Vibrissae Movements Research Articles

Effect of direct current electrical stimulation on the recovery of facial nerve crush injury

This study aimed to evaluate the effect of noninvasive electrical stimulation (ES) using transcutaneous direct current on facial nerve crush injury by assessing in vitro cellular responses including proliferation and differentiation using PC12 cells as well as by performing in vivo functional and morphological assessments. Compared to the non-treated cells, the cells subjected to ES treatment showed clear in vitro neurite outgrowth and enhanced expression of differentiation genes. In this animal model, functional assessment of recovery was performed using vibrissa movement orientation and electrically stimulated muscle action potential. Moreover, histological observation was performed using a transmission electron microscope. A higher score of recovered vibrissa movement and more significant reduction of the threshold of electrically evoked muscle action potential were observed in the ES group than in the control group. Furthermore, histomorphometric evaluation showed that the experimental group had statistically significantly higher axon counts than did the control group. Regenerative nerve fibers were prominent in the distal segments of the ES group.

Parallel Inhibitory and Excitatory Trigemino-Facial Feedback Circuitry for Reflexive Vibrissa Movement

Animals employ active touch to optimize the acuity of their tactile sensors. Prior experimental results and models lead to the hypothesis that sensory inputs are used in a recurrent manner to tune the position of the sensors. A combination of electrophysiology, intersectional genetic viral labeling and manipulation, and classical tracing allowed us to identify second-order sensorimotor loops that control vibrissa movements by rodents. Facial motoneurons that drive intrinsic muscles to protract the vibrissae receive a short latency inhibitory input, followed by synaptic excitation, from neurons located in the oralis division of the trigeminal sensory complex. In contrast, motoneurons that retract the mystacial pad and indirectly retract the vibrissae receive only excitatory input from interpolaris cellsthat further project to the thalamus. Silencing this feedback alters retraction. The observed pull-push circuit at the lowest-level sensorimotor loop provides a mechanism for the rapid modulation ofvibrissa touch during exploration of peri-personal space.

Muscle-Nerve-Muscle Grafting for Facial Reanimation in Rats.

Facial paralysis is a devastating condition leaving patients with a myriad of aesthetic and functional consequences. Muscle-nerve-muscle (MNM) neurotization is a reinnervation technique that involves implanting an autogenous nerve graft as a conduit between an innervated "donor" muscle and a denervated "recipient" muscle. We investigated the use of MNM reinnervation, alone or in combination with electrical stimulation (ES) and testosterone propionate (TP) in comparison to nerve reanastomosis (RE), on functional recovery following rat facial nerve injury. Thirty-one male, Sprague-Dawley rats were assigned to groups: no graft (control), MNM grafting alone (MNM), MNM grafting with ES and TP (MNM+ES+TP), or RE. Harvested right facial nerve branches were used as the MNM graft. Functional recovery was assessed by behavioral observations and electromyographic recordings. The MNM grafting improved muscle tone and vibrissae movement. The ES+TP treatment further enhanced muscle tone as well as reduced recovery time for coordinated movement in a manner that is comparable to those of RE. Electromyographic recordings demonstrated electrical conductance across all MNM grafts. These data have important implications for patients with unilateral paralysis from facial or laryngeal nerve injury, particularly those who are not candidates for nerve reanastomosis.

Neural stem/progenitor cells on collagen with anchored basic fibroblast growth factor as potential natural nerve conduits for facial nerve regeneration.

Neural stem/progenitor cells (NS/PCs) were beneficial for the treatment of nervous system diseases. However, after transplantation, the beneficial was limited because the number of living NS/PCs decreased rapidly due to insufficient signaling molecules, such as growth factors, in the microenvironments surrounding transplanted cells. In the present study, we constructed collagen-based nerve conduit with anchored bFGF to achieve higher numbers of NS/PCs for repairing facial nerve injury. Compared with other methods involving neutral salt treatment or dialysis, the fabrication method of collagen scaffolds was simple, low-cost and safe, requiring a relatively short time to prepare. At 12weeks after transplantation, the functional and histological results of natural nerve conduits treated group showed significant similarities to the gold standard method of nerve autografting.

