Ketamine potentiates TRPV1 receptor signaling in the peripheral nociceptive pathways.

TRPV1 is a cation channel expressed in peripheral nociceptive pathways and its activation can trigger nociception signals to the brain. Ketamine is an intravenous anesthetic routinely used for anesthesia induction and with potent analgesic activity. Despite its proven depressant action on peripheral sensory pathways, the relationship between ketamine and TRPV1 receptors is still unclear. In this study, we evaluated the effect of ketamine injected peripherally in a rat model of spontaneous pain induced by capsaicin. We also investigated the effect of ketamine on Ca2+ transients in cultured dorsal root ganglia (DRG) neurons and HEK293 cells expressing the TRPV1 receptor (HEK-TRPV1 cells). Intraplantar administration of ketamine caused an unexpected increase in nocifensive behavior induced by capsaicin. Incubation of HEK-TRPV1 cells with 10 µM ketamine increased TRPV1 and PKCє phosphorylation. Ketamine potentiated capsaicin-induced Ca2+ transients in HEK-TRPV1 cells and DRG neurons. Ketamine also prevented TRPV1 receptor desensitization induced by successive applications of capsaicin. єV1-2, a PKCє inhibitor, reduced potentiation of capsaicin-induced Ca2+ transients by ketamine. Taken together, our data indicate that ketamine potentiates TRPV1 receptor sensitivity to capsaicin through a mechanism dependent on PKCє activity.

Glycine transporters type 1 inhibitor promotes brain preconditioning against NMDA-induced excitotoxicity.

Brain preconditioning is a protective mechanism, which can be activated by sub-lethal stimulation of the NMDA receptors (NMDAR) and be used to achieve neuroprotection against stroke and neurodegenerative diseases models. Inhibitors of glycine transporters type 1 modulate glutamatergic neurotransmission through NMDAR, suggesting an alternative therapeutic strategy of brain preconditioning. The aim of this work was to evaluate the effects of brain preconditioning induced by NFPS, a GlyT1 inhibitor, against NMDA-induced excitotoxicity in mice hippocampus, as well as to study its neurochemical mechanisms. C57BL/6 mice (male, 10-weeks-old) were preconditioned by intraperitoneal injection of NFPS at doses of 1.25, 2.5 or 5.0 mg/kg, 24 h before intrahippocampal injection of NMDA. Neuronal death was evaluated by fluoro jade C staining and neurochemical parameters were evaluated by gas chromatography-mass spectrometry, scintillation spectrometry and western blot. We observed that NFPS preconditioning reduced neuronal death in CA1 region of hippocampus submitted to NMDA-induced excitotoxicity. The amino acids (glycine and glutamate) uptake and content were increased in hippocampus of animals treated with NFPS 5.0 mg/kg, which were associated to an increased expression of type-2 glycine transporter (GlyT2) and glutamate transporters (EAAT1, EAAT2 and EAAT3). The expression of GlyT1 was reduced in animals treated with NFPS. Interestingly, the preconditioning reduced expression of GluN2B subunits of NMDAR, whereas did not change the expression of GluN1 or GluN2A in all tested doses. Our study suggests that NFPS preconditioning induces resistance against excitotoxicity, which is associated with neurochemical changes and reduction of GluN2B-containing NMDAR expression.