Oral and pharyngeal reflexes in the mammalian nervous system: their diverse range in complexity and the pivotal role of the tongue

The interactions between different tastes on initiation of reflex swallow elicited by electrical stimulation in humans

The act of eating is a source of pleasure for people and is a major factor in maintaining a good quality of life. Several types of products for dysphagia patients are available to decrease aspiration of food that often accompanies daily food intake. The final goal of these products is to improve the ease of forming a food bolus and/or the safety of the swallowing process; however, tastes of products are not a major concern with initiation of swallowing. In the present study, we investigated the effect of bitter taste stimuli (quinine) and the combination of quinine and umami (monosodium glutamate: MSG) applied to the oropharynx on reflex swallows evoked by electrical stimulation to the oropharyngeal mucosa. Each of the distilled water (DW), quinine and quinine-MSG mixture solution (volume of each solutions, 100 µl) was applied 1 s prior to electrical stimulation. No swallow was evoked when each of the solutions was applied without electrical stimulation. The application of DW and lower concentration of quinine (<100 µM) did not affect the latency of reflex swallow, but 100 µM quinine application increased the latency of the reflex swallow. In addition, application of quinine-MSG mixture solution counteracted the increase in latency induced by quinine application alone. These findings suggest that MSG enhances the initiation of swallowing along with its well-known increase in appetite stimulation. Adding MSG might be effective when creating food to promote swallowing.

Central nervous system integration of sensorimotor signals in oral and pharyngeal structures: oropharyngeal kinematics response to recurrent laryngeal nerve lesion

Safe, efficient liquid feeding in infant mammals requires the central coordination of oropharyngeal structures innervated by multiple cranial and spinal nerves. The importance of laryngeal sensation and central sensorimotor integration in this system is poorly understood. Recurrent laryngeal nerve lesion (RLN) results in increased aspiration, though the mechanism for this is unclear. This study aimed to determine the effect of unilateral RLN lesion on the motor coordination of infant liquid feeding. We hypothesized that 1) RLN lesion results in modified swallow kinematics, 2) postlesion oropharyngeal kinematics of unsafe swallows differ from those of safe swallows, and 3) nonswallowing phases of the feeding cycle show changed kinematics postlesion. We implanted radio opaque markers in infant pigs and filmed them pre- and postlesion with high-speed videofluoroscopy. Markers locations were digitized, and swallows were assessed for airway protection. RLN lesion resulted in modified kinematics of the tongue relative to the epiglottis in safe swallows. In lesioned animals, safe swallow kinematics differed from unsafe swallows. Unsafe swallow postlesion kinematics resembled prelesion safe swallows. The movement of the tongue was reduced in oral transport postlesion. Between different regions of the tongue, response to lesion was similar, and relative timing within the tongue was unchanged. RLN lesion has a pervasive effect on infant feeding kinematics, related to the efficiency of airway protection. The timing of tongue and hyolaryngeal kinematics in swallows is a crucial locus for swallow disruption. Laryngeal sensation is essential for the central coordination in feeding of oropharyngeal structures receiving motor inputs from different cranial nerves.

Hard to swallow: Developmental biological insights into pediatric dysphagia

Pediatric dysphagia-feeding and swallowing difficulties that begin at birth, last throughout childhood, and continue into maturity--is one of the most common, least understood complications in children with developmental disorders. We argue that a major cause of pediatric dysphagia is altered hindbrain patterning during pre-natal development. Such changes can compromise craniofacial structures including oropharyngeal muscles and skeletal elements as well as motor and sensory circuits necessary for normal feeding and swallowing. Animal models of developmental disorders that include pediatric dysphagia in their phenotypic spectrum can provide mechanistic insight into pathogenesis of feeding and swallowing difficulties. A fairly common human genetic developmental disorder, DiGeorge/22q11.2 Deletion Syndrome (22q11DS) includes a substantial incidence of pediatric dysphagia in its phenotypic spectrum. Infant mice carrying a parallel deletion to 22q11DS patients have feeding and swallowing difficulties that approximate those seen in pediatric dysphagia. Altered hindbrain patterning, craniofacial malformations, and changes in cranial nerve growth prefigure these difficulties. Thus, in addition to craniofacial and pharyngeal anomalies that arise independently of altered neural development, pediatric dysphagia may result from disrupted hindbrain patterning and its impact on peripheral and central neural circuit development critical for feeding and swallowing. The mechanisms that disrupt hindbrain patterning and circuitry may provide a foundation to develop novel therapeutic approaches for improved clinical management of pediatric dysphagia.

Cross-activation and detraining effects of tongue exercise in aged rats

Voice and swallowing deficits can occur with aging. Tongue exercise paired with a swallow may be used to treat swallowing disorders, but may also benefit vocal function due to cross-system activation effects. It is unknown how exercise-based neuroplasticity contributes to behavior and maintenance following treatment. Eighty rats were used to examine behavioral parameters and changes in neurotrophins after tongue exercise paired with a swallow. Tongue forces and ultrasonic vocalizations were recorded before and after training/detraining in young and old rats. Tissue was analyzed for neurotrophin content. Results showed tongue exercise paired with a swallow was associated with increased tongue forces at all ages. Gains diminished after detraining in old rats. Age-related changes in vocalizations, neurotrophin 4 (NT4), and brain derived neurotrophic factor (BDNF) were found. Minimal cross-system activation effects were observed. Neuroplastic benefits were demonstrated with exercise in old rats through behavioral improvements and up-regulation of BDNF in the hypoglossal nucleus. Tongue exercise paired with a swallow should be developed, studied, and optimized in human clinical research to treat swallowing and voice disorders in elderly people.

A muscle stem cell for every muscle: variability of satellite cell biology among different muscle groups

The human body contains approximately 640 individual skeletal muscles. Despite the fact that all of these muscles are composed of striated muscle tissue, the biology of these muscles and their associated muscle stem cell populations are quite diverse. Skeletal muscles are affected differentially by various muscular dystrophies (MDs), such that certain genetic mutations specifically alter muscle function in only a subset of muscles. Additionally, defective muscle stem cells have been implicated in the pathology of some MDs. The biology of muscle stem cells varies depending on the muscles with which they are associated. Here we review the biology of skeletal muscle stem cell populations of eight different muscle groups. Understanding the biological variation of skeletal muscles and their resident stem cells could provide valuable insight into mechanisms underlying the susceptibility of certain muscles to myopathic disease.

