Hypoglossal Nucleus Research Articles

Neuronal expression of bitter taste receptors and downstream signaling molecules in the rat brainstem

Previous studies have shown that molecules of the taste transduction pathway may serve as biochemical markers for chemoreceptive cells in respiratory and gastrointestinal tracts. In this study, we tested the hypothesis that brainstem neurons contain signaling molecules similar to those in taste buds which may sense the chemical composition of brain extracellular fluids. We used the reverse transcription polymerase chain reaction (RT-PCR), Western blot and immunohistochemical techniques to evaluate presence of different bitter-responsive type 2 taste receptors (T2Rs), their associated G-protein α-gustducin, the downstream signaling molecules phospholipase C isoform β2 (PLC-β2) and transient receptor potential melastatin 5 (TRPM5) in the brainstem of rats. RT-PCR confirmed the mRNA coding for α-gustducin, PLC-β2, TRPM5 and rT2R1 but not that of rT2R16, rT2R26 and rT2R38 in the medulla oblongata. Western blotting confirmed the presence of α-gustducin at the protein level in rat brainstem. Immunohistochemistry identified cells expressing α-gustducin and PLC-β2 at multiple cardiorespiratory and CO2/H+ chemosensory sites, including rostral ventral medulla, facial, parapyramidal, solitary tract, hypoglossal and raphe nuclei. In the medullary raphe, α-gustducin and PLC-β2 were colocalized with a subpopulation of tryptophan hydroxylase (TPH)-immunoreactive serotonergic neurons, a subset of which has respiratory CO2/H+ chemosensitivity. Presence of the T2R1 gene and other genes and proteins of the bitter taste transduction pathway in the brainstem implies additional functions for taste receptors and their effector molecules apart from their gustatory function.

Regulation of hindbrainPyyexpression by acute food deprivation, prolonged caloric restriction, and weight loss surgery in mice

PYY is a gut-derived putative satiety signal released in response to nutrient ingestion and is implicated in the regulation of energy homeostasis. Pyy-expressing neurons have been identified in the hindbrain of river lamprey, rodents, and primates. Despite this high evolutionary conservation, little is known about central PYY neurons. Using in situ hybridization, PYY-Cre;ROSA-EYFP mice, and immunohistochemistry, we identified PYY cell bodies in the gigantocellular reticular nucleus region of the hindbrain. PYY projections were present in the dorsal vagal complex and hypoglossal nucleus. In the hindbrain, Pyy mRNA was present at E9.5, and expression peaked at P2 and then decreased significantly by 70% at adulthood. We found that, in contrast to the circulation, PYY-(1-36) is the predominant isoform in mouse brainstem extracts in the ad libitum-fed state. However, following a 24-h fast, the relative amounts of PYY-(1-36) and PYY-(3-36) isoforms were similar. Interestingly, central Pyy expression showed nutritional regulation and decreased significantly by acute starvation, prolonged caloric restriction, and bariatric surgery (enterogastroanastomosis). Central Pyy expression correlated with body weight loss and circulating leptin and PYY concentrations. Central regulation of energy metabolism is not limited to the hypothalamus but also includes the midbrain and the brainstem. Our findings suggest a role for hindbrain PYY in the regulation of energy homeostasis and provide a starting point for further research on gigantocellular reticular nucleus PYY neurons, which will increase our understanding of the brain stem pathways in the integrated control of appetite and energy metabolism.

