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.
Department of Psychobiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, São Paulo, Brazil. suchecki@psicobio.epm.br
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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