The capacity for volitional control of pharyngeal swallowing in healthy adults

INTRODUCTION

Previous research has documented that pressure and duration of brainstem-generated pharyngeal swallowing can be cortically modulated. But there is a commonly held belief that the sequence of pharyngeal pressure remains constant. However, Huckabee et al. [19] reported a patient cohort who demonstrated reduced latency of peak pressure in the proximal and distal pharynx, disproportionate and sometimes inversely correlated with overall swallowing duration, suggesting independent timing of underlying muscle contraction within the overall pharyngeal response. This study examined if healthy adults can volitionally produce altered latency of pharyngeal closure in isolation following intensive training, thereby evaluating the capacity for pharyngeal adaptation in a healthy system.

METHOD

Six healthy participants were seen for intensive training, consisting of daily one-hour sessions over two weeks (10 days) using pharyngeal manometry as a visual biofeedback modality. The participants were instructed to produce simultaneous pressure in the pharyngeal sensors when swallowing. The temporal separation of peak proximal and distal pharyngeal pressure was measured with discrete-sensor pharyngeal manometry at baseline, during training with biofeedback, and following training without biofeedback.

RESULTS

Following intensive training, participants were able to reduce temporal separation of peak pressure between the proximal and distal pharyngeal sensors from a baseline median of 188 ms (IQR=231 ms) to 68 ms (IQR=92 ms; p=0.002). In contrast, there was no significant change in overall swallowing duration during training (p=0.41). However, change in pharyngeal pressure latency was moderately correlated with both change in swallowing duration (r=0.444) and amplitude (r=0.571) during training, and there was a reduction in swallowing duration post-training (p=0.03).

CONCLUSION

Given intensive manometric biofeedback training, participants substantially reduced temporal separation of peak proximal and distal pharyngeal pressure when volitionally swallowing. However, correlation with overall pressure and duration measures suggest the adaptation was one of modulating the cumulative pharyngeal response rather than altering discrete components of timing of pharyngeal pressure in isolation. This is inconsistent with the pattern of behaviour documented by Huckabee et al. [19] in the patient population. Further research on modulatory control over targeted aspects of the pharyngeal swallow is needed, and may provide avenues for rehabilitative treatment of patients with dysphagia.

Electrolyte and plasma responses after pickle juice, mustard, and deionized water ingestion in dehydrated humans

CONTEXT

Some athletes ingest pickle juice (PJ) or mustard to treat exercise-associated muscle cramps (EAMCs). Clinicians warn against this because they are concerned it will exacerbate exercise-induced hypertonicity or cause hyperkalemia. Few researchers have examined plasma responses after PJ or mustard ingestion in dehydrated, exercised individuals.

OBJECTIVE

To determine if ingesting PJ, mustard, or deionized water (DIW) while hypohydrated affects plasma sodium (Na(+)) concentration ([Na(+)]p), plasma potassium (K(+)) concentration ([K(+)]p), plasma osmolality (OSMp), or percentage changes in plasma volume or Na(+) content.

DESIGN

Crossover study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 9 physically active, nonacclimated individuals (age = 25 ± 2 years, height = 175.5 ± 9.0 cm, mass = 78.6 ± 13.8 kg).

INTERVENTION(S)

Participants exercised vigorously for 2 hours (temperature = 37°C ± 1°C, relative humidity = 24% ± 4%). After a 30-minute rest, a baseline blood sample was collected, and they ingested 1 mL/kg body mass of PJ or DIW. For the mustard trial, participants ingested a mass of mustard containing a similar amount of Na(+) as for the PJ trial. Postingestion blood samples were collected at 5, 15, 30, and 60 minutes.

MAIN OUTCOME MEASURE(S)

The dependent variables were [Na(+)]p, [K(+)]p, OSMp, and percentage change in plasma Na(+) content and plasma volume.

RESULTS

Participants became 2.9% ± 0.6% hypohydrated and lost 96.8 ± 27.1 mmol (conventional unit = 96.8 ± 27.1 mEq) of Na(+), 8.4 ± 2 mmol (conventional unit = 8.4 ± 2 mEq) of K(+), and 2.03 ± 0.44 L of fluid due to exercise-induced sweating. They ingested approximately 79 mL of PJ or DIW or 135.24 ± 22.8 g of mustard. Despite ingesting approximately 1.5 g of Na(+) in the PJ and mustard trials, no changes occurred within 60 minutes postingestion for [Na(+)]p, [K(+)]p, OSMp, or percentage changes in plasma volume or Na(+) content (P > .05).

CONCLUSIONS

Ingesting a small bolus of PJ or large mass of mustard after dehydration did not exacerbate exercise-induced hypertonicity or cause hyperkalemia. Consuming small volumes of PJ or mustard did not fully replenish electrolytes and fluid losses. Additional research on plasma responses pre-ingestion and postingestion to these treatments in individuals experiencing acute EAMCs is needed.

Defatting Vestibuloplasty for Functional and Esthetic Reconstruction of Tongue

The radial forearm free flap (RFFF) is a thin and pliable tissue with many advantages for tongue reconstruction. However, tongues reconstructed with RFFF occasionally need revision surgery because inadequate defect measurement at primary surgery can lead to bulkiness and limited movement of reconstructed tongue. In this case, the patient underwent partial glossectomy and RFFF reconstruction for treatment of tongue cancer five years prior. We could not make a lower denture for the patient, because the alveolo-lingual sulcus of tongue was almost lost. So we performed vestibuloplasty with a modified Kazanjian method on the lingual vestibule of the mandibular right posterior area, and defatting surgery to debulk the flap. After surgery, we observed that the color and texture of the revised tongue changed to become similar with adjacent tissue. The patient obtained a more functional and esthetic outcome. Accordingly, we present a case report with a review of relevant literature.

