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.

Mang, Christian F., Sebastian Truempler, Doris Erbelding, and Heinz Kilbinger. Modulation by NO of acetylcholine release in the ileum of wild-type and NOS gene knockout mice. Am J Physiol Gastrointest Liver Physiol 283: G1132-G1138, 2002 10.1152/ajpgi.00192.2002 inhibits the release of acetylcholine and cholinergic contractions in the small intestine of several species, but no information is available about the mouse ileum. This study examines the effects of NO on the electrically evoked release of 3 H]acetylcholine release and cholinergic contractions in preparations from wild-type mice and from eNOS knockout mice. Effects of L-NNA were specifically antagonized by L-arginine. In contrast, L-NNA and ODQ did not modify the release and contractions in preparations from nNOS knockout mice. The NO donor S-nitroso-N-acetyl-DLpenicillamine inhibited the electrically evoked release of [ 3 H]acetylcholine and longitudinal muscle contractions in a quantitatively similar manner in wild-type preparations as well as in nNOS and eNOS knockout preparations. We conclude that endogenous NO released by electrical field stimulation tonically inhibits the release of acetylcholine. Furthermore, data suggest that nNOS and not eNOS is the enzymatic source of NO-mediating inhibition of cholinergic neurotransmission in mouse ileum. neuronal nitric oxide synthase knockout mice; endothelial nitric oxide synthase knockout mice; cholinergic neurotransmission NITRIC OXIDE (NO) is a nonadrenergic, noncholinergic neurotransmitter that causes inhibition of intestinal motility (for review, see Ref. 24). The relaxant action of NO is probably not confined to its direct action on smooth muscle, because NO decreases intestinal motility also indirectly by inhibiting the release of the functionally most prominent excitatory enteric neurotransmitters acetylcholine and substance P. For example, exogenous NO (31) and NO donors (5) inhibit the electrically evoked release of acetylcholine from guinea pig ileum. Vice versa, NO synthase (NOS) inhibitors enhance the evoked release of acetylcholine from the ileum of guinea pig (10,20) and dog (7) as well as the electrically evoked cholinergic and tachykininergic contractions of guinea pig ileum (6,32). This suggests that endogenous NO, released by field stimulation, decreases the evoked release of acetylcholine from enteric neurones. There are, however, tissue and species differences in the neuromodulatory effect of NO: NO or NOS inhibitors do not modify the electrically evoked acetylcholine release from the colon of guinea pig and dog (22,29) and from stomach preparations of man (13

No abstract

The effects of GABA receptor agonists were investigated on guinea-pig isolated ileum longitudinal muscle with intact myenteric plexus. Electrical field stimulation (1 Hz, 10 s) of the histamine (1 microM)-precontracted preparation caused a contraction followed by a relaxation. Relaxations were inhibited by L-N(G)-nitroarginine (L-NA; EC50 3 microM) in a concentration-dependent manner. The inhibitory action of 10 microM L-NA was blocked by 10 microM L-arginine but not by D-arginine, which indicates that the relaxation was largely mediated by endogenous nitric oxide (NO). Tetrodotoxin (1 microM) reduced the relaxation only by about 50%. GABA and the GABA(B) agonist, baclofen, inhibited the field stimulation-induced longitudinal muscle relaxation in a concentration-dependent manner. The GABA(B) receptor antagonist, saclofen (10 microM), antagonised the effect of baclofen (apparent pA2 of saclofen: 5.6). Muscimol (10 microM) similarly inhibited the relaxation, and this inhibition was prevented by bicuculline (1 microM). It is concluded that nitrergic nerves of the guinea-pig myenteric plexus are endowed with GABA(A) and GABA(B) receptors which mediate inhibition of NO release.