Molecular Pain最新文献

Sleep deprivation can trigger migraine, and migraineurs often choose to sleep to relieve headaches during acute migraine. This study aimed to explore the effect of acute sleep deprivation on hyperalgesia induced by nitroglycerin in mice. In part one, after either 6-h sleep deprivation or 6-h normal sleep, mice were intraperitoneally injected with nitroglycerin or saline. The mechanical pain threshold and withdrawal latency of the hindpaw were measured every 30 min for 6 h. Next, the same sleep deprivation and injection procedure was performed with new mice, and mice were sacrificed 4.5 h after injection. The trigeminal nucleus caudalis and upper cervical spinal segments were taken for immunofluorescence Fos staining. In part two, after injection of saline or nitroglycerin, the mice were either deprived of sleep for 6 h or allowed to sleep without interference. The mechanical and thermal pain threshold were measured after 6 h. In part three, we compared the sleep time of mice after intraperitoneal injection of saline or nitroglycerin without interference. Sleep deprivation for 6 h did not cause any changes in the baseline pain thresholds in mice. However, pretreatment with 6-h sleep deprivation significantly prolonged the duration of hyperalgesia induced by nitroglycerin. Additionally, the expression of Fos at 4.5 h was significantly higher in the 6-h sleep deprivation and nitroglycerin group than in the other three groups. When intraperitoneal injection was given first, the mechanical pain threshold of the hind paw was significantly lower in the group that received nitroglycerin with 6-h sleep deprivation than in the other groups. Compared to the saline injection, one-time nitroglycerin injection would result in a significant increase in sleep latency and decrease in sleep duration for the normal mice. Acute sleep deprivation significantly aggravated the hyperalgesia induced by nitroglycerin in mice, which highlights the importance of sleep disorders for migraine.

Background: Kappa-opioid receptor (KOR) agonists are known for having opposite and/or different effects compared with Mu-opioid receptor (MOR) agonists. This study is aimed at clarifying the analgesic effect and tolerance of nalbuphine combined with morphine, and quantifying the mRNA and protein expression of spinal MOR and KOR in a mouse bone cancer pain (BCP) model treated with nalbuphine and morphine.

Method: BCP model was prepared in C3H/HeNCrlVr Mice by implanting the sarcoma cells into the intramedullary space of the femur. The paw withdrawal thermal latency (PWL) measured by thermal radiometer was used to assess thermal hyperalgesia. PWL testing was performed after implantation and drug administration according to the protocol. Hematoxylin-eosin staining in the spinal cord and x-ray in the femoral intramedullary canal was detected. Real-time PCR and western blot analysis played a role in detecting spinal MOR and KOR expression changes.

Results: In tumor-implanted mice, the spinal MOR and KOR protein and mRNA expression was down-regulated when compared to that in sham-implanted mice (p < 0.05). Morphine therapy can lead to a decrease in spinal μ receptor expression. Similarly, the nalbuphine therapy can lead to a decrease in the expression of κ receptor protein and mRNA at the spinal cord level (p < 0.05). Morphine, nalbuphine, or nalbuphine co-administration with morphine all can extend the paw withdrawal thermal latency (PWL) to radiant thermal stimulation in tumor-implanted mice (p < 0.05). Compared with the morphine treatment group, nalbuphine co-administration with morphine delayed the reduction of PWL value again (p < 0.05).

Discussion: BCP itself may induce down-regulation of the spinal MOR and KOR expression. A low dose of nalbuphine co-administration with morphine led to the delayed emergence of morphine tolerance. The part of the mechanism may be due to the regulation of spinal opioid receptors expression.

Background: Remifentanil-induced postoperative hyperalgesia (RIH) refers to a state of hyperalgesia or aggravated pre-existing pain after remifentanil exposure. There has been considerable interest in understanding and preventing RIH. However, the mechanisms responsible for RIH are still not completely understood. Toll-like receptor 4 (TLR4), a classic innate immune receptor, has been detected in sensory neurons and participates in various nociceptive conditions, whereas its role in RIH remains unclear. Transient receptor potential ankyrin 1 (TRPA1) always serves as a nociceptive channel, whereas its role in RIH has not yet been investigated. This study aimed to determine whether the TLR4 signaling pathway in sensory neurons engaged in the development of RIH and the possible involvement of TRPA1 during this process. Methods: A rat model of remifentanil-induced postoperative hyperalgesia (RIH) was established, which presented decreased paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL). The mRNA and protein expression levels of TLR4, phosphorylated NF-κB, and TRPA1 in the dorsal root ganglion (DRG) from RIH model were analyzed by real-time PCR, western blot, and immunofluorescence. The TLR4 antagonist TAK-242 and the TRPA1 antagonist HC-030031 were applied to determine the role of sensory neuron TLR4 signaling and TRPA1 in RIH. Results: Compared with control, PWMT and PWTL were significantly decreased in RIH model. Moreover, the mRNA and protein expression of TLR4 and TRPA1 in DRG were upregulated after remifentanil exposure together with increased NF-κB phosphorylation. TLR4 antagonist TAK-242 mitigated mechanical pain in RIH together with downregulated expression of TLR4, phosphorylated NF-κB, and TRPA1 in DRG neurons. In addition, TRPA1 antagonist HC-030031 also alleviated mechanical pain and decreased TRPA1 expression in RIH without affecting TLR4 signaling in DRG. Conclusions: Taken together, these results suggested that activation of TLR4 signaling pathway engaged in the development of RIH by regulating TRPA1 in DRG neurons. Blocking TLR4 and TRPA1 might serve as a promising therapeutic strategy for RIH.

