Facial Nucleus Research Articles

Use of a tissue clearing technique combined with retrograde trans-synaptic viral tracing to evaluate changes in mouse retinorecipient brain regions following optic nerve crush.

Successful establishment of reconnection between retinal ganglion cells and retinorecipient regions in the brain is critical to optic nerve regeneration. However, morphological assessments of retinorecipient regions are limited by the opacity of brain tissue. In this study, we used an innovative tissue cleaning technique combined with retrograde trans-synaptic viral tracing to observe changes in retinorecipient regions connected to retinal ganglion cells in mice after optic nerve injury. Specifically, we performed light-sheet imaging of whole brain tissue after a clearing process. We found that pseudorabies virus 724 (PRV724) mostly infected retinal ganglion cells, and that we could use it to retrogradely trace the retinorecipient regions in whole tissue-cleared brains. Unexpectedly, PRV724-traced neurons were more widely distributed compared with data from previous studies. We found that optic nerve injury could selectively modify projections from retinal ganglion cells in the hypothalamic paraventricular nucleus, intergeniculate leaflet, ventral lateral geniculate nucleus, central amygdala, basolateral amygdala, Edinger-Westphal nucleus, and oculomotor nucleus, but not the superior vestibular nucleus, red nucleus, locus coeruleus, gigantocellular reticular nucleus, or facial nerve nucleus. Our findings demonstrate that the tissue clearing technique, combined with retrograde trans-synaptic viral tracing, can be used to objectively and comprehensively evaluate changes in mouse retinorecipient regions that receive projections from retinal ganglion cells after optic nerve injury. Thus, our approach may be useful for future estimations of optic nerve injury and regeneration.

Trigeminal Sensory Supply Is Essential for Motor Recovery after Facial Nerve Injury

Recovery of mimic function after facial nerve transection is poor. The successful regrowth of regenerating motor nerve fibers to reinnervate their targets is compromised by (i) poor axonal navigation and excessive collateral branching, (ii) abnormal exchange of nerve impulses between adjacent regrowing axons, namely axonal crosstalk, and (iii) insufficient synaptic input to the axotomized facial motoneurons. As a result, axotomized motoneurons become hyperexcitable but unable to discharge. We review our findings, which have addressed the poor return of mimic function after facial nerve injuries, by testing the hypothesized detrimental component, and we propose that intensifying the trigeminal sensory input to axotomized and electrophysiologically silent facial motoneurons improves the specificity of the reinnervation of appropriate targets. We compared behavioral, functional, and morphological parameters after single reconstructive surgery of the facial nerve (or its buccal branch) with those obtained after identical facial nerve surgery, but combined with direct or indirect stimulation of the ipsilateral infraorbital nerve. We found that both methods of trigeminal sensory stimulation, i.e., stimulation of the vibrissal hairs and manual stimulation of the whisker pad, were beneficial for the outcome through improvement of the quality of target reinnervation and recovery of vibrissal motor performance.

Target Site of Prepulse Inhibition of the Trigeminal Blink Reflex in Humans.

