Serotonin Signalling in Flatworms: An Immunocytochemical Localisation of 5-HT7 Type of Serotonin Receptors in Opisthorchis felineus and Hymenolepis diminuta

Abstract

The study is dedicated to the investigation of serotonin (5-hydroxytryptamine, 5-HT) and 5-HT7 type serotonin receptor of localisation in larvae of two parasitic flatworms Opisthorchis felineus (Rivolta, 1884) Blanchard, 1895 and Hymenolepis diminuta Rudolphi, 1819, performed using the immunocytochemical method and confocal laser scanning microscopy (CLSM). Using whole mount preparations and specific antibodies, a microscopic analysis of the spatial distribution of 5-HT7-immunoreactivity(-IR) was revealed in worm tissue. In metacercariae of O. felineus 5-HT7-IR was observed in the main nerve cords and in the head commissure connecting the head ganglia. The presence of 5-HT7-IR was also found in several structures located on the oral sucker. 5-HT7-IR was evident in the round glandular cells scattered throughout the larva body. In cysticercoids of H. diminuta immunostaining to 5-НТ7 was found in flame cells of the excretory system. Weak staining to 5-HT7 was observed along the longitudinal and transverse muscle fibres comprising the body wall and musculature of suckers, in thin longitudinal nerve cords and a connective commissure of the central nervous system. Available publications on serotonin action in flatworms and serotonin receptors identification were reviewed. Own results and the published data indicate that the muscular structures of flatworms are deeply supplied by 5-HT7-IR elements. It suggests that the 5-HT7 type receptor can mediate the serotonin action in the investigated species and is an important component of the flatworm motor control system. The study of the neurochemical basis of parasitic flatworms can play an important role in the solution of fundamental problems in early development of the nervous system and the evolution of neuronal signalling components.

Single-cell transcriptomics identifies a p21-activated kinase important for survival of the zoonotic parasiteFasciola hepatica

“…This pattern clearly fits the nature of invertebrate muscle fibers described above. Next to these structural molecules, we found expression of a gene coding for the 5-HT receptor 1 (D915_001848), (Fig 6 A), which is thought to be involved in the serotonin-dependent activation of muscle fibers in flatworms 56,57 , as well as other central regulators of cell signaling. Among these were protein kinase C, G-protein coupled receptors and phosholipase C, for which signaling in response to FMRFamides was previously suggested for Fasciola muscle fibers 58 .…”

Genome-Wide Identification of 5-HT Receptor Gene Family in Razor Clam Sinonovacula constricta and Their Circadian Rhythm Expression Analysis

“…5-hydroxytryptamine (5-HT), or serotonin, a kind of canonical neurotransmitter, can increase a delighted atmosphere and is therefore called "the hormone of happiness" along with dopamine and norepinephrine [1]. As neurotransmitters, neuromodulators and neurohormones, and ancient signaling molecules, 5-HT widely exists in the plant and animal kingdoms [2,3] and plays important roles in mood, appetite, sleep, sex and temperature regulation [4], which are required to be combined with specific 5-HT receptors (5-HTRs) located on the surface of cell membrane.…”

“…At present, 5-HT and its receptors have been identified in nematodes [11,12], flatworms [3], insects [13,14], mollusks [15,16] and so on. In flatworms, 5-HT7 was highly expressed in the muscle and nervous systems, which provided evidence for the subsequent research on neurodevelopment [1]. Due to the distinct functions of the various 5-HTRs, most studies have been focused on single receptors of 5-HT.…”