Adipose-Derived Stem Cells Enhance Axonal Regeneration through Cross-Facial Nerve Grafting in a Rat Model of Facial Paralysis.

Cross-face nerve grafting combined with functional muscle transplantation has become the standard in reconstructing an emotionally controlled smile in complete irreversible facial palsy. However, the efficacy of this procedure depends on the ability of regenerating axons to breach two nerve coaptations and reinnervate endplates in denervated muscle. The current study tested the hypothesis that adipose-derived stem cells would enhance axonal regeneration through a cross-facial nerve graft and thereby enhance recovery of the facial nerve function. Twelve rats underwent transection of the right facial nerve, and cross-facial nerve grafting using the sciatic nerve as an interpositional graft, with coaptations to the ipsilateral and contralateral buccal branches, was carried out. Rats were divided equally into two groups: a grafted but nontreated control group and a grafted and adipose-derived stem cell-treated group. Three months after surgery, biometric and electrophysiologic assessments of vibrissae movements were performed. Histologically, the spectra of fiber density, myelin sheath thickness, fiber diameter, and g ratio of the nerve were analyzed. Immunohistochemical staining was performed for the evaluation of acetylcholine in the neuromuscular junctions. The data from the biometric and electrophysiologic analysis of vibrissae movements, immunohistochemical analysis, and histologic assessment of the nerve showed that adipose-derived stem cells significantly enhanced axonal regeneration through the graft. These observations suggest that adipose-derived stem cells could be a clinically translatable route toward new methods to enhance recovery after cross-facial nerve grafting.

The injury of marginal mandibular branch unexpectedly promotes the repair of buccal branch of facial nerve in a rat model

Conclusions: The results indicate that the injury of the marginal mandibular branch improved the recovery of the buccal branch in a rat model.Objective: The aim of this study was to investigate whether the injury or intactness of the marginal mandibular branch affects the regeneration of the facial nerve buccal branch in a rat model.Methods: This experiment was conducted on 30 adult rats, which were randomly and equally divided into two groups. The buccal branch of the facial nerve was transected and reconstructed, with the marginal mandibular branch damaged (group A) or intact (group B). The vibrissae movement of rats was assessed since the 4th week after operation. At the 8th and 12th week, compound muscle action potentials (CMAPs) and morphological changes of injured buccal branches were evaluated.Results: After the operation, vibrissae movement of rats was eliminated in group A, but it was similar to the health side in group B. CMAPs were recorded from regenerated buccal branches in group A since the 8th week, but no CMAPs could be recorded in group B at each time point. Additionally, the diameter of nerve fibers, the thickness of myelin sheath, and the density of regenerated fibers in group A were significantly larger than those in group B (p < 0.05).

Analysis of the Vibrissa Parametric Resonance Causing a Signal Amplification during Whisking Behaviour

The paper deals with the mechanical vibrational motion of vibrissae during natural exploratory behaviour of mammals. The theoretical analysis is based on a mechanical model of a cylindrical beam with circular natural configuration under an applied periodic force at the tip, which corresponds to the surface roughness of an investigated object. The equation of motion of the beam is studied using the Euler-Bernoulli beam theory and asymptotic methods of mechanics. It is shown that from the mechanical point of view the phenomenon of parametric resonance of the vibrissa is possible. It means that the amplitude of forced vibrations of a vibrissa increases exponentially with time, if it is stimulated within a specific resonance frequency range, which depends on biomechanical parameters of the vibrissa. The most intense parametric resonance occurs, when the excitation frequency is close to the doubled natural frequency of free vibrations. Thus, it may be used to distinguish and amplify specific periodic components of a complex roughness profile during texture discrimination.

