Inverse Association of Locus Coeruleus MRI Integrity With Structural Volume and Its Impact on Individual's Inattentiveness

We compared locus coeruleus (LC) structural integrity, as measured by neuromelanin-sensitive magnetic resonance imaging (NM-MRI), between patients with Parkinson's disease (PD) and those with multiple system atrophy (MSA) and tested whether orthostatic hypotension (OH) impacted differences in LC volume between PD and MSA. Substantia nigra (SNc) volumes were compared between these groups to determine whether effects observed in LC were specific to that structure. Last, we tested whether LC integrity is associated with orthostatic hemodynamic responses. Presence or absence of (±)OH was determined with active stand testing. Automated segmentation of LC and SNc volumes took place using NM-MRI. Structural volumes were first compared between PD and MSA groups and, second, after stratification by OH status. Last, correlations between LC volumes and orthostatic vitals were calculated. Of 71 patients with PD, 19 were (+)OH. Of 19 patients with MSA, 12 were (+)OH. LC volumes were larger in PD than MSA (p = 0.002), and LC volumes in PD(-)OH were larger than PD(+)OH and MSA(±)OH (p < 0.05). All comparisons involving SNc were nonsignificant. Primarily in PD(-)OH, LC volumes correlated negatively with supine mean arterial pressure (MAP) and positively with supine heart rate. In PD(+OH) and MSA(+)OH, lower LC volumes were correlated with greater orthostatic falls in MAP. Similar levels of LC neurodegeneration were observed in PD(+)OH and MSA(±)OH. Therefore, LC measurement may be useful to differentiate PD(-)OH from MSA.Lower LC volumes additionally correlated with greater drops in MAP in both PD(+)OH and MSA(+)OH, suggesting thatLC neurodegeneration may contribute to OH in both conditions.

Introduction The locus coeruleus (LC), an important sleep/wake regulating structure and site of early change in neurodegenerative disease, is best measured in humans with ultra-high field 7-Tesla MRI due to its small size. We hypothesized that obstructive sleep apnea (OSA) would negatively influence LC structural integrity and volume in cognitively normal elderly individuals. Methods We examined the LC using 7T MRI with a computational LC localization and segmentation algorithm in 30 cognitively normal older subjects: 17 with a new OSA clinical diagnosis and 13 from the community without sleep complaints. Obstructive sleep apnea was assessed by WatchPAT home sleep study or in-lab polysomnography. We evaluated associations between OSA severity/hypoxic burden and LC structural metrics: absolute volume, volume normalized to brainstem or whole brain volume, and LC integrity, a relative measure of MRI contrast enhanced neuromelanin. Results Of the 30 subjects, mean age was 66 years and 53% were women. The cohort was dichotomized using an OSA cutoff of AHI4%&amp;gt;=5 (OSA+, n=22, OSA-, n = 8). Total sleep time was not significantly different between the OSA- and OSA+ groups. As expected, AHI4%, REM AHI4%, and min. oxygen saturation during sleep were all significantly different in the OSA- and OSA+ groups, though time below 90% oxygen saturation (T90) was not. We observed a significant negative association between LC integrity and T90 [R=-0.45, p=0.035] in the OSA+ group, but not the OSA- group [R=0.58, p=0.132]. We did not observe differences between the OSA+ and OSA- groups for the absolute LC volume [OSA-: 145± 63mm3, OSA+: 132± 74, p=0.44], LC volume normalized to brainstem volume [OSA-: 0.0052± 0.0032, OSA+: 0.0055± 0.0032, p=0.83], LC volume normalized to whole brain volume [OSA-: 8.0e-05± 4.8e-05, OSA+: 7.6-05± 4.7e-05, p=0.83], or LC integrity [OSA-: 1.60± 0.09, OSA+: 1.58± 0.14, =0.94]. Conclusion This study presents some of the first evidence that greater hypoxic burden as assessed by T90 is associated with reduced LC integrity in older adults, potentially implicating a role for nocturnal hypoxemia in the pathological decline of the LC with aging. Support (if any) AASMF Bridge award, AARGD award, NIH

