Ultrastructural evaluation of calcitonin gene-related peptide immunoreactivity in the human cochlea and vestibular endorgans

Trigeminal cervical complex: A neural network affecting the head and neck

OBJECTIVES

To introduce the trigeminal cervical complex (TCC) as a comprehensive framework for understanding the anatomical and functional scope of the afferences and efferences of the trigeminal nerve and explaining common otolaryngologic symptoms, including head and neck myofascial pain syndrome. Additionally, it explores how the bidirectional transmission of neurotransmitters contributes to the sensitization of the TCC and motor nuclei.

METHODS

The study was conducted as a narrative review. The authors performed a comprehensive search of multiple databases, including Medline/OVID, Embase, Scopus, and PubMed, covering publications from inception until August 2023. Both keywords and medical subject headings related to the TCC were utilized in the search. Information from 66 studies was extracted based on predetermined inclusion and exclusion criteria.

RESULTS

This review discusses the multiple afferent connections from cranial nerves, specifically VII, IX, X, and XI, to the TCC, and their respective efferent pathways. These connections may explain various clinical manifestations in the head and neck that cannot be attributed to other medical conditions. Additionally, the review highlights the dual sensory and motor nature of cranial nerves, emphasizing the bidirectional transmission of neurotransmitters in head and neck areas, which leads to the sensitization of both the TCC and motor nuclei innervating the cervicofacial muscles.

CONCLUSION

The authors hypothesize that the central and peripheral sensitization and the intricate connections of the TCC can elucidate the pathophysiology of conditions such as otalgia, tinnitus, hearing loss, vertigo, headache, cervicogenic dizziness, bruxism, and other symptoms affecting the head and neck.

Adverse event profile of CGRP monoclonal antibodies: findings from the FDA adverse event reporting database

BACKGROUND

Four CGRP Monoclonal Antibodies (mAbs) have been approved for migraine prophylaxis by the Food and Drug Administration (FDA) since 2018. However, there are concerns about the safety of these four drugs for real-world use.

OBJECTIVE

To compare the adverse event profiles of four CGRP-mAbs with FAERS data.

METHODS

The study was based on records from the FAERS database. Only reports containing one of the active ingredients with CGRP-mAbs were included in this study. Disproportionality analyses including but not limited to reporting odds ratio (ROR) and information components (IC) were conducted to identify drug-AE associations.

RESULTS

In total, 58110 reports were identified for CGRP-mAbs. 80 overlapping signals were disproportionately reported. They affected a range of organs and systems, including the gastrointestinal and cardiovascular systems, skin, and hair. Additionally, the rare cardiovascular adverse events were significantly different among the four CGRP-mAbs.

CONCLUSION

We identified numerous shared underlying signals (overlapping signals) for CGRP-mAbs as suspected drugs in multiple systems and organs. The unlabeled common signals may indicate potential safety issues. In addition, the underlying safety signals varied among the four CGRP-mAbs, particularly in the cardiovascular system, and further studies are needed to confirm these associations and the potential clinical implications.

Will Vestibular Migraine Pathology Lead to Ischemic Changes in Brain Tissue in Later Age?

Migraine has been considered to be an episodic, multifactorial, neurovascular disorder without long-term consequences to the brain, although numerous studies have shown a possible association between vestibular migraine and ischemic changes in the brain. 3 Case based scenarios of previously diagnosed patients with vestibular migraine on treatment, associated  with clinical changes of ischemia, infarction and white matter lesions are reviewed and integrated with the results based on MRI study. There is a need for proper diagnosis to address the complaints and manage symptoms during acute attacks of vestibular migraine and prophylaxis. In addition these cases highlight the ongoing need for proper systemic evaluation, therapeutic management, regular follow up, compliance of medication and life style modification. Pathological sequelae of long standing vestibular migraine are ischemic changes of the brain tissue, which requires further evaluation and extensive study of these symptom complexes.

