Locus Coeruleus Magnetic Resonance Imaging in Neurological Diseases

Locus coeruleus MRI contrast, cerebral perfusion, and plasma Alzheimer's disease biomarkers in older adults

The locus coeruleus (LC) is among the first brain structures impacted by Alzheimer's disease (AD), and noradrenergic denervation may contribute to early neurovascular dysfunction in AD. Mechanistic links between the LC and cerebral perfusion have been demonstrated in rodents, but there have been no similar studies in aging humans. Community-dwelling older adults with no history of stroke or dementia (N=66) underwent structural (T1-MPRAGE; T1-FSE) and perfusion (resting pCASL) MRI. Plasma AD biomarkers levels were evaluated for Aβ42/40 ratio (n=56) and pTau181 (n=60). Higher rostral LC structural MRI contrast was associated with lower perfusion in entorhinal and limbic regions but higher perfusion in lateral and medial orbitofrontal cortices. Relationships between LC structure and regional cerebral perfusion were attenuated in older adults with higher plasma pTau levels and lower plasma Aβ42/40 ratios. Previously unstudied links between LC structure and cerebral perfusion are detectible in older adults using MRI and are attenuated in those showing greater AD pathophysiologic change, suggesting an uncoupling of LC-cerebral perfusion relationships in older adults with aggregating AD-related pathophysiology.

The Neuroanatomy of Induced Pluripotent Stem Cells: In Vitro Models of Subcortical Nuclei in Neurodegenerative Disorders

Neuromodulatory subcortical systems (NSSs) are monoaminergic and cholinergic neuronal groups that are markedly and precociously involved in the pathogenesis of many neurodegenerative disorders (NDDs), including Parkinson's and Alzheimer's diseases. In humans, although many tools have been developed to infer information on these nuclei, encompassing neuroimaging and neurophysiological methods, a detailed and specific direct evaluation of their cellular features in vivo has been difficult to obtain until recent years. The development of induced pluripotent stem cell (iPSC) models has allowed research to deeply delve into the cellular and molecular biology of NSS neurons. In fact, iPSCs can be produced easily and non-invasively from patients' fibroblasts or circulating blood monocytes, by de-differentiating those cells using specific protocols, and then be re-differentiated towards neural phenotypes, which may reproduce the specific features of the correspondent brain neurons (including NSS ones) from the same patient. In this review, we summarized findings obtained in the field of NDDs using iPSCs, with the aim to understand how reliably these might represent in vitro models of NSS. We found that most of the current literature in the field of iPSCs and NSSs in NDDs has focused on midbrain dopaminergic neurons in Parkinson's disease, providing interesting results on cellular pathophysiology and even leading to the first human autologous transplantation. Differentiation protocols for noradrenergic, cholinergic, and serotoninergic neurons have also been recently defined and published. Thus, it might be expected that in the near future, this approach could extend to other NSSs and other NDDs.

Locus coeruleus integrity and neuropsychiatric symptoms in a cohort of early- and late-onset Alzheimer's disease

INTRODUCTION

Early-onset Alzheimer's disease (EOAD) shows a higher burden of neuropsychiatric symptoms than late-onset Alzheimer's disease (LOAD). We aim to determine the differences in the severity of neuropsychiatric symptoms and locus coeruleus (LC) integrity between EOAD and LOAD accounting for disease stage.

METHODS

One hundred four subjects with AD diagnosis and 32 healthy controls were included. Participants underwent magnetic resonance imaging (MRI) to measure LC integrity, measures of noradrenaline levels in cerebrospinal fluid (CSF) and Neuropsychiatric Inventory (NPI). We analyzed LC-noradrenaline measurements and clinical and Alzheimer's disease (AD) biomarker associations.

RESULTS

EOAD showed higher NPI scores, lower LC integrity, and similar levels of CSF noradrenaline compared to LOAD. Notably, EOAD exhibited lower LC integrity independently of disease stage. LC integrity negatively correlated with neuropsychiatric symptoms. Noradrenaline levels were increased in AD correlating with AD biomarkers.

DISCUSSION

Decreased LC integrity negatively contributes to neuropsychiatric symptoms. The higher LC degeneration in EOAD compared to LOAD could explain the more severe neuropsychiatric symptoms in EOAD.

HIGHLIGHTS

LC degeneration is greater in early-onset AD (EOAD) compared to late-onset AD. Tau-derived LC degeneration drives a higher severity of neuropsychiatric symptoms. EOAD harbors a more profound selective vulnerability of the LC system. LC degeneration is associated with an increase of cerebrospinal fluid noradrenaline levels in AD.

Fully Automated MRI-based Analysis of the Locus Coeruleus in Aging and Alzheimer's Disease Dementia using ELSI-Net

INTRODUCTION

The Locus Coeruleus (LC) is linked to the development and pathophysiology of neurodegenerative diseases such as Alzheimer's Disease (AD). Magnetic Resonance Imaging based LC features have shown potential to assess LC integrity in vivo.

