Hypoglossal Neurons Research Articles

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.

Opioids and obstructive sleep apnea.

Freire C, Sennes LU, Polotsky VY. Opioids and obstructive sleep apnea. J Clin Sleep Med. 2022;18(2):647-652.

Central functional reorganization and recovery following facial-hypoglossal neurorrhaphy for facial paralysis

ObjectiveFunctional deficits induced by nerve injuries can be restored by achieving effective reinnervation of the denervated targets and functional reorganization of the central nervous system after nerve reconstruction. In this study, we investigated the effect and extent of cortical functional reorganization related to the ability of transferred hypoglossal neurons to restore facial function in facial paralysis patients after a surgical bridge of neurorrhaphy ectopically between the ipsilateral hypoglossal nerve and injured facial nerve. MethodsWe treated 23 patients (35.4 ± 10.3 years, 10 males) and followed them up for 2.9 ± 0.61 years. We used motor-task-related functional magnetic resonance imaging to map activation change at multiple time points before and after neurorrhaphy; 20 normal subjects were included as control. ResultsAll patients regained facial function to some extent after neurorrhaphy. Enhanced activation in motor-related cortices gradually returned to normal levels and was positively correlated with regained facial function. The related cortical functional areas included the left middle temporal gyrus, left inferior frontal gyrus, insula, bilateral motor cortex and the supplementary motor area extending to the paracingulate involved in intensive eye closing, as well as the left superior temporal gyrus, right putamen and the bilateral motor cortex involved in lip pursing. Intriguingly, significant correlations were found between the pre-surgery activation while intensive eye closing in bilateral motor cortex and recovery of facial nerve function induced by the neurorrhaphy treatment. ConclusionThis is the first study mapping activation change in motor cortices at multiple time points before and after repair of the facial nerve. The cortex functional reorganization found may suggest potential treatment targets in the central nervous system for adjuvant therapies such as repetitive transcranial magnetic stimulation to further improve functional recovery.

Tongue and hypoglossal morphology after intralingual cholera toxin B-saporin injection.

We recently developed an inducible model of dysphagia using intralingual injection of cholera toxin B conjugated to saporin (CTB-SAP) to cause death of hypoglossal neurons. In this study we aimed to evaluate tongue morphology and ultrastructural changes in hypoglossal neurons and nerve fibers in this model. Tissues were collected from 20 rats (10 control and 10 CTB-SAP animals) on day 9 post-injection. Tongues were weighed, measured, and analyzed for microscopic changes using laminin immunohistochemistry. Hypoglossal neurons and axons were examined using transmission electron microscopy. The cross-sectional area of myofibers in the posterior genioglossus was decreased in CTB-SAP-injected rats. Degenerative changes were observed in both the cell bodies and distal axons of hypoglossal neurons. Preliminary results indicate this model may have translational application to a variety of neurodegenerative diseases resulting in tongue dysfunction and associated dysphagia.

Upregulation of Nucleotide-Binding Oligomerization Domain-, LRR- and Pyrin Domain-Containing Protein 3 in Motoneurons Following Peripheral Nerve Injury in Mice

Neuronal injuries are accompanied by release and accumulation of damage-associated molecules, which in turn may contribute to activation of the immune system. Since a wide range of danger signals (including endogenous ones) are detected by the nucleotide-binding oligomerization domain-, LRR- and pyrin domain-containing protein 3 (NLRP3) pattern recognition receptor, we hypothesized that NLRP3 may become activated in response to motor neuron injury. Here we show that peripheral injury of the oculomotor and the hypoglossal nerves results in upregulation of NLRP3 in corresponding motor nuclei in the brainstem of mice. Although basal expression of NLRP3 was observed in microglia, astroglia and neurons as well, its upregulation and co-localization with apoptosis-associated speck-like protein containing a caspase activation and recruitment domain, suggesting inflammasome activation, was only detected in neurons. Consequently, increased production of active pro-inflammatory cytokines interleukin-1β and interleukin-18 were detected after hypoglossal nerve axotomy. Injury-sensitive hypoglossal neurons responded with a more pronounced NLRP3 upregulation than injury-resistant motor neurons of the oculomotor nucleus. We further demonstrated that the mitochondrial protector diazoxide was able to reduce NLRP3 upregulation in a post-operative treatment paradigm. Our results indicate that NLRP3 is activated in motoneurons following acute nerve injury. Blockade of NLRP3 activation might contribute to the previously observed anti-inflammatory and neuroprotective effects of diazoxide.

