Excitability Of Facial Motoneurons Research Articles

Trigeminal afferent input alters the excitability of facial motoneurons in hemifacial spasm.

To investigate whether skin or muscle afferent input via the trigeminal nerve alters the excitability of facial motoneurons in hemifacial spasm (HFS). Botulinum toxin type A (BTX) was injected only to the orbicularis oculi (O. oculi) muscle of 21 patients with idiopathic HFS, and the excitability of the orbicularis oris (O. oris) motoneurons was monitored. The synkinetic response (SR) of the blink reflex and abnormal muscle response (AMR) were recorded from the O. oris before and after treatment. BTX injections produced marked to moderate improvement in the O. oculi of all 21 patients and in the O. oris of 17 (81%). The rectified areas of SR1 and SR2 were smaller after treatment. In particular, the AMR area showed a reduction (p = 0.02). The significant lessening of spasms in the O. oris after BTX injection to the O. oculi and the concomitant reduction in excitability of O. oris neurons are consistent with the hypothesis that in HFS, skin or muscle afferent volleys via the trigeminal nerve enhance the excitability of facial nerve motoneurons.

Movement disorders in patients with peripheral facial palsy.

Acute unilateral facial paralysis is usually a benign neurological condition that resolves in a few weeks. However, it can also be the source of a transient or long-lasting severe motor dysfunction, featuring disorders of automatic and voluntary movement. This review is organized according to the two most easily recognizable phases in the evolution of facial paralysis: (1). Just after presentation of facial palsy, patients may exhibit an increase in their spontaneous blinking rate as well as a sustained low-level contraction of the muscles of the nonparalyzed side, occasionally leading to blepharospasm-like muscle activity. This finding may be due to an increase in the excitability of facial motoneurons and brainstem interneurons mediating trigeminofacial reflexes. (2). If axonal damage has occurred, axonal regeneration beginning at approximately 3 months after the lesion leads inevitably to clinically evident or subclinical hyperactivity of the previously paralyzed hemifacial muscles. The full-blown postparalytic facial syndrome consists of synkinesis, myokymia, and unwanted hemifacial mass contractions accompanying normal facial movements. The syndrome has probably multiple pathophysiological mechanisms, including abnormal axonal branching after aberrant axonal regeneration and enhanced facial motoneuronal excitability. Although the syndrome is relieved with local injections of botulinum toxin, fear of such uncomfortable contractions may lead the patients to avoid certain facial movements, with the implications that this behavior might have on their emotional expressions.

Reflex excitability of facial motoneurons at onset of muscle reinnervation after facial nerve palsy.

We studied 18 patients with complete unilateral denervation of the facial muscles after idiopathic facial nerve palsy to determine whether motoneuronal excitability is enhanced in the few motor units that are active at onset of muscle reinnervation. The study was carried out between 75 and 90 days after the facial nerve lesion. We used two needle electrodes to record simultaneously the spontaneous and voluntary activity of the orbicularis oris (OOris) and orbicularis oculi (OOculi) muscles, as well as the responses to ipsilateral and contralateral facial and supraorbital nerve stimuli. All patients showed involuntary firing of motor unit action potentials (MUAPs) in at least one of the muscles. Synkinetic activation of motor units in the OOris was induced by spontaneous blinking in all patients, and by inhalation and swallowing in some. Electrical stimulation of the ipsilateral facial nerve induced a direct M response in only 4 patients. In contrast, long-latency reflex responses were induced in both muscles by electrical stimulation of ipsilateral and contralateral facial and supraorbital nerves in all patients, at latencies ranging between 44 and 132 ms. The shape of such MUAP reflex responses was the same as that of the MUAPs seen to fire at rest. These findings provide evidence of enhanced excitability of facial motoneurons in our patients. Such hyperexcitability may be partly responsible for the postparalytic motor dysfunction syndrome that occurs after facial palsy with severe axonal damage.

Electromyography and recovery of the blink reflex in involuntary eyelid closure: a comparative study.

