Chronic lead (Pb) exposure affects the circadian physiological processes regulated by suprachiasmatic nucleus (SCN), which is synchronized (entrainment) by light. Disorders in the entrainment capacity of an organism alter its performance to interact with the environment, thus affecting its health status. The objectives of the present study were to evaluate whether chronic early Pb exposure affects the entrainment of the circadian rhythm of locomotor activity by light and to explore the possible mechanisms involved. Adult male Wistar rats, control and chronically exposed to Pb (320 ppm) in drinking water from gestation to adult age, were used. Assessment of the metal level showed a significant increase of Pb in the blood, hypothalamus and prefrontal cortex of the experimental rats. Continuous registrations of locomotor activity (12 h:12 h light-dark cycle) depicted that Pb induces important delay of this activity when the light was turned off. The Pb exposed animals entrained faster with a photoperiod delay of 6 h, (lights on at 13:00 h), and maintained the significant delay in the onset of activity at lights out. In continuous darkness, the animals were exposed to a light pulse at circadian time 23. This resulted in a significant decrease of photo-stimulated neurons (immunoreactivity to c-Fos) in the SCN of the metal-exposed animals. These results show that chronic early Pb exposure alters the photic entrainment of the rhythm of locomotor activity, which is evidenced by a significant decrease in both the number of photo-stimulated neurons and neuronal population (Nissl stain) of the SCN.

慢性铅 (Pb) 暴露会影响由光同步（夹带）的视交叉上核 (SCN) 调节的昼夜生理过程。生物体夹带能力的紊乱会改变其与环境相互作用的表现，从而影响其健康状况。本研究的目的是评估慢性早期铅暴露是否会影响光对运动活动的昼夜节律的夹带，并探讨可能的机制。使用成年雄性 Wistar 大鼠，对照和长期暴露于从妊娠到成年的饮用水中的 Pb (320 ppm)。金属水平的评估显示实验大鼠血液、下丘脑和前额叶皮层中的铅显着增加。运动活动的连续记录（12 小时：12 小时明暗循环）描绘了当灯关闭时，Pb 会导致该活动的重要延迟。暴露于 Pb 的动物以 6 小时的光周期延迟（13:00 时亮灯）更快地夹带，并在熄灯时保持活动开始的显着延迟。在连续黑暗中，动物在昼夜节律时间 23 时暴露于光脉冲。这导致暴露于金属的动物的 SCN 中的光刺激神经元（对 c-Fos 的免疫反应性）显着减少。这些结果表明，慢性早期铅暴露改变了运动活动节律的光夹带，这可以通过 SCN 的光刺激神经元和神经元群（尼氏染色）的数量显着减少来证明。