Matsumoto S, Basil J, Jetton A E, Lehman M N, Bittman E L
Department of Biology, University of Massachusetts, Amherst 01003, USA.
J Biol Rhythms. 1996 Jun;11(2):145-62. doi: 10.1177/074873049601100207.
The influence of exogenous signals on circadian rhythms restored by transplants of the suprachiasmatic nucleus (SCN) of the hypothalamus has received little study. The authors tested the responsiveness of hamsters bearing SCN transplants to photic and pharmacological treatments. Light intensities as high as 6,500 lux were insufficient to produce entrainment, although masking was observed frequently. Triazolam failed to produce statistically significant phase shifts when administered during the subjective day, but 2 animals bearing functional SCN grafts responded to this benzodiazapine during the subjective night. The authors next tested the hypothesis that the host can retain circadian aftereffects that influence the period of the circadian system reconstituted by the graft. Intact hamsters were entrained to light:dark cycles of short (23.25-h) and long (25-h) period (T) for at least 3 months. Control hamsters released into constant darkness exhibited profound and long-lasting aftereffects of entrainment to T cycles. Hamsters that received SCN lesions after exposure to these T cycles and SCN grafts 3 weeks later exhibited marginal but statistically significant aftereffects that disappeared within 3 months. On subsequent transfer to constant light, tau lengthened by 0.25 +/- 0.6 h in hamsters with intact SCN (p < .05). Animals bearing SCN grafts continued to free run in constant light but differed from intact animals in that circadian period did not lengthen. Functional SCN grafts contained vasoactive intestinal polypeptide (VIP), neurophysin (NP), and cholecystokinin (CCK) immunoreactive (ir) cells. Inputs of neuropeptide Y-and serotonin-ir fibers from the host brain to grafted SCN peptide cell clusters were variable. Limited observations using retrograde and anterograde tracers do not support the existence of extensive input to the graft. Retinal input overlapped only rarely with clusters of VIP-ir, CCK-ir, or NP-ir cells. The authors conclude that the circadian system reinstated by SCN transplants is relatively impervious to photic influences that exert parametric and nonparametric influences in intact hamsters. The transient expression of aftereffects induced in the host before transplantation indicates that extra-SCN systems of the host can influence the period of the reconstituted circadian system to at least a limited degree.
外源性信号对通过下丘脑视交叉上核（SCN）移植恢复的昼夜节律的影响鲜有研究。作者测试了接受SCN移植的仓鼠对光照和药物治疗的反应性。尽管经常观察到掩盖效应，但高达6500勒克斯的光强度不足以产生同步化。三唑仑在主观白天给药时未能产生具有统计学意义的相位偏移，但2只带有功能性SCN移植物的动物在主观夜间对这种苯二氮䓬有反应。作者接下来测试了一个假设，即宿主可以保留昼夜节律后效应，这种后效应会影响由移植物重建的昼夜节律系统的周期。将完整的仓鼠置于短（23.25小时）和长（25小时）周期（T）的明暗循环中至少3个月。释放到持续黑暗中的对照仓鼠表现出对T周期同步化的深刻而持久的后效应。在暴露于这些T周期后接受SCN损伤并在3周后接受SCN移植的仓鼠表现出轻微但具有统计学意义的后效应，这些后效应在3个月内消失。在随后转移到持续光照下时，完整SCN的仓鼠的tau延长了0.25±0.6小时（p<0.05）。带有SCN移植物的动物在持续光照下继续自由活动，但与完整动物不同的是，昼夜周期没有延长。功能性SCN移植物包含血管活性肠肽（VIP）、神经垂体素（NP）和胆囊收缩素（CCK）免疫反应性（ir）细胞。来自宿主脑的神经肽Y和5-羟色胺ir纤维向移植的SCN肽细胞簇的输入是可变的。使用逆行和顺行示踪剂的有限观察结果不支持向移植物存在广泛输入的观点。视网膜输入仅很少与VIP-ir、CCK-ir或NP-ir细胞簇重叠。作者得出结论，SCN移植恢复的昼夜节律系统相对不受在完整仓鼠中施加参数性和非参数性影响的光照影响。移植前在宿主中诱导的后效应的短暂表达表明，宿主的SCN外系统可以至少在有限程度上影响重建的昼夜节律系统的周期。
