THE NERVOUS SYSTEM OF THE PARASITE ACROLICHANUS AURICULATUS (TREMATODA: ALLOCREADIIDAE) OF ACIPENSERIDS: IMMUNOCYTOCHEMICAL ANALYSIS

The trematode Acrolichanus auriculatus is a widely distributed intestine parasite of acipenserides. In this research, the presence and localization of the serotonergic nerve elements of the parasite was studied using immunocytochemical technique and confocal laser scanning microscopy. Trematodes A. auriculatus isolated from sterlets were used. The helminths were fixed in paraformaldehyde in a phosphate buffer solution and then preserved in a phosphate buffered sucrose solution. The study revealed biogenic amine and serotonin in the central and peripheral parts of the A. auriculatus nervous system, namely, in neurons and neurites of the brain ganglia, the brain commissure, the longitudinal nerve trunks and the commissures connecting them. The musculature of the attachment organs, pharynx, esophagus, and distal regions of the reproductive system was found to be innervated by the serotonergic nerve elements. The comparative analysis of the results obtained for A. auriculatus and the data available in the literature for other trematodes found both conservative and distinctive features in the organization of the serotonergic nervous system in various trematode species. The differences involve the number and size of serotonergic neurons in the brain ganglia, the nerve trunks, and the body, as well as the distribution of transverse commissures that connect the nerve trunks.