Figure 4. Exogenous dopamine application increases cone input and decreases rod input to goldfish retinal L-type cone horizontal cells.

A, superfusion of dopamine (100 nm) during the subjective night increased cone input and eliminated rod input to the cells, so that light responses closely resembled those typically observed during the day. B, superfusion of dopamine (100 nm) during the subjective day produced a slight increase in the size of the light responses. C, destruction of dopaminergic cells following pre-treatment with 6-hydroxydopamine (see Methods) increased rod input and decreased cone input during the subjective day. Light responses during the subjective night were not affected. Similar results were obtained from 9 (A), 8 (B), and 13 (C) cells. Subjective day data in this and all subsequent figures were obtained under conditions of constant darkness during the second cycle at ZT 3 and 9. No differences were observed between ZT 3 and 9. Subjective night data in this and all subsequent figures were obtained at ZT 15 and 21; no differences were observed between ZT 15 and 21.