Sleep deprivation and memory consolidation 265 in synaptic plasticity (Guzman-Marin et al.,2006;Ribeiro contextual fear memory and hippocampal long-term potentiation in et al.,1999,2002)and,ultimately,memory storage (Vecsey rats.Neurobiol.Learn.Mem.,2009,91:260-265. etal.,2009). Bernabeu,R.,Bevilaqua,L.,Ardenghi,P.et al.Involvement of hippocampal cAMP/cAMP-dependent protein kinase signaling It is often suggested that effects of SD on memory pathways in a late memory consolidation phase of aversively consolidation in animals may be a consequence of the SD motivated learning in rats.Proc.Natl Acad.Sci.USA,1997,94 procedure rather than to sleep loss per se.However,it is highly 7041-7046. unlikely that the findings in the present study are an indirect Blanchard.R.J.and Blanchard,D.C.Crouching as an index of fear. effect of the SD procedure,as we have shown previously that J.Comp.Physiol.Psychol.,1969.67:370-375. Bourtchuladze,R..Frenguelli,B..Blendy,J.,Cioffi,D.,Schutz,G.and the effects of SD on consolidation of contextual fear memory Silva,A.J.Deficient long-term memory in mice with a targeted are not related to the amount of stimulation the animals mutation of the cAMP-responsive element-binding protein.Cell. received to keep them awake (Hagewoud et al.,2010c).That 1994,79:59-68. study also showed that it is not likely that effects are related to Chen,C.,Kim,J.J.,Thompson,R.F.and Tonegawa,S.Hippocampal stress,as plasma CORT levels were not elevated after SD. lesions impair contextual fear conditioning in two strains of mice. Behav..Neurosci.,1996,110:1177-1180. In addition,contrary to the view that stress has adverse effects Ellenbogen,J.M.Cognitive benefits of sleep and their loss due to sleep on learning and memory processes,it is well known that deprivation.Neurology,2005,64:E25-E27. glucocorticoids contribute to contextual fear conditioning in Fanselow,M.S.Conditioned and unconditional components of post- a positive way.Indeed,administration of glucocorticoid shock freezing.Pavlov.J.Biol.Sci.,1980,15:177-182. receptor antagonists immediately before or after training,as Fanselow,M.S.Contextual fear,gestalt memories,and the hippo- campus.Behav.Brain Res.,2000.110:73-81. well as adrenalectomy,impairs the formation of contextual Fendt,M.and Fanselow,M.S.The neuroanatomical and neuro- fear memory (Pugh et al.,1997a,b),whereas administration of chemical basis of conditioned fear.Neurosci.Biobehav.Rev..1999. glucocorticoids immediately following fear conditioning facil- 23:743-760. itates the formation of contextual fear (Abrari et al.,2009). Graves,L.A.,Heller,E.A.,Pack,A.I.and Abel,T.Sleep deprivation Therefore.if the SD-induced effect was due to a small acute selectively impairs memory consolidation for contextual fear condi- tioning.Learn.Mem..2003.10:168-176. increase of glucocorticoids instead of sleep loss per se,we Guan.Z..Peng,X.and Fang.J.Sleep deprivation impairs spatial would probably have found results opposite to the present memory and decreases extracellular signal-regulated kinase phos- findings. phorylation in the hippocampus.Brain Res.,2004,1018:38-47. In conclusion,6 h of SD immediately following training Guzman-Marin,R..Ying.Z..Suntsova,N.et al.Suppression of disrupts the consolidation of contextual fear memory,which is hippocampal plasticity-related gene expression by sleep deprivation in rats.J.Physiol.,2006.575:807-819. reflected in an attenuated behavioural freezing response and a Hagewoud,R.,Havekes,R.,Novati,A.,Keijser,J.N.,Van der Zee,E. reduced HPA axis response.Furthermore,our study reports A.and Meerlo,P.Sleep deprivation impairs spatial working that this impaired fear memory is associated with a reduction memory and reduces hippocampal AMPA receptor phosphoryla- of the normal pCREB increase in the CAl area of the tion.J.Sleep Res.,2010a,19:280-288. hippocampus and the amygdala,brain regions that are Hagewoud,R..Havekes.R..Tiba,P.A.et al.Coping with sleep deprivation:shifts in regional brain activity and learning strategy. important for the formation,retrieval and expression of fear Sleep,2010b:in press. memory Hagewoud,R.,Whitcomb,S.N.,Heeringa,A.N.,Havekes,R.. Koolhaas,J.M.and Meerlo,P.A time for learning and a time for sleep:the effect of sleep deprivation on