Cannabinoid type 1 receptors (CB1r) are an important modulatory site for emotional behavior. However,
little is known on the effects of CB1r ligands on emotionality aspects of primates, even with their highly
similar behavioral response and receptor density/distribution as humans. Thus, we analyzed the effects of
the CB1r agonist WIN 55,212-2 (WIN; 1 mg/kg) and the antagonist AM 251 (AM; 2 mg/kg), systemically
administered prior to a single brief (15 min) exposure to a novel open-field (OF) environment, on the
behavior of individually tested adult black tufted-ear marmosets. Both WIN- and AM-treated subjects,
compared to vehicle controls, had significantly lower rates of long (contact) calls and exploration, while
higher levels of vigilance-related behaviors (scan/glance); these are indicators of anxiolysis in this setup.
Changes in locomotion were not detected. However, in the vehicle and AM-groups, sojourn in the peripheral
zone of the OF was significantly higher than in its central region. WIN-treated marmosets spent an
equivalent amount of time in both zones. Therefore, activation or blockade CB1r function prior to a short
and individual exposure to an unfamiliar environment exerted a significant and complex influence on
different behavioral indicators of anxiety in these monkeys (i.e., a partially overlapping anxiolytic-like
profile). AM 251, however, has no anxiolytic effect when the time spent in the center of the OF is considered.
This is a major difference when compared to the WIN-treated group. Data were compared to the
response profile reported in other pre-clinical (rodent) and clinical studies.