Direct Activation of Orexin Neurons Attenuates Central Post‐Stroke Pain in Mice

BACKGROUND: Central post-stroke pain (CPSP) is a refractory complication that occurs after stroke and is classified as central neuropathic pain. Its pathophysiological mechanisms remain unclear and effective pharmacological treatments are limited. Previously, we demonstrated that hypothalamic orexin expression is reduced in a bilateral carotid artery occlusion (BCAO) mouse model of CPSP. Here, we investigated whether impairment of orexinergic signalling contributes to the pathophysiology of CPSP and whether chemogenetic activation of lateral hypothalamic (LH) orexin neurons alleviates mechanical hypersensitivity after cerebral ischaemia. METHODS: Mice were subjected to BCAO for 30 min. The von Frey test assessed mechanical hypersensitivity. To specifically activate orexin-expressing LH neurons, we bilaterally injected Flp-dependent adeno-associated viruses expressing excitatory DREADD hM3Dq into the LH of orexin-Flp mice. RESULTS: BCAO mice showed significantly increased withdrawal responses to mechanical stimulation on Day 3 after a stroke. Hypothalamic prepro-orexin mRNA expression was significantly decreased in BCAO mice. Cleaved caspase-3-positive cells and glial activation were observed in the hypothalamus, including the LH. Chemogenetic activation of orexin neurons significantly attenuated BCAO-induced mechanical hypersensitivity in heterozygous Orexin-Flp mice but not in homozygous Orexin-Flp mice. The antinociceptive effect was inhibited by pretreatment with SB334867, an orexin receptor 1 antagonist. CONCLUSION: These findings suggest that impaired hypothalamic orexinergic signalling may contribute to the pathophysiology of CPSP and that modulation of orexinergic signalling may represent a potential therapeutic strategy for post-stroke pain. SIGNIFICANCE STATEMENT: Central post-stroke pain (CPSP) lacks effective therapies, and its underlying mechanisms remain poorly understood. Using a mouse model of BCAO, we found reduced hypothalamic prepro-orexin expression together with neuroinflammatory and apoptotic changes in the hypothalamus. Chemogenetic activation of lateral hypothalamic orexin neurons attenuated mechanical hypersensitivity, at least in part through orexin receptor 1 signalling. These findings suggest that impaired hypothalamic orexinergic signalling contributes to the pathophysiology of CPSP and identify the orexinergic system as a potential therapeutic target for post-stroke pain.