Morphological plasticity in the neural circuitry responsible for seasonal breeding in the ewe
Morphological plasticity in the neural circuitry responsible for seasonal breeding in the ewe
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DOI：
10.1210/en.2006-0408
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发表时间：
2006-10-01
期刊：
影响因子：
4.8
通讯作者：
Lehman, Michael N.
中科院分区：
文献类型：
--
作者：
Adams, Van L.;Goodman, Robert L.;Lehman, Michael N.
GnRH 神经元对雌激素负反馈反应的增加是导致母羊季节性不发情的原因，但其潜在的神经机制仍然很大程度上未知。神经可塑性可能发挥重要作用，因为 GnRH 神经元的突触输入密度随季节变化。此外，从繁殖季节到发情季节的过渡需要甲状腺激素，这也是神经元发育所必需的。在第一个实验中，我们通过电子显微镜分析比较甲状腺切除和甲状腺完整对照的突触输入，检查 GnRH 神经元突触的减少是否对于绝情过渡至关重要。甲状腺切除的母羊仍处于繁殖季节，但其 GnRH 细胞上的突触接触数量与未发情的甲状腺完整母羊没有不同。下一个实验通过共聚焦显微镜分析 A15 神经元上的突触蛋白阳性密切接触，测试了在动情期间介导雌激素负反馈的 A15 多巴胺能神经元的形态是否存在季节性变化。在发情期，A15 神经元树突上的这些紧密接触增加了 2 倍，并且每年这个时候 A15 树突的长度也相应增加。树突长度的增加被甲状腺切除术阻断，但该手术并没有显着影响 A15 神经元的突触输入。这些结果提供了初步证据，表明 GnRH 神经元突触的季节性变化不足以过渡到发情期，但介导雌激素负反馈的 A15 多巴胺能神经元的可塑性可能有助于这种季节性变化。
An increase in the response of GnRH neurons to estrogen negative feedback is responsible for seasonal anestrus in the ewe, but the underlying neural mechanisms remain largely unknown. Neural plasticity may play an important role because the density of synaptic input to GnRH neurons changes with seasons. Moreover, the transition from breeding to anestrous season requires thyroid hormones, which are also required for neuronal development. In the first experiment, we examined whether the decrease in synapses on GnRH neurons is critical for the transition to anestrus by comparing synaptic input in thyroidectomized and thyroid-intact controls, using electron microscopic analysis. Thyroidectomized ewes remained in the breeding season, but the number of synaptic contacts on their GnRH cells was not different from those in thyroid-intact ewes that were anestrus. The next experiment tested whether there was a seasonal change in morphology of the A15 dopaminergic neurons that mediate estrogen negative feedback during anestrus by analyzing synapsin-positive close contacts onto A15 neurons with confocal microscopy. There was a 2-fold increase in these close contacts onto dendrites of A15 neurons in anestrus and a corresponding increase in the length of A15 dendrites at this time of year. The increase in dendritic length was blocked by thyroidectomy, but this procedure did not significantly affect synaptic input to A15 neurons. These results provide initial evidence that the seasonal change in synapses on GnRH neurons is not sufficient for the transition into anestrus but that plasticity of the A15 dopaminergic neurons mediating estrogen negative feedback may contribute to this seasonal alteration.