Prof. Mitsuo Terasawa
Faculty of Engineering, Tamagawa University
<ABSTRACT>
Experiments were held in a plexiglas cage where the lamp was turned
off and on every twenty seconds. One group of rats was the control group
which could eat pellets freely without having to press a lever. The second
group of rats could eat a pellet every time they pushed a lever. The third
group of rats could eat a pellet when they pressed a lever while a lamp
was lit. We found that the thiamine is stocked in the brain of the rats
by learning and the part of the brain where it is stored depends on the
type of learning.
1. Introduction
In one of the previous experiments we looked at the relationship between
cognitive development of rats and a vitamin B1 deficient diet. Rats fed
on a B1-deficient diet were electrically stimulated so as to repeatedly
undertake a lever-pressing task. Their ability to accomplish the task decreased
the longer they were on the vitamin B1 deficient diet1)
In another experiment we looked at the effect of learning with rewards
on the vitamin B1 concentration in the brain. The rats fed on a normal
diet undertook the lever pressing task. They were rewarded with a pellet
whenever they pres sed the lever. After dissection we discovered that the
rats had a significantly higher concentration of vitamin B1 in their cerebellum
and brainstem than a control group of rats that did not undertake the task.
7)-8) This lead us to further investigate the correlation between
the complexity of tasks and the levels of thiamine found in the portions
of the brain. We conducted a lever pressing experiment with the lamp alternately
turned on and off to find the correlation.
2. Methodology
The procedure of the lever-pressing experiment withthe lamp alternately
turned on and off was as follows:
2.1 Experimental procedures
1) The weight of each rat was measured to ascertain its condition and
state of health.
2) The rats in Group A were one by one put into an experimental cage
that has no lever or tasks after a feeder had been filled with 20 reward
pellets. The rats in Group B and Group C were put into their respective
experimental cages after the feeders had been filled with 20 pellets, Afterwards,
the amount of time to eat the pellets was gradually reduced.
3) To obtain information on each rat’s learning ability we measured
the feeding time of rats in Groups B and C. The time for each rat to finish
eating twenty pellets was counted as one trial.
4) To maintain the rats’ weight, a controlled diet of a powdered type
was given to the rats each day after the experiments. The quantity of feed
and thiamin intake was therefore the same for rats in all of the three
groups.
After the completion of the experiments, all of the rats' blood, brains and livers were removed. The thiamin levels in the removed parts were measured.
2.2Experimental Equipment
We used a black acrylic cage of 250 mm x 250 mm x 300 mm that was shielded
from external light. The equipment is shown in Fig.1. A lamp was placed
in the cage and was switched on and off every 20 seconds. The rats were
divided into three groups. The experiment was conducted under the following
conditions:
2.3 The experimental animals and the learning experiment
Fifteen 5-week-old male rats were used. Four rats wereused in Group
A, five in Group B and six in Group C.
Group A: The rats did not have to press a lever for their feed and
were free to eat (exactly the same
amount of feed as that of Groups B and C).
Group B: The rats were trained to get a pellet every time a lever was
pressed, regardless of whether the
lamp was switched on or not (Lever-pressing learning).
Group C: The rats were trained to press the lever in order to get a
pellet, but only while the lamp was on.
If it was off, they would not be rewarded with a pellet (Lever-pressing
learning).
The time it took for each rat to finish eating (the expected amount
of feed), and the rat’s weight were measured and recorded. This experiment
was conducted over a period of 59 days.
2.4 Feed
The feed used in this learning experiment was of a pellet type, 0.05
g in weight and 3mm in diameter. Twenty pellets a day were given to each
rat at the outset. The number of tasks was increased to promote the rats’
learning abilities according to each rat’s progress. Therefore the quantity
was incresed by adding a supplement (in the form of powdered feed) as the
experiment progressed.
In order to keep the rat’s weight at around 140g, the quantity of
feed was adjusted by 6-8g. This was given in a combined pellet and powdered
form.
2.5 Measurement of the thiamin concentration in different parts of
the rat’s body
Upon conclusion of the experiments, the rats’ blood, brains and livers
were removed. The thiamin levels contained in 1ml of blood, 1g of the cerebrum,
1g of the brain stem and 1g of the cerebellum were measured by the fluorometric
method of thiochrome reaction. The significance of the results was determined
by Dunkan’smultiple range test.
3. Results
The results from the various lever- pressing experiment with the lamp
alternately turned on and off are:
3.1 Rats’ weight and the experiment duration
The relationship between the rats’ weight and the duration of the
experiment is shown in Fig.2. We controlled the quantity of feed given
to the rats to keep the average weight of the rats in each group at around
of 140 grams.
3.2 Rats’ eating time and progress of the experiment
The relationship between the time required for the rat to finish eating
twenty pellets (eating time) and the progress of the experiment is shown
in Fig.3. The eating time became shorter as the experiment progressed.
