Study of the influence of the posttraumatic stress disorder on vulnerability to drugs in DBA/2 mice

Posttraumatic stress disorder (PTSD) and drug addiction are two comorbid conditions bound in a complex bidirectional relationship. On one hand, the mechanisms by which PTSD promotes the occurrence of drug addiction are not fully understood. On the other hand, methodological and ethical limitations inherent to human studies do not allow a full understanding of the influence of drug addiction on the expression of PTSD symptoms. In an effort to contribute to the resolution of these two issues, the present thesis based on an animal model with DBA/2J mice, combined sequentially, in both directions, a drug-induced locomotor sensitization procedure and an animal model of PTSD based on an electric shock. Locomotor sensitization was achieved by repeated administrations of ethanol or cocaine at the same dose over several days. The PTSD-like symptoms were assessed several weeks after the electric shock with conditioned fear, sensitized fear and anxiety tests. Overall, the various experiments have shown, on one hand, that a PTSD-like experience in mice does not significantly increase the intensity of drug-induced locomotor sensitization. However, this PTSD-like experience indirectly strengthen drug sensitization through an interaction with some of its modulating factors. On the other hand, drug-induced locomotor sensitization does not directly affect the expression of PTSD in this animal model. However, drug sensitization can be considered as a form of stress sensitization. It induces on its own stress behaviors that add to the effects of the PTSD experience. Further studies on the subject would provide a better understanding of the co-morbidity between PTSD and drug addiction