Estudo da modulação da via PI3Kγ/AKT/NOS/NO/GCs/GMPc e canais para potássio sobre a dor neuropática em ratos submetidos a constrição do nervo ciático

Abstract

Neuropathic pain is induced by an injury to the somatosensory nervous system closely related to changes in defective neuronal plasticity, which keeps the pain chronic and intense. Associated with maladaptive plasticity responses, changes also occur in endogenous pain control systems. Many analgesic systems have as one of their mechanisms of action the activation of receptors coupled to Gi protein, which signals via PI3Kγ / Akt / NOS / NO / GCs / cGMP. This signal transduction promotes the opening of the channels for potassium and the efflux of this ion, inducing neuronal hyperpolarization, preventing the conduction of nerve impulses. Thus, the present work evaluated the participation of the PI3Kγ / Akt / NOS / NO / GCs / GMPc pathway and of the potassium channels in the endogenous modulation of neuropathic pain. For this, Wistar rats, weighing 180 g, were used for sciatic nerve constriction surgery. These animals were treated with intraplantar injection of AS605240 (90 μg / paw), PI3Kγ enzyme inhibitor, ODQ (100 μg / paw), soluble guanylate cyclase enzyme inhibitor and channel blockers for potassium, dequalinium (50 μg / paw) which blocks sensitive to low conductance calcium, Paxilin (50 μg / paw) which blocks sensitive to high conductance calcium, tetraethylammonium (30 μg / paw) which blocks voltage dependent and glibenclamide (80 μg / paw) that blocks ATP-sensitive channels. After the treatments were applied, they were submitted to an algesimetric paw compression test. Akt, inducible nitric oxide synthase and ATP-sensitive potassium channels in the midbrain and in the paws of healthy and neuropathic animals were also quantified by the western blot technique. Finally, the levels of nitric oxide in the paw and midbrain of neuropathic and healthy animals were indirectly quantified through the Griess Reaction. Initially, we found that neuropathic pain induces a very intense hypoalgesia that gradually declines reaching the baseline threshold around the 5th day, with hyperalgesia being observed from the 6th day after constriction. The nociceptive threshold continues to gradually decrease until around the 10th day, remaining constant, indicating that neuropathic pain is consolidated. Thus, we inhibit some components of the PI3Kγ / Akt / NOS / NO / GCs / cGMP pathway and potassium channels on days 6 and 12 post-constriction to assess induction and already consolidated neuropathic pain, respectively. With the inhibition of the components of the studied pathway, we verified that PI3Kɣ participates in analgesic processes both in induction and in consolidated neuropathy, nNOS already participates in analgesic processes in induction and of hyperalgesics in neuropathy while iNOS and soluble guanylate cyclase always play an analgesic role. With the blocking of the channels, we observed that the voltage-gated potassium channels do not participate in neuropathy at any time. Low- conductance calcium-dependent channels participate in analgesia, but only in the induction phase, while high-conductance channels participate in hyperalgesic events in consolidated neuropathy. The ATP-sensitive potassium channels, on the other hand, participate in all phases of analgesic processes. Akt quantification reveals a high concentration at the time of induction both in the paw and in the midbrain, but the levels are not maintained in consolidated neuropathy. The same occurs with iNOS in the paw, but in the midbrain the concentrations are already low on the 6th day after the sciatic nerve constriction. The quantification of potassium channels sensitive to ATP showed an increase in these paws in neuropathic animals compared to healthy animals on the first day and on the 6th, the levels returned to the values of non-neuropathic animals. Meanwhile, in the midbrain there was a gradual increase and on the 12th day it reached the highest levels in relation to the days evaluated in this study. When dosing NO through the measurement of nitrite, we observed that, in the paw and in the midbrain, the concentration increases during induction, but returns to non-neuropathic levels during consolidated neuropathy. Therefore, we can conclude that there is a dual role for the IP3Kγ / Akt / NOS / NO / GCs / GMPc pathway, in which at some moments components of this pathway can act in analgesic processes and at other times in hyperalgesic processes. And finally, we also observed that the ATP-sensitive potassium channels participate in the modulation of neuropathic pain in an analgesic way and the support of the high levels of this channel in the central nervous system may indicate a possibility of direct treatment, without going through the dualities of the studied pathways. FINANCIAL SUPPORT: CAPES, CNPq, FAPEMIG. CEUA Protocol: 173/2014.