Department of Neuroscience Biomedicine and Movement, Section of Physiology and Psychology, University of Verona, 37134 Verona, Italy.
National Institute of Neuroscience, 37134 Verona, Italy.
Mol Metab. 2017 Apr 22;6(6):594-601. doi: 10.1016/j.molmet.2017.04.005. eCollection 2017 Jun.
In the mouse model of obesity, chronic absence of leptin causes a significant increase of orexin (OX) production by hypothalamic neurons and excessive food intake. The altered OX level is linked to a dramatic increase of the inhibitory innervation of OX producing neurons (OX neurons) and the over expression of the endocannabinoid 2-arachidonoylglycerol (2-AG) by OX neurons of mice. Little is known about the function of the excitatory synapses of OX neurons in mice, and their modulation by 2-AG. In the present study, we fill this gap and provide the first evidence of the overall level of activation of OX neurons in the mice.
We performed whole-cell patch-clamp recordings on OX neurons located in the perifornical area of the lateral hypothalamus in acute brain slices of wt and mice. We identified OX neurons on the basis of their electrophysiological membrane properties, with 96% of concordance with immunohistochemisty.
We found that OX neurons of mice are innervated by less efficient and fewer excitatory synapses than wt mice. Consequently, OX neurons show more negative resting membrane potential and lower action potential firing frequency than wt. The bath application of the cannabinoid type-1 receptor agonist WIN55,212-2, depresses both the excitatory and the inhibitory synapses in animals, but only the excitatory synapses in wt animals. Finally, the physiologic release of 2-AG induces a prevalent depression of inhibition (disinhibition) of OX neurons in animals but not in wt.
In mice, chronic absence of leptin induces a 2-AG mediated functional disinhibition of OX neurons. This helps explain the increase of OX production and, consequently, the excessive food intake of mice.
在肥胖症的 小鼠模型中，瘦素的慢性缺失会导致下丘脑神经元中食欲素（OX）的产生显著增加，并导致过度摄食。改变后的 OX 水平与 OX 产生神经元（OX 神经元）的抑制性神经支配的剧烈增加以及 小鼠中 OX 神经元中超表达内源性大麻素 2-花生四烯酰甘油（2-AG）有关。关于 小鼠中 OX 神经元的兴奋性突触的功能及其被 2-AG 调节的了解甚少。在本研究中，我们填补了这一空白，并提供了 小鼠中 OX 神经元整体激活水平的第一个证据。
我们在 wt 和 小鼠的急性脑切片中，对位于外侧下丘脑穹窿周围区域的 OX 神经元进行全细胞膜片钳记录。我们根据其电生理膜特性来鉴定 OX 神经元，其与免疫组织化学的一致性达到 96%。
我们发现， 小鼠的 OX 神经元被效率较低且数量较少的兴奋性突触所支配。因此， OX 神经元的静息膜电位更负，动作电位发放频率更低。大麻素 1 型受体激动剂 WIN55,212-2 的浴内应用可抑制 动物中的兴奋性和抑制性突触，但仅抑制 wt 动物中的兴奋性突触。最后，2-AG 的生理性释放会导致 动物中 OX 神经元的抑制（去抑制）主要被抑制，但 wt 动物中则不会。
在 小鼠中，瘦素的慢性缺失会诱导 2-AG 介导的 OX 神经元功能去抑制。这有助于解释 OX 产生增加，以及 小鼠过度摄食的原因。
