Night-to-night variability in sleep and amyloid beta burden in normal aging

INTRODUCTION

Alzheimer's disease is associated with sleep disturbances and accumulation of cerebral amyloid beta. The objective was to examine whether actigraphy-detected sleep parameters might be biomarkers for early amyloid burden.

METHODS

Participants underwent a week of actigraphy and an amyloid positron emission tomography (PET) scan. Sleep duration and continuity disruption (sleep fragmentation and nocturnal awakenings) were extracted and compared between amyloid-positive and amyloid-negative participants. Then multiple linear regressions were used between mean or night-to-night intra-individual variability (standard deviation) of sleep parameters and brain amyloid burden in a voxel-wise analysis.

RESULTS

Eighty-six subjects were included (80.3 ± 5.4 years; 48.8% of women). Amyloid-positive participants had a higher variability of sleep fragmentation compared to amyloid-negative participants. This parameter was associated with a higher amyloid burden in the frontal and parietal regions, and in the precuneus, in the whole sample.

DISCUSSION

This study highlights the relevance of using variability in sleep continuity as a potential biomarker of early amyloid pathogenesis.

Age-related positivity effect: Distinct mechanisms for lexical access and episodic memory of emotional words

The age-related positivity effect is the tendency of older adults to preferentially process positive information over negative information when compared to younger adults (e.g., Reed & Carstensen, 2012). The aim of the study was to determine whether common and/or distinct mechanisms underlie the age-related positivity effect in lexical access and episodic memory. Fifty young and 50 older adults successively performed a progressive demasking task incorporating memory instructions, an immediate free recall task, a memory recognition task, and delayed free recalls at 20 min and 7 days. The materials included 60 words that varied in emotional valence (positive, neutral, negative) and arousal (low, high). The results revealed that distinct processes underlie the age-related positivity effect in lexical access and episodic memory. In progressive demasking, this effect emerged for both low- and high-arousal words, suggesting that it depends on automatic processes. In immediate and delayed free recall and recognition, this effect emerged for low-arousal words only, suggesting that it depends on more controlled processes. Moreover, in older adults, positivity scores correlated with well-being scores for episodic memory. These results are discussed in relation to affective aging theories. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Attention-deficit/hyperactivity and obsessive-compulsive symptoms in adult patients with primary restless legs syndrome

Comorbidity between Restless Legs Syndrome and Attention-Deficit/Hyperactivity Disorder remains a matter of debate. This putative association, possibly reflecting a shared brain iron homeostasis and dopaminergic dysfunction, supports the hypothesis of a neurodevelopmental component in Restless Legs Syndrome pathogenesis. The aim of this study was to investigate Attention-Deficit/Hyperactivity Disorder and Obsessive-Compulsive Disorder symptoms prevalence in adult patients with primary Restless Legs Syndrome compared to another ill group of patients with obstructive sleep apnea syndrome to control for the disease specific effects on psychiatric symptoms and a healthy individuals control group. Clinical data were obtained through standardized and validated self-administrated questionnaires evaluating Attention-Deficit/Hyperactivity Disorder and Obsessive-Compulsive Disorder symptoms frequencies in 139 outpatients with idiopathic Restless Legs Syndrome, 111 patients with treated obstructive sleep apnea syndrome and 136 healthy subjects. Our findings demonstrate a higher prevalence of Attention-Deficit/Hyperactivity Disorder symptoms among both male and female patients with Restless Legs Syndrome, compared to obstructive sleep apnea syndrome patients and healthy subjects (33.3 and 43.5%, respectively, p < 0.001). Only women presented a strong relationship between Attention-Deficit/Hyperactivity Disorder and Restless Legs Syndrome severity (p < 0.001). Male and female in the three groups showed similar Obsessive-Compulsive Disorder symptom prevalence. These findings indicate that Attention-Deficit/Hyperactivity Disorder symptoms among adult patients with Restless Legs Syndrome populations are a robust phenomenon. These data provide arguments in favor of an enlargement of the clinical neuropsychological presentation of Restless Legs Syndrome and question the role of decreased brain iron of these psychiatric symptoms.

The age-related positivity effect: forgetting the negative and/or remembering the positive? An inter-task study

A growing number of studies have shown that when compared to younger adults, older adults are better at recalling positive information than negative information. However, it is not yet clear whether this age-related positivity effect relies on a greater ability to recall positive information or on a decreased ability to recall negative information. We therefore aimed to study the specific mechanisms underlying the age-related positivity effect using different memory tasks. We used an emotional word memory paradigm including immediate free recall, recognition, and delayed free recall tasks. Forty-five young adults (m = 20.0 years) and 45 older adults (m = 69.2 years) participated, all of whom were native French speakers. Thirty-six French low-arousal words (12 positve, 12, negative, 12 neutral) were selected from an emotional lexical database (Gobin et al. 2017) and divided into three equal groups of positive, neutral and negative terms. For the recognition task, 36 new words were selected. The results show that the age-related positivity effect specifically depended on a decrease in negativity preference (i.e., the comparison between negative and neutral words) in older adults, in comparison with younger adults, both in the immediate and delayed free recall tasks. In these tasks, younger adults recalled more negative than neutral words, whereas there was no difference in older adults. During the recognition task, no age-related positivity effect was observed. The results also show that, for the immediate recall task, the greater the memory ability of older adults, the lower their negativity preference. This correlation was not significant in the delayed recall task. These results suggest that, when compared with younger adults, older adults disengage from processing negative words that require costly cognitive processes. A low negativity preference indicates that memory abilities are well-maintained. The results are discussed within the framework of socio-emotional selectivity theory.

Assessment of dream-related aspects and beliefs in a large cohort of French students using a validated French version of the Mannheim Dream questionnaire

Focusing on a specific population when studying dream characteristics can shed light on underlying mechanisms and correlates of dreaming. The aim of this study is to establish a clearer description of specific dream aspects and beliefs in a large cohort of students using a validated questionnaire, and to further investigate the role of sociodemographic variables such as age, gender and field of study. Participants were 1137 students aged from 18 to 34 (mean age: 22.2) who responded to an online version of the questionnaire. Our results showed a difference between humanities and science students, and a differential effect of gender on dream variables. Our results are discussed in light of previous investigations using the same questionnaire or focusing on the same population.

Attention-Deficit Hyperactivity and Obsessive-Compulsive Symptoms in Adult Patients With Primary Restless Legs Syndrome: Different Phenotypes of the Same Disease?

OBJECTIVES

To investigate the prevalence of attention deficit hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD) symptoms in adult patients with primary restless legs syndrome (RLS) and to determine the iron biological correlates of these comorbidities.

PARTICIPANTS AND METHODS

We obtained demographic and clinical data from consecutive 105 outpatients with idiopathic RLS who answered validated questionnaires designed to assess the presence of ADHD and OCD symptoms. In these patients, iron blood parameters were routinely checked.

RESULTS

Of the total sample, 42.86% of the patients with RLS showed symptoms reminiscent either of ADHD or OCD. Prevalence of ADHD and OCD symptoms was 27.62% and 7.62%, respectively. Compared to other groups, a significantly higher percentage of RLS patients with ADHD symptoms was on antidepressant (p = 0.012); and women with ADHD symptoms, either alone or combined with OCD symptoms, showed significant reduced ferritin concentrations compared to men with either isolated ADHD symptoms or with combined ADHD and OCD symptoms (p = 0.028 and p = 0.025, respectively).

CONCLUSIONS

Our findings highlight the high prevalence of ADHD and OCD symptoms in adult patients with primary RLS and independently of serum iron stores decrease, except for women with ADHD symptoms either alone or in combination with OCD symptoms. This may suggest an overlapping neurobiological dopaminergic and serotoninergic dysfunction in ADHD, OCD, and RLS, and question the expression of different RLS phenotypes. The efficacy of dopamine agonists in these groups of patients should be questioned in future studies.

3-D motion capture for long-term tracking of spontaneous locomotor behaviors and circadian sleep/wake rhythms in mouse

BACKGROUND

Locomotor activity provides an index of an animal's behavioral state. Here, we report a reliable and cost-effective method that allows long-term (days to months) simultaneous tracking of locomotion in mouse cohorts (here consisting of 24 animals).

