Astrocyte-to-neuron communication: functional relevance for synaptic transmission in the respiratory network?

星形胶质细胞现在已经被确定为正常脑功能的关键角色。据推测，最重要的是它们对神经元环境稳定的贡献，因为它们有能力调节细胞外钾和神经递质的浓度。此外，星形胶质细胞本身也可以利用和释放递质（所谓的胶质递质）向神经元发出信号。这种星形胶质细胞与神经元之间的通讯依赖于星形胶质细胞释放谷氨酸或ATP等钙依赖性物质，因此，星形胶质细胞能够直接影响突触传递。然而，在呼吸中枢，我们对星形胶质细胞衍生的传递分子在呼吸神经元突触中的作用的理解仍然是初级的。在拟建的项目中，我们将回答以下关于尾侧延髓腹侧呼吸组（VRG）中星形胶质细胞与神经元间通讯的问题：VRG中的星形胶质细胞是否向邻近的呼吸神经元和突触释放胶质递质？自发星形胶质细胞钙振荡触发VRG星形胶质细胞的胶质递质释放吗？需要哪些条件才能影响整个网络？为了回答这些问题，我们将结合电生理和光学技术。我们将对已识别的星形胶质细胞和邻近的呼吸神经元进行双全细胞记录。这一方面允许使用电刺激直接操纵星形胶质细胞，打开第二信使或特定拮抗剂的细胞内灌注，另一方面通过记录抑制性或兴奋性突触后电流来监测突触传递。同时，我们将在正在进行的呼吸网络活动中成像和调节星形细胞钙信号。

Astrocytes have now been identified as key players for normal brain function. Presumably most important is their contribution to the stabilization of the environment of neurons, due to their capability to regulate the extracellular concentration of potassium as well as neurotransmitters. Moreover, it has become evident that astrocytes themselves can utilize and release transmitter (so called gliotransmitters) to signal to neurons. This kind of astrocyte-to-neuron communication has been shown to depend on a calcium-dependent release of e.g. glutamate or ATP from astrocytes, thus, astrocyte are capable to influence synaptic transmission directly. In the respiratory centre, however our understanding of the role of astrocyte-derived transmitter molecules for synapses between respiratory neurons is still rudimentary. In the proposed project we shall answer the following questions regarding astrocyte-to-neuron communication in the ventral respiratory group (VRG) of the caudal medulla: Do astrocytes in the VRG release gliotransmitters to neighboring respiratory neurons and synapses? Do spontaneous astrocytic calcium oscillations trigger gliotransmitter release in VRG astrocytes? Which conditions are required to influence the entire network? To answer these questions we will combine electrophysiological and optical techniques. We will perform dual whole-cell recordings from pairs of identified astrocytes and neighboring respiratory neurons. This allows on the one side a direct manipulation of the astrocyte using electrical stimulation, un-caging of second messengers or intracellular perfusion of specific antagonists and on the other to monitor synaptic transmission by recording inhibitory or excitatory postsynaptic currents. In parallel we will image and modulate astrocytic calcium signals during ongoing respiratory network activity.