Retinal Inputs to the Thalamus Are Selectively Gated by Arousal.

The brain can flexibly filter out sensory information in a manner that depends on behavioral state. In the visual thalamus and cortex, arousal and locomotion are associated with changes in the magnitude of responses to visual stimuli. Here, we asked whether such modulation of visual responses might already occur at an earlier stage in this visual pathway. We measured neural activity of retinal axons using wide-field and two-photon calcium imaging in awake mouse thalamus across arousal states associated with different pupil sizes. Surprisingly, visual responses to drifting gratings in retinal axonal boutons were robustly modulated by arousal level in a manner that varied across stimulus dimensions and across functionally distinct subsets of boutons. At low and intermediate spatial frequencies, the majority of boutons were suppressed by arousal. In contrast, at high spatial frequencies, boutons tuned to regions of visual space ahead of the mouse showed enhancement of responses. Arousal-related modulation also varied with a bouton's preference for luminance changes and direction or axis of motion, with greater response suppression in boutons tuned to luminance decrements versus increments, and in boutons preferring motion along directions or axes of optic flow. Together, our results suggest that differential modulation of distinct visual information channels by arousal state occurs at very early stages of visual processing, before the information is transmitted to neurons in visual thalamus. Such early filtering may provide an efficient means of optimizing central visual processing and perception across behavioral contexts.

Embryonic Intravitreous Injection in Mouse.

Axons of retinal ganglion cells (RGCs) relay visual information from the retina to lateral geniculate nucleus (LGN) and superior colliculus (SC), which are two major image-forming visual nuclei. Wiring of these retinal projections completes before vision begins. However, there are few studies on retinal axons at embryonic stage due to technical difficulty. We developed a method of embryonic intravitreous injection of dyes in mice to visualize retinal projections to LGN and SC. This study opens up the possibility of understanding early visual circuit wiring in mice embryos.

Anaglyph of retinal stem cells and developing axons: selective volume enhancement in microscopy images.

Retinal stem cell culture has become a powerful research tool, but it requires reliable methods to obtain high-quality images of living and fixed cells. This study describes a procedure for using phase contrast microscopy to obtain three-dimensional (3-D) images for the study of living cells by photographing a living cell in a culture dish from bottom to top, as well as a procedure to increase the quality of scanning electron micrographs and laser confocal images. The procedure may also be used to photograph clusters of neural stem cells, and retinal explants with vigorous axonal growth. In the case of scanning electron microscopy and laser confocal images, a Gaussian procedure is applied to the original images. The methodology allows for the creation of anaglyphs and video reconstructions, and provides high-quality images for characterizing living cells or tissues, fixed cells or tissues, or organs observed with scanning electron and laser confocal microscopy. Its greatest advantage is that it is easy to obtain good results without expensive equipment. The procedure is fast, precise, simple, and offers a strategic tool for obtaining 3-D reconstructions of cells and axons suitable for easily determining the orientation and polarity of a specimen. It also enables video reconstructions to be created, even of specimens parallel to the plastic base of a tissue culture dish, It is also helpful for studying the distribution and organization of living cells in a culture, as it provides the same powerful information as optical tomography, which most confocal microscopes cannot do on sterile living cells.

Expression of Nogo-A on the new born retinal ganglion cells and their axons of mouse embryos / 解剖学报

Objective To investigate the expression of Nogo-A in the retinal ganglion cells (RGCs) and their axons of mouse embryos and its time course changes. Methods Sections of retinofugal pathway of C57 mouse embryos at different developmental stages were immunostained with Nogo-A specific antibody and observed by a confocal microscopy. The identity of Nogo-A positive cells was partially revealed by double-staining together with Tuj-1. Results At the early stage of E12, Nogo-A was densely expressed in some radially-orientated cells in retina. The immunopositive signals appeared in the cytoplasm, on the cell membrane and axons. The double-labeling together with Tuj-1, a neuronal marker, showed that nearly all the RGCs and their axons expressed Nogo-A protein. At the later stage of E13, the number of Nogo-A positive neurons in retina decreased dramatically. And those Nogo-A positive RGCs were specifically located in the ventricular part and the ciliary margin zone of the retina. At this stage, only a very few axons maintained their Nogo-A expression in the fiber layer of the retina, while most lost their Nogo-A distribution. When most RGCs had fully differentiated at E15, there was no detectable Nogo-A immunopositive staining in the retina and only a few retinal fibers were Nogo-A immunopositive. The similar expression patterns of Nogo-A was found in a few axons along the optic disc, optic stalk, optic chiasm and optic tract. Worthy of note, the retinal axons with Nogo-A distribution in the optic tract were exclusively found in the superficial area, where the newly-arrived axons were traveling through during development. Conclusion The expression pattern and its time course change suggested that Nogo-A was an important protein expressed by the newly differentiated RGC neurons and their projecting axons, whilst the mature RGCs down-regulated their expression. Nogo-A in the new born RGCs might play some cell-intrinsic roles such as decreasing axon branching in vivo.