Inflammatory markers are associated with inhibitory avoidance memory deficit induced by sleep deprivation in rats

Behavioural Brain Research 221 (2011) 7–12

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Inflammatory markers are associated with inhibitory avoidance memory deficit induced by sleep deprivation in rats L.A. Esumi, B.D. Palma ∗ , V.L. Gomes, S. Tufik, D.C. Hipólide Department of Psychobiology, Universidade Federal de São Paulo (UNIFESP), Rua Napoleão de Barros, 925, 04024-002, Vila Clementino, São Paulo, SP, Brazil

a r t i c l e

i n f o

Article history: Received 13 December 2010 Received in revised form 4 February 2011 Accepted 21 February 2011 Keywords: Inhibitory avoidance task Lipopolysaccharide Interleukin-6 Body weight

a b s t r a c t Sleep deprivation (SD) causes detrimental effects to the body, such as memory impairment and weight loss. SD also changes the concentration of inflammatory mediators such as cytokines, which, in turn, can affect cognitive functioning. Thus, the objective of this study was to investigate the involvement of these inflammatory mediators in inhibitory avoidance memory deficit in sleep-deprived rats. Male Wistar rats were deprived of sleep by the modified multiple platform method for 96 h, while their respective controls remained in their housing cages. To assess memory after SD, all animals underwent training, followed by the inhibitory avoidance task test 24 h later. Also, the weight of each animal was recorded daily. In the first experiment, animals received an acute administration of lipopolysaccharide (LPS, 50 or 75 ␮g/kg i.p.) 3 h before the inhibitory avoidance training. In the experiment 2, the animals received acute or chronic administration of anti-IL-6 antibody (Ab, 2 ␮g/kg i.p.). The acute administration was performed 3 h before the inhibitory avoidance training, while the chronic treatment administrations were performed daily during the SD period. The 75 ␮g/kg dose of LPS, but not the 50 ␮g/kg dose, caused a significant attenuation of memory impairment in the sleep-deprived animals. Although the treatments with the anti-IL-6 Ab did not produce any significant changes in cognitive performance, the Ab attenuated weight loss in sleep-deprived animals. Taken together, these results suggest the involvement of inflammatory mediators in the modulation of memory deficit and weight loss that are observed in sleep-deprived rats. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Sleep-deprived animals show several changes, such as memory deficit [1–3], weight loss [4–6], and immunological changes [7,8], indicating a possible relationship between sleep and these functions. Several lines of evidence indicate that sleep is necessary for the consolidation of memories [9], especially with respect to hippocampus-dependent memory [10]. Memory impairment in sleep-deprived rodents has already been noted in several behavioral tasks, such as contextual fear conditioning [3], the spatial version of the Morris water maze [2], and inhibitory avoidance task [1], where all of these are dependent on the hippocampus. Cognitive impairment can be related to the excessive production of cytokines. This effect is observed in certain pathological conditions, such as infection [11], neurodegenerative diseases [12], and neuropsychiatric disorders [13]. Current data indicate that cytokines also influence cognition under some physiological situations [14–16]. Studies have shown that memory, a component of cognitive function, changes when the concentration of cer-

∗ Corresponding author. Tel.: +55 11 2149 0155; fax: +55 11 5572 5092. E-mail address: [email protected] (B.D. Palma). 0166-4328/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2011.02.025

tain cytokines changes. The administration of cytokines has been reported to alter rodent performance during memory tasks that are dependent on the hippocampus. For example, the central administration of IL-6 induces a decrease in performance on a passive avoidance task [17]. Knockout (KO) animals for certain cytokines also exhibit modified behavior in memory tasks, and in the case of an IL-6 KO, the lack of IL-6 was related to improved performance [18]. Other studies showed that cytokines modify synaptic plasticity mechanisms involved in the memory formation process [19]. For example, long-term potentiation (LTP) is inhibited by IL-6 [20,21]. This data together indicate that IL-6 is involved in memory deficit. However, a study developed by Benedict et al. [33] showed that nasal administration of IL-6 in humans promote consolidation of emotional memories. SD also causes alterations in the concentration of cytokines such as IL-1␤, TNF-␣, and IL-6 [22–24]. These cytokines not only participate in functions related to the immune system, but also in complex functions of the central nervous system such as cognition [14]. Based on the data showing the influence of cytokines on memory, the objective of this study was to evaluate the involvement of these inflammatory mediators in the inhibitory avoidance memory deficit observed in sleep-deprived rats. Thus, we studied the effects of LPS, a potent stimulator of cytokine secretion, and IL-6

