The 5-HT6 Receptors in the Ventrolateral Orbital Cortex Attenuate Allodynia in a Rodent Model of Neuropathic Pain

Neuroprotective Effect of Hydrogen Sulfide Subchronic Treatment Against TBI-Induced Ferroptosis and Cognitive Deficits Mediated Through Wnt Signaling Pathway

Emerging evidence shows that targeting ferroptosis may be a potential therapeutic strategy for treating traumatic brain injury (TBI). Hydrogen sulfide (H2S) has been proven to play a neuroprotective role in TBI, but little is known about the effects of H2S on TBI-induced ferroptosis. In addition, it is reported that the Wnt signaling pathway can also actively regulate ferroptosis. However, whether H2S inhibits ferroptosis via the Wnt signaling pathway after TBI remains unclear. In this study, we first found that in addition to alleviating neuronal damage and cognitive impairments, H2S remarkably attenuated abnormal iron accumulation, decreased lipid peroxidation, and improved the expression of glutathione peroxidase 4, demonstrating the potent anti-ferroptosis action of H2S after TBI. Moreover, Wnt3a or liproxstatin-1 treatment obtained similar results, suggesting that activation of the Wnt signaling pathway can render the cells less susceptible to ferroptosis post-TBI. More importantly, XAV939, an inhibitor of the Wnt signaling pathway, almost inversed ferroptosis inactivation and reduction of neuronal loss caused by H2S treatment, substantiating the involvement of the Wnt signaling pathway in anti-ferroptosis effects of H2S. In conclusion, the Wnt signaling pathway might be the critical mechanism in realizing the anti-ferroptosis effects of H2S against TBI. TBI induces ferroptosis-related changes characterized by iron overload, impaired antioxidant system, and lipid peroxidation at the chronic phase after TBI. However, NaHS subchronic treatment reduces the susceptibility to TBI-induced ferroptosis, at least partly by activating the Wnt signaling pathway.

The 5-HT7 receptors in the VLO contribute to the development of morphine-induced behavioral sensitization in rats

The 5-hydroxytryptamine 7 receptor (5-HT₇R) is one of the most recently cloned serotonin receptors which have been implicated in many physiological and pathological processes including drug addiction. Behavioral sensitization is the progressive process during which re-exposure to drugs intensified the behavioral and neurochemical responses to drugs. Our previous study has demonstrated that the ventrolateral orbital cortex (VLO) is critical for morphine-induced reinforcing effect. The aim of the present study was to investigate the effect of 5-HT₇Rs in the VLO on morphine-induced behavioral sensitization and their underlying molecular mechanisms. Our results showed that a single injection of morphine, followed by a low challenge dose could induce behavioral sensitization. Microinjection of the selective 5-HT₇R agonist AS-19 into the VLO during the development phase significantly increased morphine-induced hyperactivity. Microinjection of the 5-HT₇R antagonist SB-269970 suppressed acute morphine-induced hyperactivity and the induction of behavioral sensitization, but had no effect on the expression of behavioral sensitization. In addition, the phosphorylation of AKT (Ser 473) was increased during the expression phase of morphine-induced behavioral sensitization. Suppression of the induction phase could also block the increase of p-AKT (Ser 473). In conclusion, we demonstrated that 5-HT₇Rs and p-AKT in the VLO at least partially contribute to morphine-induced behavioral sensitization.

Phosphorylation of Neurofilament Light Chain in the VLO Is Correlated with Morphine-Induced Behavioral Sensitization in Rats

Neurofilament light chain (NF-L) plays critical roles in synapses that are relevant to neuropsychiatric diseases. Despite postmortem evidence that NF-L is decreased in opiate abusers, its role and underlying mechanisms remain largely unknown. We found that the microinjection of the histone deacetylase (HDAC) inhibitor Trichostatin A (TSA) into the ventrolateral orbital cortex (VLO) attenuated chronic morphine-induced behavioral sensitization. The microinjection of TSA blocked the chronic morphine-induced decrease of NF-L. However, our chromatin immunoprecipitation (ChIP)-qPCR results indicated that this effect was not due to the acetylation of histone H3-Lysine 9 and 14 binding to the NF-L promotor. In line with the behavioral phenotype, the microinjection of TSA also blocked the chronic morphine-induced increase of p-ERK/p-CREB/p-NF-L. Finally, we compared chronic and acute morphine-induced behavioral sensitization. We found that although both chronic and acute morphine-induced behavioral sensitization were accompanied by an increase of p-CREB/p-NF-L, TSA exhibited opposing effects on behavioral phenotype and molecular changes at different addiction contexts. Thus, our findings revealed a novel role of NF-L in morphine-induced behavioral sensitization, and therefore provided some correlational evidence of the involvement of NF-L in opiate addiction.

Migraine signaling pathways: amino acid metabolites that regulate migraine and predispose migraineurs to headache

Migraine is a common, debilitating disorder for which attacks typically result in a throbbing, pulsating headache. Although much is known about migraine, its complexity renders understanding the complete etiology currently out of reach. However, two important facts are clear, the brain and the metabolism of the migraineur differ from that of the non-migraineur. This review centers on the altered amino acid metabolism in migraineurs and how it helps define the pathology of migraine.

5-HT7 Receptor Is Involved in Electroacupuncture Inhibition of Chronic Pain in the Spinal Cord

Knee osteoarthritis (KOA) is a common and disabling condition characterized by attacks of pain around the joints, and it is a typical disease that develops chronic pain. Previous studies have proved that 5-HT₁, 5-HT₂, and 5-HT₃ receptors in the spinal cord are involved in electroacupuncture (EA) analgesia. The 5-HT₇ receptor plays antinociceptive role in the spinal cord. However, it is unclear whether the 5-HT₇ receptor is involved in EA analgesia. The 5-HT₇ receptor is a stimulatory G-protein (Gs)-coupled receptor that activates adenylyl cyclase (AC) to stimulate cyclic adenosine monophosphate (cAMP) formation, which in turn activates protein kinase A (PKA). In the present study, we found that EA significantly increased the tactile threshold and the expression of the 5-HT₇ receptor in the dorsal spinal cord. Intrathecal injection of 5-HT₇ receptor agonist AS-19 mimicked the analgesic effect of EA, while a selective 5-HT₇ receptor antagonist reversed this effect. Moreover, intrathecal injection of AC and PKA antagonists prior to EA intervention prevented its anti-allodynic effect. In addition, GABA_A receptor antagonist bicuculline administered (intrathecal, i.t.) prior to EA intervention blocked the EA effect on pain hypersensitivity. Our data suggest that the spinal 5-HT₇ receptor activates GABAergic neurons through the Gs–cAMP–PKA pathway and participates in EA-mediated inhibition of chronic pain in a mouse model of KOA.