Testosterone (T) has repeatedly been shown to have anxiolytic properties in rodents, but findings in primates are more mixed. To examine the effects of exogenous T on anxiety, we tested pharmacologically-castrated adult male rhesus monkeys in a modified version of the Human Intruder Paradigm, which measured defensive responses to an unfamiliar human staring directly at them for 2 min. Monkeys were tested at 2 week intervals during 4 experimental conditions lasting 4 weeks each: at baseline, during treatment with the gonadotropin releasing hormone (GnRH) agonist leuprolide acetate (200 μg/kg; Lupron phase), during treatment with Lupron+T enanthate (TE, 5 mg/kg; TE phase) and during treatment with Lupron+oil vehicle (oil phase). We found that the number of anxious behaviors was lower during periods of low T (Lupron only and Lupron+oil phases) than during the Lupron+TE phase. No change in pacing or watching behavior was observed. Thus, in contrast to rodent data, we found no evidence for anxiolytic properties of T in male rhesus monkeys. Rather, T supplementation restored baseline levels of anxiety in Lupron-treated monkeys. These discrepant findings may be best explained by the low levels of gonadotropins achieved by the GnRH agonist. We suggest that Lupron-induced luteinizing hormone (LH) suppression reduced anxiety and that this effect was abolished by T administration. This interpretation is consistent with the view that T increases emotional reactivity to a potential threat and facilitates adaptive arousal response in face of immediate social challenge.Highlights
▸ Suppression of testosterone (T) by a GnRH agonist lowers anxiety in male rhesus monkeys tested in a 2-min stare condition of the Human Intruder Paradigm; exogenous T restores baseline anxiety levels. ▸ Reduced LH may underlie the beneficial effects of the GnRH on anxiety. ▸ T promotes an adaptive arousal response in face of an immediate social threat.