VOL. XVI, No. 3
JULY,
1939
THE ACTION OF DRUGS, ESPECIALLY ACETYLCHOLINE, ON THE ANNELID BODY WALL
{LUMBRICUS, ARENICOLA)
BY K. S. WU
From the Department of Zoology, University College, London
[Received n October 1938)
(With Three Text-figures)
IN the course of a recently published investigation (Wu, 1939) it was found that the
gut of the earthworm differed from the well-known preparation of the dorsal
musculature of the leech (Fiihner, 1918; Minz, 1932), as regards its reactions to
acetylcholine, in the following respects: (1) in the absence of eserine the body wall
of the leech is very much less sensitive to acetylcholine than is the gut (crop and
gizzard) of the earthworm, the lowest effective concentration of the drug being io" 4
to io" 5 for the former and io~B to io- 10 for the latter; (2) treatment with eserine
increases the sensitivity to acetylcholine of the leech dorsum enormously and that
of the earthworm gut only slightly, so that the former (lowest effective concentration
io~8 to io"10) is now nearly as sensitive as the latter (io~10 to io~ u ); (3) adopting
the classification of Dale (1914), the action of acetylcholine on the leech is a
"nicotine-action" (abolished by large doses of nicotine) while that on the earthworm gut is a " muscarine-action " (abolished by small doses of atropine). The question therefore arises, are these differences due to the fact that we are dealing with
two species, earthworm and leech, or with two organs, body wall and gut? To
answer this question, the writer has studied the action of acetylcholine and certain
other relevant drugs on the body wall of the earthworm (Lumbricus terrestris) and of
the lugworm (Aremcola marina). By putting these results beside those already
established for the leech, a comparison can be drawn between the reactions of the
body wall in representatives of all of the three great divisions of the annelid phylum.
As regards the gut, the data of Wu (1939) on the earthworm and of Wells (1937)
on the lugworm are also available for comparison.
MATERIAL
Most of the experiments were done on longitudinal strips including tissue from
several segments of the worm. In Lumbricus, either dorsal, ventral or lateral strips
were used. All of these strips showed spontaneous rhythmic activity, whether they
contained the ventral nerve cord or not. In Arenicola, the strips were ventral,
dorsal or ventro-lateral; in the latter case the ventral nerve cord was present in some
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K. S. Wu
experiments and absent in others. In contrast to the earthworm strips, those of
Arenicola only showed spontaneous activity if the ventral nerve cord was present.
The ventral strips were very active and often showed outbursts of rhythmic activity
alternating with more quiet periods, rather like the behaviour pattern of the
isolated oesophagus and extrovert preparations of Wells (1937) but not so regular.
In addition to the longitudinal strips, experiments were also made on circular
strips of Arenicola body wall. Rings were cut including two or three segments and
converted into strips by dividing them in the mid-dorsal line. The oblique muscles
were also cut through. These strips showed a very regular continuous rhythm.
ESERINE
It was found that eserine alone exerted a striking exciting action on the earthworm body wall (Fig. 1). The effect is shown by dorsal, ventral and lateral strips,
Fig. 1. Lateral strip of the earthworm (Lumbricus terrestris). The record begins in Ringer, at signal
eserine io~* is added. In all records: read from left to right; upstroke of lever means shortening of
preparation; time signal marks once a minute.
and can be detected even with concentrations of eserine down to io~7. In the case
of Arenicola, the effect is seen only in the case of longitudinal strips containing the
nerve cord. The dorsal and lateral strips, which showed no spontaneous rhythm,
were not excited by eserine; neither were the circular strips, although they contained nerve cord and were spontaneously rhythmic.
Action of Drugs on the Annelid Body Wall
253
ACETYLCHOLINE
The characteristic effect of acetylcholine on all the annelid muscles under consideration (body wall or gut) is the evocation of a swift tonic contraction. In all the
earthworm and lugworm strips, the concentration of acetylcholine required to produce a contraction in the absence of eserine is from 10-4 to io" 5 ; they therefore
quantitatively resemble the leech body wall in this respect. Moreover, eserine
greatly sensitizes the earthworm and lugworm body wall to acetylcholine, the effect
being nearly, but not quite, as great as in the leech. Eserine was applied in the
following concentrations: io~6 or io~7 for the earthworm and io~B or 1/5 x io~*
for Arenicola. After eserine, the lowest effective concentrations of acetylcholine
were found to be io~6 to io~8 for Lumbricus, io~9 for Arenicola when the strips were
longitudinally ventral and io~7 to io~* for Arenicola for longitudinally dorsal and
circular strips, a8 compared with io" 8 to io~10 for the leech.