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on the performance of the animals in the inhibitory avoidance task. The body weight of sleep-deprived animals was also assessed. 2. Methods 2.1. Animals Three-month-old male Wistar rats that were obtained from the Center of Development of Animal Models for Medicine and Biology (CEDEME) at the Universidade Federal de São Paulo (UNIFESP) were used in all experiments. They were habituated to laboratory conditions at least one week before the procedures. All rats were housed in plastic cages in groups of four or five in a room under controlled temperature (21 ± 2 ◦ C) and light/dark cycle (lights on from 7:00 to 19:00) and had free access to food and water throughout the experiment. All procedures were approved by the Ethics Committee in Research of the UNIFESP (0590/08). 2.2. Experimental procedures 2.2.1. Sleep deprivation Animals were sleep-deprived for 96 h (beginning at 13:00) using the modified multiple platform method [25]. The rats were placed in a water tank (123 cm × 44 cm × 44 cm) containing circular platforms with a 6.5 cm diameter. The water level remained approximately 2 cm below the surface of the platforms, and the number of platforms always exceeded the number of animals to avoid movement restriction. This method relies on the muscle atonia that accompanies paradoxical sleep. When the rats on the platforms reach this sleep stage, they lose muscle tone, touch or fall into the surrounding water, and then awaken [26]. The modified multiple platform method completely abolishes paradoxical sleep and also decreases slow wave sleep by approximately 35% [27]. The control group remained in their home cages in the same room where the SD procedure took place. To avoid unnecessary drops in the water, animals were habituated to the SD method for two days (1 h/day) before onset of the experiments. 2.2.2. Inhibitory avoidance task The inhibitory avoidance apparatus consisted of two acrylic boxes connected by a sliding door. One of the boxes was the safe compartment, with white acrylic walls, whereas the other box was the aversive compartment, with black acrylic walls. The ceiling was made of transparent acrylic, and the floor was made of parallel metallic rods (each 0.4 cm in diameter, 1.2 cm apart) connected to an electric shock generator. The inhibitory task was performed in two sessions, the training and the test. In the training session, each animal was placed in the safe compartment of the apparatus with the sliding door closed. Ten seconds later, the door was opened. Due to the natural preference of rats for a dark environment, they tended to cross to the dark compartment. As soon as the animal entered the aversive compartment, the door was closed, the latency to enter was recorded, and the animal received five foot shocks of 0.8 mA/1 s, with 15 s intervals between them. After the shocks, the animal was removed from the apparatus and returned to the home cage. The test session was carried out 24 h after the training session. Each animal was first placed in the safe compartment of the apparatus, and then the sliding door was opened 10 s later. The latency to cross to the aversive compartment was recorded. Each animal was allowed 300 s to cross to the aversive compartment. If it failed to do so, the animal was removed from the apparatus, and a latency of 300 s was recorded. 2.2.3. Drugs 2.2.3.1. LPS. LPS (Escherichia coli, serotype O111:B4, 500,000 endotoxin units/mg, L2630, Sigma, St. Louis, MO) was dissolved in bidistilled water and diluted to concentrations of 50 and 75 ␮g/mL before use. The rats were injected intraperitoneally (i.p.) with either LPS or vehicle (bidistilled water) using a volume of 1 mL/kg (LPS doses of 50 and 75 ␮g/kg) [28,29]. 2.2.3.2. Anti-IL-6 antibody. Lyophilized anti-IL-6 Ab (100 ␮g, AF506, R&D Systems, Minneapolis, MN) was reconstituted in 10 mL of phosphate buffered saline (PBS) to obtain an Ab concentration of 10 ␮g/mL. On each administration day, the stock solution was diluted again to yield a final solution with Ab concentration of 2 ␮g/mL. The rats were injected i.p. with either the anti-IL-6 Ab or vehicle (PBS) at a volume of 1 mL/kg [30,31]. 2.3. Experimental design 2.3.1. Experiment 1 The animals were divided into four groups for each LPS dose: control animals (CT) injected with vehicle or LPS (CT + Vehicle and CT + LPS) and sleep-deprived animals (SD) injected with vehicle or LPS (SD + Vehicle and SD + LPS). After habituation, the SD groups were sleep-deprived for 96 h, whereas the CT groups remained in their home cages and were exposed to the SD tank daily (30 min/day). On the last day of the 96-h period, the animals were injected with either the vehicle or LPS (50 or 75 ␮g/kg, i.p.) at 10:00 and were submitted to the inhibitory avoidance training session at 13:00. After the test, all animals were returned to their home cages and allowed to sleep for 24 h. After that 24-h period, the animals were submitted to

