Keverne, E. B., Martensz, N. D., Tuite, B. 1989. Beta-endorphin concentrations in cerebrospinal fluid of monkeys are influenced by grooming relationships . Psychoneuroendocrinology 14(1-2), 155-161 .

This report presents changes in the brain's opioid system contingent on grooming in monkeys.When isolated monkeys were permitted to interact in pairs, the most significant feature of their interaction was increased time spent grooming their partner. In all except one pair this was reciprocal. In all monkeys except one pair, there was an increase in CSF beta-endorphin concentrations, ranging from 17% to 186%.The finding that CSF beta-endorphin increased following social contact in previously isolated monkeys strongly implicates an action of affiliative behaviour on the endogenous opioid system. The drug-induced changes in grooming and seeking of close social contact (grooming invitations) are particularly interesting in view of the hypothesis that the positive affect arising from social bonds may be mediated by cerebral endorphin-containing systems.