The dynamic characteristics of the feedback signal from horizontal cells to cones in the goldfish retina

Abstract

The dynamic properties of the microcircuitry formed by cones and horizontal cells in the isolated goldfish retina were studied. Cones project to horizontal cells and horizontal cells feed back to cones via a relatively slow negative feedback pathway. The time constant of the feedback signal in cones and of the effect this feedback signal had on the responses of second‐order neurons was determined using whole‐cell patch clamp and intracellular recording techniques. It was found that the feedback signal in cones had a time constant of around 80 ms, whereas the time constant of the effect this feedback signal had on the second‐order neurons ranged from 36 to 116 ms. This range of time constants can be accounted for by the non‐linearity of the Ca2+ current in the cones. In depolarized cones, the feedback‐mediated response in second‐order neurons had a similar time constant to that of the direct light response of the cone, whereas in hyperpolarized cones, the time constant of the feedback‐mediated response in second‐order neurons was considerably larger. Further, it was shown that there was no delay in the feedback pathway. This is in contrast to what has been deduced from the response properties of second‐order neurons. In one type of horizontal cell, the responses to red light were delayed relative to the responses to green light. This delay in the second‐order neurons can be accounted for by the interaction of the direct light response of the medium‐wavelength‐sensitive cones (M‐cones) with the feedback response of the M‐cones received from the horizontal cells.

Lateral Gain Control in the Outer Retina Leads to Potentiation of Center Responses of Retinal Neurons

“…The time constant of feedback-induced responses depends on the membrane potential of the cone and thus on the stimulus intensity (Kamermans et al, 2001b). If negative feedback from HCs to cones leads to gain enhancement, the amplitude of HC responses to the sinusoidally modulated spot of light should increase with a time constant similar to that of the feedback-induced responses.…”

“…This secondary depolarization or "roll-back" response is correlated with negative feedback from HCs to cones (Wu, 1994;Witkovsky et al, 1995;Kamermans et al, 2001a,b). Since feedback develops relatively slowly (Kamermans et al, 2001b), feedback will be weak early and pronounced late in the response. To test whether the synaptic gain changes in parallel with the strength of feedback, HCs were stimulated with a 1000 ms flash of sine wave-modulated light (Fig.…”

“…Detailed analysis of the feedback responses in cones and the roll-back responses in HCs (Kamermans et al, 2001b) has shown that the feedback pathway is relatively slow and that the feedbackinduced responses in both cones and HCs do not have a fixed time constant. The time constant of feedback-induced responses depends on the membrane potential of the cone and thus on the stimulus intensity (Kamermans et al, 2001b).…”

“…The red symbols show the time constant of the feedback signal measured in cones as a function of intensity. This curve is based on Kamermans et al (2001b). They measured the relation between stimulus intensity and cone membrane potential and the relation between cone membrane potential and time constant of feedback.…”

Teleost polarization vision: how it might work and what it might be good for

“…HCs integrate the visual scene spatially [64,65], spectrally [65 -67] and temporally [68]. They make a time-averaged estimate of the global intensity and colour.…”