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Annette E Allen, Riccardo Storchi, Daniel H Elijah, Franck P Martial, Robert J Lucas; The spatial and temporal contributions of melanopsin to mouse vision. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5866.
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© ARVO (1962-2015); The Authors (2016-present)
The emerging role of melanopsin and intrinsically photosensitive retinal ganglion cells (ipRGCs) in perceptual vision demands a more quantitative description of melanopsin’s input to these pathways in visually intact animals. Particularly lacking is a description of the spatial and temporal information conveyed by ipRGCs that arises exclusively from melanopsin’s photon capture, and what functional impact this may have on image forming vision.
We have modified a commercially available projection system so that each of the R, G and B channels is instead a combination of up to five, independently controlled wavelengths (λmax 405, 455, 525, 561, 630nm). This allows us to present patterned stimuli that only present spatial/temporal contrast for particular photopigments. We have used multi-channel recording electrodes to record light-evoked activity in the dorsal lateral geniculate nucleus (dLGN) of urethane anaesthetised Opn1mwR mice; these mice display a long-wavelength shifted spectral sensitivity of green cones, which allows us to achieve maximal contrast for each photopigment.
We have recorded evoked activity in the dLGN in response to spatially structured stimuli, that originate from melanopsin in isolation (49% Michelson contrast); rod opsin & cone opsins (33% Michelson contrast); or melanopsin, rod and cone opsins (49% and 33%, respectively). We have measured the spatial receptive fields in each of these conditions; when measurable, isolated melanopsin receptive fields tend to be large, extending beyond the size of rod/cone driven receptive fields recorded in the same dLGN cell. The temporal properties of these responses are also distinct from rod/cone evoked responses. Moreover, comparisons of the responses evoked by rod/cone stimuli presented with or without concurrent melanopsin contrast reveal a defined input of melanopsin that is quite distinct from rod and cone-evoked responses.
Visual responses arising exclusively with melanopsin are detectible at the level of the dLGN at relatively modest contrasts, and on a physiologically relevant spatial and temporal scale. Although these signals are outside the range required for high spatiotemporal acuity vision, they instead occupy a distinct sensory niche that may still be useful for pattern vision.
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