Role of solitarial GABAergic mechanisms in control of swallowing

The role of solitarial gamma-aminobutyric acid (GABA)-ergic mechanisms in deglutition was investigated in urethane-anesthetized rats. When applied to the dorsal extraventricular surface of the nucleus tractus solitarii (NTS), muscimol reversibly inhibited 1) buccopharyngeal swallows evoked by either electrical or chemical stimulation of the NTS and 2) esophageal peristalsis evoked by muscarinic agonists. Bicuculline (5-1,000 pmol) applied to the NTS surface evoked rhythmic swallowing, which was reversibly blocked by DL-2-amino-7-phosphonoheptanoic acid (5-500 pmol). Methscopolamine (5-100 pmol) applied at the same site abolished the esophageal component of the response. Intrasolitarial application of bicuculline at s-glutamate-responsive loci in the intermediate and central subnuclei gave rise to buccopharyngeal and esophageal responses, respectively, and to a concomitant facilitation of glutamate-evoked responses. In subliminal doses ejected at esophageal loci, bicuculline induced deglutitive esophageal peristalsis during elicitation of buccopharyngeal swallowing by chemical (kainate or norepinephrine) or electrical stimulation of the NTS. We conclude that solitarial GABA neurons exert a tonic inhibition of the medullary deglutitive pattern generator and control buccopharyngeal-esophageal coupling.