In discussing migraine, it is imperative to distinguish an acute migraine from other headache classes, as well as chronic migraine from chronic headaches. Headache is a subjective symptom which is commonly reported among patients and ranges in severity from mild to severe. Its impact on health is so profound that it ranked in 2019 according to the Global Burden of Disease Study among the top ten conditions for disability-adjusted life-years (DALYs). DALYs are a measure of the number of years lost due to poor health, disability or early death to express disease burden (GBD 2019; Diseases and Injuries Collaborators, 2020). To facilitate diagnosing criteria for different types of headache, the International Headache Society (IHS) is responsible for publishing the International Classification of Headache Disorders and their third edition was published in 2018 based on emerging scientific evidence on headaches (Headache Classification Committee of the International Headache Society (IHS), 2018). Primary headaches are headaches without an underlying cause, and migraine in addition to tension-type headache are the two most common primary headache disorders with a quantifiable impact on global population health (Steiner and Stovner, 2023). It is also worth noting that migraines have been shown to be the second highest cause of disability among all populations globally using age-standardized years of life lived with disability (YLD) as a metric (Stovner et al., 2018; Steiner and Stovner, 2023). The loss of productivity associated with migraines is evident since the group most affected form the largest proportion of the workforce that drives national economies. The migraine disability assessment (MIDAS) questionnaire is a 5-point validated questionnaire that is also used to grade migraine associated disability using a scoring system (Stewart et al., 2000, 2001). According to the MIDAS tool, disability associated with migraine is described as the number of days missed at work or school, reduced productivity at home, work, and school as well as reduced social activities within 3 months (Stewart et al., 2000, 2001). After summing the number of days associated with headache/migraine-related disability, the total obtained is used to categorize severity into grades as shown in Table 1.

Acute migraine is described as headache that occurs unilaterally with a pulsating sensation, which lasts between 4 to 72 h and is associated with nausea and/or light sensitivity (photophobia) and sound sensitivity (phonophobia) (Headache Classification Committee of the International Headache Society (IHS), 2018). This headache class may be of moderate to severe intensity and may be exacerbated by physical activity. In some instances, the headache may be described as pressure, stabbing or aching (Kelman and Tanis, 2006). A patient who experiences headache, but not necessarily a migraine, on 15 or more days within a month for more than 3 months, with features of migraine headache on at least 8 days per month, can be said to have chronic migraine based on the ICHD-3 (Headache Classification Committee of the International Headache Society (IHS), 2018). Importantly, a challenge that these diagnostic criteria poses is the reliance on the patient’s ability to recall number of headache days accurately. It has been argued that the current definition of chronic migraine be reconsidered, and the threshold of days lowered since there are patients that have about 8 to 14 headache days per month but with a similar disease burden as 15 days or above (Ishii et al., 2021). These patients that experience a lower threshold may fail to get the needed medical treatment and represents another challenge in the treatment of chronic migraine.

According to the studies, there are two types of migraine classified based on the presence or absence of aura, i.e., migraine with aura and migraine without aura (Rasmussen and Olesen, 1992; Headache Classification Committee of the International Headache Society (IHS), 2018). An aura describes reversible neurological symptoms that have a short duration and may manifest before a migraine headache or occur concurrently with the headache. These may include one or more of the following symptoms: visual (an absolute or partial blind spot at a fixed point with zigzag pattern, which has a distorted and bright edge of convex shape), sensory disturbances (numbness, migratory pins and needles sensation on body, face and/or tongue), speech disturbance (aphasia characterized by difficulty in expressing oneself), motor weakness, brainstem symptoms (tinnitus, vertigo/dizziness, diplopia/double vision, dysarthria/difficulty speaking, decreased consciousness).

Other classifications of migraine exist which are based on their unique clinical presentations which may differ in onset, frequency, or associated symptoms. For instance, hemiplegic migraine describes migraine with associated motor weakness, while migrainous infarction is a type of migraine that co-occurs with ischemic infarctions in the brain. A detailed list of these classifications is given by the International Headache Society in the International Classification of Headaches, 3rd Edition and are out of the scope of this review.

