Modulation of 22-kHz Postejaculatory Vocalizations by Conditioning to New Place: Evidence for Expression of a Positive Emotional State

It has been assumed that the 22-kHz ultrasonic vocalizations (USVs) are emitted by adult rats as a result of a negative emotional state. However, emission of the 22-kHz vocalizations by male rats has been also observed following ejaculation, which has a high rewarding value as shown by a conditioned place preference test. These observations suggest that 22-kHz USVs may also occur in response to a positive emotional state. The aim of this study was to determine whether the postejaculatory 22-kHz USVs are related to conditioning processes. The 22 kHz USVs were recorded in Sprague-Dawley males in the postejaculatory refractory period during conditioning processes to a new chamber unrelated to copulation. During the first session in the clean recording chamber, males vocalized marginally and exhibited intensive rearing behavior. From the second to fourth sessions, vocalization duration increased and the number of rearing decreased. Following established conditioning process, odor cues from foreign males, but not the familiar ones, resulted in decreased duration of 22-kHz USVs and increased the number of rearing. On the other hand, in the presence of mating cues (copulatory chamber and presence of the female), males exhibited increased duration of postejaculatory 22-kHz USVs and reduced number of rearing. These results demonstrated that the conditioning to the cues, both unrelated and related to copulation, is important for evoking postejaculatory 22-kHz USVs as well as the relaxation state. Furthermore, these results confirmed the postejaculatory 22-kHz USVs' involvement in expression of the positive emotional state.