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The Journal of Experimental Biology 204, 2527-2534 (2001)
© 2001 The Company of Biologists Limited

Review

Ultraviolet colour opponency in the turtle retina

D. F. Ventura1,*, Y. Zana1, J. M. de Souza1 and R. D. DeVoe2

1 Departamento de Psicologia Experimental, Instituto de Psicologia and Centro de Neurociências e Comportamento, Universidade de São Paulo, São Paulo 05508-900, Brazil and
2 School of Optometry, Indiana University, Bloomington, Indiana, USA

*Author for correspondence (e-mail: dventura{at}usp.br)

Accepted April 19, 2001

We have examined the functional architecture of the turtle Pseudemys scripta elegans retina with respect to colour processing, extending spectral stimulation into the ultraviolet, which has not been studied previously in the inner retina. We addressed two questions. (i) Is it possible to deduce the ultraviolet cone spectral sensitivity function through horizontal cell responses? (ii) Is there evidence for tetrachromatic neural mechanisms, i.e. UV/S response opponency? Using a constant response methodology we have isolated the ultraviolet cone input into the S/LM horizontal cell type and described it in fine detail.

Monophasic (luminosity), biphasic L/M (red-green) and triphasic S/LM (yellow-blue) horizontal cells responded strongly to ultraviolet light. The blue-adapted spectral sensitivity function of a S/LM cell peaked in the ultraviolet and could be fitted to a porphyropsin cone template with a peak at 372nm.

In the inner retina eight different combinations of spectral opponency were found in the centre of the receptive field of ganglion cells. Among amacrine cells the only types found were UVSM-L+ and its reverse. One amacrine and four ganglion cells were also opponent in the receptive field surround.

UV/S opponency, seen in three different types of ganglion cell, provides a neural basis for discrimination of ultraviolet colours. In conclusion, the results strongly suggest that there is an ultraviolet channel and a neural basis for tetrachromacy in the turtle retina.

Key words: ultraviolet vision, spectral sensitivity, colour vision, turtle, retina, intracellular recording.


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© The Company of Biologists Ltd 2001