Effects of Calcitonin-Gene-Related-Peptide on Auditory Nerve Activity

Calcitonin-gene-related peptide (CGRP) is a lateral olivocochlear (LOC) efferent neurotransmitter. Depression of sound-driven auditory brainstem response amplitude in CGRP-null mice suggests the potential for endogenous CGRP release to upregulate spontaneous and/or sound-driven auditory nerve (AN) activity. We chronically infused CGRP into the guinea pig cochlea and evaluated changes in AN activity as well as outer hair cell (OHC) function. The amplitude of both round window noise (a measure of ensemble spontaneous activity) and the synchronous whole-nerve response to sound (compound action potential, CAP) were enhanced. Lack of change in both onset adaptation and steady state amplitude of sound-evoked distortion product otoacoustic emission (DPOAE) responses indicated CGRP had no effect on OHCs, suggesting the origin of the observed changes was neural. Combined with results from the CGRP-null mice, these results appear to confirm that endogenous CGRP enhances auditory nerve activity when released by the LOC neurons. However, infusion of the CGRP receptor antagonist CGRP (8–37) did not reliably influence spontaneous or sound-driven AN activity, or OHC function, results that contrast with the decreased ABR amplitude measured in CGRP-null mice.

Diverse identities and sites of action of cochlear neurotransmitters

Accurate encoding of acoustic stimuli requires temporally precise responses to sound integrated with cellular mechanisms that encode the complexity of stimuli over varying timescales and orders of magnitude of intensity. Sound in mammals is initially encoded in the cochlea, the peripheral hearing organ, which contains functionally specialized cells (including hair cells, afferent and efferent neurons, and a multitude of supporting cells) to allow faithful acoustic perception. To accomplish the demanding physiological requirements of hearing, the cochlea has developed synaptic arrangements that operate over different timescales, with varied strengths, and with the ability to adjust function in dynamic hearing conditions. Multiple neurotransmitters interact to support the precision and complexity of hearing. Here, we review the location of release, action, and function of neurotransmitters in the mammalian cochlea with an emphasis on recent work describing the complexity of signaling.

New Insight on the Safety of Erenumab: An Analysis of Spontaneous Reports of Adverse Events Recorded in the US Food and Drug Administration Adverse Event Reporting System Database

AIM

The aim of this article was to provide an overview of adverse events reported for erenumab in post-marketing through the Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) and perform a disproportionality analysis with other drugs used for acute or preventative treatment of migraine as controls.

METHODS

FAERS was screened from the first quarter of 2018 to the second quarter of 2020 (latest data update 30 June 2020). Clinical and demographic characteristics of cases were described along with the seriousness and outcome of adverse events. Disproportionality analyses were performed using the reporting odds ratio (ROR).

RESULTS

In total, 23,312 cases were reported during the study period, 67.0% by consumers. Cases in the age range 18-64 years (10,922 cases; 45.8%), in female sex (15,099 cases; 64.8%), and with adverse events that were classified as non-serious (19,626 cases; 84.2%) were the most prevalent in the database. After the exclusion of duplicates, 146 fatal cases were identified. A total of 1303 unlabeled adverse events were reported, of which 49 had statistically significant disproportionality of reporting in comparison with other drugs used for acute or preventative treatment of migraine. Identified disproportionality signals included alopecia, depression, anxiety, myocardial infarction, increased heart rate, pulmonary embolism, weight alteration, insomnia, tinnitus, and influenza-like symptoms. Injection-site reactions (labeled events) were co-reported with errors in administration procedures.

CONCLUSION

Adverse events reported during the first 2 years of post-marketing surveillance were mostly non-serious and with a favorable prognosis. However, new safety aspects emerged for which further studies are needed to confirm the associations, prioritizing unlabeled events with consistent disproportionality signals (e.g., emerging in at least 4 out of 6 analyses).

Activation of GABAB receptors results in excitatory modulation of calyx terminals in rat semicircular canal cristae

Previous studies have found GABA in vestibular end organs. However, existence of GABA receptors or possible GABAergic effects on vestibular nerve afferents has not been investigated. The current study was conducted to determine whether activation of GABAB receptors affects calyx afferent terminals in the central region of the cristae of semicircular canals. We used patch-clamp recording in postnatal day 13-18 (P13-P18) Sprague-Dawley rats of either sex. Application of GABAB receptor agonist baclofen inhibited voltage-sensitive potassium currents. This effect was blocked by selective GABAB receptor antagonist CGP 35348. Application of antagonists of small (SK)- and large-conductance potassium (BK) channels almost completely blocked the effects of baclofen. The remaining baclofen effect was blocked by cadmium chloride, suggesting that it could be due to inhibition of voltage-gated calcium channels. Furthermore, baclofen had no effect in the absence of calcium in the extracellular fluid. Inhibition of potassium currents by GABAB activation resulted in an excitatory effect on calyx terminal action potential firing. While in the control condition calyces could only fire a single action potential during step depolarizations, in the presence of baclofen they fired continuously during steps and a few even showed repetitive discharge. We also found a decrease in threshold for action potential generation and a decrease in first-spike latency during step depolarization. These results provide the first evidence for the presence of GABAB receptors on calyx terminals, showing that their activation results in an excitatory effect and that GABA inputs could be used to modulate calyx response properties.NEW & NOTEWORTHY Using in vitro whole cell patch-clamp recordings from calyx terminals in the vestibular end organs, we show that activation of GABAB receptors result in an excitatory effect, with decreased spike-frequency adaptation and shortened first-spike latencies. Our results suggest that these effects are mediated through inhibition of calcium-sensitive potassium channels.

