The role of social experience in the development of sexual competence in Rattus norvegicus.

To clarify the hitherto ambiguous role of pubertal social experience in determining adult sexual competence in male Rattus norvegicus , the quality of the subjects' social interactions was manipulated. In Experiment 1, subjects were raised from weaning onwards in male-only groups, in groups with limited periods of social deprivation at various ages, or in total isolation. Only the latter showed a significant degree of sexual impairment. In Experiment 2, subjects were raised in mixed-sex groups, in total physical (but not visual or olfactory) isolation from a surrounding mixed-sex group, or in physical isolation except for one hour's social contact per day with a peer. All of these subjects were sexually competent as adults. It thus appears that, in the laboratory rat, social deprivation must consist of total physical and visual and/or olfactory isolation in order to produce a significant degree of sexual impairment.

Effects of early social experience on activity and object investigation in the ferret.

Earlier experiments have shown that many of the effects of early social isolation in the rat may be due to deprivation of social play. The isolated ferret, like the isolated rat, is hyperactive; furthermore, its hyperactivity appears to be related to deprivation of social play. However, the relationship between object investigation and social rearing is more complex in the ferret than it is in the rat.

Isolation has permanent effects upon the behavior of the rat, but not the mouse, gerbil, or guinea pig.

In the rat isolation has both short- and long-term influences upon behavior. Rats isolated at any age will show increases in timidity and aggression, but both effects can be reversed by periods of social housing. However, isolation before 50 days of age has permanent effects upon behavior. We have previously found that rats between 25 and 45 days of age may be protected from the deleterious effects of isolation by short daily periods of social contact if, during these daily contact periods, the rats engage in intense bouts of rough-and-tumble play. In this study we examined the permanence of the effects of isolation on the rat, mouse, guinea pig and gerbil. As predicted by the play hypothesis, species which do not engage in extensive social play do not show permanent deficits if isolated prior to 50 days. Only rats which engage in long bouts of rough-and-tumble play between 20 and 50 days show any permanent behavioral effects of isolation during this period.

Environmentally induced differences in susceptibility of rats to CNS stimulants and CNS depressants: evidence against a unitary explanation.

It has been suggested that socially isolated rats are more aroused then rats raised in social groups. This hypothesis was tested by examining amphetamine-induced activity and stereotypy in social and isolated rats of both sexes in both the active and inactive phases of their diurnal activity cycle. In socially raised rats it was possible to produce behavioural profiles similar to those of isolated rats by increasing the arousal level of the social rat. However, the complex interaction of housing conditions, diurnal variation and gender with drug dose suggests that one intervening variable such as arousal is too simplistic an explanation. In subsequent experiments, stereotypy was enhanced by a familiar environment, and there was a clear dissociation between the effects of CNS stimulants and CNS depressants. The increased susceptibility of isolates to CNS stimulants depends on social isolation for a short period before 45 days of age; the decreased susceptibility of isolates to CNS depressants may be produced by isolation at any age. We conclude that there is no evidence that isolated rats are hyperaroused.

A critical period for social isolation in the rat.

Rats housed in social isolation show heightened levels of object-contact in an open-field and are slower than socially-housed controls to emerge from a small enclosure into an unfamiliar environment. Isolation between 25 and 45 days of age produced an irreversible effect upon object contact but had no lasting effect if between 16 and 25 days or after 45 days. In contrast to object contact, emergence was affected by isolation at any age and the effect was reversed by subsequent social housing. Thus the effects of isolation upon object contact and upon emergence apparently do not depend upon a single underlying variable.