Cat odour-induced anxiety--a study of the involvement of the endocannabinoid system.

ABSTRACT

RATIONALE Recent evidence suggests the involvement of the endocannabinoid (EC) system in the regulation of anxiety. OBJECTIVES: The aim of present work was to study the role of the EC system in cat odour-induced anxiety in rats. Materials and methods Male Wistar rats were exposed to cat odour in home and motility cages. Exposure of rats to elevated zero-maze was used to determine changes in anxiety. Effect of rimonabant (0.3-3 mg/kg), antagonist of CB1 receptors, was studied on cat odour-induced alterations in exploratory behaviour. Real-time PCR was used to determine gene expression levels of EC-related genes in the brain. RESULTS: Anxiogenic-like action of cat odour was evident in the elevated zero-maze. Cat odour increased the expression of FAAH, the enzyme responsible for the degradation of anandamide, in the mesolimbic area. By contrast, in the amygdala and periaqueductal grey (PAG) levels of NAPE-PLD, the enzyme related to the synthesis of anandamide, and FAAH were remarkably decreased. Cat odour also decreased the expression of enzymes related to metabolism of 2-archidonoyl-glycerol in the amygdala and PAG. Pre-treatment of rats with rimonabant (0.3-3 mg/kg) reduced the exploratory behaviour of rats, but did not affect cat odour-induced changes. CONCLUSION: Exposure to cat odour induces anxiogenic-like effect on the behaviour in rats. Cat odour also causes moderate increase in expression of EC-related genes in the mesolimbic area, whereas significant down-regulation is established in the amygdala and PAG. Relation of predator odour-induced anxiety to the inhibition of the EC system in the amygdala and PAG is supported by behavioural studies where blockade of CB1 receptors by rimonabant induces anxiogenic-like action.