Neural responses of rat area postrema to stimuli producing nausea.

To identify a neuron within the area postrema (AP) that participates in producing nausea, neural responses of the rat AP to noxious, excessive distension of the stomach were recorded electrophysiologically under urethane-chloralose anesthesia. There were two types of the neural responses; one is characterized by increasing the frequency of discharges responding to the stomach distension (excitatory type), while the other shows the opposite response (decreasing the frequency) to the same stimulation (inhibitory type). After this identification, the effect of LiCl or apomorphine superfused on the floor of IVth ventricle was examined to ascertain a convergence of afferents responding to chemical (LiCl or apomorphine) as well as mechanical noxious stimulation (stomach distension) on the same AP neuron. It was revealed that the rat AP involves multimodality neurons responsive to various emetic stimuli, so indicating their participation in producing nausea.