Neuropathic pain (NP) is often accompanied by psychiatric comorbidities and currently lacks effective treatment. Prior research has shown that HDAC6 plays a crucial role in pain sensitization, but the specific mechanisms remain unclear. HDAC6 inhibitors have been found to alleviate mechanical allodynia caused by inflammation and peripheral nerve damage. In this study, we investigated the cellular mechanisms of HDAC6 in the development and maintenance of neuropathic pain. Our findings indicate that HDAC6 expression in the spinal cord (SC) is upregulated in a time-dependent manner following chronic constriction injury (CCI). HDAC6 is primarily expressed in neurons and microglia in the spinal cord. CCI-induced HDAC6 production was abolished by intrathecal injection of a microglia inhibitor. ACY-1215, a specific HDAC6 inhibitor, significantly reduced CCI-induced mechanical allodynia, but not thermal hyperalgesia. ACY-1215 also inhibited neuron activation and suppressed CCI-induced pyroptosis and neuroinflammatory responses. In summary, our results suggest that HDAC6 contributes to the development and maintenance of NP through neuronal activation and neuroinflammation. HDAC6 may be a promising target for treating NP.

STOML3 is a membrane bound scaffolding protein that has been shown to facilitate the opening of mechanically sensitive ion channels and contribute to noxious mechanical sensation, allodynia and hyperalgesia. In this study, we aimed to determine the role of STOML3 in noxious mechanical sensitivity of bone afferent neurons and carrageenan-induced acute inflammation in the bone. An in vivo, electrophysiological bone-nerve preparation was used to make recordings of the activity and sensitivity of bone afferent neurons that innervate the tibial marrow cavity in anaesthetised rats, in response to noxious mechanical stimuli delivered to the marrow cavity, before and after injection of either the STOML3 oligomerisation inhibitor OB-1 or vehicle, in either naïve animals or animals with carrageenan-induced inflammation of the marrow cavity. A dynamic weight-bearing apparatus was used to measure weight bearing in response to inflammatory pain before and after injection of OB-1 or saline into the tibial marrow cavity in the presence of carrageenan-induced inflammation. Electrophysiological recordings revealed that Aδ, but not C bone afferent neurons have a reduced discharge frequency in response to mechanical stimulation, and that carrageenan-induced sensitisation of Aδ, but not C bone afferent neurons was attenuated by inhibition of STOML3 oligomerisation with OB-1. Animals treated with OB-1 spent a significantly greater amount of time on the limb injected with carrageenan than animals treated with saline. Our findings demonstrate that inhibition of STOML3 oligomerisation reduces inflammatory bone pain by reducing the sensitivity of Aδ bone afferent neurons to mechanical stimulation. Targeting STOML3 may be an effective approach to reduce pain from noxious pressure and/or painful inflammatory pathology in bone.

Background: Trigeminal nerve injury causes orofacial pain that can interfere with activities of daily life. However, the underlying mechanism remains unknown, and the appropriate treatment has not been established yet. This study aimed to examine the involvement of interferon gamma (IFN-γ) signaling in the spinal trigeminal caudal subnucleus (Vc) in orofacial neuropathic pain. Methods: Infraorbital nerve (ION) injury (IONI) was performed in rats by partial ION ligation. The head-withdrawal reflex threshold (HWT) to mechanical stimulation of the whisker pad skin was measured in IONI or sham rats, as well as following a continuous intracisterna magna administration of IFN-γ and a mixture of IFN-γ and fluorocitrate (inhibitor of astrocytes activation) in naïve rats, or an IFN-γ antagonist in IONI rats. The IFN-γ receptor immunohistochemistry and IFN-γ Western blotting were analyzed in the Vc after IONI or sham treatment. The glial fibrillary acid protein (GFAP) immunohistochemistry and Western blotting were also analyzed after administration of IFN-γ and the mixture of IFN-γ and fluorocitrate. Moreover, the change in single neuronal activity in the Vc was examined in the IONI, sham, and IONI group administered IFN-γ antagonist. Results: The HWT decreased after IONI. The IFN-γ and IFN-γ receptor were upregulated after IONI, and the IFN-γ receptor was expressed in Vc astrocytes. IFN-γ administration decreased the HWT, whereas the mixture of IFN-γ and fluorocitrate recovered the decrement of HWT. IFN-γ administration upregulated GFAP expression, while the mixture of IFN-γ and fluorocitrate recovered the upregulation of GFAP expression. IONI significantly enhanced the neuronal activity of the mechanical-evoked responses, and administration of an IFN-γ antagonist significantly inhibited these enhancements. Conclusions: IFN-γ signaling through the receptor in astrocytes is a key mechanism underlying orofacial neuropathic pain associated with trigeminal nerve injury. These findings will aid in the development of therapeutics for orofacial neuropathic pain.