METHODS

We present a Deep Learning based LC segmentation and feature extraction method: ELSI-Net and apply it to healthy aging and AD dementia datasets. Agreement to expert raters and previously published LC atlases were assessed. We aimed to reproduce previously reported differences in LC integrity in aging and AD dementia and correlate extracted features to cerebrospinal fluid (CSF) biomarkers of AD pathology.

RESULTS

ELSI-Net demonstrated high agreement to expert raters and published atlases. Previously reported group differences in LC integrity were detected and correlations to CSF biomarkers were found.

DISCUSSION

Although we found excellent performance, further evaluations on more diverse datasets from clinical cohorts are required for a conclusive assessment of ELSI-Nets general applicability.

The degeneration of locus coeruleus occurring during Alzheimer's disease clinical progression: a neuroimaging follow-up investigation

The noradrenergic nucleus Locus Coeruleus (LC) is precociously involved in Alzheimer's Disease (AD) pathology, and its degeneration progresses during the course of the disease. Using Magnetic Resonance Imaging (MRI), researchers showed also in vivo in patients the disruption of LC, which can be observed both in Mild Cognitively Impaired individuals and AD demented patients. In this study, we report the results of a follow-up neuroradiological assessment, in which we evaluated the LC degeneration overtime in a group of cognitively impaired patients, submitted to MRI both at baseline and at the end of a 2.5-year follow-up. We found that a progressive LC disruption can be observed also in vivo, involving the entire nucleus and associated with clinical diagnosis. Our findings parallel neuropathological ones, which showed a continuous increase of neuronal death and volumetric atrophy within the LC with the progression of Braak's stages for neurofibrillary pathology. This supports the reliability of MRI as a tool for exploring the integrity of the central noradrenergic system in neurodegenerative disorders.

Automatic geometry-based estimation of the locus coeruleus region on T1-weighted magnetic resonance images

The locus coeruleus (LC) is a key brain structure implicated in cognitive function and neurodegenerative disease. Automatic segmentation of the LC is a crucial step in quantitative non-invasive analysis of the LC in large MRI cohorts. Most publicly available imaging databases for training automatic LC segmentation models take advantage of specialized contrast-enhancing (e.g., neuromelanin-sensitive) MRI. Segmentation models developed with such image contrasts, however, are not readily applicable to existing datasets with conventional MRI sequences. In this work, we evaluate the feasibility of using non-contrast neuroanatomical information to geometrically approximate the LC region from standard 3-Tesla T1-weighted images of 20 subjects from the Human Connectome Project (HCP). We employ this dataset to train and internally/externally evaluate two automatic localization methods, the Expected Label Value and the U-Net. For out-of-sample segmentation, we compare the results with atlas-based segmentation, as well as test the hypothesis that using the phase image as input can improve the robustness. We then apply our trained models to a larger subset of HCP, while exploratorily correlating LC imaging variables and structural connectivity with demographic and clinical data. This report provides an evaluation of computational methods estimating neural structure.

Locus coeruleus features are linked to vagus nerve stimulation response in drug-resistant epilepsy

The locus coeruleus-norepinephrine system is thought to be involved in the clinical effects of vagus nerve stimulation. This system is known to prevent seizure development and induce long-term plastic changes, particularly with the release of norepinephrine in the hippocampus. However, the requisites to become responder to the therapy and the mechanisms of action are still under investigation. Using MRI, we assessed the structural and functional characteristics of the locus coeruleus and microstructural properties of locus coeruleus-hippocampus white matter tracts in patients with drug-resistant epilepsy responding or not to the therapy. Twenty-three drug-resistant epileptic patients with cervical vagus nerve stimulation were recruited for this pilot study, including 13 responders or partial responders and 10 non-responders. A dedicated structural MRI acquisition allowed in vivo localization of the locus coeruleus and computation of its contrast (an accepted marker of LC integrity). Locus coeruleus activity was estimated using functional MRI during an auditory oddball task. Finally, multi-shell diffusion MRI was used to estimate the structural properties of locus coeruleus-hippocampus tracts. These characteristics were compared between responders/partial responders and non-responders and their association with therapy duration was also explored. In patients with a better response to the therapy, trends toward a lower activity and a higher contrast were found in the left medial and right caudal portions of the locus coeruleus, respectively. An increased locus coeruleus contrast, bilaterally over its medial portions, correlated with duration of the treatment. Finally, a higher integrity of locus coeruleus-hippocampus connections was found in patients with a better response to the treatment. These new insights into the neurobiology of vagus nerve stimulation may provide novel markers of the response to the treatment and may reflect neuroplasticity effects occurring in the brain following the implantation.