Safety and tolerability of monthly galcanezumab injections in patients with migraine: integrated results from migraine clinical studies

BACKGROUND

Galcanezumab, a humanized monoclonal antibody that selectively binds to calcitonin gene-related peptide, has demonstrated a significant reduction in monthly migraine headache days in phase 2 and 3 trials. In these analyses, we aimed to evaluate the safety and tolerability of galcanezumab compared with placebo for prevention of episodic or chronic migraine.

METHODS

Data were integrated from three double-blind clinical studies for the up to 6-month galcanezumab exposure group (N = 1435), and from five clinical studies for the up to 1-year all-galcanezumab exposure group (N = 2276). Patients received a monthly 120 mg subcutaneous injection of galcanezumab (with a 240 mg loading dose in month 1), 240 mg galcanezumab, or placebo. Outcomes measured were treatment-emergent adverse events (TEAEs), serious AEs (SAEs), and discontinuation due to AEs (DCAEs). Laboratory results, vital signs, electrocardiogram (ECG), suicidal ideation and behavior results were evaluated.

RESULTS

TEAEs that occurred more frequently in galcanezumab-treated patients included injection site pain, injection site reactions excluding pain, constipation, vertigo, and pruritus. The proportion of DCAEs among galcanezumab-treated patients ranged between 1.8 and 3.0%, and differed from placebo group for galcanezumab 240 mg (P < 0.05). Fewer than 2.0% of patients in either galcanezumab dose-group compared with 1.0% of placebo-treated patients reported a SAE. There were no clinically meaningful differences between galcanezumab and placebo in laboratory measures, vital signs including blood pressure, ECGs, cardiovascular-related AEs, or suicidal ideation and behavior.

CONCLUSIONS

Galcanezumab demonstrated a favorable safety and tolerability profile for up to 1 year of treatment for the prevention of migraine.

TRIAL REGISTRATION

Clinical Trials CGAB = NCT02163993, EVOLVE-1 = NCT02614183, EVOLVE-2 = NCT02614196, REGAIN = NCT02614261, and CGAJ = NCT02614287. All were first posted on 25 November 2015, except CGAB posted on 16 June 2014, and before enrolling the first patient.

Neuropeptides in sensory signal processing

Peptides released from trigeminal fibers fulfill well-understood functions in neuroinflammatory processes and in the modulation of nociceptive signal processing. In particular, calcitonin gene-related peptide (CGRP) and substance P (SP), released from afferent nerve terminals, exert paracrine effects on the surrounding tissue and this has been recently highlighted by the prominent parcrine role of CGRP in the development of headache and migraine. Some recent communications suggest that these sensory neuropeptides may also modulate the workings of sensory organs and influence afferent signals from nose, tongue, eyes and ears. Here, we briefly review the evidence for modulatory effects of CGRP and SP in the sensory periphery.

The role of the brainstem in migraine: Potential brainstem effects of CGRP and CGRP receptor activation in animal models

Background

Migraine is a severe debilitating disorder of the brain that is ranked as the sixth most disabling disorder globally, with respect to disability adjusted life years, and there remains a significant unmet demand for an improved understanding of its underlying mechanisms. In conjunction with perturbed sensory processing, migraine sufferers often present with diverse neurological manifestations (premonitory symptoms) that highlight potential brainstem involvement. Thus, as the field moves away from the view of migraine as a consequence of purely vasodilation to a greater understanding of migraine as a complex brain disorder, it is critical to consider the underlying physiology and pharmacology of key neural networks likely involved.

Discussion

The current review will therefore focus on the available evidence for the brainstem as a key regulator of migraine biology and associated symptoms. We will further discuss the potential role of CGRP in the brainstem and its modulation for migraine therapy, given the emergence of targeted CGRP small molecule and monoclonal antibody therapies.

