Juvenile Lymnaea ventilate, learn and remember differently than do adult Lymnaea
Calgary Brain Institute, Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada
* Author for correspondence (e-mail: lukowiak{at}ucalgary.ca)
Accepted 15 February 2005
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: aerial respiration, learning and memory, in vitro semiintact preparation, Lymnaea, operant conditioning, associative learning, long-lasting memory
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In adult Lymnaea aerial respiratory behaviour can be operantly
conditioned and this learning can be consolidated into long-term memory (LTM;
Lukowiak et al., 1996,
2003a
). Neural correlates of
memory formation have been found in RPeD1 (Spencer et al.,
1999
,
2002
), one of the three CPG
neurons that drive this behaviour. Moreover, this neuron is a necessary site
for the processes of memory consolidation, reconsolidation, extinction and
forgetting (Scheibenstock et al.,
2002
; Sangha et al.,
2003a
,b
,c
,
2005
) Interestingly in
juvenile Lymnaea RPeD1 spontaneous activity is significantly higher
than in adults (McComb et al.,
2003
). Whether this higher level of RPeD1 activity is coincident
with altered learning and memory ability has not been experimentally
tested.
Typically, younger animals (vertebrate and invertebrate) `perseverate' (the
inappropriate or unintentional repetition of a response or behaviour)
(Cider, 1997) on learning tasks
where they are required to withhold a behavioural response
(Denenberg and Kine, 1958
;
Peretz and Lukowiak, 1975
;
Blozovski and Cudennec, 1980
;
Mattingly and Zolman, 1980
;
Dickel et al., 1997
,
2000
). The neuronal basis of
behavioural perseveration is not known. Since adult trained snails learn and
remember not to perform aerial respiratory behaviour and since RPeD1 activity
in juveniles is different than it is in adults we hypothesize that juvenile
Lymnaea, on this specific task, will learn and remember more poorly
than adults.
Age-dependent changes in neural circuitry have previously been shown to
affect learning and memory abilities in a wide variety of preparations. In
Aplysia, for example, the ability of the gill withdrawal reflex to
undergo habituation, dishabituation and sensitization is subject to a specific
ontogenic timetable (Rankin and Carew,
1987; Rankin et al.,
1987
; Carew, 1989
;
Marcus et al., 1994
;
Mauelshagen et al., 1996
;
Stark and Carew, 1999
). In
vertebrates, the inability to withhold responding is ascribed to the presumed
delay in the maturation of inhibitory control over frontal brain structures
(Mabry and Campbell, 1973
;
Myslivecek and Hassmannova,
1983
; Band and van der Molen,
2000
). By contrast, learning and memory ability, in both
vertebrates and invertebrates (including Lymnaea) on essential tasks
(e.g. taste aversion) or where animals are required to `perform' a specific
behaviour in response to a positive reinforcing stimulus may be similar across
ontogenesis (Solyom and Miller,
1965
; Roberts,
1966
; Yamanaka et al.,
1999
). In addition to the differences in learning ability they are
also age-related differences in the ability to consolidate the acquired
behaviour (i.e. learning) into memory. For example, Liston and Kagan
(2002
) have shown in human
infants that long-term retention (>24 h) of a learned event increases
during the second year of life coincident with the maturation of the
hippocampus and frontal lobe. We show here that juvenile Lymnaea
exhibit poorer learning compared with adults and are unable to form LTM.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Newly hatched Lymnaea (N200) were maintained in an
aquarium lined with crushed oyster shells and filled with well-aerated pond
water (de-chlorinated City of Calgary tap water). They were fed on
molluscide-free Romaine lettuce ad libitum. Every week 33 snails from
this population were randomly selected and their shell lengths measured before
they were returned to the aquarium. An experimenter `blind' to the purposes of
the study performed the weekly selection of animals to be measured. An age
vs growth curve for snails reared in the laboratory was constructed
(Fig. 1). Newly laid egg masses
were never observed in aquaria until snails reached an average shell length of
22.5 cm, which we took to indicate that they were now adults.
|
In eumoxic conditions (i.e. atmospheric air was continuously bubbled into the test beaker; PO2>9.9 kPa) there is approximately 6 ml O2 l1 and adult Lymnaea perform aerial respiration infrequently, once every 1020 min. Under hypoxic conditions, when 100% N2 is continuously bubbled into the test beaker for at least 20 min, there is less than 0.1 ml O2 l1 and both the frequency and amount of aerial respiratory behaviour increase significantly in adults under such hypoxic conditions (PO2<0.9 kPa).
