Investigação da participação dos receptores serotoninérgicos 5-HT5A, 5-HT6 e 5-HT7 na extinção da memória de medo condicionado ao contexto

• Main Author: Assis Brasil, Eduardo Silva de
• Publication Date: 2019
• Format: Doctoral thesis
• Language: por
• Source: Biblioteca Digital de Teses e Dissertações da PUC_RS
• Download full: http://tede2.pucrs.br/tede2/handle/tede/8817
• topic: Memória; Medo Condicionado ao Contexto; Extinção; Serotonina; Hipocampo; Amígdala; Memory; Conditioned Fear; Extinction; Serotonin; Hippocampus; Amygdala; CIENCIAS DA SAUDE::MEDICINA

Fear memories can lead to exaggerated defensive behavior in response to threats, such as Post Traumatic Stress Disorder (PTSD). Extinction is the learned inhibition of retrieval, it may be useful in restricting the expression of fear memories to appropriate situations. The hippocampus and basolateral amygdala (ABL) are essential for extinction to occur. This process can be modulated by different drugs and neurotransmitters, for example, serotonin. The serotonergic system has receptors located in several areas in the brain and its role is well documented in various behavioral tasks. It is known that the most recently described receptors 5-HT5A, 5-HT6 and 5-HT7 are related to the formation of some types of memory, however the role of these receptors in the process of extinction of fear memory remains unknown. Therefore, this study aims to investigate the role of 5-HT5A, 5-HT6 and 5-HT7 receptors in the extinction of context-conditioned fear memory. For this, male Wistar rats with cannulas implanted in the CA1 region of the hippocampus or ABL were submitted to the context-dependent fear memory extinction protocol and received infusions of agonists and antagonists of the 5-HT5A, 5-HT6 and 5-HT7 receptors immediately or 3 hours after extinction and tested 24 hours later. When the drugs were infused in CA1 immediately or 3 h after extinction training, the animals did not present difference in relation to the control group. However, when 5-HT5A and 5-HT7 receptor antagonists were infused immediately or 3 h after extinction training in the ABL, the process of extinction was facilitated, this effect was also seen when infused 5-HT6 antagonist only immediately after extinction training in the ABL, the groups that received the agonists of these receptors did not differ from the control group. In summary, the antagonists of the 5-HT5A, 5-HT6 and 5-HT7 receptors in the ABL, but not in the CA1 region of the hippocampus, was able to facilitate de extinction consolidation.