Serotonergic elements in the nervous system of parasite of acipenserid fishes, Acrolichanus auriculatus (Digenea: Allocreadiidae)

The trematode Acrolichanus auriculatus is a widely distributed intestine parasite of acipenserid fishes. For the first time the localization and distribution of the serotonergic nerve elements in A. auriculatus was studied using immunocytochemical method and confocal laser scanning microscopy. The study revealed the presence of biogenic amine, serotonin, in the central and peripheral nervous systems of A. auriculatus, that is in the neurons and neurites of the brain ganglia, brain commissure, the longitudinal nerve cords, and the connective nerve commissures. The innervation of the attachment organs, pharynx, oesophagus and distal regions of the reproductive system by the serotonergic nerve elements is observed. The distribution of serotonergic neurons in A. auriculatus is schematically marked. The comparative analysis of findings obtained in A. auriculatus with those recorded for other digeneans reveals the presence of both conservative and distinctive features in the organization of the serotonergic nervous system in various representatives of trematodes.

Neuromuscular system of the causative agent of dicrocoeliosis, Dicrocoelium lanceatum. II. Neuropeptide FMRFamide immunoreactivity in nervous system

The parasitic flatworm, trematoda Dicrocoelium lanceatum or lancet fluke is the causative agent of a widespread parasite disease of grazing ruminants, dicrocoeliosis. The aim of this work is the study of the presence and localization of neuropeptide FMRFamide immunoreactive elements in the nervous system of D. lanceatum using immunocytochemical technique and confocal scanning laser microscopy. For the first time the data on the presence and distribution of the FMRFamide-immunopositive components in the central and peripheral departments of the nervous system of D. lanceatum has been obtained. FMRFamidergic neurons and neurites were identified in paired brain ganglia, in the brain commissure, longitudinal nerve cords and connective nerve commissures. The innervation of the oral and ventral suckers by peptidergic nerve structures was revealed. The distal part of the reproductive system is innervated by FMRFamide immunopositive neurites. The data obtained suggest that the neuropeptides of FMRFamide family can be involved in the regulation of functions of the attachment organs and the reproductive system in D. lanceatum. The study of neurotransmitters and their functions in flatworms expand our knowledge on the structure and function of the nervous system of trematodes of various taxonomic groups. The results obtained on the morphological organization of D. lanceatum nervous system support the exploitation of the FMRFamidergic components as an anthelmintic target.

Neuromuscular organization and haptoral armament of Polyclithrum ponticum (Monogenea: Gyrodactylidae)

Most gyrodactylids have a haptor armed with a pair of hamuli, two connecting bars and 16 marginal hooks. In some gyrodactylids, however, the haptor is disc-shaped and reinforced by additional sclerites. The genus Polyclithrum has arguably the most elaborate haptor in this group. This study aimed to gain better understanding of the anatomy of Polyclithrum by examining neuromusculature and haptoral armament of Polyclithrum ponticum, a species parasitizing Mugil cephalus in the Black Sea, with emphasis on haptoral sclerites and musculature in connection with host-attachment mechanisms. Musculature was stained by phalloidin, the nervous system by anti-serotonin and anti-FMRFamide antibodies, and haptoral sclerites were visualized in reflected light. The study provided new information on sclerites: in addition to previously described supplementary sclerites (A1-6), ear-shaped sclerites (ESSs) and two paired groups of ribs, reflected light revealed a rod-shaped process on the ESSs and a pair of small posterior sclerites. The sclerites were shown to be operated by 16 muscles, the most prominent of which were two transverse muscles connecting the hamular roots, three muscles attached to sclerite A2, the muscle fibres of anterior ribs and a set of extrinsic muscles. The nervous system consists of a pair of cerebral ganglia connected by a commissure and three pairs of nerve cords that unite in the haptor to form a loop between the opposite cords. The arrangement of sclerites and muscles suggests that Polyclithrum initiates the attachment by clamping a host's surface with longitudinally folded haptor and then secures its position with marginal hooks.

Neuromuscular system of the causative agent of dicrocoeliosis, Dicrocoelium lanceatum. I. 5-Hydroxytryptamine in the nervous system

The trematode Dicrocoelium lanceatum known as lancet fluke, is a causative agent of dicrocoeliosis, a widespread parasitic disease of the grazing ruminants. The investigation of the major neurotransmitters and their functions are an important step in the development of a new pharmacological strategy of the struggle against the dicrocoeliosis affecting the neuronal signal substances and the functions of its nervous system. The aim of this work was to study the presence and localization of the neurotransmitter serotonin (5-HT, 5-Hydroxytryptamine) in the nervous system of D. lanceatum using immunocytochemical technique and confocal laser scanning microscopy. For the first time the data on the presence and distribution of serotonin-immunopositive components in the central and peripheral compartments of the nervous system of D. lanceatum has been obtained. Serotonin-immunopositive neurons and neurites were identified in paired brain ganglia, in the brain commissure, longitudinal nerve cords and connective nerve commissures. The innervation of the oral and ventral suckers by serotonergic nerve structures was revealed. The distal part of the reproductive system and the region of the reproductive pore were intensively innervated by serotonergic neurites. Serotonin-immunopositive neurons and neurites were also revealed in the proximal region of the reproductive system. The data obtained suggest that the serotonergic nervous system is involved in the regulation of the attachment organs and the reproductive system functions in D. lanceatum. The new results on the morphological and functional organization of the D. lanceatum nervous system increase our knowledge of the structure and function of nervous system of trematodes of various taxonomic groups and support the possibility of the exploitation of the serotonergic system of the parasite as a target for anthelmintic drugs.

Musculature and neurotransmitters of internal organs of trematodes (the digestive, reproductive and excretory systems)

The article analyzes the results on the presence and organization of the muscle elements in the visceral organs of parasitic flatworms, trematodes, as well as their innervations. The different regions of the digestive, reproductive and excretory systems of trematodes contain circular, longitudinal and diagonal muscle fibers. The results of immunocytochemical investigations and confocal scanning laser microscopy show the presence of serotonin and FMRFamide-like immunoreactivity in the nervous system elements in various parts of the digestive, reproductive and excretory systems of trematodes. The data suggest that serotonergic and FMRFamide-immunopositive components of parasite's nervous system are involved in the regulation of the muscle activity of the digestive, reproductive and excretory systems. Comparative analysis of the results presented for trematodes from different taxonomic groups indicates that the organization of muscle elements in the visceral organs in trematodes and their innervation by serotonergic and peptidergic components are highly conserved.