Serotonergic neurotransmission is involved in controlling arousal levels in humans and other animals. Here, the effects of serotonergic receptor antagonists on the induction and depth of anaesthesia produced by three different general anaesthetics were investigated. Rats were pretreated (i.p.) with either methiothepin (1.5 mg kg(-1)), mianserin (5 mg kg(-1)), ketanserin (7 mg kg(-1)) or saline....