Behavioral profile of rats submitted to session 1-session 2 in the elevated plus-maze during diurnal/nocturnal phases and under different illumination conditions
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Abstract
The elevated plus-maze (EPM) model usually employs nocturnal species (e.g. rats and
mice) and the tests are almost exclusively performed during the diurnal phase (lights
on), leading some laboratories to perform experiments with animals under a reversed
light cycle to overcome this problem. However, it is questionable whether the artificial
reversal of the light cycle for short periods guarantees modifications in all the
physiological parameters found in normal subjects. The present study evaluated the
session 1-session 2 (S1-S2) EPM profile in rats during their normal diurnal or nocturnal
phase using different illumination conditions. Prior exposure to the EPM decreased
open arm exploration for all groups in S2, regardless of the circadian phase and illumination
condition; however, this behavior was decreased in subjects tested during the nocturnal
phase, when compared to the diurnal phase. Risk assessment (RA) behavior was decreased
under high illumination for both circadian phases in S1 and increased in the first
minute of S2, when compared to the last minute of S1. Although open arm exploration
and RA behavior were decreased under high illumination, when compared to low illumination
conditions in both circadian phases, general locomotor activity was only decreased
during the nocturnal phase. The results are discussed in terms of circadian variations
in the behavioral profile and as a possible source of variability in pre-clinical
models of anxiety.