al., 2007) and also decrease the recovery of conditioned fear responses in rats (Chhatwal et al., 2005) if given prior to extinction learning. Conversely, co-administration of CB1 antagonists, such as AM251 and rimonabant [SR141716], block the extinction enhancing effects of these CB1 agonists and reuptake/metabolism inhibitors (Chhatwal et al., 2005; de Oliveira Alvares et al., 2008; Varvel et al., 2007). When administered alone, CB1 antagonists lead to a profound disruption of extinction retention when given either prior to extinction learning or immediately following extinction learning, suggesting that CB1 receptor activation is necessary during extinction learning and for consolidation of extinction memories in order to successfully retrieve these memories at a later time (Chhatwal et al., 2005; de Oliveira Alvares et al., 2008; Lin et al., 2009; Marsicano et al., 2002; Pamplona et al., 2008; Pamplona et al., 2006; Suzuki et al., 2004). Consistent with these results are findings that extinction of fear is impaired in CB1 receptor knockout mice when compared to wild-type mice (Kamprath et al., 2006; Marsicano et al., 2002; Varvel et al., 2005).
