Effects of calcium antagonists on biogenic amines in discrete brain areas

Discrete brain sections were obtained from rats given i.p. verapamil, nifedipine, diltiazem or flunarizine (0, 10, 20 or 40 mg/kg). The biogenic amines and metabolites in the hypothalamus, brainstem hippocampus, striatum, thalamus-midbrain and cortex were determined by high-performance liquid chromatography with electrochemical detection. The treatments induced several changes in the levels of neurotransmitters and metabolites, displaying regional specificity and differences according to the various compounds. It was speculated that some effects could have been due to indirect actions and/or to interactions of the compounds with receptors other than the voltage-sensitive calcium channels. However blockade of these channels could account for the following effects. (a) The nifedipine-induced increases in the 5-hydroxy-3-indoleacetic acid levels and, in general, the signs of activation of the serotonergic systems. (b) The fall in the 3,4-dihydroxyphenylacetic acid levels and, in general, the signs of attenuation of dopaminergic neurotransmission induced by nifedipine, verapamil and diltiazem. (c) The fall in the norepinephrine levels induced by all the compounds studied.