Behavioural ontogeny of looptail mice

Anim. Behav ., 1968, 16, 1-4

BEHAVIOURAL ONTOGENY OF LOOPTAIL MICE BY J . H . F . VAN ABEELEN Genetics Laboratory, University of Nijmegen, The Netherlands

neither trait is fully penetrant, there remains a slight chance of incorrect classification even in the case of mice phenotypically normal in both respects . The mutant (Lp/+) and the nonmutant (+/+) group each comprised sixteen males . They were marked with dye. After each observation session the dye was renewed and the animals were returned to their mothers .

Williams & Scott (1954), after observing the overt behaviour of young mice, have established natural stages of development, each with its own repertoire of acts and postures . These periods are : neonatal (1 to 4 days), transitional (5 to 11 days), socialization (12 to 25 days), and juvenile (26 to 40 days). Applying reflexological criteria, Fox (1965a) distinguishes the following periods : perinatal (1 to 3 days), neonatal (3 to 8 days), postnatal transitional (9 to 14 days), postnatal infantile (15 to 26 days), and juvenile (from 26 days until sexual maturity) . The basic information on normal development given by these authors can be employed for studying behavioural deviations in mutant mice (see also Fox, 1965b ; Thiessen, 1965) . The effects of the looptail-allele (Lp) on physical development have been dealt with by Griineberg (1952, p. 144 and 1963, p . 153) . Adult heterozygotes which display wobbly head movements show enlargement of the ventricles of the telencephalon and deformation of the caudate nucleus-putamen complex, hippocampus, and septal area (van Abeelen & Raven, in press) . Apart from their head shaking, van Abeelen (1966) has detected other behavioural characteristics in 3-month old heterozygotes, viz . diminished frequencies of rearing, climbing, and vibrating with the forelegs . For these reasons a detailed analysis of the behavioural ontogeny of this mutant would seem of interest . This study compares the development of behavioural components in looptail mice with that in normal house mice .

Apparatus For observing mice under the age of 1 month a plastic cage measuring 17 cm x 11 cm x 13 cm and without a lid was used . A sheet of filter-paper covered its floor, with five wheat pellets scattered over it. One-month old mice were observed in a large cage similar to the one described elsewhere (van Abeelen, 1966), but of a different size : 133 cm x 53 cm x 58 cm. Locomotory activity was recorded by means of three light beams directed upon three photoelectric cells which were connected to electric counters . The temperature in the observation room varied around 21'C. Illumination was provided by eight 40 W fluorescent tubes . Procedure Infant mice were separated from their mother and placed singly in the centre of the observation cage . Each animal was observed directly and continuously for 15 min on the afternoons of days 3 (neonatal period), 8 and 10 (transitional), 14 and 17 (socialization), and approximately 31 (juvenile). The frequencies of twentyeight behavioural components were registered on check-lists . For the neonatal period these acts included body flexion, twitching, crawling, pivoting, head waving, stretching, yawning, squealing, face cleaning, scratching, and sniffing at pellet (Williams & Scott, 1954 ; most of these have also been described in neonate rats by Bolles & Woods, 1964) . For the later stages of development the following components were also surveyed : sniffing at hopper, walking, backing, jumping, climbing, leaning against wall, rearing, lifting one foreleg, eating, defecating, urinating, licking, vibrating forelegs, furshaking, digging (scraping and kicking back), and freezing (for descriptions and figures see van Abeelen, 1963).

Method Subjects The mice came from a non-inbred stock in which the only major gene segregating was Lp . Six litters born early in the morning were used . After removal of the females and an occasional runt, the remaining four, five, or six male pups were raised by their wild-type mother in a plastic breeding cage. The cages were provided with a bedding of peat dust and some wood shavings for nesting material, and placed in an air-conditioned mouse room . The mice were classified using tail twists as well as adult head-shaking as criteria . Since 1

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ANIMAL BEHAVIOUR, 16,

Nonparametric statistical tests were applied for evaluation of the results : the Kruskal-Wallis test for litter effects, the Mann-Whitney U test for group comparisons with regard to components of which the total number of zero scores was less than 16, Fisher's exact test for components with 16 zeros or more, and Kendall's ranking test for correlations between a few components (Siegel, 1956).