α-Synuclein Pathology in the Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex in the Kii Peninsula, Japan

α-Synuclein pathology was examined in the brains and spinal cords of 10 patients with amyotrophic lateral sclerosis (ALS)/parkinsonism-dementia complex (PDC) in the Kii Peninsula, Japan. Various types of phosphorylated α-synuclein-positive structures including neuronal cytoplasmic inclusions, dystrophic neurites, and glial cytoplasmic inclusions were found in all ALS/PDC cases. There were phosphorylated α-synuclein-positive neurons in 8 cases (80%), and the amygdala was most severely affected. Phosphorylated α-synuclein was distributed mainly in the limbic system and brainstem; tau pathology was more prevalent than α-synuclein pathology in most affected areas. In the substantia nigra, periaqueductal gray, locus coeruleus, raphe nuclei, dorsal nucleus of the vagus nerve, hypoglossal nucleus or ventral horn, and intermediolateral nucleus of the spinal cord, α-synuclein pathology was more predominant than tau pathology in only 1 or 2 patients. Phosphorylated α-synuclein- positive structures were not found in the molecular layer of the cerebellum. Phosphorylated α-synuclein frequently colocalized with tau in neuron cell bodies, neurites, and glia. Immunoblots of sarkosyl-insoluble fractions extracted from the brain of 1 patient showed a triplet of α-synuclein-immunoreactive bands that were ubiquitinated. These results suggest that interaction between tau and α-synuclein be involved in the pathogenesis of Kii ALS/PDC.

Expression and distribution of TRPV2 in rat brain

Transient receptor potential (TRP) proteins are non-selective cation channels that mediate sensory transduction. The neuroanatomical localization and the physiological roles of isoform TRPV2 in the rodent brain are largely unknown. We report here the neuroanatomical distribution of TRPV2 in the adult male rat brain focusing on the hypothalamus and hindbrain regions involved in osmoregulation, autonomic function and energy metabolism. For this we utilized immunohistochemistry combined with brightfield microscopy. In the forebrain, the densest immunostaining was seen in both the supraoptic nucleus (SON) and the magnocellular division of the paraventricular nucleus (PVN) of the hypothalamus. TRPV2 immunoreactivity was also seen in the organum vasculosum of the lamina terminalis, the median preoptic nucleus and the subfornical organ, in addition to the arcuate nucleus of the hypothalamus (ARH), the medial forebrain bundle, the cingulate cortex and the globus pallidus to name a few. In the hindbrain, intense staining was seen in the nucleus of the solitary tract, hypoglossal nucleus, nucleus ambiguous, and the rostral division of the ventrolateral medulla (RVLM) and some mild staining in the area prostrema. To ascertain the specificity of the TRPV2 antibody used in this paper, we compared the TRPV2 immunoreactivity of wildtype (WT) and knockout (KO) mouse brain tissue. Double immunostaining with arginine vasopressin (AVP) using confocal microscopy showed a high degree of colocalization of TRPV2 in the magnocellular SON and PVN. Using laser capture microdissection (LCM) we also show that AVP neurons in the SON contain TRPV2 mRNA. TRPV2 was also co-localized with dopamine beta hydroxylase (DBH) in the NTS and the RVLM of the hindbrain. Based on our results, TRPV2 may play an important role in several CNS networks that regulate body fluid homeostasis, autonomic function, and metabolism.

Postnatal developmental profile of neurons and glia in motor nuclei of the brainstem and spinal cord, and its comparison with organotypic slice cultures

In vitro preparations of the neonatal rat spinal cord or brainstem are useful to investigate the organization of motor networks and their dysfunction in neurological disease models. Long-term spinal cord organotypic cultures can extend our understanding of such pathophysiological processes over longer times. It is, however, surprising that detailed descriptions of the type (and number) of neurons and glia in such preparations are currently unavailable to evaluate cell-selectivity of experimental damage. The focus of the present immunohistochemical study is the novel characterization of the cell population in the lumbar locomotor region of the rat spinal cord and in the brainstem motor nucleus hypoglossus at 0-4 postnatal days, and its comparison with spinal organotypic cultures at 2-22 days in vitro. In the nucleus hypoglossus, neurons were 40% of all cells and 80% of these were motoneurons. Astrocytes (35% of total cells) were the main glial cells, while microglia was <10%. In the spinal gray matter, the highest neuronal density was in the dorsal horn (>80%) and the lowest in the ventral horn (≤57%) with inverse astroglia numbers and few microglia. The number of neurons (including motoneurons) and astrocytes was stable after birth. Like in the spinal cord, motoneurons in organotypic spinal culture were <10% of ventral horn cells, with neurons <40%, and the rest made up by glia. The present report indicates a comparable degree of neuronal and glial maturation in brainstem and spinal motor nuclei, and that this condition is also observed in 3-week-old organotypic cultures.

