Sex-Related Gene Expression in the Posterodorsal Medial Amygdala of Cycling Female Rats Along with Prolactin Modulation of Lordosis Behavior

The rat posterodorsal medial amygdala (MePD) is sexually dimorphic, has a high concentration of receptors for gonadal hormones and prolactin (PRL), and modulates reproduction. To unravel genetic and functional data for this relevant node of the social behavior network, we studied the expression of ERα, ERβ, GPER1, Kiss1, Kiss1R, PRGR, PRL, PRLR, EGR1, JAK2, STAT5A, and STAT5B in the MePD of males and females along the estrous cycle using the RT-qPCR technique. We also investigated whether PRL in the MePD would affect the sexual behavior display of proestrus females by microinjecting saline, the PRL receptor antagonist Del1-9-G129R-hPRL (1 µM and 10 µM), or PRL (1 nM) and Del1-9-G129R-hPRL (10 µM) 3h before the onset of the dark-cycle period. The estrogen-dependent lordosis behavior, indicative of sexual receptivity of proestrus females, was recorded and compared before (control) and after (test) microinjections in these groups. Sex differences were found in the right and left MePD gene expression. ERα and Kiss1R, as well as PRL, Short PRLR , and STAT5B expression, is higher in cycling females than males. Kiss1 expression is higher in males than females, and GPER1 is higher during diestrus than proestrus. Furthermore, Del1-9-G129R-hPRL in the MePD significantly reduced the full display and quotient of lordosis in proestrus females, an effect restored by the co-microinjection of PRL. In conjunction, the expression of studied genes showed specific sex and estrous cycle phase features while, in proestrus, PRL action in the MePD plays an essential role in the display of lordosis during the ovulatory period. Highlights The MePD expression of Kiss1 is higher in males than females. ERα and Kiss1R expression is higher in cycling females than males. PRL, Short PRLR, and STAT5B expression is higher in cycling females than males. GPER1 expression is higher during diestrus than in proestrus. Del1-9-G129R-hPRL action in the MePD reduced lordosis quotient during proestrus.