Nelson J F, Felicio L S, Randall P K, Sims C, Finch C E
Biol Reprod. 1982 Sep;27(2):327-39. doi: 10.1095/biolreprod27.2.327.
Cycle frequency, length, and vaginal cytology were measured longitudinally in three cohorts of singly housed virgin mice staggered across a 3-year interval. The age profiles of these parameters were qualitatively similar, but quantitatively different, among cohorts. Cycle frequency was initially low (Phase I), due to prolonged cycles and late-starting cycles, and did not peak (Phase II) until mice were 3-5 months old. Phase II lasted for 7-10 months, depending on the cohort. Thereafter cycle frequency declined steadily (Phase III). The average age of cessation of cyclicity varied among cohorts, occurring between 13 and 16 months of age. Age changes in cycle length paralleled those of cycle frequency. During Phase II, median cycle length was less than 5 days and variance was lowest. During Phases I and III, variance was about twofold greater and median cycle length was greater than 5 days. Although median cycle length remained stable for several months during Phase II, the peak period of 4-day cycles was much shorter. In all cohorts, 4-day cycles did not peak until 7-8 months of age and began to decline by 9 months. The decrease in 4-day cycles was associated with a progressive lengthening of cycles-first from 4 to 5 days, then to longer cycles. The fraction of cycles with extended cornification (greater than 2 days) increased with advancing age from less than 0.35 during the initial period of cycle lengthening to a maximum of 0.60. The observation that the initial phase o cycle prolongation was not usually associated with extended cornification is consistent with earlier evidence that this period is characterized by a delayed, rather than prolonged, preovulatory rise of estradiol. However, the increased fraction of prolonged cycles with extended cornification at later ages suggests that the preovulatory elevation of estradiol may ultimately be prolonged.
在三年时间间隔内，分三个队列纵向测量了单笼饲养的处女小鼠的周期频率、长度和阴道细胞学。这些参数的年龄分布在各队列之间在质量上相似，但在数量上不同。周期频率最初较低（第一阶段），这是由于周期延长和开始较晚，直到小鼠3至5个月大时才达到峰值（第二阶段）。第二阶段持续7至10个月，具体取决于队列。此后，周期频率稳步下降（第三阶段）。各队列间月经周期停止的平均年龄有所不同，发生在13至16个月龄之间。周期长度的年龄变化与周期频率的变化平行。在第二阶段，中位周期长度小于5天，方差最低。在第一阶段和第三阶段，方差大约大两倍，中位周期长度大于5天。尽管在第二阶段中位周期长度在几个月内保持稳定，但4天周期的高峰期要短得多。在所有队列中，4天周期直到7至8个月龄时才达到峰值，并在9个月时开始下降。4天周期的减少与周期的逐渐延长有关——首先从4天延长到5天，然后延长到更长的周期。角化延长（大于2天）的周期比例随着年龄的增长而增加，从周期延长初期的小于0.35增加到最大值0.60。周期延长的初始阶段通常与角化延长无关，这一观察结果与早期证据一致，即这一时期的特征是雌二醇排卵前升高延迟而非延长。然而，在较晚年龄，角化延长的延长周期比例增加，这表明雌二醇排卵前的升高最终可能会延长。
