Calcium entry blockers and oxiracetam have opposite effects on the density of dihydropyridine receptors in rat cerebral cortex.

Ca2+ entry blockers riodipine, D-cis-diltiazem and verapamil, when administered i.p. to rats at a dose of 10 mg/kg, produced two-fold decreases in the density of 1,4-dihydropyridine (DHP) receptors in rat cerebral cortex, as revealed by Scatchard plot analysis of radioligand binding made 24 h after the first injection. Thereafter, the number of DHP binding sites increased up to the initial level on day 4 of the treatment. The nootropic drug oxiracetam, when injected simultaneously with Ca2+ channel blockers at a dose of 10 mg/kg, prevented this transient decrease in DHP receptor density in brain. These results can explain the opposite modulation of memory retention by calcium antagonists and nootropic drugs that has been observed previously.