Nitric oxide acts as an excitatory neurotransmitter at hypoglossal motor nucleus

The study is to observe the effect of nitric oxide (NO) donor and scavenger to the hypoglossal motor nucleus (HMN) activity and explore the underlying mechanism. Male adult anesthetized Wistar rats were anesthetized. The activity of genioglossus (GG), diaphragma, blood pressure (BP) and respiratory rate (RR) were recorded when constant microdialysis perfusion of artificial cerebrospinal fluid (ACSF) to HMN as control, followed with diethylamine NONOate sodium salt hydrate (DEA), a NO donor, and 2-(4-carboxyphenyl)-4,4,5,5-tetra-methylimidazoline-1-oxyl-3-oxide potassium salt (carboxy-PTIO), a NO scavenger. Compared with ACSF, application of DEA and carboxy-PTIO at HMN increased and decreased the GG activity respectively and significantly (P<0.05), mainly respiratory-related activity. The tonic GG, diaphragma activity, BP and RR had not been affected statistically between 30-120 min when microdialysis perfusion of both DEA and carboxy-PTIO were delivered. Acting as an excitatory neurotransmitter of HMN, NO may contribute to the patency of upper airway physiologically.

Nitric oxide activates hypoglossal motoneurons by cGMP‐dependent inhibition of TASK channels and cGMP‐independent activation of HCN channels

Nitric oxide (NO) is an important signaling molecule; however mechanism(s) underlying NO modulation of motoneurons (MNs) remain obscure. Here, we used a combination of in vivo and in vitro recording techniques to examine NO modulation of MNs in the hypoglossal motor nucleus (HMN). Microperfusion of DEA (NO donor) into the HMN of anesthetized adult rats increased genioglossus muscle activity. In the brain slice, whole‐cell current‐clamp recordings from hypoglossal MNs show that exposure to DEA depolarized membrane potential and increased responsiveness to depolarizing current injections. Under voltage‐clamp conditions, we found that NO inhibited a Ba2+‐sensitive background K+ conductance and activated a Cs+‐sensitive hyperpolarization‐activated inward current (Ih). The NO‐sensitive K+ conductance exhibited properties similar to TWIK‐related acid‐sensitive K+ (TASK) channels and was blocked by ODQ (soluble guanylyl cyclase antagonist) and KT5823 (PKG antagonist). In Ba2+, NO activated both the instantaneous (Iinst) and time‐dependent (Iss) components of Ih. Interestingly, at more hyperpolarized potentials NO preferentially increased Iinst, and this was retained in ODQ but blocked by a cysteine‐specific oxidant. These results suggest that NO activates hypoglossal MNs by cGMP‐dependent inhibition of a TASK‐like current and S‐nitrosylation‐ dependent activation of Ih.

Gap‐junction coupling in a computational model of the hypoglossal motor nucleus

Hypoglossal motoneurons (HMs) innervate the tongue muscles and play an important role in the maintenance of upper airway patency. Various studies have focused on investigating the biophysical properties of individual HMs, and recent work from our laboratory has focused on developing a series of mathematical HM models that accurately simulate the spiking behaviors and electrophysiological properties recorded experimentally in single HMs. As part of our HM modeling efforts, we have developed a computational model of a large‐scale network of HMs that simulates the entire hypoglossal motor nucleus (nXII) of the rat (approximately 1700 neurons). The HMs are connected with each other through gap junctions, and we analyze different aspects of their coupling mechanisms. Among other results, we noticed the emergence of different firing groups in a rather homogenous population of HMs. We also examined the network with less homogenous HMs composed of slight differences in their biophysical properties, and created a series of networks with different connectivity topologies. Finally, we analyzed the synchrony of our (nXII) model via numerous computer simulations. Supported by HL63175 and NS049310

