Cholinergic influence on vestibular stimulation-induced focus coeruleus inhibition in rats

In our previous study, caloric stimulation (CS) of the vestibular apparatus inhibited noradrenergic neuronal activity in the locus coeruleus (LC) in u rethane-anaesthetized rats. Therefore, the inhibition of LC noradrenergic n eurons is involved in vestibule-autonomic responses. Since motion sickness can be cured by scopolamine, cholinergic neuron system may also be involved in vestibule-autonomic responses. The present study examined the effects o f intracerebroventricular injection of ethylcholine mustard aziridinium ion (AF64A), a presynaptic cholinergic neurotoxin, on CS-induced LC inhibition . In AF64A-treated rats, the CS-induced LC inhibition was less pronounced t han in normal rats. In a subsequent series of experiments, the intravenous injection of scopolamine blocked the CS-induced LC inhibition. These findin gs suggest that central cholinergic neurons are associated with noradrenerg ic neuronal inhibition during the vestibulo-autonomic reflex.