Ageing-related decline in adenosine A1 receptor binding in the rat brain: An autoradiographic study

The stress of losing sleep: Sex-specific neurobiological outcomes

Sleep is a vital and evolutionarily conserved process, critical to daily functioning and homeostatic balance. Losing sleep is inherently stressful and leads to numerous detrimental physiological outcomes. Despite sleep disturbances affecting everyone, women and female rodents are often excluded or underrepresented in clinical and pre-clinical studies. Advancing our understanding of the role of biological sex in the responses to sleep loss stands to greatly improve our ability to understand and treat health consequences of insufficient sleep. As such, this review discusses sex differences in response to sleep deprivation, with a focus on the sympathetic nervous system stress response and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We review sex differences in several stress-related consequences of sleep loss, including inflammation, learning and memory deficits, and mood related changes. Focusing on women's health, we discuss the effects of sleep deprivation during the peripartum period. In closing, we present neurobiological mechanisms, including the contribution of sex hormones, orexins, circadian timing systems, and astrocytic neuromodulation, that may underlie potential sex differences in sleep deprivation responses.

Purinergic signaling in cognitive impairment and neuropsychiatric symptoms of Alzheimer's disease

About 10 million new cases of dementia develop worldwide each year, of which up to 70% are attributable to Alzheimer's disease (AD). In addition to the widely known symptoms of memory loss and cognitive impairment, AD patients frequently develop non-cognitive symptoms, referred to as behavioral and psychological symptoms of dementia (BPSDs). Sleep disorders are often associated with AD, but mood alterations, notably depression and apathy, comprise the most frequent class of BPSDs. BPSDs negatively affect the lives of AD patients and their caregivers, and have a significant impact on public health systems and the economy. Because treatments currently available for AD are not disease-modifying and mainly aim to ameliorate some of the cognitive symptoms, elucidating the mechanisms underlying mood alterations and other BPSDs in AD may reveal novel avenues for progress in AD therapy. Purinergic signaling is implicated in the pathophysiology of several central nervous system (CNS) disorders, such as AD, depression and sleep disorders. Here, we review recent findings indicating that purinergic receptors, mainly the A₁, A_2A, and P2X7 subtypes, are associated with the development/progression of AD. Current evidence suggests that targeting purinergic signaling may represent a promising therapeutic approach in AD and related conditions. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Role of Adenosine in Epilepsy and Seizures

Adenosine is an endogenous anticonvulsant and neuroprotectant of the brain. Seizure activity produces large quantities of adenosine, and it is this seizure-induced adenosine surge that normally stops a seizure. However, within the context of epilepsy, adenosine plays a wide spectrum of different roles. It not only controls seizures (ictogenesis), but also plays a major role in processes that turn a normal brain into an epileptic brain (epileptogenesis). It is involved in the control of abnormal synaptic plasticity and neurodegeneration and plays a major role in the expression of comorbid symptoms and complications of epilepsy, such as sudden unexpected death in epilepsy (SUDEP). Given the important role of adenosine in epilepsy, therapeutic strategies are in development with the goal to utilize adenosine augmentation not only for the suppression of seizures but also for disease modification and epilepsy prevention, as well as strategies to block adenosine A_2A receptor overfunction associated with neurodegeneration. This review provides a comprehensive overview of the role of adenosine in epilepsy.

PET Imaging of Adenosine Receptors in Diseases

Adenosine receptors (ARs) are a class of purinergic G-protein-coupled receptors (GPCRs). Extracellular adenosine is a pivotal regulation molecule that adjusts physiological function through the interaction with four ARs: A1R, A2AR, A2BR, and A3R. Alterations of ARs function and expression have been studied in neurological diseases (epilepsy, Alzheimer's disease, and Parkinson's disease), cardiovascular diseases, cancer, and inflammation and autoimmune diseases. A series of Positron Emission Tomography (PET) probes for imaging ARs have been developed. The PET imaging probes have provided valuable information for diagnosis and therapy of diseases related to alterations of ARs expression. This review presents a concise overview of various ARs-targeted radioligands for PET imaging in diseases. The most recent advances in PET imaging studies by using ARs-targeted probes are briefly summarized.

