Exteroceptive suppression patterns of masseter and temporalis muscles in central and peripheral headache disorders

Change in the second exteroceptive suppression period of the temporalis muscle during erenumab treatment

Comparative studies on the second exteroceptive suppression period (ES2) of the masseter or temporalis muscle in migraineurs and controls have provided conflicting results. As the interneurons responsible for ES2 are probably close to the trigeminal nucleus caudalis and receive afferents also from the anti-nociceptive system, the study of ES2 could provide information on neural circuits involved in migraine pathophysiology. The aim of this observational, pilot study was to assess whether erenumab treatment may affect the exteroceptive suppression reflex of the temporalis muscle activity in migraineurs. The exteroceptive suppression reflex of the temporalis muscle activity was previously studied in a small case series of three chronic female migraineurs and after 4 months of beneficial erenumab treatment, administered according to current clinical indications. There was a statistically significant decrease in ES2 latency (p-value 0.039) and duration (p-value 0.030) after treatment. The change observed in the temporalis ES2 during erenumab treatment indicates that ES2 may play some kind of role as a neurophysiological marker and that this monoclonal antibody can modulate the brainstem circuits involved in migraine pathophysiology, at least indirectly. Further studies are required to confirm this intriguing hypothesis.

Sensory Thresholds and Peripheral Nerve Responses in Chronic Tension-Type Headache and Neuropsychological Correlation

Chronic tension-type headache (CTTH) is a common disease with no fully defined pathophysiological processes. We designed a study to value electrophysiological responses in these patients and their correlation with possible psychopathological manifestations in order to deepen understanding of central and peripheral mechanisms of CTTH. In 40 patients with CTTH and 40 healthy controls, we used electrical stimulation to determine sensory threshold (SPT) and pain perception threshold (PPT) and the characteristics of the electrophysiological sensory nerve action potential (SNAP): initial sensory response (ISR) and supramaximal response (SMR). We then calculated the intensity differences between thresholds (IDT), namely SPT-PPT, ISR-SMR and SMR-PPT, and correlated these IDTs with psychological characteristics: trait and state anxiety, depression, and emotional regulation. The SPT, together with the ISR and SMR thresholds, were higher (p < 0.01) in CTTH patients. The SMR-PPT IDT was smaller and correlated with significantly higher indicators of depression, state and trait anxiety, and poorer cognitive reappraisal. CTTH patients have less capacity to recognize non-nociceptive sensory stimuli, greater tendency toward pain facilitation, and a poor central pain control requiring higher stimulation intensity thresholds to reach the start and the peak amplitude of the SNAP. This is consistent with relative hypoexcitability of the Aβ nerve fibers in distant regions from the site of pain, and therefore, it could be considered a generalized dysfunction with a focal expression. Pain facilitation is directly associated with psychological comorbidity.

Exteroceptive Suppression of Masseter Muscle Activity in Juvenile Migraineurs

The second exteroceptive suppression period (ES2) of masseter or temporalis muscle activity may be reduced in adults with chronic tension-type headache. In adults with migraine, ES2 was found normal or tended to be protracted. To date, no studies on exteroceptive suppression in children and adolescents with headaches have been published. We investigated the exteroceptive suppression of masseter muscle activity in 14 migraineurs and 19 controls between 6 and 18 years of age. It was elicited by electrical stimulation at the labial commissure. No differences were found regarding the first suppression period, but ES2 was significantly longer in the migraine group than in controls. The results of the migraine group suggest overactivity of the interneurons of the reflex loop due to impaired inhibitory control from superior antinociceptive systems already at the beginning of this headache disorder.

Pearls and pitfalls: electrophysiology for primary headaches

BACKGROUND

Primary headaches are functional neurological diseases characterized by a dynamic cyclic pattern over time (ictal/pre-/interictal). Electrophysiological recordings can non-invasively assess the activity of an underlying nervous structure or measure its response to various stimuli, and are therefore particularly appropriate for the study of primary headaches. Their interest, however, is chiefly pathophysiological, as interindividual, and to some extent intraindividual, variations preclude their use as diagnostic tools.

AIM OF THE WORK

This article will review the most important findings of electrophysiological studies in primary headache pathophysiology, especially migraine on which numerous studies have been published.

RESULTS

In migraine, the most reproducible hallmark is the interictal lack of neuronal habituation to the repetition of various types of sensory stimulations. The mechanism subtending this phenomenon remains uncertain, but it could be the consequence of a thalamocortical dysrythmia that results in a reduced cortical preactivation level. In tension-type headache as well as in cluster headache, there seems to be an impairment of central pain-controlling mechanisms but the studies are scarce and their outcomes are contradictory. The discrepancies between studies might be as a result of methodological differences as well as patients' dissimilarities, which are also discussed.

CONCLUSIONS AND PERSPECTIVES

Electrophysiology is complementary to functional neuroimaging and will undoubtedly remain an important tool in headache research. One of its upcoming applications is to help select neurostimulation techniques and protocols that correct best the functional abnormalities detectable in certain headache disorders.

