Elevated Plus Maze. Fig. 2. The (rat) elevated plus-maze consists of two opposite open-arms (surrounded by a small ledge), and two enclosed-arms, about 50-cm above the ground (a). Its use to measure anxiety is relatively simple: one may score the number of entries and the time spent on the open-arms (b). Besides these spatiotemporal measures, there are more subtle postures associated with anxiety such as the stretched-attend (c). They are collectively referred to as risk assessment behaviors. An "anxious" animal is one that displays risk assessment behavior very often, and rarely ventures out on the open-arms. In general, as can be seen in bottom panels, anxiolytics (e.g., midazolam, MDZ) increase open-arm exploration (e,f) and reduced stretched-attend postures (g) whereas anxiogenic drugs (e.g., pentylenetetrazole, PTZ) produce the opposite effect (e, f and g). One possible complication that an animal might not come out because it is inherently inactive, rather than anxious, can be dealt with by scoring the number of enclosed-arms entries, an index of general exploratory activity in this test (d, h).
Neurobiology of anxiety Screening for new anxiolytics
Genetical, biochemical and/or behavioral manipulations
Elevated Plus Maze. Fig. 3. The main focus of published papers using the elevated-plus maze test in 2008, according to the search performed on PubMed site (www.ncbi.nlm.nih. gov/pubmed).
variables (Hogg 1996), it would be imperative that laboratories using, or planning to use this test dedicate time and effort in order to define the optimal experimental conditions before starting their respective studies (Rodgers and Cole 1994).
Regarding possible apparatus limitations, it has been pointed out that within the rodent repertoire of defensive behaviors, the EPM is able to detect inhibitory avoidance and risk assessment. The expression of overt defensive behaviors such as ► freezing or flight, however, is not necessarily in the EPM range detection. Although both responses could be elicited by anxiogenic-like drugs, freezing could also be confounded with the enclosed reduced activity found in subjects treated with anxiolytics at sedative-like doses. Likewise, flight behavior induced by anxiogenics could also be confounded with the higher open-arms activity normally detected in animals treated with anxiolytic-like drugs. Overall, this limitation can also be applied as a note of caution when testing genetically modified organisms in the EPM. In fact, it might be extended to all organismic and procedural variables listed above.
A tendency towards automatic scoring of behavioral measures has been proposed to avoid subjective interpretation of the animals' behavior. Although these computer programs permit the analysis of spatiotemporal patterns of exploration in the EPM, some relevant (risk assessment) behaviors cannot be automatically recorded (Carobrez and Bertoglio 2005).
Furthermore, inconsistent results obtained in this test may indicate that the associated emotional state/reaction is critically dependent on stimulus parameters (Hogg 1996; Rodgers et al. 1997). Clearly, the behavioral expressions displayed in the EPM test represent a combination of exploratory and avoidance behaviors, as well as general activity, all of which are influenced by both genetic and environmental factors (Carobrez and Bertoglio 2005).
► Anxiety: Animal Models
► Anxiogenic-like Drugs
► Anxiolytic-like Drugs
Carobrez AP, Bertoglio LJ (2005) Ethological and temporal analyses of anxiety-like behavior: The elevated plus-maze model 20 years on. Neurosci Biobehav Rev 29:1193-1205 Cruz AP, Frei F, Graeff FG (1994) Ethopharmacological analysis of rat behavior on the elevated plus-maze. Pharmacol Biochem Behav 49:171-176
Handley SL, Mithani S (1984) Effects of alpha-adrenoceptor agonists and antagonists in a maze-exploration model of 'fear'-motivated behaviour. Naunyn-Schmiedeberg's Arch Pharmacol 327:1-5 Hogg S (1996) A review of the validity and variability of the elevated plus maze as an animal model of anxiety. Pharmacol Biochem Behav 54:21-30
Lister R (1990) Ethologically-based animal models of anxiety disorders.
Pharmacol Ther 46:321-340 Montgomery KC (1955) The relation between fear induced by novel stimulation and exploratory behavior. J Comp Physiological Psychology 48:254-260 Pellow S, Chopin P, File SE, 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 Rodgers RJ, Cole JC (1994) The elevated plus-maze: pharmacology, methodology and ethology. In: Cooper SJ, Hendrie CA (eds) Ethology and psychopharmacology. Wiley, Chichester, pp 9-44 Rodgers RJ, Cao BJ, Dalvi A, Holmes A (1997) Animal models of anxiety: an ethological perspective. Braz J Med Biol Res 30:289-304
Elevated Prolactin (Luteotropic Hormone)
1 Elevated X-Maze
► Elevated Plus Maze
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