Targeted Hypoglossal Nerve Stimulation for Patients With Obstructive Sleep Apnea: A Randomized Clinical Trial

Importance

Evidence is lacking from randomized clinical trials of hypoglossal nerve stimulation in obstructive sleep apnea (OSA).

Objective

To evaluate the safety and effectiveness of targeted hypoglossal nerve stimulation (THN) of the proximal hypoglossal nerve in patients with OSA.

Design, Setting, and Participants

This randomized clinical trial (THN3) was conducted at 20 centers and included 138 patients with moderate to severe OSA with an apnea-hypopnea index (AHI) of 20 to 65 events per hour and body mass index (calculated as weight in kilograms divided by height in meters squared) of 35 or less. The trial was conducted from May 2015 through June 2018. Data were analyzed from January 2022 through January 2023.

Intervention

Implant with THN system; randomized 2:1 to activation at month 1 (treatment) or month 4 (control). All received 11 months of THN with follow-up at months 12 and 15, respectively.

Main Outcomes and Measures

Primary effectiveness end points comprised AHI and oxygen desaturation index (ODI) responder rates (RRs). Treatment responses at months 4 and 12/15 were defined as a 50% or greater reduction in AHI to 20 or less per hour and an ODI decrease of 25% or greater. Coprimary end points comprised (1) month 4 AHI and ODI RR in the treatment greater than the control group and (2) month 12/15 AHI and ODI RR in the entire cohort exceeding 50%. Secondary end points included sleep apnea severity (AHI and ODI) and patient-reported outcomes (Epworth Sleepiness Scale, Functional Outcomes of Sleep Questionnaire, and EQ-5D visual analog scale).

Results

Among 138 participants, the mean (SD) age was 56 (9) years, and 19 (13.8%) were women. Month 4 THN RRs were substantially greater in those in the treatment vs control group (AHI, 52.3% vs 19.6%; ODI, 62.5% vs 41.3%, respectively) with treatment-control standardized mean differences of 0.725 (95% CI, 0.360-1.163) and 0.434 (95% CI, 0.070-0.843) for AHI and ODI RRs, respectively. Months 12/15 RRs were 42.5% and 60.4% for AHI and ODI, respectively. Improvements in AHI, ODI, Epworth Sleepiness Scale, Functional Outcomes of Sleep Questionnaire, and EQ-5D visual analog scale scores were all clinically meaningful (medium to large effect size). Two serious adverse events and 100 nonserious related adverse events were observed from the implant procedure or study protocol.

Conclusions and Relevance

This randomized clinical trial found that THN demonstrated improvements in sleep apnea, sleepiness, and quality of life in patients with OSAs over an extended AHI and body mass index range without prior knowledge of pharyngeal collapse pattern. Clinically meaningful improvements in AHI and patient-reported responses compared favorably with those of distal hypoglossal nerve stimulation trials, although clinically meaningful differences were not definitive for ODI.

Trial Registration

ClinicalTrials.gov Identifier: NCT02263859.

Association between anxiety, depression, and emotional distress and hypoglossal nerve stimulator adherence

PURPOSE

To evaluate relationships between hypoglossal nerve stimulator (HNS) adherence and the presence of anxiety, depression, and emotional distress.

METHODS

This is a cross-sectional study of subjects with moderate to severe obstructive sleep apnea (OSA), who had HNS implanted and activated at The Ohio State University Medical Center (OSUMC). Patient usage data from the previous 6 months was obtained from 33 patients. Adherence was defined as ≥28 h of use per week. Generalized Anxiety Disorder-7 (GAD-7) and Patient Health Questionnaire-9 (PHQ-9) were administered, and the Patient Health Questionnaire Anxiety and Depression Scale (PHQ-ADS) score was calculated for all subjects.

RESULTS

Sixty-five percent were adherent with average usage of 46.5±11.7 h per week vs 7.7±7.5 h per week in the non-adherent group. The average GAD-7 were 3.90±3.98 in the adherent group vs. 8.27±6.69 in the non-adherent group (p=0.049). PHQ-9 score was 6.15±4.31 vs. 10.09±7.53 (p=0.118), and PHQ-ADS was 10.05±7.49 vs. 19.20±9.80 (p=0.035). There were no statistically significant differences in age, gender, pre-treatment AHI, and post-treatment AHI between the two groups, though there was a trend to higher age in the adherent group.

CONCLUSIONS

This study demonstrated higher GAD-7 and PHQ-ADS scores in the non-adherent group compared to those who were adherent to HNS supporting that anxiety and emotional distress may contribute to HNS therapy adherence. To our knowledge, this is the first study evaluating the relationship between anxiety, depression, emotional distress, and HNS adherence. Screening patients with the GAD-7 and PHQ-9 prior to implantation may be helpful when evaluating patient adherence to therapy.

Hypoglossal Nerve Stimulation Therapy for the Treatment of Obstructive Sleep Apnea

Hypoglossal nerve stimulation (HGNS) therapy was approved in 2014 for the treatment of obstructive sleep apnea in patients who are intolerant to continuous positive airway pressure (CPAP) therapy, which is reported in up to 40-60% of patients. This therapy works via direct neurostimulation of the hypoglossal nerve in synchrony with respiration, to open the airway via tongue stiffening and protrusion. Studies have demonstrated significant reductions in both respiratory parameters such as disordered breathing indices, as well as subjective sleep complaints, such as daytime sleepiness, with the use of this therapy. This has increased the repertoire of treatment options for sleep providers to recommend to those patients that are intolerant to CPAP therapy.

Ultrasound Localization and Percutaneous Electrical Stimulation of the Hypoglossal Nerve and Ansa Cervicalis

OBJECTIVE

Hypoglossal nerve stimulation for obstructive sleep apnea (OSA) can be effective for appropriately selected patients, but current patient selection criteria are complex and still result in a proportion of nonresponders. Ansa cervicalis stimulation of the infrahyoid cervical strap muscles has recently been proposed as a new form of respiratory neurostimulation (RNS) therapy for OSA treatment. We hypothesized that percutaneous stimulation of both nerves in humans with temporary electrodes would make testing of the physiologic response to different RNS strategies possible.

STUDY DESIGN

Nonrandomized acute physiology study.

SETTING

Tertiary care hospital.

METHODS

Fifteen participants with OSA underwent ultrasonography and placement of percutaneous electrodes proximal to the medial division of the hypoglossal nerve and the branch of the ansa cervicalis innervating the sternothyroid muscle (ACST). Procedural success was documented in each participant, as were any failures or procedural complication.

RESULTS

The hypoglossal nerve was successfully localized in 15 of 15 (100%) participants and successfully stimulated in 13 of 15 (86.7%). The ACST was successfully localized in 15 of 15 (100%) participants and successfully stimulated in 14 of 15 (93.3%). Stimulation failure of the hypoglossal nerve was due to suboptimal electrode placement in 1 participant and electrode displacement in the other 2 cases. No complications occurred.

CONCLUSIONS

The hypoglossal nerve and ACST can be safely stimulated via percutaneous electrode placement. Larger trials of percutaneous stimulation may help to identify responders to different RNS therapies for OSA with temporary or permanent percutaneous electrodes. Techniques for electrode design, nerve localization, and electrode placement are described.

