The neuroendocrine control of gonadotrophin release in the Japanese quail. III. The role of the tuberal and anterior hypothalamus in the control of ovarian development and ovulation.

Abstract

Reproduction in the Japanese quail (Coturnix coturnix japonica), as in many other species, is controlled by the length of the daily photoperiod. The present experiments have investigated the neuroendocrine regulation of both the photoperiodically induced 'tonic' gonadotrophin secretion, which causes the development and maintenance of the ovary, and the 'cyclic' surge release of luteinizing hormone (LH), which stimulates ovulation. Areas within the anterior and tuberal hypothalamus were destroyed by means of electrolytic lesions while a small knife was used to isolate, to various degrees, the tuberal hypothalamus. Information was obtained on the regulation of 'tonic' and 'cyclic' secretion of gonadotrophin by using immature and mature laying females, respectively. The results indicate that the neuroendocrine regulation of photoperiodically induced gonadotrophin secretion in immature quail appears to be controlled by two discrete hypothalamic centres, the infundibular nuclear complex (i.n.c.) and the preoptic region (po.r.). The supraoptic region (so.r.) appears to have no influence on photoperiodically induced ovarian development. Deafferentation reveals that afferents from the anterior hypothalamus enter the tuberal region in a diffuse manner from both anterior and lateral directions. As in the developing animals, destruction of either the i.n.c. or the po.r. in mature birds results in a complete block to 'tonic' gonadotrophin release and to regression of the ovaries. When the supraoptic region is destroyed, the 'cyclic' ovulatory surge of LH is blocked and a polyfollicular syndrome ensues in which the ovaries, still under the influence of 'tonic' gonadotrophin release, grow to a very large size, but no ovulation takes place. An intramuscular injection of progesterone stimulates a release of LH in both untreated mature females and in sham-operated females, but not in so.r.-lesioned birds. Priming these lesioned females with oestrogen and progesterone restores, in some birds, the ability to respond positively to progesterone stimulation.