Figure 3.

Effect of inactivating the K_ATP channel on VMN neuron responses to leptin. VMN neurons were first characterized as being GE, GI, or NG by their responses to glucose-induced (2.5 to 0.5 to 2.5 mmol/liter) changes in [Ca²⁺]_i oscillations. Neurons held at 2.5 mmol/liter glucose were then exposed to 1 pmol/liter leptin and then to 200 μmol/liter tolbutamide plus 1 pmol/liter leptin. A, Leptin inhibition of NG neuron is antagonized by tolbutamide. B, Glucose-inhibited neuron excited by leptin is unaffected by addition of tolbutamide. C, Compiled responses of VMN neurons to tolbutamide (Tol) alone and in the presence of leptin. There were significant differences in the tolbutamide responsive vs. nonresponsive leptin-inhibited neurons (P < 0.001), whereas none of the leptin-excited neurons responded to tolbutamide. Tolbutamide alone affected only a small percentage of neurons. 2.5 G, 2.5 mmol/liter glucose.