Sleep-wake behavior and responses of interleukin-6-deficient mice to sleep deprivation

Interleukin (IL)-1 and tumor necrosis factor (TNF) are involved in the regulation of non-rapid eye movements sleep (NREMS). Accumulating evidence suggests IL-6 modulates sleep under some pathophysiologic conditions. We used mice lacking a functional IL-6 gene to investigate further a potential role for IL-6 in the regulation of sleep. IL-6 knockout mice (B6.129S6-Il6tm1Kopf; n=10) and C57BL/6J mice (n=10) were purchased from the Jackson Laboratory (Bar Harbor, ME). Twenty-four-hour baseline recordings were obtained from mice in the absence of any experimental manipulation. Mice were then subjected to 6-h sleep deprivation beginning at light onset. Recordings were obtained during the deprivation period and for 18 h thereafter. During baseline conditions there were no differences between mouse strains with respect to the duration, timing or intensity of NREMS. However, across the 24-h recording period IL-6 knockout mice spent approximately 30% more time in rapid eye movements sleep (REMS) than did C57BL/6J mice. Relative to C57BL/6J mice, core body temperatures of IL-6 knockout mice were higher during the light period of the light:dark cycle. Both strains responded to sleep deprivation by spending more time in NREMS and REMS. Although the total increase in the amount of NREMS after sleep deprivation was the same in both strains, IL-6 knockout mice took 6h longer to accumulate this additional sleep. Under the conditions of this study, IL-6 does not appear necessary for the full manifestation of NREMS, although this cytokine may influence the dynamics of responses to sleep deprivation. That mice lacking IL-6 spend more time in REMS suggests that interactions between IL-6 and REMS regulatory mechanisms may differ from those of IL-1 and/or TNF.     

Hypothalamic self-stimulation in three inbred strains of mice

Male mice from 3 inbred strains (DBA/2 Orl, BALB/c Orl and C57 BL/6 Orl) were implanted with a bipolar electrode in the hypothalamus and tested for self-stimulation. The 3 strains differed in performances: the BALB/c mice showed higher scores than the DBA/2 mice which themselves showed higher rates than the C57 BL/6 mice. These strains also differed in frequency, threshold and the nature of seizures suspending their self-stimulation behavior.Moreover, for each strain, a comparison between dorsal and ventral hypothalamus implantation was made. In the 3 strains dorsal implantation gave higher self-stimulation scores than ventral. On the other hand the seizures occured more frequently with ventral implantations.     

Effect of environmental temperature on sleep, locomotor activity, core body temperature and immune responses of C57BL/6J mice

Ambient temperature exerts a prominent influence on sleep. In rats and humans, low ambient temperatures generally impair sleep, whereas higher temperatures tend to promote sleep. The purpose of the current study was to evaluate sleep patterns and core body temperatures of C57BL/6J mice at ambient temperatures of 22, 26 and 30 degrees C under baseline conditions, after sleep deprivation (SD), and after infection with influenza virus. C57BL/6J mice were surgically implanted with electrodes for recording electroencephalogram (EEG) and electromyogram (EMG) and with intraperitoneal transmitters for recording core body temperature (T(c)) and locomotor activity. The data indicate that higher ambient temperatures (26 and 30 degrees C) promote spontaneous slow wave sleep (SWS) in association with reduced delta wave amplitude during SWS in C57BL/6J mice. Furthermore, higher ambient temperatures also promote recuperative sleep after SD. Thus, in mice, higher ambient temperatures reduced sleep depth under normal conditions, but augmented the recuperative response to sleep loss. Mice infected with influenza virus while maintained at 22 or 26 degrees C developed more SWS, less rapid eye movement sleep, lower locomotor activity and greater hypothermia than did mice maintained at 30 degrees C during infection. In addition, despite equivalent viral titers, mice infected with influenza virus at 30 degrees C showed less leucopenia and lower cytokine induction as compared with 22 and 26 degrees C, respectively, suggesting that less inflammation develops at the higher ambient temperature.     

