Neuropharmacology
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Descending brainstem control of spinal nociceptive processing permits a dynamic and adaptive modulation of ascending sensory information. Chronic pain states are frequently associated with enhanced descending excitatory drive mediated predominantly through serotonergic neurones in the rostral ventromedial medulla. In this study, we examine the roles of spinal 5-HT2A and 5-HT3 receptors in modulating ascending sensory output in normal and neuropathic states. ⋯ The inhibitory profiles of both drugs were altered in SNL rats; ondansetron additionally inhibited neuronal responses to lower intensity punctate mechanical stimuli and noxious heat evoked responses, whereas ketanserin inhibited innocuous and noxious evaporative cooling evoked responses. Neither drug had any effect on dynamic brush evoked responses nor on spontaneous firing rates in both sham and SNL rats. These data identify novel modality and intensity selective facilitatory roles of spinal 5-HT2A and 5-HT3 receptors on sensory neuronal processing within the spinothalamic-somatosensory cortical pathway.
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Previous studies have revealed that neuropeptide VGF (non-acronymic) C-terminal peptide TLQP-62 rapidly activates brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB)/α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor/mammalian target of rapamycin (mTOR) signaling and produces antidepressant-like actions in rodents. In addition, acute TLQP-62 infusion also markedly changes the AMPA receptor GluA1 subunit phosphorylation at Ser 845 (pGluA1 Ser845) in the PFC of mice, indicating that the GluA1 may contributes to the rapid antidepressant-like effects of TLQP-62. However, how to regulate the TrkB-mediated signaling and GluA1 changes in the prefrontal cortex (PFC) by TLQP-62 remains unclear. ⋯ Further investigation demonstrated that this effect of TLQP-62 was mediated by activation of TrkB and mTOR, which proceeded to decrease bicaudal C homolog 1 gene (BICC1) and increase synaptic protein expression, including GluA1 subunit and pGluA1 Ser845. Notably, we further found that beneficial effects of TLQP-62 on depression-like behaviors and TrkB/mTOR/BICC1 signaling, GluA1 phosphorylation and GluA1 activation in the PFC of mice were significantly abolished by TrkB antagonist ANA-12. In conclusion, our findings indicate that TrkB/mTOR/BICC1 signaling, GluA1 phosphorylation and GluA1 activation in the PFC may involve in the rapid-acting antidepressant-like actions of TLQP-62 in mice.