Electromyographic (EMG) activity of orbicularis oculi and levator palpebrae muscles was recorded to study the origin of involuntary eyelid closure in 33 patients. The evoked blink reflex in all patients and in 23 controls was also studied. To examine the excitability of facial motoneurons and bulbar interneurons in individual patients and to compare the results with EMG findings, R1 and R2 recovery indices were calculated in all subjects, as the average of recovery values at 0.5, 0.3, and 0.21 second interstimulus intervals. Based on EMG patterns, the patients were divided into three subclasses: EMG subclass 1, 10 patients with involuntary discharges solely in orbicularis oculi muscle; EMG subclass 2, 20 patients with involuntary discharges in orbicularis oculi and either involuntary levator palpebrae inhibition or a disturbed reciprocal innervation between orbicularis oculi and levator palpebrae; EMG subclass 3, three patients who did not have blepharospasm, but had involuntary levator palpebrae inhibition in association with a basal ganglia disease. The total patient group showed an enhanced recovery of both R1 and R2 components compared with controls. Although 30 out of 33 patients had blepharospasm (EMG subclasses 1 and 2), R1 recovery index was normal in 64% and R2 recovery index was normal in 54%. Patients with an abnormal R2 recovery index had an abnormal R1 recovery index significantly more often. All patients from EMG subclass 1 had an abnormal R2 recovery index, whereas all patients from EMG subclass 3 had normal recovery indices for both R1 and R2 responses. Seventy five per cent of the patients from EMG subclass 2 had normal recovery indices. The results provide further evidence that physiologically blepharospasm is not a homogeneous disease entity, and indicate that different pathophysiological mechanisms at the suprasegmental, or segmental level, or both are involved.

Orbicularis oculi responses to stimulation of nerve afferents from upper and lower limbs in normal humans

A brief mechanical or electrical stimulus to peripheral nerve afferents from the upper and lower limbs elicited a small and inconsistent EMG response of the orbicularis oculi muscles. This response was facilitated when the stimuli were delivered at fixed leading time intervals, of 45–300 ms, with respect to a supraorbital nerve electrical stimulus. Also, the peripheral nerve stimulus modified the conventional blink reflex responses, inducing facilitation of R1 and inhibition of R2. These results suggest a complex processing of sensory inputs from the face and the limbs at the brainstem, where they are probably integrated in a network of interneurons influencing the excitability of facial motoneurons.

Vasopressin generates a persistent voltage-dependent sodium current in a mammalian motoneuron

During the period of life that precedes weaning, the facial nucleus of the newborn rat is rich in 3H-vasopressin binding sites, and exogenous arginine vasopressin (AVP) can excite facial motoneurons by interacting with V1 (vasopressor-type) receptors. We have investigated the mode of action of this peptide by carrying out single-electrode voltage-clamp recordings in coronal brainstem slices from the neonate. Facial motoneurons were identified by antidromic invasion following electrical stimulation of the genu of the facial nerve. When the membrane potential was held at or near its resting level, vasopressin generated an inward current whose magnitude was concentration related; the lowest peptide concentration still effective in eliciting this effect was 10 nM. The vasopressin-induced current, IAVP, was resistant to tetrodotoxin (TTX) and was insensitive to a reduction in extracellular calcium concentration. It was sustained, was inward at all potentials tested (-120 to -25 mV), and increased in magnitude during depolarization. IAVP was not generated by the blockade of a potassium current, because it did not reverse at hyperpolarized potentials, was not affected by a two-fold increase in the transmembrane potassium gradient, and was not modified by the potassium channel blockers tetraethylammonium bromide (TEA), 4-aminopyridin (4-AP), barium, cesium, quinine, glibenclamide, and apamin. Also, IAVP was not affected by changes in the transmembrane chloride gradient. In contrast, it could be reduced by partially substituting extracellular sodium with equimolar N-methyl-D-glucamine or Tris. Our results suggest that vasopressin increases the excitability of facial motoneurons by generating a persistent sodium-dependent membrane current that is voltage gated and TTX resistant.

Enhanced excitability of facial motoneurons in post-paralytic facial synkinesis

Enhanced excitability of facial motoneurons in post-paralytic facial synkinesis

Long-term increases in excitability of facial motoneurons and other neurons in and near the facial nuclei after presentations of stimuli leading to acquisition of a pavlovian conditioned facial movement

Levels of neuronal excitability to injected current were measured intracellularly in facial motoneurons and other neurons in and near the facial nuclei of three groups of awake cats: (1) a “Conditioned” group consisting of animals that had previously received sufficient numbers of paired presentations of click CSs and glabella tap USs to produce eyeblink CRs; (2) a “US-only” group that had received presentations of the USs only; and (3) a “Naive” group that had received neither of these stimuli. Thresholds of intracellularly applied, depolarizing pulse currents required to elicit repeatable spike activity were significantly lower in the “Conditioned” and “US-only” groups than in the “Naive” group. The increased levels of neuronal excitability were correlated with increases in neuronal input resistance. Levels of neuronal excitability remained elevated when measured more than a month after presentations of both CSs and USs, whereas the increases in neuronal excitability decayed within a few weeks in animals given USs only. The increases in neuronal excitability and input resistance following repetitive presentations of glabella tap USs alone appeared to support a latent facilitation of motor performance reflected by an absence of a blink CR to click CS after such presentations but an increased rate of acquisition of subsequent eyeblink conditioning using paired click CS and tap US. The rate of eyeblink conditioning was found to be accelerated in a group of cats given repetitive presentations of tap USs seven days prior to conditioning with paired CSs and USs, compared to a group that was not given USs or CSs before similar conditioning. These findings provide direct, in vivo evidence that increases in the excitability and input resistance of neurons in and near the facial nucleus can occur in cats following presentations of the stimuli used for conditioning.

