Serotonin-immunoreactive neural system and contractile system in the hydroid Cladonema (Cnidaria, Hydrozoa)

Abstract

Serotonin is a widespread neurotransmitter which is present in almost all animal phyla including lower metazoans such as Cnidaria. Serotonin detected in the polyps of several cnidarian species participates in the functioning of a neural system. It was suggested that serotonin coordinates polyp behavior. For example, serotonin may be involved in muscle contraction and/or cnidocyte discharge. However, the role of serotonin in cnidarians is not revealed completely yet. The aim of this study was to investigate the neural system of Cladonema radiatum polyps. We detected the net of serotonin-positive processes within the whole hydranth body using anti-serotonin antibodies. The hypostome and tentacles had denser neural net in comparison with the gastric region. Electron microscopy revealed muscle processes throughout the hydranth body. Neural processes with specific vesicles and neurotubules in their cytoplasm were also shown at an ultrastructural level. This work demonstrates the structure of serotonin-positive neural system and smooth muscle layer in C. radiatum hydranths.

Atlas of the neuromuscular system in the Trachymedusa Aglantha digitale: Insights from the advanced hydrozoan

“…In contrast to other hydrozoans, where 5-HT-IR is reported both in planulae and polyps (Mayorova & Kosevich, 2013;Zega, Pennati, Fanzago, & De Bernardi, 2007), we did not detect serotonin (5-HT) immunoreactivity in Aglantha. It suggests the secondarily loss of this transmitter in the lineage leading to Aglantha.…”

The genetic factors of bilaterian evolution

“…Specifically, robust clustering results and HMM-HMM comparisons place the origin of monoamine neurotransmitter receptors for serotonin, adrenaline, and dopamine to the bilaterian root ( Supplementary file 1 –Supplementary Table 17, Supplementary file 1 –Supplementary Table 18), in line with a recent publication that dated back the evolutionary history of adrenergic signalling to the bilaterian ancestor ( Bauknecht and Jékely, 2017 ). Histochemical, biochemical, and functional data are in conflict with this finding and argue for the presence of serotonin, dopamine, and other small molecule neurotransmitters in cnidarians, the bilaterian sister group ( Carlberg and Anctil, 1993 ; Kass-Simon and Pierobon, 2007 ; Mayorova and Kosevich, 2013 ). However, receptors for these molecules could not be identified unambiguously in cnidarians ( Anctil, 2009 ; Bosch et al, 2017 ), maintaining the possibility that they indeed constitute bilaterian innovations.…”

Neural versus alternative integrative systems: molecular insights into origins of neurotransmitters

“…Ctenophores [185], sponges [66,[186][187][188][189][190][191], placozoans and cnidarians [192][193][194][195][196][197][198][199][200][201][202][203][204][205][206][207][208][209][210] might synthesize additional catecholamines and indolamines, but their locations and potential transmitter functions should be subject to careful investigations. There are several, mostly early, reports for the presence of serotonin, dopamine and noradrenaline in cnidarians [197,200,[211][212][213][214][215][216][217][218][219][220], but it was not consistent with genomic data about predicted synthetic enzymes [176,177,179]. Although some gene royalsocietypublishing.org/journal/rstb Phil.…”