Electrical activity following cellular recognition of self and non-self in a sea anemone.

The sea anemone Anthopleura elegantissima lives in clonal colonies and possesses a cellular recognition system of remarkable specificity, by which it can recognize members of its own clone; other anemones, including individuals of the same species which are not syngeneic, are attacked. Attack is initiated by contact with a foreign anthozoan and involves the inflation of specialized tentacle-like structures known as acrorhagi, which contain numerous stinging cells. These stinging cells only discharge when the tip of the acrorhagus is in physical contact with the surface of a foreign anthozoan; contact with syngeneic individuals, organisms other than anthozoans and inanimate objects does not elicit discharge. We show here that the recognition of allogeneic tissue is accompanied by a novel form of local electrical activity in the acrorhagus that is usually, but not invariably, followed by nematocyst discharge. This type of electrical activity was not found during contact with syngeneic tissue or inanimate objects and seemed to be a consequence of the recognition of allogeneic surface markers by cells at the tip of the acrorhagus.

Colonial nervous control of lophophore retraction in cheilostome Bryozoa.

Nervous impulses causing lophophore retraction over large areas of Membranipora membranacea and Electra pilosa were recorded with external electrodes. The response propagates at about 100 centimeters per second, presumably through the colonial nerve plexus of Hiller and Lutaud. Impulses are rapid up to 200 per second. A second impulse was recorded from individual zooids, probably generated by the polypide's nervous system. The retractor muscle shortens at more than 20 times its own length per second and is apparently the most rapidly contracting muscle known.

Colonial conduction systems in the Anthozoa: Octocorallia.

1. The octocorals Alcyonium digitatum, Pennatula phosphorea and Virgularia mirabilis each have a through-conducting nerve net. The nerve net demonstrated electrophysiologically may well be the same as that previously shown by the use of histological techniques. 2. It exhibits both facilitation and defacilitation in the rate of conduction of pulses. 3. The distance of spread of nerve net activity is not limited by the number of stimuli applied. 4. The nerve net controls fast muscle contractions; the frequency of pulses is important in determining which muscles contract and in which sequence. 5. The nerve net is 'spontaneously' active. 6. A previously undescirbed slow system has been identified in Pennatula. It has many of the properties of slow systems in sea anemones and may well be ectodermal. It is suggested that multiple conduction systems are of common occurrence in the Anthozoa.

The transmission of impulses in the ectodermal slow conduction system of the sea anemone Calliactis parasitica (Couch).

1. The SS 1 fatigues in response to repetitive electrical stimulation. This fatigue is manifested by an increased conduction delay and a decreased SS 1 pulse amplitude. 2. Continued repetitive stimulation leads to the failure of the system. Recovery may take many seconds. Narrow strips of column fail more rapidly than wide strips. 3. The increased conduction delay is explained in terms of a decrease in the population of spiking cells. 4. A computer model is described and analysed. It suggests that conduction between electrically coupled ectoderm cells could be the basis for the SS1. The SS 1 may have properties not so far experimentally demonstrated; for example, under certain conditions it could behave as a local system.