ABSTRACT
Rod and cone photoreceptors support vision across large light intensity ranges. Rods, active under dim illumination, are thought to saturate at higher (photopic) irradiances. The extent of rod saturation is not well defined; some studies report rod activity well into the photopic range. Using electrophysiological recordings from retina and dorsal lateral geniculate nucleus of cone-deficient and visually intact mice, we describe stimulus and physiological factors that influence photopic rod-driven responses. We find that rod contrast sensitivity is initially strongly reduced at high irradiances, but progressively recovers to allow responses to moderate contrast stimuli. Surprisingly, rods recover faster at higher light levels. A model of rod phototransduction suggests that phototransduction gain adjustments and bleaching adaptation underlie rod recovery. Consistently, exogenous chromophore reduces rod responses at bright background. Thus, bleaching adaptation renders mouse rods responsive to modest contrast at any irradiance. Paradoxically, raising irradiance across the photopic range increases the robustness of rod responses.
Subject(s)
Adaptation, Physiological , Light Signal Transduction/physiology , Light/adverse effects , Photobleaching/radiation effects , Retinal Rod Photoreceptor Cells/physiology , Animals , Color Vision/physiology , Geniculate Bodies/physiology , Mice , Mice, Transgenic , Models, Animal , Photic Stimulation , Retinal Cone Photoreceptor Cells/physiologyABSTRACT
The collective activity pattern of retinal ganglion cells, the retinal code, underlies higher visual processing. How does the ambient illuminance of the visual scene influence this retinal output? We recorded from isolated mouse and pig retina and from mouse dorsal lateral geniculate nucleus in vivo at up to seven ambient light levels covering the scotopic to photopic regimes. Across each luminance transition, most ganglion cells exhibited qualitative response changes, whereas they maintained stable responses within each luminance. We commonly observed the appearance and disappearance of ON responses in OFF cells and vice versa. Such qualitative response changes occurred for a variety of stimuli, including full-field and localized contrast steps and naturalistic movies. Our results suggest that the retinal code is not fixed but varies with every change of ambient luminance. This finding raises questions about signal processing within the retina and has implications for visual processing in higher brain areas.
Subject(s)
Lighting , Retina/physiology , Animals , Cyclic Nucleotide-Gated Cation Channels/genetics , Cyclic Nucleotide-Gated Cation Channels/physiology , Electrophysiological Phenomena/drug effects , Electrophysiological Phenomena/physiology , Environment , GABA Antagonists/pharmacology , Mice , Mice, Inbred C57BL , Mice, Knockout , Photoreceptor Cells, Vertebrate/physiology , Retina/drug effects , Retinal Ganglion Cells/physiology , Swine , gamma-Aminobutyric Acid/physiologyABSTRACT
Multi-electrode arrays are a state-of-the-art tool in electrophysiology, also in retina research. The output cells of the retina, the retinal ganglion cells, form a monolayer in many species and are well accessible due to their proximity to the inner retinal surface. This structure has allowed the use of multi-electrode arrays for high-throughput, parallel recordings of retinal responses to presented visual stimuli, and has led to significant new insights into retinal organization and function. However, using conventional arrays where electrodes are embedded into a glass or ceramic plate can be associated with three main problems: (1) low signal-to-noise ratio due to poor contact between electrodes and tissue, especially in the case of strongly curved retinas from small animals, e.g. rodents; (2) insufficient oxygen and nutrient supply to cells located on the bottom of the recording chamber; and (3) displacement of the tissue during recordings. Perforated multi-electrode arrays (pMEAs) have been found to alleviate all three issues in brain slice recordings. Over the last years, we have been using such perforated arrays to study light evoked activity in the retinas of various species including mouse, pig, and human. In this article, we provide detailed step-by-step instructions for the use of perforated MEAs to record visual responses from the retina, including spike recordings from retinal ganglion cells and in vitro electroretinograms (ERG). In addition, we provide in-depth technical and methodological troubleshooting information, and show example recordings of good quality as well as examples for the various problems which might be encountered. While our description is based on the specific equipment we use in our own lab, it may also prove useful when establishing retinal MEA recordings with other equipment.
