The effects of okadaic acid on Enchytraeus crypticus (Annelida: Oligochaeta)

We describe the morpho-functional effects of different concentrations of okadaic acid (OA) on specimens of Enchytraeus crypticus. The results demonstrate that this experimental model is very sensitive to the treatment and presents time- and dose-related effects mainly involving an immune response associated with a reaction in the chloragogenous tissue. At the lower dose (100 nM), the main organs do not appear particularly affected except for a swelling of the coelomatic cavity and an increased number of circulating coelomocytes. At the higher dose (200 nM), the chloragogenous tissue extends in volume to occupy the body cavity almost completely, while the circulating amoebocytes and chloragocytic cells undergo conformational changes. At the highest OA dose (400 nM), there is a general cell suffering in the main animal organs. In control animals, the immunocytochemical reaction with anti-IL-6 antibody is positive in neuron cell bodies and fibres from the ventral nerve cord and in circulating amoebocytes. Following OA treatment, fewer immunoreactive cells are seen in the damaged nervous tissue, and the high number of recruited amoebocytes is also positive.