Migraine is characterized by severe pain and somatic symptoms like allodynia and photophobia, driven by neuroinflammation that sensitizes the trigeminal vascular system (TVS). This study investigated how neuroinflammation induced by systemic lipopolysaccharide (LPS) affects migraine-related nociceptive signaling. Using a chronic migraine model in rats with nitroglycerin (NTG), we compared prenatal and acute postnatal LPS administration. Rats with prenatal LPS exhibited lower mechanical thresholds and enhanced allodynia and photophobia after NTG. Acute LPS also increased allodynia, but not photophobia. Both LPS groups showed increased mast cell degranulation in the dura mater. Plasma CGRP after NTG administration was elevated in the acute LPS group. Electrophysiology revealed enhanced trigeminal afferent responses to serotonin in both acutely and prenatally LPS-treated rats. Calcium imaging demonstrated increased neuronal responses to serotonin and capsaicin, suggesting an upregulation of serotonin and TRPV1 receptors. Our findings show that LPS-induced neuroinflammation, whether prenatal or acute, promotes sensitization of peripheral and central nociceptive pathways, involving serotoninergic mechanisms.

Migraines are a common neurological disorder that significantly reduces quality of life. The sensitization of trigeminal afferents is a key factor in the development of the pain syndrome associated with migraine. Carbon monoxide (CO) is produced endogenously by heme oxygenase (HO), widely expressed in structures involved in pain processing. In our study, the role of CO in an acute and chronic nitroglycerin (NTG)-induced rat migraine model was investigated using behavioral, electrophysiological, biochemical and histological methods. The repeated administration of a CO donor (CORM-2) or an HO-1 inducer (CoPP) decreased mechanical hypersensitivity and photophobia of rats in the NTG-induced migraine model. Additionally, CORM-2 and CoPP prevented an increase in trigeminal afferent excitability, which was evaluated by the frequency of action potentials in response to KCl application. Preliminary CORM-2 or CoPP injections promoted mast cell stability in the meninges and prevented NTG-induced CGRP elevation in blood plasma. Our results suggest that exogenously or endogenously produced CO has a protective potential in preventing inflammation and the sensitization of peripheral trigeminal afferents, the activity of which underlies the occurrence of pain in migraine. This could contribute to the development of new approaches for migraine prevention.

The trigeminovascular system plays a pivotal role in the generation of nociceptive activity, which underlies pain in migraine and includes trigeminal nerve afferents, dura mater vessels, and mast cells. Adenosine triphosphate (ATP) is one of the main mediators of the interaction between vessels, nerve endings, and mast cells. ATP activates P2X3 receptors of trigeminal nerve afferents and P2X7 receptors of mast cells. 24-Hydroxycholesterol is the primary brain cholesterol metabolite synthesized by neurons and is capable of freely entering the bloodstream by crossing the blood–brain barrier. The purpose of this study was to examine the impact of 24-hydroxycholesterol on the electrical activity of trigeminal nerve afferents triggered by ATP application and on the mast cells degranulation in rat brain meninges. The electrical activity of the trigeminal nerve was recorded using an extracellular electrode in a rat hemiskull preparation, mast cells were stained with toluidine blue. 24-Hydroxycholesterol had no direct effect on the frequency of action potentials of trigeminal nerve but suppressed the response triggered by ATP application. Furthermore, incubation of meninges in 24-hydroxycholesterol resulted in a reduction in mast cell degranulation in response to ATP. Therefore, 24-hydroxycholesterol prevented the activation of trigeminal afferents either directly by reducing the activity of ionotropic ATP receptors or indirectly by stabilizing mast cells.

Carbon monoxide (CO) is an endogenous molecule that plays a regulatory role in a number of physiological and pathological processes. It is known that exposure to CO causes headaches. CO is involved in the processes of nociception, neurotransmission and cerebral haemodynamics, and there is also evidence of its anti-nociceptive role. However, the mechanisms through which CO exerts its effects on the meninges and the interaction between CO and ATP, a major inducer of nociceptive activity in trigeminal nerve afferents, remain to be elucidated. The objective of this study was to examine the effect of an exogenous CO on ATP-evoked activity in peripheral afferents using electrophysiological recording of action potentials from the trigeminal nerve in rat half-cranial preparations. The application of a CO donor, specifically CORM-2, like a solution saturated with CO gas, resulted in the activation of afferents and this effect was prevented by the inhibitor of soluble guanylate cyclase (GC)–ODQ. Preliminary CO application suppressed ATP-evoked excitation of trigeminal nerve afferents, and this effect was not mediated by the activation of soluble guanylate cyclase and cyclic nucleotides 8-Br-cGMP and 8-Br-cAMP. We suggest that CO increases the activity of trigeminal afferents through sGC activation and prevents the pro-nociceptive activity of ATP independent of the intracellular levels of cyclic nucleotides.