An airway-to-brain sensory pathway mediates influenza-induced sickness.

Pathogen infection causes a stereotyped state of sickness that involves neuronally orchestrated behavioural and physiological changes1,2. On infection, immune cells release a 'storm' of cytokines and other mediators, many of which are detected by neurons3,4; yet, the responding neural circuits and neuro-immune interaction mechanisms that evoke sickness behaviour during naturalistic infections remain unclear. Over-the-counter medications such as aspirin and ibuprofen are widely used to alleviate sickness and act by blocking prostaglandin E2 (PGE2) synthesis5. A leading model is that PGE2 crosses the blood-brain barrier and directly engages hypothalamic neurons2. Here, using genetic tools that broadly cover a peripheral sensory neuron atlas, we instead identified a small population of PGE2-detecting glossopharyngeal sensory neurons (petrosal GABRA1 neurons) that are essential for influenza-induced sickness behaviour in mice. Ablating petrosal GABRA1 neurons or targeted knockout of PGE2 receptor 3 (EP3) in these neurons eliminates influenza-induced decreases in food intake, water intake and mobility during early-stage infection and improves survival. Genetically guided anatomical mapping revealed that petrosal GABRA1 neurons project to mucosal regions of the nasopharynx with increased expression of cyclooxygenase-2 after infection, and also display a specific axonal targeting pattern in the brainstem. Together, these findings reveal a primary airway-to-brain sensory pathway that detects locally produced prostaglandins and mediates systemic sickness responses to respiratory virus infection.

Perineural Invasion and Perineural Tumor Spread in Head and Neck Cancer.

Perineural invasion (PNI), the neoplastic invasion of nerves, is a common pathologic finding in head and neck cancer that is associated with poor clinical outcomes. PNI is a histologic finding of tumor cell infiltration and is distinct from perineural tumor spread (PNTS), which is macroscopic tumor involvement along a nerve extending from the primary tumor that is by definition more advanced, being radiologically or clinically apparent. Despite widespread acknowledgment of the prognostic significance of PNI and PNTS, the mechanisms underlying its pathogenesis remain largely unknown, and specific therapies targeting nerve invasion are lacking. The use of radiation therapy for PNI and PNTS can improve local control and reduce devastating failures at the skull base. However, the optimal volumes to be delineated with respect to targeting cranial nerve pathways are not well defined, and radiation can carry risks of major toxicity secondary to the location of adjacent critical structures. Here we examine the pathogenesis of these phenomena, analyze the role of radiation in PNI and PNTS, and propose guidelines for radiation treatment design based on the best available evidence and the authors' collective experience to advance understanding and therapy of this ominous cancer phenotype.

Comparison of sympathetic nerve activity normalization procedures in conscious rabbits.

One of the main constraints associated with recording sympathetic nerve activity (SNA) in both humans and experimental animals is that microvolt values reflect characteristics of the recording conditions and limit comparisons between different experimental groups. The nasopharyngeal response has been validated for normalizing renal SNA (RSNA) in conscious rabbits, and in humans muscle SNA is normalized to the maximum burst in the resting period. We compared these two methods of normalization to determine whether either could detect elevated RSNA in hypertensive rabbits compared with normotensive controls. We also tested whether either method eliminated differences based only on different recording conditions by separating RSNA of control (sham) rabbits into two groups with low or high microvolts. Hypertension was induced by 5 wk of renal clipping (2K1C), 3 wk of high-fat diet (HFD), or 3 mo infusion of a low dose of angiotensin (ANG II). Normalization to the nasopharyngeal response revealed RSNA that was 88, 51, and 34% greater in 2K1C, HFD, and ANG II rabbits, respectively, than shams (P < 0.05), but normalization to the maximum burst showed no differences. The RSNA baroreflex followed a similar pattern whether RSNA was expressed in microvolts or normalized. Both methods abolished the difference between low and high microvolt RSNA. These results suggest that maximum burst amplitude is a useful technique for minimizing differences between recording conditions but is unable to detect real differences between groups. We conclude that the nasopharyngeal reflex is the superior method for normalizing sympathetic recordings in conscious rabbits.

