Connection to Anxiolytic Behavior and Reflex Movements
Some testing methods used for the assessment of the emotional state in rodents are based on the conflict between exploration and aversion, that is, on the capacity of situational aversiveness to reduce or block exploratory responses. These methods include the elevated plus maze test, the black–white transition test, and the emergence-from-cage test. The elevated plus maze apparatus consists of an elevated maze with intersecting arms, of which two are open and two are closed. This test is based on the assumption that rats and mice prefer to be in an enclosed environment, compared with an open space. This test provides information concerning anxiety-like behavior in these animals. The animal is placed in the center of the maze and has free access to all arms. Entries into open and closed arms and time spent in open and closed arms are scored by incidence. This test has been validated behaviorally and pharmacologically (Pellow et al. 1985; Pellow and File 1986). Anxiogenic compounds, such as pentylenetetrazole and FG 7142, further decrease the percentage of entries into and time spent in the open arms, whereas anxiolytic drugs, such as benzodiazepines, elicit opposite effects. The elevated plus maze test has been frequently used for the assessment of emotional changes produced in rodents by developmental exposure to psychoactive compounds. Recent results obtained in rats exposed prenatally to a benzodiazepine derivative may be cited as an example (Kellogg et al. 1991). Adult male rats exposed in utero to diazepam spent significantly more time in the open arms than did rats exposed in utero to vehicle. The total amount of time spent in either the open or the closed arms, however, was not affected by prenatal drug treatment. Such data could be interpreted as indicating a decrease in the emotional reactivity of animals exposed to diazepam during gestation.
KeywordsElevated Plus Maze Maze Test MeHg Exposure Developmental Exposure Situational Aversiveness
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