There are some patients who experience a prodromal phase (also referred to as premonitory phase) that heralds an impending migraine headache (Giffin et al., 2003) and may start hours or a few days to the attack; it may manifest as tiredness, photophobia and/or phonophobia, or nausea. Yawning was shown to be a common prodromal symptom in a cross-sectional study of 2,714 patients conducted by Laurell et al. (2016). It must be noted that this prodromal phase is different from an aura since it does not involve neurological symptoms. A post-dromal phase has also been described and occurs following headache resolution. But it can last as long as 48 h and some of its symptoms include fatigue, difficulty in concentration and stiffness of the neck (Headache Classification Committee of the International Headache Society (IHS), 2018). In a study of 11,388 migraine patients, cutaneous allodynia was reported among about 63% of patients (Lipton et al., 2008). Cutaneous allodynia tends to be frequently associated with migraine and may occur with or without migraine headaches and some unilateral autonomic symptoms such as nasal congestion, lacrimation and eyelid edema which are associated with trigeminal autonomic cephalalgias have also been reported among migraine patients (Barbanti et al., 2002). Other symptoms reported include diarrhea, taste abnormality, osmophobia (Kelman and Tanis, 2006).

Migraine patients have self-reported factors that trigger attacks. In a survey conducted on patients with migraine, triggers identified were classified into precipitating and aggravating factors. Some precipitating triggers which were predominant among migraine patients included weather changes, smell, smoke and light, while aggravating factors also included physical activity, noise and motion that involved straining and bending over (Spierings et al., 2001). Other triggers include stress and fatigue, lack of sleep, not eating on time, menstruation, and this has been corroborated in other studies (Ierusalimschy and Moreira Filho, 2002; Andress-Rothrock et al., 2010; Hauge et al., 2010). Recognizing the predominance of migraines in females and menstruation as a trigger, ICHD-3 has a category for menstrual migraine which is differentiated based on whether migraines occur during menstruation only, during and outside the menstruation period, or outside the menstruation period. Some foods are also an identified trigger for migraine although a mechanism remains elusive. A survey conducted in an outpatient’s neurology clinic in Turkey on 146 migraine patients showed that migraine headache was triggered by intake of chocolate, coffee, alcohol, milk and cheese although this was in a small percentage of participants (Hauge et al., 2010). In a randomized controlled trial among 38,370 females that sought to quantify the triggering of migraine on consuming some foods such as alcohol, ice cream, citrus fruits, milk and processed meat, it was found that dairy products and chocolate could be linked to the onset of migraine with aura (Rist et al., 2015). This study relied upon the consumption of low food quantities as being a marker of the food being a potential trigger for migraine, which was a limitation. It could be that the low intake of these foods was due to other factors such as general dislike for the food, and there is no evidence to suggest that food intake contributed to the migraine headache experienced.

Currently, LU AG09222 is an investigational monoclonal antibody that targets PACAP38 and has completed a phase 2 clinical trial to evaluate their use in migraine headache prevention (Rasmussen et al., 2023). Cannabidiol in combination with cannabigerol and tetrahydrocannabinol is in a Phase 4 clinical trial to investigate its use as an adjuvant therapy to medication commonly used to prevent migraine (Kaup, 2023). These clinical trials demonstrate that additional targets may prove to be fruitful to examine and may yield novel migraine therapeutics.

In addition to these, some drugs have been repurposed and investigated in clinical trials to be used as monotherapy or combination therapy for acute and chronic migraine. Examples include lidocaine which is a local anesthetic and indomethacin which is an NSAID (Di Monda et al., 2003; Schwenk et al., 2022). Ketamine (NMDA receptor antagonist) and bupivacaine (local anesthetic) are other repurposed drugs also used to manage acute migraine (Afridi et al., 2013; Cady et al., 2015; Cohen et al., 2018). A summary of experimental therapeutics is provided in Table 5.

Status migrainosus is an intractable and severe form of migraine that persists beyond 72 h and may occur with or without an aura (Headache Classification Committee of the International Headache Society (IHS), 2018). To date, there is no established effective treatment for this migraine complication (Iljazi et al., 2020). This condition, while not fatal, is responsible for frequent hospitalizations and increased healthcare costs. A study by Harnod et al. (2018) also highlighted the tendency for suicide among status migrainosus patients (Harnod et al., 2018).