New approaches to quantifying sympathetic nerve activity.

The importance of the sympathetic nervous system in the pathophysiology of human and experimental models of hypertension is well established. Underpinning recent advances has been direct recording from sympathetic nerves via implanted electrodes in animals or microneurography in human subjects. However, the limited life of a recording electrode and the prolonged nature of the development of hypertension bring with it the difficulty of comparing sympathetic nerve activity between groups. New developments in high-frequency radiotelemetry in animals have heralded a new age in long-term sympathetic recordings ideal for hypertension research. Standard multifiber recordings in human and animal studies have provided information about the frequency and amplitude of sympathetic bursts. Characterization of sympathetic output is now possible from new techniques of determining single-unit firing frequency, firing probability, and the number of spikes generated per cardiac interval. These have led to a better understanding of sympathoactivation in hypertension and its underlying mechanisms.

Voluntary versus spontaneous swallowing in man.

This review examines the evidence regarding the clinical and neurophysiological differences between voluntary and spontaneous swallows. From the clinical point of view, voluntary swallow (VS) occurs when a human has a desire to eat or drink during the awake and aware state. Spontaneous swallow (SS) is the result of accumulated saliva and/or food remnants in the mouth. It occurs without awareness while awake and also during sleep. VS is a part of eating behavior, while SS is a type of protective reflex action. In VS, there is harmonized and orderly activation of perioral, lingual, and submental striated muscles in the oral phase. In SS, the oral phase is bypassed in most cases, although there may be partial excitation. Following the oral phase, both VS and SS have a pharyngeal phase, which is a reflex phenomenon that protects the upper airway from any escape of food and direct the swallowed material into the esophagus. This reflexive phase of swallowing should not be confused with SS. VS and SS are similar regarding their dependence on the swallowing Central Pattern Generator (CPG) at the brainstem, which receives sensory feedback from the oropharynx. There are differences in the role of the corticobulbar input between VS and SS.

Unmyelinated fibers of the anterior ethmoidal nerve in the rat co-localize with neurons in the medullary dorsal horn and ventrolateral medulla activated by nasal stimulation.

The anterior ethmoidal nerve (AEN) innervates the nasal passages and external nares, and serves as the afferent limb of the nasopharyngeal and diving responses. However, although 65% of the AEN is composed of unmyelinated fibers, it has not been determined whether this afferent signal is carried by unmyelinated or myelinated fibers. We used the transganglionic tracers WGA-HRP, IB4-HRP, and CTB-HRP to trace the central projections of the AEN of the rat. Interpretation of the labeling patterns suggests that AEN unmyelinated fibers project primarily to the ventral tip of the ipsilateral medullary dorsal horn (MDH) at the level of the area postrema. Other unmyelinated projections were to the ventral paratrigeminal nucleus and ventrolateral medulla, specifically the Bötzinger and RVLM/C1 regions. Myelinated AEN fibers projected to the ventral paratrigeminal and mesencephalic trigeminal nuclei. Stimulating the nasal passages of urethane-anesthetized rats with ammonia vapors produced the nasopharyngeal response that included apnea, bradycardia and an increase in arterial blood pressure. Central projections of the AEN co-localized with neurons within both MDH and RVLM/C1 that were activated by nasal stimulation. Within the ventral MDH the density of AEN terminal projections positively correlated with the rostral-caudal location of activated neurons, especially at and just caudal to the obex. We conclude that unmyelinated AEN terminal projections are involved in the activation of neurons in the MDH and ventrolateral medulla that participate in the nasopharyngeal response in the rat. We also found that IB4-HRP was a much less robust tracer than WGA-HRP.

Role of the hypoglossal nerve in equine nasopharyngeal stability.

