Lu Xin-Yun, Shieh Kun-Ruey, Kabbaj Mohamed, Barsh Gregory S, Akil Huda, Watson Stanley J
University of Michigan School of Medicine, Mental Health Research Institute, Ann Arbor 48109, USA.
Endocrinology. 2002 Oct;143(10):3905-15. doi: 10.1210/en.2002-220150.
In the present study we examined the diurnal patterns of agouti-related protein (AGRP) and proopiomelanocortin (POMC) mRNA expression in the arcuate nucleus and their relation to circulating glucocorticoids and food intake. Animals were killed at 4-h intervals throughout the 24-h diurnal cycle, and the expression of AGRP and POMC mRNA was evaluated by semiquantitative in situ hybridization analysis. We observed a significant diurnal rhythm in AGRP mRNA expression, with a marked peak at 2200 h (4 h after lights off) and a trough at 1000 h (4 h after lights on), consistent with the overall day-night rhythm of food intake. In contrast, POMC mRNA levels did not show a significant fluctuation across the diurnal cycle, although there was a tendency for levels to decrease after the onset of the dark cycle. Corticosterone secretion temporally coincided with the rising phase of AGRP mRNA expression. Depletion of corticosterone by adrenalectomy abolished the AGRP diurnal rhythm by suppressing the nighttime expression, but did not alter the feeding rhythm. Exposure of adrenalectomized rats to constant corticosterone replacement (10 or 50 mg continuous release corticosterone pellet) resulted in fixed AGRP mRNA expression throughout the 12-h light, 12-h dark cycle. A relatively high level of corticosterone (50 mg) significantly increased AGRP mRNA expression, with a positive correlation between these two measures. These results indicate that 1) the diurnal expression of AGRP mRNA is regulated by corticosterone independently of the light/dark cue; and 2) a normal endogenous corticosterone rhythm is required for generating the diurnal AGRP rhythm.
在本研究中，我们检测了弓状核中刺鼠相关蛋白（AGRP）和阿黑皮素原（POMC）mRNA表达的昼夜模式，以及它们与循环糖皮质激素和食物摄入的关系。在整个24小时昼夜周期内，每隔4小时处死动物，通过半定量原位杂交分析评估AGRP和POMC mRNA的表达。我们观察到AGRP mRNA表达存在显著的昼夜节律，在22:00（熄灯后4小时）有一个明显的峰值，在10:00（开灯后4小时）有一个谷值，这与食物摄入的总体昼夜节律一致。相比之下，POMC mRNA水平在昼夜周期中没有显示出显著波动，尽管在黑暗周期开始后有下降的趋势。皮质酮分泌在时间上与AGRP mRNA表达的上升阶段一致。肾上腺切除导致皮质酮耗竭，通过抑制夜间表达消除了AGRP的昼夜节律，但没有改变进食节律。给肾上腺切除的大鼠持续给予皮质酮替代物（10或50毫克持续释放皮质酮丸剂），导致在12小时光照、12小时黑暗周期中AGRP mRNA表达固定。相对较高水平的皮质酮（50毫克）显著增加了AGRP mRNA表达，这两个指标之间呈正相关。这些结果表明：1）AGRP mRNA的昼夜表达受皮质酮调节，与光/暗线索无关；2）正常的内源性皮质酮节律是产生AGRP昼夜节律所必需的。
