Effects of intra-nasally administered testosterone on sexual proceptive behavior in female capuchin monkeys (Cebus apella).

Sexual dysfunction in the female has been associated with a decrease in androgen levels, which can be reversed by testosterone treatment, however, bearing the risk of adverse side effects. Nasally administered testosterone could be an effective method for androgenic treatment avoiding the first-pass intestinal and hepatic metabolism and side effects. Here we examined the effects of chronic intranasal administration of testosterone on sexual behavior in female capuchin monkeys (Cebus apella) that lived with male cohorts. During 8 days of baseline 10 females were observed for their sexual and non-sexual behavior without drug. They then received daily intranasal testosterone (0.24 mg per nostril, n=5 per group) or placebo gel for 5 days, followed by 5 days of wash out, followed by 5 days of daily intranasal application, whereby the animals that had received testosterone before, now received placebo and vice versa. Diverse sexual and non-sexual behaviors were scored. Blood samples were collected and analyzed for testosterone, estradiol, dihydrotestosterone and progesterone using EIAs. The results revealed an increase in sexual behavior (eyebrow raising, chest rubbing, courtship behavior, masturbation) in the females during testosterone treatment, which seemed to be prolonged even when testosterone treatment was discontinued. These behavioral results were accompanied by an increase in plasma testosterone levels. This study demonstrates the efficacy of testosterone in enhancing sexual behavior in female capuchin monkeys by means of intranasal application, which may be a useful alternative compared to other forms of administration.

Influence of stimuli size on color discrimination in capuchin monkeys.

Large-field trichromacy is a general feature of protanope and deuteranope humans, provided that the stimuli size extends to an 8 degrees visual angle. In this study we compared the performance of five male and three female tufted capuchin monkeys (Cebus apella) in discriminating pairs of Munsell color papers. Human subjects were also studied in two-choice discrimination tests, using the same stimuli and apparatus employed for the monkeys. The results show that although the dichromatic humans showed improved discrimination with larger versions of the stimuli, the dichromatic monkeys exhibited the same performance for both stimuli sizes. Thus, Cebus apella apparently do not present large-field trichromacy-at least for the conditions in the present experiments.

Color vision perception in the capuchin monkey (Cebus apella): a re-evaluation of procedures using Munsell papers.

In previous experiments based on color vision discrimination of Munsell chips, Pessoa et al. (Behav Brain Res 1997;89:285-8) presented evidence of trichromatic color vision in capuchin monkeys. However, the possibility of subjects using brightness cues was not eliminated. The purpose of the present study was to reassess the color perception in Cebus apella in a similar behavioral paradigm, but using a range of brightness values at each tested hue. We now report that male capuchins show a dichromatic behavior. The results are discussed in terms of the hypothesis of male dichromatism in the New World monkey, the biological role of color vision and cognitive abilities of capuchin monkeys.