NO nerves in trematodes, too! NADPH-diaphorase activity in adult Fasciolopsis buski.

The free radical nitric oxide (NO) is a unique molecule with an avidity to react with other molecules and is known to function as a neuronal messenger. This nitrergic transmitter with diverse functions in signal transduction, being a gas, is not stored in synaptic vesicles but is generated in various neuronal cells by a family of nitric oxide synthases (NOSs). The NADPH-d histochemical reaction is regarded as a selective marker for NOS in the neuronal tissue. With histochemical detection of NADPH-d, the presence of NOS is demonstrated in the digenetic trematode, Fasciolopsis buski. Strong NADPH-d staining was observed in the neuronal cell bodies in the two cerebral ganglia, the brain commissure and the nerve fibers in the main nerve cords. NADPH-d staining was also detectable in the innervation of the pharynx, the cirrus sac and the ventral sucker besides being observable sporadically in the nerve tributaries in the general parenchyma. NO released by the whole worm kept in PBS at 37 degrees C could also be measured biochemically. The NOS activity was assayed in the whole worm homogenate and also in the tissue homogenate containing only the anterior pre-acetabular part of the parasite body. The presence of NOS in this digenean parasite confirms that a nitrergic innervation occurs in the trematode group also as in other groups of exclusively parasitic helminths and that NO represents an old signal molecule in evolutionary scale.