The role of the median eminence in control of photoperiodically induced testicular growth in the white-crowned sparrow. Zonotrichia leucophrys gambelii.

Abstract

Midline electrolytic lesions were created in the basal hypothalamus of adult white-crowned sparrows, Zonotrichia leucophrys gambelii, in order to explore further the neuroendocrine basis of photoperiodic control of testicular growth. Lesions that destroyed the anterior and posterior divisions of the median eminence (AME and PME) prevented photoperiodically induced testicular growth, confirming the previously reported experiments of Wilson (1967) on this species. Destruction of the PME alone also abolished photoperiodic testicular growth. Destruction of the AME usually had no inhibitory effect. Moreover, extraeminential lesions that interrupted a majority of the fibers of the supraoptico-hypophysial tract thereby causing a marked depletion of stainable neurosecretory material from the AME had, in all but two birds, no noticeable effect on testicular growth. On the other hand, destruction of selected regions of the infundibular nucleus, without involvement of the median eminence, suppressed the photoperiodic testicular response. Destruction of the posterior region of the infundibular nucleus, causing antegrade degeneration of tubero-hypophysial fibers into the PME, also suppressed the testicular response. These results suggest that the infundibular nucleus may be composed of separate cellular populations functioning in the control of photoperiodically induced testicular growth and that only one of these may contribute neuronal elements to the neurohemal organs of the PME.