Acetylcholinesterase activity in juvenile Ciona intestinalis (Ascidiacea, Urochordata) after exposure to tributyltin

The acetylcholinesterase (AChE) activity has been studied in 4-day post-fertilization juveniles of Ciona intestinalis exposed to tributyltin (TBT) at 10(-5) M using the histochemical method of Karnovsky and Roots. Relative to vertebrate tissues and organs, the development of adult form of ascidians is interesting, because the analysis of many nuclear genes indicated that the ascidians are the closest living relatives of the vertebrates. Therefore, toxicity research using different approaches could provide data for comparative studies with vertebrates. AChE is over-expressed under chemical stress and in some diseases of vertebrates. Therefore, AChE is considered a biomarker of environmental contamination. Recently, we showed that eggs and embryos of ascidians over-express AChE activity after TBT exposure. Thus, the aim of the present study is to extend our previous findings by evaluating the effects of TBT on AChE activity in the embryos of this chordate and their suitability as good materials for comparative ecotoxicological studies. Our results demonstrate an increased expression of AChE activity in nervous-, blood progenitors- and tunic cells. The specific AChE inhibitor, BW284C51, inhibited this enzymatic activity. The presence of AChE activity in these cells has no obvious relations to their classical functions and seems to show a behavior similar to that of other chordates under changing stimuli. These preliminary descriptions provide a basis for further studies on cellular and molecular mechanism underlying the development of adult organs and tissues of this chordate, under chemical and physiological stress conditions.