NEW METHOD

The technique is based on a motion capture system used mainly for human movement study. A reflective marker was placed on the head of each mouse using a surgical procedure and labeled animals were returned to their individual home cages. Camera-recorded data of marker displacement resulting from locomotor movements were then analyzed with custom built software. To avoid any data loss, data files were saved every hour and automatically concatenated. Long-term recordings (up to 3 months) with high spatial (<1mm) and temporal (up to 100Hz) resolution of animal movements were obtained.

RESULTS

The system was validated by analyzing the spontaneous activity of mice from post-natal day 30-90. Daily motor activity increased up to 70days in correspondence with maturational changes in locomotor performance. The recorded actigrams also permitted analysis of circadian and ultradian rhythms in cohort sleep/wake behavior.

COMPARISON WITH EXISTING METHOD(S)

In contrast to traditional session-based experimental approaches, our technique allows locomotor activity to be recorded with minimal experimenter manipulation, thereby minimizing animal stress.

CONCLUSIONS

Our method enables the continuous long-term (up to several months) monitoring of tens of animals, generating manageable amounts of data at minimal costs without requiring individual dedicated devices. The actigraphic data collected allows circadian and ultradian analysis of sleep/wake behaviors to be performed.

Affective Prosody and Depression After Stroke: A Pilot Study

BACKGROUND AND PURPOSE

Poststroke depression (PSD) is a frequent complication of stroke with detrimental consequences in terms of quality of life and functional outcomes. In individuals with major depression, several studies have demonstrated an alteration of affective prosody. The aim of this study is to identify prosodic markers that may be predictive of PSD.

METHODS

Patient voices were recorded at baseline and 3 months after stroke. We extracted prosodic parameters, including fundamental frequency, percentage of voice breaks, and shimmer. Depression and anxiety symptoms were assessed 3 months later.

RESULTS

Among the 49 patients included in the study, 22.5% developed PSD 3 months after stroke. A significant decrease was observed concerning the fundamental frequency among patients who developed PSD. Discriminant analysis demonstrated that initial voice breaks coupled with shimmer are strongly predictive of subsequent PSD.

CONCLUSIONS

Early alterations of affective prosody are associated with a higher risk of PSD 3 months after a stroke. This new physiological approach overcomes traditional barriers associated with clinical instruments and contributes to the prediction of this disorder.

123I-Iodobenzovesamicol SPECT Imaging of Cholinergic Systems in Dementia with Lewy Bodies

Cholinergic alterations in dementia with Lewy bodies (DLB) have been widely documented in postmortem studies, whereas in vivo studies are sparse, particularly at the subcortical level. We used ¹²³I-iodobenzovesamicol, a SPECT radiotracer of the vesicular acetylcholine transporter, to evaluate in vivo in DLB the integrity of the 3 main cholinergic pathways-the Ch1 (septohippocampal), the Ch4 (innominatocortical), and the Ch5 (pontothalamic) cholinergic pathways-as well as the striatal cholinergic interneurons. In addition, we assessed the involvement of the cholinergic system in cognitive and neuropsychiatric disorders in DLB patients.

METHODS

Twelve healthy volunteers (median age, 72 y; interquartile range, 6.25 y) and 11 DLB patients (median age, 76 y; interquartile range, 10.50 y) underwent a dynamic ¹²³I-iodobenzovesamicol SPECT scan and an MRI scan. MR images were automatically segmented, providing the volumes of several regions of interest, including the striatum and cholinergic terminals in Ch1 (hippocampus), Ch4 (cortical lobes), and Ch5 (thalamus). For each region of interest and each subject, pharmacokinetic modeling allowed calculation of the nondisplaceable binding potential (BP_ND) values for the binding of ¹²³I-iodobenzovesamicol to the vesicular acetylcholine transporter. A neuropsychological evaluation of participants was performed with the Mini-Mental State Examination and the Grober-Buschke, Set, visual discrimination, Benton, and Wechsler tests, and cognitive fluctuations and apathy were also assessed.

RESULTS

Compared with BP_ND values for healthy subjects, BP_ND values for DLB patients were significantly lower in the Ch4 terminal regions of the anterior cingulate cortex and the superior and inferior parietal cortices (P = 0.0006, 0.0015, and 0.0023, respectively), in the Ch5 terminal region of the thalamus (P = 0.0003), and in the striatum (P = 0.0042). All of the neuropsychological test scores were significantly lower in DLB patients than in healthy subjects. Four DLB patients with apathy and 4 DLB patients without apathy were identified. For the anterior cingulate cortex, compared with BP_ND values in healthy subjects, BP_ND values were significantly lower in patients with apathy (P = 0.004) and were unchanged in patients without apathy.

CONCLUSION

Our results confirm the existence in DLB of cholinergic alterations, reaching both cortical and subcortical levels, including the Ch5 pathway and the striatum. Alterations in cholinergic transmission in the anterior cingulate cortex could be closely associated with the development of apathy.

Mood Influences the Concordance of Subjective and Objective Measures of Sleep Duration in Older Adults

Objective/Background: Sleep plays a central role in maintaining health and cognition. In most epidemiologic studies, sleep is evaluated by self-report questionnaires but several reports suggest that these evaluations might be less accurate than objective measures such as polysomnography or actigraphy. Determinants of the discrepancy between objective and subjective measures remain to be investigated. The aim of this pilot-study was to examine the role of mood states in determining the discrepancy observed between objective and subjective measures of sleep duration in older adults.

Patients/Methods: Objective sleep quantity and quality were recorded by actigraphy in a sample of 45 elderly subjects over at least three consecutive nights. Subjective sleep duration and supplementary data, such as mood status and memory, were evaluated using ecological momentary assessment (EMA).

Results: A significant discrepancy was observed between EMA and actigraphic measures of sleep duration (p < 0.001). The magnitude of this difference was explained by the patient’s mood status (p = 0.020). No association was found between the magnitude of this discrepancy and age, sex, sleep quality or memory performance.

Conclusion: The discrepancy classically observed between objective and subjective measures of sleep duration can be explained by mood status at the time of awakening. These results have potential implications for epidemiologic and clinical studies examining sleep as a risk factor for morbidity or mortality.

Simplified Quantification Method for In Vivo SPECT Imaging of the Vesicular Acetylcholine Transporter with 123I-Iodobenzovesamicol

(123)I-iodobenzovesamicol is a SPECT radioligand selective for the vesicular acetylcholine transporter (VAChT) and used to assess the integrity of cholinergic pathways in various neurologic disorders. The current noninvasive method for quantitative analysis of (123)I-iodobenzovesamicol, based on multilinear reference tissue model 2 (MRTM2), requires repeated scans for several hours, limiting its application in clinical trials. Our objective was to validate a simplified acquisition method based on a single (123)I-iodobenzovesamicol static scan preserving the quantification accuracy. Three acquisition times were tested comparatively to a kinetic analysis using MRTM2.

METHODS

Six healthy volunteers underwent a dynamic SPECT acquisition comprising 14 frames over 28 h and an MR imaging scan. MR images were automatically segmented, providing the volumes of 19 regions of interest (ROIs). SPECT datasets were coregistered with MR images, and regional time-activity curves were derived. For each ROI, a complete MRTM2 pharmacokinetic analysis, using the cerebellar hemispheres as the reference region, led to the calculation of a (123)I-iodobenzovesamicol-to-VAChT binding parameter, the nondisplaceable binding potential (BP(ND-MRTM2)). A simplified analysis was also performed at 5, 8, and 28 h after injection, providing a simplified BP(ND), given as BP(ND-t) = C(ROI) - C(cerebellar hemispheres)/C(cerebellar hemispheres), with C being the averaged radioactive concentration.

