Blockade of 5-HT3 receptors with granisetron does not affect trigeminothalamic nociceptive transmission in rats: Implication for migraine

D2 dopamine receptor-mediated mechanisms of dopaminergic system modulation in in vivo and in vitro experimental models of migraine

The dopaminergic system is implicated in the pathophysiology of migraine. However, the underlying mechanisms remain unclear. We explored the effects and mechanisms of dopaminergic system modulation in the in vivo and in vitro rat models of migraine. Dopaminergic agonist apomorphine, D2 receptor antagonists metoclopramide and haloperidol and 5-HT3 receptor antagonist ondansetron alone and together were tested in nitroglycerin-induced migraine model, in vivo. Likewise, the combinations of drugs were also tested on basal calcitonin gene-related peptide (CGRP) release in vitro hemiskull preparations. Mechanical allodynia was tested by von Frey filaments. CGRP concentrations in trigeminovascular structures and in vitro superfusates and c-Fos levels in the brainstem were determined by enzyme-linked immunosorbent assay. Meningeal mast cells were evaluated with toluidine blue staining. Apomorphine further enhanced nitroglycerin-induced mechanical allodynia, brainstem c-fos expression, trigeminal ganglion and brainstem CGRP concentrations and meningeal mast cell degranulation, in vivo. Haloperidol completely antagonised all apomorphine-induced effects and also alleviated changes induced by nitroglycerin without apomorphine. Metoclopramide and ondansetron partially attenuated apomorphine- or nitroglycerin-induced effects. A combination of haloperidol and ondansetron decreased basal CGRP release, in vitro, whereas the other administrations were ineffective. Apomorphine-mediated dopaminergic activation exacerbated nitroglycerin-stimulated nociceptive reactions by further enhancing c-fos expression, CGRP release and mast cell degranulation in strategical structures associated with migraine pain. Metoclopramide partially attenuated the effects of apomorphine, most likely because it is also a 5-HT3 receptor antagonist. Haloperidol with pure D2 receptor antagonism feature appears to be more effective than metoclopramide in reducing migraine-related parameters in dopaminergic activation- and/or NTG-induced migraine-like conditions.

Menthol dural application alters meningeal arteries tone and enhances excitability of trigeminocervical neurons in rats

Headaches, including migraines, can have a causal relationship to exposure to cold, and this relationship may be both positive and negative, as cold can both provoke and alleviate cephalgia. The role of thermoreceptors responsible for transduction of low temperatures belongs to the transient receptor potential cation channel subfamily melastatin member 8 (TRPM8). These channels mediate normal cooling sensation and have a role in both cold pain and cooling-mediated analgesia; they are seen as a potential target for principally new anti-migraine pharmaceuticals. Using a validated animal migraine models, we evaluated effects of menthol, the TRPM8-agonist, on trigeminovascular nociception. In acute experiments on male rats, effects of applied durally menthol solution in various concentrations on the neurogenic dural vasodilatation (NDV) and firing rate of dura-sensitive neurons of the trigeminocervical complex (TCC) were assessed. Application of menthol solution in concentrations of 5 % and 10 % was associated with NDV suppression, however amplitude reduction of the dilatation response caused not by the vascular dilatation degree decrease, but rather due to the significant increase of the meningeal arterioles' basal tone. In electrophysiological experiments the 1 % and 30 % menthol solutions intensified TCC neuron responses to the dural electrical stimulation while not changing their background activity. Revealed in our study excitatory effects of menthol related to the vascular as well as neuronal branches of the trigeminovascular system indicate pro-cephalalgic effects of TRPM8-activation and suggest feasibility of further search for new anti-migraine substances among TRPM8-antagonists.

5-hydroxytryptamine in migraine: The puzzling role of ionotropic 5-HT3 receptor in the context of established therapeutic effect of metabotropic 5-HT1 subtypes

5-hydroxytryptamine (5-HT; serotonin) is traditionally considered as a key mediator implicated in migraine. Multiple 5-HT receptor subtypes contribute to a variety of region-specific functional effects. The raphé nuclei control nociceptive inputs by releasing 5-HT in the brainstem, whereas dural mast cells provide the humoral source of 5-HT in the meninges. Triptans (5-HT_1B/D agonists) and ditans (5-HT_1F agonists) are the best established 5-HT anti-migraine agents. However, activation of meningeal afferents via ionotropic 5-HT₃ receptors results in long-lasting excitatory drive suggesting a pro-nociceptive role for these receptors in migraine. Nevertheless, clinical data do not clearly support the applicability of currently available 5-HT₃ antagonists to migraine treatment. The reasons for this might be the presence of 5-HT₃ receptors on inhibitory interneurons dampening the excitatory drive, a lack of 5-HT₃ A-E subunit-selective antagonists and gender/age-dependent effects. This review is focusing on the controversial role of 5-HT₃ receptors in migraine pathology and related pharmacological perspectives of 5-HT ligands.

