Hypothalamic and hormonal control of the photoperiodically induced vernal functions in the white-crowned sparrow, Zonotrichia leucophrys gambelii. 1. The effects of hypothalamic lesions and exogenous hormones.

To assess the role of the hypothalamo-hypophysial complex in the control of photoperiodically induced vernal premigratory responses in the White-crowned Sparrow, the effects of hypothalamic lesions and systemic administration of several hormones on these responses were investigated. Lesions that destroyed the posterior median eminence (PME) or the entire median eminence (ME) inhibited photoperiodically induced testicular growth, premigratory fattening and Zugunruhe. Lesions in the basal infundibular nucleus (IN) that resulted in complete inhibition of testicular growth abolished Zugunruhe, but allowed varying degrees of fattening. The systemic administration of prolactin, testosterone propionate (TP) or the combination thereof in the PME-lesioned birds induced fattening similar to that observed in photostimulated controls but did not induce Zugunruhe. It is concluded that testosterone and prolactin are the most important hormones involved in the control of vernal premigratory fattening. The role of these hormones in the induction of vernal Zugunruhe is not positively proven.