Profiles of orofacial dysfunction in different diagnostic groups using the Nordic Orofacial Test (NOT-S)--a review

OBJECTIVE

The Nordic Orofacial Test-Screening (NOT-S) was developed as a comprehensive method to assess orofacial function. Results from the screening protocol have been presented in 11 international publications to date. This study reviewed these publications in order to compile NOT-S screening data and create profiles of orofacial dysfunction that characterize various age groups and disorders.

MATERIALS AND METHODS

NOT-S results of nine reports meeting the inclusion criteria were reviewed. Seven of these studies not only provided data on the mean and range of total NOT-S scores, but also on the most common domains of orofacial dysfunction (highest rate of individuals with dysfunction scores), allowing the construction of orofacial dysfunction profiles based on the prevalence of dysfunction in each domain of NOT-S.

RESULTS

The compiled data comprised 669 individuals, which included healthy control subjects (n = 333) and various patient groups (n = 336). All studies reported differences between individuals with diagnosed disorders and healthy control subjects. The NOT-S data could measure treatment effects and provided dysfunction profiles characterizing the patterns of orofacial dysfunction in various diagnoses.

CONCLUSIONS

This review corroborates previous results that the NOT-S differentiates well between patients and healthy controls and can also show changes in individuals after treatment. NOT-S could be used as a standard instrument to assess orofacial dysfunction, evaluate the outcomes of oral habilitation and rehabilitation and improve comparability in clinical practice and research.

Cortical innervation of the hypoglossal nucleus in the non-human primate (Macaca mulatta)

The corticobulbar projection to the hypoglossal nucleus was studied from the frontal, parietal, cingulate, and insular cortices in the rhesus monkey by using high-resolution anterograde tracers and stereology. The hypoglossal nucleus received bilateral input from the face/head region of the primary (M1), ventrolateral pre- (LPMCv), supplementary (M2), rostral cingulate (M3), and caudal cingulate (M4) motor cortices. Additional bilateral corticohypoglossal projections were found from the dorsolateral premotor cortex (LPMCd), ventrolateral proisocortical motor area (ProM), ventrolateral primary somatosensory cortex (S1), rostral insula, and pregenual region of the anterior cingulate gyrus (areas 24/32). Dense terminal projections arose from the ventral region of M1, and moderate projections from LPMCv and rostral part of M2, with considerably fewer hypoglossal projections arising from the other cortical regions. These findings demonstrate that extensive regions of the non-human primate cerebral cortex innervate the hypoglossal nucleus. The widespread and bilateral nature of this corticobulbar connection suggests recovery of tongue movement after cortical injury that compromises a subset of these areas, may occur from spared corticohypoglossal projection areas located on the lateral, as well as medial surfaces of both hemispheres. Since functional imaging studies have shown that homologous cortical areas are activated in humans during tongue movement tasks, these corticobulbar projections may exist in the human brain.

The effect of bilateral superior laryngeal nerve lesion on swallowing: a novel method to quantitate aspirated volume and pharyngeal threshold in videofluoroscopy

The purpose was to determine the effect of bilateral superior laryngeal nerve (SLN) lesion on swallowing threshold volume and the occurrence of aspiration, using a novel measurement technique for videofluoroscopic swallowing studies (VFSS) in infant pigs. We used a novel radiographic phantom to assess volume of the milk containing barium from fluoroscopy. The custom made phantom was firstly calibrated by comparing image intensity of the phantom with known cylinder depths. Secondly, known volume pouches of milk in a pig cadaver were compared to volumes calculated with the phantom. Using these standards, we calculated the volume of milk in the valleculae, esophagus and larynx, for 205 feeding sequences from four infant pigs feeding before and after had bilateral SLN lesions. Swallow safety was assessed using the tested and validated IMPAS (Dysphagia 28(2):178-187, 2013). The log-linear correlation between image intensity values from the phantom filled with barium milk and the known phantom cylinder depths was strong (R (2) > 0.95), as was the calculated volumes of the barium milk pouches. The threshold volume of bolus in the valleculae during feeding was significantly larger after bilateral SLN lesion than in control swallows (p < 0.001). The IMPAS score increased in the lesioned swallows relative to the controls, indicating substantially impaired swallowing (p < 0.001). Bilateral SLN lesion dramatically increased the aspiration incidence and the threshold volume of bolus in valleculae. The use of this phantom permits quantification of the aspirated volume of fluid, allowing for more accurate 3D volume estimation from 2D X-ray in VFSS.

Variability of the pharyngeal phase of swallow in the cat

Objective

The pharyngeal phase of swallow has been thought to be a stereotypical motor behavior.

Study Design

This is a prospective, preclinical, hypothesis driven, one group by three-task design.

Methods

We sought to compare the effects of pharyngeal swabbing, water only, and water plus punctate mechanical stimulation on the spatiotemporal features of the pharyngeal phase of swallow in the cat. Swallow was elicited under these three conditions in six anaesthetized cats. Electromyographic activity was recorded from seven muscles used to evaluate swallow: mylohyoid, geniohyoid, thyrohyoid, thyroarytenoid, thyropharyngeus, cricopharyngeus, and parasternal.

Results

Pharyngeal swabbing in comparison to the other stimulus conditions, results in decreases in post-swallow cricopharyngeus activity (upper esophageal sphincter); a significant increase in parasternal (schluckatmung; swallow breath) activity; and increases in thyrohyoid (laryngeal elevator), thyroarytenoid (laryngeal adductor) and parasternal muscles burst duration. Pearson correlations were found of moderate strength between 19% of burst duration comparisons and weak to moderate relationships between 29% of burst amplitude comparisons. However, there were no positive significant relationships between phase durations and electromyogram amplitudes between any of the muscles studied during swallow.

Conclusions

The results support the concept that a stereotypical behavior, such as pharyngeal swallowing in animal models, can be modified by sensory feedback from pharyngeal mucosal mechanoreceptors. Furthermore, differences in swallow phase durations and amplitudes provide evidence that separate regulatory mechanisms exist which regulate spatial and temporal aspects of the behavior.

