ISSN EDICIÓN EN PAPEL: 0214-9915
1999. Vol. 11, nº 1, pp. 75-81
OPEN-FIELD EXPLORATION AND EMOTIONAL REACTIVITY IN MICE
Generós Ortet y Manuel Ignacio Ibáñez
University of Castelló
Ambulation (exploratory behaviour) and defecation (emotional
reactivity) in the Garcia-Sevilla's (1984) low-frightening open field have been
proposed as analogous in rats to extraversión and neuroticism personality
dimensions. The present study was designed to study these behaviours with the
modified version of the open field test in mice. However, ambulation was considered
as a possible parallel of human sensation-seeking. According to the previous
experiments, no significant negative correlations were found between ambulation
and defecation, as usually found between sensation-seeking and anxiety/neuroticism
in man. Moreover, a significant decrease of ambulation was also found between
the first and forth day of exposure to the test, as the repeated exposure to
the same environment seem to lower interest in human high-sensation seekers.
Finally, the animals' weight was independent of ambulation in both mouse strains
used, and was independent of defecation for Swiss Albino mice.
La exploración y la reactividad emocional del ratón
en el campo abierto. La deambulación (conducta exploratoria) y la
defecación (reactividad emocional) en el campo abierto poco amenazador
de García-Sevilla (1984) se han propuesto como análogos en ratas
de las dimensiones de personalidad extraversión y neuroticismo. Este
estudio se diseñó para estudiar estas conductas en esta versión
modificada del campo abierto con ratones. Sin embargo, la deambulación
se consideró como un posible paralelo de la búsqueda de sensaciones
humana. Al igual que en experimentos previos, encontramos correlaciones negativas
no significativas entre deambulación y defecación, como generalmente
ocurre entre búsqueda de sensaciones y ansiedad/ neuroticismo en humanos.
Además se encontró un decremento significativo de la deambulación
entre el primer y cuarto día de exposición al test, del mismo
modo que la exposición repetida al mismo ambiente parece disminuir su
interés para los altos buscadores de sensaciones humanos. Finalmente,
el peso de los animales fue independiente de la deambulación en ambas
cepas de ratones, así como de la defecación en los ratones Swiss
Correspondencia: Generós Ortet
Department of Psychology
Jaume I University of Castelló
12080 Castelló (Spain)
Nowadays there is an important amount of empirical evidence
related to the contribution of genetic factors to basic personality traits.
The behaviour-genetic studies represent two traditions (Goldsmith, 1989): human
family, twin, and adoption studies of a variety of traits, usually assessed
via questionnaires (e.g. Plomin and Daniels, 1987; Plomin, Chipuer and Loehlin,
1990; Eysenck, 1990; Zuckerman, 1991; Loehlin and Rowe, 1992; Goldsmith, Losoya,
Bradshaw and Campos, 1994; Pedersen, 1994); and laboratory research of animal
models of personality (e.g. Chamove, Eysenck and Harlow, 1972; Garcia-Sevilla,
1984; Mather and Anderson, 1993; Gold and Maple, 1994; Draper, 1995; Forkman,
Furuhaug and Jensen, 1995; Dellu, Piazza, Mayo, Le Moal and Simon, 1996). The
first line of research has had an important development and there are already
studies related to the identification of specific genetic locus that contributes
to personality traits (Benjamín, Li, Patterson, Greenberg, Murphy and
Hamer, 1996; Ebstein et al., 1996). The second line of research, animal models
of human personality traits or dimensions has had a less impressive progress,
especially among animal psychologists (see Eysenck and Eysenck, 1985; Zuckerman,
1991 for a review). These researchers consider that the main personality traits
may be understood as genetically based behaviour patterns developed in terms
of Darwinian evolutionary principles and based on common physiological structures
and hormonal activity.
García-Sevilla (1984) and Garau, Martí, Pérez-Mourelo
and Garcia-Sevilla (1991) describe a full series of studies related to parallels
of Eysenck's extraversion and neuroticism in rats. In these investigations,
ambulation (more related to exploratory than activity measures) and defecation
(emotional reactivity) in a low-frightening open field were proposed as measures
of extraversion and neuroticism respectively. This open field was created modifying
the one standardised by Broadhurst (1957) with the elimination of the 78 dB
white noise. Under these conditions, ambulation and defecation measures were
not correlated to each other or showed a low negative correlation (Garcia-Sevilla,
However, it has been argued that the core of extraversion is
sociability (Zuckerman, 1991) and this dimension, together with agreeableness,
appears as very relevant to interpersonal behaviour (McCrae and Costa, 1989).
So, it seems that the social behaviour of animals in controlled colony environments
may be a better parallel of human extraversion; and ambulation in the open field
may be a more appropriate measure of sensation seeking, especially as an analogous
to the adventure seeking type in the human (Zuckerman, 1994). Accordingly, Garau
(1984), using factor analyses of rodent behaviour in the low-frightening open
field and other tests (e.g., Y maze, dark-light, hole-board), found that the
ambulation appeared to be associated with the extraversion trait stimulation
seeking (sensation seeking).
