Pharmacological modification of experimental depression in infant macaques.

This study provides evidence that mother--infant separation in macaques is a useful experimental model of depression. At the age of 6--8 months, seven M.fascicularis infants underwent two consecutive separations from their mothers lasting 21 and 15 days, respectively. The frequency and duration of a set of individual and social behaviours were recorded throughout each of the following experimental conditions: baseline, separation, reunion. In response to maternal separation, the infants showed marked increased in frequency of behaviours reflecting distress, self-directed activity or anxiety (e.g. vocalization, locomotion, body play). Both individual and social play behaviours were markedly suppressed in separated infants. During the second separation, one group of subjects was given, in a 'double blind' fashion, daily doses of 5 mg/kg of an antidepressant, desmethylimipramine (DMI), i.m. Treatment with DMI markedly diminished most of the behavioural alterations induced by separation. In particular, the increases in distress and self-directed behaviours as well as the suppression of play activities were prevented or antagonized. Plasma levels of DMI after 5 days of administration were in the range of 50--150 ng/ml.