Studies on the location and release of cholecystokinin and vasoactive intestinal peptide in rat and cat spinal cord

Abstract

By radioimmunoassay vasoactive intestinal peptide (VIP) and cholecystokinin (CCK) are found in the cat lumbar spinal ganglion and spinal cord with levels in dorsal > ventral horn. Unilateral rhizotomy, but not cervical hemisection produced a significant but incomplete depletion of CCK and VIP immunoreactivity in dorsal, but not ventral horn. Intrathecal capsaicin (0.5 mg) had no effect on the levels of spinal VIP or CCK. Intrathecal colchicine (0.5 mg) produced a significant increase in the levels of VIP in the dorsal and ventral horn but had no effect on the levels of CCK. The present experiments, using a preparation which permits in situ superfusion of the spinal cord, demonstrated in the chloralose-urethanized cat and rat the presence of measurable levels of VIP and CCK. In rats, the addition of potassium (40 mM in excess) resulted in a 138% and 46% increase in the levels of CCK and VIP, respectively above resting levels (3.7 ± 1.2fmol/ml/10 min and1.7 ± 0.5fmol/ml/10 min, respectively). The deletion of calcium and substitution of cobalt (2 mM) resulted in a significant reduction in the potassium-evoked release. Intrathecal picrotoxin doubled the levels of CCK, but had no effect on the levels of VIP in the spinal superfusates. Capsaicin (3 × 10 −4 M) had no effect on the levels of either peptide in rat spinal superfusate. In cats, bilateral electrical stimulation of the sciatic nerve at high, but not low intensity, resulted in a 218% and 132% increase above prestimulation baseline in the levels of CCK and VIP, respectively. Separation of immunoreactivity on a Sephadex G-50 superfine column of the spinal superfusates and the extracted material from cat spinal cord, revealed that the immunoreactive CCK species in tissue co-migrated with the 8 and 33 amino acid peptide fragments. In the release samples, however, all the radioimmunoassayable activity migrated with the peak corresponding with CCK 8. No other peaks were detected. Column separation of spinal cord and the superfusate obtained during basal and evoked release, revealed that all activity in both the tissue and perfusate samples, travelled in a single peak which co-migrated with authentic VIP 28.