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

Abstract

In modern society, people are living under constant pressure. On the one hand, mild “healthy” stressors can be a motivator, leading to increased individual productivity and creativity. On the other hand, however, constant, excessive stress over a long period of time can impair not only the mind but the overall well‐being of a person. The burden of aforementioned societal pressure is shown by the increasing number of stress‐associated health issues around the globe. Mood‐ and psychiatric disorders are just a small part of the wide range of diseases related to stress. Biologically, the brain is the region that is most affected by highly stressful situations. Neurotransmitter signaling, neuroendocrine function, and neuronal signaling are lowered during periods of chronic stress, and if left unchecked, these neurologic changes are amongst the causes of depressive symptoms and the first step towards clinical depression. Alteration of brain‐derived neurotrophic factor (BDNF) concentration is one of many biochemical changes associated with depression. The main goal of this thesis is to better understand how socially stressful situations are able to change BDNF concentration and modify depression‐related factors. For that the use of Positron Emission Tomography (PET) to observe such factors in vivo in an animal model has been used, with a significant focus on social stress‐dependent neuroinflammation. In conclusion, social stimuli had an impact in the brain, as shown by differences in behavior, neurotrophin, and synaptic plasticity markers, both in positive and negative social environments. It appears that the longer the stimulation, and the shorter the analysis period, the more pronounced is the behavioral change. Longer stress protocols are needed in order to achieve a chronic state of anxiety‐ and depressive‐like behaviors in an animal model of stress, allied with possibly a shorter interval between stressor and analysis. The same pattern found in the behavior of these animals can also influence the analysis of neuroinflammation and neurotrophic biomarkers that were analyzed in this thesis.