Facilitation of facial nerve regeneration using chitosan-β-glycerophosphate-nerve growth factor hydrogel

Conclusion C/GP hydrogel was demonstrated to be an ideal drug delivery vehicle and scaffold in the vein conduit. Combined use autologous vein and NGF continuously delivered by C/GP-NGF hydrogel can improve the recovery of facial nerve defects. Objective This study investigated the effects of chitosan-β-glycerophosphate-nerve growth factor (C/GP-NGF) hydrogel combined with autologous vein conduit on the recovery of damaged facial nerve in a rat model. Methods A 5 mm gap in the buccal branch of a rat facial nerve was reconstructed with an autologous vein. Next, C/GP-NGF hydrogel was injected into the vein conduit. In negative control groups, NGF solution or phosphate-buffered saline (PBS) was injected into the vein conduits, respectively. Autologous implantation was used as a positive control group. Vibrissae movement, electrophysiological assessment, and morphological analysis of regenerated nerves were performed to assess nerve regeneration. Results NGF continuously released from C/GP-NGF hydrogel in vitro. The recovery rate of vibrissae movement and the compound muscle action potentials of regenerated facial nerve in the C/GP-NGF group were similar to those in the Auto group, and significantly better than those in the NGF group. Furthermore, larger regenerated axons and thicker myelin sheaths were obtained in the C/GP-NGF group than those in the NGF group.

Facial nerve identification with fluorescent dye in rats.

PURPOSE The parotidectomy technique still has an elevated paresis and paralysis index, lowering patient life's quality. The correct identification of the facial nerve can prevent nerve damage. Fluorescent dye identifies nerves in experimental studies but only few articles focused its use on facial nerve study in parotidectomies. We aimed to stain the rat facial nerve with fluorescent dye to facilitate visualization and dissection in order to prevent injuries. METHODS Forty adult male Wistar rats were submitted to facial injection of saline solution (Gsf-control group, 10) or fluorescent dye solution (Gdye group, 30) followed by parotidectomy preserving the facial nerve, measuring the time for localization and facility of localization (LocTime and LFN). Nerve function was assessed using the Vibrissae Movements (PMV) and Eyelid Closure Motion (PFP) scores. RESULTS Nerve localization was faster in Gdye group, with 83% Easy LFN rate. The Gdye group presented with low nerve injury degree and better PMV and PFP scores, with high sensitivity and accuracy. CONCLUSIONS This experimental method of facial nerve fluorescence was effective for intraoperative nerve visualization, identification and preservation. The technique may be used in future facial nerve studies, translated to humans, contributing to the optimization of parotid surgery in the near future.

Evidence for a trigeminal mesencephalic-hypoglossal nuclei loop involved in controlling vibrissae movements in the rat.

Previous studies performed in rats showed that the whisker-pad motor innervation involves not only the facial nerve, but also some hypoglossal neurons whose axons travel within the trigeminal infraorbital nerve (ION) and target the extrinsic muscles surrounding the whisker-pad macrovibrissae. Furthermore, the electrical stimulation of the ION induced an increase in the EMG activity of these muscles, while the hypoglossal nucleus stimulation elicited evoked potentials and single motor unit responses. However, the existence of a neural network able to involve the XIIth nucleus in macrovibrissae whisking control was totally unknown until now. Since other recent experiments demonstrated that: (1) the mesencephalic trigeminal nucleus (Me5) neurons respond to both spontaneous and artificial movements of macrovibrissae, and (2) the Me5 peripheral terminals provide a monosynaptic sensory innervation to the macrovibrissae, the present study was aimed at analyzing a possible role of the Me5 nucleus as a relay station in the sensory-motor loop that involves the XIIth nucleus neurons in rhythmic whisking control. Two tracers were used in the same animal: Fluoro Gold, which was injected into the whisker pad to retrogradely label the hypoglossal whisker-pad projection neurons, and Dil, which was instead injected into the Me5 to label its projections to these hypoglossal neurons. Results demonstrated that terminals of the Me5 neurons monosynaptically target the hypoglossal whisker-pad projection neurons. The functional role of this sensory-motor connection is discussed, with particular regard to a hypothesized proprioceptive reflex in whisker-pad extrinsic muscles that can be elicited by the activation of the Me5 macrovibrissae receptors.

Juxtacellular Monitoring and Localization of Single Neurons within Sub-cortical Brain Structures of Alert, Head-restrained Rats.

