Glucocorticoids are not responsible for paradoxical sleep deprivation-induced memory impairments.
OBJECTIVE
To evaluate whether paradoxical sleep deprivation-induced memory impairments are due to release of glucocorticoids, by means of corticosterone inhibition with metyrapone.


METHODS
The design was a 2 (Groups [control, paradoxical sleep-deprived]) x 2 (Treatments [vehicle, metyrapone]) study, performed in 2 experiments: Acute treatment (single injection given immediately after 96 hours of sleep deprivation) and chronic treatment (8 injections, twice per day, throughout the sleep-deprivation period). Animals were either paradoxical sleep-deprived or remained in their home cages for 96 hours before training in contextual fear conditioning and received intraperitoneal injections of a corticosterone synthesis inhibitor, metyrapone. Memory performance was tested 24 hours after training.


METHODS
Three-month old Wistar male rats.


METHODS
Freezing behavior was considered as the conditioning index, and adrenocorticotropic hormone and corticosterone plasma levels were determined from trunk blood of animals sacrificed in different time points. Animals were weighed before and after the paradoxical sleep-deprivation period.


RESULTS
Acute metyrapone treatment impaired memory in control animals and did not prevent paradoxical sleep deprivation-induced memory impairment. Likewise, in the chronic treatment, paradoxical sleep-deprived animals did not differ from control rats in their corticosterone or adrenocorticotropic hormone response to training, but still did not learn as well, and did not show any stress responses to the testing. Chronic metyrapone was, however, effective in preventing the weight loss typically observed in paradoxical sleep-deprived animals.


CONCLUSIONS
Our results suggest that glucocorticoids do not mediate memory impairments but might be responsible for the weight loss induced by paradoxical sleep deprivation.
Tiba
Paula Ayako
PA
Department of Psychobiology, Universidade Federal de São Paulo, São Paulo, Brazil.
Oliveira
Maria Gabriela de Menezes
MG
Rossi
Vanessa Contatto
VC
Tufik
Sergio
S
Suchecki
Deborah
D
D000324:Adrenocorticotropic Hormone / Q000097:blood* / Q000378:metabolism; D000818:Animals; D003213:Conditioning, Psychological; D003345:Corticosterone / Q000097:blood* / Q000378:metabolism; D004334:Drug Administration Schedule; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D005239:Fear; D006207:Half-Life; D008297:Male; D008569:Memory Disorders / Q000188:drug therapy / Q000209:etiology*; D008797:Metyrapone / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D012892:Sleep Deprivation / Q000150:complications*
D004791:Enzyme Inhibitors; D000324:Adrenocorticotropic Hormone; D006899:Mixed Function Oxygenases; D003345:Corticosterone; D008797:Metyrapone