Hypoglossal Transection Research Articles

Hypoglossal-Facial Anastomosis for Facial Nerve Reconstruction: Outcomes using the Side-to-End Surgical Technique

Abstract Introduction The side-to-end hypoglossal-facial anastomosis (HFA) technique is an excellent alternative technique to the classic end-terminal anastomosis, because it may decrease the symptoms resulting from hypoglossal-nerve transection. Methods Patients with facial nerve palsy (House-Brackmann [HB] grade VI) requiring facial reconstruction from 2014 to 2017were retrospectively included in the study. Results In total, 12 cases were identified, with a mean follow-up of 3 years. The causes of facial paralysis were due to resection of posterior-fossa tumors and trauma. There was improvement in 91.6% of the patients (11/12) after the HFA. The rate of improvement according to the HB grade was as follows: HB III - 58.3%; HB IV - 16.6%; and HB II - 16.6%. The first signs of improvement were observed in the patients with the shortest time between the paralysis and the anastomosis surgery (3.5 months versus 8.5 months; p = 0.011). The patients with HB II and III had a shorter time between the diagnosis and the anastomosis surgery (mean: 5.22 months), while the patients with HB IV and VI had a longer time of paresis (mean: 9.5 months; p = 0.099). We did not observe lingual atrophy or changes in swallowing. Discussion and Conclusion Hypoglossal-facial anastomosis with the terminolateral technique has good results and low morbidity in relation to tongue motility and swallowing problems. The HB grade and recovery appear to be better in patients operated on with a shorter paralysis time.

Involvement of hypoglossal and recurrent laryngeal nerves on swallowing pressure.

Swallowing pressure generation is important to ensure safe transport of an ingested bolus without aspiration or leaving residue in the pharynx. To clarify the mechanism, we measured swallowing pressure at the oropharynx (OP), upper esophageal sphincter (UES), and cervical esophagus (CE) using a specially designed manometric catheter in anesthetized rats. A swallow, evoked by punctate mechanical stimulation to the larynx, was identified by recording activation of the suprahyoid and thyrohyoid muscles using electromyography (EMG). Areas under the curve of the swallowing pressure at the OP, UES, and CE from two trials indicated high intrasubject reproducibility. Effects of transecting the hypoglossal nerve (12N) and recurrent laryngeal nerve (RLN) on swallowing were investigated. Following bilateral hypoglossal nerve transection (Bi-12Nx), OP pressure was significantly decreased, and time intervals between peaks of thyrohyoid EMG bursts and OP pressure were significantly shorter. Decreased OP pressure and shortened times between peaks of thyrohyoid EMG bursts and OP pressure following Bi-12Nx were significantly increased and longer, respectively, after covering the hard and soft palates with acrylic material. UES pressure was significantly decreased after bilateral RLN transection compared with that before transection. These results suggest that the 12N and RLN play crucial roles in OP and UES pressure during swallowing, respectively. We speculate that covering the palates with a palatal augmentation prosthesis may reverse the reduced swallowing pressure in patients with 12N or tongue damage by the changes of the sensory information and of the contact between the tongue and a palates. NEW & NOTEWORTHY Hypoglossal nerve transection reduced swallowing pressure at the oropharynx. Covering the hard and soft palates with acrylic material may reverse the reduced swallowing function caused by hypoglossal nerve damage. Recurrent laryngeal nerve transection reduced upper esophageal sphincter negative pressure during swallowing.

Decreased hippocampal brain-derived neurotrophic factor and impaired cognitive function by hypoglossal nerve transection in rats.

