Tobacco components other than nicotine might participate in the behavioural effects of smoking. In this study, in-vivo recordings of serotonergic dorsal raphe neurons were performed in the anesthetized rat, whereas tobacco extracts, cigarette smoke extracts, nicotine, nornicotine or anabasine were intravenously injected. All substances inhibited the neurons, and all inhibitions were completely blocked by the nicotine receptor antagonist mecamylamine. The effects of the extracts were much more potent than those of individual substances. These results support the hypothesis that the acute inhibition of serotonin neurons by tobacco compounds is completely related to an effect on nicotine receptors. Tobacco extracts and tobacco smoke extracts may be useful tools for the study of the effects of central effects of smoking.