Differential distribution and energy status-dependent regulation of the four CART neuropeptide genes in the zebrafish brain.

The cocaine- and amphetamine-regulated transcript (CART) neuropeptide has been implicated in the neural regulation of energy homeostasis across vertebrate phyla. By using gene-specific in situ hybridization, we have mapped the distribution of the four CART mRNAs in the central nervous system of the adult zebrafish. The widespread neuronal expression pattern for CART 2 and 4 suggests a prominent role for the peptide in processing sensory information from diverse modalities including olfactory and visual inputs. In contrast, CART 1 and 3 have a much more restricted distribution, predominantly located in the nucleus of the medial longitudinal fasciculus (NMLF) and entopeduncular nucleus (EN), respectively. Enrichment of CART 2 and 4 in the preoptic and tuberal areas emphasizes the importance of CART in neuroendocrine functions. Starvation resulted in a significant decrease in CART-positive cells in the nucleus recessus lateralis (NRL) and nucleus lateralis tuberis (NLT) hypothalamic regions, suggesting a function in energy homeostasis for these neurons. Similarly, the EN emerges as a novel energy status-responsive region. Not only is there abundant and overlapping expression of CART 2, 3, and 4 in the EN, but also starvation induced a decrease in CART-expressing neurons in this region. The cellular resolution mapping of CART mRNA and the response of CART-expressing nuclei to starvation underscores the importance of CART neuropeptide in energy processing. Additionally, the regional and gene-specific responses to energy levels suggest a complex, interactive network whereby the four CART gene products may have nonredundant functions in energy homeostasis.