Celia L. Moore

The Role of Maternal Stimulation in the Development of Sexual Behavior and Its Neural Basis

Both sexual differentiation, which is a matter of individual development, and sexual dissimilation, which is a matter of individual differences, result from developmental processes that are open to input from the early maternal environment. There are reliable features in both the dam and the young that ensure that males receive more perineal stimulation from maternal licking than is necessary for survival and normal growth. This stimulation contributes toward the development of masculine sexual behavior and mechanisms in the central nervous system that control copulatory reflexes. Because of differences in signals that they produce, males receive more stimulation than females. This bias in early stimulation accounts for some of the dissimilarity between the sexes in nervous system morphology and behavior. The same processes that produce sex differences can also produce individual differences among males. These differences are likely to have significant functional consequences in rats, a species in which males have a high level of intrasexual reproductive competition. Future research will be directed toward testing this functional hypothesis and toward exploring the extent of stimulative effects on the development of the sexually dimorphic brain regions that function in sexual behavior.

An olfactory basis for maternal discrimination of sex of offspring in rats (rattus norvegicus)

Abstract Lactating Long-Evans rats ( Rattus norvegicus ) were presented with three-day-old male and female pups that were either untreated, coated with collodion in the anogenital region or on the neck, or perfumed; or with female pups odorized with either male or female pup urine. As measured by related t -tests of maternal anogenital licking, male and female pups were discriminated in the untreated condition, but not when masking stimuli were present. Female pups treated with male urine elicited more licking than female pups treated with female urine. Overall, maternal licking was decreased by olfactory masking agents and increased by pup urine. It was concluded that olfactory stimuli from pups both stimulate maternal licking and serve as a basis for discriminating male and female offspring.

Sex differences in self-grooming of rats: Effects of gonadal hormones and context

When prepubescent males and females were placed alone in a novel cage, males were found to groom their genitals, but not other body regions, more than females. This sex difference was present in untreated and in testosterone-treated gonadectomized rats as well as in intact rats. Neither the presence of gonads nor testosterone treatment affected grooming in this context. However, when similarly treated rats of the same age were observed in groups in the home cage, no sex difference in genital grooming of intact or gonadectomized rats was found. Testosterone significantly increased nongenital grooming in both sexes and genital grooming in males. Thus, both the presence of sex differences and the effects of testosterone on self-grooming depend on the behavioral context.

Another psychobiological view of sexual differentiation

Abstract The major psychobiological theory of sex differences is based on the hypothesis that hormones induce sex differences in neural organization. Hormonally masculinized or feminized brains are thought to underlie subsequent behavioral sex differences. This theory and the constructs, arguments, and evidence used in its support are closely examined. Some conceptual problems with widely used arguments are identified and discussed. Behavioral, physiological, and anatomical evidence from studies of animal sexual behavior is reviewed. It is concluded that the evidence fails to support generally accepted views that early hormones affect behavior through direct effects on brain differentiation and that behavioral differences must be located in the brain. It is argued instead that hormones coact and interact with other factors throughout development, that brain differences may result from as well as cause functional differences, and that hormone-based sources of sex differences may be located throughout the body and in the social surround. Directions for new research are suggested and implications for interpretation of human sex differences are discussed.

Contributions of reproductive experience to observation maintained crop growth and incubation in male and female ring doves.

Previous work has established that experienced male ring doves (Streptopelia risoria) can maintain prolactin-dependent crop growth and readiness to incubate by observing an incubating partner. We report that this is also true for female ring doves. The role of experience in this phenomenon was examined in separate experiments with males and females. Observation of an incubating mate from 3 days after completion of egg laying is sufficient to maintain crop growth and incubation in both male and female ring doves in their second, but not in their first, reproductive cycle. Male and female doves in their first cycle must incubate for a greater part of the cycle before observation of an incubating mate is an effective stimulus; there are no differences between first and second cycle doves separated by a glass plate from the mate and nest 8 days after laying. Experience obtained within the first cycle apparently ensures that previously neutral stimuli come to elicit prolactin secretion. The effectiveness of these stimuli is reinstated early in a second cycle.

Stimuli associated with pregnancy prepare for maternal behavior in rats.

Cohabitation with pregnant females decreased the time required for reproductively naive female rats to become maternal with constant stimulation by pups. Experience with a companions parturition did not add to experience related to her pregnancy. Exposure to pregnancy-related stimuli also increased nestbuilding as an initial response of virgins to pups. Social isolation for 9 days before exposure to pups decreased both contact with pups and cannibalism.