1

The quantitative data are set forth in Table I . In general, the number of animals performing a given component on a particular day was about the same for the two genotypes, except for scratching on day 10 and leaning against the wall on days 10, 14, and 17. The values for twitching suggest that this component declines more rapidly in looptail mice than in normals during the transitional period. Neonate looptails rated lower for pivoting on day 3 (the rather high score on day 8 was largely due to one subject : 13 times) . Head waving decreased virtually synchronously in mutants and nonmutants. Although the difference reached significance on day 17 only, Lp-mice scored almost consistently lower for face cleaning than normals (Fig . 1), with both groups showing a peak on day 14. Mutants seemed to scratch less often than normals, at least at the end of the transitional period ; after the peaks in this period the curves for both groups drop sharply (Fig . 2) . Licking at various body parts appeared relatively late in development, with an indication of mutants doing it less frequently .

Results The tests for litter effects did not reveal any significant differences between litters. Since fifteen components occurred rarely or not at all in mutants as well as nonmutants, these acts are omitted from the table . Of these, crawling was seen on days 3, 8, and 10 ; by day 8 about half of the animals walked on all fours, and jumping was observed for the first time on day 14. On day 10 the eyes were still closed, but open on day 14 . Eating did not appear until day 17 . A conspicuous feature of day 17 was freezing, which was displayed by eleven mice in each group . Wobbly head movements became discernible in mutants by day 10 .

Table I. Looptail versus Wild-type : Frequencies of Behavioural Components Performed by Solitary Males withIn 15 Min at Different Ages Day 3

Day 8

Day 10

Day 14

Day 17

1 Month

Components Twitch

LP

+

LP

+

LP

+

LP

+

LP

+

419

339

72

118*

48

68

16

12

4

0

LP

+

77*

58

74

10

46

67

49

37

223

284

Pivot

21

42*

45

31

6

1

2

0

0

0

Head wave

86

88

59

62

26

27

0

0

0

0

Face clean

11

4

4

12

5

23

65

91

47

Scratch

2

0

37

67

7

50(*)

17

14

4

Lick

0

0

0

0

0

0

18

35

16

49(*)

Sniff pellet

5

7

2

2

5

12

18

24

38

39

Lean

0

0

1

2

1

13(*)

37

205*

98

330**

433

447

Rear

0

0

0

0

0

4

17

179

144

188

216

Sniff hopper

0

0

6(*)

Climb

58

108*

Vibrate

0

10*

Scrape Activity count

73

96

1572

1581

The number of animals in each group is sixteen, except for the age of 1 month (n=15 ; here the animals were observed in a different situation) . **P<0 .01 ; *P<0 .05 ; (*)P<0 .10 .

VAN

ABEELEN : BEHAVIOURAL ONTOGENY OF LOOPTAIL MICE

It was hypothesized that for some acts there might exist a common causative factor. For twitching (day 3) and locomotor activity (1 month) this could be a general excitability of the brain ; head waving (day 3) and rearing (1 month) might both represent a tendency for orientation in an upward direction . In neither case a correlation between early and later acts was found .

100

M

3

20

3

8

10

14

17 DAYS

Fig . 1 . Development of face-cleaning in Lpl+ (---) and +/+ (-) mice .

Sniffing at pellet occurred only occasio nal ly in the small cage, but very often in the large one . Lp-mice clearly demonstrated a retarded development of leaning against the wall ; at I month, however, they seemed to have caught up with the normals . There is an indication that they started rearing later ; at 1 month they did not differ from normals in this respect . It turned out that mutants aged I month rated lower for climbing and vibrating with the forelegs than wild-type mice . The values for locomotor activity were very close . 100 00

