Vom nervensystem der ctenophoren

Heider, Karl G.

doi:10.1007/bf00408582

Cited by 16 publications

(9 citation statements)

References 11 publications

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“…Classical light microscopic methods such as vital staining with methylene blue and silver impregnation revealed a branching polygonal lattice on the body surface of ctenophores, called the ectodermal or subepithelial nerve net (Hertwig ; Bethe ; Heider ,; Korn ; Hernandez‐Nicaise ,b, ). However, classic nerve stains are notoriously unreliable when applied to ctenophores, and can stain comb plate cells, muscles, intracellular fibrils, spaces between cells and other non‐nervous structures (Horridge & Mackay ; Horridge ).…”

Section: Integrative Pathwaysmentioning

confidence: 99%

Cilia and the life of ctenophores

Tamm

2014

Invertebrate Biology

112

189

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Section: Integrative Pathwaysmentioning

confidence: 99%

Cilia and the life of ctenophores

Tamm

2014

Invertebrate Biology

112

189

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“…These studies were extended using Methylene Blue vital staining and silver impregnation (Bethe, 1895;Heider, 1927a;Heider, 1927b;Korn, 1959) but with only moderate success. In fact, ctenophore neurons are very elusive cells to stain with convenient histological dyes.…”

Section: Neural Systems In Ctenophoresmentioning

confidence: 99%

“…Although nerve cells in ctenophores were initially described more than 130 years ago , some follow up studies were unable to demonstrate even the existence of a nervous system in ctenophores (Samassa, 1892). For nearly a century, the only way to map neurons was vital staining with Methylene Blue and silver impregnation with Golgi stains (Bethe, 1895;Heider, 1927a;Heider, 1927b;HernandezNicaise, 1973a). The majority of described neuronal cell bodies and their processes form a polygonal lattice on the body surface known as a subepidermal nerve net (Fig.…”

Section: Enigmatic Ctenophore Neuronsmentioning

confidence: 99%

Convergent evolution of neural systems in ctenophores

Moroz

2015

Journal of Experimental Biology

121

139

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Neurons are defined as polarized secretory cells specializing in directional propagation of electrical signals leading to the release of extracellular messengers -features that enable them to transmit information, primarily chemical in nature, beyond their immediate neighbors without affecting all intervening cells en route. Multiple origins of neurons and synapses from different classes of ancestral secretory cells might have occurred more than once during ~600 million years of animal evolution with independent events of nervous system centralization from a common bilaterian/cnidarian ancestor without the bona fide central nervous system. Ctenophores, or comb jellies, represent an example of extensive parallel evolution in neural systems. First, recent genome analyses place ctenophores as a sister group to other animals. Second, ctenophores have a smaller complement of pan-animal genes controlling canonical neurogenic, synaptic, muscle and immune systems, and developmental pathways than most other metazoans. However, comb jellies are carnivorous marine animals with a complex neuromuscular organization and sophisticated patterns of behavior. To sustain these functions, they have evolved a number of unique molecular innovations supporting the hypothesis of massive homoplasies in the organization of integrative and locomotory systems. Third, many bilaterian/cnidarian neuron-specific genes and 'classical' neurotransmitter pathways are either absent or, if present, not expressed in ctenophore neurons (e.g. the bilaterian/cnidarian neurotransmitter, γ-amino butyric acid or GABA, is localized in muscles and presumed bilaterian neuronspecific RNA-binding protein Elav is found in non-neuronal cells). Finally, metabolomic and pharmacological data failed to detect either the presence or any physiological action of serotonin, dopamine, noradrenaline, adrenaline, octopamine, acetylcholine or histamineconsistent with the hypothesis that ctenophore neural systems evolved independently from those in other animals. Glutamate and a diverse range of secretory peptides are first candidates for ctenophore neurotransmitters. Nevertheless, it is expected that other classes of signal and neurogenic molecules would be discovered in ctenophores as the next step to decipher one of the most distinct types of neural organization in the animal kingdom.

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“…The reason why the bridge was not described by previous investigators (Chun, 1880;Hertwig, 1880;Heider, 1927;Horridge, 1965;Hernandez-Nicaise, 1991), including ourselves (Tamm, 1982), is probably due to tissue geometry. The refractile statolith completely masks the underlying bridge in views of the apical organ from the aboral surface of the animal.…”

Section: Discussionmentioning

confidence: 75%

Novel bridge of axon‐like processes of epithelial cells in the aboral sense organ of ctenophores

Tamm

2002

Journal of Morphology

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We describe by light and electron microscopy a novel structure in the aboral sense organ (apical organ) of cydippid (Pleurobrachia) and lobate (Mnemiopsis) ctenophores. An elevated bundle of long, thin, microtubule-filled processes arises from the apical ends of two groups of epithelial cells located on opposite sides of the apical organ along the tentacular plane of the body. This bundle of axon-like processes arches over the epithelial floor like a bridge, with branches at both ends running toward opposing pairs of ciliary balancers that are motile pacemakers for the rows of locomotory ciliary comb plates. The bridge in Pleurobrachia is ϳ40 m long and 3-4 m wide and consists of ϳ60 closely packed processes, 0.2-0.8 m thick, containing vesicles and numerous microtubules running parallel to their long axes. There are ϳ30 epithelial cells in each of the two groups giving rise to the bridge and each cell forms a single process, so roughly half of the processes in the bridge must originate from cells on one side and diverge into branches to a pair of balancers on the opposite side of the apical organ. The 150 -200 cilia in each balancer arise from morphologically complex cellular projections with asymmetric lateral extensions directed towards a fork of the bridge. Presynaptic triad structures and vesicles are found in this region but clear examples of synaptic contacts between bridge processes and balancer cells have not yet been traced. Cydippid larvae of Mnemiopsis have a conspicuous bridge along the tentacular plane of the apical organ. Beroid ctenophores that lack tentacles at all stages do not have a bridge. We discuss the possibility that the bridge is an electrical conduction pathway to balancers that coordinates tentacle-evoked swimming responses of ctenophores, such as global ciliary excitation.

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Vom nervensystem der ctenophoren

Cited by 16 publications

References 11 publications

Cilia and the life of ctenophores

Cilia and the life of ctenophores

Convergent evolution of neural systems in ctenophores

Novel bridge of axon‐like processes of epithelial cells in the aboral sense organ of ctenophores

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