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... data (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) 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: &# 61607; Rats reach sexual maturity at 5 weeks of age &# 61607; Females of breeding age come into heat every 4 - 5 days. &# 61607; Female rats don't come into heat if they are pregnant or nursing. &# 61607; The best time to breed a female is after 4 months of age. &# 61607; The gestation period is normally 22 days. &# 61607; 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 1 would 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.
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. 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 13 x 13 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 12 x 12 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 370 g 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: 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 270 g 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 (anesthetized only). Lesions in surgical groups: 3. Amygdala-striatal transition zone 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).
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