Chemosensory pathways in the capitate tentacles of the hydroid Cladonema

Abstract

The introduction of an extract of Artemia into the sea water bathing tentacles from the hydroid Cladonema triggers a burst of electrical activity that can be recorded intracellularly from cnidocytes in the capitate tentacles. These bursts, which are composed of a variety of events, including action potentials and EPSPs, are Ca2+ dependent, and are abolished by pretreatment with NiCl2, suggesting that voltage-gated Ca2+ channels are involved in their generation or transmission. Intracellular injection of Lucifer Yellow and recordings from pairs of cnidocytes reveal that the cnidocytes are electrically coupled to one another, but that they are not uncoupled by heptanol. The role of these chemosensory pathways in priming the cnidocytes for discharge is discussed.

Hydrozoan nematocytes send and receive synaptic signals induced by mechano-chemical stimuli

“…However, chemical stimuli have been known to change the sensitivity of nematocytes via distinct chemoreceptor cells in anthozoans (Pantin, 1942;Watson and Hessinger, 1989), suggesting intercellular communication. More recently, electrical responses have been recorded in hydrozoan nematocytes in response to watersoluble chemical stimuli and these responses were proposed to be postsynaptic (Purcell and Anderson, 1995;Price and Anderson, 2006). Similarly, we have observed that mechanical stimulation of cnidocils induces electrical responses in neighbouring nematocytes (Brinkmann, 1994;Brinkmann et al, 1995;Thurm et al, 1998b;Thurm et al, 2004), suggestive of synaptic signalling between nematocytes.…”

“…(2) T-potentials: the time course and occurrence is comparable with those of action potentials as they have stereotyped impulse-like waveforms with a variable number and frequency of repetitions. Are T-potentials actually action potentials as Price and Anderson (Price and Anderson, 2006) proposed for T-potential-like responses of Cladonema, a capitate hydroid closely related to the species examined in this study? Their 'Class I' and 'Class II' potentials were induced in nematocytes by water-borne chemosensory stimulation of the isolated tentacle.…”

Cloning and functional expression of voltage-gated ion channel subunits from cnidocytes of the Portuguese Man O'War Physalia physalis

“…There was no significant difference in the rate of inactivation under the two conditions. pathway composed of sensory cells (Holtmann and Thurm, 2001;Westfall, 2004), neurons (Kass-Simon andScappaticci, Jr, 2004;Price and Anderson, 2006) and in some instances, supporting cells (Watson and Roberts, 1995). One consequence of the fact that multiple cell types are involved in the regulation of discharge has been the challenge of localizing the site of action of some experimental manipulations.…”

“…Previous work with cnidocytes in the tentacles of Physalia showed that cnidocytes impaled with microelectrodes will not discharge in response to intracellular current injection (Anderson and McKay,1987), implying that discharge does not involve any voltage-dependent phenomena. Furthermore, cnidocytes isolated from the hydroid Cladonema have been shown to produce action potentials (Anderson and McKay, 1987;Price and Anderson, 2006), yet neither those action potentials, nor imposed changes in membrane potential, both of which would be expected to activate any endogenous voltage-gated Ca 2+ channels, trigger discharge. It is, of course, possible that the presence of the microelectrode or the isolation procedure may have compromised the cells' abilities to discharge, but it is also possible that the Ca 2+ channels reported here may play other roles.…”

“…However, although neurons are not always required for cnidocyte discharge (Aerne et al, 1991), cnidocytes are innervated by peptidergic (Anderson et al, 2004) and other classes of neuron (Kass-Simon and Scappaticci, Jr, 2004). Consequently, the effects of Ca 2+ -free media and Ca 2+ channel blockers could be manifest through their block of synaptic activity within the nerve nets that surround cnidocytes (Anderson et al, 2004;Price and Anderson, 2006), or at the level of synapses onto the cnidocytes themselves.…”