Retinotopy in Mouse Superior Colliculus Mapped with Single-Cell Precision using Hyperscope
Introduction
A recent paper in Nature by researchers from the Epigenetics and Neurobiology Unit at the European Molecular Biology Laboratory used the Scientifica HyperScope for in vivo two-photon imaging.
About the study
Retinotopy, like all long-range projections, can arise from the axons themselves or their targets. The underlying connectivity pattern, however, remains elusive at the fine scale in the mammalian brain. To address this question, we functionally mapped the spatial organization of the input axons and target neurons in the female mouse retinocollicular pathway at single-cell resolution using in vivo two-photon calcium imaging.
The research found a near-perfect retinotopic tiling of retinal ganglion cell axon terminals, with an average error below 30 μm or 2° of visual angle. The precision of retinotopy was relatively lower for local neurons in the superior colliculus. Subsequent data-driven modelling ascribed it to a low input convergence, on average 5.5 retinal ganglion cell inputs per postsynaptic cell in the superior colliculus. These results indicate that retinotopy arises largely from topographically precise input from presynaptic cells, rather than elaborating local circuitry to reconstruct the topography by postsynaptic cells.
Retinotopy in the superior colliculus (SC; color-coded) can arise from either precisely retinotopic projection of retinal ganglion cell (RGC) axons, innervating exact target locations in SC (Model 1); or roughly retinotopic projection of RGC axons while SC neurons identify appropriate partners to recover the retinotopy (Model 2). In Model 1, retinotopy can be more precise for RGC axons than for SC somata if the synaptic connectivity is not topographically well organized. In Model 2, in contrast, SC somata should show more precise retinotopy than RGC axons.
"Performing Ca2+ recordings of visual responses in awake mice always require to have extra room under the microscope to set up a treadmill and visual stimulation arrangements. In our case Scientifica HyperScope was very convenient in that regard and currently it is our in vivo imaging workhorse. I also like HyperScope's simplicity, reliability and easy access features which saved us a lot of time."
Dmitry Molotkov EMBLView the full paper
Molotkov, D., Ferrarese, L., Boissonnett, T., & Asari, H. (2023) 'Topographic axonal projection at single-cell precision supports local retinotopy in the mouse superior colliculus,' Nature Communications, 14(1). https://doi.org/10.1038/s41467...
Scientifica HyperScope
A customisable multiphoton microscope, proven to perform two-photon and three-photon laser scanning microscopy with exceptional performance. Upgradeable to a Spatial Light Modulator (SLM) system, this dual scan head microscope is ideal for in vivo and in vitro fluorescence imaging.