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Aggression in low and high brainweight mice following septal lesions
Physiology ~nd B c ~ v i o r , Voi. 12, pp. 8 1 3 - 8 1 8 , Brain Research Publications Inc.. 1974. Printed in the U.S.A.
Aggression in Low and High Brainweight Mice Following Septal Lesions JOHN C. GONSIOREK=, PETER J. DONOVICK, RICHARD G. BURRIGHT AND JOHN L. F U L L E R
Department o/Psychology, State University o / N e w York at B~nghamton, Binghamton, New York 13901
(Received 9 November 1973) GONSIOREK, J. C., P. J. DONOVICK, R. G. BURRIGHT AND J. L. FULLER. Aggression in low and high brain. werght m~ce following septal le~nx PHYSIOL. BEHAV. 12(5) 813-818, 1974. - Septal lesions or control operations were performed on adult male mice genetically selected for either high or low bramweight. FoUowmg recovery from surgery, pairs of animals with a s~milar genetic and surgical tustory were matched in tests of agomstic behavior. Irrespective of strain, pairs of mice wlth septal lesions fought less than pairs of control animals. However, submissive postures and social explorabon showed a clear interaction between gcnotype and surgical history. The importance of interactions between variables such as genotype, experience, and brain damage is dbcu.med. Genotype
Bramweight
Ag~ession
Septal lesions
IT HAS BECOME increasingly clear to us that septal lesions alter the intensity rather than the nature of species typical responses to environmental stimulation. As noted by Brady and Nauta [3], compared to control animals, rats with septal lesions over respond to sudden stimulation in any sensory modality. It is not surprising then, that septal lesions also alter response patterns related to basic homeostatic mechanisms. The way a septal-lesioned rat regulates consummatory behavior {I0], responds to water deprivation {8], and copes with alterations in environmental temperature [20], is an exaggeration of the response pattern normally seen in brain-intact animals. Similarly, rats with septal lesions exhibit an exaggerated form of exploratory behavior [ l 1,16]. One might expect that social behavior would also be altered by septal lesions. Increased aggression in males following septal lesioning has been reported in the golden hamster [19] and cotton rats [5]. Increased fighting has also been noted in albino rats with septal lesions when they were tested under shock-induced aggression situations [1, 2, 12]. However, Jonason and Enloe [15] reported that hooded rats with septal lesions spend more time in nonaggressive contact with another rat than either control or amygdalectormzed rats. Further, Slotnick and McMullen [18] indicate that there is a decrease in aggression in albino mice following septal lesioning. Finally, Bunnell and Smith [5] found that in the cotton rat there was an increased number of contacts between animals following septal lesionmg, but social rank did not change as a function of brain damage; rather there was a decreased latency for both flight and fight.
Clearly, these studies varied in many ways. The setting and procedures for testing social-aggressive behavior, the past experience of the animals, and the strain and the species of experimental animal were rarely the same. We recently showed that a rat's presursical experience determines, in part, how septal lesioning will affect its behavior [9]. It seems likely that genetic background might also modify the behavioral effects of septal lesions. Indeed, the variability often noted following septal lesions (6] strongly suggests the importance of experiential and genetic factors in determining the effects of brain damage on behavior. The genetic substrate and experiential history of the animal do, in part, determine behavioral characteristics such as aggressiveness. For instance, Hahn, Haber, and Fuller [13] measured agonistic behavior in mice selected for differences in brainweight. Males of the low brainweight strata were more a w e s s i v e only when isolated for a period of ten days immediately after weaning. There have been numerous studies showing such interaction between genotype and experience [14) but few on the interaction between genetic variation and brain damage. Such genetic manipulations can ~e used to examine the differential effects of brain damage superimposed on animals of the same species but genetically selected for specific characteristics. W e adopted such an approach to investipte the possible interactions between septal lesions and genetic history on agonistic behavior. Specifically, septal lesions were performed on male mice of the Binghamton B W S - L and B W S - H Lines selected for low and high bralnweight respectively (cf., [ I 3 ) ). Pairs of animals of similar genetic
This research was supported in part by a grant from the State Universlty of New York Foundation to Peter J. Donovick and NSF GB 24287 to John L. Fuller. Reprint requests should be sent to Peter J. Donovick at the Department of Psychology, State Umversity of New York at Binshamton, Binghamton, New York 13901. = Present address: Department of Psychology, University of Minnesota. 813
814
G O N S I O R E K , DONOVICK, B U R R I G H T AND F U L L E R
and surgical history were m a t c h e d in tests of agonistic behavior. We f o u n d t h a t b o t h g e n o t y p e and lesion were involved in d e t e r m i n i n g the degree of aggressiveness displayed in male mice. ..METHOD
Animals Forty-eight e x p e r i m e n t a l l y naive male mice were tested for agom.stic behavior. T w e n t y - f o u r o f the mice were from the low b r a m w e i g h t strain while the rest were from the high brainweight strain (cf., [ 13 ] ). All of the mice were b o r n in t h i s l a b o r a t o r y where t e m p e r a t u r e s were m a i n t a i n e d between 23* and 24"C and the Lights are o n from 0 8 0 0 to 2000 hr. Water and Charles River Mouse Chow were available ad lib from birth. The animals used in this e x p e r i m e n t were from the eighth generation of selection. The brainweight and b o d y w e i g h t s o f c o m p a r a b l e male mice measured at 4 2 days after b i r t h were 546 mg and 31 g for the high brainweight ammals and 477 mg and 26.9 g for the low bralnweight anmaals. There is essentially no overlap in bralnweight o f these groups, but some overlap in bodyweight. See Hahn, Haber, and FuUer [13] for a more c o m p l e t e description of these strains and their derivation. Litters were cuUed to a p p r o x i m a t e l y eight pups per mother. The mice were weaned at 21 days of age and group housed with same sex siblings until 50 (lays of age when all animals were switched to individual cages where they were kept until surgery was performed.