Despite the clinical significance of prepulse inhibition (PPI), the mechanisms are not well understood. Herein, we present our investigation of PPI in the R1 component of electrically induced blink reflexes. The effect of a prepulse was explored with varying prepulse test intervals (PTIs) of 20-600 ms in 4 females and 12 males. Prepulse-test combinations included the following: stimulation of the supraorbital nerve (SON)-SON [Experiment (Exp) 1], sound-sound (Exp 2), the axon of the facial nerve-SON (Exp 3), sound-SON (Exp 4), and SON-SON with a long trial-trial interval (Exp 5). Results showed that (1) leading weak SON stimulation reduced SON-induced ipsilateral R1 with a maximum effect at a PTI of 140 ms, (2) the sound-sound paradigm resulted in a U-shaped inhibition time course of the auditory startle reflex (ASR) peaking at 140 ms PTI, (3) facial nerve stimulation showed only a weak effect on R1, (4) a weak sound prepulse facilitated R1 but strongly inhibited SON-induced late blink reflexes (LateRs) with a similar U-shaped curve, and (5) LateR in Exp 5 was almost completely absent at PTIs >80 ms. These results indicate that the principal sensory nucleus is responsible for R1 PPI. Inhibition of ASR or LateR occurs at a point in the startle reflex circuit where auditory and somatosensory signals converge. Although the two inhibitions are different in location, their similar time courses suggest similar neural mechanisms. As R1 has a simple circuit and is stable, R1 PPI helps to clarify PPI mechanisms.SIGNIFICANCE STATEMENT Prepulse inhibition (PPI) is a phenomenon in which the startle response induced by a startle stimulus is suppressed by a preceding nonstartle stimulus. This study demonstrated that the R1 component of the trigeminal blink reflex shows clear PPI despite R1 generation within a circuit consisting of the trigeminal and facial nuclei, without startle reflex circuit involvement. Thus, PPI is not specific to the startle reflex. In addition, PPI of R1, the auditory startle reflex, and the trigeminal late blink reflex showed similar time courses in response to the prepulse test interval, suggesting similar mechanisms regardless of inhibition site. R1 PPI, in conjunction with other paradigms with different prepulse-test combinations, would increase understanding of the underlying mechanisms.

Changes of signaling molecules in the axotomized rat facial nucleus

Axotomy of the rat facial nerve causes downregulation of motoneuron-specific molecules, including choline acetyltransferase and the vesicular acetylcholine transporter, in surviving motoneurons. Subsequently, resident microglia are activated and proliferate. These cellular responses are thought to promote the survival, repair and regeneration of motoneurons. However, it is still unclear which signaling molecules are involved in these responses. In this study, we investigated the changes and localizations of several signaling molecules, including immediate early genes (IEGs) such as c-Jun and c-Fos, transcription factors such as cAMP responsive element binding protein (CREB) and activating transcription factor 2 (ATF2), and mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and p38. Immunoblotting and immunohistochemical analyses revealed the following. Among the IEGs, c-Jun was increased in injured motoneurons, but c-Fos did not respond to neuronal injury. Among the CREB/ATF family members, phosphorylated CREB (p-CREB) was significantly decreased in injured motoneurons. The levels of p-CREB/CREB and ATF2 were immunohistochemically increased in microglia. Among MAPKs, p-ERK1/2 and p-JNK1 were decreased in injured motoneurons at the late stage. p-p38 and p38 were markedly increased in microglia. In vitro experiments revealed that p38 and CREB were activated in proliferating microglia. These results strongly suggested that c-Jun is involved in the survival, repair and regeneration of motoneurons, but p-CREB/CREB, p-ERK/ERK and p-JNK/JNK are associated with the downregulation of motoneuron-specific molecules. On the other hand, p-p38/p38 and p-CREB/CREB were suggested to be closely involved in the activation/proliferation of microglia.

Elephant facial motor control.

We studied facial motor control in elephants, animals with muscular dexterous trunks. Facial nucleus neurons (~54,000 in Asian elephants, ~63,000 in African elephants) outnumbered those of other land-living mammals. The large-eared African elephants had more medial facial subnucleus neurons than Asian elephants, reflecting a numerically more extensive ear-motor control. Elephant dorsal and lateral facial subnuclei were unusual in elongation, neuron numerosity, and a proximal-to-distal neuron size increase. We suggest that this subnucleus organization is related to trunk representation, with the huge distal neurons innervating the trunk tip with long axons. African elephants pinch objects with two trunk tip fingers, whereas Asian elephants grasp/wrap objects with larger parts of their trunk. Finger "motor foveae" and a positional bias of neurons toward the trunk tip representation in African elephant facial nuclei reflect their motor strategy. Thus, elephant brains reveal neural adaptations to facial morphology, body size, and dexterity.

Expression of Glial Cell-Derived Neurotrophic Factor Receptors Within Nucleus Ambiguus During Rat Development.

