Abstract
The amount of neurosecretory material (NSM) in the median eminence (ME) and the morphological changes in NSM of the supraoptic nuclei were investigated over a 24-hour period in Japanese quails, which were held on 8-hour daily photoperiods from 37 days to 55 days of age and then subjected to continuous illumination for 32 hours before sacrifice. Daily rhythmic changes were found in the amount and the concentration of NSM in ME, as well as in the volume of the stainable portion of ME. The rhythmic changes of the concentration of NSM in ME was inversely related to that of the volume of the stainable portion of ME. These rhythms in ME as well as in the morphological observation of NSM in the supraoptic nuclei suggest that the onsets of light and dark periods activate the hypothalamic neurosecretory system resulting in the initiation of synthesis and release of NSM. Biological meanings of these phenomena are discussed in relation to the avian gonadal growth induced by photoperiodical manipulation.