RESULTS

No significant difference was found among BP(ND-5 h), BP(ND-8 h), and BP(ND-MRTM2) in any of the extrastriatal regions explored. BP(ND-28 h) was significantly higher than BP(ND-5 h), BP(ND-8 h), and BP(ND-MRTM2) in 9 of the 17 regions explored (P < 0.05). BP(ND-5 h), BP(ND-8 h), and BP(ND-28 h) correlated significantly with BP(ND-MRTM2) (P < 0.05; ρ = 0.99, 0.98, and 0.92, respectively). In the striatum, BP(ND-28 h) was significantly higher than BP(ND-5 h) and BP(ND-8 h). BP(ND-5 h) differed significantly from BP(ND-MRTM2) (P < 0.05), with BP(ND-5 h) being 43.6% lower.

CONCLUSION

In the extrastriatal regions, a single acquisition at 5 or 8 h after injection provides quantitative results similar to a pharmacokinetic analysis. However, with the highest correlation and accuracy, 5 h is the most suitable time to perform an accurate (123)I-iodobenzovesamicol quantification. In the striatum, none of the 3 times has led to an accurate quantification.

Circadian sleep/wake rhythm abnormalities as a risk factor of a poststroke apathy

BACKGROUND

Poststroke apathy affects 19-55% of patients following stroke and has a negative impact on functional recovery, general health, and quality of life, as well as being a source of significant burden for caregivers.

AIMS

A major clinical issue is the delayed diagnosis of poststroke apathy, and so the aim of our study is to evaluate the relationship between early poststroke alterations of circadian rhythms of sleep/wake cycles and the occurrence of poststroke apathy.

METHODS

Forty-six patients with a recent magnetic resonance imaging confirmed stroke were included. Main exclusion criteria were a mild to severe disability impeding home discharge from the hospital and the presence of apathy or dementia before stroke. Cerebrovascular lesions were evaluated by magnetic resonance imaging. At hospital discharge, an actigraph was used to measure patient's global activity as well as parameters of circadian rhythmicity (relative amplitude, interdaily stability, intradaily variability) and sleep (sleep duration, sleep efficiency, fragmentation index) over seven-days. Apathy was assessed at hospital discharge as well as at three-months using the Apathy Inventory and the Lille Apathy Rating Scale.

RESULTS

Of the 46 patients evaluated, 10 (22%) showed apathy three-months after stroke (median Apathy Inventory = 4·5). Before inclusion, these 10 subjects did not differ significantly from other patients concerning their sleep and, at inclusion, they did not differ concerning apathy, anxiety, depression, or cognitive and functional abilities. However, actigraphy measured at discharged identified significant alterations of sleep (P < 0·005). Future poststroke apathy patients exhibited a decrease in sleep efficiency (actual sleep time expressed as a percentage of time in bed) and an increase in the fragmentation index (degree of fragmentation during the sleep period) at three-months. No association was observed between poststroke apathy and the characteristics of cerebrovascular lesions (stroke location, extent of leucoencephalopathy, number of lacunes and microbleeds).

CONCLUSION

These results indicate that early poststroke alterations of sleep/wake circadian rhythms--easily evaluated by actigraphy--are associated with a higher risk of poststroke apathy at three-months. In terms of clinical outcomes, our results provide targets for very early identification of patients at risk to develop apathy after stroke and for assessing when to start specific therapy to optimize rehabilitation efficiency.

[(123)I]-IBVM SPECT imaging of cholinergic systems in multiple system atrophy: A specific alteration of the ponto-thalamic cholinergic pathways (Ch5-Ch6)

We evaluated in vivo the integrity of brain cholinergic pathways in Multiple System Atrophy (MSA) and the relationship between cholinergic dysfunction and motor disturbances, by measuring the vesicular acetylcholine transporter (VAChT) expression using Single Photon Emission Computed Tomography (SPECT) and [(123)I]-iodobenzovesamicol ([(123)I]-IBVM).

METHODS

Nine patients with probable MSA and 12 healthy volunteers underwent a dynamic [(123)I]-IBVM SPECT-CT scan and a magnetic resonance imaging (MRI) scan. All patients were examined with the Unified MSA Rating Scale (UMSARS; subscale I = activities of daily living (ADL), II = motor and IV = disability). CT and MRI images were used to register the dynamic SPECT image to the Montreal Neurological Institute brain template, which includes the regions of interest (ROI) of striatum and Ch1 (medial septum nucleus-hippocampus), Ch4 (nucleus basalis of Meynert-cortex) and Ch5-Ch6 (pedunculopontine and laterodorsal tegmental nuclei-thalamus) cholinergic pathways. For each ROI, pharmacokinetic modeling of regional time activity curves led to the calculation of [(123)I]-IBVM to VAChT binding potential (BPND) value, proportional to VAChT expression.

RESULTS

When compared to controls, BPND values for MSA in Ch5-Ch6 were significantly decreased in both the pedunculopontine-laterodorsal nuclei and the thalamus (p = 0.004 and p = 0.006, respectively). Additionally, thalamus BPND values were correlated with UMSARS ADL (p = 0.006), motor (p = 0.002) and disability (p = 0.02) sub-scores. UMSARS motor subscale items 13 (postural instability) and 14 (gait) were also correlated with thalamus BPND values (p = 0.04).

CONCLUSION

Ch5-Ch6 are the most affected cholinergic pathways in MSA at both cell bodies and thalamic cholinergic terminals. These results underscore the relevant role of [(123)I]-IBVM SPECT for improving our understanding of the pathophysiology in MSA.

Improvement of in vivo quantification of [123I]-Iodobenzovesamicol in single-photon emission computed tomography/computed tomography using anatomic image to brain atlas nonrigid registration

Brain anatomy variability is a major problem in quantifying functional images in nuclear medicine, in particular relative to aging and neurodegenerative diseases. The aim of this study was to compare affine and elastic model-based methods for magnetic resonance imaging (MRI) to brain atlas registration and to assess their impact on the quantification of cholinergic neurotransmission. Patients with multiple system atrophy (MSA) and age-matched healthy subjects underwent an MRI and a single-photon emission computed tomographic (SPECT) examination using [123I]-iodobenzovesamicol (IBVM). Both affine and elastic methods were compared to register the subjects' MRI with the Montreal Neurological Institute brain atlas. Performance of the registration accuracy was quantitatively assessed and the impact on the IBVM quantification was studied. For both subject groups, elastic registration achieved better quantitative performance compared to the affine model. For patients suffering from neurogenerative disease, this study demonstrates the importance and relevance of MRI to atlas registration in quantification of neuronal integrity. In this context, in comparison with rigid registrations, an elastic model-based registration provides the best relocation of the brain structures to the atlas for accurately quantifying cholinergic neurotransmission.

Cerebellum involvement in post-stroke mood: a combined ecological and MRI study

This study evaluated a new approach combining magnetic resonance imaging and the experience sampling method in the understanding of post-stroke mood pathophysiology. Findings revealed that emotional cognition after stroke may be related to phenotypic characteristics such as cerebellar volume, thereby suggesting that this combined approach could provide new insights into the pathophysiology of post-stroke mood disorders as well as other forms of comorbidity.

Progressive supranuclear palsy: in vivo SPECT imaging of presynaptic vesicular acetylcholine transporter with [123I]-iodobenzovesamicol

PURPOSE

To evaluate the integrity of brain cholinergic pathways in vivo in patients with progressive supranuclear palsy (PSP) by measuring the vesicular acetylcholine transporter expression at single photon emission computed tomography (SPECT) with [123I]-iodobenzovesamicol.

MATERIALS AND METHODS

All participants provided informed written consent according to institutional human ethics committee guidelines. Ten patients with PSP and 12 healthy volunteers underwent dynamic [123I]-iodobenzovesamicol SPECT and magnetic resonance (MR) imaging. CT and MR images were used to register the dynamic SPECT image to the Montreal Neurologic Institute brain template, which includes the regions of interest of the striatum and the septo-hippocampal, innominato-cortical, and ponto-thalamic cholinergic pathways. For each region of interest, pharmacokinetic modeling of regional time activity curves was used to calculate [123I]-iodobenzovesamicol to vesicular acetylcholine transporter binding potential value, proportional to vesicular acetylcholine transporter expression.