Neural Stem/Progenitor Cells Transplanted to the Hypoglossal Nucleus Integrates with the Host CNS in Adult Rats and Promotes Motor Neuron Survival

Transplantation of neural stem cells and the mobilization of endogenous neuronal precursors in the adult brain have been proposed as therapeutic strategies for central nervous system disorders and injuries. The aim of the present study was to investigate the possible survival and integration of grafted neural progenitor cells (NPCs) from the subventricular zone (SVZ) in a hypoglossal nerve avulsion model with substantial neuronal loss. Adult neural progenitor cells (NPCs) from the subventricular zone (SVZ) were cultured from inbred transgenic eGFP Lewis rats and transplanted to the hypoglossal nucleus of inbred Lewis rat from the same family but that were not carrying the eGFP strain after avulsion of the hypoglossal nerve. Grafted cells survived in the host more than 3 months and differentiated into neurons [βIII tubulin (Tuj-1 staining)] with fine axon- and dendrite-like processes as well as astrocytes (GFAP) and oligodendrocytes (O4) with typical morphology. Staining for synaptic structures (synaptophysin and bassoon) indicated integration of differentiated cells from the graft with the host CNS. Furthermore, transplantation of NPCs increased the number of surviving motoneurons in the hypoglossal nucleus after nerve avulsion that, if untreated, result in substantial neuronal death. The NPCs used in this study expressed VEGF in vitro as well as in vivo following transplantation that may mediate the rescue effect of the axotomized motoneurons.

Early postnatal alcohol exposure (PAE) causes a partial loss of motoneurons (MNs) in the ventral part of the hypoglossal nucleus (XIIn) in rats

Early postnatal alcohol exposure (PAE) causes a partial loss of motoneurons (MNs) in the ventral part of the hypoglossal nucleus (XIIn) in rats

Neurochemical Properties of the Synapses in the Pathways of Orofacial Nociceptive Reflexes

The brainstem premotor neurons of the facial nucleus (VII) and hypoglossal (XII) nucleus can integrate orofacial nociceptive input from the caudal spinal trigeminal nucleus (Vc) and coordinate orofacial nociceptive reflex (ONR) responses. However, the synaptoarchitectures of the ONR pathways are still unknown. In the current study, we examined the distribution of GABAergic premotor neurons in the brainstem local ONR pathways, their connections with the Vc projections joining the brainstem ONR pathways and the neurochemical properties of these connections. Retrograde tracer fluoro-gold (FG) was injected into the VII or XII, and anterograde tracer biotinylated dextran amine (BDA) was injected into the Vc. Immunofluorescence histochemical labeling for inhibitory/excitatory neurotransmitters combined with BDA/FG tracing showed that GABAergic premotor neurons were mainly distributed bilaterally in the ponto-medullary reticular formation with an ipsilateral dominance. Some GABAergic premotor neurons made close appositions to the BDA-labeled fibers coming from the Vc, and these appostions were mainly distributed in the parvicellular reticular formation (PCRt), dorsal medullary reticular formation (MdD), and supratrigeminal nucleus (Vsup). We further examined the synaptic relationships between the Vc projecting fibers and premotor neurons in the VII or XII under the confocal laser-scanning microscope and electron microscope, and found that the BDA-labeled axonal terminals that made asymmetric synapses on premotor neurons showed vesicular glutamate transporter 2 (VGluT2) like immunoreactivity. These results indicate that the GABAergic premotor neurons receive excitatory neurotransmission from the Vc and may contribute to modulating the generation of the tonic ONR.

