Differences in effects of Ca2+ channel antagonists on dopamine metabolism in the limbic and extrapyramidal dopaminergic structures.

The effect of single and multiple administration of Ca2+ channel antagonists, nifedipine and verapamil, on concentrations of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), was investigated in the mesolimbic (cortex, nucleus accumbens) and extrapyramidal (striatum) structures in Wistar rats. A single dose of nifedipine (10 mg/kg IP) produced some activation of the dopaminergic system in both cortex (increase in DOPAC) and n. accumbens (increase in HVA); verapamil (20 mg/kg IP) produced an increase in HVA in the cortex only. Chronic treatment with either Ca2+ channel antagonist produced more marked activation of dopamine metabolism in the cortex and nucleus accumbens. Those changes were most expressed 1 h after the last treatment, but lasted for at least 24 h. No changes in dopamine metabolism were observed in the striatum. The present data suggest that Ca2+ channel antagonists after chronic treatment specifically activate the dopaminergic system in limbic structures.