RESULTS

When compared with control participants, patients with PSP had binding potential values that were unchanged in the striatum and septohippocampal pathway, significantly lower in the anterior cingulate cortex (P=.017) in the innominatocortical pathway, and significantly decreased in the thalamus (P=.014) in the pontothalamic cholinergic pathway. In addition, binding potential values in the thalamus were positively correlated with those in the pedunculopontine nucleus (ρ=0.81, P<.004) and binding potential values in both the thalamus (ρ=-0.88, P<.001) and pedunculopontine nucleus (ρ=-0.80, P<.010) were inversely correlated with disease duration.

CONCLUSION

Cholinergic pathways were differentially affected in the PSP group, with a significant alteration of pontothalamic pathways that increased with disease progression at both cell body and terminal levels, while the innominatocortical pathway was only mildly affected, and the septohippocampal pathway and the striatum were both preserved.

Paradoxical effect of severe dietary restriction on Long-Evans rat life span

It has been firmly established that the longevity of 20- to 60%-calorie-restricted rodents, with malnutrition (essential nutrients deficiency) being avoided, is increased when compared to ad libitum fed rodents. However, the effects on life span of severe dietary restriction (i. e. malnutrition), with limited weight loss, remained unknown. The purpose of this 4-year study was to investigate the effects on longevity of a severe form of dietary restriction, with limited and controlled weight loss. To this end, a group of male Long-Evans rats severely dietary restricted (SDR group), with a weight loss throughout the experiment<or=25% of their weight before the onset of the experiment at 9 weeks of age, was compared to a control group of rats 30- to 40%-calorie-restricted (C group). Our results show that a severe dietary restriction, excessive weight loss being prevented, paradoxically increased rat longevity by nearly 50%. The life span increase observed in our SDR rats is in accordance with some other studies investigating the effects on longevity of partial essential nutrients deficiencies (tryptophan, methionine, and fat, for example).

Photoluminescence and Sims Studies of Hydrogen Passivation of Mg-Doped P-Type Gallium Nitride

The effects of hydrogen passivation in MOCVD grown Mg doped p-type GaN were studied using low temperature (5K) photoluminescence (PL) and secondary-ion-mass spectroscopy (SIMS). GaN films with different Mg doping level were annealed at 700° C in N2 ambient with different annealing times. The SIMS results indicate that the hydrogen concentration increases with increasing Mg doping level in the as-grown Mg:GaN film. After 20 minutes of annealing, most of the hydrogen escapes from the film. The 3.455 eV PL peak before annealing and the 3.446 eV peak after annealing found in the Mg doped samples were attributed to the exciton bound to the Mg-H complex and to the Mg acceptor, respectively. The shift of the bound exciton peak to higher energy (3.465 eV) in the lightly doped sample is due to an effective n-type compensation associated with an annealing-induced increase in the nitrogen vacancies. In heavily doped Mg:GaN, the decreases in the integrated PL intensity after 700° C annealing may be associated with the hydrogen depassivation of nonradiative recombination centers in the film. The increase of PL intensity in the lightly doped sample after annealing is attributed to the reduction of defects by the annealing process.

Using Layered Manufacturing to Create Textured Microstructures in Si3N4 Ceramics

In recent years, seeding has been shown to be an effective method to create textured microstructures in Si 3N4, Al2O3 and PZT ceramics. The objective of this research is to create anisotropic and textured Si3N4 parts using the Fused Deposition of Ceramics (FDC) process. This technique is currently being developed to fabricate high performance structural Si 3N4 based components. In order to create the textured microstructures, rod-like β-Si3N4 seed particles are introduced into the FDC feedstock filaments. In this study, anisometric β-Si3N4 seeds were introduced into the starting α-Si3N4 powder (Honeywell's AS800 grade) at a 10 vol.% loading. The effects of the seeds (aspect ratio ∼4) on the viscosity and resultant microstructure were evaluated using capillary rheology, scanning electron microscopy, coefficient of thermal expansion (CTE) measurements, and x-ray diffraction. It is observed that the seeds do align during filament extrusion and a significant texture has been detected by x-ray diffraction and CTE measurements in FDC feedstock filaments and sintered FDC parts.

Low brain allopregnanolone levels mediate flattened circadian activity associated with memory impairments in aged rats

BACKGROUND

Sleep and cognitive impairments are two of the most prevalent neuropsychiatric disorders in the aged population. Age-related memory dysfunctions can result from alterations in sleep/wake circadian rhythm. However, the underlying mechanism of these alterations is unknown. Here, we demonstrate the role of alterations in brain steroid levels in age-related sleep-dependent memory impairment in rats.

METHODS

Sleep/wake circadian activity and spatial memory performance were evaluated in adult, middle-aged, and aged rats, and steroid levels were measured in brain structures involved in mediating sleep-dependent memory processes using gas chromatography/mass spectrometry. The causal relationship between circadian activity and allopregnanolone levels was assessed using an inhibitor of allopregnanolone synthesis (indomethacin).

RESULTS

Similar to observations in humans, a subpopulation of middle-aged and aged rats show flattened amplitude of circadian activity associated with impaired spatial long-term memory performance. Sleep-dependent memory dysfunction was associated with a low level of allopregnanolone in the hypothalamus, pedunculopontine nucleus, and ventral striatum. Inhibition of allopregnanolone synthesis in young rats decreased allopregnanolone in the hypothalamus and produced flattened amplitude of circadian activity similar to aged rats.

CONCLUSIONS

These findings identify brainstem and basal forebrain allopregnanolone as an essential endogenous substrate involved in mediating sleep-dependent memory function in young and aged rats. Allopregnanolone may play a critical role in preserving individuals from age-induced alterations in sleep and memory processes and may represent a novel target for attenuating age-related declines in sleep and memory.

Chronic exposure of rats to noise: Relationship between long-term memory deficits and slow wave sleep disturbances

Noise is now recognized as a serious health problem in our modern societies. Although its deleterious and direct effects on cognitive tasks (long-term memory, mental arithmetic activity, visual tasks, etc.) are clearly admitted, no studies have determined a delayed indirect effect of noise on cognitive processes. Furthermore, the link between sleep disturbances related to environmental noise (EN) exposure and these indirect deteriorations of human performances has never been demonstrated. This could be due to inappropriate evaluation of sleep as well as to uncontrolled and confounding factors such as sex, age, and also inter-individual vulnerability. Based on a recently validated animal model [Rabat A, Bouyer JJ, Aran JM, Le Moal M, Mayo W. Chronic exposure to an environmental noise permanently disturbs sleep in rats: inter-individual vulnerability. Brain Res 2005;1059:72-82], aims of the present study were (i) to determine long-term memory (LTM) deficits following a chronic exposure to EN and (ii) to link these behavioral problems to sleep disturbances related to EN. For this purpose in a first experiment, LTM performances were evaluated before and following 9 days of EN. Results show LTM deficits following a chronic exposure to EN with inter-individual vulnerability. Vulnerability profile was related to the psychobiological profile of rats. Results of the second experiment show LTM deficits correlated to both debt of slow wave sleep (SWS) and to daily decrease of SWS bout duration. Our results demonstrate that chronic exposure to noise indirectly disturbs LTM possibly through SWS disturbances and suggest a possible role of the stress hormonal axis in these biological effects of noise.

Neurosteroids and cholinergic systems: implications for sleep and cognitive processes and potential role of age-related changes

RATIONALE

The neurosteroids pregnenolone sulfate (PREGS), dehydroepiandrosterone sulfate (DHEAS) and allopregnanolone (3alpha,5alpha THPROG) have been implicated as powerful modulators of memory processes and sleep states in young and aged subjects with memory impairment. As these processes depend on the integrity of cholinergic systems, a specific effect of neurosteroids on these systems may account for their effects on sleep and memory.

OBJECTIVE

To review the evidence for a specific and differential effect of neurosteroids on cholinergic systems.

METHODS

We carried out keyword searches in "Medline" to identify articles concerning (1) the effects of neurosteroids on cholinergic systems, sleep and memory processes, and (2) changes in neurosteroid concentrations during aging. Few results are available for humans. Most data concerned rodents.

