Increased release of immunoreactive CCK-8 by electroacupuncture and enhancement of electroacupuncture analgesia by CCK-B antagonist in rat spinal cord.

Cholecystokinin octapeptide (CCK-8) in CNS has been shown to function as a neuropeptide with potent anti-opioid activity. It hinders opioid analgesia and facilitates opioid tolerance. The present study showed that electroacupuncture (EA) stimulation produced a marked increase of the CCK-8 immunoreactivity (ir) in the perfusate of the rat spinal cord. The increase of CCK-8-ir was most marked in response to EA of 100 Hz and 15 Hz, and less marked in response to EA of 2 Hz. Since CCK-8 has been shown to possess potent anti-opioid activity at the spinal level, blockade of the spinal CCK effect would be expected to potentiate EA-induced analgesia which is known to be opioid-mediated. Intrathecal (i.t.) administration of CCK-B antagonist L-365,260 per se did not affect tail flick latency (TFL) to any significant extent, yet it potentiated EA induced analgesia in a dose- and frequency-dependent manner. The potentiation was most marked at a dose range of 2.5-5.0 ng (i.t.) and at a frequency rank order of 100 Hz > 15 Hz > 2 Hz. The results suggest that an increased release of CCK-8 following EA may limit the effect of opioid peptides, and that the CCK-B receptor mediates the anti-opioid effect of CCK-8 in rat spinal cord.