The nucleus ambiguus (NAmb) is a column of neurons in the medulla oblongata, involved in bulbar functions. Expression of Glial Cell-Derived Neurotrophic Factor (GDNF) and its receptors (GDNFR) is observed within the cell bodies during reinnervation following recurrent laryngeal nerve (RLN) injury. Little is known regarding GDNFR expression in the formation of the NAmb and the laryngeal innervation during embryogenesis. Understanding the timing and pattern of GDNFR expression in embryogenesis versus after RLN injury may provide insights into therapeutic targets for regeneration after RLN injury. Laboratory experiment. Rat brainstems at E14.5/E16.5/E18.5/E20.5/adult were stained for GDNFR: GFRα-1/GFRα-2/GFRα-3/Ret. Islet1 and choline acetyltransferase were used as cell body markers. Sections were observed using fluorescent microscopy and quantified through manual cell counting. Expression of GFRα-1, GFRα-3, and Ret was identified within the NAmb, hypoglossal, and facial nuclei of the adult medulla. During development, GFRα-1 immunoreactivity was seen at E20.5. GFRα-2 expression was not observed at any timepoint. GFRα-3 expression began at E16.5. Ret expression within nerve fibers in the NAmb were observed beginning at E14.5, but never in the cell bodies. Embryonic GDNFR expression in the NAmb differs from that of the adult after RLN injury. The developing brainstem experienced upregulation at discrete timepoints with signaling sustained through adulthood. In contrast, adult RLN-transected rats experienced patterns of up and down regulation. GFRα-1 may contribute to muscle targeting and neuromuscular junction maturation, GFRα-3 may contribute to both, as well as axon guidance. It is likely that GDNF is functioning via a Ret-independent pathway. NA Laryngoscope, 133:2240-2247, 2023.

Cellular Sources and Neuroprotective Roles of Interleukin-10 in the Facial Motor Nucleus after Axotomy.

Facial motoneuron (FMN) survival is mediated by CD4+ T cells in an interleukin-10 (IL-10)-dependent manner after facial nerve axotomy (FNA), but CD4+ T cells themselves are not the source of this neuroprotective IL-10. The aims of this study were to (1) identify the temporal and cell-specific induction of IL-10 expression in the facial motor nucleus and (2) elucidate the neuroprotective capacity of this expression after axotomy. Immunohistochemistry revealed that FMN constitutively produced IL-10, whereas astrocytes were induced to make IL-10 after FNA. Il10 mRNA co-localized with microglia before and after axotomy, but microglial production of IL-10 protein was not detected. To determine whether any single source of IL-10 was critical for FMN survival, Cre/Lox mouse strains were utilized to selectively knock out IL-10 in neurons, astrocytes, and microglia. In agreement with the localization data reflecting concerted IL-10 production by multiple cell types, no single cellular source of IL-10 alone could provide neuroprotection after FNA. These findings suggest that coordinated neuronal and astrocytic IL-10 production is necessary for FMN survival and has roles in neuronal homeostasis, as well as neuroprotective trophism after axotomy.

Phosphodiesterase 10A deactivation induces long-term neurological recovery, Peri-infarct remodeling and pyramidal tract plasticity after transient focal cerebral ischemia in mice

The phosphodiesterase (PDE) superfamily comprises enzymes responsible for the cAMP and cGMP degradation to AMP and GMP. PDEs are abundant in the brain, where they are involved in several neuronal functions. High PDE10A abundance was previously observed in the striatum; however its consequences for stroke recovery were unknown. Herein, we evaluated the effects of PDE10A deactivation by TAK-063 (0.3 or 3 mg/kg, initiated 72 h post-stroke) in mice exposed to intraluminal middle cerebral artery occlusion. We found that PDE10A deactivation over up to eight weeks dose-dependently increased long-term neuronal survival, angiogenesis, and neurogenesis in the peri-infarct striatum, which represents the core of the middle cerebral artery territory, and reduced astroglial scar formation, whole brain atrophy and, more specifically, striatal atrophy. Functional motor-coordination recovery and the long-distance plasticity of pyramidal tract axons, which originate from the contralesional motor cortex and descend through the contralesional striatum to innervate the ipsilesional facial nucleus, were enhanced by PDE10A deactivation. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) revealed a set of dopamine receptor-related and neuronal plasticity-related PDE10A targets, which were elevated (e.g., protein phosphatase-1 regulatory subunit 1B) or reduced (e.g., serine/threonine protein phosphatase 1α, β-synuclein, proteasome subunit α2) by PDE10A deactivation. Our results identify PDE10A as a therapeutic target that critically controls post-ischemic brain tissue remodeling and plasticity.

