Mendonça M T, Tousignant A J, Crews D
Department of Zoology, University of Texas at Austin 78712, USA.
Gen Comp Endocrinol. 1995 Nov;100(2):226-37. doi: 10.1006/gcen.1995.1152.
We report seasonal and annual variation in the daily cycle of plasma melatonin levels in male red-sided garter snakes, Thamnophis sirtalis parietalis. In autumn of 1989 and 1990, levels averaged a maximum of 210 pg/ml during scotophase and a minimum of 45 pg/ml during photophase and had a similar diel pattern. Under hibernation conditions (4 degrees, 0:24 L:D), melatonin was undetectable and a diel cycle could not be determined. In Spring 1990, melatonin levels rose rapidly and precipitously within an hour of emergence (while in photophase), peaked at levels significantly higher than those seen in the autumn (approximately 900 pg/ml) and remained significantly high for 24 hr after emergence (though the majority of animals did have decreased levels at the 0400 sample). By the 10th day after emergence, a diel cycle was reestablished and absolute melatonin levels had decreased. The next spring (1991), melatonin again rose within an hour after emergence, while in photophase, but not as high as the previous year. Also unlike the previous year, a diel cycle was observed within 24 hr of emergence. Melatonin levels at emergence were significantly higher than those observed 10 days later. Disruption of a diel rhythm of plasma melatonin (by pinealectomy the previous autumn) inhibits courtship behavior by males the next spring, implying a role for melatonin in the stimulation of sexual behavior. Males in 1991 (with quickly established melatonin cycles) courted much sooner after emergence than did males in 1990. Therefore, the initial day/night difference in melatonin levels at emergence (i.e., establishment of a normal diel cycle) may function in synchronizing and modulating reproductive behavior in male red-sided garter snakes.
我们报告了雄性红侧带蛇（Thamnophis sirtalis parietalis）血浆褪黑素水平日周期的季节性和年度变化。在1989年和1990年秋季，暗期血浆褪黑素水平平均最高可达210 pg/ml，光期平均最低为45 pg/ml，且具有相似的昼夜模式。在冬眠条件下（4摄氏度，0:24光暗比），无法检测到褪黑素，也无法确定昼夜周期。1990年春季，褪黑素水平在出蛰后一小时内（处于光期时）迅速急剧上升，峰值显著高于秋季水平（约900 pg/ml），出蛰后24小时内一直保持在较高水平（尽管大多数动物在凌晨4点采样时水平有所下降）。到出蛰后第10天，重新建立了昼夜周期，褪黑素的绝对水平有所下降。次年春天（1991年），褪黑素在出蛰后一小时内（处于光期时）再次上升，但不如前一年高。与前一年不同的是，出蛰后24小时内就观察到了昼夜周期。出蛰时的褪黑素水平显著高于10天后观察到的水平。破坏血浆褪黑素的昼夜节律（前一年秋季进行松果体切除）会抑制次年春天雄性的求偶行为，这意味着褪黑素在刺激性行为中发挥作用。1991年的雄性（具有快速建立的褪黑素周期）出蛰后比1990年的雄性更早开始求偶。因此，出蛰时褪黑素水平的初始昼夜差异（即建立正常的昼夜周期）可能在同步和调节雄性红侧带蛇的生殖行为中发挥作用。