Migrainous infarction is a rare migraine complication diagnosed as an ischemic infarction, occurs in a patient experiencing migraine with aura that persists for more than 1 h, and the stroke onset coincides with the migraine attack (Headache Classification Committee of the International Headache Society (IHS), 2018). It must be highlighted that ischemic stroke may occur later in a migraine patient and will not be classified as a migrainous infarct because of its onset. However, stroke is also a migraine complication, with early research suggesting a possible link between the two (Murphy, 1955). Some studies have suggested that migraine could serve as a risk for developing ischemic stroke (Henrich and Horwitz, 1989) but with a higher association among women below 45 years of age (Tzourio et al., 1993).

In addition, magnetic resonance imaging studies point to an increased risk of migraine patients developing subclinical brain infarcts (Monteith et al., 2014) which is associated with higher migraine attack frequency (Kruit et al., 2004). There is evidence that points to migraine patients having ischemic white matter abnormalities (WMAs) seen as hyperintense lesions and suspected to be linked to microvascular damage (Ashina et al., 2021). It has been reported that as much as 59% of migraine patients could have white matter abnormalities (Bashir et al., 2013) and the CAMERA-1 study highlighted a higher prevalence of infratentorial cerebellar infarcts in patients with migraine with aura (Kruit et al., 2005). Compared to women without migraine women with migraine without aura had a higher deep white matter hyperintensity volume (Palm-Meinders et al., 2012). However, no link between WMAs and migraine frequency, migraine severity and migraine type has been found, but these changes may explain why migraine patients are at a risk of stroke-related conditions (Palm-Meinders et al., 2012). There are also studies that highlight an association between migraine and developing cardiovascular disease with relatively higher correlation among patients who experience migraine with aura, especially women (Bigal et al., 2010; Kurth et al., 2020; Ng et al., 2022). Some theories proposed to understand why migraines could lead to stroke include the pre-existence of a patent foramen ovale (PFO) in migraine patients (Lechat et al., 1988; West et al., 2018) although some studies do not confirm this association (Garg et al., 2010). PFO is a condition that is congenital and characterized by the presence of an open channel in the septum of the heart’s atrial wall that causes deoxygenated blood to shunt from the right atrium into the left atrium due to failure to close after birth. The foramen ovale is in the region of the fossa ovalis, a valve that closes under an increase in left atrial pressure at birth. This is different from atrial septal defect which is a structural defect in the wall that separates the right and left atrial chambers (Hari et al., 2015). It has also been proposed that CSD in migraine patients leads to stroke and migrainous infarction (Dohmen et al., 2008; Lauritzen et al., 2011). This hypothesis may not be correct, as while there is an apparent increase of stroke related cases among migraine patients, most studies do not demonstrate that treating migraine treatment also leads to reduced stroke events (Sacco and Carolei, 2011).

Depression is also a recognized migraine complication. In a prospective study conducted to understand the relationship between migraine and major depression, it was found that migraine could cause major depression and vice-versa (Breslau et al., 1994, 2003). Interestingly, this pattern was not observed with other forms of headache. There is some evidence that points to patients who have migraine with aura, especially women, having a higher predisposition to depression, as well as depression with comorbid anxiety, compared to migraine without aura patients (Oedegaard et al., 2006). The mental health complications of migraine also include a tendency for suicide and drug abuse potential (Breslau et al., 1991, 2012) as well as bipolar disorder, panic disorder and agoraphobia (Fasmer and Oedegaard, 2001). Brain activity studies of migraineurs point to an elevated intrinsic brain activity in the left medial prefrontal cortex with a decrease in the right gyrus rectus, observations also seen in patients with depression. Due to the involvement of the right gyrus rectus in emotional regulation, alterations in this region may also underlie the observation that migraine patients have higher concomitant emotional disorder and addiction diagnosis correlations (Ma et al., 2018). Serotonin modulation has also been proposed as a link between depression and migraine because of its role in both disease states (D’Andrea et al., 1989; Meltzer, 1989).

