ESTROGEN RECEPTOR DETECTED IN THE FACIAL NUCLEUS OF NEWBORN RATS.

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Distribution and ontogeny of estrogen receptor (ER) -containing neurons in the newborn rat brain was examined. Neurons containing ER were classified into two types, i.e.,(1) Adult-type : the ER neurons appear in the same regions in the newborn as those in the adult ;(2) Newborn-type : the ER appears transiently only during the fetal to newborn period. The adult-type was observed in the preoptic nucleus, in the bed nucleus of the stria terminalis, in the hypothalamic arcuate, ventromedial and periventricular nuclei, in the midbrain central gray, in the lateral habenular nucleus, and medial and cortical nuclei of the amygdala. On the other hand, the newborn-type appears only in the ventromedial subnucleus of the facial nucleus and the layr 5 of the primary auditory cortex. Estrogen administration decreases ER immunoreactivity in the both types of ER.ER mRNA expression was detected by in situ hybridization in both cases. However, the area where former group was found contains aromatase immunoreactivity, which indicates androgen is converted to estradiol, while that for the latter does not. Sex difference was found only the former group. Thus, ER directly related to sex differentiation of the brain was suggested as the former (adult-type), while the latter (newborn-type) might be related to stimulating effects of estrogen in the developing brain. By retrograde track-tracing, double immunohistochemical staining of ER and choline acetyltransferase, and electron microscopic immunocytochemistry, the cells which contain ER transiently in the newborn life were suggested as immature motoneurons.