contextual fear conditioning ACKNOWLEDGEMENTS at different times of the day.Sleep,2010c.33:1315-1322. We thank Michele Azzolini,Caroline Coppens,Wanda Hall,J..Thomas,K.L.and Everitt,B.J.Cellular imaging of zif268 expression in the hippocampus and amygdala during contextual and Douwenga,Amarins Heeringa and Shamiso Whitcomb for cued fear memory retrieval:selective activation of hippocampal CAl their help with the SD.Arianna Novati for her help with the neurons during the recall of contextual memories.Neurosci.. blood sampling,Jan Bruggink for the CORT analysis and Jan 2001a.21:2186-2193. Keijser for his help with the pCREB analysis.This work was Hall.J..Thomas,K.L.and Everitt,B.J.Fear memory retrieval induces CREB phosphorylation and Fos expression within the supported by the Netherlands Organization for Scientific amygdala.Eur.J.Neurosci.,2001b,13:1453-1458. Research (NWO Vidi grant 84.04.002 to Peter Meerlo). Hublin,C..Kaprio,J.,Partinen,M.and Koskenvuo,M.Insufficient sleep-a population-based study in adults.Sleep,2001.24:392-400. Karni.A.,Tanne.D..Rubenstein,B.S..Askenasy.J.J.and Sagi.D. DISCLOSURE Dependence on REM sleep of overnight improvement of a percep- tual skill.Science,1994,265:679-682 This was not an industry-financed study.None of the authors Kida,S.,Josselyn.S.A..Pena de,O.S.et al.CREB required for the has any financial interest or conflicts of interest related to this stability of new and reactivated fear memories.Nat.Neurosci.,2002. work. 5:348-355. Kim,J.J.and Fanselow,M.S.Modality-specific retrograde amnesia of fear.Science,1992.256:675-677. REFERENCES Mamiya,N..Fukushima,H..Suzuki,A.et al.Brain region-specific gene expression activation required for reconsolidation and extinc- Abrari,K.,Rashidy-Pour,A.,Semnanian,S.and Fathollahi,Y.Post- tion of contextual fear memory.J.Neurosci..2009.29:402-413. training administration of corticosterone enhances consolidation of 2010 European Sleep Research Society.J.Sleep Res.,20.259-266in synaptic plasticity (Guzman-Marin et al., 2006; Ribeiro et al., 1999, 2002) and, ultimately, memory storage (Vecsey et al., 2009). It is often suggested that effects of SD on memory consolidation in animals may be a consequence of the SD procedure rather than to sleep loss per se. However, it is highly unlikely that the findings in the present study are an indirect effect of the SD procedure, as we have shown previously that the effects of SD on consolidation of contextual fear memory are not related to the amount of stimulation the animals received to keep them awake (Hagewoud et al., 2010c). That study also showed that it is not likely that effects are related to stress, as plasma CORT levels were not elevated after SD. In addition, contrary to the view that stress has adverse effects on learning and memory processes, it is well known that glucocorticoids contribute to contextual fear conditioning in a positive way. Indeed, administration of glucocorticoid receptor antagonists immediately before or after training, as well as adrenalectomy, impairs the formation of contextual fear memory (Pugh et al., 1997a,b), whereas administration of glucocorticoids immediately following fear conditioning facil￾itates the formation of contextual fear (Abrari et al., 2009). Therefore, if the SD-induced effect was due to a small acute increase of glucocorticoids instead of sleep loss per se, we would probably have found results opposite to the present findings. In conclusion, 6 h of SD immediately following training disrupts the consolidation of contextual fear memory, which is reflected in an attenuated behavioural freezing response and a reduced HPA axis response. Furthermore, our study reports that this impaired fear memory is associated with a reduction of the normal pCREB increase in the CA1 area of the hippocampus and the amygdala, brain regions that are important for the formation, retrieval and expression of fear memory. ACKNOWLEDGEMENTS We thank Michele Azzolini, Caroline Coppens, Wanda Douwenga, Amarins Heeringa and Shamiso Whitcomb for their help with the SD, Arianna Novati for her help with the blood sampling, Jan Bruggink for the CORT analysis and Jan Keijser for his help with the pCREB analysis. This work was supported by the Netherlands Organization