Impaired long-trace eyeblink conditioning in a Tg2576 mouse model of Alzheimer's disease

Eyeblink conditioning has been used for assessing cognitive performance in cases of human neurodegenerative diseases including Alzheimer's disease (AD). Here, we tested and compared the delay and long-trace interval (TI = 500 ms) eyeblink conditionings in a Tg2576 mouse model of AD, at the age of 3, 6, and 12 months. Tg2576 mice exhibited significant impairment in trace conditioning at 6 months of age. In contrast, delay conditioning was not impaired in Tg2576 mice even at 12 months. These findings indicate that the long-TI eyeblink conditioning is more susceptible to age-related cognitive deterioration than delay conditioning in Tg2576 mice. The long-trace eyeblink conditioning could be a potential tool for detecting early cognitive deficits in AD mouse model.     

Behavioral characterization of the Tg2576 transgenic model of Alzheimer's disease through 19 months

Behavioral characterization of Alzheimer's disease (AD) transgenic models over multiple time points during aging has been largely inadequate, usually being limited to one or two cognitive-based tasks. In this context, the present study utilized a comprehensive 6-week behavioral battery to characterize sensorimotor and cognitive performance of Tg2576 AD transgenic (Tg+) mice and nontransgenic (Tg-) controls aged 3, 9, 14, and 19 months. Compared collectively to Tg- mice over all four time points, Tg+ mice were impaired in Y-maze spontaneous alternation, visible platform recognition, and several sensorimotor tasks; Tg+ mice also showed an overall increase in activity measures. The deficits in visible platform became evident by 9 months of age, while those in sensorimotor tasks became clearly manifest by 14 months. Although the behavioral impairments exhibited by Tg+ mice were usually progressive through 19 months, Tg- animals also showed similar progressive decline in the same behavioral measures; thus, no task revealed a progressive behavioral decline exclusive to Tg+ mice. Moreover, although the 6-week behavioral battery included six cognitively based tasks (i.e., Y-maze, visible platform, Morris water maze, circular platform, passive avoidance, and active avoidance), behavioral analysis through 19 months revealed Tg+ mice to be impaired in only the Y-maze and visible platform tasks. Consequently, Tg2576 mice do not exhibit widespread, profound cognitive impairment, even into old age. This may reflect their predominant C57BL/6 background and an apparent inability of the mutant transgene to profoundly alter performance therein.     

Decreased phosphatidylethanolamine binding protein expression correlates with Abeta accumulation in the Tg2576 mouse model of Alzheimer's disease

Phosphatidylethanolamine binding protein (PEBP) is a multifunctional protein, with proposed roles as the precursor protein of hippocampal cholinergic neurostimulating peptide (HCNP), and as the Raf kinase inhibitor protein (RKIP). Previous studies have demonstrated a decrease in PEBP mRNA in CA1 region of AD hippocampus. The current study demonstrates that PEBP is decreased in the hippocampus of 11 month Tg2576 mice, in the absence of change in mRNA levels compared to non-transgenic littermates. The level of PEBP in transgenic mouse hippocampus significantly decreases at 11 months (a time point when Abeta begins accumulating) and 15 months (when Abeta plaques have formed). There was a significant correlation between decreased PEBP expression and accumulation of Abeta. Immunohistochemical studies on Tg2576 and AD brain sections demonstrate that PEBP immunoreactivities are present at the periphery of dense multicore Abeta plaques, and in selective astrocytes, primarily surrounding plaques. These findings suggest that PEBP expression may be influenced by accumulation of Abeta. Down-regulation of PEBP may result in lower levels of HCNP or altered coordination of signal transduction pathways that may contribute to neuronal dysfunction and pathogenesis in AD.     

