Differential agonistic behavior in mice selected for brain weight

Physiology and Behavior, Vol. I0, pp. 759-762. Brain Research Publications Inc., 1973. Printed in the U.S.A.

Differential Agonistic Behavior in Mice Selected for Brain Weight' MARTIN E. HAHN, SONJA B. HABER 2 AND JOHN L. F U L L E R

State University o f N e w York at Binghamton, Binghamton, N e w York 13901

(Received 14 August 1972)

HAHN, E., S. B. HABER AND J. L. FULLER. Differentialagonistic behavior in mice selected for brain weight. PHYSIOL. BEHAV. 10(4) 759-762, 1973.-Mice selected for high, medium and low brain weight were weaned at 21 days and placed with siblings for 10 days then isolated or isolated immediately after weaning. At seventy-two days of age pairs from the same line and condition were fought. Behavioral measures such as: fighting, tail lashing, defense posture, nosing, genital sniffing and latencies to contact, aggression and dominance were recorded. Results indicated significant line and interaction effects for agonistic behaviors only in the groups receiving no experience with siblings after weaning. The results are discussed with reference to differential developmental patterns in the lines. Agonistic behavior

Brain weight

Early experience

GENETIC selection for a behavioral p h e n o t y p e is not a new area of research. In a pioneering study, Tryon [9] selectively bred rats based on performance in a multiunit maze. By inbreeding dull and bright animals, nearly nonoverlapping lines, with respect to maze performance, were obtained within eight generations. Since Tryon, successful selection has been carried out for numerous behavioral and physiological phenotypes [ 1,5 ]. Often, the lines or strains produced by selection have been analyzed to determine what types of change in biochemical or physiological processes have accompanied the observed changes. F o r example, Feuer and Broadhurst [3] investigated the Maudsley Reactive and Nonreactive strains (selectively bred for emotional defecation) and found, among other differences, lower amounts o f thyroid hormones in the thyroid glands of the high defecating strain. More recently, Lagerspetz et al. [8] after selecting mice for high and low aggressiveness found correlated differences in serotonin content of the forebrain, adrenal function and testicle weight. An alternate approach to the above t y p e of analysis is exemplified by Wimer and Prater [10] and Wimer et aL [ 11 ] who have selected for a neurological character (brain weight) and found associated modifications in behavior. In mice selected for high and low brain weight, behavioral differences were observed in open-field activity and some types of learning abilities. In addition to these behavioral differences, Fuller and Geils [4] have found differences in motor, sensory and brain growth patterns. Finally, Collins

Behavior genetics

Developmental patterns

[2] has discovered an apparent difference in aggressiveness in these same selected lines. She housed groups of 10 mice of either heavy or light brain lines together and observed differential amounts of wounding in the two lines. The light line animals carried significantly more wounds than did their heavy line counterparts. The present experiment set out to explore the apparent relationship between brain weight and aggressiveness reported by Collins, using independently selected lines, a more direct and detailed system of observing aggressive behavior and rearing conditions that might isolate differing susceptibility to social stimulation. METHOD

A nirnals Animals for the experiment were drawn from three lines selected on the basis of brain weight (BWS lines). The base population for the selection program was an eight-way cross of eight inbred strains originally made by Roderick and maintained by him, and later by us, with a breeding system which minimizes inbreeding and thus maintains genetic variability. These strains were: LP/J, BALB/cJ, MA/J, SM/J, C57BL/6J, LG/J, 129/J and DBA/2J. Our selection for brain weight was initiated at the eighth generation of the heterogeneous stock (HET) following the first cross in which genes from all eight foundation strains were potentially present in a single individual. In all three lines the basis for selection has been brain weight at 42 days adjusted to a standard b o d y weight for

This research was supported by National Science Foundation Grant GB-24827 and National Institute of Mental Health Grant MH-22005. 2Presently at the Department of Psychology, Miami University, Oxford, Ohio. 759

