Androgen receptor levels in hypothalamic and vocal control nuclei in the male zebra finch

Abstract

Using a synthetic, non-metabolizable ligand, R1881 (methyltrienolone), an in vitro binding assay was developed to quantify levels of cytosol androgen receptors in microdissected nuclei from the finch brain. Saturable, high affinity binding in the nanomolar range was demonstrated in the brain areas examined, and receptor levels were unaffected by freezing the tissue samples. The assay was specific for androgen receptors when 10 μM triamcinolone acetonide was added to inhibit the binding of R1881 to glucocorticoid and progestin receptors. Levels of cytosol androgen receptors were quantified in 3 hypothalamic and 3 vocal control nuclei presumed to contain high concentrations of androgen receptors on the basis of previous autoradiography. All nuclei examined showed significant levels of androgen receptors ranging from 5.8 to 35.8 fmol/mg protein. Hypothalamic nuclei had higher concentrations than vocal control nuclei.