Catecholaminergic responses to rotational stress in rat brain stem: implications for amphetamine therapy of motion sickness.

The fact that amphetamine, a noradrenaline releaser, prevents motion sickness leads the hypothesis of Wood and Graybiel that the noradrenergic neuron system in the brain stem acts against the development of motion sickness. To evaluate the hypothesis, the effects of rotational stress on the turnovers of noradrenaline and dopamine in the rat brain stem were examined. Rats were rotated about two axes simultaneously (double rotational) or about one axis (single rotation) for 60 min. Measurement of kaolin intake (pica) induced by rotation, as an index of motion sickness, showed that double rotation produced motion sickness, whereas single rotation did not. Both single and double rotation significantly increased the turnovers of noradrenaline and dopamine in the brain stem. However, there were no significant differences between the increases in catecholamine turnover induced by double and single rotations. Moreover, pretreatment of rats with methamphetamine (5 mg/kg) just before double rotation, which prevented the induction of motion sickness by double rotation, did not affect increases of the catecholamine turnover in the brain stem by double rotation. These findings do not support the hypothesis of Wood and Graybiel, suggesting that the catecholaminergic neuron systems in the brain stem are not involved in motion sickness and that the therapeutic effect of methamphetamine is not due to its direct effect on the brain stem.