Olfactory-hypoglossal connections.

Natural olfactory stimulation with amyl acetate significantly modulates the electrical activity of hypoglossal neurons and the electromyographic responses of the tongue musculature. The aim of the present study was to identify and characterize, using neuroanatomical and neurophysiological approaches, the pathways involved in the transmission of the olfactory information to the hypoglossal nucleus (XIIn). The neuroanatomical findings provided the initial demonstration that olfactory information is conveyed from the olfactory bulb to the hypoglossal nucleus via the interpeduncular nucleus (IPn) by both fast disynaptic and different polysynaptic pathways. The latter, in particular, involve many of the brain structures that process olfactory information. The electrophysiological studies demonstrated that the IPn neurons respond with a variety of patterns to natural stimulation of the olfactory receptors, thus supporting the hypothesis that the IPn is a crucial relay station for the elaboration and transmission of olfactory stimuli to XIIn.