Changes in Primate Social Behavior After Treatment with Alpha-Methyl-Para-Tyrosine

Abstract

The catecholamine hypothesis of the affective disorders relates the depressive syndromes in man to a deficiency of dopamine and norepinephrine. Two subjects within a social group of nonhuman primates were treated with alpha-methyl-paratyrosine, an inhibitor of the synthesis of these catecholamines. Quantifiable social interactions and appearance changed with drug treatment. Both treated animals initiated fewer total social interactions, including grooming, threats and attacks. Total social responses and social-sexual presentations remained stable. The animals showed retarded motor activity and assumed withdrawn postures, huddled with arms crossed and heads hung low. Their social-affective responses and facial expressions suggested a lack of concern with the environment. These behaviors, similar in some ways to the depressive state as seen in man, were reversible, and were accompanied by a decreased excretion of two metabolites of norepinephrine. An attempt to reverse the syndrome in 1 animal using L-DOPA was unsuccessful. This model may provide some insight into the neurochemical mechanisms of the human depressive syndromes. Further efforts to reverse the syndrome may have therapeutic relevance as well.