Neurochemical coding of myenteric neurones in the human gastric fundus S. PIMONT,*à S. BRULEY DES VARANNES,* à J. C. LE NEEL, à P. AUBERT,* J. P. GALMICHE,* à & M. NEUNLIST* *INSERM U 539, Place Alexis Ricordeau, Nantes, France  CIC-INSERM, Place Alexis Ricordeau, Nantes, France àDepartment of Gastroenterology and Surgery, University Hospital Ho ˆ tel-Dieu, Nantes, France Abstract The major functions of the stomach are under the control of the enteric nervous system (ENS), but the neuronal circuits involved in this control are largely unknown in humans. Enteric neurones can be characterized by their neuromediator or marker content, i.e. by neurochemical coding. The purpose of this study was to characterize the presence and co-localization of neurotransmitters in myenteric neurones of the human gastric fundus. Choline ace- tyltransferase (ChAT), neurone-specific enolase (NSE), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), substance P (SP) were detected by immunohistochemical methods in whole mounts of gastric fundus myenteric plexus (seven patients). Antibodies against ChAT and NOS labelled the majority of myenteric neurones identified by NSE (57.2 ± 5.6% and 40.8 ± 4.5%, respectively; mean ± SD). The proportions of VIP- and SP-immunoreactive neurones were significantly smaller, constituting 19.6 ± 6.9% and 16.0 ± 3.7%, respectively. Co-local- ization studies revealed five major populations repre- senting over 75% of the myenteric neurones: ChAT/-, 30.1 ± 6.1%; NOS/-, 24.2 ± 4.4%; ChAT/SP/-, 8.3 ± 3.1%; NOS/VIP/-, 7.2 ± 6.0%; ChAT/VIP/-, 4.9 ± 2.6. Some similarities are apparent in the neurochemical coding of myenteric neurones in the stomach and intestine of humans, and between the stomach of humans and animals, but striking differences exist. The precise functional role of the neurochemically identi- fied classes of neurones remains to be determined. Keywords human gastric fundus, myenteric plexus, neurochemical coding. INTRODUCTION The functions of the human stomach are wide ranging and include accommodation, mixing, and acid and mucus secretion. The fine-tuning of these functions is achieved via various humoral and neuronal pathways. The extrinsic nervous system is crucial for neuronal regulation of the stomach and control of gastric accom- modation and acid secretion. 1,2 However, the enteric nervous system (ENS) is another key neural regulator of gastric functions in animals and humans. In fact, mechanically induced reflexes can be evoked in isolated stomach devoid of extrinsic neuronal control. 3,4 In the stomach of small animals (guinea-pig, mouse), in contrast to other gut regions, the vast majority of enteric neurones are located in the myenteric plexus. 5 As tracing studies have shown that gastric myenteric neurones innervate both muscle and the mucosal target, 6–8 myenteric neurones might be involved in the control of motor as well as mucosal functions. Although a small ganglionated submucosal plexus exists in larger animals and humans, the vast majority of enteric neurones are still located in the myenteric plexus. 5 In the guinea-pig, enteric neurones have been clas- sified according to their morphology, innervation tar- get, neuromediator and marker content (i.e. their neurochemical code), and electrophysiological charac- teristics. 9–12 The neuronal retrograde tracing method, in combination with immunohistochemical methods, has made it possible to establish a correlation between the neurochemical code of enteric neurones and their putative functions in the stomach. 6–8 For instance, myenteric neurones immunoreactive for ChAT/SP or ChAT/ENK/GRP might function preferentially as muscle motor neurones, while ChAT/NPY and Address for correspondence Michel Neunlist, PhD, INSERM U539, University Hospital Ho ˆ tel Dieu, Place Alexis Ricordeau, 44035 Nantes Cedex, France. Tel.: +33(0)240087515; fax: +33(0)240087506; e-mail: michel.neunlist@sante.univ-nantes.fr Received: 21 March 2003 Accepted for publication: 30 July 2003 Neurogastroenterol Motil (2003) 15, 655–662 Ó 2003 Blackwell Publishing Ltd 655