Postnatal development of Na+–K+–2Cl− co-transporter 1 and K+–Cl− co-transporter 2 immunoreactivity in multiple brain stem respiratory nuclei of the rat

Previously, we reported that in rats, GABAA and glycine receptor immunoreactivity increased markedly in multiple brain stem respiratory nuclei around postnatal days (P) 12–13, a critical period when abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory network and when the system is under greater inhibition than excitation. Since Na+–K+–2Cl− co-transporter 1 (NKCC1) and K+–Cl− co-transporter 2 (KCC2) play pivotal roles in determining the responses of GABAA and glycine receptors, we hypothesized that NKCC1 and KCC2 undergo significant changes during the critical period. An in-depth immunohistochemical and single neuron optical densitometric study of neurons in seven respiratory-related nuclei (the pre-Bötzinger complex [PBC], nucleus ambiguus [Amb], hypoglossal nucleus [XII], ventrolateral subnucleus of solitary tract nucleus [NTSVL], retrotrapezoid nucleus/parafacial respiratory group [retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG)], dorsal motor nucleus of the vagus nerve [dorsal motor nucleus of the vagus nerve (DMNX)], and inferior olivary nucleus [IO]) and a non-respiratory cuneate nucleus (CN, an internal control) was undertaken in P0–P21 rats. Our data revealed that (1) NKCC1 immunoreactivity exhibited a developmental decrease from P0 to P21 in all eight nuclei examined, being relatively high during the first 1½ postnatal weeks and decreased thereafter. The decrease was abrupt and statistically significant at P12 in the PBC, Amb, and XII; (2) KCC2 immunoreactivity in these eight nuclei showed a developmental increase from P0 to P21; and (3) the significant reduction in NKCC1 and the greater dominance of KCC2 around P12 in multiple respiratory nuclei of the brain stem may form the basis of an enhanced inhibition in the respiratory network during the critical period before the system stabilizes to a more mature state.

Direction of innervation after interpositional nerve graft between facial and hypoglossal nerves in individuals with or without facial palsy: A rat model for treating incomplete facial palsy

The use of an interpositional nerve graft (IPNG) between the facial and hypoglossal nerves for incomplete facial palsy has recently been reported. However, its mechanism has not been elucidated. We established a rat model of IPNG to study incomplete facial palsy and confirmed the direction of innervation through the grafted nerve with or without facial nerve injury. Twenty rats were divided into five groups (n=4): a control group (group A), an incomplete facial palsy group (group B), an IPNG-treated group (group C), an incomplete facial palsy group treated with IPNG (group D) and an incomplete hypoglossal nerve palsy group treated with IPNG (group E). After surgery, mimetic muscle movement was evaluated using an original scoring system. Twelve weeks after surgery, the mimetic muscles of the tongue were injected with Fast Blue and DiI. Retrograde-labelled neurons were counted through the facial and hypoglossal nuclei, and mimetic muscle specimens stained with Masson's trichrome were examined. Fast Blue-labelled neurons were noted in the hypoglossal nucleus in groups C and D, and DiI-labelled neurons within the facial nucleus were noted in groups C and E. The group D facial palsy score statistically exceeded the group B score. The results revealed that axonal regeneration through IPNG is bi-directional and is preferentially directed towards the injured side. Innervation from the hypoglossal nerve to mimetic muscles through IPNG prevents muscle atrophy and helps counter facial palsy.

Kölliker–Fuse neurons send collateral projections to multiple hypoxia-activated and nonactivated structures in rat brainstem and spinal cord.