ATROPINE
It was shown previously (Wu, 1939) that atropine from 1 : 5000 to io~B has a
slight exciting action, and can abolish the action of acetylcholine, on the earthworm
gut. On the earthworm body wall, atropine io~B has a slight excitatory action and
reduces the response to acetylcholine, but does not completely abolish it. Similarly
the sensitivity to acetylcholine of the longitudinal and circular strips of Arenicola
body wall is reduced by previous application of atropine io~s but the response is
not abolished altogether by atropine either in this concentration or 1/5 x io" 4 .
The annelid body wall seems to resemble the rectus abdominis of the frog, in
which the response to acetylcholine is diminished but not abolished by atropine
(Riesser & Neuschloss, 1921; Bfown, 1937).
NICOTINE
Both in the earthworm and in the lugworm, nicotine by itself causes contraction
of the body wall. In Lumbricus, nicotine io~B causes a single, quick twitch-like contraction followed by slow relaxation. In Arenicola, with high concentrations (io~ 3
to 10-4) there are two contractions—first a quick rise and fall, and then a slow contraction and relaxation (Fig. 2). The first, quick, contraction seems to be due to an
action of the drug on the nerves. It is much more powerful in strips which contain
the nerve cord than in those which do not. With lower nicotine concentrations only
the slow phase is seen.
Both in Lumbricus and in Arenicola, the action of acetylcholine can be abolished
by high nicotine concentrations. In Lumbricus, nicotine io~* was found to abolish
the action of acetylcholine (io~ 3 without eserine). In Arenicola, nicotine 10-4 or
io~ 3 completely antagonizes low concentrations of acetylcholine (io~ 6 with eserine).
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K. S. Wu
Higher acetylcholine concentrations now evoke a slow tone rise, quite unlike the
swift normal response to the drug (Fig. 2),
Fig. 2. Strips of the lugworm (Aremcola marina). A, ventro-lateral atrip, without nerve cord, 7-11
segments. The record begins in sea water, at signal nicotine io" 4 is added. B, dorsal strip, posterior
third. The record begins in eserine io~* in sea water, at signal the game and acetylcholine 10"' is
added. C, continuation of B. The record is taken after the preparation has been paralysed by nicotine
io~*. Beginning is in nicotine io"' and eserine io~', at first signal Ach io~* + nicotine 10"' +eserine
io~* and at second signal Ach io~* + nicotine io~* + e»erine io~* are applied, at third signal sea
water.
ADRENALINE
Although the main object of these experiments was to elucidate the action of
acetylcholine, experiments were also made on the action of adrenaline on the
Arenicola body wall. It was shown by Wells (1937) that adrenaline inhibits the
rhythm of a circular muscle strip. This result was confirmed. The inhibition is very
clear and constant. It is diminished, but not abolished, by ergotoxine 1/5 x io~*.
The action of adrenaline on the longitudinal strips was not so clear. The dorsal
strips, which show no spontaneous rhythm, responded by loss of tone to adrenaline
application in some experiments; in others, there was no definite effect. The spontaneously active ventral strip was inhibited by adrenaline in some experiments, but
clearly excited in others (Fig. 3). This variability of behaviour can be attributed to
the complexity of the preparation and the number of points at which the drug
could act.
Action of Drugs on the Annelid Body Wall
255
Fig. 3. Ventral strip of the lugworrri, 11-15 segments. The record (above) begins in sea water, at
signal adrenaline io~5 is applied. The lower continues in adrenaline io~', at first signal adrenaline
1 : 80,000 is added, at second signal return to sea water.
DISCUSSION
Two questions may be discussed: (1) the contrast between gut and body wall,
and (i) differences between the three species of worms.
(1) It is clear that the three body walls (Hirudo, Lumbricus, Arenicold) differ
from the earthworm gut in two respects. First, in the body wall there is a factor
—probably a high concentration of choline esterase—which blocks the action of
acetylcholine and is antagonized by eserine. All three are relatively insensitive to
acetylcholine alone, and greatly sensitized by eserine. The earthworm gut, on the
other hand, is very sensitive to acetylcholine alone and eserine only causes a slight
increase in sensitivity. The Aremcola gut seems to resemble that of Lumbricus in this
regard. Working with the front part of the lugworm gut ("isolated extrovert"),
Wells (1937, and private communication) found that acetylcholine alone was
effective down to about io~ 8 and that eserine only lowered the threshold
to about io~7. Second, the action of acetylcholine on the body wall is a
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K. S. Wu
"nicotine action", while that on the gut, of the earthworm at least, is a
'' muscarine-action''.
