The Role of the Ventral Hippocampus on Contextual Learning and Avoidance Behavior: Implications for PTSD

Abstract

A hallmark coping mechanism of post-traumatic stress disorder (PTSD) is avoidance, which is a behavior that decreases the likelihood of encountering a perceived threatening stimulus. Seventy-five Sprague Dawley rats were obtained for two way signaled active avoidance (SAA) in which the rat must completely cross to the other side of the conditioning box during a tone CS to prevent a footshock US and terminate the CS. In the first experiment, the rats were trained in one of two contexts for either 4 or 8 days and then tested under extinction conditions in both contexts. Rats tested in a different context from the one they were trained in showed significantly reduced levels of avoidance responding and increased freezing compared to their responding in the same context as training. In a second experiment, rats were trained for 4 days in the two-way SAA. To test if ventral hippocampus is responsible for the behavioral effect, the ventral hippocampus was inactivated with muscimol or injected with vehicle as a control. Rats given vehicle injections showed the same context shift deficit when tested in a novel context. However, rats given muscimol injections had similar levels of avoidance responses in both the novel and original contexts for testing. These results exemplify that ventral hippocampus is important for constraining avoidance to the training context and improper functioning of this brain area could lead to context dysregulation of avoidance.