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When exposed to an unfamiliar open space, animals experience fear and attempt to find an escape route. Anxiety emerges when animals are confronted with a challenging obstacle to this fear motivated escape. High anxiety animals do not take risks; they avoid the challenge. The present experiments investigated this risk avoidant behavior in mice. In experiment 1, BALB/c, C57BL/6J and CD-1 mice were exposed to a large platform with downward inclined steep slopes attached on two opposite sides. The platform was elevated 75 and 100cm from the ground, in a standard (SPDS) and in a raised (RPDS) configuration, respectively. In experiment 2, the platform was elevated 75cm from the ground. Mice had to climb onto a stand at the top of upward inclined slopes (SPUS). In experiment 3, BALB/c mice were exposed to SPDS with steep or shallow slopes either in early morning or in late afternoon. In all 3 test configurations, mice spent more time in the areas adjacent to the slopes than in the areas adjacent to void, however only C57BL/6J and CD-1 crossed onto the slopes in SPDS, and crossed onto the stands in SPUS whereas BALB/c remained on the platform in SPDS and explored the slopes in SPUS. Elevation of the platform from the ground reduced the crossings onto the slopes in C57BL/6J and CD-1, and no differences were observed between BALB/c and C57BL/6J. BALB/c mice demonstrated no difference in anxiety when tested early morning or late afternoon; they crossed onto shallow slopes and avoided the steep one., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Familiarity can imply a reduction of fear and anxiety, which may render learning and memory performance insensitive to NMDA receptor antagonism. Our previous study indicates that MK-801 (dizocilpine), NMDA antagonist, increased anxiety and prevented the acquisition of a spatial memory task. Here, we examined whether MK-801 will produce anxiety in mice that were familiar with the test environment. Male C57BL/6J mice were exposed, one session a day for 7days, to a 3D maze, which consisted of nine arms attached to upward inclined bridges radiating from a nonagonal platform. In this maze, high anxiety mice avoid the arms in the first sessions. One group of mice received saline (SAL) while a second group received MK-801 (MKD1), both on day one. A third group received saline in the first 3 sessions, and MK 801 in subsequent sessions (MKD4). Saline and MK-801 (0.1mg/kg) were administered intraperitoneally 30min before the test. MKD4 mice demonstrated an increase in bridge and arm visits, and reached arm/bridge entries ratio close to 1 in session 5. SAL mice also crossed frequently onto the arms, and reached a comparable ratio, but this was achieved with a lower number of arm visits. MKD1 mice demonstrated a reduced number of arm visits in each session compared to SAL and MKD4 mice. Dizocilpine produced anxiety in mice treated from day 1 of the test, but not in those treated from day 4. It also impaired habituation in animals familiar with the test environment; it produced sustained non-habituating hyperactivity., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Here we used a 3-dimensional (3D) maze, a modification of the radial maze, to assess the effects of treatment for two weeks with a single daily dose of fluoxetine (20 mg/kg, i.p.) on anxiety in male BALB/c mice. We examined whether anxiolytic effects of fluoxetine can be detected over three daily test sessions. We examined also whether repeated handling associated with chronic treatment interferes with effects of fluoxetine on anxiety responses. The 3D maze comprises nine arms, each connected to an upward inclined bridge radiating from a central platform. In this maze, BALB/c mice cross frequently into the bridges but avoid the arms. This avoidance is used as an index of anxiety. Two separate groups received once a day either saline (SALCH, n = 8) or fluoxetine (FLUCH, n = 8) for 14 days, and up to 30 min before the test during the subsequent 3 days. A third group received saline (SALAC, n = 8) 30 min before the test, once a day for 3 days. SALAC mice did not cross into the arms, and continued this avoidance over 3 sessions. SALCH mice avoided the arms in session 1 whereas FLUCH mice did cross into the arms, and like SALCH mice, increased number of crossings into and time on the arms in subsequent sessions. Fluoxetine evidently had an anxiolytic effect but only in the first session. These results indicate that handling experience decreased fear and anxiety in the mice, which may have masked the anxiolytic effect of fluoxetine in the second and third test sessions.