There are a variety of techniques to monitor extracellular activity of single neuronal units. However, monitoring this activity from deep brain structures in behaving animals remains a technical challenge, especially if the structures must be targeted stereotaxically. This protocol describes convenient surgical and electrophysiological techniques that maintain the animal's head in the stereotaxic plane and unambiguously isolate the spiking activity of single neurons. The protocol combines head restraint of alert rodents, juxtacellular monitoring with micropipette electrodes, and iontophoretic dye injection to identify the neuron location in post-hoc histology. While each of these techniques is in itself well-established, the protocol focuses on the specifics of their combined use in a single experiment. These neurophysiological and neuroanatomical techniques are combined with behavioral monitoring. In the present example, the combined techniques are used to determine how self-generated vibrissa movements are encoded in the activity of neurons within the somatosensory thalamus. More generally, it is straightforward to adapt this protocol to monitor neuronal activity in conjunction with a variety of behavioral tasks in rats, mice, and other animals. Critically, the combination of these methods allows the experimenter to directly relate anatomically-identified neurophysiological signals to behavior.

A novel videographic method for quantitatively tracking vibrissal motor recovery following facial nerve injuries in rats

BackgroundPrevious studies of vibrissal movements employ either optoelectronic recording techniques in the head fixed rodent, or videographic recordings in freely moving animals. However, both approaches have shortcomings for quantitatively tracking the process of vibrissal motor recovery. New methodA critical feature of our videographic method is to measure tagged vibrissae movements while leaving all others intact in body restrained rats without head fixation. Thirty two adult rats underwent facial nerve manipulation and testing. All animals underwent baseline preoperative whisking testing. In the experimental groups, the right facial nerve was either crushed, or transected and sutured. In the control groups, the left facial nerve underwent either sham surgery, or transection denervation. Whisking function was measured for the ensuing 2 to 12 weeks. Data were analyzed for whisking recovery. ResultsBaseline preoperative whisking testing showed that majority of free whisking on the both sides is synchronous and symmetric, which allows us to compare vibrissal motor data between intact and manipulated side after facial nerve injury. As expected, the recovery of whisking function following crush is better and earlier than that with transection and suture. Comparison with existing method(s)To our knowledge, this novel videographic method is a significant simplification over currently employed optoelectronic recording techniques and videographic methods. ConclusionsOur novel videographic method may be a powerful tool to investigate motor recovery from facial nerve manipulation in the rat model.

Feedback in the brainstem: an excitatory disynaptic pathway for control of whisking.

Sensorimotor processing relies on hierarchical neuronal circuits to mediate sensory-driven behaviors. In the mouse vibrissa system, trigeminal brainstem circuits are thought to mediate the first stage of vibrissa scanning control via sensory feedback that provides reflexive protraction in response to stimulation. However, these circuits are not well defined. Here we describe a complete disynaptic sensory receptor-to-muscle circuit for positive feedback in vibrissa movement. We identified a novel region of trigeminal brainstem, spinal trigeminal nucleus pars muralis, which contains a class of vGluT2+ excitatory projection neurons involved in vibrissa motor control. Complementary single- and dual-labeling with traditional and virus tracers demonstrate that these neurons both receive primary inputs from vibrissa sensory afferent fibers and send monosynaptic connections to facial nucleus motoneurons that directly innervate vibrissa musculature. These anatomical results suggest a general role of disynaptic architecture in fast positive feedback for motor output that drives active sensation.

The effect of etanercept and methylprednisolone on functional recovery of the facial nerve after crush injury.