Modulation of exteroceptive suppression periods in human jaw-closing muscles by subanaesthetic dose of propofol

Exteroceptive suppression (ES) periods in human jaw-closing muscles can be conditioned by a wide range of somatosensory stimuli and cognitive states. The aim of this study was to examine the effects of subanaesthetic doses of midazolam, ketamine and propofol on the short latency (ES1) and long latency (ES2) reflex in the jaw-closing muscles. First, we tried to evaluate the various methodological criteria for ES recording. We then examined the effect of subanaesthetic doses of midazolam (0·035 mg kg(-1)), ketamine (0·30 mg kg(-1)) and propofol (0·35 mg kg(-1)) on these reflexes of recording left masseter and temporalis muscle. ES duration did not differ greatly in the present study, recorded with the correct adjustment of stimulating and recording conditions. None of the subanaesthetic doses of the agents influenced ES1, and no significant effects on ES2 were observed with midazolam and ketamine. However, significant inhibitory change was observed in ES2 with propofol. ES2 is thought to be mediated by afferents, which descend in the spinal trigeminal tract and connect with a polysynaptic chain of excitatory interneurones located in the lateral reticular formation. Our observations indicate that propofol is uniquely effective not only through involvement of the gamma-aminobutyric acid type A receptor, but also through a range of other effects.

The second exteroceptive suppression is affected by psychophysiological factors

OBJECTIVE

The second exteroceptive suppression (ES2) is assumed to be an indicator of central antinociceptive processing, although some conflicting data have been produced. We examined the impact of experimentally induced psychophysiological conditions on the latency and duration of the ES2. Also, the association to the subjective evaluation of the painful electrical stimulation by which the ES2 is elicited was studied.

METHODS

ES2 was assessed in 46 healthy volunteers running through four experimentally induced psychophysiological conditions: stress, relaxation, depressed mood, and heterotopic pressure pain. Conditions were presented in a repeated measure design in permuted sequences. Ten stimulation-recording sequences per condition were averaged. ES2 parameters were compared to a baseline condition and correlated to subjective pain perception.

RESULTS

ES2 duration was found to be prolonged and ES2 latency to be shortened under the impact of relaxation and depressed mood. The subjective perception of the painful electrical stimulation was affected by the experimental conditions.

CONCLUSION

Data lend support to the hypothesis that the repeatedly observed limited stability of ES2 parameters might be caused by the variability of individual psychophysiological states. Against expectation, subjective pain perception is not systematically correlated with ES2 parameters. Thus it can be questioned whether the ES2 is directly associated with pain processing at all.

Tension-type headache: current research and clinical management

Tension-type headache (TTH) is the most common form of headache, and chronic tension-type headache (CTTH) is one of the most neglected and difficult types of headache to treat. The pathogenesis of TTH is multifactorial and varies between forms and individuals. Peripheral mechanisms (myofascial nociception) and central mechanisms (sensitisation and inadequate endogenous pain control) are intermingled: the former predominate in infrequent and frequent TTH, whereas the latter predominate in CTTH. Acute therapy is effective for episodes of TTH, whereas preventive treatment--which is indicated for frequent and chronic TTH--is, on average, not effective. For most patients with CTTH, the combination of drug therapies and non-drug therapies (such as relaxation and stress management techniques or physical therapies) is recommended. There is clearly an urgent need to improve the management of patients who are disabled by headache. This Review summarises the present knowledge on TTH and discusses some of its more problematic features.

Occlusal tooth wear in female F344/N rats with aging

OBJECTIVES

This study was conducted to ascertain whether laboratory rats are an adequate animal model for aging oral cavity research, especially on occlusal tooth wear (OTW), which progresses with aging and causes abnormal occlusions. Mastication has been reported to relate to cognition in the elderly. Thus, it is important to care for the oral cavity, especially in the frail elderly, for the maintenance of all-round quality of life. Adequate and appropriate animal models are essential for basic and clinical research on the oral cavity.

METHODS

Dried maxilla and mandible specimens from 98 young, aging or aged female F344/N rats were used.

RESULTS

The levels of OTW of all molars were monitored with aging. The molar tooth began to wear at 1-month old (M) and progressed rapidly till 12M. Subsequently, OTW progressed slowly till 30M, and then rapidly again after 35M.

CONCLUSIONS

This study showed that progress of OTW is well correlated with the entire life span of the rat, and suggested that the rat aged over 12M would be an adequate animal model for research on OTW in middle-aged and elderly people.

Effect of low-level clenching and subsequent muscle pain on exteroceptive suppression and resting muscle activity in human jaw muscles

OBJECTIVE

To investigate the effects of muscle fatigue induced by low-level isometric jaw-clenching and subsequent glutamate-evoked muscle pain on the exteroceptive suppression (ES) response and resting electromyographic (EMG) activities in human jaw muscles.

METHODS

The resting EMG activity and the ESs were recorded before (baseline), after low-level jaw-clenching (Post1), after subsequent glutamate or isotonic saline injections into the left masseter (Post2), and 60 min after the clenching (Post3) in 23 healthy volunteers.