Dellu, Mayo, Piazza, Le Moal and Simon (1993) and Dellu, Piazza,
Mayo, Le Moal and Simon (1996) have proposed that individual differences of
locomotor reactivity to novelty in rats (assessed by a test that consists of
a circular corridor) as a possible parallel of sensation seeking. They found
that the high responders (HR) rodents, opposed to low responders (LR), are highly
reactive in different behavioural tests that measure the free-choice response
to novel environments (i.e., exploration in a Ymaze, exploration in a 16-arm
radial maze, and a darklight emergence test). These authors consider that the
response to novelty is crucial to the definition of sensation seeking, and suggest
an animal model with characteristics that are analogous to some of the factors
found in this human trait. Moreover, HR rats have been found to be predisposed
to drug-taking, like sensation seeking is related to drug use (Zuckerman, 1994),
and rapidly develop intravenous self-administration of amphetamine while the
LR do not (Piazza, Demière, Le Moal, and Simon, 1989). However, Gong,
Neill and Justice (1996) found that HR rats did not developed place-preference
conditioning with cocaine more readily than LR rats. Dellu et al. (1993; 1996)
have pointed out that there are also neurochemical and neuroendocrinological
differences between HR and LR rats related to dopaminergic activity in the nucleus
accumbens and the level of corticosteroids. Accordingly, HR rats (and high sensation
seekers as defended by Zuckerman, 1994) may seek novelty situations for the
reinforcing properties of the neurochemical and neuroendocrinological activity
enhanced by intense, varied, novel and complex sensations, and risk-taking activities.
The main aim of the present research was to study exploration
and emotional reactivity with the Garcia-Sevilla's (1984) lowfrightening open
field in mice. For this purpose, ambulation (exploration) in the open field
was considered as an indication of the adventure seeking type of sensation seeking,
and defecation (emotional reactivity) was considered as an indication of neuroticism/anxiety.
According to Zuckerman's (1994) sensation seeking concept, it was predicted
that correlations between ambulation and defecation would be low negative in
the two strains of mice used, as it is usually found between sensation seeking
and neuroticism/anxiety in humans. Because repeated exposure to the same open
field environment decreases its novelty, conversely it was predicted that ambulation
would decrease across the four days of testing. In addition, it was predicted
that ambulation and defecation in the open field would be independent of other
biological measures, such as animal's weight.
Twenty four male mice from outbred (12 Swiss Albino) and inbred
(12 C57BL/6) strains obtained from Interfauna Ibérica, S.A., Barcelona,
Spain (Sprague Dawley Co.) served as subjects. Animals were 4 weeks old at the
start of testing and were hou-sed, 4 per cage, on arrival with food and water
freely available. All mice were maintained in a room temperature of 22°C with
controlled humidity, where 12 hr light-dark schedule with light off 08:00-20:00
was in effect. Experimentation took place during the dark phase of the cycle.
Apparatus and behavioural testing
Low frightening open field. The apparatus was a square transparent
plastic cage (50 x 50 x 40 cm high) divided into 25 equal squares. A lamp with
three fluorescent 36W bulbs, hanging 1 m above the centre of the open field,
provided the illumination. One week after arrival, animals were placed at the
centre of the open feld and observed during 5 min. Testing was repeated at the
same time on four subsequent days. After testing, subjects were weighed and
returned to the home cage. The number of lines crossed by the hind legs were
recorded as a measure of ambulation (exploratory behaviour), and the number
of boli deposited were recorded as a measure of defecation (emotional reactivity).
The normality of the 2 strain distribution on the behavioural
and weight measures was verified using Kolmogorov-Smirnov test. The consistency
of behavioural responses was analysed by using Cronbach's coefficient alpha.
Student's t-test was used to compare between strains. An analysis of
variance (ANOVA) for repeated measures was used for comparisons among the behavioral
measures during the four days. All measures were correlated using Pearson's
correlation coefficient. The accepted level of significance was P <
0.05 for all statistical test.
The normality of the two samples for the three variables was
verified: Swiss Albino (ambulation, Z= 0.51, p = 0.9; defecation, Z
= 0.60, p =0.9; weight, Z = 0.38, p = 0.9); C57BL/6 (ambulation,
Z = 0.58, p = 0.9; defecation, Z = 0.57, p = 0.9;
weight, Z = 0.54, p =0.9). Table 1 shows, for the two mouse strains,
means and standard errors of mean of ambulation, defecation and weight along
with the mean comparisons and reliability coefficients. It shows that significant
differences between strains were only found for weight. Alpha reliability coefficients
were high for both behavioural measures for Swiss Albino strain, however it
was very low for defecation by C57BL/6 group, being ambulation the most consistent
Table 2 presents the correlation coefficients between the behavioural
and weight measures. Although most correlations were high, only the coefficient
between defecation and weight for C57BL/6 strain was significant.
