Differential effects of anandamide on acetylcholine release in the guinea‐pig ileum mediated via vanilloid and non‐CB₁ cannabinoid receptors

Abstract

3). The concentration-response curves for anandamide were shifted to the right by 1 mM capsazepine (pK B 7.5 and 7.6), and by the combined blockade of NK 1 and NK 3 tachykinin receptors with the antagonists CP99994 plus SR142801 (each 0.1 mM). The CB 1 and CB 2 receptor antagonists, SR141716A (1 mM) and SR144528 (30 nM), did not modify the facilitatory eects of anandamide.3 Anandamide inhibited the electrically-evoked release of [ 3 H]-acetylcholine (pEC 50 5.8) and contractions (pEC 50 5.2). The contractile response to the muscarinic agonist methacholine was not signi®cantly aected by 10 mM anandamide. 4 The inhibitory eects of anandamide were not changed by either capsazepine (1 mM), SR144528 (30 nM) or CP99994 plus SR142801 (each 0.1 mM). SR141716A (1 mM) produced rightward shifts in the inhibitory concentration-response curves for anandamide yielding pK B values of 6.6 and 6.2. 5 CP55940 inhibited the evoked [ 6 The experiments con®rm the existence of release-inhibitory CB 1 receptors on cholinergic myenteric neurones. We conclude that anandamide inhibits the evoked acetylcholine release via stimulation of a receptor that is dierent from the CB 1 and CB 2 receptor. Furthermore, anandamide increases basal acetylcholine release via stimulation of vanilloid receptors located at primary aerent ®bres.

Cannabidiol Reverses MK-801-Induced Disruption of Prepulse Inhibition in Mice

“…Coexpression of CB 1 and TRPV1 receptors has been demonstrated in rat dorsal root ganglion neurons (Ahluwalia et al, 2000;Bridges et al, 2003) and in rat mesencephalic cultures (Kim et al, 2005). Tonic activation of CB 1 receptors exerts an inhibitory control over TRPV1 receptors, as anandamide or capsaicin-induced TRPV1 receptor-mediated effects are potentiated in the presence of a CB 1 receptor antagonist (Maccarrone et al, 2000;Mang et al, 2001;Lever and Malcangio, 2002). Furthermore, cell death induced by capsaicin and the CB 1 agonist HU-210 in rat mesencephalic culture was reversed by the CB 1 receptor antagonist AM 251 and capsazepine, respectively, suggesting functional crosstalk between the two receptors (Kim et al, 2005).…”

Pharmacological characterization of cannabinoid receptor activity in the rat‐isolated ileum myenteric plexus‐longitudinal muscle preparation

“…Each pulse at any given frequency was of 0.5 ms duration and at a voltage that was 10% greater than that required to elicit maximal contractions. Supramaximal voltage was employed to ensure that the neurones sensitive to the respective frequency within the field of stimulus were stimulated, and that the EFS conditions were comparable with previous studies Coutts and Pertwee, 1997;Mang et al, 2001;Borelli et al, 2004).…”

“…Results from these studies have suggested that psychotropic cannabinoids decrease intestinal motility by reducing the release of contractile neurotransmitters, such as acetylcholine (ACh) from the myenteric plexus (Coutts and Pertwee, 1997;Mang et al, 2001), through an activation of the cannabinoid CB 1 receptors (nomenclature follows Alexander et al, 2008) located on the somatodendritic and terminal regions of the neurones . Although the guinea pig ileum has long served as a useful bioassay for describing the inhibitory action of cannabinoids on intestinal transit observed in the mouse or rat in vivo, it is important that isolated ileal tissues from the latter species are used for studying cannabinoid effects.…”

“…The former action has been invariably studied by evaluating either the distance travelled or the delay in the time taken for the transit of an orally or intra-duodenally administered non-absorbable marker from the pylorus to the caecum of the animal. While in vivo bioassays have played an important role in characterizing the pharmacology of cannabinoids on intestinal motility under both physiological and pathophysiological states, the mechanism of the depressant action has been inferred from in vitro studies performed on segments or strips of the isolated ileum of the guinea pig Coutts and Pertwee, 1997;Izzo et al, 1998;Mang et al, 2001), and, to a lesser extent, of a human Manara et al, 1998;Guagnini et al, 2006). Therefore, to date, the guinea pig ileum has been the standard in vitro bioassay for screening cannabinoids on the small intestine.…”

“…Therefore, to date, the guinea pig ileum has been the standard in vitro bioassay for screening cannabinoids on the small intestine. The in vitro studies on this tissue have focussed on the ability of cannabinoids to inhibit either the peristaltic reflex in segments of whole ileum (Heinemann et al, 1999;Izzo et al, 2000), synaptic transmission (Lopez-Redondo et al, 1997), or the low frequency electrical field simulation (EFS)-evoked release of neurotransmitters (Coutts and Pertwee, 1997;Mang et al, 2001;Begg et al, 2002a,b) or subsequent contraction of the longitudinal Coutts and Pertwee, 1997;Mang et al, 2001) or circular (Izzo et al, 1998) smooth muscle layers.…”