Effects of cholecystokinin peptides and GV 150013, a selective cholecystokinin(B) receptor antagonist, on electrically evoked endogenous GABA release from rat cortical slices

Abstract

The effects of cholecystokinin (CCK) agonists and antagonists on spontaneous and electrically evoked endogenous GABA release from rat cerebral cortex slices were evaluated. Neither the nonselective and CCK(B)-selective receptor agonists CCK-8S (3-1,000 nM) and CCK-4 (3-1,000 nM), respectively, nor the selective CCK(B) and CCK(A) receptor antagonists GV 150013 (3-30 nM) and L-364,718 (10-100 nM), respectively, significantly affected spontaneous GABA release. CCK-8S (1-1,000 nM) and CCK-4 (1-1,000 nM) increased the electrically (5 and 10 Hz)-evoked GABA release. On the contrary, GV 150013 (10 and 30 nM) significantly decreased the electrically evoked GABA release only when the slices were stimulated at the higher 10 Hz frequency. The CCK- 8S- and CCK-4-induced increases in electrically evoked GABA release were counteracted by GV 150013, but not by L-364,718. Furthermore, GV 150013 at 3 nM shifted to the right the CCK-4 concentration-response curve, whereas at the higher 10 nM concentration it dramatically flattened the curve. Finally, in cortical slices obtained from rats chronically treated with GV 150013, the concentration-response curve of CCK-4 was shifted to the left and the peak effect of the peptide was significantly higher than that observed in naive animals. These results suggest that CCK increases electrically evoked, but not spontaneous, endogenous GABA release from rat cortical slices, possibly by activating local CCK(B) receptors. In addition, chronic treatment with the novel CCK(B) receptor antagonist GV 150013 leads to an enhanced responsiveness of cortical slices to CCK-4 application.