Characterization of behavioral and physiological changes associated with early life stress in experimental models of epilepsy and psychiatric comorbidities

Author(s)

Lívea Dornéla Godoy

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2019-01-25

Examining board members

Norberto Garcia Cairasco; Ricardo Mauricio Xavier Leão; Rafael Naime Ruggiero; Deborah Suchecki

• Advisor: Norberto Garcia Cairasco

Abstract

Recent studies have strongly associated the pathophysiology of depression with chronic stress and its consequences, from altered behavior to HPA axis disruption and changes in gene expression. Depression is a disease that affects millions of people around the world, causing a major impact on the quality of life of patients. Evidence suggests the contributory role of early life stress (ELS) for Major Depression (MD). The variable chronic stress paradigm is widely used, but its impacts were not studied early in life. Therefore, to better understand this condition, male Wistar rat pups (P1-P21) were exposed to the Multimodal ELS paradigm. Plasma levels of corticosterone (CORT) and organs related to the HPA axis were evaluated. Additionally, these were evaluated during adulthood in the sucrose consumption test (SCT), the forced swimming test (FST) and the light-dark box test (LDT). The results indicate that pups did not habituate to multimodal ELS. In P21, the weight of the adrenal glands of the ELS animals is significantly greater, and the thymus and body weight decreased, when compared with the control group. The thymus also remains significantly reduced when compared to the control group in P90. In addition, adult rats submitted to the ELS protocol presented lower intake of sucrose and greater latency to light compartment in the LDT when compared to the control group. Another animal model that presents intermittent stress and has been widely used is the constraint model of nest material. In this model, the reduction of nest material promotes disruption in maternal care and causes changes in the encephalic and behavioral development of offspring. ELS leads to an early onset of contextual fear inhibition and accelerated maturation of the hippocampus. We postulate that CORT plays a functional role in regulating the maturation time of the regions underlying the learning and expression of threats, including the hippocampus and amygdala. Our hypothesis is that changes in plasma CORT levels may affect the timed brain and behavioral maturation processes. Therefore, our objective was to evaluate how a CORT synthesis blocker (Metyrapone; MET) alters conditioned fear behavior and BDNF expression in animals reared under control conditions or submitted to the ELS model of limited nesting bed. Both in control and ELS groups included Naïve animals or animals that received vehicle or MET; 50 mg/kg in P12. In P18, P21 or P28 independent groups of mice were exposed to a single session of fear conditioning, followed 24 hours later by a single context test. Analysis of the freezing behavior in the context test revealed that MET treatment blocked the acceleration of contextual fear suppression at P22 induced by ELS, with no difference between the P19 or P29 groups. This effect was observed mainly in female mice. Interestingly, in control male pups treated with MET, there was an altered contextual fear developmental curve. MET showed significant reduction in freezing in PND22, increase in freezing in PND29 followed by delayed suppression in P39. We observed that MET behavioural data were further supported by BDNF expression in limbic regions (ventral hippocampal and basolateral amygdala). Based on the current results, CORT probably plays an important role at the time of typical development and changes associated with ELS in the behavior and maturation of the brain. Epilepsy is a chronic neurological condition characterized by a persistent predisposition to epileptic seizures, and by neurobiological, cognitive, psychological and social consequences. Depression is a very common psychiatric comorbidity in patients with epilepsy. Increasingly data suggest that epilepsy, depression and other possible psychiatric disorders such as anxiety share pathogenic mechanisms. In this sense, abnormalities in the WAR strain (Wistar Audiogenic Rat) have been found that make it an interesting model for the study of stress, Epilepsy and neuropsychiatric comorbidities involved. Based on this, the present study aimed to evaluate in the WAR strain: 1. Maternal care under control and under stress conditions 2. Basal depressive type behaviors and after audiogenic kindling (chronic seizures-KAu).xvi Godoy, L.D. There was no difference for active breastfeeding posture, licking/grooming or time of mother in the nest and in the number of attacks and aggressive behaviors in maternal aggression test. WAR rats showed a higher latency to recover pup in pup retrieval test, whereas 100% of the Wistar rats grouped the entire litter, and in WAR it was only 40%. 2. In order to evaluate the depressive type behaviors, the rats were submitted to 20 acoustic stimuli twice a day (AuK) (Wistar-AuK, WAR-AuK), while the respective control groups remained without stimulus (Wistar, WAR). Subsequently, the groups were submitted to sucrose consumption test (SCT) and forced swim test (FST). There was no difference between the WAR and Wistar groups in the SCT, however the WAR-KAu group presented an increase in sucrose consumption in relation to the control groups 3 or 13 dasy after the AuK. In FST, both WAR and WARKAu groups showed a significant decrease in the test session when compared to Wistar. Taken together, these findings indicate that ELS may induce susceptibility to psychiatric comorbidities associated with stress, and that the current experimental models allow investigating how the effects of glucocorticoids are related to neurodevelopment, specifically in the maturation of fear behavior and limbic structures. In addition, preliminary data indicate that, although the WAR strain does not show maternal behavioral differences at baseline, it may present changes under stressful events. Also, based on the findings, the susceptibility of seizures may be related to changes in behavioral strategies in stressful situations in adult life, which may also constitute vulnerability to psychiatric comorbidities. (AU)

• FAPESP's process: 14/17959-1 - Characterization of depressive behaviors and morphological aspects involved in early life stress and audiogenic kindling in war strain
• Grantee: Lívea Dornela Godoy
• Support Opportunities: Scholarships in Brazil - Doctorate