Intracranial administration of the G-protein coupled estrogen receptor 1 antagonist, G-15, selectively affects dimorphic characteristics of the song system in zebra finches (Taeniopygia guttata).

In zebra finches (Taeniopygia guttata), estradiol contributes to sexual differentiation of the song system but the receptor(s) underlying its action are not exactly known. Whereas mRNA and/or protein for nuclear estrogen receptors ERα and ERβ are minimally expressed, G-protein coupled estrogen receptor 1 (GPER1) has a much greater distribution within neural song regions and the syrinx. At present, however, it is unclear if this receptor contributes to dimorphic development of the song system. To test this, the specific GPER1 antagonist, G-15, was intracranially administered to zebra finches for 25 days beginning on the day of hatching. In males, G-15 significantly decreased nuclear volumes of HVC and Area X. It also decreased the muscle fiber sizes of ventralis and dorsalis in the syrinx. In females, G-15 had no effect on measures within the brain, but did increase fiber sizes of both muscle groups. In sum, these data suggest that GPER1 can have selective and opposing influences on dimorphisms within the song system, but since not all features were affected additional factors are likely involved.