Breathing observations were performed in either eumoxic or hypoxic conditions. For both conditions, a 1 l beaker was filled with 500 ml of pond water and either atmospheric air or N2 was bubbled through the beaker continuously during the observation period. Individually labeled animals were placed into the pond water and given a 10 min acclimatization period during which they could freely open their pneumostome. At the end of this period, all snails were gently pushed under the water, signaling the beginning of the 45 min observation session. The opening and closing times for each breath were recorded and the number of breaths, the average duration of each breath, and the total breathing time (calculated by the sum of the duration of each individual breath) were obtained.
Operant conditioning: training and testing procedures
Briefly, animals were placed in a 1 l beaker filled with 500 ml of pond
water, made hypoxic (<0.1 ml O2 l1) by
bubbling N2 through it 20 min prior to, and during, training
sessions. Before each training session, snails were given a 10 min
acclimatization period during which they were free to open their pneumostomes.
At the end of this 10 min period, animals were gently pushed beneath the water
surface, signaling the beginning of the training session. During each training
and test session, animals received a gentle tactile stimulus to the
pneumostome each time it began to open. This stimulus resulted in the
immediate closure of the pneumostome but did not induce the snail to retract
its body into the shell, known as the whole-body withdrawal behaviour. Snails
typically remain at the surface following the application of the tactile
stimulus. The time of each stimulus was recorded and tabulated. With operant
conditioning training, animals learned to associate pneumostome opening with
the negative reinforcement of receiving a tactile stimulus. In the interval
between training and test sessions, animals were placed in eumoxic pond water
where they could open their pneumostomes freely (see Lukowiak et al.,
1996,
2003b
;
Spencer et al., 1999
;
Sangha et al., 2005
for
details).
Tactile stimuli delivered to adults and juveniles
Juvenile snails exhibited a stronger behavioural response compared with
adults when they were given tactile stimuli of the same intensity. The force
of the stimulation to the pneumostome area was therefore adjusted in the
experiments dealing with juveniles so that the same behavioural responses were
elicited in both juveniles and adults. That is the stimulus did not cause the
snail to withdraw into the shell.
Training procedure for long-term memory (LTM)
Snails received two 45 min training sessions separated by a 1 h interval. A
`savings' test session (MT) was given 24 h after the last training session to
test for LTM. Long-term memory in adults was present at least 24 h after
training (Lukowiak et al.,
2000).
Yoked controls
Yoked control experiments were performed to demonstrate that the changes in
aerial respiratory behaviour with training were the result of operant
conditioning. The day before training commenced, all snails (those to be
conditioned and those to serve as yoked controls) received a 45 min pre-test
session in hypoxia. During this session, snails received a stimulus to the
pneumostome each time it began to open. It was previously shown that one 45
min hypoxic training session is not sufficient to produce long-term memory
(Lukowiak et al., 2000). On
the following day, snails either received the operant conditioning training
procedure (see above) or the yoked control procedure. In the yoked control
procedure animals received a tactile stimulus to the pneumostome area every
time the snails to which they were `yoked' attempted to open their
pneumostomes. One hour after session 2 all animals (i.e. operantly trained and
yoked) were given a 45 min post-test session in hypoxia. During this session,
animals received a tactile stimulus to the pneumostome each time it began to
open. To determine if tactile stimuli alone (i.e. non-contingent) resulted in
a diminution of the response, the number of tactile stimuli pre-test and
post-test sessions were compared. This type of yoked control procedure has
been used successfully before (e.g.
Lukowiak et al., 2003a
).
Enforced submersion experiment
Animals were placed in an aquarium filled with pond water made hypoxic by
bubbling N2 through it, prior to and during the experiment. Snails
were prevented from reaching the water surface and performing aerial
respiration by a submerged, perforated barrier. Animals were submerged for 30
minimmediately prior to performing breathing observations or associative
training. This enforced submersion `caused these snails to perform aerial
respiration significantly more often; hence we term these animals
`motivated-snails'.
Operational definitions of learning and memory
Associative learning was defined as being present if: (1) there was a
significant effect of training on the number of attempted pneumostome
openings, and (2) the number of attempted openings in the final training
session was significantly less than the number of attempted openings in the
first training session.
LTM was defined as being present if: (1) the number of attempted pneumostome openings in the memory-test session was not significantly greater than the last training session; and (2) the number of attempted openings in the memory-test session was significantly less than the number of attempted openings in the first training session.