The equine upper airway is highly adapted to provide the extremely high oxygen demand associated with strenuous aerobic exercise in this species. The tongue musculature, innervated by the hypoglossal nerve, plays an important role in airway stability in humans who also have a highly adapted upper airway to allow speech. The role of the hypoglossal nerve in stabilizing the equine upper airway has not been established. Isolated tongues from eight mature horses were dissected to determine the distal anatomy and branching of the equine hypoglossal nerve. Using this information, a peripheral nerve location technique was used to perform bilateral block of the common trunk of the hypoglossal nerve in 10 horses. Each horse was subjected to two trials with bilateral hypoglossal nerve block and two control trials (unblocked). Upper airway stability at exercise was determined using videoendoscopy and measurement of tracheal and pharyngeal pressure. Three main nerve branches were identified, medial and lateral branches and a discrete branch that innervated the geniohyoid muscle alone. Bilateral hypoglossal block induced nasopharyngeal instability in 10/19 trials, and none of the control trials (0/18) resulted in instability (P<0.001). Mean treadmill speed (+/-SD) at the onset of instability was 10.8+/-2.5 m/s. Following its onset, nasopharyngeal instability persisted until the end of the treadmill test. This instability, induced by hypoglossal nerve block, produced an expiratory obstruction similar to that seen in a naturally occurring equine disease (dorsal displacement of the soft palate, DDSP) with reduced inspiratory and expiratory pharyngeal pressure and increased expiratory tracheal pressure. These data suggest that stability of the equine upper airway at exercise may be mediated through the hypoglossal nerve. Naturally occurring DDSP in the horse shares a number of anatomic similarities with obstructive sleep apnea. Study of species with extreme respiratory adaptation, such as the horse, may provide insight into respiratory functioning in humans.

The anterior ethmoidal nerve is necessary for the initiation of the nasopharyngeal response in the rat.

Stimulation of the nasal passages with ammonia vapors can initiate a nasopharyngeal response that resembles the diving response. This response consists of a sympathetically mediated increase in peripheral vascular resistance, parasympathetically mediated bradycardia and an apnea. The current study investigated the role of the anterior ethmoidal nerve (AEN) in the nasopharyngeal response in the rat, as it is thought that the AEN provides the main sensory innervation of the nasal passages. When both AENs were intact, nasal stimulation caused significant bradycardia, hypertension, and apnea and produced Fos label ventrally within the ipsilateral medullary dorsal horn (MDH) and paratrigeminal nucleus just caudal to the obex. This labeling presumably represents activation of second-order trigeminal neurons. When only one AEN was intact, the nasopharyngeal response was slightly attenuated, and a similar pattern of Fos labeling was only seen in the trigeminal nucleus ipsilateral to the intact AEN. The trigeminal labeling contralateral to the intact AEN was significantly reduced. When both AENs were cut, the nasopharyngeal response to nasal stimulation consisted of only a slight apnea and an increase in arterial pressure; the resultant Fos labeling within the trigeminal nucleus was significantly reduced. Cutting both AENs but not stimulating the nasal passages also produced some Fos labeling within the trigeminal nucleus. These findings suggest that a single AEN can provide sufficient afferent input to initiate the cardiorespiratory changes consistent with the nasopharyngeal response. We conclude that the AEN provides a unique afferent contribution that is capable of producing the diving response.

Brain-stem components of high-frequency somatosensory evoked potentials are modulated by arousal changes: nasopharyngeal recordings in healthy humans.

OBJECTIVE: Until now, the demonstration that early components of high-frequency oscillations (HFOs) evoked by electrical upper limb stimulation are generated in the brain-stem has been based on the results of scalp recordings. To better define the contribution of brain-stem components to HFOs building, we recorded high-frequency somatosensory evoked potentials (SEPs) in 6 healthy volunteers by means of a nasopharyngeal (NP) electrode. Moreover, since HFOs are highly susceptible to arousal fluctuations, we investigated whether eyes opening can influence HFOs at this level. METHODS: We recorded right median nerve SEPs from the ventral surface of the medulla by means of a NP electrode as well as from the scalp, in 6 healthy volunteers under two different arousal states (eyes opened versus eyes closed). SEPs have been further analyzed after digital narrow bandpass filtering (400-800 Hz). RESULTS: NP recordings demonstrated in all subjects a well-defined burst, occurring in the same latency window of the low-frequency P13-P14 complex. Eyes opening induced a significant amplitude increase of the NP-recorded HFOs, whereas scalp-recorded HFOs as well as low-frequency SEPs remained unchanged. CONCLUSIONS: Our findings demonstrate that slight arousal variations induce significant changes in brain-stem components of HFOs. According to the hypothesis that HFOs reflect the activation of central mechanisms, which modulate sensory inputs depending on variations of arousal state, our data suggest that this modulation is already effective at brain-stem level.