RESULTS

The late ES (ES2) showed more inhibition at Post1 compared with baseline (P<0.05). It was less inhibited after both types of injections (Post2), and increased at Post3 again (P<0.05) with no significant difference between the glutamate and isotonic saline sessions. The resting EMG activity increased at Post1 and Post2 (P<0.05). The glutamate injection further increased the resting EMG activity in the injected muscle (P<0.01).

CONCLUSIONS

Muscle fatigue influences inhibitory reflex pathways in jaw-closing muscles and subsequent acute muscle pain potentiates the local increase in the resting EMG activity of the painful muscle.

SIGNIFICANCE

Muscle fatigue which can be observed in patients with oral dysfunctions may interact with nociceptive regulation and influence the clinical presentation of jaw symptoms and function.

Exteroceptive suppression of temporalis muscle activity in subjects with high and low aggression traits

STUDY AIM

There is evidence that the second exteroceptive suppression period of temporalis muscle activity (ES2) is modulated by the 5-HT neuronal activity in the brainstem, and the aggression trait is also connected with the cerebral 5-HT neuronal innervation. We therefore studied the temporalis ES2 in subjects with high and low aggression traits.

METHODS

Sixty-five subjects with either low or high aggression trends, judged by clinical interview, answered the Zuckerman-Kuhlman Personality Questionnaire (ZKPQ), the Zuckerman Sensation Seeking Scales (SSS) and the Plutchik-van Praag Depression Inventory (PVP). These also underwent a temporalis ES2 test procedure. Twenty-two subjects with a high ZKPQ aggression trait score and 27 with a low score were selected for data analysis.

RESULTS

On average, the high aggression group displayed significantly reduced temporalis ES2 duration, elevated ZKPQ Impulsive Sensation Seeking, Neuroticism-Anxiety and Aggression-Hostility, and PVP scores. The personality traits were not related with either latency or duration of temporalis ES2 in any group. The PVP score, however, was negatively correlated with ES2 duration in all 49 subjects.

CONCLUSIONS

This study demonstrates neurophysiologic signs of brainstem dysfunction in subjects with high aggression traits.

Impairment of pain inhibition in chronic tension-type headache

Evidence has been accumulated suggesting that a dysfunction in pain inhibitory systems, i.e. in 'diffuse noxious inhibitory controls' (DNIC)-like mechanisms, might be-amongst other factors-responsible for the development of anatomically generalized chronic pain like fibromyalgia. The aim of the present study was to look for similar impairments in chronic tension-type headache (CTTH) as a regionally specific pain syndrome. Twenty-nine CTTH patients and 25 age- and sex-matched healthy control subjects participated in the study. After baseline assessment of electrical detection and pain thresholds, tonic heat stimuli were concurrently applied by a thermode to the thigh to induce DNIC-like pain inhibition. Tonic heat stimuli were applied either slightly above ('pain' condition) or slightly below ('heat' condition) pain threshold. For determination of electrical detection and pain thresholds, electrocutaneous stimuli were administered either to the forearm (extra-cranial site) or to the temple (cranial site), using a multiple staircase procedure. The increase in the electrical detection and pain thresholds induced by concurrent tonic heat stimulation was significantly smaller in the CTTH patients than in the control subjects. This group difference was present during the 'pain' as well as the 'heat' condition. Furthermore, the electrical detection and pain thresholds were affected in this group-specific manner both at the forearm and at the temple. These findings suggest that patients with CTTH suffer from deficient DNIC-like pain inhibitory mechanisms in a similar manner, as do patients with anatomically generalized chronic pain like fibromyalgia.

Cutaneous silent periods of the vastus medialis evoked by the stimulation of lateral femoral cutaneous nerve

OBJECTIVE

Cutaneous silent period (CSP), which is a spinal reflex mediated by A-delta cutaneous afferents, is transient suppression of the electromyographic activity. In this study, our aim is to investigate CSPs of vastus medialis muscle (vm-CSP) evoked by the stimulation of the lateral femoral cutaneous nerve (LFCN) in healthy controls and in patients with meralgia paresthetica (MP).

METHODS

Twenty-one patients with MP (17 unilateral, 4 bilateral) and 27 healthy controls were included. Nerve conduction studies of LFCN and vm-CSP were analyzed in all subjects. A stimulus train consisting of five electrical shocks was applied to the skin at the anterolateral side of the thigh for recording of the vm-CSP.

RESULTS

Nerve conduction abnormalities of LFCN were observed in all patients with MP. Mean duration of vm-CSP was 69.7+/-9.2ms, and mean onset latency was 44.7+/-6.9 in healthy controls. Onset latency of vm-CSP was significantly prolonged and the duration of vm-CSP was significantly shortened in patients with MP. Vm-CSP abnormalities were observed in 20/25 extremities with MP.

CONCLUSIONS

Dysfunction of A-delta afferents may cause these findings in patients with MP. Additionally, spinal modulation of pain may also play a role in the explanation of our findings.

SIGNIFICANCE

The present study demonstrates the CSP alterations in the patients with entrapment neuropathy of a cutaneous nerve.