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

Abstract

It has long been known that the oesophageal distension produced by swallowing elicits a powerful proximal gastric relaxation (Cannon & Leib, 1911). This reflex was termed the 'receptive relaxation reflex' and is an important mechanism which increases gastric volume and reduces intragastric pressure to ensure that swallowed food is efficiently transported to the stomach. Results from several laboratories (Abrahamsson & Jansson, 1969;Jansson, 1969;Miolan & Roman, 1984;Sengupta et al. 1989) have shown that this potent gastroinhibition results from stimulation of low threshold mechanoreceptive afferents of the vagus nerve, and that the reflex requires intact vagal connections between the brainstem, oesophagus and stomach. Recent tract-tracing techniques have shown that vagal afferents from the upper alimentary canal, including the oesophagus, are viscerotopically represented within the nucleus of the solitary tract. In particular, oesophageal vagal afferents were found to terminate specifically within the central

Excitatory and inhibitory local circuit input to the rat dorsal motor nucleus of the vagus originating from the nucleus tractus solitarius

“…Electrophysiological and anatomical experiments imply the existence of a connection between the NTS and DMV, which alters functional output of the vagus nerve onto, for example, gastrointestinal viscera [5,18,21,23,32,35]. Although most have focused on an inhibitory connection, [11,18,25,32] the existence of an excitatory connection has also been suggested [5,32].…”

“…Although most have focused on an inhibitory connection, [11,18,25,32] the existence of an excitatory connection has also been suggested [5,32]. Anatomical evidence for the existence of a direct connection between the NTS and DMV is based primarily on dye injections into the NTS [23], retrograde transneuronal viral labeling of NTS neurons after infection of terminal fields in the viscera [6,12], ormorphological identification of neurons known to project to DMV [12]. However, these studies do not directly demonstrate synaptic connections between the nuclei and provide little information about the function or organization of connectivity with individual DMV cells.…”

Characterization of neurons of the nucleus tractus solitarius pars centralis

“…This reduced heterogeneity of morphological features may be ascribed to the relatively homogeneous sensory input from esophagus impinging on the cNTS [1,6,8,16,27].…”

“…We have shown that esophageal distension induces gastric relaxation and increases the firing rate and cFos expression in cNTS neurons [27,28]. Furthermore, the majority of neurons that express induced cFos activity contain tyrosine-hydroxylase immunoreactivity (TH-IR) and are more likely located in the outer, rather than the inner, core of cNTS [28].…”

“…The overlap of these viscerotopically organized areas makes the distinction of cells devoted to a particular function quite problematic, even though a recent report suggested that innovative techniques may be used to distinguish NTS neurons receiving discrete projections in a brainstem slice preparation [13]. The subnucleus centralis (cNTS), which is located adjacent to the tractus solitarius [5], receives inputs from vagal afferent fibers originating almost exclusively from the esophagus [1,6,8,16,27], making it an excellent model for the study of a population of second order neurons controlling esophageal-mediated reflexes.…”