Complex neuromodulatory processes in the locus coeruleus neuron-astrocyte network

脑干中的蓝斑（LC）通过释放化学神经递质去甲肾上腺素（NA）来控制记忆，焦虑，疼痛感或呼吸等行为的突触来支配大多数大脑区域。据认为，LC是一个“简单”的脑回路，其中自发动作电位（“尖峰”）放电是同步的，以促进目标区域中的NA节律性释放。然而，最近在体内的研究表明，LC是一个相当复杂的网络，能够产生不同的尖峰“突发”模式内的神经元簇，从其他脑区突触输入，涉及不同的神经递质接收。因此，这种假定的“LC模块”可以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，它们都是脑细胞通讯的关键。星形胶质细胞的神经元附近的胶质细胞可能有助于复杂的LC活动，在其他脑区。事实上，有证据表明，LC神经元兴奋的乳酸从相邻的星形胶质细胞释放。所有这些都表明LC不是一个简单的电路。拟议的研究旨在测试覆盖假设：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尖峰爆发输出模式，从而影响脉冲NA释放的功效。基于我们之前对自发活性神经元-星形胶质细胞网络（例如，脊髓、海马、皮质或呼吸中心）的广泛体外研究，我们有资格进行本研究。为此，我们将联合收割机药理学操作与局部场电位（LFP）和单个细胞膜电位的电生理记录以及信号传导因子的成像相结合。例如，我们用化学染料对细胞内钙或膜电位的变化进行成像，几年来，我们还用基因工程荧光蛋白传感器进行成像。关于拟议的研究，我们最近报道，新生大鼠脑切片中的LC神经元自发产生锁相，非同步尖峰。此外，尖峰在单个神经元重叠，形成钟形LFP爆发和LC人口爆发模式的变化深刻的响应谷氨酸或激活剂的离子型谷氨酸受体（iGluR）亚型。我们的初步研究结果表明，阿片类和NA受体亚型的激活以不同的方式改变LC爆发模式。在这里，我们将确定的机制，其中（i）神经递质受体调节LC活动和（ii）从星形胶质细胞释放的乳酸刺激LC神经元。我们的研究将表明，LC有内在的机制，以适应其放电模式的影响下，特定的神经递质和信号的星形胶质细胞。这种复杂的行为可能是关键，使这个小的大脑结构能够具体影响参与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.