Influences of Photoperiod on Nuclear Androgen Receptor Occupancy in Neuroendocrine Tissues of the Golden Hamster

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Abstract
Day length regulates the negative feedback potency of gonadal steroids upon luteinizing hormone (LH) in seasonal breeders such as the golden hamster. We have used an exchange assay employing 3H-R1881 to determine whether nuclear androgen plus receptor levels in the preoptic area, medial basal hypothalamus, or anterior pituitary differ between male hamsters maintained in long or short days. Cell nuclear androgen plus receptor levels in brain and anterior pituitary were significantly lower in intact males maintained in short days; these differences reflected significant decreases in testis size and serum testosterone (T) levels upon exposure to inhibitory photoperiods. In castrated males in which serum T levels were ''clamped'' by the insertion of T-filled Silastic capsules, exposure to short days was not correlated with an increase in preoptic area, medial basal hypothalamus, or anterior pituitary receptor occupancy even though T''s negative feedback actions upon LH were clearly enhanced. In contrast, there were instances in which androgen receptor occupation was elevated in males exposed to long days. Our results suggest that in the male golden hamster, the well-documented increase in the ability of T to suppress LH secretion in short photoperiods cannot be attributed to an increase in receptor-mediated uptake and nuclear accumulation of androgen in target cells in the brain and anterior pituitary gland.