Complex neuromodulatory processes in the locus coeruleus neuron-astrocyte network

脑干中的蓝斑（LC）通过突触支配大部分大脑区域，释放化学神经递质去甲肾上腺素（NA）来控制记忆、焦虑、疼痛感觉或呼吸等行为。人们认为LC是一个“简单”的大脑回路，其中自发的动作电位（“尖峰”）放电是同步的，以促进目标区域有节奏的NA释放。然而，最近的体内研究表明，LC是一个相当复杂的网络，能够在神经元簇内产生不同的spike“burst”模式，这些神经元簇接收来自其他脑区涉及多种神经递质的突触输入。因此，这些假定的“LC模块”可能表达不同的神经递质受体，例如谷氨酸、多巴胺或内源性阿片类物质，它们都是脑细胞通信的关键。神经元附近的星形胶质细胞可能与大脑其他区域一样参与复杂的LC活动。事实上，有证据表明，LC神经元被邻近星形胶质细胞释放的乳酸兴奋。所有这些都表明LC不是一个简单的电路。提出的研究旨在验证总体假设：LC是一个复杂的神经调节网络，其中神经递质和神经元-星形胶质细胞相互作用形成脉冲NA释放的脉冲脉冲输出模式。基于我们之前在体外对自发活动的神经元-星形胶质细胞网络的广泛研究，例如脊髓、海马、皮层或呼吸中枢，我们有资格进行这项研究。为此，我们将药理学操作与单个细胞局部场电位（LFP）和膜电位的电生理记录以及信号因子成像结合起来。例如，我们用化学染料成像细胞内钙或膜电位的变化，几年来，用基因工程荧光蛋白传感器。针对我们提出的研究，我们最近报道了新生大鼠脑切片中的LC神经元自发地产生锁相的非同步尖峰。此外，单个神经元的尖峰重叠形成钟形LFP爆发，这种LC群体爆发模式在谷氨酸或嗜离子性谷氨酸受体（iGluR）亚型激活剂的作用下发生深刻变化。我们的初步研究结果表明，阿片受体和NA受体亚型的激活以不同的方式改变了LC爆发模式。在这里，我们将确定(i)神经递质受体调节LC活性和（ii）星形胶质细胞释放的乳酸刺激LC神经元的机制。我们的研究将表明，LC在特定神经递质和星形胶质细胞信号的影响下具有适应放电模式的内在机制。这种复杂的行为很可能是关键，使这个小的大脑结构能够具体影响涉及不同行为的许多目标大脑区域的不同活动。

The locus coeruleus (LC) in the brainstem innervates most brain areas with synapses that release the chemical neurotransmitter noradrenaline (NA) to control behaviors like memory, anxiety, pain sensation or breathing. It is thought that the LC is a `simple' brain circuit in which spontaneous action potential (`spike') discharge is synchronous to facilitate rhythmic NA release in the target areas. However, recent in vivo studies indicate that the LC is rather a complex network capable of generating different spike `burst' patterns within neuron clusters that receive from other brain areas synaptic input involving diverse neurotransmitters. Accordingly, such presumptive `LC modules' may express different neurotransmitters receptors, e.g. for glutamate, dopamine or endogenous opioids that are all pivotal for brain cell communication. Astrocytic glial cells in the vicinity of the neurons might contribute to complex LC activities as in other brain areas. Indeed, there is evidence that LC neurons are excited by lactate released from adjacent astrocytes. All this indicates that the LC is NOT a simple circuit. The proposed research aims at testing the Overarching Hypothesis: The LC is a complex neuromodulatory network in which neurotransmitters and neuron-astrocyte interactions shape spike burst output patterns and thus the efficacy of pulsed NA release. We are qualified for this research based on our previous extensive in vitro studies of spontaneously active neuron-astrocyte networks, e.g. in the spinal cord, hippocampus, cortex or breathing center. For this, we combine pharmacological manipulations with electrophysiological recording of local field potentials (LFP) and membrane potential from an individual cell plus imaging of signaling factors. For example, we image changes of intracellular calcium or membrane potential with chemical dyes and, since several years, with genetically-engineered fluorescent protein sensors. Regarding the proposed research, we reported recently that LC neurons in newborn rat brain slices spontaneously generate phase-locked, non-synchronous spikes. Moreover, spikes in single neurons overlap to form bell-shaped LFP bursts and this LC population burst pattern changes profoundly in response to glutamate or activators of ionotropic glutamate receptor (iGluR) subtypes. Our preliminary findings show that activation of opioid and NA receptor subtypes transforms the LC burst pattern in different fashion. Here, we will identify mechanisms by which (i) neurotransmitter receptors modulate LC activity and (ii) lactate released from astrocytes stimulates LC neurons. Our research will show that the LC has intrinsic mechanisms for adapting its discharge pattern under the influence of specific neurotransmitters and signals from astrocytes. This complex behavior is likely pivotal to enable this small brain structure to affect specifically the different activities of numerous target brain areas that are involved in distinct behaviors.