Synaptic plasticity such as Long-term potentiation (LTP) is a key mechanism for learning in central synapses including the cortex. There are two least two major forms of LTPs: presynaptic LTP and postsynaptic LTP. For postsynaptic LTP, the potentiation of AMPA receptor-mediated responses through protein phosphorylation is thought to be a key mechanism. Silent synapses have been reported in the hippocampus, but it is thought to be mainly present in the cortex during early development, and may contribute to maturation of the cortical circuit. However, recent several lines of evidence demonstrate that silent synapses may exist in mature synapses of adult cortex, and they can be recruited by LTP-inducing protocols, as well as chemical-induced LTP. In pain-related cortical regions, silent synapses may not only contribute to cortical excitation after peripheral injury, but also the recruitment of new cortical circuits as well. Thus, it is proposed that silent synapses and modification of functional AMPA receptors and NMDA receptors may play important roles in chronic pain, including phantom pain.

Important neurotrophic factors that are potentially involved in degenerative intervertebral disc (IVD) disease of the spine's lumbosacral (L/S) region include glial cell-derived neurotrophic factor (GDNF) and growth associated protein 43 (GAP-43). The aim of this study was to determine and compare the concentrations of GAP-43 and GDNF in degenerated and healthy IVDs and to quantify and compare the GAP-43-positive and GDNF-positive nerve fibers. The study group consisted of 113 Caucasian patients with symptomatic lumbosacral discopathy (confirmed by a specialist surgeon), an indication for surgical treatment. The control group included 81 people who underwent postmortem examination. GAP-43 and GDNF concentrations were significantly higher in IVD samples from the study group compared with the control group, and the highest concentrations were observed in the degenerated IVDs that were graded 4 on the Pfirrmann scale. In the case of GAP-43, it was found that as the degree of IVD degeneration increased, the number of GAP-43-positive nerve fibers decreased. In the case of GDNF, the greatest number of fibers per mm² of surface area was found in the IVD samples graded 3 on the Pfirrmann scale, and the number was found to be lower in samples graded 4 and 5. Hence, GAP-43 and GDNF are promising targets for analgesic treatment of degenerative IVD disease of the lumbosacral region of the spine.

Activation of neurons and glial cells in the dorsal root ganglion is one of the key mechanisms for the development of hyperalgesia. The aim of the present study was to examine the role of neuroglial activity in the development of opioid-induced hyperalgesia. Male rats were treated with morphine daily for 3 days. The resultant phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 in the dorsal root ganglion was analyzed by immunohistochemistry and Western blotting. Pain hypersensitivity was analyzed using behavioral studies. The amount of cytokine expression in the dorsal root ganglion was also analyzed. Repeated morphine treatment induced hyperalgesia and marked induction of phosphorylated ERK1/2 in the neurons and satellite glial cells on day 3. An opioid receptor antagonist, toll like receptor-4 inhibitor, MAP/ERK kinase (MEK) inhibitor and gap junction inhibitor inhibited morphine-induced hyperalgesia and ERK1/2 phosphorylation. Morphine treatment induced alteration of cytokine expression, which was inhibited by the opioid receptor antagonist, toll like receptor-4 inhibitor, MEK inhibitor and gap junction inhibitor. Dexamethasone inhibited morphine-induced hyperalgesia and ERK1/2 phosphorylation after morphine treatment. The peripherally restricted opioid receptor antagonist, methylnaltrexone, inhibited hyperalgesia and ERK1/2 phosphorylation. Morphine activates ERK1/2 in neurons and satellite glial cells in the dorsal root ganglion via the opioid receptor and toll like receptor-4. ERK1/2 phosphorylation is gap junction-dependent and is associated with the alteration of cytokine expression. Inhibition of neuroinflammation by activation of neurons and glia might be a promising target to prevent opioid-induced hyperalgesia.