The third histamine (H 3 ) receptor was first described as a presynaptic autoreceptor located in the central nervous system. 1 Subsequently, H 3 receptors were also shown to be located presynaptically as heteroreceptors on nonhistamine-containing neurons. 2 A number of potential therapies for disorders associated with sleep−wake cycle, cognition, memory, food intake, and thermoregulation using modulators of H 3 receptors have been proposed on the basis of ...