Abstract
Subcutaneous injection of ovine luteinizing and follicle-stimulating hormones in photoperiodically stimulated female White-crowned Sparrows, Zonotrichia leucophrys gambelii, was followed by significant increments in growth of the ovary and oviduct and a significant depression in the level of assayable pituitary gonadotropins. Simultaneous injections of ovine prolactin did not significantly alter the effects of treatment with gonadotropins, nor did they modify the rate of photoperiodically induced growth of the ovary. It appears that plasma gonadotropins and/or ovarian hormones exert an inhibitory feedback effect on the hypothalamohypophysial system. In photorefractory females 10 daily injections of luteinizing and follicle-stimulating hormones caused a small, but significant, growth of the ovaries that was unaffected by simultaneous injections of prolactin. The level of pituitary gonadotropins was not affected by these injections of hormones. These data are consistent with the hypothesis that photorefractoriness is a neural or hypophysial phenomenon.
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