Identification and functional characterization of an oxytocin neuronal population coordinating lactation

下丘脑神经肽催产素(OT)是启动和维持哺乳期的必需分子，哺乳期是哺乳动物典型的后代营养的一种独特功能状态。中枢OT系统由两种不同的细胞类型组成--大细胞和小细胞OT神经元。大细胞催产素神经元是乳汁分泌系统的主要细胞成分，因为其独特的同步爆发活动，促使催产素释放到血液循环系统，诱导乳汁从乳腺排出。然而，这种同步性背后的基本机制在很大程度上仍不清楚。我们最近在处女大鼠身上的发现表明，OT系统的其他细胞组件，即小细胞OT神经元，可以直接控制OT大细胞神经元的活动和全身OT对感觉刺激的释放。根据这一发现并基于本方案中未发表的初步结果，我们在此旨在证明微小细胞OT神经元也有助于调节哺乳期大细胞神经元的活动。在我们的前瞻性研究过程中，我们将利用我们在德国和瑞士的实验室的互补专业知识，使用新开发的光和药物遗传学方法的病毒载体，结合监测哺乳期大鼠的哺乳行为，利用体内多单位光电记录来研究微小细胞OT神经元的重要性。这些技术将首先用于进行功能丧失的化学和光遗传学实验，以证明微小细胞OT神经元活动与哺乳期幼崽体重增加和大细胞OT神经元爆裂之间的因果关系。接下来，在功能获得设置中，我们将通过微小细胞OT神经元的光基因激活，挽救由乳头感觉剥夺诱导的母乳喂养和大细胞OT神经元放电活动的变化。最后，应用单突触逆行传播病毒的鸡尾酒，我们将重建乳腺和微小细胞OT神经元之间的神经通路，并用上述方法检验它们在诱导哺乳中的功能重要性。总之，我们的工作将剖析新的催产素网络启动和/或维持哺乳，这将是重要的，我们将进一步了解生殖生理的基本机制。

The hypothalamic neuropeptide oxytocin (OT) is an essential molecule for initiation and maintenance of lactation - a unique functional state of offspring nourishing typical for mammals. The central OT system is composed of two distinct cell types - magnocellular and parvocellular OT neurons. Magnocellular OT neurons are the main cellular components of the system due to their unique synchronous bursting activity, eliciting release of OT into blood circulatory system to induce milk let-down from the mammary glands. The basic mechanisms underlying this synchronicity are still, however, largely unknown. Our recent finding in virgin rats demonstrated that the other cellular components of the OT system, the parvocellular OT neurons, can directly control both OT magnocellular neuron activity and systemic OT release in response to sensory stimulation. Following this finding and also based on unpublished preliminary results included in the present proposal, we here aim to demonstrate that the parvocellular OT neurons also contribute to the regulation of magnocellular neuron activity during lactation. In the course of our prospective study we will use complementary expertise of our laboratories in Germany and Switzerland, using newly developed viral vectors for opto- and pharmacogenetic approaches to study the importance of parvocellular OT neurons using in vivo multi-unit opto-electrode recordings in combination with the monitoring of suckling behaviour in lactating rats. These techniques will first be implemented to perform loss-of-function chemo,- and optogenetic experiments to prove the causal relation between the activity of parvocellular OT neurons and changes in weight gain of suckling pups and bursting of magnocellular OT neurons during lactation. Next, in a gain-of-function setup we will rescue changed in breast feeding and magnocellular OT neuron firing activity that are induced by nipple sensory deprivation, via optogenetic activation of parvocellular OT neurons. Finally, applying a cocktail of monosynaptic retrogradely transmitted viruses we will reconstruct the neural pathways between mammary glands and parvocellular OT neurons and with the above described approaches, examine their functional importance for inducing lactation. Collectively, our work will dissect novel OT network initiating and/or maintaining lactation, which will be important to further our understanding of the basic mechanisms of reproductive physiology.