Role of the orexinergic system on lead-induced neuronal and behavioral alterations in a marine teleost.

Lead (Pb) is one of the most dangerous pollutants leading to abnormal motor performances in aquatic vertebrates. At date, information regarding the role of Pb neurotoxicity on some neuronal complexes such as the orexinergic (ORX) system, which are involved with the control of some vital physiological activities is still lacking. In order to evaluate behavioral effects of Pb on cross-talking with the ORX neuroreceptor system, food-seeking and swimming behaviors were monitored in ornate wrasses (Thalassoma pavo) exposed for 96 h to Pb Maximum Acceptable Toxicant (MAT) concentrations (1.6 mg/L) +/- intraperitoneal administrations of the most effective ORX-A dose (100 ng/g BW) with respect to controls (NaCl 0.9%). Behavioral analyses revealed that ORX-A caused moderate reductions (p<0.05) of Pb-induced hyperactivities and very great enhancements (p<0.001) of the time spent in feeding maneuvers, so completely inverting Pb anorexigenic effects. When we checked for possible behavioral correlations with ORX receptor mRNA expression, in situ hybridization analyses displayed very great and great (p<0.01) up-regulations of ORX receptor transcription in most Pb-exposed fish brain areas such as the optic tectum (+90%) and nucleus of the lateral recess (+69%) respectively, a trend that was significantly reduced in ORX-A-treated fish. Conversely, the evident neurodegenerative signs revealed by amino cupric silver stains in Pb-exposed fish were not reduced by ORX-A co-treatments. Overall, our results suggest for the first time a pivotal neuroprotective role of the ORXergic system against lead-dependent transcriptional and behavioral alterations despite its lack of protection on neurodegenerative events in the ornate wrasse.