Figure 3.

IGF-1 inhibits the activity of SON neurons in vitro by activating an outward current. A, Application of IGF-1 induced a rapid hyperpolarization associated with a decrease or cessation of firing of all isolated SON neurons (left). The hyperpolarizing effect of IGF-1 was independent of electrical activity, because it was still observed after injection of a constant negative current that lowered the membrane potential and shut down spontaneous activity (right). Current-clamp recordings of an acutely isolated neuron are shown. B, The hyperpolarization induced by IGF-1 under current clamp (left) is associated in the same neuron with a small outward current under voltage clamp (holding potential, -70 mV), accompanied by a decrease in noise amplitude (right).