Electrical activity of silent RPa3, LPa2, LPa3, LPa8, LP11 neurons and spontaneously active RPa1 neuron was investigated as affected by iontophoretic intracellular cAMP injection. It is shown that in all cases the cAMP injection caused depolarization of the membrane; cAMP injection into the neuron when its membrane potential is clamped at the resting potential level evoked the appearance of transmembrane current (cAMP-current). External theophylline (1 mM/1) increased the amplitude and duration of vAMP-current approximately by 50%. It is concluded that variation in the cAMP concentration inside the neuron may alter the ionic permeability of its membrane, thus changing its electrical activity.