RESULTS

Peripheral and central administrations of PREGS, DHEAS, and 3alpha,5alpha THPROG modulate the basal forebrain and brainstem projection cholinergic neurons but not striatal cholinergic interneurons. Local administration of neurosteroids to the basal forebrain and brainstem cholinergic neurons alters sleep and memory in rodents. There are a few conflicting reports concerning the effects of aging on neurosteroid concentrations in normal and pathological conditions.

CONCLUSIONS

The specific modulation of basal forebrain and brainstem cholinergic systems by neurosteroids may account for the effects of these compounds on sleep and memory processes. To improve our understanding of the role of neurosteroids in cholinergic systems during normal and pathological aging, we need to determine whether there is specific regionalization of neurosteroids, and we need to investigate the relationship between neurosteroid concentrations in cholinergic nuclei and age-related sleep and memory impairments.

Motherhood-induced memory improvement persists across lifespan in rats but is abolished by a gestational stress

Motherhood modifies the biology and behavior of the female, a process which prepares the mother's cognitive systems that are needed for nurturance. It has recently been shown that motherhood enhances hippocampal-mediated spatial learning and synaptic plasticity. Deleterious and long-term effects of a stress experienced during gestation have been demonstrated on progeny. Surprisingly little is known about the effect of such stress on mothers. Here, we investigated the effect of gestational stress on the adaptive changes due to motherhood. Female rats were mated and stressed during the last week of gestation. Two weeks after weaning, they were submitted to behavioral tests or electrophysiological study. A group of females were then kept for 16 months after motherhood experience to study the long-term effect of gestational stress and motherhood on memory when they were 22 months old. We confirm that a single motherhood experience selectively increases hippocampal-mediated spatial memory during the entire lifespan of female rats and protects them from age-associated memory impairments. However, we demonstrate that a stressful experience during gestation totally abolishes the positive effects of motherhood both on spatial memory and on hippocampal synaptic plasticity (long-term potentiation). Environmental factors that induce biological vulnerability have negative effects even for fundamental biological behaviors.

Chronic exposure to an environmental noise permanently disturbs sleep in rats: Inter-individual vulnerability

Chronic exposure to an environmental noise (EN) induces sleep disturbances. However, discrepancies exist in the literature since many contradictory conclusions have been reported. These disagreements are largely due to inappropriate evaluation of sleep and also to uncontrolled and confounding factors such as sex, age and also inter-individual vulnerability. Based on a recently validated animal model, aims of the present study were (i) to determine the effects of a chronic exposure to EN on sleep and (ii) to evaluate the inter-individual vulnerability of sleep to EN. For this purpose, rats were exposed during 9 days to EN. Results show that a chronic exposure to EN restricts continually amounts of slow wave sleep (SWS) and paradoxical sleep (PS) and fragments these two sleep stages with no habituation effect. Results also evidence the existence of subpopulations of rats that are either resistant or vulnerable to these deleterious effects of EN on sleep and especially on SWS amounts, bouts number and bout duration. Furthermore, importance of SWS debt and daily decrease of SWS bout duration are correlated to each others and both correlate to the amplitude of the locomotor reactivity to novelty, a behavioral measure of reactivity to stress. This last result suggests that this psychobiological profile of subjects, known to induce profound differences in neural and endocrine systems, could be responsible for their SWS vulnerability under a chronic EN exposure.

New insights into the role of neuroactive steroids in cognitive aging

The aim of this article is to describe neuroactive steroid research that has been focused on their physiological role in cognitive aging, an attractive new field in experimental gerontology. Neuroactive steroids have been recently proposed as biomarkers of cognitive aging, however, their specific functions have not yet been fully established. For instance, data emerging from human and animal studies suggest a complex relationship between neuroactive steroids and/or metabolites and cognitive processes during aging. Thus, a better knowledge of neuroactive steroid brain distribution and function could broaden our understanding of their physiological roles and lead to novel and more effective treatments for the management of age-related brain disorders. To this end, newly developed sensitive, specific, and accurate mass spectrometry assays may allow the quantification of neuroactive steroids in discrete brain regions and greatly contribute to unravel their role in age-related cognitive deficits.

Pregnenolone sulfate enhances neurogenesis and PSA-NCAM in young and aged hippocampus

Age-dependent cognitive impairments have been correlated with functional and structural modifications in the hippocampal formation. In particular, the brain endogenous steroid pregnenolone-sulfate (Preg-S) is a cognitive enhancer whose hippocampal levels have been linked physiologically to cognitive performance in senescent animals. However, the mechanism of its actions remains unknown. Because neurogenesis is sensitive to hormonal influences, we examined the effect of Preg-S on neurogenesis, a novel form of plasticity, in young and old rats. We demonstrate that in vivo infusion of Preg-S stimulates neurogenesis and the expression of the polysialylated forms of NCAM, PSA-NCAM, in the dentate gyrus of 3- and 20-month-old rats. These influences on hippocampal plasticity are mediated by the modulation of the gamma-aminobutyric acid receptor complex A (GABA(A)) receptors present on hippocampal neuroblasts. In vitro, Preg-S stimulates the division of adult-derived spheres suggesting a direct influence on progenitors. These data provide evidence that neurosteroids represent one of the local secreted signals controlling hippocampal neurogenesis. Thus, therapies which stimulate neurosteroidogenesis could preserve hippocampal plasticity and prevent the appearance of age-related cognitive disturbances.

Deleterious effects of an environmental noise on sleep and contribution of its physical components in a rat model

Sleep disturbances induced by environmental noise (EN) exposure are now well admitted. However, many contradictory conclusions and discrepancies have been reported, resulting from uncontrolled human factors or the use of artificial noises (pure tone). Thus, the development of an animal model appears to be a useful strategy for determining whether EN is deleterious to sleep. The aims of this study were: (i) to confirm the effects of noise on sleep in a rat model; and (ii) to determine the most deleterious physical component of noise regarding sleep structure. For this purpose, rats were exposed during 24 h either to EN or to artificial broad-band noises [either continuous broad-band noise (CBBN) or intermittent broad-band noise (IBBN)]. All the noises decrease both slow wave sleep (SWS) and paradoxical sleep (PS) amounts during the first hours of exposure. However, CBBN acts indirectly on PS through a reduction of SWS bout duration, whereas IBBN and EN disturb directly and more strongly both SWS and PS. Finally, EN fragments SWS and decreases PS amount during the dark period, whereas IBBN only fragments PS. These results demonstrate the validity and suitability of a rodent model for studying the effects of noise on sleep and definitively show that sleep is disturbed by EN exposure. Two physical factors seem to be implicated: the intermittency and the frequency spectrum of the noise events, which both induce long-lasting sleep disturbances. An additive effect of frequency spectrum to intermittency tends to abolish all possible adaptations to EN exposure. Since sleep is involved in cognitive processes, such disturbances could lead to cognitive deficits.

Sleep-wake states and cortical synchronization control by pregnenolone sulfate into the pedunculopontine nucleus

Cholinergic neurons of the pedunculopontine tegmentum nucleus (PPT) are crucial for initiation and maintenance of electroencephalographic (EEG) desynchronization states like paradoxical sleep and wakefulness. These neurons are regulated by classical neurotransmitter systems from the pontomesencephalic reticular formation and basal ganglia. In addition to this regulation, PPT neuron activity could be modulated by endogenous neurosteroids and particularly by pregnenolone sulfate (PREG-S) because synthesis enzymes of this neurosteroid are present in this area and peripheral administrations of PREG-S affect sleep-wakefulness states. To test this hypothesis, we studied the effects of different doses of PREG-S infusion into the PPT on sleep-wakefulness states in rats. Our results show dose-dependent effects of PREG-S on sleep-wakefulness states. Low concentration of PREG-S (5 ng) increased the amount of paradoxical sleep without any modification of slow wave sleep and wakefulness. High level of PREG-S (10 and 20 ng) increased paradoxical sleep and slow wave sleep together with an increase of delta power and a decrease of theta power during wakefulness. Dependent on the doses used, PREG-S thus can promote paradoxical sleep alone or the global propensity to fall asleep, impairing the quality of wakefulness. These results unveil a new regulation pathway for PPT neurons and strengthen the role of PREG-S in sleep-wakefulness regulation.