Nitric oxide controls excitatory/inhibitory balance in the hypoglossal nucleus during early postnatal development

Synaptic remodeling during early postnatal development lies behind neuronal networks refinement and nervous system maturation. In particular, the respiratory system is immature at birth and is subjected to significant postnatal development. In this context, the excitatory/inhibitory balance dramatically changes in the respiratory-related hypoglossal nucleus (HN) during the 3 perinatal weeks. Since, development abnormalities of hypoglossal motor neurons (HMNs) are associated with sudden infant death syndrome and obstructive sleep apnea, deciphering molecular partners behind synaptic remodeling in the HN is of basic and clinical relevance. Interestingly, a transient expression of the neuronal isoform of nitric oxide (NO) synthase (NOS) occurs in HMNs at neonatal stage that disappears before postnatal day 21 (P21). NO, in turn, is a determining factor for synaptic refinement in several physiopathological conditions. Here, intracerebroventricular chronic administration (P7–P21) of the broad spectrum NOS inhibitor l-NAME (N(ω)-nitro-l-arginine methyl ester) differentially affected excitatory and inhibitory rearrangement during this neonatal interval in the rat. Whilst l-NAME led to a reduction in the number of excitatory structures, inhibitory synaptic puncta were increased at P21 in comparison to administration of the inactive stereoisomer d-NAME. Finally, l-NAME decreased levels of the phosphorylated form of myosin light chain in the nucleus, which is known to regulate the actomyosin contraction apparatus. These outcomes indicate that physiologically synthesized NO modulates excitatory/inhibitory balance during early postnatal development by acting as an anti-synaptotrophic and/or synaptotoxic factor for inhibitory synapses, and as a synaptotrophin for excitatory ones. The mechanism of action could rely on the modulation of the actomyosin contraction apparatus.

Optimizing the Translational Value of Mouse Models of ALS for Dysphagia Therapeutic Discovery

The goal of this study was to compare dysphagia phenotypes in low and high copy number (LCN and HCN) transgenic superoxide dismutase 1 (SOD1) mouse models of ALS to accelerate the discovery of novel and effective treatments for dysphagia and early amyotrophic lateral sclerosis (ALS) diagnosis. Clinicopathological features of dysphagia were characterized in individual transgenic mice and age-matched controls utilizing videofluoroscopy in conjunction with postmortem assays of the tongue and hypoglossal nucleus. Quantitative PCR accurately differentiated HCN-SOD1 and LCN-SOD1 mice and nontransgenic controls. All HCN-SOD1 mice developed stereotypical paralysis in both hindlimbs. In contrast, LCN-SOD1 mice displayed wide variability in fore- and hindlimb involvement. Lick rate, swallow rate, inter-swallow interval, and pharyngeal transit time were significantly altered in both HCN-SOD1 and LCN-SOD1 mice compared to controls. Tongue weight, tongue dorsum surface area, total tongue length, and caudal tongue length were significantly reduced only in the LCN-SOD1 mice compared to age-matched controls. LCN-SOD1 mice with lower body weights had smaller/lighter weight tongues, and those with forelimb paralysis and slower lick rates died at a younger age. LCN-SOD1 mice had a 32% loss of hypoglossal neurons, which differed significantly when compared to age-matched control mice. These novel findings for LCN-SOD1 mice are congruent with reported dysphagia and associated tongue atrophy and hypoglossal nucleus pathology in human ALS patients, thus highlighting the translational potential of this mouse model in ALS research.

