Neurons of the motor trigeminal nucleus project to the hypoglossal nucleus in the rat

Abstract

The hypoglossal nucleus (Mo12) contains motoneurons that innervate the tongue, while the motor trigeminal nucleus (Mo5) contains motoneurons that elevate or depress the mandible. Previous studies have revealed lateral and medial tegmental field neuronal afferents to the Mo12 adjacent to, but not within, the motor trigeminal nucleus (Mo5). The current studies demonstrate the presence of retrogradely labeled neuronal afferents to the Mo12 within the Mo5 produced by as little as 10 nl of Fast Blue (FB) injected into the Mo12. Retrograde labeling of Mo5 afferents to the Mo12 with injections of Diamidino Yellow (DY) combined with injections of FB into the lumbar spinal cord showed these neuronal afferents to the Mo12 are not part of the diffuse projections to motoneurons from the nucleus subcoeruleus. Retrograde labeling of Mo5 afferents to the Mo12 with DY combined with injections of FB into the masseter revealed these neuronal afferents to the Mo12 are not trigeminal motoneurons. These results indicate that Mo5 interneurons are part of the lateral tegmental field projections to the Mo12, and are likely to comprise part of the neural substrate coordinating the motor activity of the jaw and tongue.

Colocalization of substance P or enkephalin in serotonergic neuronal afferents to the hypoglossal nucleus in the rat

“…While the injection sites were all well localized to the XII, we cannot exclude from consideration underestimation of the injection site limits due to absorption and transport of the tracer; however, the short survival times utilized make this unlikely. The overall distribution of rhodamine latex beads agrees with previous retrograde studies in our laboratory employing two other fluorescent tracers (Manaker et al, 1992;Manaker and Tischler, 1993), although the current study produced higher absolute numbers of retrogradely labeled neurons using rhodamine latex beads. These differences in absolute numbers of retrogradely labeled neurons may be attributed to the different inherent transport properties of various retrograde tracers (Illert et al, 1982;Craig et al, 1989;Richmond et al, 1994).…”

“…The distribution of neurons projecting to the XII observed by the injection of rhodamine-conjugated microspheres in the present study (Tables 1 and 2; Figs. 2 and 3) was similar to previous reports using other retrograde tracers (Takada et al, 1984;Aldes, 1990;Manaker et al, 1992;Manaker and Tischler, 1993). In all eight cases, dense rhodamine labeling was localized bilaterally throughout the lateral tegmental field, especially the parvicellular reticular nuclei.…”

Ultrastructural anatomy of physiologically identified jaw-muscle spindle afferent terminations onto retrogradely labeled jaw-elevator motoneurons in the rat

“…This finding is consistent with the somatotopic arrangement of the trigeminal motor nucleus in rats (Mizuno et al, 1975;Limwongse and DeSantis, 1977;Sasamoto, 1979;Lynch, 1985;Rokx et al, 1985a,b;Mong et al, 1988), but not all neurons in this region of the trigeminal motor nucleus contained HRP reaction product. Previous studies have reported intranuclear neurons (Shigenaga et al, 1988) and projection (Langer et al, 1985;Røste, 1989;Manaker et al, 1992) and commissural (Mizuno et al, 1978(Mizuno et al, , 1981Ter Horst et al, 1990) interneurons spread throughout the trigeminal motor nucleus. It is likely, therefore, that some of the unlabeled neurons found scattered among the retrogradely labeled neurons in this study are comparable interneurons.…”

“…This level of discrimination has become increasingly important when studying trigeminal motoneuronal circuitry because of the diversity of physiological inputs to Vmo (Kidokoro et al, 1968;Nakamura et al, 1973;Ohta and Sasamoto, 1980;Chandler and Goldberg, 1982;Shigenaga et al, 1988;Donga and Lund, 1991;Olsson and Westberg, 1991;Takata et al, 1991;Grimwood et al, 1992;Taylor et al, 1992;Yohsida et al, 1994) and the accumulating evidence indicating that neurons within the trigeminal motor nucleus are not homogeneous. Not only motoneurons, but a variety of interneurons (Mizuno et al, 1978(Mizuno et al, , 1981Shigenaga et al, 1988;Ter Horst et al, 1990;Kolta, 1997) and projection neurons (Langer et al, 1985;Røste, 1989;Manaker et al, 1992) are located within the anatomical confines of the trigeminal motor nucleus. Because some of these interneurons are large enough that they overlap the size range of trigeminal motoneurons (Kotchabhakdi and Walberg, 1977;Mizuno et al, 1981;Ter Horst et al, 1990), the identification of motoneurons should go beyond mere localization within the cytological boundaries of Vmo.…”

Oromotor Nuclei

“…Other, presumably non-motoneuronal cells within 5N have central projections, and were retrogradely labeled following injections of retrograde tracers into the cerebellum (cat: Kotchabhakdi and Walberg, 1977;Roste, 1989; rabbit: Bukowska and Grottel, 1997), or hypoglossal nucleus (Manaker et al, 1992). In addition, a small projection from neurons in the jaw-closing region of 5N to the homologous region on the contralateral side could contribute to bilateral jaw closing (Jüch et al, 1993;Ter Horst et al, 1990).…”