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Ventromedial tegmental lesions abolish offense without disturbing predation or defense
Physiology & Behavior, Vol. 38, pp. 165--168.Copyright©Pergamon Press Ltd., 1986. Printed in the U.S.A.
0031-9384/86 $3.00 + .00
Ventromedial Tegmental Lesions Abolish Offense Without Disturbing Predation or Defense D A V I D B. A D A M S
D e p a r t m e n t o f Psychology, Wesleyan University, Middletown, CT 06457 R e c e i v e d 28 A p r i l 1986 ADAMS, D. B. Ventromedial tegmental lesions abolish offense without disturbing predation or defense. PHYSIOL BEHAV 38(2) 165-168, 1986.--Offense, defense, and predation, three kinds of aggressive behavior, are differentially affected by lesions of the ventromedial tegmentum of the brainstem of the rat. The lesions abolish offense while leaving defense and predation undisturbed. The offense behavior against another strange male, including bite-and-kick attack, offensive sideways posture, and offensive upright posture, was totally abolished, while the rats showed intact motor patterns of defensive upright posture, chasing, and killing bite in the tests for defense and predation. It is argued that these results support a motivational systems analysis of mammalian aggressive behavior. According to such an analysis, offense, defense, and predation are controlled by discrete motivational mechanisms located in different brainstem regions. Offense
Aggression
Rat
Predation
Defense
IT is generally agreed that there are at least several different types of aggressive behavior in mammals, and, in recent years, interest has focused especially upon three common types: offense, defense, and predation [7,19]. Offense is characterized by a bite-and-kick attack and offensive sideways posture, and it may be elicited by confronting a mature male cat, rat, or mouse with an unfamiliar male opponent of the same species. Offense may also be elicited in either males or females by giving one piece of food to two hungry mice [11] or rats [21]. Defense is characterized by a lungeand-bite attack or upright posture with boxing movements of the forelimbs in the mouse or rat [3] and by hissing, arching of the back and striking with the forelimbs in the cat [14]. Both offense and defense involve extensive autonomic arousal. Predation is exemplified by the mouse-killing of the rat and the killing of mice or rats by the cat, a behavior that involves minimal autonomic arousal and has therefore been called "quiet attack" [ 10]. Reviewing the literature until 1979, I proposed that offense and defense could be distinguished in terms of their neural organization and that probably predation could be distinguished as well, although it was less well understood [2]. A more specific prediction was that it should be possible to abolish offense by making a specific lesion in the brainstem, since it had already been shown that defense could be abolished by lesions of the midbrain central gray [8]. The reason that brainstem rather than forebrain regions were predicted was because studies had shown that the forebrain is not necessary for any of these behaviors. Predation is retained after surgical isolation of the hypothalamus [9]; offense is retained after cross-sectional destruction of the hypothalamus [2]; and defense is also retained after crosssectional destruction of the hypothalamus [1].
165
The experimental clue that guided the direction of the present study was provided by a previous report [13] that median raphe lesions abolish offense in mice. It is the only study in the literature that claims to abolish offense with brain stem lesions [2]. Although we failed in pilot studies to replicate those findings in the rat, we did find that larger lesions that destroyed part of the tegmentum on either side of the median raphe were sufficient to abolish offense. The present study replicates our pilot results and extends the testing procedure to include defense and predation as well as offense. The experimental subjects were adult male rats of a hybrid strain (DA by $2). Preoperatively, they were tested for predation by introducing an unrestrained adult male mouse into their home cage, and they were tested for offense by introducing an adult male rat of a different strain into their home cage. Ten rats, approximately 10% of all the rats given behavioral testing, fulfilled the testing criteria which were three consecutive kills of a mouse within 20 minutes, each test being on a different day, and three consecutive tests with a bite-and-kick attack against a rat intruder within 20 minutes, again each test being on a different day. The percentage of animals showing predation and offense was consistent with findings in other rat strains [4,12]. The scoring of offense and predation were as follows. Predation was scored in terms of the latency to kill the mouse, or, in a few tests when no kill occurred, the latency to a non-lethal biting attack directed at the mouse. Offense was given an "offense score" consisting of one point for the presence of offensive sideways posture, which is a low level of offense, and additional points for each occurrence of bite-and-kick attack, which is a higher level of offense [15]. Offense tests were 20 minutes in duration and predation tests
ADAMS
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FIG. 1. Effect of bilateral lesions of the ventromedial t e g m e n t u m in five rats upon predation, offense, and defense behaviors. L e s i o n s are illustrated at their maximal extent on plates drawn from the stereotaxic atlas o f Paxinos and W a t s o n [17]. T h e anterior levels o f the plates are given for reference only; the lesions are illustrated in t e r m s o f the actual brain structures w h e r e they were located. Predation is m e a s u r e d in t e r m s o f latency to kill, and offense is m e a s u r e d in t e r m s of an " o f f e n s e s c o r e " (see text for details). Defense is m e a s u r e d only at the conclusion of other behavioral testing and is quantified in t e r m s o f the percent o f trials with boxing at each shock intensity presented on a titration schedule [8]. O p e n circles in predation data indicate the latency to attack the m o u s e on trials w h e n no kill was achieved.