Morphometric study of the neurons in human hypoglossal nerve nucleus during early gestation

Hypoglossal nerve, XII cranial nerve is responsible for the motor innervation of the tongue muscles, which assists in various motor activities such as chewing, swallowing, vocalization. Thus, weakness of this nerve will lead to weakness and deviation of the tongue to one side. Clinically besides these functions it is also responsible for the most important function such as modulation of respiration and drinking behavior. Thus, a detailed study about the cell dynamics, which involves the development of neurons in the hypoglossal nerve nucleus becomes essential. 12 foetuses [Gestational age 10 – 24 weeks] were included in the study. They were divided into 4 groups based on their gestational age and CRL measurements. Hypoglossal nucleus extends throughout the length of medulla oblongata in the para-median plane. Tissues were collected from hind brain section and section of medulla. The tissues will be processed by routine histological procedure were stained with hematoxylin & eosin and also with Holmer’s Silver nitrate to study the histological details. Morphometric study covered the cell dimensions and volumes of hypoglossal neurons and its nucleus. From these data, coefficients were drawn to identify the proportion of growth between cell and nuclear volume. Morphometric analysis of hypoglossal nerve neurons in human from 10th to 24th gestational week concludes that the primitive migratory cells seen in the initial period and later it will become round neuroblast. In the initial 16 weeks nucleus occupied the entire volume of the cell.Keywords: Hypoglossal nerve nucleus, Deglutition, Mastication, Morphometry, Histogenesis

The mesencephalic-hypoglossal nuclei loop as a possible central pattern generator for rhythmical whisking in rats.

It has been previously demonstrated that the Me5 nucleus is involved in the genesis of reflex activities at whisker pad level. Specific Me5 neurons, which provide sensory innervation of the macrovibrissae, are monosynaptically connected with small hypoglossal neurons innervating the extrinsic muscles that control macrovibrissal movements. Artificial whisking, induced by the electrical stimulation of the peripheral stump of the facial nerve and the electrical stimulation of the XII nucleus or the infraorbital nerve, induced evoked responses in the whisker pad extrinsic motor units, along with a significant increase in the electromyographic activity of the extrinsic pad muscles (Mameli et al. in Acta Oto-Laryngol 126:1334-1338, 2006; in Pfűgers Arch Eur J Physiol 456:1189-1198, 2008; in Brain Res 1283:34-40, 2009; in Exp Brain Res 234:753-761, 2016). In anaesthetized rats, we evaluated the possible involvement of this Me5-XII loop in the genesis of rhythmical whisking. The anatomical findings showed that in addition to the ipsilateral, even the contralateral Me5 nucleus could be retrogradely labeled by the Dil tracer injected into the whisker pad of one side, they, furthermore, showed labeled axons extending across the midline between the two nuclei. The electrophysiological findings agreed with the neuroanatomical results, since the mechanical or artificially induced deflection of the whiskers of one side, evoked in the Me5 contralateral nucleus different patterns of responses. The hypothesis that the Me5-XII loops, along with their cross-linked relationship, could act as a "central generator" responsible for the stereotyped symmetrical pattern of macrovibrissal movements such as rhythmical whisking has been discussed.

Altered neurobiological function of brainstem hypoglossal neurons in DiGeorge/22q11.2 Deletion Syndrome

DiGeorge/22q11.2 Deletion Syndrome (22q11DS) is a common genetic microdeletion syndrome that underlies several neurodevelopmental disorders including autism, attention deficit/hyperactivity disorder, and schizophrenia. In addition to cognitive impairments, those with 22q11DS have disrupted feeding and swallowing from birth onward. This perinatal dysphagia significantly compromises nutritional status, impairs appropriate weight gain, and can lead to life threatening aspiration-based infections. Appropriately timed excitation and inhibition of brainstem hypoglossal motor neurons, which innervate tongue muscles, is essential for proper feeding and swallowing. In this study we have examined changes in hypoglossal motor neuron function in the LgDel mouse model of 22q11DS. Hypoglossal motor neurons from LgDel mouse pups have action potentials with afterhyperpolarizations, mediated by a large conductance charybdotoxin-sensitive Ca-activated K current, that are significantly shorter in duration and greater in magnitude than those in wild-type pups. In addition, the amplitude, but not frequency, of glutamatergic excitatory glutamatergic postsynaptic currents (EPSCs) is diminished, and GABAergic, but not glycinergic, neurotransmission to hypoglossal motor neurons was reduced in LgDel animals. These observations provide a foundation for understanding the neurological changes in hypoglossal motor neuron function and their contribution to swallowing abnormalities that occur in DiGeorge/22q11.2 Deletion Syndrome.

