Lightly stroking the lips or gently poking some skin regions can evoke mechanical itch in healthy human subjects. Sensitization of mechanical itch and persistent spontaneous itch are intractable symptoms in chronic itch patients. However, the underlying neural circuits are not well defined. We identified a subpopulation of excitatory interneurons expressing Urocortin 3::Cre (Ucn3 + ) in the dorsal spinal cord as a central node in the pathway that transmits acute mechanical itch and mechanical itch sensitization as well as persistent spontaneous itch under chronic itch conditions. This population receives peripheral inputs from Toll-like receptor 5-positive (TLR5 + ) Ab low-threshold mechanoreceptors and is directly innervated by inhibitory interneurons expressing neuropeptide Y::Cre (NPY + ) in the dorsal spinal cord. Reduced synaptic inhibition and increased intrinsic excitability of Ucn3 + neurons lead to chronic itch sensitization. Our study sheds new light on the neural basis of chronic itch and unveils novel avenues for developing mechanism-specific therapeutic advancements.

Novel treatments against migraine are an urgent medical requirement. The α6 subunit-containing GABA receptors (α6GABARs) are expressed in trigeminal ganglia (TG), the hub of the trigeminal vascular system (TGVS) that is involved in the pathogenesis of migraine. Here we reveal an unprecedented role of α6GABARs in ameliorating TGVS activation using several pharmacological approaches in an animal model mimicking pathological changes in migraine. TGVS activation was induced by intra-cisternal (i.c.) instillation of capsaicin in Wistar rats. Centrally, i.c. capsaicin activated the trigeminal cervical complex (TCC) measured by the increased number of c-Fos-immunoreactive (c-Fos-ir) TCC neurons. Peripherally, it elevated calcitonin gene-related peptide immunoreactivity (CGRP-ir) in TG and depleted CGRP-ir in the dura mater. Pharmacological approaches included a recently identified α6GABAR-selective positive allosteric modulator (PAM), the pyrazoloquinolinone Compound 6, two α6GABAR-active PAMs (Ro15-4513 and loreclezole), an α6GABAR-inactive benzodiazepine (diazepam), an α6GABAR-selective antagonist (furosemide), and a clinically effective antimigraine agent (topiramate). We examined effects of these compounds on both central and peripheral TGVS responses induced by i.c. capsaicin. Compound 6 (3-10 mg/kg, i.p.) significantly attenuated the TCC neuronal activation and TG CGRP-ir elevation, and dural CGRP depletion induced by capsaicin. All these effects of Compound 6 were mimicked by topiramate, Ro15-4513 and loreclezole, but not by diazepam. The brain-impermeable furosemide antagonized the peripheral, but not central, effects of Compound 6. These results suggest that the α6GABAR in TG is a novel drug target for TGVS activation and that α6GABAR-selective PAMs have the potential to be developed as a novel pharmacotherapy for migraine.

Background: Stress-induced analgesia (SIA) is an evolutionarily conserved phenomenon during stress. Neuropeptide S (NPS), orexins, substance P, glutamate and endocannabinoids are known to be involved in stress and/or SIA, however their causal links remain unclear. Here, we reveal an unprecedented sequential cascade involving these mediators in the lateral hypothalamus (LH) and ventrolateral periaqueductal gray (vlPAG) using a restraint stress-induced SIA model. Methods: Male C57BL/6 mice of 8-12 week-old were subjected to intra-cerebroventricular (i.c.v.) and/or intra-vlPAG (i.pag.) microinjection of NPS, orexin-A or substance P alone or in combination with selective antagonists of NPS receptors (NPSRs), OX 1 receptors (OX 1 Rs), NK 1 receptors (NK 1 Rs), mGlu 5 receptors (mGlu 5 Rs) and CB 1 receptors (CB 1 Rs), respectively. Antinociceptive effects of these mediators were evaluated via the hot-plate test. SIA in mice was induced by a 30-min restraint stress. NPS levels in the LH and substance P levels in vlPAG homogenates were compared in restrained and unrestrained mice. Results: NPS (i.c.v., but not i.pag.) induced antinociception. This effect was prevented by i.c.v. blockade of NPSRs. Substance P (i.pag.) and orexin-A (i.pag.) also induced antinociception. Substance P (i.pag.)-induced antinociception was prevented by i.pag. Blockade of NK 1 Rs, mGlu 5 Rs or CB 1 Rs. Orexin-A (i.pag.)-induced antinociception has been shown previously to be prevented by i.pag. blockade of OX 1 Rs or CB 1 Rs, and here was prevented by NK 1 R or mGlu 5 R antagonist (i.pag.). NPS (i.c.v.)-induced antinociception was prevented by i.pag. blockade of OX 1 Rs, NK 1 Rs, mGlu 5 Rs or CB 1 Rs. SIA has been previously shown to be prevented by i.pag. blockade of OX 1 Rs or CB 1 Rs. Here, we found that SIA was also prevented by i.c.v. blockade of NPSRs or i.pag. blockade of NK 1 Rs or mGlu 5 Rs. Restrained mice had higher levels of NPS in the LH and substance P in the vlPAG than unrestrained mice.

