Estrogen Alters Oxytocin mRNA Levels in the Preoptic Area

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Abstract
Estrogen has numerous effects on immunoreactive levels of oxytocin (OXT) centrally, particularly in the preoptic lateral subcommissural nucleus (LSN). In this study in situ hybridization of a 38‐base oligodeoxyribonucleotide (38mer) complementary to OXT mRNA revealed that estrogen treatment altered the pattern of OXT production in the rostral LSN and the more caudal anterior commissural nucleus. Rats were injected with 20 ng estradiol benzoate or sesame oil vehicle im 4 and 5 days after ovariectomy. On the sixth day all animals were perfused with paraformaldehyde‐glutaraldehyde and their brains sectioned to 10 μm thickness in a −10 °C cryostat. Coronal brain sections were taken from four parallel levels of the preoptic‐anterior hypothalamic area. These sections were mounted and hybridized in situ to a [l125]‐labeled 38mer for 16 h at 37 °C. Washed and dried slides were processed for autoradiography and analyzed with a light microscope. The effect of estrogen on OXT production differed between the rostral and caudal sections in both the LSN and periventricular (PeV) areas. Estrogen significantly increased OXT mRNA levels in LSN cells while decreasing hybridization in the anterior commissural nucleus cells. Changes in frequency patterns in the PeV paralleled those in the LSN with a significant drop of hybridization in the caudal PeV. Neurons hybridizing 38mer probe were also found in several other areas including the ventral medial preoptic area, lateral hypothalamus, bed nucleus of the stria terminalis and the nucleus triangularis septi. OXT mRNA levels were affected by estrogen treatments and this effect differed between the preoptic area and anterior hypothalamus. The sensitivity of LSN oxytocinergic cells to estrogen has implications for estrogen‐sensitive OXT‐enhanced reproductive behaviors.