Locations of the Motor Endplate Band and Motoneurons Innervating the Sternomastoid Muscle in the Rat

Abstract

Sternocleidomastoid (SCM) is a long muscle with two bellies, sternomastoid (SM) and cleidomastoid (CM) in the lateral side of the neck. It has been widely used as muscle and myocutaneous flap for reconstruction of oral cavity and facial defects and as a candidate for reinnervation studies. Therefore, exact neuroanatomy of the SCM is critical for guiding reinnervation procedures. In this study, SM in rats were investigated to document banding pattern of motor endplates (MEPs) using whole-mount acetylcholinesterase (AChE) staining and to determine locations of the motoneurons innervating the muscle using retrograde horseradish peroxidase (HRP) tracing technique. The results showed that the MEPs in the SM and CM were organized into a single band which was located in the middle portion of the muscle. After HRP injections into the MEP band of the SM, ipsilaterally labeled motoneurons were identified in the caudal medulla oblongata (MO), C1, and C2. The SM motoneurons were found to form a single column in lower MO and dorsomedial (DM) nucleus in C1. In contrast, the labeled SM motoneurons in C2 formed either one (DM nucleus), two [DM and ventrolateral (VL) nuclei], or three [DM, VL, and ventromedial (VM)] columns. These findings are important not only for understanding the neural control of the muscle but also for evaluating the success rate of a given reinnervation procedure when the SM is chosen as a target muscle. Anat Rec, 294:295-304, 2011. V V C 2010 Wiley-Liss, Inc.

Nerve-Muscle-Endplate Band Grafting

“…As reported, the SM motoneurons were typically located in the lower MO and spinal ventral grey horn in the C1-C2. 59 For example, the SM motoneurons in C1 were concentrated predominantly in the dorsomedial (DM) region, whereas the SH motoneurons at this level were located mainly in the VM region of the ventral horn (Figure 9C). …”

“…The details regarding HRP labeling have been given in our recent publication. 59 Briefly, 30 % HRP (type VI A, Sigma Chemical, St. Louis, MO) solution was injected at two points (5μL/point) into the MEP band in the right NMEG reinnervated SM muscle and the left SH muscle (control) with Hamilton microsyringe. After a survival time of 48 hours, the animals were deeply anesthetized with sodium pentobarbital (60 mg/kg i.p.)…”

Comparison of muscle force after immediate and delayed reinnervation using nerve-muscle-endplate band grafting

“…The present study showed that NMEG produced a better recovery of muscle force and larger muscle weight as compared with conventional EEA nerve repair. Retrograde horseradish peroxidase (HRP) tracing [46] confirmed that the XI nerve-innervated SM muscles were reinnervated by motoneurons from the SH nerve pool in C1-C2 in the NMEG group. The mean weight of the NMEG reinnervated muscle (with immediate reinnervation after denervation) measured at 3 months after reinnervation was 87% of the control (intact SM on the opposite site).…”

Muscle reinnervation with nerve-muscle-endplate band grafting technique: correlation between force recovery and axonal regeneration

“…We recently developed a new reinnervation technique called “nerve-muscle-endplate band grafting (NMEG)” [28] and conducted a series of experiments in a rat model [29–33]. The development of this technique is based on the concept that a healthy motor endplate band with a nerve branch and terminals that innervates an expendable muscle can be transplanted to a more functionally important denervated muscle for restoring its motor function.…”