A exposição à novidade modula a extinção da memória aversiva e a sua persistência

Abstract

The recall of a traumatic memory can be inhibited through a process called extinction. The extinction has a great therapeutic applicability in the treatment of phobias such as PTSD. However, although widely used in clinical practice, extinction still does not yield satisfactory results in terms of its long-term results. The aim of this research was to evaluate the modulatory effects of novelty on the extinction of aversive memory, as well as the persistence of these effects and possible involvement of dopaminergic system. Male Wistar rats (n = 37) were divided into five groups according to the intervention used. The animals were trained in inhibitory avoidance (IA), an aversive behavioral task, and 24 hours later underwent three extinction training sessions with a 90 min interval between them. Twenty-four hours, 3, 7, 14 and 21 days after the animals were submitted to retention tests. Some animals were exposed for 5 min to a novelty (unknown open field) 30 minutes before the first extinction session. Other animals received an intra-hippocampal microinjection of dopamine 30 minutes before the first extinction session. In the 24 h retention test, we observed that novelty and the dopamine were able to promote the extinction of aversive memory, while control animals did not extinguish the original memory. In the 3, 7, 14 and 21 days tests the same results were observed, what demonstrates the persistence of extinction memory. Unlike the new open field, the exposure to a familiar open field had no effect. These results allow us to conclude that exposure to a new environment promotes the extinction of aversive memory, an effect that is related to exposure to novelty, since exposure to a familiar environment did not promote the same effect. In addition, the novelty effect was persistent and mimicked by the infusion of dopamine into the hippocampus, what allows to infer that the participation of this neurotransmitter is an important mechanism for the observed effects.