Figure 1 shows that daily repeated exposure lo the low-frightening
open field decreased the number of crossings (ambulation). ANOVA showed that,
for both strains, the highest ambulation was observed during the first day,
while the lowest was scored on the forth day [Swiss Albino: F(3,33) =
3.50, P < 0.05; C57BL/6: F( 3,33) = 13.79, P < 0.001].
Figure 2 shows that repeated exposure had no effect on defecation
for Swiss Albino mice [F(3,33) = 2.36, P = NS], but the ANOVA
showed significant differences for C57BL/6 mice [F(3,33) = 4.12, P
< 0.05]. Thus, for C57BL/6 the highest score was observed during day 2 and
the lowest during day 1.
Results showed that two behavioural measures, ambulation and
defecation, in the low-frightening open field provided an acceptable level of
internal consistency for Swiss Albino and C57BL/6 mouse strains. The only exception
was defecation for the second group. The obtained reliability coefficients are
similar to those found in previous studies with rats (cf. Garau, 1984; Goma
and Tobeña, 1978). There were no significant differences between the
behavioural measures in the two strains of mice. However, Swiss Albino rodents
were clearly bigger than C57BL/6.
Results were consistent with those found by Garcia-Sevilla
(1984) and Garau et al. (1991) with rats. That is, correlations between ambulation
(exploration) and defecation (emotional reactivity) in the lowfrightening open
field were negative but not significant for both mouse strains. In relation
to our hypothesis, these data can be better interpreted in the fine of the low
negative correlations usually found between sensation seeking and anxiety/neuroticism
dimensions in humans (Zuckerman, 1994). Ambulation measure is considered as
a possible analogous to sensation seeking (especially the adventure seeking
type) in humans. In keeping with previous studies with rats (e.g. Garcia-Sevilla,
1984), ambulation and defecation were independent of other biological measures,
such as the animal's body weight in Swiss Albino mice. Also, ambulation was
not significantly correlated to weight for C57BL/6. However, a positive significant
correlation between defecation and weight was found for C57BL/6 strain which
would indicate an unpredicted direct relationship between defecation and body
According to our expectations, a significant decrease in ambulation
between the first and forth day of exposure to the lowfrightening open field
was also found in mice (cf. Garau, 1984; Garau et al., 1991). As it was hypothesised,
repeated exposure to the same environment decreased its novelty, as a result
exploratory behaviour (ambulation) also decreased (cf. Dellu et al., 1993).
Results have characteristics that resemble the relevance of novelty in human
sensation seeking. Furthermore, the current study found no significant differences
in defecation among the four days of exposure for Swiss Albino mice. This may
be due to the low-frightening characteristics of the test. This open field is
designed to enhance low levels of fear, so the repeated exposure would not influence
the habituation of the animal's emotional reactivity to the experimental situation.
Nonetheless, an unexpected pattern with significant differences among sessions
was found for this measure by C57BL/6 strain which is difficult to interpret.
Overall, results found in this study on the low-frightening
open field test supported most of our predictions. These were: 1) no significant
negative correlations between ambulation and defecation were found, 2) a significant
decrease of ambulation between the first and forth day of exposure was observed,
and 3) an independence between ambulation and defecation of body weight was
obtained, especially with the Swiss Albino strain.
More experiments are needed to take exploratory behaviour (ambulation)
and emotional reactivity (defecation) of mice in García-Sevilla's (1984)
low-frightening open field as analogous measures to sensation-seeking and anxiety
traits in humans. Other studies with bigger and varied samples of animals are
required. Moreover, it seems necessary to compare the low-frightening open field
test with other exploratory (e.g., Dellu et al.'s, 1993, novelty-induced locomotor
activity or Lister's, 1987, hole-board) and emotional reactivity (e.g., Lister's,
1987, plus-maze) behavioural tests in mice. And last but not least, studies
about the hereditary, and the neurochemical and neuroendocrinological characteristics
of exploration and emotional reactivity in the lowfrightening open field test
are required in relation to biological correlates of sensation seeking (e.g.,
dopaminergic activity) and anxiety (e.g., serotonergic activity) proposed in
We thank Diane M. Walker, Juan Carlos Oliver, Carlos G. Aragón
and Micaela Moro for their help in preparing this manuscript. This research
was supported by Grant No. GV B-ES-17-003-96 from the Conselleria de Cultura,
Educació i Ciència, Generalitat Valenciana. Correspondence should
be addressed to Generós Ortet, Department of Psychology, Jaume I University
of Castelló, 12080 Castelló, Spain. E-mail: firstname.lastname@example.org
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Aceptado el 6 de mayo de 1998
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| Table 1. Means ( SEM of ambulation and defecation in the low-frightening open field, and weight by Swiss Albino (N=12) and C57BL/6 (N=12) mice, mean comparisons between the two strains, and coefficients alpha of behavioural measures).|| |
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| Table 2. Correlations between the two measures obtained from the low-frigtening open field and weight by Swiss Albino (N= 12, above diagonal) and C57BL/6 (N= 12, below diagonal) mice.|| |
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| Figure 1. Ambulation (exploration) in the low-frightening open field.|| |
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| Figure 2. Defecation (emotional reactivity) in the low-frightening open field.|