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Anxiety-related
Anxiety is a body’s natural response to stress. Often it is associated with feelings of fear or uneasiness and can range from mild to severely debilitating. Measuring anxiety in animals provides researchers insight into the underlying mechanisms and brain structures responsible for establishing beneficial treatment and prevention.
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“Fear is an emotion indispensable for survival.” – Hannah Arendt
Feeling fearful can be an important warning sign for possible threats. Being out in in brightly lit spaces makes rodents easy pickings for predators. On the other hand, too much fear prevents an animal from exploring their surroundings, another important feature of survival. Therefore, the ratio of approach and avoidance of open spaces is dependent on anxiety-related states in the animal.
To assess anxiety-related approach and avoidance behavior of open spaces, animals are put on the so-called plus-maze. The maze contains two arms enclosed by opaque walls that provide protection against potential predators and two open arms that pose possible threat. Entries and time spent in the different areas give information about the anxious state of the animal. Anxious animals, for example, spend more time in the closed areas.
When given anxiety-reducing drugs (e.g. benzodiazepines), animals show enhanced exploratory behavior towards the open arms. When challenged with anxiety-enhancing treatment, the exploratory behavior decreases, respectively.
Literature
Karrenbauer, B. D., Müller, C. P., Ho, Y. J., Spanagel, R., Huston, J. P., Schwarting, R. K. W., & Pawlak, C. R. (2011). Time-dependent in-vivo effects of interleukin-2 on neurotransmitters in various cortices: relationships with depressive-related and anxiety-like behaviour. Journal of neuroimmunology, 237(1-2), 23-32.
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The open field test is a well-known and often used behavioral assay used to examine the general locomotor activity, anxiety levels and exploratory behavior in animals such as rodents. For example, rats and mice have an innate preference to avoid open, brightly lit areas but being that they are also innately curious animals, they also have an urge to explore possibly threatening stimuli. Decreased anxiety will lead to more exploratory behavior and an increase in locomotor activity whereas increased anxiety will result in less activity and a preference to remain close to the walls. When assessing open field behavior, typically, the experimenter will place the rat or mouse in the open arena for a pre-determined amount of time and then record the amount of time the animal spends in the centre as opposed to the edges as well as the number of entries the animal makes from the edges to the centre. Rearing behavior can also be assessed as a measure of anxiety, as the higher the level of anxiety the less the animal will rear to explore the surrounding area. The open field assessment can be combined with genetic (e.g SERT and CACNA1C), electrical, neurobiological and/or pharmacological manipulations - for example, Amphetamine - to help uncover underlying mechanisms, possible deficits as well as potential treatments. Ultrasonic vocalizations can also be assessed during open field behavior.
Literature
Wöhr, M., Rippberger, H., Schwarting, R. K.W, & van Gaalen, M. (2015). Critical involvement of 5-HT2C receptor function in amphetamine-induced 50-kHz ultrasonic vocalizations in rats. Psychopharmacology, 232(10), 1817-1829.
Rippberger, H., van Gaalen, M., Schwarting, R.K.W., & Wöhr, M. (2015). Environmental and pharmacological modulation of amphetamine-induced 50-kHz ultrasonic vocalizations in rats. Current neuropharmacology, 13(2), 220-232.