Microstructural integrity of the locus coeruleus and its tracts reflect noradrenergic degeneration in Alzheimer's disease and Parkinson's disease

BACKGROUND

Degeneration of the locus coeruleus (LC) noradrenergic system contributes to clinical symptoms in Alzheimer's disease (AD) and Parkinson's disease (PD). Diffusion magnetic resonance imaging (MRI) has the potential to evaluate the integrity of the LC noradrenergic system. The aim of the current study was to determine whether the diffusion MRI-measured integrity of the LC and its tracts are sensitive to noradrenergic degeneration in AD and PD.

METHODS

Post-mortem in situ T1-weighted and multi-shell diffusion MRI was performed for 9 AD, 14 PD, and 8 control brain donors. Fractional anisotropy (FA) and mean diffusivity were derived from the LC, and from tracts between the LC and the anterior cingulate cortex, the dorsolateral prefrontal cortex (DLPFC), the primary motor cortex (M1) or the hippocampus. Brain tissue sections of the LC and cortical regions were obtained and immunostained for dopamine-beta hydroxylase (DBH) to quantify noradrenergic cell density and fiber load. Group comparisons and correlations between outcome measures were performed using linear regression and partial correlations.

RESULTS

The AD and PD cases showed loss of LC noradrenergic cells and fibers. In the cortex, the AD cases showed increased DBH + immunoreactivity in the DLPFC compared to PD cases and controls, while PD cases showed reduced DBH + immunoreactivity in the M1 compared to controls. Higher FA within the LC was found for AD, which was correlated with loss of noradrenergic cells and fibers in the LC. Increased FA of the LC-DLPFC tract was correlated with LC noradrenergic fiber loss in the combined AD and control group, whereas the increased FA of the LC-M1 tract was correlated with LC noradrenergic neuronal loss in the combined PD and control group. The tract alterations were not correlated with cortical DBH + immunoreactivity.

CONCLUSIONS

In AD and PD, the diffusion MRI-detected alterations within the LC and its tracts to the DLPFC and the M1 were associated with local noradrenergic neuronal loss within the LC, rather than noradrenergic changes in the cortex.

Neurogenic orthostatic hypotension in Parkinson's disease: is there a role for locus coeruleus magnetic resonance imaging?

Locus coeruleus (LC) is the main noradrenergic nucleus of the brain, and degenerates early in Parkinson's disease (PD). The objective of this study is to test whether degeneration of the LC is associated with orthostatic hypotension (OH) in PD. A total of 22 cognitively intact PD patients and 52 age-matched healthy volunteers underwent 3 T magnetic resonance (MRI) with neuromelanin-sensitive T1-weighted sequences (LC-MRI). For each subject, a template space-based LC-MRI was used to calculate LC signal intensity (LC contrast ratio-LCCR) and the estimated number of voxels (LCVOX) belonging to LC. Then, we compared the LC-MRI parameters in PD patients with OH (PDOH+) versus without OH (PDOH-) (matched for sex, age, and disease duration) using one-way analysis of variance followed by multiple comparison tests. We also tested for correlations between subject's LC-MRI features and orthostatic drop in systolic blood pressure (SBP). PDOH- and PDOH+ did not differ significantly (p > 0.05) based on demographics and clinical characteristics, except for blood pressure measurements and SCOPA-AUT cardiovascular domain (p < 0.05). LCCR and LCVOX measures were significantly lower in PD compared to HC, while no differences were observed between PDOH- and PDOH+. Additionally, no correlation was found between the LC-MRI parameters and the orthostatic drop in SBP or the clinical severity of autonomic symptoms (p > 0.05). Conversely, RBD symptom severity negatively correlated with several LC-MRI parameters. Our results failed to indicate a link between the LC-MRI features and the presence of OH in PD but confirmed a marked alteration of LC signal in PD patients.

Automatic Geometry-based Estimation of the Locus Coeruleus Region on T1-Weighted Magnetic Resonance Images

The locus coeruleus (LC) is a key brain structure implicated in cognitive function and neurodegenerative disease. Automatic segmentation of the LC is a crucial step in quantitative non-invasive analysis of the LC in large MRI cohorts. Most publicly available imaging databases for training automatic LC segmentation models take advantage of specialized contrast-enhancing (e.g., neuromelanin-sensitive) MRI. Segmentation models developed with such image contrasts, however, are not readily applicable to existing datasets with conventional MRI sequences. In this work, we evaluate the feasibility of using non-contrast neuroanatomical information to geometrically approximate the LC region from standard 3-Tesla T1-weighted images of 20 subjects from the Human Connectome Project (HCP). We employ this dataset to train and internally/externally evaluate two automatic localization methods, the Expected Label Value and the U-Net. We also test the hypothesis that using the phase image as input can improve the robustness of out-of-sample segmentation. We then apply our trained models to a larger subset of HCP, while exploratorily correlating LC imaging variables and structural connectivity with demographic and clinical data. This report contributes and provides an evaluation of two computational methods estimating neural structure.

