Long latency spinal cord dorsum potential; suppression by intrathecal morphine and enkephalin analog.

We have developed a new method which combines intrathecal recordings of spinal cord dorsum potentials (CDPs) with application of drugs to the spinal cord via an intrathecal catheter. With this technique we have discovered a late component (LC) in the CDP which has not been previously described. The LC is evoked by high intensity electrical stimulation of the rat tail. Whereas previous reports describe early components in the CDP evoked by low intensity A-fiber stimulation, ours is the first to describe a late evoked potential implicating C-fiber activation of the cord. Moreover, we show that the LC is blocked by intrathecal application of morphine sulphate or D-Ala-Met-enkephalinamide in a naloxone reversible manner. We postulate that this LC represents, at least in part, the spinal cord evoked response to C-polymodal nociceptive afferent inputs.