Statistics
To determine whether operant conditioning training had an effect when
compared with the yoked control group a repeated measures one-way ANOVA was
performed for both juvenile and adult snails testing both between (e.g. yoked
vs operantly conditioned groups) and within group differences
(Zar, 1999). If the ANOVA was
significant (P<0.05) a post-hoc Fisher's LSD
t-test was performed to show which individual sessions were
significantly different from each other [i.e. for learning session 1
vs session 2; for memory the savings test session (MT) vs
session 1 and MT vs session 2]. Significance was at the
P<0.05.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In 45 min observation periods (see Materials and methods) we examined aerial respiratory behaviour in juvenile and adult snails in both eumoxic and hypoxic conditions (Fig. 1B). In eumoxic conditions the mean number of breaths in adults (N=43; 4.33±0.47) was significantly greater (P<0.001) than in juveniles (N=43; 2.3±0.32). The total breathing time for adults in eumoxia (89.8±10.6 s) was significantly greater (P<0.001) than it was in juveniles (41.5±7.9 s); but the average time per breath in eumoxia in adults (22.4±1.9 s) was not significantly different (P>0.05) from that in juveniles (17.5±2.4 s).
In hypoxia, somewhat similar results were obtained. That is, the mean number of breaths in adults (10.67±0.47) was significantly greater (P<0.001) than in juveniles (6.69±0.57); the total breathing time for adults (356.42±34 s) was significantly greater (P<0.001) than it was in juveniles (157.3±15 s) but now the average breathing time was also significantly (P<0.05) greater in adults (41.6±7.7 s) than it was in juveniles (23.8±2.2 s).
We conclude that juveniles perform aerial respiration less often than adults in both hypoxic and eumoxic conditions. However, in hypoxia juveniles too, significantly increase aerial respiratory behaviour compared with their performance in eumoxia.
To demonstrate that the changes in aerial respiratory behaviour that result
from our training procedure (see Materials and methods) are a bona
fide example of associative learning we compared the data from operantly
conditioned and yoked control preparations in both adults and juveniles
(Fig. 2). We first examined
four cohorts (N=12 in each) of snails (two juvenile groups
yoked and contingent and two adult groups yoked and contingent). We
compared, as we have previously done
(Lukowiak et al., 2003a) the
number of attempted openings in the pre-training session to the number of
attempted openings in the post-training session. Thus, both between and within
group comparisons were made. The ANOVA for the complete data set (i.e. the
four cohorts) showed that there was a significant effect of training
(F56,7=155.5801, P<0.001). We then performed a
post hoc Fisher's LSD protected t-test on the various test
sessions making both within and between group analyses. Consistent with
previous findings we found in adult snails that there was a significant
decrease in the number of attempted pneumostome openings between the pre-test
session and the post-test session (P<0.01) while in the yoked
control cohort the post-test session was not significantly less than the
pre-test session (P>0.05). Furthermore, the number of attempted
openings in the pre-test session was not different between the yoked control
and contingent cohort (P>0.05) while the number of attempted
openings in the post-test session of the operantly trained cohort was
significantly less than in the yoked control cohort (P<0.01).
Similar findings were found for the juvenile snails. That is, in the operantly
conditioned cohort the number of attempted pneumostome openings in the
post-test session was significantly smaller than in the pre-test session
(P<0.01); while in the yoked control the post-test session was not
significantly less than the pre-test session (P>0.05). When we
compared the number of attempted openings between the yoked and operant
conditioning juvenile cohorts we found that there was no significant
difference between the cohorts in the pre-test session (P>0.05);
while the number of attempted openings in the post-test session of the
operantly conditioned juveniles was significantly smaller than in the yoked
control cohort (P<0.01). Finally, the number of attempted openings
in both of the adult pre-test sessions was significantly greater than the
number of attempted openings in the pre-test sessions of the juvenile cohorts
(P>0.01 for both comparisons). These analyses showed that
associative learning occurs in both adults and juveniles.
|
To begin to determine whether there were age-related differences in learning ability between juvenile and adult Lymnaea we subjected a relatively large number of juvenile and adult snails (N=280 snails each) to the operant conditioning procedure. In both adult and juvenile snails learning was demonstrated (Fig. 3A). That is, the number of attempted pneumostome openings in session 2 was significantly less than in session 1 (P<0.01). Normalized data of learning ability revealed that adults and juveniles reduced their attempted openings in the second training session by 46% and 30%, respectively (Fig. 3B).