C57BL/6J mice were introduced to a nine arm radial maze without prior habituation and trained in the acquisition of a working memory task in 16 sessions, one session per day. In this maze mice need to climb onto an upward inclined bridge in order to reach and cross onto an arm. They received in each session an i.p. injection of MK-801 (0.1 mg/kg) 30 min before training or immediately after training. MK-801 pre-treated mice made significantly more entries onto the bridges, fewer entries onto the arms and took significantly longer time to make a first arm visit compared to saline and MK-801 post-treated mice during the first 3 session blocks (4 sessions per block). These results indicate that MK-801 induced anxiety which was extended throughout the first 3 session blocks. MK-801 pre-treated mice made also significantly more errors and required more sessions to reach the criterion compared to saline and MK-801 post-treated mice. Administration of MK-801 after training did not affect the acquisition of the task. The present results indicate that MK-801 pre-treatment impaired the acquisition of a spatial task and this can be accounted for by its effect on the baseline level of anxiety which was elevated. The introduction of mice to the acquisition of the task without prior habituation demonstrates that a drug treatment can affect learning and memory by increasing and/or prolonging anxiety. Such effect may be confounded with learning and memory performance and not detected with pre-habituation training procedures, particularly when the number of sessions is determined a-priori., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Balb/c mice were exposed to an elevated platform that is extended on two opposite sides with lowered steep slopes. They were tested for 12min per session in 6 successive days. They received i.p. administration of either saline or one dose of diazepam (DZP 0.5, 1, 3mg/kg) in sessions 1-3, and saline in sessions 4 and 5. All groups of mice received a single dose of DZP (1mg/kg) in session 6. DZP produced inverted U-shaped dose-responses on the number of entries into different areas of the apparatus, with a peak in mean response at 1mg/kg whereas its effect on the duration of entries was mostly comparable between the 3 doses. It increased the number of crossings on the surface of the platform and facilitated entries onto the slopes. DZP-treated mice crossed frequently onto and spent longer time on the slopes in sessions 1-3 whereas saline-treated mice remained on the platform in sessions 1-6. Withdrawal of DZP in sessions 4-5 increased the latency of first entry and decreased the number and duration of entries onto the slopes which was reversed with the administration of 1mg/kg of DZP in the next session. This ON-OFF the drug may be due to the half-life of DZP which is very short in mice and rats ( approximately 0.88h). It also indicates that DZP-treated mice did not benefit from previous experience of entries onto the slopes which suggests a possible "state-dependent" effect. Administration of DZP after repeated exposures to the test did not facilitate entries onto the slopes but instead increased significantly the number of crossings on the surface of the platform; this increase was much higher than that observed in mice initially treated with DZP and exposed to the test. There is no evidence of habituation in saline-treated mice: the number of crossings on the platform was comparable between the first 5 sessions of the test. These results demonstrate that repeated exposures to the same anxiogenic environment resulted in avoidance responses developing tolerance and approach responses developing sensitization. They suggest that tolerance and sensitization are two opposite sides of the habituation process to the same stimulus and may account for the maintained state of anxiety.

In the present report we describe the behavior of two albinos (BALB/c and CD-1) and one pigmented (c57/BL6) strains of mice exposed to a novel open space anxiety test in a single 12 min session. The test is based on exposure of mice to an unfamiliar elevated platform which is extended on two opposite sides with steep slopes presented downward or upward. In the first experiment, the behavior of mice was examined on the elevated platform at two different heights (75 and 100 cm) with downward slopes. In the second experiment, we examined the behavior of mice on the platform at the lowest height (75 cm) but with upward slopes which lead to a stand. In the third experiment, we examined the behavior of Balb/c mice on the platform at the lowest height (75 cm) with downward slopes, and a hub enclosure providing a protected space located in the centre of the platform. The least anxious strain of mice was expected to take risks and cross onto the slopes (experiments 1 and 3) and onto the stands (experiment 2). The results of experiment 1 show that Balb/c mice did not cross onto the slope, and CD-1 mice made more crossings into and spent more time on the slopes than c57 mice. The increase in the heights of the platform reduced the number of crossings on the platform in all three strains of mice, and decreased the time spent on the platform before first entry onto a slope in c57 and in CD-1 mice. It also decreased the number of entries and duration of entries onto the slopes in CD-1 mice. In experiment 2, Balb/c mice did cross onto the upward slopes but significantly less than c57 and CD-1 mice but they did not cross onto the stands attached to the end of the slopes. CD-1 mice made more entries onto and spent more time on the stands than c57 mice. In the third experiment, Balb/c and c57 mice spent most of their time inside a protective space (cylinder) placed in the centre of the platform demonstrating strong avoidance responses of the outer area of the platform, and only three c57 mice crossed onto the slopes for a very brief duration in one or two entries. In all three experiments, mice entered more frequently and spent more time in the outer areas than in the inner areas of the platform, particularly in the areas adjacent to slopes than in the areas adjacent to a void space. CD-1 mice appears the least anxious taking more risks by venturing onto the slopes and onto the stands while Balb/c appears the most anxious spending a large amount of time in the areas adjacent to the slopes. The different configurations of the test apparatus (experiments 1 and 2) seem to provide different incentives for the drive to explore and escape which may account for differences in anxiety responses whereas the presence of a protective space (experiment 3) appears to encourage avoidance responses., (Copyright 2009 Elsevier B.V. All rights reserved.)