TEGMENTAL LESIONS ABOLISH OFFENSE were 20 minutes in duration or until the killing of the mouse, whichever came first. In the ten rats that fulfilled pre-operative testing criteria, brain lesions were placed bilaterally in the ventromedial tegmentum. The lesions were placed by stereotaxic procedure using the coordinates 0.5 mm anterior, 0.7 mm vertical and 1.0 mm left and right and passing radio frequency current of 6 mA through the tip of an insulated electrode for 40 sec. Surgery was performed only after the animal had been fully anesthetized with Chloropent anesthesia, using 140 mg per kg. At the conclusion of the experiment, the lesions were reconstructed from serial frozen sections of the brain referring to the stereotaxic atlas of Paxinos and Watson [17]. It should be noted that a discrepancy was found between the labeling of the sections in the atlas and the stereotaxic coordinates employed in the study, such that is would appear that the atlas sections are mislabeled almost a millimeter too far anterior for our strain of rats (i.e., the section labeled 1.2 mm in the atlas describes the anatomical plane where we placed lesions using a setting of 0.5 mm anterior to the ear bar). In the figure, the lesions are illustrated in terms of the brain structures of that section rather than the anterior-posterior level which is given only for reference to the atlas. Post-operative tests of offense and predation were conducted in eight rats (two had died from surgical complications) in the same manner as pre-operative tests. Three post-operative tests for offense and predation, respectively, were conducted on at least three separate days from 2-13 days after surgery. In one case, offense testing was continued for a total of six tests over 21 days to ensure that there was no recovery of offense in that period. Following all offense and predation testing, the rat was tested for defense according to the method of shock-elicited boxing, and thresholds were determined by the titration method [8]. The testing for defense was not done until after all testing for offense and predation because of the possibility of interaction between offense and defense systems [15]. Offense was abolished in five rats whose lesions are illustrated in Fig. 1. These lesions destroyed much of the ventromedial tegmentum at a level including and slightly anterior to the reticular tegmental nucleus. The median raphe was damaged or destroyed in three of the animals and spared in two others. The lesions were tear-shaped and extended at their maximal width for 0.7 mm anterior and posterior to the shaded area shown in Fig. 1 which represents the largest cross-sectional area of the lesion in the stereotaxic plane. In addition to these five rats, there were three other rats in which offense was not abolished; it was found that their lesions were all posterior to the ones illustrated here and they involved no damage at the tegmental levels illustrated in Fig. 1. Data from those animals are not considered in this study. Lesions were not placed in other regions of the tegmentum in this study, since our pilot work has shown that other such tegmental lesions do not abolish offense. The behavioral results were the same in all five rats shown in Fig. 1: offense was abolished, while predation remained unchanged and the rats were capable of showing shock-elicited defensive boxing at the conclusion of the testing. Not only was the bite-and-kick attack of offense abolished, but also there was no offensive sideways posture or offensive upright posture. Other social behaviors remained unaffected by the lesion: there were no decrements in the frequency of olfactory investigation or grooming of the intruder.
