Humans and other animals interact with other social targets around them. They reproduce, raise offspring and defend their territory through social interaction. Among these, sexual behaviors are crucial in maintaining species and passing on genes to offspring. Therefore, an understanding of neural mechanisms underlying sexual behavior has been deemed important for decades.
Previous studies have indicated that the medial preoptic area (MPA) is a one of the control centers of this behavior. However, the detailed mechanisms are still unknown. The purpose of this study is to clarify the neural mechanisms related to sexual behavior within the MPA region. Firstly, we did immunohistochemistry (IHC) of an immediate early gene (IEG), cFos to gain information about the area’s neural firing dynamics. After female exposure, we found that neuronal activity in MPA significantly increased. Neurons in the core region of MPA (Medial preoptic nucleus; MPN) were activated further in male animals after intromission. This results suggested that neurons in the MPA are functionally differentiated for reproductive behavior in male mice.
Also, previous reports suggested that sexual behaviors are mediated by GABAergic neurons. We next focused on the role of excitatory (glutamatergic) neurons in sexual behavior. We used optogenetic stimulation to activate these neurons in MPA. Differential activation of glutamatergic neurons in dlMPA and MPN and in various conditions did not facilitate sexual behavior in either group, with some mice seeming to ignore the provided female. Surprisingly, dlMPA stimulation induced hyperactivity and abnormal jumping behavior in an intensity independent and frequency dependent manner. High frequency (20Hz) stimulation induced a high increment of hyperactivity. Glutamatergic neuronal inhibition using the DREADD system did not alter sniffing behavior but produced small differences in USV. When we stimulated dopamine receptor d2 neurons, sexual behavior was inhibited without affecting general activity levels. This results suggest that glutamatergic neurons in MPA do not directly stimulate or inhibit sexual behavior but may have a role in behaviors that involve up regulation of ractivity levels like searching, foraging, or escaping behavior in some sense.