Hypoglossal Nucleus Research Articles

Intrinsic and Extrinsic Tongue Muscles are Driven by Physiologically Distinct Motoneuron Pools

The hypoglossal motor nucleus innervates six of the seven tongue muscles responsible for wide-ranging behaviors including speech, breathing, and swallowing. Despite the task-specific nature of tongue movements, neurophysiologic research has historically treated hypoglossal motoneurons as a homogeneous population. Our previous work showed that hypoglossal motoneurons innervating specific tongue muscles had different firing thresholds and resting membrane potential. Here, we extend this work by comparing potassium conductance in motor neurons innervating the superior longitudinalis (SL; intrinsic) and genioglossus (GG; extrinsic), tongue muscles with opposing actions of tongue retraction and tongue protrusion, respectively. Experiments were performed using N=10 neonatal rat pups aged post-natal day 0-5 ( n=5 each of SL and GG). Motoneurons were back-labeled by injection of dextran rhodamine conjugated to Texas Red into either the SL or GG muscle. > 24-hours after injection, animals were anesthetized on ice and decapitated. The brainstem and spinal cord were removed and 250 μm transverse slices of the medulla containing the hypoglossal nucleus were obtained. SL or GG motor neurons were visualized under a fluorescence microscope and resting membrane potential, rheobase current, frequency-current relation and potassium currents were recorded using whole-cell patch clamp. Statistical analysis revealed that SL motoneurons were ~11 mV more depolarized than GG motoneurons (resting membrane potential of -49 vs -60 mV, p<0.05). Rheobase current (the minimal electrical current required to evoke an action potential) was greater in GG motoneurons than SL motoneurons (approximately 300 vs 150 pA, p<0.05). SL motoneurons had a higher firing rate than GG motoneurons in response to current injection ( p<0.05). Evaluation of neuronal potassium channel conductance showed that the magnitude of transient ( p < 0.01) and sustained (p < 0.01) potassium currents were greater in GG than SL motoneurons, consistent with our finding that resting membrane potential was more negative, and firing rate was slower, in GG than SL motoneurons. Finally, additional SL motoneuron recordings were performed to evaluate for potential sex differences in N=12 (6 male) rat pups aged post-natal day 0-5. Preliminary analysis revealed no significant difference in resting membrane potential between male (-49 mV) and female (-52 mV) SL motoneurons, suggesting that the properties of a specific hypoglossal motoneuron pool are consistent across sexes. Overall, these results demonstrate that GG motoneurons are less excitable than SL motoneurons, which supports the idea that intrinsic and extrinsic tongue muscles are driven by physiologically distinct motoneuron pools. This work has potential to guide development of therapeutics for disordered speech, breathing, and swallowing, all of which depend on proper neuromotor control of the tongue. This work was funded by NIH 5R01DC020889-02. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Vocal and tongue exercise in early to mid-stage Parkinson disease using the Pink1-/- rat

Vocal and swallowing deficits are common in Parkinson disease (PD). Because these impairments are resistant to dopamine replacement therapies, vocal and lingual exercise are the primary treatment, but not all individuals respond to exercise and neural mechanisms of treatment response are unclear. To explore putative mechanisms, we used the progressive Pink1-/- rat model of early to mid-stage PD and employed vocal and lingual exercises at 6- and 10-months of age in male Pink1-/- and wild type (WT) rats. We hypothesized that vocal and lingual exercise would improve vocal and tongue use dynamics and increase serotonin (5HT) immunoreactivity in related brainstem nuclei. Rats were tested at baseline and after 8 weeks of exercise or sham exercise. At early-stage PD (6 months), vocal exercise resulted in increased call complexity, but did not change intensity, while at mid-stage (10 months), vocal exercise no longer influenced vocalization complexity. Lingual exercise increased tongue force generation and reduced relative optical density of 5HT in the hypoglossal nucleus at both time points. The effects of vocal and lingual exercise at these time points are less robust than in prodromal stages observed in previous work, suggesting that early exercise interventions may yield greater benefit. Future work targeting optimization of exercise at later time points may facilitate clinical translation.

Impact of ovariectomy on neurotransmitter receptors BDNF/TrkB and endoplasmic reticulum molecular chaperones in rat hypoglossal nucleus.

The online version contains supplementary material available at 10.1007/s41105-024-00520-5.

Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part II. Age-associated alterations in serotonin receptor binding profiles within medullary nuclei supporting cardiorespiratory homeostasis.

The failure of chemoreflexes, arousal, and/or autoresuscitation to asphyxia may underlie some sudden infant death syndrome (SIDS) cases. In Part I, we showed that some SIDS infants had altered 5-hydroxytryptamine (5-HT)2A/C receptor binding in medullary nuclei supporting chemoreflexes, arousal, and autoresuscitation. Here, using the same dataset, we tested the hypotheses that the prevalence of low 5-HT1A and/or 5-HT2A/C receptor binding (defined as levels below the 95% confidence interval of controls-a new approach), and the percentages of nuclei affected are greater in SIDS versus controls, and that the distribution of low binding varied with age of death. The prevalence and percentage of nuclei with low 5-HT1A and 5-HT2A/C binding in SIDS were twice that of controls. The percentage of nuclei with low 5-HT2A/C binding was greater in older SIDS infants. In >80% of older SIDS infants, low 5-HT2A/C binding characterized the hypoglossal nucleus, vagal dorsal nucleus, nucleus of solitary tract, and nuclei of the olivocerebellar subnetwork (important for blood pressure regulation). Together, our findings from SIDS infants and from animal models of serotonergic dysfunction suggest that some SIDS cases represent a serotonopathy. We present new hypotheses, yet to be tested, about how defects within serotonergic subnetworks may lead to SIDS.

A predisposed motor bias shapes individuality in vocal learning.

The development of individuality during learned behavior is a common trait observed across animal species; however, the underlying biological mechanisms remain understood. Similar to human speech, songbirds develop individually unique songs with species-specific traits through vocal learning. In this study, we investigate the developmental and molecular mechanisms underlying individuality in vocal learning by utilizing F1 hybrid songbirds (Taeniopygia guttata cross with Taeniopygia bichenovii), taking an integrating approach combining experimentally controlled systematic song tutoring, unbiased discriminant analysis of song features, and single-cell transcriptomics. When tutoring with songs from both parental species, F1 hybrid individuals exhibit evident diversity in their acquired songs. Approximately 30% of F1 hybrids selectively learn either song of the two parental species, while others develop merged songs that combine traits from both species. Vocal acoustic biases during vocal babbling initially appear as individual differences in songs among F1 juveniles and are maintained through the sensitive period of song vocal learning. These vocal acoustic biases emerge independently of the initial auditory experience of hearing the biological father's and passive tutored songs. We identify individual differences in transcriptional signatures in a subset of cell types, including the glutamatergic neurons projecting from the cortical vocal output nucleus to the hypoglossal nuclei, which are associated with variations of vocal acoustic features. These findings suggest that a genetically predisposed vocal motor bias serves as the initial origin of individual variation in vocal learning, influencing learning constraints and preferences.

Angiotensin II, blood-brain barrier permeability, and microglia interplay during the transition from pre-to hypertensive phase in spontaneously hypertensive rats.

Hypertension is characterized by upregulation of the renin-angiotensin system, increased blood-brain barrier (BBB) permeability, microglia activation within autonomic nuclei, and an intense sympathoexcitation. There is no information on the interplay of these events during the development of neurogenic hypertension. We sought to identify the interaction and time-course changes of Ang II availability, barrier dysfunction, microglia activation, and autonomic imbalance within autonomic areas during the development of neurogenic hypertension. Sequential changes of hemodynamic/autonomic parameters, BBB permeability, microglia structure/density (IBA-1), and angiotensin II (Ang II) immunofluorescence were evaluated within the paraventricular hypothalamic nucleus, nucleus of the solitary tract, and rostral ventrolateral medulla of Wistar and spontaneously hypertensive rats (SHRs) aged 4 weeks, 5 weeks, 6 weeks, 8 weeks, and 12weeks. The somatosensory cortex and hypoglossal nucleus were also analyzed as non-autonomic control areas. Increased brain Ang II availability (4th-5thweek) was the first observed change, followed by the incipient BBB leakage and increased microglia density (6thweek). From the 5th-6thweeks on, BBB leakage, Ang II, and IBA-1 densities increased continuously, allowing a parallel increase in both Ang II-microglia colocalization and the transition of microglial cells from highly ramified in the basal surveillant condition (4th-5thweek) to shorter process arbors, fewer endpoints, and enlarged soma in the disease-associate condition (6th week to the 12th week). Simultaneously with increased Ang II-microglia colocalization and microglia morphologic phenotypic changes, sympathetic activity and pressure variability increased, autonomic control deteriorated, and blood pressure increased. These responses were not specific for autonomic nuclei but also occurred at a lower magnitude in the somatosensory cortex and hypoglossal nucleus, indicating the predominance of hypertension-induced effects on autonomic areas. No changes were observed in age-matched controls where Ang II density did not change. Brain Ang II density is the initial stimulus to drive coordinated changes in BBB permeability and microglial reactivity. Increased BBB dysfunction allows access of plasma Ang II and increases its local availability and the colocalization and activation of microglial cells. It is a potent stimulus to augments vasomotor sympathetic activity, autonomic imbalance, and pressure elevation during the establishment of hypertension.