How the brainstem controls orofacial behaviors comprised of rhythmic actions

Mammals perform a multitude of well-coordinated orofacial behaviors such as breathing, sniffing, chewing, licking, swallowing, vocalizing, and in rodents, whisking. The coordination of these actions must occur without fault to prevent fatal blockages of the airway. Deciphering the neuronal circuitry that controls even a single action requires understanding the integration of sensory feedback and executive commands. A far greater challenge is to understand the coordination of multiple actions. Here, we focus on brainstem circuits that drive rhythmic orofacial actions. We discuss three neural computational mechanisms that may enable circuits for different actions to operate without interfering with each other. We conclude with proposed experimental programs for delineating the neural control principles that have evolved to coordinate orofacial behaviors.

Adrenoreceptor modulation of oromotor pathways in the rat medulla

Regulation of feeding behavior involves the integration of multiple physiological and neurological pathways that control both nutrient-seeking and consummatory behaviors. The consummatory phase of ingestion includes stereotyped oromotor movements of the tongue and jaw that are controlled through brain stem pathways. These pathways encompass not only cranial nerve sensory and motor nuclei for processing feeding-related afferent signals and supplying the oromotor musculature but also reticular neurons for orchestrating ingestion and coordinating it with other behaviors that utilize the same musculature. Based on decerebrate studies, this circuit should be sensitive to satiety mechanisms mediated centrally by A2 noradrenergic neurons in the caudal nucleus of the solitary tract (cNST) that are potently activated during satiety. Because the first observable phase of satiety is inhibition of oromotor movements, we hypothesized that norepinephrine (NE) would act to inhibit prehypoglossal neurons in the medullary reticular formation. Using patch-clamp electrophysiology of retrogradely labeled prehypoglossal neurons and calcium imaging to test this hypothesis, we demonstrate that norepinephrine can influence both pre- and postsynaptic properties of reticular neurons through both α1- and α2-adrenoreceptors. The α1-adrenoreceptor agonist phenylephrine (PE) activated an inward current in the presence of TTX and increased the frequency of both inhibitory and excitatory miniature postsynaptic currents. The α2-adrenoreceptor agonist dexmedetomidine (DMT) inhibited cNST-evoked excitatory currents as well as spontaneous and miniature excitatory currents through presynaptic mechanisms. The diversity of adrenoreceptor modulation of these prehypoglossal neurons may reflect their role in a multifunctional circuit coordinating both ingestive and respiratory lingual function.

Monosynaptic premotor circuit tracing reveals neural substrates for oro-motor coordination

Feeding behaviors require intricately coordinated activation among the muscles of the jaw, tongue, and face, but the neural anatomical substrates underlying such coordination remain unclear. In this study, we investigate whether the premotor circuitry of jaw and tongue motoneurons contain elements for coordination. Using a modified monosynaptic rabies virus-based transsynaptic tracing strategy, we systematically mapped premotor neurons for the jaw-closing masseter muscle and the tongue-protruding genioglossus muscle. The maps revealed that the two groups of premotor neurons are distributed in regions implicated in rhythmogenesis, descending motor control, and sensory feedback. Importantly, we discovered several premotor connection configurations that are ideally suited for coordinating bilaterally symmetric jaw movements, and for enabling co-activation of specific jaw, tongue, and facial muscles. Our findings suggest that shared premotor neurons that form specific multi-target connections with selected motoneurons are a simple and general solution to the problem of orofacial coordination.DOI: http://dx.doi.org/10.7554/eLife.02511.001.

The facial motor system

Facial movements support a variety of functions in human behavior. They participate in automatic somatic and visceral motor programs, they are essential in producing communicative displays of affective states and they are also subject to voluntary control. The multiplicity of functions of facial muscles, compared to limb muscles, is reflected in the heterogeneity of their anatomical and histological characteristics that goes well beyond the conventional classification in single facial muscles. Such parcellation in different functional muscular units is maintained throughout the central representation of facial movements from the brainstem up to the neocortex. Facial movements peculiarly lack a conventional proprioceptive feedback system, which is only in part vicariated by cutaneous or auditory afferents. Facial motor activity is the main marker of endogenous affective states and of the affective valence of external stimuli. At the cortical level, a complex network of specialized motor areas supports voluntary facial movements and, differently from upper limb movements, in such network there does not seem to be a prime actor in the primary motor cortex.

Protein kinase A regulates the long-term potentiation of intrinsic excitability in neonatal trigeminal motoneurons

Although much is known about neuronal plasticity in the mammalian hippocampus and other cortical neurons, the subcellular mechanisms underlying plasticity at the level of motor pools are less well characterized. Protein kinase A (PKA) activation plays an essential role in long-term potentiation of intrinsic excitability (LTP-IE) in layer V (LV) visual cortical neurons and may be involved in other systems as well. Trigeminal motoneurons (TMNs) participate in rhythmical motor behaviors, such as suckling, chewing, and swallowing. Using the whole-cell patch clamp method and various kinase inhibitors and activators, we investigated the mechanism of LTP-IE in neonatal rat TMNs. Ca(2+) depletion using ACSF with 0mM Ca(2+) or the Ca(2+) chelator bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) blocked the long-lasting increase in intrinsic excitability in TMNs, showing that intracellular Ca(2+) during the induction protocol is necessary for the induction of LTP-IE. We next used specific inhibitors of PKA, protein kinase C, and calcium/calmodulin-dependent protein kinase II during the induction protocol. Only the PKA inhibitor H-89 blocked the increase in the firing rate induced by the induction protocol. In addition, forskolin, which activates PKA, induced a long-lasting increase in excitability that resembled the excitability produced by the induction protocol. Thus, we conclude that LTP-IE in TMNs is calcium-dependent, and PKA is the primary regulator of this process.

Ultrasound imaging of infant sucking dynamics during the establishment of lactation

BACKGROUND

Infant sucking problems are frequently implicated in early weaning during breastfeeding, yet our understanding of early sucking dynamics is limited.

OBJECTIVE

This study aimed to describe infant sucking patterns during breastfeeding at secretory activation and determine whether they changed by the time of established lactation.