Surgical and Histological Procedures Within each b r m n w e i g h t strain, surgery was p e r f o r m e d on sets of four same-aged littermates. Two received septal lesions and the o t h e r two u n d e r w e n t c o n t r o l operations. ALl mice were deprived of water for 24 hours prior to surgery. Large bilateral septa/ lesions were p r o d u c e d u n d e r aseptic c o n d i t i o n s while the a m m a l was a n e s t h e t i z e d with sodium p e n t o b a r b i t a l (85 mg/kg) s u p p l e m e n t e d by local application of lidocaine h y d r o c h l o r i d e . Electrolytic lesions were p r o d u c e d by passing 1 mA anodal d.c. c u r r e n t for 6 sec t h r o u g h the a n i n s u l a t e d tip of a =0 insect pin to rectal cathode. A Kopf stereotaxic i n s t r u m e n t , with a modified head holder, was used to position the electrode. The modification consisted of a nose clamp to immobilize the head and m a i n t a i n the surface of the skull in a llorizontal plane. The h e a d h o l d e r does not make use of earbars and thus ear damage was not incurred. The tip of the lesion electrode was lowered 3.5 m m from the surface o f the dura at a point 0.6 m m a n t e r i o r to bregma and -- 0.4 m m lateral to the midline. Control animals u n d e r w e n t the same procedures, including exposure of the ~tura. except the electrodes were not lowered. Upon c o m p l e t i o n of the e x p e r i m e n t all ammals were overdoSed with sodium p e n t o b a r b i t a l and perfused intracardially with isotomc saline followed by 10% Formalin. Lemoned brains were fixed in 10% Formalin for at ~east three days after which frozen tissue technique was used .'o section the brain. The sections were ~ 0 , thick and every briner section t h r o u g h o u t the lemon was stained with a m e t a c h r o m a t i c stain for nuclear and fiber regaons [7) and microscoptcal.ly e x a m m e d to d e t e r m i n e the e x t e n t of damage.
Behavioral Testing The behavioral tests were p e r f o r m e d 20 days after surgery when the anamals were 70 days of age. Two days prior to testing a pair of mice were placed, one on each side, in a clean cage divided in half, lengthwise, by a metal partition. Pairs were always same age siblings with similar surgical history. The divided cages were kept in the main vivarium for two days, and t h e n moved into a small testing room. The testing room was sound deadened and dimly illuminated ( 10 footcandles of i l l u m i n a t i o n at the tloor of the test cage was provided by one 15 "~ incandescent bulb). The 30 rain testing sessions began b e t w e e n 1500 and 1 8 0 0 h r and were initiated by removing the partition b e t w e e n the animals. Simultaneously, a stop watch a n d a 10 c h a n n e l Esterline-Angus recorder (chart speed 1 m m i s e c ) were switched on and behavioral recording was begun, using a ten key control panel. A battery of measures previously described in detail [131 were recorded. They were: the latency to, (1) contact, ( 2 ) f i g h t , ( 3 ) d o m i n a n c e ; and the frequency and time spent in, (4) nosing, (5) gemtal sniffing, (6) social grooming, (7) tail lashing, ~8) fighting, (9) squeaking, and (10) defense posturing. A t t a i n m e n t of a d o m i n a n c e - s u b o r d i n a t i o n relationship was defined as the first s i m u l t a n e o u s occurrence of defense posture and squeaking in one m e m b e r of the p a i r . . M t h o u g h d o m i n a n c e usually followed fighting, ammals could, and did, achieve d o m i n a n c e w i t h o u t any actual fighting.
