Haloperidol in large doses reduces the cataleptic response and increases noradrenaline metabolism in the brain of the rat

The results indicate that noradrenergic hyperfunction in the frontal cortex or thalamus induced by large doses of haloperidol may reduce the cataleptogenic effect of the drug via indirect stimulation of a dopaminoceptive neuron in the striatum or mesolimbic area.

Abstract

The neurochemical basis for the clinical observation that some patients receiving a large dose of haloperidol exhibit no extrapyramidal side effects was investigated in rats. Haloperidol at doses of 1, 2.5, 5, 7.5 and 10 mg/kg (i.p.) caused a dose-dependent decrease in the duration of catalepsy. Haloperidol at a dose of 10 mg/kg induced catalepsy lasting for only 20% of that obtained with 1 mg/kg. Haloperidol decreased the content of noradrenaline in the frontal cortex and thalamus in a dose-dependent manner, while the content of 3-methoxy-4-hydroxyphenylglycol (MHPG) showed a dose-dependent increase in the same areas of the brain. Thus, there was an inverse relationship between the duration of catalepsy and the ratio of 3-methoxy-4-hydroxyphenylglycol to noradrenaline in the frontal cortex or thalamus. The concomitant administration of 20 mg/kg of phenoxybenzamine with 10 mg/kg of haloperidol induced a long-lasting catalepsy. The result may indicate that the increased metabolism of noradrenaline by large doses of haloperidol was not secondary to the blocking of dopaminergic receptors. In contrast, haloperidol caused a dose-dependent decrease in the content of homovanillic acid and 3,4-dihydroxyphenylacetic acid in the striatum and mesolimbic area. These results indicate that noradrenergic hyperfunction in the frontal cortex or thalamus induced by large doses of haloperidol may reduce the cataleptogenic effect of the drug via indirect stimulation of a dopaminoceptive neuron in the striatum or mesolimbic area.