Mistargeted retinal axons form synaptically segregated subcircuits in the visual thalamus of albino mice.

A Hebbian model of circuit remodeling predicts that two sets of inputs with sufficiently distinct activity patterns will synaptically capture separate sets of target cells. Mice in which a subset of retinal ganglion cells (RGCs) target the wrong region of the dorsal lateral geniculate nucleus (dLGN) provide the conditions for testing this prediction. In albino mice, mistargeted RGC axons form an island of terminals that is distinct from the surrounding neuropil. Blocking retinal activity during development prevents the formation of this island. However, the synaptic connectivity of the island was unknown. Here, we combine light and electron microscopy to determine if this activity-dependent island of axon terminals represent a synaptically segregated subcircuit. We reconstructed the microcircuitry of the boundary between the island and non-island RGCs and found a remarkably strong segregation within retinogeniculate connectivity. We conclude that, when sets of retinal input are established in the wrong part of the dLGN, the developing circuitry responds by forming a synaptically isolated subcircuit from the otherwise fully connected network. The fact that there is a developmental starting condition that can induce a synaptically segregated microcircuit has important implications for our understanding of the organization of visual circuits and for our understanding of the implementation of activity dependent development.

Diversity in homeostatic calcium set points predicts retinal ganglion cell survival following optic nerve injury in vivo.

Retinal ganglion cell (RGC) degeneration drives vision loss in blinding conditions. RGC death is often triggered by axon degeneration in the optic nerve. Here, we study the contributions of dynamic and homeostatic Ca2+ levels to RGC death from axon injury. We find that axonal Ca2+ elevations from optic nerve injury do not propagate over distance or reach RGC somas, and acute and chronic Ca2+ dynamics do not affect RGC survival. Instead, we discover that baseline Ca2+ levels vary widely between RGCs and predict their survival after axon injury, and that lowering these levels reduces RGC survival. Further, we find that well-surviving RGC types have higher baseline Ca2+ levels than poorly surviving types. Finally, we observe considerable variation in the baseline Ca2+ levels of different RGCs of the same type, which are predictive of within-type differences in survival.

Galactosylated hydroxyl-polyamidoamine dendrimer targets hepatocytes and improves therapeutic outcomes in a severe model of acetaminophen poisoning-induced liver failure.

Toxicity to hepatocytes caused by various insults including drugs is a common cause of chronic liver failure requiring transplantation. Targeting therapeutics specifically to hepatocytes is often a challenge since they are relatively nonendocytosing unlike the highly phagocytic Kupffer cells in the liver. Approaches that enable targeted intracellular delivery of therapeutics to hepatocytes have significant promise in addressing liver disorders. We synthesized a galactose-conjugated hydroxyl polyamidoamine dendrimer (D4-Gal) that targets hepatocytes efficiently through the asialoglycoprotein receptors in healthy mice and in a mouse model of acetaminophen (APAP)-induced liver failure. D4-Gal localized specifically in hepatocytes and showed significantly better targeting when compared with the non-Gal functionalized hydroxyl dendrimer. The therapeutic potential of D4-Gal conjugated to N-acetyl cysteine (NAC) was tested in a mouse model of APAP-induced liver failure. A single intravenous dose of a conjugate of D4-Gal and NAC (Gal-d-NAC) improved survival in APAP mice, decreased cellular oxidative injury and areas of necrosis in the liver, even when administered at the delayed time point of 8 h after APAP exposure. Overdose of APAP is the most common cause of acute hepatic injury and liver transplant need in the United States, and is treated with large doses of NAC administered rapidly within 8 h of overdose leading to systemic side effects and poor tolerance. NAC is not effective when treatment is delayed. Our results suggest that D4-Gal is effective in targeting and delivering therapies to hepatocytes and Gal-D-NAC has the potential to salvage and treat liver injury with a broader therapeutic window.

Transpupillary Two-photon In vivo Imaging of the Mouse Retina.

The retina transforms light signals from the environment into electrical signals that are propagated to the brain. Diseases of the retina are prevalent and cause visual impairment and blindness. Understanding how such diseases progress is critical to formulating new treatments. In vivo microscopy in animal models of disease is a powerful tool for understanding neurodegeneration and has led to important progress towards treatments of conditions ranging from Alzheimer's disease to stroke. Given that the retina is the only central nervous system structure inherently accessible by optical approaches, it naturally lends itself towards in vivo imaging. However, the native optics of the lens and cornea present some challenges for effective imaging access. This protocol outlines methods for in vivo two-photon imaging of cellular cohorts and structures in the mouse retina at cellular resolution, applicable for both acute- and chronic-duration imaging experiments. It presents examples of retinal ganglion cell (RGC), amacrine cell, microglial, and vascular imaging using a suite of labeling techniques including adeno-associated virus (AAV) vectors, transgenic mice, and inorganic dyes. Importantly, these techniques extend to all cell types of the retina, and suggested methods for accessing other cellular populations of interest are described. Also detailed are example strategies for manual image postprocessing for display and quantification. These techniques are directly applicable to studies of retinal function in health and disease.

Cell-type-specific binocular vision guides predation in mice.

Predators use vision to hunt, and hunting success is one of evolution's main selection pressures. However, how viewing strategies and visual systems are adapted to predation is unclear. Tracking predator-prey interactions of mice and crickets in 3D, we find that mice trace crickets with their binocular visual fields and that monocular mice are poor hunters. Mammalian binocular vision requires ipsi- and contralateral projections of retinal ganglion cells (RGCs) to the brain. Large-scale single-cell recordings and morphological reconstructions reveal that only a small subset (9 of 40+) of RGC types in the ventrotemporal mouse retina innervate ipsilateral brain areas (ipsi-RGCs). Selective ablation of ipsi-RGCs (<2% of RGCs) in the adult retina drastically reduces the hunting success of mice. Stimuli based on ethological observations indicate that five ipsi-RGC types reliably signal prey. Thus, viewing strategies align with a spatially restricted and cell-type-specific set of ipsi-RGCs that supports binocular vision to guide predation.