Davis F C, Darrow J M, Menaker M
Am J Physiol. 1983 Jan;244(1):R93-105. doi: 10.1152/ajpregu.1983.244.1.R93.
The circadian pacemaker that underlies the wheel-running activity of hamsters was studied in males and females. Sex differences were found in the mechanism by which the pacemaker entrains to light-dark cycles and in the timing of activity onset. When exposed to a light-dark cycle with a period of 24.75 h (with 1 h of light/cycle), males show a greater ability to maintain entrainment than do females. This difference in the upper limit of entrainment appears due to a sex difference in the magnitude of light-induced phase shifts. A small difference in free-running period may also contribute to the sex difference in entrainment. Two weeks after castration of adults, the sex difference in entrainment is not affected, indicating that the difference does not depend on circulating gonadal steroids or on estrous cyclicity of the female. However, castration of females at an early age increases their ability to entrain, whereas long-term castration of males seems to reduce entrainment ability. During entrainment to a 24-h light-dark cycle (LD 14:10), females were found to begin their daily activity before males and before castrated females. This difference is consistent with a sex difference in the magnitude of light-induced phase shifts and in entrainment of the pacemaker. However, evidence is given that the sex difference in activity onset might also be caused by a sex difference in the relationship of locomotor activity to the pacemaker in intact males and females.
对雄性和雌性仓鼠的昼夜节律起搏器进行了研究，该起搏器是仓鼠轮子转动活动的基础。在起搏器与明暗周期同步的机制以及活动开始的时间方面发现了性别差异。当暴露于周期为24.75小时（每个周期1小时光照）的明暗周期时，雄性比雌性表现出更强的维持同步的能力。这种同步上限的差异似乎是由于光诱导相移幅度的性别差异所致。自由运行周期的微小差异也可能导致同步方面的性别差异。成年仓鼠阉割两周后，同步方面的性别差异不受影响，这表明该差异不依赖于循环性腺类固醇或雌性的发情周期。然而，幼年雌性仓鼠阉割会提高它们的同步能力，而雄性仓鼠长期阉割似乎会降低同步能力。在与24小时明暗周期（LD 14:10）同步期间，发现雌性比雄性以及阉割后的雌性更早开始每日活动。这种差异与光诱导相移幅度以及起搏器同步方面的性别差异一致。然而，有证据表明，活动开始的性别差异也可能是由于完整雄性和雌性中运动活动与起搏器关系的性别差异所致。