Events Occurring in the Axotomized Facial Nucleus.

Transection of the rat facial nerve leads to a variety of alterations not only in motoneurons, but also in glial cells and inhibitory neurons in the ipsilateral facial nucleus. In injured motoneurons, the levels of energy metabolism-related molecules are elevated, while those of neurofunction-related molecules are decreased. In tandem with these motoneuron changes, microglia are activated and start to proliferate around injured motoneurons, and astrocytes become activated for a long period without mitosis. Inhibitory GABAergic neurons reduce the levels of neurofunction-related molecules. These facts indicate that injured motoneurons somehow closely interact with glial cells and inhibitory neurons. At the same time, these events allow us to predict the occurrence of tissue remodeling in the axotomized facial nucleus. This review summarizes the events occurring in the axotomized facial nucleus and the cellular and molecular mechanisms associated with each event.

Brain-Inspired Spiking Neural Network Controller for a Neurorobotic Whisker System.

It is common for animals to use self-generated movements to actively sense the surrounding environment. For instance, rodents rhythmically move their whiskers to explore the space close to their body. The mouse whisker system has become a standard model for studying active sensing and sensorimotor integration through feedback loops. In this work, we developed a bioinspired spiking neural network model of the sensorimotor peripheral whisker system, modeling trigeminal ganglion, trigeminal nuclei, facial nuclei, and central pattern generator neuronal populations. This network was embedded in a virtual mouse robot, exploiting the Human Brain Project's Neurorobotics Platform, a simulation platform offering a virtual environment to develop and test robots driven by brain-inspired controllers. Eventually, the peripheral whisker system was adequately connected to an adaptive cerebellar network controller. The whole system was able to drive active whisking with learning capability, matching neural correlates of behavior experimentally recorded in mice.

The Unconventional Growth Factors Cerebral Dopamine Neurotrophic Factor and Mesencephalic Astrocyte-Derived Neurotrophic Factor Promote Post-ischemic Neurological Recovery, Perilesional Brain Remodeling, and Lesion-Remote Axonal Plasticity.

Considerable efforts are currently made to develop strategies that boost endogenous recovery once a stroke has occurred. Owing to their restorative properties, neurotrophic factors are attractive candidates that capitalize on endogenous response mechanisms. Non-conventional growth factors cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) promote neuronal survival and reduce neurological deficits in the acute phase of ischemic stroke in mice. Their effects on endogenous repair and recovery mechanisms in the stroke recovery phase were so far unknown. By intracerebroventricular delivery of CDNF or MANF starting 3days post-stroke (1µg/day for 28days via miniosmotic pumps), we show that delayed CDNF and MANF administration promoted functional neurological recovery assessed by a battery of behavioral tests, increased long-term neuronal survival, reduced delayed brain atrophy, glial scar formation, and, in case of CDNF but not MANF, increased endogenous neurogenesis in the perilesional brain tissue. Besides, CDNF and MANF administration increased long-distance outgrowth of terminal axons emanating from the contralesional pyramidal tract, which crossed the midline to innervate ipsilesional facial nucleus. This plasticity promoting effect was accompanied by downregulation of the axonal growth inhibitor versican and the guidance molecules ephrin B1 and B2 in the previously ischemic hemisphere at 14 dpi, which represents a sensitive time-point for axonal growth. CDNF and MANF reduced the expression of the proinflammatory cytokines IL1β and TNFα in both hemispheres. The effects of non-conventional growth factors in the ischemic brain should further be examined since they might help to identify targets for restorative stroke therapy.

Lesion Localization and Prognosis Using Electrodiagnostic Studies in Facial Diplegia: A Rare Variant of Guillain-Barre Syndrome.