Fig. 1. Experimental design of experiments 1 and 2. The control (CT) and sleepdeprived (SD) groups are shown. The grey bars represent the training session, and the black bars represent the test session of the inhibitory avoidance task. The black arrows indicate the acute administrations, and the white triangles represent the chronic administrations. the inhibitory avoidance test session. Body weight was measured daily during the habituation and experimental days (Fig. 1). 2.3.2. Experiment 2 The animals were divided into four groups for the acute and chronic administration protocols: control animals (CT) injected with vehicle or anti-IL-6 Ab (CT + Vehicle and CT + Ab) and sleep-deprived animals (SD) injected with vehicle or anti-IL-6 Ab (SD + Vehicle and SD + Ab). After habituation, the SD groups were sleep-deprived for 96 h, whereas the CT groups remained in their home cages and were exposed to the SD tank daily (30 min/day). Animals on the chronic protocol were injected daily with either the vehicle or anti-IL-6 Ab (2 ␮g/kg, i.p.) during the SD period. Animals on the acute protocol received injections only on the last day. On the last day of the 96-h period, the rats were submitted to the inhibitory avoidance training session 3 h after the final administration of either the vehicle or Ab. After the test, all animals were returned to their home cages and allowed to sleep for 24 h. After that 24-h period, the animals were submitted to the inhibitory avoidance test session. Body weight was measured daily during the habituation and experimental days (Fig. 1). 2.4. Statistical analysis Body weight and latency on the inhibitory avoidance task were analyzed using ANOVA repeated measures. When a significant effect was obtained for the behavioral and body weight data, Duncan and Bonferroni’s tests were used for post hoc analysis, respectively. The data are displayed as the mean and standard error. The significance level was p ≤ 0.05.

3. Results 3.1. Inhibitory avoidance task For both LPS treatments, the ANOVA revealed significant effects of group (50 ␮g/kg: F3,36 = 3.859, p = 0.017; 75 ␮g/kg: F3,44 = 16.130, p < 0.001), time (50 ␮g/kg: F1,36 = 227.766, p < 0.001; 75 ␮g/kg: F1,44 = 383.042, p < 0.001) and the interaction between group and time (50 ␮g/kg: F3,36 = 5.383, p = 0.003; 75 ␮g/kg: F3,44 = 14.113, p < 0.001). Duncan post hoc analyses showed no significant difference between the latencies during the training session but a significant increase during the test session (50 ␮g/kg: p < 0.001 for all groups; 75 ␮g/kg: p < 0.001 for all groups). In the test session, the sleep-deprived groups displayed significantly lower latencies compared with their respective controls (50 ␮g/kg: p = 0.001 for SD + Vehicle, p = 0.001 for SD + LPS; 75 ␮g/kg: p < 0.001 for SD + Vehicle and SD + LPS). The SD + LPS group showed significantly higher latencies compared with the SD + Vehicle group (p = 0.002) only at the 75 ␮g/kg dose (Fig. 2). In the acute treatment with the anti-IL-6 Ab, the ANOVA revealed significant effects of time (F1,37 = 99.889, p < 0.001) and the interaction between group and time (F3,37 = 3.208, p = 0.03) but no effect of group. In the chronic treatment, the ANOVA revealed significant effects of group (F3,32 = 11.565, p < 0.001), time (F1,32 = 303.979, p < 0.001) and the interaction between group and time (F3,32 = 21.882, p < 0.001). For both treatments, Duncan post hoc analyses showed no significant difference between the latencies during the training session and a significant increase during the

