Selective enhancement in striatal [(3)H]nitrendipine binding following chronic treatment with morphine.
Two parameters of Ca(2+) dynamics in brain preparations ((45)Ca-uptake to slices and [(3)H]nitrendipine binding to membrane fractions) were measured in naive and chronic morphine-administered rats. While morphine did not have any effect on (45)Ca-uptake to striatal slices in normal Krebs-Ringer solution, it inhibited K(+)-stimulated (45)Ca-uptake to slices. Furthermore, the effect of morphine was antagonized by naloxone. Inhibition of K(+)-stimulated (45)Ca-uptake to striatal slices by morphine was not observed in preparations obtained from chronic morphine-administered rats (6 mg/kg/b.i.d./7 days). In membrane fractions, [(3)H]nitrendipine binding increased by 34% in striatum following chronic morphine treatment, whereas no change was observed in the cortex and hippocampus. The results will be discussed in relation to the phenomena underlying chronic morphine administration.
Saito
K
K
Department of Pharmacology, Faculty of Dentistry, Osaka University, Yamadaoka 1-8, Suita 565, Japan.
Ishii
K
K
Fujita
N
N
Nakahiro
M
M
Inoki
R
R