Oh Sung-Gyoon, Hwang Young-Gi, Lee Hyun-Sook
Dept of Anatomy, School of Medicine, Konkuk University, 05029 Seoul, Republic of Korea.
Dept of Anatomy, School of Medicine, Konkuk University, 05029 Seoul, Republic of Korea; Research Institute of Medical Science, School of Medicine, Konkuk University, 05029 Seoul, Republic of Korea.
Brain Res. 2020 Dec 1;1748:147125. doi: 10.1016/j.brainres.2020.147125. Epub 2020 Sep 12.
There was a recent report suggesting that LIM homeobox 6 (Lhx6)+ GABA-releasing neurons of the ventral zona incerta (ZI) promote sleep. We demonstrated in the previous study that Lhx6+ ZI neurons are activated during paradoxical sleep (PS) hypersomnia which was induced by 48-hour PS deprivation, implying their roles in the control of PS like melanin-concentrating hormone (MCH) cells. Since the core portion of the lateral supramammillary nucleus (SUMl) is the major hypothalamic area activating the dentate gyrus as well as other limbic cortices during PS, we examined in the present study whether Lhx6+ ZI cells provide efferent projections to the SUMl, using the retrograde-tracing method. The majority of Lhx6+ neurons projecting to the SUMl occupied the ventral border (or ventral one-third) of the ventral ZI. Based on the quantitative analysis, the mean number of retrogradely-labeled Lhx6+ neurons was comparable to that of retrogradely-labeled MCH cells in the ZI. However, the total (i.e., single- plus double-labeled) number of Lhx6+ cells was approximately three times larger than that of MCH cells in the ZI. Thus, the proportion (about 7.8%) of retrogradely-labeled Lhx6+ neurons over the total Lhx6+ cells was approximately one-third of the percentage (about 20.9%) of retrogradely-labeled MCH neurons over the total MCH cells. On the other hand, a combination of retrogradely-labeled, Lhx6 and MCH cells occupied approximately 43.7% of the total retrogradely-labeled neurons in the ventral ZI. The present observations suggested that Lhx6+ neurons in the ventral ZI might play an important role in the regulation of PS, partly via the neural network involving the SUMl.
最近有一份报告表明，腹侧未定带（ZI）中表达LIM同源框6（Lhx6）的释放γ-氨基丁酸（GABA）的神经元可促进睡眠。我们在先前的研究中证明，在由48小时快速眼动睡眠（PS）剥夺诱导的异相睡眠（PS）过度嗜睡期间，Lhx6+ ZI神经元被激活，这意味着它们在PS控制中发挥的作用类似于促黑素细胞激素（MCH）细胞。由于外侧乳头体上核（SUMl）的核心部分是在下丘脑PS期间激活齿状回以及其他边缘皮质的主要区域，因此在本研究中，我们使用逆行追踪法检查了Lhx6+ ZI细胞是否向SUMl提供传出投射。投射到SUMl的大多数Lhx6+神经元占据腹侧ZI的腹侧边界（或腹侧三分之一）。基于定量分析，ZI中逆行标记的Lhx6+神经元的平均数量与逆行标记的MCH细胞的平均数量相当。然而，ZI中Lhx6+细胞的总数（即单标记加双标记）大约是MCH细胞总数的三倍。因此，逆行标记的Lhx6+神经元在Lhx6+细胞总数中所占的比例（约7.8%）约为逆行标记的MCH神经元在MCH细胞总数中所占百分比（约20.9%）的三分之一。另一方面，逆行标记的Lhx6和MCH细胞的组合约占腹侧ZI中逆行标记神经元总数的43.7%。目前的观察结果表明，腹侧ZI中的Lhx6+神经元可能在PS调节中发挥重要作用，部分是通过涉及SUMl的神经网络。