Locus Coeruleus and Noradrenergic Pharmacology in Neurodegenerative Disease

Adrenoceptors (ARs) throughout the brain are stimulated by noradrenaline originating mostly from neurons of the locus coeruleus, a brainstem nucleus that is ostensibly the earliest to show detectable pathology in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. The α1-AR, α2-AR, and β-AR subtypes expressed in target brain regions and on a range of cell populations define the physiological responses to noradrenaline, which includes activation of cognitive function in addition to modulation of neurometabolism, cerebral blood flow, and neuroinflammation. As these heterocellular functions are critical for maintaining brain homeostasis and neuronal health, combating the loss of noradrenergic tone from locus coeruleus degeneration may therefore be an effective treatment for both cognitive symptoms and disease modification in neurodegenerative indications. Two pharmacologic approaches are receiving attention in recent clinical studies: preserving noradrenaline levels (e.g., via reuptake inhibition) and direct activation of target adrenoceptors. Here, we review the expression and role of adrenoceptors in the brain, the preclinical studies which demonstrate that adrenergic stimulation can support cognitive function and cerebral health by reversing the effects of noradrenaline depletion, and the human data provided by pharmacoepidemiologic analyses and clinical trials which together identify adrenoceptors as promising targets for the treatment of neurodegenerative disease.

Imaging Biomarkers in Prodromal and Earliest Phases of Parkinson's Disease

Assessing imaging biomarker in the prodromal and early phases of Parkinson's disease (PD) is of great importance to ensure an early and safe diagnosis. In the last decades, imaging modalities advanced and are now able to assess many different aspects of neurodegeneration in PD. MRI sequences can measure iron content or neuromelanin. Apart from SPECT imaging with Ioflupane, more specific PET tracers to assess degeneration of the dopaminergic system are available. Furthermore, metabolic PET patterns can be used to anticipate a phenoconversion from prodromal PD to manifest PD. In this regard, it is worth mentioning that PET imaging of inflammation will gain significance. Molecular imaging of neurotransmitters like serotonin, noradrenaline and acetylcholine shed more light on non-motor symptoms. Outside of the brain, molecular imaging of the heart and gut is used to measure PD-related degeneration of the autonomous nervous system. Moreover, optical coherence tomography can noninvasively detect degeneration of retinal fibers as a potential biomarker in PD. In this review, we describe these state-of-the-art imaging modalities in early and prodromal PD and point out in how far these techniques can and will be used in the future to pave the way towards a biomarker-based staging of PD.

Exploring the Role of Locus Coeruleus in Alzheimer's Disease: a Comprehensive Update on MRI Studies and Implications

PURPOSE OF REVIEW

Performing a thorough review of magnetic resonance imaging (MRI) studies assessing locus coeruleus (LC) integrity in ageing and Alzheimer's disease (AD), and contextualizing them with current preclinical and neuropathological literature.

RECENT FINDINGS

MRI successfully detected LC alterations in ageing and AD, identifying degenerative phenomena involving this nucleus even in the prodromal stages of the disorder. The degree of LC disruption was also associated with the severity of AD cortical pathology, cognitive and behavioral impairment, and the risk of clinical progression. Locus coeruleus-MRI has proved to be a useful tool to assess the integrity of the central noradrenergic system in vivo in humans. It allowed to test in patients preclinical and experimental hypothesis, thus confirming the specific and marked involvement of the LC in AD and its key pathogenetic role. Locus coeruleus-MRI-related data might represent the theoretical basis on which to start developing noradrenergic drugs to target AD.

Noradrenergic neuromodulation in ageing and disease

The locus coeruleus (LC) is a small brainstem structure located in the lower pons and is the main source of noradrenaline (NA) in the brain. Via its phasic and tonic firing, it modulates cognition and autonomic functions and is involved in the brain's immune response. The extent of degeneration to the LC in healthy ageing remains unclear, however, noradrenergic dysfunction may contribute to the pathogenesis of Alzheimer's (AD) and Parkinson's disease (PD). Despite their differences in progression at later disease stages, the early involvement of the LC may lead to comparable behavioural symptoms such as preclinical sleep problems and neuropsychiatric symptoms as a result of AD and PD pathology. In this review, we draw attention to the mechanisms that underlie LC degeneration in ageing, AD and PD. We aim to motivate future research to investigate how early degeneration of the noradrenergic system may play a pivotal role in the pathogenesis of AD and PD which may also be relevant to other neurodegenerative diseases.

