Study of GABAergic modulation in the circuitry involved in analgesia induced by the electrical stimulation of the insular cortex

Abstract

Neuropathic pain is one of the most rebellious conditions to the analgesic treatment, making the search for new therapies for this type of pain extremely urgent. The protocol of the electrical stimulation of the insular cortex (ESI) standardized by our group was effective for the treatment of rats with neuropathic pain, which was also able to alter the neuronal activity of regions that are known to constitute endogenous modulation of pain, such as anterior cingulate cortex (ACC) and periaquedutal gray matter (PAG). The aim of this project is to evaluate the modulation promoted by the gabaergic system in the circuitry constituted by Insular Cortex-ACC-PAG- rostral ventromedial medulla (RVM)- spinal cord- dorsal root ganglion (DRG) in the analgesia induced by five ESI sessions in a neuropathic pain model induced by the chronic constriction of the sciatic nerve (CCI), as well as its influence on the endogenous control of pain mediated by encephalin in the spinal cord and DRG. Throughout this study, male rats, Sprague Dawley (280-340g; CEUA ICB/USP No. 3447131117), will be submitted to CCI in the right hindpaw and a concentric electrode will be implanted in the left insular cortex for subsequent consecutive daily electrical stimulation (15 min / session, 60 Hz , 210 ¼s, 1.0 V). Treatment with Bicuculina methiodide 0.01 ¼g (Tocris ®), a selective GABAA receptor antagonist, will be performed to evaluate the influence of the gabaergic system on the antinociceptive effect generated by the ESI, using the paw pressure test, and in the general locomotor activity of the animals, through the open field test. The levels of GAD67 will be analyzed by Immunofluorescence and Western Blotting in the regions of interest; and the levels of PENK (gene prepro-enkephalin) in the spinal cord and DRG quantified by rt-PCR. The results obtained will allow us to understand how the insula influences the nociceptive system and what neurophysiological mechanisms delineate the antinociceptive effect of ESI. (AU)