Suspected chemoreceptors in coelenterates and ctenophores

Kass-Simon, G.; Hufnagel, Linda A.

doi:10.1002/jemt.1070220305

Cited by 27 publications

(12 citation statements)

References 85 publications

(161 reference statements)

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“…This neurosensory ectoderm thus functionally corresponds to a ganglion-associated sensory organ of a higher animal. A comparable situation has been reported for the subunits of the tentacles of Hydra, the battery cell complexes (Hufnagel et al, 1985;Kass-Simon and Hufnagel, 1992).…”

supporting

confidence: 59%

Mono‐ and oligo‐vesicular synapses and their connectivity in a Cnidarian sensory epithelium (Coryne tubulosa)

Holtmann

Thurm

2001

J of Comparative Neurology

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The spherical end-knobs of the tentacles of capitate hydropolyps are an evolutionarily early paradigm of a chemo- and mechanosensory epithelium composed of four types of sensory cells and one type of chemo-mechanosensitive nematocytes (stinging cells), all separated by supporting cells. The epithelium discriminates sites and compositions of stimuli and induces various kinds of behavior. Recent electrophysiological studies demonstrated rapid chemo-synaptic signal transmission of nematocytes and mechanosensory hair cells, graded in amplitude and duration. The present electron microscopic work, applying serial sectioning, analyses the ultrastructural basis of signal transmission and efference control in the tentacular spheres of Coryne tubulosa, a species also used in preceding studies. Neurites of sensory cells and of proximal ganglion cells constitute a nerve plexus at the base of the ectodermal cells. No ganglion cells are located within the spheres. Chemical synapses of the usual configuration connect neurites or are efferent to nematocytes and hair cells. Each of these synapses contains only 3-10 clear and/or dense-core vesicles of 70-150 nm diameter (oligo-vesicular synapses). For the graded afferent signal transmission of nematocytes and hair cells, the only candidates are regularly occurring zones of neurite contacts at the base of these cells. At their presynaptic side, mostly one (more seldom two to four) large vesicles (160-1100-nm-diameter magno-vesicles) are attached to a surface membrane density. In order to reconcile structural and functional data, a transient fusion and partial depletion of stationary vesicles is considered for the release of transmitter in mono-vesicular synapses, similar to recent findings for vertebrate endocrine secretion. The same principle is discussed for the usual oligo-vesicular synapses of Cnidaria.

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supporting

confidence: 59%

Mono‐ and oligo‐vesicular synapses and their connectivity in a Cnidarian sensory epithelium (Coryne tubulosa)

Holtmann

Thurm

2001

J of Comparative Neurology

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“…To designate the recognized signal as mucus-specific, homogenized trout muscle tissue was offered. This substrate caused relatively low discharge rates even at very high concentrations (Table 1 ( cercariae (reviewed by Haas and Haberl, 1997 ;Haas, 2003 -Simon and Hufnagel, 1992).…”

Section: Methodsmentioning

confidence: 99%

Polar filament discharge of Myxobolus cerebralis actinospores is triggered by combined non-specific mechanical and chemical cues

Kallert

El‐Matbouli²,

Haas

2005

Parasitology

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S U M M A R YThis study presents initial evidence for the requirement of both chemical and mechanical stimuli to discharge polar capsules of Myxobolus cerebralis actinospores, the causative agent of salmonid whirling disease. The obligate need for combined discharge triggers was concluded from data obtained in a before/after experimental set-up carried out with individual locally immobilized actinospores. Homogenized rainbow trout mucus as chemostimulus and tangency of the apical region of the spores to achieve mechanical stimulation were applied subsequently. The actinospores showed discharged polar filaments exclusively when mucus substrate application was followed by touching the polar capsule-bearing region, but not when either stimulus was offered solely to the same individuals. We measured filament discharge rates to mucus preparations in a microscopic assay using supplementary vibration stimuli to ensure mechanical excitation. The actinospores responded similarly to different frequencies, which suggested a touch-sensitive recognition mechanism. Discharge specificity for salmonid mucus could not be confirmed, as mucus of common carp and bream could trigger similar filament expulsion rates. To a lesser extent homogenized frog epidermis and bovine submaxillary mucin could also stimulate the attachment reaction. In contrast, mucus of a pulmonate freshwater snail elicited no response.

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“…Sensory cells carrying a recessed cilium not associated with microvilli have been described for several Hydrozoa (Jha and Mackie, 1967;Weis et al, 1985;Thomas et al, 1987). They are most plausibly considered chemoreceptive (Kass-Simon and Hufnagel, 1992). The organization of the vesicle-rich cells of C. tubulosa is consistent with a chemoreceptive function for water-soluble substances; the cuticle covering the ciliary cavity is known to be permeable for substances up to small peptides (Brinkmann, 1994).…”

Section: Sensory Featuresmentioning

confidence: 91%

Variations of concentric hair cells in a Cnidarian sensory epithelium (Coryne tubulosa)

Holtmann

Thurm

2001

J of Comparative Neurology

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In capitate hydropolyps, the spherical end-knobs of the short tentacles present an exceptional concentration of sensory functions in one of the evolutionarily oldest nervous systems. The tentacular spheres are the basis of sensation and discrimination of objects and of capturing of prey-objects by the discharge of nematocytes (stinging cells). Recent electrophysiological studies of the spheres revealed combined chemo/mechanosensory functioning of the nematocytes and mechanosensitivity of further types of cells. The present electron microscopical study made use of the small size of the spheres of Coryne tubulosa to characterize all cells of some spheres. Five types of ectodermal cells were found to have sensory structural features and to be separated by or enclosed in supporting cells: 1) nematocytes of the stenotele type; 2) short and 3) long ciliated concentric hair cells, which carry a cilium-stereovilli bundle, similar to the cnidocil apparatus of nematocytes; 4) cells having a recessed cilium-microvilli complex equipped with a thick cell-traversing rootlet (rootlet cells); and 5) cells having a recessed short cilium with no microvilli and only a short rootlet and containing, apically as well as basally, aggregations of dense-core vesicles (vesicle-rich cells). Types 1-4 vary the configuration of a concentric cilium-microvilli complex (variations of a concentric hair bundle) and were demonstrated or inferred to be mechanosensitive. Apical exocytotic activity, which is well known for the nematocytes (discharge of their cnidocyst), is indicated by ultrastructure for the nematocyte-resembling concentric hair cells and for the vesicle-rich cells. The tentacular spheres are considered an early paradigm of a sensory epithelium. Its synaptic structures and extensive connectivity are the subject of a subsequent paper.

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Suspected chemoreceptors in coelenterates and ctenophores

Cited by 27 publications

References 85 publications

Mono‐ and oligo‐vesicular synapses and their connectivity in a Cnidarian sensory epithelium (Coryne tubulosa)

Mono‐ and oligo‐vesicular synapses and their connectivity in a Cnidarian sensory epithelium (Coryne tubulosa)

Polar filament discharge of Myxobolus cerebralis actinospores is triggered by combined non-specific mechanical and chemical cues

Variations of concentric hair cells in a Cnidarian sensory epithelium (Coryne tubulosa)

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