Lateral Thoracic Nerve Research Articles

Aberrant arrangement of the musculocutaneous and median nerves in the thoracic limbs of a mixed-breed dog cadaver.

In the left thoracic limb of a male cadaver (adult mixed-breed dog), the median nerve (MN) after departing from the common median/ulnar nerve (UN) trunk received two branches. One from the lateral thoracic nerve (LTN) and the other from the musculocutaneous nerve (MCN). These both passed cranial to the axillary artery at the level of the lateral thoracic artery and joined the median nerve. Thus, in the proximal brachium, the axillary artery was cradled by this union, similar to the ansa axillaris of large animals and similar formations reported in human and non-human primates. In the distal brachium, the communicating branch ran unusually from the MN to the MCN on the left, and in both directions on the right. Awareness of such anatomical variations of the terminal branches of the brachial plexus (BP) in addition to the embryonic and evolutionary aspects can be useful in explaining neuroarterial signs with unknown origin, as those reported in human medicine.

The Structure of the Brachial Plexus of the Djungarian Hamster (Phodopus sungorus)

Hamsters are often chosen as companion animals but are also a group of animals frequently subjected to laboratory tests. As there are no scientific publications providing information on the anatomical architecture of the brachial plexus of the Djungarian hamster, this study analyses the structure of this part of the nervous system of this species. It is important to know the details of this structure not only for cognitive reasons, but also due to the increasing clinical significance of rodents, which are often used in scientific research. The study was conducted on 55 specimens. Like in humans, the brachial plexus of the Djungarian hamster has three trunks. The following individual nerves innervating the thoracic limb of the Djungarian hamster: the radial nerve, median nerve, ulnar nerve, musculocutaneous nerve, axillary nerve, suprascapular nerve, thoracodorsal nerve, cranial pectoral nerves, caudal pectoral nerve, lateral thoracic nerve, long thoracic nerve, and subscapular nerves. Similarly to other mammals of this order, the brachial plexus of the Djungarian hamster ranges widely (C5-T1). However, its nerves are formed from different ventral branches of the spinal nerves than in other mammals.

Long-term intermittent high-amplitude subcutaneous nerve stimulation reduces sympathetic tone in ambulatory dogs

Reducing sympathetic efferent outflow from the stellate ganglia (SG) may be antiarrhythmic. The purpose of this study was to test the hypothesis that chronic thoracic subcutaneous nerve stimulation (ScNS) could reduce SG nerve activity (SGNA) and control paroxysmal atrial tachycardia (PAT). Thoracic ScNS was performed in 8 dogs while SGNA, vagal nerve activity (VNA), and subcutaneous nerve activity (ScNA) were monitored. An additional 3 dogs were used for sham stimulation as controls. Xinshu ScNS and left lateral thoracic nerve ScNS reduced heart rate (HR). Xinshu ScNS at 3.5 mA for 2 weeks reduced mean average SGNA from 5.32 μV (95% confidence interval [CI] 3.89-6.75) at baseline to 3.24 μV (95% CI 2.16-4.31; P = .015) and mean HR from 89 bpm (95% CI 80-98) at baseline to 83 bpm (95% CI 76-90; P = .007). Bilateral SG showed regions of decreased tyrosine hydroxylase staining with increased terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive nuclei in 18.47% (95% CI 9.68-46.62) of all ganglion cells, indicating cell death. Spontaneous PAT episodes were reduced from 9.83 per day (95% CI 5.77-13.89) in controls to 3.00 per day (95% CI 0.11-5.89) after ScNS (P = .027). Left lateral thoracic nerve ScNS also led to significant bilateral SG neuronal death and significantly reduced average SGNA and HR in dogs. ScNS at 2 different sites in the thorax led to SG cell death, reduced SGNA, and suppressed PAT in ambulatory dogs.

