title: Evidence for a trigeminal mesencephalic-hypoglossal nuclei loop involved in controlling vibrissae movements in the rat.
abstract: Previous studies performed in rats showed that the whisker-pad motor innervation involves not only the facial nerve, but also some hypoglossal neurons whose axons travel within the trigeminal infraorbital nerve (ION) and target the extrinsic muscles surrounding the whisker-pad macrovibrissae. Furthermore, the electrical stimulation of the ION induced an increase in the EMG activity of these muscles, while the hypoglossal nucleus stimulation elicited evoked potentials and single motor unit responses. However, the existence of a neural network able to involve the XIIth nucleus in macrovibrissae whisking control was totally unknown until now. Since other recent experiments demonstrated that: (1) the mesencephalic trigeminal nucleus (Me5) neurons respond to both spontaneous and artificial movements of macrovibrissae, and (2) the Me5 peripheral terminals provide a monosynaptic sensory innervation to the macrovibrissae, the present study was aimed at analyzing a possible role of the Me5 nucleus as a relay station in the sensory-motor loop that involves the XIIth nucleus neurons in rhythmic whisking control. Two tracers were used in the same animal: Fluoro Gold, which was injected into the whisker pad to retrogradely label the hypoglossal whisker-pad projection neurons, and Dil, which was instead injected into the Me5 to label its projections to these hypoglossal neurons. Results demonstrated that terminals of the Me5 neurons monosynaptically target the hypoglossal whisker-pad projection neurons. The functional role of this sensory-motor connection is discussed, with particular regard to a hypothesized proprioceptive reflex in whisker-pad extrinsic muscles that can be elicited by the activation of the Me5 macrovibrissae receptors.
authors.affiliation: Human Physiology Division, Department of Clinical and Experimental Medicine, University of Sassari, viale San Pietro 8, 07100, Sassari, Italy. fisiou@uniss.it.
authors.forename: Ombretta
authors.initials: O
authors.lastname: Mameli
authors.affiliation: Human Physiology Division, Department of Clinical and Experimental Medicine, University of Sassari, viale San Pietro 8, 07100, Sassari, Italy.
authors.forename: Marcello Alessandro
authors.initials: MA
authors.lastname: Caria
authors.affiliation: Institute of Neurological Sciences, National Research Council, Section of Catania, 95125, Catania, Italy.
authors.forename: Rosalia
authors.initials: R
authors.lastname: Pellitteri
authors.affiliation: Department of Biomedical Sciences and Biotechnology, Catania University, 95125, Catania, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Russo
authors.affiliation: Department of Biological, Geological and Environmental Sciences, Catania University, 95100, Catania, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Saccone
authors.affiliation: Department of Biomedical Sciences and Biotechnology, Catania University, 95125, Catania, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Stanzani
mesh_terms: D000818:Animals; D007002:Hypoglossal Nerve / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013681:Tegmentum Mesencephali / Q000502:physiology*; D014738:Vibrissae / Q000502:physiology*
keywords: Hypoglossal neurons; Me5-XIIth sensory-motor circuit; Mesencephalic trigeminal nucleus; Proprioceptive reflex; Rat; Whisker-pad extrinsic muscles