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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HORMONES OF PREGNANCY AND LACTATION
The lactating female is especially aggressive in muroid rodents. This is true not only in laboratory species, but also in many wild species, including Rattus rattus (Ewer, 1971), Cricetomys gambianus (Ewer, 1967), Micromys (Frank, 1957), Lemmus lemmus (Arvola, limen, & Koponen, 1962), Microtus agrestis (Clarke, 1956), Neotoma fuscipes (Linsdale & Tevis, 1951), Dicrostonyx groenlandicus (Brooks & Banks, 1973), and Apodemus sylvaticus (Gurnell, 1977).
The pregnant or pseudopregnant female may also be especially aggressive. Noirot, Goyens, and Buhot (1975) have described high rates of "impulsive attacking" against male intruders by pregnant and pseudopregnant mice. Erskine, Barfield, and Goldman ( 1980b ) have noted increased aggressiveness by rats during what appeared to be pseudopregnancy. And in our laboratory we have seen increased rates of competitive fighting (offense) by females during pseudo-pregnancy (Adams, unpublished observations).
The enhanced aggressiveness of pregnant and lactating females may be due to activation of both the defense and offense motivational systems. In laboratory species, various reports have described both lunge-and-bite and bite-and-kick attacks by lactating females. In lactating Mus musculus, the bite-and-kick attack has been described as "grasping and rolling about while biting" (Rosenson & Asheroff, 1975, p. 221) and the lunge-and-bite attack as "the lactating female would immediately lunge and bite" (Gandelman, 1972, p. 24). In lactating Peromyscus leucopus, the bite-and-kick attack has been described as an "attack-fight sequence" while the lunge-and-bite was defined as a "lunge" attack (Rowley & Christian, 1976). In Rattus norvegicus, we have noted in our laboratory that the lactating female may alternate between lunge-and-bite attacks (defense) and bite-and-kick attacks with offensive sideways posture (offense) against an unfamiliar intruder .
The aggressiveness of pregnant or pseudopregnant females may also involve both enhanced defense and offense. As noted above, we have seen enhanced offense during pseudopregnancy in the rat. The observations of Erskine et al. (1980b) on pseudopregnant rats are consistent with an increase in offense, since they described offensive sideways posture and bites that were directed at the dorsal neck area of the intruder. On the other hand, the "impulsive attacking" described by Noirot et al. (1975) may have been a defensive lunge-and-bite attack.
Two hormones, progestins and prolactin, have been investigated with regard to their possible role in the aggressiveness of pregnancy and lactation. Progestin levels are high during pregnancy and low during lactation, while prolactin levels increase periodically during pregnancy and reach their highest levels during lactation.
Despite some reports that prolactin is critical for aggressiveness during lactation, other recent work has cast doubt on this notion. In favor of a role for prolactin are data that administration of ergocornine, which inhibits the release of prolactin, also suppresses maternal aggression in the hamster (Wise & Pryor , 1977) and mouse (Politch & Herrenkohl, 1980). Also it has been reported that prolactin injection can increase maternal aggression in mice (Hansult & Kessler , 1977), and that ectopic pituitary grafts that raise prolactin levels can increase aggressiveness in hamsters (Buntin, Catanzaro, & Lisk, 1979). On the other hand, the effectiveness of ergocornine as a suppressor of maternal aggression in mice has been contradicted by Mann, Michael, and Svare (1980), and it has been found that maternal aggression survives hypophysectomy, which removes the major source of circulating prolactin (Erskine, Barfield, & Goldman, 1980a).
Progestins may play a role in the enhanced aggressiveness of pregnant and pseudopregnant females. In certain species of muroid rodents, the aggresssiveness of the female may be reduced by ovariectomy and restored by progestin, but not estrogen, administration. In a study on Lemmus trimucronatus (Huck, Carter, & Banks, 1979), the attacks were clearly defensive lunge-and-bite ("female assumes a posture with head elevated, mouth open, and teeth prominently displayed. In this posture female vocalizes and lunges towards the male." p. 42). In similar studies involving Peromyscus leucopus (Gleason, Michael, & Christian, 1979) and Mesocricetus auratus (Payne & Swanson, 1971), it was not clear from the published accounts whether the attacks affected by progestins were bite-and-kick or lunge-and-bite attacks. In the former species, there was a simultaneous inhibitory effect of the progestin on submissive behavior (Gleason et at., 1979).
Progestin has another effect: It synergizes with estrogen in the estrous inhibition of offense by muroid rodent females against male opponents. Thus, injection of progestin leads to a greater effect than injection of estrogen alone, described earlier (Floody & Pfaff, 1977). Although progestin administration has been reported to inhibit offense in males (Soares, Kalberer, & Erpino, 1978), this may not have any behavioral significance since progestins do not normally circulate in significant levels in the male (Bartke, Smith, Michael, Peron, & Dalterio, 1977).
In view of a recent report that the posterior pituitary hormone secreted during lactation, oxytocin, may be involved in stimulating other behaviors associated with lactation (Pedersen, 1980), one would want to determine if it may also play a role in the enhanced aggressiveness of the lactating female.
It may be hypothesized that the hormones of pregnancy and lactation act on offense and defense/submission by influencing the offense motivational mechanism and the consociate modulator, as illustrated in Figure 1. The effect on the offense motivational mechanism would be excitatory and that on the consociate modulator would be inhibitory, thereby releasing defense from its suppressive modulation.
The evidence for the sites of action of progestin in the brain are consistent with its hypothesized roles in offense and defense/submission. Progestins are taken up in two locations in the hypothalamus, the preoptic region and the ventromedial region (Stumpf & Sar, 1976). The effects on offense might be expected to take place in the preoptic hypothalamus, as noted above in the section on estrogens. An inhibitory effect of progestin on the consociate modulator might be expected to occur in the ventromedial hypothalamus, which may be the site of the neurons of the consociate modulator (Adams, 1979a).
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