BackgroundNeuropathological studies indicate that locus coeruleus(LC) volume decreases in Alzheimer’s disease(AD) by 8% at each stage, (from Braak 0‐1), whereas in normal aging, the LC remains unchanged. These changes make LC volumetry by neuroimaging a promising way to track AD progression even before symptoms appear. However, LC’s small size and location make it prone to imaging artifacts. To assess the accuracy of neuroimaging sequences designed for LC volumetry, we used an in‐house histological computational method to compare histology and neuroimaging on a voxel‐by‐voxel basis.MethodWe investigated three cases (two Braak 1s, and a Braak 5). The whole brain underwent 7T MRI postmortem, pre‐autopsy, at the University of Sao Paulo. Upon autopsy, the brains were processed at UCSF and the histological LC was 3D reconstructed. In parallel, the GRE and TFL MRI sequence LCs were segmented (Figure 1). We applied affine&amp; spline registration to match histology to MRI‐T1 volumes (voxel size=0.75mm)(Figure 1). To measure registration accuracy, we calculated DICE coefficients using T1 visible structures (Figure 2). Next, we analyzed the percentage overlap of voxels to investigate how accurately MRI sequences detected histology LC borders.ResultOverall, the DICE values for brainstem registration are high. Table 1 shows the overlapping percentages that are quite low, from 2.5%‐23%. For our Braak 1 cases, the least overlap of GRE MRI and histology LC borders is in rostral region, while in both TFL and GRE sequence for the Braak 5 case, the least LC overlap was in the caudal region (Table 1).ConclusionThese results suggest that accurately detecting LC borders using MRI remains a challenging task due to small size, imaging artifacts, and neuromelanin dependency, which is low at baseline in caudal LC. However, our overlap results did match previous findings on specific regional LC volume loss seen rostrally in early AD, despite no neuronal loss, and in later stages of AD, volume loss caudally. This points to the MRI LC signal being potentially clinically useful for disease monitoring. Our study will continue to examine the MRI signal picked up in the LC across Braak as regions of LC degeneration shift compared to the histology counterpart.

BackgroundNeuropathological studies indicate that locus coeruleus(LC) volume decreases in Alzheimer’s disease(AD) by 8% at each stage, (from Braak 0‐1), whereas in normal aging, the LC remains unchanged. These changes make LC volumetry by neuroimaging a promising way to track AD progression even before symptoms appear. However, LC’s small size and location make it prone to imaging artifacts. To assess the accuracy of neuroimaging sequences designed for LC volumetry, we used an in‐house histological computational method to compare histology and neuroimaging on a voxel‐by‐voxel basis.MethodWe investigated three cases (two Braak 1s, and a Braak 5). The whole brain underwent 7T MRI postmortem, pre‐autopsy, at the University of Sao Paulo. Upon autopsy, the brains were processed at UCSF and the histological LC was 3D reconstructed. In parallel, the GRE and TFL MRI sequence LCs were segmented (Fig 1). We applied affine&amp; spline registration to match histology to MRI‐T1 volumes(voxel size = 0.75mm)(Fig 1). To measure registration accuracy, we calculated DICE coefficients using T1 visible structures (Fig 2). Next, we analyzed the percentage overlap of voxels to investigate how accurately MRI sequences detected histology LC borders.ResultOverall, the DICE values for brainstem registration are high. Table 1 shows the overlapping percentages that are quite low, from 2.5%‐23%. For our Braak 1 cases, the least overlap of GRE MRI and histology LC borders is in rostral region, while in both TFL and GRE sequence for the Braak 5 case, the least LC overlap was in the caudal region (Table 1).ConclusionThese results suggest that accurately detecting LC borders using MRI remains a challenging task due to small size, imaging artifacts, and neuromelanin dependency, which is low at baseline in caudal LC. However, our overlap results did match previous findings on specific regional LC volume loss seen rostrally in early AD, despite no neuronal loss, and in later stages of AD, volume loss caudally. This points to the MRI LC signal being potentially clinically useful for disease monitoring. Our study will continue to examine the MRI signal picked up in the LC across Braak as regions of LC degeneration shift compared to the histology counterpart.

The Locus Coeruleus (LC) is in the brainstem and supplies key brain structures with noradrenaline, including the forebrain and hippocampus. The LC impacts specific behaviors such as anxiety, fear, and motivation, as well as physiological phenomena that impact brain functions in general, including sleep, blood flow regulation, and capillary permeability. