Histaminergic influence on vestibular stimulation-induced locus coeruleus inhibition in rats

In previous reports we have shown that caloric stimulation (CS) of the vest ibular apparatus inhibits locus coeruleus (LC)-noradrenergic neuronal activ ity in urethane-anaesthetized rats. The present study examined the effect o f neural histamine depletion by alpha-fluoromethylhistidine (alpha-FMH) on CS-induced LC inhibition. In alpha-FMH treated rats, LC neuronal inhibition caused by CS was still observed. This finding indicates that the central h istaminergic neuron system does not participate in the CS-induced LC-noradr energic inhibition. It is suggested that the noradrenergic neuron system is involved in the development of vestibule-autonomic response, independent o f the histaminergic neuron system.