Chapter 4.11 Measuring rodent exploratory behavior

w.E. Crusio and R.T. Gerlai (Eds.) Handbook of Molecular-Genetic Techniquesfor Brain and Behavior Research (Techniques in the Behavioral and Neural Sciences, Vol. 13) 9 1999 Elsevier Science BV. All rights reserved. CHAPTER

4.11

Measuring rodent exploratory behavior Catherine Belzung Laboratoire d'Ethologie et de Pharmacologie du Comportement ( L E P C O ) , Facultd des Sciences, Parc Grandmont, F-37200 Tours, France

Introduction

Exploration generally refers to behaviors that are triggered off by novelty. It has been extensively studied using many test paradigms such as confrontation with novel objects (Misslin and Ropartz, 1981a, 1981b, 1981c; Misslin, 1982; Poucet et al., 1986), unknown conspecifics (File, 1980; Figler and Einhorn, 1983) or novel places (Katzir, 1982; Miller et al., 1986; Misslin and Cigrang, 1986; Griebel et al., 1993a; Blois-Heulin and Belzung, 1995), especially in small rodents such as mice or rats (Berlyne, 1950; Hughes, 1968; Barnett and Smart, 1975; Barnett and Cowan, 1976; Misslin and Cigrang, 1986). When these animals have free access to a novel place, they first exhibit an orienting response (Berlyne, 1960; Sokolov, 1960; Vinogradova, 1970) followed by approach responses toward the novel stimulus, called novelty-seeking behavior, and then by marked preference for the novel place (Hughes, 1968; Misslin and Ropartz, 1981c). Many explanations of this behavior have been proposed. For example, exploration permits the animal to gain information about a novel environment, which may have an adaptative value because it allows an optimization of foraging and escape from predators (Birke and Archer, 1983; Renner, 1990). However, as exploration exists outside of the direct context of foraging or of threat, another possible motivation may be related to the reinforcing properties of this behavior. Indeed,

the opportunity to discover complex novel places may act as an effective reward in learning tasks (Montgomery, 1954). Exploration-related responses include a large number of behavioral items such as scanning, sniffing, walking, rearing, leaning, jumping, digging, dragging objects (Blois-Heulin and Belzung, 1995; Renner and Seltzer, 1991). However, the expression of such a rich behavioral repertoire depends upon the experimental paradigm employed. For example, approach toward novelty cannot be exhibited when a subject is forced into novelty. Digging or eating is not possible when sawdust or food are not available. Most laboratory studies have been undertaken using experimental paradigms allowing the expression of very few behaviors and in which only a limited number of items such as locomotion or rearing have been registered, thus permitting the automatic recording of behaviors using photoelectric cells. Exploration depends upon different determinants, such as size of the apparatus (rodents are agoraphobic and therefore avoid large spaces), lighting conditions (exploration is inhibited under brightly-lit conditions) (File, 1980), presence of attractive or aversive stimuli within the environment (for example, exploration is inhibited by presence of a predator's olfactory marks) (Berton et al., 1998), free or forced access novelty (forced access is stressful, when compared to free access) (Misslin and Cigrang, 1986), complexity of the environment (Taylor, 1974), level of discrepancy

739

between unknown and familiar space (Birke and Archer, 1983), degree of satiety (exploration is largely increased in food deprived rodents), etc. This chapter describes several experimental paradigms useful for the study of exploration in rodents. These tests are widely used in behavioral neurobiology and differences between inbred strains have been repeatedly reported using these devices. Therefore, they may be useful to detect behavioral differences between transgenic, knockout or knockdown mice and their respective wildtype genotypes.

Exploration of novel places

Openfields (Fig. 1A) The open-field test consists of the measurement of behaviors elicited by placing a rodent in a novel arena from which escape is prevented by surrounding walls (Walsh and Cummins, 1976). This paradigm has been originally described by Hall (1934) for the study of emotionality. Hall's device consisted of a brightly-illuminated circular arena of about 1.2 rn diameter bound by a wall 0.45 m high, with linoleum floor marked out by radial lines and concentric circles. Hall placed rats in the outer ring of the arena and observed its movements for 2 min, during daily repeated trials. Sometimes, rats were tested after 24 or 48 h food deprivation. Hall observed that rats walked further when food deprived, but not all of them did eat. Rats that did not eat were called emotional. When compared to non-emotional ones, they exhibited lower number of entries in the central part of the arena and higher levels of defecation. The open-field test is now one of the most popular devices used in animal psychology. Different versions are available, differing in their shape (circular, square or rectangular), lighting (zenithal lighting by placing a bulb above the open-field or underneath lighting using a bulb placed under a transparent floor), presence of objects within the

arena such as platforms, columns, tunnels (see for example Takahashi and Kalin, 1989), etc. Procedure generally consists in forced confrontation of a rodent with the situation. The animal is placed in the center or the periphery of the apparatus and the following behavioral items are recorded, for a period ranging from 2 to 20 min (usually 5 min): horizontal locomotion (number of crossings of the lines marked on the floor), frequency of rearing or leaning (sometimes termed as vertical activity), grooming (long duration washing of the fur). In such a situation, rodents spontaneously exhibit a preference for the periphery of the apparatus when compared with activity in the central parts of the open-field. Indeed, mice and rats walk close to the walls, a behavior called thigmotaxis. Increase of time spent in the central part as well as of the ratio central/total locomotion or a decrease of the latency to enter the central part are an indication of anxiolysis. Some authors used a procedure in which subjects were allowed free access to the open-field, from a familiar cage (see for example Kopp et al., 1997). In this case, number of risk assessment postures toward the open-field may provide a good measure of the approach response toward novelty, that is, of exploration. All the other measures cited above are not really measures of exploration but rather of activity or anxiety. Differences in inbred mouse strain behavior have been rather well described using the open-field (De Fries et al., 1978; Crabbe, 1986; Crusio et al., 1989; Mathis et al., 1994). It is to be noticed that generally albino inbred strains such as the BALB/c or the A / J exhibit low activity and high avoidance of the central part when compared to non albinos such as C57BL/6 (Defries et al., 1966; Defries, 1969). Furthermore, genotype x lighting interactions have been shown, the BALB/c and the C57BL/6 strain not differing any more when tested under red light conditions. Therefore, in the case of a mutation affecting pigmentation, a modification of open-field activity under brightly-lighted conditions should be interpreted with caution. Using recombinant inbred

740

I

9

i

/

i ~ l B l m

~

.

