Distribution And Circadian Rhythm Of AVP, Mel_1a Receptor In The Brain Of The Rhinolophus Affinis

Arginine vasopressin (AVP), one of neurophyophyseal hormone, is considered as an important candidate for output signal and modulator of the SCN of mammalians. The melatonin is synthesized and secreted by the pineal gland. Under the SCN regulation, the secretion of the melatonin presents a circadian thythm of low-level by daytime and high-level by night. High affinity melatonin receptor subtype Mel1a mainly expresses in the SCN, which is consistent with its role in the response to the melatonin periodicity signals. It is possible that it has relationship with the function on light-feeling and signals-transmission of the melatonin.Bats are the only flying nocturnal mammals, visual degradation, and have special light-feeling system. There is rare study on AVP, Mel1a receptor and other neuroendocrine hormones in this animal. In view of this, we studied the distribution and circadian rhythm of the AVP and Mel1a receptor neurons in Rhinolophus affinis brain, expecting to accumulate data for exploring the physiological function and mutually effects of AVP and Mel1a receptor, and mechanisms for circadian hythm regulation in the nocturnal mammals.1. Nissl and HE stain were applied to exhibit the structure of the Rhinolophus affinis brain. Immunohistochemical method was used to respectively display distribution characteristics and configuration of the immunoreactive AVP, Mel1a cells in Rhinolophus affinis brain. Compared with distribution characteristics in the diurnal mammals, the result could be seen obviously in the hypothalamus suprachiasmatic nucleus, paraventricular nucleus, supraoptic nucleus, lateral hypothalamic area, median eminence and posterior pituitary, etc. And their cell configuration was similar. The cells were mainly polygonal, round and pyriform in types, and immunoreactivity was observed in the perikarya granularly, but not in the nucleus. This suggested that it was highly conservative about respective distribution in the different mammalian hypothalamus, and mechanisms of physiological function are similar in this area. However, some differences were observed on cells density and localization of the edge systems. For example, positive cells density in the nuclei is lower than that in the diurnal mammals'corresponding structure. Positive cells in the edge nuclei, such as septohippocampal nucleus, amygdaloid nucleus and lateral septum, as observed in the diurnal mammals, were not detected. It was possible that functional mechanisms of circadian rhythms is different in nocturnal and diurnal mammals.2. Using static analysis, Secretions of the AVP-IR, Mel1a-IR exhibted a circadian thythm of high-level by daytime and low-level by night in Rhinolophus affinis SCN. Secretion of groups treated at 8:00 and at 16:00 were more than that at 24:00, and there was obvious difference (P<0.05). But there was no obvious difference between daytime groups and night groups (P>0.05). Using double-labeling immunofluorescence method, cells in the SCN with AVP also contained Mel1a receptor. These data suggested that the SCN AVP cells may respond to melatonin signals, raising the possibility that the SCN AVP output mediates some of the effects of melatonin on circadian or seasonal responses.