Gi/o-Protein Coupled Receptors in the Aging Brain

Cells translate extracellular signals to regulate processes such as differentiation, metabolism and proliferation, via transmembranar receptors. G protein-coupled receptors (GPCRs) belong to the largest family of transmembrane receptors, with over 800 members in the human species. Given the variety of key physiological functions regulated by GPCRs, these are main targets of existing drugs. During normal aging, alterations in the expression and activity of GPCRs have been observed. The central nervous system (CNS) is particularly affected by these alterations, which results in decreased brain functions, impaired neuroregeneration, and increased vulnerability to neuropathologies, such as Alzheimer's and Parkinson diseases. GPCRs signal via heterotrimeric G proteins, such as G_o, the most abundant heterotrimeric G protein in CNS. We here review age-induced effects of GPCR signaling via the G_i/o subfamily at the CNS. During the aging process, a reduction in protein density is observed for almost half of the G_i/o-coupled GPCRs, particularly in age-vulnerable regions such as the frontal cortex, hippocampus, substantia nigra and striatum. G_i/o levels also tend to decrease with aging, particularly in regions such as the frontal cortex. Alterations in the expression and activity of GPCRs and coupled G proteins result from altered proteostasis, peroxidation of membranar lipids and age-associated neuronal degeneration and death, and have impact on aging hallmarks and age-related neuropathologies. Further, due to oligomerization of GPCRs at the membrane and their cooperative signaling, down-regulation of a specific G_i/o-coupled GPCR may affect signaling and drug targeting of other types/subtypes of GPCRs with which it dimerizes. G_i/o-coupled GPCRs receptorsomes are thus the focus of more effective therapeutic drugs aiming to prevent or revert the decline in brain functions and increased risk of neuropathologies at advanced ages.

Functional coupling between adenosine A1 receptors and G-proteins in rat and postmortem human brain membranes determined with conventional guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTPγS) binding or [35S]GTPγS/immunoprecipitation assay

Adenosine signaling plays a complex role in multiple physiological processes in the brain, and its dysfunction has been implicated in pathophysiology of neuropsychiatric diseases such as schizophrenia and affective disorders. In the present study, the coupling between adenosine A₁ receptor and G-protein was assessed by means of two [³⁵S]GTPγS binding assays, i.e., conventional filtration method and [³⁵S]GTPγS binding/immunoprecipitation in rat and human brain membranes. The latter method provides information about adenosine A₁ receptor-mediated Gα_i-3 activation in rat as well as human brain membranes. On the other hand, adenosine-stimulated [³⁵S]GTPγS binding determined with conventional assay derives from functional activation of Gα_i/o proteins (not restricted only to Gα_i-3) coupled to adenosine A₁ receptors. The determination of adenosine concentrations in the samples used in the present study indicates the possibility that the assay mixture under our experimental conditions contains residual endogenous adenosine at nanomolar concentrations, which was also suggested by the results on the effects of adenosine receptor antagonists on basal [³⁵S]GTPγS binding level. The effects of adenosine deaminase (ADA) on basal binding also support the presence of adenosine. Nevertheless, the varied patterns of ADA discouraged us from adding ADA into assay medium routinely. The concentration-dependent increases elicited by adenosine were determined in 40 subjects without any neuropsychiatric disorders. The increases in %E_max values determined by conventional assay according to aging and postmortem delay should be taken into account in future studies focusing on the effects of psychiatric disorders on adenosine A₁ receptor/G-protein interaction in postmortem human brain tissue.