睡眠剥夺对小鼠脑内细胞型朊蛋白表达水平的影响及可能的意义

目的 探讨小鼠正常昼夜节律下以及睡眠剥夺后大脑海马组织细胞型朊蛋白(PrP^C)和β-淀粉样前体蛋白(Aβ)表达水平的变化及PrP^C在睡眠剥夺诱导的认知损害中发挥的作用。方法 成年C57BL/6小鼠置于光照和黑暗交替环境中饲养2周后分别在开灯后4、8、12、16、20、24 h等6个时间点处死小鼠,每个时间点各8只,分别取海马、皮层2个部位的组织样本,采用酶联免疫吸附法检测PrP^C和Aβ的表达水平。成年小鼠按体重大小排序,完全随机分成3组,分别为正常对照组、环境对照组、睡眠剥夺组,采用改良水平台法对小鼠进行72h快速眼动睡眠剥夺,断头处死小鼠获取海马,分别采用Western Blot法和酶联免疫吸附法检测PrP^C和Aβ的表达水平变化。Halberg余弦分析PrP^C和Aβ在海马与皮层的昼夜节律变化特征。结果 单余弦分析显示PrP^C在皮层具有昼夜节律性(F=11.22,P<0.05)。Aβ在海马具有昼夜节律性(F=26.72,P<0.05); 睡眠剥夺后睡眠剥夺组海马PrP^C的表达水平(0.22±0.05)较正常对照组(0.64±0.16)和环境对照组(0.58±0.09)明显下调(F=4.366,P<0.05),睡眠剥夺组Aβ的表达水平(13.03±0.71)较正常对照组(8.22±0.8)和环境对照组(8.6±0.57)明显上调(F=14.511,P<0.05)。结论 正常小鼠大脑PrP^C和Aβ具有昼夜节律特征,快速眼动睡眠剥夺后PrP^C的表达水平下调,而Aβ表达水平上调,且这可能是睡眠剥夺后认知功能障碍的潜在机制之一。     

Effects of sleep deprivation on sleep and sleep EEG in three mouse strains: empirical data and simulations

Gene targeted mice can be used as models to investigate the mechanisms underlying sleep regulation. Three commonly used background strains for gene targeting (129/Ola, 129/SvJ and C57BL/6J) were subjected to 4-h and 6-h sleep deprivation (SD), and their sleep and sleep EEG were continuously recorded. The two-process model of sleep regulation has predicted the time course of slow-wave activity (SWA) in nonREM sleep after several sleep-wake manipulations in humans and the rat [3] [9]. We tested the capacity of the model to predict SWA in nonREM sleep on the basis of the temporal organization of sleep in mice. The strains differed in the amount and distribution of sleep and the time course of SWA. After spontaneous waking episodes of 10-30 min as well as after SD, SWA was invariably increased. Simulations of the time course of SWA were successful for 129/SvJ and C57BL/6J, but were not satisfactory for 129/Ola. Since the time constants are assumed to reflect the dynamics of the physiological processes involved in sleep regulation, the results provide a basis for the use of gene targeted mice to investigate the underlying mechanisms.     

Neural mechanisms distinguishing the neocortical EEG of C57BL/6 mice from that of DBA/2 mice

C57BL/6 inbred mice lack the 1-5 sec bursts of 6-7 cps spindles characteristic of the neocortical EEG of DBA/2 mice during waking. C57BL/6 mice (1) may be unable to generate any synchronized cortical EEG activity, (2) may lack the thalamocortical circuitry required to generate these brief spindle episodes (BSEs), (3) may lack mechanisms that can activate this circuitry or (4) may possess a potent mechanism to suppress BSE initiation and generation. Possibilities 1 and 2 have been eliminated because C57BL/6 mice generate pentobarbital, rostropontine-induced and sleep spindles, and because certain C57BL/6 sleep spindles resembled the BSEs seen in DBA/2 mice. Possibilities 3 and 4 were examined in the experiments reported here. In DBA/2 mice, pentylenetetrazol activates BSEs at subconvulsant doses. In contrast, neither 20 nor 50 mg/kg, IP, pentylenetetrazol activated BSEs in C57BL/6 mice, although the higher dose provoked 4-5 cps slow waves and myoclonic jerks. In DBA/2 mice, the beta-noradrenergic antagonist propranolol has been reported to powerfully release BSEs. In C57BL/6 mice, 10 and 15 mg/kg propanolol weakly released BSEs; fewer than 3 per hour occurred. Hence neither possibilities 3 and 4 are sufficient in themselves to explain the lack of BSEs during waking in C57BL/6 mice. However, simultaneous administration of 10 mg/kg propranolol and 20 mg/kg pentylenetetrazol provoked numerous BSEs in C57BL/6 mice. This suggests that perhaps C57BL/6 mice, as compared to DBA/2 mice, possess both a more powerful noradrenergic mechanism to suppress spindles and a more weakly functioning mechanism to activate BSEs. Hence possibilities 3 and 4 may both be correct.(ABSTRACT TRUNCATED AT 250 WORDS)     

