Figure 2. Depolarization-induced inhibition of light-evoked EPSCs and EPSPs.

All records were obtained in Mg²⁺-free Ringer solution. A, in voltage clamp mode light responses were recorded before (continuous line) and 100 ms after (dotted line) the termination of a 400 ms depolarizing step (ΔV) from -70 to 0 mV. B, light-evoked EPSCs recorded every 30 s without and with a depolarizing pre-pulse from -70 to 0 mV that induced reversible inhibition. The presentation, but not the timing, of the depolarizing pre-pulse is represented above the middle trace. C, light-evoked EPSPs were recorded in current clamp mode before (continuous line) and after a depolarizing current of +50 pA (dotted line). EPSPs were reduced following the injection of current. The resting membrane potential was -65 mV. CsCl and TEA in the pipette solution were replaced by KCl. D, histogram of the depolarization-induced inhibition (means ±s.e.m.) of EPSC and EPSP amplitudes. The number of cells studied is indicated above each bar. In this and subsequent figures, the bath solution contained 20 μm strychnine and 50 μm picrotoxin.