Data Analysis In all caSes, we scored the behavior of the pair of animals rather than individual activity. Since b o t h m e m b e r s of the pair were of identical g e n o t y p e and lesion history, the social unit was the most a p p r o p r i a t e basis for statistical analysis. It should be n o t e d t h a t scoring of the behavior of an individual does not negate the i m p a c t of the o t h e r m e m b e r of a parr on the measure. An e x a m i n a t i o n of all o f o u r pair data suggested that n o n p a r a m e t r i c statistical techniques were most a p p r o p r i a t e for data analysis. Therefore. an analysis of variance on ranks, mvolving the partitioning of the K.ruskal-Watlis H statistic [171 was e m p l o y e d for between group comparisons (of., [ 1 3 l ) . Two tailed :ests were always employed. "l'his t e c h m q u e allowed us to statistically assess the reliability of b o t h lesion (L) and genotype (G) mare effects and their interactxon. There were six paurs of animals per group m this 2 x 2 e x p e n m e n t a l design. TypicaLly the frequency and d u r a t i o n measures retlected the same p a t t e r n of behavior across groups. Thus we will only discuss the most relevant aspects of these two related measures. RESULTS
Histology Microscopic e x a m i n a t i o n of the bastoioglcal material indicated that the septai lesions p r o d u c e d in b o t h the Iow and high b r a m w e i g h t stratus of mice were quite comparable to those typically reported by us for rats. Figure 1 indicates the m a x i m u m e x t e n t of a septal lesion in one of the high bralnweight mice. Typically. lesions were large and bilaterally destroyed the major portion of the precommkssural septum. The lesions usually first appeared at the genu ot the corpus caUosum and e x t e n d e d to a point just posterior to tiae crossing of the a n t e n o r commmsure. No damage was seen in the p r e o p u c nuclei.
AGGRESSION. BRAINWEIGHT AND SEPTAL LESIONS
815
FIG. 1. A typical septtd lesion; maximum extent of septal lesion in mouse 72-11-7(l ).
Behavioral Observations Generally, when the divider separating the two mice was removed both aiumaLs remained immobile for several seconds. This was followed by a period of intense exploration of the cage which resulted in contact between pairmates. The initial contact occurred within the first 30 sec for 10 out of 12 pairs of control mice and 7 out of 12 pairs of septal mice. Interestingly, while all control mice and high brainweight septai mice made initial contact with their pair mate within the f'ast two rain, four out of six pairs of low bramweight septals took 5 or more rain to achieve contact. The initial contact usually consisted of nosing and sometimes genital sniffing. The first occurrence of tail lashing was also sometimes observed at this time, but fighting was generally not seen. Frequently there were several similar encounters prior to the first spontaneous bout of fighting. GeneraLly, high bramweight mice had a lower latency to the first fight than low bramweight mice (G. H = 5.47, d r = 1, p<0.05). This difference was clearest in the lesioned animals, although the interaction between genorype and brain damage failed to reach statistical significance. Once a pair of ammaLs fought, there was a clear difference in the behavior patterns of lesioned and control pairs. As can be seen in Fig. 2 regardless of bralnweight, mice with septal lesions fought less frequently than their control counterparts (L: H = 4.44, dr= 1, p<0.05). The number of tail lashes also indicated that the control animals engaged m more aggressive behavior than the lesioned mice (L: H =4.81, dr= 1. p<0.05). There was also a tendency for low bramweight mice to be lower than high brainweight mxce on this measure (G: H = 3.10, d r = 1, 0.05
both brainweight control groups and the low bramweight septal group exhibited about the same number of defense postures, high brainweight mice with septal lesions were observed in a defense posture much more frequently than either control group or the low brainweight septal group (G x L: H = 4.32, d[= 1, p<0.05). As might be expected then, there was a difference in the number of pairs which reached a dominance relationship among the various groups. Indeed none of the high brainweight controls and orfly t w o of the six pau's of l o w b r a n weight controLs reached dominance in the t h i r t y minute test session. The failure to meet dominance was always associated with a great deal of aggressive behavior in control mice. On the other hand, three out of six pairs of low brainweight septal mice and all six pairs of high bralnweight septal mice reached dominance (Latency to dominance, L: H = 6 . 7 5 . elf= 1, p<0.01: G x L : H=3.63; d[=l, 0.05
816
GONSIOREK, DONOVICK, BURRIGHT AND FULLER i
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G O N S I O R E K , DONOVICK, BURR.IGHT AND F U L L E R
(G x L: H = 5.74, d r = I, p
