Emerging studies in rodents suggest that activation of the cannabinoid (CB) system within the brain may also regulate extinction learning and retention, similar to the effects of DCS. For example, activation of type 1 CB receptors, via agonists like Δ9-tetrahydrocannabinol (THC), facilitates extinction learning, whereas fear extinction does not occur when these receptors are disabled by pharmacological blockade or genetic deletion (Bitencourt et al., 2008; Chhatwal et al., 2005; de Oliveira Alvares et al., 2008; Lafenetre et al., 2007; Lin et al., 2008; Lin et al., 2009; Lutz, 2007; Marsicano et al., 2002; Pamplona et al., 2008; Pamplona et al., 2006; Roche et al., 2007). Pharmacologically enhancing endogenous cannabinoid (eCB) levels during extinction can enhance extinction retention and block return of extinguished fear in rats (Chhatwal et al., 2005). These studies suggest that the efficacy of extinction learning and retention can be enhanced via increasing activity of CB1 receptors.
