Center for Studies in Reproduction, Department of Physiology, School of Medicine, University of Maryland, Baltimore, Maryland 21201, USA.
J Neuroendocrinol. 1992 Oct;4(5):599-603. doi: 10.1111/j.1365-2826.1992.tb00209.x.
Norepinephrine (NE) turnovers (an index of secretion) increase in the hypothalamus of proestrous rats concomitant with luteinizing hormone surges, whereas, neither of these events are observed in diestrous nor in androgen-sterilized rats. Increased hypothalamic NE release may occur as a consequence of the withdrawal of local inhibitory γ-aminobutyric acid and opiate controls on specific presynaptic NE terminals and/or as a result of an increase in activity within noradrenergic neurons. Tyrosine hydroxylase (TH) is the rate-limiting enzyme for the synthesis of NE and our earlier studies revealed that increases in TH mRNA in A1 and locus ceruleus (LC) neurons can serve as an index of increased activity within these cells. In the present study, we evaluated whether TH message levels change in A1 and LC neurons prior to and during the hours when luteinizing hormone surges and increased NE turnovers are observed. As controls, TH mRNA levels in A1 and LC neurons were evaluated at the same hours of day in diestrous day 2 and in androgen-sterilized rats. In situ hybridization histochemistry and quantitative image analysis methods were used to measure changes in TH mRNA levels. Luteinizing hormone surges in proestrous rats began at 1500 h, peaked between 1600 and 1700 h and declined, thereafter, to 2000 h. In contrast, plasma luteinizing hormone remained basal throughout the day in diestrous and androgen-sterilized rats. While A1 neuronal TH mRNA levels did not differ in the three groups of rats during the morning (0930 to 1030 h), these message levels were significantly elevated in proestrous rats during the afternoon (1645 to 1715 h) and remained high at 2000 to 2030 h. In contrast, no changes in TH mRNA levels were observed in A1 neurons throughout the afternoon in diestrous animals or androgen-sterilized rats. TH mRNA levels in the LC did not differ in the three groups of rats and they remained unchanged throughout the afternoon hours we examined. From these observations we conclude that concomitant with afternoon proestrous luteinizing hormone surges and the accompanying increase in hypothalamic NE secretion, there is an increase in activity within A1 but not LC neurons. These data suggest that the proestrous increase in hypothalamic NE turnover we previously observed is not due solely to withdrawal of local inhibitory controls of presynaptic NE release but it also involves an increase in activity within A1 but not LC neurons.
去甲肾上腺素（NE）的周转率（分泌的指标）在发情期大鼠的下丘脑增加伴随着促黄体激素激增，然而，这些事件都没有在发情期或雄激素绝育的大鼠中观察到。下丘脑 NE 释放的增加可能是由于局部抑制性γ-氨基丁酸和阿片类物质对特定的突触前 NE 末梢的控制的撤回，和/或由于去甲肾上腺素能神经元内的活性增加。酪氨酸羟化酶（TH）是 NE 合成的限速酶，我们之前的研究表明，A1 和蓝斑（LC）神经元中 TH mRNA 的增加可以作为这些细胞内活性增加的指标。在本研究中，我们评估了促黄体激素激增和增加的 NE 周转率出现之前和期间，A1 和 LC 神经元中的 TH 信使 RNA 水平是否发生变化。作为对照，在发情期第 2 天和雄激素绝育的大鼠中，同一时间评估 A1 和 LC 神经元中的 TH mRNA 水平。使用原位杂交组织化学和定量图像分析方法来测量 TH mRNA 水平的变化。发情期大鼠的促黄体激素激增于 1500 时开始，在 1600 到 1700 时达到峰值，然后下降到 2000 时。相比之下，发情期和雄激素绝育的大鼠的血浆促黄体激素在全天都保持基础水平。虽然 A1 神经元中的 TH mRNA 水平在三组大鼠的上午（0930 至 1030 时）没有差异，但这些消息水平在发情期大鼠的下午（1645 至 1715 时）显著升高，并在 2000 至 2030 时保持高水平。相比之下，发情期动物或雄激素绝育的大鼠在整个下午的 A1 神经元中都没有观察到 TH mRNA 水平的变化。LC 中的 TH mRNA 水平在三组大鼠中没有差异，并且它们在我们检查的整个下午时间都保持不变。从这些观察结果中，我们得出结论，伴随着下午发情期促黄体激素激增和伴随而来的下丘脑 NE 分泌增加，A1 但不是 LC 神经元内的活性增加。这些数据表明，我们之前观察到的下丘脑 NE 周转率的发情期增加不仅是由于对突触前 NE 释放的局部抑制性控制的撤回，而且还涉及 A1 但不是 LC 神经元内的活性增加。