Respiratory pattern and phrenic and hypoglossal nerve activity during normoxia and hypoxia in 6-OHDA-induced bilateral model of Parkinson's disease

Respiratory disturbances present in Parkinson's disease (PD) are not well understood. Thus, studies in animal models aimed to link brain dopamine (DA) deficits with respiratory impairment are needed. Adult Wistar rats were lesioned with injection of 6-hydroxydopamine (6-OHDA) into the third cerebral ventricle. Two weeks after hypoxic test was performed in whole-body plethysmography chamber, phrenic (PHR) and hypoglossal (HG) nerve activities were recorded in normoxic and hypoxic conditions in anesthetized, vagotomized, paralyzed and mechanically ventilated rats. The effects of activation and blockade of dopaminergic carotid body receptors were investigated during normoxia in anesthetized spontaneously breathing rats. 6-OHDA injection affected resting respiratory pattern in awake animals: an increase in tidal volume and a decrease in respiratory rate had no effect on minute ventilation. Hypoxia magnified the amplitude and minute activity of the PHR and HG nerve of 6-OHDA rats. The ratio of pre-inspiratory to inspiratory HG burst amplitude was reduced in normoxic breathing. Yet, the ratio of pre-inspiratory time to total time of the respiratory cycle was increased during normoxia. 6-OHDA lesion had no impact on DA and domperidone effects on the respiratory pattern, which indicate that peripheral DA receptors are not affected in this model. Analysis of monoamines confirmed substantial striatal depletion of dopamine, serotonin and noradrenaline (NA) and reduction of NA content in the brainstem. In bilateral 6-OHDA model changes in activity of both nerves: HG (linked with increased apnea episodes) and PHR are present. Demonstrated respiratory effects could be related to specific depletion of DA and NA.

[Hypoglossal nerve stimulation for obstructive sleep apnoea; technique, indication and future prospects]

Hypoglossal nerve stimulation for obstructive sleep apnoea; technique, indication and future prospects Continuous positive airway pressure (CPAP) is the treatment of first choice in patients with moderate to severe obstructive sleep apnoea (OSA); however, 1 in 3 patients does not tolerate CPAP. Upper airway stimulation (UAS) is an alternative for CPAP. This is a new treatment, intended for patients with CPAP intolerance or failure. The muscles responsible for protrusion of the tongue are activated by unilateral stimulation of the hypoglossal nerve, resulting in opening up of the pharynx. Since April 2017, UAS treatment has been reimbursed for a select group of patients by the National Healthcare Institute in the Netherlands, leading to an increase in demand for UAS.

Chemogenetic stimulation of the hypoglossal neurons improves upper airway patency

Obstructive sleep apnea (OSA) is characterized by recurrent upper airway obstruction during sleep. OSA leads to high cardiovascular morbidity and mortality. The pathogenesis of OSA has been linked to a defect in neuromuscular control of the pharynx. There is no effective pharmacotherapy for OSA. The objective of this study was to determine whether upper airway patency can be improved using chemogenetic approach by deploying designer receptors exclusively activated by designer drug (DREADD) in the hypoglossal motorneurons. DREADD (rAAV5-hSyn-hM3(Gq)-mCherry) and control virus (rAAV5-hSyn-EGFP) were stereotactically administered to the hypoglossal nucleus of C57BL/6J mice. In 6-8 weeks genioglossus EMG and dynamic MRI of the upper airway were performed before and after administration of the DREADD ligand clozapine-N-oxide (CNO) or vehicle (saline). In DREADD-treated mice, CNO activated the genioglossus muscle and markedly dilated the pharynx, whereas saline had no effect. Control virus treated mice showed no effect of CNO. Our results suggest that chemogenetic approach can be considered as a treatment option for OSA and other motorneuron disorders.

Coordinated Respiratory Motor Activity in Nerves Innervating the Upper Airway Muscles in Rats

Maintaining the patency of the upper airway during breathing is of vital importance. The activity of various muscles is related to the patency of the upper airway. In the present study, we examined the respiratory motor activity in the efferent nerves innervating the upper airway muscles to determine the movements of the upper airway during respiration under normocapnic conditions (pH = 7.4) and in hypercapnic acidosis (pH = 7.2). Experiments were performed on arterially perfused decerebrate rats aged between postnatal days 21–35. We recorded the efferent nerve activity in a branch of the cervical spinal nerve innervating the infrahyoid muscles (CN), the hypoglossal nerve (HGN), the external branch of the superior laryngeal nerve (SLN), and the recurrent laryngeal nerve (RLN) with the phrenic nerve (PN). Inspiratory nerve discharges were observed in all these nerves under normocapnic conditions. The onset of inspiratory discharges in the CN and HGN was slightly prior to those in the SLN and RLN. When the CO₂ concentration in the perfusate was increased from 5% to 8% to prepare for hypercapnic acidosis, the peak amplitudes of the inspiratory discharges in all the recorded nerves were increased. Moreover, hypercapnic acidosis induced pre-inspiratory discharges in the CN, HGN, SLN, and RLN. The onset of pre-inspiratory discharges in the CN, HGN, and SLN was prior to that of discharges in the RLN. These results suggest that the securing of the airway that occurs a certain time before dilation of the glottis may facilitate ventilation and improve hypercapnic acidosis.

[Effect of prenatal alcohol exposure on rhythmic respiratory discharge activity in medullary slices of neonatal rats]

OBJECTIVE

To investigate the effects of prenatal alcohol exposure on rhythmic respiratory discharge activity (RRDA) in the medullary slices of neonatal rats.

METHODS

Ten pregnant female SD rats were exposed to 0, 4%, 6%, 8%, and 10% alcohol in drinking water from 1 week before till 3 days after delivery. The medullary slices of the neonatal rats containing the medial region of the nucleus retrofacialis (mNRF) with the hypoglossal nerve rootlets were prepared and perfused with modified Kreb's solution to record RRDA from the hypoglossal nerve rootlets using suction electrodes.

RESULTS

No significant difference was found in RRDA in 50 min among the neonatal rats with prenatal exposure to 0, 4%, 6%, and 8% alcohol, but the RRDA in 10% alcohol exposure group became irregular. Prenatal exposure to increased alcohol concentrations caused attenuated RRDA attenuated in the neonatal rats, shown by shortened inspiratory time (TI), decreased respiratory frequency (RF), and reduced integral amplitude (IA) as compared with those in the control group.

CONCLUSION

Prenatal alcohol exposure inhibits RRDA in medullary slices of neonatal rats, which might be a mechanism by which maternal alcohol exposure causes suppressed offspring respiratory functions.

Respiratory activity in the 6-hydroxydopamine model of Parkinson's disease in the rat

Respiratory disturbances accompany Parkinson's disease. Weakness of the respiratory muscles or lowering of central respiratory drive might be responsible for respiratory disability. Striatal injection of 6-hydroxydopamine (6-OHDA) simulates motor symptoms of Parkinson's disease in the rat. Present study investigated whether unilateral infusion of 6-OHDA into the striatum may evoke respiratory disorders and therefore be a model for the study of the respiratory aspects of Parkinson's disease. Two weeks after the infusion the animals were anesthetized, vagotomized, paralyzed and artificially ventilated. Neural respiratory activity in the vehicle and 6-OHDA treated groups of animals was assessed from the peak amplitude of the phrenic and hypoglossal bursts, frequency of bursts and minute activity during baseline ventilation and acute intermittent hypoxia composed of five 1.5 minute long episodes of 11 percent oxygen introduced every 3 minutes. An impairment of dopaminergic pathways by 6-OHDA evoked separate effects on phrenic and hypoglossal activity. Under baseline conditions the respiratory parameters taken from the integrated phrenic nerve activity unchanged, while the preinspiratory part of the hypoglossal activity (pre-I HG) was reduced both in terms of its onset and amplitude. 6-OHDA did not affect the phrenic response to acute intermittent hypoxia but it increased the hypoglossal response (Fig. 2). Hypoxia activated the pre-I HG in both experimental groups. Although the pre-I HG increased strongly during hypoxic stimulation, the ratio of the pre-inspiratory hypoglossal amplitude to the inspiratory hypoglossal amplitude never achieved similar values as in the sham group. This ratio decreased significantly during secondary decline of the hypoxic respiratory response. A decline of the hypoxic response was more intense in the hypoglossal activity than in the phrenic activity and moved into hypoxic apnoea more frequently in the Parkinson's disease model. The results indicate a differential modulation of the phrenic and hypoglossal neural output with increased chemical drive when dopaminergic pathways were impaired by 6-OHDA suggesting that such a mechanism may contribute to respiratory insufficiency in Parkinson's disease. An involvement of a modified mechanism of dopamine efflux and of serotonin and orexin during hypoxia is suggested in the observed changes in the hypoglossal activity in the 6-OHDA model of PD.