Structural and functional characterization of the locus coeruleus in young and late middle-aged individuals

INTRODUCTION

The brainstem locus coeruleus (LC) influences a broad range of brain processes, including cognition. The so-called LC contrast is an accepted marker of the integrity of the LC that consists of a local hyperintensity on specific Magnetic Resonance Imaging (MRI) structural images. The small size of the LC has, however, rendered its functional characterization difficult in humans, including in aging. A full characterization of the structural and functional characteristics of the LC in healthy young and late middle-aged individuals is needed to determine the potential roles of the LC in different medical conditions. Here, we wanted to determine whether the activation of the LC in a mismatch negativity task changes in aging and whether the LC functional response was associated to the LC contrast.

METHODS

We used Ultra-High Field (UHF) 7-Tesla functional MRI (fMRI) to record brain response during an auditory oddball task in 53 healthy volunteers, including 34 younger (age: 22.15y ± 3.27; 29 women) and 19 late middle-aged (age: 61.05y ± 5.3; 14 women) individuals.

RESULTS

Whole-brain analyses confirmed brain responses in the typical cortical and subcortical regions previously associated with mismatch negativity. When focusing on the brainstem, we found a significant response in the rostral part of the LC probability mask generated based on individual LC images. Although bilateral, the activation was more extensive in the left LC. Individual LC activity was not significantly different between young and late middle-aged individuals. Importantly, while the LC contrast was higher in older individuals, the functional response of the LC was not significantly associated with its contrast.

DISCUSSION

These findings may suggest that the age-related alterations of the LC structural integrity may not be related to changes in its functional response. The results further suggest that LC responses may remain stable in healthy individuals aged 20 to 70.

The Central Noradrenergic System in Neurodevelopmental Disorders: Merging Experimental and Clinical Evidence

The aim of this article is to highlight the potential role of the locus-coeruleus-noradrenergic (LC-NA) system in neurodevelopmental disorders (NdDs). The LC is the main brain noradrenergic nucleus, key in the regulation of arousal, attention, and stress response, and its early maturation and sensitivity to perinatal damage make it an interesting target for translational research. Clinical data shows the involvement of the LC-NA system in several NdDs, suggesting a pathogenetic role in the development of such disorders. In this context, a new neuroimaging tool, LC Magnetic Resonance Imaging (MRI), has been developed to visualize the LC in vivo and assess its integrity, which could be a valuable tool for exploring morphological alterations in NdD in vivo in humans. New animal models may be used to test the contribution of the LC-NA system to the pathogenic pathways of NdD and to evaluate the efficacy of NA-targeting drugs. In this narrative review, we provide an overview of how the LC-NA system may represent a common pathophysiological and pathogenic mechanism in NdD and a reliable target for symptomatic and disease-modifying drugs. Further research is needed to fully understand the interplay between the LC-NA system and NdD.

Lithium engages autophagy for neuroprotection and neuroplasticity: translational evidence for therapy

Here an overview is provided on therapeutic/neuroprotective effects of Lithium (Li⁺) in neurodegenerative and psychiatric disorders focusing on the conspicuous action of Li⁺ through autophagy. The effects on the autophagy machinery remain the key molecular mechanisms to explain the protective effects of Li⁺ for neurodegenerative diseases, offering potential therapeutic strategies for the treatment of neuropsychiatric disorders and emphasizes a crossroad linking autophagy, neurodegenerative disorders, and mood stabilization. Sensitization by psychostimulants points to several mechanisms involved in psychopathology, most also crucial in neurodegenerative disorders. Evidence shows the involvement of autophagy and metabotropic Glutamate receptors-5 (mGluR5) in neurodegeneration due to methamphetamine neurotoxicity as well as in neuroprotection, both in vitro and in vivo models. More recently, Li⁺ was shown to modulate autophagy through its action on mGluR5, thus pointing to an additional way of autophagy engagement by Li⁺ and to a substantial role of mGluR5 in neuroprotection related to neural e neuropsychiatry diseases. We propose Li⁺ engagement of autophagy through the canonical mechanisms of autophagy machinery and through the intermediary of mGluR5.