In s u p p o r t o f earlier findings [ 18], we found that mice with septal lesions were less aggressive than their control counterparts. We f o u n d this reduction in aggression in pm.rs o f septal lesioned mice while Slotnick and McMullen [181 found a similar change when a lesioned mouse was tested with a control mouse. Our findings aJso lend s u p p o r t to the c o n t e n t i o n [ 181 that the decrease m aggression induced by septal lesions is a general species characteristic of mice. Although different lines o f mice were used (Slotnick's were o u t b r e d CF-I and ours were selected from a cross of inbred lines) the lesion effect was similar. However, some comp o n e n t s of the behavior patterns observed are clearly influenced by genetic variation w i t h m the same species. "I'aus submissive postures and social e x p l o r a t i o n associated with social c o n t a c t s s h o w e d a clear interaction of g e n o t y p e with septal lesions. The i m p o r t a n c e of such findings are clear. The variability in behavior o f t e n associated with septal lesions may be related to u n k n o w n genetic differences among experimental animals. In interpreting the r e p o r t e d differences between species in aggression following septal lesions, care must be taken in
differentiating b e t w e e n the species' specific s y m p t o m s and the underlying neural d y s f u n c t i o n . At face value, the increase m aggression seen following septal lesions in rats [4,5] and hamsters [ 1 9 ] , and the decrease in aggression in mice with septal lesions [ 18, and present investigation] would appear to be contradictory. However, it" one views the effects o f septal lesions in terms of a shift in the reactivity to controlling stimuli [21] then the apparent contradiction may be less i m p o r t a n t . That is, the lesioned mice exhibited an exaggerated pattern of some aspects of the normal animal's behavior. To fully u n d e r s t a n d such shifts in behavior we must eventually identify the controlling stimuli of the situation. The comparative and behavior genetic approach provides a means for dissection of the biotogacally d e t e r m i n e d characteristics of the nervous system and their interactions with brmn damage. A further cautionary note is necessary however. The effects of septal lesions are also altered by the pre-surgacal past experiential history, of the animal [9,19]. Higtxly c o m p l e x interactions of genetic, experientaI, and b r a n damage ,Mstory are to be expected. One example is apparent in the present data. Hahn, Haber and Fuller [13] found that the differential aggression at 70 days of age in high and low bramweight mice was only observed in mice which had been isolated at 21 days of age. Animals o f the two lines group housed until 31 days and then tested at 70 days o f age were not different in aggression. These findings suggest sensitive periods for the interaction b e t w e e n genetic and environmental d e t e r m m a n t s o f behavior. In the present e x p e r i m e n t , mice were housed in group cages until 50 days of age and yet there were clear differences in the agonlstic behavior o f high and low brainweight control animals. It would thus appear that variables such as duration o f group rearmg, and the time of separation are not related in a simple manner.
REFERENCES I.
2. 3.
.t. 5. 6. 7. 8. 9.
10.
Ahmad, S. S, and J. A. Harvey. Long-term effects of septal lesions and experienc, on shock.elicited fighting m rats. J. camp. physzol. 1~'y.ehol. 66: 596-602, 1968. Blanchard, R. J. and D. C. Blanchard. Limbic lesions and reflexive fightmg. J. camp. phytzol, t~-ychol. 66: 603-605. 1968. Brady, J. V. and W. J. H. Nauta. Subcortlcal mechanisms in emotional behavior: affecttve changes followmg septal forebrain lesions in the albino rat. J. camp. phystoL Prychot. 46: 339-346, L953. Bunnell, B. N.. J. R. Bemporad and C. K. Flasher. Septal forebrain lesions and social dominance behavior m the hooded rat. Psychon. ScL 6: 207. 1966. Bunneil, B, N. and M. H. Smith. Septal lesions and aggressiveness in the Cotton Rat. Sigmodon htspidu~ Pryenon. ScL 6: 443-444, 1966. 8urriznt, R. G.. P. J. DonovicK and E. Zuromsl~x. Se~tai lesions and experientaJ influences on saline and saccharin preferenceaversion functions. Ph>'~toi. Behav m press. 197-t. Donosack. P. J. A metachromatic stain for neural :issue. Scan Technology, in press, 197-I.. Dono~ck, P. I. and R. G. Burrlght. Water consumpuon of rats •ruth septal lesions t'ollowang two days of water deprivation. Physiol. Behav. 3: 285-288, 1968. Dono~ck, P. J.. R. G. Burnght and M. A. Sw~dler. Presurmcal rearmg environment alters exploration, fluid consumption, and leammg of septat lesioned and control rats. t~y%iot. Behav l I: 543-5.5¢3. 1973. Donovack, P. I.. R. G. Burright and E. ZUromsk~. Localization 3f qumme aversion wlthm the se~tum, habenula, and raterpeduncular nucleus of the rat..L camp. ~ny%tot. Prvchoi. 71: 376-383. 1970.
l.I.
