At the behavioural level, this decline in AEA also appears to relate to changes in emotional behaviour. Specifically, exposure to predator odor stress is known to produce a behavioural phenotype of defensive burying that is believed to represent an anxiety-like behaviour (McGregor et al., 2004). Administration of an AEA uptake/FAAH inhibitor prior to stress exposure significantly attenuates the induction of this burying behaviour in a similar manner to anxiolytic agents (Hill et al., 2006). These data would suggest that the decline in AEA signaling that occurs in response to stress contributes to the increase in emotional and anxiety-like behaviours that accompanies stress exposure. Interestingly, this hypothesis may help to explain the anxiolytic effects of FAAH inhibitors. Specifically, a series of studies has consistently demonstrated that inhibition of FAAH does not produce anxiolytic effects unless the environmental conditions in which testing occurs are particularly aversive (Haller et al., 2009; Naidu et al., 2007). This finding suggests that inhibition of FAAH under stable conditions does little to modulate emotional behaviour, but following exposure to aversive environmental conditions, FAAH activity may increase which