|
Learning and memory, while related, are not a unitary process. We therefore determined if they were also age-dependent differences in the ability to consolidate the associative learning into LTM (Fig. 4). We hypothesized that the reduced learning ability in juveniles (only a 30% vs a 46% change) compared with adults would result in poorer memory retention. To investigate the retention of LTM, adults and juveniles were given two 45 min training sessions (separated by 1 h) followed by a savings-test 24 h later. Adults, but not juveniles, met the criteria for long-term memory when tested 24 h after the last training session. That is, in adult snails the number of attempted openings in the savings-test session was significantly different from the number of openings in session 1 (P<0.01), but was not significantly different from the number of openings in session 2 (P>0.05). In juveniles, however, there was no significant difference in the number of attempted openings between the savings-test session (MT) and session 1 (P>0.05; i.e. memory not demonstrated), while there was a significant difference between the number in MT and session 2 (P<0.01). Thus while the criteria for memory were met in adults they were not met in juvenile snails. Adults were found to show a 51% reduction in their attempted openings between session 1 and MT. By contrast, juveniles demonstrated only a slight decrease (6%) in the number of attempted pneumostome openings between session 1 and MT. We conclude that only adults possess the capacity of consolidating the learned behaviour into LTM.
|
On inspection of the data in the previous figures it can be readily seen that juveniles perform, or attempt to perform, aerial respiration less often than adults and, thus, receive fewer reinforcing stimuli. It could be argued this could be a reason why there is `less' robust learning and no memory in juveniles compared with adults. To determine whether the differences in learning ability and LTM formation between juveniles and adults were due solely to differences in the number of reinforcing stimuli delivered during training, we performed additional experiments and additional re-analyses of the data shown above.
To increase the number of reinforcing stimuli delivered to juvenile snails to levels approximating those in adults, juveniles were submerged in hypoxic conditions for 30 min prior to performing breathing observations. Submersion (i.e. the prevention of aerial respiration; see Materials and methods) significantly increased total breathing time in juveniles to a level that was not significantly different from adults (P>0.05) (Fig. 5A). In these `motivated' juvenile snails the number of attempted openings in session 1 was not significantly different from adults (P>0.05) (Fig. 5B). However, while submersion significantly increased the number of reinforcing stimuli received by the `motivated' juvenile snails it did not affect learning ability in juveniles. That is, learning ability was still found to be significantly poorer in the motivated snails compared with adults (P<0.05). Moreover, the `motivated' juvenile snails did not learn any better than the `un-motivated' juvenile snails (P>0.05). Submerged and non-submerged juveniles showed a 27% and 24% reduction in attempted openings between sessions 1 and 2, respectively. Based on these results we conclude that the difference in learning between juveniles and adults was not caused by the juveniles receiving fewer reinforcing stimuli than adults during training.
|
We also re-examined the data presented in Fig. 4 but post-hoc extracted and re-analyzed the top 25% juvenile responders (N=20; `high responders'). These data are plotted in Fig. 6, as well as data from adults (N=20) randomly chosen from the adult cohort used in Fig. 4. We first performed a two-sample t-test comparing the number of attempted pneumostome openings in session 1 between the juvenile high responders (N=20) and the randomly chosen adults (N=20) and found that statistically they were not different (P>0.05). Thus, the juvenile `high responders' received statistically the same number of reinforcing stimuli as the randomly chosen adults. We then determined if the juvenile `high performers' have the ability to form LTM. An ANOVA showed that there was a significant effect of training on the two cohorts (high responders and randomly chosen adults; (F39,5=156.6676, P<0.001). We then performed a post hoc Fisher's LSD protected t-test on the various test sessions making both within and between group analyses. Confirming our previous analyses we found that the adult snails have the ability to form LTM. That is, the number of attempted openings in the memory test session (MT) was significantly less than the number of attempted openings in session 1 (P<0.01) but was not significantly greater than the number in session 2 (P>0.05). On the other hand, the within group analysis of the juvenile `high-responders' showed that memory was not formed. That is the number of attempted openings in MT was not significantly less than the number in session 1 (P>0.05) while the number of attempted openings in MT was significantly greater than session 2 (P<0.01). The criteria for us to conclude that memory was present were not met. The between group analyses showed that the responses in session 1 between adults and these juveniles were statistically similar (P>0.05), but the responses in MT were different, the randomly chosen adults received significantly fewer reinforcing stimuli (P<0.01) than the juvenile high responders. That is, the adult snails exhibited memory whereas the juvenile high responders did not exhibit memory.
|
Approaching the argument from the other direction we also re-analyzed the data from adult `low-responders' (i.e. the 25% that received the fewest number of stimuli in session 1). The number of reinforcing stimuli these adult snails received in session 1 was 6.78±0.65. Yet, these snails when tested in MT (4.1±0.32) exhibited LTM. That is, the number of attempted openings in MT was significantly less than in session 1 (P<0.01) but was not significantly different than the number of attempted openings in session 2 (3.9±0.29; P>0.05). Thus, these adult `low responders' have the capacity to form LTM.