[The influence of intermittent hypoxia on long-term facilitation of hypoglossal nerve discharge in spontaneously breathing rats]

OBJECTIVE

To explore the impact of intermittent hypoxia on long-term facilitation (LTF) of hypoglossal nerve discharge.

METHODS

Twelve adult SD rats were divided into the experimental group (CIH group, n = 6) and the control group (normoxia group, n = 6) by the random number table. The rats in the CIH group were fed in the intermittent hypoxia animal chambers, while the control group was placed in the normoxia animal chambers for 8 h per day (from 8:00 AM to 4:00 PM) for 4 consecutive weeks. After that, 5 min×3 stimulations of acute intermittent hypoxia (AIH) were administered and the hypoglossal never signals were recorded before and after AIH.

RESULTS

The baseline frequency and average peak amplitude of hypoglossal nerve discharge in the CIH experimental group were significantly greater than those in the control group. The discharge frequency in the CIH and the control groups was (73 ± 13) Hz, and (58 ± 11) Hz, respectively(P < 0.05); and the discharge amplitude in the 2 groups was (4.6 ± 1.1) µV, and (3.3 ± 0.7) µV, respectively(P < 0.05). After intervention with AIH, the frequency and the average peak amplitude of the hypoglossal nerve discharge in the experimental and the control groups were significantly increased(all P < 0.05). The increased discharge lasted more than 1 h and this typical phenomenon was referred to as LTF. In the CIH group, the discharge frequency before and after exposure to AIH was (68 ± 16) Hz and (133 ± 20) Hz, respectively; and the discharge amplitude was (4.6 ± 1.1) µV and (8.9 ± 1.4) µV, respectively. In the control group, the discharge frequency before and after AIH was (59 ± 12) Hz and (102 ± 16) Hz, respectively; and the discharge amplitude was (3.3 ± 0.7) µV and (4.5 ± 0.7) µV, respectively(P < 0.05). After AIH stimulation, the enhanced respiratory intensity of rats in CIH group was much higher than that in the control group [(408 ± 149)% vs (242 ± 31)%, P < 0.05].

CONCLUSION

Both AIH and CIH can induce LTF of the hypoglossal nerve discharge, while the induction of LTF by AIH can be strengthened by CIH.

Motor unit recruitment in human genioglossus muscle in response to hypercapnia

STUDY OBJECTIVES

single motor unit recordings of the genioglossus (GG) muscle indicate that GG motor units have a variety of discharge patterns, including units that have higher discharge rates during inspiration (inspiratory phasic and inspiratory tonic), or expiration (expiratory phasic and expiratory tonic), or do not modify their rate with respiration (tonic). Previous studies have shown that an increase in GG muscle activity is a consequence of increased activity in inspiratory units. However, there are differences between studies as to whether this increase is primarily due to recruitment of new motor units (motor unit recruitment) or to increased discharge rate of already active units (rate coding). Sleep-wake state studies in humans have suggested the former, while hypercapnia experiments in rats have suggested the latter. In this study, we investigated the effect of hypercapnia on GG motor unit activity in humans during wakefulness.

SETTING

sleep research laboratory.

PARTICIPANTS

sixteen healthy men.

MEASUREMENTS AND RESULTS

each participant was administered at least 6 trials with P(et)CO(2) being elevated 8.4 (SD = 1.96) mm Hg over 2 min following a 30-s baseline. Subjects were instrumented for GG EMG and respiratory measurements with 4 fine wire electrodes inserted subcutaneously into the muscle. One hundred forty-one motor units were identified during the baseline: 47% were inspiratory modulated, 29% expiratory modulated, and 24% showed no respiratory related modulation. Sixty-two new units were recruited during hypercapnia. The distribution of recruited units was significantly different from the baseline distribution, with 84% being inspiratory modulated (P < 0.001). Neither units active during baseline, nor new units recruited during hypercapnia, increased their discharge rate as P(et)CO(2) increased (P > 0.05 for all comparisons).

CONCLUSIONS

increased GG muscle activity in humans occurs because of recruitment of previously inactive inspiratory modulated units.

Development of synaptic inhibition in glycine transporter 2 deficient mice

Mice deficient for the neuronal glycine transporter subtype 2 (GlyT2) die during the second postnatal week after developing neuromotor deficiencies, which resembles severe forms of human hyperekplexia. This phenotype has been attributed to a dramatic reduction in glycinergic neurotransmission. In the present study we analyzed the development of GABAergic and glycinergic synaptic transmission in GlyT2-knockout mice during early postnatal life. Anti-glycine immunohistochemistry in spinal cord and brainstem slices and whole-cell voltage-clamp recordings of glycinergic inhibitory postsynaptic currents (IPSCs) from hypoglossal motoneurons revealed strikingly reduced levels of synaptic glycine already at birth. Since GABA and glycine use the same vesicular inhibitory amino acid transporter (VIAAT or VGAT) we also analysed GABAergic neurotransmission. No increase of GABA immunoreactivity was observed in the spinal cord and brainstem of GlyT2(-/-) mice at any stage of postnatal development. Correspondingly no up-regulation of GABAergic IPSCs was detected in GlyT2(-/-) hypoglossal motoneurons. These data suggest that in the first postnatal week, loss of the glycine transporter 2 is neither compensated by glycine de-novo synthesis nor by up-regulation of the GABAergic transmission in GlyT2(-/-) mice.

Simulated apnoeas induce serotonin-dependent respiratory long-term facilitation in rats

Long-term facilitation (LTF) is a form of respiratory neuroplasticity frequently induced by acute intermittent isocapnic hypoxia (AIH, three 5 min isocapnic hypoxic episodes). Although repetitive apnoeas are a frequent natural occurrence producing brief (< 30 s) episodes of hypoxia and hypercapnia, it is unknown if repetitive apnoeas also elicit LTF. Apnoea-induced LTF may preserve upper airway patency during sleep, thereby limiting further apnoeic events. We tested the hypothesis that repeated, brief ventilator-induced apnoeas are sufficient to induce serotonin-dependent phrenic and hypoglossal (XII) LTF in anaesthetized rats. Anaesthetized, male Sprague-Dawley rats were exposed to three or six 25 s ventilator apnoeas with 5 min intervals, and compared to time control and AIH-treated rats. Three and six ventilator apnoeas induced phrenic and XII LTF with a magnitude similar to AIH. Both apnoea-induced and AIH-induced LTF were associated with a decreased CO(2) recruitment threshold for phrenic and XII activity (approximately 4 mmHg). Spinal methysergide, a serotonin receptor antagonist, blocked apnoea-induced LTF but not changes in the CO(2)-recruitment threshold. Thus, brief ventilator apnoeas elicit phrenic and XII LTF. Similar to AIH-induced LTF, apnoea-induced LTF is serotonin dependent, and the relevant serotonin receptors for phrenic LTF are located in the cervical spinal cord. Apnoea-induced LTF may have implications for the maintenance of breathing stability, particularly during sleep.

