FREE ESSAY ON ALTERATIONS IN FEEDING BEHAVIOUR

ALTERATIONS IN FEEDING BEHAVIOUR

__________________________________________________________________
Alterations in feeding behaviour of female rats at varying phases of their reproductive
sequence as a result of lesions in various parts of the amygdala
Rachel K MacDonald
City University
The topic of this proposed research is the role of the amygdala in hunger and satiety
following damage in female infant and adult rats as a result of sexual and maternal
activity. Data will be collected from 200 female albino rats, 50 infants and 150 adults
of the Sprague-Dawley strain. Hunger and satiety will be analysed following feeding
behaviour analysis of body weight regulation, spontaneous food and water intake, and the
responses to glucose gavage and long-term food deprivation. The results should provide
evidence that the aforementioned feeding mechanisms are affected by lesions in some parts
of the amygdala and should lead to the safe conclusion that the amygdala does play an
equal role in hunger and satiety as it does in appetite.
Specific aims: (abstract/summary)
The broad, long-term objectives of this research include; assessing the role of the
amygdala (See Figure.1 for location) on feeding behaviour in the female rat. In order to
realise the role of neural mechanisms and signals underlying hunger and satiation. This
specific research is intended to accomplish a greater understanding of the effect of
lesions in varying areas of the amygdala on body weight regulation, unprompted food and
water intake, responses to glucose gavage and long-term food deprivation. These feeding
factors will be analysed at various points throughout the rats' reproductive and maternal
activities and the sample will therefore include infant female rats and adult female
rats.
As the amygdala is comprised of a collection of nuclei in the temporal lobe the
basolateral complex is in red, and the lateral nucleus is in yellow. The hippocampus is
also displayed in blue, with its cell bodies in black. 
The green is a collection of various nerve fibres contributing to the internal and
external capsulae and corpus callosum.
The main assumptions underlying this research are that lesions in altered parts of the
amygdala will affect feeding behaviour of the rats in diverse ways as different parts of
the amygdala are responsible for divergent functions and these differences will alter
depending on whether the female rat in 'in heat', pregnant, or nursing as the amygdala
plays roles in reproductive behaviour as well is ingestion.
The general goal is therefore to observe both similarities and differences in feeding
behaviour observed in Schoenfeld & Hamilton's (1981) report by therefore extending their
prior research and applying the findings to a larger rat population. A further goal is to
verify or refute Schoenfeld & Hamilton's vague statement that "Body weight regulation,
spontaneous food and water intake, and the responses to glucose gavage and long-term food
deprivation were not altered by lesions in the amygdala. Hence the wide-ranging research
question the proposed study attempts to answer is 'what exact role does the amygdala play
in feeding in the female rat as a function of age and sexual eminence.' This question
shall be answered by firstly asking which of the following behavioural tests; body weight
regulation, spontaneous food and water intake, the responses to glucose gavage and
feeding response to long-term food deprivation, are altered by lesions in the amygdala of
female rats. This latter question enables us to assess the role the amygdala plays in
hunger and satiety in the female rat. 
It is consequently important to make the distinction between appetite, hunger, and
satiety, as the latter ones are the only ones that require thorough testing. This is
because although various theories have been put forward generally the whole topic in
question is poorly understood. To understand the complexities it is essential to
recognize what the terms hunger, appetite and satiety mean. Hunger is the craving for
food that is associated with objective sensations. It is a general sensation localised to
the stomach region; it appears when the stomach is empty and coincides with contractions
detected by mechanoreceptors in the stomach wall. Appetite is the desire for specific
types and quantity of food. Satiety is the opposite of hunger and results from a filling
meal. Schoenfeld & Hamilton (1984) felt that some of the tests they conducted did not
show disruption of satiety or hunger at all, just appetite. This proposed research will
put that assumption to test again, with another variable of gender and reproductive
phase.
These questions are important because it is imperative to learn if Schoenfeld &
Hamilton's (1981) conclusions extend to female rats, and also whether lesions of the
amygdala affect the feeding behaviour of the rat differently in different reproductive
stages. The first experiment, on food deprivation is fundamental as although the topic
has been a critical factor in research on amygdaloid mechanisms in feeding behaviour.
Food deprivation in rats is still largely misunderstood, especially as concerning female
rats.
