Porreca, Frank

Abstract Mild traumatic brain injury (mTBI) commonly induces transient acute (APTH) or persistent (PPTH) post-traumatic headache (PTH) that often resembles migraine. As orexin B sensitizes male but not female murine, nonhuman primate, and human dorsal root ganglion neurons and supradural orexin B/orexin receptor 2 (OX2R) signaling elicits migraine-like pain in naïve male, but not female, mice we explored possible sexually dimorphic contributions of orexin B/OX2R to PTH. In mice of both sexes, mTBI-induced transient cephalic allodynia, a surrogate measure of APTH. After APTH resolution, allodynia was reinstated by exposure to normally innocuous stress or by inhalational delivery of a subthreshold concentration of umbellulone, a TRPA1 agonist, suggesting the expression of PPTH. In contrast to these nonselective stimuli, subthreshold supradural orexin B induced PPTH only in male mTBI mice. Intranasal delivery of a CRISPR/Cas9 plasmid to edit trigeminal OX2R expression prevented APTH and development of PPTH selectively in male mTBI mice. Daily oral suvorexant, a dual orexin receptor antagonist (DORA), beginning immediately after mTBI, prevented APTH as well as PPTH. Critically, starting suvorexant treatment after resolution of APTH also prevented stress- or umbellulone-induced PPTH. EEG/EMG-defined sleep architecture or immobility-defined sleep was not disrupted in this mTBI model suggesting that suvorexant benefits are unlikely related to sleep modulation. Our findings reveal a male-specific mechanism of PTH maintained by orexin B/OX2R signaling and suggest that approved DORAs may be beneficial in treating APTH and preventing transition to PPTH in men. Importantly, DORAs may also be effective in men with established PPTH.

Background Headache is a common symptom following mild traumatic brain injury (mTBI). Post-traumatic headache (PTH), a secondary headache disorder that develops after mTBI, often persists for months or years. To identify potential recovery mechanisms and prognostic biomarkers, the present study investigated whether longitudinal changes in pain-induced brain activation differ between healthy controls (HC) and PTH participants showing headache improvement and those without improvement. Methods Thirty-three participants who met International Classification of Headache Disorders, 3rd edition, criteria for acute PTH within 59 days post-mTBI and 33 HC participants were included with no significant differences in demographics. All participants underwent functional magnetic resonance imaging scans at baseline, four weeks, and 16 weeks post-enrollment using a thermal stimulation paradigm with noxious and non-painful heat stimuli. ‘Painful vs. Non-Painful Heat’ contrasts were generated using SPM12. PTH improvement was assessed at three months post-enrollment via electronic headache diaries. Two-sample t -tests compared the brain activation between HC and PTH at baseline. Linear mixed-effects models examined longitudinal changes for HC, PTH improvement and non-improvement groups across visits. Generalized linear models compared these groups within visits. Results Baseline analysis revealed several regions with significantly higher activation in acute PTH compared to HC, including bilateral postcentral gyrus, right superior temporal gyrus, right middle temporal gyrus, left inferior parietal gyrus, right superior parietal gyrus, left ventral striatum, left olfactory cortex, left gyrus rectus, and left middle occipital gyrus. Over time, the PTH improvement group demonstrated progressive normalization across all identified brain regions, whereas the non-improvement group showed only partial normalization in left ventral striatum, left olfactory cortex, and left gyrus rectus. Sustained elevated activation in specific regions distinguished PTH participants without headache improvement from those with headache improvement, suggesting potential biomarkers for persistent PTH. Conclusions Our findings demonstrate significantly altered pain-induced brain activations in participants with acute PTH compared to HC. Longitudinal analysis revealed distinct recovery trajectories: progressive normalization in the improvement group versus persistent alterations in the non-improvement group. These neuroimaging patterns may serve as biomarkers for identifying individuals at risk for persistent PTH, with implications for early intervention and personalized treatment approaches.