Advantages of imaging photoplethysmography for migraine modeling: new optical markers of trigemino-vascular activation in rats

Background

Existent animal models of migraine are not without drawbacks and limitations. The aim of our study was to evaluate imaging photoplethysmography (PPG) as a method of assessing intracranial blood flow in rats and its changes in response to electrical stimulation of dural trigeminal afferents.

Methods

Experiments were carried out with 32 anesthetized adult male Wistar rats. Trigeminovascular system (TVS) was activated by means of electrical stimulation of dural afferents through a closed cranial window (CCW). Parameters of meningeal blood flow were monitored using a PPG imaging system under green illumination with synchronous recording of an electrocardiogram (ECG) and systemic arterial blood pressure (ABP). Two indicators related to blood-flow parameters were assessed: intrinsic optical signals (OIS) and the amplitude of pulsatile component (APC) of the PPG waveform. Moreover, we carried out pharmacological validation of these indicators by determining their sensitivity to anti-migraine drugs: valproic acid and sumatriptan. For statistical analysis the non-parametric tests with post-hoc Bonferroni correction was used.

Results

Significant increase of both APC and OIS was observed due to CCW electrical stimulation. Compared to saline (n = 11), intravenous administration of both the sumatriptan (n = 11) and valproate (n = 10) by using a cumulative infusion regimen (three steps performed 30 min apart) lead to significant inhibitory effect on the APC response to the stimulation. In contrast, intravenous infusion of any substance or saline did not affect the OIS response to the stimulation. It was found that infusion of either sumatriptan or valproate did not affect the response of ABP or heart rate to the stimulation.

Conclusions

Imaging PPG can be used in an animal migraine model as a method for contactless assessment of intracranial blood flow. We have identified two new markers of TVS activation, one of which (APC) was pharmacologically confirmed to be associated with migraine. Monitoring of changes in APC caused by CCW electrical stimulation (controlling efficiency of stimulation by OIS) can be considered as a new way to assess the peripheral mechanism of action of anti-migraine interventions.

The Influence of Metoclopramide on Trigeminovascular Nociception: Possible Anti-migraine Mechanism of Action

Metoclopramide is widely used as an abortive migraine therapy due to the advantage of having not only antiemetic, but also analgesic properties. Despite the proven clinical efficacy of metoclopramide in acute migraine, the mechanism of its anti-cephalalgic action has not been entirely elucidated. Taking into account the key role of the trigeminovascular system activation in migraine pathophysiology, we aimed to investigate metoclopramide effects on the excitability of central trigeminovascular neurons and neurogenic dural vasodilation using valid electrophysiological and neurovascular models of trigeminovascular nociception. Extracellular recordings of the activity of second-order dura-sensitive neurons were made in the trigeminocervical complex (TCC) of 16 anaesthetised rats. Cumulative metoclopramide infusion (three steps in 30 min intervals, 5 mg/kg i.v. per step, n = 8) significantly and dose-dependently suppressed both ongoing firing of the TCC neurons and their responses to dural electrical stimulation, maximally to 30%[0-49%] (median[Q1-Q3]) and 4%[0-30%] of the initial level, respectively (both p = 0.001, compared to saline (n = 8)). By contrast, the neurogenic dural vasodilation studied in a separate group of 12 rats was not significantly affected by cumulative infusion of metoclopramide (5 mg/kg i.v. per step, n = 6) compared to both baseline values and the vehicle group (n = 6) (all p > 0.05). These results provide evidence that metoclopramide is unable to affect the peripheral response to trigeminovascular activation, but it does suppress the central response, which is highly predictive of anti-migraine action. Thus, here we show the neurophysiological mechanism underlying the therapeutic efficacy of metoclopramide in migraine.

Emergent management of primary headache: a review of current literature

PURPOSE OF REVIEW

The current article reviews recent data on treatment of acute headache patients in the acute care setting.

RECENT FINDINGS

Intravenous fluid hydration, a common component of emergency department (ED) migraine therapy, does not improve pain outcomes and leads to longer ED lengths of stay. Therefore, intravenous fluids should be administered only to migraine patients with clinical evidence of dehydration. Similarly, intravenous ketamine has garnered interest as a treatment for acute pain but does not provide substantial relief to migraine patients. New studies on the serotonin (5-HT3; 5-hydroxytryptamine-3) antagonist granisetron, intranasal lidocaine, and high-flow oxygen have reported conflicting results for migraine patients. Finally, although experts recommend avoiding opioids in migraine treatment, opioid administration remains prevalent in the ED. A new study has demonstrated that patients who receive intravenous hydromorphone in the ED are much less likely to attain acute headache relief. Standardized headache protocols may decrease opioid use and provide significant pain relief for patients.

SUMMARY

Recent data have clarified the role of opioids and ketamine in the ED (do not use!). The role of treatment protocols and intravenous fluids is still ill-defined. Subpopulations of migraine patients may benefit from high-flow oxygen and intranasal lidocaine.