The hypoglossal nerve controls tongue movements, and damages of it result in difficulty in mastication and food intake. Mastication has been reported to maintain hippocampus‐dependent cognitive function. This study was conducted to examine the effect of tongue motor loss on the hippocampus‐dependent cognitive function and its underlying mechanism. Male Sprague Dawley rats were subjected to the initial training of Morris water maze task before or after the bilateral transection of hypoglossal nerves (Hx). When the initial training was given before the surgery, the target quadrant dwelling time during the probe test performed at a week after the surgery was significantly reduced in Hx rats relative to sham‐operated controls. When the initial training was given after the surgery, Hx affected the initial and reversal trainings and probe tests. Brain‐derived neurotrophic factor (BDNF) expression, cell numbers and long‐term potentiation (LTP) were examined in the hippocampus on the 10th day, and BrdU and doublecortin staining on the 14th day, after the surgery. Hx decreased the hippocampal BDNF and cells in the CA1/CA3 regions and impaired LTP. BrdU and doublecortin staining was decreased in the dentate gyrus of Hx rats. Results suggest that tongue motor loss impairs hippocampus‐dependent cognitive function, and decreased BDNF expression in the hippocampus may be implicated in its underlying molecular mechanism in relation with decreased neurogenesis/proliferation and impaired LTP.

Impact of Sensory and Motor Defects on Oral Function in an Animal Model.

To evaluate the combined functional impact on swallowing of tongue sensory and motor loss using a rat model. Rats underwent selective neurectomies with transection of the motor (hypoglossal) nerve or motor and sensory (lingual) nerves. Postoperative functional parameters were followed for 2 weeks. Translational research. Thirty-six adolescent male Wistar rats were divided into 4 groups: anesthetic (n = 6), sham surgery (n = 8), hypoglossal transection (n = 10), and hypoglossal and lingual transection (n = 12). Each morning on postoperative days 1 to 14, the water and food intake were quantified and the animal weighed. Two-way analyses of variance (SigmaPlot; SYSTAT, San Jose, California) were performed with factors of "group" and "postoperative day" (POD) to analyze whether a significant difference existed between water intake, pellet consumption, and weight change. The hypoglossal and lingual group consumed significantly less water during PODs 1 to 2 and significantly less food during PODs 1 to 3 than any other group. This established a significant difference in body weight between the hypoglossal and lingual group and all other groups for the duration of the study. Measured parameters in the hypoglossal group better approximated those of the control anesthetic and sham groups. The addition of a sensory loss to a motor deficit involving the oral tongue results in a measurably significant difference in weight gain, a marker of function, compared with rats with only a motor deficit. Additional studies are needed to determine if there would be similar findings in a model of sensate vs asensate oral tongue reconstruction.

Atrophy of the tongue following complete versus partial hypoglossal nerve transection in a canine model.

The hypoglossal nerve (XII) has been used as a donor nerve in facial and laryngeal reinnervation. The purpose of this study was to investigate the neuromuscular changes that occur within the tongue following partial or complete transection of XII using a canine model. Histopathological comparison of tongue denervation following two types of XII resection in a canine model. Ten adult canines underwent complete unilateral resection of XII or resection of only the medial terminal branch of the hypoglossal nerve (mXII). After 6 months of recovery, tongue specimens were analyzed histopathologically using whole cross-sections. Routine histologic sections were assessed by two neuropathologists blinded to the type of denervation. The cross-sectional area was calculated of both sides of the tongue, and the amount of myosin was quantified morphometrically using immunohistochemistry for myosin (antimyosin heavy chain, fast isotype). Statistical comparison between partial and complete denervation was performed using the Student t test. Six months following XII transection, quantitative measures of the cross-sectional area of the tongue and content of myosin demonstrated severe muscle atrophy on the operated side of the tongue for both groups, compared to the nonoperated side. For partial transection involving only mXII, the degree of atrophy was less severe (P < .05). This study provides new histological information demonstrating that partial resection of the hypoglossal nerve, sacrificing only the proximal medial branch of the hypoglossal nerve (mXII), results in less severe atrophy of the tongue than complete transection of the entire hypoglossal nerve. NA Laryngoscope, 126:2689-2693, 2016.

