No abstract

Guinea pig pups exhibit a two-stage, active/passive response during isolation in a novel environment that resembles the "protest" and "despair" stages observed in some species of primates. The present study examined social and developmental influences on the expression of the passive stage of responsiveness in young guinea pigs. Both preweaning and periadolescent guinea pigs displayed the passive stage during isolation in a novel environment. In preweaning pups and periadolescents that had been housed with the mother since birth, the presence of the mother in the novel environment prevented the passive stage from occurring. Levels of passive responses in the presence of an unfamiliar adult female were generally intermediate to those in the other two test conditions; however, periadolescents housed only with a peer between weaning and testing exhibited the passive stage of responsiveness not only when alone but also when with the mother or an unfamiliar female. The findings indicate that the passive responses can occur in periadolescent guinea pigs and that the test conditions under which they occur depend upon the periadolescents' social housing conditions prior to testing. Further, the results are consistent with the hypothesis that responses during the second stage constitute "stress-induced sickness behaviors."

The bile acid pools of developing rats were measured by gas-liquid chromatography. From shortly after birth the bile acid pools fell to a nadir on the 10th day of life (0.295 ± 0.031 mg · g^-1 body weight at 2 days to 0.144 ± 0.012 mg · g^-1 body weight at 10 days, p < 0.001). The pool re-expanded rapidly between the 12th and 15th day. After weaning and during puberty there was a further temporary increase in pool size, during which females had larger pools than males. By adulthood the pool size had returned to the 2-day-old and weanling (15- and 18-day-old) levels, expressed per gramme body weight, and there was no longer a significant sex difference. These results show that changes in pool size are occurring at times when there are major physiological changes in the developing animal. The changes during puberty suggest hormonal control.