To establish whether etanercept, a TNF-α antagonist, is an alternative and effective treatment on facial nerve after crush injury. Fifty-four rats underwent exposure of the left main trunk of the facial nerve followed by a standard crush injury. Animals were randomly divided into 3 groups: control group, methylprednisolone-treated group, and etanercept-treated group. All these groups were divided into 2 subgroups; animals were sacrificed on the 4th day after facial crush injury in the first subgroup and on the 28th day in the second subgroup. Functional recovery of vibrissae movement, eye blink reflex, and vibrissae orientation was measured on a 3-point scale (1 = no recovery, 2 = partial recovery, and 3 = complete recovery) during the recovery process. Facial nerve, from the main trunk at the stylomastoid foramen to the zygomatic, buccal, and marginal branches, were dissected and postfixed in the same fixative. The paraffin sections were studied with macrophage marker, GAP-43 and T Cell Marker. Animals receiving etanercept demonstrated significantly better functional recovery compared with control and methylprednisolone-treated animals. The etanercept-treated group showed highest GAP-43 immunoreactivity in the nerves. After the macrophage marker and T cell marker staining, the etanercept and methylprednisolone groups demonstrated statistically significant difference compared with the control group (p < 0.001). The present study demonstrates accelerated functional recovery associated with etanercept treatment after facial nerve crush injury in rats.

Activation and measurement of free whisking in the lightly anesthetized rodent.

The rodent vibrissa system is a widely used experimental model of active sensation and motor control. Vibrissa-based touch in rodents involves stereotypic, rhythmic sweeping of the vibrissae as the animal explores its environment. Although pharmacologically induced rhythmic movements have long been used to understand the neural circuitry that underlies a variety of rhythmic behaviors, including locomotion, digestion and ingestion, these techniques have not been available for active sensory movements such as whisking. However, recent work that delineated the location of the central pattern generator for whisking has enabled pharmacological control over this behavior. Here we specify a protocol for the pharmacological induction of rhythmic vibrissa movements that mimic exploratory whisking. The rhythmic vibrissa movements are induced by local injection of a glutamatergic agonist, kainic acid. This protocol produces coordinated rhythmic vibrissa movements that are sustained for several hours in the anesthetized mouse or rat and thus provides unprecedented experimental control in studies related to vibrissa-based neuronal circuitry.

Effect of topical dexamethasone in reducing dysfunction after facial nerve crush injury in the rat

ObjectiveTo date, the effect of topical steroid after a crush injury to rat facial nerve has rarely been reported on. The aim of this study was to investigate the effects of topical dexamethasone on recovery after a crush injury to the rat facial nerve, by functional, electrophysiological, and morphological evaluation. Materials and methodsWe investigated the effects of topical dexamethasone on recovery after a crush injury to rat facial nerve by functional, electrophysiological and morphological evaluation. ResultsThe functional recovery using vibrissae movement was significantly high scores in the experimental group than control group at two and three weeks post-crush. The recovery of the threshold of muscle action potential was significantly lowered in the experimental group compared to the control (p<0.05). However, there was no statistical significance in the nerve conduction velocity. The dexamethasone treatment groups showed a larger axon diameter and thicker myelin sheath than the control group. ConclusionFrom our results, topical dexamethasone accelerates recovery of the crush-injured facial nerve.

Involvement of trigeminal mesencephalic nucleus in kinetic encoding of whisker movements

In previous experiments performed on anaesthetised rats, we demonstrated that whisking neurons responsive to spontaneous movement of the macrovibrissae are located within the trigeminal mesencephalic nucleus (Me5) and that retrograde tracers injected into the mystacial pad of the rat muzzle extensively labelled a number of Me5 neurons. In order to evaluate the electrophysiological characteristics of the Me5-whisker pad neural connection, the present study analysed the Me5 neurons responses to artificial whisking induced by electrical stimulation of the peripheral stump of the facial nerve. Furthermore, an anterograde tracer was injected into the Me5 to identify and localise the peripheral terminals of these neurons in the mystacial structures. The electrophysiological data demonstrated that artificial whisking induced Me5 evoked potentials as well as single and multiunit Me5 neurons responses consistent with a direct connection. Furthermore, the neuroanatomical findings showed that the peripheral terminals of the Me5 stained neurons established direct connections with the upper part of the macrovibrissae, at the conical body level, with fibres spiralling around the circumference of the vibrissae shaft. As for the functional role of this sensory innervation, we speculated that the Me5 neurons are possibly involved in encoding and relaying proprioceptive information related to vibrissae movements to other CNS structures.

