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.

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.

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.

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.

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.

Postnatal development of palatal and laryngeal taste buds in the hamster.

Mammalian taste buds are distributed within several distinct subpopulations, innervated by branches of three cranial nerves. These taste bud populations originate and mature at different times in various mammalian species and are thought to play differential roles in the control of taste-mediated behaviors. The hamster is a common animal for the electrophysiological study of the gustatory system, and it has been shown that taste buds innervated by the IXth nerve develop postnatally in this species. To delineate further the development of the gustatory system of hamsters, we quantified the number of taste buds appearing on the palatal, nasopharyngeal, and laryngeal epithelium from birth through 120 days of age. Taste buds are present in almost adult numbers on the soft palate at birth, but only 39% of these are mature. Distinct taste pores, indicative of mature taste buds, increase in number until about 20-30 days of life, at which time all of the taste buds on the soft palate and on the nasoincisive papillae are fully developed. Taste buds are concentrated primarily on the posterior and medial portions of the soft palate. Taste buds located on the laryngeal surface of the epiglottis and the aryepiglottal folds are absent at birth and originate and mature over the following 120 days. Laryngeal taste buds are more concentrated on the aryepiglottal folds than on the epiglottis. On the soft palate and in the epiglottal region, the maturation of taste buds is well characterized by a logarithmic function (Y = a log X + B) relating the number of mature taste buds to postnatal age. On the soft palate, the length of the taste buds from base to apex correlates with the thickness of the epithelium, which increases with development. The diameter of mature taste buds on the soft palate does not change with age. In contrast to many mammalian species, in rodents taste bud development occurs mostly after birth. Rapid postnatal development progresses at a time when ingestive behavior is undergoing a number of significant changes. Taste buds in the larynx have been implicated in a number of laryngeal reflexes (i.e., apnea, swallowing) in several nonrodent species. The electrophysiological properties of superior laryngeal nerve fibers would suggest a similar function for epiglottal taste buds in the hamster.

Distribution of auditory brainstem potentials over the scalp and nasopharynx in humans.

Auditory brainstem potentials were recorded from various scalp and nasopharyngeal sites referenced both to a noncephalic site and to certain scalp locations in normal humans. The distribution of amplitudes and latencies of the components were defined. There were significant amplitude, polarity, and latency asymmetries over the scalp in both referential and differential recordings. The data indicated that several of the ABR components have generator sources that are lateralized and move through the brainstem in particular orientations.

Cardiovascular responses to gustatory and mechanical stimulation of the nasopharynx in rats.

The effects of natural (mechanical and gustatory) stimulation of the nasopharynx or electrical stimulation of the pharyngeal branch of the glossopharyngeal (PH-IXth) nerve on the changes in heart rate (HR) and arterial blood pressure (BP) were investigated in paralyzed and anesthetized rats. Afferent responses in the PH-IXth nerve were also investigated. Electrical stimulation of the PH-IXth nerve elicited a tachycardia and an increase in BP. Among the gustatory (1.0 M NaCl, 0.03 M HCl, 0.03 M QHCl, 1.0 M sucrose, H2O, and 0.9% NaCl) and mechanical stimuli applied to the nasopharynx, 1.0 M sucrose and 0.9% NaCl were ineffective in changing HR and BP; the rest of the stimuli were strongly effective as was the case with electrical stimulation of the PH-IXth nerve. Responses were evoked in the PH-IXth nerve by nasopharyngeal stimulation with the stimuli which were effective in producing cardiovascular responses. On the other hand, 1.0 M sucrose and 0.9% NaCl, which were ineffective stimuli for cardiovascular responses, did not produce any response in the PH-IXth nerve. There was a high correlation between the magnitude of the responses in the PH-IXth nerve and those of the cardiovascular system. These results indicate that gustatory and mechanical information carried in the PH-IXth nerve innervating the nasopharynx plays an important role in cardiovascular regulation as well as the sense of taste.

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.

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.

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.

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.

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.