Topographical study of transdural motor cortex stimulation-induced analgesia of rats: somatotopy of behavioral response and neuronal activation

Abstract

Subliminal stimulation of the motor cortex has been extensively used to treat patients with neuropathic pain resistant to other conventional treatments. Experimental data suggest that the motor cortex is also involved in the modulation of nociception in normal animals, however, the mechanisms underlying this effect has not been, until now, understood. Data obtained by our group demonstrated that transdural electrical stimulation of the motor cortex of normal rats induces significant analgesia in an experimental model of pain sensitivity, by acting on opioid system. Recent results obtained by our group showed that analgesia induced by cortical stimulation inhibits neuronal firing in the periaqueductal gray (PAG), an important center of pain inhibitory system, whereas the inhibition of the expression of proto-oncogene Egr-1. This study will investigate the possible topography of the antinociceptive effect induced by stimulation of the motor cortex in rats and to evaluate the possible pathways involved in this effect. The methodology includes in vivo assays of painful sensitivity evaluation for the study of the topography. Possible pathways involved, will be evaluated on in vitro assays of immunohistochemistry for Fos expression in the PAG, thalamic nuclei in the ventral posterior lateral and posterior medial and at the posterior column of the spinal cord which will signal the degree of protein synthesis providing data on local effects and distance circuits of cortical stimulation. Also, the participation of opoid receptors will be evaluated at the same areas cited above by ELISA in slices. The results may potentially allow a better understanding of mechanisms involved on motor cortex stimulation-induced analgesia and its possible topographical organization, a phenomenon that still hasn't been described. (AU)