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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ANDROGENS
Androgens facilitate both the offense and patrol/marking motivational systems in muroid rodents. This is indicated by the higher levels of the bite-and- kick attack (offense) and scent-marking motor patterns (patrol/marking) in dominant intact males than in subordinates, castrates, or females, and by the restoration of higher levels in castrates by administration of androgens. In the case of offense, the effect of androgens is well known and has often been reviewed (Bronson & Desjardins, 1971; Edwards & Rowe, 1975; Leshner, 1975; Whalen, 1974). In the case of patrol/marking it has not been as extensively reviewed but has been shown experimentally in rats (Price, 1975), gerbils (Thiessen, Friend, & Lindzey, 1968), and mice (Bronson, 1976).
There is little evidence that androgens affect the defense and submission motivational systems. In the laboratory rat there are higher rates of upright posture and boxing during shock-elicited fighting in males, an effect that is dependent on neonatal androgens (Conner & Levine, 1969) and reduced by castration (Hutchinson, Ulrich, & Azrin, 1965). However, we have found no difference in the rate of upright posture and boxing between males and females in response to bite-and-kick attack by a partner during competitive fighting (Adams, unpublished observations). Also, the defensive responses to handling by an experimenter do not differ between the sexes (Korn & Moyer, 1968), nor do the submissive postures during defeat (Nock & Leshner, 1976).
The effect of androgens on offense is apparently exerted on sensory analyzers for motivating stimuli rather than on the motivational mechanism. This is indicated by the fact that offense due to certain motivating stimuli, such as those associated with competitive fighting, is not dependent on androgens in the mouse (Fredericson & Birnbaum, 1954) or rat (Zook & Adams, 1975). Also, there is offense by females as well as males in wild rats (Telle, 1966), wild mice (Ebert & Hyde, 1976), and other muroid rodent species such as the gerbil (Swanson, 1974) and hamster (Vandenbergh, 1971). It has been suggested that within the laboratory, the mouse and rat are special cases in which other motivating stimuli are not effective in eliciting offense and only the sensory analyzer dependent on androgens is functional (Adams, 1980).
The location of the neural substrate for the action of androgen on the offense motivational system has been determined. Studies by Bermond (1978) and by Bean and Conner (1978) have shown that injection of androgen into the preoptic hypothalamus facilitates the intermale offense of the laboratory rat after it has been reduced by prior castration. An earlier study by Owen, Peters, and Bronson (1974) had found that septal implants of androgen were effective, but they did not test implants in the preoptic area, which is adjacent and which might have been affected by spread of the hormones from the septal implant. Neurons of the preoptic area show a differential uptake of androgen (Stumpf & Sar, 1976), and their firing patterns in response to olfactory stimulation are altered by androgen (Pfaff & Pfaffman, 1969).
The intermale fighting of laboratory rats and mice, it may be hypothesized, depends on an androgen-organized and androgen-activated sensory analyzer, located at least partly in the preoptic hypothalamus, that is tuned to androgen-dependent pheromones and that activates the offense motivational mechanism. Part of the basis for this hypothesis derives from the preceding paragraphs. Other relevant evidence comes from the fact that the fighting depends on olfaction (Adams, 1976) and on the presence of androgen in the opponent (Mugford & Nowell, 1970; Thor & Flannelly, 1976). Also, androgens must be present not only in the adult (i.e., an activating role) but also in the perinatal period (an organizing role), as has been shown in the mouse (Edwards, 1969) and rat (Barr, Gibbons, & Moyer, 1976).
There is another aspect of the intermale fighting of muroid rodents that may be androgen-dependent: an inhibition of attack on adult conspecific females. In experiments using urine from a donor animal, the inhibition depends on estrogen-dependent pheromones of the donor animal (Haag, Jerhoff, & Kirkpatrick, 1974). One may suppose that the effect is due to the action of these pheromones on an androgen-activated sensory analyzer that is tuned to estrogen- dependent pheromones and that inhibits the offense motivational mechanism. Its neural substrate has not been investigated, but it may be related to the other mechanism described above.
The effects of androgens on patrol/marking are apparently exerted at two points, both on the motivational mechanism itself and on sensory analyzers for motivating stimuli of patrol/marking.
The facilitation of the motivational mechanism of patrol/marking by androgens is indicated by experiments in which effects on motivating stimuli are ruled out. Thus, androgens are apparently responsible for the "spontaneous" patrolling of males that occurs even in the absence of relevant motivating stimuli (Shillito, 1963). Also, androgen administration can reinstate the ventral-rub marking of gerbils after its motivating stimuli have been rendered ineffective by olfactory deafferentation (Thiessen, Lindzey, & Nyby, 1970).
There are also effects of androgens on the sensory analyzers of motivating stimuli for patrol/marking. There may be two such analyzers, similar to or identical with the analyzers that process motivating stimuli of offense: (1) a sensory analyzer tuned to odors of androgen-dependent pheromones, activated by androgens, and inhibiting the patrol/marking motivational mechanism; and (2) a sensory analyzer tuned to odors of estrogen-dependent pheromones, activated by androgens and facilitating the patrol/marking motivational mechanism. They determine the fact that intact males explore and scent-mark in reaction to conspecific females but not in reaction to males. The data for various muroid rodent species has recently been reviewed in detail (Adams, 1980).
The effects of androgens on patrol/marking, like their effects on offense, apparently take place in the preoptic hypothalamus. Therefore, this brain area may contain either the motivational mechanism of patrol/marking, its sensory analyzers, or both. Lesions of this area abolish the approach locomotion that is normally enhanced by androgen in males (Singer, 1968), and implantation of androgen in this area reinstates the ventral-rub scent-marking of male gerbils after it has been reduced by castration (Vahr, 1977). Neurons of this area respond differentially to urine odors that may normally function as motivating stimuli for patrol/marking, and they may be sensitized by the administration of androgen (Pfaff & Pfaffman, 1969). Also, they have been shown to have a high uptake of radioactive androgen, as noted above (Stumpf & Sar, 1976). We have obtained data showing that medial preoptic neurons are differentially active during approach by a male rat toward an estrous female (Mink et al., in press).
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