Electroencephalographic and respiratory activities during acute intermittent hypoxia in anesthetized rats

Cortical activity and respiratory responses to intermittent hypoxia were studied in anesthetized, paralyzed, vagotomized, and artificially ventilated rats. Respiratory responses to hypoxic exposure consisted of stimulation of phrenic and hypoglossal activity and a subsequent decline of the activity up to apnea. The respiratory response to hypoxia was accompanied by a gradual decrement of the total power of EEG. Relative EEG power increased in the delta frequency range and decreased in the remaining frequency ranges. During hypoxic bradypnea or apnea, the total power of EEG strongly diminished or ceased. Each episode of hypoxia caused similar respiratory and cortical effects. However, in comparison with the baseline level, the total power of EEG decreased gradually while the power of the delta frequency range increased in subsequent hypoxic episodes. EEG activity after the last hypoxic exposure recovered within 40-60 min. We conclude that hypoxia initially induces modest changes in the cortical activity that grow with the severity of hypoxia. The persistence of changes in EEG activity following intermittent hypoxia may contribute to disorders present in the sleep apnea syndrome.

Effect of aging on tongue protrusion forces in rats

The purpose of this study was to ascertain the effect of aging on muscle contractile properties associated with tongue protrusion in a rat model. Fischer 344/Brown Norway hybrid rats, ten young (9 months old) and ten old (32 months old), were used to measure protrusive contractile properties. Results showed a significant reduction in tetanic forces in the old animals. The following measures of muscle contraction were not different between age groups: mean twitch contraction force, twitch contraction time, twitch contraction half-decay time, and a calculated measure of fatigability. In conclusion, aging influenced protrusive tongue muscle contractions in a rat model such that tetanic forces were reduced. The reduction of tetanus force may parallel findings in human subjects relative to isometric tongue force generation and may be associated with age-related disorders of swallowing.

Cortico-hypoglossal and corticospinal conduction abnormality in Bickerstaff's brainstem encephalitis

The Miller Fisher syndrome, Guillain-Barre syndrome and Bickerstaff's brainstem encephalitis are related conditions in which anti-GQ1b antibody positivity occur in varied frequencies. This report demonstrates the presence of corticobulbar and corticospinal dysfunction in BBE, by means of a novel transcranial magnetic stimulation technique. It further supports the presence of protean manifestations in anti-GQ1b IgG antibody-positive spectrum of disorders.

Respiratory motor activity: influence of neuromodulators and implications for sleep disordered breathing

Sleep, especially rapid-eye-movement sleep, causes fundamental modifications of respiratory muscle activity and control mechanisms, modifications that can predispose individuals to sleep-related breathing disorders. One of the most common of these disorders is obstructive sleep apnea (OSA) that affects approximately 4% of adults. OSA is caused by repeated episodes of pharyngeal airway obstruction that can occur hundreds of times per night, leading to recurrent asphyxia, arousals from sleep, daytime sleepiness, and adverse cardiovascular and cerebrovascular consequences. OSA is caused by the effects of sleep on pharyngeal muscle tone in individuals with already narrow upper airways. Moreover, since OSA occurs only in sleep, this disorder by definition is a state-dependent process ultimately caused by the influence of sleep neural mechanisms on the activity of pharyngeal motoneurons. This review synthesizes recent findings relating to control of pharyngeal muscle activity across sleep-wake states, with special emphasis on the influence of neuromodulators acting at the hypoglossal motor nucleus that inervates the genioglossus muscle of the tongue. The results of such basic physiological studies may be relevant to identifying and developing new pharmacological strategies to augment pharyngeal muscle activity in sleep, especially rapid-eye-movement sleep, as potential treatments for OSA.

Implications of ALS focality: rostral-caudal distribution of lower motor neuron loss postmortem

BACKGROUND

Because motor manifestations of ALS begin focally and progress contiguously, the anatomic distribution of underlying lower motor neuron and upper motor neuron degeneration should correlate to onset.

OBJECTIVES

To assess the rostral-caudal distribution of lower motor neuron loss in relation to the region of clinical onset.

METHODS

We evaluated 19 ALS postmortem nervous systems from patients whose motor manifestations had begun in different body regions. In each, we looked at four neuraxis levels: hypoglossal nucleus and cervical, thoracic, and lumbar spinal cord. We used light microscopy and devised a technique of particle counting that indexed lower motor neuron loss.

RESULTS

The average overall loss of lower motor neurons in ALS nervous systems was 55%, and the range of loss had a normal distribution that ranged between 8% and 90%. The distribution of lower motor neuron loss was graded within the nervous system relative to onset (p = 0.02 by analysis of variance). In 14 of the 19 nervous systems, the regional lower motor neuron loss within the nervous systems was graded radially away from the region of onset. In 1, radial degeneration seemed likely but did not meet significance. In 2, radial degeneration was apparent but loss was greatest in a region different than that identified as the region of onset. In the remaining 2, lower motor neuron loss was minimal and not graded (both from patients whose motor manifestations had been predominantly upper motor neuron).

CONCLUSION

Lower motor neuron degeneration in ALS is a focal process that advances contiguously, summates over time, and creates graded loss. Stage of degeneration in the nervous system is a function of anatomic location.

Suture of transected nerve suppresses expression of BH3-only protein Noxa in nerve-transected motor neurons of C57BL/6J mouse

Disrupted peripheral nerves are typically sutured as spontaneous recovery does not always occur. However, the molecular mechanisms involved in nerve regeneration following end-to-end nerve suture are obscure. Here, we investigated effects of end-to-end nerve suture after peripheral nerve transection on motor neurons, using the C57BL/6J mouse hypoglossal nerve injury model. In this animal model, 60-80% of injured motor neurons gradually progress to neuronal death, while the remaining injured neurons survive and regenerate. Mice were divided into the Cut and Suture groups. In the Cut group, the right hypoglossal nerve was transected. In the Suture group, the right hypoglossal nerve was transected and then was repaired using end-to-end nerve suture. We assessed differences between the Cut and Suture groups by analyzing the neuronal survival rate by thionine staining and the nerve terminal regeneration rate by vesicular acetylcholine transporter (VAChT) immunohistochemistry, which is a marker for cholinergic presynaptic terminal. We found that 82.9% of motor neurons survived in the Suture group, whereas only 39.2% of motor neurons did in the Cut group 56 days after surgery. At that time point, 86% of presynaptic terminals compared to controls were regenerated in the Suture group, and 21% were regenerated in the Cut group. These results demonstrate that peripheral nerve suture prevented death of nerve-transected motor neurons and promoted nerve regeneration. We also examined expression profiles of major survival and death signal-associated genes in hypoglossal nuclei using in situ hybridization and real-time polymerase chain reaction (PCR). Although most of the survival- and death-associated genes were regulated in a similar manner in both groups, expression of BH3-only protein Noxa mRNA was significantly lower in the Suture than in the Cut group. A significant suppression of Noxa expression by the Suture may be a major reason why nerve suture induces survival and regeneration of nerve-injured motor neurons.