12. 13. 14. 1.5. 16. 17. 18. 19. 20. 21.
Donovack, F. J. and K. Wakeman. Open-~eld luminance and "Septal Hyperemotionality." .4him. Behav. 17: l~6-190. 1969. Eicheiman. B. S. Effect o(subcortical lesions on shock-reduced aggression in the rat. J. camp. physiol. Psychol. 74: 331-339, 1971. Harm. M., S. Haoet and J. L. FuUer. Dtfferentiai agonIstlc behavior in mice ~elected ."or brain weight./~ysio/. Behav. 10: "59-762, 1973. Henderson. N. D. The confounding effects of genetic 'J~labies in early e.xpenence research: Can we ~,g'nore ~laem? Dev. P~3~chobtol. 1: 1-1.6-152. ~968. Jonason. K. R. and L. J. Enloe. -klteratlons m socmi behavter followmg ~eptal and amygdaloid lesions m the rat. Z camp. ~ny%lol. P~ychol. 75: 256-301, 1971. Nielson, H. C.. A. H. Mclver and R. S. Bos',ved. Effect o( septaJ iesions on learning, emouonality, activity, and expioratory behaviorm rats. Expl.VeuroL 11: 147-157. 1965. Scheirer, C. J. and W. S. Ray. A ranks anaJysis of data derived from a completely randomized design, in prep~auon. Slotnick, B. M. and M. F .'*lcMullen. lntraspec~fic fightmg In albino mice wath septal forebraJn lesions. Ph.vszoL Beimv. ~: 333-337, ~972. Sodetz, F" J. and B. N. Bunned. Septal ablauon a.nd :he socl~ beha~qor ,gf the _~olden hamster. P~r-,siol. 8enav. 5 : " 9 - ~ 8 1970. Wakeman. K. A.. P. J. DonovlcK and R. G. Burngnt. Sepia. lesions increase bar pressing for heat in annals m~ntamed ~r the cold. Ph.vszoL 8chap. 5: i 193- ~!95. ig"ro. Zuroms~. E. S.. P. J. DonovlcK .rod R. G. ~3urnght. Ba; pressing for illumination change :n albino tats wltn sepia lesions. J. camp. pn>'stot, r~vehoL 78: .~3-90. "972.
Aggression in Low and High Brainweight Mice Following Septal Lesions JOHN C. GONSIOREK=, PETER J. DONOVICK, RICHARD G. BURRIGHT AND JOHN L. F U L L E R
Department o/Psychology, State University o / N e w York at B~nghamton, Binghamton, New York 13901
(Received 9 November 1973) GONSIOREK, J. C., P. J. DONOVICK, R. G. BURRIGHT AND J. L. FULLER. Aggression in low and high brain. werght m~ce following septal le~nx PHYSIOL. BEHAV. 12(5) 813-818, 1974. - Septal lesions or control operations were performed on adult male mice genetically selected for either high or low bramweight. FoUowmg recovery from surgery, pairs of animals with a s~milar genetic and surgical tustory were matched in tests of agomstic behavior. Irrespective of strain, pairs of mice wlth septal lesions fought less than pairs of control animals. However, submissive postures and social explorabon showed a clear interaction between gcnotype and surgical history. The importance of interactions between variables such as genotype, experience, and brain damage is dbcu.med. Genotype
Bramweight
Ag~ession
Septal lesions
IT HAS BECOME increasingly clear to us that septal lesions alter the intensity rather than the nature of species typical responses to environmental stimulation. As noted by Brady and Nauta [3], compared to control animals, rats with septal lesions over respond to sudden stimulation in any sensory modality. It is not surprising then, that septal lesions also alter response patterns related to basic homeostatic mechanisms. The way a septal-lesioned rat regulates consummatory behavior {I0], responds to water deprivation {8], and copes with alterations in environmental temperature [20], is an exaggeration of the response pattern normally seen in brain-intact animals. Similarly, rats with septal lesions exhibit an exaggerated form of exploratory behavior [ l 1,16]. One might expect that social behavior would also be altered by septal lesions. Increased aggression in males following septal lesioning has been reported in the golden hamster [19] and cotton rats [5]. Increased fighting has also been noted in albino rats with septal lesions when they were tested under shock-induced aggression situations [1, 2, 12]. However, Jonason and Enloe [15] reported that hooded rats with septal lesions spend more time in nonaggressive contact with another rat than either control or amygdalectormzed rats. Further, Slotnick and McMullen [18] indicate that there is a decrease in aggression in albino mice following septal lesioning. Finally, Bunnell and Smith [5] found that in the cotton rat there was an increased number of contacts between animals following septal lesionmg, but social rank did not change as a function of brain damage; rather there was a decreased latency for both flight and fight.