BackgroundThe etiology of facial nerve palsy is diverse and includes herpes zoster virus, Guillain-Barre syndrome (GBS), otitis media, Lyme disease, sarcoidosis, human immunodeficiency virus, etc. The lower motor neuron type facial nerve palsy is usually caused by an ipsilateral facial nerve lesion; however, it may be caused by a central lesion of the facial nerve nucleus and tract in the pons. Facial diplegia is an extremely rare condition that occurs in approximately 0.3% to 2.0% of all facial palsies. Electrodiagnostic studies including direct facial nerve conduction, facial electromyography (EMG), and blink reflex studies are useful for the prognosis and lesion localization in facial nerve palsy.MethodologyThis retrospective, observational study was conducted at the Neurophysiology Unit, Hamad General Hospital, Doha, Qatar. This study included 11 patients with bilateral facial weakness who visited for electrodiagnostic studies in the neurophysiology laboratory.ResultsIn total, eight (72.7%) patients had facial diplegia, eight (72.7%) had hypo/areflexia, seven (63.6%) had facial numbness, and five (45.5%) had cerebrospinal fluid albuminocytological dissociation. The most frequent cause of facial diplegia in this study was GBS (81.9%). Direct facial nerve conduction stimulation showed that nine (81.8%) patients had bilateral facial nerve low compound muscle action potential amplitudes. The bilateral blink reflex study showed that eight (88.8%) patients had absent bilateral evoked responses. Finally, the EMG study showed that five (55.5%) patients had active denervation in bilateral sample facial muscles.ConclusionsBilateral facial nerve palsy is an extremely rare condition with a varied etiology. Electrodiagnostic studies are useful in detecting the underlying pathophysiologic processes, prognosis, and central or peripheral lesion localization in patients with facial diplegia.

Treatment With Nimodipine or FK506 After Facial Nerve Repair Neither Improves Accuracy of Reinnervation Nor Recovery of Mimetic Function in Rats.

PurposeNimodipine and FK506 (Tacrolimus) are drugs that have been reported to accelerate peripheral nerve regeneration. We therefore tested these substances aiming to improve the final functional outcome of motoric reinnervation after facial nerve injury.MethodsIn 18 female rats, the transected facial nerve was repaired by an artificial nerve conduit. The rats were then treated with either placebo, nimodipine, or FK506, for 56 days. Facial motoneurons were pre-operatively double-labeled by Fluoro-Gold and again 56 days post-operation by Fast-Blue to measure the cytological accuracy of reinnervation. The whisking motion of the vibrissae was analyzed to assess the quality of functional recovery.ResultsOn the non-operated side, 93–97% of those facial nerve motoneurons innervating the vibrissae were double-labeled. On the operated side, double-labeling only amounted to 38% (placebo), 40% (nimodipine), and 39% (FK506), indicating severe misdirection of reinnervation. Regardless of post-operative drug or placebo therapy, the whisking frequency reached 83–100% of the normal value (6.0 Hz), but whisking amplitude was reduced to 33–48% while whisking velocity reached 39–66% of the normal values. Compared to placebo, statistically neither nimodipine nor FK506 improved accuracy of reinnervation and function recovery.ConclusionDespite previous, positive data on the speed and quantity of axonal regeneration, nimodipine and FK506 do not improve the final functional outcome of motoric reinnervation in rats.

5‐HT7 receptors expressed in the mouse parafacial region are not required for respiratory chemosensitivity

