Abstract
Background: Central sensitization is an important mechanism of chronic migraine (CM) and is related to the inflammatory response of microglia. The NOD-like receptor protein 3 (NLRP3) inflammasome may regulate the inflammatory process of microglia in several neurological diseases, but its role in CM is largely unknown. Therefore, the aim of this study was to identify the precise role of microglial NLRP3 in CM. Methods: An experimental CM mouse model was established by repeated intraperitoneal (i.p) injection with nitroglycerin (NTG). We evaluated the expression levels of NLRP3 and its downstream interleukin (IL)-1β protein in the trigeminal nucleus caudalis (TNC; which is a central area relevant to migraine pain) at different time points. To further examine the effects of the NLRP3 inflammasome pathway on central sensitization of CM, we examined MCC950, an NLRP3 inflammasome-specific inhibitor, and IL-1ra, an IL-1β antagonist, whether altered NTG-induced mechanical hyperalgesia of the periorbital area and hind paw. The effect of MCC950 and IL-1ra on c-Fos, phosphorylated extracellular signal-regulated kinase (p-ERK) and calcitonin gene-related peptide (CGRP) expression in the TNC were also analyzed. The cell localization of NLRP3 and IL-1β in the TNC was evaluated by immunofluorescence staining. Results: Repeated NTG administration induced acute and chronic mechanical hyperalgesia and increased expression of NLRP3 and IL-1β. Blockade of NLRP3 or IL-1β reduced NTG-induced hyperalgesia, and this effect was accompanied by a significant inhibition of the NTG-induced increase in p-ERK, c-Fos and CGRP levels in the TNC. Immunofluorescence staining revealed that NLRP3 and IL-1β were mainly expressed in microglia in the TNC, and the IL-1β receptor, IL-1R, was mainly expressed in neurons in the TNC. Conclusions: These results indicate that NLRP3 activation in the TNC participates in the microglial-neuronal signal by mediating the inflammatory response. This process contributes to the central sensitization observed in CM.