167 The predation and defense, which were undisturbed after the lesions, served as behavioral controls, indicating that there was no simple motor incapacity that interfered with the performance of offense. Predation includes approach, chasing, and biting attack similar in many respects to the biteand-kick attack of offense. Defense included a defensive upright posture that is quite similar to offensive upright posture. For offense and predation, each animal's pre-operative results served as behavioral controls, the offense being abolished and the predation remaining unchanged. With regard to defense, a separate series of tests were conducted on unlesioned rats of the same strain and housing conditions and tested in the same shock-testing apparatus. The range of thresholds was similar, being 0.18 to 0.75 mA for the lesioned animals and 0.35 to 0.75 mA for the unlesioned controls. By fulfilling the prediction that brain stem lesions should be found that would abolish offense rather than other types of aggressive behavior, these results support the motivational systems analysis upon which the prediction was based [2]. The motivational systems analysis suggests that offense, defense, and predation represent three distinct systems organized around discrete sets of neurons, called motivational mechanisms, whose activation is responsible for the motivational state of the organism. The model for this analysis comes from defense, where the motivational mechanism was said to be located in the midbrain central gray, a location where: (1) lesions permanently abolish defense; (2) electrical and chemical stimulation produce defense; and (3) single neurons are differentially active during defense [2]. More recent data have shown that offense is not abolished by midbrain central gray lesions [16]. Although predation is interrupted by central gray lesions, the interruption affects only the final killing bite and not the other motivated components of the behavior such as orienting, tracking, and lunging towards the prey [20]. Further research is needed to determine if the ventromedial tegmentum contains the neurons of a motivational mechanism for offense, in the same sense that the central gray appears to have such a mechanism for defense. The fact that brain lesions of the ventromedial tegmentum abolish offense and not other types of aggression is one of the necessary criteria, but others remain untested as yet. Is the lesion effect permanent? Can offense be elicited by electrical and chemical stimulation of the ventromedial tegmentum, and are single neurons differentially active in that region during offense? In conclusion, it is now possible to distinguish offense, defense, and predation on the basis of brain stem lesions that differentially abolish these behaviors. Both offense and defense can be abolished by discrete lesions in the ventromedial tegmentum and midbrain central gray, respectively, that do not abolish the other types of aggression. It remains to be determined if predation can be abolished by a brainstem lesion that does not disturb offense or defense. Temporary or partial abolition of predation has been reported as a result of various brainstem lesions, but none have been shown to abolish predation totally and permanently [5, 6, 18, 20]. ACKNOWLEDGEMENTS For their work on the pilot project for this study, the author wishes to thank especially Gloria Herrera, Janice Robinson, Bill Goldman and Gary Edwards.
168
ADAMS
REFERENCES 1. Adams, D. B. Defence and territorial behaviour dissociated by hypothalamic lesions in the rat. Nature 232: 573-574, 1971. 2. Adams, D. B. Brain mechanisms for offense, defense, and submission. Behav Brain Sci 2: 201-241, 1979. 3. Adams, D. B. Motivational systems of agonistic behavior in muroid rodents: A comparative review and neural model. Aggress Behav 6: 295-346, 1980. 4. Bandler, R. J., Jr. and K. E. Moyer. Animals spontaneously attacked by rats. Cornmun Behuv Biol 5: 177-182, 1970, 5. Berntson, G. G. Blockade and release of hypothalamically and naturally elicited aggressive behaviors in cats following midbrain lesions. J Comp Physiol Psychol 81: 541-554, 1972. 6. Chaurand, J. P., P. Schmitt and P. Karli. Effets de lesions du tegmentum ventral du mesenc6phale sur le comportement d'agression Rat-Souris. Physiol Behav 10: 507-515, 1973. 7. Depaulis, A. and M. Vergnes. Relationship between mousekilling and conspecific aggression in the male rat. Ag,~re.ss Behm" 9: 25%268, 1983. 8. Edwards, M. A. and D. B. Adams. Role of midbrain central gray in pain-induced defensive boxing of rats. Physiol Behav 23: 113-121, 1974. 9. Ellison, G. D. and J. P. Flynn. Organized aggressive behavior in cats after surgical isolation of the hypothalamus. Arch ltal Biol 106: 1-20, 1968. 10. Flynn, J. P. Neural basis of threat and attack. In: Biological Foundations o f Psychiatry. edited by R. G. Grenell and S. Gabay. New York: Raven Press, 1976, pp. 273-295. 11. Fredericson, E. The effects of food deprivation upon competitive and spontaneous combat in C57 black mice. J Psyehol 29: 8%100, 1950.