Conclusion

The brainstem forms a functional unit with several hypothalamic nuclei that are capable of modulating diverse functions including migraine-relevant trigeminal pain processing, appetite and arousal regulatory networks. As such, the brainstem has emerged as a key regulator of migraine and is appropriately considered as a potential therapeutic target. While currently available CGRP targeted therapies have limited blood brain barrier penetrability, the expression of CGRP and its receptors in several key brainstem nuclei and the demonstration of brainstem effects of CGRP modulation highlight the significant potential for the development of CNS penetrant molecules.

Migraine Related Vertigo

Migraine related vertigo (MRV) is largely accepted in the vestibular community and probably represents the second most common cause of vertigo after benign positional vertigo by far exceeding Meniere's disease. The data on vestibular migraine management is still relatively poor, despite its enormous importance in daily practice. A 55-year old male presented with history of giddiness, imbalance, sweating and sensation of nausea with severe pulsating headache of one day duration. Ear, Nose and Throat examination was normal. Neurological tests were negative. Audiogram and Electronystagmography were within normal limits. Nystagmus was positive on turning his head to left side. By reviewing the available literature on MRV, the report aims to outline a protocol for future management. The patient and caretakers were thoroughly counseled and educated, started on Flunarizine 10 mg and Dimenhydrinate 50 mg; advice healthy life style, necessary precautions, compliance to treatment. Patient was reportedly followed up and was symptom free over a period of 9 years. There is a call for proper diagnosis to address the complaint and manage of symptoms in acute attack and prophylaxis. In addition, this case highlight the ongoing need for proper systematic evaluation, therapeutic management, follow up by ensuring compliance to medication, necessary precautions and life style modification.

Efferent Vestibular Neurons Show Homogenous Discharge Output But Heterogeneous Synaptic Input Profile In Vitro

Despite the importance of our sense of balance we still know remarkably little about the central control of the peripheral balance system. While previous work has shown that activation of the efferent vestibular system results in modulation of afferent vestibular neuron discharge, the intrinsic and synaptic properties of efferent neurons themselves are largely unknown. Here we substantiate the location of the efferent vestibular nucleus (EVN) in the mouse, before characterizing the input and output properties of EVN neurons in vitro. We made transverse serial sections through the brainstem of 4-week-old mice, and performed immunohistochemistry for calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT), both expressed in the EVN of other species. We also injected fluorogold into the posterior canal and retrogradely labelled neurons in the EVN of ChAT:: tdTomato mice expressing tdTomato in all cholinergic neurons. As expected the EVN lies dorsolateral to the genu of the facial nerve (CNVII). We then made whole-cell current-, and voltage-clamp recordings from visually identified EVN neurons. In current-clamp, EVN neurons display a homogeneous discharge pattern. This is characterized by a high frequency burst of action potentials at the onset of a depolarizing stimulus and the offset of a hyperpolarizing stimulus that is mediated by T-type calcium channels. In voltage-clamp, EVN neurons receive either exclusively excitatory or inhibitory inputs, or a combination of both. Despite this heterogeneous mixture of inputs, we show that synaptic inputs onto EVN neurons are predominantly excitatory. Together these findings suggest that the inputs onto EVN neurons, and more specifically the origin of these inputs may underlie EVN neuron function.

The expression of calcitonin gene-related Peptide and acetylcholine in the vestibular-related nucleus population of wild-type mice and retinal degeneration fast mice after rotary stimulation

Due to the lack of an appropriate animal model, few studies have addressed the integration of visual and vestibular information in the visual system. Using a mouse model with a visual defect (retinal degeneration fast, rdf), we have verified that the prepositus hypoglossal nucleus (PrH) and the Kooy cap of the inferior olive medial nucleus (IOK) are key regions in which visual and vestibular information integrate. Although the integration regions were identified, the precise mechanisms of integration require further investigation. The rdf mice and wild-type Kunming mice were randomly assigned to experimental and control subgroups, respectively. Mice in the experimental groups were exposed to rotary motion for 30 min three times at 24-h intervals, whereas mice in the control groups were not exposed to rotary motion. Differences in the number of calcitonin gene-related peptide positive (CGRP-positive) and choline acetyltransferase positive (ChAT-positive) neurons in the vestibular-related nucleus populations of two types of mice were determined. After rotatory stimulus, the number of CGRP-positive and ChAT-positive neurons in the PrH and the IOK was significantly less in rdf mice compared with that in wild-type mice. There were differences in the number of CGRP-positive and ChAT-positive neurons in the other vestibular-related regions, but the differences were not significant, except the difference in the number of ChAT-positive neurons in the medial vestibular nucleus. The expression patterns of CGRP and ChAT were similar to that of Fos in the vestibular-related regions in the two types of mice after rotatory stimulus. The number of CGRP-positive and ChAT-positive neurons and the number of active nerve cells were consistent in those regions in the two types of mice after rotary stimulus. Therefore, we speculated that CGRP and Ach generated and released by neurons in the PrH and the IOK may play roles in the sensory integration of visual and vestibular information in mice.