The relevant theoretical framework to the proposed research involves producing lesions
bilaterally in the various sites in and around the amygdala and then assessing brain
damage using standardized gridded plates from a rat brain atlas, to see if lesions in
particular areas affect feeding behaviour in differing ways.
The hypotheses will be tested thoroughly by using similar methods as stated in Schoenfeld
& Hamilton's method section but using female rats instead of male, and at different
points in their life cycles. The factor of age will be carefully controlled as will the
factor of weight.
Background and Significance:
The theoretical and empirical background for this proposed research chiefly originates
from Schoenfeld & Hamilton's (1981) investigation into disruption of appetite following
small lesions in the amygdala of male rats. 
Klüver and Bucy (1939) are most often cited as having initially suggested that the
amygdala plays an important role in feeding behaviour. They came to this conclusion
through observing the functions of the temporal lobes in monkeys.
Others researchers that have worked on similar problems include; Nachman and Ashe (1974),
however they extended the original idea to the study of rats. Unfortunately, the methods
used in these previous studies led to a lack of specificity. The consequences of the
research led to more unanswered questions, as no conclusions had been uncovered about the
fixed limits or boundary of the amygdala's involvement in feeding behaviour. Even though
Nachman and Ashe did manage to incorporate behavioural specificity with anatomical
specificity in a reasonable way it is still unclear whether differences in results
between experiments are due to differing procedures, anatomical destruction, or some
other distinction. For this reason the proposed experimental procedure shall closely
follow Schoenfeld & Hamilton's, as displayed in their 1981 publication.
The results and conclusions of previous research are quite contradictory. For instance
Pubols (1966) study, and Kemble & Schwartzbaum's (1969) study on the effect of lesions on
the response to brief exposure to 8% sucrose solutions yielded completely inconsistent
findings even though they were extremely similar experiments. Another important
contradiction relates to the theory behind experiment 1. Dacey and Grossman (1977)
compared the effects of lesions restricted to only the amygdala and only to the striatus.
They found that lesions of the central amygdaloid nucleus do not alter spontaneous
feeding and drinking.
Conversely, observations by Box and Mogenson (1975) were conflicting. Clearly, further
tests need to be carried out in order to shed more light on the subject.
The proposed study will therefore be limited to the investigation of infant and adult
female rats with lesions in various part of their amygdala (see Table 1), on subsequent
testing in four measures of their feeding behaviour.
Experiment Lesions sites:
Experiment 1:  Ventromedial area
 Transition zone
 Caudoventral area
 Midlateral area
 Central nucleus
Experiment 2:  Lateral amygdala
 Medial amygdala
 Amygdalaostriatal transition zone
 Striatum 
Table 1. Area of brain damage in each experiment
The work that I intend to execute will take this previous research and not only extend it
but also challenge some of its core conclusions. It will also explore a previously
ignored area of research by investigating the interaction between reproductive behaviour
and appetite following brain damage of the amygdala. Following thorough analysis and
evaluation of the current knowledge available, it becomes apparent that the research
proposed would fill in an imperative gap in the literature, i.e. the absent data from
females of the Sprague-Dawley strain, at differing stages of reproductive age and
activity. Pfaff and Keiner (1972) found that the amygdala contains some cell groups,
which are targets for estrogens. It is therefore sensible to assume that lesions in
particular areas will cause interference of feedings behaviour in most female rats
(except for the ones that are not sexually mature). The future study will also challenge
prior knowledge by retesting the claim that "the amygdala may play a greater role in
appetite than in hunger or satiety." This extended assessment will only analyse the
previously dismissed feeding behaviour, which damage to different parts of the amygdala
was concluded as having not been changed.
In summary, this proposal comprises a replication of the Schoenfeld & Hamilton (1981)
study plus an essential gender extension. 
Research Design and Methods:
The experimental design is completely between.
The main factor that will be manipulated is the region of damage within the amygdala (See
Table.1).
However the main independent variable is of reproductive status. This has 4 levels:
(1) 6 weeks of age or younger (therefore not sexually mature)
(2) 4 months and above (undergoing usual reproductive cycles)
(3) Pregnant
(4) Nursing
The dependant variable differs within each experiment with consideration of the behaviour
under inspection.