Cough, expiration and aspiration reflexes following kainic acid lesions to the pontine respiratory group in anesthetized cats.

The importance of neurons in the pontine respiratory group for the generation of cough, expiration, and aspiration reflexes was studied on non-decerebrate spontaneously breathing cats under pentobarbitone anesthesia. The dysfunction of neurons in the pontine respiratory group produced by bilateral microinjection of kainic acid (neurotoxin) regularly abolished the cough reflexes evoked by mechanical stimulation of both the tracheobronchial and the laryngopharyngeal mucous membranes and the expiration reflex mechanically induced from the glottis. The aspiration reflex elicited by similar stimulation of the nasopharyngeal region persisted in 73% of tests, however, with a reduced intensity compared to the pre-lesion conditions. The pontine respiratory group seems to be an important source of the facilitatory inputs to the brainstem circuitries that mediate cough, expiration, and aspiration reflexes. Our results indicate the significant role of pons in the multilevel organization of brainstem networks in central integration of the aforementioned reflexes.

Neurons in amygdala mediate ear pinna vasoconstriction elicited by unconditioned salient stimuli in conscious rabbits.

We determined whether functional integrity of neurons in the amygdala is necessary for sudden episodes of cutaneous vasoconstriction that occur when the conscious animal detects a salient alerting stimulus. To inhibit neuronal function, muscimol (5 nmol in 300 nl), a long acting and potent GABA-A receptor agonist that hyperpolarizes neurons, was injected bilaterally into the amygdala or into a more dorsal control site in conscious rabbits. Cutaneous blood flow was measured in the ear pinna flow using an ultrasonic Doppler probe chronically implanted around the central ear artery. Ear flow responses to salient unconditioned alerting stimuli (fur touch, slight cage movement. removal of drape covering cage) were examined before and after injection of the muscimol, and the effects compared with effects of muscimol on the ear flow response to more nociceptive stimuli, including ear pinch. Muscimol injections into the dorsal control site did not significantly alter alerting-related episodes of ear pinna vasoconstriction. Muscimol injections into the amygdala almost completely abolished ear vasoconstriction elicited by fur touch (0/5 positive responses), drape removal (0/7 positive responses) and cage movement (0/7 positive responses). Muscimol injections into the amygdala reduced the mean ear flow coefficient of variation for a 15 min observation period from 47+/-5 before injection to 15+/-33% after injection (P<0.01, n=7 rabbits). Muscimol injections into the amygdala did not alter the vigorous ear pinna vasoconstriction elicited by ear pinch (7/7 positive responses). Our results indicate that neuronal function in the amygdala, probably the central nucleus of the amygdala, is necessary for the occurrence of ear pinna vasoconstriction episodes elicited by unconditioned salient stimuli but not for the occurrence of corresponding vasoconstriction elicited by nociceptive stimuli.

The trigeminal nerve. Part III: The maxillary division.

The maxillary nerve gives sensory innervation to all structures in and around the maxillary bone and the midfacial region including the skin of the midfacial regions, the lower eyelid, side of nose, and upper lip; the mucous membrane of the nasopharynx, maxillary sinus, soft palate, palatine tonsil, roof of the mouth, the maxillary gingivae, and maxillary teeth. This vast and complex division of the trigeminal nerve is intimately associated with many sources of orofacial pain, often mimicking maxillary sinus and/or temporomandibular joint involvement. For those who choose to treat patients suffering with orofacial pain and temporomandibular disorders, knowledge of this nerve must be second nature. Just providing the difficult services of a general dental practice should be stimulus enough to understand this trigeminal division, but if one hopes to correctly diagnose and treat orofacial pain disorders, dedication to understanding this nerve cannot be overstated. In this, the third of a four part series of articles concerning the trigeminal nerve, the second or maxillary division will be described and discussed in detail.