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We first tested the hypothesis that juveniles show different aerial respiratory behaviour in both eumoxic and hypoxic conditions compared with adults. Juveniles exhibited significantly less ventilatory behaviour compared with adults during 45 min breathing observations in both hypoxia (0.1 ml O2 l1) and eumoxia (6 ml O2 l1). That is, total breathing time, the average time per breath, and the mean number of breaths were reduced in juveniles compared with adults. We conclude that juvenile snails satisfy their respiratory needs to a lesser extent than adults via aerial respiration. That is, in juveniles cutaneous respiration satisfies their respiratory needs to a greater extent than it does in adults.
These results are not surprising, considering juvenile Lymnaea
have a larger surface area to volume ratio than adults and this could result
in more efficient cutaneous respiration. That is, juveniles presumably obtain
a higher percent of their ongoing oxygen requirements via cutaneous
respiration, reducing their need to perform ventilatory behaviour. In eumoxia,
adult Lymnaea on average spend approximately 4% of their time
performing aerial respiration whereas juveniles spend less than 15% of their
time engaged in this activity. Adult Lymnaea spend about 15% of their
time performing aerial respiration in hypoxic conditions; under similar
conditions juveniles spend only 5% of their time engaged in aerial
respiration. In a hypoxic environment there is less dissolved oxygen in the
pond-water causing inadequate cutaneous respiration in both juvenile and adult
snails. Thus both juvenile and adult Lymnaea when challenged with
hypoxic conditions must significantly increase ventilatory behaviour in order
to preserve respiratory homeostasis.
Studies in land snails (Herreid,
1977), air-breathing fish
(Munshi and Dube, 1973
), and
Xanthid crabs (Leffler, 1973
)
have shown that metabolic rates, measured by oxygen consumption, are higher in
smaller animals. Therefore, one would expect small (juvenile) snails to have
higher metabolic requirements compared with larger (adult) snails. Yamanaka et
al. (1999
) examined voluntary
activity in Lymnaea of different ages and found that `immatures'
(shell length
1.01.5 cm) showed significantly more activity
compared with `adults' (shell length >2.0 cm). Based on the above reports,
one would expect juvenile snails to have higher metabolic requirements
compared with larger, adult snails. But then the obvious question is: why do
juveniles exhibit less aerial respiratory behaviour compared with adults? Even
if juveniles do have higher oxygen requirements compared with adults, they
have a more favourable surface area to volume ratio and, possibly, more
efficient cutaneous respiration, which enables juveniles to meet their
respiratory needs without having the need to increase aerial respiratory
behaviour. It may be that there is positive survival value (i.e. less
predation or less chance to desiccate) for not having to spend time at the
surface opening and closing the pneumostome. Cutaneous respiration may also
metabolically `cost' less than aerial respiration and, thus, juveniles would
have to expend less of their energy intake on breathing and more on
maturational processes. Higher levels of activity have been found to
correspond to higher metabolic rates
(Herreid, 1977
). Cutaneous
respiration must therefore adequately satisfy the presumed increased metabolic
needs of the juveniles. It may be that there is a higher positive survival
value for not having to spend more time at the surface opening and closing the
pneumostome in juveniles than in adults.
Having found an age-related difference in the need to perform aerial
respiration we next turned our attention to the question as to whether there
would be an age-related impairment in juvenile snail's ability to learn and/or
form memory in an associative learning task involving aerial respiratory
behaviour. We found that juvenile Lymnaea are significantly poorer
learners on this task compared with adults and, importantly, as a group are
unable to consolidate the learning into LTM. This should not be taken to mean
that juvenile Lymnaea are incapable of learning or forming LTM.
Juvenile Lymnaea, as do other animals, have the capacity to learn and
form LTM on tasks not involving the withholding of a behaviour. Thus for
example, juvenile Lymnaea learn and form memory for appetitive food
behaviours (Yamanaka et al.,
2000).
A possible explanation for explaining why juveniles have a greater difficulty acquiring learning and then consolidating this change into LTM than do adults is that the juveniles do not receive a sufficient number of reinforcing stimuli during the training sessions. We concluded, however, that this was not the explanation. We arrived at this conclusion because we found that: (1) `motivated' juveniles (i.e. the ones in the submersion experiments) received as many reinforcing stimuli in session 1 as adults yet continue to exhibit poorer learning compared with adults; (2) the `motivated' juvenile snails do not learn any better than un-motivated' juvenile snails, thus more reinforcing stimuli does not necessarily result in better learning; (3) when we analyzed the ability of the highest responding juveniles (i.e. the `high responders' in Fig. 4) to form memory, we found that they did not, that is, even though statistically they received the same number of reinforcing stimuli as randomly selected adults, they still did not form memory; (4) adult `low responders' formed LTM even though they received fewer reinforcing stimuli than the juveniles; (5) finally, Smyth et al., 2002 showed that adult snails that were trained using three 15 min training sessions (each session separated by a 1 hinterval) procedure exhibited LTM. These adult snails received fewer reinforcing stimuli (average in session 1 was 4.8) than did the juveniles here, yet LTM was established.
