Bosc M J, Nicolle A
Reprod Nutr Dev (1980). 1980;20(4A):939-48. doi: 10.1051/rnd:19800604.
Parturition time has been chosen to investigate whether a photoinducible phase exists during the light-dark cycle in the rat. A 1-hr light stimulation was given during the dark phase at various times after the beginning of the principal photoperiod or conventional dawn. The rats kept under 8 hrs of light and 16 hrs of darkness from mating (day 1 of pregnancy) gave birth to most of their pups on the afternoon of day 22 of pregnancy when the light pulse was applied 9 to 18 hrs or 22 to 23 hrs after dawn. Parturition was delayed till day 23 when the light pulse was given 18 to 22 hrs after dawn. In the same manner, under 16 hrs of light and 8 of darkness, most of the parturitions occurred on day 23 of pregnancy when a light pulse was given 22 hrs after dawn; they extended over two preferential periods--one on day 22 (about 50 p. 100) and the other on day 23 when the light pulse was given 16 to 17 hrs or 18 to 19 hrs after dawn. Thus, the stimulation of the photoinducible phase, found at the end of the dark period, resulted in retarded parturition. That delay was also observed when the light pulse was only given during the final days of pregnancy. Most parturitions occurred on day 22 of pregnancy under a short photoperiod to which 5 hrs of light were added during the dark phase at a time not coinciding with the photoinducible phase. This suggested that the effect of the principal light regime and the stimulation of the photoinducible phase could be dissociated.
选择分娩时间来研究大鼠在明暗周期中是否存在光诱导期。在主要光周期或常规黎明开始后的不同时间，于黑暗期给予1小时的光照刺激。从交配（妊娠第1天）开始就处于8小时光照和16小时黑暗环境下饲养的大鼠，当在黎明后9至18小时或22至23小时给予光脉冲时，它们大多在妊娠第22天下午分娩。当在黎明后18至22小时给予光脉冲时，分娩会延迟至第23天。同样，在16小时光照和8小时黑暗环境下，当在黎明后22小时给予光脉冲时，大多数分娩发生在妊娠第23天；它们分布在两个优先时间段——一个在第22天（约占100分之50），另一个在第23天，此时光脉冲是在黎明后16至17小时或18至19小时给予的。因此，在黑暗期结束时发现的光诱导期的刺激导致分娩延迟。当仅在妊娠的最后几天给予光脉冲时，也观察到了这种延迟。在短光周期下，妊娠第22天发生了大多数分娩，在黑暗期添加5小时光照，且添加时间与光诱导期不重合。这表明主要光照模式的影响和光诱导期的刺激可能是可以分开的。