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Fig. 2. Latency in the inhibitory avoidance task of the control (CT) and sleep-deprived (SD) rats treated with vehicle or LPS. (A) Treatment with 50 ␮g/kg of LPS (* vs. training session: p < 0.001 for CT + Vehicle, CT + LPS, SD + Vehicle and SD + LPS; # vs. respective CT group during test session: p < 0.001 for SD + Vehicle and SD + LPS). (B) Treatment with 75 ␮g/kg of LPS (* vs. training session: p < 0.001 for CT + Vehicle, CT + LPS, SD + Vehicle and SD + LPS; # vs. respective CT group during test session: p < 0.001 for SD + Vehicle and SD + LPS; $ p = 0.002 vs. SD + Vehicle group during test session) (mean ± SEM).

test session (acute: p < 0.001 for CT + Vehicle and CT + Ab, p = 0.006 for SD + Vehicle, p < 0.001 for SD + Ab; chronic: p < 0.001 for all groups). During the test session, the sleep-deprived groups displayed significant lower latencies compared with their respective controls (acute: p = 0.029 for SD + Vehicle, p = 0.046 for SD + Ab; chronic: p < 0.001 for SD + Vehicle and SD + Ab) (Fig. 3).

3.2. Body weight The ANOVA revealed significant effects of group (F3,36 = 2.920, p = 0.047), time (F2,72 = 106.257, p < 0.001) and the interaction between group and time (F6,72 = 48.393, p < 0.001) for the treatment with 50 ␮g/kg LPS. The ANOVA revealed significant effects of

Fig. 3. Latency in the inhibitory avoidance task of the control (CT) and sleep-deprived (SD) rats treated with vehicle or anti-IL-6 Ab. (A) Acute treatment (* vs. training session: p < 0.001 for CT + Vehicle and CT + Ab, p = 0.006 for SD + Vehicle, p < 0.001 for SD + Ab; # vs. respective CT group during test session: p = 0.029 for SD + Vehicle, p = 0.046 for SD + Ab). (B) Chronic treatment (* vs. training session: p < 0.001 for all groups; # vs. respective CT group during test session: p < 0.001 for all groups) (mean ± SEM).

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Fig. 4. Body weight of control (CT) and sleep-deprived (SD) rats treated with vehicle or LPS at three time points: basal, after the 96-h sleep deprivation period, and after the 24-h recovery period (RP). The arrows indicate the administrations. (A) Treatment with 50 ␮g/kg of LPS (* vs. 0 h: p = 0.002 for CT + Vehicle, p = 0.003 for CT + LPS, p < 0.001 for SD + Vehicle and SD + LPS; # vs. 96 h: p < 0.001 for CT + LPS and SD + LPS). (B) Treatment with 75 ␮g/kg of LPS (* vs. 0 h: p = 0.002 for CT + Vehicle, p < 0.001 for CT + LPS, p < 0.001 for SD + Vehicle and SD + LPS; # vs. 96 h: p < 0.001 for all groups) (mean ± SEM).

time (F2,92 = 287.075, p < 0.001) and the interaction between group and time (F6,92 = 75.813, p < 0.001)) for the treatment with 75 ␮g/kg LPS. There was no effect of group. For both treatments, Bonferroni post hoc analyses showed no significant difference in body weights at the basal time point (0 h). After 96 h, there were significant increases in the body weights of the control groups (50 ␮g/kg: p = 0.002 for CT + Vehicle, p = 0.003 for CT + LPS; 75 ␮g/kg: p = 0.002 for CT + Vehicle, p < 0.001 for CT + LPS) and significant decreases in the sleep-deprived groups (50 ␮g/kg: p < 0.001 for SD + Vehicle and SD + LPS; 75 ␮g/kg: p < 0.001 for SD + Vehicle and SD + LPS). On the day after the administrations, there were significant reductions in body weight for the animals in the 50-␮g/kg LPS treatment group (CT + LPS and SD + LPS, p < 0.001) and for all the animals in the 75␮g/kg LPS treatment group (p < 0.001 for all groups) (Fig. 4). For both Ab treatments, the ANOVA revealed significant effects of group (acute: F3,37 = 3.320, p = 0.030; chronic: F3,34 = 4.404, p = 0.010), time (acute: F2,74 = 210.929, p < 0.001; chronic: F5,170 = 17.364, p < 0.001) and the interaction between group and time (acute: F6,74 = 61.893, p < 0.001; chronic: F15,170 = 11.542, p < 0.001). Bonferroni post hoc analyses showed no significant difference in body weights at the basal time point (0 h). In the acute treatment, there were significant decreases in the body weights of the sleep-deprived groups after the 96-h time point (p < 0.001 for SD + Vehicle and SD + Ab). On the day after the administrations, both control groups and the SD + Vehicle group also displayed significant reductions in body weight (p = 0.001 for CT + Vehicle and CT + Ab, p = 0.002 for SD + Vehicle). In the chronic treatment, both sleep-deprived groups had significant reductions in body weights after the 48-h time point compared with that at the basal time point (0 h) (p < 0.001 for all time-points). There was also a