One of the major challenges in migraine drug discovery is robust translational model development that encompasses all the typical features of acute/chronic migraine with or without aura. While there have been attempts made to produce such a complete model, none exists currently. In humans, one strategy often utilized to induce an experimental migraine is the administration of nitroglycerin at a continuous infusion rate not exceeding 0.5 ug/kg/min to induce predictable migraine headache (Iversen et al., 1989; Onderwater et al., 2021) or as a sublingual tablet (Juhasz et al., 2003). Another is the administration of sildenafil orally which does not provoke vasodilation in the middle cerebral artery but is able to evoke migraine-like headache (Kruuse et al., 2003). However, this model has not been shown to induce migraine aura (Butt et al., 2022). Histamine has also been infused intravenously to induce migraine but is not commonly used to test experimental compound efficacy (Krabbe and Olesen, 1980; Lassen et al., 1995).

Like the human model, algogenic substances that trigger migraine-like headaches have been evaluated on rodents. Nitroglycerin-induced migraine is also a commonly used preclinical experimental model, especially rodents, due to the relative ease in route of administration, usually intraperitoneally (Pradhan et al., 2014; Marone et al., 2018). It may also be administered subcutaneously but this route of administration is not frequently used (Akerman et al., 2019). It also induces peptide and inflammatory marker expression, and has been shown to induce headache-like features that are similar to the temporal nature of migraine, described as a persistent headache (De Logu et al., 2019). Nitroglycerin administration also allows the development of acute and chronic migraine models. A dose of 10 mg/kg nitroglycerin given on alternating days for 9 days (5 doses) in mice as a chronic model of migraine has been shown to induce mechanical allodynia whose effects were suppressed with the administration of topiramate (Pradhan et al., 2014).

One challenge associated with nitroglycerin as a preclinical migraine model is that with this model, the nitroglycerin dose used in animals (i.e., 10 mg/kg), tends to be extremely high compared to the usual nitroglycerin dose administered to humans, approximately 0.5 ug/kg/min for 20 min (10 ug/kg) (Akerman et al., 2019). To address this issue, some studies utilize priming agents that sensitize rodents prior to lower nitroglycerin dose administration (Sureda-Gibert et al., 2022). In addition, some Sprague-Dawley rats are predisposed to lower thresholds of pain and develop spontaneous allodynia at lower (i.e., 0.1 mg/kg) nitroglycerin doses (Oshinsky et al., 2012). Another disadvantage of the preclinical nitroglycerin model is that CSD cannot be reliably induced (Bates et al., 2010) and it is unsuitable for studying the effects of migraine medications on migraine aura.

Most studies utilizing a chronic migraine model often involve the concomitant administration of nitroglycerin with the drug intervention under study, separated by at least 1 h (Pradhan et al., 2014). This chronic preclinical model does not directly parallel the human migraine state where the patient has a basally existing migraine predisposition and migraine attacks occur spontaneously. In addition, migraine therapies are usually clinically given after acute migraine headache or in the case of preventive therapy, daily treatment is given in the migraine patient to reduce future spontaneous migraine occurrence or for newer biologics, monthly or quarterly administration (Diener et al., 2007; Dodick et al., 2009; Pringsheim et al., 2010; Herd et al., 2018; Steiner et al., 2019; Pozo-Rosich et al., 2023). The current chronic migraine nitroglycerin model lacks this spontaneous nature and the seminal experiments utilizing this model showed a return to baseline about 6 days after discontinuing nitroglycerin administration, representing a “loss of chronicity” (Pradhan et al., 2014). In animal care, it is understandable that a state of perpetual nociception might be undesired, but this model is not technically “chronic.” Although such a model has not been developed, an ideal modified preclinical model would be a model that predisposes an animal to spontaneous migraine, coupled with the use of therapeutic preventative treatment administration, which would allow for the exposure of the animal to migraine stimuli, and would determine if the therapeutic reduces migraine headache frequency.

