Biomaterial Database

Light adaptation of cone photoresponses studied at the photoreceptor and ganglion cell levels in the frog retina. 1998

K Donner, and S Hemilä, and A Koskelainen

Department of Biosciences, University of Helsinki, Finland. kkdonner@touko.helsinki.fi

The sensitivity and time scale of the dominant (562 nm) cone system of the frog, Rana temporaria, were studied as functions of steady adapting illuminance (IB). Photoreceptor responses to brief flashes of light were recorded as aspartate-isolated ERG mass potentials from the isolated retina. The characteristics of the cone signal after transmission through the retina were derived from response thresholds and stimulus--intensity-response--latency functions for extracellularly recorded spike discharges of single ganglion cells in the eyecup. At 14 degrees C, the single-photon response of dark-adapted cones, extrapolated from ERG intensity-response functions, had an amplitude of 0.5% of the saturated response (Umax) and peaked at tp approximately 0.4 sec. Steady background illumination decreased both tp and flash sensitivity (SF), starting from apparent "dark lights" of, respectively, less than 10 (for time scale) and about 100 (for sensitivity) photoisomerisations per cone per second [P*sec-1]. From there upwards, two distinct ranges of background adaptation were apparent. Under moderate backgrounds (up to IB approximately 10(4) - 10(5) P*sec-1), sensitivity fell according to the relation SF alpha IB-0.64 and time scale shortened according to tp alpha IB-0.16. Under brighter backgrounds, from approx. 10(5) P*sec-1 up to the limit of our light source at 10(7) P*sec-1, the decrease in SF was significantly stronger than predicted by the Weber relation (SF alpha IB-1), while the decrease in tp levelled out and even tended to reverse. All these changes were virtually identical at the photoreceptor and ganglion cell levels, although the absolute time scale of cone signals apparent at the latter level was 2-fold longer. Our general conclusion is that photoreceptors have several distinct regimes for light adaptation, and traditional descriptions of functional changes (in sensitivity and kinetics) relevant to vision need to be restated with higher resolution, in view also of recent insights into the diversity of underlying mechanisms.

UI	MeSH Term	Description	Entries
D010775	Photic Stimulation	Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity.	Stimulation, Photic,Visual Stimulation,Photic Stimulations,Stimulation, Visual,Stimulations, Photic,Stimulations, Visual,Visual Stimulations
D011896	Rana temporaria	A species of the family Ranidae occurring in a wide variety of habitats from within the Arctic Circle to South Africa, Australia, etc.	European Common Frog,Frog, Common European,Common European Frog,Common Frog, European,European Frog, Common,Frog, European Common
D011930	Reaction Time	The time from the onset of a stimulus until a response is observed.	Response Latency,Response Speed,Response Time,Latency, Response,Reaction Times,Response Latencies,Response Times,Speed, Response,Speeds, Response
D004596	Electroretinography	Recording of electric potentials in the retina after stimulation by light.	Electroretinographies
D000221	Adaptation, Ocular	The adjustment of the eye to variations in the intensity of light. Light adaptation is the adjustment of the eye when the light threshold is increased; DARK ADAPTATION when the light is greatly reduced. (From Cline et al., Dictionary of Visual Science, 4th ed)	Light Adaptation,Adaptation, Light,Adaptations, Light,Adaptations, Ocular,Light Adaptations,Ocular Adaptation,Ocular Adaptations
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D012684	Sensory Thresholds	The minimum amount of stimulus energy necessary to elicit a sensory response.	Sensory Threshold,Threshold, Sensory,Thresholds, Sensory
D017949	Retinal Cone Photoreceptor Cells	Photosensitive afferent neurons located primarily within the FOVEA CENTRALIS of the MACULA LUTEA. There are three major types of cone cells (red, blue, and green) whose photopigments have different spectral sensitivity curves. Retinal cone cells operate in daylight vision (at photopic intensities) providing color recognition and central visual acuity.	Cone Photoreceptors,Cones (Retina),Cone Photoreceptor Cells,Photoreceptors, Cone,Retinal Cone,Retinal Cone Cells,Retinal Cone Photoreceptors,Cell, Cone Photoreceptor,Cell, Retinal Cone,Cells, Cone Photoreceptor,Cells, Retinal Cone,Cone (Retina),Cone Cell, Retinal,Cone Cells, Retinal,Cone Photoreceptor,Cone Photoreceptor Cell,Cone Photoreceptor, Retinal,Cone Photoreceptors, Retinal,Cone, Retinal,Cones, Retinal,Photoreceptor Cell, Cone,Photoreceptor Cells, Cone,Photoreceptor, Cone,Photoreceptor, Retinal Cone,Photoreceptors, Retinal Cone,Retinal Cone Cell,Retinal Cone Photoreceptor,Retinal Cones
D017950	Ganglia, Sensory	Clusters of neurons in the somatic peripheral nervous system which contain the cell bodies of sensory nerve axons. Sensory ganglia may also have intrinsic interneurons and non-neuronal supporting cells.	Sensory Ganglia,Ganglion, Sensory,Sensory Ganglion