B B

0

E

D

F

Fig. 1. Illustration of some testing situations used to study exploratory behavior in rodents. (A) Circular open-field. (B) Holeboard. (C) Y-maze used to study spontaneous exploration. (D) Elevated plus maze. (E) Light/dark choice test. (F) Free exploratory test. (Photographs from Serge Barreau.)

741 strains (Plomin et al., 1991; Mathis et al., 1995) or linkage-testing strains (Flint et al., 1995; Clement et al., 1995; 1997), different authors found some genetic markers associated with open-field activity. In some cases, behavioral consequences of the pharmacological inhibition of the function of a given protein parallels the behaviors induced by mutations of the gene coding for the same protein. For example, open-field activity is increased by specific dopamine transporter inhibitors (Garreau et al., 1997) as well as in knockout mice deficient for the dopamine transporter (Giros et al., 1996). However, this is not always the case. No difference in open-field behavior appears between mice lacking the serotonin 5-HT1B receptor and their wildtype controls, but after challenge with a 5-HT~B receptor agonist, activity is increased in controls and not in mutant mice (Saudou et al., 1994).

Holeboards (Fig. 1B) The holeboard test has been first described by Boissier and Simon (1962). It consists of a wooden board, elevated above the floor of the testing room, in which sixteen holes (3cm in diameter) have been drilled. During 3 or 5 min sessions, experimenters record the frequency of head dipping in the holes and the number of iterative head dipping in the same hole. It is to be noticed that all these variables are inter-correlated (Belzung and Le Pape, 1994) and therefore the concomitant recording of more than one of them may lead to redundancies. Differences in holeboard behavior have been found between normal and Lurcher mutant mice (Lalonde et al., 1993), between different strains of rats (Rex et al., 1996), and between haloperidol sensitive and haloperidol resistant gerbils (Upchurch and Schallert, 1983), indicating a genotype influence. Huntington's disease transgenic mice exhibit a decrease in exploratory head-dips (File et al., 1998). Recently, this test has been used to show exploration alterations in

transgenic mice expressing high levels of brain tumor necrosis factor-a (Fiore et al., 1998).

Spontaneous alternation procedures (Fig. 1C) The natural tendency that rodents exhibit, when moving from one place to another, to enter the least visited area or an area which has changed in some way, has been demonstrated by Tolman (1925) and is known as "spontaneous alternation" (see Dember and Fowler, 1958; Berlyne, 1960; Barnett, 1975 for further details). Spontaneous alternation has been often studied using non-reinforced T-mazes: rats or mice are placed in the start arm and allowed to enter one of the goal arms. The subject is then replaced in the start arm and, if a second opportunity is given to enter one of the goal arms, the animal may enter the arm that had not been chosen during the first trial. If other trials are given the animal, an alternation between right and left arm choices will appear. More recently, Y-mazes are used to study spontaneous alternation because they eliminate the necessity of handling the rodents between two consecutive trials, the goal compartment becoming the start box for the next trial (Roullet and Lasalle, 1993). The Y maze apparatus consists of three arms, with a 120 ~ angle between two adjacent arms. Each arm is ended by a start/goal compartment that can be separated from the rest of the maze by a removable door. At the beginning of the session, animals are confined in the start compartment during 1 min. The door is then opened, providing free access to the maze. The rodents can then freely move until a given number of choices (ranging from 6 to 30) have been completed. An alternative procedure consists in a forced first choice followed by a second free choice. By imposing a delay between two consecutive choices or rotating the apparatus between two choices, it is also possible to use this paradigm to study memory or spatial processes (Bertholet and Crusio, 1991). An experimenter records the choice (right or left arm)

742

made by the animal which will permit to calculate the percent of spontaneous alternation, the number of choices of the preferred side and the longest series of same side choices. Spontaneous alternation is usually observed in 60-70% of the choices. Spontaneous alternation differences have been found between several inbred mouse strains (Bertholet and Crusio, 1991) and between the Roman high and Roman low avoidance strains of rats (Willig et al., 1992), suggesting that performance in this procedure is genotype-dependent. Furthermore, spontaneous alternation deficits have been observed in several cerebellar mutant mice such as nervous mutants (Lalonde and al., 1986a), lurcher mutants (Lalonde et al., 1986b; Lalonde et al., 1988; Caston et al., 1997), staggerer mutants (Lalonde, 1987), hot foot mutants (Filali et al., 1996) and Purkinje cell degeneration mutants (Lalonde et al., 1987). Note that all these cerebellar mutants exhibit motor deficits, which may explain spontaneous alternation deficits because animals cannot control their movements. Deficits are also observed in some animal models of human neurodegenerative disorders associated with mental retardation or dementia, such as transgenic mice carrying multiple copies of the human gene for S100/3, which is a model of Down syndrome (Gerlai et al., 1994) or in models of Alzheimer's disease such as transgenic mice expressing the 751-amino acid isoform of the human beta-amyloid precursor protein (Moran et al., 1995) or mice carrying both amyloid precursor protein and presenilin 1 transgenes (Holcomb et al., 1998). However, in this procedure exploration deficits are difficult to distinguish from working memory deficits. This is emphasized by the fact that most of the behavioral genetic studies that showed differences between strains in spontaneous alternation have used models of mental retardation, dementia or of cerebellar dysfunction which exhibit amnesic deficits. In order to study exploration rather then memory, it is necessary not to impose a delay between two consecutive choices.

