Endocannabinoid modulation of circadian- and stress-dependent effects on rat short-term memory

Cannabinoid drugs often induce biphasic effects on cognitive and emotional behavior depending on the level of stress and emotional arousal at the time of drug consumption. The effects of stress on endocannabinoids appear to be regionally specific and time-dependent relative to exposure to stress. Stress-induced changes in corticosterone affect memory. We evaluated how different stress intensities after encoding influence rat short-term memory in an object recognition task, whether the effects depend on circadian variation of corticosterone and if exogenous augmentation of anandamide levels could restore any observed impairment. Mild forced swimming stress selectively impaired memory retention in rats tested in the morning, while the stronger forced swimming stress caused memory impairments, independently of the testing time. The anandamide hydrolysis inhibitor URB597 reverted these impairing effects of stress on memory performance, leaving memory unaltered in the non-impaired groups.