Age-Related Decrease in Male Extra-Striatal Adenosine A1 Receptors Measured 11C-MPDX PET

Adenosine A₁ receptors (A₁Rs) are widely distributed throughout the entire human brain, while adenosine A_2A receptors (A_2ARs) are present in dopamine-rich areas of the brain, such as the basal ganglia. A past study using autoradiography reported a reduced binding ability of A₁R in the striatum of old rats. We developed positron emission tomography (PET) ligands for mapping the adenosine receptors and we successfully visualized the A₁Rs using 8-dicyclopropylmethyl-1-¹¹C-methyl-3-propylxanthine (¹¹C-MPDX). We previously reported that the density of A₁Rs decreased with age in the human striatum, although we could not observe an age-related change in A_2ARs. The aim of this study was to investigate the age-related change of the density of A₁Rs in the thalamus and cerebral cortices of healthy participants using ¹¹C-MPDX PET. We recruited eight young (22.0 ± 1.7 years) and nine elderly healthy male volunteers (65.7 ± 8.0 years). A dynamic series of decay-corrected PET scans was performed for 60 min starting with the injection of ¹¹C-MPDX. We placed the circular regions of interest of 10 mm in diameter in ¹¹C-MPDX PET images. The values for the binding potential (BP_ND) of ¹¹C-MPDX in the thalamus, and frontal, temporal, occipital, and parietal cortices were calculated using a graphical analysis, wherein the reference region was the cerebellum. BP_ND of ¹¹C-MPDX was significantly lower in elderly participants than young participants in the thalamus, and frontal, temporal, occipital, and parietal cortices. In the human brain, we could observe the age-related decrease in the distribution of A₁Rs.

Sex differences in age-related changes in the sleep-wake cycle

Age-related changes in sleep and circadian regulation occur as early as the middle years of life. Research also suggests that sleep and circadian rhythms are regulated differently between women and men. However, does sleep and circadian rhythms regulation age similarly in men and women? In this review, we present the mechanisms underlying age-related differences in sleep and the current state of knowledge on how they interact with sex. We also address how testosterone, estrogens, and progesterone fluctuations across adulthood interact with sleep and circadian regulation. Finally, we will propose research avenues to unravel the mechanisms underlying sex differences in age-related effects on sleep.

Purinergic signalling during development and ageing

Extracellular purines and pyrimidines play major roles during embryogenesis, organogenesis, postnatal development and ageing in vertebrates, including humans. Pluripotent stem cells can differentiate into three primary germ layers of the embryo but may also be involved in plasticity and repair of the adult brain. These cells express the molecular components necessary for purinergic signalling, and their developmental fates can be manipulated via this signalling pathway. Functional P1, P2Y and P2X receptor subtypes and ectonucleotidases are involved in the development of different organ systems, including heart, blood vessels, skeletal muscle, urinary bladder, central and peripheral neurons, retina, inner ear, gut, lung and vas deferens. The importance of purinergic signalling in the ageing process is suggested by changes in expression of A1 and A2 receptors in old rat brains and reduction of P2X receptor expression in ageing mouse brain. By contrast, in the periphery, increases in expression of P2X3 and P2X4 receptors are seen in bladder and pancreas.

Sleep is more sensitive to high doses of caffeine in the middle years of life

During the middle years of life, sleep becomes more fragile and its sensitivity to psychostimulants may increase. This study evaluated the effects of 200 mg and 400 mg of caffeine on sleep in young and middle-aged adults. The sleep of 22 young (23.5 ± 1.9 years) and 24 middle-aged (51.7 ± 11.5 years) adults was recorded using polysomnography in two conditions (placebo and caffeine) in a double-blind cross-over design. Compared to placebo, caffeine increased sleep latency, shortened total sleep duration and reduced sleep efficiency. At the higher dose, these effects were more pronounced in middle-aged than in young adults. Furthermore, the higher dose of caffeine increased absolute stage 1 sleep in young adults, whereas it decreased absolute stage 2 sleep in middle-aged adults. Caffeine also induced dose-dependent increases in relative stage 1 sleep and reductions in absolute and relative slow wave sleep and absolute rapid eye movement sleep in both age groups. There was no dose- or age-related modulation of the effects of caffeine on quantified electroencephalographic measures. These results indicate that, compared to young adults, middle-aged adults are generally more sensitive to the effects of a high dose of caffeine on sleep quantity and quality.

