Hormonal and behavioural responses of paradoxical sleep-deprived rats to the elevated plus maze.
Activation of the hypothalamic-pituitary-adrenal (HPA) axis is observed immediately after 96 h of paradoxical sleep (PS) deprivation. However, when individually or group PS-deprived rats are challenged with a mild stressor, they exhibit a facilitation of the corticosterone response, and a faster return to basal levels than control rats. Because the housing condition influences coping behaviour, we tested whether the type of PS deprivation (individually or in group) influenced anxiety-like behaviour in the elevated plus-maze and the accompanying adrenocorticotropin (ACTH) and corticosterone responses. Individually (I-DEP) or group deprived (G-DEP) rats and their appropriate control groups were either killed immediately after 96 h of sleep deprivation (time-point 0 or 'basal') or exposed to a 5-min test on the elevated plus maze and sampled 5, 20 or 60 min after test onset. Control of I-DEP rats showed reduced locomotor activity and augmented anxiety-like behaviour, replicating the effects of social isolation. Although I-DEP rats exhibited higher motor activity than cage control rats, these groups did not differ in regard to the percentage of entry and time spent in the open arms. G-DEP rats, in turn, ambulated more, entered and remained longer in the open arms, exhibiting less anxiety-like behaviour. PS-deprived rats exhibited higher ACTH and corticosterone 'basal' secretion than control rats. For all groups, peak ACTH secretion was reached at the 5-min time-point, returning to unstressed basal levels 60 min after the test, except for G-DEP rats, which showed a return at 20 min. Peak levels of corticosterone occurred at 5 min for PS-deprived groups and at 20 min for control groups. G-DEP rats showed a return to 'basal' unstressed levels at 20 min, whereas the I-DEP and control groups did so at 60 min. A negative correlation between exploration in the open arms and hormone concentrations was observed. These data indicate that housing condition influences the subsequent behaviour of PS-deprived rats in the EPM which, in turn, seems to determine the secretion profile of ACTH and corticosterone in response to the test.
Suchecki
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Department of Psychobiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, São Paulo, Brazil. suchecki@psicobio.epm.br
Tiba
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Tufik
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D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D003345:Corticosterone / Q000097:blood* / Q000378:metabolism; D008297:Male; D018782:Maze Learning / Q000502:physiology*; D009043:Motor Activity / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012892:Sleep Deprivation / Q000503:physiopathology*; D012895:Sleep, REM / Q000502:physiology*
D000324:Adrenocorticotropic Hormone; D003345:Corticosterone