Neuronal control of the gastric sling muscle of the guinea pig

The gastric sling (oblique) muscle (GSM), located close to the lower esopha geal sphincter (LES), is involved in gastric motor function and may coopera te with the LES in controlling propulsion between the esophagus and stomach . Neuronal pathways and transmission to the GSM were investigated in isolat ed esophagus-stomach preparations by using intracellular recording with the focal electrical stimulation and neuroanatomical tracing method. Focal sti mulation on the GSM evoked inhibitory junction potentials (IJPs) that were reduced to 45% by 100 mu M N-nitro-L-arginine and subsequently blocked by 0 .5 mu M apamin, thereby unmasking excitatory junction potentials (EJPs), wh ich were abolished by 1 mu M hyoscine. Vagal and esophageal stimulation evo ked IJPs that were blocked by 100 mu M hexamethonium. Vagal stimulation als o evoked EJPs after blockade of IJPs. Application of 1,1'-didodecyl-3,3,3', 3'-tetramethyl indocarbocyanine perchlorate to the GSM labeled muscle motor neurons located in the stomach mainly close to the GSM, with a few neurons (2%) in the esophagus. The majority (79%) of labeled neurons were immunore active for choline acetyltransferase and, hence, excitatory motor neurons. Inhibitory motor neurons (nitric oxide synthase immunoreactive; 15%) were c lustered in the midline near the gastroesophageal region. These results dem onstrate that the GSM is innervated primarily by gastric excitatory and inh ibitory motor neurons and some esophageal neurons. Both excitatory (acetylc holine) and inhibitory (nitric oxide and apamin-sensitive component) transm ission can be activated via vagal-enteric pathways. J. Comp. Neurol. 412:66 9-680, 1999. (C) 1999 Wiley-Liss, Inc.