Neonatal manipulation of oxytocin affects expression of estrogen receptor alpha

In adult females many of the effects of the neuropeptide oxytocin are steroid, and especially estrogen dependent. Here we demonstrate for the first time that neonatal manipulation of oxytocin can affect the expression of estrogen receptor alpha. On the first day of postnatal life male and female prairie voles (Microtus ochrogaster) were randomly assigned to receive one of four treatments; (a) 50μl i.p. injection of 3μg oxytocin (approximately 1μg/g), (b) 0.3μg of an oxytocin antagonist (approximately 0.1μg/g), or (c) isotonic saline. A fourth group was handled, but not injected. On postnatal day 8 or 21, brain tissue was collected, fixed and sectioned. Free-floating sections were stained for estrogen receptor alpha using immunocytochemistry, and estrogen receptor alpha immunoreactive neurons were compared by age, treatment, and sex. To compare the temporal expression of estrogen receptor alpha an additional set of brains was collected from untreated males and females on the day of birth. The effects of oxytocin manipulations were age dependent, sexually dimorphic, and site-specific. While there were no significant treatment effects on postnatal day 8, by postnatal day 21 females that received oxytocin showed a significant increase in the number of cells expressing estrogen receptor alpha-immunoreactivity in the ventromedial nucleus of the hypothalamus. Treatment with oxytocin antagonist resulted in a significant decrease in estrogen receptor alpha-immunoreactivity in the medial preoptic area in postnatal day 21 females. While there were no significant effects in males, males treated with oxytocin antagonist trended toward a reduction in estrogen receptor alpha-immunoreactivity in the medial amygdala. The results indicate that oxytocin can have organizational effects on the expression of estrogen receptor alpha, that these effects are sexually dimorphic, and finally that during the preweaning period the development of estrogen receptor alpha is sexually dimorphic.