Kao C, Schaeffer D J, Jackson G L
Department of Veterinary Biosciences, University of Illinois, Urbana 61801.
Biol Reprod. 1992 Mar;46(3):425-34. doi: 10.1095/biolreprod46.3.425.
The objective of this study was to determine whether two photoperiod regimens that induce anestrus in the ewe-short-day photorefractoriness (SDPR) and long-day photosuppression (LDPS)--act by different neuronal mechanisms. In separate experiments, ovary-intact (INTACT), ovariectomized (OVX), and ovariectomized estradiol-treated (OVX + E) ewes were subjected to three different photoperiodic regimens that resulted in reproductive quiescence: (1) exposure to long days (16L:8D), which caused photosuppression (INTACT, n = 9; OVX, n = 6; OVX + E, n = 5; (2) prolonged exposure to short days (10L:14D)), which caused photorefractoriness (INTACT, n = 10; OVX, n = 6; OVX + E, n = 5); (3) exposure to natural photoperiod, which induced seasonal anestrus (INTACT, n = 11; OVX, n = 6; OVX + E, n = 5). Effect of photoregimen was monitored by measuring progesterone or LH. Drug challenges were made after two sequential estrous cycles were missed in INTACT ewes, after mean LH concentrations dropped below 1 ng/ml in OVX + E ewes, and after LH interpulse intervals increased in OVX ewes. Effects of drug on LH pulse pattern were determined by taking blood samples at 12-min intervals for 8 h after i.v. diluent injection; then for 8 h after i.v. injection of cyproheptadine, a serotonin antagonist (3 mg/kg); and again 7 days later after i.v. injection of diluent or pimozide, a dopamine antagonist (0.25 mg/kg). Cyproheptadine had little effect except to decrease (p = 0.05) mean LH in INTACT anestrous ewes and decrease (p less than 0.01) pulse amplitude in OVX + E SDPR ewes. Pimozide did not affect LH pulse frequency in LDPS ewes. However, pimozide increased LH pulse frequency (p less than 0.005) and mean concentrations (p less than 0.005) in SDPR OVX + E ewes, whereas it suppressed LH pulse frequency (p less than 0.05) and amplitude (p less than 0.03) in SDPR INTACT and SDPR OVX ewes. The results suggest that (1) the role of the dopaminergic system differs in SDPR and LDPS ewes, and that different neuronal systems may effect SDPR and LDPS, (2) the effect of pimozide in SDPR ewes is altered by ovarian steroids, and (3) the serotonergic system has relatively little role in regulating pulsatile LH secretion in any of the three different states of anestrus.
本研究的目的是确定诱导母羊发情间期的两种光照周期方案——短日照光不应性（SDPR）和长日照光抑制（LDPS）——是否通过不同的神经元机制起作用。在单独的实验中，将保留卵巢（INTACT）、切除卵巢（OVX）以及切除卵巢并经雌二醇处理（OVX + E）的母羊置于三种不同的导致生殖静止的光照周期方案下：（1）暴露于长日照（16小时光照：8小时黑暗），这会引起光抑制（INTACT组，n = 9；OVX组，n = 6；OVX + E组，n = 5）；（2）长时间暴露于短日照（10小时光照：14小时黑暗），这会引起光不应性（INTACT组，n = 10；OVX组，n = 6；OVX + E组，n = 5）；（3）暴露于自然光照周期，这会诱导季节性发情间期（INTACT组，n = 11；OVX组，n = 6；OVX + E组，n = 5）。通过测量孕酮或促黄体生成素（LH）来监测光照方案的效果。在INTACT母羊错过两个连续发情周期后、OVX + E母羊的平均LH浓度降至1 ng/ml以下后以及OVX母羊的LH脉冲间期增加后进行药物激发试验。通过在静脉注射稀释剂后每隔12分钟采集血样8小时来确定药物对LH脉冲模式的影响；然后在静脉注射5 - 羟色胺拮抗剂赛庚啶（3 mg/kg）后8小时采集血样；7天后再次在静脉注射稀释剂或多巴胺拮抗剂匹莫齐特（0.25 mg/kg）后采集血样。赛庚啶除了使INTACT发情间期母羊的平均LH降低（p = 0.05）以及使OVX + E SDPR母羊的脉冲幅度降低（p < 0.01）外，几乎没有其他作用。匹莫齐特对LDPS母羊的LH脉冲频率没有影响。然而，匹莫齐特使SDPR OVX + E母羊的LH脉冲频率增加（p < 0.005）和平均浓度增加（p < 0.005），而在SDPR INTACT和SDPR OVX母羊中，它抑制LH脉冲频率（p < 0.05）和幅度（p < 0.03）。结果表明：（1）多巴胺能系统在SDPR和LDPS母羊中的作用不同，并且不同的神经元系统可能影响SDPR和LDPS；（2）卵巢类固醇改变了匹莫齐特在SDPR母羊中的作用；（3）在三种不同的发情间期状态下，5 - 羟色胺能系统在调节LH脉冲式分泌中作用相对较小。
