The effects of stress on serotonergic signalling and brain development

Pre- and early postnatal stress has been shown to affect brain development and adult behaviour, and is a known risk factor for the onset of anxiety and depression in later life. These conditions have been linked to serotonin signalling, a neurotransmitter that acts as a neuromodulator in the adult brain. Serotonin also affects neuronal growth during development, and there is evidence that changes in serotonin signalling during this period can lead to anxious and depressive behaviour. We hypothesise that developmental stress affects serotonergic signalling during critical periods of brain development resulting in behavioural changes in later life. Here we will explore this hypothesis using zebrafish as a model system. In particular, we will study the influence of developmental stress on serotonergic signalling during development. We will also investigate whether stress hormone exposure or pharmacological alteration of serotonin signalling during development can mimic the effects of developmental stress on serotonin receptor expression, brain development and behaviour.

The project has the following specific objectives:
• To study the effects of developmental stress or pharmacological activation of stress hormone receptors on the expression of serotonin receptors and serotonin signalling-related genes
• To characterise the effects of developmental stress and stress hormone receptor activation on brain development and behaviour
• To investigate whether pharmacological disruption of serotonin signalling, especially via 5HT1A and 5HT7 receptors, can mimic the effects of developmental stress on brain development and behaviour
• To explore whether pharmacological interventions targeting serotonin signalling can mitigate the effects of developmental stress

Zebrafish are an ideal model system for this project as fertilisation and development occurs externally, which provides opportunities for experimental manipulations during early development. In the first phase of the project, zebrafish larvae (from gastrulation onwards) will either be exposed to established stress protocols (prolonged rotation, high temperature) or various concentrations of stress hormone receptor agonists (corticosterone, dexamethasone). Subsequently, mRNA will be extracted at various time points during development (48 – 120 hpf) and changes in the expression of serotonin receptor and serotonin signalling-related genes will be analysed using qPCR techniques. The qPCR analysis will be complemented by in situ hybridisation to map the distribution of 5HT receptor and 5HT signalling-related mRNAs in the brain. In parallel, zebrafish larvae will also be prepared for immunohistochemistry and labelled with synapse- and neuron-specific antibodies to characterise changes in neuronal structures and synaptic connectivity. Finally, larvae that have experienced developmental stress or been exposed to stress hormones will be assessed for anxiety levels and related behavioural traits using established behavioural tests (e.g. novel tank diving) at both juvenile (one-month) and adult stages (from three months onwards). In the second phase of the project, we will test the hypothesis that changes in serotonin signalling can mimic the effects of developmental stress on behaviour in later life. This will establish a causal link between developmental stress, serotonin signalling and subsequent behavioural changes. We will also explore whether manipulation of serotonin signalling can mitigate any behavioural effects of developmental stress.

The work in zebrafish will be complemented by using bioinformatics to analyse publicly available gene expression data following stress hormone receptor activation in other species. This will help to establish common principles that are applicable across different vertebrate species.