Trigeminal proprioceptive projections to the hypoglossal nucleus and the cervical ventral gray column.

Abstract

AbstractTrigeminal proprioceptive projections to the hypoglossal nucleus and the cervical ventral gray column in the cat were investigated by means of neuroanatomical and neurophysiological methods. Degeneration studies (Nauta and Fink‐Heimer methods) involved circumscribed electrolytic lesions of the trigeminal mesencephalic nucleus and/or the supratrigeminal nucleus. Degenerated fibers in Probst's tract, which is composed of the central processes of trigeminal mesencephalic neurons, terminated in the ventrolateral portion of the ipsilateral hypoglossal nucleus and in the medial part of the ventral gray column of C1–C4. The descending juxtatrigeminal fascicle, a separate bundle of degenerated fibers, originated from the supratrigeminal region, which is known to receive processes from trigeminal mesencephalic neurons. This descending fascicle contributed fibers to the spinal trigeminal nucleus and the juxtatrigeminal reticular formation, from which region interneurons connect to the hypoglossal nucleus. Probst's tract, as well as the descending juxtatrigeminal fascicle, could be considered as parts of two separate polysynaptic pathways from trigeminal proprioceptors to those motoneurons responsible for the innervation of the tongue and infrahyoid musculature. Electrophysiological experiments revealed that proprioceptive muscle afferents from the masseter muscle project directly to the ipsilateral hypoglossal nucleus and to the ipsilateral upper cervical ventral column.