MORPHOLOGICAL AND FUNCTIONAL ANALYSIS OF THE NEURONAL MELANOCORTIN CIRCUITRY

To enable the effective treatment of patients with obesity and metabolic disorders, it is essential to elucidate the mechanisms of this system. Our aim is to determine how melanocortin neurons are modulated by nutritional state and to identify the connected neural networks. The melanocortin system is composed of two principal neuronal populations, pomc- and agrp-expressing neurons. pomc-expressing neurons signal via melanocortin receptor-expressing cells, thereby suppressing feeding behaviour and promoting energy expenditure. In contrast, agrp-expressing neurons exert opposing effects and stimulate feeding behaviour. Because the melanocortin system is evolutionarily conserved between mammals and fish, we employ zebrafish larvae as a model organism. These larvae are optically transparent and therefore well suited for microscopic experimentation. In zebrafish, an additional whole genome duplication has generated paralogues of genes relevant to melanocortin circuitry. In this project, we seek to assess the morphology, expression levels, projection targets, and synaptic partners of melanocortin neurons in order to define their functional roles. Building on previous work from our laboratory and a single-cell projectome generated through microinjections in zebrafish larvae, we know that pomca neurons frequently project to sensory regions such as the optic tectum and the olfactory bulbs. The Torus Semicircularis, a centre for mechanosensory processing, also receives input from pomca-cells. By combining hybridisation chain reaction (HCR) with transgenic lines generated using CRISPR–Cas9 knock-in strategies, we can characterise axonal morphology and melanocortin receptor expression. Functional analyses will be performed using in vivo calcium imaging and behavioural paradigms to elucidate pomca neuron function within the Torus Semicircularis.