Application of Neuromelanin MR Imaging in Parkinson Disease

MRI has been used to develop biomarkers for movement disorders such as Parkinson disease (PD) and other neurodegenerative disorders with parkinsonism such as progressive supranuclear palsy and multiple system atrophy. One of these imaging biomarkers is neuromelanin (NM), whose integrity can be assessed from its contrast and volume. NM is found mainly in certain brain stem structures, namely, the substantia nigra pars compacta (SNpc), the ventral tegmental area, and the locus coeruleus. Another major biomarker is brain iron, which often increases in concert with NM degeneration. These biomarkers have the potential to improve diagnostic certainty in differentiating between PD and other neurodegenerative disorders similar to PD, as well as provide a better understanding of pathophysiology. Mapping NM in vivo has clinical importance for gauging the premotor phase of PD when there is a greater than 50% loss of dopaminergic SNpc melanized neurons. As a metal ion chelator, NM can absorb iron. When NM is released from neurons, it deposits iron into the intracellular tissues of the SNpc; the result is iron that can be imaged and measured using quantitative susceptibility mapping. An increase of iron also leads to the disappearance of the nigrosome-1 sign, another neuroimage biomarker for PD. Therefore, mapping NM and iron changes in the SNpc are a practical means for improving early diagnosis of PD and in monitoring disease progression. In this review, we discuss the functions and location of NM, how NM-MRI is performed, the automatic mapping of NM and iron content, how NM-related imaging biomarkers can be used to enhance PD diagnosis and differentiate it from other neurodegenerative disorders, and potential advances in NM imaging methods. With major advances currently evolving for rapid imaging and artificial intelligence, NM-related biomarkers are likely to have increasingly important roles for enhancing diagnostic capabilities in PD. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 2.

Magnetic resonance imaging Locus Coeruleus abnormality in amnestic Mild Cognitive Impairment is associated with future progression to dementia

BACKGROUND AND PURPOSE

Human neuropathological studies indicate that the pontine nucleus Locus Coeruleus (LC) undergoes significant and early degeneration in Alzheimer's disease. This line of evidence alongside experimental data suggests that the LC functional/structural decay may represent a critical factor for Alzheimer's disease pathophysiological and clinical progression. In the present prospective study, we used Magnetic Resonance Imaging (MRI) with LC-sensitive sequence (LC-MRI) to investigate in vivo the LC involvement in Alzheimer's disease progression, and whether specific LC-MRI features at baseline are associated with prognosis and cognitive performance in amnestic Mild Cognitive Impairment.

METHODS

LC-MRI parameters were measured at baseline by a template-based method on 3.0-T magnetic resonance images in 34 patients with Alzheimer's disease dementia, 73 patients with amnestic Mild Cognitive Impairment, and 53 cognitively intact individuals. A thorough neurological and neuropsychological assessment was performed at baseline and 2.5-year follow-up.

RESULTS

In subjects with Mild Cognitive Impairment who converted to dementia (n = 32), the LC intensity and number of LC-related voxels were significantly lower than in cognitively intact individuals, resembling those observed in demented patients. Such a reduction was not detected in Mild Cognitive Impairment individuals, who remained stable at follow-up. In Mild Cognitive Impairment subjects converting to dementia, LC-MRI parameter reduction was maximal in the rostral part of the left nucleus. Structural equation modeling analysis showed that LC-MRI parameters positively correlate with cognitive performance.

CONCLUSIONS

Our findings highlight a potential role of LC-MRI for predicting clinical progression in Mild Cognitive Impairment and support the key role of LC degeneration in the Alzheimer clinical continuum.

Association between neuronal degeneration and supraphysiological doses of two types of anabolic steroids in rat brain

The anabolic androgenic steroids (AAS) are natural compounds that are precursors or derivatives of testosterone and, as a consequence of indiscriminate use, cause irreversible neuronal effects. For this study, 70 brain samples were used from male Wistar rats, separated into 14 groups, divided into: control, sedentary, and exercise groups; in the concentrations: 5 mg, 10 mg, and 15 mg. Two different AAS were used: Testosterone Cypionate (TC) and Nandrolone Decanoate (ND). The encephali followed all the conventional histological procedures, for further analysis of the estimates of neuron bodies of the Locus coeruleus; also being carried out the techniques of the Tunnel Assay and Von Kossa staining. The results obtained show significant values different from the control group: Testosterone Cypionate (TCS): 5 mg (25,00 ± 4,47); 10 mg (23,67 ± 4,45) and 15 mg (21,93 ± 5,65), as well as for Nandrolone Decanoate (ND) in the doses: 5 mg (23,40 ± 3,81); 10 mg (22,80 ± 3,80) and 15 mg (22,80 ± 4,54) being the values of the control group (CGS) 34,27 ± 6,06. For the groups that exercised, the values were: TCT 5 mg 20,87 ± 3,23; TCT 10 mg 21,93 ± 4,91 and TCT 15 mg 21,47 ± 4,36 while, the Nandrolone Decanoate (ND) groups, in the different doses were: NDT 5 mg 21,53 ± 4,34; NDT 10 mg 23,53 ± 1,68 and NDT 15 mg 23,40 ± 2,20, also expressing significant values different from the control group. When comparing the sedentary control group with the animals that exercised, a statistically significant difference was observed being: CGS 34,27 ± 6,06; TCT 5 mg; 20,87 ± 3,23; NDT 5 mg 21,53 ± 4,34; TCT 10 mg 21,93 ± 4,91; NDT 10 mg 23,53 ± 1,68; TCT 15 mg 21,47 ± 4,36 and NDT 15 mg 23,40 ± 2,20. The results of this study, point out that both steroids drastically reduce neuronal density in the Locus coeruleus area inferring that, the possible cause of neuronal death is necrosis, caused by intracellular calcium imbalance.