Clearly, these studies varied in many ways. The setting and procedures for testing social-aggressive behavior, the past experience of the animals, and the strain and the species of experimental animal were rarely the same. We recently showed that a rat's presursical experience determines, in part, how septal lesioning will affect its behavior [9]. It seems likely that genetic background might also modify the behavioral effects of septal lesions. Indeed, the variability often noted following septal lesions (6] strongly suggests the importance of experiential and genetic factors in determining the effects of brain damage on behavior. The genetic substrate and experiential history of the animal do, in part, determine behavioral characteristics such as aggressiveness. For instance, Hahn, Haber, and Fuller [13] measured agonistic behavior in mice selected for differences in brainweight. Males of the low brainweight strata were more a w e s s i v e only when isolated for a period of ten days immediately after weaning. There have been numerous studies showing such interaction between genotype and experience [14) but few on the interaction between genetic variation and brain damage. Such genetic manipulations can ~e used to examine the differential effects of brain damage superimposed on animals of the same species but genetically selected for specific characteristics. W e adopted such an approach to investipte the possible interactions between septal lesions and genetic history on agonistic behavior. Specifically, septal lesions were performed on male mice of the Binghamton B W S - L and B W S - H Lines selected for low and high bralnweight respectively (cf., [ I 3 ) ). Pairs of animals of similar genetic
This research was supported in part by a grant from the State Universlty of New York Foundation to Peter J. Donovick and NSF GB 24287 to John L. Fuller. Reprint requests should be sent to Peter J. Donovick at the Department of Psychology, State Umversity of New York at Binshamton, Binghamton, New York 13901. = Present address: Department of Psychology, University of Minnesota. 813
814
G O N S I O R E K , DONOVICK, B U R R I G H T AND F U L L E R
and surgical history were m a t c h e d in tests of agonistic behavior. We f o u n d t h a t b o t h g e n o t y p e and lesion were involved in d e t e r m i n i n g the degree of aggressiveness displayed in male mice. ..METHOD
Animals Forty-eight e x p e r i m e n t a l l y naive male mice were tested for agom.stic behavior. T w e n t y - f o u r o f the mice were from the low b r a m w e i g h t strain while the rest were from the high brainweight strain (cf., [ 13 ] ). All of the mice were b o r n in t h i s l a b o r a t o r y where t e m p e r a t u r e s were m a i n t a i n e d between 23* and 24"C and the Lights are o n from 0 8 0 0 to 2000 hr. Water and Charles River Mouse Chow were available ad lib from birth. The animals used in this e x p e r i m e n t were from the eighth generation of selection. The brainweight and b o d y w e i g h t s o f c o m p a r a b l e male mice measured at 4 2 days after b i r t h were 546 mg and 31 g for the high brainweight ammals and 477 mg and 26.9 g for the low bralnweight anmaals. There is essentially no overlap in bralnweight o f these groups, but some overlap in bodyweight. See Hahn, Haber, and FuUer [13] for a more c o m p l e t e description of these strains and their derivation. Litters were cuUed to a p p r o x i m a t e l y eight pups per mother. The mice were weaned at 21 days of age and group housed with same sex siblings until 50 (lays of age when all animals were switched to individual cages where they were kept until surgery was performed.
Surgical and Histological Procedures Within each b r m n w e i g h t strain, surgery was p e r f o r m e d on sets of four same-aged littermates. Two received septal lesions and the o t h e r two u n d e r w e n t c o n t r o l operations. ALl mice were deprived of water for 24 hours prior to surgery. Large bilateral septa/ lesions were p r o d u c e d u n d e r aseptic c o n d i t i o n s while the a m m a l was a n e s t h e t i z e d with sodium p e n t o b a r b i t a l (85 mg/kg) s u p p l e m e n t e d by local application of lidocaine h y d r o c h l o r i d e . Electrolytic lesions were p r o d u c e d by passing 1 mA anodal d.c. c u r r e n t for 6 sec t h r o u g h the a n i n s u l a t e d tip of a =0 insect pin to rectal cathode. A Kopf stereotaxic i n s t r u m e n t , with a modified head holder, was used to position the electrode. The modification consisted of a nose clamp to immobilize the head and m a i n t a i n the surface of the skull in a llorizontal plane. The h e a d h o l d e r does not make use of earbars and thus ear damage was not incurred. The tip of the lesion electrode was lowered 3.5 m m from the surface o f the dura at a point 0.6 m m a n t e r i o r to bregma and -- 0.4 m m lateral to the midline. Control animals u n d e r w e n t the same procedures, including exposure of the ~tura. except the electrodes were not lowered. Upon c o m p l e t i o n of the e x p e r i m e n t all ammals were overdoSed with sodium p e n t o b a r b i t a l and perfused intracardially with isotomc saline followed by 10% Formalin. Lemoned brains were fixed in 10% Formalin for at ~east three days after which frozen tissue technique was used .'o section the brain. The sections were ~ 0 , thick and every briner section t h r o u g h o u t the lemon was stained with a m e t a c h r o m a t i c stain for nuclear and fiber regaons [7) and microscoptcal.ly e x a m m e d to d e t e r m i n e the e x t e n t of damage.
