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 antag onists, nifedipine and verapamil, on concentrations of dopamine and it s metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), was investigated in the mesolimbic (cortex, nucleus accum bens) and extrapyramidal (striatum) structures in Wistar rats. A singl e dose of nifedipine (10 mg/kg IP) produced some activation of the dop aminergic 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 antagon ist produced more marked activation of dopamine metabolism in the cort ex and nucleus accumbens. Those changes were most expressed 1 h after the last treatment, but lasted for at least 24 h. No changes in dopami ne metabolism were observed in the striatum. The present data suggest that Ca2+ channel antagonists after chronic treatment specifically act ivate the dopaminergic system in limbic structures.