Exploration tests used to measure anxiety (Fig. 1D and E)

Some anxiety models are based upon the fear-induced inhibition of exploration. They involve forced confrontation with an unfamiliar environment characterized by an important contrast between two areas, the one of which is attractive and the other one aversive. In such a situation, the rodent is confronted with two opposite spontaneous motivations: on the one hand, to escape from the unknown paradigm (forced confrontation is stressful) and thus entering all parts of the apparatus to find an exit, and on the other hand avoiding the aversive part of the apparatus. Two such models have been designed for the measurement of exploration or anxiety: the elevated plus maze (Handley and Mithani, 1984; Pellow et al., 1985; Lister, 1987), based on the contrast between two arms closed by lateral walls and two perpendicular open arms, and the light/dark choice test (Crawley and Goodwin, 1980; Crawley, 1981), based on the contrast between a brightly lit (2/3 of the surface) and a dark part (1/3 of the surface) of an area (for further details on the methods, see the in Chapter by Crawley). The percent of entries in the open arms and the number of transitions from the dark to the lit arena have been described as good measures of anxiety: the higher the value of these variables, the lower the anxiety level of a given subject. Measurement of other variables permits to obtain further information. For example, in a modified version of the light/dark choice test which consists of two equal size boxes linked by a tunnel, the time spent in the lit area is a variable that is sensitive to the anxiolytic as well as to the anxiogenic effects of drugs (Belzung et al., 1987) and that does not depend upon activity. Therefore, if it is predicted that a given genotype may express an anxious phenotype, it is necessary to measure the time spent in the lit area and not only the transitions, because these last ones do not allow to measure anxiogenesis. In the elevated plus maze, animals initially exhibit a high

743 level of risk assessment from the central platform toward the open arms (Rodgers et al., 1992). Interestingly, anxiolytic compounds acting via a GABAergic mechanism decrease the percentage of entries in the open arms as well as risk assessment while anxiolytic agents acting via other pharmacological targets such as serotoninergic function do not consistently modify the percentage of open arm entries at non sedative doses while they decrease risk assessment (Rodgers, 1997). Therefore, when testing the effects of a genetic manipulation interfering with serotoninergic function, it will be necessary to study effects on risk assessments as well. In the elevated plus maze or the light/dark choice tests, different factors can modify the baseline of controls such as illumination level, isolation or daytime of testing (Misslin et al., 1989; Griebel et al., 1993b). These factors must be controlled by the experimenter. Strain distributions have been described for the elevated plus maze (Trullas and Skolnick, 1993) and the light/dark apparatus (Crawley and Davis, 1982; Mathis et al., 1994; Crawley et al., 1997). Furthermore, high level of anxiety has been reported in Fyn tyrosine kinase deficient mice (Miyakawa et al., 1994) and in mice lacking the adenosine Aza receptor (Ledent et al., 1997) using the light/dark choice test. Using the elevated plus maze, high level of anxiety has been reported in transgenic mice overexpressing the corticotropin- releasing factor (Stenzel-Poore et al., 1994), in adenosine Aza receptor knockout mice (Ledent et al., 1997), in mice lacking the serotonin 1A receptor (Parks et al., 1998; Ramboz et al., 1998) while a low level of anxiety has been found in young transgenic mice overexpressing the bovine growth hormone gene (Meliska et al., 1997), in dopamine D3 receptor deficient mice (Steiner et al., 1997), in transgenic mice with impaired glucocorticoid (type II) receptor function (Rochford et al., 1997), in Huntington's disease transgenic mice (File et al., 1998) or using antisense targeting of CRH (Skutella et al., 1996).

Free access to novelty (Fig. IF)

These situations consist in permitting an animal free access to an unknown place from their home cage or another place to which they have been familiarized for at least 24 h. Various paradigms have been designed, including free access to a runway (Blois Heulin and Belzung, 1995; Berton et al., 1998) or to an open field (Kopp et al., 1997) from the home cage in which mice have previously been isolated for 24 h. However, the sole situation that has been extensively validated is the free exploratory test. This test has first been described by Hughes (1968) for rats and adapted to mice by Misslin and Ropartz (198 lc). The paradigm used in the mouse is a rectangular box (20 x 30 • 20cm) that can be divided in two equal parts (10 • 30 x 20cm each)by removable doors. Each of these two parts is divided in three "exploratory boxes" (10 x 10 x 20 cm). Mice are introduced in one part of the apparatus 24 h before testing with the doors closed, in order to get familiarized with this side. The floor of this part of the apparatus is covered with sawdust, and food and water are available ad libitum. The other part remains empty. Twenty-four hours later, the animals are given the opportunity to choose between this familiar part and the other part by removal of the temporary partitions. During 10 min, an experimenter records the number of attempts (risk assessment posture the rodent exhibits toward the novel place, while remaining in the familiar part with at least one paw), the time spent on the novel side, the number of boxes entered (locomotion) and the number of rearings. In such a situations, most strains of mice exhibit a preference for the novel side (Misslin and Cigrang, 1986; Beuzen and Belzung, 1995), probably because the procedure implies the entries in very small (10 • 10cm) spaces and not in large areas. However, some strains such as BALB / c (Griebel et al., 1993a; Belzung et al., 1994; Belzung and Berton, 1997) show neophobic behavior characterized by a higher number of attempts and a preference for the familiar side. This neophobic behavior can be reversed

744 by benzodiazepines such as diazepam or chlordiazepoxide (Griebel et al., 1993a; Belzung and Berton, 1997). Knock out for the 72 subunit of the GABAA receptor, which display a reduction of 25% of the number of benzodiazepine binding sites, exhibit increased neophobia in this situation (Crestani et al., 1996).

has been reported among inbred strains of mice (Lassalle et al., 1991; Roullet and Lassalle, 1990). Moreover, in such a situation, Janus et al. (1995) showed that transgenic mice over-expressing a human calcium-binding protein (the S100 /3 protein) exhibit a decrease in object exploration.

