Figure 3. EGABA in magnocellular neurons from wild-type rats. A, Scatter plot showing mean EGABA values measured in unidentified magnocellular neurons (n = 16) from wild-type rats. The EGABA values distribute into two distinct groups, one with values of EGABA more negative than the resting membrane potential (Negative EGABA, n = 6) and the other with values of EGABA more positive than the resting membrane potential (Positive EGABA, n = 11). B, Evoked synaptic GABA current amplitudes plotted against holding potentials in the cells shown in A divided into two groups, negative-EGABA and positive-EGABA. C, Average rectification index from the negative-EGABA (Neg-E) and positive-EGABA groups (Pos-E) of unidentified magnocellular neurons recorded in slices from wild-type rats (negative-EGABA, n = 8; positive-EGABA, n = 20, p < 0.01) (left). Average rectification index from the GFP-negative and GFP-positive magnocellular neurons recorded in slices from VP-GFP rats (GFP-negative, n = 5; GFP-positive n = 9, p < 0.01) (right). A1: Rectification measured between voltage steps of −45 mV and −85 mV; A2: rectification measured between voltage steps of −125 mV and −85 mV (shown in D and E); **p < 0.01. D, Cells with outward currents at resting membrane potential showed a nonlinear I–V relationship (n = 8). Membrane currents were elicited by a series of voltage steps from a holding potential of −45 mV (inset). The current measurements in the I–V plot were obtained from values averaged over 10 ms at the end of the voltage steps (dashed red line). E, Cells with inward currents at resting membrane potential showed a linear I–V relationship generated with a series of voltage steps from a holding potential of −45 mV (n = 20) (inset). F, Representative biocytin-labeled, immunohistochemically identified magnocellular neurons from wild-type rats that generated inward synaptic GABA currents (top) and outward synaptic GABA currents (bottom) at resting membrane potential. The magnocellular neuron that generated inward synaptic currents (blue, top) at resting potential was immunopositive for vasopressin (green, top) and negative for OT (red, top), identifying it as a VP-expressing neuron. The magnocellular neuron that generated outward synaptic currents at resting potential (blue, bottom) was immunonegative for VP (green, bottom) and positive for OT (red, bottom), identifying it as an OT-expressing neuron. Scale bars: 50 μm.