[Effect of epidural capsaicin on substance P in the dorsal horn in adult rats using epidural tubing].

Male Sprague-Dawley rats weighing 280-300g were used. To achieve the long-term administration of drugs into the epidural space without anesthesia, a new method of epidural tubing was used. A polyethylene catheter was inserted for 1.5cm into the epidural space through a slit made in the ligamentum flavum of L2-L3 intervertebral space. When 0.1ml of contrast media was injected through this catheter, the media spread from lumbar to upper thoracic vertebral region, as demonstrated with X-ray pictures. The rats with an epidural catheter were injected with 0.1ml of 2% capsaicin solution into the epidural space once a day for 4 days. Control rats were administered with the same volume of capsaicin-free vehicle. The depression of substance P at the dorsal horn (C6, Th7, L1) was investigated by the indirect immunofluorescence technique of Coons. One day after the end of capsaicin administration the depression of substance P was remarkable at laminae I-II in dorsal horn. But 14 days after the end of administration, substance P content at laminae I-II returned to the level of control rats. It was concluded that the depression of substance P by consecutive epidural capsaicin is reversible.