Predatory stress as an experimental strategy to measure fear and anxiety-related behaviors in non-human primates

Natural defense-inducing stimuli are being increasingly exploited as a means to investigate the neural mechanisms underlying normal and pathological anxiety, as well as for the screening of new compounds with potential therapeutic use in human anxiety disorders. Such an approach, frequently used in rodents, has recently been employed in the Marmoset Predator Confrontation Test (MPCT). In this method, marmoset monkeys are individually confronted with a taxidermized predator (wild oncilla cat) in a previously habituated maze environment, while several easily discernable fear/anxiety-related behaviors are measured. Confrontation with the cat stimulus significantly altered ongoing behaviors, each habituating distinctively during repeated exposures; e.g. complete rapid habituation (alarm call), complete slow habituation (exploration, vigilance) or only partial habituation (proximity avoidance). Pharmacological validating studies with diazepam and buspirone induced a significant dose-dependent reversal of the fear-induced proximic avoidance and scratching/scent-marking behaviors, while exploration (smell/lick the maze, leg stand) was found to increase. The neuropeptide substance P and the selective 5-HT1A receptor antagonist WAY100635 resulted in a similar anxiolytic-like profile. The response pattern observed was not influenced by social isolation, handling/manual restraint, novel environment exposure or habituation to the stimulus or its location. Persistent defensive behavior and response pattern to diazepam was observed when naive versus MPCT-experienced marmosets were tested following a recent predatory stress. Taken together, the results indicate that the MPCT is a valuable experimental procedure to measure fear and anxiety-related behaviors in non-human primates.