760

HAHN, HABER AND FULLER

males and females separately. Ten to twelve matings have been measured in each generation and approximately one-half have been selected for propagation of the next generation. In the BWS-H line, selection is based on a high brain weight relative to body weight; in the BWS-L line, selection is based on low brain weight. In contrast to this directional selection the BWS-M line is subjected to stabilizing selection with breeders chosen from litters with intermediate brain weights relative to body weight. After six generations of selection, the lines differ significantly from one another in brain weight. There is no difference between males and females and no interaction between sex and line. Table 1 is a summary of the brain weights of the three lines at this stage. The data in Table 1 describe our sixth generation population of brain selected mice. Animals for the present experiment were a random sample from this population. A total of 82 male mice, 30 (15 pairs) from the BWS-L group, 28 (14 pairs) from the BWS-M group and 24 (12 pairs) from the BWS-H group were used.

posture, nosing and squeaking were gories have been previously defined lasted until dominance was achieved as the simultaneous occurrence of squeaking) or for a maximum of 30 not achieved. Animals participated in RESULTS

After all pairs had been tested, the event recorder charts were scored for the frequency of occurrence and duration in seconds of each behavior category. In order to compare data from pairs which fought for different lengths, per rain scores were obtained for each test pair, i.e. raw frequency and duration data were divided by the number of minutes the particular test lasted. Only duration of behaviors will be presented since frequency data are essentially identical. Figure 1 depicts the results for four behavior categories and two latency measures. There is a pattern of results common to all measures illustrated. Mice in the 21-10-39 condition behaved similarly regardless of their brain size.

TABLE 1 75

BRAIN WEIGHTS OF BWS LINES -- GENERATION 6* 6.0

Line H M F N Mean Brain Wt. S.D.

22 522.9 16.2

15 526.3 24.7

Line MF M 33 486.0 22.8

27 479.7 19.6

4.$

MLine L F

38 477.4 17.3

42 468.6 18.9

recorded. These cateby Hahn [6]. A test within a pair (defined defense posture and min if dominance was one test only.

"~

li!! ! 00I I

8

]0

1.5

1,0

,

:in

L

H

*Brain weight in milligrams

Procedure At 21 days of age, all of the animals were weaned and placed at random into one of two experimental conditions. Even numbers of animals, approximately half the litters of each line, were placed in a 21-0-49 group, i.e. were weaned at 21 days, given 0 days with siblings and 49 days of isolation. The remainder (21-10-39 group) were given 10 days of sibling contact, before isolation. Animals in both groups remained in isolation until 70 days of age (replicates the procedure of King [7] in obtaining 70 day fighters) at which time two siblings from the same condition were placed into a Carworth Polycarbonate Isocage for mice separated by a divider attached to the top. They remained in this situation for two days and at 72 days of age were tested. On the test day a pair of males (set up in a divided cage 48 hr previously) was placed in an acoustically deadened room with one 15 W bulb providing 10 ft-c of illumination. The divider top was removed and a clear piece of PIexiglas was placed over the cage top to prevent escape. Simultaneously, a stopwatch and a 10 channel Esterline-Angus event recorder (chart speed 1 ram/see) were switched on and behavioral recording was begun, using a ten key control panel. Three time measures, latencies to contact, aggression and dominance and seven behavioral measures; fighting, social grooming, genital sniffing, tail lashing, defense

0 L

M

H

le

0

L

~00"

750

IOQI

~ 250

IO

0

M

I0 H

ii 0

lO L

0

10 M

0

10 H

0

iO L

iO

b

0

!0

PA

FIG. 1. Mean values for behavioral measures byline and condition. Conditions 21-0-49 and 21-10-39 abbreviated 0 and 10 respectively. Brain weight groups abbreviated L(low), M(medium) and H(high). In graphs A-D, the vertical scale represents time spent in the indicated activity in seconds per minute. In graphs E-F, the vertical scale indicates latency to the event indicated in seconds.