Why, then, can't juveniles form LTM? We do not have a definitive answer but
have a number of testable hypotheses. We know in adult Lymnaea
(Scheibenstock et al., 2002;
Sangha et al., 2003a
;
Sangha et al., 2005
) that
RPeD1 is a necessary site for LTM formation. We also know that there are
significant differences in the levels of spontaneous RPeD1 between juvenile
and adults (McComb et al.,
2003
). RPeD1 is, in juveniles, significantly smaller than it is in
adults and its smaller cell size coupled with significant differences in a
number of its intrinsic membrane properties (i.e. membrane resistance, time
constant and rheobase current) contribute to its increased neuronal
excitability. That is, RPeD1 is significantly more active in juveniles than it
is in adults. This increased excitability of juvenile RPeD1s paradoxically
results in a decreased ability to elicit respiratory rhythmogenesis, as the
neuron is firing outside of its optimal range to induce rhythmic activity in
the neuronal circuit that controls aerial respiratory behaviour
(McComb et al., 2003
;
Turrigiano, 1999
). This
increased excitability of RPeD1 in juveniles may contribute to their poor
learning and memory formation abilities. That is, since LTM formation depends
on altered gene activity and new protein synthesis in RPeD1; it is possible
that the transcription factors that must be activated and/or inhibited in
RPeD1 to initiate the molecular cascade necessary for the formation of LTM may
also be dependent on some optimal level of RPeD1 activity. However, further
experimentation (e.g. altering the activity of RPeD1 by the injection of
hyperpolarizing current during the course of training) in an in vitro
preparation will be necessary before we can accept this hypothesis.
Our data concerning the acquisition of learning and its lack of
consolidation into LTM are consistent with previous data from juveniles that
typically perseverate on tasks where they have to withhold a response,
including habituation (Peretz and
Lukowiak, 1975; Lukowiak,
1980
), suppression of attack responses
(Wells, 1962
;
Dickel et al., 1997
), passive
avoidance (Blozovski and Cudennec,
1980
; Mattingly and Zolman,
1980
), spatial discrimination
(Bronstein and Spear, 1972
) and
the classical conditioning of Lymnaea's whole-body withdrawal
response (Ono et al., 2002
).
We now have the possibility of determining whether the inability to form LTM
for associative learning is dependent partly or completely on differences in a
single neuron.
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Band, G. P. H. and van der Molen, M. W. (2000). The ability to activate and inhibit speeded responses: separate developmental trends. J. Exp. Child Psych. 75,263 -290.[CrossRef][Medline]
Blozovski, D. and Cudennec, A. (1980). Passive avoidance learning in the young rat. Dev. Psychobiol. 13,513 -518.[Medline]
Bronstein, P. M. and Spear, N. E. (1972). Acquisition of a spatial discrimination task by rats as a function of age. J. Comp. Physiol. Psych. 78,208 -212.[Medline]
Carew, T. J. (1989). Developmental assembly of learning in Aplysia. Trends Neurosci. 12,389 -394.[CrossRef][Medline]
Carew, T. J. and Sutton, M. A. (2001). Molecular stepping stones in memory consolidation. Nat. Neurosci. 4,769 -771.[CrossRef][Medline]
Cider, A. (1997). Perseveration in Schizophrenia. Schizo. Bull. 3, 63-74.
Denenberg, V. H. and Kine, N. J. (1958). The relationship between age and avoidance learning in the hooded rat. J. Comp. Physiol. Psych. 51,488 -491.[Medline]
Dickel, L., Boal, J. G. and Budelmann, B. U. (2000). The effect of early experience on learning and memory in cuttlefish. Dev. Psychobiol. 36,101 -110.[CrossRef][Medline]
Dickel, L., Chichery, M. P. and Chichery, R. (1997). Postembryonic maturation of the vertical lobe complex and early development of predatory behavior in the cuttlefish (Sepia officinalis). Neurobiol. Learn. Mem. 67,150 -160.[CrossRef][Medline]
Herreid, C. F., II (1977). Metabolism of land snails (Otala lactea) during dormancy, arousal, and activity. Comp. Biochem. Physiol. A 56,211 -215.[CrossRef][Medline]
Inoue, T., Haque, Z., Lukowiak, K. and Syed, N. I.