0143 CARBACHOL INHIBITS GLUTAMATERGIC INPUT TO MOUSE HYPOGLOSSAL MOTOR NEURONS - A MECHANISM FOR REM SLEEP SUPPRESSION OF GENIOGLOSSUS ACTIVITY

In REM sleep, the genioglossus (GG) muscle undergoes a dramatic suppression of activity. A current hypothesis is that the loss of GG activity during REM sleep is mediated by a combination of 1) monoaminergic disfacilitation and 2) a cholinergic inhibition of hypoglossal motor neurons. Strikingly, blockade of cholinergic receptors in the hypoglossal motor nucleus fully restores REM sleep tonic and inspiratory-modulated components of GG activity (Grace et al., 2013), suggesting that the cholinergic signal is largely responsible for the REM sleep suppression of GG activity. Respiratory rhythm generator neurons of the pre-Bötzinger complex drive the activation of hypoglossal motor neurons through glutamatergic premotor neurons in the parahypoglossal region (PH). In the current study, we investigate how cholinergic signaling affects the PH glutamatergic input to hypoglossal motor neurons. We stereotaxically injected the PH region of vGluT2-cre mice with a cre-dependent AAV-ChR2-mCherry to expressed channelrhodopsin2 (ChR2) in PH glutamatergic premotor neurons. We then performed whole-cell recordings in hypoglossal neurons while photostimulating PH glutamatergic inputs expressing ChR2. Photostimulation of the glutamatergic PH input evoked AMPA-mediated EPSCs in hypoglossal motor neurons. These photoevoked EPSCs were maintained in TTX, indicating direct connectivity between stimulated terminals and recorded hypoglossal motoneurons. Bath application of carbachol strongly inhibited the PH glutamatergic excitation of hypoglossal neurons via muscarinic receptors. The effect of carbachol on photoevoked EPSCs was maintained when 1) we blocked postsynaptic G-mediated effects by adding GDP-β-S in the recording pipette and 2) when we blocked action potential mediated transmission by adding TTX in the extracellular bath solution. These results indicate that carbachol inhibits PH input to hypoglossal motoneurons through a presynaptic mechanism. Our results provide a possible mechanism for cholinergic inhibition of the hypoglossal motor neurons in REM sleep. We propose that the cholinergic presynaptic suppression of the excitatory drive from the PH premotor neurons can be responsible for the reduction in activity of hypoglossal motor neurons in REM sleep. P01HL095491.

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.

Stereological assessment of the total number of hypoglossal neurons after repeated crush injuries to the hypoglossal nerve in adult rats

Objective: Retrograde neuronal cell death does not occur in mature motoneurons following the axonal injury of peripheral nerves. However, a previous study suggested that retrograde neuronal cell death does occur in adult rats after the creation of double lesions on the hypoglossal (XII) nerve based on a substantial decrease in the number of XII neurons. Using stereological methods, we examined neuronal apoptosis in XII neurons and the total number of XII neurons following repeated crush injuries to the XII nerve.Methods: The right XII nerve of adult rats was crushed three times at one-week intervals with a brain aneurysm clip. At 4 weeks after the final crush, the total numbers of XII neurons on the injured right and uninjured left sides were estimated stereologically.Results: After repeated crush injuries, no apoptosis was evident in XII neurons as indicated by immunostaining for cleaved caspase-3. Moreover, immunohistochemistry for the vesicular acetylcholine transporter revealed axonal elongation in the tongue 4 weeks after repeated crush injuries. At 4 weeks, the total numbers of XII neurons were 7800 ± 290 on the injured right side and 8000 ± 230 on the uninjured left side, and no significant difference was evident between the injured and uninjured sides.Conclusion: Neuronal cell death does not occur in XII neurons and the total number of XII neurons does not decrease after repeated crush injuries of the XII nerve in adult rats.

An optogenetic mouse model of rett syndrome targeting on catecholaminergic neurons.

