in two groups of immature rats of both sexes: in the naive group, juveniles aged from 18 to 30 days were given one test and showed clear -cut sex differences. The experience group was submitted to repeated t ests from 18 to 30 days of age, thus eliminating the effects of novelt y: as a result, all differences between sexes disappeared. A second ex periment was designed in 24-day-old females to differentiate the effec ts of repeated handling and exposure to the test situation from that o f repeated exposure to pups; moreover, the effects of an anxiety-reduc ing drug (diazepam) were studied. Exposure to pups is particularly eff icient in facilitating maternal response. Diazepam injection was also effective, but its control showed that the injection per se was respon sible for the effect. In conclusion, our results stress the importance of response to novelty and suggest that sex differences in maternal b ehavior of immature rats may be modulated by different emotional respo nses by males and females. In fact, emotionality competes with, and ma y exert an inhibitory effect on, the expression of a vast array of beh aviors. (C) 1994 Wiley-Liss, Inc.