Macrophage participation in influenza-induced sleep enhancement in C57BL/6J mice

Mice develop changes in sleep during the nonspecific immune response that occurs during the initial few days after inoculation with influenza virus. T lymphocytes, neutrophils, macrophages, and natural killer (NK) cells all participate in the early host response to influenza infection. All of these cell types are potential sources of endogenous substances that modulate sleep, but the contributory role of each cell type to the alteration of somnolence during infection has not been determined. To investigate which cell types contribute to the sleep enhancement that develops during influenza infection in mice, the sleep patterns of C57BL/6J mice with perturbations of particular facets of host immune response capabilities were assessed before and after influenza infection. Targeted mutation of the gene Ccl3 (macrophage inflammatory protein 1 alpha) prevented development of the dark phase sleep enhancement that is characteristic of C57BL/6J mice after influenza infection. Other experimental treatments that impair macrophage or monocyte function also produced significant (administration of pentoxifylline or CNI-1493) or marginally significant (deletion of the interferon-gamma gene or intranasal administration of carrageenan) changes in influenza-induced sleep enhancement in C57BL/6J mice. In contrast, functional impairments of NK cells, neutrophils, and T lymphocytes did not significantly influence sleep responses. These data therefore support a contributory role for macrophages, but not for NK cells, neutrophils, and T lymphocytes, in eliciting the sleep response typical of influenza-infected C57BL/6J mice.     

Wheel running sleep in two strains of mice: plasticity and rigidity in the expression of circadian rhythmicity.

The effects of 12--12 h, 6--6 h, 3--3 h and 1--1 h light--dark (L-D) cycles and of constant light (L--L) on wheel-running activity and electrograhically defined sleep were studied in two strains of mice, C57BL/6 and SEC/1Re. Wheel-running activity was inhibited by light and enhanced by darkness; however, in the C57 strain the L-D-induced changes were less pronounced and superimposed to a clear circadian rhythm. Under the L-L schedule clear patterns of daily rhythmicity were evident in the C57 strain but not in the SEC strain. Sleep was enhanced by light and inhibited by darkness. The L-D-induced changes of sleep were superimposed on the circadian rhythm in both strains; however, in the C57 strain these changes were larger in the circadian phase in which the animals were active. Under the L-L-schedule the C57 strain was characterized by more clear-cut patterns of daily rhythmicity than SEC mice. These phenomena are discussed in terms of plasticity of free-running rhythms of sleep and activity and of the genetic factors involved in the expression of circadian rhythmicity.     

C1473G polymorphism in mouse tph2 gene is linked to tryptophan hydroxylase‐2 activity in the brain,intermale aggression,and depressive‐like behavior in the forced swim test

Tryptophan hydroxylase‐2 (TPH2) is the rate‐limiting enzyme of brain serotonin synthesis. The C1473G polymorphism in the mouse tryptophan hydroxylase‐2 gene affects the enzyme's activity. In the present study, we investigated the linkage between the C1473G polymorphism, enzyme activity in the brain, and behavior in the forced swim, intermale aggression, and open field tests using mice of the C57BL/6 (C/C) and CC57BR/Mv (G/G) strains and the B6‐1473C (C/C) and B6‐1473G (G/G) lines created by three successive backcrossings on C57BL/6. Mice of the CC57BR/Mv strain had decreased brain enzyme activity, aggression intensity, and immobility in the forced swim test, but increased locomotor activity and time spent in the central part of the open field arena compared with animals of the C57BL/6 strain. Mice of the B6‐1473G line homozygous for the 1473G allele had lower TPH2 activity in the brain, aggression intensity, and immobility time in the forced swim test compared with animals of the B6‐1473C line homozygous for the 1473C allele. No differences were found between the B6‐1473G and B6‐1473C mice in locomotor activity and time spent in the central part of the arena in the open field test. Thus, the C1473G polymorphism is involved in the determination of TPH2 activity and is linked to aggression intensity and forced‐swim immobility in mice. At the same time, the polymorphism does not affect locomotion and anxiety‐related behavior in the open field test. The B6‐1473C and B6‐1473G mice represent a valuable experimental model for investigating molecular mechanisms of serotonin‐related behavior. © 2008 Wiley‐Liss, Inc.     

