Prenatal stress alters reproductive responses of rats in behavioral estrus and paced mating of hormone-primed rats

Adult female offspring of dams exposed to gestational stress (prenatal stress, PNS) may show altered reproductive behavior, exploration in novel environments, and/or social interactions than do their non-PNS counterparts. These behavioral differences may be more readily observed in a seminatural, paced mating paradigm, in which females have greater control of their sexual contacts, than in a standard mating situation. Adult offspring of dams exposed to restraint and lights for 45 min on Gestational Days 14-20 (PNS) were compared with those not subjected to stress (non-PNS, control condition). The motor, reproductive, and sociosexual behaviors of hormone-primed (Experiment 1) or cycling adult offspring in behavioral estrus (Experiment 2) were examined following 20 min of restraint stress under bright lights (postnatal stress). Hormone-primed PNS rats displayed less motor behavior in a novel arena than did non-PNS rats. In a standard mating test, hormone-primed PNS females tended to be more aggressive toward the male than were non-PNS rats. In a seminatural mating situation, hormone-primed PNS females showed increased avoidance behavior, such as longer latencies to the initial intromission, greater return latencies following mounts and intromissions, and more exiting subsequent to mounts and intromissions, than did non-PNS rats. PNS rats in behavioral estrus had decreased incidence and intensity of lordosis, and fewer solicitation behaviors, in both standard or paced mating situations, in which latency to and number of mounts were also increased. Thus, hormone-primed PNS rats exposed to restraint showed more avoidance behaviors in paced mating situations, while cycling PNS rats in behavioral estrus had greater disruption of reproductive responses in standard or paced mating paradigms than did non-PNS control rats.     

Effects of age,rearing, and separation stress on immunoglobulin levels in rhesus monkeys

The study reported here examined the effect of different rearing conditions and psychological stress on immunoglobulin levels in rhesus monkey infants. In the first experiment, 24 rhesus neonates were placed in one of the three following rearing conditions: Separated from their mothers and reared in the laboratory nursery; kept with their biological mothers; or removed at birth from their biological mothers and cross-fostered to adoptive rhesus mothers. Plasma samples were obtained from the nursery-reared infants immediately after birth and at weekly intervals for the next 30 days. Samples were also obtained from mother-reared and foster-reared infants on days 15 and 29. All samples were tested for IgG and IgM levels. The results indicated that neither rearing nor diet affected Ig levels. IgG levels were highest at birth and decreased progressively for the first 30 days, suggesting that placental transfer of maternal IgG is the critical determinant of IgG levels in primate infants as in humans. IgM changes were also similar to those in human infants: Low levels at birth, a significant increase from birth to day 15, and a moderate decline from day 15 to day 30. When IgG levels and IgM levels were correlated across the first month, many significant correlations were found which were consistent with human data relating both infant IgG and IgM levels to infant maturation. In the second experiment, 11 of the previously tested nursery infants were subjected to four consecutive social separations from peer groups at 6 months of age. Plasma samples were obtained before and after the first and fourth weeks of separation and tested for IgG and IgM levels. Small but significant decreases in both immunoglobulins were detected after 4 days of separation, particularly on the fourth week.     

Reactions of nuclear-family–reared rhesus macaques to the births of younger siblings

A group of juvenile rhesus macaques (Macaca mulatta) living in a nuclear-family laboratory environment was studied to determine their responses to the births of siblings. The frequencies of interactions with family members (mothers, fathers, and new siblings) and nonfamily (peers, unrelated infants, and unrelated adults) were studied over both the year preceding and the year following sibling birth. The frequencies of specific behaviors in each of those interactions and the frequencies of interactions in each area of the nuclear-family unit (home cage, play area, or other families' cage) were also examined. After new siblings arrived, several measures of interactions with mothers, fathers, and new siblings increased significantly; by contrast interactions with peers decreased substantially over the post-birth year. Although the frequency of interactions in home cages remained stable over the 2-year period, interactions outside of the subjects' home cages decreased significantly after siblings were born. An additional subject group whose mothers became pregnant but failed to deliver viable offspring showed no significant changes in total levels of interactions with peers; they did, however, exhibit increases in some interactions with unrelated infants and adults. Female juveniles interacted with new siblings significantly more often than did males when siblings were less than 6 months old, but as siblings grew older (6–12 months), females' levels of interaction with them fell to a level equal to that of males. In the nuclear-family social structure, the birth of a sibling resulted in an increased emphasis on family interactions at the expense of peer interactions.     

Social development in nursery-reared pigtailed macaques (Macaca nemestrina)

The social development of 240 nursery-reared pigtailed macaques (Macaca nemestrina) was studied from postnatal weeks 4 to 32. The objectives of the study were to document developmental trends and evaluate social behavior in laboratory-reared M. nemestrina raised at the University of Washington Infant Primate Laboratory, and to identify husbandry factors that might affect early social development. Only infants who had not undergone invasive postnatal experimental manipulation and had no chronic illness or injuries were included in the study. Infants were separated from their mothers and housed singly, but had access to peers for 30 min a day, 5 days a week, in a large playroom. Play and social behaviors emerged early in development, increased during the developmental period studied and occupied a large portion of the infants' time budgets. Although disturbance behaviors occurred with some frequency and duration early in development, they occupied a very small portion of the infants' time budget at 8 months of age. Weaning from infant formula at 16–19 weeks retarded development of play behavior. Permanent removal of a cloth comforter (diaper) during weeks 20–24 had no long-term behavioral effects. It was concluded that at 8 months of age these infants showed relatively normal species-typical behavioral repertoires. Am J Primatol 41:23–35, 1997. © 1997 Wiley-Liss, Inc.     

Neuronal actions of glucocorticoids: focus on depression

Stress, acting through glucocorticoids (GC), has profound effects on brain physiology and pathology and is causally implicated in depressive illness. Here, we consider the information derived from genetic models generated to probe the role of the hypothalamo–pituitary–adrenal axis in depression. This essay also briefly reviews the status of knowledge regarding GC actions on neuronal birth, survival and death from the perspective of the importance of these phenomena in depression.     

Abnormal behaviors in nursery-reared squirrel monkeys (Saimiri sciureus)

Seventeen squirrel monkeys (Saimiri sciureus), 11 nursery-reared and six mother-reared, were monitored to clarify the type and degree of deviant behaviors that result from rearing this species in the nursery. Two observation periods were used: the first when the subjects averaged 6.7 months of age, the second when they averaged 15.5 months. Thirteen activities involving variations of nonnutritive orality, stereotypic posturing, and agitated behaviors were seen in the nursery-reared subjects, but never in the mother-reared subjects. No consistent gender, subspecies, or age differences were evident. Squirrel monkeys, like chimpanzees and some Old World monkeys, do develop atypical self-directed behaviors when deprived of normal stimulation during early development.