Intracranial supramaximal facial nerve stimulation: A murine model

PurposeSupramaximal facial nerve stimulation is an applied current sufficient to evoke a maximal electromyographic response of facial musculature. It is used during cerebellopontine angle surgery for prognostication of postoperative nerve function. We utilized a rat model to examine safe parameters for intracranial electrical stimulation. Materials and methodsIntracranial facial nerve stimulation with electromyographic monitoring of 14 rats was performed. Supramaximal current level was determined and 50 additional pulses of supramaximal (4 rats), 3 times supramaximal (4), 10 times supramaximal (3), or zero (3) current were applied. To monitor progression of facial nerve injury, video recordings of vibrissae movements and eye closure were captured at 1, 3 and 28days after surgery; animals were sacrificed on day 28, when nerve morphometry was performed. ResultsOne rat in the supramaximal stimulation group (of 4), and one rat in the 10 times supramaximal stimulation group (of 3) demonstrated persistent impairment of facial nerve function as evidenced by decreased amplitude of vibrissae sweeping and eye closure impairment. The remainder of rats in all experimental groups demonstrated symmetric and normal facial nerve function at all time points. ConclusionsA novel animal model for supramaximal stimulation of the rat intracranial facial nerve is described. A small proportion of animals demonstrated functional evidence of nerve injury postoperatively. Function was preserved in some animals after stimulation with current order of magnitude higher than supramaximal levels. Further study with this model is necessary to definitively isolate the effects of surgical trauma from those of supramaximal electrical stimulation.

ReaChR: a red-shifted variant of channelrhodopsin enables deep transcranial optogenetic excitation

Channelrhodopsins are used to optogenetically depolarize neurons. We engineered a variant of channelrhodopsin, denoted Red-activatable Channelrhodopsin (ReaChR), that is optimally excited with orange to red light (λ ~ 590 to 630 nm) and offers improved membrane trafficking, higher photocurrents, and faster kinetics compared with existing red-shifted channelrhodopsins. Red light is more weakly scattered by tissue and absorbed less by blood than the blue to green wavelengths required by other channelrhodopsin variants. ReaChR expressed in vibrissa motor cortex was used to drive spiking and vibrissa motion in awake mice when excited with red light through intact skull. Precise vibrissa movements were evoked by expressing ReaChR in the facial motor nucleus in the brainstem and illuminating with red light through the external auditory canal. Thus, ReaChR enables transcranial optical activation of neurons in deep brain structures without the need to surgically thin the skull, form a transcranial window, or implant optical fibers.

Phenotypic characterization of orofacial movement topography in mutants with disruption of amino acid mechanisms: Glutamate N2A/B/D [GluRε1/2/4] subtypes and the GABA synthesizing enzyme GAD65

To investigate the role of glutamate receptor subtypes and GABA in orofacial function, six individual topographies of orofacial movement, both spontaneous and induced by the dopamine D1-like receptor agonist [R/S]-3-methyl-6-chloro-7,8-dihydroxy-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF 83959), were quantified in mutant mice with deletion of (a) GluN2A, B or D receptors, and (b) the GABA synthesizing enzyme, 65-kD isoform of glutamate decarboxylase (GAD65). In GluN2A mutants, habituation of head movements was disrupted and vibrissae movements were reduced, with an overall increase in locomotion; responsivity to SKF 83959 was unaltered. In GluN2B mutants, vertical and horizontal jaw movements and incisor chattering were increased, with an overall decrease in locomotion; under challenge with SKF 83959, head and vibrissae movements were reduced. In GluN2D mutants, horizontal jaw movements, incisor chattering and vibrissae movements were increased, with reduced tongue protrusions and no overall change in locomotion; under challenge with SKF 83959, horizontal jaw movements were increased. In GAD65 mutants, vertical jaw movements were increased, with disruption to habituation of locomotion; under challenge with SKF 83959, vertical and horizontal jaw movements and incisor chattering were decreased. Effects on orofacial movements differed from their effects on regulation of overall locomotor behavior. These findings (a) indicate novel, differential roles for GluN2A, B and D receptors and for GAD65-mediated GABA in the regulation of individual topographies of orofacial movement and (b) reveal how these roles differ from and/or interact with the established role of D1-like receptors in pattern generators and effectors for such movements.