Genioglossus muscle activity and serotonergic modulation of hypoglossal motor output in obese Zucker rats

Obese Zucker rats have a narrower and more collapsible upper airway compared with lean controls, similar to obstructive sleep apnea (OSA) patients. Genioglossus (GG) muscle activity is augmented in awake OSA patients to compensate for airway narrowing, but the neural control of GG activity in obese Zucker rats has not been investigated to determine whether such neuromuscular compensation also occurs. This study tests the hypotheses that GG activity is augmented in obese Zucker rats compared with lean controls and that endogenous 5-hydroxytryptamine (5-HT) contributes to GG activation. Seven obese and seven lean Zucker rats were implanted with electroencephalogram and neck muscle electrodes to record sleep-wake states, and they were implanted with GG and diaphragm wires for respiratory muscle recordings. Microdialysis probes were implanted into the hypoglossal motor nucleus for perfusion of artificial cerebrospinal fluid and the 5-HT receptor antagonist mianserin (100 microM). Compared with lean controls, respiratory rates were increased in obese rats across sleep-wake states (P=0.048) because of reduced expiratory durations (P=0.007); diaphragm activation was similar between lean and obese animals (P=0.632). Respiratory-related, tonic, and peak GG activities were also similar between obese and lean rats (P>0.139). There was no reduction in GG activity with mianserin at the hypoglossal motor nucleus, consistent with recent observations of a minimal contribution of endogenous 5-HT to GG activity. These results suggest that despite the upper airway narrowing in obese Zucker rats, these animals have a sufficiently stable airway such that pharyngeal muscle activity is normal across sleep-wake states.

Altered expression of Smad family members in injured motor neurons of rat

We examined changes in the expression of Smad family members, which transduce signals from TGF-beta superfamily ligands, following hypoglossal nerve injury. RT-PCR and in situ hybridization revealed that Smad1, 2, 3 and 4 mRNAs were significantly up-regulated in injured side, whereas Smad8 mRNA was down-regulated. Immunohistochemistry and Western blotting analysis confirmed the alterations of Smad1, 2 and 4 in injured neurons. These results suggest that the Smad signaling may be important for nerve regeneration.

Partial neurolysis of the hypoglossal nerve for selective lingual atrophy in a porcine model

OBJECTIVES

Obstructive sleep apnea in children is most commonly treated with adenotonsillectomy; however, in cases of significant tongue base prolapse, this may prove inadequate. Surgical procedures used to increase the retroglossal airway have significant morbidities and low patient acceptability. We theorized that effective reduction of the tongue base can be achieved through partial denervation of the hypoglossal nerve, which is easily accessed in the submandibular space with minimal morbidity.

METHODS

We performed a prospective, experimental study in which topographic innervation maps of porcine tongue were generated by stimulating the hypoglossal main trunk and peripheral branches. The effects of complete unilateral nerve sectioning on tongue base volume and linear dimensions were measured and compared to the contralateral control side. In the final stage, only the peripheral nerve that was determined as the main supply to the tongue base was sectioned, and the results were compared to those in the matched controls.

RESULTS

A medial branch of the hypoglossal nerve was consistently identified as the main motor supply to the tongue base. Complete denervation resulted in a measurable decrease in the volume of the tongue base as compared to that of controls. Partial neurolysis produced inconsistent changes in 2 subjects, with decreases in linear dimensions that were not proportional to the decrease in volume. Histologically, complete denervation was followed by a significantly greater replacement of muscle with fat and connective tissue as compared with partial neurolysis.

CONCLUSIONS

There were inconsistent changes in volume and linear dimensions of the tongue base following partial neurolysis of the hypoglossal nerve over the 3-month experimental period.

Time-frequency coherence analysis of phrenic and hypoglossal activity in the decerebrate rat during eupnea, hyperpnea, and gasping

Fast respiratory rhythms include medium- (MFO) and high-frequency oscillations (HFO), which are much faster than the fundamental breathing rhythm. According to previous studies, HFO is characterized by high coherence (Coh) in phrenic (Ph) nerve activity, thereby providing a means of distinguishing between these two types of oscillations. Changes in Coh between the Ph and hypoglossal (XII) nerves during the transition from normal eupnic breathing to gasping have not been characterized. Experiments were performed on nine unanesthetized, chemo- and barodenervated, decerebrate adult rats, in which sustained asphyxia elicited hyperpnea and gasping. A gated time-frequency Coh analysis was developed and applied to whole Ph and medial XII nerve recordings. The results showed dynamic Ph-Ph Coh during eupnea, including MFO and HFO. XII-XII Coh during eupnea was broadband and included four distinct peaks, with low-frequency Coh dominating the epochs preceding the onset of Ph activity. During gasping, only MFO-peaks were present in Ph-Ph Coh. Bilateral XII activity showed a significant reduction in Coh and a shift toward lower frequencies during gasping. In contrast, contralateral Ph-XII Coh progressively increased during state changes from eupnea to gasping, a tendency mirrored in the startup part of the Ph activity. These data suggest significant hypoxia/hypercapnia-induced alterations in synchronization between respiratory outputs during the transition from eupnea to gasping, reflecting a reconfiguration of the respiratory network and/or alterations in the circuitry associated with the motor pools, including dynamic coupling between outputs.

Selective loss of high-frequency oscillations in phrenic and hypoglossal activity in the decerebrate rat during gasping

Respiratory motor outputs contain medium-(MFO) and high-frequency oscillations (HFO) that are much faster than the fundamental breathing rhythm. However, the associated changes in power spectral characteristics of the major respiratory outputs in unanesthetized animals during the transition from normal eupneic breathing to hypoxic gasping have not been well characterized. Experiments were performed on nine unanesthetized, chemo- and barodenervated, decerebrate adult rats, in which asphyxia elicited hyperpnea, followed by apnea and gasping. A gated fast Fourier transform (FFT) analysis and a novel time-frequency representation (TFR) analysis were developed and applied to whole phrenic and to medial branch hypoglossal nerve recordings. Our results revealed one MFO and one HFO peak in the phrenic output during eupnea, where HFO was prominent in the first two-thirds of the burst and MFO was prominent in the latter two-thirds of the burst. The hypoglossal activity contained broadband power distribution with several distinct peaks. During gasping, two high-amplitude MFO peaks were present in phrenic activity, and this state was characterized by a conspicuous loss in HFO power. Hypoglossal activity showed a significant reduction in power and a shift in its distribution toward lower frequencies during gasping. TFR analysis of phrenic activity revealed the increasing importance of an initial low-frequency “start-up” burst that grew in relative intensity as hypoxic conditions persisted. Significant changes in MFO and HFO rhythm generation during the transition from eupnea to gasping presumably reflect a reconfiguration of the respiratory network and/or alterations in signal processing by the circuitry associated with the two motor pools.

Unusual presentations of craniovertebral junction tuberculosis: a report of 2 cases and literature review

BACKGROUND

CVJ tuberculosis is a described entity requiring challenging ways of management. Severe neck pain, causing restricted neck movements and torticollis, is a characteristic presentation of neurologically asymptomatic suboccipital Pott's disease.

CASE DESCRIPTION

Two patients with unusual CVJ tuberculosis form the basis for the present communication. The first patient presented with tubercular otitis media, causing progressive erosion of the petrous part of temporal bone, and destruction of the occipital condyle, along with the lateral mass of atlas, leading to CVJ instability. This is a first report of such a presentation, according to our knowledge. Detailed bony architectural destruction demonstrable on CT scan has been described. The second patient, with CVJ tuberculosis, presented with skull base syndrome and with multiple cranial nerve palsies. Both patients were managed without surgical intervention and showed clinical and radiological recovery.

