Avaliação da participação dos receptores potencial transiente vanilóide do tipo 1 e Toll like 4 e células gliais talâmicas durante a dor neuropática em camundongos

Abstract

Glial cells are involved in several chronic pains, including neuropathic pain (NP). They potentiate neuronal discharges arising from peripheral injury in the thalamus, by increasing the expression of receptors that activate intracellular signaling cascades, with consequent synthesis and release of pro-inflammatory cytokines. Thus, the present study investigated the participation of glial cells in the activation of TLR4 (Tolllike receptor 4) and TRPV1 (transient receptor of vanilloid potential 1) receptors and the MAPK p38 (p38 mapkinase)/NFκB (nuclear factor kappa B) pathway in the ventrobasal thalamus of mice with NP. For this, male C57BL6 mice were used, and chronic constriction injury (CCI) was used to induce mechanical allodynia. The evaluation of the motor coordination of neuropathic animals after treatment with pharmacological inhibitors was performed on the 14th day of neuropathy using the rota rod test. We examined the participation of glial cells, TLR4 and TRPV1 receptors, MAPK p38 and NFκB in the maintenance of mechanical allodynia in the thalamus of animals with 14 days of neuropathy. The thalamus was extracted to analyze the expression and protein synthesis of glial markers, Iba1 (ionized calcium-binding adapter molecule 1), TMEM119 (transmembrane protein 119) and GFAP (glial fibrillary acidic protein), of the TLR4 and TRPV1 receptors and of the p38 MAPK pathway using the Western Blot and RT-PCR technique, as well as the levels of TNFα and IL1β cytokines through ELISA. TLR4 activation in glial cells from neuropathic animals was also examined in the thalamus by means of immunofluorescence. As a result, manipulated microinjections in the ventrobasal thalamus contralateral to the CCI lesion significantly reduced mechanical allodynia without motor changes. Increased expression and protein synthesis for Iba1/TMEM119, GFAP and TLR4 were demonstrated in the ventrobasal thalamus, after 14 days of CCI, with increased levels of TNFα, corroborating the co-localization between glial markers and TLR4. Therefore, we suggest that glial cells play a decisive role in the neuromodulation of neuropathic pain at the thalamic level through activation of the TLR4 receptor, allowing NFκB gene transcription to produce TNFα, which contributes to the persistent state of pain.