Colocalization of 5-HT1F receptor and glutamate in neurons of the vestibular nuclei in rats

Inhibition of glutamatergic trigeminal nucleus caudalis- vestibular nucleus projection neurons attenuates vestibular dysfunction in the chronic-NTG model of migraine

BACKGROUND

Prior clinical studies suggest a shared mechanism between vestibular symptoms and migraine headache. However, the specific neuroanatomical substrate connecting vestibular symptoms with migraine remains to be largely unknown. Thus, the aim of this study was to further investigate the mechanisms that whether and how trigeminovestibular neurons produce effects on neuronal activation in vestibular nucleus (VN).

METHODS

A chronic-NTG rat model was established by recurrent intermittent administration of nitroglycerin (NTG). Pain- and vestibular-related behaviors were assessed. To selectively inhibit the glutamatergic neurons and trigeminal nucleus caudalis (TNC) to VN projection neurons, the AAVs encoding engineered Gi-coupled hM4D receptor were administered in the TNC or VN area.

RESULTS

We identify a glutamatergic projection from TNC to VN that mediates vestibular dysfunction in a chronic-NTG rat model. Inhibition of the Glutamate^TNC neurons alleviates vestibular dysfunction in the chronic-NTG rat. Calcitonin gene-related peptide (CGRP)-expressing neurons in the VN received glutamatergic projections from TNC neurons. Silencing the glutamatergic TNC-VN projection neurons attenuates vestibular dysfunction in the chronic-NTG rat.

CONCLUSIONS

Together, we reveal a modulatory role of glutamatergic TNC-VN projection neurons in vestibular dysfunction of migraine.

Whole-brain monosynaptic outputs and presynaptic inputs of GABAergic neurons in the vestibular nuclei complex of mice

GABAergic neurons in the vestibular nuclei (VN) participate in multiple vital vestibular sensory processing allowing for the maintenance and rehabilitation of vestibular functions. However, although the important role of GABA in the central vestibular system has been widely reported, the underlying neural circuits between VN GABAergic neurons and other brain functional regions remain elusive, which limits the further study of the underlying mechanism. Hence, it is necessary to elucidate neural connectivity based on outputs and inputs of GABAergic neurons in the VN. This study employed a modified rabies virus retrograde tracing vector and cre-dependent adeno-associated viruses (AAVs) anterograde tracing vector, combined with a transgenic VGAT-IRES-Cre mice, to map the inputs and outputs of VN GABAergic neurons in the whole brain. We found that 51 discrete brain regions received projections from VN GABAergic neurons in the whole brain, and there were 77 upstream nuclei innervating GABAergic neurons in the VN. These nuclei were mainly located in four brain regions, including the medulla, pons, midbrain, and cerebellum. Among them, VN GABAergic neurons established neural circuits with some functional nuclei in the whole brain, especially regulating balance maintenance, emotion control, pain processing, sleep and circadian rhythm regulation, and fluid homeostasis. Therefore, this study deepens a comprehensive understanding of the whole-brain neural connectivity of VN, providing the neuroanatomical information for further research on the neural mechanism of the co-morbidities with vestibular dysfunction.