A brainstem homeostatic system senses CO2/H+ to regulate ventilation, blood gases and acid‐base balance. Neurons of the retrotrapezoid nucleus (RTN) and medullary raphe are both implicated in this mechanism as respiratory chemosensors, but recent pharmacological work suggested that the CO2/H+‐sensitivity of RTN neurons is mediated indirectly – by raphe‐derived serotonin acting on 5‐HT7 receptors. To investigate this further, we characterized Htr7 transcript expression in phenotypically identified RTN neurons using multiplex single cell qRT‐PCR and RNAscope. Although present in multiple neurons in the parafacial region of the ventrolateral medulla, Htr7 expression was undetectable in most RTN neurons (Nmb+/Phox2b+) concentrated in the densely packed cell group ventrolateral to the facial nucleus. Where detected, Htr7 expression was modest and often associated with RTN neurons that extend dorsolaterally to partially encircle the facial nucleus. These more dorsolateral Nmb+/Htr7+ neurons tended to express high levels of Nmb and low levels of the intrinsic RTN proton detectors, Gpr4 and Kcnk5. In mouse brainstem slices, CO2‐stimulated firing in RTN neurons was mostly unaffected by a 5‐HT7 receptor antagonist, SB269970 (n=11/12). At the whole animal level, microinjection of SB269970 into the RTN of conscious mice blocked respiratory stimulation by co‐injected LP‐44, a 5‐HT7 receptor agonist, but had no effect on CO2‐stimulated breathing in those same mice. We conclude that Htr7 is expressed by a minor subset of RTN neurons with a molecular profile distinct from the established chemoreceptors and that 5‐HT7 receptors have negligible effects on CO2‐evoked firing activity in RTN neurons or on CO2‐stimulated breathing in mice.

Neonatal opioid withdrawal syndrome disrupts the ventral swallow pattern generator in germline‐GCaMP6F mouse

Opioid exposure during gestation can lead to neonatal opioid withdrawal syndrome (NOWS) at birth. A feature of NOWS is dysphagia. To better understand the contribution of dysregulated central control to dysphagia in NOWs infants, we compared fictive swallow in neonate (P2‐P6) control mice and mice exposed to methadone from E14.5 onwards. Propriobulbar interneuronal and cranial premotoneuronal networks that coordinate orofacial and laryngeal activity during feeding, as well as constituents of the ventral respiratory column were recorded optically in mice expressing the genetically encoded Ca2+ indicator GCaMP6F in the germline. In the sagittally‐sectioned isolated brainstem, swallow can be evoked by electrical stimulation of command neurons along the dorsomedial edge of the preparation. In vitro swallow is defined as a burst at the hypoglossal nerve (XIIn) unaccompanied by phrenic (C4) motor output. In control animals evoked swallow was accompanied by sequential activation of networks dorsal and medial to the facial nucleus (VIIn), a nucleus in the intermediate reticular formation implicated in vibrissal control (vIRT), and (pre‐)motoneurons along the nucleus ambiguus (NA). In opioid‐exposed pups fictive swallow could reliably be evoked, but only networks dorsomedial to VIIn were reliably activated, while vIRT and NA networks were silent. The distribution of ChAT+, phox2b+, and SST+ neurons was the same in control and MTD‐exposed mice, as were the networks active during inspiration. These findings suggest that dysphagia may at least in part be due to network‐level dysregulation of central networks mediating swallow, but not to gross developmental abnormality of these networks. Because neonate feeding behaviors are highly conserved in mammals, these findings suggest that the sagittally‐sectioned mouse hindbrain provides a platform to investigate the contribution of central networks to dysphagia in NOWS infants.

5-HT7 receptors expressed in the mouse parafacial region are not required for respiratory chemosensitivity.

