Submitted on April 9, 2008
Revised on May 6, 2008
Accepted on May 12, 2008
Cannabinoid CB2 receptors in the enteric nervous system modulate gastrointestinal contractility in lipopolysaccharide-treated rats
Marnie Duncan1, Abdeslam Mouihate2, Ken Mackie3, Catherine M Keenan1, Nancy E Buckley4, Joseph S. Davison5, Kamala D Patel PhD1, Quentin J. Pittman1, and Keith A Sharkey1*
1 University of Calgary
2 Health Sciences Centre, Faculty of Medicine, University of Calgary
3 Indiana University
4 California State Polyechnic University
5 University of Calgary, Faculty of Med.
* To whom correspondence should be addressed. E-mail: ksharkey{at}ucalgary.ca.
Enhanced intestinal transit due to lipopolysaccharide (LPS) is reversed by cannabinoid (CB)2 receptor agonists in vivo, but the site and mechanism of action is 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 (2h; 65µg/kg, i.p.) 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, though 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. Taken together, we conclude that activation of CB2 receptors in the enteric nervous system of the gastrointestinal tract dampens endotoxin-induced enhanced intestinal contractility.