(2001). Hypoxia-induced respiratory patterned activity in
Lymnaea originates in the periphery. J.
Neurophysiol. 86,156
-163.
Janse, C., Wildering, W. C. and Popelier, C. M. (1989). Age-related changes in female reproductive activity and growth in the mollusc Lymnaea stagnalis. J. Gerontol. 44,B148 -B155.[Medline]
Jones, H. D. (1961). Aspects of respiration in Planorbis corneus (L) and Lymnaea stagnalis (L) (Gastropoda: Pulmonata). Comp. Biochem. Physiol. 4, 1-29.[CrossRef][Medline]
Leffler, C. W. (1973). Metabolic rate in relation to body size and environmental oxygen concentration in two species of Xanthid crabs. Comp. Biochem. Physiol. A 44,1047 -1052.[CrossRef][Medline]
Liston, C. and Kagan, J. (2002). Brain development: memory enhancement in early childhood. Nature 419,896 .[CrossRef][Medline]
Lukowiak, K. (1980). CNS control over gill reflex behaviors in Aplysia: satiation causes an increase in the suppressive control in older but not young animals. J. Neurobiol. 11,591 -611.[CrossRef][Medline]
Lukowiak, K., Adatia, N., Krygier, D. and Syed, N. I.
(2000). Operant conditioning in Lymnaea: evidence for
intermediate- and long-term memory. Learn. Mem.
7, 140-150.
Lukowiak, K., Haque, Z., Spencer, G., Varshney, N., Sangha, S.
and Syed, N. (2003a). Long-term memory survives nerve
injury and subsequent regeneration process. Learn.
Mem. 10,44
-54.
Lukowiak, K., Ringseis, E., Spencer, G., Wildering, W. and Syed,
N. I. (1996). Operant conditioning of aerial respiratory
behaviour in Lymnaea stagnalis. J. Exp. Biol.
199,683
-691.
Lukowiak, K., Sangha, S., McComb, C., Varshney, N., Rosenegger,
D., Sadamoto, H. and Scheibenstock, A. (2003b).
Associative learning, long-term memory, and the assignment of `marks' in the
pond snail, Lymnaea. J. Exp. Biol.
206,2097
-2103.
Mabry, P. D. and Campbell, B. A. (1973). Ontogeny of serotonergic inhibition of behavioral arousal in the rat. J. Comp. Physiol. Psych. 86,193 -201.
Marcus, E. A., Emptage, N. J., Marois, R. and Carew, T. J. (1994). A comparison of the mechanistic relationships between development and learning in Aplysia. Prog. Brain Res. 100,179 -188.[Medline]
Mattingly, B. A. and Zolman, J. F. (1980). Ontogeny of passive avoidance learning in young chicks: punishment of key-peck and running responses. J. Comp. Physiol. Psych. 94,718 -733.[Medline]
Mauelshagen, J., Parker, G. R. and Carew, T. J.
(1996). Dynamics of induction and expression of long-term
synaptic facilitation in Aplysia. J. Neurosci.
16,7099
-7108.
McComb, C., Meems, R., Syed, N. and Lukowiak, K.
(2003). Electrophysiological differences in the neuronal circuit
controlling aerial respiratory behaviour between juvenile and adult
Lymnaea. J. Neurophysiol.
90,983
-992.
Milsom, W. K. (1990). Mechanoreceptor
modulation of endogenous respiratory rhythms in vertebrates. Am. J.
Physiol. Reg. Int. Comp. Physiol.
259,R898
-R910.
Munshi, J. S. D. and Dube, S. C. (1973). Oxygen uptake capacity of gills in relation to body size of the air-breathing fish, Anabas testudineus (Bloch). Acta. Physiol. Acad. Sci. Hung. 44,113 -123.[Medline]
Myslivecek, J. and Hassmannova, J. (1983). The development of inhibitory learning and memory in hooded and albino rats. Behav. Brain Res. 8,151 -166.[CrossRef][Medline]
Ono, M., Kawai, R., Horikoshi, T., Yasuoka, T. and Sakikabara, M. (2002). Associative learning acquisition and retention depends on developmental stage in Lymnaea. Neurobiol. Learn. Mem. 78,53 -64.[CrossRef][Medline]
Peretz, B. and Lukowiak, K. (1975). Age-dependent CNS control of the habituating gill withdrawal reflex and of correlated activity in identified neurons in Aplysia. J. Comp. Physiol. 103,1 -17.
