Abstract
To understand regulation circuits controlling swallowing, we used fish brain since fish swallowing simply consists of upper esophageal relaxation and pharyngeal contraction. However, regulation of esophageal relaxation has not been clear even in fish. Recently we have reported that spontaneous activities of motoneurons innervating the upper esophageal sphincter (UES) in the middle part of the glossopharyngeal-vagal motor complex (mGVC, i.e. the nucleus ambiguus) are suppressed by catecholamines (CAs). In the present study we explored catecholaminergic inputs to the mGVC neurons in eel. The eel brain sections retrogradely stained with a neuronal tracer injected into the UES were immunostained against tyrosin hydroxylase (TH). Around retrogradely labeled mGVC neurons, TH-immunoreactive fibers were predominantly distributed and a source of the fibers was traced back the commissural nucleus of Cajal (NCC, i.e. the nucleus of solitary tract). To examine the neuronal connection between the NCC and the mGVC in eel, electric field stimulation was applied to the NCC and the response was recorded from the mGVC extracellularly. Spontaneous firings of the mGVC neurons were transiently inhibited by the NCC stimulation. Such inhibition was suppressed after treatment with prazosin. Since prazosin is shown previously to block the inhibitory effects of CAs in the eel GVC, this result indicates that the NCC innervates the mGVC catecholaminergically. [J Physiol Sci. 2008;58 Suppl:S158]
