Electrophysiological and ultrasonic correlates of reproductive behavior in the male rat

The purpose of the present study was to examine the electrophysiological correlates of copulatory behavior in the rat and correlate brain electroencephalographic (EEG) activity with the ultrasonic vocalizations that have been shown to play a major role in the integration of mating behavior. Ultrasonic vocalizations of male rats with chronically implanted hippocampal and cortical electrodes were monitored during mating with a female rat. Hippocampal theta rhythms were significantly correlated with high activity, mounting, intromissions, and preejaculatory excitatory behavior and were also significantly associated with 50-kHz short ultrasonic vocalizations. Postmount or postintromission behaviors (grooming, exploration) were closely correlated with an absence of ultrasonic vocalizations and the onset of irregular low-amplitude hippocampal EEG recordings. Long 22-kHz vocalizations occurred in all tests during the postejaculatory refractory period. Shorter 22-kHz vocalizations occurred during mating and were associated with unsuccessful intromissions or mounting attempts. Postejaculatory long 22-kHz vocalizations were significantly associated with irregular high-amplitude hippocampal EEG tracings, and preejaculatory short 22-kHz vocalizations were also accompanied by sleep-like irregular high-amplitude hippocampal EEG tracings with cortical spindling. The correlation of ultrasonic vocalizations with electroencephalographic and behavioral manifestations of central arousal and inhibitory processes suggests that these vocalizations are indicators of the sexual arousal of the mating pair.