Exploration of novel conspecifics Exploration of novel objects Behavioral reactions of mice toward novel objects has been studied in several experimental paradigms such as open-fields. However, exploration of novel objects depends upon the discrepancy between novelty of the object and novelty of the background. Indeed, a novel object placed in a familiar environment induces avoidance and burying behaviors (neophobic behavior) whereas the same object placed in a novel environment may induce approach responses (neophylic behavior) (Misslin, 1982; Misslin and Ropartz, 198 la). Reactions of mice toward novel objects have been extensively studied using a small environment (10 x 30 cm), divided in three exploratory units (10 x 10cm each). The floor of the apparatus is covered with sawdust and unlimited access to food and water is given the animals during a 24-h period. After this familiarization period, a novel object is introduced in this familiar environment and the behavior of the mice recorded under red light during 10 min. Strong avoidance responses such as burying of the novel object are observed (Misslin and Ropartz, 198 l a, 198 lb; Misslin, 1982). Snell Dwarf mice and staggerer mutants do not display this avoidance response (Misslin et al., 1986; Bouchon et al., 1987). In another device called spatial open-field, object exploration is used to provide an index of long-term memory of spatial representation (Wiltz and Bolton, 1971; Thinus-Blanc et al., 1992). In such studies, a set of novel objects is introduced in an open-field: the habituation of object exploration over daily sessions as well as the reaction of mice to the spatial rearrangement of the objects on the last session are tested. Variation of response

Rodents are a social species which are able to identify individuals within a given group via their capacity to recognize the olfactory properties of a subject (Rawleigh et al., 1993). This implies that a rat or a mouse is able to distinguish a familiar from a non familiar animal. When confronted to an unknown conspecific, rodents can exhibit a large pattern of responses, ranging from investigatory to agonistic behaviors, depending on various factors such as social status (dominant or not), type of breeding (grouped vs isolated subjects), place of confrontation (familiar place vs new place, territory of a given animal), experimental design (high or low lighting), gender (male vs female) etc. Some abnormalities of conspecific exploration have been found in S100/3 transgenic mice (Roder et al., 1996) using a T-maze. Moreover, female mice exhibiting corticotropin-releasing factor over-expression display active rejection of sexually experienced males, which has been interpreted as a reduction in social interactions (Heinrichs and al., 1997). However, a modification of social exploration needs some caution in interpretation. For example, some genetic modifications affect social behaviors in rodents, but cannot be interpreted in terms of modification of exploration of novel conspecifics (Lijam et al., 1997).

Methodological and interpretational cautions Methodological cautions First, it is very important to remember that exploration refers to behaviors triggered off by confrontation with novelty. So, every novelty-related

745

experiment can interact with the rodent's exploratory behavior. Therefore, bedding, cage or room changing should be avoided during the 24 h that precede the test session. It is also necessary not to allow animals to move freely outside of that breeding cage before the experiments. Animals can only be tested once in a given apparatus. Furthermore, rodents are very sensitive to the rhythm of activity of persons working in the laboratory, which generally decreases during weekends. After experiencing two relative quiet days, animals generally behave differently on Mondays than on subsequent weekdays (Lassalle and Wahlsten, 1992). Other factors can directly modify exploration and therefore it is important to control them in the experimental designs. Indeed, open-field behavior is modified by isolation, handling, illumination, ceiling height, cross-fostering, floor texture, age of testing and litter size (Nagy and Glaser, 1970; Nagy and Holm, 1970; Whitford and Zipf, 1975; Deitchman et al., 1976; Dixon and Mayeda, 1976; Misslin et al., 1976; Le Pape and Lassalle, 1984). For example, a mutation could modify fertility: such litter size-induced modification of open-field behavior may not be interpreted in terms of modified exploration! As maternal effects have been demonstrated by cross-fostering for open-field behavior (Reading, 1966; Poley and Royce, 1970), it may be important that the experimental design used allows the distinction between genetic and epigenetic factors. Therefore, one may recommend when comparing two genotypes, to use mice issued from a + / - x + / - cross, rather then animals issued respectively from + / + • + / + and - / x -/pairings, which differ not only for genotype but also for maternal effects. It should be noticed that important intra-group variability can appear in experiments investigating exploratory behavior. Therefore, it is required to use a parallel group design in which different genotypes are tested simultaneously. If it is not possible to run all animals at the same time, a small number of subjects of each group should be tested at each session. This should then be repeated until

all animals have been observed. Furthermore, as circadian activity changes occur in these species, it is necessary to randomize time of test over genotypes. Animals should be kept under a 12 / 12 h reversed light/dark cycle, in order to observe them during their high activity period, that is when lights are off.

Cautions in interpretation of results First of all, the word "exploration" can only be employed referring to behaviors measured when a subject is freely confronted to a novel environment. This excludes behaviors exhibited in the breeding cage and in situations in which rodents are forced into novel situations. Second, modifications of behavioral responses toward novel environments can be elicited by other factors than changes of exploration per se. This can include modification in sensorial processing or in motor execution. For example, a mutation that induces peripheral or central modifications of visual processing may alter behavior in a light/dark choice test. One may emphasize that several strains of mice used as genetic background in knock out experiments possess some sensorial deficiency. For example, C57BL/6 mice show a specific anosmia (Wysocki et al., 1977) while 129/Ev mice exhibit barbering behavior, which results in lack of facial whiskers and hairs (Lijam et al., 1997). Behavior in the free exploratory paradigm largely depends upon olfaction (Giebel et al., 1993a) while mice without vibrissae do not avoid open arms in the elevated plus maze (unpublished results). This may mask effects of a given mutation. Consequently, it is very important to study the effect of a given gene using several experimental paradigms based upon different sensory modalities and using at least two different genetic backgrounds. References Barnett, S.A. (1975) The Rat: a study in Behavior. Chicago: University of Chicago Press.

