DIFFERENT SUBPOPULATIONS OF CHOLINERGIC AND NITRERGIC MYENTERIC NEURONS PROJECT TO MUCOSA AND CIRCULAR MUSCLE OF THE GUINEA-PIG GASTRIC FUNDUS

Since the stomach lacks a well-developed ganglionated submucous plexus , the somata of enteric neurones innervating the muscle or the mucosa have to be localised within the myenteric plexus. The aim of this stud y was to determine the projection pathways and the neurochemical codin g of myenteric neurones innervating these different targets in the gas tric fundus. Myenteric cell bodies projecting to the mucosa or the cir cular muscle were retrogradely labelled by mucosa or muscle applicatio n of the fluorescent tracer DiI and subsequently characterised by thei r immunoreactivity for choline acetyltransferase (ChAT), nitric oxide synthase (NOS), substance P (SP) and/or neuropeptide Y (NPY). On avera ge 143+/-91 and 89+/-49 myenteric neurones were labelled from the muco sa and the circular muscle, respectively. DiI-labelled neurones were e ither ChAT- or NOS-positive. DiI-labelled ChAT-positive neurones were mainly ascending and outnumbered NOS-positive neurones, which were mai nly descending (79.3+/-6.2% vs 20.7+/-6.2% for mucosa neurones; 69.3+/ -11.1% vs 30.7+/-11.1% for muscle neurones). Three ChAT-positive subpo pulations (ChAT/-, ChAT/SP, ChAT/NPY) and two NOS-positive subpopulati ons (NOS/-, NOS/NPY) were found. ChAT/SP neurones projected mainly to the circular muscle (36.1+/-11.9% of the cholinergic muscle neurones; mucosa projection: 8.0+/-2.1%), whereas ChAT/NPY neurones projected ma inly to the mucosa (38.1+/-9.2% of the cholinergic mucosa neurones; mu scle projection: 5.7+/-2.4%). NOS/-cells projected predominantly to th e muscle. This study demonstrates polarised pathways in the myenteric plexus consisting nf ascending ChAT and descending NOS that innervate the circular muscle and the mucosa of the gastric fundus. The ChAT/SP neurones might function as circular muscle motor neurones, whereas ChA T/NPY neurones might represent secretomotor neurones.