Chronic intermittent hypoxia attenuates noradrenergic innervation of hypoglossal motor nucleus

The state-dependent noradrenergic activation of hypoglossal motoneurons plays an important role in the maintenance of upper airway patency and pathophysiology of obstructive sleep apnea (OSA). Chronic intermittent hypoxia (CIH), a major pathogenic factor of OSA, contributes to the risk for developing neurodegenerative disorders in OSA patients. Using anterograde tracer, channelrhodopsin-2, we mapped axonal projections from noradrenergic A7 and SubCoeruleus neurons to hypoglossal nucleus in DBH-cre mice and assessed the effect of CIH on these projections. We found that CIH significantly reduced the number of axonal projections from SubCoeruleus neurons to both dorsal (by 68%) and to ventral (by73%) subregions of the hypoglossal motor nucleus compared to sham-treated animals. The animals’ body weight was also negatively affected by CIH. Both effects, the decrease in axonal projections and body weight, were more pronounced in male than female mice, which was likely caused by less sensitivity of female mice to CIH as compared to males. The A7 neurons appeared to have limited projections to the hypoglossal nucleus. Our findings suggest that CIH-induced reduction of noradrenergic innervation of hypoglossal motoneurons may exacerbate progression of OSA, especially in men.

Motor neuron symptoms and pathology burden in de medulla oblongata of FTLD‐TDP brain donors

AbstractBackgroundmotor neuron symptoms (MNS) are the hallmark of amyotrophic lateral sclerosis (ALS), which is clinically and pathologically related to frontotemporal dementia (FTD). Up to 20% of FTD patients are diagnosed with ALS (1). However, MNS are observed in a larger proportion of FTD patients (FTD‐MNS), which do not fulfill clinical diagnostic criteria for concomitant ALS (FTD‐ALS) (2). The burden of TDP‐43 pathology in the hypoglossal nucleus (HN) is higher in FTD‐ALS compared to pure FTD brain donors (3), but little is known about the distribution of TDP‐43 pathology in the medulla oblongata in FTD‐MNS.MethodMNS occurring at any disease stage were assessed from the records of FTLD‐TDP brain donors from the Netherlands Brain Bank (n = 38). The total amount of neurons and the percentage of neurons showing TDP‐43 pathology were counted in the HN, nucleus ambiguus (NA) and inferior olivary nucleus (ION). ANOVA was performed between pure FTD, FTD‐ALS, and FTD‐MNS.Resulta pure FTD syndrome was recorded in 12/38 FTLD‐TDP brain donors. A concomitant FTD‐ALS diagnosis had been established during life for 4/38 brain donors, while 16/38 had FTD‐MNS. The most common MNS were dysphagia (63%), spasticity (29%) and wasting (24%). A higher TDP‐43 burden in the HN and NA was observed in FTD‐ALS compared to FTD (p < 0.05). TDP‐43 burden in the HN and in the ION was significantly higher in FTD‐MNS compared to FTD brain donors (p < 0.05).ConclusionMNS are common in FTD, even in the absence of ALS. MNS in FTD are linked to TDP‐43 burden in the HN, NA and ION.

