Adult rats emit two categories of ultrasonic vocalizations, 22 kHz calls and 50 kHz calls. These vocalizations communicate animal's emotional state to other members of the social group. Production of social vocalizations is an evolutionary old activity in vertebrates, and is regulated by well-preserved brain circuitries. The 22 kHz calls express negative, aversive state and are initiated by activity of the mesolimbic cholinergic system originating from laterodorsal tegmental nucleus. The 50 kHz calls express positive, appetitive state and are initiated by activity of the mesolimbic dopaminergic system originating from the ventral tegmental area. The 22 kHz calls serve as warning and alarm calls, while the 50 kHz calls serve as affiliative and social-cooperating calls. These specie-specific vocalizations play role of ethological transmitters, termed ethotransmitters, that is, they are species-specific signals that are selectively recognized by receivers and have capability of changing emotional state of the receivers. Copyright © 2013 Elsevier Ltd. All rights reserved.