Effects of positive emotionality and chronic variable stress on brain monoamine levels and behaviour in rats

Abstract

Background: Positive emotional states have been shown to play the role in modifying stress response both in animal models and in humans. Additionally positive emotional states have been related to higher resilience against many psychiatric disorders at population level. The main goal of current master’s thesis was to experimentally analyze the effects of positive emotionality measured by 50 kHz ultrasonic vocalizations (USVs) in stress response both at behavioral level and also at the level of monoaminergic signaling by using chronically variable stress (CVS) animal model. Method: Male Wistar rats were tickled for 2 weeks and based on USVs elicited by tickling divided in low chirping (LC) and high chirping (HC) group that was followed by CVS condition. After the end of CVS half of the animals were subjected to open field and social preference tests, while others were sacrificed to assess the level of main monoamine neurotransmitters and their metabolites in amygdala and prefrontal cortex. Results: CVS decreased 5-HT turnover in frontal cortex of HC animals, while increasing it in LC animals. In open field test the HC animals displayed less anxious phenotype than LC animal at basal level but this difference was eliminated by CVS. In social preference test the HC differed from LC animals by having higher activity toward unanimated objects and spending larger proportion of time in active socialization out of total time spent near other rat. HC animals had higher sucrose preference 3 weeks after tickling, while this difference was not seen in following 3 tests. CVS affected the weight gain and increased the stress induced hyperthermia response.