Muscle compound motor action potentials from esophago-vertebral electrical stimulation of the spinal cord in the normal awake man.

In 15 normal alert subjects, electrical stimulation of the spinal cord at various levels by a nasopharyngeal probe (cathode) and a vertebral surface electrode (anode) was performed with different orientation of the stimulating dipole. Maximum spinal cord compound motor action potentials (SCCMAPmax) simultaneously recorded from homologous muscles of the upper arm of both sides were not significantly different in amplitude and latency. By stimulating the spinal cord at the cervico-dorsal level it was possible to obtain simultaneous recordings of SCCMAP from muscles of the upper and lower limbs and trunk at a stimulus intensity of 50-70 mA. Stimulating the spinal cord and the peripheral nerve at Erb's point it was also possible to calculate motor propagation velocity of the peripheral nerve of limb-girdle muscles. Central latency of the F wave exceeded by 0.5 to 0.7 ms that of the SCCMAP, suggesting that esophago-vertebral stimulation is able to directly excite the motor neurons. By threshold current intensity, it is possible to obtain a threshold SCCMAP (SCCMAPth) of the same latency as SCCMAPmax and different in shape, duration and amplitude from the CMAP obtained by cortical stimulation with threshold magnetic stimuli. SCCMAPth was different in shape from the motor unit action potential activated at weak voluntary effort, SCCMAPth latency and amplitude were unchanged after voluntary homo- and contralateral activation.

Reflexogenic areas for velopharyngeal closure in rabbits.

Responsive areas for velopharyngeal closure were examined by recording diaphragmatic and superior pharyngeal constrictor activities of anesthetized rabbits. Pressure stimulation was applied with a cotton applicator to the mucosae of three pharyngeal areas: the anterior (palatal) and posterior walls of the nasopharynx and the posterior wall of the oropharynx. The intensity and duration of the stimulation were around 9.0 gf and 0.43 sec, respectively. Velopharyngeal closure was elicited more frequently from the posterior wall of the nasopharynx than the other two areas tested. The higher responsiveness of the posterior wall of the nasopharynx for velopharyngeal closure is suggested to be attributed to higher density and/or lower threshold of pressure receptors in this area than those in the other two areas tested. Possible physiological implications of the present results are discussed.

Anatomic and magnetic resonance imaging bases for the naso-maxillo-cheek flap technique.

A transfacial approach to the deep cranio-maxillo-facial areas by the naso-maxillo-cheek flap technique (NMCF) is indicated for the treatment of some bulky tumors of the naso-pharynx. The procedure requires precise preoperative imaging. This study presents the morphologic bases of this surgical access and the reasonable limits of the excision preoperatively determined by magnetic resonance imaging (MRI). 18 facial and skull specimens were submitted to surgical facial dismantling by the NMCF technique according to Curioni's method. The clinical application in a 66-year-old patient suffering from a neuroblastoma of the olfactory nerve extended into the naso-pharynx is presented. Pre- and postoperative MRI correlations were made in transverse, sagittal and frontal acquisitions. Several structures were preserved in the procedure: facial reliefs, inferior orbital rim and orbital floor, posterior wall of the maxillary sinus covering the pterygopalatine fossa, lateral and medial pterygoid plates and pterygopalatine ganglion with its branches, lateral facial neurovascular pedicle, teeth and soft palate. Other structures were sacrificed: arteries and nerves located at the sites of skin and mucosal incision, and at the sites of osteotomies, ie the infraorbital nerve, the distal part of the greater palatine nerve, the nerves supplying the naso-pharynx, the nasal septum and the nasal conchae, nasolacrimal groove and lacrimal canal. The NMCF technique gives wide access to the deep nasal and nasopharyngeal areas. It is essential to preserve the lateral facial neurovascular pedicle to prevent necrosis of the midface structures. Preservation of the bony architecture surrounding the osteotomy sites is of great importance to allow precise final bone reassembly. Preoperative MRI appears of paramount importance to determine the borders of the lesion and the possibility of block resection.

