Effects of drugs influencing monoamine mechanisms on the increase in brain dopamine produced by axotomy or treatment with gammahydroxybutyric acid.

Abstract

The influence of blockade or stimulation of dopamine (DA) receptors on the selective increase in brain DA seen after axotomy or injection of gammahydroxybutyric acid (sodium form, 1.5 g/kg i.p.) was studied in rats. The increases were not changed after blockade of the DA receptors by haloperidol but were slightly reduced after stimulation of these receptors by apomorphine. Since pretreatment with haloperidol counteracted this effect of apomorphine, a diminished stimulation of DA receptors may partially be responsible for the increase in brain DA seen when the nerve impulse flow has been blocked in the DA neurones by axotomy or treatment with gammahydroxybutyric acid. The NA content was usually somewhat lowered on the lesioned side and this reduction was not changed after treatment with haloperidol, apomorphine or amphetamine. The increase in brain DA usually observed after axotomy was not found when the rats were also treated with reserpine and nialamide. This effect indicates that the negative feed-back of cytoplasmic DA on the DA synthesis operates also in the absence of nerve impulses. Injection of amphetamine before or after axotomy or treatment with gammahydroxybytyric acid markedly inhibited the increase in brain DA, probably due to release of newly synthesized DA.