Oscillations in rod and horizontal cell membrane potential: evidence for feed-back to rods in the vertebrate retina.

1. Rods and horizontal cells were studied with intracellular recordings in the retina of the toad, Bufo marinus; 161 cells were from the eyecup preparation and thirty were from the isolated perfused retina. 2. Of these cells, 39% exhibited either transient or sustained oscillations of membrane potential. Light flashes either evoked transient oscillations or temporarily abolished sustained oscillations. The amplitudes of the oscillations could be as large as 27 mV. The frequency of the oscillations at 25 degrees C was between 1-5 and 3-5 Hz and was strongly dependent on temperature and background illumination. 3. The rod oscillation amplitude and the peak of the horizontal cell light response increased similarly with increasing test flash diameters. They continued to grow for diameters much larger than those which increased the peak of the rod light response. 4. Perfusion of the isolated retina with 2 mM aspartate had only a small effect on the rod light response but it completely eliminated the horizontal cell light response as well as the oscillations recorded in both rods and horizontal cells. 5. It is believed that the oscillations result from a reverberating interaction between rods and neurones post-synaptic to rods. Thus, rods can be both post- as well as presynaptic retinal elements.