Pharmacological evidence for a selective antidopaminergic action of gamma-hydroxybutyric acid

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Abstract
D-Amphetamine (Amph) and p-chloroamphetamine (PCA) induced dose-dependent increases in oropharyngeal myocloniform twitch activity (MTA) in rats anesthetized with urethane. In doses of 80–120 mg/kg, gamma-hydroxybutyric acid (GHB) blocked Amph-induced MTA. The blockade was readily surmountable. Pretreatment with reserpine markedly enhanced the myoclonigenic effect of Amph and rendered it insensitive to blockade by GHB, 160 mg/kg. PCA and tryptamine also effectively stimulated MTA, but unlike Amph were antagonized by low doses of the serotonin (5-HT) antagonist methysergide. In doses which blocked Amph, GHB failed to antagonize the myoclonigenic effect of PCA. It is concluded that: (a) the actions of Amph and PCA on MTA are mediated by dopamine (DA) and 5-HT, respectively; (b) 5-HT-mediated MTA is less sensitive to GHB blockade than DA-mediated MTA; and (c) the GHB-Amph antagonism may be of a functional nature,i.e. result from a depression of the firing activity of DA neurons produced by GHB. Since reserpinization abolished the GHB effect on Amph-induced MTA, the functional integrity of granular DA binding and releasing mechanisms appears to be a pre-requisite for the antagonism between GHB and Amph.