12. Karli, P. The Norway rafts killing response to the white mouse. An experimental analysis. Behaviour 20: 81-103. 1956. 13. Kostowski, A. and L. Valzelli. Biochemical and behavioral effects of lesions of the raphe nuclei in aggressive mice. Pharmacol Biochem Behav 2: 277-280, 1974. 14. Leyhausen, P. Verhaltensstudien an Katzen. Z 7ierpsychol 2: 1-120, 1956. 15. Mink, J. W. and D. B. Adams. Why offense is reduced when rats are tested in a strange cage. Phy,siol Behav 26: 567-573, 1981. 16. Mos, J., J. H. C. M. Lammers, A. M. van der Poel, B. Bermon, W. Meelis and M. R. Kruk. Effects of midbrain central gray lesions on spontaneous and electrically induced aggression in the rat. Aggres,~ Behav 9: 133-155, 1983. 17. Paxinos. G. and C. Watson. 7he Rat Brain in Stereota.~ic C,~ordinates. New York: Academic Press, 1982. 18. Proshansky, E. and R. J. Bandler. Midbrain-hypothalamic interrelationships in the control of aggressive behavior. Aggre.s~s Behm' 1: 135-155, 1975. 19. Ursin, H. Neuroanatomical basis of aggression. In: Multidisciplima3" Approaches t o Aggression Research, edited by P. F. Brain and D. Benton. Amsterdam: Elsevier/North Holland, 1981, pp. 269-293. 20. Waldbillig, R. J. Offense, defense, submission, and attack: Problems of logic and lexicon. Behav Brain Sci 2: 227-228, 1979. 21. Zook, J. M. and D. B. Adams. Competitive fighting in the rat. J Comp Physiol Psvchal 88:418-423, 1975.
0031-9384/86 $3.00 + .00
Ventromedial Tegmental Lesions Abolish Offense Without Disturbing Predation or Defense D A V I D B. A D A M S
D e p a r t m e n t o f Psychology, Wesleyan University, Middletown, CT 06457 R e c e i v e d 28 A p r i l 1986 ADAMS, D. B. Ventromedial tegmental lesions abolish offense without disturbing predation or defense. PHYSIOL BEHAV 38(2) 165-168, 1986.--Offense, defense, and predation, three kinds of aggressive behavior, are differentially affected by lesions of the ventromedial tegmentum of the brainstem of the rat. The lesions abolish offense while leaving defense and predation undisturbed. The offense behavior against another strange male, including bite-and-kick attack, offensive sideways posture, and offensive upright posture, was totally abolished, while the rats showed intact motor patterns of defensive upright posture, chasing, and killing bite in the tests for defense and predation. It is argued that these results support a motivational systems analysis of mammalian aggressive behavior. According to such an analysis, offense, defense, and predation are controlled by discrete motivational mechanisms located in different brainstem regions. Offense
Aggression
Rat
Predation
Defense
IT is generally agreed that there are at least several different types of aggressive behavior in mammals, and, in recent years, interest has focused especially upon three common types: offense, defense, and predation [7,19]. Offense is characterized by a bite-and-kick attack and offensive sideways posture, and it may be elicited by confronting a mature male cat, rat, or mouse with an unfamiliar male opponent of the same species. Offense may also be elicited in either males or females by giving one piece of food to two hungry mice [11] or rats [21]. Defense is characterized by a lungeand-bite attack or upright posture with boxing movements of the forelimbs in the mouse or rat [3] and by hissing, arching of the back and striking with the forelimbs in the cat [14]. Both offense and defense involve extensive autonomic arousal. Predation is exemplified by the mouse-killing of the rat and the killing of mice or rats by the cat, a behavior that involves minimal autonomic arousal and has therefore been called "quiet attack" [ 10]. Reviewing the literature until 1979, I proposed that offense and defense could be distinguished in terms of their neural organization and that probably predation could be distinguished as well, although it was less well understood [2]. A more specific prediction was that it should be possible to abolish offense by making a specific lesion in the brainstem, since it had already been shown that defense could be abolished by lesions of the midbrain central gray [8]. The reason that brainstem rather than forebrain regions were predicted was because studies had shown that the forebrain is not necessary for any of these behaviors. Predation is retained after surgical isolation of the hypothalamus [9]; offense is retained after cross-sectional destruction of the hypothalamus [2]; and defense is also retained after crosssectional destruction of the hypothalamus [1].
