Harney J P, Scarbrough K, Rosewell K L, Wise P M
Department of Physiology, University of Kentucky College of Medicine, Lexington 40536-0084, USA.
Endocrinology. 1996 Sep;137(9):3696-701. doi: 10.1210/endo.137.9.8756535.
In mammals, the suprachiasmatic nuclei (SCN) regulate the timing of LH surges. Recent evidence suggests that vasoactive intestinal peptide (VIP), an abundantly expressed neuropeptide of the SCN, communicates time of day information from the SCN to GnRH neurons. VIP levels in the SCN decrease with age and may be responsible for alterations in LH surges that become apparent in middle-aged rats. We wished to determine whether suppression of VIP synthesis, through antisense oligonucleotides (oligos) directed at the SCN, results in 1) selective suppression of VIP levels in the SCN and 2) aging-like changes in the secretion of LH and PRL. To test the specificity of antisense oligo treatment, rats were ovariectomized and treated with estradiol. Antisense or control random oligos were infused into the peri-SCN region through stereotaxically placed bilateral cannulas. Beginning at lights off, rats were maintained in constant dim red illumination throughout the remainder of the experiment. They were killed at specific times, brains were microdissected, and VIP concentrations in the SCN, paraventricular nuclei, and cortex were assayed. As a control for the specificity of antisense VIP treatment, we monitored the levels of arginine vasopressin in the SCN. To test the effects of antisense treatment on the pattern of plasma LH and PRL secretion, blood samples were collected from atrial catheters from 1200-2000 h, and plasma samples were assayed for LH and PRL. The results indicate that the effects of antisense treatment were discrete, as they suppressed VIP concentrations in the SCN, but had no effect on VIP concentrations in the paraventricular nuclei or cortex or on arginine vasopressin concentrations in the SCN. Peak LH levels during the surge were delayed and attenuated in antisense-treated animals compared to random oligo-treated control rats in a manner strikingly similar to that observed previously in middle-aged rats. Likewise, PRL, which was unaffected in middle-aged rats, was also unaffected by targeted suppression of VIP. In summary, our findings clearly demonstrate that antisense VIP oligos suppress VIP levels in the SCN and do not affect peptide concentrations in other regions of the brain or other neuropeptides in the SCN. Further, we show that suppression of a single neuropeptide in the SCN can mimic the effects of age on the estradiol-induced surges of LH and PRL. These data support a central role for suprachiasmatic VIP in the regulation of the LH surge and suggest that age-related perturbations in the integrity of this axis may account for alterations in the pattern of LH secretion observed during middle age.
在哺乳动物中，视交叉上核（SCN）调节促黄体生成素（LH）高峰的时间。最近的证据表明，血管活性肠肽（VIP）是SCN中大量表达的一种神经肽，它将一天中的时间信息从SCN传递给促性腺激素释放激素（GnRH）神经元。SCN中的VIP水平会随着年龄增长而降低，这可能是中年大鼠中明显出现的LH高峰变化的原因。我们希望确定通过针对SCN的反义寡核苷酸（oligos）抑制VIP合成是否会导致：1）SCN中VIP水平的选择性抑制；2）LH和催乳素（PRL）分泌出现类似衰老的变化。为了测试反义寡核苷酸治疗的特异性，对大鼠进行卵巢切除并给予雌二醇治疗。通过立体定位放置的双侧套管将反义或对照随机寡核苷酸注入SCN周围区域。从熄灯开始，在实验的剩余时间里，将大鼠置于持续昏暗的红光照明下。在特定时间处死大鼠，对大脑进行显微解剖，并测定SCN、室旁核和皮质中的VIP浓度。作为反义VIP治疗特异性的对照，我们监测了SCN中精氨酸加压素的水平。为了测试反义治疗对血浆LH和PRL分泌模式的影响，在1200 - 2000 h从心房导管采集血样，并测定血浆样本中的LH和PRL。结果表明，反义治疗的效果是离散的，因为它抑制了SCN中的VIP浓度，但对室旁核或皮质中的VIP浓度或SCN中的精氨酸加压素浓度没有影响。与随机寡核苷酸处理的对照大鼠相比，反义处理的动物在LH高峰期间的峰值水平延迟且减弱，其方式与先前在中年大鼠中观察到的惊人相似。同样，中年大鼠中未受影响的PRL，也不受靶向抑制VIP的影响。总之，我们的研究结果清楚地表明，反义VIP寡核苷酸抑制了SCN中的VIP水平，且不影响大脑其他区域的肽浓度或SCN中的其他神经肽。此外，我们表明抑制SCN中的单一神经肽可以模拟年龄对雌二醇诱导的LH和PRL高峰的影响。这些数据支持视交叉上核VIP在调节LH高峰中起核心作用，并表明该轴完整性的年龄相关扰动可能是中年期间观察到的LH分泌模式变化的原因。
