FAAH and Anxiety: The endocannabinoids are important modulators of stress reactivity in humans and experimental animals.19,30 In rodent experiments, this modulation depends on the adverseness of environmental conditions, such as the intensity of ambient lighting.13,31,32 To test whether the prosocial actions of FAAH inhibition in BTBR mice might be due to a general reduction in anxiety, we asked whether URB597 exerted anxiolytic-like effects in the elevated plus maze test under the same dim lighting conditions used for the social approach test (5 lux).