Fig. 1. Norepinephrine increases the frequency of spontaneous “GABAergic” inhibitory postsynaptic currents (IPSCs). Records shown were obtained from one neuron. (A ) At a holding potential of 0 mV, IPSCs were recorded as upward deflections in the membrane current trace. Bath application of norepinephrine (20 μM) evoked repetitive large-amplitude IPSCs. In this cell, a prominent summation of IPSCs produced a persistent elevation of the baseline current. The bar above each trace indicates the application of norepinephrine. (B ) Two sets of traces show IPSCs recorded in control and during application of norepinephrine on an expanded time base.