CGRP Administration Into the Cerebellum Evokes Light Aversion, Tactile Hypersensitivity, and Nociceptive Squint in Mice

Abstract

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.

Involvement of the cerebellum in migraine

“…However, the precise sites of CGRP action in the central nervous system that contribute to migraine attacks remain to be fully elucidated. Recent studies have presented the posterior thalamus (Sowers et al, 2020 ) and the cerebellum (Wang et al, 2022a , b ) as candidate sites for CGRP action in migraine pathophysiology.…”

“…Based on the expression of CGRP receptor subunits RAMP1 and CLR in the MN (Warfvinge and Edvinsson, 2019 ), a recent study investigated the effect of CGRP delivery into the MN on migraine-like behaviors (Wang et al, 2022b ). CGRP administration into the MN induced light-aversive behavior in both male and female mice, significant anxiety-like and squinting responses in female mice and more robust tactile hypersensitivity in female mice (Wang et al, 2022b ). This discovery suggests that CGRP can act in the cerebellum to induce migraine-like behaviors (Wang et al, 2022b ).…”

“…CGRP administration into the MN induced light-aversive behavior in both male and female mice, significant anxiety-like and squinting responses in female mice and more robust tactile hypersensitivity in female mice (Wang et al, 2022b ). This discovery suggests that CGRP can act in the cerebellum to induce migraine-like behaviors (Wang et al, 2022b ). Later, Wang et al ( 2022a ) discovered that optical stimulation of CGRP neurons in the MN induced light aversion only in female mice and tactile sensitivity in both sexes.…”

Stimulation of CGRP-expressing neurons in the medial cerebellar nucleus induces light and touch sensitivity in mice

“…Specifically, stimulation of MN CGRP neurons led to light aversion in female mice, and significant tactile hypersensitivity in ipsilateral hind paws in both sexes. A previous publication reported that direct injection of CGRP into the MN induced light aversion in both sexes, anxiety and squinting behavior in female mice, and more robust contralateral cutaneous allodynia in females than males ( Wang et al, 2022 ). Interestingly, with both studies, the responses tended to be more predominant in female mice.…”

“…These findings suggest that the MN, specifically CGRP and its receptors in the MN, may be associated with migraine pathophysiology. A previous study has demonstrated that CGRP injections into the MN induced migraine-like behaviors, including light aversion, anxiety-like, cutaneous allodynia and nociceptive squinting behaviors ( Wang et al, 2022 ). Due to the CGRP distribution in the MN, we pursued the idea of the CGRP-expressing neurons of the MN (MN CGRP ) being involved in migraine pathophysiology.…”