Fig. 5. Body weight of control (CT) and sleep-deprived (SD) rats treated with vehicle or 2 ␮g/kg of anti-Interleukin-6 Ab at three time points: basal, after the 96-h sleep deprivation period, and after the 24-h recovery period (RP). The arrows indicate the administrations. (A) Acute treatment (* vs. 0 h: p < 0.001 for SD + Vehicle and SD + Ab; # vs. 96 h: p = 0.001 for CT + Vehicle and CT + Ab, p = 0.002 for SD + Vehicle). (B) Chronic treatment (* vs. 0 h: p < 0.001 for all time-points; # vs. 24 h: p = 0.003 for SD + Vehicle at 48 h, p < 0.001 for SD + Vehicle at 72 h, 96 h and RP; p = 0.009 for SD + Ab at 96 h, p = 0.03 for SD + Ab at SR) (mean ± SEM).

significant weight reduction in the SD + Vehicle group at the later time points compared with the 24-h time point (p = 0.003 for 48 h; p < 0.001 for 72 h, 96 h and RP). In the SD + Ab group, however, only the body weights at the 96-h and RP time points were significantly different from those at the 24-h time point (p = 0.009 for 96 h, p = 0.03 for SR) (Fig. 5). 4. Discussion This study demonstrated that the administration of 75 ␮g/kg LPS attenuated the loss in performance of sleep-deprived rats in the inhibitory avoidance task. Although treatment with anti-IL-6 Ab did not alter animal performance in the inhibitory avoidance task, it attenuated the weight loss of the sleep-deprived groups. Memory impairment is known to be one of the classic behavioral effects of SD [1–3]. In this study, rats that were deprived of sleep for 96 h using the multiple platform method had impaired performance in the inhibitory avoidance task, a result that corroborates data from the literature [1]. The mechanisms responsible for the SD amnesic effect remain to be clarified; however, some studies have indicated a possible involvement of inflammatory mediators. SD alters several immune parameters [7,8,23], and studies have already demonstrated that inflammatory mediators altered by SD also participate in cognitive processes such as memory [14–16]. In this study, the administration of LPS at a dose of 75 ␮g/kg attenuated the decrease in the performance of the sleep-deprived animals in the inhibitory avoidance task when compared with sleep-deprived animals treated only with vehicle. We suggest three possible mechanisms to explain this effect: First, given the evidence supporting the involvement of the immune system in cognitive processes [14–16], the LPS administration would induce the secretion of inflammatory mediators [32], which, in turn, would act directly to improve animal performance. Studies with humans support this hypothesis. Recently, Benedict

