An estradiol-induced protein synthesized in the ventral medial hypothalamus and transported to the midbrain central gray

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Abstract
Estradiol (E2) facilitates the lordosis reflex that occurs in response to flank stimulation in female rats. Lordosis appears to be regulated in part by the synthesis of proteins in the ventral medial hypothalamus (VMH) that are transported to the midbrain central gray (MCG). We developed a strategy involving microinfusion of radioactive amino acids, followed by 2-dimensional gel electrophoresis, to identify proteins that may be regulated by E2 in the VMH and transported to the MCG. A mixture of 35S-methionine and 35S-cysteine (2:1, total 500–1000 microCi), suspended in 1 microliter PBS, was infused bilaterally into the VMH over a period of 2 hr into matched pairs of ovariectomized female rats, one of which was given a Silastic implant containing E2 at the beginning of infusion or 1 week earlier. The rats were sacrificed 12 hr after the end of infusion, and several brain regions were obtained by microdissection. Samples were analyzed by 2-dimensional gel electrophoresis, entailing isoelectric focusing in the first dimension and SDS-PAGE (molecular-weight separation) in the second dimension, followed by fluorography. We could routinely separate at least 250 spots. We consistently found a protein spot with an apparent molecular weight of 70 kDa, pI of about 5.9, which almost always appeared in the VMH and MCG of rats given E2 replacement but very rarely in samples from ovariectomized rats given no E2 replacement. A spot immediately acidic to this protein (70 kDa, pl about 5.8) appeared to vary inversely with this E2-induced protein.

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