Rhesus monkeys are regarded as suitable animals in which to investigate the behavioral problems of humans. The subjects for this study were social colonies of healthy adult monkeys aged 3-5 years, weighing 4-6 kg. Each colony comprised one male and seven females housed in 20' x 12' x 8' cages. The monkeys were kept under controlled conditions of temperature (22 ± 5ºC), humidity (55-60%), ventilation (10-15 air changes per hour) and light (300 lux intensity) in a 12-h light/dark cycle, to maintain their physiological rhythm. A balanced diet was provided in the morning and evening, and water was available ad libitum.

The animals were allowed 4-6 weeks to habituate to their new surroundings. During this habituation period, they were caught and removed from the cage once a week and administered saline, either intramuscularly or orally. Behavioral observations took place prior to and after drug or vehicle treatment, producing a baseline control. The checklist of social and solitary behavioral responses used was a modified version (Palit et al. 1997) of the parameters described by Schlemmer & Davis (1983). Behavior was observed via a video monitor placed in an adjacent room, with two 180° rotating video cameras with zoom lenses fixed in the behavioral chamber. All behavioral responses were recorded for analysis.

On any one day, only one animal from each group was injected with an antidepressant drug. All monkeys were injected on a rotational basis, and scores of their normal behavior were compared with that observed after treatment. After drugging, the subject's behavior was observed for 1 min at 10-min intervals over 2 h. Behavioral scores from these twelve 1-min intervals were summed, with the total representing the day's score for that monkey. Monkeys were also observed at 4, 6, 8 and 24 h post-treatment, to check for any significant alteration in behavior. At least 10 days passed before each monkey was reused.

Imipramine (16 mg/kg) produced mild changes in social and solitary behavior in these monkeys. Locomotion and vigilance decreased significantly, and a high degree of piloerection was observed. Fluoxetine (20 mg/kg) produced a marked decrease in social and solitary behavioral responses. Centpropazine (40 mg/kg), a new antidepressant, produced a mild decrease in social and solitary behavior. It may be concluded that imipramine and fluoxetine showed similar sedative effects, which were not observed with centpropazine.

Paper presented at Measuring Behavior 2002 , 4^th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands

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