A brainstem homeostatic system senses CO2/H+ to regulate ventilation, blood gases and acid–base balance. Neurons of the retrotrapezoid nucleus (RTN) and medullary raphe are both implicated in this mechanism as respiratory chemosensors, but recent pharmacological work suggested that the CO2/H+ sensitivity of RTN neurons is mediated indirectly, by raphe‐derived serotonin acting on 5‐HT7 receptors. To investigate this further, we characterized Htr7 transcript expression in phenotypically identified RTN neurons using multiplex single cell qRT‐PCR and RNAscope. Although present in multiple neurons in the parafacial region of the ventrolateral medulla, Htr7 expression was undetectable in most RTN neurons (Nmb +/Phox2b+) concentrated in the densely packed cell group ventrolateral to the facial nucleus. Where detected, Htr7 expression was modest and often associated with RTN neurons that extend dorsolaterally to partially encircle the facial nucleus. These dorsolateral Nmb +/Htr7 + neurons tended to express Nmb at high levels and the intrinsic RTN proton detectors Gpr4 and Kcnk5 at low levels. In mouse brainstem slices, CO2‐stimulated firing in RTN neurons was mostly unaffected by a 5‐HT7 receptor antagonist, SB269970 (n = 11/13). At the whole animal level, microinjection of SB269970 into the RTN of conscious mice blocked respiratory stimulation by co‐injected LP‐44, a 5‐HT7 receptor agonist, but had no effect on CO2‐stimulated breathing in those same mice. We conclude that Htr7 is expressed by a minor subset of RTN neurons with a molecular profile distinct from the established chemoreceptors and that 5‐HT7 receptors have negligible effects on CO2‐evoked firing activity in RTN neurons or on CO2‐stimulated breathing in mice.Key points Neurons of the retrotrapezoid nucleus (RTN) are intrinsic CO2/H+ chemosensors and serve as an integrative excitatory hub for control of breathing.Serotonin can activate RTN neurons, in part via 5‐HT7 receptors, and those effects have been implicated in conferring an indirect CO2 sensitivity.Multiple single cell molecular approaches revealed low levels of 5‐HT7 receptor transcript expression restricted to a limited population of RTN neurons.Pharmacological experiments showed that 5‐HT7 receptors in RTN are not required for CO2/H+‐stimulation of RTN neuronal activity or CO2‐stimulated breathing.These data do not support a role for 5‐HT7 receptors in respiratory chemosensitivity mediated by RTN neurons.

The Alterations and Significance of Intercellular Adhesion Molecule-1 in Mouse Brainstem During Herpes Simplex Virus Type 1-Induced Facial Palsy.

Herpes simplex virus type 1 (HSV-1) results in the development of Bell's pals but still, the pathophysiology of the facial nerve paralysis is still not fully studied. The main objective is to establish an animal model of type 1 herpes simplex virus (HSV-1)-induced face paralysis in the mouse and to investigate the pattern of changes in intercellular adhesion molecule -1(ICAM-1) expression in the facial nucleus of the brain stem in mice with facial paralysis as well as the effects of glucocorticoids on intercellular adhesion molecule -1(ICAM-1) expression. A total of 170 4-week-old Balb/c male mice were randomly divided into the virus inoculation group (n = 135), saline control group (n = 26), and blank control group (n = 9). Mice in the virus inoculation group that showed facial paralysis were divided into A, B, and C subgroups. The A group did not receive any treatments, the B group received methylprednisolone sodium succinate (MPSS) intervention, and the C group received MPSS + RU486 treatment. The mouse model of facial paralysis was established by inoculating HSV-1 to the skin at the back of the ears. The facial nerve function of mice was assessed, and real-time PCR and western blot were used to assess ICAM-1 expression in the facial nucleus of the brain stem in mice with facial paralysis after drug intervention. In the virus inoculation group, 95 mice (55.88%) showed varying degrees of facial paralysis symptoms within 2-5days after inoculation. The ICAM-1 gene and protein expression levels remained at low levels in the facial nucleus of the brain stem of mice in the saline group, which showed no significant difference compared to the normal control group (P > 0.05). However, for mice of the virus inoculation group, ICAM-1 expression increased at 6h after the occurrence of facial paralysis and peaked after 2days, differing significantly from the blank control group (P < 0.01). ICAM-1 expression subsequently decreased gradually. In the HSV-1 + MPSS group, ICAM-1 protein expression decreased significantly on the 2nd day after facial paralysis. In the HSV-1 + MPSS + RU486 group, MPSS inhibition of ICAM-1 protein expression was reduced. The results suggested that ICAM-1 is involved in the pathological processes by which HSV-1 induces facial paralysis in mice, and the treatment effects of MPSS for Bell's palsy can be achieved by the inhibition of MCP-1.

Efficacy of LED Photobiomodulation for Functional and Axonal Regeneration After Facial Nerve Section-Suture.