Wheel running and sleep in two strains of mice: Plasticity and rigidity in the expression of circadian rhythmicity

The effects of 12-12 h, 6-6 h, 3-3 h and 1-1 h light-dark (L-D) cycles and of constant light (L-L) on wheel-running activity and electrographically defined sleep were studied in two strains of mine, C57BL/6 and SEC/1Re.Wheel-running activity was inhibited by light and enhanced by darkness; however, in the C57 strain the L-D-induced changes were less pronounced and super-imposed to a clear circadian rhythm. Under the L-L schedule clear patterns of daily rhythmicity were evident in the C57 strain but not in the SEC strain.Sleep was enhanced by light and inhibited by darkness. The L-D-induced changes of sleep were superimposed on the circadian rhythm in both strains; however, in the C57 strain these changes were larger in the carcadian phase in which the animals were active. Under the L-L schedule the C57 strain was characterized by more clearcut patterns of daily rhythmicity than SEC mice.These phenomena are discussed in terms of plasticity of free-running rhythms of sleep and activity and of the genetic factors involved in the expression of circadian rhythmicity.     

The acute inhibition of rapid eye movement sleep by citalopram may impair spatial learning and passive avoidance in mice

Rapid eye movement (REM) sleep is known to be essential for memory. Hence, REM sleep deprivation impairs memory processes. The frequently prescribed selective serotonin reuptake inhibitors (SSRIs) are known to cause REM sleep deprivation and to impair cognitive performance in humans and rodents. We suggested that impaired memory processes by citalopram in C57/BL6 mice could be explained by the acute inhibition of REM sleep. We hypothesized that those acute citalopram 5 and 10 mg/kg injections induced REM sleep deprivation, altered cognitive performance in passive avoidance, impaired spatial memory compared to controls. Three experiments have been realized: (1) mice received successively physiological saline, injection of citalopram 5 and 10 mg/kg and were recorded by polysomnographic recording after each injection. (2) Cognitive performance was evaluated in the passive avoidance with two groups of mice. One group received citalopram before training and one, after training. (3) Spatial learning was evaluated with another group of animals in the Y-maze test. At 5 and 10 mg/kg, citalopram delayed REM sleep onset and decreased REM sleep amounts (vs. controls). The same doses were administrated in the passive avoidance test and have significantly shortened latency to enter the dark compartment. In the Y-maze, citalopram-treated mice showed a decreased percentage of time spent in the novel arm in contrast to the two other arms compared with controls. We showed that citalopram impaired cognitive performance in behavioral tasks. Those impairments could be linked to REM sleep deprivation induced by citalopram although causal relationship needs to be investigated in further studies.     

Increased paradoxical sleep in mice during acquisition of a shock avoidance task

Two strains of mice were subjected to a complex shock avoidance task. The C57BR (brown) strain were superior to the C57BL (black) strain in their learning ability. Both strains showed a long term increase in paradoxical sleep (PS) prior to the maximum increase in learning performance (MIP). For the brown starin, this increase was apparent in the 24 h before the MIP. For the black strain, the increase began 48 h prior to the MIP. In the brown strain the day after the MIP, a second effect appeared. PS was higher in the first half hour after sleep onset, following the training session. This increase was due to the larger numbers of slow wave sleep-paradoxical sleep (SWS-PS) cycles. The effect was not present in the black strain.It was concluded that two mechanisms are probably at work during the learning process, one during the earlier stages and one during the later stages as learning reaches criterion.     

Corticosterone facilitates extinction of fear memory in BALB/c mice but strengthens cue related fear in C57BL/6 mice

Corticosterone, the naturally occurring glucocorticoid of rodents is secreted in response to stressors and is known for its facilitating and detrimental effects on emotional learning and memory. The large variability in the action of corticosterone on processing of emotional memories is postulated to depend on genetic background and the spatio-temporal domain in which the hormone operates. To address this hypothesis, mice of two strains with distinct corticosterone secretory patterns and behavioural phenotype (BALB/c and C57BL/6J) were treated with corticosterone (250 μg/kg, i.p.), either 5 min before or directly after acquisition in a fear conditioning task. As the paradigm allowed assessing in one experimental procedure both context- and cue-related fear behaviour, we were able to detect generalization and specificity of fear. BALB/c showed generalized strong fear memory, while C57BL/6J mice discriminated between freezing during context- and cue episodes. Corticosterone had opposite effects on fear memory depending on the strain and time of injection. Corticosterone after acquisition did not affect C57BL/6J mice, but destabilized consolidation and facilitated extinction in BALB/c. Corticosterone 5 min before acquisition strengthened stress-associated signals: BALB/c no longer showed lower fear memory, while C57BL/6J mice displayed increased fear memory and impaired extinction in cue episodes. We propose that corticosterone-induced facilitation of fear memory in C57BL/6J mice can be used to study the development of fear memories, corticosterone administration in BALB/c mice presents a model to examine treatment. We conclude that genetic background and time of corticosterone action are modifiers of fear memory with interesting translational implications for anxiety-related diseases.     

