The nuerochemical basis of postoprative nausea and vomiting

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One of the most common and distressing symptoms which follow anesthesia and surgery is emetic problem. Postoperative nausea and vomiting (PONV) following same procedure occurs more frequently with some anesthetic agents, such as anitrous oxide, than with others. Several stimuli are detected by cells of the area postrema, termed the chemoreceptor trigger zone (CTZ) for emesis, which in turn activate the vomiting center. The CTZ is rich in dopamine, serotonin, acetylcholine (ACh) receptors. Anesthetics have general pharmacological effects on the brain and PONV may be an expression of such effects on the emetic reflex pathways. To provide a neurochemical basis of PONV,we investigated the effects of the anesthetics on the release of the neurotransmitters whose receptors exist in the CTZ.We studied the changes of brain monoamines and their metabolites during nitrous oxide inhalation in rats. Nitrous oxide increased the content of 3,4-dihydroxyphenylacetic acid, the metabolite of dopamine, but not dopamine, in the cerebral cortex and the medulla, which indicated the enhancement of dopaminergic neuronal activities. We studied the effects of nitrous oxide, isoflurane, and sevoflurane on the release of ACh at the cerebral cortex and the striatum using the microdialysis method in rats. Nitrous oxide increase the release of ACh in the cerebral cortex, whereas isoflurane and sevoflurane decreased it.The emetic properties of nitrous oxide may be a reflection of the activation of dopaminergic and cholinergic systems.