Another method employed to induce preclinical migraine model utilizes stereotaxic procedures to penetrate the skull of an alive animal and involves the infusion of substances directly on the dura mater This method allows for the interaction of these inflammatory substances with meningeal nociceptors to elicit a migraine-like response. However, this method to induce migraine-like behaviors is not without caveats. A new migraine model involving direct infusion of a histamine, serotonin, bradykinin, and prostaglandin E₂ (PGE₂) combination into the dural space caused periorbital allodynia (Han et al., 2017). However, in this study, the levels of PACAP were decreased rather than increased. While the authors concluded decreased PACAP was representative of decreased PACAP commonly observed clinically during the interictal phase of migraine, it is possible the application method may have been a confounder. A rat study utilizing serotonin and PGE₂ administration to the dural mater demonstrated these substances diffused into the cerebral cortex and into the cerebrospinal fluid (Zhao et al., 2017). In a similar rat study, using CGRP tagged with fluorescein, which was directly administered to the dura, the florescent marker diffused into nearby regions beyond its site of application in the cerebellum (Wang et al., 2022) and calls into question whether substances applied via stereotaxic surgery evoke responses beyond their interaction with dura mater neurons. Stereotaxic procedures commonly used to apply algogenic substances into the brain involve a level of tissue damage and stress, which may be sufficient to upregulate inflammatory markers (McCluskey et al., 2008).

In animals, behavioral changes, and biomarkers, described below in the next paragraph, that have a clinical correlation to human migraine endpoints are typically examined. Grimacing behaviors in rodents (mice and rats) have been monitored either via manual video scoring or automated via imaging software that is able to capture and score stereotypical headache-like responses, including orbital tightening, whisker changes, ear changes as well as cheek flattening after migraine-inducing agent administration (Langford et al., 2010; Sotocinal et al., 2011; Burgos-Vega et al., 2019; Viero et al., 2022). In rodents spontaneous head rubbing with the paws after migraine-inducing agent administration is also used to examine acute nociception, while allodynic responses including head or hind paw withdrawal responses via the von Frey assay is used as a surrogate for cutaneous allodynia which often occurs in migraine patients (De Logu et al., 2019). The tail flick and Hargreaves tests are used to examine thermal hyperalgesia (Bates et al., 2010; Harriott et al., 2019) which has been characterized in chronic and episodic migraine patients (Schwedt et al., 2011). Similarly, anxiety associated with migraine has been tested with the open field test and light/dark box test (Bates et al., 2010; Wang et al., 2021).

While no specific molecule unique to migraine has thus far been identified, therapeutic drugs suppress the expression of molecules implicated in migraine pathophysiology. Indeed, animal migraine models are able to induce the expression of these molecules, which strengthens the translational and face validity of these preclinical models. CGRP is frequently examined preclinically, due to its clinical overexpression in migraine patients. Immunohistochemistry, immunofluorescence or Western blot studies that utilize CGRP antibodies are often used (Lukács et al., 2015; Zhang et al., 2019). Measurement of the PACAP as well as other inflammatory substances, like PGE₂ and PGI₂, interleukin-6 (IL-6), tumor necrosis factor (TNF-α) and the c-Fos gene, all of which are typically upregulated in both clinical and preclinical migraine studies, have also been utilized (Han et al., 2017; De Logu et al., 2019). c-Fos is a proto-oncogene responsible for Fos protein production. It is expressed in the brain and plays multiple functions in brain development (Velazquez et al., 2015), inflammation (Hop et al., 2018) and stress response (Ceccatelli et al., 1989; Senba et al., 1993). It has also been implicated as a marker for pain, as it is expressed in the brain stem, hypothalamus, and spinal cord after noxious stimuli application (Harris, 1998). This gene is usually used as a marker to detect neuronal activation pathways and has aided in the confirmation that the trigeminovascular system is a significant migraine pathology contributor. In a seminal preclinical study, upon activation of the trigeminal system Fos and nitric oxide were both markedly upregulated (Hoskin et al., 1999). In addition, c-Fos expression was found to be elevated in a chronic migraine mouse model and in these mice administration of an approved CGRP antagonist, olcegepant, reduced c-Fos immunostaining in the medial prefrontal cortex and the trigeminal nucleus caudalis (Wu et al., 2022).