The Kölliker–Fuse nucleus (KFN) in dorsolateral pons has been implicated in many physiological functions via its extensive efferent connections. Here, we combine iontophoretic anterograde tracing with posthypoxia c-Fos immunohistology to map KFN axonal terminations among hypoxia-activated/nonactivated brain stem and spinal structures in rats. Using a set of stringent inclusion/exclusion criteria to align visualized axons across multiple coronal brain sections, we were able to unequivocally trace axonal trajectories over a long rostrocaudal distance perpendicular to the coronal plane. Structures that were both richly innervated by KFN axonal projections and immunopositive to c-Fos included KFN (contralateral side), ventrolateral pontine area, areas ventral to rostral compact/subcompact ambiguus nucleus, caudal (lateral) ambiguus nucleus, nucleus retroambiguus, and commissural–medial subdivisions of solitary tract nucleus. The intertrigeminal nucleus, facial and hypoglossal nuclei, retrotrapezoid nucleus, parafacial region and spinal cord segment 5 were also richly innervated by KFN axonal projections but were only weakly (or not) immunopositive to c-Fos. The most striking finding was that some descending axons from KFN sent out branches to innervate multiple (up to seven) pontomedullary target structures including facial nucleus, trigeminal sensory nucleus, and various parts of ambiguus nucleus and its surrounding areas. The extensive axonal fan-out from single KFN neurons to multiple brainstem and spinal cord structures("one-to-many relationship"’) provides anatomical evidence that KFN may coordinate diverse physiological functions including hypoxic and hypercapnic respiratory responses, respiratory pattern generation and motor output,diving reflex, modulation of upper airways patency,coughing and vomiting abdominal expiratory reflex, as well as cardiovascular regulation and cardiorespiratory coupling.

GABA/glycine signaling during degeneration and regeneration of mouse hypoglossal nerves

In the adult central nervous system (CNS), GABA and glycine (Gly) are predominant inhibitory neurotransmitters, negatively regulating glutamatergic transmission. In the immature CNS, on the other hand, they act as trophic factors, mediating morphogenesis. In the present study, to investigate their involvement in axonal regeneration, we morphologically examined changes in their signaling in mouse hypoglossal nuclei during degeneration and regeneration of hypoglossal nerves. We found that (1) expression and localization of presynaptic elements were not changed, (2) localization of gephyrin, which anchors GABA and Gly receptors, was spread on the surface of motor neuron cell bodies and dendrites, (3) KCC2-expression markedly decreased, (4) choline acetyltransferase, which mediates acetylcholine-synthesis, immediately disappeared from the motor neurons, and (5) the synaptic cleft of both excitatory and inhibitory synapses became irregularly wider, in the hypoglossal nuclei of the sutured side after the operation. These changes gradually normalized during regeneration. These results suggested that synthesis of acetylcholine may be stopped in the motor neuron after axotomy. GABA/Gly may be normally released from presynaptic terminals, be spilled over the original synaptic cleft, be diffused into the neighboring space, bind to extrasynaptically localized receptors, and mediate depolarization of the membrane potential of motor neurons during degeneration and regeneration. Furthermore, it was suggested that GABA/Gly signaling in postsynaptic motor neurons went back to being immature after axotomy, and may play an important role in axonal regeneration.

Impaired recruitment of neuroprotective microglia and T cells during acute neuronal injury coincides with increased neuronal vulnerability in an amyotrophic lateral sclerosis model

Non-cell-autonomous motor neuronal death is suggested in a mutant Cu/Zn superoxide dismutase 1 (mSOD1)-mediated amyotrophic lateral sclerosis (ALS) model, in which microglia and T cells play significant roles in disease progression. However, it remains unknown whether these cells are toxic or protective. The present study aimed to clarify the developmental age-related alterations of neuronal, glial and T cell responses to acute neuron injury in non-transgenic (N-Tg) mice, and the in vivo effects of mSOD1 on these changes by studying N-Tg and mSOD1-Tg mice subjected to unilateral hypoglossal nerve axotomy at young (8weeks) and adult (17weeks) ages. Adult N-Tg mice showed increased neuronal viability on day 21 after axotomy and trends toward increased numbers of recruited microglia on day 3 and T cells on day 7, in the hypoglossal nucleus, compared with young N-Tg mice. Quantitative comparisons between mSOD1-Tg and N-Tg mice at the same ages, on day 3 after axotomy, showed that microglial recruitment was significantly lower in mSOD1-Tg mice than in 17-week-old N-Tg mice (the disease progression stage), but the same difference was not seen in 8-week-old mice (the presymptomatic stage), despite good preservation of hypoglossal neurons. Infiltration of CD3-positive T cells, mostly CD4-positive, on day 7 and the viability rate of hypoglossal neurons on the operated side compared with the contralateral side on day 21 were significantly decreased in mSOD1-Tg mice compared with N-Tg mice aged 17weeks, but the same difference was not seen in mice aged 8weeks. On day 3 after axotomy, expression levels of IGF-1 mRNA in the operated hypoglossal nucleus were significantly lower in mSOD1-Tg mice than N-Tg mice at 17weeks of age. The observation that depressed microglial and T cell responses and expression of neurotrophic factors coincided with reduced neuronal viability in adult mSOD1-Tg mice suggests that diminished neuroprotective functions of mSOD1 microglia and T cells may contribute to exaggerated neuronal death.

