Nicotine enhances both foreground and background contextual fear conditioning

Abstract

The present study examined if nicotine enhances contextual fear conditioning when the training context is either a background stimulus or a foreground stimulus. In the background conditioning experiment, mice were trained using two auditory conditioned stimulus (CS; 30 s, 85 dB white noise)-footshock unconditioned stimulus (US; 2 s, 0.57 mA) pairings and tested 24 h later. In the foreground conditioning experiment, mice were trained with two presentations of a footshock US (2 s, 0.57 mA) and tested 24 h later. Mice received 0.09 mg/kg nicotine before training and testing. For both the foreground and background conditioning experiments, nicotine enhanced contextual conditioning. No enhancement of the auditory CS-US association was seen. These results demonstrate that nicotine enhances contextual fear conditioning regardless of whether the context is a background stimulus or a foreground stimulus during conditioning.

Fig. 1

Acute nicotine administration (0.09 mg/kg) enhances freezing to the context when the context is a background stimulus during training. There were no effects of nicotine administration on baseline freezing, immediate freezing, preCS freezing, or freezing to the CS (*p < 0.05).

Fig. 2

Nicotine (0.09 mg/kg) administration before training and testing enhances contextual fear conditioning when the context is a foreground training stimulus. There were no effects of nicotine on baseline or immediate freezing. Freezing to an altered context (preCS) and to a white noise (CS) were also examined in order to verify that freezing in mice trained with a CS results from CS–US training and is not due to a startle response. Freezing to the altered context (preCS) and freezing to the white noise (CS) were minimal. There were no differences in preCS and CS freezing between saline-treated and nicotine-treated mice (*p < 0.05).