Migraine patients are predisposed to a secondary medication overuse headache, which occurs when drugs used to treat headache worsen headache and can also lead to drug-seeking behavior as well as drug abuse (Takahashi et al., 2021). In the America symptoms and treatment (MAST) study conducted in 2017, 15% of 13,649 migraine patients reported analgesic medicine overuse, with a higher prevalence in men, and predominantly involved opioids, triptans, barbiturates as well as ergot alkaloids (Schwedt et al., 2018). While it can easily be inferred that pain persistence may be the predominate driving force behind these patients taking more analgesic medicines, it is not known whether the migrainous state causes alterations in the brain that promotes substance use disorder and drug addiction. An early study by Breslau et al. (1991) showed about two to three fold increase in risk of alcohol abuse, nicotine dependence and illicit drug use among young people who suffered from migraine with or without aura as compared to healthy controls. Identifying the interplay between substance use and migraine disorders could expand the range of drug classes used to treat migraine patients to include therapeutics that lack abuse potential or serve as dual purpose migraine and substance use disorder medications.

Cannabis (Cannabis sativa) has been reported to have some beneficial effect in reducing migraine-associated headache (Baron, 2018). One study evaluated cannabis use among migraine patients, and found that patients self-reported more frequent cannabis concentrate were used more frequently due to greater reductions in headache than flower use (Cuttler et al., 2020). Few studies have investigated clinical cannabis use as a migraine therapeutic, but several preclinical studies using various cannabinoids have yielded findings that support cannabinoids as viable migraine therapeutics. Cannabis contains ^Δ9-tetrahydrocannabidiol, which is a cannabinoid receptor 1 (CB₁R) and cannabinoid receptor 2 (CB₂R) partial agonist (Devane et al., 1988; Munro et al., 1993; Ortiz et al., 2022). As WIN 55,212-2 mesylate, a CB₁R agonist suppressed CSD in rats, it is possible that the CB₁R may also be involved in the aura pathway (Kazemi et al., 2012). Although cannabis and cannabinoid-related compound medicinal use is restricted in some geographical regions of the world, there is potential for cannabinoid-based therapeutics to become viable inclusions within the pharmacological arsenal for migraine treatment and prevention.

The 5-HT₇ receptor is another serotonin receptor found in the spinal cord and is involved in descending pain pathway modulation (Rocha-González et al., 2005). In a rat model 5-HT₇ receptor agonist activity produced antinociception, and deletion of this receptor produced reduced opioid-induced antinociception (Yanarates et al., 2010). While this study highlights the potential for 5-HT₇ receptor agonists maybe useful analgesics, 5-HT₇ receptor antagonism may be more therapeutically advantageous as a migraine therapeutic. In addition, 5-HT₇ receptors have been identified in the trigeminal ganglion, cortex, and thalamus where it is postulated to be involved in CGRP release, as well as serotonin-induced meningeal artery vasodilation (Terrón and Martínez-García, 2007). In an experimental migraine model using male Sprague-Dawley rats, SB269970, a 5-HT₇ receptor antagonist, partially decreased trigeminal ganglion mediated CGRP release (Wang et al., 2010). Currently, the study of this receptor is restricted to experimental preclinical migraine models and further human clinical migraine research is needed.

Purinergic receptors are activated by adenosine or its nucleotides, adenosine diphosphate (ADP), adenosine triphosphate (ATP) and comprise part of the non-adrenergic non-cholinergic system (Burnstock, 2007; Ghiringhelli et al., 2009). While adenosine binds the P1 receptor family, both ATP and ADP bind, with varying affinity, to the P2Y receptor family. For example, ADP primarily stimulates P2Y₁, P2Y₆, and P2Y₁₂, while ATP stimulates P2Y₂ and P2Y₄. For a detailed review over purinergic receptors and neurotransmission, see the review article by Burnstock (2007). Evidence suggests there may be a purinergic role in migraine headache development. In study involving the mouse nitroglycerin chronic migraine model P2Y₁₂ receptor upregulation was observed, and both MRS2395 and clopidogrel, P2Y₁₂ receptor antagonists reduced CGRP and c-Fos expression in the trigeminal nucleus as well as decreased periorbital allodynia (Jing et al., 2019). While therapeutic targets of the P2Y₁₂ receptor might be desirable, drug antiplatelet activity is often associated with risk of bleeding or decreased anticoagulation with prolonged therapy, which can lead to treatment discontinuation (Becker et al., 2011). In the mouse nitroglycerin-induced chronic migraine model the P2X₄ receptor, another purinergic receptor subtype was upregulated in the trigeminal nucleus caudalis, and antagonism with a P2X₄ receptor antagonist, 5-BDBD, reduced its expression (Long et al., 2018). This antagonist also reduced CGRP and c-Fos expression as well as decreased cutaneous and periorbital allodynia. While these purinergic receptors may be promising targets, their widespread bodily distribution warrants selective identification of receptor types that are migraine pathogenesis specific.