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et al. [33] showed that nasal administration of an IL-6 solution improves the consolidation of emotional memories, indicating the possible involvement of this inflammatory mediator in memory consolidation processes. Although most studies have reported that IL-6 leads to a decreased performance in memory tasks, discrepancies in the literature may be related at least in part to the use of different subjects, gender, route and doses of administration of cytokines, and the paradigm used to evaluate de memory function. Second, the necessity of sleep for memory consolidation has already been well established in the literature [9]. Certain inflammatory mediators are involved in the homeostatic regulation of sleep [34], and the administration of these mediators or substances that induce their secretion, such as LPS, causes an increase in NREM sleep (i.e., slow-wave sleep) and the suppression of REM sleep (i.e., paradoxical sleep) [35]. In this study, LPS was administered to sleep-deprived animals prior to the 24-h recovery period. During the recovery period, the animals that had been deprived of sleep generally exhibited reduced NREM and increased REM sleep, a phenomenon called sleep rebound [27]. Thus, the effects of the LPS treatment and the sleep rebound together may have altered the sleep architecture in a way that favored the consolidation of memories related to the task. Third, previously, we demonstrated that sleep-deprived animals exposed to moderate stress immediately after SD had increased corticosterone levels [36]. An increase of this hormone is also observed after LPS administration, a result of its ability to activate the hypothalamic–pituitary–adrenal (HPA) axis [37]. Other studies have shown that the administration of corticosterone or dexamethasone after training can improve performance on fear conditioning and inhibitory avoidance tasks [38,39]. Thus, the probable increase in corticosterone levels induced during the inhibitory avoidance task training session and the LPS treatment together may have facilitated the acquisition and/or consolidation of the task in the sleep-deprived animals. Among the immunological changes caused by SD, the change in the concentration of the cytokine IL-6 stands out, and this cytokine has been associated with learning and memory processes. Animal studies using the SD platform technique have also reported an increase in peripheral cytokines, including IL-6 [22,24]. Braida et al. [18] reported that IL-6 KO mice perform better in the acquisition of the radial maze task and display reduced amnesic effects after scopolamine administration. In addition, IL-6 has been shown to affect LTP. Li et al. [20] showed that IL-6 can suppress LTP induction, and Balschun et al. [21] showed that the neutralization of IL-6 enhanced LTP maintenance. These data indicate a potential involvement of IL-6 in memory impairment. In this study, however, neither an acute nor chronic block of IL-6 activity altered animal performance in the inhibitory avoidance task. This lack of effect indicates that IL-6 alone is not responsible for the memory changes observed after SD. The possibility of a synergistic action between IL-6 and other cytokines, such as IL-1␤ and TNF␣, that promotes this effect, however, cannot be discounted [16]. Another classic effect of SD in animal models is a reduction in body weight [4–6]. This weight loss occurs because there is an increase in energy expenditure [4] while food consumption remains practically unchanged [6], which results in a negative energy balance during SD [5]. In this study, acute treatment with anti-IL-6 after SD prevented significant weight reduction during the recovery period, and daily chronic treatment with the same Ab during SD attenuated the weight loss, suggesting the involvement of IL-6 in promoting this effect. This hypothesis is corroborated by data from other studies: the mRNAs of both IL-6 and its receptor are expressed in the ventral and dorsomedial regions of the hypothalamus [40], which are involved in the regulation of food intake [41]; IL-6 KO mice showed attenuated weight loss after LPS administration [42]; and the administration of serum or a monoclonal anti-IL-6

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Ab before the peripheral administration of LPS effectively attenuates the reduction in food intake and weight loss, respectively, that are promoted by LPS [43,44]. Among the changes promoted by LPS, the change in eating behavior stands out, and this effect is known to be mediated mainly by pro-inflammatory cytokines [45]. These cytokines participate in the regulation of anorexia, the promotion of metabolism, an increase in catabolism and weight loss [46,47]. These data explain the significant weight reduction observed in the control and sleepdeprived animals in observed 24 h after LPS administration in this study. As mentioned earlier, SD and LPS administration raise cytokine concentrations [22,24], and sleep-deprived animals show significant weight loss [5,6], an effect also observed in this study. Unfortunately, the role of cytokines in the SD-induced weight loss remains unclear. 5. Conclusions The results of this study demonstrate the possible involvement of inflammatory mediators in the inhibitory avoidance memory deficit observed after SD. The isolated action of IL-6 is apparently not related to the SD-induced memory impairment because the administration of an anti-IL-6 Ab did not affect the performance of the animals in the behavioral task. The results, however, do indicate that this particular inflammatory mediator is involved in promoting weight loss during SD. Given the “network” performance of cytokines, the SD-induced changes likely involve the action of other inflammatory mediators. Acknowledgments We would like to acknowledge the technical assistance provided by Tomé Pimentel dos Anjos. Research support was provided by FAPESP-CEPID (08/51656-5; 98/14303-3) and AFIP. References [1] Bueno OF, Lobo LL, Oliveira MG, Gugliano EB, Pomarico AC, Tufik S. Dissociated paradoxical sleep deprivation effects on inhibitory avoidance and conditioned fear. Physiol Behav 1994;56(4):775–9. [2] Smith C, Rose G. Evidence for a paradoxical sleep window for place learning in the Morris water maze. Physiol Behav 1996;59(1):93–7. [3] Graves LA, Heller EA, Pack AI, Abel T. Sleep deprivation selectively impairs memory consolidation for contextual fear conditioning. Learn Mem 2003;10(3):168–76. [4] Bergmann BM, Everson CA, Kushida CA, Fang VS, Leitch CA, Schoeller DA, et al. Sleep deprivation in the rat. V. Energy use and mediation. Sleep 1989;12(1):31–41. [5] Hipólide DC, Suchecki D, Pinto APD, Faria EC, Tufik S. Paradoxical sleep deprivation and sleep recovery: Effects on the hypothalamic–pituitary–adrenal axis activity, energy balance and body composition of rats. J Neuroendocrinol 2006;18(4):231–8. [6] Martins PJ, D’Almeida V, Nobrega JN, Tufik S. A reassessment of the hyperphagia/weight-loss paradox during sleep deprivation. Sleep 2006;29(9):1233–8. [7] Irwin M. Effects of sleep and sleep loss on immunity and cytokines. Brain Behav Immun 2002;16(5):503–12. [8] Bryant PA, Trinder J, Curtis N. Sick and tired: does sleep have a vital role in the immune system? Nat Rev Immunol 2004;4(6):457–67. [9] Maquet P. The role of sleep in learning and memory. Science 2001;294(5544):1048–52. [10] Marshall U, Born J. The contribution of sleep to hippocampus-dependent memory consolidation. Trends Cognit Sci 2007;11(10):442–50. [11] Dantzer R, O’Connor JC, Freund GG, Johnson RW, Kelley KW. From inflammation to sickness and depression: when the immune system subjugates the brain. Nat Rev Neurosci 2008;9(1):46–56. [12] Singh VK, Guthikonda P. Circulating cytokines in Alzheimer’s disease. J Psychiatr Res 1997;31(6):657–60. [13] Raison CL, Capuron L, Miller AH. Cytokines sing the blues: inflammation and the pathogenesis of depression. Trends Immunol 2006;27(1):24–31. [14] Maier SF, Watkins LR. Cytokines for psychologists: implications of bidirectional immune-to-brain communication for understanding behavior, mood, and cognition. Psychol Rev 1998;105(1):83–107.

