Long-Term Facilitation in a Swimming Sea Anemone

DONALD M. WILSON

doi:10.1242/jeb.36.3.526

Long-Term Facilitation in a Swimming Sea Anemone

Journal of Experimental Biology ◽

10.1242/jeb.36.3.526 ◽

1959 ◽

Vol 36 (3) ◽

pp. 526-532

Author(s):

DONALD M. WILSON

Keyword(s):

Sea Anemone ◽

Experimental Techniques ◽

Frequency Range ◽

Nerve Net ◽

Electric Shocks ◽

Electrical Shocks ◽

Probable Site ◽

A Chain ◽

Long Term Facilitation

1. Repetition-produced modifications in the behaviour of the swimming sea anemone, Stomphia coccinea, are described. Lowered threshold to number of electrical shocks on successive trials indicates a kind of ‘learning‘ called here longterm facilitation. 2. Dissection of the behaviour into its components, both by experimental techniques and observation of atypical cases, shows the swimming reaction not to be simply a chain of reflexes, but to be ‘centrally’; co-ordinated. 3. The conditions for electrical elicitation of swimming are shocks sufficient in intensity to activate the through-conducting nerve net repeated eight times in the frequency range of 1/2 sec. to 4/sec. Fewer than 8 shocks constitute a subthreshold stimulus in fresh animals; more than 8 are rarely required. 4. Repeated subthreshold stimulation by starfish or by 7 electric shocks result in a long-lasting facilitated state in which the same stimulus repeated hours later may produce a full response. The facilitated condition has been observed to last 7 days. Controls kept without stimulation do not show facilitation. 5. The probable site of this long-term facilitation is discussed. It is suggested that this site is at the point of convergence of the two types of stimulation used and between the through-conducting nerve net and the responding muscles.

Download Full-text

The Behaviour and Neuromuscular System of Gonactinia Prolifera, A Swimming Sea-Anemone

Journal of Experimental Biology ◽

10.1242/jeb.55.3.611 ◽

1971 ◽

Vol 55 (3) ◽

pp. 611-640

Author(s):

ELAINE A. ROBSON

Keyword(s):

Electrical Stimulation ◽

Mechanical Stimulation ◽

Motor Units ◽

Nerve Cells ◽

Sea Anemone ◽

Neuromuscular System ◽

Sea Anemones ◽

Nerve Net ◽

Local Contraction ◽

Electric Shocks

1. In Gonactinia well-developed ectodermal muscle and nerve-net extend over the column and crown and play an important part in the anemone's behaviour. 2. Common sequences of behaviour are described. Feeding is a series of reflex contractions of different muscles by means of which plankton is caught and swallowed. Walking, in the form of brief looping steps, differs markedly in that it continues after interruptions. Anemones also swim with rapid tentacle strokes after contact with certain nudibranch molluscs, strong mechanical disturbance or electrical stimulation. 3. Swimming is attributed to temporary excitation of a diffuse ectodermal pacemaker possibly situated in the upper column. 4. From the results of electrical and mechanical stimulation it is concluded that the endodermal neuromuscular system resembles that of other anemones but that the properties of the ectodermal neuromuscular system require a new explanation. The size and spread of responses to electric shocks vary with intensity, latency is variable and there is a tendency to after-discharge. There is precise radial localization, for example touching a tentacle or the column causes it to bend towards or away from the stimulus. 5. A model to explain these and other features includes multipolar nerve cells closely linked to the nerve-net which would act as intermediate motor units, causing local contraction of the ectodermal muscle. This scheme can be applied to other swimming anemones but there is no evidence that it holds for sea anemones generally.

Download Full-text

Neuromuscular Activity in the Swimming Sea Anemone, Stomphia Coccinea (Müller)

Journal of Experimental Biology ◽

10.1242/jeb.37.4.671 ◽

1960 ◽

Vol 37 (4) ◽

pp. 671-688

Author(s):

G. HOYLE

Keyword(s):

Puget Sound ◽

Sea Anemone ◽

Sphincter Muscle ◽

Single Shock ◽

Term Change ◽

Electric Shocks ◽

Constant Strength ◽

Repetition Interval ◽

Slow Contraction

1. The spontaneous activity and also the response mechanisms to externally applied electric shocks have been studied in the swimming sea anemone Stomphia coccinea obtained from Puget Sound, Washington. 2. Slow rhythmical activity with a repetition interval of the order of 30 min. is evident in kymograph records of whole-animal movements and also in rings of body wall isolated from the oral or basal regions. 3. By suitably placing the stimulating electrodes different parts of the musculature can be brought into contraction. Those studied were principally the parietobasilar muscles and also the longitudinal retractors, the circular muscles of the column and the isolated oral sphincter. 4. The magnitude of the response of the parieto-basilar muscles to constant-strength stimuli was very variable. Responses occur to single shocks and these increase in magnitude with increasing strength of stimulus. 5. The parietal muscles give delayed, slow contractions in response to trains of about ten stimuli at one per sec. 6. The isolated sphincter muscle shows two kinds of contraction, a quick one which occurs to single shocks and a slow one which occurs following a brief train of fairly widely separated shocks. 7. The ordinary circular muscles respond with a slow contraction to a few widely spaced shocks. They do not give quick contractions. 8. Although in many cases animals responded to eight quick shocks by giving swimming reactions this number was not found to be a precise requirement, and it varied for the same animal at different times in an unpredictable manner as well as varying from one animal to another. On one occasion a swimming response occurred after a single shock and on another after twenty-eight shocks. 9. It was found that the state of ‘facilitation’ (occurring in the response to electric shocks) of the muscles used in swimming varied a great deal but did not show any marked long-term change following a single shock or the elicitation of a swimming response.

Download Full-text