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.