12

L.A. Esumi et al. / Behavioural Brain Research 221 (2011) 7–12

[15] Wilson CJ, Finch CE, Cohen HJ. Cytokines and cognition – the case for a headto-toe inflammatory paradigm. J Am Geriatr Soc 2002;50(12):2041–56. [16] McAfoose J, Baune BT. Evidence for a cytokine model of cognitive function. Neurosci Biobehav Rev 2009;33(3):355–66. [17] Ma TC, Zhu XZ. Effects of intrahippocampal infusion of interleukin-6 on passive avoidance and nitrite and prostaglandin levels in the hippocampus in rats. Arzneimittelforschung 2000;50(3):227–31. [18] Braida D, Sacerdote P, Panerai AE, Bianchi M, Aloisi AM, Iosue S, et al. Cognitive function in young and adult IL (interleukin)-6 deficient mice. Behav Brain Res 2004;153(2):423–9. [19] Cunningham AJ, Murray CA, Oneill LAJ, Lynch MA, Oconnor JJ. Interleukin-1 beta (IL-1 beta) and tumour necrosis factor (TNF) inhibit long-term potentiation in the rat dentate gyrus in vitro. Neurosci Lett 1996;203(1):17–20. [20] Li AJ, Katafuchi T, Oda S, Hori T, Oomura Y. Interleukin-6 inhibits long-term potentiation in rat hippocampal slices. Brain Res 1997;748(1–2):30–8. [21] Balschun D, Wetzel W, Del Rey A, Pitossi F, Schneider H, Zuschratter W, et al. Interleukin-6: a cytokine to forget. FASEB J 2004;18(14):1788–90. [22] Hu J, Chen Z, Gorczynski CP, Gorczynski LY, Kai Y, Lee L, et al. Sleepdeprived mice show altered cytokine production manifest by perturbations in serum IL-1ra, TNFa, and IL-6 levels. Brain Behav Immun 2003;17(6): 498–504. [23] Everson CA. Clinical assessment of blood leukocytes, serum cytokines, and serum immunoglobulins as responses to sleep deprivation in laboratory rats. Am J Physiol Regul Integr Comp Physiol 2005;289(4):R1054–63. [24] Yehuda S, Sredni B, Carasso RL, Kenigsbuch-Sredni D. REM sleep deprivation in rats results in inflammation and Interleukin-17 elevation. J Interferon Cytokine Res 2009;29(7):393–8. [25] Suchecki D, Tufik S. Social stability attenuates the stress in the modified multiple platform method for paradoxical sleep deprivation in the rat. Physiol Behav 2000;68(3):309–16. [26] Jouvet D, Jouvet M, Vimont P, Delorme F. Etude de la privation selective de la phase paradoxale de sommeil le chat. C R Seances Soc Biol Ses Fil 1964;158(4), 756-&. [27] Machado RB, Hipolide DC, Benedito-Silva AA, Tufik S. Sleep deprivation induced by the modified multiple platform technique: quantification of sleep loss and recovery. Brain Res 2004;1004(1–2):45–51. [28] Lockey AJ, Kavaliers M, Ossenkopp KP. Lipopolysaccharide reduces tactile startle response magnitude but not prepulse inhibition in rats: a dose–response examination. Pharmacol Biochem Behav 2009;93(1):47–53. [29] Skinner GW, Mitchell D, Harden LM. Avoidance of physical activity is a sensitive indicator of illness. Physiol Behav 2009;96(3):421–7. [30] Smith C, Wilson NW, Louw A, Myburgh KH. Illuminating the interrelated immune and endocrine adaptations after multiple exposures to short immobilization stress by in vivo blocking of IL-6. Am J Physiol Regul Integr Comp Physiol 2007;292(4):R1439–47.