Decreased locus coeruleus signal associated with Alzheimer’s disease based on neuromelanin-sensitive magnetic resonance imaging technique

Objective

Neuromelanin-sensitive magnetic resonance imaging (NM-MRI) technique was used to detect the changes of the locus coeruleus (LC) signals in Alzheimer’s disease patients (AD), and to analyze its correlation with cognitive function.

Materials and methods

A total of 27 patients with AD, 15 patients with mild cognitive impairment (MCI), and 25 healthy controls (HC) were examined by NM-MRI technique. ImageJ software was used to measure the LC signals. The locus coeruleus signal contrast ratios (LC-CRs) were calculated, along with the measurement of neuropsychological scales.

Results

The LC-CRs of AD patients were significantly different from that of HC (p = 0.007, 95% CI: −0.053∼−0.007). However, such significant differences were not observed between MCI and HC (p = 1.000, 95% CI: −0.030∼0.024), AD and MCI (p = 0.050, 95% CI: −0.054∼0.000). Furthermore, a significant positive correlation was identified between LC-CRs and MMSE sub item Drawing (r = 0.484, p = 0.011) in the AD group, MoCA sub item Attention (r = 0.519, p = 0.047) in the MCI group. The area under the curve of LC-CRs in the diagnosis of AD was 0.749 (p = 0.002, 95% CI: 0.618∼0.880), with a sensitivity of 85.2% and a specificity of 56.0%.

Conclusion

The NM-MRI technique could quantify the pathological degenerations of the LC in AD. Such LC degenerations can be employed to distinguish AD from healthy elderly.

The role of the locus coeruleus/norepinephrine system in the pathogenesis of neurodegenerative disorders: An update

PURPOSE OF REVIEW

The aim of this review was to provide an update on current and emerging knowledge of the neuropathological processes affecting the locus coeruleus/norepinephrine (LC/NE) system, their effect on Alzheimer's disease and Parkinson's disease symptomatology, including efforts to translate these notions into therapeutic actions targeting the noradrenergic system.

RECENT FINDINGS

Over the past 2 years, work from multiple groups has contributed to support an early role of locus coeruleus degeneration and/or hyperactivation in the neurodegenerative process, including a trigger of neuroinflammation. Imaging advances are allowing the quantification of locus coeruleus structural features in vivo, which is critical in the early stages of disease. Nonmotor and noncognitive symptoms, often secondary to the involvement of the LC/NE system, are becoming more important in the definition of these diseases and their treatment.

SUMMARY

The diverse symptomatology of Parkinson's disease and Alzheimer's disease, which is not limited to cardinal motor and cognitive abnormalities, strongly suggests a multisystem neurodegenerative process. In this context, it is increasingly clear how the LC/NE system plays a key role in the initiation and maintenance of the neurodegenerative process.

Locus Coeruleus magnetic resonance imaging: a comparison between native-space and template-space approach

Locus Coeruleus (LC) is the main noradrenergic nucleus of the brain, which is involved in many physiological functions including cognition; its impairment may be crucial in the neurobiology of a variety of brain diseases. Locus Coeruleus-Magnetic Resonance Imaging (LC-MRI) allows to identify in vivo LC in humans. Thus, a variety of research teams have been using LC-MRI to estimate LC integrity in normal aging and in patients affected by neurodegenerative disorders, where LC integrity my work as a biomarker. A number of variations between LC-MRI studies exist, concerning post-acquisition analysis and whether this had been performed within MRI native space or in ad hoc-built MRI template space. Moreover, the reproducibility and reliability of this tool is still to be explored. Therefore, in the present study, we analyzed a group of neurologically healthy, cognitively intact elderly subjects, using both a native space- and a template space-based LC-MRI analysis. We found a good inter-method agreement, particularly considering the LC Contrast Ratio. The template space-based approach provided a higher spatial resolution, lower operator-dependency, and allowed the analysis of LC topography. Our ad hoc-developed LC template showed LC morphological data that were in line with templates published very recently. Remarkably, present data significantly overlapped with a recently published LC "metaMask", that had been obtained by averaging the results of a variety of previous LC-MRI studies. Thus, such a template space-based approach may pave the way to a standardized LC-MRI analysis and to be used in future clinic-anatomical correlations.