Spatial memory performances of aged rats in the water maze predict levels of hippocampal neurogenesis

Neurogenesis occurs within the adult dentate gyrus of the hippocampal formation and it has been proposed that the newly born neurons, recruited into the preexistent neuronal circuits, might be involved in hippocampal-dependent learning processes. Age-dependent spatial memory impairments have been related to an alteration in hippocampal plasticity. The aim of the current study was to examine whether cognitive functions in aged rats are quantitatively correlated with hippocampal neurogenesis. To this end, we took advantage of the existence of spontaneous individual differences observed in aged subjects in a hippocampal-dependent task, the water maze. We expected that the spatial memory capabilities of aged rats would be related to the levels of hippocampal neurogenesis. Old rats were trained in the water maze, and, 3 weeks after training, rats were injected with 5-bromo-2'-deoxyuridine (BrdUrd, 50 or 150 mg/kg) to label dividing cells. Cell proliferation was examined one day after the last BrdUrd injection, whereas cell survival and differentiation were determined 3 weeks later. It is shown that a quantitative relationship exists between learning and the number of newly generated neurons. Animals with preserved spatial memory, i.e., the aged-unimpaired rats, exhibited a higher level of cell proliferation and a higher number of new neurons in comparison with rats with spatial memory impairments, i.e., the aged-impaired rats. In conclusion, the extent of memory dysfunction in aged rats is quantitatively related to the hippocampal neurogenesis. These data reinforce the assumption that neurogenesis is involved in memory processes and aged-related cognitive alterations.

Steroid hormones and neurosteroids in normal and pathological aging of the nervous system

Without medical progress, dementing diseases such as Alzheimer's disease will become one of the main causes of disability. Preventing or delaying them has thus become a real challenge for biomedical research. Steroids offer interesting therapeutical opportunities for promoting successful aging because of their pleiotropic effects in the nervous system: they regulate main neurotransmitter systems, promote the viability of neurons, play an important role in myelination and influence cognitive processes, in particular learning and memory. Preclinical research has provided evidence that the normally aging nervous system maintains some capacity for regeneration and that age-dependent changes in the nervous system and cognitive dysfunctions can be reversed to some extent by the administration of steroids. The aging nervous system also remains sensitive to the neuroprotective effects of steroids. In contrast to the large number of studies documenting beneficial effects of steroids on the nervous system in young and aged animals, the results from hormone replacement studies in the elderly are so far not conclusive. There is also little information concerning changes of steroid levels in the aging human brain. As steroids present in nervous tissues originate from the endocrine glands (steroid hormones) and from local synthesis (neurosteroids), changes in blood levels of steroids with age do not necessarily reflect changes in their brain levels. There is indeed strong evidence that neurosteroids are also synthesized in human brain and peripheral nerves. The development of a very sensitive and precise method for the analysis of steroids by gas chromatography/mass spectrometry (GC/MS) offers new possibilities for the study of neurosteroids. The concentrations of a range of neurosteroids have recently been measured in various brain regions of aged Alzheimer's disease patients and aged non-demented controls by GC/MS, providing reference values. In Alzheimer's patients, there was a general trend toward lower levels of neurosteroids in different brain regions, and neurosteroid levels were negatively correlated with two biochemical markers of Alzheimer's disease, the phosphorylated tau protein and the beta-amyloid peptides. The metabolism of dehydroepiandrosterone has also been analyzed for the first time in the aging brain from Alzheimer patients and non-demented controls. The conversion of dehydroepiandrosterone to Delta5-androstene-3beta,17beta-diol and to 7alpha-OH-dehydroepiandrosterone occurred in frontal cortex, hippocampus, amygdala, cerebellum and striatum of both Alzheimer's patients and controls. The formation of these metabolites within distinct brain regions negatively correlated with the density of beta-amyloid deposits.

Individual differences in cognitive aging: implication of pregnenolone sulfate

In humans and animals, individual differences in aging of cognitive functions are classically reported. Some old individuals exhibit performances similar to those of young subjects while others are severely impaired. In senescent animals, we have previously demonstrated a significant correlation between the cognitive performance and the cerebral concentration of a neurosteroid, the pregnenolone sulfate (PREG-S). Neurotransmitter systems modulated by this neurosteroid were unknown until our recent report of an enhancement of acetylcholine (ACh) release in basolateral amygdala, cortex and hippocampus induced by intracerebroventricular (i.c.v.) or intracerebral administrations of PREG-S. Central ACh neurotransmission is known to be involved in the regulation of memory processes and is affected in normal aging and severely altered in human neurodegenerative pathologies like Alzheimer's disease. In the central nervous system, ACh neurotransmission is also involved in the modulation of sleep-wakefulness cycle, and particularly the paradoxical sleep (PS). Relationships between paradoxical sleep and memory are documented in the literature in old animals in which the spatial memory performance positively correlates with the basal amounts of paradoxical sleep. PREG-S infused at the level of ACh cell bodies (nucleus basalis magnocellularis, NBM, or pedunculopontine nucleus, PPT) increases paradoxical sleep in young animals.Finally, aging related cognitive dysfunctions, particularly those observed in Alzheimer's disease, have also been related to alterations of mechanisms underlying cerebral plasticity. Amongst these mechanisms, neurogenesis has been extensively studied recently. Our data demonstrate that PREG-S central infusions dramatically increase neurogenesis, this effect could be related to the negative modulator properties of this steroid at the GABA(A) receptor level. Taken together these data suggest that neurosteroids can influence cognitive processes, particularly in senescent subjects, through a modulation of ACh neurotransmission associated with paradoxical sleep modifications; furthermore, our recent data suggest a critical role for neurosteroids in the modulation of cerebral plasticity, mainly on hippocampal neurogenesis.

The effect of education on cognitive performances and its implication for the constitution of the cognitive reserve

Some studies have suggested that people with a high educational level have a lower risk of developing dementia compared to people with a low educational level. This protective effect of education has been explained by the constitution of a cognitive reserve which might delay the cognitive and functional expression of neurodegenerative illnesses. The aim of this study is, on the one hand, to evaluate the impact of education on cognitive functioning, which is thought to support the cognitive reserve capacity, and on the other, to determine the extent to which cognitive functioning is affected by other explanatory variables. The analysis was conducted on 1022 individuals without physical or neurological disorders in the Personnes Ages Quid study. These participants were aged 66 and over and had completed a neuropsychological battery. The effect of some demographic and socioeconomic variables on cognitive performance was also analyzed. Multivariate analysis showed a significant effect of education on most neuropsychological performances, independently of the other variables, and more particularly, in the high-attention-demanding tests. A principal component analysis demonstrated that education specifically increases 2 cognitive components: controlled processes and conceptualization ability. More-over, mental stimulation occurring after the education years, such as high-complex-activity occupations, seems to increase the controlled component. All these results suggest that the effect of education on cognitive reserve may be explained by an in-crease in controlled processes and conceptualization abilities. These 2 cognitive components might delay the clinical expression of neurodegenerative illnesses by maintaining global cognitive efficiency. Of these 2 components, controlled processes were also influenced by high attention-demanding occupations.

Neuroactive steroids: new biomarkers of cognitive aging

Intensive studies in animals established that neuroactive steroids display neuronal actions and influence behavioral functions. We describe here investigations on the role of neuroactive steroids in learning and memory processes during aging and suggest their role as biomarkers of cognitive aging. Our work demonstrated the role of the steroid pregnenolone (PREG) sulfate as a factor underlying an individual's age-related cognitive decline in animals. As new perspectives of research we argue that knowing whether neuroactive steroids exist as endogenous neuromodulators and modulate physiologically behavioral functions is essential. To this end, a new approach using the sensitive, specific, and accurate quantitative determination of neuroactive steroids by mass spectrometry seems to have potential for examining the role of each steroid in discrete brain areas in learning and memory alterations, as observed during aging.