Tongue and laryngeal exercises improve tongue strength and vocal function outcomes in a Pink1-/- rat model of early Parkinson disease

Parkinson disease (PD) causes voice and swallow dysfunction even in early stages of the disease. Treatment of this dysfunction is limited, and the neuropathology underlying this dysfunction is poorly defined. Targeted exercise provides the greatest benefit for offsetting voice and swallow dysfunction, and previous data suggest the hypoglossal nucleus and noradrenergic-locus coeruleus (LC) may be involved in its early pathology. To investigate relationships between targeted exercise and neuropathology of voice and swallow dysfunction, we implemented a combined exercise paradigm that included tongue force and vocalization exercises early in the Pink1-/- rat model. We tested the hypotheses that (1) tongue and vocal exercise improves tongue force and timing behaviors and vocalization outcomes, and (2) exercise increases optical density of serotonin (5-HT) in the hypoglossal nucleus, and tyrosine hydroxylase immunoreactive (Th-ir) cell counts in the LC. At two months of age Pink1-/- rats were randomized to exercise or non-exercise treatment. Age-matched wildtype (WT) control rats were assigned to non-exercise treatment. Tongue force and timing behaviors and ultrasonic vocalizations were measured at baseline (two months) and final (four months) timepoints. Optical density of 5-HT in the hypoglossal nucleus and TH-ir cell counts in the LC were obtained. Pink1-/- rats produced greater tongue forces, faster tongue contraction, and higher-intensity vocalization following exercise. There were no differences in LC TH-ir. The non-exercised Pink1-/- group had reduced density of 5-HT in the hypoglossal nucleus compared to the WT control group. The changes to tongue function and vocalization after targeted exercise suggests exercise intervention may be beneficial in early PD.

An interesting case of crossed syndrome: ipsilateral facial paralysis with contralateral glossoplegia

BackgroundStroke is rarely accompanied with peripheral facial paralysis and supranuclear palsy of the hypoglossal nerve. Both sides of the motor cortex innervate the hypoglossal nucleus; therefore, unilateral lesions of the upper motor neurons rarely result in contralateral lingual paresis. We report a rare case of crossed syndrome with associated hyperacute peripheral hemifacial paralysis and contralateral lingual paresis after a lower pontine tegmentum ischemic stroke.Case presentation: A 73-year-old man presented with symptoms of hyperacute peripheral hemifacial paralysis. Upon protrusion, the patient’s tongue deviated to the contralateral side, without fasciculation or atrophy. Brain imaging showed focal ischemic stroke in the pontine tegmentum. However, lingual hemiparesis and multimodal neuroimaging findings differed.ConclusionsWe suggest that cortico-hypoglossal fibers pass through the dorsal pontine. This case of crossed syndrome is a rare report of a lower pontine tegmentum ischemic stroke resembling an upper motor neuron lesion of the contralateral hypoglossal nerve.

The medullary serotonergic centres involved in cardiorespiratory control are disrupted by fetal growth restriction.

Fetal growth restriction (FGR) is associated with cardiovascular and respiratory complications after birth and beyond. Despite research showing a range of neurological changes following FGR, little is known about how FGR affects the brainstem cardiorespiratory control centres. The primary neurons that release serotonin reside in the brainstem cardiorespiratory control centres and may be affected by FGR. At two time points in the last trimester of sheep brain development, 110 and 127days of gestation (0.74 and 0.86 of gestation), we assessed histopathological alterations in the brainstem cardiorespiratory control centres of the pons and medulla in early-onset FGR versus control fetal sheep. The FGR cohort were hypoxaemic and asymmetrically growth restricted. Compared to the controls, the brainstem of FGR fetuses exhibited signs of neuropathology, including elevated cell death and reduced cell proliferation, grey and white matter deficits, and evidence of oxidative stress and neuroinflammation. FGR brainstem pathology was predominantly observed in the medullary raphé nuclei, hypoglossal nucleus, nucleus ambiguous, solitary tract and nucleus of the solitary tract. The FGR groups showed imbalanced brainstem serotonin and serotonin 1A receptor abundance in the medullary raphé nuclei, despite evidence of increased serotonin staining within vascular regions of placentomes collected from FGR fetuses. Our findings demonstrate both early and adaptive brainstem neuropathology in response to placental insufficiency. KEY POINTS: Early-onset fetal growth restriction (FGR) was induced in fetal sheep, resulting in chronic fetal hypoxaemia. Growth-restricted fetuses exhibit persistent neuropathology in brainstem nuclei, characterised by disrupted cell proliferation and reduced neuronal cell number within critical centres responsible for the regulation of cardiovascular and respiratory functions. Elevated brainstem inflammation and oxidative stress suggest potential mechanisms contributing to the observed neuropathological changes. Both placental and brainstem levels of 5-HT were found to be impaired following FGR.

