Transcutaneous trigeminal nerve stimulation induces a long-term depression-like plasticity of the human blink reflex.

The beneficial effects of trigeminal nerve stimulation (TNS) on several neurological disorders are increasingly acknowledged. Hypothesized mechanisms include the modulation of excitability in networks involved by the disease, and its main site of action has been recently reported at brain stem level. Aim of this work was to test whether acute TNS modulates brain stem plasticity using the blink reflex (BR) as a model.

A comprehensive assessment of the cross-training effect in ankle dorsiflexors of healthy subjects: A randomized controlled study.

Purpose: To investigate the cross-training effect, induced on ankle dorsiflexors (AD) by unilateral strength-training of the contralateral muscles, as transfer of peak torque (PT) and muscle work (MW) and their relative contributions to muscle performance.

Methods: Thirty healthy volunteers were randomly assigned to a training or control group. The trained group sustained a 4-week maximal isokinetic training of the stronger AD at 90 and 45°/s.

Abnormalities of vestibular-evoked myogenic potentials in idiopathic Parkinson's disease are associated with clinical evidence of brainstem involvement.

Brainstem degeneration in Parkinson's disease (PD) may explain the occurrence of many non-motor symptoms in this condition. Purposes of the present work were to investigate brainstem function in PD through a battery of vestibular-evoked myogenic potentials (VEMP) allowing a comprehensive brainstem exploration and to correlate VEMP findings with symptoms related to brainstem involvement. Cervical (cVEMP), masseter (mVEMP) and ocular (oVEMP) VEMPs were investigated in 24 PD patients and compared with those recorded in 24 age-matched controls.

Exploring brainstem function in multiple sclerosis by combining brainstem reflexes, evoked potentials, clinical and MRI investigations.

Objective: To investigate vestibulo-masseteric (VMR), acoustic-masseteric (AMR), vestibulo-collic (VCR) and trigemino-collic (TCR) reflexes in patients with multiple sclerosis (MS); to relate abnormalities of brainstem reflexes (BSRs) to multimodal evoked potentials (EPs), clinical and Magnetic Resonance Imaging (MRI) findings.

Methods: Click-evoked VMR, AMR and VCR were recorded from active masseter and sternocleidomastoid muscles, respectively; TCR was recorded from active sternocleidomastoid muscles, following electrical stimulation of the infraorbital nerve. EPs and MRI were performed with standard techniques.

Reflex responses of masseter muscles to sound.

Acoustic stimuli can evoke reflex EMG responses (acoustic jaw reflex) in the masseter muscle. Although these were previously ascribed to activation of cochlear receptors, high intensity sound can also activate vestibular receptors. Since anatomical and physiological studies, both in animals and humans, have shown that masseter muscles are a target for vestibular inputs we have recently reassessed the vestibular contribution to masseter reflexes.

Effects of volitional contraction on intracortical inhibition and facilitation in the human motor cortex.

Short-interval intracortical inhibition (SICI), intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) were assessed in the cortical motor area of the first dorsal interosseous muscle (FDI) of 16 healthy subjects. Paired-pulse TMS was delivered to the left hemisphere at the following interstimulus intervals (ISIs): 2 and 3 ms for SICI, 10 and 15 ms for ICF and 1-5 ms for SICF. Motor-evoked potentials were recorded from the resting and active right FDI.

Intracortical modulation of cortical-bulbar responses for the masseter muscle.

Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated in the masseter muscles of 12 subjects and the cortical silent period (SP) in nine subjects. Motor evoked potentials (MEPs) were recorded from contralateral (cMM) and ipsilateral (iMM) masseters, activated at 10% of maximal voluntary contraction (MVC). Interstimulus intervals (ISIs) were 2 and 3 ms for SICI, 10 and 15 ms for ICF.

Origin of sound-evoked EMG responses in human masseter muscles.

Sound is a natural stimulus for both cochlear and saccular receptors. At high intensities it evokes in active masseter muscles of healthy subjects two overlapping reflexes: p11/n15 and p16/n21 waves, whose origin has not yet been demonstrated. Our purpose was to test which receptor in the inner ear is responsible for these reflexes.

A sound-evoked vestibulomasseteric reflex in healthy humans.

Averaged responses to loud clicks were recorded in the unrectified and rectified masseter electromyogram (EMG) of 18 healthy subjects. Unilateral clicks (0.1 ms, 3 Hz, 70-100 dB NHL), delivered during a steady masseter contraction, evoked bilateral responses that appeared to consist of 2 components on the basis of threshold, latency, and their appearance in rectified EMG.

Nitric oxide increases the spontaneous firing rate of rat medial vestibular nucleus neurons in vitro via a cyclic GMP-mediated PKG-independent mechanism.

The effects of nitric oxide (NO) on the discharge rate of medial vestibular nucleus neurons (MVNn) were investigated in rat brainstem slices. The NO-donor sodium nitroprusside (SNP, 200 microM) caused a marked enhancement (+36.7%) of MVNn spontaneous firing rate, which was prevented by the NO-scavenger, carboxy-PTIO (300 microM).

A short latency vestibulomasseteric reflex evoked by electrical stimulation over the mastoid in healthy humans.

We describe EMG responses recorded in active masseter muscles following unilateral and bilateral electrical vestibular stimulation (EVS, current pulses of 5 mA intensity, 2 ms duration, 3 Hz frequency). Averaged responses in unrectified masseter EMG induced by unilateral EVS were examined in 16 healthy subjects; effects induced by bilateral (transmastoid) stimulation were studied in 10 subjects. Results showed that unilateral as well as bilateral EVS induces bilaterally a clear biphasic response (onset latency ranging from 7.

Melatonin inhibits rat medial vestibular nucleus neuron activity in vitro.

The present study evaluated the effects of melatonin on the discharge rate of tonically active medial vestibular nucleus (MVN) neurons in an in vitro slice preparation of the rat dorsal brainstem. The results demonstrated that, when melatonin was applied to the slice for a period of 7-10 min, a decrease in MVN neuron firing rate was observed in 21/58 (36%) of the cells sampled. The inhibitory effects of melatonin were present in synaptic uncoupling condition and were mimicked by 2-iodomelatonin, a non-selective agonist with high affinity for melatonin membrane receptor subtypes (MT(1), MT(2), MT(3)).

Modulation of masseter exteroceptive suppression by non-nociceptive upper limb afferent activation in humans.

The effects induced by non-noxious electrical stimulation of upper limb nerves on exteroceptive suppression (ES) of masseter muscle EMG activity were studied in 15 healthy subjects. EMG activity of masseter muscles was recorded bilaterally and great care was taken to minimise the activation of afferents other than the stimulated ones. Masseter ES was elicited by applying a non-noxious electrical stimulus to the skin above the mental nerve (Mt) of one side, during a voluntary contraction of masseter muscles at a prescribed steady clenching level.

Non-nociceptive upper limb afferents modulate masseter muscle EMG activity in man.

Recent electrophysiological data obtained in anaesthetized rats evidenced jaw muscle excitatory responses to the electrical stimulation of type II limb somatosensory afferents. In the present work, we describe an inhibitory reflex evoked in human masseter muscles by stimulation of non-nociceptive fibres travelling in the median and radial nerves (MED and RAD, respectively). Eighteen healthy volunteers participated in the study.