Diurnal variation of lipopolysaccharide-induced alterations in sleep and body temperature of interleukin-6-deficient mice

Infectious challenge triggers a broad array of coordinated changes within the host organism, including alterations in sleep-wake behavior and body temperature. Pro-inflammatory cytokines orchestrate many of the behavioral, metabolic, and endocrine responses to immune challenge. Although interleukin (IL)-6 mediates several aspects of sickness behavior, a role for this cytokine as a mediator of alterations in sleep in response to immune challenge has not been established. We evaluated sleep-wake behavior and core body temperature of IL-6-deficient (IL-6 KO; B6.129S6-Il6tm1Kopf) mice and C57BL/6J control mice after intraperitoneal (IP) administration of 10 microg lipopolysaccharide (LPS). Because feedback mechanisms that regulate responses to immune challenge exhibit circadian rhythms, we evaluated responses to LPS administered at the beginning of both the light and dark portions of the light:dark cycle. LPS-induced increases in non-rapid eye movements sleep (NREMS) of both mouse strains, but this increase was less pronounced in IL-6 KO mice than in C57BL/6J mice. Strain differences in LPS-induced increases in NREMS were greatest after light-onset administration. During the 12 h light period, NREMS of C57BL/6J mice increased from 53.0+/-1.7% of recording time after vehicle to 65.4+/-1.4% of recording time after LPS. During this same time period, NREMS of IL-6 KO mice increased from 50.5+/-1.8% after vehicle to only 52.4+/-1.8% of recording time after LPS. REMS of both mouse strains was suppressed to the same extent after LPS, irrespective of timing of administration. LPS-induced fever in C57BL/6J mice, with peak magnitude of 1.4+/-0.3 degrees C and 1.8+/-0.2 degrees C after dark onset and light onset administration, respectively. In contrast, this dose of LPS-induced profound hypothermia in IL-6 KO mice, with nadirs of hypothermia reaching 4.9+/-1.0 degrees C after injection at dark onset and 2.2+/-0.5 degrees C after administration at light onset. These results indicate that IL-6 mediates some of the effects of LPS on NREMS and body temperature of mice, and that the magnitude and duration of these effects differ as a function of the time at which the challenge is given.     

Genetic studies of daily variations of first-step enzymes of monoamines metabolism in the brain of inbred strains of mice and hybrids. I. Daily variations of tryptophan hydroxylase activity in the nuclei raphe dorsalis, raphe centralis and in the striatum

A daily variation of tryptophan hydroxylase (TrH) activity was observed in the raphe dorsalis (RD), raphe centralis (RC) and striatum (St) of 3 inbred strains of mice (BALB/c, C57BL/6, C57BR) and of the reciprocal hybrids obtained from Balb/c and C57BL6. Significant differences of the characteristics of these rhythms have been found in the same strain between different structures and for the same structure between different strains. In RD and RC hybridization led to less defined daily variations which, in the striatum, remained well synchronized and could be controlled by a dominant genetic mechanism part. These results help to discuss evidence for selective control mechanisms of regulation responsible for daily variation of TrH in the 5-HT cell bodies and terminals and their relative independence.     

Strain differences in the development of susceptibility to audiogenic seizures after acoustic priming but not after hearing loss

Either exposure to an initial auditory stimulus (IAS) or external ear plugging (EEP) was used to produce susceptibility to audiogenic seizures in C57BL/6Bg and DBA/1Bg mice. After the IAS, increments in seizure susceptibility occurred by 5 h in C57BL/6Bg mice and by 24 h in DBA/1Bg-ras mice, whereas after EEP, increments in seizure susceptibility occurred by 48 h in C57BL/6Bg and by 24 h in DBA/1Bg-ras mice. Because both the IAS and EEP produce hearing loss, the strain differences in the effect of the IAS on the development of susceptibility and the strain similarities in the effect of the EEP on the development of susceptibility support the hypothesis that acoustic priming in the C57BL/6Bg at 19 days of age involves another mechanism in addition to that of hearing loss and disuse supersensitivity. It was suggested elsewhere that the other mechanism is mediated by a post-IAS decrease in the concentration of brain γ-aminobutyric acid and requires brain protein synthesis for a brief period post-IAS.     

