Capsaicin-sensitive nonadrenergic and noncholinergic depressor response to spinal cord stimulation in the pithed rat

The effects of capsaicin on nonadrenergic, noncholinergic depressor responses to spinal cord stimulation were studied in pithed rats. Mean blood pressure (MBP was maintained at a level of 100 mmHg by continuous infusion of methoxamine and hexamethonium to block autonomic outflow. Electrical stimulation of the lower thoracic region (T9-12) via a pithing rod produced a frequency (1-8 Hz)-dependent fall in elevated MBP. The depressor response was abolished by tetrodotoxin, whereas atropine, propranolol, and cimetidine plus pyrilamine did not affect the response. Capsaicin treatment abolished the depressor response. These results suggest that spinal cord stimulation causes neurogenic vasodilation which is mediated by capsaicin-sensitive nonadrenergic and noncholinergic vasodilator nerves.