METHODS

Sucking patterns and milk intake of 15 breastfeeding infants were assessed on day 3.2 ± 0.8 and later at follow-up, 16.0 (11.3-22.8) days postpartum. Nipple diameters, tongue movement, nipple position, and suck rate during nutritive sucking (NS) and non-nutritive sucking (NNS) were measured from ultrasound scans of the intra-oral cavity during breastfeeding. Milk intake and LATCH scores were also recorded.

RESULTS

As the tongue lowered during a suck cycle, the nipple increased in size (P < .001), milk flowed into the intra-oral space and the nipple moved closer to the hard-soft palate junction (P < .001). During NS, nipple diameters and the mid-tongue movement were greater than during NNS (P < .001). As the infant aged, the mid-tongue lowered further (P = .002), suck rates became faster (P < .001) and milk intake increased (P = .004), however, no differences were seen for LATCH scores (P = .34).

CONCLUSION

Differences in tongue movement between NS and NNS suggest that there is an altered sucking action when milk flow is absent. Similar sucking patterns at day 3 and during established lactation imply that infants have a mature sucking pattern in the early postpartum period.

Tactile stimulation of the oropharynx elicits sympathoexcitation in conscious humans

Tactile stimulation of the oropharynx (TSO) elicits the gag reflex and increases heart rate (HR) and mean arterial pressure (MAP) in anesthetized patients. However, the interaction between upper-airway defense reflexes and the sympathetic nervous system has not been investigated in conscious humans. In Experiment 1, beat-by-beat measurements of HR, MAP, muscle sympathetic nerve activity (MSNA), and renal vascular resistance (RVR) were measured during TSO and tactile stimulation of the hard palate (Sham) in the supine posture. In Experiment 2, TSO was performed before (pre) and after (post) inhalation of 4% lidocaine via nebulizer. Rate pressure product (RPP) was determined. Compared with Sham, TSO elicited the gag reflex and increased RPP [absolute change (Δ)36 ± 6 vs. 17 ± 5%], MSNA (Δ122 ± 39 vs. 19 ± 19%), and RVR (Δ55 ± 11 vs. 4 ± 4%). This effect occurred within one to two cardiac cycles of TSO. The ΔMAP (12 ± 3 vs. 6 ± 1 mmHg) and the ΔHR (10 ± 3 vs. 3 ± 3 beats/min) were also greater following TSO compared with Sham. Lidocaine inhalation blocked the gag reflex and attenuated increases in MAP (Δpre: 16 ± 2; Δpost: 5 ± 2 mmHg) and HR (Δpre: 12 ± 3; Δpost: 2 ± 2 beats/min) in response to TSO. When mechanically stimulated, afferents in the oropharynx not only serve to protect the airway but also cause reflex increases in MSNA, RVR, MAP, and HR. An augmented sympathoexcitatory response during intubation and laryngoscopy may contribute to perioperative cardiovascular morbidity and mortality.

Morphological evidence of local reflex arc in the rat's tongue

Lingual components of the autonomic nervous system are considered to be the most rostral portion of the enteric nervous system. Therefore our aim was to study the intrinsic nerve cell bodies and synapses using immunohisto-, immunocytochemical methods. Several small groups of ganglia with cell bodies immunoreactive (IR) for vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and substance P (SP) were observed just below the gustatory epithelium. A few somatostatin and galanin IR nerve cell bodies were also found. Many IR cell bodies were also demonstrated in the glands and next to blood vessels. Some of these cell bodies were multipolar and some of them were small neurons with an ovoid shape having only one process. Cell bodies positive for calcitonin gene-related peptide (CGRP) were detected neither in the superficial nor in the deep portion. Electronmicroscopical analysis demonstrated different IR nerve fibres having axo-somatic and axo-dendritic synapses with other immunonegative cells. In a few cases VIP IR nerve processes were found to synaptize with other VIP positive nerve cell bodies. These results support the existance of intralingual reflex in the tongue, where the ganglia might have an integrative role of the different neuropeptide containing nerve fibres.

Assessment of masticatory performance, bite force, orthodontic treatment need and orofacial dysfunction in children and adolescents

OBJECTIVES

Few studies have evaluated the relationship between morphological and functional characteristics of the masticatory apparatus in young subjects. Thus, the aim of this study was to evaluate masticatory performance (MP), maximal bite force (BF), orthodontic treatment need and orofacial dysfunction in children and adolescents.

DESIGN

The sample consisted of 316 subjects of both genders, with an age range 6-16years divided into 4 groups: early mixed, intermediate mixed, late mixed and permanent dentition. MP was evaluated by the individual's ability to comminute a chewable test material in order to determine median particle size (X(50)) and distribution of particles in different sieves ("b"). BF was determined using a digital gnatodynamometer with fork strength of 10mm. Orofacial function and orthodontic treatment need were screened using the Nordic Orofacial Test-Screening (NOT-S) protocol and Index of Orthodontic Treatment Need (IOTN), respectively. The results were submitted to descriptive statistics, normality test, analysis of variance and stepwise multiple linear regression to test relationship between MP and studied independent variables.

RESULTS

Variance of X(50) and b between groups was statistically significant. But evaluation of variables that significantly contributed to MP variation showed that age, body mass index (BMI), BF and the presence of sleep bruxism were negatively related to X(50) and the NOT-S clinical exam scores showed a positive relationship with X(50).

CONCLUSION

In the studied sample, age, BMI, BF and the presence of sleep bruxism were related to better MP; but the increase in NOT-S scores was significantly related to poorer MP.

A survey of oral cavity afferents to the rat nucleus tractus solitarii

Visualization of myelinated fiber arrangements, cytoarchitecture, and projection fields of afferent fibers in tandem revealed input target selectivity in identified subdivisions of the nucleus tractus solitarii (NTS). The central fibers of the chorda tympani (CT), greater superficial petrosal nerve (GSP), and glossopharyngeal nerve (IX), three nerves that innervate taste buds in the oral cavity, prominently occupy the gustatory-sensitive rostrocentral subdivision. In addition, CT and IX innervate and overlap in the rostrolateral subdivision, which is primarily targeted by the lingual branch of the trigeminal nerve (LV). In the rostrocentral subdivision, compared with the CT terminal field, GSP appeared more rostral and medial, and IX was more dorsal and caudal. Whereas IX and LV filled the rostrolateral subdivision diffusely, CT projected only to the dorsal and medial portions. The intermediate lateral subdivision received input from IX and LV but not CT or GSP. In the caudal NTS, the ventrolateral subdivision received notable innervation from CT, GSP, and LV, but not IX. No caudal subnuclei medial to the solitary tract contained labeled afferent fibers. The data indicate selectivity of fiber populations within each nerve for functionally distinct subdivisions of the NTS, highlighting the possibility of equally distinct functions for CT in the rostrolateral NTS, and CT and GSP in the caudal NTS. Further, this provides a useful anatomical template to study the role of oral cavity afferents in the taste-responsive subdivision of the NTS as well as in subdivisions that regulate ingestion and other oromotor behaviors.

