Neuropharmacology of motion sickness and emesis. A review.

Histamine H1-receptors are involved in the development of the symptoms and signs of motion sickness, including emesis. On provocative motion stimulus, a signal for sensory conflict activates the histaminergic neuron system, and the histaminergic descending impulse stimulates H1-receptors in the emetic center of the brain stem. The histaminergic input to the emetic center through H1-receptors is independent of dopamine D2-receptors in the chemoreceptor trigger zone and serotonin 5HT3-receptors in the visceral afferent, which are also involved in the emetic reflex. Antihistamines block emetic H1-receptors to prevent motion sickness. Acetylcholine muscarinic receptors are involved in the generation of signals for sensory conflict. Anti-cholinergic drugs prevent motion sickness by modifying the neural store to facilitate the acquisition of habituation to provocative motion.