Corticotropin-releasing factor and neuropeptide Y mRNA levels are elevated in the preoptic area of socially subordinate rainbow trout.

The objectives of this study were to characterize rainbow trout (Oncorhynchus mykiss) corticotropin-releasing factor (CRF) and neuropeptide Y (NPY) cDNAs and to determine their mRNA levels in response to social stress. Standard cloning techniques were used to obtain cDNAs, sequences for trout NPY and two CRF isoforms. At the predicted amino acid level, our NPY sequence differs from the trout amino acid sequence reported by. A phylogenetic analysis suggests that the two CRF isoforms result from a gene duplication that occurred in a common ancestor of salmonids. A tissue distribution demonstrated that the mRNAs of both CRF isoforms are predominantly present in the preoptic area of the trout brain, whereas NPY mRNA is more abundant in the telencephalon. Pairs of sized-matched juvenile female trout were allowed to interact for 72 h and social ranks were assigned on the basis of behavioural observations. Mean plasma cortisol levels were 13-fold higher in subordinate than in dominant trout. As measured by ribonuclease protection assay, CRF1 and NPY mRNA levels were respectively 51 and 32% higher in the preoptic area of subordinate trout; in addition, CRF1 and NPY mRNA levels were positively correlated (R2=0.44). These results suggest that subordinate rainbow trout chronically maintain high levels of CRF mRNA during social stress and that NPY may be involved in the control of the stress axis in trout.