The variable concerning the reproductive aspect of the rats is based on the following
specifics:
 Rats reach sexual maturity at 5 weeks of age
 Females of breeding age come into heat every 4-5 days.
 Female rats don't come into heat if they are pregnant or nursing.
 The best time to breed a female is after 4 months of age.
 The gestation period is normally 22 days.
 Babies can be weaned at 4-5 weeks.
The proposed experiment will contain two independent studies:
Experiment 1 - brief food consumption following food deprivation or glucose gavage.
Experiment 2 - body weight regulation and spontaneous consumption of food pellets and
water. The latter study will be a single focus of behavioural observation, unlike in
Schoenfeld & Hamilton's study when in was analysed within other experiments.
The procedures apparent within the proposed research will closely follow Schoenfeld and
Hamilton's (1981) techniques. (See main method below for divergences)
The data will be analysed like such:
Figure 2. A flow diagram of the proposed data analysis
Outcomes that are inconsistent with the results that are expected could arise due to
differing procedural details or differing anatomical destruction and should be
consequently interpreted as ambiguous. Alternatively, inconsistent findings could arise
due to the gender of the rats; this aspect is therefore not contradictory as some
dissimilarity between the two sexes should be expected due to the differing role of the
amygdala in male and female reproductive behaviour as this brain structure is sexually
dimorphic.
Any refutations would suggest that Schoenfeld & Hamilton were correct in postulating that
lesions in any areas of the amygdala do not alter certain feeding behaviours, i.e. food
deprivation and body weight regulation. Results that portray no difference between male
and female rats, regardless of reproductive state would simply imply that the amygdala is
more similar in males and females that we might otherwise have thought. Even these
findings would for that reason would still add relevant data to the general problem of
the role of amygdala in rats.
Outcomes that are consistent with the hypotheses include relevant evidence that lesions
in particular areas of the amygdala do affect body weight regulation, spontaneous food
and water intake, response to glucose gavage and long term food deprivation. This
substantiating data would imply that the amygdala (or certain areas within it) do play a
role in hunger and/or satiety and not just appetite.
In experiment 1 rats with Caudoventral area damage will have increased intake following
deprivation but to a decreased level if an infant (under 6 weeks). In accordance with
Cole's (1974) findings it is likely that the amygdaloid lesions in a dorsomedial region
will result in less absolute food consumption following overnight deprivation than that
shown by controls. Increased food consumption will take place in pregnant rats due to
increased activation of the medial amygdala. Lesions of the ventromedial area will also
produce this result. Schoenfeld & Hamilton stated that male rats "overeat to a brief
period of food restriction". This shall be demonstrated in female rats, except the ones
that are pregnant or nursing. This experiment will display hunger (rather than just
appetite) if rats respond to long-term deprivation with a normal increase in food
intake.
In experiment 2 a difference in nursing and pregnant rats from the other groups would be
expected if their lesions were in the medial amygdala. This is because cells In the
medial amygdala contain estrogen receptors and it is reasonable to assume that this will
interact with the feeding mechanisms controlled by the medial amygdala. However as the
medial nucleus of the amygdala plays an important role in reproductive behaviour the
results from the rats in usual reproductive cycles may differ significantly.
The medial nucleus of the amygdala receives olfactory information from the olfactory bulb
and accessory olfactory bulb. As it is involved in the effects of odors and pheromones on
reproductive behaviour lesions in this area could cause different results in rats with a
normal reproductive cycle. This is especially true if they are 'in heat' and/or a male
rat is brought close to them.
The results that are expected from experiment 1would illustrate that body weight loss is
more closely associated with damage to the amygdala itself. Especially in pregnant or
nursing rats, as the medial amygdala plays a central role in reproduction. Also a high
level of body weight and intake should be associated with the control group only,
regardless of age, but more so in pregnant rats. The body weight levels of animals with
amygdaloid lesions should differ significantly from the controls. Also in experiment 2:
unless the rat is six weeks or under, the body weight of the striatal damaged rats will
drop significantly.
General Method
Subjects - Two hundred female albino rats of the Sprague-Dawley strain will be used.
Fifty of these will be approximately 6 weeks of age (infant, not reached sexual maturity)
and 150 will be approximately 4 months (adult). The animals will be housed individually
with Purina Lab Chow and tap water freely available except as noted.
