FIGURE 1.

NE generates hyperpolarization in layer III pyramidal neurons with no effects in layer V/VI of the EC. A, a picture taken under an infrared microscope (Olympus BX51WI) with differential interference contrast optics in low magnification showing different layers of the medial EC in slices. B, action potentials recorded from a layer III pyramidal neuron prior to, during, and after application of NE (100 μm). Note that NE reversibly inhibited the firing frequency of action potentials. C, summarized time course of action potential firing frequency recorded from 12 layer III pyramidal neurons. The number of action potentials at each minute was normalized to that recorded at 1 min prior to the application of NE. D, concentration-response curve of NE-induced inhibition of action potential firing frequency. Numbers in parenthesis are numbers of cells recorded at each concentration. E, application of NE (100 μm)-generated membrane hyperpolarization and reduced input resistance in a layer III pyramidal neuron of the EC. Resting membrane potential was recorded in current-clamp mode and a hyperpolarizing current (-50 pA, 500 ms) was injected every 5 s to measure the input resistance. Note that NE generated hyperpolarization and reduced input resistance. Inset, voltage traces taken before (thin) and during (thick) the application of NE. F, summarized data for NE-induced changes in resting membrane potentials. G, application of NE (100 μm) induced an outward holding current (n = 10). Neurons were held at -55 mV, and the holding currents were recorded every 3 s in the extracellular solution supplemented with bicuculline (10 μm), CGP55845 (1 μm), 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (10 μm), dl-2-amino-5-phosphonovaleric acid (50 μm), and tetrodotoxin (0.5 μm). The holding currents were averaged per min, and NE-induced changes in holding currents were calculated by subtracting the averaged holding currents at each min from the holding current just prior to application of NE. Inset, holding currents prior to (a) and during (b) the application of NE. H, application of NE (100 μm) failed to change the holding currents recorded at -55 mV from the principal neurons in layer V (n = 15) and layer VI (n = 10).