Fig. 2. The effects of bicuculline and tetrodotoxin on norepinephrine-induced inhibitory postsynaptic currents (IPSCs). Records shown were obtained from two different neurons (A  and B ). (A ) Three sets of traces show IPSCs recorded with control, norepinephrine (20 μM), and norepinephrine with bicuculline (BIC, 20 μM) bath solutions. Norepinephrine increased the frequency of IPSCs, and all IPSCs were eliminated by the simultaneous application of bicuculline. (B ) Norepinephrine (30 μM) increased IPSC frequency. Increased IPSC frequency was reduced, but not completely blocked, by tetrodotoxin (1 μM). Norepinephrine increased the frequency of spontaneous IPSCs from 6.5 to 47.3 Hz, and the norepinephrine-induced increase in IPSC frequency was reduced by tetrodotoxin to 10.6 Hz. Note that norepinephrine-induced IPSCs with large amplitude were not seen in control and that these large IPSCs were eliminated by tetrodotoxin.