Title & Introduction
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Offense, Defense & Patrol/Marking
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Neural Circuitry & Motivational Mechanisms
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How Circulating Hormones May Affect Behavior
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Pregnancy and Lactation
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ACTH, etc.
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Reproductive States
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Conclusion
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References
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ESTROGENS
The effect of estrogens on offense is apparently exerted, at least in part, directly on the offense motivational mechanism, since offense is reduced during estrus against all types of opponents. Apparently the effect is mediated by estrogen and facilitated by progestins (Floody & Pfaff, 1977). One set of contradictory data have been obtained in a preliminary study in our laboratory that suggested that competitive fighting by females is not reduced during estrus. It is possible, however, that the motivating-stimulus inputs for competitive fighting are facilitated by estrogen, since females usually show more competitive fighting than males, and that during estrus there are two opposing influences of estrogens that more or less cancel each other out.
More work remains to be done on the effects of estrogens upon the neural substrate of offense in female muroid rodents. The major data come from only one species, the hamster. Although there are data on the mouse and rat, the reduction of offense during estrus in the one study on the mouse was not highly significant for chasing and attack (Hyde & Sawyer, 1977), and preliminary reports on reduction of offense during estrus on the rat have not yet been fully published. Furthermore, there may be an additional inhibitory effect depending on male gonadal hormones in the opponent, which could explain why females of many wild rodent species are less likely to attack strange males than they are to attack strange females.
The effects of estrogens on patrol/marking, like those of androgens, are apparently exerted at two points, both on the motivational mechanism itself and on sensory analyzers for motivating stimuli.
The facilitation of the motivational mechanism of patrol/marking by estrogens is indicated by experiments in which possible effects on motivating stimuli are apparently ruled out. When female muroid rodents of various species are in estrus, they show higher levels of locomotion, apparently due to patrol/marking activation (Richards, 1966; Stinson, 1952; Vick & Banks, 1969; Wang, 1923). This locomotion increase may be obtained from females that are isolated in cages that exclude the normal motivating stimuli of patrol/marking.
Estrogens also may activate a sensory analyzer that is tuned to androgen-dependent pheromones and that facilitates patrol/marking in the female when she encounters another male. This may be the same analyzer that is responsible for her decreased offense against such a male. In the rat, adult females approach, urine-mark, and sniff more in the presence of male odors than in the presence of the odors of castrates or females, and the effect is abolished by ovariectomy (Brown, 1977). In the mouse, females are attracted to the odors of adult male preputial glands and the effect is enhanced by estrogen injections (Caroom & Bronson, 1971). Also, they locomote more in response to odors from intact males than to odors from castrates (Ropartz, 1970), and they urine-mark more in the presence of male odors than of castrate odors (Maruniak, Owen, Bronson, & Desjardins, 1975), Although the latter authors found no differences as a function of the estrous cycle or ovariectomy, their data have recently been contradicted and an estrous effect has been described that would be consistent with estrogen activation (Wolff & Powell, 1979).
Estrogens, like androgens, apparently exert at least some of their effects on patrol/marking by acting on neurons of the preoptic region. Lesions of the preoptic region reduce approach locomotion that is produced by systemic estrogen injections (King, 1979). Implantation of estrogen into the preoptic region facilitates locomotor activity of ovariectomized rats (Colvin & Sawyer, 1969; Wade & Zucker, 1970). Neurons in this region have also been shown to have a high uptake of radioactive estrogens (Pfaff, Lewis, Diakow, & Keiner, 1973). Whether the region contains the motivational mechanism of patrol/marking or its sensory analyzers or both is a question that cannot yet be answered.
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