Facial nerve damage can lead to partial or total facial nerve palsy. Photobiomodulation has been reported to improve and accelerate functional recovery following peripheral nerve lesion, depending on the type of lesion and the light exposure parameters used. The aim of this study was to investigate the effects of infrared exposure on functional and axonal regeneration after section-suture of the distal branches of the facial nerve: the buccal and marginal mandibular branches and the distal pes. The animals underwent surgery and were irradiated with infrared light at 850 nm twice daily from day 1 to day 16. The recovery of facial function was then studied at both the behavioral and morphological levels. Behavioral analyses were performed by videoscoring with a high-speed camera and using various devices to assess the recovery of whisker movement on the lesioned side from day 1 to day 30. We also assessed nasal deviation toward the intact side and the ability to close the ipsilateral eyelid completely from day 1 to day 38 and from day 1 to day 50, respectively. For morphological analyses, we assessed the re-establishment of facial motoneuron labeling with Fluorogold®, an immunofluorescent retrograde marker of axonal transport injected into the vibrissae, on D10, D14 and D30. We found that whisker movements recovery was significantly faster in treated than in control mice. A complete disappearance of nasal deviation was observed at 2 weeks in infrared-treated lesioned mice and at 5 weeks in controls. Complete eyelid closure was observed 3 weeks after surgery in treated animals and 6 weeks after surgery in controls. Finally, normal fluorogold labeling of the facial nuclei complex was restored 30 days after surgery in the treated animals, but no such restoration was ever observed in control animals. In conclusion, our data show that IR treatment at a distal site has a significant positive effect on facial nerve recovery. These findings pave the way for the clinical use of infrared photobiomodulation in patients with nerve lesions.

Motoneuron-Specific PTEN Deletion in Mice Induces Neuronal Hypertrophy and Also Regeneration after Facial Nerve Injury.

In postmitotic neurons, several tumor suppressor genes (TSGs), including p53, Rb, and PTEN, modulate the axon regeneration success after injury. Particularly, PTEN inhibition is a key driver of successful CNS axon regeneration after optic nerve or spinal cord injury. In contrast, in peripheral neurons, TSG influence in neuronal morphology, physiology, and pathology has not been investigated to the same depth. In this study, we conditionally deleted PTEN from mouse facial motoneurons (Chat-Cre/PtenloxP/loxP ) and analyzed neuronal responses in vivo with or without peripheral facial nerve injury in male and female mice. In uninjured motoneurons, PTEN loss induced somatic, axonal, and nerve hypertrophy, synaptic terminal enlargement and reduction in physiological whisker movement. Despite these morphologic and physiological changes, PTEN deletion positively regulated facial nerve regeneration and recovery of whisker movement after nerve injury. Regenerating PTEN-deficient motoneurons upregulated P-CREB and a signaling pathway involving P-Akt, P-PRAS40, P-mTOR, and P-4EBP1. In aged mice (12 months), PTEN deletion induced hair loss and facial hyperplasia of the epidermis. This suggests a time window in younger mice with PTEN loss stimulating axon growth after injury, however, at the risk of hyperplasia formation at later time points in the old animal. Overall, our data highlight a dual TSG function with PTEN loss impairing physiological neuron function but furthermore underscoring the positive effects of PTEN ablation in axon regeneration also for the PNS.SIGNIFICANCE STATEMENT Tumor suppressor genes (TSGs) restrict cell proliferation and growth. TSG inhibition, including p53 and PTEN, stimulates axon regeneration after CNS injury. In contrast, in PNS axon regeneration, TSGs have not been analyzed in great depth. Herein we show enhanced peripheral axon regeneration after PTEN deletion from facial motoneurons. This invokes a signaling cascade with novel PTEN partners, including CREB and PRAS40. In adult mice, PTEN loss induces hyperplasia of the skin epidermis, suggesting detrimental consequences when reaching adulthood in contrast to a beneficial TSG role for regeneration in young adult mice. Thus, our data highlight the double-edged sword nature of interfering with TSG function.

Advances and future directions in the care of patients with facial paralysis

Advances and future directions in the care of patients with facial paralysis