Herpes zoster oticus: a clinical model for a transynaptic, reflex pathways, viral transmission hypotheses

Reactivation of the varicella-zoster virus (VZV) along the sensory nerves innervating the ear, including the geniculate ganglion, is responsible for herpes zoster oticus (HZO). In some cases, HZO is associated with polyneuropathy of the cranial nerves, although the mechanism of this involvement is not known. To explain this phenomenon and based on some clinical considerations, the present authors hypothesize an intersynaptic spread of VZV along the reflex pathways of the brainstem.

Regional variation in geniohyoid muscle strain during suckling in the infant pig

The geniohyoid muscle (GH) is a critical suprahyoid muscle in most mammalian oropharyngeal motor activities. We used sonomicrometry to evaluate regional strain (i.e., changes in length) in the muscle origin, belly, and insertion during suckling in infant pigs, and compared the results to existing information on strain heterogeneity in the hyoid musculature. We tested the hypothesis that during rhythmic activity, the GH shows regional variation in muscle strain. We used sonomicrometry transducer pairs to divide the muscle into three regions from anterior to posterior. The results showed differences in strain among the regions within a feeding cycle; however, no region consistently shortened or lengthened over the course of a cycle. Moreover, regional strain patterns were not correlated with timing of the suck cycles, neither (1) relative to a swallow cycle (before or after) nor (2) to the time in feeding sequence (early or late). We also found a tight relationship between muscle activity and muscle strain, however, the relative timing of muscle activity and muscle strain was different in some muscle regions and between individuals. A dissection of the C1 innervations of the geniohyoid showed that there are between one and three branches entering the muscle, possibly explaining the variation seen in regional activity and strain. In combination, our findings suggest that regional heterogeneity in muscle strain during patterned suckling behavior functions to stabilize the hyoid bone, whereas the predictable regional strain differences in reflexive behaviors may be necessary for faster and higher amplitude movements of the hyoid bone.

Posterior lingual lidocaine: A novel method to improve tolerance in upper gastrointestinal endoscopy

AIM: To evaluate the effect of posterior lingual lidocaine swab on patient tolerance to esophagogastroduodenoscopy, the ease of performance of the procedure, and to determine if such use will reduce the need for intravenous sedation.

METHODS: Eighty patients undergoing diagnostic esophagogastroduodenoscopy in a tertiary care medical center were randomized to either lidocaine swab or spray. Intravenous meperidine and midazolam were given as needed during the procedure.

RESULTS: Patients in the lidocaine swab group (SWG) tolerated the procedure better than those in the spray group (SPG) with a median tolerability score of 2 (1, 4) compared to 4 (2, 5) (P < 0.01). The endoscopists encountered less difficulty performing the procedures in the SWG with lower median difficulty scores of 1 (1, 5) compared to 4 (1, 5) in the SPG (P < 0.01). In addition, the need for intravenous sedation was also lower in the SWG compared to the SPG with fewer patients requiring intravenous sedation (13/40 patients vs 38/40 patients, respectively, P < 0.01). The patients in the SWG were more satisfied with the mode of local anesthesia they received as compared to the SPG. In addition, the endoscopists were happier with the use of lidocaine swab.

CONCLUSION: The use of a posterior lingual lidocaine swab in esophagogastroduodenoscopy improves patient comfort and tolerance and endoscopist satisfaction and decreases the need for intravenous sedation.

Ontogenetic changes in Mammalian feeding: insights from electromyographic data

All infant mammals make a transition from suckling milk to eating solid foods. Yet, the neuromuscular implications of the transition from a liquid-only diet to solid foods are unknown even though the transport and swallowing of liquids is different from that of solids. We used legacy electromyography (EMG) data to test hypotheses concerning the changes in motor pattern and neuromuscular control that occur during the transition from an all-liquid diet to consumption of solid food in a porcine model. EMG signals were recorded from five oropharyngeal muscles in pigs at three developmental stages (infants, juveniles, and adults) feeding on milk, on food of an intermediate consistency (porridge), and on dry chow (juveniles and adults only). We measured cycle frequency and its variation in "transport cycles" and "swallow cycles". In the swallow cycles, a measure of variation of the EMG signal was also calculated. Variation in cycle frequency for transport and swallow cycles was lowest in adults, as predicted, suggesting that maturation of feeding mechanisms occurs as animals reach adulthood. Infants had lower variation in transport cycle frequency than did juveniles drinking milk, which may be due to the greater efficiency of the infant's tight oral seal against the teat during suckling, compared to a juvenile drinking from a bowl where a tight seal is not possible. Within juveniles, variation in both transport and swallow cycle frequencies was directly related to food consistency, with the highest variation occurring when drinking milk and the lowest when feeding on solid food. There was no difference in the variation of the EMG activity between intact infants and juveniles swallowing milk, although when the latter swallow porridge the EMG signals were less variable than for milk. These results suggest that consistency of food is a highly significant determinant of the variation in motor pattern, particularly in newly weaned animals.

