Development of steroid-receptor systems in guinea pig brain. I. Cytoplasmic estrogen receptors.

The development of the cytoplasmic estrogen receptor (CER) system in male and female guinea pigs was examined to determine whether attainment of sensitivity to estrogen action related to lordosis behavior is correlated with increases in brain CER concentrations. Ovariectomized neonatal (7 days old) guinea pigs failed to display lordosis after priming with 10 micrograms estradiol benzoate (EB) and 0.5 mg progesterone (P). The percentage of ovariectomized steroid-treated females displaying lordosis increased at 29-33 days of age. At 50-65 days of age this percentage increased even further. Plasma levels of estrogen in 4-6 day old animals at 4, 8 and 12 h after 10 micrograms EB were at least equal to those seen in 50-65 day old animals. Neither the concentration nor the affinity of CER in hypothalamus (HYPO), preoptic area (POA), amygdala (AMYG) and cortex ( CORT ) were different in 4-6 day olds vs 50-65 day olds. The rank order for concentrations of CER in brain regions was: POA greater than HYPO greater than AMYG greater than CORT . A sex difference in CER was found in HYPO (females greater than males), but not POA, AMYG or CORT of 4-6 day olds.