Rett syndrome (RTT) is a neurodevelopmental disorder affecting multiple functions, including the norepinephrine (NE) system. In the CNS, NE is produced mostly by neurons in the locus coeruleus (LC), where defects in intrinsic neuronal properties, NE biosynthetic enzymes, neuronal CO2 sensitivity, and synaptic currents have been reported in mouse models of RTT. LC neurons in methyl-CpG-binding protein 2 gene (Mecp2) null mice show a high rate of spontaneous firing, although whether such hyperexcitability might increase or decrease the NE release from synapses is unknown. To activate the NEergic axonal terminals selectively, we generated an optogenetic mouse model of RTT in which NEergic neuronal excitability can be manipulated with light. Using commercially available mouse breeders, we produced a new strain of double-transgenic mice with Mecp2 knockout and channelrhodopsin (ChR) knockin in catecholaminergic neurons. Several RTT-like phenotypes were found in the tyrosine hydroxylase (TH)-ChR-Mecp2(-/Y) mice, including hypoactivity, low body weight, hindlimb clasping, and breathing disorders. In brain slices, optostimulation produced depolarization and an increase in the firing rate of LC neurons from TH-ChR control mice. In TH-ChR control mice, optostimulation of presynaptic NEergic neurons augmented the firing rate of hypoglossal neurons (HNs), which was blocked by the α-adrenoceptor antagonist phentolamine. Such optostimulation of NEergic terminals had almost no effect on HNs from two or three TH-ChR-Mecp2(-/Y) mice, indicating that excessive excitation of presynaptic neurons does not benefit NEergic modulation in mice with Mecp2 disruption. These results also demonstrate the feasibility of generating double-transgenic mice for studies of RTT with commercially available mice, which are inexpensive, labor/time efficient, and promising for cell-specific stimulation. © 2016 Wiley Periodicals, Inc.

Evidence for a trigeminal mesencephalic-hypoglossal nuclei loop involved in controlling vibrissae movements in the rat.

Previous studies performed in rats showed that the whisker-pad motor innervation involves not only the facial nerve, but also some hypoglossal neurons whose axons travel within the trigeminal infraorbital nerve (ION) and target the extrinsic muscles surrounding the whisker-pad macrovibrissae. Furthermore, the electrical stimulation of the ION induced an increase in the EMG activity of these muscles, while the hypoglossal nucleus stimulation elicited evoked potentials and single motor unit responses. However, the existence of a neural network able to involve the XIIth nucleus in macrovibrissae whisking control was totally unknown until now. Since other recent experiments demonstrated that: (1) the mesencephalic trigeminal nucleus (Me5) neurons respond to both spontaneous and artificial movements of macrovibrissae, and (2) the Me5 peripheral terminals provide a monosynaptic sensory innervation to the macrovibrissae, the present study was aimed at analyzing a possible role of the Me5 nucleus as a relay station in the sensory-motor loop that involves the XIIth nucleus neurons in rhythmic whisking control. Two tracers were used in the same animal: Fluoro Gold, which was injected into the whisker pad to retrogradely label the hypoglossal whisker-pad projection neurons, and Dil, which was instead injected into the Me5 to label its projections to these hypoglossal neurons. Results demonstrated that terminals of the Me5 neurons monosynaptically target the hypoglossal whisker-pad projection neurons. The functional role of this sensory-motor connection is discussed, with particular regard to a hypothesized proprioceptive reflex in whisker-pad extrinsic muscles that can be elicited by the activation of the Me5 macrovibrissae receptors.

Contribution of the Runx1 transcription factor to axonal pathfinding and muscle innervation by hypoglossal motoneurons.

The runt-related transcription factor Runx1 contributes to cell type specification and axonal targeting projections of the nociceptive dorsal root ganglion neurons. Runx1 is also expressed in the central nervous system, but little is known of its functions in brain development. At mouse embryonic day (E) 17.5, Runx1-positive neurons were detected in the ventrocaudal subdivision of the hypoglossal nucleus. Runx1-positive neurons lacked calcitonin gene-related peptide (CGRP) expression, whereas Runx1-negative neurons expressed CGRP. Expression of CGRP was not changed in Runx1-deficient mice at E17.5, suggesting that Runx1 alone does not suppress CGRP expression. Hypoglossal axon projections to the intrinsic vertical (V) and transverse (T) tongue muscles were sparser in Runx1-deficient mice at E17.5 compared to age-matched wild-type littermates. Concomitantly, vesicular acetylcholine transporter-positive axon terminals and acetylcholine receptor clusters were less dense in the V and T tongue muscles of Runx1-deficient mice. These abnormalities in axonal projection were not caused by a reduction in the total number hypoglossal neurons, failed synaptogenesis, or tongue muscles deficits. Our results implicate Runx1 in the targeting of ventrocaudal hypoglossal axons to specific tongue muscles. However, Runx1 deficiency did not alter neuronal survival or the expression of multiple motoneuron markers as in other neuronal populations. Thus, Runx1 appears to have distinct developmental functions in different brain regions.

