Neuromodulatory Circuits of Feeding Drive

Abstract

Neural circuits of innate behaviors which are necessary for survival are redundant and hardwired as they are shaped by selective pressure. However, functional organization of these circuits is poorly understood. Here we focus on Cocaine- and Amphetamine- Regulated Transcript (CART) neural circuitry in regulation of feeding drive. Using gene specific, in situ hybridization, we have mapped the expression pattern of the four CART genes in the adult zebrafish brain. CART 2 and 4 were expressed in many regions involved in sensory processing, neuroendocrine regulation, and motor control while CART 1 and 3 showed restricted expression in nucleus of the medial longitudinal fasciculus (NMLF) and in the entopeduncular nucleus (EN) respectively. We have identified CART expressing neuronal groups which respond to changes in energy levels. In hypothalamus, upon starvation, CART 2 expression in the nucleus recessus lateralis (NRL) was completely abolished and CART 4 expression was reduced in the nucleus lateralis tuberis (NLT) suggesting their important role in energy homeostasis. EN in telencephalon emerges as a novel non-hypothalamic nucleus involved in energy homoeostasis as CART 2 expression was significantly reduced upon starvation. These nuclei could serve as an entry point for circuit specific investigation of feeding behavior. To that end we have optimized a high throughput behavioral assay to quantify feeding behavior in zebrafish larvae using fluorescently labeled paramecia. Energy homoeostasis may modulate olfactory sensitivity towards food related odorants. We have optimized electro-olfactogram (EOG) for zebrafish and our preliminary data suggests an increased olfactory sensitivity in starved fish.