Peripheral motor action of glucagon-like peptide-1 through enteric neuronal receptors A. AMATO,* L. CINCI ,  A. ROTONDO,*, à R. SERIO,* M. S. FAUSSONE-PELLEGRINI ,  M. G. VANNUCCHI   1 & F. MULE ` * *Dipartimento di Biologia cellulare e dello Sviluppo, Universita ` di Palermo, Palermo Italy  Dipartimento di Anatomia, Istologia e Medicina legale, Universita ` di Firenze, Firenze, Italy àDipartimento di Medicina, Pneumologia, Fisiologia e Nutrizione Umana, Universita ` di Palermo, Palermo Italy Abstract Background Glucagon-like peptide-1 (GLP-1) is a proglucagon-derived peptide expressed in the ente- roendocrine-L cells of small and large intestine and released in response to meal ingestion. Glucagon-like peptide-1 exerts inhibitory effects on gastrointestinal motility through vagal afferents and central nervous mechanisms; however, no data is available about a direct influence on the gastrointestinal wall. Our aim was to investigate the effects of GLP-1 on the spontaneous and evoked mechanical activity of mouse duodenum and colon and to identify the presence and distribution of GLP-1 receptors (GLP-1R) in the muscle coat. Methods Organ bath recording technique and immunohistochemistry were used. Key Results Glucagon-like peptide-1 (up to the con- centration of 1 lmol L )1 ) failed to affect spontaneous mechanical activity. It caused concentration-depen- dent reduction of the electrically evoked cholinergic contractions in circular smooth muscle of both intes- tinal segments, without affecting the longitudinal muscle responses. Glucagon-like peptide-1 inhibitory effect was significantly antagonized by exendin (9–39), an antagonist of GLP-1R. In both intestinal prepara- tions, GLP-1 effect was not affected by guanethidine, a blocker of adrenergic neurotransmission, but it was significantly reduced by N x -nitro-L-arginine methyl ester, inhibitor of nitric oxide (NO) synthase. Gluca- gon-like peptide-1 failed to affect the contractions evoked by exogenous carbachol. Immunohistochem- istry demonstrated GLP-1R expression in the enteric neurons. Furthermore, 27% of GLP-1R immunoreac- tive (IR) neurons in the duodenum and 79% of GLP- 1R-IR neurons in the colon, co-expressed nNOS. Conclusions & Inferences The present results suggest that GLP-1 is able to act in the enteric nervous system by decreasing the excitatory cholinergic neurotrans- mission through presynaptic GLP-1Rs, which modu- late NO release. Keywords acetylcholine, colon, duodenum, enteric nervous system, GI hormones, immunohistochemis- try, nitric oxide. Abbreviations: ACh, acetylcholine; ChAT, acetylcholine transferase; EFS, electrical field stimulation; GLP-1, glu- cagon-like peptide-1; GLP-1R, glucagon-like peptide-1 receptor; IPANs, intrinsic primary afferent neurons; NO, nitric oxide; nNOS, neuronal nitric oxide-synthase; IR, immunoreactivity; L-NAME, N x -nitro-L-arginine methyl ester; CCh, carbachol; TTX, tetrodotoxin. Glucagon-like peptide-1 (GLP-1) is a proglucagon- derived peptide expressed in the endocrine pancreas and in the L-type enteroendocrine cells mainly located in duodenum, distal small intestine and colon. 1,2 Glucagon-like peptide-1 is considered an important incretin, which, at physiological concentrations, pot- entiates glucose-induced insulin release and inhibits glucagon release, properties that provide the rationale for reducing glycaemia and for its potential use as a therapeutic agent in the treatment of diabetes. 3,4 However, several studies have suggested multiple additional effects, including a regulatory role in the control of the appetite and energy intake. 5,6 This hormone may contribute to the so-called Ôileal breakÕ, a mechanism by which the presence of nutrients in the distal small intestine causes inhibition of the upper Address for correspondence Flavia Mule `, Dipartimento di Biologia cellulare e dello Sviluppo, Laboratorio di Fisiologia generale, Universita ` di Palermo, Viale delle Scienze, 90128 Palermo, Italy. Tel: 39 091 23897515; fax: 39 091 6577501; e-mail: fmule@unipa.it 1 The author is the coordinator of the immunohistochemical studies. Received: 28 September 2009 Accepted for publication: 29 September 2009 Neurogastroenterol Motil (2010) 22, 664–e203 doi: 10.1111/j.1365-2982.2010.01476.x Ó 2010 Blackwell Publishing Ltd 664