The looming stimulus-evoked flight response to approaching predators is a defensive behavior in most animals. However, how looming stimuli are detected in the retina and transmitted to the brain remains unclear. Here, we report that a group of GABAergic retinal ganglion cells (RGCs) projecting to the superior colliculus (SC) transmit looming signals from the retina to the brain, mediating the looming-evoked flight behavior by releasing GABA. GAD2-Cre and vGAT-Cre transgenic mice were used in combination with Cre-activated anterograde or retrograde tracer viruses to map the inputs to specific GABAergic RGC circuits. Optogenetic technology was used to assess the function of SC-projecting GABAergic RGCs (scpgRGCs) in the SC. FDIO-DTA (Flp-dependent Double-Floxed Inverted Open reading frame-Diphtheria toxin) combined with the FLP (Florfenicol, Lincomycin & Prednisolone) approach was used to ablate or silence scpgRGCs. In the mouse retina, GABAergic RGCs project to different brain areas, including the SC. ScpgRGCs are monosynaptically connected to parvalbumin-positive SC neurons known to be required for the looming-evoked flight response. Optogenetic activation of scpgRGCs triggers GABA-mediated inhibition in SC neurons. Ablation or silencing of scpgRGCs compromises looming-evoked flight responses without affecting image-forming functions. Our study reveals that scpgRGCs control the looming-evoked flight response by regulating SC neurons via GABA, providing novel insight into the regulation of innate defensive behaviors.
Animals ; Superior Colliculi/physiology* ; Retinal Ganglion Cells/physiology* ; GABAergic Neurons/physiology* ; Mice, Transgenic ; Mice ; Optogenetics ; Visual Pathways/physiology* ; Mice, Inbred C57BL ; Photic Stimulation/methods* ; gamma-Aminobutyric Acid/metabolism* ; Male

Objective:To utilize four viral tracer tools with different properties, to visualize cell morphology and connectome in visual pathways and explore and summarize the applications of different viral tracer tools in visual circuit, basing on the technology of neural circuitry tracing with viral vectors.Methods:For cell tracing, C57BL/J mice were injected by fluorogold, adeno-associated virus (AAV), pseudorabies virus (PRV) or herpes simplex virus 1 strain 129 (H129). GAD2-Cre mice were injected by AAV. Thy1-Cre mice were injected by rabies virus (RV). Four mice were contained in every group.Retrograde tracing: mice were injected with fluorogold, AAV, PRV or RV in SC regions.After a certain period, their retinas were isolated, expanded into flat-mounted on slides to observe the morphology and distribution of labelled retinal cells.Anterograde tracing: mice were injected with H129 in vitreous cavities.After a certain period, their brains were isolated to observe the morphology and distribution of labelled brain cells. Results:The number of cells labelled by fluorogold was larger than that labelled by AAV.The morphology of cells labelled by AAV possessed more details than that by fluorogold.H129 and PRV injection could display numerous cells with synaptic connections in the visual circuit.Recombined RV could mono-transsynaptically spread and label cells with the support of helper virus.Conclusions:AAV is more helpful in studying cell morphology.HSV-1, PRV and RV can be used to study cell connectomes.Cooperated with Cre/loxP system, Caspase-3, DTA, Gcamp or other neuroscience tools, viral tracer tools can be used to regulate the function of cells that belong to a specific cell type.

Adeno-associated viral vector (AAV) is the most important viral tool and has been widely used in gene therapy. Because of its small size, non-enveloped, non-pathogenic and other characteristics, so it is one of the main means to treat hereditary retinal diseases. Aiming at MERTK for retinitis pigmentosa, ND4 for Leber hereditary optic neuropathy or RPE1 for choroideremia, AAV gene therapy improved half patients' visual acuity in clinic tests. Besides, there are some clinic tests in progress for Leber’s congenital amaurosis, X-linked retinoschisis, Achromatopsia, age-related macular degeneration. But more researches need to be found before clinic test for Stargardt disease, Usher syndrome and nanophthalmos. At present, AAV gene therapy is mainly used for recessive hereditary retinal diseases, and technology is needed to intervene for dominant retinal diseases. For the treatment of hereditary retinal diseases, this will be an important and complex systematic project, which requires more human and material resources to participate in and study together, and we expect to have a great breakthrough in the near future.