Expression of calcitonin gene-related peptide in efferent vestibular system and vestibular nucleus in rats with motion sickness

Motion sickness presents a challenge due to its high incidence and unknown pathogenesis although it is a known fact that a functioning vestibular system is essential for the perception of motion sickness. Recent studies show that the efferent vestibular neurons contain calcitonin gene-related peptide (CGRP). It is a possibility that the CGRP immunoreactivity (CGRPi) fibers of the efferent vestibular system modulate primary afferent input into the central nervous system; thus, making it likely that CGRP plays a key role in motion sickness. To elucidate the relationship between motion sickness and CGRP, the effects of CGRP on the vestibular efferent nucleus and the vestibular nucleus were investigated in rats with motion sickness.

Neurologic bases for comorbidity of balance disorders, anxiety disorders and migraine: neurotherapeutic implications

The comorbidity among balance disorders, anxiety disorders and migraine has been studied extensively from clinical and basic research perspectives. From a neurological perspective, the comorbid symptoms are viewed as the product of sensorimotor, interoceptive and cognitive adaptations that are produced by afferent interoceptive information processing, a vestibulo-parabrachial nucleus network, a cerebral cortical network (including the insula, orbitofrontal cortex, prefrontal cortex and anterior cingulate cortex), a raphe nuclear-vestibular network, a coeruleo-vestibular network and a raphe-locus coeruleus loop. As these pathways overlap extensively with pathways implicated in the generation, perception and regulation of emotions and affective states, the comorbid disorders and effective treatment modalities can be viewed within the contexts of neurological and psychopharmacological sites of action of current therapies.

Retrograde neuron tracing with microspheres reveals projection of CGRP-immunolabeled vestibular afferent neurons to the vestibular efferent nucleus in the brainstem of rats

OBJECTIVE

A new retrograde neuron-tracing technique with microspheres was used to explore the possible innervation of calcitonin gene-related peptide (CGRP)-immunolabeled vestibular afferent neurons in the vestibular efferent immunolabeled nucleus in the brainstem.

METHODS

0.1 microl of 5% microfluorospheres was injected into the area of the vestibular efferent nucleus, which is located lateral to the genu of the facial nerve. CGRP immunohistochemistry was processed in serial sections of the brainstem at the facial nerve genu level. Double-labeled neurons with both CGRP immunoreactivity and microfluorospheres were examined with fluorescence and confocal laser microscopy.

RESULTS

Three types of labeled neurons were observed: (1) neurons only retrogradely microfluorosphere-labeled that were mainly located in the medial vestibular nucleus, lateral vestibular nucleus, superior vestibular nucleus and parvicellular reticular nucleus on the ipsilateral side of the injection; (2) neurons that were both immunolabeled with CGRP and also retrogradedly labeled with microfluorospheres, indicating that they are CGRP cells projecting to the area of vestibular efferent nucleus, these cells were mainly distributed in the superior vestibular nucleus and dorsal vestibular nucleus, and (3) cells only immunolabeled for CGRP that were scattered extensively in the brainstem.

CONCLUSION

The presented methodical contribution demonstrates the suitability of fluorescein-labeled microspheres for retrograde neuronal tracing. The vestibular nuclei contain numerous afferent neurons that send projections to the vestibular efferent nucleus, some of which are CGRP cells. This afferent innervation provides morphological evidence that the vestibular efferent neurons receive input from the vestibular afferent neurons including CGRP cells. These vestibular primary CGRP afferent neurons may have an influence on vestibular efferent neurons. CGRP acts as an important co-transmitter or modulator in the afferent-mediated activity of vestibular efferent neurons, which in turn affect afferents in the vestibular end organs.