The neurosteroid pregnenolone sulfate infused into the medial septum nucleus increases hippocampal acetylcholine and spatial memory in rats

The effects of an infusion of the neurosteroid pregnenolone sulfate into the medial septum on acetylcholine release in the hippocampus and on spatial memory were evaluated in two experiments. Results show that pregnenolone sulfate enhanced acetylcholine release by more than 50% of baseline and improved recognition memory of a familiar environment. Therefore, our results suggest that the septo-hippocampal pathway could be involved in the promnesic properties of this neurosteroid.

The neurosteroid allopregnanolone increases dopamine release and dopaminergic response to morphine in the rat nucleus accumbens

Neurosteroids are a subclass of steroids that can be synthesized in the central nervous system independently from peripheral sources. Clinical studies in humans have associated these hormones with depression and postpartum mood disorders. In rodents, allopregnanolone (AlloP) has been shown to have anxiolytic and rewarding properties. These observations suggest that neurosteroids could interact with mood and motivation. However, the possible neural substrates of these effects remain unknown. In this report, we have studied the action of AlloP on the activity of the mesencephalic dopaminergic (DA) projection to the nucleus accumbens, which is considered one of the biological substrates of motivation and reward. This study was conducted by measuring extracellular concentrations of dopamine (DA) in the nucleus accumbens by means of microdialysis in freely moving rats. We studied both the direct effect of AlloP and the influence of this hormone on the DA response to an injection of morphine. AlloP dose-dependently increased the release of DA in the nucleus accumbens. Furthermore, this hormone doubled the DA response to morphine. These effects were observed for AlloP doses of 50 and 100 pmol injected intracerebroventricularly. These results suggest that the stimulatory effect of AlloP on DA could mediate some of the behavioural effects of neurosteroids and, in particular, the interaction of these hormones with mood and motivation.

Individual vulnerability to substance abuse and affective disorders: role of early environmental influences

One of the most important questions raised by modern psychiatry and experimental psychopathology is the origin of mental diseases. More concisely, clinical and experimental neurosciences are increasingly concerned with the factors that render one individual more vulnerable than another to a given pathological outcome. Animal models are now available to understand the sources of individual differences for specific phenotypes prone to behavioral disadaptations. Over the last 10 years we have explored the consequences of environmental perinatal manipulations in the rat. We have shown that prenatal stress is at the origin of a wide range of physiological and behavioral aberrances such as alterations in the activity of the hormonal stress axis, increased vulnerability to drug of abuse, emotional liability, cognitive impairments and predisposition to pathological aging. Taken together, these abnormalities define a bio-behavioral syndrome. Furthermore, the cognitive disabilities observed in prenatally-stressed rats were recently related to an alteration of neurogenesis in the dentate gyrus, thus confirming the impact of early life events on brain morphology. A second model (handling model) has also been developed in which pups are briefly separated from their mothers during early postnatal life. In contrast with prenatally-stressed animals, handled rats exhibited a reduced emotion response when confronted with novel situations and were protected against age-induced impairments of both the hormonal stress axis and cognitive functions. Taken together, the results of these investigations show that the bio-behavioral phenotype that characterizes each individual is strongly linked to the nature and timing of perinatal experience. Furthermore, data collected in prenatally-stressed animals indicate that this model could be used profitably to understand the etiology and pathophysiology of affective disorders.

The effect of restraint stress on paradoxical sleep is influenced by the circadian cycle

It is well known that the physiological impact imposed by events or behaviors displayed during the waking period determines the way organisms sleep. Among the situations known to affect sleep both in its duration and quality, stress has been widely studied and it is now admitted that its effects on sleep architecture depend on several factors specific to the stressor or the individual itself. Although numerous reports have highlighted the prominent role of the circadian cycle in the physiological, endocrine and behavioral consequences of restraint stress, a possible circadian influence in the effects of stress on the sleep-wake cycle has never been studied. Thus the present study was designed to compare the effects on sleep of a 1 h-lasting restraint stress applied at light onset to those observed after the same stressor was applied at light offset. We report that in both conditions stress induced a marked paradoxical sleep increase, whereas wakefulness displayed a moderate decrease and slow wave sleep a moderate augmentation. Although the effects of stress at lights on were of similar magnitude than those of stress at lights off, important differences in the sleep rebound latencies were observed: whatever the time of day the stress was applied, its effects on sleep always occurred during the dark period. This result thus shows that restraint stress could be efficiently used to study the interaction between the circadian and homeostatic components of sleep regulation.

Neurosteroids in learning and memory processes

The discovery that neurosteroids could be synthesized de novo in the brain independent from the periphery and display neuronal actions led to great enthusiasm for the study of their physiological role. Pharmacological studies suggest that neurosteroids may be involved in several physiological processes, such as learning and memory. This chapter summarizes the effects of the administration of neurosteroids on learning and memory capabilities in rodents and in models of amnesia. We address the central mechanisms involved in mediating the modulation of learning and memory processes by neurosteroids. In this regard, the neurosteroid-modulated neurotransmitter systems, such as gamma-aminobutyric acid type A, N-methyl-D-aspartate, and cholinergic and sigma opioid systems, appear to be potential targets for the rapid memory alteration actions of neurosteroids. Moreover, given that some neurosteroids affect neuronal plasticity, this neuronal change could be involved in the long-term modulation of learning and memory processes. To understand the role of endogeneous neurosteroids in learning and memory processes, we present some physiological studies in rodents and humans. However, the latter do not successfully prove a role of endogenous neurosteroids in age-related memory impairments. Finally, we discuss the relative implication of a given neurosteroid vs its metabolites. For this question, a new approach using the quantitative determination of traces of neurosteroids by mass spectrometry seems to have potential for examining the role of each neurosteroid in discrete brain areas in learning and memory alterations, as observed during aging.

Anti-S-nitrosocysteine antibodies are a predictive marker for demyelination in experimental autoimmune encephalomyelitis: implications for multiple sclerosis

Multiple sclerosis (MS) is characterized by inflammation within the CNS. This inflammatory response is associated with production of nitric oxide (NO) and NO-related species that nitrosylate thiols. We postulated that MS patients would exhibit an antibody (Ab) response directed against proteins containing S-nitrosocysteine (SNO-cysteine) and showed that anti-NO-cysteine Abs of the IgM isotype are in fact present in the sera of some MS patients (Boullerne et al., 1995). We report here the presence of a seemingly identical Ab response directed against SNO-cysteine in an acute model of MS, experimental autoimmune encephalomyelitis (EAE) induced in Lewis rats with the 68-84 peptide of guinea pig myelin basic protein (MBP(68-84)). Serum levels of anti-SNO-cysteine Abs peaked 1 week before the onset of clinical signs and well before the appearance of anti-MBP(68-84) Abs. The anti-SNO-cysteine Ab peak titer correlated with the extent of subsequent CNS demyelination, suggesting a link between Ab level and CNS lesion formation. In relapsing-remitting MS patients, we found elevated anti-SNO-cysteine Ab at times of relapse and normal values in most patients judged to be in remission. Two-thirds of patients with secondary progressive MS had elevated anti-SNO-cysteine Ab levels, including those receiving interferon beta-1b. The data show that a rise in circulating anti-SNO-cysteine Ab levels precedes onset of EAE. Anti-SNO-cysteine Abs are also elevated at times of MS attacks and in progressive disease, suggesting a possible role for these Abs, measurable in blood, as a biological marker for clinical activity.

Role of pregnenolone, dehydroepiandrosterone and their sulfate esters on learning and memory in cognitive aging

Aging is a general process of functional decline which involves in particular a decline of cognitive abilities. However, the severity of this decline differs from one subject to another and inter-individual differences have been reported in humans and animals. These differences are of great interest especially as concerns investigation of the neurobiological factors involved in cognitive aging. Intensive pharmacological studies suggest that neurosteroids, which are steroids synthesized in the brain in an independent manner from peripheral steroid sources, could be involved in learning and memory processes. This review summarizes data in animals and humans in favor of a role of neurosteroids in cognitive aging. Studies in animals demonstrated that the neurosteroids pregnenolone (PREG) and dehydroepiandrosterone (DHEA), as sulfate derivatives (PREGS and DHEAS, respectively), display memory-enhancing properties in aged rodents. Moreover, it was recently shown that memory performance was correlated with PREGS levels in the hippocampus of 24-month-old rats. Human studies, however, have reported contradictory results. First, improvement of learning and memory dysfunction was found after DHEA administration to individuals with low DHEAS levels, but other studies failed to detect significant cognitive effects after DHEA administration. Second, cognitive dysfunctions have been associated with low DHEAS levels, high DHEAS levels, or high DHEA levels; while in other studies, no relationship was found. As future research perspectives, we propose the use of new methods of quantification of neurosteroids as a useful tool for understanding their respective role in improving learning and memory impairments associated with normal aging and/or with pathological aging, such as Alzheimer's disease.

