Signal transmission from red cones to horizontal cells in the turtle retina.

Abstract

1. Intracellular recordings were made from L‐type horizontal cells in the retina of the turtle Pseudemys scripta elegans. The responses were evoked by 500 msec pulses of 'white' light. 2. L‐type horizontal cells were classified as either, 'small receptive field' s.r.f. or 'large receptive field' l.r.f. based upon (1) receptive field size and (2) kinetics of responses to test flashes covering small and big spots. 3. Constant illumination of the entire receptive field, with any intensity studied, evoked a response that reached a peak and then slowly sagged back to a steady‐state level that was about half the peak response. 4. Termination of backgrounds resulted in a very fast recovery of the membrane potential that overshot the dark‐adapted potential. This 'off' response had faster kinetics in horizontal cells than in red cones. 5. The intensity‐response curve measured around any background intensity was shifted along the log intensity axis toward higher test intensities. The curves obtained under light‐adapted conditions were sharper than the curve measured in the dark‐adapted state. 6. The photoresponses of red cones and s.r.f. horizontal cells were compared under similar states of adaptation. In the dark‐adapted state of the gain, expressed as the millivolt change in the horizontal cell per millivolt change in the cone, was not linearly related to cone potential, and was highest for dim stimuli. Light‐adaption modified the synaptic transmission to make the horizontal cells most sensitive to light modulation around the background illumination. 7. The mechanisms by which signal transmission can be modified by light‐adaptation are discussed in terms of transmitter release by the presynaptic terminals and its binding to post‐synaptic sites.

Dopamine D2 receptor‐mediated modulation of rod‐cone coupling in the Xenopus retina

“…This wavelength-dependent difference indicates an input from another red-sensitive cell type. The shape of the transient included a sharp depolarization at light off, which is not a characteristic of the rod's light response but is typical of a cone's response to light when the stimulus duration exceeds about 100 msec (Normann and Perlman, 1979). Figure 2 illustrates that there is a positive correlation between the ability to follow higher frequency sinusoids and the fractional size of the rod transient.…”

Improvement in human vision under bright light: grain or gain?

“…The physiological picture with respect to non-linearity is more ambiguous, perhaps partly due to species differences and rod-cone differences. The required adaptation dependence is clear in turtle horizontal cells, but not in turtle cones (Normann & Perlman, 1979). It appears to be absent in some recordings of the rod-dominated responses of cat ganglion cells (Sakmann & Creutzfeldt, 1969), but present in others (Barlow & Levick, 1960 a).…”

Membrane properties of solitary horizontal cells isolated from goldfish retina.

“…However, several possibilities are suggested: (1) amplification of the graded potentials generated by the subsynaptic membrane (Byzov et al 1977), RETINAL HORIZONTAL CELLS IN CULTURE (2) maintenance of the length constant by compensating the conductance decrease of the subsynaptic membrane during the light response (Werblin, 1975), (3) economy of transmitter release from photoreceptors since only a small amount of current is sufficient to keep the horizontal cell membrane depolarized, (4) delay of initiating the feed-back effect on photoreceptors due to hysteresis, (5) improved discrimination under light adaptation, that is, the conductance of the postsynaptic membrane is small due to the decrease of transmitter release from photoreceptors under light adaptation; thus the non-linearity of the horizontal cell membrane becomes explicit, resulting in the sharper slope of light intensity-response curve (ref. Normann & Perlman, 1979).…”