Dreaming during non-rapid eye movement sleep in the absence of prior rapid eye movement sleep

STUDY OBJECTIVES: There is a long-standing controversy surrounding the existence of dream experiences during non-rapid eye movement (NREM) sleep. Previous studies have not answered the question whether this "NREM dream" originates from the NREM sleep mechanism because the subject might simply be recalling experiences from the preceding rapid eye movement (REM) sleep. METHODS: We scheduled 11 healthy men to repeat 20-minute nap trials separated by 40-minute periods of enforced wakefulness across a period of 3 days. At the end of the nap trial, each participant answered questions regarding the formal aspects of his dream experiences during the nap trial, using the structured interviews. RESULTS: We obtained a total of 172 dream reports after naps containing REM sleep (REM naps) and 563 after naps consisting of only NREM sleep (NREM naps). Dream reports from NREM naps were less remarkable in quantity, vividness, and emotion than those from REM naps and were obtained more frequently during the morning hours when the occurrences of REM sleep were highest. CONCLUSIONS: These results suggest that the polysomnographic manifestations of REM sleep are not required for dream experiences but that the mechanisms driving REM sleep alter experiences during NREM sleep in the morning. A subcortical activation similar to REM sleep may occur in human NREM sleep during the morning when REM sleep is most likely to occur, resulting in dream experiences during NREM sleep.     

Melanin-concentrating hormone neurons promote rapid eye movement sleep independent of glutamate release

Brain Structure and Function - Neurons containing melanin-concentrating hormone (MCH) in the posterior lateral hypothalamus play an integral role in rapid eye movement sleep (REMs) regulation. As...     

Activation of pedunculopontine tegmental PKA prevents GABAB receptor activation-mediated rapid eye movement sleep suppression in the freely moving rat

The pedunculopontine tegmental (PPT) GABAergic system plays a crucial role in the regulation of rapid eye movement (REM) sleep. I recently reported that the activation of PPT GABA(B) receptors suppressed REM sleep by inhibiting REM-on cells. One of the important mechanisms for GABA(B) receptor activation-mediated physiological action is the inhibition of the intracellular cAMP-dependent protein kinase A (cAMP-PKA) signaling pathway. Accordingly, I hypothesized that the PPT GABA(B) receptor activation-mediated REM sleep suppression effect could be mediated through inhibition of cAMP-PKA activation. To test this hypothesis, a GABA(B) receptor selective agonist, baclofen hydrochloride (baclofen), cAMP-PKA activator, Sp-adenosine 3',5'-cyclic monophosphothioate triethylamine (SpCAMPS), and vehicle control were microinjected into the PPT in selected combinations to determine effects on sleep-waking states of chronically instrumented, freely moving rats. Microinjection of SpCAMPS (1.5 nmol) induced REM sleep within a short latency (12.1 +/- 3.6 min) compared with vehicle control microinjection (60.0 +/- 6.5 min). On the contrary, microinjection of baclofen (1.5 nmol) suppressed REM sleep by delaying its appearance for approximately 183 min; however, the suppression of REM sleep by baclofen was prevented by a subsequent microinjection of SpCAMPS. These results provide evidence that the activation of cAMP-PKA within the PPT can successfully block the GABA(B) receptor activation-mediated REM sleep suppression effect. These findings suggest that the PPT GABA(B) receptor activation-mediated REM sleep regulating mechanism involves inactivation of cAMP-PKA signaling in the freely moving rat.     

A novel role of pedunculopontine tegmental kainate receptors: a mechanism of rapid eye movement sleep generation in the rat

