Jane J. Turner

Seasonal testicular function in male rhesus monkeys

Some studies report seasonal patterns of testicular function in male rhesus monkeys even when they are housed away from females, while others suggest that exposure to sexually active females is essential for male seasonality. We conducted the present experiment (1) to test claims that seasonal testicular activation occurs in the absence of females and (2) to determine whether regular exposure to and copulation with females enhances, or is without effect upon, seasonal increases in testicular function. We studied two groups of male monkeys housed in a colony room containing no females. Males in the Female Exposure group (n = 7) were paired twice weekly with estradiol-implanted females and copulated vigorously. Males in the second group (n = 7) were placed in the same test chamber (at least 16 h after it had been scrubbed with disinfectant) but were never exposed to females. Serum testosterone levels and testis volume were monitored for both groups. Each group displayed a seasonal pattern of testosterone and of testis volume comparable in timing and magnitude to seasonal increases previously reported in group-housed males, but the two groups did not differ from each other. Our findings confirm that seasonal changes in testosterone and testis size occur in the absence of sexual interaction and demonstrate that moderate levels of sexual activity do not enhance this response.

Ejaculation is important for mating-induced testosterone increases in male rhesus monkeys

Abstract Sexual behavior of male and estrogen-treated female rhesus monkeys was observed at 1000 and 1400 hr within and outside the breeding season. Blood samples for analysis of testosterone were taken before and after these 1 hr behavioral tests. Group testosterone levels increased significantly only during the one condition in which over half of the males ejaculated (in season afternoon), and only in those males actually ejaculating. In other time and seasonal conditions, increases in testosterone were observed when tests without ejaculation were eliminated from analysis. Furthermore, males in which testosterone levels increased following ejaculation displayed no increase when caged alone for an equivalent time period, or when tested with an untreated, ovariectomized female. These results suggest that ejaculation (rather than other aspects of the test setting) may be critical for the occurrence of androgen increases.

Endocrine changes induced by venipuncture in rhesus monkeys

An animal-worn, remotely activated blood collection device was used to obtain estimates of baseline levels of testosterone (T), growth hormone (GH) and prolactin (PRL) from unrestrained and active male rhesus monkeys. As soon as possible after this baseline period, the males were captured and a final venipuncture sample was obtained. Venipuncture produced elevated GH levels compared to values obtained using the blood collection device, but was without detectable effect upon levels of T and PRL. Cortisol values, available only from a single animal, displayed an increase in response to venipuncture, much like that seen for GH.

Fluctuations in testosterone levels of male rhesus monkeys during copulatory activity

Abstract We examined the effect of copulatory activity on testosterone levels in rhesus monkeys using an animal-worn, radio-activated blood sampling device which enabled us to collect samples without interrupting sexual behavior. Two animals showed significant increases in serum levels of testosterone averaging 108% and 203% above the pre-ejaculation baseline. A third animal showed little change in serum testosterone levels during sexual behavior. The data demonstrate that the technique of remotely activated blood sample collection may prove valuable in psychoendocrine research.

A low-cost lightweight jacket for the protection of chronically indwelling jugular catheters in rhesus monkeys

A jacket for long-term protection of chronically indwelling jugular catheters in rhesus monkeys is described. The jacket is made of lightweight, durable, and inexpensive material and is easily modified to fit animals of different sizes. It has been used successfully on over 25 animals.

A ten-month study of endogenous testosterone levels and behaviour in outdoor-living female rhesus monkeys (Macaca mulatta)

Endogenous testosterone levels were measured in association with sexual, aggressive, and social/affiliative behaviors in 11 outdoor-housed female rhesus monkeys over a ten-month period. Several behaviors (sex directed toward the male, sex received from the male, aggression directed toward the male, submission directed toward the male, submission directed toward the female, and groom another female) were significantly (p<0.05) positively correlated with testosterone in from one to five females. No trends were strong enough across all females to suggest that any of these correlations have species-wide significance. Factor analysis revealed clearcut clusters of behaviors, but elevations in testosterone were not strongly associated with any of these clusters. It is concluded that endogenous testosterone levels have little measurable effect on overt behavior in female rhesus monkeys.

Effects of a gonadotropin-releasing hormone agonist on sexual behavior in male rhesus monkeys (Macaca mulatta)

Low levels of sexual behavior persist in male rhesus monkeys treated with GnRH-a despite very low levels of T and gonadotropin that occur during such treatment. The behavior of male rhesus monkeys treated with GnRH-a resembles the behavior of surgically castrated male rhesus monkeys more closely than it does the behavior of reproductively quiescent males during the normal nonmating season. The normal, seasonal cessation of sexual behavior in male rhesus monkeys may result from changes in behavioral sensitivity to circulating androgens.