Optical and pharmacological manipulation of hypoglossal motor nucleus identifies differential effects of taltirelin on sleeping tonic motor activity and responsiveness

Pharyngeal muscle activity and responsiveness are key pathophysiological traits in human obstructive sleep apnea (OSA) and strong contributors to improvements with pharmacotherapy. The thyrotropin-releasing hormone (TRH) analog taltirelin is of high pre-clinical interest given its neuronal-stimulant properties, minimal endocrine activity, tongue muscle activation following microperfusion into the hypoglossal motor nucleus (HMN) or systemic delivery, and high TRH receptor expression at the HMN compared to rest of the brain. Here we test the hypothesis that taltirelin increases HMN activity and/or responsivity to excitatory stimuli applied across sleep–wake states in-vivo. To target hypoglossal motoneurons with simultaneous pharmacological and optical stimuli we used customized “opto-dialysis” probes and chronically implanted them in mice expressing a light sensitive cation channel exclusively on cholinergic neurons (ChAT–ChR2, n = 12) and wild-type mice lacking the opsin (n = 10). Both optical stimuli applied across a range of powers (P < 0.001) and microperfusion of taltirelin into the HMN (P < 0.020) increased tongue motor activity in sleeping ChAT–ChR2 mice. Notably, taltirelin increased tonic background tongue motor activity (P < 0.001) but not responsivity to excitatory optical stimuli across sleep–wake states (P > 0.098). This differential effect on tonic motor activity versus responsivity informs human studies of the potential beneficial effects of taltirelin on pharyngeal motor control and OSA pharmacotherapy.

0038 Genioglossus muscle (GG) activity evoked by pharmacological stimulation of alpha1-adrenoceptors in pre-hypoglossal region (PHR)

Abstract Introduction The sleep-related withdrawal of noradrenergic excitation and increased cholinergic inhibition of hypoglossal motoneurons (HM), which control the tone of the GG, the largest protruder muscle of the tongue, play a critical role in obstructive sleep apnea pathophysiology. In an animal model of REM sleep, antagonism of alpha1 noradrenergic signaling by microinjections of prazosin into the hypoglossal nucleus (HN) strongly decreased hypoglossal nerve activity. However, a significant delay of this decrease prompted a hypothesis that prazosin must diffuse outside the HN to block alpha1-adrenoceptors that are located on interneurons, which mediate noradrenergic drive to HM. Here, we aimed to map the PHR by microinjecting alpha1 drugs for possible location of these interneurons. Methods Adult C57bl/6J mice (n=28) of both sexes were anesthetized with either ketamine/xylazine (120/20 mg/kg, i.p.) or 1.5-2.0% isoflurane inhaled through a nose mask. Electromyogram electrodes were implanted into GG and diaphragm to record their activity. We microinjected phenylephrine (alpha1-adrenoceptor agonist, 5-10 nl, 1 mM) in both ketamine/xylazine- and isoflurane-anesthetized mice, while prazosin (10 nl, 0.2 mM) was injected only in mice under isoflurane anesthesia. The injection sites were marked with Pontamine Skye Blue. After the completion of experiments, all animals were perfused, and brains removed for histological analysis. Results The activity of GG showed spontaneous phasic inspiratory modulation with minimal tonic component under both anesthesia conditions although its amplitude was markedly lager in animals anesthetized by isoflurane. Effective microinjections of phenylephrine elicited short-lasting (approximately 15 minutes) excitatory GG responses. When injected into the HN, phenylephrine strongly excited GG as compared to injections to the PHR in ketamine/xylazine-anesthetized mice. However, in isoflurane-anesthetized animals, microinjections of phenylephrine into the PHR induced greater activation of GG than injections onto the HN. Microinjections of prazosin in isoflurane-anesthetized mice produced long-lasting disfacilitation of GG activity. However, prazosin injections into the PHR elicited responses with the shortest latencies (0-120 s). Conclusion These results suggest that the putative interneurons that mediate noradrenergic drive to HM are located in the PHR. This finding is important for deciphering the neuronal network that controls the state-dependent activity of GG, which may provide new therapeutic targets for OSA treatment. Support (if any) NIHR01HL133847, NIAR01AG065233.