Length-dependent axo-terminal degeneration at the neuromuscular synapses of type II muscle in SOD1 mice

In motor neuron diseases, there is a prolonged period of time before any clinical symptoms begin to appear. During this time, distal axonal degeneration, or “dying back” axonopathy, begins to occur before the onset of clinical symptoms and motor neuron death. This preclinical degeneration is a hallmark of motor neuron diseases in both animal models and human patients. Generally, in muscles with mixed fiber types, distal degeneration occurs in fast-fatigable α-motor axons innervating type IIb muscle fibers before axons innervating slow, type I muscle fibers. We investigated whether the “dying back” axonopathy in a pure fast-fatigable α-motor axon nerve is a length-dependent process. The lateral thoracic nerve (LTN) exclusively consists of motor nerves that innervate the very thin cutaneous maximus muscle (CMM) that solely contains type II neuromuscular synapses. We characterized the LTN and CMM synapses both morphologically and physiologically in the superoxide dismutase 1 (SOD1) mutant mouse model of amyotrophic lateral sclerosis (ALS). By 60days of age, there was a significant “dying back” phenomenon at the caudal region while the rostral region remained intact. The longer axons innervating the caudal region appear to be more susceptible to degeneration in the SOD1 mouse indicating that the axonal degeneration of motor neurons innervating type II fibers is a length-dependent process. Additionally, we identified how the simplicity of the LTN–CMM system offers a better method to investigate axon degeneration in an ALS mouse model and may be used to investigate possible therapeutic compounds for axon protection and regeneration.

The lateral thoracic nerve and the cutaneous maximus muscle—A novel in vivo model system for nerve degeneration and regeneration studies

We report a novel in vivo mouse model system to study regeneration of injured motor nerve and spatiotemporal pattern of denervation in experimental nerve diseases. The lateral thoracic nerve (LTN), as a pure motor nerve, innervates the cutaneous maximus muscle (CMM) by some of the shortest and the longest motor nerve fibers in the mouse body. Its branches and nerve terminals can be imaged in whole mount preparations. Here we describe the branching pattern of the LTN and its innervation of the CMM, and characterize degeneration and regeneration over time after a LTN crush by morphological and electrophysiological analyses. We demonstrate the utility of this model in a well-established neurotoxicity paradigm and in a genetic disease model of the peripheral neuropathy. Furthermore, this system enables punch biopsies that allow repeated and multi-location examinations for LTN regeneration and CMM reinnervation over time. The presence of the LTN and the CMM in a variety of species and its easy accessibility suggests that this in vivo model system offers considerable promise for future nerve degeneration and regeneration research.

Coexistent malignant peripheral nerve sheath tumor and lateral spinal meningoceles

Malignant peripheral nerve sheath tumor (MPNST) is a malignant spindle cell tumor of the soft tissue thought to be derived from the components of nerve sheath. MPNSTs are mainly located in the buttocks, thighs, brachial plexus, and paraspinal region. The objective of this article is to describe a case of neurofibromatosis type 1 who developed neurofibrosarcoma of the right lateral thoracic nerve with thoracic meningoceles, a rare coincidental finding which has not yet been reported in the English medical literature, and how both the conditions were managed in the same sitting.

Restoration of elbow flexion by performing contralateral lateral thoracic and thoracodorsal nerve transfers after experimental musculocutaneous nerve transection

The immediate transfer of the right lateral thoracic nerve (LTN) and the thoracodorsal nerve (TDN) to the transected left musculocutaneous nerve (MCN), leading to nerve cross-neurotization, was performed in cats to evaluate reinnervation of the biceps brachii muscle (BBM). Surgery to produce cross-neurotization of the MCN was performed in 12 cats (treatment group). Transection of the MCN was performed without attempts at neurotization in three cats (control group). Reinnervation of the BBM was assessed by performing electromyography (EMG) 6 months (14 cats) and 26 months (one cat) postsurgery. True Blue retrograde axonal tracing studies, tensile force measurements (muscle extensometry), and histopathological analyses were performed. All cats in the treatment group recovered voluntary contraction of the BBM and regained elbow flexion. Electromyography revealed no abnormal spontaneous activity in the BBM. Muscle evoked potentials were recorded in that muscle after right C-8 ventral branch stimulation. The muscle contraction strength in the left BBM varied from 108 to 557 g. The BBMs regained their normal appearances. The region of the MCN distal to the anastomosis displayed a normal histological appearance. Fluorescence was detected in the ventral horn of the spinal cord in the right C-8 and T-1 segments. In contrast, in all cats in the control group there was atrophy of the BBM, no EMG signal, and no clinical sign of recovery. There was no contraction of the BBM, no labeled neuron in the spinal cord, and the MCN displayed major degenerative changes. These findings demonstrate that the LTN and TDN can be used to neurotize injured contralateral brachial plexus nerves and obtain successful reinnervation in cats.