Behavioral Testing The behavioral tests were p e r f o r m e d 20 days after surgery when the anamals were 70 days of age. Two days prior to testing a pair of mice were placed, one on each side, in a clean cage divided in half, lengthwise, by a metal partition. Pairs were always same age siblings with similar surgical history. The divided cages were kept in the main vivarium for two days, and t h e n moved into a small testing room. The testing room was sound deadened and dimly illuminated ( 10 footcandles of i l l u m i n a t i o n at the tloor of the test cage was provided by one 15 "~ incandescent bulb). The 30 rain testing sessions began b e t w e e n 1500 and 1 8 0 0 h r and were initiated by removing the partition b e t w e e n the animals. Simultaneously, a stop watch a n d a 10 c h a n n e l Esterline-Angus recorder (chart speed 1 m m i s e c ) were switched on and behavioral recording was begun, using a ten key control panel. A battery of measures previously described in detail [131 were recorded. They were: the latency to, (1) contact, ( 2 ) f i g h t , ( 3 ) d o m i n a n c e ; and the frequency and time spent in, (4) nosing, (5) gemtal sniffing, (6) social grooming, (7) tail lashing, ~8) fighting, (9) squeaking, and (10) defense posturing. A t t a i n m e n t of a d o m i n a n c e - s u b o r d i n a t i o n relationship was defined as the first s i m u l t a n e o u s occurrence of defense posture and squeaking in one m e m b e r of the p a i r . . M t h o u g h d o m i n a n c e usually followed fighting, ammals could, and did, achieve d o m i n a n c e w i t h o u t any actual fighting.
Data Analysis In all caSes, we scored the behavior of the pair of animals rather than individual activity. Since b o t h m e m b e r s of the pair were of identical g e n o t y p e and lesion history, the social unit was the most a p p r o p r i a t e basis for statistical analysis. It should be n o t e d t h a t scoring of the behavior of an individual does not negate the i m p a c t of the o t h e r m e m b e r of a parr on the measure. An e x a m i n a t i o n of all o f o u r pair data suggested that n o n p a r a m e t r i c statistical techniques were most a p p r o p r i a t e for data analysis. Therefore. an analysis of variance on ranks, mvolving the partitioning of the K.ruskal-Watlis H statistic [171 was e m p l o y e d for between group comparisons (of., [ 1 3 l ) . Two tailed :ests were always employed. "l'his t e c h m q u e allowed us to statistically assess the reliability of b o t h lesion (L) and genotype (G) mare effects and their interactxon. There were six paurs of animals per group m this 2 x 2 e x p e n m e n t a l design. TypicaLly the frequency and d u r a t i o n measures retlected the same p a t t e r n of behavior across groups. Thus we will only discuss the most relevant aspects of these two related measures. RESULTS
Histology Microscopic e x a m i n a t i o n of the bastoioglcal material indicated that the septai lesions p r o d u c e d in b o t h the Iow and high b r a m w e i g h t stratus of mice were quite comparable to those typically reported by us for rats. Figure 1 indicates the m a x i m u m e x t e n t of a septal lesion in one of the high bralnweight mice. Typically. lesions were large and bilaterally destroyed the major portion of the precommkssural septum. The lesions usually first appeared at the genu ot the corpus caUosum and e x t e n d e d to a point just posterior to tiae crossing of the a n t e n o r commmsure. No damage was seen in the p r e o p u c nuclei.
AGGRESSION. BRAINWEIGHT AND SEPTAL LESIONS
815
FIG. 1. A typical septtd lesion; maximum extent of septal lesion in mouse 72-11-7(l ).