Lasmiditan mechanism of action - review of a selective 5-HT1F agonist

Migraine is a leading cause of disability worldwide, but it is still underdiagnosed and undertreated. Research on the pathophysiology of this neurological disease led to the discovery that calcitonin gene-related peptide (CGRP) is a key neuropeptide involved in pain signaling during a migraine attack. CGRP-mediated neuronal sensitization and glutamate-based second- and third-order neuronal signaling may be an important component involved in migraine pain. The activation of several serotonergic receptor subtypes can block the release of CGRP, other neuropeptides, and neurotransmitters, and can relieve the symptoms of migraine. Triptans were the first therapeutics developed for the treatment of migraine, working through serotonin 5-HT1B/1D receptors. The discovery that the serotonin 1F (5-HT1F) receptor was expressed in the human trigeminal ganglion suggested that this receptor subtype may have a role in the treatment of migraine. The 5-HT1F receptor is found on terminals and cell bodies of trigeminal ganglion neurons and can modulate the release of CGRP from these nerves. Unlike 5-HT1B receptors, the activation of 5-HT1F receptors does not cause vasoconstriction.The potency of different serotonergic agonists towards 5-HT1F was correlated in an animal model of migraine (dural plasma protein extravasation model) leading to the development of lasmiditan. Lasmiditan is a newly approved acute treatment for migraine in the United States and is a lipophilic, highly selective 5-HT1F agonist that can cross the blood-brain barrier and act at peripheral nervous system (PNS) and central nervous system (CNS) sites.Lasmiditan activation of CNS-located 5-HT1F receptors (e.g., in the trigeminal nucleus caudalis) could potentially block the release of CGRP and the neurotransmitter glutamate, thus preventing and possibly reversing the development of central sensitization. Activation of 5-HT1F receptors in the thalamus can block secondary central sensitization of this region, which is associated with progression of migraine and extracephalic cutaneous allodynia. The 5-HT1F receptors are also elements of descending pain modulation, presenting another site where lasmiditan may alleviate migraine. There is emerging evidence that mitochondrial dysfunction might be implicated in the pathophysiology of migraine, and that 5-HT1F receptors can promote mitochondrial biogenesis. While the exact mechanism is unknown, evidence suggests that lasmiditan can alleviate migraine through 5-HT1F agonist activity that leads to inhibition of neuropeptide and neurotransmitter release and inhibition of PNS trigeminovascular and CNS pain signaling pathways.

Targeted 5-HT1F Therapies for Migraine

Migraine is a common neurological disease characterised by the presence of attacks of unilateral, severe head pain accompanied by other symptoms. Although it has been classified as the sixth most disabling disorder, the available therapeutic options to treat this condition have not progressed accordingly. The advance in the development of 5-HT1 receptor agonists for migraine, including 5-HT1B/D and 5-HT1F receptor agonists, has meant a major step forward towards the progression of a better treatment for migraine. Triptans have a limited efficacy, and their effect on vasoconstriction makes them unsafe for patients with cardiovascular and/or cerebrovascular diseases. Therefore, novel effective antimigraine treatments without cardiovascular effects are required, such as selective 5-HT1F receptor agonists (ditans). Lasmiditan has much higher affinity for the 5-HT1F receptor than for the vasoconstrictor 5-HT1B receptor. This has been confirmed in preclinical studies performed to date, where lasmiditan showed no effect on vasoconstriction, and in clinical trials, where healthy individuals and patients did not report cardiac events due to treatment with lasmiditan, although it should be confirmed in larger cohorts. Lasmiditan crosses the blood-brain barrier and may act both centrally and peripherally on 5-HT1F receptors expressed on trigeminal neurons. It is a well-tolerated compound that does not induce major adverse events. Although ongoing phase III clinical trials are needed to confirm its efficacy and safety, lasmiditan might offer an alternative to treat acute migraine with no associated cardiovascular risk. This review will focus on the characterisation of 5-HT1 receptor agonists and their effects as migraine therapies.

Decreased risk of stroke in patients receiving traditional Chinese medicine for vertigo: A population-based cohort study

ETHNOPHARMACOLOGICAL RELEVANCE

Patients with vertigo are reported to exhibit a higher risk of subsequent stroke. However, it remains unclear if Traditional Chinese Medicine (TCM), the most common form of complementary and alternative medicine, can help lower the risk of stroke for these patients. So the aim of the study was to investigate the effects of TCM on stroke risk among patients with vertigo.

MATERIALS AND METHODS

This longitudinal cohort study used the Taiwanese National Health Insurance Research Database to identify 112,458 newly diagnosed vertigo patients aged ≥20 years who received treatment between 1998 and 2007. Among these patients, 53,203 (47.31%) received TCM after vertigo onset (TCM users), and the remaining 59,201 patients were designated as a control group (non-TCM users). All enrollees received follow-up until the end of 2012 to measure stroke incidence. Cox proportional hazards regression was used to compute the hazard ratio (HR) of stroke in recipients of TCM services.

