OREXIN NEURORECEPTOR TRANSCRIPTIONAL RESPONSES FOLLOWING COPPER TOXICITY IN A MARINE TELEOST (THALASSOMA PAVO)

At date, a growing number of interests are focusing on the role of the orexin (ORX) system as crucial neuronal element involved with stressful conditions while little attention has been directed towards its implication during toxicity evoked by heavy metals above all in fish. On this basis, it was our purpose to evaluate if the previously shown behavioral alterations induced by two sublethal copper concentrations (CuCl2; 0,25 mg/L and 1,07 mg/L) after 48 hours are related to variations of ORX neuroreceptor (ORXR) transcriptional pattern in some brain areas of the marine teleost Thalassoma pavo. At the same time, ORXR expression were evaluated in some fish that were left to recover in Cu-free water. In situ hybridization analysis revealed up-regulatory effects in some encephalic areas such as the nucleus diffusus lobi inferioris that showed very great (p<0.001) and great (p<0.01) enhancements of mRNA levels after exposure to high (+142%) and low (+73%) Cu concentrations, respectively. Moreover, these treatments accounted for a moderate (p<0.05) down-regulation of ORXR transcription in the area ventralis telencephali, pars lateralis (-40%) of fish exposed to both concentrations while moderate decreases were detected in the optic tectum (-33%) only after the high CuCl2 concentration. After the permanence in Cu-free water most telencephalic sites supplied an inversion of their transcriptional pattern. Interestingly, amino cupric silver stain method showed that the above brain areas were heavily covered by neurodegeneration events, a condition that was reduced after the recovery period in only fish that received a low CuCl2 concentration. These results suggest, for the first time, an ORXR involvement during Cu-neurotoxicity as well as a great recovery capacity of the teleost brain that may lead to the understanding of adaptive neuronal mechanisms activated under stressful conditions.