Comparison of Direct Side-to-End and End-to-End Hypoglossal-Facial Anastomosis for Facial Nerve Repair

The hypoglossal facial anastomosis (HFA) is the gold standard for facial reanimation in patients with severe facial nerve palsy. The major drawbacks of the classic HFA technique are lingual morbidities due to hypoglossal nerve transection. The side-to-end HFA is a modification of the classic technique with fewer tongue-related morbidities. In this study we compared the outcome of the classic end-to-end and the direct side-to-end HFA surgeries performed at our center in regards to the facial reanimation success rate and tongue-related morbidities. Twenty-six successive cases of HFA were enrolled. In 9 of them end-to-end anastomoses were performed, and 17 had direct side-to-end anastomoses. The House-Brackmann (HB) and Pitty and Tator (PT) scales were used to document surgical outcome. The hemiglossal atrophy, swallowing, and hypoglossal nerve function were assessed at follow-up. The original pathology was vestibular schwannoma in 15, meningioma in 4, brain stem glioma in 4, and other pathologies in 3. The mean interval between facial palsy and HFA was 18 months (range: 0-60). The median follow-up period was 20 months. The PT grade at follow-up was worse in patients with a longer interval from facial palsy and HFA (P value: 0.041). The lesion type was the only other factor that affected PT grade (the best results in vestibular schwannoma and the worst in the other pathologies group, P value: 0.038). The recovery period for facial tonicity was longer in patients with radiation therapy before HFA (13.5 vs. 8.5 months) and those with a longer than 2-year interval from facial palsy to HFA (13.5 vs. 8.5 months). Although no significant difference between the side-to-end and the end-to-end groups was seen in terms of facial nerve functional recovery, patients from the side-to-end group had a significantly lower rate of lingual morbidities (tongue hemiatrophy: 100% vs. 5.8%, swallowing difficulty: 55% vs. 11.7%, speech disorder 33% vs. 0%). With the side-to-end HFA technique the functional restoration outcome is at least as good as that following the classic end-to-end HFA, but the complications related to the complete hypoglossal nerve transection can be avoided. Best results are achieved if this procedure is performed within the first 2 years after facial nerve injury. Patients with facial palsy of longer duration also have the chance for good functional restoration after HFA.

HRK (harakiri, BCL2 interacting protein (contains only BH3 domain))

HRK / Dp5 / Bid3 is a BH3-only member of the Bcl-2 family of apoptosis regulators. Bcl-2 family proteins regulate the mitochondrial (intrinsic) pathway of apoptosis by regulating mitochondrial outer membrane permeability. Interactions between the pro- and anti-apoptotic members of the Bcl-2 family determine the fate of cells in response to signals that induce apoptosis. BH3-only proteins are activated in response to a variety of signals including survival factor withdrawal, DNA damage, ER stress and oxidative stress. HRK expression increases following Nerve Growth Factor (NGF) withdrawal in sympathetic neurons, neuronally differentiated PC12 cells and dorsal root ganglion (DRG) neurons, KCl deprivation in cerebellar granule neurons, beta amyloid treatment in cortical neurons and following axotomy of motor neurons in vivo. Experiments with HRK-/- knockout mice have shown that HRK is not essential for normal embryonic development but does contribute to the death of DRG neurons following NGF deprivation in vitro and the death of motoneurons in vivo following hypoglossal nerve transection.

Differential involvement of perineuronal astrocytes and microglia in synaptic stripping after hypoglossal axotomy

Following peripheral axotomy, the presynaptic terminals are removed from lesioned neurons, that is synaptic stripping. To elucidate involvement of astrocytes and microglia in synaptic stripping, we herein examined the motoneuron perineuronal circumference after hypoglossal nerve transection. As reported previously, axotomy-induced slow cell death occurred in C57BL/6 mice but not in Wistar rats. Synaptophysin labeling in the hypoglossal nucleus exhibited a minor reduction in both species after axotomy. Slice patch recording showed that the mean frequency of miniature postsynaptic currents in axotomized motoneurons was significantly lower in rats than in mice. We then estimated the relative coverage of motoneuron perineuronal circumference by line profile analysis. In the synaptic environment, axotomy-induced intrusion of astrocytic processes was significantly more extensive in rats than in mice, whereas microglial intrusion into the synaptic space was significantly more severe in mice than in rats. Interestingly, in the extrasynaptic environment, the prevalence of contact between astrocytic processes and lesioned motoneurons was significantly increased in rats, while no significant axotomy-induced alterations in astrocytic contact were observed in mice. These findings indicate that astrocytic, but not microglial, reaction may primarily mediate some anti-apoptotic effects through synaptic stripping after hypoglossal nerve axotomy. In addition, enlargement of astrocytic processes in the extrasynaptic environment may also be involved in neuronal protection via the increased uptake of excessive glutamate.