Spinocerebellar ataxia type 36 exists in diverse populations and can be caused by a short hexanucleotide GGCCTG repeat expansion

ObjectiveSpinocerebellar ataxia 36 (SCA36) is an autosomal-dominant neurodegenerative disorder caused by a large (>650) hexanucleotide GGCCTG repeat expansion in the first intron of the NOP56 gene. The aim of this...

Quantitative analysis of survival of hypoglossal neurons in neonatally nerve-injured rats: Correlation with milk intake

IntroductionTongue movement innervated by the hypoglossal (XII) nerve is essential for the survival of neonatal rats. The pups with bilateral XII nerve resection failed to suckle milk and did not survive, and the pups with unilateral XII nerve resection showed disturbed suckling capability and lower survival rates. The present study was performed to investigate the relation between neuronal population and milk intake of developing rats that had received various degrees of crush injuries to the unilateral XII nerve during the neonatal period. MethodsThe right XII nerve of postnatal day 1 (P1) pups was crushed and milk intake was estimated at 3 days and 6 days after the nerve injury. As nerve injury at the neonatal stage results in death of axotomized neurons, varying degrees of crushing was estimated by the number of survived motor neurons. ResultsIn nerve-crushed rats, the populations of XII motor neurons and amounts of milk intake were reduced in a varied manner. Statistically significant positive correlations were observed between increasing XII neuron survival and increasing milk intake at 3 (r=0.62) and 6 (r=0.71) days after the nerve injury. ConclusionThe results indicate that there is a strong relationship between the number of XII motor neurons and the amount of milk intake in neonatally XII nerve-injured rats.

Lung inflammation induces IL-1β expression in hypoglossal neurons in rat brainstem

Perinatal inflammation is associated with respiratory morbidity. Immune modulation of brainstem respiratory control centers may provide a link for this pathobiology. We exposed 11-day old rats to intratracheal lipopolysaccharide (LPS, 0.5μg/g) to test the hypothesis that intrapulmonary inflammation increases expression of the proinflammatory cytokine IL-1β within respiratory-related brainstem regions. Intratracheal LPS resulted in a 32% increase in IL-1β protein expression in the medulla oblongata. In situ hybridization showed increased intensity of IL-1β mRNA but no change in neuronal numbers. Co-localization experiments showed that hypoglossal neurons express IL-1β mRNA and immunostaining showed a 43% increase in IL-1β protein-expressing cells after LPS exposure. LPS treatment also significantly increased microglial cell numbers though they did not express IL-1β mRNA. LPS-induced brainstem expression of neuronal IL-1β mRNA and protein may have implications for our understanding of the vulnerability of neonatal respiratory control in response to a peripheral proinflammatory stimulus.

Changes in reactive oxygen species (ROS) in central respiratory centers with sustained hypoxia

ROS are important for plasticity in chemoreceptors and respiratory motor neurons with acute and chronic intermittent hypoxia. Recent studies show ROS change with sustained hypoxia so we hypothesized ROS contribute to plasticity with chronic sustained hypoxia (CSH) in ventilatory acclimatization to hypoxia. To test this, we measured (1) ventilation (Vi) in conscious, unrestrained mice breathing 21% or 10% O2 using barometric pressure plethysmography, and (2) ROS levels in medullary respiratory centers by imaging dihydroethidium (DHE) fluorescence in fixed tissue sections obtained after 2 hr of DHE exposure in 4 groups of mice (n=3–5 each): normoxic control (CON) and CSH (PiO2 = 70 Torr, 7 days), treated with a superoxide scavenger (MnTMPyP 5 mg/kg ip) or saline for 10–13 days prior to study. DHE fluorescence was observed in neurons but not glia. CSH decreased ROS to 60–71% of CON in nucleus tractus solitarii and hypoglossal neurons (NTS and XII). MnTMPyP decreased ROS in NTS and XII by 37% in CON but only 6–12% in CSH. In CON, Vi increased with MnTMPyP. Vi increased with CSH as expected but was not changed by MnTMPyP. The results are consistent with ventilatory inhibition by ROS that are scavenged by MnTMPyP and decreased in CSH. Supported by NIH RO1 HL‐081823 and 1P01 HL 098053.