Intracellular studies on the effects of systemic administration of serotonin agonists on rat facial motoneurons

Intracellular recordings were made from facial motoneurons of anesthetized rats during systemitic administration of 5-methoxy-N,N-dimethyltryptamine N-dimethyltryptamine (5-MeODMT) and p-chloroamphetamine (PCA), drugs which elicit the behavioral serotonin syndrome. Both drugs caused a slow depolarization, increased input resistance, and increased excitability of facial motoneurons. These changes are identical to those caused by direct microiontophoretic application of serotonin to these neurons, and probably underlie some of the components of the behavioral serotonin syndrome.

Serotonergic synaptic input to facial motoneurons: localization by electronmicroscopic autoradiography

Serotonergic nerve terminals in the facial motor nucleus were labelled with [ 3H]5-hydroxy-tryptamine. When serotonergic nerve terminals were destroyed (by the selective neurotoxin 5,7-dihydroxytryptamine) the labelling was lost. By electron-microscopic autoradiography, labelled serotonergic terminals were found to make axo-dendritic or axo-somatic junctions with facial motor neurons. No axo-axonic junctions were observed. These morphological findings are consistent with physiological studies which indicate that 5-hydroxy-tryptamine facilitates the excitation of facial motoneurons through a direct postsynaptic action.

Intracellular determination of membrane potential of trigeminal motoneurons during sleep and wakefulness.

Intracellular determination of membrane potential of trigeminal motoneurons during sleep and wakefulness.

Hallucinogens potentiate responses to serotonin and norepinephrine in the facial motor nucleus

The present investigation was designed to determine the effect of hallucinogens on the facilitating action of serotonin (5-HT) and norepinephrine (NE) in the facial nucleus. Intravenous administration of d-lysergic acid diethylamide (LSD, 5–10 μg/kg), mescaline (0.5–1.0 mg/kg), or psilocin (0.5–1.0 mg/kg) had no effect by themselves on the glutamate-induced excitation of facial motoneurons. In contrast, the facilitation of facial neuron excitation by iontophoretically applied 5-HT and NE was enhanced 6–10 fold by these hallucinogens. The LSD-enhanced responses to 5-HT and NE continued for at least 4 hours after administration of the hallucinogen. Iontophoretic application of LSD or mescaline (low currents) also markedly potentiated the facilitating effect of 5-HT and NE. Higher currents of LSD (15–40 nA) temporarily antagonized the response to 5-HT. The nonhallucinogen ergot derivatives lisuride and methysergide failed to potentiate the facilitating effects of 5-HT or NE. These observations suggest that hallucinogens potentiate the effect of monoamines on facial motoneurons by increasing the sensitivity of 5-HT and NE receptors. A novel mechanism regarding the psychedelic effects of hallucinogens is discussed.

Effects of orbital cortical stimulation on facial motoneurons in the cat

Effects of orbital cortical stimulation on the excitability of facial motoneurons were examined in the cat by means of extracellular and intracellular recording techniques. Orbital cortical stimulation induced prolonged changes in the infraorbital facial reflex; an initial phase of facilitation was followed by long-lasting suppression. Cortical effect with the same time course was observed on the antidromic field potential of the facial nucleus. After orbital cortical stimulation, 64.2% of facial motoneurons showed an initial excitatory postsynaptic potential followed by a prolonged hyperpolarizing potential. Both antidromically and orthodromically induced spikes in these cells were facilitated or suppressed, respectively, during the depolarizing or hyperpolarizing phase induced in the motoneurons by stimulating the orbital cortex. The facilitatory or inhibitory effect of cortical stimulation on the infraorbital facial reflex and the antidromic field potential of the facial nucleus showed a close temporal correlation with the cortically induced depolarizing or hyperpolarizing postsynaptic potential in facial motoneurons.

Effect of lesions of cortical motor areas on acquisition of conditioned eye blink in the cat.

