Abstract
Similar to many marine teleost species, Atlantic cod undergo remarkable physiological changes during the early life stages with concurrent and profound changes in feeding biology and ecology. In contrast to the digestive system, very little is known about the ontogeny and the localization of the centers that control appetite and feed ingestion in the developing brain of fish. We examined the expression patterns of three appetite regulating factors (orexigenic: neuropeptide Y, NPY; prepro-orexin, pOX and anorexigenic: cocaine- and amphetamine-regulated transcript, CART) in discrete brain regions of developing Atlantic cod using chromogenic and double fluorescent in situ hybridization. Differential temporal and spatial expression patterns for each appetite regulator were found from first feeding (4 days post hatch; dph) to juvenile stage (76 dph). Neurons expressing NPY mRNA were detected in the telencephalon (highest expression), diencephalon, and optic tectum from 4 dph onward. CART mRNA expression had a wider distribution along the anterior-posterior brain axis, including both telencephalon and diencephalon from 4 dph. From 46 dph, CART transcripts were also detected in the olfactory bulb, region of the nucleus of medial longitudinal fascicle, optic tectum and midbrain tegmentum. At 4 and 20 dph, pOX mRNA expression was exclusively found in the preoptic region, but extended to the hypothalamus at 46 and 76 dph. Co-expression of both CART and pOX genes were also observed in several hypothalamic neurons throughout larval development. Our results show that both orexigenic and anorexigenic factors are present in the telencephalon, diencephalon and mesencephalon in cod larvae. The telencephalon mostly contains key factors of hunger control (NPY), while the diencephalon, and particularly the hypothalamus may have a more complex role in modulating the multifunctional control of appetite in this species. As the larvae develop, the overall progression in temporal and spatial complexity of NPY, CART and pOX mRNAs expression might be correlated to the maturation of appetite control regulation. These observations suggest that teleost larvae continue to develop the regulatory networks underlying appetite control after onset of exogenous feeding.
Highlights
Atlantic cod (Gadus morhua) has a key role in North Atlantic fisheries and several major attempts to introduce cod into aquaculture have occurred over the last decades [1, 2]
To increase our understanding of the gene distribution and putative roles of neuropeptides Neuropeptide Y (NPY), Cocaine- and amphetamine-regulated transcript (CART) and pOX in selected brain regions of Atlantic cod larvae, we examined their mRNA expression patterns in serial brain sections by using both chromogenic and dual fluorescent in situ hybridization methods
NPY transcripts were detected in the telencephalon, diencephalon and optic tectum from 4 dph and its distribution pattern varied between all stages
Summary
Atlantic cod (Gadus morhua) has a key role in North Atlantic fisheries and several major attempts to introduce cod into aquaculture have occurred over the last decades [1, 2]. At the onset of first feeding (4 dph), the larvae are 4–5 mm long and possess a simple and straight gut lumen. The intestine develops both in length and complexity including the development of elaborate folding of the mucosa layer. Larvae have been observed to continue to feed despite a full gut, especially just after onset of exogenous feeding [8] These observations raise the question whether appetite control ( satiety) and digestive processes are fully functional in early larval stages [8]. In the teleost fish investigated so far, the onset of pOX expression occurs at very early embryonic stages [15]. RT-PCR studies in Atlantic cod revealed pOX expression as early as cleavage stage [16]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
