Modulation by social status of the relationship between cerebrospinal fluid and serum cortisol levels in male talapoin monkeys.

Serum and cerebrospinal fluid (CSF) cortisol were measured by radioimmunoassay in male talapoin monkeys living in social groups. The slopes of the regressions between cortisol in the two compartments were significantly less in dominant than either the most subordinate males or those of intermediate rank. Furthermore, the dominants' CSF also contained proportionately more cortisol than was predicted from the overall regression analyses of the groups of which they were members. There was no difference in the proportion of 'free' cortisol (that is, not bound to serum proteins) between the serums of dominant or subordinate males. These findings point to an association between social status and the distribution of cortisol between blood and CSF in these monkeys.

Relationship between dominance hierarchy, cerebrospinal fluid levels of amine transmitter metabolites (5-hydroxyindole acetic acid and homovanillic acid) and plasma cortisol in monkeys.

The dominance hierarchy has repercussions for a monkey's sexual behaviour and endocrine state. Here we report on neural mechanisms that are sensitive to a monkey's status in the social hierarchy, and which may regulate not only its endocrine function but its sexual responsiveness to its own hormones. During the initial phase of group formation, 5-hydroxyindole acetic acid, the metabolite of serotonin, increases in the cerebrospinal fluid of monkeys which become subordinate (all groups), but decreases in monkeys which become dominant (two out of three groups) and shows no changes in intermediate-ranking animals (five out of seven). Homovanillic acid, a metabolite of dopamine, may also increase in the cerebrospinal fluid of monkeys that become subordinate (two out three groups). In the initial period of group formation these changes in transmitter metabolites do not parallel changes in cortisol. However, in the established social groups, both 5-hydroxyindole acetic acid and plasma cortisol are related to the social hierarchy, being greater in those monkeys that are subordinate, but homovanillic acid shows no consistent change. Although subordinate monkeys receive more aggression than others in their group, fluctuations in 5-hydroxyindole acetic acid do not correlate with aggressive behaviour, and are equally high on days when no aggression occurs. Dominant males, however, had higher 5-hydroxyindole acetic acid levels on days when they were involved in agonistic encounters. In the established social hierarchy therefore, elevated levels of the serotonin metabolite in cerebrospinal fluid seem reflect a "state"-dependent consequence of occupying a position of low social status.

Subordination in male talapoin monkeys lowers sexual behaviour in the absence of dominants.

Three experiments assessed the consequences of social status for the socio-sexual behaviour and endocrine state of adult male talapoin monkeys (Miopithecus talapoin). In the first study, each of five males was individually placed into a group of adult females. Neither behavioural responses, nor plasma levels of testosterone, cortisol, or prolactin, predicted males' rank or hormone levels when all males were subsequently placed with these females. In the second study, each of four mixed-sex social groups lived continuously in a large cage for periods ranging from 9-15 months. There were marked differences between the behaviour and hormone levels of highest- and lowest-ranking males. In the third study, each highest- and lowest-ranking male from these groups was individually placed with females. Males that had experienced social subordination for long periods (9-15 months) showed infrequent sexual behaviour and had elevated levels of cortisol and prolactin. These results indicate that the experience of chronic social subordination is a strong predictor of how males will subsequently behave, since both the endocrine and behavioural effects of subordination persist even after the dominant males are removed.

Effects of rank and novel females on behaviour and hormones in male talapoin monkeys.

Two social groups of captive talapoin monkeys (Miopithecus talapoin), each with three intact adult males and three or four ovariectomized, estrogen-treated adult females, were observed. Socio-sexual and aggressive interactions were recorded, and levels of testosterone, cortisol, and prolactin were measured in male serum. Cortisol and prolactin titers did not reflect male rank, nor did changes in one of these hormones parallel changes in the other. In both groups males formed a linear dominance hierarchy, defined in terms of the direction of aggression among animals. Highest male rank was associated with frequent socio-sexual interaction and elevated testosterone levels, even in the absence of ejaculations. Males in one group copulated with females, but no male in the other group copulated. All males of each group were then housed with all females of the other group which resulted in marked changes in males' behaviour; socio-sexual interactions increased in C group males and decreased in B group males. This illustrates the influence that females may have on male behaviour in general, and in particular outlines the potential for female dominance and the consequences this may have especially on reproductive behaviour.