In vivo studies on the basal and evoked release of cholecystokinin and vasoactive intestinal polypeptide from cat cerebral cortex and periventricular structures

In cat, radioimmunoassay revealed high concentrations of vasoactive intestinal polypeptide (VIP) and cholecystokinin (CCK) (approximately 10-90 ng/g wet weight tissue) in various regions of the cerebral cortex and in periventricular structures. Superfusion of cat cerebral cortex or perfusion from the lateral ventricle to the cisterna magna with artificial cerebrospinal fluid (CSF) was carried out in cats anesthetized with chloralose-urethane. The superfusate was assayed for VIP- and CCK-like immunoreactivity (VIP-LI and CCK-LI) simultaneously. Basal efflux of VIP-LI was 13.8 +/- 4.1 fmol/30 min/cm2 cortex and 31.6 +/- 5.0 fmol/30 min in ventriculo-cisternal superfusate. Basal efflux of CCK-LI, assayed in the same superfusate sample, was 10.7 +/- 2.5 fmol/30/min/cm2 cortex in cortical cup superfusate and 25.6 +/- 4.4 fmol/30 min in ventriculo-cisternal superfusate. The addition of potassium (50 mM) and veratridine (7.5 X 10(-5) M) to the superfusate produced significant increases in the levels of VIP-LI in both ventricular and cortical effluents. The potassium evoked release of VIP-LI and CCK-LI was inhibited by the substitution of cobalt (4 mM) for the calcium ion in the perfusion media; basal efflux was not affected. Separation of immunoreactivity by gel filtration chromatography demonstrated the CCK-LI in cat cortical tissue co-chromatographed with the COOH-terminal 4, 8, 33 and 39 amino acid peptide fragments of CCK and with a larger molecule. In contrast, the immunoreactivity in cortical and ventricular superfusate obtained during basal and evoked release co-migrated with authentic CCK octapeptide. For VIP, all immunoreactivity in tissue extract of cerebral cortex existed as a single peak which co-migrated with authentic VIP-28. The molecular pattern in cortical superfusate corresponded to that found in tissue extract.