Considerable evidence suggests that pedunculopontine tegmental cholinergic cells are critically involved in normal regulation of rapid eye movement sleep. The major excitatory input to the cholinergic cell compartment of the pedunculopontine tegmentum arises from glutamatergic neurons in the pontine reticular formation. Immunohistochemical studies reveal that both ionotropic and metabotropic receptors are expressed in pedunculopontine tegmental cells. This study aimed to identify the role of endogenous glutamate and its specific receptors in the pedunculopontine tegmentum in the regulation of physiological rapid eye movement sleep. To identify this physiological rapid eye movement sleep-inducing glutamate receptor(s) in the pedunculopontine tegmental cholinergic cell compartment, specific receptors were blocked differentially by local microinjection of selective glutamate receptor antagonists into the pedunculopontine tegmental cholinergic cell compartment while quantifying the effects on rapid eye movement sleep in freely moving chronically instrumented rats. By comparing the alterations in the patterns of rapid eye movement sleep following injections of control vehicle and selective glutamate receptor antagonists, contributions made by each receptor subtype in rapid eye movement sleep were evaluated. The results demonstrate that when kainate receptors were blocked by local microinjection of a kainate receptor selective antagonist, spontaneous rapid eye movement sleep was completely absent for the first 2 h, and for the next 2 h the total percentage of rapid eye movement sleep was significantly less compared to the control values. In contrast, when N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid, groups I, II, and III metabotropic receptors were blocked, total percentages of rapid eye movement sleep did not change compared to the control values. These findings suggest, for the first time, that the activation of kainate receptors within the cholinergic cell compartment of the pedunculopontine tegmentum is a critical step for the regulation of normal rapid eye movement sleep in the freely moving rat. The results also suggest that the different types of glutamate receptors within a small part of the brainstem may be involved in different types of physiological functions.     

Upregulation of tPA/plasminogen proteolytic system in the periphery of amyloid deposits in the Tg2576 mouse model of Alzheimer's disease

Although the tissue plasminogen activator (tPA)/plasminogen/plasmin proteolytic system is thought to modulate the catabolism of amyloid-β (Aβ), in vivo evidence remains insufficient. In the brain of human amyloid precursor protein transgenic Tg2576 mice, we found co-accumulation of tPA and plasminogen at the periphery of compact amyloid deposits, mainly Aβ42-cored plaques, as well as in the walls of blood vessels with cerebral amyloid angiopathy (CAA). This tPA/plasminogen system contained high levels of proteolytic activity. High levels of tPA were also found in reactive astrocytes with increased Aβ42 expression, whereas plasminogen was found only in neurons. When the brain sections of Tg2576 mice were treated with both tPA and plasminogen, levels of thioflavin-S fluorescence, congophilicity and birefringence in the compact amyloid plaques were significantly reduced, and the ultrastructure of Aβ42-fibrils was disrupted. These results suggest that the assembled Aβ42 may promote upregulation of the tPA/plasminogen proteolytic system, which can modulate the deposition of amyloid plaques in vivo.     

Heparan sulfate accumulation with Abeta deposits in Alzheimer's disease and Tg2576 mice is contributed by glial cells

Abstract Amyloid beta-peptide (Abeta) plaques, one of the major neuropathological lesions in Alzheimer's disease (AD), can be broadly subdivided into two morphological categories: neuritic and diffuse. Heparan sulfate (HS) and HS proteoglycans (HSPGs) are codeposits of multiple amyloidoses, including AD. Although HS has been considered a limiting factor in the initiation of amyloid deposition, the pathological implications of HS in Abeta deposits of AD remain unclear. In this study, immunohistochemistry combined with fluorescence and confocal microscopy was employed to gain deeper insight into the accumulation of HS with Abeta plaques in sporadic and familial AD. Here we demonstrate that HS preferentially accumulated around the Abeta40 dense cores of neuritic plaques, but was largely absent from diffuse Abeta42 plaques, suggesting that Abeta42 deposition may occur independently of HS. A codeposition pattern of HS with Abeta deposits in Tg2576 mice was also examined. We identified the membrane-bound HSPGs, glypican-1 (GPC1) and syndecan-3 (SDC3), in glial cells associated with Abeta deposits, proximal to sites of HS accumulation. In mouse primary glial cultures, we observed increased levels of GPC1 and SDC3 following Abeta stimulation. These results suggest that HS codeposits with Abeta40 in neuritic plaques and is mainly derived from glial cells.     