746

Barnett, S.A. and Cowan, P.E. (1976) Activity, exploration, curiosity and fear: an ethological study. Interdisciplin. Sci. Rev., 1: 43-62. Barnett, S.A. and Smart, J.L. (1975) The movements of wild and domestic house mice in an artificial environment. Behav. Biol., 15: 85-94. Belzung, C. and Berton, F. (1997) Further pharmacological validation of the BALB/c neophobia in the free exploratory paradigm as an animal model of anxiety. Behav. PharmacoL, 8:541-548. Belzung, C. and Le Pape, G. (1994) Comparison of different behavioral test situations used in psychopharmacology for measurement of anxiety. Physiol. Behav., 56: 623-628. Belzung, C., Misslin, R., Vogel, E., Dodd, R.H. and Chapouthier, G. (1987) Anxiogenic effects of methyl-fl-carboline-3-carboxylate in a light/dark choice situation. Pharmacol. Biochem. Behav., 28: 29-33. Belzung, C., Pineau, N., Beuzen, A. and Misslin, R. (1994) The effectiveness of PD 135158, a selective CCK-B receptor antagonist, in reducing "state" but not "trait" anxiety in BALB/c mice. Pharmacol. Biochem. Behav., 49: 433-436. Berlyne, D.E. (1950) Novelty and curiosity as determinants of exploratory behaviour. Br. J. Psychol., 41: 68-70. Berlyne, S.E. (1960) Conflict, arousal and curiosity, London, McGraw-Hill. Bertholet, J.Y. and Crusio, W. (1991) Spatial and non-spatial spontaneous alternation and hippocampal mossy fibre distribution in nine inbred mouse strains. Behav. Brain Res., 43: 197-202. Berton, F., Vogel, E. and Belzung, C. (1998) Modulation of mice anxiety in response to cat odour as a consequence of predators diet. Physiol. Behav., 65: 247-254. Beuzen, A. and Belzung, C. (1995) Link between emotional memory and anxiety states: A study by principal component analysis. PhysioL Behav., 58:111-118. Birke, L.I.A. and Archer, J. (1983) Some issues and problems in the study of animal exploration. In: J. Archer and L. Birke (Eds.), Exploration in animals and humans, Van Nostrand Reinhold, Berkshire, UK. Blois-Heulin, C. and Belzung, C. (1995) Effects of previous familiarization on novelty reactions in mice (Mus musculus). Behav. Proc., 34: 197-212. Boissier, J.R. and Simon, P. (1962) La r6action d'exploration chez la souris. ThOrapie, 17: 1225-1232. Bouchon, R., Misslin, R., Vogel, E. and Ropartz, P. (1987) Total recovery of responses to novelty after ectopic pituitary isografts in Snell Dwarf mice (dw/dw). Behav. Proc., 15: 155-165. Caston, J., Vasseur, F., Delhaye-Bouchaud, N. and Mariani, J. (1997) Delayed spontaneous alternation in intact and cerebellectomized control and lurcher mutant mice: differential role of cerebellar cortex and deep cerebellar nuclei. Behav. Neurosci., 111: 214-218. C16ment, Y., Martin B., Venault, P. and Chapouthier, G. (1995) Involvement of regions of the 4th and 7th chromosomes in the open-field activity in mice. Behav. Brain Res., 70:51-57.

Clement, Y., Proeschel, M.F., Bondoux, D., Girard, F., Launay, J.M. and Chapouthier, G. (1997) Genetic factors regulate processes related to anxiety in mice. Brain Res., 752: 127-135. Crabbe, J.C. (1986) Genetic differences in locomotor activity in mice. Pharmacol. Biochem. Behav. 25: 289-292. Crawley, J.N. (1981) Neuropharmacological specificity of a simple animal model for the behavioral action of benzodiazepines. Pharmacol. Biochem. Behav., 15: 695-699. Crawley, J.N., Belknap, J.K., Collins, A., Crabbe, J.C., Frankel, W., Henderson, N., Hitzemann, R.J., Maxson, S.C., Miner, L.L., Silva, A.J., Wehner, J.M., Winshaw-Boris, A. and Paylor, R. (1997) Behavioral phenotypes of inbred mouse strains: implications and recommendations for molecular studies. Psychopharmacology, 132: 107-124. Crawley, J.N. and Davis, L.G. (1982) Baseline exploratory activity predicts anxiolytic responsiveness to diazepam in five mouse strains. Brain Res. Bull., 8: 609-612. Crawley, J.N. and Goodwin, F.K. (1980) Preliminary report of a simple animal behaviour model for the anxiolytic effects of benzodiazepines. Pharmacol. Biochem. Behav., 13: 167-170. Crestani, F., Benke, D., Reyes, G., Fritschy, J.M., Liischer, B. and Mohler, H. (1996) Impairment of GABAA receptor function by subunit gene targeting in mice results in neophobia. Soc. Neurosci. Abstr., Washington. Crusio, W.E., Schwegler, H. and Van Abeelen, J.H. (1989) Behavioral responses to novelty and structural variation of the hippocampus in mice. I. Quantitative-genetic analysis of behavior in the open-field. Behav. Brain Res., 32: 75-80. De Fries, J.C. (1969) Pleitropic effects of albinism on open field behaviour in mice. Nature, 221: 65-66. De Fries, J.C., Gervais, M.C. and Thomas, E.A. (1978) Response to 30 generations of selection for open-field activity in laboratory mice. Behav. Gen. 8: 3-13. De Fries, J.C., Hegmann, J.P. and Weir, M.W. (1966) Open field behavior in mice: Evidence for a major gene effect mediated by the visual system. Science, 154: 1577-1579. Deitchman, R., Lavine, A. and Burkholder, J. (1976) Litter size, emotionality, learning, and social interaction in C57BL/6J mice. Psychol. Rep., 39: 27-31. Dember, W.N. and Fowler, H (1958) Spontaneous alternation behavior. Psychol. BulL, 55: 412-428. Dixon, L. and Mayeda, D.V. (1976) Effects of floor textures on open field behavior in selected lines of mice. Behav. Genet., 6: 87-92. Figler, M.H. and Einhorn, D.M. (1983) The territorial prior residence effect in convit cichlids (Cichlasoma Nigrofasciatum Giinther): temporal aspects of establishment and retention, and proximate mechanisms. Behaviour, 85: 157-183. Filali, M., Lalonde, R., Bensoula, A.N., Guastavino, J.M. and Lestienne, F. (1996) Spontaneous alternation, motor activity, and spatial learning in hot-foot mutant mice. J. Comp. Physiol. (A), 178: 101-104.