The Effect of Tongue Exercise on Serotonergic Input to the Hypoglossal Nucleus in Young and Old Rats

Breathing and swallowing problems affect elderly people and may be related to age-associated tongue dysfunction. Hypoglossal motoneurons that innervate the tongue receive a robust, excitatory serotonergic (5HT) input and may be affected by aging. We used a rat model of aging and progressive resistance tongue exercise to determine whether age-related alterations in 5HT inputs to the hypoglossal nucleus can be modified. We hypothesized that tongue forces would increase with exercise, 5HT input to the tongue would decrease with age, and tongue exercise would augment 5HT input to the hypoglossal nucleus. Young (9-10 months), middle-aged (24-25 months), and old (32-33 months) male F344/BN rats received tongue exercise for 8 weeks. Immunoreactivity for 5HT was measured in digital images of sections through the hypoglossal nucleus using ImageJ software. Tongue exercise resulted in increased maximum tongue forces at all ages. There was a statistically significant increase in 5HT immunoreactivity in the hypoglossal nucleus in exercised, young rats but only in the caudal third of the nucleus and primarily in the ventral half. Specificity found in serotonergic input following exercise may reflect the topographic organization of motoneurons in the hypoglossal nucleus and the tongue muscles engaged in the exercise paradigm.

Dysfunctional Nucleus Tractus Solitarius: Its Crucial Role in Promoting Neuropathogentic Cascade of Alzheimer’s Dementia—A Novel Hypothesis

The pathophysiological mechanism(s) underlying Alzheimer's disease (AD) still remain unclear, and no disease-modifying or prophylactic therapies are currently available. Unraveling the fundamental neuropathogenesis of AD is an important challenge. Several studies on AD have suggested lesions in a number of CNS areas including the basal forebrain, hippocampus, entorhinal cortex, amygdale/insula, and the locus coeruleus. However, plausible unifying studies on the upstream factors that involve these heterogeneous regions and herald the onset of AD pathogenesis are not available. The current article presents a novel nucleus tractus solitarius (NTS) vector hypothesis that underpins several disparate biological mechanisms and neural circuits, and identifies relevant hallmarks of major presumptive causative factor(s) linked to the NTS, in older/aging individuals. Aging, obesity, infection, sleep apnea, smoking, neuropsychological states, and hypothermia-all activate inflammatory cytokines and oxidative stress. The synergistic impact of systemic proinflammatory mediators activates microglia and promotes neuroinflammation. Acutely, the innate immune response is protective defending against pathogens/toxins; however, when chronic, it causes neuroinflammation and neuronal dysfunction, particularly in brainstem and neocortex. The NTS in the brainstem is an essential multiple signaling hub, and an extremely important central integration site of baroreceptor, chemoreceptor, and a multitude of sensory afferents from gustatory, gastrointestinal, cardiac, pulmonary, and upper airway systems. Owing to persistent neuroinflammation, the dysfunctional NTS exerts deleterious impact on nucleus ambiguus, dorsal motor nucleus of vagus, hypoglossal, parabrachial, locus coeruleus and many key nuclei in the brainstem, and the hippocampus, entorhinal cortex, prefrontal cortex, amygdala, insula, and basal forebrain in the neocortex. The neuronal and synaptic dysfunction emanating from the inflamed NTS may affect its interconnected pathways impacting almost the entire CNS--which is already primed by neuroinflammation, thus promoting cognitive and neuropsychiatric symptoms. The upstream factors discussed here may underpin the neuropathopgenesis of AD. AD pathology is multifactorial; the current perspective underscores the value of attenuating disparate upstream factors--in conjunction with anticholinesterase, anti-inflammatory, immunosuppressive, and anti-oxidant pharmacotherapy. Amelioration of the NTS pathology may be of central importance in countering the neuropathological cascade of AD. The NTS, therefore, may be a potential target of novel therapeutic strategies.