Effect of lesions of cortical motor areas on acquisition of conditioned eye blink in the cat.C Woody, P Yarowsky, J Owens, P Black-Cleworth, and T CrowC Woody, P Yarowsky, J Owens, P Black-Cleworth, and T CrowPublished Online:01 May 1974https://doi.org/10.1152/jn.1974.37.3.385MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByIntracellularly recorded responses of neurons of the motor cortex of awake cats to presentations of Pavlovian conditioned and unconditioned stimuliBrain Research, Vol. 969, No. 1-2Electrical properties affecting discharge of units of the mid and posterolateral thalamus of conscious catsNeuroscience, Vol. 122, No. 2Learning- and Expectation-Related Changes in the Human Brain During Motor LearningN. Ramnani, I. Toni, O. Josephs, J. Ashburner, and R. E. Passingham1 December 2000 | Journal of Neurophysiology, Vol. 84, No. 6Neuronal activity in the motor and premotor cortices before and after learning the associations between auditory stimuli and motor responsesBrain Research, Vol. 611, No. 1Changes in membrane currents during Pavlovian conditioning of single cortical neuronsBrain Research, Vol. 539, No. 1Pavlovian conditioning of discriminatively elicited eyeblink responses with short onset latency attributable to lengthened interstimulus intervalsBrain Research, Vol. 400, No. 1Intracellular injection of cGMP-dependent protein kinase results in increased input resistance in neurons of the mammalian motor cortexBrain Research, Vol. 386, No. 1-2Long-term increases in excitability of facial motoneurons and other neurons in and near the facial nuclei after presentations of stimuli leading to acquisition of a pavlovian conditioned facial movementNeuroscience Research, Vol. 3, No. 6Responses of morphologically identified cortical neurons to intracellularly injected cyclic GMPExperimental Neurology, Vol. 91, No. 3Classical conditioning of the nictitating membrane response of the rabbitExperimental Brain Research, Vol. 60, No. 1Two different mechanisms control inhibition of spike discharge in neurons of cat motor cortex after stimulation of the pyramidal tractBrain Research, Vol. 332, No. 2Depolarization-induced effects of Ca2+-calmodulin-dependent protein kinase injection, in vivo, in single neurons of cat motor cortexBrain Research, Vol. 321, No. 1Neuronal substrates of simple associative learning: classical conditioningTrends in Neurosciences, Vol. 6A conditioned eyeblink obtained by using electrical stimulation of the facial nerve as the unconditioned stimulusBrain Research, Vol. 90, No. 1 More from this issue > Volume 37Issue 3May 1974Pages 385-94 https://doi.org/10.1152/jn.1974.37.3.385PubMed4827016History Published online 1 May 1974 Published in print 1 May 1974 Metrics

Differences in excitability of cortical neurons as a function of motor projection in conditioned cats.

Differences in excitability of cortical neurons as a function of motor projection in conditioned cats.

Monosynaptic excitation of facial motoneurons during electrical stimulation of the red nucleus

Synaptic effects of the red nucleus on motoneurons of the facial nucleus were studied in cats. Impulses from the red nucleus activate motoneurons innervating the auricular, buccal, and orbicularis oculi muscles. Monosynaptic EPSPs appeared in all motoneurons which responded to stimulation. Their mean latent period was 1.5±0.04 msec, duration 12.3 ± 0.34 msec, and rise time between 1.5 and 3.2 msec. Repetitive stimulation of the red nucleus led to marked facilitation of the testing EPSP. Facilitation was maximal when the interval between stimuli was 3.5 msec; it was reduced by either a decrease or an increase in the interval. The functional role of the monosynaptic connections of neurons of the red nucleus and of the facial motoneurons is discussed.

Analysis of facial reflex facilitation and inhibition by microelectrode recording from the brain stem.

AbstractThe response in the facial nucleus to stimulation of peripheral facial and trigeminal nerve branches is described. After antidromic invasion the excitability of facial motoneurons was lowered for up to 30 ms before as well as after intravenous injections of strychnine. The depression following antidromic stimuli is thus not caused by postsynaptic inhibition of the Renshaw type but rather by positive afterpotentials in the motoneurons. Synaptic activation by tap stimulation of the face led to increased motoneuron excitability setting in after a latency of 3 ms and lasting for 30 ms. This was followed by a lowered excitability lasting for an additional period of 65 ms. The period of depression was presumed to be due to postsynaptic inhibition of motoneurons. The changes of the excitability of facial motoneurons following synaptic activation explain in part previously observed effects of conditioning afferent stimuli on facial reflexes.‐Responses to electrical stimulation of facial and hypoglossal nerve afferents were recorded from reticular neurons. These neurons responded to single stimuli with a repetitive high‐frequency discharge related to the stimulus strength and could respond to an afferent inflow from large areas of the body and limbs. It is discussed whether these reticular neurons may be interneurons in a system exerting inhibitory control of facial muscle reflexes.