165
The experimental clue that guided the direction of the present study was provided by a previous report [13] that median raphe lesions abolish offense in mice. It is the only study in the literature that claims to abolish offense with brain stem lesions [2]. Although we failed in pilot studies to replicate those findings in the rat, we did find that larger lesions that destroyed part of the tegmentum on either side of the median raphe were sufficient to abolish offense. The present study replicates our pilot results and extends the testing procedure to include defense and predation as well as offense. The experimental subjects were adult male rats of a hybrid strain (DA by $2). Preoperatively, they were tested for predation by introducing an unrestrained adult male mouse into their home cage, and they were tested for offense by introducing an adult male rat of a different strain into their home cage. Ten rats, approximately 10% of all the rats given behavioral testing, fulfilled the testing criteria which were three consecutive kills of a mouse within 20 minutes, each test being on a different day, and three consecutive tests with a bite-and-kick attack against a rat intruder within 20 minutes, again each test being on a different day. The percentage of animals showing predation and offense was consistent with findings in other rat strains [4,12]. The scoring of offense and predation were as follows. Predation was scored in terms of the latency to kill the mouse, or, in a few tests when no kill occurred, the latency to a non-lethal biting attack directed at the mouse. Offense was given an "offense score" consisting of one point for the presence of offensive sideways posture, which is a low level of offense, and additional points for each occurrence of bite-and-kick attack, which is a higher level of offense [15]. Offense tests were 20 minutes in duration and predation tests
ADAMS
166
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FIG. 1. Effect of bilateral lesions of the ventromedial t e g m e n t u m in five rats upon predation, offense, and defense behaviors. L e s i o n s are illustrated at their maximal extent on plates drawn from the stereotaxic atlas o f Paxinos and W a t s o n [17]. T h e anterior levels o f the plates are given for reference only; the lesions are illustrated in t e r m s o f the actual brain structures w h e r e they were located. Predation is m e a s u r e d in t e r m s o f latency to kill, and offense is m e a s u r e d in t e r m s of an " o f f e n s e s c o r e " (see text for details). Defense is m e a s u r e d only at the conclusion of other behavioral testing and is quantified in t e r m s o f the percent o f trials with boxing at each shock intensity presented on a titration schedule [8]. O p e n circles in predation data indicate the latency to attack the m o u s e on trials w h e n no kill was achieved.
