Envolvimento central dos receptores 5-HT1A na antinocicepção induzida pela fotobiomodulação em modelo animal de dor neuropática

Abstract

Neuropathic pain is due to injury or disease that affects the somatosensory system. It is a poorly adaptive response, has no biological value and is an important cause of permanent disability, especially when chronic. The concern to reduce neuropathic pain and its consequences has stimulated research, in animal models, with different resources. In particular, photobiomodulation has been widely used in investigations on tissue regeneration and pain reduction. However, its mechanisms of action, mainly in the central modulation of the painful stimulus, remain unclear in the literature. Studies have shown that the serotonergic system is involved in pain modulation, mainly by activating the supraspinatus pathway, however the role of photobiomodulation (FBM) in this pain modulation process is still not well understood. Thus, the aim of this study was to investigate the central involvement of 5-HT1A receptors on the nociceptive behavior of mice submitted to chronic sciatic nerve constriction (CCI) and subsequent application of FBM. Subsequently, the animals received an infusion of WAY100635 (5-HT1A receptor antagonist) or saline intracerebroventricular followed by irradiation with infrared laser (808 nm), continuous-wave mode, optical power of 100 mW, and dose of 0 J/cm2 (Control Group) and 50 J/cm2. Hyperalgesia to the thermal stimulus was evaluated by the hot plate test, while allodynia to the mechanical stimulus, by von Frey filament. After the CCI, the animals showed a reduction in the nociceptive threshold (p <0.001) when compared to the SHAM group. In the von Frey test, only the CCI + Saline + FBM 50 J/cm² group showed an increase in the nociceptive threshold after applying the FBM at all times of measurement with (p <0.001) in comparison with the other groups (2) CCI + SALINE + FBM 0 J/cm², (3) CCI + WAY100635 + FBM 50 J/cm² and (4) CCI + WAY100635 + FBM 0 J/cm². Similar results were also found in the hot plate test, where the CCI + Saline + FBM 50 J/cm² group showed an increase in the nociceptive threshold after the application of FBM in the following moments of assessment of nociceptive latency 120 and 180 minutes. In view of the results presented, it is possible to suggest the involvement of 5HT1A receptors in the CNS, since WAY100635 was able to reverse the antinociceptive effect provided by FBM in animals submitted to CCI.