It took 5 minutes and a half for the rats in Group B and 7 minutes for
the rats in Group C to finish eating the feed in the beginning. Later Group
B took only three minutes and a half, while Group C took four minutes and
a half to finish feeding.
Fig.3 The relationship between the time period of
eating pellets and the number
of experimental days
3.3 The amount of thiamin contained in the different portions of
the body induced by the lever-pressing learning
The relationship between the thiamin contained in the body and blood
of the rats which had eaten feed without undertaking the learning tasks
(control group) and the rats which had experienced the learning experiment
is shown in Figs. 4 and 5. The average thiamin levels in 1g of liver, cerebellum,
cerebrum and brain stem are shown in Fig.4. These results suggest that
thiamin contained in 1g of liver was significantly more in the rats that
had undertaken the learning tasks than those who did not (Group A), regardless
of whether the light had been switched on and off or not. The amount of
vitamin B1 contained in the cerebellum of rats in Group B was higher than
that of the non-learning rats. However no significant difference was found
between rats in Groups A and C.
The thiamin contained in 1g of cerebrum and brain stem of the rats
that carried out the task with lighting on was 5% higher than non-learning
rats.
The thiamin contained in 1ml of blood is shown in Fig.5. There was
no noticeable difference in the levels of thiamin concentration found in
the blood of rats that carried out the lever pressing task and those that
did not.
Fig.4 The amount of thiamin contained in
1g of the living tissue
of the rats
Fig.5 The amount of thiamin contained in
1ml of blood of the rats
4. Conclusion
The vitamin B1 concentration contained in cerebellums, brains stems
and cerebrums of rats who learned to press the lever to get feed only while
the light was switched on, was significantly greater than those rats who
had not been given the learning tasks. Our results indicate that vitamin
B1 is accumulated in the brain while the rats are learning tasks. The level
of vitamin B1 in the liver also increases significantly while the rats
are learning.
We compared three types of learning tasks and measured the time it
took rats to finish eating 20 pellets of feed. The most difficult task
for rats was the one in which they could only receive their reward while
a light was switched on. The concentrations of thiamin found in that particular
group of rats’ brain stems and cerebrum concentrations were significantly
higher than those rats that had not done the lever pressing tasks. However
there was no significant difference in the levels of thiamin found in the
two groups’ cerebellums. These results suggest that the brain stem and
the cerebrum are of primary importance in the rat’s cognitive development.
The thiamin levels detected in the liver were also significantly lower
in the rats that carried out the most difficult task than in the control
group. The amount of feed given and the thiamin concentration in that feed
was the same for all groups. This suggests that thiamin is supplied to
the parts of the body that need it most, i.e. the cerebrum and brain stem
rather than the cerebellum.
The brain stem is a part of nervous system which is responsible for
feelings. The higher level of thiamin found in the brain stem has a close
connection with satisfaction that rats felt when they got rewards by pressing
the lever.
The thiamin contained in the cerebrum was also found to be significantly
higher. This result suggests that the rats learned how to get feed. They
did not have to move around to get feed, but could get the feed by pressing
the lever while the la mp was on. Therefore the thiamin contained in the
cerebellum was lower, that is, the necessity to accumulate thiamin in the
cerebellum decreased.
It is also important to note that the cerebrum is located near several
parts of the nervous system that are responsible for short-term (the hippocampus
) and more long-term memories. The concentration of thiamin in the brain
stem and cerebrum of rats that carried out the lever-pressing learning
tasks with an additional level of difficulty (receiving the reward only
when a light was on), was significantly higher than rats in the other groups.
This result suggests that vitamin B1 affected only certain parts of the
nervous system (brain stem and cerebrum) while a rat carried out learning
tasks. The results also suggest that there is a correlation between thiamin
levels and the level of complexity of learning tasks carried out.
REFERENCES
1) M. Terasawa, T. Nakahara, N. Tsukada, A Sugawara, Y. Itokawa: The
Relationship between thiamine Deficiency and Performance of a Learning
Task in Rats. Metabolic Brain Disease vol. 14, No. 3, 137-148, Plenum Publishing
Corporation, 1999.
2) M. Terasawa, T. Yoneyama, N. Tsukada, T. Nakahara, Y. Itokawa: The
Relationship between the Learning by Reward and Vitamin B1 in the Nervous
Tissues of Rats, SCI’99 The 3rd World Multiconference on Systemics, Cybernetics
and Informatics and ISA99, The 5th International Conference on Information
Systems analysis and Synthesis 1999, Proceedings, Vol.8, P237-240, 1999.
3)M. Terasawa, T. Yoneyama, N. Tsukada, T. Nakahara, Y. Itokawa ：
The Relationship between the Ability to Learn and Thiamine Concentration
in the Nervous Tissues of Rats, 20th Annual International Conference of
the IEEE /EMBS, 20, Part4/6, 2084-2087, 1998.