Time dependent changes in the concentrations of immunoreactives cholecystokinin octapeptide sulfate in rat brain regions after systemic injection of picrotoxin.

Cholecystokinin octapeptide sulfate-like immunoreactivity (CCK-8S-LI) was determined by enzyme linked immunoassay (ELISA) in seven rat brain areas following injections subcutanously of the Cl(-) channel blocker, picrotoxin. Time dependent changes in the concentrations of CCK-8S-LI were seen in the hippocampus, amygdaloid complex, septum, and hypothalamus at 15-180 min after the injection. Concentrations of CCK-8S-LI in the frontal cortex, striatum, and thalamus did not show significant changes. CCK-8S-LI in the amygdaloid complex and hypothalamus was the lowest concentrations at 60 min, and the concentrations in the hippocampus and septum were the lowest at 180 min. The data on high-performance liquid chromatography of the extracts from rat amygdaloid complex showed that changes in the concentrations of CCK-8S-LI were mainly due to the concentration of CCK-8S itself. These data indicate that systemic injection of picrotoxin decreases the concentration of CCK-8S in the brain regions, and the decreases in the amygdaloid complex and hypothalamus occur earlier than that in the hippocampus and septum.