Simultaneous expression of glutathione, thioredoxin-1, and their reductases in nerve transected hypoglossal motor neurons of rat

Anti-oxidative stress responses are crucial for the survival of nerve-injured motor neurons. Herein, we examined changes in expression of glutathione reductase (GSHr), thioredoxins (TRX1 and TRX2), and thioredoxin reductases (TRXr1 and TRXr2), important constituents of anti-oxidative pathways, following rat hypoglossal nerve transection. RT-PCR and in situ hybridization demonstrated that GSHr, TRX1, and TRXr1 mRNAs were significantly up-regulated during the first few weeks in nerve-injured motor neurons, while TRX2 and TRXr2 mRNAs were unchanged throughout 8 weeks after nerve transection. The up-regulation of GSH, GSHr, TRX1, and TRXr1 proteins in injured neurons was confirmed by immunohistochemical analysis. Western blotting also demonstrated up-regulation of GSHr, TRX1, and TRXr1 in injured neurons. These data suggest that the two major redox systems, GSH/GSHr and TRX1/TRXr1, are simultaneously activated in injured neurons, and likely provide protection of injured neurons against oxidative stress.

Bilateral traumatic hypoglossal nerve transection in a blast injury

Background The hypoglossal nerve supplies motor function to the tongue. Case Description A 21-year-old man was injured in a blast injury to his mandible, resulting in severe maxillofacial hemorrhaging. Irreversible injury was evident from lack of improvement to tongue; patient underwent transplantation by end-to-end coaptation of right injured nerve 6 months after injury, with subsequent repair to left nerve 2 months later. At 11-year follow up, there was acceptable force and normal motor activity. Only speech, mastication, and swallowing did not return to normal despite prolonged physiotherapy. Conclusion In hypoglossal nerve injury, the proximity of the injury site to the primary muscle and, therefore, the short time required for the nerve fibers to repair toward the muscle are expected to predict an excellent outcome after transplantation. However, this is not usually the case, as in our patient.

Melatonin preserves superoxide dismutase activity in hypoglossal motoneurons of adult rats following peripheral nerve injury

Peripheral nerve injury (PNI) produces functional changes in lesioned neurons in which oxidative stress is considered to be the main cause of neuronal damage. As superoxide dismutase (SOD) is an important antioxidative enzyme involved in redox regulation of oxidative stress, the present study determined whether melatonin would exert its beneficial effects by preserving the SOD reactivity following PNI. Adult rats subjected to hypoglossal nerve transection were intraperitoneally injected with melatonin at ones for 3, 7, 14, 30 and 60 days successively. The potential neuroprotective effects of melatonin were quantitatively demonstrated by neuronal nitric oxide synthase (nNOS), mitochondrial manganese SOD (Mn-SOD), and cytosolic copper-zinc SOD (Cu/Zn-SOD) immunohistochemistry. The functional recovery of the lesioned neurons was evaluated by choline acetyltransferase (ChAT) immunohistochemistry along with the electromyographic (EMG) recordings of denervation-induced fibrillation activity. The results indicate that following PNI, the nNOS immunoreactivity was significantly increased in lesioned neurons peaking at 14 days. The up-regulation of nNOS temporally coincided with the reduction of ChAT and SOD in which the Cu/Zn-SOD showed a greater diminution than Mn-SOD. However, following melatonin administration, the nNOS augmentation was successfully suppressed and the activities of Mn-SOD, Cu/Zn-SOD, and ChAT were effectively preserved at all postaxotomy periods. EMG data also showed a decreased fibrillation in melatonin-treated groups, suggesting a potential effect of melatonin in promoting functional recovery. In association with its significant capacity in preserving SOD reactivity, melatonin is suggested to serve as a powerful therapeutic agent for treating PNI-relevant oxidative damage.