Recent reports support the startling conclusion that peripheral nociceptors, the first link in pain transmission, are sexually dimorphic. The mechanisms promoting pain in men and women are therefore likely to be different, suggesting the need to consider patient sex as a factor in managing pain and painful conditions such as migraine. Many patients do not achieve sufficient benefit from available therapies and migraine therefore remains a major unmet medical need. The concept of sexual dimorphism in pain mechanism reveals previously unrecognized gaps in knowledge of migraine pathophysiology and in treatment outcomes. As migraine is highly female prevalent, our knowledge is based on studies conducted predominately in women. Data from these studies have rarely been analyzed and reported based on sex, limiting our interpretation of the occurrence, timing and severity of disease symptoms as well as possible differences in treatment efficacy in men. Inclusion of a higher proportion of men in both mechanistic investigations and clinical trials is therefore needed. Advancing our knowledge and improving therapeutic outcomes will require both preclinical and clinical investigations that address the contribution of sex in headache pain and other non-painful symptoms of migraine that impact the quality of life for patients. This viewpoint highlights the importance of considering sex as a variable in advancing our understanding of migraine pathophysiology and therapy. Consideration of patient sex could influence current clinical practice and the design of clinical studies.

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 Women with endometriosis are more likely to have migraine. The mechanisms underlying this co-morbidity are unknown. Prolactin, a neurohormone secreted and released into circulation from the anterior pituitary, can sensitize sensory neurons from female, but not male, rodents, monkeys and human donors. Methods We used a syngeneic model of endometriosis to determine whether elevated prolactin levels can sensitize trigeminal ganglion neurons and increase vulnerability to migraine pain. Results Mice with endometriotic lesions showed increased serum prolactin levels and developed persistent abdominal, but not cephalic, allodynia. However, inhalation of a transient receptor potential ankyrin 1 agonist, umbellulone, a known environmental trigger of headache in some patients, elicited cephalic allodynia in mice with endometriosis but not sham controls, suggesting that endometriosis can promote sensitization of trigeminal neurons and migraine attacks. Endometriosis dysregulated the expression of prolactin receptor isoforms in trigeminal neurons and increased their excitability measured by in vitro patch clamp electrophysiology. Inhibition of pituitary prolactin following a 2-week treatment with a dopamine receptor agonist, cabergoline, prevented cephalic allodynia elicited by activation of trigeminal afferents with umbellulone. Cabergoline treatment also normalized the expression of prolactin receptor isoforms in trigeminal ganglia and the hyperexcitability of trigeminal neurons. Conclusions These data demonstrate that circulating prolactin in endometriosis promotes vulnerability to migraine through sensitization of trigeminal afferents. Clinically available dopamine receptor agonists or novel monoclonal antibodies targeting prolactin signaling may be effective for migraine prevention in women with endometriosis.

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.

Abstract Migraine and sleep disorders are common co-morbidities. Patients frequently link their sleep to migraine attacks suggesting a potential causal relationship between these conditions. However, whether migraine pain promotes or disrupts sleep or whether sleep disruption can increase the risk of migraine remains unknown. We assessed the potential impact of periorbital allodynia, a measure consistent with migraine-like pain, from multiple preclinical models on sleep quantity and quality. Additionally, we evaluated the possible consequences of sleep deprivation in promoting susceptibility to migraine-like pain. Following the implantation of electroencephalogram/electromyography electrodes to record sleep, mice were treated with either single or repeated systemic injections of nitroglycerin at the onset of their active phase (i.e. nocturnal awake period). Neither single nor repeated nitroglycerin affected the total sleep time, non-rapid eye movement sleep, rapid eye movement sleep, sleep depth or other measures of sleep architecture. To account for the possible disruptive effects of the surgical implantation of electroencephalogram/electromyography electrodes, we used immobility recordings as a non-invasive method for assessing sleep-wake behaviour. Neither single nor repeated nitroglycerin administration during either the mouse sleep (i.e. daylight) or active (i.e. night) periods influenced immobility-defined sleep time. Administration of an inflammatory mediator mixture onto the dura mater at either sleep or active phases also did not affect immobility-defined sleep time. Additionally, inhalational umbellulone-induced migraine-like pain in restraint-stressed primed mice did not alter immobility-defined sleep time. The possible influence of sleep disruption on susceptibility to migraine-like pain was evaluated by depriving female mice of sleep over 6 h with novel objects, a method that does not increase circulating stress hormones. Migraine-like pain was not observed following acute sleep deprivation. However, in sleep-deprived mice, subthreshold doses of systemic nitroglycerin or dural calcitonin gene-related peptide induced periorbital cutaneous allodynia consistent with migraine-like pain. Our data reveal that while migraine-like pain does not significantly disrupt sleep, sleep disruption increases vulnerability to migraine-like pain suggesting that a therapeutic strategy focused on improving sleep may diminish migraine attacks.

Sexual dimorphism in functional pain suggests the need of developing sex-specific therapies.

Female selective nociceptor sensitization and opioid-induced hyperalgesia result from an imbalance of prolactin receptor isoforms.