Involvement of Opioid Peptides in the Analgesic Effect of Spinal Cord Stimulation in a Rat Model of Neuropathic Pain.

Abstract

Spinal cord stimulation (SCS)-induced analgesia was characterized, and its underlying mechanisms were examined in a spared nerve injury model of neuropathic pain in rats. The analgesic effect of SCS with moderate mechanical hypersensitivity was increased with increasing stimulation intensity between the 20% and 80% motor thresholds. Various frequencies (2, 15, 50, 100, 10000 Hz, and 2/100Hz dense-dispersed) of SCS were similarly effective. SCS-induced analgesia was maintained without tolerance within 24h of continuous stimulation. SCS at 2Hz significantly increased methionine enkephalin content in the cerebrospinal fluid. The analgesic effect of 2Hz was abolished by μ or κ opioid receptor antagonist. The effect of 100Hz was prevented by a κ antagonist, and that of 10kHz was blocked by any of the μ, δ, or κ receptor antagonists, suggesting that the analgesic effect of SCS at different frequencies is mediated by different endorphins and opioid receptors.