Effect of alpha-fluoromethylhistidine on brain histamine and noradrenaline in muricidal rats.

Rats maintained on a thiamine-deficient diet for 30 days showed mouse-killing aggression (muricide). Once the muricide tendency appeared, it remained during the entire experimental period, even after subsequent administration of thiamine hydrochloride for 30 days. The effect of alpha-fluoromethylhistidine (FMH) on muricide in this animal model was examined, and histamine and noradrenaline levels in several brain regions were measured. One hour after i.p. injection of 200 mg/kg of FMH, muricide was completely abolished. Significant decrease in histamine levels was found in the hypothalamus, thalamus, amygdala, striatum and pituitary of muricidal rats. Thus, the central histaminergic neuron system may be involved in the suppressive mechanism of muricide. On the other hand, it is noteworthy that the noradrenaline level was significantly decreased only in the hypothalamus. In conclusion, it seems likely that the suppression of muricide induced by FMH was attributable to both inhibition of the histaminergic system and activation of the noradrenergic system.