Automated Mouse Pupil Size Measurement System to Assess Locus Coeruleus Activity with a Deep Learning-Based Approach

Strong evidence from studies on primates and rodents shows that changes in pupil diameter may reflect neural activity in the locus coeruleus (LC). Pupillometry is the only available non-invasive technique that could be used as a reliable and easily accessible real-time biomarker of changes in the in vivo activity of the LC. However, the application of pupillometry to preclinical research in rodents is not yet fully standardized. A lack of consensus on the technical specifications of some of the components used for image recording or positioning of the animal and cameras have been recorded in recent scientific literature. In this study, a novel pupillometry system to indirectly assess, in real-time, the function of the LC in anesthetized rodents is presented. The system comprises a deep learning SOLOv2 instance-based fast segmentation framework and a platform designed to place the experimental subject, the video cameras for data acquisition, and the light source. The performance of the proposed setup was assessed and compared to other baseline methods using a validation and an external test set. In the latter, the calculated intersection over the union was 0.93 and the mean absolute percentage error was 1.89% for the selected method. The Bland–Altman analysis depicted an excellent agreement. The results confirmed a high accuracy that makes the system suitable for real-time pupil size tracking, regardless of the pupil’s size, light intensity, or any features typical of the recording process in sedated mice. The framework could be used in any neurophysiological study with sedated or fixed-head animals.

New frontiers in Alzheimer's disease diagnostic: Monoamines and their derivatives in biological fluids

Current diagnosis of Alzheimer's disease (AD) relies on a combination of neuropsychological evaluations, biomarker measurements and brain imaging. Nevertheless, these approaches are either expensive, invasive or lack sensitivity to early AD stages. The main challenge of ongoing research is therefore to identify early non-invasive biomarkers to diagnose AD at preclinical stage. Accumulating evidence support the hypothesis that initial degeneration of profound monoaminergic nuclei may trigger a transneuronal spread of AD pathology towards hippocampus and cortex. These studies aroused great interest on monoamines, i.e. noradrenaline (NA), dopamine (D) ad serotonin (5-HT), as early hallmarks of AD pathology. The present work reviews current literature on the potential role of monoamines and related metabolites as biomarkers of AD. First, morphological changes in the monoaminergic systems during AD are briefly described. Second, we focus on concentration changes of these molecules and their derivatives in biological fluids, including cerebrospinal fluid, obtained by lumbar puncture, and blood or urine, sampled via less invasive procedures. Starting from initial observations, we then discuss recent insights on metabolomics-based analysis, highlighting the promising clinical utility of monoamines for the identification of a molecular AD signature, aimed at improving early diagnosis and discrimination from other dementia.

The connections of Locus Coeruleus with hypothalamus: potential involvement in Alzheimer's disease

The hypothalamus and Locus Coeruleus (LC) share a variety of functions, as both of them take part in the regulation of the sleep/wake cycle and in the modulation of autonomic and homeostatic activities. Such a functional interplay takes place due to the dense and complex anatomical connections linking the two brain structures. In Alzheimer's disease (AD), the occurrence of endocrine, autonomic and sleep disturbances have been associated with the disruption of the hypothalamic network; at the same time, in this disease, the occurrence of LC degeneration is receiving growing attention for the potential roles it may have both from a pathophysiological and pathogenetic point of view. In this review, we summarize the current knowledge on the anatomical and functional connections between the LC and hypothalamus, to better understand whether the impairment of the former may be responsible for the pathological involvement of the latter, and whether the disruption of their interplay may concur to the pathophysiology of AD. Although only a few papers specifically explored this topic, intriguingly, some pre-clinical and post-mortem human studies showed that aberrant protein spreading and neuroinflammation may cause hypothalamus degeneration and that these pathological features may be linked to LC impairment. Moreover, experimental studies in rodents showed that LC plays a relevant role in modulating the hypothalamic sleep/wake cycle regulation or neuroendocrine and systemic hormones; in line with this, the degeneration of LC itself may partly explain the occurrence of hypothalamic-related symptoms in AD.

Neuropathology of the Brainstem to Mechanistically Understand and to Treat Alzheimer's Disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder as yet without effective therapy. Symptoms of this disorder typically reflect cortical malfunction with local neurohistopathology, which biased investigators to search for focal triggers and molecular mechanisms. Cortex, however, receives massive afferents from caudal brain structures, which do not only convey specific information but powerfully tune ensemble activity. Moreover, there is evidence that the start of AD is subcortical. The brainstem harbors monoamine systems, which establish a dense innervation in both allo- and neocortex. Monoaminergic synapses can co-release neuropeptides either by precisely terminating on cortical neurons or, when being “en passant”, can instigate local volume transmission. Especially due to its early damage, malfunction of the ascending monoaminergic system emerges as an early sign and possible trigger of AD. This review summarizes the involvement and cascaded impairment of brainstem monoaminergic neurons in AD and discusses cellular mechanisms that lead to their dysfunction. We highlight the significance and therapeutic challenges of transmitter co-release in ascending activating system, describe the role and changes of local connections and distant afferents of brainstem nuclei in AD, and summon the rapidly increasing diagnostic window during the last few years.