Induction of rapid eye movement sleep by neurotrophin-3 and its co-localization with choline acetyltransferase in mesopontine neurons

Because neurotrophin-3 (NT-3), a neurotrophic factor closely related to nerve growth factor, is capable of modulating neuronal activity [Yamuy et al., Neuroscience 95 (2000a) 1089-1100], we sought to examine if the microinjection of NT-3 into the nucleus reticularis pontis oralis (NPO) of chronically prepared cats also induced changes in behavior. In contrast to vehicle administration, NT-3 injection induced, with a mean latency of 4.7 min, long-duration episodes (mean, 21.6 min) of a state that was polygraphically indistinguishable from naturally occurring REM sleep. If NT-3 plays a physiologic role in the generation of REM sleep, then an endogenous source for this neurotrophin that is capable of controlling the activity of NPO neurons should exist. We therefore determined whether cholinergic neurons in the latero-dorsal and pedunculo-pontine tegmental (LDT and PPT) nuclei, which are involved in the initiation of REM sleep and project to the NPO, contained NT-3. Most, if not all, of the LDT-PPT cholinergic neurons exhibited NT-3 immunoreactivity. A portion (10%) of the NT-3+ neurons in the LDT-PPT were not cholinergic. The present data indicate that NT-3 rapidly modulates the activity of NPO neurons involved in REM sleep and that cholinergic neurons in the LDT and PPT contain NT-3. Taken together, these results support the hypothesis that NT-3 may be involved in the control of naturally occurring REM sleep.     

Hypocapnia decreases the amount of rapid eye movement sleep in cats

CONTEXT: Sleep is disturbed at high altitudes. Low PO2 levels at high altitude cause hyperventilation, which results in secondary hypocapnia (low PaCO2 levels). Thus, although sleep disruption at high altitudes is generally assumed to be caused by hypoxia, it may instead be the result of hypocapnia. OBJECTIVE: To determine whether hypocapnia disrupts sleep. METHODS: Four cats were studied for a total of 345 hours of sleep recordings. Two methods were used to test this idea. First we studied their sleep when the cats breathed oxygen concentrations (15% and 10%) equivalent to those at approximately 12,000 feet and 21,000 feet. Then we studied their sleep again in response to the same hypoxic stimuli but with CO2 added to the inspirate to maintain normal CO2 levels. Second, we used mechanical hyperventilation to vary the levels of CO2 while maintaining normal O2 levels. RESULTS: Hypoxia (10% O2) decreased the amount of rapid eye movement sleep to about 20% of normal, and adding back CO2 restored rapid eye movement sleep to approximately 70% of normal. Periodic breathing and apneas were not observed during hypoxia in sleep. When mechanical hyperventilation lowered the CO2 to 85%, 75%, and 65% of normal, rapid eye movement sleep decreased progressively from a control level of 17% of total recording time to 12%, 7%, and 4%, respectively. CONCLUSION: We conclude that hypocapnia rather than hypoxia may account for most of the sleep disturbance at high altitudes.     

Brainstem glycinergic neurons and their activation during active (rapid eye movement) sleep in the cat

