ǂThe ǂrole of the stress axis in modulating behavioural flexibility in a social cichlid

Zala Ferlinc (2022) ǂThe ǂrole of the stress axis in modulating behavioural flexibility in a social cichlid. MSc thesis.

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Abstract

The hypothalamic-pituitary-interrenal (HPI) axis or the stress axis – the hypothalamicpituitary- adrenal (HPA) axis equivalent in fishes, is a major neuroendocrine system that regulates the stress response and effects many body functions including cognition. Activity of the axis is regulated by negative feedback induced by the release of glucocorticoids which bind on glucocorticoid receptors in the brain to stop the further release of glucocorticoids. The stress axis activity following acute stress is regulated via the lower affinity glucocorticoid receptors which are found in high concentrations all over the pituitary and the brain. An acute rise with a subsequent swift decline of glucocorticoid hormones induces an emergency response which enhances cognitive performance. Although memory formation and attention, two important building blocks of behavioural flexibility, are known to be influenced when exposed to stressors, whether stress mediates behavioural flexibility is less investigated. The main objective of this experiment was to investigate the role of the HPI axis in mediating behavioural flexibility in the cooperatively breeding cichlid fish Neolamprologus pulcher in an ecologically valid set-up in which the stress hormone cascade is dependent on the behavioural task under study. To verify this role, we pharmacologically blocked glucocorticoid receptors in adults using a non-invasive short-term application of a glucocorticoid antagonist mifepristone (RU486). Subsequently after the application we repeatedly exposed test fish to an ecologically relevant mild stressor and tested their behavioural flexibility in a detour task. The application of mifepristone decreased behavioural flexibility in an ecologically relevant spatial task without altering motivation to seek shelter. This highlights the role of the stress axis in determining the ability of animals to adapt to changes in the environment and emphasises the tight link between stress and cognition in general. This work is of particular relevance for current conservation issues in a world where humans rapidly alter the environment.

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