MIF, TRH, and simian social and motor behavior

MSH-release-inhibiting factor (MIF) and thyrotropin-releasing hormone (TRH) both have been reported to modify mood and activity in man. These two hypothalamic peptides were given intramuscularly across a 1000-fold dose range to 5 juvenile male M. nemestrina monkeys living in a social group. Motor activity was recorded automatically, and an observer counted various social behaviors. MIF increased motor activity for up to 11 hr. It decreased quiet foraging behavior, but did not change behaviors of social interaction. TRH did not stimulate motor behavior; high doses strongly suppressed it and produced apparent somatic distress. TRH increased behaviors of quiet rest and association and decreased environment exploration and low-intensity dominance behaviors. The lowest dose of TRH increased social play. Two monkeys showed repetitive, stereotyped behaviors even in baseline observations, and certain doses of TRH and MIF may have increased the frequency of these behaviors.