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.

Where are we? The anatomy of the murine cortical meninges revisited for intravital imaging, immunology, and clearance of waste from the brain

Rapid progress is being made in understanding the roles of the cerebral meninges in the maintenance of normal brain function, in immune surveillance, and as a site of disease. Most basic research on the meninges and the neural brain is now done on mice, major attractions being the availability of reporter mice with fluorescent cells, and of a huge range of antibodies useful for immunocytochemistry and the characterization of isolated cells. In addition, two-photon microscopy through the unperforated calvaria allows intravital imaging of the undisturbed meninges with sub-micron resolution. The anatomy of the dorsal meninges of the mouse (and, indeed, of all mammals) differs considerably from that shown in many published diagrams: over cortical convexities, the outer layer, the dura, is usually thicker than the inner layer, the leptomeninx, and both layers are richly vascularized and innervated, and communicate with the lymphatic system. A membrane barrier separates them and, in disease, inflammation can be localized to one layer or the other, so experimentalists must be able to identify the compartment they are studying. Here, we present current knowledge of the functional anatomy of the meninges, particularly as it appears in intravital imaging, and review their role as a gateway between the brain, blood, and lymphatics, drawing on information that is scattered among works on different pathologies.

Intravenous dextromethorphan/quinidine inhibits activity of dura-sensitive spinal trigeminal neurons in rats

BACKGROUND

Migraine is a chronic neurological disorder characterized by episodes of throbbing headaches. Practically all medications currently used in migraine prophylaxis have a number of substantial disadvantages and use limitations. Therefore, the further search for principally new prophylactic antimigraine agents remains an important task. The objective of our study was to evaluate the effects of a fixed combination of dextromethorphan hydrobromide and quinidine sulphate (DM/Q) on activity of the spinal trigeminal neurons in an electrophysiological model of trigemino-durovascular nociception.

METHODS

The study was performed in 15 male Wistar rats, which were anaesthetized with urethane/α-chloralose and paralysed using pipecuronium bromide. The effects of cumulative intravenous infusions of DM/Q (three steps performed 30 min apart, 15/7.5 mg/kg of DM/Q in 0.5 mL of isotonic saline per step) on ongoing and dural electrical stimulation-induced neuronal activities were tested in a group of eight rats over 90 min. Other seven animals received cumulative infusion of equal volumes of saline and served as control.

RESULTS

Cumulative administration of DM/Q produced steady suppression of both the ongoing activity of the spinal trigeminal neurons and their responses to electrical stimulation of the dura mater.

CONCLUSIONS

It is evident that the observed DM/Q-induced suppression of trigeminal neuron excitability can lead to a reduction in nociceptive transmission from meninges to higher centres of the brain. Since the same mechanism is believed to underlie the pharmacodynamics of many well-known antimigraine drugs, results of the present study enable us to anticipate the potential efficacy of DM/Q in migraine.