Brainstem pathways responsible for oesophageal control of gastric motilityand tone in the rat

1. Previous anatomical studies indicate that the nucleus of the solitary tr act, pars centralis (NSTc) contains the neurones which receive vagal affere nt input from the oesophagus. The purpose of the present study was to chara cterize the NSTc circuits in the medulla that may be responsible for oesoph ageal control of gastric motility. 2. Moderate balloon distension of the oesophagus of the rat (14-18 mmHg) pr ovoked a significant reduction in gastric motility and tone recorded with s train gauges. This receptive relaxation effect was eliminated by bilateral lesions centred on the NSTc. . NSTc cells activated by oesophageal distension were labelled extracellula rly and juxtacellularly with neurobiotin. NSTc neurones send axonal project ions throughout the entire rostral-caudal extent of the dorsal motor nucleu s of the vagus (DMN). These NSTc-DMN connections were confirmed by retrogra de transport of neurobiotin from DMN to NSTc. NSTc neurones were observed w ith dendrites arborizing within the ependymal lining of the fourth ventricl es. Thus, NSTc neurones may be in position to monitor bloodborne or ventric ular agents and to alter the function of gastric-vago-vagal reflexes in res ponse to these stimuli. 4. Neurophysiological recordings identified two subpopulations of DMN neuro nes which may be either activated or inhibited by oesophageal distension. N eurones excited by oesophageal distension were located mainly lateral and c audal in the DMN; neurones inhibited by oesophageal stimulation were locate d in medial and rostral DMN. 5. Our neurobiotin tracing results verified earlier studies showing that th e NSTc projects to the intermediate reticular nucleus and the compact divis ion of the nucleus ambiguus. Additionally, we found that the NSTc may be in volved in reciprocal connections with the anterior, rostrolateral NST. 6. These results suggest that the gastric relaxation evoked by oesophageal distension is critically dependent on intact brainstem vago-vagal circuits. The NSTc, the recipient of oesophageal afferent projections from the vagus nerve, sends axons to the entire DMN, the source of parasympathetic contro l of the stomach. DMN neurones respond differentially to oesophageal disten sion, reinforcing the view that oesophageal afferents may provoke gastric r elaxation by activating a vagal inhibitory pathway while simultaneously inh ibiting a vagal excitatory pathway.