Bertolucci C, Foà A
Dipartimento di Biologia, Università di Ferrara, Italy.
Am J Physiol. 1998 Apr;274(4):R1004-14. doi: 10.1152/ajpregu.1998.274.4.R1004.
To establish whether the capability of daily melatonin injections to entrain circadian rhythms varies with season, we examined in constant conditions the locomotor behavior of lizards Podarcis sicula collected and subjected to daily melatonin injections at different times of the year. Although in summer locomotor rhythms of both pineal-intact and pinealectomized lizards became entrained to the 24-h injection period, in the other seasons their rhythms did not entrain to the injection period. To establish whether the suprachiasmatic nuclei (SCN) mediate summer entrainment of locomotor rhythms to melatonin, we examined the behavioral effects of daily melatonin injections in lizards subjected to either bilateral (SCN-X) or unilateral (USCN-X) ablation of the SCN. SCN-X lizards became behaviorally arrhythmic, and daily melatonin injections did not restore rhythmicity. USCN-X lizards remained rhythmic, and their locomotor rhythms did entrain to the injections. Besides demonstrating for the first time in a vertebrate that daily melatonin injections are capable of entraining circadian rhythmicity in only one season (summer), the present results support the view that the SCN (and not the pineal gland) are the primary target sites of melatonin in the circadian system of P. sicula.
为了确定每日注射褪黑素调节昼夜节律的能力是否随季节变化，我们在恒定条件下研究了不同季节采集的西西里壁蜥（Podarcis sicula）的运动行为，并对其进行每日褪黑素注射。尽管在夏季，松果体完整和松果体切除的蜥蜴的运动节律都与24小时注射周期同步，但在其他季节，它们的节律并未与注射周期同步。为了确定视交叉上核（SCN）是否介导夏季运动节律对褪黑素的同步，我们研究了对SCN进行双侧（SCN-X）或单侧（USCN-X）切除的蜥蜴每日注射褪黑素的行为效应。SCN-X蜥蜴行为上变得无节律，每日注射褪黑素并未恢复节律性。USCN-X蜥蜴仍保持节律性，其运动节律确实与注射同步。除了首次在脊椎动物中证明每日注射褪黑素仅在一个季节（夏季）能够调节昼夜节律外，目前的结果支持以下观点：在西西里壁蜥的昼夜节律系统中，SCN（而非松果体）是褪黑素的主要作用靶点。
