Functional alterations in the social organization of bonnet macaques (Macaca radiata) induced by ovariectomy: an experimental analysis

Long-term ovariectomy alters social and anxious behaviors in semi-free ranging Japanese macaques

Symptoms of anxiety and depression often occur in young women after complete hysterectomy and in older women during menopause. There are many variables that are hard to control in human population studies, but that are absent to a large extent in stable nonhuman primate troops. However, macaques exhibit depressive and anxious behaviors in response to similar situations as humans such as isolation, stress, instability or aggression. Therefore, we hypothesized that examination of behavior in ovariectomized individuals in a stable macaque troop organized along matriarchal lineages and in which individuals have social support from extended family, would reveal effects that were due to the withdrawal of ovarian steroids without many of the confounds of human society. We also tested the hypothesis that ovariectomy would elicit and increase anxious behavior in a stressful situation such as brief exposure to single caging. Japanese macaques (Macaca fuscata) were ovariectomized (Ovx) or tubal-ligated (intact controls) at 3 years of age and allowed to mature for 3 years in a stable troop of approximately 300 individuals. Behaviors were recorded in the outdoor corral in the third year followed by individual temperament tests in single cages. There was no obvious difference in anxiety-related behaviors such as scratching between Ovx and tubal-ligated animals in the corral. Nonetheless, compared to tubal-ligated animals, Ovx animals exhibited a significant decrease in (1) positive social behavior, (2) initiating dominance behavior, (3) time receiving grooming, (4) locomoting, (5) mounting behavior, and in (6) consort behavior. However, Ovx females exhibited a significant increase in (1) consummatory behavior and (2) object play compared to tubal-ligated controls. In the individual temperament tests, Ovx individuals exhibited an increase in anxiety-related behaviors. There was no difference in adrenal weight/body weight suggesting that neither group was under chronic stress. These data indicate that ovarian hormones enable females to successfully navigate their social situation and may reduce anxiety in novel situations.

Behavioral responses to ovariectomy and chronic anabolic steroid treatment in female cynomolgus macaques

A pilot study was conducted to investigate the effects of ovariectomy on rates of aggressive and affiliative behavior, as well as body size, in 38 young adult female cynomolgus monkeys (Macaca fascicularis) living in isosexual social groups of four to five animals. In addition, we assessed the effects of nandrolone decanoate (an anabolic steroid used for postmenopausal hormone replacement therapy) on indices of aggression, submission, and body size. Animals were randomized into three experimental conditions: 1) sham ovariectomized, untreated (SHAM); 2) ovariectomized, untreated (OVX); and, 3) ovariectomized, treated with nandrolone decanoate for 24 months (NAN). Each individual was observed for 10 min, one to two times per month, and all instances of agonistic and affiliative behavior were recorded by means of focal animal sampling. Ovariectomized, untreated animals exhibited a two- to threefold increase in aggression compared to SHAM or NAN animals; F(2, 32) = 4.09, p = 0.026; however, the expression of prosocial or affiliative behaviors as measured by rates of grooming and initiating friendly behavior was unaffected. At an i.m. dose of 25 mg every 2 weeks, nandrolone decanoate caused a 60% increase in body weight of the animals compared to untreated intact and ovariectomized animals, F(2, 31) = 161.57, p < 0.0001.

Effects of ovariectomy, social instability and social status on female Macaca fascicularis social behavior

The effects of ovariectomy, social instability and social status on affiliative and agonistic behavior were studied in 44 females housed in 10 unimale groups. Five of the groups contained ovariectomized females and five groups contained intact females. The membership among three groups of intact females (n = 13) and three groups of ovariectomized females (n = 13) was reorganized every three months (unstable), and the other groups were left undisturbed (stable) for the 22 month study. The behavior of each female was recorded during 160 (stable) or 190 (unstable) 15 min focal observations of each subject. The social status of each female was determined by outcomes of agonistic interactions. It was hypothesized that the effects of social instability and status would be more pervasive than the effects of ovariectomy. It was found that ovariectomy reduced interfemale affiliation and increased male-female agonism. Social instability increased submissions to males and females and time spent alone, and decreased interfemale affiliation. Dominant animals were more aggressive and less submissive than subordinates. Thus, ovariectomy influenced both isosexual and heterosexual social interaction, implying mediation of these behaviors, at least in part, by ovarian hormones.