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The melatonin is an endocrine hormone secreted by the pineal gland, through the binding with its high affinity receptor, the melatonin participate in the regulation of physiological functions of many organs and systems. Up to now, most people believe that there are three types of melatonin’s high affinity receptor: MT1, MT2 and MT3. It has been confirmed that the secretion of the melatonin has a circadian rhythm of low-level by day and high-level by night, which is opposite to the photoperiod, participating in the transfer information of circadian rhythm and seasonal rhythm .The studies on the distribution of MT1 in the mammal brains show that MT1 distributes in many sections of the brain, such as SCN, PT, PVN, the Hippocampus, the Cortex and so on. Dauer F et.al has found that the melatonin receptors take on a significant circadian rhythm in the PT of the rats. Then how about distribution of MT1 receptor in the whole brain of Gecko swinhonis? Does the expression of MT1 receptor in the brain of Gecko swinhonis also present a circadian rhythm? And does this rhythm change in different photoperiods?With the application of immunohistochemical and maths-morphologic methods, we have studied the distribution of MT1 receptor in the whole brain of Gecko swinhonis, the results showed that the MT1 receptor mainly located in the paraventricular nuclei of hypothalamus(PVN), also a little distribution in the nucleus of the pallial posterior commissure, whereas the immuno-reactive cells were not found in the suprachiasmatic nuclei of hypothalamus(namely the SCN of mammal).The positive cells of MT1 in PVN are mostly round and small ,and the positive reaction located in cell membrane and cytoplasm .In addition ,the distribution of MT1 receptor can also be found in the peripheral organs of Gecko swinhonis, the immunohistochemical results showed that in the liver of Gecko swinhonis ,the MT1 receptor mainly distributes in the Kupffer′s cell, some liver cells also has the distribution and the immuno-reactive occur mostly in cell membrane and cytoplasm. However, in the spleen this reaction was not founded.Under the three different photoperiods of DD, DL and LL, we respectively choose six time spots during a 24 hours interval—CT 7(circadian time), CT 11, CT 15, CT 19, CT 23, CT 3—to make the statistic analysis of the number of MT1
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