Pretraining inactivation of the caudal pontine reticular nucleus impairs the acquisition of conditioned fear-potentiated startle to an odor, but not a light.

Recent data from developing rats suggest that structures downstream from the amygdala are involved in the acquisition of conditioned fear-potentiated startle (FPS). The authors tested this idea in adult rats by temporarily inactivating the structure critical for FPS, the caudal pontine reticular nucleus (PnC), during fear conditioning. When the conditioned stimulus (CS) was an odor, rats displayed freezing, but not FPS, at test. This effect was not due to a decrease in footshock sensitivity. Further, no savings were evident on retraining. When the CS was a light, inactivation of the PnC had no effect on the acquisition of FPS. Thus, the PnC may be crucial for the acquisition of conditioned FPS to an odor, but not a light.