Department of Anatomy, College of Medicine, Konkuk University, Hwayang-dong, Gwangjin-gu, 143-701 Seoul, Republic of Korea.
Brain Res. 2011 Nov 18;1424:20-31. doi: 10.1016/j.brainres.2011.09.051. Epub 2011 Oct 1.
Hypocretin (Hcrt or orexin) and melanin-concentrating hormone (MCH) containing neurons are located in the hypothalamus and are implicated in the regulation of feeding behavior, energy homeostasis, and sleep-wake cycle. MCH and Hcrt are not co-localized within the same neuron, but these neurons project widely throughout the brain, especially to brain regions regulating arousal. Recent data indicate that HCRT and MCH neurons located medially with respect to the fornix have a differential projection pattern compared to those located lateral to the fornix. To further elucidate the projection of these neurons in the present study we use retrograde tracing methods combined with double immunofluorescence to determine the differential distribution of Hcrt- and MCH-immunoreactive neurons projecting to the pedunculopontine tegmental (PPTg) or laterodorsal tegmental (LDTg) nuclei. In rats where the retrograde tracer was confined to the PPTg/LDTg we found that there were more MCH neurons projecting to these targets compared to HCRT neurons (P<0.01). When the retrograde tracer was confined to the PPTg, there were more retrogradely labeled MCH neurons lateral to the fornix compared to MCH neurons in the medial LH subdivision (P<0.05). On the average, only about 4.5% of MCH neurons versus 6.1% of HCRT neurons project to PPTg/LDTg. Thus, very few of the MCH or HCRT neurons project to these arousal populations. Although there were significantly more MCH neurons projecting to the mesopontine cholinergic arousal zone compared to the HCRT neurons, the HCRT neurons also exert an indirect influence via the tuberomammillary nucleus. Based on the present and previous (Hong and Lee, 2011) observations, we suggest that both MCH and HCRT neurons exert a potent influence on the PPTg/LDTg, which might play an important role in arousal.
下丘脑含有食欲素（Hcrt 或 orexin）和黑色素浓缩激素（MCH）神经元，参与调节摄食行为、能量平衡和睡眠-觉醒周期。MCH 和 Hcrt 不在同一神经元中共存，但这些神经元广泛投射到大脑中，特别是到调节觉醒的脑区。最近的数据表明，相对于穹窿内侧的 HCRT 和 MCH 神经元，位于穹窿外侧的这些神经元具有不同的投射模式。为了进一步阐明这些神经元的投射，本研究采用逆行追踪方法结合双重免疫荧光技术，确定投射到脚桥核（PPTg）或外侧背侧核（LDTg）的 Hcrt 和 MCH 免疫反应性神经元的差异分布。在逆行示踪剂仅限于 PPTg/LDTg 的大鼠中，我们发现投射到这些靶点的 MCH 神经元数量多于 HCRT 神经元（P<0.01）。当逆行示踪剂仅限于 PPTg 时，与内侧 LH 亚区的 MCH 神经元相比，穹窿外侧有更多的逆行标记 MCH 神经元（P<0.05）。平均而言，只有约 4.5%的 MCH 神经元而不是 6.1%的 HCRT 神经元投射到 PPTg/LDTg。因此，很少有 MCH 或 HCRT 神经元投射到这些觉醒神经元。尽管投射到中脑胆碱能觉醒区的 MCH 神经元数量明显多于 HCRT 神经元，但 HCRT 神经元也通过结节乳头核发挥间接影响。基于目前和之前的（Hong 和 Lee，2011）观察结果，我们认为 MCH 和 HCRT 神经元都对 PPTg/LDTg 产生强烈影响，这可能在觉醒中发挥重要作用。
