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重要分子，哺乳期是哺乳动物特有的哺育后代的功能状态。中枢OT系统由两种不同的细胞类型-大细胞和小细胞OT神经元组成。大细胞OT神经元因其独特的同步爆发活动而成为该系统的主要细胞成分，引发OT释放到血液循环系统中，从而诱导乳腺排奶。然而，这种同步性背后的基本机制在很大程度上仍然是未知的。我们最近在处女大鼠中的发现表明，OT系统的其他细胞成分，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释放响应于感觉刺激。根据这一发现，并根据未发表的初步结果包括在本提案中，我们在这里的目的是证明，小细胞OT神经元也有助于调节哺乳期间的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，使用新开发的病毒载体的光和药物遗传学方法，研究小细胞OT神经元的重要性，使用体内多单元光电极记录结合哺乳期大鼠的哺乳行为的监测。这些技术将首先被实施以进行功能丧失的化学和光遗传学实验，以证明小细胞OT神经元的活性与哺乳幼崽的体重增加变化和哺乳期间大细胞OT神经元的爆发之间的因果关系。接下来，在功能获得设置中，我们将通过小细胞OT神经元的光遗传学激活来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，我们将重建乳腺和小细胞OT神经元之间的神经通路，并与上述方法，检查其功能的重要性，诱导泌乳。总的来说，我们的工作将剖析新的OT网络启动和/或维持泌乳，这将是重要的，以进一步我们的生殖生理学的基本机制的理解。

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 Following this finding and also based on unpublished preliminary results included in the present proposal, we here aim to demonstrate that the parvocellular OT neurons also contribute to the regulation of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.