Effect of hypothalamic implantation of puromycin on photostimulated testicular growth in the Japanese quail (Coturnix coturnix japonica)

Avian photoreceptors and their role in the regulation of daily and seasonal physiology

Birds time their activities in synchronization with daily and seasonal periodicities in the environment, which is mainly provided by changes in day length (=photoperiod). Photoperiod appears to act at different levels than simply entraining the hypothalamic clock via eyes in birds. Photoreceptor cells that transmit light information to an avian brain are localized in three independent structures, the retina of eyes, pineal gland and hypothalamus, particularly in the paraventricular organ and lateral septal area. These hypothalamic photoreceptors are commonly referred to as encephalic or deep brain photoreceptors, DBPs. Eyes and pineal are known to contribute to the circadian regulation of behavior and physiology via rhythmic melatonin secretion in several birds. DBPs have been implicated in the regulation of seasonal physiology, particularly in photoperiod induced gonadal growth and development. Here, we briefly review limited evidence that is available on the roles of these photoreceptors in the regulation of circadian and seasonal physiology, with particular emphasis placed on the DBPs.

Effects of hypothalamic deafferentation on light-stimulated ovarian function in turkeys

Previous studies in the turkey have shown that lesions placed in the preoptic brain (POR) block ovulation, while lesions placed in the tuberal hypothalamus (TH) induce regression of rapidly growing ovarian follicles. In the present experiments, the nature of the neural pathways to and between these regions is explored by the method of neural transection performed with a small, stereotaxically positioned knife. Superior deafferentation of the POR allowed light-stimulated rapid growth of ovarian follicles but appeared to block or suppress ovulation. Complete deafferentation of the TH prevented development of the ovary as indicated by the failure of ovarian follicles to enter the phase of rapid growth. Partial cuts that severed anterior inputs to the TH blocked follicular growth, whereas cuts that severed lateral and posterodorsal connections or posterior connections to this region had no effect on development of a functional ovary. Deafferentation of the posterior two-thirds of the TH, which created an island including the posterodorsal region of the infundibular nuclear complex, did not block ovulation.

On hypothalamic control of ovulation in the turkey

Small bilateral lesions of the ventromedial preoptic hypothalamus consistently blocked ovulation. Lesions that completely cut the supraoptico-hypophyseal tract or that were placed throughout the tuberal hypothalamus and median eminence had no effect on ovulation. Lesions placed in the posterodorsal, medial, and ventral parts of the infundibular nuclear complex and in the medial and posteria divisions of the median eminence resulted in slight to moderate atresia of rapidly growing follicles within 38 to 40 hr after surgery.

Immunohistochemical localization of LH-producing cells in the adenohypophysis of the Japanese quail, Coturnix coturnix japonica

The cells that produce luteinizing hormone (LH) in the adenohypophysis of the Japanese quail were identified immunohistochemically using anti-chicken LH serum and horseradish peroxidase-labeled goat anti-rabbit gamma globulin serum. The LH cells are localized in the caudal lobe of the pars distalis. They are elongate in shape shape and are polarized toward the sinusoids, especially in their active states. Alterations in size of LH cells are directly related to changes in circulating LH levels as induced by castration or photostimulation. The LH cells identified immunohistochemically were only stained by alcian blue with periodic acid-Schiff (PAS), alcian blue and orange G. PAS-positive gonadotropic cells in the cephalic lobe were stained immunohistochemically only slightly if at all using anti-chicken LH serum and consequently may be FSH producing cells. In the cephalic lobe another type of basophilic cell was stained with alcian blue. These cells were also stained immunohistochemically with anti-chicken LH serum. These cells may possibly be identified as TSH cells due to the characteristics of the anti-chicken LH serum used in this study which cross react with LH and TSH but only slightly with FSH, and also on the basis of previous light and electron microscopic studies.