AGONISTIC BEHAVIOR IN MICE BRED FOR BRAIN WEIGHT Conversely, the agonistic behavior of animals in the 2143-49 condition is inversely related to their brain weight. Data summarized in Tables 2 and 3 substantiate this pattern. Although a 2x3 factorial design was employed, lack of homogeneity of variance and limited sample size eliminated a traditional analysis of variance and a non-parametric analysis based on ranks was substituted. Given that the Kruskal-Wallis H is equal to SS Treatment/MS Total, Scheirer and Ray (in preparation) have demonstrated that

761

the sum of squares for treatment can be partitioned into sums of squares associated with one or more variables, or into interaction between variables and trends, as in a traditional analysis of variance and that the resultant ratio is distributed as a random chi-square variable. Table 2 presents a summary of results obtained using this analysis. Results for nonagonistic behavioral measures: social grooming, genital sniffing, and nosing are omitted since they show no effect due to brain weight, condition or

TABLE 2 MEANS OF BRAIN WEIGHT AND REARING GROUPS FOR EACH BEHAVIORAL MEASURE AND RESULTS OF 2 x 3 KRUSKAL-WALLISANALYSES

Means

Measures

21-0-49

21-10-39

H on Ranks

df

Level

L

11.9

15.4

HBW

1.58

2

N.S.

M

44.3

32.6

HENV.

0.16

1

N.S.

H

20.7

17.3

HBW X ENV.

0.31

2

N.S.

L

59.1

163.9

HBW

4.98

2

p<0.10

M

99.3

115.4

HENV.

0.09

1

N.S.

H

406.0

283.6

HBW X ENV.

1.79

2

N.S.

L

217.6

590.8

HBW

6.58

2

p
M

312.4

495.9

HENV.

0.01

1

N.S.

H

1136.3

650.9

HBW X ENV.

1.41

2

N.S.

L

5.8

5.0

HBW

3.99

2

N.S.

M

4.5

6.6

HENV.

0.80

1

N.S.

H

3.5

5.2

HBW X ENV.

1.19

2

N.S.

L

4.8

1.2

HBW

7.98

2

p<0.02

M

1.5

1.1

HENV.

0.43

1

N.S.

H

0.4

1.2

HBW X ENV.

6.63

2

p<0.05

L

3.6

1.4

HBW

11.41

2

p
M

2.3

1.4

HENV.

0.00

1

N.S.

H

0.2

1.4

HBW X ENV.

5.11

2

p<0.10

L

1.9

0.8

HBW

1.83

2

N.S.

M

1.5

0.9

HENV.

2.84

1

p<0.10

H

0.8

0.7

HBW X ENV.

3.07

2

N.S.

Latency to Contact

Latency to Aggression

Latency to Dominance

Fighting

Tail Lashing

Defense Posture

Squeaking

762

HAHN, HABER AND F U L L E R TABLE 3

COMPARISONS BETWEEN LINES IN THE 21-0-49 CONDITION*

Measures

Differences in Means Comparison p value

Linear Trend, 1 df H p value

Latency to Contact

Overall

<0.05

1.11

N.S.

Latency to Aggression

Overall H>L

<0.05 <0.01

5.71

<0.02

Latency to Dominance

Overall H>M, H>L

<0.05 <0.05

4.45

<0.05

Fighting

Overall L>H

N.S. <0.05

3.75

<0.05

Tail Lashing

Overall L>H, L>M, M>H

<0.01 <0.01

11.57

<0.001

Defense Posture

Overall L>H, M>H

<0.01 <0.002

10.43

<0.005

Squeaking

Overall L>H, M>H

N.S.

3.75

<0.05

*Means are presented in Table 2 an interaction of the two. Latency to contact which is presented, also was uneffected by brain weight, condition or an interaction of the two. On the other hand, latency to aggression and dominance (measured either from the beginning of the test or first aggression), tail lashing and defense posture all show an effect negatively related to brain weight and both tail lashing and defense posture demonstrate an interaction between brain weight and rearing condition. Table 3 summarizes additional tests in support of our interpretation of the data. Kruskal-Wallis one-way analyses on ranks were performed between brain weight groups within conditions, and on conditions within brain weight groups. Mann-Whitney U tests were used to make individual pair comparisons. Trend analyses after Scheirer and Ray (in preparation) were used to detect linear trends within environmental conditions due to brain weight. Again, results on agonistic behaviors show increasing aggressiveness