Centrally derived gasotransmitter modulation of hypoglossal motoneuron activity

Airway obstruction during inspiration is a hallmark trait of sleep apnea (SA). In mice, genetic elimination of the CO producing enzyme, heme oxygenase-2 (HO-2), leads to a SA phenotype predominately associated with recurrent airway obstruction. This phenotype is mitigated by either inhibition or genetic ablation of the H2S producing enzyme, cystathionine g-lysase (CSE). While these observations indicate that mutual interactions between HO-2/CO and CSE/H2S are important for regulating airway clearance, the extent of contribution from these interaction in the central nervous system to airway tone are unclear. Here, we determine how HO-2/CO and CSE/H2S impact inspiratory output from the hypoglossal nucleus (XIIn) in the isolated rhythmic brainstem slice preparation. We hypothesize that these enzymes and their respective gasotransmitter products locally interact in the inspiratory circuit to modulate the input-output (I/O) relationship between preBötC and XIIn. Electrophysiological studies conducted in brainstem slices from mice (P5-12) showed that HO-2 dysregulation, using either in wildtype slices exposed to Cr (III) Mesoporphyrin IX chloride or in slices from HO-2 null mice, increased transmission failure from preBötC to XIIn and altered the I/O relationship between the rhythm generating network and XIIn. HO-2 dysregulation also increased subnetwork activity in the preBötC that was associated with a decrease in amplitude regularity. While many transmission failures to the XIIn were associated with preBötC subnetwork activity, simultaneous recordings from the preBötC, premotor area, and the XIIn revealed that preBötC subnetwork activity was reliably transmitted to the premotor field but not to the XIIn. Dual extracellular and intracellular recordings from the preBötC and individual XIIn neurons under disinhibited conditions revealed that HO-2 dysregulation reduced inspiratory drive currents received by XIIn neurons, decreased the intrinsic excitability of XIIn neurons while also reducing the amount of preBötC subnetwork activity. Additionally, targeted inhibition of CSE/H2S activity using L-PAG or by genetic elimination of CSE in HO-2 null mice mitigated these effects of HO-2 dysregulation. Thus, the mutual interactions HO-2/CSE and CSE/H2S in the medullary brainstem appear to modulate XIIn output by: (1) causing a E/I imbalance that promotes preBötC subnetwork activity; (2) suppressing inspiratory drive received in XIIn; and (3) suppressing intrinsic excitability of XIIn neurons. These findings may be key to understanding the action by which central gasotransmitters actions contribute to upper airway muscle regulation. This work was supported by NIH: P01-HL-44454; R01NS107421. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Neuronal muscarinic acetylcholine receptor subtype modulation of inspiratory bursting at hypoglossal motoneurons in developing neonatal mice in vitro

