Sleep deprivation and memory consolidation 263 (a) (c CA3 120 GA 100 80 60 40 20 HCC SDT (b) d DG 120 120 100 (33HJO 100 80 8 80 60 20 0 HCC 人 SDT HCC SDT Figure 2.Phosphorylated 3.5'-cyclic AMP response-element binding protein (pCREB)expression in the hippocampus upon re-exposure to the shock context 24 h following training.(a)Representative photomicrograph of pCREB immunoreactivity in the hippocampus.Optical density of pCREB immunoreactivity was measured for the granular cell layer of the dentate gyrus(DG)and the pyramidal cell layer of the CA3 and CAl areas of the hippocampus.The scale bar represents 500 um.Home cage controls(HCC,n =7),animals trained in the contextual fear conditioning paradigm without any interference (T,n=9)and animals subjected to 6 h of sleep deprivation immediately following training(SDT,n=10)were sacrificed I h after testing.(b-d)Testing for contextual fear did not affect pCREB immunoreactivity in the DG and CA3 areas.However,it increased pCREB expression significantly in the CAl area compared with HCC animals;6 h of SD immediately following training also increased pCREB expression in the CAl area but significantly less than in the trained group without any interference.Data are expressed as mean±standard error of the mean..◆p<0.05. CORT response and a lower neuronal activation within response upon re-exposure to the shock context 24 h after brain areas mediating contextual fear,as demonstrated by training. an attenuated increase in pCREB immunoreactivity in the Upon re-exposure to the shock context,the weaker hippocampus and amygdala. contextual memory was also associated with a reduced Several studies have demonstrated previously that brief SD neuronal activation,as shown by an attenuated increase in after training impairs the formation of fear memory (Graves pCREB expression in the hippocampus.It is noteworthy that et al.,2003;Hagewoud et al.,2010c;Vecsey et al.,2009). in the non-sleep-deprived rats,testing for contextual fear Importantly.SD does not affect the consolidation of amyg- induced an increase in pCREB expression solely in the CAl dala-dependent cued fear memory but only impairs selectively area of the hippocampus.This is in agreement with other the consolidation of hippocampus-dependent contextual fear studies,showing that recall of contextual memories induces memory (Graves et al.,2003;Vecsey et al.,2009).In other pCREB-regulated immediate early genes c-fos and zif268 words,SD does not have a general non-specific effect on fear specifically in the CAl area of the hippocampus(Hall et al., memory but,rather,impairs selectively the formation of fear 2001a:Strekalova et al.,2003).This increase in pCREB memory when this process involves the hippocampus. expression in the CAl region,compared with HCC animals, By affecting hippocampus function and interfering with the may not simply reflect memory retrieval,but may also be processing of contextual information,SD leads to a weaker involved in memory reconsolidation or extinction following association between the context and shock.Therefore,when retrieval (Mamiya et al.,2009). the rats are re-exposed to this context later on,they do not The reduced fear response,caused by impaired contextual show the full-blown fear response displayed by non-sleep- fear memory,was also associated with an attenuated activa- deprived animals.In the present study this reduced fear tion of the amygdala.While trained non-sleep-deprived response of rats in the SD group was reflected in an attenuated animals displayed a significant increase in pCREB expression behavioural freezing response and a lower adrenal CORT in the BLA and CeN.the trained SD animals did not.Indeed. 2010 European Sleep Research Society.J.Sleep Res.,20.259-266CORT response and a lower neuronal activation within brain areas mediating contextual fear, as demonstrated by an attenuated increase in pCREB immunoreactivity in the hippocampus and amygdala. Several studies have demonstrated previously that brief SD after training impairs the formation of fear memory (Graves et al., 2003; Hagewoud et al., 2010c; Vecsey et al., 2009). Importantly, SD does not affect the consolidation of amyg￾dala-dependent cued fear memory but only impairs selectively the consolidation of hippocampus-dependent contextual fear memory (Graves et al., 2003; Vecsey et al., 2009). In other words, SD does not have a general non-specific effect on fear memory but, rather, impairs selectively the formation of fear memory when this process involves the hippocampus. By affecting hippocampus function and interfering with the processing of contextual information, SD leads to a weaker association between the context and shock. Therefore, when the rats are re-exposed to this context later on, they do not show the full-blown fear response displayed by non-sleep￾deprived animals. In the present study this reduced fear response of rats in the SD group was reflected in an attenuated behavioural freezing response and a lower adrenal CORT response upon re-exposure to the shock context 24 h after training. Upon re-exposure to the shock context, the weaker contextual memory was also associated with a reduced neuronal activation, as shown by an attenuated increase in pCREB expression in the hippocampus. It is noteworthy that in the non-sleep-deprived rats, testing for contextual fear induced an increase in pCREB expression solely in the CA1 area of the hippocampus. This is in agreement with other studies, showing that recall of contextual memories induces pCREB-regulated immediate early genes c-fos and zif268 specifically in the CA1 area of the hippocampus (Hall et al., 2001a; Strekalova et al., 2003). This increase in pCREB expression in the CA1 region, compared with HCC animals, may not simply reflect memory retrieval, but may also be involved in memory reconsolidation or extinction following retrieval (Mamiya et al., 2009). The reduced fear response, caused by impaired contextual fear memory, was also associated with an attenuated activa￾tion of the amygdala. While trained non-sleep-deprived animals displayed a significant increase in pCREB expression in the BLA and CeN, the trained SD animals did not. Indeed, CA1 HCC T SDT 0 20 40 60 80 100 120 * * * HCC T SDT 0 20 40 60 80 100 120 DG HCC T SDT Optical density (% of HCC) Optical density (% of HCC) Optical density (% of HCC) 0 20 40 60 80 100 120 CA3 CA3 DG CA1 (a) (c) (b) (d) Figure 2. Phosphorylated 3¢,5¢-cyclic AMP response-element binding protein (pCREB) expression in the hippocampus upon re-exposure to the shock context 24 h following training. (a) Representative photomicrograph of pCREB immunoreactivity in the hippocampus. Optical density of pCREB immunoreactivity was measured for the granular cell layer of the dentate gyrus (DG) and the pyramidal cell layer of the CA3 and CA1 areas of the hippocampus. The scale bar represents 500 lm. Home cage controls (HCC, n = 7), animals trained in the contextual fear conditioning paradigm without any interference (T, n = 9) and animals subjected to 6 h of sleep deprivation immediately following training (SDT, n = 10) were sacrificed 1 h after testing. (b–d) Testing for contextual fear did not affect pCREB immunoreactivity in the DG and CA3 areas. However, it increased pCREB expression significantly in the CA1 area compared with HCC animals; 6 h of SD immediately following training also increased pCREB expression in the CA1 area but significantly less than in the trained group without any interference. Data are expressed as mean ± standard error of the mean. *P < 0.05. Sleep deprivation and memory consolidation 263 2010 European Sleep Research Society, J. Sleep Res., 20, 259–266