Cannabinoid CB2 receptors in the enteric nervous system modulate gastrointestinal contractility in lipopoly saccharide-treated rats.

Enhanced intestinal transit due to lipopolysaccharide (LPS) is reversed by cannabinoid (CB)₂ receptor agonists in vivo, but the site and mechanism of action are unknown. We have tested the hypothesis that CB₂ receptors are expressed in the enteric nervous system and are activated in pathophysiological conditions. Tissues from either saline- or LPS-treated (2 h; 65 µg/kg ip) rats were processed for RT-PCR, Western blotting, and immunohistochemistry or were mounted in organ baths where electrical field stimulation was applied in the presence or absence of CB receptor agonists. Whereas the CB₂ receptor agonist JWH133 did not affect the electrically evoked twitch response of the ileum under basal conditions, in the LPS-treated tissues JWH133 was able to reduce the enhanced contractile response in a concentration-dependent manner. Rat ileum expressed CB₂ receptor mRNA and protein under physiological conditions, and this expression was not affected by LPS treatment. In the myenteric plexus, CB₂ receptors were expressed on the majority of neurons, although not on those expressing nitric oxide synthase. LPS did not alter the distribution of CB₂ receptor expression in the myenteric plexus. In vivo LPS treatment significantly increased Fos expression in both enteric glia and neurons. This enhanced expression was significantly attenuated by JWH133, whose action was reversed by the CB₂ receptor antagonist AM630. Taking these facts together, we conclude that activation of CB₂ receptors in the enteric nervous system of the gastrointestinal tract dampens endotoxin-induced enhanced intestinal contractility. [ABSTRACT FROM AUTHOR]