Chemical genetics in zebrafish: modulation of cAMP and MAPK pathways in behaviour
Lundegaard, Pia Rengtved
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The prevalence of stress and anxiety disorders in modern society is increasing, but the development of new treatments decreasing due to high research costs and low success rates in clinical trials. The latest type of compounds introduced to treat anxiety and depression was the specific serotonin reuptake inhibitors (SSRI), which was introduced in 1987. Since then, no new class of compounds have been introduced, suggesting that the need to find alternative targets in treating mental disorders is needed. In this thesis I have used the zebrafish as a model organism to study the modulation of behaviours through intracellular signalling pathways, known to be involved in learning, memory and anxiety. First, using the pro-convulsant compound, pentylenetetrazole (PTZ), an automated tracking system was established to quantify and analyse swimming behaviour in larvae zebrafish. Pentylenetetrazole induces seizures in zebrafish at high concentrations, however this thesis identifies that the combination of a low level of PTZ and subjecting the fish to alternating cycles of light and dark induced a reversed response to light and dark. A group of compounds with known anti-seizure effects were subsequently screened, which found that a combinational treatment with diazepam and two types of neurosteroids reversed the PTZ-induced light dark response. Secondly, using the same automated analysis setup, the effect of cAMP modulators was studied on behaviour in zebrafish larvae. Our lab has previously established that Rolipram, a PDE4 inhibitor, causes anxiety thigmotaxis in zebrafish larvae. In this thesis we treated zebrafish larvae with Rolipram and other compounds modulating cAMP, which greatly increased the swimming activity, which was reversed by subsequently treating with PD0325901. To test if the pharmacological modulation of cAMP-levels through the inhibition of other PDEs would lead to increased locomotor activity, a small library of PDE inhibitors was screened, and 4 compounds were identified that caused an increase in locomotion – three of these compounds were PDE4-inhibitors. Finally, by using two behavioural assays, I found that in adult fish Rolipram cause anxiety-like phenotypes, which is also reversible by MAPK-inhibition.