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Introduction
Page 1
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Experiment 1:
Intro/Method
Pages 2-3
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Experiment 1:
Results
Page 4
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Experiment 1:
Discussion
Page 5
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Experiment 2:
Intro/Method
Page 6
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Experiment 2:
Results
Page 7
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Experiment 2:
Discussion
Page 8
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Experiment 3:
Intro/Methods
Page 9
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Experiment 3:
Results
Page 10
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Experiment 3:
Discussion
Page 11
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General Discussion
Page 12
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Figures 1-2-3
Pages 13-14-15
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Tables 1-2-3
Pages 16-17-18
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Competitive and territorial fighting can be elicited easily in laboratory rats, as well as other animals, although the means of eliciting the two types of fighting are quite distinct. In competitive fighting, two rats already familiar with each other will often fight over a piece of food or a single water source if they have been food or water deprived. In territorial fighting, a resident rat will often attack an unfamiliar rat that intrudes into its territory. Despite the fact that these two types of fighting occur in very different situations, they share the same motor patterns, including the bite-and-kick attack, biting attack, and offensive sideways posture. Because the two types of fighting are different in some respects, yet similar in their motor patterns, the question has arisen as to whether they are controlled by a single brain mechanism or by two separate mechanisms.
Adams (3) proposed a model that assumes that competitive and territorial fighting are controlled by the same brain mechanism which was named the offense motivational mechanism. According to the model, the motivational mechanism is activated or inhibited by motivating stimulus analyzers that are tuned to specific stimuli that elicit or inhibit the behavior. If the appropriate releasing or directing stimuli from the target animal are present during this activation, one or more of the motor patterns of offense will be produced. Separate analyzers were proposed for androgen-dependent pheromones, estrogen-dependent pheromones, unfamiliar conspecific odors, and ultrasound, as well as a competitive fighting synthesizer. It was assumed that all of these inputs (some facilitative and others inhibitory) converge in an additive fashion on the offense motivational mechanism.
The model was developed to explain data obtained from experiments on territorial fighting. These experiments (8-10) found that rats preferentially attack intruders of the same sex. In the case of males, the effect was abolished by castration and restored by androgens, while in the case of females, the effect was not abolished by ovariectomy (9).
Experiment 1 sought to test the Adams model by determining if competitive fighting, like territorial fighting, is stronger against same-sexed opponents, which would be expected if both types of fighting were under the control of one and the same motivational mechanism. As far as we know, this question has never been addressed in previous studies of competitive fighting.
The first experiment also looks at sex differences in competitive fighting. Work by Fredericson (11, 12) established that competitive fighting differs from territorial fighting in this regard. Whereas territorial fighting (which he called spontaneous fighting) was observed only in male mice, competitive fighting over food was as likely to occur in females as in males. And in rats, whereas it is well established that males are more likely to show territorial fighting, Zook and Adams (15) found as much fighting by females as by males in competitive fighting. A later study by Mink and Adams (13) found more than twice as much competitive fighting by females as by males.
To explore the hormonal basis for differences in fighting as a function of sex and opponent sex, we compared the competitive fighting of normal and gonadectomized rats. As mentioned above, previous studies have found that in territorial fighting, the male and female sex hormones play very different roles, facilitating the fighting of males against males, but not affecting the normal fighting of females.
Experiment 2 was designed to replicate the findings of previous investigators (8-10) on preferential attacks upon same-sexed opponents in territorial fighting. Because the rats used in the competitive fighting experiment are a homozygous strain, it was necessary to show that this strain showed the same effects as those found in outbred rats by previous investigators.
Experiment 3 compared the effects of food deprivation on competitive and territorial fighting. It was assumed that if the two types of fighting were mediated by a single brain mechanism, the effects of food deprivation should be similar on both of them.
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