Location of the motoneurons of the mylohyoid muscle in the rat A fluorescence and Nissl study

Objectives: To locate the neuronal motor cells of themylohyoid muscle and discuss their topographicalorganization.Methods: The present study was conducted at theDepartment of Anatomy and Histology, Faculty ofMedicine, University of Jordan, Amman, Jordan between2002 and 2003. The mylohyoid muscle in 15 albino ratswas injected with 15 ìliter of a retrogradely transportedfluorescent material DAPI-Pr. After a survival period of48 hours, animals were sacrificed, fixed in situ and brainsharvested. The caudorostral transverse sections of thehindbrains were examined under the fluorescencemicroscope to detect the fluorescing cells, which wereimmediately photographed. Sections containing thelabeled cells were charted, stained with 1% thionine andphotographs obtained through light and fluorescencemicroscopes at different magnifications. The place andshape of all labeled cells were singled out by asset oftheir charted referring photographs of hindbrain sections,which display the entire motor trigeminal nucleus.Results: The results showed that the fluorescent cellincrease was found to occupy the rostromedial part of theipsilateral motor trigeminal nucleus. The nucleus waslarge at its caudal third; the labeled cells are mainly thoseof the medial subgroup. These cells are rationallydistinct and lie alongside the internal loop of the facialnerve. At the middle third, most of the medial subgroupwas found labeled. At its middle, the nucleus found waswell developed, attained an appreciable size and itsmedial subgroup was somewhat distinct. Whereas, atthe rostral third, the nucleus was larger, the medial groupwas more distinct and all cells were labeled. The medialcellular mass of the nucleus showed reduced labeled cellsat the rostral end.Conclusion: This study demonstrates that therostromedial part of the motor trigeminal nucleusrepresents the absolute territorial domain of themylohyoid muscle motoneurons