in relation to decreasing brain weight in the 21-0-49 condition, furthermore, trend analysis reveals significant linear trends due to brain weight in all agonistic behaviors. There were no differences between groups nor any trends present in nonagonistic behaviors in the 21-0-49 condition, or within any measures in the 21-10-39 condition. DISCUSSION The results clearly demonstrate that in these lines, agonistic behavior is negatively related to brain weight. The power of this relationship is strengthened when it is recalled that the lines used are not inbred and thus vary considerably in physiological and behavioral traits. Furthermore, our results agree with those of Collins and add to the probability of a functional relationship between brain size and agonistic behavior since our subjects were derived from a completely independent program of selection. This relationship is strongly influenced by environmental factors since strain differences were found only in the 21-0-49 condition. King [7] using inbred mice, simultaneously manipulated genotype and timing of social experience and found that 10 days of postweaning sibling contact before isolation, facilitated fighting while no sibling contact before isolation inhibited fighting - exactly as found in our M and H lines. The opposite response of the L line mice to these schedules of sibling contact may indicate that this line is out of phase with the other lines on a program of fixation of behavioral characteristics. It has already been shown by Fuller and Geils [4] that differences in adult brain size are associated with differences in the temporal patterns of growth. Finally, it is interesting to note that tail lashing and defense posture showed greater between line and interaction effects than fighting itself. Hahn and Haber (in preparation) in a study on agonistic behavior in inbred strains, have demonstrated a significant correlation of 0.55 ( p < 0 . 0 t ) between amount of tail lashing and observer ratings of intensity of fighting. As a consequence, we argue that the behavioral trait negatively correlated with total brain weight is a general temperamental and motivational character. This genetic difference is more clearly brought out by measures of intensity than by those of duration and latency. Presumably, something more specific than the mass of brain is involved in the genotype - behavior pathway, and we suggest that selection based on neuroendocrine traits might be even more effective in modifying agonistic behavior.

REFERENCES 1. Broadhurst, P. L. Experiments in psychogenetics. In: Experiments in Personality. Fol. L Psychogenetics and Psych~ pharmacology, edited by H. J. Eysenik. London: Routledge, 1960, pp. 1-102. 2. Collins, R. A. Experimental modification of brain weight and behavior in mice: an enrichment study. Devl Psychobiol. 3: 145-155, 1970. 3. Feuer, G. and P. L. Broadhurst. Thyroid function in rats selectively bred for emotional elimination. I. Differences in thyroid hormones. J. Endocr. 24: 127-136, 1962. 4. Fuller, J. L. and H. D. Geils. Brain growth in mice selected for high and low brain weight. Devl Psychobiol., 1972, in press. 5. Fuller, J. L. and W. R. Thompson. Behavior Genetics. New York: John Wiley and Sons, Inc., 1960, pp. 117-269. 6. Hahn, M. E. Social relationships and their development in two strains of Mus Musculus. Unpublished doctoral dissertation, Miami Univ., 1970.

7. King, J. A. Relationships between early social experience and adult aggressive behavior in inbred mice. J. genet: Psychol. 90: 151-166, 1957. 8. Lagerspetz, K. Y. H., R. Tirri and K. M. J. Lagerspetz. Neurochemical and endocrinological studies of mice selectively bred for aggressiveness. Reports from the Institute of Psychology~ University of Turku. No. 29, 1967. 9. Tryon, R. C. Genetic differences in maze learning ability in rats. Yb nat Soc. Stud. Educ. 39: 111-119, 1940. 10. Wimer, C. and L. Prater. Some behavioral differences in mice genetically selected for high and low brain weight. Psychol. Rep. 19: 675-681, 1966. 11. Wimer, C., T. H. Roderick and R. E. Wimer. Supplementary Report: Behavioral differences in mice genetically selected for brain weight. Psychol. Rep. 25: 363-368, 1969.