Neurotensin, TIDA neurons, and the pregnancy-induced plasticity of a neuroendocrine circuit

我们的目标是了解大脑是如何让哺乳动物的身体为怀孕、哺乳和育儿行为等巨大挑战做好准备的。由于许多这些适应是由生殖激素催乳素（Prl）驱动的，因此本研究将重点放在妊娠诱导的结节基底多巴胺能（TIDA）神经元的可塑性上——这是一种高度特化的脑细胞，控制垂体释放Prl。如果通过调节Prl的释放，TIDA神经元要有效地调节生理和行为，以确保我们满足当前和未来的生殖需求，那么它们必须能够实现两件事。首先，为了积极促进有利于繁殖的条件，他们必须能够实时地对相关信息做出反应。其次，考虑到需要努力调动怀孕和父母行为所需的巨大资源，他们能够“提前计划”并预测未来的需求是至关重要的。该项目旨在研究脑肽神经紧张素（NT）在驱动显著的细胞和电路可塑性方面的作用，使TIDA网络能够完成这些计算任务。如果放任不管，产生Prl的垂体细胞就会持续释放激素。因此，TIDA神经元通过抑制来控制Prl水平，持续传递抑制性“NO”信号多巴胺（DA）。因此，当需要增加Prl时，Prl调节因子（如NT）的变化会导致TIDA神经元减少其DA输出。在基础和非怀孕条件下，Prl的增加在大小和持续时间上受到负反馈过程的强烈限制——一个抑制回路，Prl通过刺激TIDA神经元和增加NO信号来抑制其自身的释放。然而，在怀孕期间，准妈妈需要极端和持久的高泌乳素血症。相应地，TIDA回路与脑垂体之间的交流必须由负反馈变为正反馈。然而，这种对话是如何从“不”转向“去”的，仍然不得而知。目前的数据表明，在怀孕期间，TIDA系统仍然对Prl有反应，但停止释放DA，用GO因子取代NO信号。这种氧化石墨烯信号的一个重要候选者是NT，其TIDA的产生在怀孕期间急剧增加。为了研究NT在TIDA控制的反应性和预测性机制中的动态作用，我将测试以下三步假设：1)TIDA神经元可以直接对NT作出反应。2)NT神经元-控制摄食行为，代谢和应激的细胞-与TIDA神经元交谈，传递重要的生殖相关信息。3)在怀孕期间，TIDA系统经历了一个“信号开关”，将“NO”因子DA替换为“GO”信号NT——这是一个预测性的步骤，使乳酸营养轴能够驱动持久的催乳素释放，为身体为严酷的妊娠、分娩和哺乳做好准备。为了验证这些预测，我将使用经过验证的小鼠模型，这将使我能够选择性地可视化、监测和操作TIDA和NT神经元。当结合解剖学和生理学方法时，我将不仅能够确定哪些NT神经元与TIDA回路“对话”，而且能够确定NT如何影响TIDA网络的细胞和回路特性。最后，我将使用基于crispr的尖端技术来防止TIDA回路产生NT，然后观察去除这种依赖于状态的“GO”因子如何影响生育、哺乳和亲代行为。这项研究将揭示关于神经内分泌网络调节催乳素释放和生殖行为的自适应动态的新的多层次理解，并将揭示信号可塑性的新机制，神经元网络通过该机制使电路性能适应当前环境和未来需求。

Our goal is to understand how the brain prepares the mammalian body for the enormous challenges of pregnancy, nursing, and parental behaviour. As many of these adaptations are driven by the reproductive hormone prolactin (Prl), this proposal focuses upon the pregnancy induced plasticity of tuberoinfundibular dopaminergic (TIDA) neurons - the highly specialised brain cells that control the release of Prl from the pituitary. If, via their regulation of Prl release, TIDA neurons are to effectively tune physiology and behaviour to ensure we meet both immediate and future reproductive demands, then they must be able to achieve two things. First, in order to actively promote conditions conducive to reproduction, they must be able to REACT to relevant information, in real time. Second, given the effort required to marshal the enormous resources demanded by pregnancy and parental behaviours, it is essential that they be able to 'plan ahead' and PREDICT what is needed in the future. This project is designed to investigate the role of the brain peptide neurotensin (NT) in driving the remarkable cellular and circuit plasticity that enables the TIDA network to fulfil these computational tasks.If left to their own devices, the pituitary cells that produce Prl, will engage in continuous hormone release. Accordingly, TIDA neurons control Prl levels by via inhibition, continuously delivering the inhibitory 'NO' signal, dopamine (DA). As such, when an increase in Prl is required, changes in Prl regulating factors - such as NT - cause TIDA neurons to reduce their DA output. Under basal, non-pregnant conditions, such increases in Prl are powerfully restricted in size and duration by a process of negative feedback - an inhibitory loop where Prl supresses its own release by exciting TIDA neurons and increasing the 'NO' signal. During pregnancy, however, the expectant mother requires extreme and enduring hyperprolactinaemia. Correspondingly, communication between the TIDA circuit and the pituitary must change from negative to positive feedback. Yet, how this conversation switches from "NO" to "GO" remains obscure. Current data suggests that during pregnancy the TIDA system remains responsive to Prl, but ceases to release DA, replacing this NO signal with a GO factor. A prominent candidate for this GO signal is NT, the TIDA production of which increases enormously during pregnancy. To investigate the dynamic role of NT in both reactive and predictive mechanisms of TIDA control, I will test the following three step hypothesis: 1) TIDA neurons can REACT directly to NT. 2) NT neurons - cells that control ingestive behaviour, metabolism and stress - talk to TIDA neurons, relaying vital reproduction relevant information. 3) During pregnancy the TIDA system undergoes a 'signal switch', replacing the 'NO' factor DA with the 'GO' signal NT - a PREDICTIVE step that enables the lactotrophic axis to drive the enduring prolactin release needed to prepare the body for the rigors of gestation, parturition and nursing.To test these predictions, I will use validated mouse models that will enable me to selectively visualise, monitor, and manipulate, both TIDA and NT neurons. When coupled with anatomical and physiological approaches, I will be able to determine not only which NT neurons 'talk' to the TIDA circuit, but how NT affects the cellular and circuit properties of the TIDA network. Finally, I will use cutting-edge CRISPR-based techniques to prevent the TIDA circuit from producing NT and then observe how the removal of this state-dependent 'GO' factor impacts fertility, nursing and parental behaviour.This research will reveal novel multi-level understanding regarding the adaptive dynamism of the neuroendocrine networks governing prolactin release and reproductive behaviour, and will uncover new mechanisms of signal plasticity by which neuronal networks adapt circuit performance to both prevailing circumstance and future requirement.