Migraine is the third most common disease in the world (behind dental caries and tension-type headache) with an estimated global prevalence of 15%, yet its etiology remains poorly understood. Recent clinical trials have heralded the potential of therapeutic antibodies that block the actions of the neuropeptide calcitonin gene-related peptide (CGRP) or its receptor to prevent migraine. Calcitonin gene-related peptide is believed to contribute to trigeminal nerve hypersensitivity and photosensitivity in migraine, but a direct role in pain associated with migraine has not been established. In this study, we report that peripherally administered CGRP can act in a light-independent manner to produce spontaneous pain in mice that is manifested as a facial grimace. As an objective validation of the orbital tightening action unit of the grimace response, we developed a squint assay using a video-based measurement of the eyelid fissure, which confirmed a significant squint response after CGRP injection, both in complete darkness and very bright light. These indicators of discomfort were completely blocked by preadministration of a monoclonal anti-CGRP-blocking antibody. However, the nonsteroidal anti-inflammatory drug meloxicam failed to block the effect of CGRP. Interestingly, an apparent sex-specific response to treatment was observed with the antimigraine drug sumatriptan partially blocking the CGRP response in male, but not female mice. These results demonstrate that CGRP can induce spontaneous pain, even in the absence of light, and that the squint response provides an objective biomarker for CGRP-induced pain that is translatable to humans.

Objective Migraine is a prevalent and disabling neurological disease. Its genesis is poorly understood, and there remains unmet clinical need. We aimed to identify mechanisms and thus novel therapeutic targets for migraine using human models of migraine and translational models in animals, with emphasis on amylin, a close relative of calcitonin gene‐related peptide (CGRP). Methods Thirty‐six migraine without aura patients were enrolled in a randomized, double‐blind, 2‐way, crossover, positive‐controlled clinical trial study to receive infusion of an amylin analogue pramlintide or human αCGRP on 2 different experimental days. Furthermore, translational studies in cells and mouse models, and rat, mouse and human tissue samples were conducted. Results Thirty patients (88%) developed headache after pramlintide infusion, compared to 33 (97%) after CGRP (p = 0.375). Fourteen patients (41%) developed migraine‐like attacks after pramlintide infusion, compared to 19 patients (56%) after CGRP (p = 0.180). The pramlintide‐induced migraine‐like attacks had similar clinical characteristics to those induced by CGRP. There were differences between treatments in vascular parameters. Human receptor pharmacology studies showed that an amylin receptor likely mediates these pramlintide‐provoked effects, rather than the canonical CGRP receptor. Supporting this, preclinical experiments investigating symptoms associated with migraine showed that amylin treatment, like CGRP, caused cutaneous hypersensitivity and light aversion in mice. Interpretation Our findings propose amylin receptor agonism as a novel contributor to migraine pathogenesis. Greater therapeutic gains could therefore be made for migraine patients through dual amylin and CGRP receptor antagonism, rather than selectively targeting the canonical CGRP receptor. ANN NEUROL 2021;89:1157–1171

The neuropeptide calcitonin gene-related peptide (CGRP) is a major player in migraine pathophysiology. Previous preclinical studies demonstrated that intracerebroventricular administration of CGRP caused migraine-like behaviors in mice, but the sites of action in the brain remain unidentified. The cerebellum has the most CGRP binding sites in the central nervous system and is increasingly recognized as both a sensory and motor integration center. The objective of this study was to test whether the cerebellum, particularly the medial cerebellar nuclei (MN), might be a site of CGRP action. In this study, CGRP was directly injected into the right MN of C57BL/6J mice via a cannula. A battery of tests was done to assess preclinical behaviors that are surrogates of migraine-like symptoms. CGRP caused light aversion measured as decreased time in the light zone even with dim light. The mice also spent more time resting in the dark zone, but not the light, along with decreased rearing and transitions between zones. These behaviors were similar for both sexes. Moreover, significant responses to CGRP were seen in the open field assay, von Frey test, and automated squint assay, indicating anxiety, tactile hypersensitivity, and spontaneous pain, respectively. Interestingly, CGRP injection caused significant anxiety and spontaneous pain responses only in female mice, and a more robust tactile hypersensitivity in female mice. No detectable effect of CGRP on gait was observed in either sex. These results suggest that CGRP injection in the MN causes light aversion accompanied by increased anxiety, tactile hypersensitivity, and spontaneous pain. A caveat is that we cannot exclude contributions from other cerebellar regions in addition to the MN due to diffusion of the injected peptide. These results reveal the cerebellum as a new site of CGRP actions that may contribute to migraine-like hypersensitivity.

Chronic complications of traumatic brain injury represent one of the greatest financial burdens and sources of suffering in the society today. A substantial number of these patients suffer from posttraumatic headache (PTH), which is typically associated with tactile allodynia. Unfortunately, this phenomenon has been understudied, in large part because of the lack of well-characterized laboratory animal models. We have addressed this gap in the field by characterizing the tactile sensory profile of 2 nonpenetrating models of PTH. We show that multimodal traumatic brain injury, administered by a jet-flow overpressure chamber that delivers a severe compressive impulse accompanied by a variable shock front and acceleration–deceleration insult, produces long-term tactile hypersensitivity and widespread sensitization. These are phenotypes reminiscent of PTH in patients, in both cephalic and extracephalic regions. By contrast, closed head injury induces only transient cephalic tactile hypersensitivity, with no extracephalic consequences. Both models show a more severe phenotype with repetitive daily injury for 3 days, compared with either 1 or 3 successive injuries in a single day, providing new insight into patterns of injury that may place patients at a greater risk of developing PTH. After recovery from transient cephalic tactile hypersensitivity, mice subjected to closed head injury demonstrate persistent hypersensitivity to established migraine triggers, including calcitonin gene-related peptide and sodium nitroprusside, a nitric oxide donor. Our results offer the field new tools for studying PTH and preclinical support for a pathophysiologic role of calcitonin gene-related peptide in this condition.

Background Circadian patterns of migraine attacks have been reported by patients but remain understudied. In animal models, circadian phases are generally not taken into consideration. In particular, rodents are nocturnal animals, yet they are most often tested during their inactive phase during the day. This study aims to test the validity of CGRP-induced behavioral changes in mice by comparing responses during the active and inactive phases. Methods Male and female mice of the outbred CD1 strain were administered vehicle (PBS) or CGRP (0.1 mg/kg, i.p.) to induce migraine-like symptoms. Animals were tested for activity (homecage movement and voluntary wheel running), light aversive behavior, and spontaneous pain at different times of the day and night. Results Peripheral administration of CGRP decreased the activity of mice during the first hour after administration, induced light aversive behavior, and spontaneous pain during that same period of time. Both phenotypes were observed no matter what time of the day or night they were assessed. Conclusions A decrease in wheel activity is an additional clinically relevant phenotype observed in this model, which is reminiscent of the reduction in normal physical activity observed in migraine patients. The ability of peripheral CGRP to induce migraine-like symptoms in mice is independent of the phase of the circadian cycle. Therefore, preclinical assessment of migraine-like phenotypes can likely be done during the more convenient inactive phase of mice.