The sensory perception of noxious temperature and chemical stimuli in peripheral tissue has been attributed to a group of cation channels called transient receptor potential channels (Caterina et al., 1997; McKemy et al., 2002; Story et al., 2003; Jordt et al., 2004; Bautista et al., 2005). The transient receptor potential vanilloid 1 (TRPV1) channel was first found to mediate the hot sensation of chili peppers due to the agonist activity of capsaicin, a vallinyl compound, on the channel. Capsaicin activates the TRPV1 channel to open to allow the influx of sodium and calcium ions, which leads to depolarization of nociceptors and the sensation of heat (Caterina et al., 1997; Yang and Zheng, 2017). The TRP family of channels behave similarly by allowing the influx of cations although they differ in their distribution in the body, physiology, and molecular mechanisms (Liedtke et al., 2000; McKemy et al., 2002; Moran, 2018). To date, the following superfamily of TRP channels have been isolated and characterized: TRP ankyrin (TRPA), TRP canonical (TRPC), TRP melastatin (TRPM), TRP mucolipin (TRPML), TRP polycystin (TRPP) and TRP vanilloid (TRPV) (Zheng, 2013; Moran, 2018). There is now emerging evidence that supports the role of TRP channels in migraine pathophysiology due to functional roles associated with their presence on neurons as well as astrocytes within the brain (Wilkerson et al., 2022). Some clinical evidence that highlighted the possible role of TRP channels was obtained when a study conducted on 555 patients found that single nucleotide polymorphisms in TRPV3 and TRPV1 correlated with susceptibility to migraine (Carreño et al., 2012). Conversely, an experiment conducted in male Sprague-Dawley rats revealed the presence of TRPA1 and TRPM8 in the trigeminal ganglion with a higher neuronal expression of TRPM8 in this region (Kobayashi et al., 2005). A limitation of this study is the exclusion of female rats and considering the sex difference that exist in migraine pathophysiology, it is difficult to accept the result of this study as generalizable. It has also been observed in preclinical study that TRPA1 agonist activity leads to the release of CGRP in the trigeminal region (Demartini et al., 2017). In this study, a hemisected preparation of adult male Wistar rat and C57BL/6 wild-type mouse skull was used. TRPA1 and TRPV1 knock-out mice on a C57BL/6 genetic background were also included. Acrolein and mustard oil, both of which have receptor agonist activity on TRPV1 and TRPA1 channels, dose-relatedly induced CGRP release in wild type animals only (Demartini et al., 2017). It is suspected that while TRPA1 channels may play a role in migraine pain, it does not directly activate nociceptors in the meninges to cause migraine and only has a modulatory role (Benemei et al., 2010; Edelmayer et al., 2012; Demartini et al., 2017). Parthenolide is a partial agonist at the TRPA1 channel, desensitizes the channel (Materazzi et al., 2013), and is an active constituent of the feverfew plant, a natural remedy used for headaches (Cady et al., 2011). Although there are no approved migraine therapeutics that act via TRP channels, parthenolide was found to reduce the release of CGRP and associated meningeal vasodilation in adult rats (Materazzi et al., 2013). While it is unclear whether agonist or antagonist activity of TRP channels will be most beneficial in treating migraines, elucidating the role of TRP channels in migraine pathology remains worth pursuing.