Cannabinoid-1 (CB1) receptors regulate colonic propulsion by acting at motor neurons within the ascending motor pathways in mouse colon

Sibaev A, Yuce B, Kemmer M, Van Nassauw L, Broedl U, Allescher HD, Goke B, Timmermans J, Storr M. Cannabinoid-1 (CB1) receptors regulate colonic propulsion by acting at motor neurons within the ascending motor pathways in mouse colon. Am J Physiol Gastrointest Liver Physiol 296: G119-G128, 2009. First published November 25, 2008; doi:10.1152/ajpgi.90274.2008.-Cannabinoid-1 (CB1) receptors on myenteric neurons are involved in the regulation of intestinal motility. Our aim was to investigate CB1 receptor involvement in ascending neurotransmission in mouse colon and to characterize the involved structures by functional and morphological means. Presence of the CB1 receptor was investigated by RT-PCR, and immunohistochemistry was used for colabeling studies. Myenteric reflex responses were initiated by electrical stimulation (ES) at different distances, and junction potentials (JP) were recorded from circular smooth muscle cells by intracellular recording in an unpartitioned and a partitioned recording chamber. In vivo colonic propulsion was tested in wild-type and CB1-/- mice. Immunostaining with the cytoskeletal marker peripherin showed CB1 immunoreactivity both on Dogiel type I and type II neurons. Further neurochemical characterization revealed CB1 on choline acetyltransferase, calretinin-, and 5-HT-immunopositive myenteric neurons, but nitrergic neurons appeared immunonegative for CB1 immunostaining. Solitary spindle-shaped CB1-immunoreactive cells in between smooth muscle cells lacked specific markers for interstitial cells of Cajal or glial cells. ES elicited neuronally mediated excitatory JP (EJP) and inhibitory JP. Gradual increases in distance resulted in a wave-like EJP with EJP amplitudes being maximal at the location of stimulating electrode 6 and a maximal EJP projection distance of similar to 18 mm. The CB1 receptor agonist WIN 55,212-2 reduced the amplitude of EJP and was responsible for shortening the oral spreading of the excitatory impulse. In a partitioned chamber, WIN 55,212-2 reduced EJP at the separated oral sites, proving that CB1 activation inhibits interneuron-mediated neurotransmission. These effects were absent in the presence of the CB1 antagonist SR141716A, which, when given alone, had no effect. WIN 55,212-2 inhibited colonic propulsion in wild-type mice but not in SR141716A-pretreated wild-type or CB1-/- mice. Activation of the CB1 receptor modulates excitatory cholinergic neurotransmission in mouse colon by reducing amplitude and spatial spreading of the ascending electrophysiological impulses. This effect on electrophysiological spreading involves CB1-mediated effects on motor neurons and ascending interneurons and is likely to underlie the here reported in vivo reduction in colonic propulsion.