Pregnenolone sulfate and aging of cognitive functions: behavioral, neurochemical, and morphological investigations

Neurosteroids are a subclass of steroids that can be synthesized in the central nervous system independently of peripheral sources. Several neurosteroids influence cognitive functions. Indeed, in senescent animals we have previously demonstrated a significant correlation between the cerebral concentration of pregnenolone sulfate (PREG-S) and cognitive performance. Indeed, rats with memory impairments exhibited low PREG-S concentrations compared to animals with correct memory performance. Furthermore, these memory deficits can be reversed by intracerebral infusions of PREG-S. Neurotransmitter systems modulated by this neurosteroid were unknown until our recent report of an enhancement of acetylcholine (ACh) release in basolateral amygdala, cortex, and hippocampus induced by central administrations of PREG-S. Central ACh neurotransmission is involved in the regulation of memory processes and is affected in normal aging and in human neurodegenerative pathologies like Alzheimer's disease. ACh neurotransmission is also involved in the modulation of sleep-wakefulness cycle and relationships between paradoxical sleep and memory are well documented in the literature. PREG-S infused at the level of ACh cell bodies induces a dramatic increase of paradoxical sleep in young animals. Cognitive dysfunctions, particularly those observed in Alzheimer's disease, have also been related to alterations of cerebral plasticity. Among these mechanisms, neurogenesis has been recently studied. Preliminary data suggest that PREG-S central infusions dramatically increase neurogenesis. Taken together these data suggest that PREG-S can influence cognitive processes, particularly in senescent subjects, through a modulation of ACh neurotransmission associated with paradoxical sleep modifications; furthermore our recent data suggest a role for neurosteroids in the modulation of hippocampal neurogenesis.

[Early experience, stressful dysregulation of the hormonal axis and age-related vulnerability to neurodegenerative processus: a longitudinal study in the rat]

The deleterious effects of particular environmental situations have been suspected to augment the repercussions of cerebral injuries leading to increased vulnerability during ageing. The relationship between the hormones of the hypothalamo-pituitary-adrenal axis, mainly glucocorticosteroids, and cerebral structures like the hippocampus has been the subject of intense investigation in the recent years. Data suggest that long-term elevated blood levels of these hormones can induce neuronal alterations leading to cognitive dysfunction. This hypothesis has been tested with relevant animal models of normal/abnormal ageing. The models are based on the existence of considerable inter-individual differences in the degree of age-related cognitive impairments observed in rodents. Results show that long-term glucocorticosteroid exposure induces cerebral changes related to the action of these hormones on their central receptors. Experimental data are in accordance with clinical investigations suggesting that hormonal changes, and chronic life events, could be considered as a predictive factor of future cognitive dysfunction.

Long term neurodevelopmental and behavioral effects of perinatal life events in rats

Modern neurosciences are now able to open new avenues concerning an experimental approach to clinical neurosciences and psychiatry. Detection and prediction of potential vulnerabilities such as behavioral disturbances and neurodegenerative diseases, are urgent tasks leading to prevention that must be encouraged in parallel to the enormous efforts displayed for treatments. Besides possible genetic origins of diseases, environmental factors are now coming under scrutiny, and especially deleterious and challenging life events and stress occurring during prenatal and postnatal critical periods may orient brain functions towards deleterious developments. The hypothesis that will be examined is that early events might be at the origin of pathological transformations and symptoms after long periods of apparent normal abilities and behavioral homeostasis. We used models of prenatal stress and postnatal manipulations such as cross-fostering. It will be demonstrated that such events induce long-term changes, cognitive and emotional modifications appearing first, when offspring are adults, followed by cognitive defects later in life. Increased sensitivity of the hypothalamic pituitary-adrenal axis (HPA), the endocrine system controlling the secretion of stress hormones (corticoids), appears to be a major element of pathogenesis. HPA axis dysfunction appears very early after birth (3 days) and lasts for months. Cumulative exposure to high levels of hormones seems to be detrimental for some brain regions, especially the hippocampus and major neurotransmitter systems such as dopamine neurons. We evidenced that neuronal modifications in hippocampal region are correlated with behavioral and cognitive defects, relating environment, stress in early life, hormonal changes, long-term neuropathological processes and impaired cognition in aging. Moreover appears in offspring, when adults, a proneness to engage in drug dependence. These data emphasize the need to consider early environmental life events as etiological factors for delayed neuropsychiatric disturbances, neurodegenerative defects included. Moreover, they strengthen the interest for a longitudinal approach to promote experimental psychopathology.

PSA-NCAM: an important regulator of hippocampal plasticity

The Neural Cell Adhesion Molecule (NCAM) serves as a temporally and spatially regulated modulator of a variety of cell-cell interactions. This review summarizes recent results of studies aimed at understanding its regulation of expression and biological function, thereby focussing on its polysialylated isoforms (PSA-NCAM). The detailed analysis of the expression of PSA and NCAM in the hippocampal mossy fiber system and the morphological consequences of PSA-NCAM deficiency in mice support the notion that the levels of expression of NCAM are important not only for the regulation and maintenance of structural changes, such as migration, axonal growth and fasciculation, but also for activity-induced plasticity. There is evidence that PSA-NCAM can specifically contribute to a presynaptic form of plasticity, namely long-term potentiation at hippocampal mossy fiber synapses. This is consistent with previous observations that NCAM-deficient mice show deficits in spatial learning and exploratory behavior. Furthermore, our data points to an important role of the hypothalamic-pituitary-adrenal axis, which is the principle adaptive response of the organism to environmental challenges, in the control of PSA-NCAM expression in the hippocampal formation. In particular, we evidence an inhibitory influence of corticosterone on PSA-NCAM expression.

Pregnenolone sulfate increases hippocampal acetylcholine release and spatial recognition

The pregnenolone sulfate is a neurosteroid with promnesic properties. Recently, a correlation between endogenous levels of pregnenolone sulfate in the hippocampus and performance in a spatial memory task has been reported in aged rats. Cholinergic transmission is known to modulate memory processes and to be altered with age. In the present experiment we investigated the effect of increasing doses of pregnenolone sulfate on hippocampal acetylcholine release. Our results show that intracerebroventricular administrations of this neurosteroid induced a dose-dependent increase in acetylcholine release. Administration of 12 and 48 nmol of pregnenolone sulfate induced a short lasting (20 min) enhancement of acetylcholine output with a maximum around 120% over baseline and the administration of 96 and 192 nmol doses induced a long-lasting (80 min) increase that peaked around 300% over baseline. In a second experiment we have observed that the 12 nmol dose enhanced spatial memory performance, whereas the 192 nmol dose was inefficient. These results are consistent with previous work suggesting that, a modest increase in acetylcholine release facilitates memory processes, while elevation beyond an optimal level is ineffective. Nevertheless, neurosteroids may be of value for reinforcing depressed cholinergic transmission in certain age-related memory disorders.

[Corticosteroid hormones and the brain]

The anatomical and functional links between the hormone stress axis and the cortico-limbic brain regions which integrate emotion and motivation are well documented. It is important, considering the consequences of stress on the brain, to take into account the regulatory buffer capacities of the personality-cognitive processes. Another point of interest is evaluation of the long term effects of repeated life events on chronic environmental pressures which induce brain negative feedback defects and, subsequently, insidious cellular changes in regions such as the hippocampus that lead to memory or adaptive impairments. An example is provided by perinatal stress that induces, later in life, both hormonal and cognitive deleterious changes.