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Ultraviolet colour opponency in the turtle retina

D. F. Ventura^1,*, 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

View larger version (14K): [in a new window]   Fig. 1. Spectral sensitivity, S(), functions of horizontal cells measured using the constant-response method, with no background. The figure shows an average S() function of 38 dark-adapted luminosity horizontal cells (filled circles) and the corresponding standard deviations (thin line). (Modified from Fig.4 in Ventura et al., 1999, with permission of Visual Neuroscience.)

View larger version (14K): [in a new window]   Fig. 2. Average spectral sensitivity S() functions of three L/M biphasic cells measured with the flash method (filled circles, hyperpolarizing responses; open circles, depolarising responses; thin line, standard deviation).

View larger version (12K): [in a new window]   Fig. 3. Spectral sensitivity S() measurements of an S/LM cell with no background (A) and under blue adaptation (B). All curves are averages of four S() scans, collected alternately from 300 to 700nm and in the opposite direction. The polarisation reversal was detected by a phase change in the response to the flickering stimulus. (A) S() function recorded in the absence of background light (filled circles, hyperpolarizing responses, open circles, depolarising responses). (B) The S() function of the same cell under a bright blue background (Schott DIL 457nm; 1.9x1012quantas-1cm-2). The solid line is the cone porphyropsin template (Stavenga et al., 1993) with a peak at 372nm.

View larger version (20K): [in a new window]   Fig. 4. Intracellular recordings obtained in a spectrally opponent cell (G51L31C1), stained with Neurobiotin and identified as a G15 ganglion cell. Upper trace: the response to a large spot stimulus at the receptive field centre (radius, =1250µm) depolarises from 300 to 500nm and hyperpolarizes from 520 to 700nm. Lower trace: responses to equal quanta flashes at four wavelengths. (Modified from Fig.10 in Ventura et al., 1999 with permission of Visual Neuroscience.)

View larger version (39K): [in a new window]   Fig. 5. Intracellular recordings from a double opponent ganglion cell (G86R1C1). Upper trace: responses to a spot stimulus (radius, =600µm) at the centre of the receptive field are excitatory to ultraviolet (370nm), blue (450nm) and green (540nm) flashes and inhibitory to red (640nm) flashes. Lower trace: responses to an annulus (ext=1500mm, int=1050mm) reversed the excitation and inhibition seen at the centre, at all wavelengths. Note that at 540nm, where the crossover occurs, only transient responses, at the stimulus onset and offset, are reversed.

View larger version (46K): [in a new window]   Fig. 6. Intracellular recordings from a spectrally opponent ganglion cell (G81L3C1) that showed opponency between ultraviolet and blue. Upper trace: responses to a spot stimulus at the receptive field centre (radius, =300µm) were hyperpolarizing to ultraviolet (370nm) and red (640nm) and depolarising to blue (450nm) and green (540nm) flashes. Lower trace: responses to an annulus (ext=1500µm, int=1050µm) reversed the polarity to red flashes, relative to the centre responses, but not to ultraviolet, blue and green flashes. Therefore, the cell presented spatial opponency only to red stimuli.