Muscarinic acetylcholine receptor modulation contributes to changes in hypoglossal motoneuron excitability through pre- and post-synaptic effects, an important mechanism for regulation of airway tone during sleep. Previous data indicate a net excitatory effect of muscarinic modulation of inspiratory bursting in neonatal mouse brainstem slices, yet a net inhibitory effect on inspiratory bursting in adult rats. We tested the hypothesis that a developmental shift in muscarinic modulation impacts hypoglossal motoneurons, using neuroanatomical and electrophysiological methods. Immunofluorescence confirmed hypoglossal motoneurons express M1, M2, M3, and M5 muscarinic subtypes. We observed maturational decreases in M1 and M5 labeling intensity, M3 labeling intensity generally decreased with postnatal (P) age, although there was a transient increase in expression at P17. M2 labeling intensity did not change, although distribution of M2 labeling with postnatal maturation may change. Next, using the in-vitro rhythmic slice preparation from CD1 mice of either sex, local application of muscarine (100 μM) into the hypoglossal nucleus was tested in mice P0-14. The net effect of applying muscarine results in excitatory output after local application into the rhythmic slice because each data point is a positive percent change from control. The magnitude of this potentiation appears to lessen as the mice age toward P14. To evaluate the mechanisms through which the magnitude of muscarinic potentiation of inspiratory bursting changes with postnatal maturation, we next assessed the role of excitatory and inhibitory muscarinic receptor subtypes. Blocking M1 locally (pirenzepine, 100 μM) significantly decreased muscarine-mediated potentiation of inspiratory bursting (to 72±14% of control muscarine response, n=9, P0-5). Preliminary data indicate bath application of 4-DAMP (M3 antagonist) attenuated muscarinic potentiation of inspiratory bursting (range: to 7%-25% of control burst response, n=3, P0-5). Modulating M5 locally with a positive allosteric modulator VU 0238429 (1000 μM) had little effect on burst amplitude (119±4% of control burst response, n=3, P0-6). Blocking M2 locally (methoctramine, 2μM) showed no effect on inspiratory burst potentiation after applying muscarine (181±65% vs 187±69%, n=7, P0-5). Bath application of methoctramine did not have a significant effect on inspiratory burst potentiation by muscarine (179±65% vs control 182±90%, n=10) in P0-5 mice while preliminary analysis suggests an increasing effect of blocking M2 with postnatal maturation (147±56% vs control 134±30%, n=4, P9-14). These data support excitatory muscarinic receptor subtypes contributing to the excitatory response early in postnatal maturation. Based on our neuroanatomical data, we speculate the increasing inhibitory response to muscarinic modulation with postnatal maturation is due to a decreased contribution of excitatory muscarinic receptor subtypes. NIH R15HL148870 (Revill) and NIH/NHLBI R25 HL126140 (Moreno, Garcia, Parthasarathy) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Motor neuron involvement threatens survival in spinocerebellar ataxia type 1.

Motor neuron involvement threatens survival in spinocerebellar ataxia type 1.

The combination of atomoxetine and dronabinol for the treatment of obstructive sleep apnea: a dose-escalating, open-label trial.

The potential sedative effect of dronabinol and the high expression of cannabinoid receptors on the hypoglossal motor nuclei makes this agent a good candidate for obstructive sleep apnea (OSA) pharmacotherapy to be tested with atomoxetine, a noradrenergic reuptake inhibitor that reduced OSA severity in combination with oxybutynin. Here we tested the effect of atomoxetine 80 mg plus dronabinol (Ato-Dro) at 2 different doses (5 and 10 mg) vs. baseline and atomoxetine alone in a 2-center, open-label, dose-escalating trial. The primary outcome was the effect of Ato-Dro vs. baseline on OSA severity (apnea-hypopnea index, hypopneas associated with 4% oxygen desaturation). Safety of the combination and self-reported outcomes were also assessed. Fifteen patients with OSA received progressively increasing Ato-Dro doses (dose escalation was performed every week, starting from Ato-Dro 40-2.5 mg, then 80-5 mg and finally 80-10 mg). A clinical, in-lab polysomnography was performed at baseline, on Ato-Dro 80-5 and Ato-Dro 80-10 mg. Ato-Dro 80-10 mg did not significantly reduce apnea-hypopnea index, hypopneas associated with 4% oxygen desaturation, and hypoxic burden and yielded limited clinical benefit vs. baseline and atomoxetine alone. However, Ato-Dro 80-5 mg did improve OSA severity (Δapnea-hypopnea index = 8.3[0.3, 16.3] events/h; mean [confidence interval]; Δhypoxic burden = 37.7[12.5, 62.7] %min/h) and multiple self-reported outcomes vs. baseline and/or atomoxetine alone. Ato-Dro administration was characterized by several potentially harmful side effects and treatment discontinuation in 1/3 of cases. Ato-Dro 80-5 mg might be useful to reduce OSA severity and lead to self-reported improvement in those who could tolerate the combination. However, given the numerous side effects and the exploratory nature of this open-label study, our results warrant further validation in larger trials. Registry: ClinicalTrials.gov; Title: Study for Efficacy and Dose Escalation of AD313 + Atomoxetine (SEED) (SEED); URL: https://clinicaltrials.gov/ct2/show/NCT05101122; Identifier: NCT05101122. Messineo L, Norman D, Ojile J. The combination of atomoxetine and dronabinol for the treatment of obstructive sleep apnea: a dose-escalating, open-label trial. J Clin Sleep Med. 2023;19(7):1183-1190.

Gasotransmitter modulation of hypoglossal motoneuron activity.