Impairment of the mitochondrial electron transport chain due to sleep deprivation in mice

It has been demonstrated that sleep deprivation is associated with altered expression of genes related to metabolic processes, response to stress and inflammation, circadian sleep/wake cycles, regulation of cell proliferation and various signaling pathways. However, the molecular mechanisms underlying these changes remain poorly understood. Thus, the present study aims to characterize the function of the mitochondrial electron transport chain in the brain using an animal model of paradoxical sleep deprivation (PSD). The question of whether sleep recovery (rebound) can reverse changes found after PSD is also addressed. Adult male inbred C57BL/6 J mice were randomly distributed into three groups: home-cage control, PSD and sleep rebound groups. The PSD and rebound groups were subjected to PSD for 72 h. After this sleep deprivation period, the rebound group was returned to its home cage and allowed to sleep in an undisturbed and spontaneous fashion for 24 h. The mitochondrial complex I-III, complex II, succinate dehydrogenase and complex II-III activities were then measured by spectrophotometric methods in sub-mitochondrial particles extracted from the prefrontal cortex, hippocampus, striatum and hypothalamus. Our results showed a significant decrease in the activity of complex I-III in the PSD and rebound groups as compared to the control group. The complex II and II-III activity were particularly decreased in the hypothalamus of the sleep rebound group. These results are consistent with the involvement of sleep in energy metabolism and corroborate previous experiments demonstrating the importance of the hypothalamus in sleep regulation.     

Functional roles of NMDA receptor NR2A and NR2B subunits in the acute intoxicating effects of ethanol in mice

The present study examined the roles of NR2A and NR2B subunit-containing NMDA receptors in the mediation of the sedative/hypnotic effects of ethanol in mice. The ability of the competitive NMDA antagonist, CGP-37849 (0, 1, or 3 mg/kg), and the NR2B-selective antagonist, Ro 25-6981 (0, 3, or 10 mg/kg), to alter (3 g/kg) ethanol-induced sleep time was measured in C57BL/6J mice and NR2A knockout (KO) mice. The results show that pretreatment with either antagonist significantly potentiated the sedative/hypnotic effects of ethanol in C57BL/6J mice. These effects were not significantly altered in NR2A KO mice. Basal sleep time responses to ethanol were also normal in NR2A KO mice. These findings confirm a major role for NMDA receptors in the acute intoxicating actions of ethanol and provide tentative support for a prepotent role of the NR2B subunit in these effects.     

Age-related deficits in the retention of memories for cued fear conditioning are reversed by galantamine treatment

Aging has diverse effects on different behaviors and underlying neural systems. This study utilized fear conditioning to determine if aged mice have deficits in the acquisition and/or retention of memories for contextual or cued fear conditioning, and to determine if galantamine, an acetylcholinesterase (AChE) inhibitor and allosteric modulator of nicotinic acetylcholinergic receptors, would alter acquisition and/or retention of fear conditioning memories in young (2-3 months) and aged (19-20 months) C57BL/6 mice. Mice were trained with two white-noise CS (85 dB, 30 s)-footshock US (0.57 mA, 2 s) presentations. In the initial study, separate groups were tested 24, 48, or 96 h post-training. All mice were retested 1 week after the initial test. Aged mice were impaired in freezing to the CS for the 48 and 96 h train-test intervals, but not the 24-h interval. When retested 1 week after the initial test, freezing to the CS was significantly lower for all train-test intervals. No age-related deficits were found in contextual fear conditioning. In the second study, 2 mg/kg galantamine was administered to young and aged mice before fear conditioning and conditioned fear was assessed 48 h later. No age-related deficits in cued fear conditioning were seen in galantamine-treated aged mice. Thus, aged C57BL/6 mice are impaired in the long-term retention of auditory cued fear conditioning, but not the acquisition of auditory cued or contextual fear conditioning. This retention deficit for cued fear conditioning is ameliorated by treatment with the AChE inhibitor galantamine.