Gorman M R, Zucker I
Department of Psychology, University of California, Berkeley 94720, USA.
Biol Reprod. 1997 Mar;56(3):668-73. doi: 10.1095/biolreprod56.3.668.
The impact of photoperiodic history was studied in male hamsters kept from birth to 6 wk of age (Week 0) in long-day (LD; 16 h light per day) or short-day (SD; 10 h light per day) photoperiods. At Week 0, hamsters were transferred to constant light and were s.c. infused daily with melatonin (MEL; 4 ng/h) until Week 12. Groups of SD hamsters received 10-h MEL infusions or MEL infusions of durations that decreased linearly by 1-2 min/day from 10 h at Week 0 to 7.5 h at Week 12. LD hamsters were infused for 5 h/day or in patterns that decreased from 10 to 7.5 h or increased from 5 to 7.5 h during Weeks 0-12. MEL signals of decreasing duration produced opposite effects on the gonads of LD and SD hamsters: decreasing MEL durations induced complete gonadal regression in LD hamsters (testis weight = 42 +/- 3 mg) but stimulated testis growth in SD hamsters (testis weight = 276 +/- 57 mg; p < 0.05). MEL infusions that were of shorter but increasing duration induced gonadal regression in LD hamsters. The present experiments indicate that MEL signals of a given sequence and duration can produce either gonadal growth or regression depending on the hamster's photoperiodic history. The pattern of change in MEL secretion, as well as absolute duration of the MEL signal, is important for implementing seasonal cycles of reproduction.
研究了光周期历史对雄性仓鼠的影响。这些仓鼠从出生到6周龄（第0周）饲养在长日照（LD；每天16小时光照）或短日照（SD；每天10小时光照）的光周期环境中。在第0周时，将仓鼠转移到持续光照环境，并每天皮下注射褪黑素（MEL；4纳克/小时），直至第12周。SD组仓鼠接受10小时的MEL注射，或MEL注射时长从第0周的10小时以每天1 - 2分钟的线性速度递减至第12周的7.5小时。LD组仓鼠每天注射5小时MEL，或在第0 - 12周期间注射时长从10小时递减至7.5小时，或从5小时递增至7.5小时。持续时间递减的MEL信号对LD和SD仓鼠的性腺产生了相反的影响：MEL持续时间的减少导致LD仓鼠性腺完全退化（睾丸重量 = 42 ± 3毫克），但刺激了SD仓鼠睾丸生长（睾丸重量 = 276 ± 57毫克；p < 0.05）。注射时长较短但呈递增趋势的MEL导致LD仓鼠性腺退化。本实验表明，给定序列和持续时间的MEL信号可根据仓鼠的光周期历史产生性腺生长或退化的结果。MEL分泌的变化模式以及MEL信号的绝对持续时间对于实现季节性繁殖周期很重要。