CONCLUSION

In such patients with unusual clinical presentations, histopathologic examination is necessary to arrive at a correct diagnosis. The management of patients with tubercular involvement of CVJ remains controversial. In the present communication, both the patients were managed successfully with full dose of antitubercular drugs and immobilization.

Usefulness of transcervical approach for surgical treatment of hypoglossal schwannoma with paraspinal extension: case report

BACKGROUND

Usefulness of transcervical approach to hypoglossal schwannoma with paraspinal extension is described herein.

CASE DESCRIPTION

A 54-year-old woman presented with gradually worsening left hypoglossal nerve palsy. The findings were of a tumor lying in the left hypoglossal canal and paraspinal region and were consistent with hypoglossal schwannoma. Subtotal intracapsular removal of the tumor was performed via transcervical approach. The symptoms improved, and no additional symptoms were noted.

CONCLUSION

The transcervical approach and intracapsular removal of the tumor under electrophysiological monitoring provided for successful minimally invasive surgery in this case of hypoglossal schwannoma.

Determination of the changes in the hypoglossal nerve function after suspension laryngoscopy with needle electromyography of the tongue

The purpose of this study was to determine changes in the hypoglossal nerve function after suspension laryngoscopy with needle electromyography of the tongue. This study also attempted to determine the possible relationship between the predictive factors of intubation difficulty by using the intubation difficulty scale, which was introduced by Adnet et al., duration of suspension laryngoscopy and changes in hypoglossal nerve function after suspension laryngoscopy. The study was performed on 39 patients who underwent suspension laryngoscopy for benign glottic pathology. Pre-operative airway assessment was evaluated by the intubation difficulty scale and the duration of suspension laryngoscopy was recorded. Needle electromyography of the tongue was performed three or four weeks after the suspension laryngoscopy. After needle electromyography of the tongue, increased polyphasia was found in 13 patients (33 per cent), bilaterally in three of them. The interference pattern was reduced in two of these 13 patients. There was no statistically significant difference in predictive factors of intubation difficulty and the duration of the operation between these 13 patients with increased polyphasiaand the remaining 26 patients with completely normal electromyography findings. These findings show that, in spite of normal clinical tongue function, subclinical changes can be detected by needle electromyography of the tongue after suspension laryngoscopy.

Noradrenergic, serotonergic and GABAergic antagonists injected together into the XII nucleus abolish the REM sleep-like depression of hypoglossal motoneuronal activity

Recently, we reported that the suppression of hypoglossal (XII) motoneuronal activity that occurs during the carbachol-induced, rapid eye movement (REM) sleep-like state is abolished by the microinjection into the XII nucleus of a drug mix that antagonizes aminergic excitation and amino acid-mediated inhibition (prazosin, methysergide, bicuculline and strychnine). We now assess the role of glycinergic inhibition in the depression of XII motoneuronal activity and estimate the distribution of the antagonists around the XII nucleus at the time when they are effective. Towards the first goal, REM sleep-like episodes were elicited in urethane-anesthetized rats by 10 nl carbachol microinjections into the dorsomedial pons prior to, and at different times after, combined microinjections into the XII nucleus of only three antagonists (strychnine omitted). As in our previous study, the carbachol-induced depression of XII activity was abolished during tests performed 42-88 min after the antagonists, whereas other characteristic effects of carbachol (appearance of hippocampal theta, cortical activation, decreased respiratory rate) remained intact. The depressant effect of carbachol on XII motoneurons partially recovered after 2.5 h. Towards the second goal, using a drug diffusion model, we determined that the tissue concentrations of the antagonists at the time when they were effective were within the range of their selective actions, and the drugs acted within 0.9-1.4 mm from the injection sites, thus within a space containing XII motoneurons and their dendrites. We conclude that antagonism of alpha-adrenergic, serotonergic, and GABA(A) receptors are sufficient to abolish the REM sleep-like atonia of XII motoneurons.

Expression of Reg/PAP family members during motor nerve regeneration in rat

In this study, we examined the expression of mRNAs for Regenerating gene (Reg)/pancreatitis-associated protein (PAP) family members following hypoglossal nerve injury in rats. In addition to four rat family members (RegI, Reg-2/PAP I, PAP II, and PAP III) that had been identified, we newly cloned and sequenced a type-IV Reg gene in rats. Among these five family members, the expression of Reg-2/PAP I mRNA was predominantly enhanced in injured motor neurons after axotomy. Furthermore, a marked induction of PAP III mRNA was observed in the distal part of the injured nerve. A polyclonal antibody was raised against PAP III, and a Western blotting analysis using this antibody confirmed an increased level of PAP III protein in the injured nerve. These results suggest that Reg family members would be new mediators among injured neurons and glial cells, and may play pivotal roles during nerve regeneration.

Differences in time-dependent hypoxic phrenic responses among inbred rat strains

Hypoxic ventilatory responses differ between rodent strains, suggesting a genetic contribution to interindividual variability. However, hypoxic ventilatory responses consist of multiple time-dependent mechanisms that can be observed in different respiratory motor outputs. We hypothesized that strain differences would exist in discrete time-dependent mechanisms of the hypoxic response and, furthermore, that there may be differences between hypoglossal and phrenic nerve responses to hypoxia. Hypoglossal and phrenic nerve responses were assessed during and after a 5-min hypoxic episode in anesthetized, vagotomized, and ventilated rats from four inbred strains: Brown Norway (BN), Fischer 344 (FS), Lewis (LW), and Piebald-viral-Glaxo (PVG). During baseline, burst frequency was higher in PVG than LW rats ( P < 0.05), phrenic burst amplitude was higher in PVG vs. other strains ( P < 0.05), and hypoglossal burst amplitude was higher in PVG and BN vs. FS and LW ( P < 0.05). During hypoxia, burst frequency did not change in BN or LW rats, but it increased in PVG and FS rats. The phrenic amplitude response was smallest in PVG vs. other strains ( P < 0.05), and the hypoglossal response was similar among strains. Short-term potentiation posthypoxia was slowest in FS and fastest in LW rats ( P < 0.05). Posthypoxia frequency decline was absent in PVG, but it was observed in all other strains. Augmented breaths were observed during hypoxia in FS rats only. Thus genetic differences exist in the time domains of the hypoxic response, and these are differentially expressed in hypoglossal and phrenic nerves. Furthermore, genetic diversity observed in hypoxic ventilatory responses in unanesthetized rats may arise from multiple neural mechanisms.

Neck-tongue syndrome

OBJECTIVE

To discuss a case of neck-tongue syndrome (NTS) affecting a dancer/figure skater, review literature summarizing the pathogenesis and treatment, and offer new categorization of neck-tongue syndrome.

CLINICAL FEATURES

A 24-year-old female dancer/skater sought treatment for recurrent episodes of right-sided upper neck pain with associated ipsilateral numbness of her tongue following brisk active rotation. Radiographs revealed a narrowing of the left para-odontoid space. Physical examination revealed a mildly painful restriction in rotation at C1-2 with no apparent muscular hypertonicity.

INTERVENTION AND OUTCOME

The patient had sought chiropractic treatment for this condition several times since she was 8 years old. Diversified chiropractic adjustments were applied to restrictions throughout the cervical spine as determined by the clinician. No other interventions were employed. The patient experienced significant improvement in frequency and intensity of the neck and tongue symptoms following spinal manipulative therapy applied to her cervical spine.