0 40

s w 20

3

8 10

14

17 DAYS

Fig . 2. Development of scratching in Lpl+ (----) ) mice . and +/+ (

Discussion As a result of the stimulation they receive from their mother and littermates, pups are quite active in the nest, but most of the time their bodies are only partly visible. Solitary pups are much easier to observe ; however, they turn out to be rather quiet, as is evident from the rarity of several acts. The present data on the course of behavioural development in normal mice are in agreement with the findings of Williams & Scott (1954) and Fox (1965a) . Lp-mice, on the other hand, show in some respects a different pattern of temporal changes . Twitching, which appears at first as a diffuse fluttering of the whole body, but later becomes a more localized movement of the limbs, probably reflects the maturation of systems of co-ordination in the brain . Thus, the lower twitching rates in mutants during the transitional period might be a sign of already defective neurological development . The lower frequency of pivoting (according to Fox, 1965a, a searching type of locomotor activity) during the neonatal period points in the same direction . Looptails tend to lag behind normals with regard to the rates of all three kinds of grooming behaviour recorded . Execution of these components requires well-developed motor functions, and in these respects young mutants seem to be somewhat disturbed. Adult looptails, however, do not differ from normals as far as grooming is concerned (van Abeelen, 1966) . The temporary but marked decrease of scratching found within the socialization period coincides with high scores for face-cleaning and licking. No explanation is offered for this finding . Initially, leaning against the wall develops with greater difficulty in mutants . At a later age (1 month ; also at 3 months : van Abeelen, 1966), they carry out this act as easily and frequently as normals do . Apparently, mutants retain considerable developmental capacities throughout. Yet, as has been shown in the report cited above, rearing is still clearly affected in adult looptails, probably as a result of persisting choreatic movements .

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ANIMAL BEHAVIOUR, 16, 1

The differences found for climbing and vibrating with the forelegs have also been observed in the previous work with 3-month old animals . The defect in climbing in Lp-mice again indicates motor impairment . Vibrating with the forelegs can be interpreted as an intention movement for face cleaning . The latter occurred almost at all stages less often in mutants than in nonmutants ; the difference for vibrating may be just another expression of this tendency. The picture emerging is that the Lp-locus affects several segments of mouse behaviour that occur during various developmental periods . Most probably, these effects can be traced back to the abnormal ontogenesis of extrapyramidal motor systems in the forebrain, particularly those of the caudate nucleus and the putamen . However, at this stage the possibility that the Lp-locus exerts its effect on behaviour through other developmental pathways cannot be excluded . Summary 1 . For the purpose of comparing the behavioural development of looptail (Lp/+) mice and normal (+/+) mice, twenty-eight components performed by single males were screened by direct observation on days 3, 8, 10, 14, 17, and approximately 31 after birth . 2. The data on the behaviour of normal mice confirmed earlier findings . Apart from wobbly head movements, mutants showed at specific ages decreased frequencies of twitching, pivot-

ing, three grooming activities, leaning postures, rearing, climbing, and vibrating with the forelegs . 3 . These results are related to previous findings in older looptails and discussed in terms of the abnormal development of certain brain structures . REFERENCES Abeelen, J . H . F. van (1963) . Mouse mutants studied by means of ethological methods. I . Ethogram. Genetica, 34, 79-94 . Abeelen, J . H. F . van (1966) . Behavioural profiles of neurological mutant mice . Genetica, 37, 149-158 . Abeelen, J . H. F . van & Raven, S . M . J . . Enlarged ventricles in the cerebrum of loop-tail mice . Experientia (in press) . Bolles, R. C . & Woods, P . J. (1964) . The ontogeny of behaviour in the albino rat . Anim. Behav., 12, 427-441 . Fox, M . W. (1965a) . Reflex-ontogeny and behavioural development of the mouse . Anim. Behav., 13, 234-241 . Fox, M . W . (1965b). Neuro-ontogeny of neuromuscular mutant mice . J. Hered., 56, 55-60. Griineberg, H. (1952) . The Genetics of the Mouse (Bibliogr. Genet . XV) . The Hague : Nijhoff. Gruneberg, H . (1963). The Pathology of Development . A Study of Inherited Skeletal Disorders in Animals . Oxford : Blackwell Scientific Publications . Siegel, S . (1956) . Nonparametric Statistics for the Behavioral Sciences . New York : McGraw-Hill . Thiessen, D. D . (1965) . The wabbler-lethal mouse : A study in development . Anim. Behav., 13, 87-100 . Williams, E . & Scott, J . P. (1954) . The development of social behavior patterns in the mouse, in relation to natural periods . Behaviour, 6, 35-65 . (Received 6 March 1967 ; Ms . number : 733)