Measurement of the lateral thoracic reflex latency in ponies.

Lateral thoracic nerve reflex latencies values were measured in ponies using a simple, non-invasive technique. The reflex was elicited using an external triggering hammer attached to an electrodiagnostic unit. The resulting evoked, compound muscle action potentials were recorded with electrodes, which were placed over the 6th ribs or 11th rib level with the axilla. Two superimposed repeats of 4 signal-averaged sweeps of 50 or 100 milliseconds were recorded and the estimated reflex pathway was measured for each subject in order to calculate the reflex latencies and latency velocities. Mean left and right 6th rib peak latencies were not significantly different from each other (P = .609), but left 6th rib latencies were shorter than those recorded from the 11th rib (P < .0001), substantiating the existence of an indirect (central) pathway to the reflex. The calculated left and right 6th rib latency velocities were not significantly different from each other (P = .58) but left 6th rib latency velocities were different from left 11th rib (P = .009). The calculated latency velocities were within the broad range for corticospinal tract motor conduction velocities and comparable to magnetic motor evoked latency velocities. The use of lateral thoracic reflex latency measurements to objectively identify the site of spinal cord lesions is discussed.

Free Vascularized Double Muscle Transplantation for the Treatment of Facial Paralysis

Two cases of free neurovascular double muscle transplantation for facial paralysis are reported, with detailed descriptions of the operative technique and follow-up study. The latissimus dorsi muscle segment is placed between the nasolabial fold and the zygoma to substitute for the zygomatic and levator labii muscles, while the serratus anterior muscle segment is placed between the lower lip and the mandibular margin to substitute for the depressor labii muscles. The thoracodorsal nerve is sutured to the stump of the cross-face nerve graft, and the lateral thoracic nerve is sutured to a part of the hypoglossal nerve. The procedure is able to restore a relatively symmetrical smile, especially in patients with a full denture smile. The satisfactory results of this procedure are expected to lead to new prospects in the treatment of facial paralysis.

Spinal Root Origin of the Radial Nerve and Nerves Innervating Shoulder Muscles of the Dog

The ventral spinal root origin of the radial nerve, its muscle branches, and brachial plexus nerves which supply shoulder and thoracic musculature was determined in the dog. Electrophysiological signal averaging techniques measured evoked potential from specific ventral spinal roots to individual muscle nerves. The entire radial nerve received input from the sixth cervical (C6) through the second thoracic (T2) spinal roots. The most significant (p less than .05) input to triceps brachii came from C8 while the deep ramus of the radial nerve received its largest input from C7. The brachiocephalicus, suprascapular, and subscapular nerves all received their most significant (p less than .05) innervation from C6. Approximately 90% of the evoked potential to the axillary nerve originated from C7. The thoracodorsal nerve received most of its innervation from ventral roots C7 and C8. The lateral thoracic nerve which innervates the cutaneous trunci muscle was supplied by ventral roots C8-T2. Examination of innervation patterns suggests that only modest variation of spinal root input to specific nerves occurred between individual dogs.

Location of the cutaneous trunci motor nucleus in the dog

Using the methods of muscle injection of horseradish peroxidase (HRP) and application of HRP to the proximal stump of the cut lateral thoracic nerve (LTN), the motor nucleus of the cutaneous trunci muscle (CTM) has been located predominantly in C8 and T1 spinal cord segments in the ventral and ventrolateral nuclei of Rexed's Lamina IX. Cells of the nucleus are somatotopically arranged rostro-caudally to correspond to the rostro-caudal segmentation. There was a higher average number of HRP-filled cells per section and greater rostro-caudal extent of the nucleus for the cut nerve technique than for the muscle injection technique. Evidence is presented that the CTM is an appendicular muscle in spite of its obvious axial position on the trunk.