Glycinergic inputs limit the temporal responses of LEDs.

<p>(A) Average spike-time histograms generated from extracellular spike responses in 4 LEDs in control (black) and with 0.5 µM strychnine (blue). A significant increase in spiking is particularly evident at frequencies above 0.5 Hz (P<0.05). The stimulus was a 100 µm diameter spot that was sine-wave modulated from –80% to +80% contrast. The stimulus timing is shown in grey; the numbers adjacent to the records indicate the temporal frequency in Hz. (B) Upper panel: average light-evoked excitatory synaptic conductances calculated during 2 Hz stimulation with a small spot, in control (black) and with 0.5 µM strychnine (green). Lower panel: average inhibitory conductance G_i in control (black) and with 0.5 µM strychnine (red) during 2 Hz flicker stimulus. The timing of the 2 Hz stimulus timing is shown between the panels. Data averaged from 8 cells, shading shows the SEM. Suppression was not significant for excitation (P = 0.072), but was significant for inhibition (P = 0.0020). (C) Current clamp recordings made from an LED using a potassium-based intracellular solution (see Methods). The lower panel shows the same cell repatched with the addition of 1 mM ginkgolide to the internal solution. The stimulus was a 100 µm spot that was modulated at 1 Hz square wave flicker (timing shown between panels). The red vertical lines show the time of the first spike for the OFF phase of the stimulus in control. Note the shorter spike delay in the presence of ginkgolide (lower panel). (D) Average excitatory conductances (upper panel) and inhibitory conductances (lower panel) in control (black trace) and with 1 mM ginkgolide (colored traces) during 0.75 Hz square wave flicker. Average traces from two groups of 5 cells each are shown. The stimulus timing is shown between the panels. (n = 5, shading shows the standard deviation for each group of cells).