Haidar M, Guèvremont G, Zhang C, Bathgate R A D, Timofeeva E, Smith C M, Gundlach A L
The Florey Institute of Neuroscience and Mental Health, Parkville, Victoria, Australia.
Florey Department of Neuroscience and Mental Health, The University of Melbourne, Victoria, Australia.
Hippocampus. 2017 May;27(5):529-546. doi: 10.1002/hipo.22709. Epub 2017 Jan 31.
Hippocampus is innervated by γ-aminobutyric acid (GABA) "projection" neurons of the nucleus incertus (NI), including a population expressing the neuropeptide, relaxin-3 (RLN3). In studies aimed at gaining an understanding of the role of RLN3 signaling in hippocampus via its G -protein-coupled receptor, RXFP3, we examined the distribution of RLN3-immunoreactive nerve fibres and RXFP3 mRNA-positive neurons in relation to hippocampal GABA neuron populations. RLN3-positive elements were detected in close-apposition with a substantial population of somatostatin (SST)- and GABA-immunoreactive neurons, and a smaller population of parvalbumin- and calretinin-immunoreactive neurons in different hippocampal areas, consistent with the relative distribution patterns of RXFP3 mRNA and these marker transcripts. In light of the functional importance of the dentate gyrus (DG) hilus in learning and memory, and our anatomical data, we examined the possible influence of RLN3/RXFP3 signaling in this region on spatial memory. Using viral-based Cre/LoxP recombination methods and adult mice with a floxed Rxfp3 gene, we deleted Rxfp3 from DG hilar neurons and assessed spatial memory performance and affective behaviors. Following infusions of an AAV -Cre-IRES-eGFP vector, Cre expression was observed in DG hilar neurons, including SST-positive cells, and in situ hybridization histochemistry for RXFP3 mRNA confirmed receptor depletion relative to levels in floxed-RXFP3 mice infused with an AAV -eGFP (control) vector. RXFP3 depletion within the DG hilus impaired spatial reference memory in an appetitive T-maze task reflected by a reduced percentage of correct choices and increased time to meet criteria, relative to control. In a continuous spontaneous alternation Y-maze task, RXFP3-depleted mice made fewer alternations in the first minute, suggesting impairment of spatial working memory. However, RXFP3-depleted and control mice displayed similar locomotor activity, anxiety-like behavior in light/dark box and elevated-plus maze tests, and learning and long-term memory retention in the Morris water maze. These data indicate endogenous RLN3/RXFP3 signaling can modulate hippocampal-dependent spatial reference and working memory via effects on SST interneurons, and further our knowledge of hippocampal cognitive processing. © 2017 Wiley Periodicals, Inc.
海马体由不确定核（NI）的γ-氨基丁酸（GABA）“投射”神经元支配，其中包括一群表达神经肽松弛素-3（RLN3）的神经元。在旨在通过其G蛋白偶联受体RXFP3了解RLN3信号在海马体中作用的研究中，我们研究了RLN3免疫反应性神经纤维和RXFP3 mRNA阳性神经元相对于海马体GABA神经元群体的分布情况。在不同的海马体区域，检测到RLN3阳性成分与大量生长抑素（SST）和GABA免疫反应性神经元以及少量小白蛋白和钙视网膜蛋白免疫反应性神经元紧密相邻，这与RXFP3 mRNA和这些标记转录本的相对分布模式一致。鉴于齿状回（DG）门在学习和记忆中的功能重要性以及我们的解剖学数据，我们研究了该区域的RLN3/RXFP3信号对空间记忆的可能影响。使用基于病毒的Cre/LoxP重组方法和带有floxed Rxfp3基因的成年小鼠，我们从DG门神经元中删除了Rxfp3，并评估了空间记忆表现和情感行为。在注入腺相关病毒（AAV）-Cre-IRES-eGFP载体后，在DG门神经元（包括SST阳性细胞）中观察到了Cre表达，并且针对RXFP3 mRNA的原位杂交组织化学证实相对于注入AAV-eGFP（对照）载体的floxed-RXFP3小鼠，受体被耗尽。相对于对照，DG门内RXFP3的缺失在食欲性T迷宫任务中损害了空间参考记忆，表现为正确选择的百分比降低以及达到标准的时间增加。在连续自发交替Y迷宫任务中，RXFP3缺失的小鼠在第一分钟内的交替次数减少，表明空间工作记忆受损。然而，RXFP3缺失的小鼠和对照小鼠在运动活动、明暗箱和高架十字迷宫测试中的焦虑样行为以及莫里斯水迷宫中的学习和长期记忆保持方面表现相似。这些数据表明内源性RLN3/RXFP3信号可以通过对SST中间神经元的作用来调节海马体依赖性空间参考和工作记忆，并进一步加深我们对海马体认知加工的了解。© 2017威利期刊公司
