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NEUROREGULATION AND MOTILITY

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

¹Department of Internal Medicine II and ²Institute for Surgical Research Ludwig Maximilians University, Munich, Germany; ³Department of Internal Medicine, Teaching Hospital of the Ludwigs-Maximilians-University, Garmisch-Partenkirchen, Germany; ⁴Laboratory of Cell Biology & Histology, University of Antwerp, Belgium; ⁵Department of Medicine, Division of Gastroenterology, University of Calgary, Calgary, Alberta, Canada

Submitted 2 April 2008 ; accepted in final form 13 November 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 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.

peristaltic reflex; enteric nervous system; electrophysiology

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