Chronic pain is a major clinical problem with limited treatment options. Previous studies have demonstrated that activation of adenosine monophosphate-activated protein kinase (AMPK) can attenuate neuropathic pain. Inflammation/immune response at the site of complete Freund’s adjuvant (CFA) injection is known to be a critical trigger of the pathological changes that produce inflammatory pain. However, whether activation of AMPK produces an analgesic effect through inhibiting the proinflammatory cytokines, including interleukin-1β (IL-1β), in inflammatory pain remains unknown. Inflammatory pain was induced in mice injected with CFA. The effects of AICAR (5-aminoimidazole-4-carboxyamide ribonucleoside, an AMPK activator), Compound C (an AMPK inhibitor), and IL-1ra (an IL-1 receptor antagonist) were tested at day 4 after CFA injection. Inflammatory pain was assessed with von Frey filaments and hot plate. Immunoblotting, hematoxylin and eosin (H&E) staining, and immunofluorescence were used to assess inflammation-induced biochemical changes. The AMPK activator AICAR produced an analgesic effect and inhibited the level of proinflammatory cytokine IL-1β in the inflamed skin in mice. Moreover, activation of AMPK suppressed CFA-induced NF-κB p65 translocation from the cytosol to the nucleus in activated macrophages (CD68+ and CX3CR1+) of inflamed skin tissues. Subcutaneous injection of IL-1ra attenuated CFA-induced inflammatory pain. The AMPK inhibitor Compound C and AMPKα shRNA reversed the analgesic effect of AICAR and the effects of AICAR on IL-1β and NF-κB activation in inflamed skin tissues. Our study provides new information that AMPK activation produces the analgesic effect by inhibiting NF-κB activation and reducing the expression of IL-1β in inflammatory pain.

Purpose: Knee osteoarthritis (KOA) is a highly prevalent, chronic joint disorder, with chronic pain as its typical symptom. Although studies have shown that an activated peripheral CB2 receptor can reduce acute pain, whether the CB2 receptor is involved in electroacupuncture (EA) inhibiting chronic pain and the involved mechanism remains unclear. The aim of this study was to investigate whether EA may strengthen peripheral CB2 receptor-inhibited chronic pain in a mouse model of KOA. Materials and methods: KOA was induced by intra-articular injection of monosodium iodoacetate (MIA) into the left knee joint of mice. Thermal hyperalgesia was tested with the hot plate test, and mechanical allodynia was quantified using von Frey filaments. The expression of CB2 receptor and IL-1β were quantified by using immunofluorescence labeling. Results: EA treatment at 2 Hz+1 mA significantly increased the expression of CB2 receptor in fibroblasts and decreased the expression of IL-1β in the menisci compared with that in the KOA group. However, EA had no effect on the expression of IL-1β in CB2^−/− mice. At 2 Hz+1 mA, EA significantly increased mechanical threshold, thermal latency, and weight borne after KOA modeling. However, knockout of the CB2 receptor blocked these effects of EA. After 2 Hz+1 mA treatment, EA significantly reduced the Osteoarthritis Research Society International (OARSI) score after KOA modeling. However, EA had no significant effect on the OARSI score in CB2^−/− mice. Conclusion: EA reduced the expression of IL-1β by activating the CB2 receptor, thus inhibiting the chronic pain in the mouse model of KOA.

Purpose: We determined whether electroacupuncture (EA) reduces Netrin-1-induced myelinated primary afferent nerve fiber sprouting in the spinal cord and pain hypersensitivity associated with postherpetic neuralgia (PHN) through activation of μ-opioid receptors. Methods: PHN was induced by systemic injection of resiniferatoxin (RTX) in rats. Thirty-six days after RTX injection, a μ-opioid receptor antagonist, beta-funaltrexamine (β-FNA) or a κ-opioid receptor antagonist, nor Binaltorphimine (nor-BNI), was injected intrathecally 30 mins before EA, once every other day for 4 times. Mechanical allodynia was tested with von Frey filaments. The protein expression level of Netrin-1 and its receptors (DCC and UNC5H2) were quantified by using western blotting. The myelinated primary afferent nerve fiber sprouting was mapped with the transganglionic tracer cholera toxin B-subunit (CTB). Results: Treatment with 2 Hz EA at “Huantiao” (GB30) and “Yanglingquan” (GB34) decreased the mechanical allodynia at 22 days and the myelinated primary afferent nerve fiber preternatural sprouting into the lamina II of the spinal dorsal horn at 42 days after RTX injection. Also, treatment with 2 Hz EA reduced the protein levels of DCC and Netrin-1 and promoted the expression of UNC5H2 in the spinal dorsal horn 42 days after RTX injection. Furthermore, the μ-opioid receptor antagonist β-FNA, but not the κ-opioid receptor antagonist nor-BNI, reversed the effect of EA on neuropathic pain caused by RTX. In addition, morphine inhibited the Netrin-1 protein level induced by RTX in SH-SY5Y cells. Conclusions: Through activation of μ-opioid receptors, treatment with EA reduces the expression level of DCC and Netrin-1 and changes a growth-permissive environment in spinal dorsal horn into an inhibitory environment by increasing UNC5H2, thus decreasing RTX-caused primary afferent nerve sprouting in the spinal dorsal horn and neuropathic pain.

Urination, a fundamental physiological process, is intricately regulated by central neural circuits. The periaqueductal gray (PAG) is a critical hub for urination control, yet the specific neuronal subtypes involved remain undefined. Here, we identified somatostatin (SST)-expressing neurons in the lateral and ventrolateral PAG (l/vlPAG) as key regulators of urination. SST⁺ neurons in the l/vlPAG exhibited activity closely aligned with urination onset in freely moving animals. Optogenetic activation of these neurons reliably triggered urination and bladder contraction, whereas their acute inhibition at urination onset halted ongoing urination. Moreover, activation of l/vlPAG SST⁺ neurons projecting to the pontine micturition center (PMC) elicited urination and bladder contraction, effects that were absent following pelvic nerve transection. These findings reveal that l/vlPAG SST⁺ neurons regulate urination through the PAG-PMC pathway, providing new insights into bladder control and potential therapeutic targets for bladder dysfunction.

Rising global temperatures have turned heatstroke from a seasonal concern into a year-round public health crisis, yet its underlying neuropathological mechanisms remain elusive. Central to this problem are hypothalamic warm-sensitive neurons (WSNs), the master regulators that integrate central and peripheral thermal signals. This review synthesizes recent advances linking the molecular architecture of WSNs to heatstroke pathophysiology. Emerging evidence redefines WSNs not simply as temperature sensors, but as putative neuromodulatory hubs that may coordinate neuroinflammation, blood-brain barrier (BBB) disruption, and multi-organ failure through hypothesized neurotransmitter-cytokine crosstalk. By mapping the functional hierarchy of WSNs—from molecular thermoregulation to systemic control of thermoeffectors—this work proposes targeted neurotherapeutic strategies, offering a novel neural circuit-based framework for managing heatstroke.