Objectives: 

In mammals, there are pharmacologic and anatomical studies that show a link between serotonin (5-HT) and neuropeptide Y (NPY) involved in the acute regulation of feeding and energy homeostasis. Given that the actions of 5-HT and NPY on fish food intake are similar to those observed in mammals, the objective of this work was to characterize a possible short-term interaction between hypothalamic 5-HT and NPY, examining whether 5-HT regulates NPY gene expression in the hypothalamus and so trying to define part of the mechanism underlying the observed anorexigenic action of central 5-HT in the rainbow trout.

Materials: 

We examined the levels of NPY mRNA in the hypothalamus-preoptic area (HPA) using real-time RT-PCR after intraperitoneal injection (i.p.) of a single dose of dexfenfluramine (dFF, 3mg/kg) or intracerebroventricular (i.c.v.) administration of 5-HT (100 ug/kg). Three experimental groups were established: i) fed fish treated with dFF, ii) 24h fasted fish treated with dFF and iii) 24h fasted fish injected with 5-HT. Beta-actin gene was used as housekeeping gene after being validated as reference gene. In order to differentiate the effect over the NPY gene expression of the drug treatment and the RNA extraction procedure, a nested or hierarchical experimental design was performed. Relative comparison of Ct´s was performed through a nested ANOVA and by a Mann-Whitney and Kolmoronov-Smirnov non-parametrical tests.

Results: 

No significant changes in NPY gene expression were obtained 150 min after 5-HT (i.c.v.) or dexfenfluramine (i.p.) administration.

Conclusions: 

The results lead us to conclude that the anorexigenic mechanism of serotonin is not mediated by NPY neurons of the hypothalamus-preoptic area in rainbow trout.