Effects of prolonged daily photoperiods and estrogen on the hypothalamic neurosecretory system of the passerine bird, Zosterops palpebrosa japonica

Abstract

The hypothalamic neurosecretory system of the Japanese White-eye, Zosterops palpebrosa japonica, was studied. The neurosecretory cells were divided into seven groups: the neurosecretory cells of the supraoptic nucleus were subdivided into lateral and median groups; the cells of the paraventricular nucleus were subdivided into anterior, periventricular, and lateral groups. The sixth group was distributed in the peduncles, and the seventh group was located in the hilar region of the median eminence. The pathways of neurosecretory axons arising in these seven cell groups are described. The neurosecretory cells of the lateral group of the supraoptic nucleus and those of the anterior and periventricular groups of the paraventricular nucleus were stimulated by prolonged daily photoperiods, but the other groups were not. Estrogen administration activated the neurosecretory cells of the median group of the supraoptic nucleus of the long-day birds and nullified the activating effect of the prolonged daily photoperiods on the neurosecretory cells of the lateral group of the supraoptic nucleus. Functional differences among different neurosecretory cell groups in the hypothalamus are briefly discussed.