Location, morphology, and central projections of mesencephalic trigeminal neurons innervating rat masticatory muscles studied by axonal transport of choleragenoid‐horseradish peroxidase

Abstract

Retrograde and transganglionic transport of horseradish peroxidase conjugated to the B-fragment of cholera toxin (B-HRP) was used to study the location, morphology, and central projections of mesencephalic trigeminal (Me5) neurons innervating rat masticatory muscles. Labeled Me5 cell bodies were found throughout the Me5 nucleus from a level slightly caudal to the trigeminal motor nucleus to the level of the superior colliculus 5 mm further rostrally. Occasionally, labeled Me5 cells were observed in the anterior medullary velum, in the cerebellum, and in the brainstem contralateral to the B-HRP injection. The vast majority of the labeled Me5 cells were pseudounipolar, but multipolar cells were also found. Extensive central projections from labeled Me5 cells could be seen extending from the nucleus of Darkschewitsch rostrally to the C2 segment caudally. Small but consistent projections from Me5 neurons were observed in nuclear islands among the incoming Me5 root fibers. Trigeminal and hypoglossal motor nuclei received direct projections from Me5 cells, but not the facial motor nucleus. The most prominent Me5 projections appeared in the brainstem reticular formation, including the supratrigeminal nucleus. Smaller projections also extended into the main sensory trigeminal nucleus, trigeminal subnucleus oralis, and the nucleus of the solitary tract.

Synaptic Control of Motoneuronal Excitability

“…Proprioceptive information from the muscles of mastication reaches the trigeminal and hypoglossal motor nuclei via the trigeminal mesencephalic nucleus (1015). Afferent information from other peripheral sensors enters the brain stem through vagal, glossopharyngeal, and accessory nerves and is conveyed to the trigeminal, facial, and hypoglossal nuclei via premotor neurons in the nucleus of the solitary tract (83,122,759,1235,1263).…”

Superior medullary velum: anatomical- histological study in the sheep brain and a preliminary tractographic study in the human brain

“…Mesencephalic trigeminal neurons were reported to be present in the anterior medullary velum in a study in which retrograde and transganglionic transport of horseradish peroxidase was used to show the central projections of mesencephalic trigeminal neurons innervating rat masticatory muscles (21). The mesencephalic trigeminal nucleus was also reported to be located on both sides of the mesencephalic tract, mingled with cells of locus coeruleus and in the superior medullary velum (23).…”

“…These medullary vela are thin laminae composed of white substance (19). Also there are literature reports suggesting the presence of neurons, especially related to the trochlear nerve and the mesencephalic nucleus of the trigeminal nerve in the superior medullary velum (21,23).…”

Mesencephalic trigeminal nucleus neurons supplying the jaw closing muscles have no spinal projection: A fluorescent double-labeling study in birds and mammals

“…However, multipolar cells have also recently been described in the mesencephalic nucleus of some mammals, birds, reptiles, amphibians, and fish (see Liem et al, 1991;Muñ oz et al, 1993;Raappana and Arvidsson, 1993).…”

“…In the literature, the findings concerning the central projections of the MeV neurons are controversial, since RECORD 249:255-258 (1997) they largely depend on the species studied and methods used (Luo et al, 1991;Raappana and Arvidsson, 1993). The present study, carried out in an avian and two mammalian species, verified, by means of fluorescent retrograde double-labeling technique, the possibility that the MeV neurons that innervate the muscle spindles of the jaw closing muscles could also have collaterals projecting to the cervical level of the spinal cord.…”