[31] Zhao M, Chen JB, Wang WY, Wang L, Ma L, Shen H, et al. Psychological stress induces hypoferremia through the IL-6-hepcidin axis in rats. Biochem Biophys Res Commun 2008;373(1):90–3. [32] Connor TJ, Leonard BE. Depression, stress and immunological activation: the role of cytokines in depressive disorders. Life Sci 1998;62(7): 583–606. [33] Benedict C, Scheller J, Rose-John S, Born J, Marshall L. Enhancing influence of intranasal interleukin-6 on slow-wave activity and memory consolidation during sleep. FASEB J 2009;23(10):3629–36. [34] Opp MR, Cytokines sleep. Sleep Med Rev 2005;9(5):355–64. [35] Imeri L, Opp MR. How (and why) the immune system makes us sleep. Nat Rev Neurosci 2009;10(3):199–210. [36] Suchecki D, Tiba PA, Tufik S. Paradoxical sleep deprivation facilitates subsequent corticosterone response to a mild stressor in rats. Neurosci Lett 2002;320(1–2):45–8. [37] Gibb J, Hayley S, Gandhi R, Poulter MO, Anisman H. Synergistic and additive actions of a psychosocial stressor and endotoxin challenge: Circulating and brain cytokines, plasma corticosterone and behavioral changes in mice. Brain Behav Immun 2008;22(4):573–89. [38] Roozendaal B, McGaugh JL. Amygdaloid nuclei lesions differentially affect glucocorticoid-induced memory enhancement in an inhibitory avoidance task. Neurobiol Learn Mem 1996;65(1):1–8. [39] Abrari K, Rashidy-Pour A, Semnanian S, 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(3):260–5. [40] Schöbitz B, Voorhuis DA, De Kloet ER. Localization of interleukin-6 mRNA and interleukin-6 receptor mRNA in rat brain. Neurosci Lett 1992;136(2): 189–92. [41] Schwartz MW, Woods SC, Porte D, Seeley RJ, Baskin DG. Central nervous system control of food intake. Nature 2000;404(6778):661–71. [42] Bluthé RM, Michaud B, Poli V, Dantzer R. Role of IL-6 in cytokineinduced sickness behavior: a study with IL-6 deficient mice. Physiol Behav 2000;70(3–4):367–73. [43] Strassmann G, Fong M, Windsor S, Neta R. The role of interleukin-6 in lipopolysaccharide induced weight loss, hypoglycemia and fibrinogen production, in vivo. Cytokine 1993;5(4):285–90. [44] Harden LM, du Plessis I, Poole S, Laburn HP. Interleukin-6 and leptin mediate lipopolysaccharide-induced fever and sickness behavior. Physiol Behav 2006;89(2):146–55. [45] Plata-Salaman C, Cytokines feeding. Int J Obes 2001;25:S48–52. [46] Langhans W, Hrupka B. Interleukins and tumor necrosis factor as inhibitors of food intake. Neuropeptides 1999;33(5):415–24. [47] Matarese G, La Cava A. The intricate interface between immune system and metabolism. Trends Immunol 2004;25(4):193–200.