CONCLUSIONS

There are 2 categories of NTS: complicated NTS due to the presence of an underlying disease process (inflammatory or degenerative) and uncomplicated NTS (idiopathic or trauma-related). This case report is of uncomplicated NTS that responded favorably to spinal manipulative therapy directed at the cervical spine. In the absence of upper cervical instability, spinal manipulative therapy appears to be beneficial and should be considered in all cases of uncomplicated NTS.

Uncoupling of rhythmic hypoglossal from phrenic activity in the rat

During eupnoea, rhythmic motor activities of the hypoglossal, vagal and phrenic nerves are linked temporally. The inspiratory discharges of the hypoglossal and vagus motor neurones commence before the onset of the phrenic burst. The vagus nerve also discharges in expiration. Upon exposure to hypocapnia or hypothermia, the hypoglossal discharge became uncoupled from that of the phrenic nerve. This uncoupling was evidenced by variable times of onset of hypoglossal discharge before or after the onset of phrenic discharge, extra bursts of hypoglossal activity in neural expiration, or complete absence of any hypoglossal discharge during a respiratory cycle. No such changes were found for vagal discharge, which remained linked to the phrenic bursts. Intracellular recordings in the hypoglossal nucleus revealed that all changes in hypoglossal discharge were due to neuronal depolarization. These results add support to the conclusion that the brainstem control of respiratory-modulated hypoglossal activity differs from control of phrenic and vagal activity. These findings have implications for any studies in which activity of the hypoglossal nerve is used as the sole index of neural inspiration. Indeed, our results establish that hypoglossal discharge alone is an equivocal index of the pattern of overall ventilatory activity and that this is accentuated by hypercapnia and hypothermia.

Long-Term Intermittent Hypoxia

Humans with long-standing sleep apnea show mixed responses to serotonergic therapies for obstructive sleep apnea. We hypothesize that long-term intermittent hypoxia may result in oxidative injury to upper airway motoneurons, thereby diminishing serotonergic motoneuronal excitation. Unilateral serotonin and glutamate agonist and antagonist microinjections into the hypoglossal motor nuclei in adult rats exposed to 3 weeks of intermittent hypoxia showed reduced hypoglossal nerve responsiveness (logEC50) for serotonin and N-methyl-D-aspartate. However, long-term intermittent hypoxia did not appear to alter hypoglossal response to alpha-amino-3-hydroxy-methylisoxazole-4-propionic acid injections. There was no reduction in hypoglossal motoneuron soma number or in serotonergic postsynaptic receptor mRNA copy numbers within single-cells; in contrast, there was an increase in isoprostanes in the dorsal medulla. Systemic 4-hydroxyl-2,2,6,6-tetramethylpiperidin-1-oxyl (tempol) throughout exposure to intermittent hypoxia improved the EC50 for serotonin to a larger extent than glutamate and normalized medullary isoprostanes. Protein kinase C activity within the hypoglossal nucleus was increased after long-term intermittent hypoxia. These results suggest that long-term intermittent hypoxia reduces serotonergic and N-methyl-D-aspartate excitatory output of hypoglossal nerves, and that reduced excitatory responsiveness and lipid peroxidation are largely prevented with superoxide dismutase treatment throughout hypoxia/reoxygenation. Similar alterations in neurochemical responsiveness may occur in select persons with obstructive sleep apnea.

Hypoglossal and phrenic nerve responses to changes in oxygen tension during picrotoxin-induced seizures in the rat

The aim of this study was to examine the response of phrenic and hypoglossal motor outputs to hyperoxia and 11% hypoxia during picrotoxin-induced seizures. Adult rats were anesthetized with a mixture of urethane with alpha-chloralose. The animals were bilaterally vagotomized, paralyzed, and artificially ventilated. Picrotoxin was administered intravenously in a cumulative dose until seizures occurred. The response to changes in oxygen tension was studied after the convulsive dose of picrotoxin and compared with the baseline level. The results show that the picrotoxin-induced seizures evoked a complex respiratory response that consisted of an augmentation of phrenic and hypoglossal nerve activities and irregular disturbances in phasic respiratory discharges. The excitation of the hypoglossal activity appeared earlier and showed a more irregular pattern than that of the phrenic activity. Hyperoxia elicited a similar decrease in neural respiratory outputs during the control and seizure conditions, suggesting the unaltered peripheral chemoreceptor mechanism. In the pre-seizure condition, hypoxia caused an initial excitation of the phrenic and hypoglossal outputs followed by some decline of the effect. During seizures, the striking effect of hypoxia was a decrease of the respiratory rate. A biphasic response to hypoxia was maintained in the hypoglossal activity due to stimulation of the hypoglossal amplitude. In contrast, in the phrenic activity the excitatory phase of hypoxia was absent and depression ensued. The mechanism underlying the facilitation of hypoxic respiratory depression during seizures is discussed.

Subclinical cranial nerve involvement in hereditary motor and sensory neuropathy: a combined conduction study with electrical and magnetic stimulation

OBJECTIVE

To evaluate the electrophysiological findings of clinically unaffected cranial nerves (facial, accessory and hypoglossal nerves) in hereditary motor and sensory neuropathy (HMSN).

METHODS

The conduction times of the facial, accessory, and hypoglossal nerves in 10 patients with HMSN type I (HMSN I), 2 patients with HMSN Type II (HMSN II), and 20 normal controls were determined. The extra- and intracranial segments of the cranial nerves were stimulated electrically and magnetically, respectively. The relationships between the conduction parameters of the cranial nerves and limb nerves were analyzed.

RESULTS

In patients with HMSN I, the conduction times of the distal and proximal segments were significantly prolonged in all 3 cranial nerves. A positive correlation was found between the conduction parameters of the cranial nerves and the limb nerves.

CONCLUSIONS

Electrophysiological involvement of the whole segment of the facial, accessory and hypoglossal nerves is common in patients with HMSN I without clinical signs of alterations. The degree of conduction slowing of the facial, accessory, and hypoglossal nerves paralleled that of limb nerves.

Regional effects of selective pharyngeal muscle activation on airway shape

Pharyngeal airway fiberoptic imaging was performed in 10 decerebrate cats to determine the effect of selective pharyngeal muscle activation on airway shape. At intraluminal pressures from 6 to -6 cm H2O, maximum anteroposterior and lateral diameters were measured in the rostral oropharynx, caudal oropharynx, and velopharynx with and without bilateral stimulation of the medial hypoglossus (HG), lateral HG, whole HG, glossopharyngeus, and pharyngeal branch of vagus nerves. At all three airway levels without nerve stimulation, the increase in diameter with increasing pressure was greater in the lateral than anteroposterior dimension. Stimulation of the hypoglossal and glossopharyngeus nerves caused greater increases in lateral than anteroposterior diameter in all three regions with different effects across nerves and regions. Stimulation of these four nerves frequently caused greater increases in both diameters, as the airway cross-sectional area was decreased by lowering airway pressure. Stimulation of the pharyngeal branch of vagus resulted in greater decreases in lateral than anteroposterior dimension in the caudal oropharynx and velopharynx, especially as airway cross-sectional area was increased by increasing intraluminal pressure. The results indicate that selective activation of pharyngeal muscles in cats frequently results in greater changes in lateral than anteroposterior airway diameter and that these effects are dependent on airway region and cross-sectional area.

