Progesterone receptors regulate susceptibility to spreading depression

Migraine patients often experience sensory symptoms called auras accompanying the headaches. Cortical spreading depression (CSD), a slow-propagating wave of neuroglial depolarization followed by hyperpolarization is proposed to be the neurological mechanism underlying these auras. We have previously found that progesterone regulates susceptibility to migraine through progesterone receptor (PR) activation. Here, we determined if PR signaling also regulates susceptibility to CSD. We used gonadally-intact and ovariectomized, estrogen-primed female mice expressing PRs or lacking them in the brain. CSDs were induced with dural application of KCl (1 M) and recorded using saline-filled glass electrodes placed in the cortex. PRs were modulated using agonist segesterone and antagonist RU-486. PR expression in the somatosensory cortex was evaluated using mice expressing a cre recombinase under the control of Pgr promoter, stereotaxically injected with adeno-associated virus (AAV) serotype 9 encoding flexed GFP. PR expression in excitatory or inhibitory neurons and distinctions in the cortical layer-specific expression were determined. The effect of chemogenetic silencing of PR-expressing somatosensory cortical neurons on CSD susceptibility was also evaluated using AAV9 expressing cre-driven hM4Di. PRs were expressed in the excitatory neurons of the somatosensory cortex. Their expression was stronger in layer 4-6 cortical neurons than in layer 2/3 neurons. PR activation increased CSD frequency and accelerated their propagation speed. In contrast, PR antagonism or their genetic deletion suppressed CSDs. Chemogenetic silencing of PR-expressing somatosensory cortical neurons also reduced the CSD frequency. These findings demonstrate the critical role of progesterone-PR signaling in regulating CSD and enhance our understanding of female hormonal regulation of migraine pathophysiological mechanisms.