Postulated vasoactive neuropeptide autoimmunity in fatigue-related conditions: a brief review and hypothesis

Disorders such as chronic fatigue syndrome (CFS) and gulf war syndrome (GWS) are characterised by prolonged fatigue and a range of debilitating symptoms of pain, intellectual and emotional impairment, chemical sensitivities and immunological dysfunction. Sudden infant death syndrome (SIDS) surprisingly may have certain features in common with these conditions. Post-infection sequelae may be possible contributing factors although ongoing infection is unproven. Immunological aberration may prove to be associated with certain vasoactive neuropeptides (VN) in the context of molecular mimicry, inappropriate immunological memory and autoimmunity. Adenylate cyclase-activating VNs including pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) act as hormones, neurotransmitters, neuroregulators, immune modulators and neurotrophic substances. They and their receptors are potentially immunogenic. VNs are widely distributed in the body particularly in the central and peripheral nervous systems and have been identified in the gut, adrenal gland, blood cells, reproductive system, lung, heart and other tissues. They have a vital role in maintaining cardio-respiratory function, thermoregulation, memory, concentration and executive functions such as emotional responses including social cues and appropriate behaviour. They are co-transmitters for a number of neurotransmitters including acetylcholine and gaseous transmitters, are potent immune regulators with primarily anti-inflammatory activity, and have a significant role in protection of the nervous system against toxic assault as well as being important in the maintenance of homeostasis. This paper describes a biologically plausible mechanism for the development of certain fatigue-related syndromes based on loss of immunological tolerance to these VNs or their receptors following infection, other events or de novo resulting in significant pathophysiology possibly mediated via CpG fragments and heat shock (stress) proteins. These conditions extend the public health context of autoimmunity and VN dysregulation and have implications for military medicine where radiological, biological and chemical agents may have a role in pathogenesis. Possible treatment and prevention options are considered.

Trigeminal stimulation elicits a peripheral vestibular imbalance in migraine patients

OBJECTIVE

The study explored the hypothesis that spontaneous nystagmus (Ny) in migraine patients can be triggered or modulated by painful trigeminal stimulation, providing evidence of a functional connection between vestibular and trigeminal systems.

BACKGROUND

Vertigo attacks are reported by subjects with migraine or a familiar history of migraine, also independently of headache episodes. Idiopathic vertigo is three times more frequent in migraine patients than in controls. Vestibular investigations in migraine patients have consistently demonstrated spontaneous Ny both of central and peripheral origin.

DESIGN

In the first phase of the study 10 outpatients experiencing migraine without aura (MO) and 10 healthy volunteers were submitted to the registration of spontaneous primary-position Ny in the dark by Ulmer's video-ocular-nystagmographic equipment. Two electrodes for electrical stimulation were applied on the supraorbital point of one side of the head and the intensity of stimulation corresponding to pain threshold was calculated. Spontaneous ocular movements were recorded for 5 minutes at baseline and after a sequence of five electric pulses (square waves of .5 Hz frequency and 50 micros duration, at pain threshold intensity). Nystagmographic responses were expressed as latency after stimulation, direction of the quick phase, and duration. The second phase of the study explored, with the same procedure, the effects on Ny of supraorbital versus median nerve stimulation in other 10 MO patients. Responses to stimulation were considered the appearance of de novo Ny after stimulation in subjects without baseline Ny, or the change of the frequency (at last a 50% variation) or of the direction of Ny after stimulation in subjects with baseline Ny. The latency and the duration of responses to stimulation were also calculated.

RESULTS

In the first series supraorbital painful electric stimulation was able to modify or to evoke Ny in 8 of 10 migraineurs and in none of 10 volunteers (Fisher's exact test, P<.01). Both the baseline and the induced Ny were second degree, stationary persistent, with a linear slow phase and were suppressed by visual fixation. In the second series, supraorbital nerve stimulation was able to induce or modify Ny in all of 10 patients but only in 1 patient Ny was induced by median nerve stimulation. Characters of Ny were the same as previously described. Statistical comparison of the responses at the two sites of stimulation was significant (Fisher's exact test, P<.01). In those 7 patients who presented de novo Ny after stimulation it was possible to calculate Ny latency and duration. The mean latency was 25 s (SD: 16, range: 14 to 60). The mean duration was 120 s (SD: 94, range: 20 to 290).

CONCLUSION

The main result of our study is that in migraine patients painful trigeminal stimulation elicits de novo, or modifies pre-existing spontaneous Ny, generally increasing it. The finding was obtained after trigeminal stimulation, but not after median nerve stimulation. We suggest that painful trigeminal stimulation can induce an imbalance of the vestibular system in migraine patients and possibly explain their predisposition to vertigo. Our data require confirmation by other studies.