Cat cones have rod input: A comparison of the response properties of cones and horizontal cell bodies in the retina of the cat

Abstract

The responses of horizontal cell bodies and cones in the retina of the cat have been studied by means of intracellular recording and Procion dye injection in an isolated, arterially perfused eyecup preparation. Comparison of the hyperpolarizing responses of these units to red and blue stimuli of different intensities indicated that all morphological varieties of horizontal cells and, additionally, cones themselves, had mixed rod and cone input. The rod input into horizontal cell bodies is thus explained on the basis of cone physiology. The half-saturating intensity of 441 nm stimuli for the rod input into cones and horizontal cells was about 400 quanta/mum2/sec and about 160,000 quanta/mum2/sec for the cone input. Little of this difference can be related to the different quantum catching abilities of rods and cones. The spatial properties of horizontal cell bodies and cones have been characterized using stimuli consisting of long slits in conjunction with a continuous cable model. Space constants for horizontal cells ranged from 210 mum to 410 mum, whereas those for cones ranged from 50 mum, or possibly less, to 180 mum. It is argued that horizontal cell bodies of the cat retina form electrical networks, and that the sizes of the receptive fields generated in these networks may be limited by the diameters of the primary and secondary dendrites of horizontal cells. The rod and cone fields of horizontal cell bodies were found to be nearly coextensive in space, arguing against the notion that substantial rod input came from distant, rod-dominated terminal arborizations.

Microcircuitry of the dark-adapted cat retina: functional architecture of the rod-cone network

“…Steinberg (1969) gives -0.5 log td scotopic for the apparent rod threshold in horizontal cells in vivo after l-2 hr of adaptation to total darkness. This value converts to about 3 quanta pm-2 see-' at the retina (see Shapley and Enroth-Cugell, 1984), approximately the same figure as Nelson's (1977). These results suggest that the pathways leading from cones carry very little rod signal at environmental intensities below 10 quanta Mm-2 set-' at the retina, which corresponds to the low end of the mesopic range defined by Enroth-Cugell et al (1977).…”

“…old for this rod signal in cones and horizontal cells is about 10 quanta pm-2 set-I at the retina, according to Nelson's (1977) in vitro recordings. Steinberg (1969) gives -0.5 log td scotopic for the apparent rod threshold in horizontal cells in vivo after l-2 hr of adaptation to total darkness.…”

“…This corresponds to roughly 10 quanta pm-' se& at the retina. The cross-sectional area of a rod is 2.27 pm2 (Nelson, 1977); the fraction of photons at retina that is absorbed is taken to be 0.33 (Bonds and MacLeod, 1974); and the efficiency of rhodopsin isomerization by absorbed photons is taken to be about 0.5 (Baylor et al, 1979). Therefore, No.…”

“…The apparent threshold stimulus intensity for the rod signal in cones and in horizontal cells after prolonged dark adaptation is about 10 quanta pm-* set' on the retina (Nelson, 1977;Steinberg, 1969, 197 l), but the threshold for dark-adapted retinal ganglion cells is about 3 log units lower (Barlow and L,evick, 1969). This suggests that the cone bipolar pathway might carry the rod signal to the ganglion cell at higher intensities and that the rod bipolar pathway might convey the signal at lower intensities.…”

Modulation of rod photoreceptor output by HCN1 channels is essential for regular mesopic cone vision

“…On the basis of a previous work 14 (and our unpublished data with this protocol in nob mice, N.T. and M.W.S), we knew that responses to low temporal frequency stimulation (0-3 Hz) are dominated by rod system activity, those to intermediate frequency stimulation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) by cone ON system activity, and those to high-frequency stimulation (≥15 Hz) by cone OFF system activity 15,16 . The ERG data in Figure 3a,b show that low frequency stimuli were well resolved in HCN1 − / − mice despite considerably prolonged responses, whereas, to our surprise, response amplitudes decreased dramatically with increasing frequency, and essentially no responses were observable above 5 Hz.…”