Masters Degrees (Clinical Pharmacology)

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Browsing Masters Degrees (Clinical Pharmacology) by Subject "Anxiety disorders -- Animal models"

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    The role of estrogen receptors in anxiety disorders: an investigation in zebrafish
    (Stellenbosch : Stellenbosch University, 2023-11) Balshaw, Aidan Glenn; Smith, Carine; Pretorius, Lesha; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Dept. of Medicine. Division of Clinical Pharmacology
    ENGLISH ABSTRACT: Background & Aim Anxiety disorders are the most prevalent psychiatric disorders with approximately twice the prevalence in females compared to males. Clinical studies on the exacerbation of anxiety symptoms in the premenstrual phase of the menstrual cycle implicate the role of declining estradiol levels. Preclinical evidence most consistently indicating the anxiolytic effect of increased estrogen receptor beta-signalling exacerbations in anxiety symptoms have been demonstrated in clinical studies. This thesis aimed to simulate estrogen-linked anxiety behaviour in larval zebrafish to assess the role of estrogen receptors (ER) in this phenomenon. Methods Using an estradiol-treatment-withdrawal-model, behaviour of zebrafish larvae was determined in the LDTT on 7 days post-fertilisation (dpf) in a series of experiments. Firstly, the estradiol treatment withdrawal model was optimised by increasing the duration of treatment withdrawal and reducing the number of estradiol concentrations used. Further optimisation included comparing behaviour after estradiol washout with behaviour after prolonged tamoxifen, an ER modulator, administration. Secondly, ER modulators (WAY-200070, PHTPP, and tamoxifen) were administered for 45 minutes, in the presence of absence of exogenous estradiol exposure, before behavioural analysis. Thirdly, ERβ expression was determined after estradiol treatment. Lastly, redox status (hydrogen peroxide levels, antioxidant capacity, and lipid peroxidation) and behaviour of estradiol-treated larvae were evaluated. Results Estradiol withdrawal decreased basal and anxiety-like behaviour. The accuracy of the estradiol washout model was not improved by longer durations of treatment withdrawal or refinement of estradiol concentrations used. Prolonged tamoxifen administration reduced basal and anxiety-like behaviour. ER modulation did not alter anxiety-like behaviour, while basal activity slightly altered by supraphysiological concentrations of WAY-200070 in the absence of estradiol. WAY-200070 and tamoxifen altered basal activity when administered in the presence of exogenous estradiol exposure. ERβ expression was not upregulated in larvae exposed to low concentrations of estradiol. Longer exposure to low concentrations of estradiol increased antioxidant capacity and slightly decreased lipid peroxidation while hydrogen peroxide levels were unaltered. In addition, acute exposure to low concentrations of estradiol increased basal activity in the LDTT. Conclusion Current data suggest that developing zebrafish larvae are likely not suitable for modelling exacerbations in anxiety symptoms associated with fluctuating estrogen levels. Rather, current investigations demonstrated that increased activity levels were not linked to anxiety but better redox status, in the context of free estrogen availability. Considering the effect of redox status on larval behaviour, it is recommended that behavioural analysis be conducted in parallel with mechanistic studies in the context of ER signalling.
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    Understanding the effect of protocol variations in the zebrafish light/dark transition test
    (Stellenbosch : Stellenbosch University, 2023-03) Gelderblom, Michelle; Smith, Carine; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Dept. of Medicine. Division of Clinical Pharmacology.
    ENGLISH ABSTRACT: Anxiety disorders have devastating individual and societal costs, and are a major contributor to years lost to disability worldwide. They appear to be increasing in prevalence, both in South Africa and the world at large. Although there are medications to treat anxiety, there is a need for more treatment options. Anxiety is often not treated effectively due to treatment resistance or non-compliance to medication due to side effects. One of the best options for identifying novel anxiolytics is to use animal models. Zebrafish are useful for screening of potential anxiolytic treatments because they are the most well-studied vertebrate model that shares the size, cost and fecundity benefits of invertebrate models. The light/dark transition test (LDTT) is the most widely used zebrafish larvae behavioural test. It has many applications in pharmacology, particularly in toxicology and screening for potential pharmaceuticals, including treatments for anxiety disorders. It is likely to be one of the first tests used when screening for neuroactivity in zebrafish larvae. During the test, zebrafish larvae are exposed to a period of light followed by an abrupt transition to darkness which produces a hyperlocomotion response that responds to anxiolytics and anxiogenics. The design of the LDTT varies between studies, but it is unclear how common protocol variations affect the comparison of results and contextualisation of data generated using slightly varied protocols. Through both prospective experiments and retrospective data analysis, the effect of age (from 2 dpf to 5 dpf), lighting conditions during rearing (standard or continuous darkness), capture order, repeated light/dark cycles, repeated light/dark transition tests, duration of the light period (1 minute or 10 minutes), light intensity during the light period, and breeding stocks on the response to the light/dark transition test was measured. All experiments consisted of an acclimation period, and at least one cycle consisting of a light period and a dark period. Experiments were recorded using the DanioVision system and activity was measured automatically using the EthoVision XT software. Variations in age, time of day, light period and breeding stock had a significant impact on the response to the light/dark transition test and should therefore be carefully controlled. Light conditions during rearing did not have a statistically significant effect, but more research is needed to confirm that variations in light-rearing do not affect response to the light/dark transition test. Finally, capture order, repeated cycles, repeated light/dark transition tests and light/dark transition intensity did not have a significant effect, suggesting that they can vary according to logistical requirements without affecting results. This opens up the use of repeated measurements that facilitate identifying neuroactivity when the amount of time it will take for the onset of action is unknown. This informs both experimental design, and which studies are comparable. It will also facilitate the use of the light/dark transition test to screen for potential anxiolytics.