Department of Anatomy and Neuroscience, Shimane University School of Medicine, 89-1 Enya-cho, Izumo-shi, Shimane, 693-8501, Japan.
Sci Rep. 2019 Feb 26;9(1):2830. doi: 10.1038/s41598-019-39063-y.
Orexin (ORX) neurons in the hypothalamus send their axons to arousal-promoting areas. We have previously shown that glutamatergic neurons in the lateral parabrachial nucleus (LPB) innervate ORX neurons. In this study, we examined potential pathways from the LPB to ORX neurons projecting to arousal-promoting areas in the brainstem by a combination of tract-tracing techniques in male Wistar rats. We injected the anterograde tracer biotinylated dextranamine (BDA) into the LPB and the retrograde tracer cholera toxin B subunit (CTb) into the ventral tegmental area, dorsal raphe nucleus, pedunculopontine tegmental nucleus, laterodorsal tegmental area, or locus coeruleus (LC). We then analyzed the BDA-labeled fibers and ORX-immunoreactive neurons in the hypothalamus. We found that double-labeled ORX and CTb neurons were the most abundant after CTb was injected into the LC. We also observed prominently overlapping distribution of BDA-labeled fibers, arising from neurons located in the lateral-most part of the dorsomedial nucleus and adjacent dorsal perifornical area. In these areas, we confirmed by confocal microscopy that BDA-labeled synaptophysin-immunoreactive axon terminals were in contiguity with cell bodies and dendrites of CTb-labeled ORX-immunoreactive neurons. These results suggest that the LPB innervates arousal-promoting areas via ORX neurons and is likely to promote arousal responses to stimuli.
下丘脑的食欲素（ORX）神经元将其轴突发送到促进觉醒的区域。我们之前已经表明，外侧臂旁核（LPB）中的谷氨酸能神经元支配投射到脑干中促进觉醒区域的 ORX 神经元。在这项研究中，我们通过雄性 Wistar 大鼠中的组合示踪技术，研究了从 LPB 到投射到脑干中促进觉醒区域的 ORX 神经元的潜在途径。我们将顺行示踪剂生物素化葡聚糖胺（BDA）注入 LPB，并将逆行示踪剂霍乱毒素 B 亚基（CTb）注入腹侧被盖区、中缝核、脚桥核被盖部、外侧背盖区或蓝斑。然后，我们分析了下丘脑中的 BDA 标记纤维和 ORX 免疫反应性神经元。我们发现，在将 CTb 注入 LC 后，双标记的 ORX 和 CTb 神经元最为丰富。我们还观察到 BDA 标记纤维的分布明显重叠，源自位于背内侧核最外侧部分和相邻背侧peri 穹窿区域的神经元。在这些区域中，我们通过共聚焦显微镜确认 BDA 标记的突触素免疫反应性轴突末端与 CTb 标记的 ORX 免疫反应性神经元的细胞体和树突连续。这些结果表明，LPB 通过 ORX 神经元支配促进觉醒的区域，并且可能促进对刺激的觉醒反应。
