Establishing and validating an unpredictable chronic mild stress rat model in a South African laboratory

Beselaar, Leandrie Corne (2021-03)

Thesis (MSc)--Stellenbosch University, 2021.

Thesis

ENGLISH ABSTRACT: There is growing concern regarding the societal implications of the increasing burden of chronic stress. In light of this, there are countless animal studies that are currently pursuing the underlying mechanisms of chronic stress-induced disease onset and/or evaluating therapeutic interventions. The unpredictable chronic mild stress (UCMS) model is widely used globally, however to the best of our knowledge it has not yet been employed in South Africa. The present study was therefore aimed at successfully establishing the UCMS model at Stellenbosch University, with the lesser goal of evaluating to which extent the validation tests succeed in confirming a chronically stressed state in the animals. Male Wistar rats (n=14) were subjected to a nine-week UCMS protocol. The rats were randomly exposed to one or more mild stressors per day and underwent a sucrose preference test (SPT) weekly, aimed at establishing levels of anhedonia. Additionally, detailed weekly monitoring was performed to observe aggressive behaviors and determine general well-being. Following the UCMS protocol, the rats underwent an elevated plus maze (EPM) test to establish the presence of anxiety-like behaviors, after which they were euthanized by decapitation. The results revealed distinct differences in individual responses to stress, therefore the Stress group was subdivided into Stress susceptible and Stress resilient groups, based on specific criteria. Despite no change in plasma corticosterone levels, molecular analyses showed that plasma adrenocorticotropic hormone levels were significantly increased in the Stress susceptible group. However, the sucrose preference of both Stress susceptible and Stress resilient groups increased over the experimental period. The EPM results revealed anxiety-like behaviors in the Stress susceptible rats, as they spent significantly more time in the closed arms of the EPM and made significantly less entries into open arms, compared to the Stress resilient group. We hypothesize that the Stress resilient rats have some protective mechanism against the effects of chronic stress. Another theory suggests that these rats are more resistant to such effects and take longer to experience the damaging effects thereof. The results of the behavioral tests used to validate the model showed that the EPM is a more robust validation of the UCMS model than the SPT. Overall, this study contributes to the existing theory that the UCMS model is difficult to establish across different laboratories. Although anxiety-like behaviors were observed in the Stress susceptible groups, the lack of plasma corticosterone changes and anhedonia in the same group suggests that the model might not have been entirely effective at creating a state of chronic stress. The study concludes that rodent models of chronic stress should be validated by multiple tests that focus on evaluating the animal as a whole and not just rely on a single behavioral or molecular parameter.

AFRIKAANSE OPSOMMING: Daar is toenemende kommer oor implikasies wat die toenemende las van chroniese spanning. In die lig hiervan is daar tallose dierestudies wat tans die onderliggende meganismes van die ontstaan van chroniese stres-geïnduseerde siektes en/of terapeutiese intervensies evalueer. Die onvoorspelbare chroniese ligte spanning (UCMS) -model is regoor die wêreld gevestig, maar na ons beste wete is dit nog nie in Suid-Afrika gevestig nie. Hierdie studie was dus daarop gemik om die UCMS-model suksesvol aan die Universiteit Stellenbosch te vestig, met die mindere doel om te evalueer tot watter mate die valideringstoetse daarin slaag om ’n toestand van chroniese spanning in die diere te bevestig. Manlike Wistar-rotte (n=14) aan 'n onvoorspelbare chroniese stresprotokol van nege weke onderwerp. Die rotte is daagliks blootgestel aan een of meer ligte stressors en het weekliks 'n sukrose-voorkeurtoets (SPT) ondergaan. Daarmee saam is is die rotte weekliks in detail gemonitor om enige aggressiewe gedrag waar te neem en algemene welstand te bepaal. Na die stres-protokol het die rotte 'n verhoogde plus doolhof (EPM) toets ondergaan om die teenwoordigheid van angstige gedrag vas te stel. Die algehele studie-resultate het duidelike verskille getoon in individuele rotte se reaksies op stres, daarom is die Stres-groep onderverdeel in Stres-vatbare en Stres-bestande groepe, gebaseer op spesifieke kriteria. Molekulêre ontledings het geen verandering is in plasmakortikosteroonvlakke getoon nie, alhoewel dit gewys het dat plasmadrenokortikotropiese hormoonvlakke beduidend verhoog was in die Stres-vatbare groep. Gedurende die eksperimentele periode het die sukrose-voorkeur in beide die Stres-vatbare en Stres-bestande groepe toegeneem. Die EPM-resultate het gewys dat Stres-vatbare rotte anstige gedrag getoon het, aangesien hulle aansienlik meer tyd in die geslote arms van die EPM deurgebring het. Dié groep het ook aansienlik minder kere in die oop arms ingetree, in vergelyking met die Stres-bestande groep. Ons veronderstel dat die Stres-bestande rotte 'n beskermende meganisme ontwikkel het teen die effekte van chroniese spanning. 'n Ander teorie dui daarop dat hierdie rotte meer bestand is en dus langer neem om die skadelike effekte daarvan te ervaar. Die resultate van die gedragstoetse wat in dié studie gebruik is om die model te onderstuen, het getoon dat die EPM 'n meer robuuste validering van 'n chroniese stresmodel is as die SPT. Oor die algemeen dra hierdie studie by tot ‘n bestaande teorie wat stel dat die UCMS-model moeilik is om tussen verskillende laboratoriums te vestig. Alhoewel angstige gedrag waargeneem is in die Stres-vatbare groep, dui die gebrek aan plasmakortikosteroonveranderings en anhedonie in dieselfde groep daarop dat die model nie heeltemal effektief sou wees om 'n toestand van chroniese spanning te skep nie. Die studie het tot die gevolgtrekking gekom dat knaagdier-modelle van chroniese stres gevalideer moet word deur veelvuldige toetse wat daarop fokus om die dier as geheel te evalueer, en nie net 'n enkele gedrags- of molekulêre eienskap nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/110063
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