for Scientific Research (NWO Vidi grant 84.04.002 to Peter Meerlo). DISCLOSURE This was not an industry-financed study. None of the authors has any financial interest or conflicts of interest related to this work. REFERENCES Abrari, K., Rashidy-Pour, A., Semnanian, S. and Fathollahi, Y. Post￾training administration of corticosterone enhances consolidation of contextual fear memory and hippocampal long-term potentiation in rats. Neurobiol. Learn. Mem., 2009, 91: 260–265. Bernabeu, R., Bevilaqua, L., Ardenghi, P. et al. Involvement of hippocampal cAMP ⁄ cAMP-dependent protein kinase signaling pathways in a late memory consolidation phase of aversively motivated learning in rats. Proc. Natl Acad. Sci. USA, 1997, 94: 7041–7046. Blanchard, R. J. and Blanchard, D. C. Crouching as an index of fear. J. Comp. Physiol. Psychol., 1969, 67: 370–375. Bourtchuladze, R., Frenguelli, B., Blendy, J., Cioffi, D., Schutz, G. and Silva, A. J. Deficient long-term memory in mice with a targeted mutation of the cAMP-responsive element-binding protein. Cell, 1994, 79: 59–68. Chen, C., Kim, J. J., Thompson, R. F. and Tonegawa, S. Hippocampal lesions impair contextual fear conditioning in two strains of mice. Behav. Neurosci., 1996, 110: 1177–1180. Ellenbogen, J. M. Cognitive benefits of sleep and their loss due to sleep deprivation. Neurology, 2005, 64: E25–E27. Fanselow, M. S. Conditioned and unconditional components of post￾shock freezing. Pavlov. J. Biol. Sci., 1980, 15: 177–182. Fanselow, M. S. Contextual fear, gestalt memories, and the hippo￾campus. Behav. Brain Res., 2000, 110: 73–81. Fendt, M. and Fanselow, M. S. The neuroanatomical and neuro￾chemical basis of conditioned fear. Neurosci. Biobehav. Rev., 1999, 23: 743–760. Graves, L. A., Heller, E. A., Pack, A. I. and Abel, T. Sleep deprivation selectively impairs memory consolidation for contextual fear condi￾tioning. Learn. Mem., 2003, 10: 168–176. Guan, Z., Peng, X. and Fang, J. Sleep deprivation impairs spatial memory and decreases extracellular signal-regulated kinase phos￾phorylation in the hippocampus. Brain Res., 2004, 1018: 38–47. Guzman-Marin, R., Ying, Z., Suntsova, N. et al. Suppression of hippocampal plasticity-related gene expression by sleep deprivation in rats. J. Physiol., 2006, 575: 807–819. Hagewoud, R., Havekes, R., Novati, A., Keijser, J. N., Van der Zee, E. A. and Meerlo, P. Sleep deprivation impairs spatial working memory and reduces hippocampal AMPA receptor phosphoryla￾tion. J. Sleep Res., 2010a, 19: 280–288. Hagewoud, R., Havekes, R., Tiba, P. A. et al. Coping with sleep deprivation: shifts in regional brain activity and learning strategy. Sleep, 2010b: in press. Hagewoud, R., Whitcomb, S. N., Heeringa, A. N., Havekes, R., Koolhaas, J. M. and Meerlo, P. A time for learning and a time for sleep: the effect of sleep deprivation on contextual fear conditioning at different times of the day. Sleep, 2010c, 33: 1315–1322. Hall, J., Thomas, K. L. and Everitt, B. J. Cellular imaging of zif268 expression in the hippocampus and amygdala during contextual and cued fear memory retrieval: selective activation of hippocampal CA1 neurons during the recall of contextual memories. J. Neurosci., 2001a, 21: 2186–2193. Hall, J., Thomas, K. L. and Everitt, B. J. Fear memory retrieval induces CREB phosphorylation and Fos expression within the amygdala. Eur. J. Neurosci., 2001b, 13: 1453–1458. Hublin, C., Kaprio, J., Partinen, M. and Koskenvuo, M. Insufficient sleep—a population-based study in adults. Sleep, 2001, 24: 392–400. Karni, A., Tanne, D., Rubenstein, B. S., Askenasy, J. J. and Sagi, D. Dependence on REM sleep of overnight improvement of a percep￾tual skill. Science, 1994, 265: 679–682. Kida, S., Josselyn, S. A., Pena de, O. S. et al. CREB required for the stability of new and reactivated fear memories. Nat. Neurosci., 2002, 5: 348–355. Kim, J. J. and Fanselow, M. S. Modality-specific retrograde amnesia of fear. Science, 1992, 256: 675–677. Mamiya, N., Fukushima, H., Suzuki, A. et al. Brain region-specific gene expression activation required for reconsolidation and extinc￾tion of contextual fear memory. J. Neurosci., 2009, 29: 402–413. Sleep deprivation and memory consolidation 265 2010 European Sleep Research Society, J. Sleep Res., 20, 259–266