J.S1 eep Res.(2011)20,259-266 Sleep and memory doi:10.1111i.1365-2869.2010.00895.x Sleep deprivation impairs contextual fear conditioning and attenuates subsequent behavioural,endocrine and neuronal responses ROELINA HAGEWOUD,LILLIAN J.BULTSMA,R.PAULIEN BARF, JAAP M.KOOLHAAS and PETER MEERLO Department of Behavioral Physiology,Center for Behavior and Neurosciences,University of Groningen,Haren,the Netherlands Accepted in revised form 11 September 2010;received 9 July 2010 SUMMARY Sleep deprivation (SD)affects hippocampus-dependent memory formation.Several studies in rodents have shown that brief SD immediately following a mild foot shock impairs consolidation of contextual fear memory as reflected in a reduced behavioural freezing response during re-exposure to the shock context later.In the first part of this study,we examined whether this reduced freezing response is accompanied by an attenuated fear-induced activation of the hypothalamic-pituitary-adrenal (HPA)axis. Results show that 6 h of SD immediately following the initial shock results in a diminished adrenal corticosterone(CORT)response upon re-exposure to the shock context the next day.In the second part,we established whether the attenuated freezing response in SD animals is associated with reduced activation of relevant brain areas known to be involved in the retrieval and expression of fear memory.Immunohisto- chemical analysis of brain slices showed that the normal increase in phosphorylation of the transcription factor 3,5'-cyclic AMP response-element binding protein (CREB) upon re-exposure to the shock context was reduced in SD animals in the CAl region of the hippocampus and in the amygdala.In conclusion,brief SD impairs the consolidation of contextual fear memory.Upon re-exposure to the context,this is reflected in a diminished behavioural freezing response,an attenuated HPA axis response and a reduction of the normal increase of phosphorylated CREB expression in the hippocampus and amygdala. KEYWORDS cAMP response-element binding protein,glucocorticoids,hippocampus, hypothalamic-pituitary-adrenal axis,learning,sleep restriction INTRODUCTION A commonly used learning task to study the effects of SD on memory consolidation in rodents is the fear conditioning Sleep loss is a serious problem in our society(Hublin et al.,2001; paradigm.In this task animals learn to associate a specific Rajaratnam and Arendt,2001).For the people affected,this context (the test environment)or a conditioned stimulus (for may have important consequences for cognitive function and example,a tone cue)with an aversive unconditioned stimulus performance (Ellenbogen.2005:Walker,2008).Various studies (foot shock).When the animals are exposed later to the same in both humans and animals have demonstrated that sleep context or cue they will exhibit a fear-related freezing response deprivation (SD)following learning impairs memory consoli- (Blanchard and Blanchard,1969;Fanselow,1980).Both dation (Karni et al.,1994;Mograss et al.,2009;Palchykova contextual and cued fear-learning involve the amygdala. et al.,2006;Smith and Rose,1997;Stickgold et al.,2000). However,contextual fear learning also depends upon the hippocampus (Chen et al.,1996;Kim and Fanselow,1992; Correspondence:Peter Meerlo.Department of Behavioral Physiology. Center for Behavior and Neurosciences,University of Groningen,PO Phillips and LeDoux,1992).Various studies in rats and mice Box 14.9750 AA Haren,the Netherlands.Tel.:+31 (0)50 363 2334; have shown that brief SD immediately following the initial fax:+31 (0)50 363 2331:e-mail:P.Meerlo@rug.nl shock exposure impairs memory consolidation for contextual 2010 European Sleep Research Society 259doi: 10.1111/j.1365-2869.2010.00895.x Sleep deprivation impairs contextual fear conditioning and attenuates subsequent behavioural, endocrine and neuronal responses ROELINA HAGEWOUD, LILLIAN J. BULTSMA, R. PAULIEN BARF, JAAP M. KOOLHAAS and PETER MEERLO Department of Behavioral Physiology, Center for Behavior and Neurosciences, University of Groningen, Haren, the Netherlands Accepted in revised form 11 September 2010; received 9 July 2010 SUMMARY Sleep deprivation (SD) affects hippocampus-dependent memory formation. Several studies in rodents have shown that brief SD immediately following a mild foot shock impairs consolidation of contextual fear memory as reflected in a reduced behavioural freezing response during re-exposure to the shock context later. In the first part of this study, we examined whether this reduced freezing response is accompanied by an attenuated fear-induced activation of the hypothalamic–pituitary–adrenal (HPA) axis. Results show that 6 h of SD immediately following the initial shock results in a diminished adrenal corticosterone (CORT) response upon re-exposure to the shock context the next day. In the second part, we established whether the attenuated freezing response in SD animals is associated with reduced activation of relevant brain areas known to be involved in the retrieval and expression of fear memory. Immunohisto￾chemical analysis of brain slices showed that the normal increase in phosphorylation of the transcription factor 3¢,5¢-cyclic AMP response-element binding protein (CREB) upon re-exposure to the shock context was reduced in SD animals in the CA1 region of the hippocampus and in the amygdala. In conclusion, brief SD impairs the consolidation of contextual fear memory. Upon re-exposure to the context, this is reflected in a diminished behavioural freezing response, an attenuated HPA axis response and a reduction of the normal increase of phosphorylated CREB expression in the hippocampus and amygdala. keywords cAMP response-element binding protein, glucocorticoids, hippocampus, hypothalamic–pituitary–adrenal axis, learning, sleep restriction INTRODUCTION Sleep loss is a serious problem in our society (Hublin et al., 2001; Rajaratnam and Arendt, 2001). For the people affected, this may have important consequences for cognitive function and performance (Ellenbogen, 2005; Walker, 2008). Various studies in both humans and animals have demonstrated that sleep deprivation (SD) following learning impairs memory consoli￾dation (Karni et al., 1994; Mograss et al., 2009; Palchykova et al., 2006; Smith and Rose, 1997; Stickgold et al., 2000). A commonly used learning task to study the effects of SD on memory consolidation in rodents is the fear conditioning paradigm. In this task animals learn to associate a specific context (the test environment) or a conditioned stimulus (for example, a tone cue) with an aversive unconditioned stimulus (foot shock). When the animals are exposed later to the same context or cue they will exhibit a fear-related freezing response (Blanchard and Blanchard, 1969; Fanselow, 1980). Both contextual and cued fear-learning involve the amygdala. However, contextual fear learning also depends upon the hippocampus (Chen et al., 1996; Kim and Fanselow, 1992; Phillips and LeDoux, 1992). Various studies in rats and mice have shown that brief SD immediately following the initial shock exposure impairs memory consolidation for contextual Correspondence: Peter Meerlo, Department of Behavioral Physiology, Center for Behavior and Neurosciences, University of Groningen, PO Box 14, 9750 AA Haren, the Netherlands. Tel.: +31 (0) 50 363 2334; fax: +31 (0) 50 363 2331; e-mail: P.Meerlo@rug.nl J. Sleep Res. (2011) 20, 259–266 Sleep and memory 2010 European Sleep Research Society 259