Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455.
Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455
J Neurosci. 2020 Oct 7;40(41):7785-7794. doi: 10.1523/JNEUROSCI.1717-20.2020. Epub 2020 Sep 4.
The extracellular space (ECS) plays an important role in the physiology of neural circuits. Despite our detailed understanding of the cellular architecture of the mammalian retina, little is known about the organization and dynamics of the retinal ECS. We developed an optical technique based on two-photon imaging of fluorescently labeled extracellular fluid to measure the ECS volume fraction (α) in the retina of male and female mice. This method has high spatial resolution and can detect rapid changes in α evoked by osmotic challenge and neuronal activity. The measured ECS α varied dramatically in different layers of the adult mouse retina, with α equaling ∼0.050 in the ganglion cell layer, ∼0.122 in the inner plexiform layer (IPL), ∼0.025 in the inner nuclear layer (INL), ∼0.087 in the outer plexiform layer, and ∼0.026 in the outer nuclear layer (ONL). ECS α was significantly larger early in retinal development; α was 67% larger in the IPL and 100% larger in the INL in neonatal mice compared with adults. In adult retinas, light stimulation evoked rapid decreases in ECS α. Light-driven reductions in ECS α were largest in the IPL, where visual stimuli decreased α values ∼10%. These light-evoked decreases demonstrate that a physiological stimulus can lead to rapid changes in ECS α and indicate that activity-dependent regulation of extracellular space may contribute to visual processing in the retina. The volume fraction of the extracellular space (ECS α), that portion of CNS tissue occupied by interstitial space, influences the diffusion of neurotransmitters from the synaptic cleft and the volume transmission of transmitters. However, ECS α has never been measured in live retina, and little is known about how ECS α varies following physiological stimulation. Here we show that ECS α values vary dramatically between different retinal layers and decrease by 10% following light stimulation. ECS α differences within the retina will influence volume transmission and light-evoked α variations may modulate synaptic transmission and visual processing in the retina. Activity-dependent ECS α variations may represent a mechanism of synaptic modulation throughout the CNS.
细胞外空间（ECS）在神经回路生理学中起着重要作用。尽管我们对哺乳动物视网膜的细胞结构有了详细的了解，但对视网膜 ECS 的组织和动态知之甚少。我们开发了一种基于双光子成像荧光标记细胞外液的光学技术，用于测量雄性和雌性小鼠视网膜的细胞外空间体积分数（α）。该方法具有高空间分辨率，可检测渗透压挑战和神经元活动引起的α的快速变化。在成年小鼠视网膜的不同层中，测量的 ECS α 差异很大，在神经节细胞层中α等于约 0.050，在内丛状层（IPL）中α等于约 0.122，在内核层（INL）中α等于约 0.025，在外丛状层中α等于约 0.087，在外核层（ONL）中α等于约 0.026。在视网膜发育早期，ECS α 显著增大；与成年鼠相比，新生鼠 IPL 中的α增大 67%，INL 中的α增大 100%。在成年视网膜中，光刺激会迅速降低 ECS α。光驱动的 IPL 中 ECS α 的减少最大，视觉刺激使 α 值降低约 10%。这些光诱发的降低表明生理刺激会导致 ECS α 的快速变化，并表明细胞外空间的活动依赖性调节可能有助于视网膜中的视觉处理。细胞外空间（ECS α）的体积分数，即 CNS 组织中由间质空间占据的部分，影响神经递质从突触间隙的扩散和递质的容积传递。然而，活体视网膜中从未测量过 ECS α，并且对 ECS α 在生理刺激后如何变化知之甚少。在这里，我们表明 ECS α 值在不同的视网膜层之间差异很大，并且在光刺激后降低了 10%。视网膜内的 ECS α 差异将影响容积传递，而光诱发的 α 变化可能调节视网膜中的突触传递和视觉处理。活动依赖性 ECS α 变化可能代表整个中枢神经系统中突触调节的一种机制。