It is well established that, during rapid eye movement (REM) sleep, somatic motoneurons are subjected to a barrage of inhibitory synaptic potentials that are mediated by glycine. However, the source of this inhibition, which is crucial for the maintenance and preservation of REM sleep, has not been identified. Consequently, the present study was undertaken to determine in cats the location of the glycinergic neurons, that are activated during active sleep, and are responsible for the postsynaptic inhibition of motoneurons that occurs during this state. For this purpose, a pharmacologically-induced state of active sleep (AS-carbachol) was employed. Antibodies against glycine-conjugated proteins were used to identify glycinergic neurons and immunocytochemical techniques to label the Fos protein were employed to identify activated neurons. Two distinct populations of glycinergic neurons that expressed c-fos were distinguished. One population was situated within the nucleus reticularis gigantocellularis (NRGc) and nucleus magnocellularis (Mc) in the rostro-ventral medulla; this group of neurons extended caudally to the ventral portion of the nucleus paramedianus reticularis (nPR). Forty percent of the glycinergic neurons in the NRGc and Mc and 25% in the nPR expressed c-fos during AS-carbachol. A second population was located in the caudal medulla adjacent to the nucleus ambiguus (nAmb), wherein 40% of the glycinergic cells expressed c-fos during AS-carbachol. Neither population of glycinergic cells expressed c-fos during quiet wakefulness or quiet (non-rapid eye movement) sleep. We suggest that the population of glycinergic neurons in the NRGc, Mc, and nPR participates in the inhibition of somatic brainstem motoneurons during active sleep. These neurons may also be responsible for the inhibition of sensory and other processes during this state. It is likely that the group of glycinergic neurons adjacent to the nucleus ambiguus (nAmb) is responsible for the active sleep-selective inhibition of motoneurons that innervate the muscles of the larynx and pharynx.     

Dense-core plaques in Tg2576 and PSAPP mouse models of Alzheimer's disease are centered on vessel walls

Occurrence of amyloid beta (Abeta) dense-core plaques in the brain is one of the chief hallmarks of Alzheimer's disease (AD). It is not yet clear what factors are responsible for the aggregation of Abeta in the formation of these plaques. Using Tg2576 and PSAPP mouse models that exhibit age-related development of amyloid plaques similar to that observed in AD, we showed that approximately 95% of dense plaques in Tg2576 and approximately 85% in PSAPP mice are centered on vessel walls or in the immediate perivascular regions. Stereoscopy and simulation studies focusing on smaller plaques suggested that vascular associations for both Tg2576 and PSAPP mice were dramatically higher than those encountered by chance alone. We further identified ultrastructural microvascular abnormalities occurring in association with dense plaques. Although occurrence of gross cerebral hemorrhage was infrequent, we identified considerable infiltration of the serum proteins immunoglobulin and albumin in association with dense plaques. Together with earlier evidence of vascular clearance of Abeta, our data suggest that perturbed vascular transport and/or perivascular enrichment of Abeta leads to the formation of vasocentric dense plaques in Tg2576 and PSAPP mouse models of AD.     

The organization of rapid eye movement activity during rapid eye movement sleep is further impaired in very old human subjects

Rapid eye movement activity (REMA) during rapid eye movement (REM) sleep was studied in seven very old ('old-old') subjects. Beyond global quantitative features (REMA density), we evaluated the organizational aspects of REMA, that is its occurrence in burst mode, which were compared to a group of younger elderly subjects ('young-old'). REMA density in 'old-old' subjects is not significantly different from that of 'young-old' subjects. The same lack of difference in the two groups is found for the number of REMA bursts. By contrast, the duration of REMA bursts is reduced in the 'old-old' subjects, as well as the 'burst state-to-burst-state' probability, i.e. the probability for successive inter-REMA time intervals to be part of the same REMA burst. Our results clearly show that the trend towards an impairment of REMA organizational aspects continues with aging. This is consistent with the hypothesis that sleep disorganization keeps worsening with age. However, it is of interest to observe that the capability of producing REMA bursts is preserved despite aging.     

