Social stress: the good, the bad, and the neurotrophic factor:understanding the brain through PET imaging and molecular biology

The growing burden of social pressure is reflected by the increasing number of stress-associated health issues around the globe. One example of a stress-related health issue is depressive disorder. Depression is considered a major global health issue, affecting every cultural, economic and age group. The work described in this thesis aimed to investigate how different social stimuli –beneficial or harmful – can affect the brain. In this context, we mimicked different environments that are usually observed in humans in animal models, which allowed us to investigate how the brain of the animal physiologically responds to different social stressors, focusing especially on memory, inflammation of the brain, and a protein involved in proper functioning and survival of brain cells: the brain-derived neurotrophic factor (BDNF).In this thesis, we describe that social environment is able to increase or decrease BDNF levels in the hippocampus, when animals were exposed for a long time to beneficial or harmful social interactions, respectively. However, when animals were exposed to acute social and physical stress, there was no effect on BDNF concentration. We also found that animals submitted to harmful social stress showed transient effects on behavior, which had normalized after two weeks. Brain inflammation, as observed by positron emission tomography, was also normalized after two weeks. We concluded that the effect of short social stress exposure was temporary, showing an effect after a few days, but normalizing a few weeks after exposure to the stressor, but long exposue to social stimuli can induce lasting modification of brain functioning