Cocaine- and amphetamine-regulated transcript in perciforms II. Responsiveness to energetic shortage

Cocaine and amphetamine-regulated transcript (Cart) is a neuropeptide with prominent roles in appetite regulation and maintenance of energy homeostasis. Although Cart has been widely studied in vertebrates, its multigenic nature in fish elicits questions regarding the various functions affected by specific cart peptides. This is further emphasized when considering the high variation of aquatic ecosystems fish occupy. Nile tilapia (Oreochromis niloticus) and gilthead seabream (Sparus aurata) are important aquaculture species with different natural habitats, food preferences and feeding behaviors. Herein, we utilize these two species to evaluate whether food-related cart functions are species-specific. To this end, we studied how short-term (SD) or long-term (LD) food deprivation affects the central expression of the multiple cart genes of both species. Quantitative PCR analysis of cart expression demonstrated that SD resulted in decreased midbrain expression of three tilapia carts and three seabream carts while LD decreased the midbrain expression of two tilapia carts and two seabream carts. In addition, SD increased the expression of tilapia oncart1c in the anterior brain and oncart1c and oncart1b in the posterior brain while reducing the expression of seabream sacart1c. Our analyses showed that there are cart genes in each species (cart1a and cart1b for tilapia, and cart1b for seabream) that responded to both SD and LD by reduced expression in the midbrain. In addition, both conditions reduced the expression of seabream sacart1c in the posterior brain. Taken together, our current findings suggest that the major appetite regulation in each species is mediated by species-specific carts.