Rankin, C. H. and Carew, T. J. (1987). Development of learning and memory in Aplysia. II. Habituation and dishabituation. J. Neurosci. 7, 133-143.[Abstract]
Rankin, C. H., Stopner, M., Marcus, E. A. and Carew, T. J. (1987). Development of learning and memory in Aplysia. I. Functional assembly of gill and siphon withdrawal. J. Neurosci. 7,120 -132.[Abstract]
Roberts, W. A. (1966). Learning and motivation in the immature rat. Am. J. Physiol. 79, 3-24.
Sangha, S., Scheibenstock, A. and Lukowiak, K.
(2003a). Reconsolidation of a long-term memory in
Lymnaea requires new protein and RNA synthesis and the soma of right
pedal dorsal 1. J. Neurosci.
23,8034
-8040.
Sangha, S., Scheibenstock, A., Martens, K., Varshney, N., Cooke, R. and Lukowiak, K. (2005). Impairing forgetting by preventing new learning and memory. Behav. Neurosci. (In press).
Sangha, S., Scheibenstock, A., McComb, C. and Lukowiak, K.
(2003b). Intermediate and long-term memories of associative
learning are differentially affected by transcription vs translation
blockers in Lymnaea. J. Exp. Biol.
206,1605
-1613.
Sangha, S., Scheibenstock, A., Morrow, R. and Lukowiak, K.
(2003c). Extinction requires new RNA and protein synthesis and
the soma of the cell RPeD1 in Lymnaea stagnalis. J.
Neurosci. 23,9842
-9851.
Scheibenstock, A., Krygier, D., Haque, Z., Syed, N. and
Lukowiak, K. (2002). The soma of RPeD1 must be present for
LTM formation of associative learning in Lymnaea. J.
Neurophysiol. 88,1584
-1591.
Solyom, L. and Miller, S. (1965). The effect of age differences on the acquisition of operant and classical conditioned responses in rats. J. Gerontol. 20,311 -314.
Spencer, G. E., Syed, N. I. and Lukowiak, K.
(1999). Neural changes after operant conditioning of the aerial
respiratory behavior in Lymnaea stagnalis. J.
Neurosci. 19,1836
-1843.
Spencer, G., Kazmi, M., Syed, N. and Lukowiak, K.
(2002). Changes in the activity of a central pattern generator
neuron following the reinforcement of an operantly conditioned behavior in
Lymnaea. J. Neurophysiol.
88,1915
-1923.
Stark, L. and Carew, T. (1999). Developmental
dissociation of serotonin-induced spike broadening and synaptic facilitation
in Aplysia sensory neurons. J. Neurosci.
19,334
-346.
Syed, N. I., Bulloch, A. and Lukowiak, K. (1990). In vitro reconstruction of the respiratory central pattern generator (CPG) in the mollusk Lymnaea.Science 250,282 -285.[Medline]
Syed, N. I., Harrison, D. and Winlow, W. (1991). Respiratory behavior in the pond snail Lymnaea stagnalis. I. Behavioral analysis and the identification of motor neurons. J. Comp. Physiol. A 169,541 -555.
Syed, N. I., Ridgway, R., Lukowiak, K. and Bulloch, A. (1992). Transplantation and functional integration of an identified respiratory interneuron in Lymnaea stagnalis.Neuron 8,767 -774.[Medline]
Taylor, B. and Lukowiak, K. (2000). The respiratory central pattern generator of Lymnaea: A model, measured and malleable. Resp. Physiol. 122,197 -207.[CrossRef][Medline]
Taylor, B., Smyth, K., Burk, M., Lukowiak, K., Harris, M. and Remmers, J. (2003). Nitric oxide mediates metabolism as well as respiratory and cardiac responses to hypoxia in the snail Lymnaea stagnalis. J. Exp. Zool. A 295, 37-46.
Turrigiano, G. G. (1999). Homeostatic plasticity in neuronal networks: the more things change, the more they stay the same. Trends Neurosci. 22,221 -227.[CrossRef][Medline]
Wells, M. J. (1962). Early learning in Sepia. Symp. Zool. Soc. Lond. 8, 149-169.
Yamanaka, M., Hatakeyama, D., Sadamoto, H., Kimura, T. and Ito, E. (2000). Development of key neurons for learning stimulates learning ability in Lymnaea stagnalis. Neurosci. Lett. 278,113 -116.[CrossRef][Medline]
Yamanaka, M., Sadamoto, S., Hatakeyama, D., Nakamura, H., Kojima, S., Kimura, T., Yamashita, M., Urano, A. and Ito, E. (1999). Developmental changes in conditioned taste aversion in Lymnaea stagnalis. Zool. Sci. 16, 9-16.[CrossRef]
Zar, J. H. (1999). Biostatistical Analysis, 3rd edn. Upper Saddle River, NJ: Prentice Hall.