Adenosine A(2A) receptor blockade reverts hippocampal stress-induced deficits and restores corticosterone circadian oscillation

Maternal separation (MS) is an early life stress model that induces permanent changes in the central nervous system, impairing hippocampal long-term potentiation (LTP) and spatial working memory. There are compelling evidences for a role of hippocampal adenosine A(2A) receptors in stress-induced modifications related to cognition, thus opening a potential window for therapeutic intervention. Here, we submitted rats to MS and evaluated the long-lasting molecular, electrophysiological and behavioral impairments in adulthood. We then assessed the therapeutic potential of KW6002, a blocker of A(2A) receptors, in stress-impaired animals. We report that the blockade of A(2A) receptors was efficient in reverting the behavior, electrophysiological and morphological impairments induced by MS. In addition, this effect is associated with restoration of the hypothalamic-pituitary-adrenal axis (HPA-axis) activity, as both the plasma corticosterone levels and hippocampal glucocorticoid receptor expression pattern returned to physiological-like status after the treatment. These results reveal the involvement of A(2A) receptors in the stress-associated impairments and directly in the stress response system by showing that the dysfunction of the HPA-axis as well as the long-lasting synaptic and behavioral effects of MS can be reverted by targeting adenosine A(2A) receptors. These findings provide a novel evidence for the use of adenosine A(2A) receptor antagonists as potential therapy against psychopathologies.

Differential effects of age on human striatal adenosine A₁ and A(2A) receptors

The aim of this study was to investigate the effect of age on the distribution of adenosine A₁ receptors (A₁Rs) and adenosine A(2A) receptors (A(2A)Rs) in the striatum of healthy subjects using PET imaging with 8-dicyclopropylmethyl-1-[¹¹C]methyl-3-propylxanthine ([¹¹C]MPDX) and [7-methyl-¹¹C]-(E)-8-(3,4,5-trimethoxystyryl)-1,3,7-trimethylxanthine ([¹¹C]TMSX), respectively. We recruited 8 young (22.0 ± 1.7 years) and 10 elderly (65.4 ± 7.6 years) volunteers to undergo [¹¹C]MPDX PET scanning, and 11 young (22.7 ± 2.7 years) and six elderly (60.7 ± 8.5 years) volunteers to undergo [¹¹C]TMSX PET scanning. A dynamic series of decay-corrected PET scans was performed for 60 min following injection of [¹¹C]MPDX or [¹¹C]TMSX. We calculated the binding potential (BP(ND) ) of [¹¹C]MPDX and distribution volume ratio (DVR) of [¹¹C]TMSX in the striatum. The BP(ND) of [¹¹C]MPDX was significantly lower in elderly than in young subjects, both in the putamen and head of the caudate nucleus. The BP(ND) was negatively correlated with age in both the putamen and the head of the caudate nucleus. However, no difference was found between the DVR of [¹¹C]TMSX in the striata of young and elderly subjects, nor was there a correlation between age and the DVR of [¹¹C]TMSX. The effect of age on the distribution of A₁Rs in the human striatum described herein is similar to previous reports of age-related decreases in dopamine D₁ and D₂ receptors. Unlike A₁Rs, however, this study suggests that the distribution of A(2A) Rs does not change with age.

Reduced neurobehavioral impairment from sleep deprivation in older adults: contribution of adenosinergic mechanisms

