Ultrastructure and functional versatility of hirudinean botryoidal tissue

In leeches, the botryoidal tissue is composed of two different cell types - granular botryoidal cells and flattened endothelial-like cells - localized in the loose connective tissue between the gut and the body wall sac. We h ave observed that the botryoidal tissue undergoes functional and structural modifications in response to the different needs arising during the life-c ycle of the animal. In healthy, untreated leeches, botryoidal cells are org anized in cords or clusters, sometimes surrounding few, small lacunae. Conv ersely, in wounded animals we have observed the transition of the botryoida l tissue from cluster/cord-like structures to a hollow/tubular architecture , typical of pre-vascular structures. We have documented in botryoidal cell cytoplasm the presence of large calci um storage. Moreover, the cytoplasm of botryoidal cells was filled with gra nules of different form and size, containing iron or melanin, as tested by classic histochemical methods. The presence of elements like iron and calci um was confirmed by the well-established EDS analysis. In response to a sur gical wound, botryoidal tissue cells changed their shape and formed new cap illary vessels. Concurrently, botryoidal cells secreted iron from cytoplasm ic granules into the new cavity: this secretory activity appeared to be rel ated to intracellular calcium fluctuations. At the end of the angiogenic pr ocess, botryoidal cells lost their contact with the basal lamina and moved freely in the circulating fluid towards the lesioned area. Interestingly, c irculating botryoidal cells were found to carry melanin in the wounded area . This function is probably involved in defense processes. Thus, we have shown that stimulated botryoidal tissue displays a variety of striking structural, secretory and defensive activities. (C) 2000 Harcourt Publishers Ltd.