Neurons containing neuropeptide S (NPS) and orexins are activated during stress. Previously, we reported that orexins released during stress, via orexin OX1 receptors (OX1Rs), contribute to the reinstatement of cocaine seeking through endocannabinoid/CB1 receptor (CB1R)‐mediated dopaminergic disinhibition in the ventral tegmental area (VTA). Here, we further demonstrated that NPS released during stress is an up‐stream activator of this orexin‐endocannabinoid cascade in the VTA, leading to the reinstatement of cocaine seeking. Mice were trained to acquire cocaine conditioned place preference (CPP) by context‐pairing cocaine injections followed by the extinction training with context‐pairing saline injections. Interestingly, the extinguished cocaine CPP in mice was significantly reinstated by intracerebroventricular injection (i.c.v.) of NPS (1 nmol) in a manner prevented by intraperitoneal injection (i.p.) of SHA68 (50 mg/kg), an NPS receptor antagonist. This NPS‐induced cocaine reinstatement was prevented by either i.p. or intra‐VTA microinjection (i.vta.) of SB‐334867 (15 mg/kg, i.p. or 15 nmol, i.vta.) and AM 251 (1.1 mg/kg, i.p. or 30 nmol, i.vta.), antagonists of OX1Rs and CB1Rs, respectively. Besides, NPS (1 nmol, i.c.v.) increased the number of c‐Fos‐containing orexin neurons in the lateral hypothalamus (LH) and increased orexin‐A level in the VTA. The latter effect was blocked by SHA68. Furthermore, a 30‐min restraint stress in mice reinstated extinguished cocaine CPP and was prevented by SHA68. These results suggest that NPS is released upon stress and subsequently activates LH orexin neurons to release orexins in the VTA. The released orexins then reinstate extinguished cocaine CPP via an OX1R‐ and endocannabinoid‐CB1R‐mediated signaling in the VTA.

Temperature information is precisely processed in the nervous system. While progress has been made in identifying molecular thermosensors in the periphery, the neural circuits that process temperature information in the central nervous system remain unknown. Here we have identified an essential node in the neural circuitry for innocuous cool sensations. We found that a population of excitatory interneurons co-expressing Calbindin1 and Lbx1 (Calb1Lbx1) in the dorsal horn of the spinal cord is activated by innocuous cool temperatures. Genetic ablation or silencing of spinal Calb1Lbx1 neurons causes loss of innocuous cool but not noxious cold sensations. Further Brainbow labeling with expansion microscopy and electrophysiology showed that a small cluster of spinal Calb1Lbx1 interneurons in lamina I and the outer layer of lamina II represents the cooling-transmission neurons. These neurons receive monosynaptic connections from TRPM8+ primary sensory neurons and amplify the activity of cool-sensitive spinoparabrachial projection neurons. Our findings reveal a microcircuit in the dorsal spinal cord that specifically transmits innocuous cool sensations.