RESULTS

During 15-year follow-up, 5532 TCM users and 12,295 non-TCM users developed stroke, representing an incidence rate of 13.10% and 25.71% per 1000 person-years. TCM users had a significantly reduced risk of stroke compared to non-TCM users (adjusted HR=0.64; 95% confidence interval CI=0.59-0.74). The predominant effect was observed for those receiving TCM for more than 180 days (adjusted HR=0.52; 95% CI=0.49-0.56). Commonly used TCM formulae, including Ban-Xia-Bai-Zhu-Tian-Ma-Tang, Ling-Gui-Zhu-Gan-Tang, Bai Zhi (Angelica dahurica (Hoffm.) Benth. & Hook.f. ex Franch. & Sav., root), Ge Gen (Pueraria lobata (Willd.) Ohwi, root) and Hai Piao Xiao (Endoconcha Sepiae, Cuttlefish Bone) were significantly associated with lower risk of stroke.

CONCLUSIONS

Results of this population-based study support the effects of TCM on reducing stroke risk, and may provide a reference for stroke prevention strategies. The study results may also help to integrate TCM into clinical intervention programs that provide a favorable prognosis for vertigo patients.

mRNA expression of 5-hydroxytryptamine 1B, 1D, and 1F receptors and their role in controlling the release of calcitonin gene-related peptide in the rat trigeminovascular system

Triptans, a family of 5-hydroxytryptamine (5-HT) 1B, 1D, and 1F receptor agonists, are used in the acute treatment of migraine attacks. The site of action and subtypes of the 5-HT(1) receptor that mediate the antimigraine effect have still to be identified. This study investigated the mRNA expression of these receptors and the role of 5-HT(1) receptor subtypes in controlling the release of calcitonin gene-related peptide (CGRP) in rat dura mater, trigeminal ganglion (TG), and trigeminal nucleus caudalis (TNC). The mRNA for each receptor subtype was quantified by quantitative real-time polymerase chain reaction. A high potassium concentration was used to release CGRP from dura mater, isolated TG, and TNC in vitro. The immunoreactive CGRP (iCGRP) release was measured by enzyme-linked immunoassay. The mRNA transcripts of the 3 5-HT(1) receptor subtypes were detected in the trigeminovascular system. Sumatriptan inhibited iCGRP release by 31% in dura mater, 44% in TG, and 56% in TNC. This effect was reversed by a 5-HT(1B/1D) antagonist (GR127395). The 5-HT(1F) agonist (LY-344864) was effective in the dura mater (26% iCGRP inhibition), and the 5-HT(1D) agonist (PNU-142633) had a significant effect in the TNC (48%), whereas the 5-HT(1B) agonist (CP-94253) was unable to reduce the iCGRP release in all tissues studied. We found that sumatriptan reduced the iCGRP release via activation of 5-HT(1D) and 5-HT(1F) receptor subtypes. The 5-HT(1F) receptor agonist was effective only in peripheral terminals in dura mater, whereas the 5-HT(1D) agonist had a preferential effect on central terminals in the TNC.

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.

A possible explanation for dizziness following SSRI discontinuation

Dizziness is the most commonly reported symptom of abrupt discontinuation from the selective serotonin reuptake inhibitor (SSRI) category of antidepressants. The reported dizziness is exacerbated by even slight head movement, and therefore is likely to be vestibular in origin. The SSRIs most implicated are those with short half-lives and which are most selective for serotonin (as opposed to noradrenaline), e.g. paroxetine and sertraline. Since the vestibular nucleus complex (VNC) has an abundance of serotonin receptors, the abrupt withdrawal from an SSRI is likely to have a substantial impact on the electrophysiological activity of neurons within it. Here we suggest that the abrupt withdrawal from an SSRI is likely to cause a sudden decrease in serotonin in the VNC, which will disrupt the function of VNC neurons bilaterally, causing dizziness without vertigo.