Abstract
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 −10M), low capacity ( n= 0.8 to 6.0fmol/mg cytosol protein) and binding specificity. The bound estradiol-17β which adhered to DNA-cellulose was sensitive to excess synthetic and natural estrogens (DES, E 2, E 1 and E 3) but not to progesterone and androgens (5α-DHT and T). Specific estradiol-17β 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.
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