A night without sleep is followed by enhanced sleepiness, increased low-frequency activity in the waking EEG, and reduced vigilant attention. The magnitude of these changes is highly variable among healthy individuals. Findings in young men of low and high subjective caffeine sensitivity suggest that adenosinergic mechanisms contribute to inter-individual differences in sleep deprivation-induced changes in EEG theta activity, as well as optimal performance on the psychomotor vigilance task (PVT). In comparison to young subjects, healthy adults of older age typically feel less sleepy after sleep deprivation, and show fewer response lapses, and faster reaction times on the PVT, especially in the morning after the night without sleep. We hypothesized that age-related changes in adenosine signal transmission underlie reduced vulnerability to sleep deprivation in older individuals. To test this hypothesis, the combined effects of prolonged wakefulness and the adenosine receptor antagonist, caffeine, on an antero-posterior power gradient in EEG theta activity and PVT performance were analyzed in healthy older and caffeine-insensitive and -sensitive young men. The results show that age-related differences in sleep loss-induced changes in brain rhythmic activity and neurobehavioral functions are mirrored in young individuals of low and high sensitivity to the stimulant effects of caffeine. Moreover, the effects of sleep deprivation and caffeine on regional theta power and vigilant attention are inversely correlated across older and young age groups. Genetic variants of the adenosine A_2A receptor gene contribute to individual differences in neurobehavioral performance in rested and sleep deprived state, and modulate the actions of caffeine in wakefulness and sleep. Based upon this evidence, we propose that age-related differences in A_2A receptor-mediated signal transduction could be involved in age-related changes in the vulnerability to acute sleep deprivation.

Age-related changes in sleep in inbred mice are genotype dependent

Aging produces major changes in sleep structure and intensity which might be linked to cognitive impairment in the elderly. In this study, the genetic contribution to age-related changes in sleep was assessed in three inbred mouse strains of various ages. Baseline sleep and the response to 6 hours sleep deprivation (SD) achieved by gentle handling were quantified in young, middle-aged, and older male mice using electroencephalography. Total sleep time initially increased with age but then decreased in the oldest group mainly due to changes in sleep duration during the active phase. The effect of age on electroencephalographic (EEG) delta power depends on genotype and sleep pressure level with SD increasing the age-related differences. The strong effect of age upon the spectral profile of the different behavioral states was modulated by genetic background. Overall, our results suggest that sleep pressure can modulate the effect of age, that most sleep variables do not monotonically change with age in contrast to previous reports in humans and other species, and that genetic factors have a major impact on the aging processes affecting sleep.

The wake-promoting effects of hypocretin-1 are attenuated in old rats

Disruption of sleep is a frequent complaint among elderly humans and is also evident in aged laboratory rodents. The neurobiological bases of age-related sleep/wake disruption are unknown. Given the critical role of the hypocretins in sleep/wake regulation, we sought to determine whether the wake-promoting effect of hypocretin changes with age in Wistar rats, a strain in which age-related changes in both sleep and hypocretin signaling have been reported. Intracerebroventricular infusions of hypocretin-1 (10 and 30 μg) significantly increased wake time relative to vehicle in both young (3 mos) and old (25 mos) Wistar rats. However, the magnitude and duration of the wake-promoting effects were attenuated with age. An increase of parameters associated with homeostatic sleep recovery after sleep deprivation, including non-rapid eye movement (NR) sleep time, NR delta power, the ratio of NR to rapid eye movement (REM) sleep, and NR consolidation, occurred subsequent to Hcrt-induced waking in young but not old rats. ICV infusions of hypocretin-2 (10 and 30 μg) produced fewer effects in both young and old rats. These data demonstrate that activation of a major sleep/wake regulatory pathway is attenuated in old rats.

Adenosine receptors and neurological disease: neuroprotection and neurodegeneration

