Olfactory modulation of hypoglossal neuron activity.

Amyl acetate stimulation of the neuroepithelial cells of the olfactory mucosa induced significant responses in the olfactory bulb and modulated the spontaneous electrical activity of the hypoglossal neurons localized in the mediocaudal part of the XIIth nucleus. Olfactory stimulation induced several patterns of responses characterized by excitation, inhibition and combined effects frequently dependent upon the stimulation intensity. In addition, olfactory inputs converge with the visual inputs on the same part of the XIIth nucleus. The olfactory inputs inducing hypoglossal excitatory responses increased the hypoglossal excitation produced by visual stimuli and decreased its inhibition. Viceversa, the olfactory inputs inducing hypoglossal inhibitory responses decreased excitation and increased hypoglossal inhibition to photic stimulation of the retinae. The possible pathways involved in carrying the olfactory inputs towards the hypoglossal nucleus, and the olfactory or non-olfactory origin of the hypoglossal responses were considered. With regard to the role played by this input in the economy of the hypoglossal function, it was concluded that olfactory inputs, alone or together with visual inputs, may induce tongue reflex adjustments associated with the oral phase of digestion to prepare the oral cavity for food reception.