Behavioral Observations Generally, when the divider separating the two mice was removed both aiumaLs remained immobile for several seconds. This was followed by a period of intense exploration of the cage which resulted in contact between pairmates. The initial contact occurred within the first 30 sec for 10 out of 12 pairs of control mice and 7 out of 12 pairs of septal mice. Interestingly, while all control mice and high brainweight septai mice made initial contact with their pair mate within the f'ast two rain, four out of six pairs of low bramweight septals took 5 or more rain to achieve contact. The initial contact usually consisted of nosing and sometimes genital sniffing. The first occurrence of tail lashing was also sometimes observed at this time, but fighting was generally not seen. Frequently there were several similar encounters prior to the first spontaneous bout of fighting. GeneraLly, high bramweight mice had a lower latency to the first fight than low bramweight mice (G. H = 5.47, d r = 1, p<0.05). This difference was clearest in the lesioned animals, although the interaction between genorype and brain damage failed to reach statistical significance. Once a pair of ammaLs fought, there was a clear difference in the behavior patterns of lesioned and control pairs. As can be seen in Fig. 2 regardless of bralnweight, mice with septal lesions fought less frequently than their control counterparts (L: H = 4.44, dr= 1, p<0.05). The number of tail lashes also indicated that the control animals engaged m more aggressive behavior than the lesioned mice (L: H =4.81, dr= 1. p<0.05). There was also a tendency for low bramweight mice to be lower than high brainweight mxce on this measure (G: H = 3.10, d r = 1, 0.05
both brainweight control groups and the low bramweight septal group exhibited about the same number of defense postures, high brainweight mice with septal lesions were observed in a defense posture much more frequently than either control group or the low brainweight septal group (G x L: H = 4.32, d[= 1, p<0.05). As might be expected then, there was a difference in the number of pairs which reached a dominance relationship among the various groups. Indeed none of the high brainweight controls and orfly t w o of the six pau's of l o w b r a n weight controLs reached dominance in the t h i r t y minute test session. The failure to meet dominance was always associated with a great deal of aggressive behavior in control mice. On the other hand, three out of six pairs of low brainweight septal mice and all six pairs of high bralnweight septal mice reached dominance (Latency to dominance, L: H = 6 . 7 5 . elf= 1, p<0.01: G x L : H=3.63; d[=l, 0.05
816
GONSIOREK, DONOVICK, BURRIGHT AND FULLER i
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In s u p p o r t o f earlier findings [ 18], we found that mice with septal lesions were less aggressive than their control counterparts. We f o u n d this reduction in aggression in pm.rs o f septal lesioned mice while Slotnick and McMullen [181 found a similar change when a lesioned mouse was tested with a control mouse. Our findings aJso lend s u p p o r t to the c o n t e n t i o n [ 181 that the decrease m aggression induced by septal lesions is a general species characteristic of mice. Although different lines o f mice were used (Slotnick's were o u t b r e d CF-I and ours were selected from a cross of inbred lines) the lesion effect was similar. However, some comp o n e n t s of the behavior patterns observed are clearly influenced by genetic variation w i t h m the same species. "I'aus submissive postures and social e x p l o r a t i o n associated with social c o n t a c t s s h o w e d a clear interaction of g e n o t y p e with septal lesions. The i m p o r t a n c e of such findings are clear. The variability in behavior o f t e n associated with septal lesions may be related to u n k n o w n genetic differences among experimental animals. In interpreting the r e p o r t e d differences between species in aggression following septal lesions, care must be taken in
differentiating b e t w e e n the species' specific s y m p t o m s and the underlying neural d y s f u n c t i o n . At face value, the increase m aggression seen following septal lesions in rats [4,5] and hamsters [ 1 9 ] , and the decrease in aggression in mice with septal lesions [ 18, and present investigation] would appear to be contradictory. However, it" one views the effects o f septal lesions in terms of a shift in the reactivity to controlling stimuli [21] then the apparent contradiction may be less i m p o r t a n t . That is, the lesioned mice exhibited an exaggerated pattern of some aspects of the normal animal's behavior. To fully u n d e r s t a n d such shifts in behavior we must eventually identify the controlling stimuli of the situation. The comparative and behavior genetic approach provides a means for dissection of the biotogacally d e t e r m i n e d characteristics of the nervous system and their interactions with brmn damage. A further cautionary note is necessary however. The effects of septal lesions are also altered by the pre-surgacal past experiential history, of the animal [9,19]. Higtxly c o m p l e x interactions of genetic, experientaI, and b r a n damage ,Mstory are to be expected. One example is apparent in the present data. Hahn, Haber and Fuller [13] found that the differential aggression at 70 days of age in high and low bramweight mice was only observed in mice which had been isolated at 21 days of age. Animals o f the two lines group housed until 31 days and then tested at 70 days o f age were not different in aggression. These findings suggest sensitive periods for the interaction b e t w e e n genetic and environmental d e t e r m m a n t s o f behavior. In the present e x p e r i m e n t , mice were housed in group cages until 50 days of age and yet there were clear differences in the agonlstic behavior o f high and low brainweight control animals. It would thus appear that variables such as duration o f group rearmg, and the time of separation are not related in a simple manner.
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