Evidence of changes in functional spreading of neural information within the myenteric reflex by Cannabinoid-1 receptor activation

Background: Propulsion along the intestine appears to occur by the action of a series of local reflexes which cause oral contraction and anal relaxation of circular muscle. This is associated with typical electrophysiological changes.

Aim: Aim of the study was to investigate influence of local electrical field stimulation (EFS) on gastrointestinal electrophysiology of murine large bowel using a 12 channel stimulation electrode in a newly designed model of the ascending peristaltic reflex with simultaneous intracellular recording.

Methods: Isolated proximal colon without mucosa and submucosa was investigated. Reflex responses were initiated by EFS (12 electrodes (SE) 0.45mm apart from each other/1mm electrode-width) and excitatory (EJP) and inhibitory (IJP) junction potentials were recorded from circular smooth muscle cells by intracellular recording.

Results: Circular smooth muscle cells display a stable resting membrane potential (–56.7±6.9mV, n=13). EFS (single pulses, 0.3ms; 15V) elicited TTX-sensitive, neuronal induced EJP (atropine-sensitive) and IJP (biphasic: fast (fIJP, apamin-sensitive) and slow (sIJP, LNNA sensitive)) which showed characteristic responses dependent on the distance between stimulation and recording site. The EJP was maximal when stimulation-site SE6/7 was used (141±34% compared to SE1). A wave like EJP can be recorded over the different SE resulting in a maximal EJP at SE6/7 with a maximal projection distance of 17mm. Both components of IJP were maximal during direct stimulation (SE1) and gradually decreased to SE7. EFS at a distance of more than 8mm from the recording site do not produce IJP. The specific CB-1 receptor agonist WIN 55,212–2 concentration dependently reduced amplitude of EJP and IJP and cause an “oral-shift“ of the ascending part of myenteric peristaltic reflex demonstrating the involvement of CB1-receptors by influencing neurotransmission and reflex-timing.

Conclusions: Spatial projections of neurones within the peristaltic reflex can be determined using a electrophysiological setup with multiple closely spaced stimulation sites along the colon. In this functional setting excitatory and inhibitory influences project under basal condition maximally 17mm. These functional projections can be modified pharmacological e.g. by cannabinoid-1 receptor activation. This principle offers a new explanation for the development and mechanisms of propagated contractile activity.