Male rat sexual behavior and the role of the ventral pallidum

Rat sexual behavior is a natural reward behavior that offers the unique opportunity to control the timing of exposure for the first time. A certain level of sexual motivation is required to turn desire into approach, leading to copulation and ejaculation. A coordinated transition between these phases is essential for a successful completion of the cycle. Moreover, gaining sexual experience enables a more efficient sexual cycle by markedly improving the patterning of behavioral responses. The neural regulation of this behavior and the transitions between phases requires different neurons to control their activity at times, to induce the favorable responses to the rewarding stimulus. The ventral pallidum (VP) plays a unique role in reward processing. Besides encoding reward values of stimuli, the VP is crucial in regulating both conditioned and unconditioned reward responses. Still, it is unknown how the VP is involved in regulating sexual behavior and gaining sexual experience. Using fiber photometry and chemogenetics, we found that the VP encodes sexual behavior by an increase in neural activity from the start of an intromission or ejaculation and lasts until the end of the copulation. Incremental levels of sexual experience were not found to be connected to different levels of neural activity. In addition, we found that silencing of the VP does not alter male rat sexual behavior in a naïve state nor in an experienced state. These results indicate that the VP is activated during sexual behavior, but is non-essential for the naturally rewarding behavior.