Differential expression of calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT) in the axotomized motoneurons of normoxic and hypoxic rats

We employed a double injury model (axotomy along with hypoxia) to determine how nerve injury and hypoxic insult would affect the expression of calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT) in the hypoglossal nucleus (HN) and nucleus ambiguus (NA). Adult rats were subjected to unilateral vagus and hypoglossal nerve transection, following which half of the animals were kept in an altitude chamber ( PO 2 = 380 Torr). The immunoexpression of CGRP and ChAT (CGRP-IR/ChAT-IR) were examined by quantitative immunohistochemistry at 3, 7, 14, 30 and 60 days post-axotomy. The results revealed that CGRP-IR in the HN was increased at 3 days but decreased to basal levels at 7 days following nerve injury. The decline was followed by a second rise in CGRP-IR at 30 days post-axotomy, followed again by a return to basal levels at 60 days. In the NA, CGRP-IR was up-regulated at 3 days and remained increased for up to 60 days after nerve injury. Animals treated with a double injury showed a greater CGRP-IR than normoxic group in both nuclei at all post-axtomized periods. In contrast to CGRP, ChAT-IR was markedly reduced in the HN and NA at 3 days reaching its nadir at 14 days following nerve injury. Hypoxic animals showed a stronger reduction of ChAT-IR in both nuclei at all post-axtomized periods. Results of cell counting showed that neuronal loss was somewhat obvious in hypoxic HN than that of normoxic ones. The present results suggest that up-regulation of CGRP-IR may exert its trophic effects while down-regulation of ChAT-IR may correlate with the poor neurotransmission within the injured neurons. It is speculated that the enhanced expression of CGRP-IR and the pronounced reduction of ChAT-IR in hypoxic rats may result from a drastic shift of intracellular metabolic pathways, which in turn could lead to more metabolic loading to the severely damaged neurons following the double insult.

Systemic Administration of Serotonin 2A/2C Agonist Improves Upper Airway Stability in Zucker Rats

The effects of [+/-]-2,5-dimethoxy-4-iodoaminophentamine, a serotonin(2A/2C) receptor agonist, on pharyngeal airflow mechanics were examined in isoflurane-anesthetized lean and obese Zucker rats. The pharyngeal pressure associated with flow limitation, maximum inspiratory flow, oronasal resistance, genioglossus muscle activity, and arterial blood pressure (BP) were measured before and after the intravenous administration of the agonist. A robust activation of the genioglossus muscle in all lean and obese rats was associated with decreased upper airway (UA) collapsibility (p < 0.05), unchanged maximum flow, and increased oronasal resistance (p < 0.05) in both groups. The changes in UA mechanics and BP after the drug were similar in lean and obese rats. The serotonin agonist had no effect on UA mechanics in a group of paralyzed (pancuronium bromide) rats, despite similar elevations in BP. There was a smaller decrease (p < 0.05) in UA collapsibility that was also associated with increased upstream resistance when the drug was administered after bilateral hypoglossal nerve transection. We conclude that systemic administration of a serotonin(2A/2C) receptor agonist improves UA collapsibility predominantly, but not exclusively, via stimulation of the hypoglossal nerves and also increases upstream resistance, at least in part, through activation of nonhypoglossal motoneuronal pools innervating the UA muscles.