TEGMENTAL LESIONS ABOLISH OFFENSE were 20 minutes in duration or until the killing of the mouse, whichever came first. In the ten rats that fulfilled pre-operative testing criteria, brain lesions were placed bilaterally in the ventromedial tegmentum. The lesions were placed by stereotaxic procedure using the coordinates 0.5 mm anterior, 0.7 mm vertical and 1.0 mm left and right and passing radio frequency current of 6 mA through the tip of an insulated electrode for 40 sec. Surgery was performed only after the animal had been fully anesthetized with Chloropent anesthesia, using 140 mg per kg. At the conclusion of the experiment, the lesions were reconstructed from serial frozen sections of the brain referring to the stereotaxic atlas of Paxinos and Watson [17]. It should be noted that a discrepancy was found between the labeling of the sections in the atlas and the stereotaxic coordinates employed in the study, such that is would appear that the atlas sections are mislabeled almost a millimeter too far anterior for our strain of rats (i.e., the section labeled 1.2 mm in the atlas describes the anatomical plane where we placed lesions using a setting of 0.5 mm anterior to the ear bar). In the figure, the lesions are illustrated in terms of the brain structures of that section rather than the anterior-posterior level which is given only for reference to the atlas. Post-operative tests of offense and predation were conducted in eight rats (two had died from surgical complications) in the same manner as pre-operative tests. Three post-operative tests for offense and predation, respectively, were conducted on at least three separate days from 2-13 days after surgery. In one case, offense testing was continued for a total of six tests over 21 days to ensure that there was no recovery of offense in that period. Following all offense and predation testing, the rat was tested for defense according to the method of shock-elicited boxing, and thresholds were determined by the titration method [8]. The testing for defense was not done until after all testing for offense and predation because of the possibility of interaction between offense and defense systems [15]. Offense was abolished in five rats whose lesions are illustrated in Fig. 1. These lesions destroyed much of the ventromedial tegmentum at a level including and slightly anterior to the reticular tegmental nucleus. The median raphe was damaged or destroyed in three of the animals and spared in two others. The lesions were tear-shaped and extended at their maximal width for 0.7 mm anterior and posterior to the shaded area shown in Fig. 1 which represents the largest cross-sectional area of the lesion in the stereotaxic plane. In addition to these five rats, there were three other rats in which offense was not abolished; it was found that their lesions were all posterior to the ones illustrated here and they involved no damage at the tegmental levels illustrated in Fig. 1. Data from those animals are not considered in this study. Lesions were not placed in other regions of the tegmentum in this study, since our pilot work has shown that other such tegmental lesions do not abolish offense. The behavioral results were the same in all five rats shown in Fig. 1: offense was abolished, while predation remained unchanged and the rats were capable of showing shock-elicited defensive boxing at the conclusion of the testing. Not only was the bite-and-kick attack of offense abolished, but also there was no offensive sideways posture or offensive upright posture. Other social behaviors remained unaffected by the lesion: there were no decrements in the frequency of olfactory investigation or grooming of the intruder.
167 The predation and defense, which were undisturbed after the lesions, served as behavioral controls, indicating that there was no simple motor incapacity that interfered with the performance of offense. Predation includes approach, chasing, and biting attack similar in many respects to the biteand-kick attack of offense. Defense included a defensive upright posture that is quite similar to offensive upright posture. For offense and predation, each animal's pre-operative results served as behavioral controls, the offense being abolished and the predation remaining unchanged. With regard to defense, a separate series of tests were conducted on unlesioned rats of the same strain and housing conditions and tested in the same shock-testing apparatus. The range of thresholds was similar, being 0.18 to 0.75 mA for the lesioned animals and 0.35 to 0.75 mA for the unlesioned controls. By fulfilling the prediction that brain stem lesions should be found that would abolish offense rather than other types of aggressive behavior, these results support the motivational systems analysis upon which the prediction was based [2]. The motivational systems analysis suggests that offense, defense, and predation represent three distinct systems organized around discrete sets of neurons, called motivational mechanisms, whose activation is responsible for the motivational state of the organism. The model for this analysis comes from defense, where the motivational mechanism was said to be located in the midbrain central gray, a location where: (1) lesions permanently abolish defense; (2) electrical and chemical stimulation produce defense; and (3) single neurons are differentially active during defense [2]. More recent data have shown that offense is not abolished by midbrain central gray lesions [16]. Although predation is interrupted by central gray lesions, the interruption affects only the final killing bite and not the other motivated components of the behavior such as orienting, tracking, and lunging towards the prey [20]. Further research is needed to determine if the ventromedial tegmentum contains the neurons of a motivational mechanism for offense, in the same sense that the central gray appears to have such a mechanism for defense. The fact that brain lesions of the ventromedial tegmentum abolish offense and not other types of aggression is one of the necessary criteria, but others remain untested as yet. Is the lesion effect permanent? Can offense be elicited by electrical and chemical stimulation of the ventromedial tegmentum, and are single neurons differentially active in that region during offense? In conclusion, it is now possible to distinguish offense, defense, and predation on the basis of brain stem lesions that differentially abolish these behaviors. Both offense and defense can be abolished by discrete lesions in the ventromedial tegmentum and midbrain central gray, respectively, that do not abolish the other types of aggression. It remains to be determined if predation can be abolished by a brainstem lesion that does not disturb offense or defense. Temporary or partial abolition of predation has been reported as a result of various brainstem lesions, but none have been shown to abolish predation totally and permanently [5, 6, 18, 20]. ACKNOWLEDGEMENTS For their work on the pilot project for this study, the author wishes to thank especially Gloria Herrera, Janice Robinson, Bill Goldman and Gary Edwards.
