First published online March 31, 2005
Journal of Experimental Biology 208, 1459-1467 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01544
Juvenile Lymnaea ventilate, learn and remember differently than do adult Lymnaea
Chloe McComb,
Nishi Varshney and
Ken Lukowiak*
Calgary Brain Institute, Department of Physiology and Biophysics,
University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1,
Canada
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Fig. 1 Shell length, age and ventilatory behaviour in Lymnaea. (A) The
growth of snails (as measured by shell length) was linear between 3.5–13
weeks of age (post-hatching). Snails were maintained in standard conditions
and a cohort (N=33) of randomly selected snails from the over 200
snails in the aquarium were measured weekly. The snails displayed continuous
shell growth at a rate of 0.25 mm day–1. Based on this growth
curve adults (2.5 cm) and juveniles (1.5 cm) are approximately 13 and 8 weeks
old, respectively. (B) Increased aerial respiration in hypoxia. Both adult
(N=43 each) and juvenile snails significantly (P<0.01 in
both cases) increase their total breathing time when exposed to the hypoxic
environment. However in both eumoxia and hypoxia the total breathing time in
adults was significantly greater (P<0.001) than in juveniles.
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Fig. 2. Juveniles exhibit reduced learning ability compared with adults. (A) Adults
and juveniles (N=280 each) were trained using two 45 min training
sessions separated by 1 h. Both age groups met the criteria for learning (i.e.
a significant reduction in the number of attempted openings between sessions 1
and 2; P<0.001). (B) Normalization of the data plotted in A. The
adults show a larger percentage decrease in the number of attempted openings
in session 2 compared with juveniles.
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Fig. 3. Yoked control data for adult and juvenile snails. Plotted are the number of
attempted pneumostome openings in the `pre' yoked training session and the
`post' yoked control-training sessions for both operantly conditioned (grey
bars) and yoked control (white bars) preparations. Also shown are the results
of operant training on the number of attempted pneumostome openings during the
course of training. The number of attempted openings in the `post' session 1 h
after the session 2 of both adult and juvenile snails did not significantly
decrease in the yoked control snails as it did for the snails that received
the operant conditioning training procedure.
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Fig. 4. Adults exhibit LTM but juveniles do not. (A) Adult (N=75) snails
subjected to the LTM training procedure exhibited LTM when tested 24 h after
the last training session (MT). That is, the criteria for LTM (the number of
attempted openings in MT was significantly less than in session 1 but was not
significantly greater than in session 2) were met. (B) Juvenile
(N=75) snails trained and tested in the same manner as the adults in
A did not meet the criteria necessary for LTM.
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Fig. 5. Motivated juveniles do not exhibit better learning than control juveniles.
To motivate juvenile snails we submerged them in hypoxic pond water for 30 min
before training. (A) Preventing juvenile snails from performing aerial
respiration for 30 min (i.e. submerged juveniles) before the observation
period significantly increases their total breathing time. Plotted are the
total breathing time (mean ± S.E.D.)
for adults (N=15, clear bar), juveniles (N=15, grey bar) and
submerged juveniles (N=12, striped bar). The submerged juveniles
breathe significantly longer than control juveniles (P<0.01) and
statistically the same as adults. (B) Submerged juveniles (N=28,
striped bars) received operant conditioning training immediately after being
submerged. The number of attempted openings of the submerged juveniles in
session 1 was not significantly different to adults (P>0.05).
These snails had a 27% reduction in the number of attempted openings in
session 2 compared with session 1. Control juvenile snails exhibited a 24%
reduction in session 2 compared with session 1.
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Fig. 6. Juvenile `high responders' do not exhibit LTM. (A) Data from the 20
juvenile `high responders' previously plotted in
Fig. 4 do not demonstrate LTM
even though they received the same number of reinforcing stimuli as the adults
in B. (B) The data from 20 randomly chosen adult snails from the data in
Fig. 4 show LTM when tested 24
h after the last training session (MT).
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© The Company of Biologists Ltd 2005