Obstructive sleep apnea (OSA) is characterized by sporadic collapse of the upper airway leading to periodic disruptions in breathing. Upper airway patency is governed by genioglossal nerve activity that originates from the hypoglossal motor nucleus. Mice with targeted deletion of the gene Hmox2, encoding the carbon monoxide (CO) producing enzyme, heme oxygenase-2 (HO-2), exhibit OSA, yet the contribution of central HO-2 dysregulation to the phenomenon is unknown. Using the rhythmic brainstem slice preparation that contains the preBötzinger complex (preBötC) and the hypoglossal nucleus, we tested the hypothesis that central HO-2 dysregulation weakens hypoglossal motoneuron output. Disrupting HO-2 activity increased the occurrence of subnetwork activity from the preBötC, which was associated with an increased irregularity of rhythmogenesis. These phenomena were also associated with the intermittent inability of the preBötC rhythm to drive output from the hypoglossal nucleus (i.e. transmission failures), and a reduction in the input-output relationship between the preBötC and the motor nucleus. HO-2 dysregulation reduced excitatory synaptic currents and intrinsic excitability in inspiratory hypoglossal neurons. Inhibiting activity of the CO-regulated H2S producing enzyme, cystathionine-γ-lyase (CSE), reduced transmission failures in HO-2 null brainstem slices, which also normalized excitatory synaptic currents and intrinsic excitability of hypoglossal motoneurons. These findings demonstrate a hitherto uncharacterized modulation of hypoglossal activity through mutual interaction of HO-2/CO and CSE/H2S, and support the potential importance of centrally derived gasotransmitter activity in regulating upper airway control.

Serotonergic current responses of neurons in rat oculomotor neural integrators.

The prepositus hypoglossi nucleus (PHN) and the interstitial nucleus of Cajal (INC) are involved in controlling horizontal and vertical gaze, respectively. Previous studies have shown that PHN neurons exhibit depolarized or hyperpolarized responses to serotonin (5-hydroxytryptamine, 5-HT). However, serotonergic modulation of INC neurons has not been examined. Furthermore, the relationship between 5-HT-induced responses and neuron types based on neurotransmitter phenotypes has not been clarified. In this study, we investigated 5-HT-induced current responses in PHN and INC neurons and the distributions of distinct current responses in different neuron types, using whole cell recordings of wild-type and transgenic rat brain stem slices. Local application of 5-HT to the cell soma confirmed that slow inward (SI) and slow outward (SO) currents were mediated by 5-HT2 and 5-HT1A receptors, respectively. Furthermore, fast inward (FI) currents that were mediated by 5-HT3 receptors were observed. These three current responses were observed in both PHN and INC neurons. Analyses of the distributions of the three current responses revealed that fluorescently identified glutamatergic and inhibitory neurons in the PHN showed high proportions of SI and SO currents, respectively, whereas glutamatergic and inhibitory neurons in the INC showed mainly SO currents. When PHN and INC neurons were characterized on the basis of firing patterns, the proportions of the currents depended on the firing patterns. The different distributions of 5-HT-induced currents suggest distinct serotonergic modulation modes specific to horizontal and vertical gaze control.NEW & NOTEWORTHY Serotonergic modulation of vertical gaze control (interstitial nucleus of Cajal, INC) is less understood than that of horizontal gaze control (prepositus hypoglossal nucleus, PHN). Here, we report 5-HT-induced fast inward currents in addition to the previously reported slow inward and outward currents. The distributions of these currents in INC neurons based on neurotransmitter phenotypes differ from those in PHN neurons. These results suggest distinct serotonergic modulation modes in horizontal and vertical gaze control centers.

An Aberrant branch of Hypoglossal Nerve-A Rare Anatomical Variation

Introduction: Hypoglossal nerve is formed from the hypoglossal nucleus situated in the medulla oblongata. It leaves the medulla through the anterolateral sulcus. It carries general somatic efferent fibres that means purely motor in nature. Landmark of the nerve is of paramount importance to avoid the damage during neck surgeries. Variations in the extracranial course may lead to the iatrogenic injuries to the important structures related to it. In our case, we found an aberrant branch from the hypoglossal nerve. Conclusion: Very few cases are reported of an aberrant hypoglossal nerve. Therefore, finding such rare cases is helpful for the surgeon before the operative procedures in the region to prevent serious injuries leading to neurological deficits