Corticomotor plasticity induced by tongue-task training in humans: a longitudinal fMRI study

Corticomotor pathways may undergo neuroplastic changes in response to acquisition of new motor skills. Little is known about the motor control strategies for learning new tongue tasks. The aim of this study was to investigate the longitudinal effect of novel tongue-task training on corticomotor neuroplasticity. Thirteen healthy, right-handed men, aged 24-35 years (mean age ± SD: 27.3 ± 0.3 years), performed a training task consisting of standardized tongue protrusion onto a force transducer. The tongue task consisted of a relax-protrude-hold-relax cycle with 1.0 N as the target at the hold phase lasting for 1.5 s. Subjects repeated this task for 1 h. Functional magnetic resonance imaging was carried out before the tongue-task training (baseline), 1-h after the training, and one-day and one-week follow-up. During scanning, the subjects performed tongue protrusion in blocks interspersed with rest. A region-of-interest (ROI) approach and an explorative search were implemented for the analysis of corticomotor activity across conditions. All subjects completed the tongue-task training (mean success rate 43.0 ± 13.2%). In the baseline condition, tongue protrusion resulted in bilateral activity in regions most typically associated with a motor task including medial frontal gyrus (supplementary motor area [SMA]), precentral gyrus (tongue motor cortex), putamen, thalamus, and cerebellum. The ROI analysis revealed increased activity in the precentral gyrus already 1 h post-training. One day after the training, increased activity was observed in the precentral gyrus, SMA, putamen, and cerebellum. No increase was found 1 week after training. Correlation analyses between changes in success rates and changes in the numbers of voxels showed robust associations for left Area 4a in primary motor cortex 1 h, 1 day, and 1 week after the tongue-task training and for the left Area 4p in primary motor cortex and the left lateral premotor cortex 1 day after the training. In the unrestricted analysis, increased activity was found in the parahippocampal gyrus 1 h after the tongue-task training and remained for a week. Decreased activity was found in right post-central and middle frontal gyri 1 h and 1 week post-training. The results verified the involvement of specific corticomotor areas in response to tongue protrusion. Short-term tongue-task training was associated with longer-lasting (up to 1 week) changes in motor-related brain activity. The results suggested that primary motor areas are involved in the early and late stages, while other motor areas mainly are engaged in the later stage of corticomotor neuroplasticity of the tongue.

Efficacy survey of swallowing function and quality of life in response to therapeutic intervention following rehabilitation treatment in dysphagic tongue cancer patients

PURPOSE

This quasi-experimental parallel cluster study was carried out to investigate the utility of interdisciplinary swallowing therapy exercises in improving swallowing function and quality of life (QOL) in dysphagic cancer patients following tongue resection and subsequent rehabilitation treatment.

METHODS

All subjects in the experimental group underwent a structured swallowing training program. The subjects in the experimental group (n = 23) received 30 min of swallowing training each day, 6 days per week for 2 weeks. The control group (n = 23) received no training. Analysis of variance was used, and the M.D. Anderson Dysphagia Inventory (MDADI) discriminated between groups of subjects.

RESULTS

Patients who underwent structured swallowing training (n = 23) showed improvement in the overall MDADI score (P < 0.01) compared with the control population. Furthermore, a separate analysis of individual domains of the MDADI (global, emotional, functional, and physical) demonstrated improved QOL. Although the mean score for tongue rehabilitation indicated that ≥50% subjects in the functional subscale were improved compared with the control population, the difference was not statistically significant (P > 0.05).

CONCLUSIONS

This study used objectively timed swallowing tests, an interdisciplinary swallowing therapy protocol, and a swallowing questionnaire to evaluate the effects of swallowing training. We found that implementation of swallowing education and exercises improved dysphagia and QOL in cancer patients following tongue resection and rehabilitation. Furthermore, this study indicated that swallowing safety and dysphagia training for nursing professionals is effective.

Substance P Modulation of Hypoglossal Motoneuron Excitability During Development: Changing Balance Between Conductances

Although Substance P (SP) acts primarily through neurokinin 1 (NK1) receptors to increase the excitability of virtually all motoneurons (MNs) tested, the ontogeny of this transmitter system is not known for any MN pool. Hypoglossal (XII) MNs innervate tongue protruder muscles and participate in several behaviors that must be functional from birth including swallowing, suckling and breathing. We used immunohistochemistry, Western immunoblotting, and whole cell recording of XII MNs in brain stem slices from rats ranging in age from postnatal day zero (P0) to P23 to explore developmental changes in: NK1 receptor expression; currents evoked by SPNK1 (an NK1-selective SP receptor agonist) and; the efficacy of transduction pathways transforming ligand binding into channel modulation. Despite developmental reductions in XII MN NK1 receptor expression, SPNK1 current density remained constant at 6.1 ± 1.0 (SE) pA/pF. SPNK1 activated at least two conductances. Activation of a pH-insensitive Na+ conductance dominated in neonates (P0–P5), but its contribution fell from ∼80 to ∼55% in juveniles (P14–P23). SPNK1 also inhibited a pH-sensitive, two-pore domain K+ (TASK)-like K+ current. Its contribution increased developmentally. First, the density of this pH-sensitive K+ current doubled between P0 and P23. Second, SPNK1 did not affect this current in neonates, but reduced it by 20% at P7–P10 and 80% in juveniles. In addition, potentiation of repetitive firing was greatest in juveniles. These data establish that despite apparent reductions in NK1 receptor density, SP remains an important modulator of XII MN excitability throughout postnatal development due, in part, to increased expression of a pH-sensitive, TASK-like conductance.

Vagal gustatory reflex circuits for intraoral food sorting behavior in the goldfish: cellular organization and neurotransmitters

The sense of taste is crucial in an animal's determination as to what is edible and what is not. This gustatory function is especially important in goldfish, who utilize a sophisticated oropharyngeal sorting mechanism to separate food from substrate material. The computational aspects of this detection are carried out by the medullary vagal lobe, which is a large, laminated structure combining elements of both the gustatory nucleus of the solitary tract and the nucleus ambiguus. The sensory layers of the vagal lobe are coupled to the motor layers via a simple reflex arc. Details of this reflex circuit were investigated with histology and calcium imaging. Biocytin injections into the motor layer labeled vagal reflex interneurons that have radially directed dendrites ramifying within the layers of primary afferent terminals. Axons of reflex interneurons extend radially inward to terminate onto both vagal motoneurons and small, GABAergic interneurons in the motor layer. Functional imaging shows increases in intracellular Ca++ of vagal motoneurons following electrical stimulation in the sensory layer. These responses were suppressed under Ca(++)-free conditions and by interruption of the axons bridging between the sensory and motor layers. Pharmacological experiments showed that glutamate acting via (+/-)-alpha-amino-3-hydroxy- 5-ethylisoxazole-4-propioinc acid (AMPA)/kainate and N-methyl-D-aspartic acid (NMDA) receptors mediate neurotransmission between reflex interneurons and vagal motoneurons. Thus, the vagal gustatory portion of the viscerosensory complex is linked to branchiomotor neurons of the pharynx via a glutamatergic interneuronal system.

