Kaur Satvinder, Thankachan Stephen, Begum Suraiya, Liu Meng, Blanco-Centurion Carlos, Shiromani Priyattam J
Veterans Affairs Boston Healthcare System, and Harvard Medical School, West Roxbury, MA, USA.
PLoS One. 2009 Jul 22;4(7):e6346. doi: 10.1371/journal.pone.0006346.
Ten years ago the sleep disorder narcolepsy was linked to the neuropeptide hypocretin (HCRT), also known as orexin. This disorder is characterized by excessive day time sleepiness, inappropriate triggering of rapid-eye movement (REM) sleep and cataplexy, which is a sudden loss of muscle tone during waking. It is still not known how HCRT regulates REM sleep or muscle tone since HCRT neurons are localized only in the lateral hypothalamus while REM sleep and muscle atonia are generated from the brainstem. To identify a potential neuronal circuit, the neurotoxin hypocretin-2-saporin (HCRT2-SAP) was used to lesion neurons in the ventral lateral periaquaductal gray (vlPAG). The first experiment utilized hypocretin knock-out (HCRT-ko) mice with the expectation that deletion of both HCRT and its target neurons would exacerbate narcoleptic symptoms. Indeed, HCRT-ko mice (n = 8) given the neurotoxin HCRT2-SAP (16.5 ng/23nl/sec each side) in the vlPAG had levels of REM sleep and sleep fragmentation that were considerably higher compared to HCRT-ko given saline (+39%; n = 7) or wildtype mice (+177%; n = 9). However, cataplexy attacks did not increase, nor were levels of wake or non-REM sleep changed. Experiment 2 determined the effects in mice where HCRT was present but the downstream target neurons in the vlPAG were deleted by the neurotoxin. This experiment utilized an FVB-transgenic strain of mice where eGFP identifies GABA neurons. We verified this and also determined that eGFP neurons were immunopositive for the HCRT-2 receptor. vlPAG lesions in these mice increased REM sleep (+79% versus saline controls) and it was significantly correlated (r = 0.89) with loss of eGFP neurons. These results identify the vlPAG as one site that loses its inhibitory control over REM sleep, but does not cause cataplexy, as a result of hypocretin deficiency.
十年前，睡眠障碍发作性睡病被认为与神经肽下丘脑泌素（HCRT）有关，后者也被称为食欲素。这种疾病的特征是白天过度嗜睡、快速眼动（REM）睡眠的不适当触发以及猝倒，猝倒是指清醒时肌肉张力突然丧失。目前仍不清楚HCRT如何调节REM睡眠或肌肉张力，因为HCRT神经元仅位于下丘脑外侧，而REM睡眠和肌肉张力缺失是由脑干产生的。为了确定潜在的神经回路，神经毒素下丘脑泌素-2-皂草素（HCRT2-SAP）被用于损毁腹外侧导水管周围灰质（vlPAG）中的神经元。第一个实验使用了下丘脑泌素基因敲除（HCRT-ko）小鼠，预期同时缺失HCRT及其靶神经元会加剧发作性睡病症状。事实上，在vlPAG中注射神经毒素HCRT2-SAP（每侧16.5 ng/23 nl/秒）的HCRT-ko小鼠（n = 8），其REM睡眠水平和睡眠碎片化程度比注射生理盐水的HCRT-ko小鼠（+39%；n = 7）或野生型小鼠（+177%；n = 9）高得多。然而，猝倒发作并未增加，清醒或非REM睡眠水平也没有改变。实验2确定了在存在HCRT但vlPAG中的下游靶神经元被神经毒素损毁的小鼠中的影响。该实验使用了一种FVB转基因小鼠品系，其中绿色荧光蛋白（eGFP）可识别GABA能神经元。我们对此进行了验证，并确定eGFP神经元对HCRT-2受体呈免疫阳性。这些小鼠的vlPAG损伤使REM睡眠增加（与生理盐水对照组相比增加了79%），并且与eGFP神经元的丧失显著相关（r = 0.89）。这些结果表明，由于下丘脑泌素缺乏，vlPAG是一个对REM睡眠失去抑制控制但不会导致猝倒的位点。
