Figure 5.

κ-Opioid-mediated inhibition does not require presynaptic potassium channels. A, Application of 2 mm 4-AP produces a robust increase in the evoked EPSC charge transfer (250 ± 74% at 20 min, n = 7, p = 0.028) and prevents U69593-mediated inhibition. EPSCs in A are taken from time points 10 min after 4-AP, 15 and 30 min after U69593 application. A lower concentration of 4-AP (100 μm) is also effective at preventing the U69593 inhibition (U69593 inhibition in 100 μm 4-AP: 32 ± 13%, p = 0.003 compared with control inhibition, n = 6). C, D, If a low Ca²⁺ containing ACSF is washed in 15 min after application of 100 μm 4-AP and followed by U69593, the κ-opioid-mediated inhibition is again unmasked (79 ± 5% inhibition, n = 3, p = 0.61). In C, low Ca²⁺ refers to 0.3 mm Ca²⁺/3.7 mm Mg²⁺ containing ACSF. E, There is no change in mEPSC frequency after bath application of 2 mm 4-AP (101 ± 21% control frequency after 15 min, n = 6, p = 0.87). In addition, after a minimum of 15 min application of 2 mm 4-AP, U69593 is still equally effective at decreasing mEPSC frequency (43 ± 9% reduction at 15 min, n = 9, p < 0.0001; F).