Induction of Migraine-Like Photophobic Behavior in Mice by Both Peripheral and Central CGRP Mechanisms

• Published in: The Journal of neuroscience 2017-01, Vol.37 (1), p.204-216
• Main Authors: Mason, Bianca N, Kaiser, Eric A, Kuburas, Adisa, Loomis, Maria-Cristina M, Latham, John A, Garcia-Martinez, Leon F, Russo, Andrew F
• Format: Article
• Language: English
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.2967-16.2017

The neuropeptide calcitonin gene-related peptide (CGRP) is a key player in migraine. Although migraine can be treated using CGRP antagonists that act peripherally, the relevant sites of CGRP action remain unknown. To address the role of CGRP both within and outside the CNS, we used CGRP-induced light-aversive behavior in mice as a measure of migraine-associated photophobia. Peripheral (intraperitoneal) injection of CGRP resulted in light-aversive behavior in wild-type CD1 mice similar to aversion seen previously after central (intracerebroventricular) injection. The phenotype was also observed in C57BL/6J mice, although to a lesser degree and with more variability. After intraperitoneal CGRP, motility was decreased in the dark only, similar to motility changes after intracerebroventricular CGRP. In addition, as with intracerebroventricular CGRP, there was no general increase in anxiety as measured in an open-field assay after intraperitoneal CGRP. Importantly, two clinically effective migraine drugs, the 5-HT sub(1B/D)agonist sumatriptan and a CGRP-blocking monoclonal antibody, attenuated the peripheral CGRP-induced light aversion and motility behaviors. To begin to address the mechanism of peripheral CGRP action, we used transgenic CGRP-sensitized mice that have elevated levels of the CGRP receptor hRAMP1 subunit in nervous tissue (nestin/hRAMP1). Surprisingly, sensitivity to low light was not seen after intraperitoneal CGRP injection, but was seen after intracerebroventricular CGRP injection. These results suggest that CGRP can act in both the periphery and the brain by distinct mechanisms and that CGRP actions may be transmitted to the CNS via indirect sensitization of peripheral nerves.