747

File, S.E. (1980) The use of social interaction as a method for detecting anxiolytic activity in chlordiazepoxide-like drugs. J. Neurosci. Meth., 2: 219-238. File, S.E., Mahal, A., Mangiarini, L. and Bates, G.P. (1998) Striking changes in anxiety in Huntington's disease transgenic mice. Brain Res., 805: 234-240. Fiore, M., Alleva, E., Probert, L., Kollias, G., Angeluci, F. and Aloe, L. (1998) Exploratory and displacement behavior in tmasgenic mice expressing high levels of brain TNF-a. Physiol. Behav., 63: 571-576. Flint, J., Corley, R., De Fries, J.C., Fulker, D.W., Gray, J.A., Miller, S. and Collins, A.C. (1995) A simple genetic basis for a complex psychological trait in laboratory mice. Science, 269: 1432-1435. Garreau, L., Emond, P., Belzung, C., Guilloteau, D., Frangin, Y., Besnard, J.C. and Chalon, S. (1997) N-(3-iodoprop-2E-enyl)-2fl-carbomethoxy-3fl-(3',4'-dichlorophenyl) nortro-pane or fl-CDIT, a tropane derivative: pharmacological characterization as a specific ligand for the dopamine transporter in rodent brain. JPET, 282: 467-474. Gerlai, R., Marks, A. and Roder, J. (1994) T-maze spontaneous alternation rate is decreased in S100 beta transgenic mice. Behav. Neurosci., 108:100-106. Giros B., Jaber, M., Jones, S.R., Wightman, R.M. and Caron, M.G. (1996) Hyperlocomotion and indifference to cocaine and amphetamine in mice lacking the dopamine transporter. Nature, 379:606-612 Griebel, G., Belzung, C., Misslin, R. and Vogel, E. (1993a) The free exploratory paradigm: an effective method for measuring neophobic behaviour in mice and testing potential neophobia reducing drugs. Behav. Pharmacol., 4: 637-644. Griebel, G., Moreau, J.L., Jenck, F., Martin, J.R. and Misslin, R. (1993b) Some critical determinants of the behaviour of rats in the elevated plus-maze. Behav. Proc., 29: 37-48. Hall, C.S. (1934) Emotional behavior in the rat. I. Defecation and urination as measures of individual differences in emotionality. J. Comp. Psychol., 18: 385-403. Handley, S.L. and Mithani, S. (1984) Effects of alpha-adrenoceptor agonists and antagonists in a maze exploration model of 'fear'-motivated behaviour. Naunyn-Schmiedeberg's Archives of Pharmacology, 327: 1-5. Heinrichs, S.C., Min, H., Tamraz, S., Carmouche, M., Boehme, S.A. and Vale, W.W. (1997) Anti-sexual and anxiogenic behavioral consequences of corticotropin-releasing factor over-expression are centrally mediated. Psychoneuroendocrinol., 22: 215-224. Holcomb, L., Gordon, M.N., McGowan, E., Yu, X., Benkovic, S., Jantzen, P., Wright, K., Saad, I., Mueller, R., Morgan, D., Sanders, S., Zehr, C., O'Campo, K., Hardy, J., Prada, C.M., Eckman, C., Younkin, S., Hsiao, K. and Duff, K. (1998) Accelerated Alzheimer-type phenotype in transgenic mice carrying both mutant amyloid precursor protein and presenilin 1 transgenes. Nat. Med., 4: 97-100.

Hughes, R.N. (1968) Behaviour of male and female rats with free choice of two environments differing in novelty. Anim. Behav., 16: 92-96. Janus, C., Janus, M. and Roder, J. (1995) Spatial exploration in transgenic mice expressing human beta-S100. Neurobiol. Learn. Mem., 64: 58-67. Katzir, G. (1982) Relationships between social structure and response to novelty in captive jackdaws, Corvus monedula 1.response to novel space. Behaviour, 81:231-239. Kopp, C., Misslin, R., Vogel, E., Rettori, M.C., Delagrange, P. and Guardiola-Lema]tre, B. (1997) Effects of day-length variations on emotional responses towards unfamiliarity in Swiss mice. Behav. Proc., 41: 151-157. Lalonde, R. (1987) Exploration and spatial learning in staggerer mutant mice. J. Neurogenet., 4: 285-291. Lalonde, R., Botez, M.I. and Boivin, D. (1986a) Spontaneous alternation and habituation in a T-maze in nervous mutant mice. Behav. Neurosci., 100: 350-352. Lalonde, R., Joyal, C.C., Guastavino, J.M. and Botez, M.I. (1993) Hole poking and motor coordination in lurcher mutant mice. Physiol. Behav., 54: 41-44. Lalonde, R., Lamarre, Y., Smith, A.M. and Botez, M.I. (1986b) Spontaneous alternation and habituation in lurcher mutant mice. Brain Res., 362:161-164. Lalonde, R., Lamarre, Y. and Smith, A.M. (1988) Does the mutant mouse lurcher have deficits in spatially oriented behaviours? Brain Res., 455: 24-30. Lalonde, R., Manseau, M. and Botez, M.I. (1987) Spontaneous alternation and habituation in Purkinje cell degeneration mutant mice. Brain Res., 411: 187-189. Lassalle, J.M.: Wahlsten, D. (1992) Behavioral paradigms: general procedures and spatial memory. In: D. Goldowitz, D. Wahlsten and R.E. Wimer (Eds.), Techniques for the Genetic Analysis of Brain and Behavior, Elsevier Science Publishers. Lassalle, J.M., Bulman-Fleming, B. and Wahlsten, D. (1991) Hybrid vigour and maternal environment in mice. II. Water escape learning, open-field activity and spatial memory. Behav. Proc., 23: 35-45. Le Pape, G. and Lassalle, J.M. (1984) A developmental genetic analysis of locomotor activity in mice: Maternal effects in the BALB/c and C57BL/6 strains and heredity in F1 hybrids. Behav. Genet., 14: 21-29. Ledent, C., Vaugeois, J.M., Schiffmann, S.N., Pedrazzini, T., E1 Yacoubi, M., Vanderhaeghen, J.J., Costentin, J., Heath, J.K., Vassart, G. and Parmentier, M. (1997) Aggressiveness, hypoalgesia and high blood pressure in mice lacking the adenosine m2a receptor. Nature, 388: 674-678. Lijam, N., Paylor, R., McDonald, M.P., Crawley, J.N., Deng, C.X., Herrup, K., Stevens, K.E., Maccaferri, G., McBain, C.J., Sussman, D.J. and Wynshaw-Boris, A. (1997) Social interaction and sensorimotor gating abnormalities in mice lacking Dvll. Cell, 90: 895-905. Lister, R.G. (1987) The use of a plus-maze to measure anxiety in the mouse. Psychopharmacology, 92: 180-185.

