Lee, Grace J.

Abstract Migraine attacks can be provoked in people with underlying primary headache disorders by multiple peripheral mechanisms suggesting the possible convergence of trigeminal nociceptive inputs onto a common, unknown central circuit. As calcitonin gene-related peptide (CGRP) expressing cells in the parabrachial nucleus (PBN) have been implicated in nociplastic pains, we hypothesized that (a) PBN CGRP-expressing neurons and their projections to the central amygdala (CeA) may be an essential central relay of multiple peripheral inputs promoting injury-free migraine headache and (b) this pathway may prioritize threat from activation of cranial afferents over other nociceptive inputs. Periorbital cutaneous allodynia (CA) was determined following supradural application of a cocktail of inflammatory mediators (IM), CGRP or pituitary adenylate cyclase-activating polypeptide (PACAP), or systemic administration of nitroglycerin (NTG) in CalcaCre or wild-type mice. Decreased rearing and photophobia were respectively evaluated as measures of ongoing headache and light-evoked migraine-like pain. Phosphorylation of extracellular signal-regulated kinases (pERK) was evaluated to assess regional neuronal activation. Compared with vehicle, supradural IM increased pERK in the trigeminal nucleus caudalis and PBN, but not in the paraventricular thalamus. Chemogenetic activation (Gq-DREADD) of PBN CGRP neurons elicited CA and photophobia while decreasing rearing. Lesioning of PBN neurons with ibotenic acid suppressed CA produced by supradural IM. Chemogenetic silencing (Gi-DREADD) or expression of tetanus toxin (TeNT) in PBN Calca neurons to prevent neurotransmitter release also inhibited CA elicited by supradural IM, CGRP, PACAP or systemic NTG. CRISPR/Cas9 editing of CeA receptor-associated membrane protein-1 (Ramp1) prevented IM-induced migraine-like symptoms revealing CGRP/CGRP-receptor activation from PBN→CeA projections. In contrast, PBN lesions, chemogenetic manipulation, and TeNT expression in PBN Calca cells and CeA Ramp1 CRISPR/Cas9 editing did not affect acute pain responses induced by hind paw IM injection, intraperitoneal acetic acid, or acute nociceptive behaviors from IM stimulation of the maxillary (V2) and mandibular (V3) branches of the trigeminal nerve. These data reveal a central pathway composed of PBN Calca neurons and CeA CGRP receptor signaling that is both sufficient to elicit migraine-like pain in naive mice and necessary to promote migraine-like pain following activation of the ophthalmic (V1) branch of the trigeminal nerve. Importantly, this pathway is essential for acute pain arising from V1 trigeminal, but dispensable for acute stimuli from other nociceptive afferents. The prioritization of V1 acute nociception suggests evolutionary importance for detecting threats to the head to promote survival through advantageous behaviors such as defensive coping observed in migraine.

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 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.