特发性和继发性快速眼动睡眠行为障碍的睡眠结构研究

目的：探讨快速眼动睡眠行为障碍（REM sleep behavior disorder,RBD）患者的睡眠结构改变。方法：纳入的22例患者符合国际睡眠障碍协会（第2版）的RBD诊断标准,16例患者符合RBD主要诊断标准以及英国脑库的PD、2005年国际路易体痴呆协作组或者2008年多系统萎缩第2版的诊断标准。同时纳入年龄、性别匹配的健康对照19例。利用日本光电32信道9200K脑电图机,所有患者均完成多项睡眠图监测（PSG）,记录脑电图、眼球运动、下颌和肢体肌电活动、心电图、经鼻气流、胸腹部呼吸运动、血氧、鼾声等多个项目,并录像监测患者的行为。使用Polysmith软件和视觉评估分析睡眠结构、呼吸、运动等相关指标。结果：RBD患者展现了典型临床表现和电生理改变。特发性RBD组（72．7％）较继发性RBD组（43．8％）显示有更多的夜间活动和言语,差异有统计学意义（P=0．071）。特发性RBD在睡眠结构并未发生明显改变,仅有周期性腿动（PLM）指数增高。继发性RBD与特发性RBD和健康对照相比,总体睡眠时间缩短、睡眠效率减低、睡眠潜伏期和REM潜伏期延迟、Ⅱ期和REM睡眠减少、Ⅰ期睡眠增加、低通气指数增高、PLM指数增高。结论：特发性RBD患者具有更多的夜间行为异常,而睡眠结构无改变,仅有PLM指数增加;而继发性RBD出现明显的睡眠结构紊乱、呼吸紊乱以及PLM异常。     

Antiserum to prolactin decreases rapid eye movement sleep (REM sleep) in the male rat.

Previous reports suggest that blood-born prolactin (PRL) may selectively promote rapid eye movement sleep (REMS). To study the possible involvement of endogenous PRL in sleep regulation, rats were systemically injected with either antiserum to PRL or normal rabbit serum, and the sleep-wake activity was determined during the subsequent 12-h light cycle. The administration of normal rabbit serum in physiological saline did not alter sleep-wake activity compared to control recordings, whereas the PRL antiserum caused a modest and selective suppression in REMS. Immunoreactive PRL was eliminated from the serial plasma samples obtained between 6 to 11 h after the injection of the antiserum. Brain temperature was not affected by the antiserum. The results indicate that physiological pituitary PRL secretion has a slight REMS-promoting activity in the male rat. It is speculated that an increased release of pituitary PRL or the PRL-like substance previously demonstrated in the brain may significantly stimulate REMS.     

Phasic activities of rapid eye movement sleep in vegetative state patients

STUDY OBJECTIVES: To assess the phasic components of rapid eye movement (REM) sleep in patients in vegetative state and to evaluate the possible relationship of these activities to patient outcome. SETTING: Sleep disorders unit at a major rehabilitation hospital. DESIGN: Comparative control study. PATIENTS: Eleven patients in vegetative state (10 males and 1 female) aged 17-53 years. INTERVENTIONS: Continuous 24-hour polysomnographic recording. MEASUREMENTS AND RESULTS: All the patients had REM sleep periods during the 24-hr recording session. Mean total REM sleep time for the whole session was 66.5 +/- 34.9 min, and for the nocturnal hours only, 37.3 +/- 19.7 min. Comparison with the control group (79.2 +/- 11.5 min) yielded a significant difference only for nocturnal REM sleep time (p<0.0003). The duration of the REM sleep periods was significantly shorter in the patients than the controls for the whole 24-hr session (10.9 +/- 6.0 vs.19.6 +/- 4.9 min, p<0.008), but not for the nocturnal period alone. Compared to controls, the density of rapid eye movements (REMs) (p=0.001), chin twitches (p=0.002), and leg muscle twitches (p=0.023) was significantly lower in the patient group. The density of the sawtooth waves was also lower in the patients, but the difference did not reach significance (p=0.069). Similar results were obtained when the comparison was done only for the nocturnal period. There was no significant difference for any of the REM sleep characteristics or REM sleep phasic activities (24-hr, nocturnal and diurnal periods) between the patients who recovered consciousness and those who did not. CONCLUSIONS: The present study shows that patients in vegetative state have a significant reduction in the phasic activities of REM sleep. However, the amount of these activities is unrelated to recovery from the clinical condition. These findings may reflect possible damage to the pedunculopontine tegmentum cholinergic mechanisms in vegetative state.