Adenosine receptors modulate neuronal and synaptic function in a range of ways that may make them relevant to the occurrence, development and treatment of brain ischemic damage and degenerative disorders. A(1) adenosine receptors tend to suppress neural activity by a predominantly presynaptic action, while A(2A) adenosine receptors are more likely to promote transmitter release and postsynaptic depolarization. A variety of interactions have also been described in which adenosine A(1) or A(2) adenosine receptors can modify cellular responses to conventional neurotransmitters or receptor agonists such as glutamate, NMDA, nitric oxide and P2 purine receptors. Part of the role of adenosine receptors seems to be in the regulation of inflammatory processes that often occur in the aftermath of a major insult or disease process. All of the adenosine receptors can modulate the release of cytokines such as interleukins and tumor necrosis factor-alpha from immune-competent leukocytes and glia. When examined directly as modifiers of brain damage, A(1) adenosine receptor (AR) agonists, A(2A)AR agonists and antagonists, as well as A(3)AR antagonists, can protect against a range of insults, both in vitro and in vivo. Intriguingly, acute and chronic treatments with these ligands can often produce diametrically opposite effects on damage outcome, probably resulting from adaptational changes in receptor number or properties. In some cases molecular approaches have identified the involvement of ERK and GSK-3beta pathways in the protection from damage. Much evidence argues for a role of adenosine receptors in neurological disease. Receptor densities are altered in patients with Alzheimer's disease, while many studies have demonstrated effects of adenosine and its antagonists on synaptic plasticity in vitro, or on learning adequacy in vivo. The combined effects of adenosine on neuronal viability and inflammatory processes have also led to considerations of their roles in Lesch-Nyhan syndrome, Creutzfeldt-Jakob disease, Huntington's disease and multiple sclerosis, as well as the brain damage associated with stroke. In addition to the potential pathological relevance of adenosine receptors, there are earnest attempts in progress to generate ligands that will target adenosine receptors as therapeutic agents to treat some of these disorders.

Nitric oxide mediated recovery sleep is attenuated with aging

Nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) in the cholinergic basal forebrain (BF) during sleep deprivation (SD) is implicated in adenosine (AD) release and induction of recovery sleep. Aging is associated with impairments in sleep homeostasis, such as decrease in non-rapid eye movement sleep (NREM) intensity following SD. We hypothesized that age related changes in sleep homeostasis may be induced by impairments in NO-mediated sleep induction. To test this hypothesis we measured levels of NO and iNOS in the BF during SD as well as recovery sleep after SD and NO-donor (DETA/NO) infusion into the BF in three age groups of rats (young, 4 months; middle-aged, 14 months; old, 24 months). We found that in aged rats as compared to young (1) recovery NREM sleep intensity was significantly decreased, (2) neither iNOS nor NO increased in the BF during SD, and (3) DETA/NO infusion failed to induce sleep. Together, these results support our hypothesis that aging impairs the mechanism through which NO in the BF induces sleep.

Is homeostatic sleep regulation under low sleep pressure modified by age?

STUDY OBJECTIVES

We have previously shown that healthy older volunteers react with an attenuated frontal predominance of sleep electroen-cephalogram (EEG) delta activity in response to high sleep pressure. Here, we investigated age-related changes in homeostatic sleep regulation under low sleep pressure conditions, with respect to regional EEG differences and their dynamics.

DESIGN

Analysis of the sleep EEG during an 8-hour baseline night, during a 40-hour multiple nap protocol (150 minutes of wakefulness and 75 minutes of sleep) and during the following 8-hour recovery night under constant posture conditions.

SETTING

Centre for Chronobiology, Psychiatric University Clinics, Basel, Switzerland

PARTICIPANTS

Sixteen young (20-31 years) and 15 older (57-74 years) healthy volunteers

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

All-night EEG spectra revealed an increase in spindle activity (13-15.25 Hz) for both age groups, but only in the young did we find a significant decrease of delta activity (0.5-1.25 Hz) in response to low sleep pressure conditions, predominantly in occipital brain regions. However, delta activity during the first non-rapid eye movement (NREM) sleep episode was equally reduced in both age groups. This response lasted significantly longer in the young (across the first 2 NREM sleep episodes) than in the older participants (only the first NREM sleep episode).

CONCLUSION

The initial EEG delta response to low sleep pressure was similar in healthy older and young participants. Therefore, age-related sleep deteriorations cannot solely be attributed to alterations in the homeostatic sleep-regulatory system. It is, rather, the interplay of circadian and homeostatic factors of sleep regulation, which is changed with aging.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Test–retest stability of cerebral A1 adenosine receptor quantification using [18F]CPFPX and PET

PURPOSE

The goal of the present study was to evaluate the reproducibility of cerebral A1 adenosine receptor (A1AR) quantification using [18F]CPFPX and PET in a test-retest design.