Changes of high-affinity choline transporter CHT1 mRNA expression during degeneration and regeneration of hypoglossal nerves in mice

The high-affinity choline transporter CHT1 works for choline uptake in the presynaptic terminals of cholinergic neurons. We examined its expression in the hypoglossal nucleus after unilateral hypoglossal nerve transection in mice by fluorescent in situ hybridization. One week after axotomy, CHT1 mRNA expression was lost in all hypoglossal motoneurons in the lesioned side. Two weeks after axotomy, CHT1 mRNA started to be re-expressed in a few motoneurons that recovered connections to tongue muscles as revealed by retrograde labeling with Fast Blue. After 4 weeks, most of axotomized hypoglossal motoneurons were reconnected and re-expressed CHT1 mRNA as strongly as control neurons, and the regenerating cholinergic axons established mature neuromuscular junctions. These results suggest that the establishment of motor innervation is critical for CHT1 mRNA expression in hypoglossal neurons after axotomy.

Expression of c-Jun N-terminal kinases after axotomy in the dorsal motor nucleus of the vagus nerve and the hypoglossal nucleus

c-Jun N-terminal kinases (JNKs)/stress-activated protein kinases (SAPKs) are a subgroup of mitogen-activated protein kinases (MAPKs), and important mediators of signal transduction from the cell surface to the nucleus. JNK phosphorylates the transcription factor c-Jun. c-Jun is one of the earliest and most consistent markers for neurons that respond to nerve-fiber transection. To elucidate the c-Jun metabolism after axotomy, we investigated the expression of JNKs mRNA and of JNKs and c-Jun proteins following vagus and hypoglossal nerve transection. We found that JNK 1, JNK 2 and JNK 3 mRNA were positive in the cytoplasm of neuronal and glial cells. JNK 1 and JNK 2 protein were distributed mainly in the cytoplasm of neurons and glial cells, while only JNK 3 immunoreactivity was observed intensely in the nuclei of neuronal cells. Activated JNK was also observed intensely in the nuclei of neuronal cells. In sham-operated animals, the cytoplasm of a few glial cells showed moderate immunoreactivity for activated JNK, while after axotomy the cytoplasm of all perineuronal microglial cells were stained intensely. Up-regulated c-Jun and phosphorylated c-Jun immunoreactivities were found in the nuclei of neuronal cells in the severed side of both the dorsal motor and hypoglossal nuclei. These results indicate that the principal activity of JNKs in neurons is contributed largely by JNK 3 under both normal and axotomized conditions, and that JNKs play an important role in signal transduction of perineuronal microglial cells after axotomy.

外傷性両側舌下神経断裂の治療経験

Bilateral hypoglossal nerve transection is a rare complication of neck trauma because this injury generally results in death due to hemorrhage from a disrupted internal carotid artery or internal juglar vein. We report a case of bilateral hypoglossal nerve transection. The patient was 20-year-old man who suffered suprahyoid lacerations. He received emergency treatment, and two weeks after injury he underwent nerve grafting using the greaterauricular nerve on the right side and end to end anastomosis of the nerve on the left side. One and a half months after operation, weak tongue movement appeared. Two months after operation, he could move his tongue toward the right side. Three and a half months after operation, he could move his tongue toward the left side. One year after operation, he had good quality of life with out dysphagia or dysarthria.

Melatonin attenuates neuronal NADPH-d/NOS expression in the hypoglossal nucleus of adult rats following peripheral nerve injury

Oxidative stress and massive production of nitric oxide (NO) have been implicated in the neuropathogenesis following peripheral nerve injury. This study was aimed to ascertain whether melatonin would exert its neuroprotective effect on the lesioned hypoglossal neurons after peripheral axotomy, since it is known to reduce the oxidative damage in a variety of experimental neuropathologies in which NO is involved. Right-sided hypoglossal nerve transection was performed in adult rats following which the animals were given two different doses of melatonin administered intraperitoneally for 3, 7, 14, 21 and 30 successive days. Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and neuronal nitric oxide synthase (nNOS) immunohistochemistry were carried out to detect the neuronal NADPH-d/NOS expression in the hypoglossal nucleus (HN). At various time intervals following axotomy, the neurons in the affected HN were induced to express NADPH-d/NOS reactivity on the lesioned side peaking at 14 days. However, the enzyme expression was markedly depressed by melatonin treatment in a dose-dependent manner in terms of frequency of labelled neurons and staining intensity. It is suggested that the suppressive effect of melatonin on NADPH-d/NOS expression may be attributed to its antioxidant properties. Hence, in consideration of therapeutic strategies for reducing the oxidative stress following peripheral nerve injury, melatonin may prove to be beneficial.

