Specific cerebral heat shock proteins and histamine receptor cross-talking mechanisms promote distinct lead-dependent neurotoxic responses in teleosts

Recent interests are beginning to be directed towards toxic neurobiological dysfunctions caused by lead (Pb) in aquatic vertebrates. In the present work, treatment with a maximum acceptable toxic concentration of this heavy metal was responsible for highly significant (pb0.01) abnormal motor behaviors such as hyperactive movements in the teleost Thalassoma pavo and the same treatment accounted for significantly (pb0.05) enhanced hyperventilating states. On the other hand, greater abnormal motor behaviors were detected in the presence of the histamine (HA) receptor subtype 2 (H2R) antagonist cimetidine (Cim), as shown by the very robust (pb0.001) increases of the two behavioral states. Interestingly, elevated expression levels of stress-related factors, i.e. heat shock protein70/90 (HSP90/70) orthologs were reported for the first time in hypothalamic and mesencephalicareas of Pb-treated teleosts. In particular, an up- regulation of HSP70 was readily detected when this heavy metal was given concomitantly with Cim,while the histamine subtype 3 antagonist (H3R) thioperamide (Thio), instead, blocked Pb-dependent up-regulatory trends of both chaperones inmostly hypothalamic areas. Moreover, intense neuronal damages of the above brain regions coincided with altered expressions of HSP70 and HSP90 when treated only with Cim. Overall these first results show that distinct HnR are able to exert a net neuroprotective role arising from their interactionwith chaperones in fish exposed to Pb-dependent stressful conditions making this a potentially key interaction especially for T. pavo, aquatic specieswhich plays an important ecological role towards the survival of other commercially vital fishes.