Endogenous Rho-Kinase Signaling Maintains Synaptic Strength by Stabilizing the Size of the Readily Releasable Pool of Synaptic Vesicles

Rho-associated kinase (ROCK) regulates neural cell migration, proliferation and survival, dendritic spine morphology, and axon guidance and regeneration. There is, however, little information about whether ROCK modulates the electrical activity and information processing of neuronal circuits. At neonatal stage, ROCKα is expressed in hypoglossal motoneurons (HMNs) and in their afferent inputs, whereas ROCKβ is found in synaptic terminals on HMNs, but not in their somata. Inhibition of endogenous ROCK activity in neonatal rat brainstem slices failed to modulate intrinsic excitability of HMNs, but strongly attenuated the strength of their glutamatergic and GABAergic synaptic inputs. The mechanism acts presynaptically to reduce evoked neurotransmitter release. ROCK inhibition increased myosin light chain (MLC) phosphorylation, which is known to trigger actomyosin contraction, and reduced the number of synaptic vesicles docked to active zones in excitatory boutons. Functional and ultrastructural changes induced by ROCK inhibition were fully prevented/reverted by MLC kinase (MLCK) inhibition. Furthermore, ROCK inhibition drastically reduced the phosphorylated form of p21-associated kinase (PAK), which directly inhibits MLCK. We conclude that endogenous ROCK activity is necessary for the normal performance of motor output commands, because it maintains afferent synaptic strength, by stabilizing the size of the readily releasable pool of synaptic vesicles. The mechanism of action involves a tonic inhibition of MLCK, presumably through PAK phosphorylation. This mechanism might be present in adults since unilateral microinjection of ROCK or MLCK inhibitors into the hypoglossal nucleus reduced or increased, respectively, whole XIIth nerve activity.

Mapping of FGF1 in the Medulla Oblongata of &lt;i&gt;Macaca fascicularis&lt;/i&gt;

FGF1 is highly expressed in neurons and it has been proposed to play a role in the neuroprotection and in regeneration. Low FGF1 expression in neurons has been linked to increased vulnerability in cholinergic neurons. Previous reports have shown that the expression of FGF1 in rat brain is localized to the cholinergic nuclei of the medulla oblongata, with low ratio of neurons positive for FGF1 in the dorsal motor nucleus of the vagus (DMNV). The role of FGF1 in the primate brain has yet to be clarified. In this study, we mapped FGF1 immunoreactivity in the medulla oblongata of cynomolgus monkey brainstems. Our results demonstrated that FGF1 immunoreactivity follows the pattern of distribution of cholinergic nuclei in the medulla oblongata; with strong localization of FGF1 to cholinergic neurons of the hypoglossal nucleus, the facial nucleus and the nucleus ambiguus. In contrast, the DMNV shows markedly lower FGF1 immunoreactivity. Localization of FGF1 to cholinergic neurons was only observed in the lateral region of the DMNV, with higher immunoreactivity in the rostral ventral-lateral region of the DMNV. These findings are consistent with the distribution of FGF1 immunoreactivity in previous studies of the rat brain.