Barber, Kara R.

Background Traumatic brain injury (TBI) commonly elicits acute (APTH) and/or persistent (PPTH) post-traumatic headache. Calcitonin gene related peptide (CGRP) has been implicated as a contributor to PTH pathophysiology. We explored the possibility of sexual dimorphism in the effects of CGRP receptor (CGRP-R) blockade in a preclinical model of PTH induced by a mild TBI (mTBI) in male or female mice. Methods Mice were lightly anesthetized and placed on a tissue paper stage prior to receiving a sham procedure or mTBI resulting from a closed-head weight drop injury. Behavioral responses to periorbital and hindpaw tactile (von Frey filaments) or thermal (hot plate) stimuli over the first 14 days post-mTBI were evaluated as measures of APTH. The PPTH phase was studied following the resolution of mTBI-induced APTH at days 14 and 28. PPTH was precipitated by exposure to bright lights (i.e., bright light stress, BLS). Olcegepant was delivered subcutaneously either repeatedly beginning 2 h after mTBI to produce a sustained block of CGRP-R signaling across the APTH phase, or as a single administration on days 14 or 28 post-mTBI to evaluate possible effects during the PPTH phase. Results mTBI, but not sham-procedure, produced periorbital and hindpaw tactile allodynia, as well as thermal hypersensitivity in mice of both sexes. APTH-related hypersensitivity was transient and resolved by day 14 post-injury. No sex differences were observed in the magnitude or duration of APTH-related pain behaviors. Sustained CGRP-R blockade was, however, significantly more effective in female than male mice in inhibiting pain behaviors in the APTH phase and in preventing the emergence of BLS-induced PPTH. CGRP-R blockade following the resolution of mTBI-induced APTH pain behaviors, on either day 14 or 28, minimally altered BLS-induced PPTH in either sex. Conclusions Sustained CGRP-R blockade starting soon after mTBI significantly inhibited APTH and prevented the expression of PPTH with greater analgesic effects in females compared to males. Delayed CGRP-R blockade beginning after resolution of APTH phase was minimally effective in preventing expression of PPTH in either sex. These data are consistent with previous observations that CGRP induces pain behaviors preferentially in females. Early and continuous CGRP blockade following mTBI may represent a viable treatment option for PTH treatment and the prevention of PTH persistence, especially in females.

Background Acute therapies targeting calcitonin gene-related peptide (CGRP) for episodic migraine (EM) demonstrate efficacy in women, but evidence of efficacy in men remains to be established. By contrast, CGRP targeting therapies for migraine prevention are effective in both men and women with frequent EM or chronic migraine (CM). Preclinical studies have shown that supradural application of CGRP preferentially produces migraine-like pain behaviors in female rodents. We hypothesized that, in male mice, increased frequency of migraine-like pain may sensitize to nociceptive effects of CGRP and this might be associated with altered expression of CGRP in trigeminal ganglion (TG) neurons and/or in their dural projections. Methods CM was modeled in male and female mice by repeated administration of nitroglycerin (NTG). Medication overuse headache (MOH), a form of CM, was modeled by repeated daily administration of sumatriptan. Following resolution of transient cutaneous allodynia (CA) elicited by NTG or sumatriptan, mice received a sex specific subthreshold dose of supradural CGRP that does not elicit CA in naïve male or female mice, and CA was evaluated. CGRP-positive cell bodies in the ophthalmic V1 region of the trigeminal ganglion (TGV1) and CGRP-positive nerve fibers innervating the dura mater were assessed. Results Supradural administration of 1 pg of CGRP produced migraine-like pain behaviors in female, but not male, mice; a ten-fold lower dose was established as subthreshold in naïve female mice. Repeated NTG or sumatriptan produced transient CA in both female and male mice that resolved within 8–11 days after treatment cessation. Following resolution of CA, previously subthreshold doses of CGRP elicited CA in CM and MOH models in mice of both sexes, with no effects observed in vehicle treated controls. A higher number of CGRP-positive neurons in the TGV1 was found in naïve female compared to male mice. The number of CGRP-positive TGV1 neurons was increased in both sexes following repeated NTG. Similar nerve fiber density was observed in the dura mater of male and female mice and no differences were detected following repeated NTG. Conclusions As previously reported, CGRP produced female-selective migraine-like pain behaviors in naïve mice. Consistent with behavioral effects, female mice demonstrated a higher number of CGRP-positive cells in the TGV1. These findings appear relevant to clinical observations of female efficacy of CGRP-receptor antagonists for acute treatment in EM patients. In models of CM or MOH that are characterized by increased frequency of migraine-like pain, previously subthreshold doses of supradural CGRP now elicited migraine-like nociceptive behaviors in mice of both sexes. The increased pain responses were accompanied by increased number CGRP positive TGV1 cells in the NTG model in both female and male mice. These data suggest that increased frequency of migraine promotes physiological changes including increased expression of TGV1 CGRP along with sensitization to CGRP-induced nociception in both males and females. Thus, as EM transforms to CM, CGRP-dependent mechanisms may become increasingly important, consistent with observations of efficacy of CGRP targeting therapies for migraine prevention in both men and women. Our results also suggest the possibility of enhanced efficacy of CGRP-receptor antagonists for the acute treatment of migraine in men as migraine frequency increases.

Background We wished to explore possible sexual dimorphism in mechanisms sensitizing or activating meningeal nociceptors that can promote the headache phase of migraine. Methods Male and female C57BL6J mice received either supradural orexin B and an inflammatory mediator cocktail (IM) with migraine-like pain behaviors and photophobia recorded. Expression of orexin 2 receptor (OX2R) in trigeminal ganglion (TG) and phosphorylated extracellular signal-regulated kinases (ERK) levels in trigeminal nucleus caudalis (TNC) were evaluated. Orexin B-induced excitability of TG cells was assessed with patch-clamp electrophysiology. Intranasal delivery of CRISPR/Cas9 plasmids was used to edit the expression of OX2R in the TG. Results Supradural orexin B induced migraine-like pain behaviors, photophobia and increased TNC ERK phosphorylation exclusively in males. Blockade of orexin signaling with supradural suvorexant, a dual orexin receptor antagonist, prevented, but did not reverse, migraine-like pain in males induced by supradural IM cocktail. OX2R expression was higher in male TG and orexin B increased TG neuron excitability in males. Intranasal OX2R CRISPR/Cas9 reduced TG receptor expression and orexin B-induced TNC ERK phosphorylation and prevented migraine-like pain induced by supradural orexin B in males. Conclusions Our studies reveal a male-specific mechanism of TG nociceptor sensitization and migraine-like pain behavior mediated by orexin B/OX2R signaling. Sexually dimorphic mechanisms of trigeminal nociceptor sensitization and activation offer opportunities to improve patient outcomes by considering patient sex and may influence clinical trial design and interpretation.