Fig. 5.
Intracellular buffering of residual free Ca2+ blocks dynorphin release. A, Typical records of mossy fiber field potentials before and after the addition of 200 μm EGTA-AM. Each trace is an average of 10 synaptic responses. To compare the paired-pulse facilitation change, the mossy fiber response to the first pulse in EGTA-AM was scaled to the corresponding control response (right panel).B, Time course of heterosynaptic inhibition in control Ringer’s solution (n = 11; filled circles) and in 200 μm EGTA-AM (n = 6; open circles). EGTA-AM blocks heterosynaptic depression of mossy fiber transmission. For each set of data, the responses were normalized to 100%. C, Dynorphin inhibition of mossy fiber synaptic responses is not blocked by EGTA-AM. The time course of 500 nm dynorphin reduction of synaptic transmission (Control; n = 9; same data as plotted in Fig. 3A) is superimposed to that induced after 200 μm EGTA-AM (n = 3; open circles). These results indicate that the EGTA-AM blockade of heterosynaptic depression is attributable to a reduction in dynorphin release rather than to a decrease in dynorphin effect.