The medial prefrontal cortex (mPFC) is involved in several aspects of drug addiction, including rewarding effects of cocaine and mechanisms underlying addiction and craving. In humans, the mPFC is activated during cocaine withdrawal and also by cue-induced cocaine craving. In rodents, the mPFC is necessary for the development of behavioral sensitization following chronic cocaine exposure. In previous investigations we have demonstrated that repeated cocaine administration alters membrane properties and ion channel function of rat mPFC pyramidal neurons after short-term withdrawal from cocaine, increasing the number of spikes evoked by depolarization.  Recently, evidence has accumulated suggesting that nitric oxide (NO), a diffusible neuromodulator, plays a major role in initiating and maintaining the behavioral effects of psychostimulant drugs. Pharmacological or genetic disruption of neuronal NO synthase (NOS) activity attenuates the development of sensitization, conditioned place preference and self-administration of psychostimulants. Moreover, acute cocaine administration increases in vivo NO release in the mPFC in a manner which is attenuated by neuronal NOS inhibition. Furthermore, changes in NO transmission modulate neuronal excitability and synaptic plasticity in several brain structures including the mPFC. However, the role of NO in the mechanisms by which cocaine affects membrane excitability is not well studied.  In this study we performed visualized whole-cell current-clamp recordings in brain slices taken from the mPFC of rats administered (once per day for 5 days) either vehicle (10% Cremophor EL in saline (0.9%) solution), cocaine (15 mg/kg, i.p.), or cocaine and the selective neuronal NOS inhibitor 7-NI (50 mg/kg, i.p.).  The impact of each treatment on the membrane excitability of pyramidal neurons in the mPFC was examined after short-term withdrawal (1 day) from repeated cocaine/vehicle administration. We found that cocaine sensitization increased the membrane excitability of pyramidal cells as evidenced by increases in the number of evoked spikes and reductions in inward and outward rectification. Interestingly, co-administration of 7-NI prevented the changes in membrane excitability previously observed in mPFC pyramidal neurons after short-term withdrawal from cocaine. These results indicate that activation of NO signaling plays a critical role in the neuroadaptations associated with the development of behavioral sensitization and the withdrawal effects observed following chronic cocaine exposure.