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Ultraviolet colour opponency in the turtle retina.
D F Ventura1, Y Zana, J M de Souza
1Departamento de Psicologia Experimental, Instituto de Psicologia and Centro de Neurociências e Comportamento, Universidade de São Paulo, Brazil. dventura@usp.br
The Journal of Experimental Biology
|August 21, 2001
Summary
This study reveals ultraviolet color processing in turtle retinas, identifying an ultraviolet channel and tetrachromacy. These findings provide a neural basis for discriminating ultraviolet colors in Pseudemys scripta elegans.
Area of Science:
- Neuroscience
- Vision Science
- Comparative Physiology
Background:
- The spectral sensitivity of the turtle retina, particularly in the ultraviolet range, remains largely uncharacterized.
- Previous studies have not investigated ultraviolet light's impact on the inner retina's color processing mechanisms.
Purpose of the Study:
- To investigate ultraviolet cone spectral sensitivity through horizontal cell responses in the turtle retina.
- To determine if tetrachromatic neural mechanisms, specifically UV/S (ultraviolet/short-wavelength) response opponency, exist in this species.
Main Methods:
- Utilized a constant response methodology to isolate and characterize ultraviolet cone input to S/LM horizontal cells.
- Recorded responses from various horizontal cell types (monophasic, biphasic, triphasic) to spectral stimulation.
- Analyzed spectral opponency in the receptive fields of amacrine and ganglion cells.
Main Results:
- Isolated ultraviolet cone input to S/LM horizontal cells, with a blue-adapted spectral sensitivity function peaking at 372 nm, consistent with porphyropsin.
- Observed strong responses to ultraviolet light in monophasic, biphasic L/M, and triphasic S/LM horizontal cells.
- Identified eight combinations of spectral opponency in ganglion cell receptive fields, including UV/S opponency in three ganglion cell types, and specific amacrine cell types (UVSM-L+).
Conclusions:
- The findings strongly suggest the presence of a distinct ultraviolet visual channel in the turtle retina.
- UV/S opponency in ganglion cells provides a neural substrate for the discrimination of ultraviolet colors.
- The study provides evidence for a neural basis of tetrachromacy in the turtle retina, indicating a four-color visual system.