748

Mathis, C., Neumann, P.E., Gershenfeld, H., Paul, S.M. and Crawley, J.N. (1995) Genetic analysis of anxiety-related behaviors and response to benzodiazepine-related drugs in AXB and BXA recombinant inbred mouse strains. Behav. Genet., 25: 557-568. Mathis, C., Paul, S.M. and Crawley, J.N. (1994) Characterization of benzodiazepine-sensitive behaviors in the A/J and C57BL/6J inbred strains of mice. Behav. Genet. 24:171-180. Meliska, C.J., Burke, P.A., Bartke, A. and Jensen, R.A. (1997) Inhibitory avoidance and appetitive learning in aged normal mice: comparison with transgenic mice having elevated plasma growth hormone levels. Neurobiol. Learn. Mem., 68: 1-12. Miller, C.L., Bard, K.A., Juno, C.J. and Nadler, R.D. (1986) Behavioural responsiveness of young chimpanzees (Pan troglodytes) to a novel environment. Folia Primatol., 47: 128-142. Misslin, R. (1982) Aspects du d6terminisme des r6actions de la Souris ~ un objet nouveau. Biol. Comport., 3: 209-214. Misslin, R., Belzung, C. and Vogel, E. (1989) Behavioural validation of a light/dark choice procedure for testing anti-anxiety agents. Behav. Proc., 18: 119-132. Misslin, R., Bouchon, R. and Ropartz, P. (1976) Signification de certains param&res comportementaux chez la souris plac6e dans un open-field. Physiol. Behav., 17: 767-770. Misslin, R., Cigrang, M. and Guastavino, J.M. (1986) Responses to novelty in staggerer mutant mice. Behav. Proc., 12: 51-56.

Misslin, R. and Cigrang, M (1986) Does neophobia necessarily imply fear or anxiety? Behav. Proc., 12: 45-50. Misslin, R. and Ropartz, P. (1981a) Responses in mice to a novel object. Behaviour, 78: 169-177. Misslin, R. and Ropartz, P. (1981b) Olfactory regulation of responsiveness to novelty in mice. Behav. Neur. Biol., 33: 230-236. Misslin, R. and Ropartz, P. (1981c) Effects of lateral amygdala lesions on response to novelty in mice. Behav. Proc., 6: 329-336. Miyakawa, T., Yagi, T., Watanabe, S. and Niki, H. (1994) Increased fearfulness of Fyn tyrosine kinase deficient mice. Brain Res. Mol. Brain Res., 27: 179-182. Montgomery, K.C. (1954) The role of the exploratory drive in learning. J. Comp. Physiol. Psychol., 47: 60-64. Moran, P.M., Higgins, L.S., Cordell, B. and Moser, P.C. (1995) Age-related learning deficits in transgenic mice expressing the 751-amino acid isoform of human beta-amyloid precursor protein. Proc. Natl. Acad. Sci. USA, 92: 5341-5345. Nagy, Z.M. and Glaser, H.D. (1970) Open field behavior of C57BL/6J mice: Effect of illumination, age and number of test days. Psychon. Sci., 19: 143-145. Nagy, Z.M. and Holm, M. (1970) Open field behavior in C3H mice: Effect of early handling, field illumination, and age at testing. Psychon. Sei., 19: 273-275.

