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

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. Positiivse emotsionaalsuse ja kroonilise varieeruva stressi moju rottide kaitumisele ja aju monoamiinsete virgatsainete tasemele Taust: Eelnevates uurimustes on naidatud, et nii loommudelites kui ka inimeste puhul muudavad positiivsed emotsioonid organismi stressile reageerimist ja selle mojusid. Lisaks sellele on populatsioonipohistes uuringutes naidatud, et korgem positiivsete emotsioonide kogemise tase on seotud madalama psuhhiaatriliste hairete esinemise riskiga. Magistritoo eesmargiks oli uurida loommudelit kasutades positiivse emotsionaalsuse moju stressireaktsioonile nii kaitumise kui ka monoamiinsete virgatsainete tasemel. Meetod: Isaseid Wistari rotte kodistati kaks nadalat ning lahtuvalt nende piuksumisaktiivsustes jagati nad vahepiuksujate (LC) voi paljupiuksujate (HC) ruhma. Kodistamisele jargnes kroonilise varieeruva stressi protseduur, misjarel pooled loomad labisid avarvalja ja sotsiaalse eelistuse kaitumiskatsed ja teine pool loomi ohverdati, et moota monoamiinsete virgatsainete ja nende peamiste metaboliitide taset mandeltuumast ja frontaalkoorest. Tulemused: Katsetest selgus, Positive emotionality, chronic variable stress model, monoamines 4 et stress vahendab frontaalkoore serotoniini kaivet HC loomadel, aga suurendab sama naitajat LC loomadel. Avarvalja katses olid HC loomad baastasemelt vahem areva kaitumisega kui LC loomad. Stressi mojul aga LC ja HC loomade erinevused areva kaitumise tasemes kadusid. Sotsiaalse eelistuse testis iseloomustas HC loomi vorreldes LC loomadega suurem aktiivsus elutute objektide suhtes ning suurem aktiivset sotsiaalset uudistamise osakaal teise roti lahisuhtlusalas viidetud ajast. HC rottide suhkrueelistus oli 3 nadalat parast kodistamist korgem kui LC rottidel, erinevus aga kadus kolmes jargnevas mootmises. Kasutatud kroonilise stressi režiim toi kaasa muutused kaalutousus ja suurendas akuutsest stressist tingitud hupertermilist reaktsiooni. Positive emotionality, chronic variable stress model, monoamines 5