168
ADAMS
REFERENCES 1. Adams, D. B. Defence and territorial behaviour dissociated by hypothalamic lesions in the rat. Nature 232: 573-574, 1971. 2. Adams, D. B. Brain mechanisms for offense, defense, and submission. Behav Brain Sci 2: 201-241, 1979. 3. Adams, D. B. Motivational systems of agonistic behavior in muroid rodents: A comparative review and neural model. Aggress Behav 6: 295-346, 1980. 4. Bandler, R. J., Jr. and K. E. Moyer. Animals spontaneously attacked by rats. Cornmun Behuv Biol 5: 177-182, 1970, 5. Berntson, G. G. Blockade and release of hypothalamically and naturally elicited aggressive behaviors in cats following midbrain lesions. J Comp Physiol Psychol 81: 541-554, 1972. 6. Chaurand, J. P., P. Schmitt and P. Karli. Effets de lesions du tegmentum ventral du mesenc6phale sur le comportement d'agression Rat-Souris. Physiol Behav 10: 507-515, 1973. 7. Depaulis, A. and M. Vergnes. Relationship between mousekilling and conspecific aggression in the male rat. Ag,~re.ss Behm" 9: 25%268, 1983. 8. Edwards, M. A. and D. B. Adams. Role of midbrain central gray in pain-induced defensive boxing of rats. Physiol Behav 23: 113-121, 1974. 9. Ellison, G. D. and J. P. Flynn. Organized aggressive behavior in cats after surgical isolation of the hypothalamus. Arch ltal Biol 106: 1-20, 1968. 10. Flynn, J. P. Neural basis of threat and attack. In: Biological Foundations o f Psychiatry. edited by R. G. Grenell and S. Gabay. New York: Raven Press, 1976, pp. 273-295. 11. Fredericson, E. The effects of food deprivation upon competitive and spontaneous combat in C57 black mice. J Psyehol 29: 8%100, 1950.
12. Karli, P. The Norway rafts killing response to the white mouse. An experimental analysis. Behaviour 20: 81-103. 1956. 13. Kostowski, A. and L. Valzelli. Biochemical and behavioral effects of lesions of the raphe nuclei in aggressive mice. Pharmacol Biochem Behav 2: 277-280, 1974. 14. Leyhausen, P. Verhaltensstudien an Katzen. Z 7ierpsychol 2: 1-120, 1956. 15. Mink, J. W. and D. B. Adams. Why offense is reduced when rats are tested in a strange cage. Phy,siol Behav 26: 567-573, 1981. 16. Mos, J., J. H. C. M. Lammers, A. M. van der Poel, B. Bermon, W. Meelis and M. R. Kruk. Effects of midbrain central gray lesions on spontaneous and electrically induced aggression in the rat. Aggres,~ Behav 9: 133-155, 1983. 17. Paxinos. G. and C. Watson. 7he Rat Brain in Stereota.~ic C,~ordinates. New York: Academic Press, 1982. 18. Proshansky, E. and R. J. Bandler. Midbrain-hypothalamic interrelationships in the control of aggressive behavior. Aggre.s~s Behm' 1: 135-155, 1975. 19. Ursin, H. Neuroanatomical basis of aggression. In: Multidisciplima3" Approaches t o Aggression Research, edited by P. F. Brain and D. Benton. Amsterdam: Elsevier/North Holland, 1981, pp. 269-293. 20. Waldbillig, R. J. Offense, defense, submission, and attack: Problems of logic and lexicon. Behav Brain Sci 2: 227-228, 1979. 21. Zook, J. M. and D. B. Adams. Competitive fighting in the rat. J Comp Physiol Psvchal 88:418-423, 1975.