Obtained measures of eating, drinking, irritability, aggression, and copulation in 57 hooded male rats before and after they were subjected to midbrain knife cuts or control operations. Slight hypophagia resulted from cuts through the supramammillary and ventral tegmental decussations. Severe-to-moderate hyposexuality resulted from cuts involving either the medial lemniscus and zona incerta or the ventral reticular formation. Cuts through the central gray or dorsal reticular formation produced no significant behavioral effects. It is suggested that the medial lemniscus and the ventral reticular formation convey an ascending sensory-arousal influence that facilitates copulation. (25 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)