Nicotine and extinction of fear conditioning.

Despite known health risks, nicotine use remains high, especially in populations diagnosed with mental illnesses, including anxiety disorders and Post-Traumatic Stress Disorder (PTSD). Smoking in these populations may relate to the effects of nicotine on emotional memories. The current study examined the effects of nicotine administration on the extinction of conditioned fear memories. C57BL/6J mice were trained with two white noise conditioned stimulus (CS; 30 s, 85 dB)-foot shock (2 s, 0.57 mA) pairings. Extinction sessions consisted of six presentations of the CS (60 s) across multiple days. Mice were either tested in an AAA design, in which all stages occurred in the same context, or in an ABA design to identify if context changes alter extinction. Saline or nicotine was administered 5 min before training and/or extinction. In the AAA design, nicotine administration before training did not alter extinction. Nicotine administered prior to extinction sessions enhanced extinction and nicotine administered before training and extinction decreased extinction. In the ABA design, nicotine administered before extinction enhanced extinction and blocked context renewal of conditioned fear, while nicotine administered during training and extinction did not alter extinction but enhanced the context renewal of conditioned fear. Nicotine has a differential effect on extinction of fear conditioning depending on when it is administered. Administration during extinction enhances extinction whereas administration during training and extinction may strengthen contextual fear memories and interfere with extinction.