Cerebral blood flow in rabbits during the nasopharyngeal reflex elicited by inhalation of noxious vapor.

We used chronically implanted Doppler ultrasonic flow probes to measure internal carotid and vertebral blood flow during the nasopharyngeal reflex elicited by inhalation of formaldehyde vapor in conscious rabbits. Internal carotid flow gradually increased to 157 +/- 5% of baseline and vertebral artery increased to 123 +/- 9% of baseline, with maximum values reached approximately 20-40 s after administration of vapor, at a time when arterial pO2 had decreased from 80 +/- 3 to 53 +/- 4 mmHg. Increases in flow were associated with increases in vascular conductance. The delayed increases in cerebral blood flow contrasted with rapid decreases in ear and distal aortic flows, measured at the same time. Our results indicate that forebrain vascular conductance increases in response to inhalation of noxious vapor, possibly reflecting cerebrovascular events associated with hypoxemia.

Trigeminally-mediated alteration of cardiorespiratory rhythms during nasal application of carbon dioxide in the rat.

Stimulation of the upper respiratory tract with air-borne irritants can result in dramatic alterations of cardiorespiratory rhythms that include apnea, bradycardia and selective peripheral vasoconstriction. Since carbon dioxide can stimulate receptors in the nasal passages, we wanted to determine if this odorless gas can induce the same autonomic changes as air-borne irritants. Passing 100% carbon dioxide through the nasal passages of rats anesthetized with chloralose-urethane produced apnea, a vagally-mediated bradycardia and a sympathetically-mediated increase in mean arterial blood pressure. Application of atropine blocked the bradycardia without affecting respiratory or blood pressure changes, while injection of prazosin eliminated blood pressure responses but did not affect heart rate or apnea. There were no significant autonomic responses to nasal application of 10, 25 or 50% carbon dioxide. The responses were mediated through the trigeminal innervation of the nasal mucosa since they could be blocked when the anesthetic procaine was applied to the nasal cavity. We conclude that these cardiorespiratory responses are due to stimulation of trigeminal nociceptors located within the nasal mucosa.

[Anatomy and pathophysiology of deglutition disorders]. / Anatomie und Pathophysiologie von Schluckstörungen.

In the nervous system there are many automatized functions that require multilevel control. Some of them are more important because of their link with some vital functions. Only two are crucial to survival: respiration and the pumping of the heart. Swallowing is integrated within the respiratory system, explaining the need for great reliability and justifying the complexity of the organization described. The progress of medical imaging techniques has created new conditions for practicing radiologists, who need to know much more anatomy than in the past. Therefore, it is easier to learn anatomical details if there details are understood as part of an intelligent construction. We hope to have been able to demonstrate that swallowing is one good example of the real competency of the constructor of this system.

Velopharyngeal insufficiency following palatine tonsillectomy.

Although adenotonsillectomy is usually considered a minor operation, numerous uncommon but severe complications have been described. Even tonsillectomy alone can cause velopharyngeal insufficiency (VPI). We describe two cases in which severe VPI was noted after palatine tonsillectomy was performed because of recurrent peritonsillar abscesses. The patients underwent clinical examination, nasalance measurements, videonasopharyngoscopy and videofluoroscopy. Findings in both patients were consistent with lesions of branches of the vagus and glossopharyngeal nerves through lingual rami, while one of the patients probably also had a lesion of the hypoglossal nerve. Endoscopic and videofluoroscopic examinations demonstrated essential differences in the patients' preoperative state of velopharyngeal anatomy. Findings demonstrate the value of careful postoperative endoscopic and videofluoroscopic examination in cases with VPI after tonsillectomy to identify factors affecting subsequent VPI and to design possible treatment.