Click to download
Difference between c57/BL6 and Balb/c mice in a novel Open Space Anxiety Test (OSAT) - effects of Chlordiazepoxide and Amphetamine The present report describes a novel apparatus for assessing anxiety in mice and examines the effects of Chlordiazepoxide (CDZ) (5, 10 and 15 mg/kg ip) and Amphetamine (AMP) (1, 2.5, 5 and 10 mg/kg ip), over 3 daily sessions (s1-3). The apparatus consists of a large platform (80 cm x 80cm) elevated 100 cm from the ground. On two opposite sides of the platform, steep inclined panels (SLP) made of rigid wire mesh are attached with ends 50cm from the ground. Separate groups of Balb/c mice were used for each dose of CDZ or AMP. One group of Balb/c mice and one group of c57 mice received saline injection. Balb/c mice were selected because of their high anxiety in our test conditions. A group of c57 mice was included for comparison as this strain of mice displays less anxiety and can be used as a reference to assess the anxiolytic properties of a pharmacological compound. An anxiolytic effect is reported when performance of anxious animals become comparable or superior to that of c57 but also when the frequency and time spent on the panels tend to equal the frequency and time spent on the areas of the platform that are adjacent to the panels. Our results confirm the difference between c57 and Balb/c mice: c57 adventured onto SLP which were avoided by Balb/c (n = 8 each, Entries: 8.57±1.88 vs. 0.44±0.44; Duration: 90.42±19.46s vs 4.14±4.14s). CDZ did not show any significant effect in the number and duration of entries onto the SLP. These results confirm our previous report on the effects of benzodiazepines in another novel OSAT (Ennaceur et al., 2008). None of the AMP-treated mice adventured even once onto the SLP. However, AMP clearly affected motor activity and the pattern of exploratory activity in a dose-dependent manner with the highest dose inducing hyperactivity on the platform (Total number of crossings, c57, s1=104.5, s2=84.7, s3=73.7, Balbc, s1=64, s2=42.3, s3=25.6, AMP1mg, s1=69.2, s2=59.1, s3= 67.6; AMP2.5mg, s1=70.2, s2=77.7, s3=89.5; AMP5mg, s1=143.6, s2=194.7, s3=224.0; AMP10mg, s1=152.7, s2=65.0). In a series of experiments in a novel OSAT, we provided evidence that benzodiazepines have no clear anxiolytic properties and may only mask symptoms through its sedating and myorelaxing effects. Both clinicians and neuroscientists would argue that the evidence is overwhelming, but clinical evidence is not convincing and is not equivalent to experimental demonstrations whereas animal studies are supported by poorly validated behavioural tasks. We suggested recently (eg. Ennaceur et al., 2008) that the plus-maze (PM), the open-field (OF) and the light-dark box (LDB) do not provide direct measures of anxiety but rather provide measures of fear which induces escape or avoidance responses. The basis of this suggestion is that these tests offer animals a choice between two alternatives and therefore an observer can only measure entries into a protected space (avoidance or escape responses) and entries into an unprotected space (approaches) separately while in anxiety the experience of conflict between approach and avoidance are compounded; what can be considered an approach to a place or an object can also be considered as avoidance of that place or that object. In addition, in these tests, it seems that anxiety is associated with animals that do not take risk. Animals that adventure in an open space of a PM, an OF, an LDB or animals that approach a novel object in a familiar environment are reported to be less anxious than those remaining in a protected space. In our test conditions, animals are forced to explore an unfamiliar open space and have no alternative choices. |
|
