Central nervous system control mechanisms of swallowing: a neuropharmacological perspective

Neuropharmacological in vivo and in vitro investigations are beginning to provide insight into chemical signaling processes within brainstem networks controlling the individual stages of swallowing. Different subtypes of excitatory amino acid (EAA) receptors operate at the level of solitarial interneurons programming the buccopharyngeal and esophageal stage, as well as motoneurons innervating esophageal striated musculature. Muscarinic cholinoceptors (MAChRs), probably activated via a propriobulbar input, are critically involved in generating output from solitarial neurons to esophageal motoneurons. Inhibition to tonically active GABAA-receptor mediated afferents to solitarial premotor neurons results in rhythmic deglutitive output, reflecting disinhibition of EAA and MACh receptor activity. Motoneuronal EAA receptors may be regulated by a somatostatinergic input arising from solitarial premotoneurons. The available evidence is consistent with a transmitter heterogeneity in esophageal premotor neurons that may operate to provide chemical coding of afferents to the motor output stage of the pattern generator for esophageal peristalsis.