In both points, the annelid body wall resembles vertebrate skeletal muscle while
the annelid gut resembles the mammalian intestine. According to Dale & Gasser
(1926), Matthes (1930), Euler & Gaddum (1931), Chang & Gaddum (1933),
Gaddum (1935) and Brown (1937), the action of acetylcholine on the cat's gastrocnemius and the frog's rectus abdominis is a "nicotine action", while that on the
rabbit's intestine is a "muscarine action". Moreover, the lowest effective concentration of acetylcholine without eserine is much higher in skeletal muscle (frog's
rectus abdominis) than in the intestine, and the potentiating action of eserine is
much greater in the former than in the latter. It is interesting that the pharmacological contrast between somatic and visceral muscle apparently applies to animals
of both phyla. In this connexion, the conclusion of Riesser (1933), that the reactions
to drugs of the somatic muscles of a number of invertebrates bear a general resemblance to those of vertebrate skeletal muscle, is worth pointing out.
(2) On comparing the various body-wall preparations, certain points of difference appear. The most striking is the exciting effect of eserine on some of the
preparations. This effect is clearly shown by the following longitudinal strips: earthworm dorsal, lateral and ventral, and Arenicola ventral. It is not shown by longitudinal dorsal strips of Arenicola or by the leech dorsum. Its incidence, as regards
longitudinal strips, corresponds with the power of spontaneous rhythmic movement.
However, in the Arenicola circular muscle strip, which is spontaneously rhythmic,
the effect is not seen. The difference between the circular and longitudinal strips in
Arenicola is also brought out by the experiments with adrenaline, which invariably
depresses the circular strip but may excite the longitudinal ventral.
SUMMARY
1. The actions of certain drugs (acetylcholine, eserine, atropine, nicotine,
adrenaline) on strips of the body wall of the earthworm (Lumbricus terrestris) and
lugworm (Arenicola marina) are described.
2. The body wall of the earthworm and lugworm resembles the dorsum of the
leech, and also vertebrate skeletal muscle, in the following points: relatively insensitive to acetylcholine alone, sensitivity to acetylcholine greatly increased by
eserine, response to acetylcholine abolished by nicotine. In these points, the
muscles mentioned contrast with the earthworm gut and the mammalian intestine,
which are: very sensitive to acetylcholine alone, sensitivity not greatly increased by
eserine, response to acetylcholine abolished by atropine.
3. The various types of body wall strip differ among themselves as regards
spontaneous activity, response to eserine alone, and response to adrenaline.
My thanks are due to Mr G. P. Wells for his suggestion of the problem and for
his continued interest throughout the investigation, and to Dr Kemp and his staff
for their kindness during my visit to Plymouth, where the experiments on Arenicola
were carried out.
Action of Drugs on the Annelid Body Wall
257
REFERENCES
BROWN, G. L. (1937). J. Pkytiol. 89, 438.
CHANG, H. C. & GADDUM, J. H. (1933). J. Pkytiol. 79, 255.
DALB, H. H. (1914). J. Pharmacol. 6, 147.
DALB, H. H. & GASSKR, H. S. (1926). J. Pharmacol. 29, 53.
EULKR, U. S. & GADDUM, J. H. (1931). J. Phytiol. 72, 74.
FOHNKR, H. (1918). Arch. exp. Path. Pharmak. 82, 51, 81 and Biochem. Z. 92, 347.
GADDUM, J. H. (1935). Aim. Rev. Bioch. 4, 311.
MATTHES, K. (1930). J. Phytiol. 70, 338.
MINZ, B. (193a). Arch. exp. Path. Pharmak. 168, a93.
RIESSER, O. (1933). Arch. exp. Path. Pharmak. 172, 194.
RIESSER, O. & NEUSCHLOSS, S. M. (1921). Arch. exp. Path. Pharmak. 91, 34a.
WELLS, G. P. (1937). J. exp. Biol. 14, 117.
Wu, K. S. (1939). J. exp. Biol. 16, 2.