Conditioned eye blink using electrical stimulation of coronal-precruciate cortex as conditional stimulus.

Conditioned eye blink using electrical stimulation of coronal-precruciate cortex as conditional stimulus.C D Woody, and P J YarowskyC D Woody, and P J YarowskyPublished Online:01 Mar 1972https://doi.org/10.1152/jn.1972.35.2.242MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByIntracellularly recorded responses of neurons of the motor cortex of awake cats to presentations of Pavlovian conditioned and unconditioned stimuliBrain Research, Vol. 969, No. 1-2Local adaptations of two naturally occurring neuronal conductances, gK+(A) and gK+(Ca), allow for associative conditioning and contiguity judgements in artificial neural networksBiological Cybernetics, Vol. 66, No. 1Changes in membrane currents during Pavlovian conditioning of single cortical neuronsBrain Research, Vol. 539, No. 1Long-term increases in excitability of facial motoneurons and other neurons in and near the facial nuclei after presentations of stimuli leading to acquisition of a pavlovian conditioned facial movementNeuroscience Research, Vol. 3, No. 6Effects of acetylcholine and cyclic GMP on input resistance of cortical neurons in awake catsBrain Research, Vol. 158, No. 2 More from this issue > Volume 35Issue 2March 1972Pages 242-52 https://doi.org/10.1152/jn.1972.35.2.242PubMed5028661History Published online 1 March 1972 Published in print 1 March 1972 Metrics

Changes in evoked responses from facial nucleus of cat with conditioning and extinction of an eye blink.

Changes in evoked responses from facial nucleus of cat with conditioning and extinction of an eye blink.C D Woody, and G BrozekC D Woody, and G BrozekPublished Online:01 Sep 1969https://doi.org/10.1152/jn.1969.32.5.717MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByIntracellularly recorded responses of neurons of the motor cortex of awake cats to presentations of Pavlovian conditioned and unconditioned stimuliBrain Research, Vol. 969, No. 1-2Learning- and Expectation-Related Changes in the Human Brain During Motor LearningN. Ramnani, I. Toni, O. Josephs, J. Ashburner, and R. E. Passingham1 December 2000 | Journal of Neurophysiology, Vol. 84, No. 6Reverse Effects of Conditioning Produced by Two Different Unconditioned Stimuli on Thalamocortical TransmissionEl Mehdi Meftah, and Lucie Rispal-Padel1 April 1997 | Journal of Neurophysiology, Vol. 77, No. 4A system for quantitative analysis of associative learning. Part 1. Hardware interfaces with cross-species applicationsJournal of Neuroscience Methods, Vol. 54, No. 1Long-term habituation of the acoustic startle response: Role of the cerebellar vermisNeuroscience, Vol. 35, No. 1Long-term increases in excitability of facial motoneurons and other neurons in and near the facial nuclei after presentations of stimuli leading to acquisition of a pavlovian conditioned facial movementNeuroscience Research, Vol. 3, No. 6Depolarization-induced effects of Ca2+-calmodulin-dependent protein kinase injection, in vivo, in single neurons of cat motor cortexBrain Research, Vol. 321, No. 1Mechanisms regulating the activity of facial nucleus motoneurones—1. Antidromic activationNeuroscience, Vol. 9, No. 4Neuronal responses of the rabbit brainstem during performance of the classically conditioned nictitating membrane (NM)/eyelid responseBrain Research, Vol. 271, No. 1Concomitant classical conditioning of the rabbit nictitating membrane and eyelid responses: Correlations and implicationsPhysiology & Behavior, Vol. 28, No. 5Differentiated short latency response increases after conditioning in inferior colliculus neurons of alert ratBrain Research, Vol. 130, No. 2A conditioned eyeblink obtained by using electrical stimulation of the facial nerve as the unconditioned stimulusBrain Research, Vol. 90, No. 1Classical eyeblink conditioning in the bilaterally hemispherectomized catExperimental Neurology, Vol. 44, No. 3Cortical representation of conditioned eye blink in the rabbit studied by a functional ablation techniqueBrain Research, Vol. 40, No. 2 More from this issue > Volume 32Issue 5September 1969Pages 717-25 https://doi.org/10.1152/jn.1969.32.5.717PubMed4309025History Published online 1 September 1969 Published in print 1 September 1969 Metrics