Development of a Novel Method of Spinal Electrophysiological Assessment via Intrathecal Administration at Analgesic Doses.

Abstract

Background/Objectives: Chronic pain is a significant global health challenge and is associated with diverse conditions, such as diabetic neuropathic pain and spinal stenosis. Understanding the mechanisms of pain transmission is crucial, for both the peripheral and central pathways. However, there are limitations in spinal electrophysiological techniques in terms of the injection method. Traditional methods such as spinal injections may differ in the distributions and concentrations of drugs compared with intrathecal administration during the behavior test. So, we developed a new intrathecal administration method for electrophysiological recordings. Methods: Sprague-Dawley rats were injected with lidocaine intrathecally, and the analgesic effect was evaluated by the von Frey test. In vivo extracellular single-unit recordings of the superficial dorsal horn neurons were performed following a newly developed technique. Lidocaine was intrathecally injected into the arachnoid membrane after laminectomy. After that, the neural responses in the superficial dorsal horn were measured. Results: Newly developed intrathecally administered dye reached the spinal cord and the cauda equina. Intrathecally administrated lidocaine increased the paw withdrawal threshold and suppressed spinal neuronal firing. This suppression correlated with increases in paw withdrawal thresholds. Conclusions: This innovative method provides insights into the central effects of analgesics, which will help the development of therapies for chronic pain.