Akt/Protein Kinase B Prevents Injury-Induced Motoneuron Death and Accelerates Axonal Regeneration

Motoneurons require neurotrophic factors for their survival and axonal projection during development, as well as nerve regeneration. By using the axotomy-induced neuronal death paradigm and adenovirus-mediated gene transfer, we attempted to gain insight into the functional significances of major growth factor receptor downstream cascades, Ras-extracellular signal-regulated kinase (Ras-ERK) pathway and phosphatidylinositol-3 kinase-Akt (PI3K-Akt) pathway. After neonatal hypoglossal nerve transection, the constitutively active Akt-overexpressing neurons could survive as well as those overexpressing Bcl-2, whereas the constitutively active ERK kinase (MEK)-overexpressing ones failed to survive. A dominant negative Akt experiment demonstrated that inhibition of Akt pathway hastened axotomy-induced neuronal death in the neonate. In addition, the dominant active Akt-overexpressing adult hypoglossal neurons showed accelerated axonal regeneration after axotomy. These results suggest that Akt plays dual roles in motoneuronal survival and nerve regeneration in vivo and that PI3K-Akt pathway is probably more vital in neuronal survival after injury than Ras-ERK pathway.

Morphological changes and expression of protein kinase CK2 beta subunit in the microglia after hypoglossal nerve transection.

Following hypoglossal nerve transection, the microglia of the rat hypoglossal nucleus expressed protein kinase CK2 beta subunit immunoreactivity. CK2 beta immunostaining occurred on the operated side from postoperative day 3; on day 5 we observed strong immunoreactivity and the immunopositive microglial cell processes surrounded the injured neurones. Thereafter, the immunoreactivity decreased gradually and on day 10 the immunopositive cells surrounded only a few injured neurones. Electron microscopic observations on the hypoglossal nucleus revealed microglia-neuronal contact within 3 hours of nerve injury, and by day 3 all the injured neurones were in contact with microglial cells. These observations indicated that microglia-neuronal contact occurred earlier than the CK2 beta subunit immunoreactivity. CK2 may not be implicated during the initial migration of the microglia to the injured neurones; however, it may enhance the growth and elongation of the microglial cell processes around the injured neurones.

Analysis of neurotrophic effects of hepatocyte growth factor in the adult hypoglossal nerve axotomy model.

Recent studies have shown that hepatocyte growth factor (HGF) promotes the survival of embryonic motor neurons. However, it remains unclear whether HGF has trophic effects on mature motor neurons. In the present study, we examined the effects of HGF on adult motoneurons using the hypoglossal nerve transection model. In adult rats, neurons in the hypoglossal nucleus show a dramatic loss of choline acetyltransferase (ChAT) protein and mRNA after the axotomy. This reduction of ChAT was markedly prevented when HGF was administered continuously at the cut end of the nerve using an osmotic pump. The HGF receptor, c-met, protein and mRNA, which were faintly expressed in hypoglossal neurons under normal conditions, gradually increased and reached maximal levels 2 weeks after the axotomy. Administration of HGF reduced this c-met upregulation almost to normal levels. We also quantified HGF mRNA in the tongue and hypoglossal nucleus. The tongue contained abundant HGF mRNA, whereas the nucleus contained only low levels. Interestingly, the HGF mRNA level in the nucleus did not increase after the axotomy. These findings suggest that HGF is principally produced in the tongue and contributes to maintain ChAT expression in the nucleus. HGF produced in the hypoglossal nucleus alone after disconnection from the tongue may not be sufficient for the maintenance of the motor neuron function. Thus, exogenously applied HGF was effective to prevent the downregulation of ChAT activities. These findings provide a strong rationale for the potential clinical use of HGF for the treatment of motor neuron degenerative disease.