Different nematocytes have different synapses in the sea anemoneAiptasia pallida (Cnidaria, Anthozoa)

Abstract

Sea anemones feed by discharging nematocysts into their prey, but the pathway for control of nematocyst discharge is unknown. The purpose of this study was to investigate the ultrastructural evidence of neuro‐nematocyte synapses and to determine the types of synaptic vesicles present at different kinds of nematocyst‐containing cells. The tip and middle of tentacles from small specimens of Aiptasia pallida were prepared for electron microscopy and serial micrographs were examined. We found clear vesicles in synapses on mastigophore‐containing nematocytes and dense‐cored vesicles in synapses on basitrich‐containing nematocytes and on one cnidoblast with a developing nematocyst. In addition, we found reciprocal neuro‐neuronal and sequential neuro‐neuro‐nematocyte synapses in which dense‐cored vesicles were present. It was concluded that : (1) neuro‐nematocyte synapses are present in sea anemones, (2) different kinds of synaptic vesicles are present at cells containing different types of nematocysts, (3) synapses are present on cnidoblasts before the developing nematocyst can be identified and these synapses may have a trophic influence on nematocyst differentiation, and (4) both reciprocal and sequential synapses are present at the nematocyte, suggesting a complex pathway for neural control of nematocyst discharge. J. Morphol. 238:53–62, 1998. © 1998 Wiley‐Liss, Inc.

The behavioral and developmental physiology of nematocysts

“…In this regard, Westfall et al (1971b), Carré and Carré (1980), Hufnagel and Kass-Simon (1988), and Westfall (1988and Westfall ( , 1998 have presented ultrastructural evidence of nerves synapsing onto nematocytes. In Apiptasia pallida, colleagues (1998, 1999) present striking and detailed electron micrographs showing synapses on mastigophore and basitrich nematocytes, nematoblasts, and spiroctyes.…”

“…This view of nematocyst functioning has prevailed among many biologists over the years. However, there is a growing body of evidence that indicates that nematocytes are innervated and responsive to signals received and transduced elsewhere, in other parts of the animal (Ewer 1947;Ross and Sutton 1964;Hufnagel and Kass-Simon 1988;Kass-Simon 1988;Westfall 1988;Westfall et al 1998Westfall et al , 1999, which argues against the hypothesis and suggests that nematocyst behavior is at least modulated, if not completely controlled, by the nervous system.…”

Ultrastructural evidence for two‐cell and three‐cell neural pathways in the tentacle epidermis of the sea anemone Aiptasia pallida

“…Hence, it is easier to trace a sensory cell to its synapse on a spirocyte than to locate a sensory cell-nematocyte synapse. Although neuro-nematocyte synapses have been described previously in sea anemones, their cells of origin have not yet been identified (Westfall et al, 1998).…”

A molecular filter for the cnidarian stinging response

“…Considering in vivo cellular and discharge activity requires the presence of prey-derived chemicals with simultaneous mechanical stimulation, chemoreception may occur indirectly through functionally-coupled cells (Price and Anderson, 2006). Previous studies suggest the presence of synaptic connections between nematocytes and other unknown cell types (Westfall et al, 1998, Oliver et al, 2008. To test this possibility, we screened isolated nematocytes for responses to well-conserved neurotransmitters and found only acetylcholine (ACh) evoked large outward currents ( Fig.…”