GLP-2 receptor expression in excitatory and inhibitory enteric neurons and its role in mouse duodenum contractility L. CINCI ,* M. S. FAUSSONE-PELLEGRINI ,* A. ROTONDO,  F. MULE `  & M. G. VANNUCCHI * *Department of Anatomy, Histology and Forensic Medicine, Section of Histology, University of Florence, Viale G. Pieraccini 6, Florence, Italy  STEMBIO Department, Physiology Laboratory, University of Palermo, Viale delle Scienze, Palermo, Italy Abstract Background Glucagon-like peptide 2 (GLP-2), a nutri- ent-responsive hormone, exerts various actions in the gastrointestinal tract that are mediated by a G-protein coupled receptor called GLP-2R. A little information is available on GLP-2R expression in enteric neurons and nothing on the interstitial cells of Cajal (ICC). Methods We investigated presence and distribution of the GLP-2R in the mouse duodenum by immunohis- tochemistry and the potential motor effects of GLP-2 on the spontaneous and neurally evoked mechanical activity. Key Results The GLP-2R was expressed by the myenteric and submucosal neurons. Labelling was also present in nerve varicosities within the circular mus- cular layer and at the deep muscular plexus (DMP). No immunoreactive nerve fiber was seen within the longi- tudinal muscle layer. The GLP-2R-positive neurons were either excitatory (SP- and choline-acetyltransfer- ase-positive) or inhibitory (vasoactive intestinal poly- peptide and nNOS-positive). The ICC, both at the myenteric plexus and at the DMP, never expressed GLP- 2R but, especially those at the DMP, were surrounded by GLP-2R-positive nerve varicosities co-expressing either excitatory or inhibitory neurotransmitters. Quantitative analysis demonstrated a consistent prev- alence of GLP-2R on the excitatory pathways. In agreement, the functional results showed that the administration of GLP-2 in vitro caused decrease of the spontaneous contractions mediated by nitric oxide release and reduction of the evoked cholinergic contractions. Conclusions & Inferences The present findings indicate that the GLP-2R is expressed by inhibitory and excitatory neurons, the GLP-2 inhibits the muscle contractility likely decreasing cholinergic neurotransmission and increasing nitric oxide pro- duction, and this effect is possibly mediated by the ICC-DMP recruitment. Keywords enteric neurons, excitatory neurotrans- mitters, glucagon-like hormones, immunohisto- chemistry, inhibitory neurotransmitters, intestinal motility. INTRODUCTION Glucagon- like peptide 2 (GLP-2), first recognized as an intestinal growth factor, 1 is a 33-amino-acid peptide mainly produced by the enteroendocrine L-cells located in the duodenum, distal small intestine, and colon. 2,3 There are several evidences that GLP-2 inhibits gastro- intestinal motility in laboratory mammals 4–6 whereas results from human studies are conflicting. In fact, while Meier and co-workers 7 showed that GLP-2 did not influence gastric emptying, another study demon- strated a dose-dependent increase in gastric emptying time after GLP-2 infusion compared to controls. 8 The GLP-2 effects are due to the interaction with a specific receptor (GLP-2R) coupled to a G protein and belonging to the class B glucagon-secretin receptor family. 9 GLP-2 binding to the transfected receptor caused an increase in adenosine 3¢,5¢-cyclic monophos- phate (cAMP) consistent with findings from studies of related members of the glucagon/GLP-1R family. 9,10 Furthermore, it has also been demonstrated that Address for Correspondence Prof. Maria Giuliana Vannucchi MD PhD, Department of Anatomy, Histology and Forensic Medicine, Section of Histology, University of Florence, Viale Pieraccini, 6, 50139 Florence, Italy. Tel: +39 055 4271389; fax: +39 055 4271385; e-mail: mariagiuliana.vannucchi@unifi.it Received: 14 February 2011 Accepted for publication: 13 June 2011 Neurogastroenterol Motil (2011) 23, e383–e392 doi: 10.1111/j.1365-2982.2011.01750.x Ó 2011 Blackwell Publishing Ltd e383