This report describes the emotional responses of mice exposed to an unfamiliar elevated platform that is extended on two opposite sides by downward lowered steep slopes. Balb/c mice were exposed to the test for 12 min per session in 3 successive days. They received i.p. administration of diazepam (0, 0.5, 1 and 3 mg/kg) or amphetamine (0, 1, 2.5, 5 and 10 mg/kg) 30 min prior to test sessions. Separate groups of Balb/c mice were used for each dose of the drugs. Both drugs increased the number of crossings on the platform, indicating increased motor activity, and the effects were dose-dependent. Diazepam also significantly increased the number and duration of entries onto the slopes indicating an anxiolytic effect, whereas none of the saline or amphetamine-treated mice adventured onto the slopes. Amphetamine and diazepam produced an inverted U-shaped dose-response effect on different parameters of the test and demonstrate that the drug concentration which elicited a peak in mean number of entries is different from the drug concentration which elicited a peak in mean duration of entries. This study demonstrates the sensitivity and discriminatory power of an open space anxiety test for future pharmacological studies.

Three set of experiments were performed in an enclosed space (open-field) and in an open space (elevated platform). The surface of the open-field and the elevated platform were divided in nine equal squares. Rats were exposed (without previous habituation) in a unique session (experiment 1) or three consecutive sessions (experiment 2) either to an open-field (enclosed space) or to an elevated platform (open space) with and without an object on the centre of the field. In experiment 3, rats were exposed (without previous habituation) either to an enclosed or an open space on five consecutive sessions, one session a day. They were tested in an object recognition test in sessions 1, 3 and 5. In sessions 2 and 4, no objects were present. In experiment 1, we recorded the latency, frequency and duration of entries into different areas of the field. In experiment 3, we recorded the latency, frequency and duration of contacts with objects in addition to entries into different areas of the field. The first experiment demonstrates that rats exposed for the first time to an enclosed or an open space do not express neophobia toward novel objects in the absence of walls that surround an open-field. They crossed frequently into and spent more time in areas occupied with an object than in unoccupied areas. After two sessions of habituation to an empty open space or an empty enclosed space, the latency of first approach to a novel object is reduced while the frequency and duration of approaches are increased. The third experiment on object recognition confirmed that rats do not avoid novel objects; they made frequent visit and spent more time in the corner of the field occupied with an object than in empty corners. Recording of crossings provided detailed information about the patterns of exploratory behavior of rats but failed to reveal discrimination between novel and familiar objects which was evident in both open and enclosed space with recording of contacts with objects on the fifth exposure.

The effects of diazepam and chlordiazepoxide were assessed in a 3D maze which is a modification of an 8-arm radial maze. Each arm of the maze is attached to a bridge radiating from a central platform. Animals exposed for the first time to the maze do not venture beyond the line that separate a bridge from an arm. The prime criteria set for an anxiolytic effect is whether mice would increase the frequency of entries onto arms and increase arm/bridge entries ratio. C57 mice readily cross the line on first exposure and make more than 8 arm visits onto arms on second exposure, while other strains (CD-1 and Balb/c) hold back and rarely cross the line on first exposure and require more sessions to make more than 8 arm entries. An anxiolytic drug is expected to encourage intermediate (CD-1) and high (Balb/c) anxiety mice to adventure onto the arms of the maze and make more visits to the arms to comparable levels seen with low anxiety c57 mice. In the present report, administration of different doses of diazepam (0.625, 1.25, 2.5 and 5 mg kg(-1) i.p.) and chlordiazepoxide (5, 10 and 15 mg kg(-1) i.p.) did not reduce anxiety in animals, with the lowest dose of diazepam increasing motor activity in Balb/c and increasing anxiety in c57 mice while the highest doses of both diazepam (2.5 and 5 mg kg(-1) i.p.) and chlordiazepoxide (15 mg kg(-1) i.p.) induced mild sedation. Our results raise some concerns about the methodological foundations in the current assessment of anxiety and anxiolytic compounds both in animal and human studies.

