Thyroid hormones and estrogen affect oxytocin gene expression in hypothalamic neurons

Area of Science:

• Neuroendocrinology
• Molecular Endocrinology

Background:

• The oxytocin (OT) gene promoter contains a composite hormone response element.
• Nuclear receptors for steroid and thyroid hormones can interact with this element in vitro.

Purpose of the Study:

• To investigate the in vivo interaction between estrogen and thyroid hormones on OT mRNA expression in rat hypothalamus.
• To determine if thyroid hormones modulate estrogen's effect on OT gene expression in specific brain regions.

Main Methods:

• In situ hybridization histochemistry was used to quantify OT mRNA levels in rat hypothalamus.
• Ovariectomized (OVX) and thyroidectomized (TX) rats were treated with triiodothyronine (T3) and/or estradiol benzoate (EB).

Main Results:

• Triiodothyronine (T3) alone elevated OT mRNA in the paraventricular nucleus (PVN) of OVX rats.
• Estradiol benzoate (EB) treatment significantly increased OT mRNA in TX/OVX rats, indicating thyroid hormone interference.
• Co-administration of T3 and EB reduced EB-induced OT gene expression in both OVX and TX/OVX animals.

Conclusions:

• Endogenous and exogenous thyroid hormones interfere with estrogen's stimulation of oxytocin (OT) gene expression in the hypothalamus.
• Differential responses in PVN subdivisions suggest neuronal heterogeneity in hormone signaling.
• Evidence of competition between nuclear proteins and transcription factors in hypothalamic neurons regulating OT gene expression.