Barbiturates and meprobamate: Decreases in catecholamine turnover of central dopamine and noradrenaline neuronal systems and the influence of immobilization stress

Abstract

Summary The effects of barbiturates and meprobamate on the central DA and NA neurones of non-stressed and stressed rats were studied using histochemical and biochemical analysis of DA and NA. Changes induced by the different drug and/or stress treatments in the rate of depletion of the CA stores 4 h after tyrosine hydroxylase inhibition were regarded as changes in turnover. Barbiturates, but not meprobamate, clearly decreased the turnover of NA in the cortical NA nerve terminals. No clear effects were found in the hypothalamus with the two drugs. Stress increased NA turnover in all parts of the brain studied, and these increases could be counteracted by both barbiturates and meprobamate. The net effect on DA turnover in the nerve terminals of the neostriatum and the median eminence was a reduction after 4 h of immobilization stress. The stress-induced decrease in turnover of the DA terminals in the neostriatum was further decreased by pretreatment with barbiturates or meprobamate. In the median eminence, on the other hand, these drugs accelerated DA turnover in the external layer as demonstrated histochemically. The present results indicate that the effects observed on CA turnover are related to the sedative and anti-stress actions of barbiturates and meprobamate. It is unlikely that the specific differences in turnover changes observed between different areas of the brain are the result of a general depressant action on the central nervous system. The effects of barbiturates and meprobamate on CA turnover found in the present study are essentially similar to the effects of the minor tranquillizers of the benzodiazepine group as found in a previous study.