METHODS

Eleven healthy volunteers were studied twice. Eight brain regions ranging from high to low receptor binding were examined. [18F]CPFPX was injected as a bolus with subsequent infusion over 120 min. Various outcome parameters were compared based on either metabolite-corrected venous blood sampling [e.g. apparent equilibrium total distribution volume (DVt')] or a reference region [ratio of specific to non-specific distribution volume (BP2)].

RESULTS

Test-retest variability was low in the outcome measure BP2 (on average 5.9%) and moderate in DVt' (on average 13.2%). Regarding reproducibility, the outcome parameter BP2 showed an intra-class correlation coefficient (ICC) of 0.94 +/- 0.1. For DVt' the between-subject coefficient of variation (%CV) was similar to the within-subject %CV (around 10%), resulting in a poor ICC of 0.06 +/- 0.2.

CONCLUSION

Our results suggest that quantification of [18F]CPFPX imaging is reproducible and reliable for PET studies of the cerebral A1AR. Among the outcome parameters the non-invasive measures were of superior test-retest stability over the invasive.

Challenging sleep in aging: the effects of 200 mg of caffeine during the evening in young and middle-aged moderate caffeine consumers

The aim of this study was to evaluate the effects of a 200-mg administration of caffeine on polysomnographic sleep variables and quantitative sleep electroencephalography (EEG) in 12 young (20-30 years) and 12 middle-aged (40-60 years) moderate caffeine consumers (one to three cups of coffee per day). All subjects were submitted to both a caffeine (200 mg) and placebo (lactose) condition in a double-blind cross-over design. The conditions were separated by 1 week. Compared with the placebo condition, the evening ingestion of caffeine lengthened sleep latency, reduced sleep efficiency, and decreased sleep duration and amount of stage 2 sleep in both age groups. Caffeine also reduced spectral power in delta frequencies in frontal, central and parietal brain areas, but not in prefrontal (PF) and occipital regions. Moreover, caffeine increased spectral power in beta frequencies in frontal and central brain areas in both age groups. A suppression of spectral power in the PF area in low delta frequencies (0.5-1.00 Hz) and a rise in spectral power in the parietal region in high alpha (10.00-12.00 Hz) and beta frequencies (17.00-21.00, 23.00-25.00, 27.00-29.00 Hz) occurred solely in middle-aged subjects. No such changes were noticeable in young subjects. Generally, caffeine produced similar effects in young and middle-aged subjects. Only a few frequency bins showed more effects of caffeine in middle-aged subjects compared with young subjects. Furthermore, sleep EEG results do not entirely support the hypothesis that caffeine fully mimics the effects of a reduction of homeostatic sleep propensity when following a normal sleep-wake cycle.

Effect of aging on cerebral A1 adenosine receptors: A [18F]CPFPX PET study in humans

Cerebral A(1) adenosine receptors (A(1)AR) fulfill important neuromodulatory and homeostatic functions. The present study examines possible age-related A(1)AR changes in living humans by positron emission tomography (PET) and the A(1)AR ligand [(18)F]CPFPX. Thirty-six healthy volunteers aged 22-74 years were included. The apparent binding potential (BP'2) of [(18)F]CPFPX in various cerebral regions was calculated non-invasively using the cerebellum as reference region. In addition, the total distribution volume (DV't) was assessed in 10 subjects undergoing arterial blood sampling. There was no significant association between regional DV't and age, gender, caffeine consumption or sleep duration. BP'2 showed a significant age-dependent decrease in all regions except cingulate gyrus (p=0.062). The BP'2 decline ranged from -17% (striatum) to -34% (postcentral gyrus), the average cortical decline being -23%. There was no significant effect of gender, caffeine consumption and sleep duration on BP'2. In line with in vitro animal studies, the present in vivo PET study detected an age-dependent A(1)AR loss in humans that may be of pathophysiological importance in various neurological diseases associated with aging. Because of the discrepant results of the invasive (DV't) and the non-invasive (BP'2) analyses the present study needs further validation.