Parks, C.L., Robinson, P.S., Sibille, E., Shenk, T. and Toth, M. (1998) Increased anxiety of mice lacking the serotoninlg receptor. Proc. Natl. Acad. Sci. USA, 95: 10734-10739. Pellow, S. Chopin, P., File, S.E. and Briley, M. (1985) Validation of open:closed arm entries in an elevated plus maze as a measure of anxiety in the rat. J. Neurosci. Meth., 14: 149-167. Plomin, R., MacClearn, G.E., Gora-Maslak, G. and Neiderhiser, J.M. (1991) Use of recombinant inbred strains to detect quantitative trait loci associated with behavior. Behav. Genet., 21: 99-116. Poley, W. and Royce, J.R. (1970) Genotype, maternal stimulation and factors of mouse emotionality. J. Comp. Physiol. Psychol., 71: 246-250. Poucet, B., Chapuis, N., Durup, M. and Thinus-Blanc, C. (1986) A study of exploratory behaviour as an index of spatial knowledge in hamsters. Anon. Learn. Behav., 14: 93-100. Ramboz, S., Oosting, R., Ai't Amara, D., Kung, H.F., Blier, P., Mendelsohn, M., Mann, J.J., Brunner, D. and Hen, R. (1998) Serotonin receptor 1A knockout: An animal model of anxiety-related disorder. Proc. Natl. Acad. Sci. USA, 95: 14476-14481. Rawleigh, J.M., Kemble, E.D. and Ostrem, J. (1993) Differential effects of prior dominance or subordination experience on conspecific odor preference in mice. Physiol. Behav., 54: 35-39. Reading, A.J. (1966) Effect of maternal environment on the behavior of inbred mice. J. Comp. Physiol. Psychol., 62: 437-440. Renner, M.J. (1990) Neglected aspects of exploratory and investigatory behavior. Psychobiol., 18: 16-22. Renner, M.J. and Seltzer, C.P. (1991) Molar characteristics of exploratory and investigatory behavior in the rat (Rattus norvegieus). J. Comp. Psychol. 105: 326-339. Rex, A., Sondern, U., Voigt, J.P., Franck, S. and Fink, H. (1996) Strain differences in fear-motivated behavior of rats. Pharmacol. Biochem. Behav., 54: 107-111. Rochford, J., Beaulieu, S., Rousse, I., Glowa, J.R. and Barden, N. (1997) Behavioral reactivity to aversive stimuli in a transgenic mouse model of impaired glucocorticoid (type II) receptor function: effects of diazepam and FG-7142. Psychopharmacol., 132: 145-152. Roder, J.K., Roder, J.C. and Gerlai, R. (1996) Conspecific exploration in the T-maze: abnormalities in S100fl transgenic mice. PhysioL Behav., 60,: 31-36. Rodgers, R.J. (1997) Animal models of 'anxiety': where next? Behav. Pharmacol., 8: 477-496. Rodgers, R.J., Cole, J.C., Cobain, M.R., Daly, P., Doran, P.J., Eells, J.R. and Wallis, P. (1992) Anxiogenic-like effects of fluprazine and eltoprazine in the mouse elevated plus maze: profile comparisons with 8-OH-DPAT, CGS12066B, TFMPP and mCPP. Behav. PharmacoL, 3: 621-634. Roullet, P. and Lassalle, J.M. (1990) Genetic variation, hippocampal fibres distribution, novelty reactions and spatial representation in mice. Behav. Brain Res, 41:61-69.

749

Roullet, P. and Lassalle J.M., (1993) Spontaneous exploration, response plus position learning and hippocampal mossy fibre distribution: a correlational study. Behav. Proc., 29: 217-228. Saudou, F.,/kit Amara, D., Dierich, A., Lemeur, M., Ramboz, S., Segu, L., Buhot, M.C. and Hen, R. (1994) Enhanced aggressive behavior in mice lacking 5-HT~B receptor. Science, 265: 1875-1878. Skutella, T., Probst, J.C., Behl, C. and Holsboer, F. (1996) Antisense targeting of corticotropin-releasing hormone and corticotropin-releasing hormone receptor type I. In: R.B. Raffa and F. Porreca (Eds.), Antisense strategies for the study of receptor mechanisms, Springer, R.G. Landes Company, Austin. Sokolov, E.K. (1960) Neuronal models and the orienting reflex. In: M.A.B. Brazier (Ed.), The Central Nervous System and Behaviour, New York: Josiah Macy Jr. Foundation. Steiner, H., Fuchs, S. AND Accili, D. (1997) D3 dopamine receptor-deficient mouse: evidence for reduced anxiety. Physiol. Behav., 63: 137-141. Stenzel-Poore, M.P., Heinrichs, S.C., Rivest, S., Koob, G.F. and Vale, W.W. (1994) Overproduction of corticotropin-releasing factor in transgenic mice: a genetic model of anxiogenic behavior. J. Neurosci., 14: 2579-2584. Takahashi, L.K. and Kalin, N.H. (1989) Role of corticotropin-releasing factor in mediating the expression of defensive behavior. In: R.J. Blanchard, P.F. Brain, D.C. Blanchard and S. Parmigiani (Eds.), Ethoexperirnental approaches to the study of behavior, NATO ASI Series, Kluwer Academic Publishers, pp. 580-594. Taylor, G.T. (1974) Stimulus change and complexity in exploratory behavior. Anita. Learn. Behav., 2:115-118.

Thinus-Blanc, C., Durup, M. and Poucet, B. (1992) The spatial parameters encoded by hamsters during exploration: a further study. Behav. Proc., 26: 43-57. Tolman, E.C. (1925) Purpose and cognition: the determiners of animal learning. Psychol. Rev., 32: 285-297. Trullas, R. and Skolnick, P. (1993) Differences in fear motivated behaviors among inbred mouse strains. Psychopharmacol., 111: 323-331. Upchurch, M. and Schallert, T. (1983) A behavior analysis of the offspring of "haloperidol-sensitive" and "haloperidol-resistant" gerbils. Behav. Neural Biol., 39: 221-228. Vinogradova, O.S. (1970) Registration of information and the limbic system. In: G. Horn and R.A. Hinde (Eds.), Short term changes in Neural Activity and Behaviour, Cambridge: Cambridge University Press. Walsh, R.N. and Cummins, R.A. (1976) The open field test: A critical review. Psychol. Bull., 83: 481-504. Whitford, F.W. and Zipf, S.G. (1975) Open-field activity in mice as a function of ceiling height: A genotype-environment interaction. Behav. Genet., 5: 275-280. Willig, F., Van De Velde, D., Laurent, J., M'Harzi, M. and Delacour, J. (1992) The Roman strains of rats as a psychogenetic tool for pharmacological investigation of working memory: example with RU 41656. Psychopharmacol., 107: 415--424. Wilz, K.J. and Bolton, R.L. (1971) Exploratory behaviour in response to the spatial rearrangement of familiar stimuli. J. Comp. Physiol. Psychol., 92: 312-321. Wysocki, C.J., Whitney, C. and Tucker, D. (1977) Specific anosmia in the Laboratory Mouse. Behav. Genet., 7: 171-188.