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Classical and melanopsin photoreception in irradiance detection: negative masking of locomotor activity by light
Stewart Thompson1, Russell G Foster, Edwin M Stone
1Howard Hughes Medical Institute, Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa 52242, USA. stewart-thompson@uiowa.edu
Abstract:
Studies in mice lacking either classical or melanopsin photoreception have been useful in describing the photoreceptor contribution to irradiance detection in accessory visual responses. However, application of these findings to irradiance detection in intact animals is problematical because retinal degeneration or manipulation can induce secondary changes in the retina. Among responses dependent on irradiance detection, the suppression of activity by light (negative masking) has had limited study. To further understand the function of classical and melanopsin photoreceptors we studied irradiance and spectral sensitivity of masking by light, primarily in mice with intact retinae. The sensitivity of negative masking was equivalent for medium ( approximately 500 nm) and short wavelengths ( approximately 365 nm) in three strains of wild-type mice, identifying a marked short-wavelength-sensitive-cone input. At medium wavelengths, spectral sensitivity above 500 nm had closest fit to the nomogram for the medium-wavelength-sensitive-cone, but a combined input of cone and melanopsin photoreceptors in wild-type mice seems likely. Under white light a decompression of the irradiance range of masking in C3H rd/rd cl mice, lacking rods and cones, identified a functional deficiency presumably resulting from the absence of classical photoreceptor input. Together the evidence demonstrates a pronounced and sustained classical photoreceptor input to irradiance detection for negative masking, and suggests one role of classical photoreceptor input is to constrain dynamic range.
Insights
Classical photoreceptors significantly contribute to light-induced activity suppression (negative masking) by regulating the dynamic range of irradiance detection. This study clarifies their role in intact mouse retinas.
Area of Science:
- Vision Science
- Photoreceptor Physiology
- Animal Behavior
Background:
- Accessory visual responses, like negative masking, depend on irradiance detection.
- Studies using manipulated retinas have limitations due to secondary changes.
- The specific roles of classical and melanopsin photoreceptors in negative masking are not fully understood.
Purpose of the Study:
- To investigate the irradiance and spectral sensitivity of negative masking in mice with intact retinae.
- To elucidate the contributions of classical and melanopsin photoreceptors to negative masking.
- To understand the dynamic range regulation of negative masking.
Main Methods:
- Studied negative masking in wild-type mice and C3H rd/rd cl mice (lacking rods and cones).
- Assessed irradiance and spectral sensitivity of masking across different wavelengths.
- Compared masking responses under varying light conditions.
Main Results:
- Negative masking showed equivalent sensitivity to medium (~500 nm) and short (~365 nm) wavelengths in wild-type mice, indicating short-wavelength-sensitive cone input.
- Spectral sensitivity at medium wavelengths suggested a combined input from cones and melanopsin photoreceptors.
- Mice lacking rods and cones exhibited a functional deficiency in masking, highlighting the importance of classical photoreceptors.
Conclusions:
- Classical photoreceptors provide a pronounced and sustained input for irradiance detection in negative masking.
- Classical photoreceptor input plays a crucial role in constraining the dynamic range of negative masking.
- This research clarifies the distinct contributions of different photoreceptor types to visual responses.
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