Surgery and Histology
These initial lesion-making procedures will be taken directly from Schoenfeld &
Hamilton's (1981) procedure, p. 566. However for Experiment 1, reproduced grid plates of
the damage will be composed of 13x13 mm squares, each of which will correspond to an area
of 1 mm? represented on the atlas plates. Yet, for experiment 2, the grid will be
composed of 12x12 mm squares, each of which will correspond to an area of 8 mm? on the
atlas plates. Lesions scores from corresponding sites or squares on each side will be
combined to make one bilateral score for each site in each rat, by using the two
hypotheses followed in 
Schoenfeld & Hamilton's article. The exact same procedures for the statistical analyses
(p. 567) will also be employed.
Experiment 1- Response to food deprivation and glucose gavage
This experiment shall examine the role of the amygdala in the response to hunger and
satiety. Food deprivation and glucose gavage shall be used to approximate these states.
Subjects - one hundred rats (25 at 6 weeks, 25 at 4 months, 25 pregnant, and 25 nursing),
weighing approx 370g will be assigned to one of 5 surgical groups, or a control group.
The procedure is as stated on p. 579 of Schoenfeld & Hamilton's publication. A large
number of lesions sites will be analysed because Schoenfeld & Hamilton found that
"changes in behaviour was correlated with damage that encompassed several sites rather
then just one".
Six experimental groups will be formed:
1. Ventromedial area
2. Transition zone
3. Caudoventral area
4. Midlateral area
5. Central nucleus
6. Operated controls
Four of each category of rat will be in each group.
Experiment 2 - Body weight and spontaneous intake
This experiment will examine the extent to which actual damage to amygdaloid tissues may
account for symptoms of reduced intake and lowered body weight following lesions in the
amygdala itself to lesions invading striatal tissues dorsal to the amygdala.
Subjects - one hundred rats, weighing approximately 270g at the beginning of the
experiment will be used. The pregnant rats will undergo testing at the beginning of their
pregnancy so they will not weigh significantly more than subjects in other groups.
Twenty-five will be roughly 6 weeks old (not sexually mature), 25 will be 4 months old
and in usual reproductive cycle, 25 will be pregnant, and 25 will be nursing at the time
of testing.
Subjects will be randomly assigned to 4 surgical groups or a control group (anaesthetized
only). Lesions in surgical groups:
1. Lateral amygdala
2. Medial amygdala
3. Amygdala-striatal transition zone
4. Striatum
There will consequently be 5 rats (of different sort) randomly assigned to one of the
surgical groups or the control group. The procedure for this experiment will also be
carried out as dictated in Schoenfeld & Hamilton's article (p. 568).
References: 
Box, B. M., & Mogenson, G.J. Alterations in ingestive behaviours after bilateral lesions
of the amygdala in the rat. Physiology and Behaviour, 1975, 15, 679-688
Dacey, D.M., & Grossman, S.P. Aphagia, adipsia, and sensory-motor deficits produced by
amygdala lesions: a function of extra-amygdaloid damage. Physiology and Behaviour, 1977,
19, 389-395.
Fonberg, E. The relation between alimentary and emotional amygdalar regulation. In D.
Novin, W. Wyrwicka, & G.Bray (Eds.) Hunger: Basic mechanisms and clinical implications.
New York: Raven Press, 1976.
Klüver, H., & Bucy, P.C. Preliminary analysis of functions of the temporal lobes in
monkeys. Archives of Neurology and Psychiatry, Chicago, 1939, 42, 979-1000
Nachman, M., & Ashe, J.H. Effects of basolateral amygdala lesions on neophobia, learned
taste aversion, and sodium appetite in rats. Journal of Comparative and Physiological
Psychology, 1974, 87, 622-643.
Phaff, D.W., & Keiner, M. Estradiol-concentrating cells in the rat amygdala as part of a
limbic-hypothalamic hormone-sensitive system. In B.E. Eleftheriou (Ed.), The neurobiology
of the amygdala. New York: Plenum Press, 1972.
Schoenfeld, T.A., & Hamilton, L.W. Disruption of Appetite but not Hunger or Satiety
following small lesions in the Amygdala of Rats. Journal of Comparative and Physiological
Psychology, vol. 95, No.4, 565-587.