CGRP-dependent sensitization of PKC-δ positive neurons in central amygdala mediates chronic migraine

Background To investigate specific brain regions and neural circuits that are responsible for migraine chronification. Methods We established a mouse model of chronic migraine with intermittent injections of clinically-relevant dose of nitroglycerin (0.1 mg/kg for 9 days) and validated the model with cephalic and extracephalic mechanical sensitivity, calcitonin gene-related peptide (CGRP) expression in trigeminal ganglion, and responsiveness to sumatriptan or central CGRP blockade. We explored the neurons that were sensitized along with migraine chronification and investigated their roles on migraine phenotypes with chemogenetics. Results After repetitive nitroglycerin injections, mice displayed sustained supraorbital and hind paw mechanical hyperalgesia, which lasted beyond discontinuation of nitroglycerin infusion and could be transiently reversed by sumatriptan. The CGRP expression in trigeminal ganglion was also upregulated. We found the pERK positive cells were significantly increased in the central nucleus of the amygdala (CeA), and these sensitized cells in the CeA were predominantly protein kinase C-delta (PKC-delta) positive neurons co-expressing CGRP receptors. Remarkably, blockade of the parabrachial nucleus (PBN)-CeA CGRP neurotransmission by CGRP(8-37) microinjection to the CeA attenuated the sustained cephalic and extracephalic mechanical hyperalgesia. Furthermore, chemogenetic silencing of the sensitized CeA PKC-delta positive neurons reversed the mechanical hyperalgesia and CGRP expression in the trigeminal ganglion. In contrast, repetitive chemogenetic activation of the CeA PKC-delta positive neurons recapitulated chronic migraine-like phenotypes in naive mice. Conclusions Our data suggest that CeA PKC-delta positive neurons innervated by PBN CGRP positive neurons might contribute to the chronification of migraine, which may serve as future therapeutic targets for chronic migraine.

Automated summary

Our study investigated the specific brain regions and neural circuits responsible for chronic migraine. We established a mouse model of chronic migraine by injecting nitroglycerin and found that the central nucleus of the amygdala (CeA) and PKC-delta positive neurons play important roles in migraine chronification. Blocking CGRP neurotransmission from the parabrachial nucleus (PBN) to CeA attenuated the mechanical hyperalgesia, while chemogenetic silencing of sensitized CeA PKC-delta positive neurons reversed the hyperalgesia. These findings suggest potential therapeutic targets for chronic migraine.