The present report describes the emotional responses of different strains of mice to exposure to a novel open space model of anxiety using a 3D spatial navigation task. The 3D maze is modification of the radial maze with flexible arms that can be raised above or lowered below the horizontal level of a central platform. To access the arms animals need to cross a bridge linking the arms to the central platform. In this model, mice are exposed to novelty in an unfamiliar open space setting with no safe alternative. Fear from novelty is compounded with the need to explore. The drive to escape and the drive to approach are intermingled making this open space model radically different from the current models of anxiety which provide animals with the choice between safe and anxiogenic spaces. In a series of experiments, we examined the behaviour of different groups of mice from C57, C3H, CD1 and Balb/c strains. In the first experiment, different groups of C57 mice were tested in one of the three arms configurations. In the second experiment, C57 mice were compared to C3H mice. In the third experiment, C57 mice were compared to CD1 and Balb/c mice in the raised arm configuration over three successive sessions. In the fourth experiment, we examined the behaviour of C57 mice in the lowered arm configuration with an open and an enclosed central. In the final experiment, we examined the difference between C57 and C3H mice of both genders. Using several spatio-temporal parameters of the transition responses between central platform, bridges and arms, we have been able to show consistent results demonstrating significant differences between C57 and C3H mice, and between Balb/c and both C57 and CD1 mice. C3H appear more anxious than C57 mice, and Balb/c mice seem more anxious than C57 and CD1 mice. We also observed significant differences between sexes in C3H mice but not in C57 mice. C3H male mice appear more anxious than C3H female mice and than both C57 male and female mice. In the lowered arm configuration with an enclosed central platform, C57 mice took longer time to make a first entry to an arm, made more visits to bridges before first entry to an arm and required longer time between re-entries to arms, spent longer time on the central platform and shorter time on arms compared to mice in the other arm configurations. They also made frequent entries to the centre and bridges compared to mice in the lowered arm with an open central platform. These results demonstrate not only the sensitivity of the parameters of the test but also the consistencies and concordances of the results which make this 3D maze a valuable new tool in the study of the underlying neural mechanisms of anxiety responses in addition to learning and memory, and in assessing the effects of potential anxiolytic drugs. In this report we examine methodological issues related to the design of animal behavioural paradigms and question the value and the construct validity of the current models of human anxiety.

Exposure to novelty has been shown to induce anxiety responses in a variety of behavioural paradigms. The purpose of the present study was to investigate whether exposition of naïve rats to novelty would result in a comparable or a different pattern of responses in an open space versus enclosed space with or without the presence of an object in the centre of the field. Lewis and Wistar rats of both genders were used to illustrate and discuss the value and validity of these anxiety paradigms. We examined a wide range of measures, which cover several aspects of animals' responses. The results of this study revealed significant differences between the behaviour of animals in an open space and in the enclosed space. It also revealed significant differences in animal's responses to the presence and absence of an object in the open space and in the enclosed space. In the enclosed space, rats spent most of their time in the outer area with lower number of exits and avoided the object area except when there was an object, while in the open space rats displayed frequent short duration re-entries in the outer area and spent longer time in the object area in presence of an object. The time spent in the inner area (away from the outer area and the object area) was significantly longer and the number of faecal boli was significantly higher in the open space than in the enclosed space. In the present report, we will discuss the fundamental differences between enclosed space and open space models, and we will examine some methodological issues related to the current animal models of human behaviour in anxiety. In the enclosed space, animals can avoid the potential threat associated with the centre area of a box and chose the safety of walls and corners, whereas, in the open space animals have to avoid every parts of the field from which there was no safe escape. The response of animals to novelty in an open space model appears more relevant to anxiety than in an enclosed space. The present studies revealed no correlations between the measures of behaviour in enclosed space and the measures of behaviour in open space, which suggest that these two models do not involve the same construct. Our results suggest that the enclosed space model involves avoidance responses while the open space model involves anxiety responses. The open space model can be very useful in understanding the underlying neural mechanisms of anxiety responses, and in assessing the effects of potential anxiolytic drugs.