Measuring fear and anxiety in the marmoset (Callithrix penicillata) with a novel predator confrontation model: effects of diazepam.

This report describes a new experimental method for measuring fear and anxiety in Cerrado marmosets (Callithrix penicillata). In order to test the sensitivity of the behavioral parameters to an anxiolytic substance, the effects of the benzodiazepine diazepam on the anxiety measures were examined. The strategy was to use a naturally occurring stimulus known to elicit anxiety and fear in this species. A taxidermized predator (the wild cat Felis tigrina) was chosen as the stimulus to induce anxiety-related behaviors on the basis of a preceding study in which various stimuli were systematically compared in their effectiviness to induce fear responses. The apparatus consisted of three parallel arms of equal dimensions, joining two perpendicular arms at each end, thus comprising a figure eight-like or five-arm continuous rectangular maze. The wild-cat was placed outside of one corner of the maze's outer parallel arms. Each subject was submitted to six treatments given in random order: three drug sessions (diazepam 1, 2 and 3 mg/kg, i.m.), saline, sham (injection control), and a control session, involving neither manipulation nor injection. Subjects were placed into the back of the chamber, out of sight of the 'predator', 20 min after a treatment and given free access to the maze for 30 min. The behavioral repertoire was recorded via videocamera. The following behaviors were considered to be possible indices of emotionality relevant to exposure to the predator in the paradigm used: scratching, scent marking, exploration, frequency and time spent in each of 13 defined sections of the maze. Administration of diazepam induced a significant reduction in scratching and an increase in the time spent in the vicinity of the 'predator', as well as in the frequency of exploratory behaviors, indicative of an anxiolytic effect. Gender did not influence the effect of treatment. These results suggest that this new ethologically-based test may be a useful method for studying anxiety and fear-induced avoidance in non-human primates and for pre-clinical research on psychoactive drugs.