Traumatic events, particularly during early life, have far-reaching consequences including increasing an individual's vulnerability to depression and anxiety disorders. However, there is a paucity of information concerning the impact of early traumatic experiences on the development of neural circuitry, and its relation to adult vulnerability to neuropsychiatric disorders. Moreover, it is known that there is considerable heterogeneity in response to traumatic stress in relation to later development of neuropsychiatric disorders. In the US, 20-30% of individuals exposed to traumatizing events subsequently exhibit symptoms of post- traumatic stress disorder (PTSD). Nonetheless, the characteristics of neural circuitries associated with either risk or resilience to these disorders re unknown. Understanding these issues is now possible with the advent of a novel approach capable of imaging resting-state functional connectivity (RSFC) in awake animals. This advancement is unique in its noninvasiveness, whole-brain coverage and high sensitivity to neuroplasticity, and thus is ideal for studying the dynamic changes of neural circuitry across brain development and under selective perturbations. By utilizing this approach, we propose to investigate the impact of early trauma on the development of the neural circuits implicated in stress-induced disorders in an animal model. Specifically, with a longitudinal design in which traumatic stress is administered during juvenile, adolescence or adulthood, we will characterize the impact of early trauma on the developmental trajectories of the neural circuits of medial prefrontal cortex (mPFC), amygdala (AMYG) and hippocampus (HP). In addition, we will examine the difference in these circuits in animals exhibiting high vulnerability to developing PTSD-like behaviors. This vulnerability will be evaluated based on cut-off criteria of an established PTSD animal model. Our preliminary data showed that the neural circuits of mPFC, AMYG and HP are still immature during adolescence. We also demonstrated that trauma exposure can induce long-lasting effects on the same neural circuits in adult rats. Importantly, vulnerable rats showed much weaker RSFC strength within the mPFC-AMYG circuit compared to resilient rats, implying that RSFC may predict vulnerability to PTSD. Based on these pilot data, we plan to accomplish the research objectives by pursuing three specific aims.
In Aim 1, we will characterize the normal developmental trajectories of the neural circuits of mPFC, AMYG and HP.
In Aim 2, we will evaluate the impact of early trauma exposure on the developmental trajectories of these neural circuits.
In Aim 3 we will assess the neural substrate underlying the vulnerability to PTSD in an animal model. The proposed work is innovative, because it combines novel neuroimaging tools and behavioral measurement to investigate the development of critical neural circuits and their vulnerability to traumatic stress. The impact of this research is highly significant because understanding the role of early trauma in neuroplastic changes in the circuitries subserving mood and anxiety disorders is critical to earlier diagnosis and treatment of these disorders.
Early adverse life experiences have been associated with long-lasting psychophysiological consequences across the lifespan. However there are many critical gaps in our understanding of the neural mechanisms that may sub-serve these processes. The proposed research projects will have significant impact on expanding our understanding of the role of adverse early life events and its' impact on adult psychopathology. These studies will provide a potential circuitry-level biomarker for the identification of vulnerability to stress-related disorders, and can help early diagnosis and treatment of dysfunctions induced by exposure to early stress.
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