Goodman R L, Meyer S L
Biol Reprod. 1984 Mar;30(2):374-81. doi: 10.1095/biolreprod30.2.374.
In the ewe, seasonal anestrus appears to result from two effects of inhibitory photoperiod: 1) estradiol gains the capacity to suppress luteinizing hormone (LH) pulse frequency and hence becomes a potent inhibitor of tonic LH secretion and 2) a steroid-independent decrease in LH pulse frequency occurs in ovariectomized ewes. In this study, we have obtained evidence, using pentobarbital anesthesia, that both these actions of photoperiod reflect the activation, in anestrus, of an inhibitory neural system. Administration of pentobarbital to intact anestrous ewes produced a dramatic, 3-fold increase in LH pulse frequency during the 6 h of anesthesia. In contrast, during the breeding season, pentobarbital inhibited LH pulse frequency in luteal phase animals. There was also a seasonal variation in the effects of pentobarbital in ovariectomized ewes. During the breeding season this drug again suppressed LH secretion, inhibiting both LH pulse amplitude and frequency. In anestrus, pentobarbital also suppressed pulse amplitude, but it produced a transitory increase (lasting 3 h) in pulse frequency. To account for the stimulatory actions of pentobarbital, we propose that in anestrus, but not the breeding season, LH pulse frequency is held in check by a set of estradiol-sensitive inhibitory neurons. Further, we suggest that these neurons are activated by inhibitory photoperiod and account for both the steroid-dependent and steroid-independent actions of photoperiod.
在母羊中，季节性发情似乎是由抑制性光周期的两种效应导致的：1）雌二醇获得了抑制促黄体生成素（LH）脉冲频率的能力，因此成为促性腺激素释放激素（GnRH）分泌的有效抑制剂；2）在切除卵巢的母羊中，LH脉冲频率出现了与类固醇无关的下降。在本研究中，我们使用戊巴比妥麻醉获得了证据，表明光周期的这两种作用都反映了在发情间期抑制性神经系统的激活。给完整的发情间期母羊注射戊巴比妥，在麻醉的6小时内LH脉冲频率显著增加了3倍。相比之下，在繁殖季节，戊巴比妥抑制了黄体期动物的LH脉冲频率。戊巴比妥对切除卵巢的母羊的影响也存在季节性变化。在繁殖季节，这种药物再次抑制LH分泌，同时抑制LH脉冲幅度和频率。在发情间期，戊巴比妥也抑制了脉冲幅度，但它使脉冲频率出现了短暂的增加（持续3小时）。为了解释戊巴比妥的刺激作用，我们提出，在发情间期而非繁殖季节，LH脉冲频率受到一组对雌二醇敏感的抑制性神经元的控制。此外，我们认为这些神经元被抑制性光周期激活，并解释了光周期的类固醇依赖性和类固醇非依赖性作用。
