Serotonergic Regulation of the Development of Affective Behavior

Early life stress (ELS), or exposure to stressful events during childhood, has been shown to lead to both short- and long-term effects on an organism\u27s physiology, including the central nervous system (Syed et al., Chronic Stress (Thousand Oaks), 2017). Due to the high levels of neuronal plasticity found in the early-life critical period, stress during this time period can alter neural circuits to increase susceptibility to mental illnesses later in life (Sheth et al., Chronic Stress (Thousand Oaks), 2017). It has been linked with the development of several psychiatric disorders later in adulthood, such as major depression and generalized anxiety disorder (Syed et al., Chronic Stress (Thousand Oaks), 2017).  Furthermore, ELS is associated with deficits in cognitive and affective functions, such as memory, processing of social and affective stimuli, and reward processing (Pechtel, P. & Pizzagalli, D.A., Psychopharmacology, 2011). While research has clearly shown that ELS increases susceptibility to psychiatric disorders, it is still unclear what circuits in the brain are responsible for this. To gain a better understanding, we focused on the dorsal raphae nucleus (DRN), a serotonin- rich region located in the midbrain and pons. The DRN has been strongly connected with mood disorders, as well as involvement in neuroplasticity, and projects to several regions throughout the brain. In this project, we concentrated on the DRN\u27s relationship with the development of affective behavior via two animal behavior assays. These tests were carried out at three points in early life at four, six, and eight weeks to determine how these behaviors mature. A forced swim test was conducted to study the animal\u27s choice between active or passive response to stress, both with and without the administration of selective serotonin reuptake inhibitors (SSRIs). Similarly, a looming disk test was performed to learn how animals respond to innate threats. Both of these behaviors depend on serotonin, and are altered by ELS. Our future studies will focus on links between ELS, maturation of the DRN, and the development of affective behavior