title: Antinociception induced by epidural motor cortex stimulation in naive conscious rats is mediated by the opioid system.
abstract: Epidural motor cortex stimulation (MCS) has been used for treating patients with neuropathic pain resistant to other therapeutic approaches. Experimental evidence suggests that the motor cortex is also involved in the modulation of normal nociceptive response, but the underlying mechanisms of pain control have not been clarified yet. The aim of this study was to investigate the effects of epidural electrical MCS on the nociceptive threshold of naive rats. Electrodes were placed on epidural motor cortex, over the hind paw area, according to the functional mapping accomplished in this study. Nociceptive threshold and general activity were evaluated under 15-min electrical stimulating sessions. When rats were evaluated by the paw pressure test, MCS induced selective antinociception in the paw contralateral to the stimulated cortex, but no changes were noticed in the ipsilateral paw. When the nociceptive test was repeated 15 min after cessation of electrical stimulation, the nociceptive threshold returned to basal levels. On the other hand, no changes in the nociceptive threshold were observed in rats evaluated by the tail-flick test. Additionally, no behavioral or motor impairment were noticed in the course of stimulation session at the open-field test. Stimulation of posterior parietal or somatosensory cortices did not elicit any changes in the general activity or nociceptive response. Opioid receptors blockade by naloxone abolished the increase in nociceptive threshold induced by MCS. Data shown herein demonstrate that epidural electrical MCS elicits a substantial and selective antinociceptive effect, which is mediated by opioids.
authors: Division of Functional Neurosurgery, Institute of Psychiatry, Hospital das Clínicas, Department of Neurology, School of Medicine, University of São Paulo, São Paulo, Brazil. fonoffet@usp.br
authors: Erich Talamoni
authors: ET
authors: Fonoff
authors: Camila Squarzoni
authors: CS
authors: Dale
authors: Rosana Lima
authors: RL
authors: Pagano
authors: Carina Cicconi
authors: CC
authors: Paccola
authors: Gerson
authors: G
authors: Ballester
authors: Manoel Jacobsen
authors: MJ
authors: Teixeira
authors: Renata
authors: R
authors: Giorgi
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003243:Consciousness / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology*; D009044:Motor Cortex / Q000187:drug effects / Q000502:physiology*; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013003:Somatosensory Cortex / Q000187:drug effects / Q000502:physiology
chemical_list: D009292:Narcotic Antagonists; D009270:Naloxone