In vitro release of cholecystokinin octapeptide-like immunoreactivity from rat brain synaptosomes

Enriched synaptosome fractions prepared by differential centrifugation and ultracentrifugation of homogenates of rat cortex, striatum, thalamus and hypothalamus contained over 65% of the total immunoreactive cholecystokinin octapeptide (CCK-8) in each area. A calcium-dependent release of immunoreactive CCK-8 from these fractions in vitro in response to 2 depolarizing stimuli (60 mM KCl and 75 microM veratrine) has been demonstrated. Released CCK-8 immunoreactivity showed parallelism when dilutions were compared with the CCK-8 dose-response curve and eluted similarly to synthetic CCK-8 on Sephadex G-50 superfine chromatography. These results provide further evidence for a neurotransmitter or neuromodulator role for CCK-8 in brain.