Zhang C, Baimoukhametova D V, Smith C M, Bains J S, Gundlach Andrew L
The Florey Institute of Neuroscience and Mental Health, 30 Royal Parade, Parkville, VIC, 3052, Australia.
Florey Department of Neuroscience and Mental Health, The University of Melbourne, Parkville, VIC, 3010, Australia.
Psychopharmacology (Berl). 2017 Jun;234(11):1725-1739. doi: 10.1007/s00213-017-4575-z. Epub 2017 Mar 17.
Relaxin-3/RXFP3 signalling is proposed to be involved in the neuromodulatory control of arousal- and stress-related neural circuits. Furthermore, previous studies in rats have led to the proposal that relaxin-3/RXFP3 signalling is associated with activation of the hypothalamic-pituitary-adrenal axis, but direct evidence for RXFP3-related actions on the activity of hypothalamic corticotropin-releasing hormone (CRH) neurons is lacking. In this study, we investigated characteristics of the relaxin-3/RXFP3 system in mouse hypothalamus. Administration of an RXFP3 agonist (RXFP3-A2) intra-cerebroventricularly or directly into the paraventricular nucleus of hypothalamus (PVN) of C57BL/6J mice did not alter corticosterone levels. Similarly, there were no differences between serum corticosterone levels in Rxfp3 knockout (C57BL/6J) and wild-type mice at baseline and after stress, despite detection of the predicted stress-induced increases in serum corticosterone. We examined the nature of the relaxin-3 innervation of PVN in wild-type mice and in Crh-IRES-Cre;Ai14 mice that co-express the tdTomato fluorophore in CRH neurons, identifying abundant relaxin-3 fibres in the peri-PVN region, but only sparse fibres associated with densely packed CRH neurons. In whole-cell voltage-clamp recordings of tdTomato-positive CRH neurons in these mice, we observed a reduction in sEPSC frequency following local application of RXFP3-A2, consistent with an activation of RXFP3 on presynaptic glutamatergic afferents in the PVN region. These studies clarify the relationship between relaxin-3/RXFP3 inputs and CRH neurons in mouse PVN, with implications for the interpretation of current and previous in vivo studies and future investigations of this stress-related signalling network in normal and transgenic mice, under normal and pathological conditions.
松弛素-3/RXFP3信号通路被认为参与了与觉醒和应激相关神经回路的神经调节控制。此外，先前在大鼠中的研究提出，松弛素-3/RXFP3信号通路与下丘脑-垂体-肾上腺轴的激活有关，但缺乏RXFP3对下丘脑促肾上腺皮质激素释放激素（CRH）神经元活性相关作用的直接证据。在本研究中，我们调查了小鼠下丘脑松弛素-3/RXFP3系统的特征。向C57BL/6J小鼠的脑室内或直接向下丘脑室旁核（PVN）注射RXFP3激动剂（RXFP3-A2），并未改变皮质酮水平。同样，尽管检测到应激诱导血清皮质酮水平升高，但Rxfp3基因敲除（C57BL/6J）小鼠和野生型小鼠在基线和应激后的血清皮质酮水平并无差异。我们检查了野生型小鼠以及在CRH神经元中共表达tdTomato荧光团的Crh-IRES-Cre;Ai14小鼠中PVN的松弛素-3神经支配性质，发现在PVN周围区域有丰富的松弛素-3纤维，但与密集排列的CRH神经元相关的纤维很少。在这些小鼠中tdTomato阳性CRH神经元的全细胞膜片钳记录中，我们观察到局部应用RXFP3-A2后微小兴奋性突触后电流（sEPSC）频率降低，这与PVN区域突触前谷氨酸能传入神经上RXFP3的激活一致。这些研究阐明了小鼠PVN中松弛素-3/RXFP3输入与CRH神经元之间的关系，对解释当前和先前的体内研究以及未来在正常和病理条件下对正常和转基因小鼠中这个与应激相关的信号网络的研究具有重要意义。