Potential therapeutic targets in obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is a disease of ever-increasing importance due to its association with multiple impairments and rising prevalence in an increasingly susceptible demographic. The syndrome is linked with loud snoring, disrupted sleep and observed apnoeas. Serious co-morbidities associated with OSA appear to be reversed by continuous positive airway pressure (CPAP) treatment; however, CPAP is variably tolerated leaving many patients untreated and emphasising the need for alternative treatments. Virtually all OSA patients have airways that are anatomically vulnerable to collapse, but numerous pathophysiological factors underlie when and how OSA is manifested. This review describes how the complexity of OSA requires multiple treatment approaches that are individually targeted. This approach may take the form of more specific diagnoses in terms of the mechanisms underlying OSA as well as rational pharmacological treatment directed toward such disparate ends as arousal threshold and ventilatory control/chemosensitivity, and mechanical treatment in the form of surgery and augmentation of lung volumes.

Integration of the reflex pharyngeal swallow into rhythmic oral activity in a neurologically intact pig model

Mammalian swallowing involves the coordinated and sequential activity of many oropharyngeal muscles. Using synchronous electromyography (EMG) and videofluorography, we recorded the pattern of EMG activity for 12 muscles during swallowing in neurologically intact suckling pigs. We tested the hypothesis that this EMG pattern corresponded to the established pattern of activity for the isolated, reflexive pharyngeal swallow of the decerebrate infant pig. The EMG activity associated with the normal swallow of the intact animal had two components: a staggered pattern of single EMG bursts that were prominent in the stylohyoid, thyrohyoid, cricothyroid, and omohyoid muscles and double bursts of activity in some muscles, including geniohyoid and genioglossus, with the same underlying periodicity as suckling. Most of the staggered activity pattern, a linear sequence of progressively delayed activities in different muscles, was not statistically different from that previously found in the reflexive pharyngeal swallow of the decerebrate. However, not all components of the linear sequence of the reflexive swallow were inserted unchanged into the intact swallow. Some components appeared to be delayed or advanced, bringing them into phase with the underlying rhythmic activity. The difference between swallows of intact and of decerebrate animals was not solely due to the presence of rhythmic activity in the former. The timing of some EMG activities in intact animals also differed from the same activities in the few decerebrates that exhibited rhythmic tongue and jaw activity. These results suggest cerebral function influences the EMG pattern of the pharyngeal swallow, which has traditionally been considered a purely reflex pattern.

Subdiaphragmatic vagotomy prevents drinking-induced reduction in plasma corticosterone in water-restricted rats

Dehydrated rats exhibit a rapid inhibition of the hypothalamic-pituitary-adrenal axis after rehydration. Drinking activates vagal afferents that project to neurons in the nucleus tractus solitarius (NTS). We hypothesized that when dehydrated rats drink, vagal afferents stimulate NTS neurons initiating inhibition of hypothalamic-pituitary-adrenal activity. Experiments assessed NTS activity by measuring Fos expression. Rats were water restricted for 1 or 6 d, limiting access to water to 30 min/d in the morning. Drinking after single or repeated restriction increased Fos, demonstrating increased NTS activity. We next examined the contribution of the vagus by comparing hormonal responses after total subdiaphragmatic vagotomy or sham surgery. Water restriction for 6 d increased plasma arginine vasopressin (AVP), ACTH, and adrenal and plasma corticosterone in both groups. In sham rats, drinking reduced plasma AVP, ACTH, adrenal and plasma corticosterone by 7.5 min. In total subdiaphragmatic vagotomy rats, whereas drinking reduced plasma AVP, ACTH, and adrenal corticosterone, drinking did not reduce plasma corticosterone. To identify the source of vagal activity, hormonal responses to restriction-induced drinking were measured after common hepatic branch vagotomy (HBV). Although pituitary hormonal responses were not affected by HBV, the adrenal and plasma corticosterone responses to water restriction were reduced; in addition, drinking in HBV rats decreased adrenal corticosterone without changing plasma corticosterone. These data indicate that an intact vagus is necessary to reduce plasma corticosterone when water-restricted rats drink and that the common hepatic vagal branch contributes to the response. These findings implicate the vagus in augmenting rapid removal of circulating corticosterone during relief from stress.

Coordination of Mastication, Swallowing and Breathing

The pathways for air and food cross in the pharynx. In breathing, air may flow through either the nose or the mouth, it always flows through the pharynx. During swallowing, the pharynx changes from an airway to a food channel. The pharynx is isolated from the nasal cavity and lower airway by velopharyngeal and laryngeal closure during the pharyngeal swallow. During mastication, the food bolus accumulates in the pharynx prior to swallow initiation. The structures in the oral cavity, pharynx and larynx serve multiple functions in breathing, speaking, mastication and swallowing. Thus, the fine temporal coordination of feeding among breathing, mastication and swallowing is essential to provide proper food nutrition and to prevent pulmonary aspiration. This review paper will review the temporo-spatial coordination of the movements of oral, pharyngeal, and laryngeal structures during mastication and swallowing, and temporal coordination between breathing, mastication, and swallowing.

Dysphagia in the elderly

The capacity to swallow or eat is a basic human need and can be a great pleasure. Older adults look forward to sharing mealtimes and participating in social interactions. The loss of capacity to swallow and dine can have far-reaching implications. With age, the ability to swallow undergoes changes that increase the risk for disordered swallowing, with devastating health implications for older adults. With the growth in the aging population, dysphagia is becoming a national health care burden and concern. Upward of 40% of people in institutionalized settings are dysphagic. There is a need to address dysphagia in ambulatory, acute care, and long-term care settings.