Analgesic effect of intrathecal morphine demonstrated in ascending nociceptive activity in the rat spinal cord an in effectiveness of caerulein and cholecystokinin octapeptide.

The effect of intrathecal injections of morphine and the two peptides, caerulein and cholecystokinin octapeptide (CCK-8), on the activity in ascending axons of the spinal cord evoked by electrical stimulation of primary nociceptive afferents was studied in spinal rats with decerebration. Morphine (20 microgram) depressed the spontaneous activity and the activity evoked from either A delta-or C-fibres. The co-activation by A delta-fibre stimulation of ascending axons activated by stimulation of C-fibres and the activity in ascending axons activated by stimulation of afferent A beta-fibres were not influenced by morphine. C-Fibre-evoked ascending activity was also depressed by morphine (10 microgram and 5 microgram). Ascending nociceptive activity was not changed by caerulein (30 ng) and CCK-8 300 ng, but it was depressed by a subsequent injection of morphine (20 microgram). The depressant effects of morphine were abolished by an intravenous injection of concluded that: (i) an intrathecal injection of morphine selectively depressed the ascending nociceptive activity; (ii) the depression produced by morphine is an equivalent for spinal analgesia following intrathecal injection of morphine to man; and (iii) the two components of the spinal nociceptive system, the motor and the sensory path, can independently be influenced by drugs.