Quantitative evaluation of cytosol and nuclear [3H]-estradiol specific binding in the fetal brain of guinea pig during fetal ontogenesis

Estrogen binding macromolecules in hypothalamus-preoptic area of male and female gray short-tailed opossums (Monodelphis domestica)

Estrogen binding sites in the hypothalamus-preoptic area (HPOA) of adult male and female gray opossums (Monodelphis domestica) were characterized by incubating cytosols from gonadectomized animals with [3H]estradiol (E2) in the presence or absence of excess unlabeled E2. Scatchard analyses revealed that HPOA cytosols from both males and females contained high concentrations (25-30 fmol/mg protein) of binding sites with a very high affinity (Kd = 0.08-0.12 nM) for E2. There was no sex difference in either the number or the affinity of estrogen binding sites. Competition studies indicated that estrogen agonists and antagonists displaced [3H]E2 from binding sites in HPOA cytosols more effectively than did progestins, androgens, or adrenal corticoids. These data suggest that the HPOA of both male and female gray opossums contains macromolecules with several of the steroid binding properties characteristic of estrogen receptors.

Sexual differentiation of the human midtrimester brain

It is firmly believed that sexual differentiation of the brain is linked with external genital differentiation in timing as an in utero event in the human. An extensive search for oestrogen, androgen and progestin receptors failed to show their presence despite adequate controls in cytosols from human fetal brain of gestational ages 14-20 weeks. It is possible that the receptors are present in levels so low that they are undetectable by present-day methods. Our results would indicate that hormonally influenced in utero brain sexual differentiation is most unlikely to occur as a mid-trimester event.

Characterization of estrogen receptors in the hamster brain

Although the hamster is frequently used as an experimental animal for studying reproductive neuroendocrinology and sex behavior, estrogen receptors (ER) in the central nervous system have not been fully characterized. Using Sephadex LH-20 gel filtration and DNA-cellulose affinity chromatography, estrogen binding macromolecules having the physicochemical properties of classical ER were identified in cytosolic and nuclear extracts of brain tissues. These receptors exhibited high affinity for estradiol (Kd = 10(-9) M), limited capacity (30-50 fmol/g tissue), and estrogen specificity; however, competition studies indicate that brain and uterine ER have different binding kinetics. The neuroanatomic distribution of ER was similar in males and females with highest levels in the limbic brain and consistently low levels in remaining forebrain and mid/hindbrain. No sex differences in receptor number or other binding parameters were evident. Sucrose gradient centrifugation showed that cytosolic ER sedimented in the 7-8S region of a 5-20% linear gradient (no salt), whereas nuclear ER had a sedimentation coefficient of 5S under high ionic strength. On DNA-cellulose affinity columns, these receptors had an elution maximum of 0.18 M NaCl. After a single injection of estradiol, nuclear ER increased and cytosolic ER were depleted. The lower estradiol binding affinity and receptor levels in hamster brain as compared to the rat are consistent with observed species differences in neural sensitivity to estrogen. We expect these data in hamsters, a markedly photosensitive species, to provide a basis for future studies examining the role of receptors in mediating the effects of day-length on steroid dependent feedback and behavioral responses.

Estrogen receptors in the turtle brain

Estrogen binding activity in the CNS of the freshwater turtle, Chrysemys picta, was investigated using DNA-cellulose affinity chromatography. An estrogen binding component (EBC) with the characteristics of an estrogen receptor species was demonstrated in the brain cytosol extracts from both sexes. This EBC exhibited high affinity (K d = 10 -10 M), low capacity (n = 0.8 to 6.0 fmol/mg cytosol protein) and binding specificity. The bound estradiol-17 beta which adhered to DNA-cellulose was sensitive to excess synthetic and natural estrogens (DES, E2, E1 and E3) but not to progesterone and androgens (5 alpha- DHT and T). Specific estradiol-17 beta binding was not detected in plasma or non-target tissues such as lung, kidney and muscle. The topographic distribution of cytoplasmic EBC was similar in males and females, with binding highest in the hypothalamus-preoptic areas (HPOA) followed by the remaining forebrain (RFB). The mid/hindbrain (HB), consisting of the optic lobes, cerebellum and underlying brain stem had significantly lower concentrations of EBC. Monthly data (from May to October) suggest that variations in EBC concentrations occur during the year.

Embryonic rodent brain contains estrogen receptors

Estradiol-binding proteins with the properties of putative estrogen receptors are present in cytosol extracts of embryonic mouse hypothalamus and other brain regions. These embryonic estrogen receptors are adultlike in their high affinity and limited capacity for estradiol, sensitivity to diethylstilbestrol, ability to adhere to DNA, and behavior during DNA-cellulose affinity chromatography. As early as 4 days before birth, mouse hypothalamus has approximately 40 percent of the adult concentration of hypothalamic estrogen receptors with these properties. These observations raise the possibility that embryonic rodent brain has the biochemical potential to respond to sex hormones and that the critical period of brain sexual differentiation could be initiated prenatally.