Deletion of the mouse glycine transporter 2 results in a hyperekplexia phenotype and postnatal lethality

The glycine transporter subtype 2 (GlyT2) is localized in the axon terminals of glycinergic neurons. Mice deficient in GlyT2 are normal at birth but during the second postnatal week develop a lethal neuromotor deficiency that resembles severe forms of human hyperekplexia (hereditary startle disease) and is characterized by spasticity, tremor, and an inability to right. Histological and immunological analyses failed to reveal anatomical or biochemical abnormalities, but the amplitudes of glycinergic miniature inhibitory currents (mIPSCs) were strikingly reduced in hypoglossal motoneurons and dissociated spinal neurons from GlyT2-deficient mice. Thus, postnatal GlyT2 function is crucial for efficient transmitter loading of synaptic vesicles in glycinergic nerve terminals, and the GlyT2 gene constitutes a candidate disease gene in human hyperekplexia patients.

Convergence of cervical and trigeminal sensory afferents

Cranial nociceptive perception shows a distinct topographic distribution, with the trigeminal nerve receiving sensory information from the anterior portions of the head, the greater occipital nerve, and branches of the upper cervical roots in the posterior regions. However, this distribution is not respected during headache attacks, even if the etiology of the headache is specific for only one nerve. Nociceptive information from the trigeminal and cervical territories activates the neurons in the trigeminal nucleus caudalis that extend to the C2 spinal segment and lateral cervical nucleus in the dorsolateral cervical area. These neurons are classified as multimodal because they receive sensory information from more than one afferent type. Clinically, trigeminal activation produces symptoms in the trigeminal and cervical territory and cervical activation produces symptoms in the cervical and trigeminal territory. The overlap between the trigeminal nerve and cervical is known as a convergence mechanism. For some time, convergence mechanisms were thought to be secondary to clinical observations. However, animal studies and clinical evidence have expanded our knowledge of convergence mechanisms. In this paper, the role of convergence mechanisms in nociceptive physiology, physiopathology of the headaches, clinical diagnosis, and therapeutic conduct are reviewed.

Hypoglossal-facial nerve anastomosis: dynamic insight into the cross-innervation phenomenon

The authors investigated the evolution of the dynamic features of the cross-innervation process in patients with complete facial palsy due to facial nerve transection during surgery for acoustic neuroma removal followed by a hypoglossal-facial nerve anastomosis (HFA). Clinical and electrophysiologic investigations were carried out before and over a 3-year period after HFA. Cross-innervation had started by the 10th day, progressed to the seventh to eighth month, then decreased and finally disappeared by the 12th month after HFA. Ipsilateral reinnervation was observed by the fourth month, progressed to the 12th to 18th month, and remained stable for the remainder of the follow-up period.

Activity of neurons in ventrolateral respiratory groups during swallowing in decerebrate rats

To elucidate the neuronal basis of the coordination between swallowing and respiration, we examined the swallowing-related activity of respiratory neurons in the ventrolateral respiratory groups of the medulla oblongata of decerebrate, paralyzed and artificially ventilated rats (n = 14). Extracellular recording was made during fictive swallowing evoked by the electrical stimulation of the superior laryngeal nerve from a total of 141 neurons with respiratory rhythm (99 expiratory and 42 inspiratory neurons). The burst of discharge by the hypoglossal nerve was used to monitor the pharyngeal phase of swallowing. The decrementing-expiratory (E-DEC) neurons (n = 62) were activated during (n = 46) or after (n = 10) the hypoglossal bursts, or showed no swallowing-related activity (n = 6). All of the augmenting-expiratory (E-AUG) neurons (n = 37) were silent during the hypoglossal bursts but were activated after each swallow. Inspiratory neurons showed either no swallowing-related bursts (n = 27), or were activated after the hypoglossal bursts (n = 15). Activation of the majority of E-DEC neurons may be related to the arrest of respiration during swallowing, and the post-swallow activation of E-AUG neurons may correspond to the expiratory phase that follows swallowing. We suggest that these behaviors of expiratory neurons are essential in the phase resetting of the respiratory cycle in association with the swallowing.

Upper airway muscle paralysis reduces reflex upper airway motor response to negative transmural pressure in rat

The reflex upper airway (UA) motor response to UA negative pressure (UANP) is attenuated by neuromuscular blockade. We hypothesized that this is due to a reduction in the sensitivity of laryngeal mechanoreceptors to changes in UA pressure. We examined the effect of neuromuscular blockade on hypoglossal motor responses to UANP and to asphyxia in 15 anesthetized, thoracotomized, artificially ventilated rats. The activity of laryngeal mechanoreceptors is influenced by contractions of laryngeal and tongue muscles, so we studied the effect of selective denervation of these muscle groups on the UA motor response to UANP and to asphyxia, recording from the pharyngeal branch of the glossopharyngeal nerve (n = 11). We also examined the effect of tongue and laryngeal muscle denervation on superior laryngeal nerve (SLN) afferent activity at different airway transmural pressures (n = 6). Neuromuscular blockade and denervation of laryngeal and tongue muscles significantly reduced baseline UA motor nerve activity (P < 0.05), caused a small but significant attenuation of the motor response to asphyxia, and markedly attenuated the response to UANP. Motor denervation of tongue and laryngeal muscles significantly decreased SLN afferent activity and altered the response to UANP. We conclude that skeletal muscle relaxation reduces the reflex UA motor response to UANP, and this may be due to a reduction in the excitability of UA motor systems as well as a decrease of the response of SLN afferents to UANP.

[Spontaneous unit activity of locus coeruleus neurons after destruction of some nuclei of the medulla oblongata]

Bilateral lesions of the nuclei prepositus hypoglossi produced a more than twofold decrease in the mean frequency discharges in the neurons of the nucleus coeruleus. The number of neurons with burst activity and the number of polymodal neurons substantially increased. Lesion of the nucleus tractus solitarius resulted in an increase in the number of neurons with regular activity and certain decrease in the mean discharge frequency of coeruleus neurons. The results confirm the suggestion about a substantial role of the nucleus prepositus hypoglossi in relaying afferent effects to the activity of locus coeruleus neurons.

Vocal cord palsy resulting from spontaneous carotid dissection

OBJECTIVES/HYPOTHESIS

Vocal cord palsy has a variety of causes, such as malignant tumors of the thyroid, lung, or upper mediastinum, aortic aneurysm, surgery of the thyroid, and infectious diseases.

STUDY DESIGN

Case report.

METHODS

A 43-year-old biologist had a holocephalic headache and right-sided neck pain for 1 day. Five days later, he developed paralysis of the right-side vocal cord. In addition, an angiotensin converting enzyme (ACE) inhibitor was administered because the patient had high systolic and diastolic blood pressures, which were formerly not known to the patient. Five days after admission, a temporary sensorimotor hemiparesis occurred.

RESULTS

Neurological examination revealed, in addition to the known paralysis of the right-side vocal cord, right-side palatoplegia, right-side hypoglossal nerve palsy, and mild dysphagia. Duplex sonography showed evidence of lumen narrowing of the right-side internal carotid artery caused by an hypoechogenic mural hematoma. Magnetic resonance imaging (0.5 T, Philips Gyroscan) revealed a circumscribed dissection of the right-side internal carotid artery from the carotid bifurcation to the petrosal segment. The diffusion-weighted magnetic resonance imaging scan of the brain also demonstrated multiple embolic ischemic lesions in the right hemisphere.

CONCLUSION

Internal carotid artery dissection must be included in the differential diagnosis of lower cranial nerve palsy and should be assessed by duplex ultrasonography and magnetic resonance imaging.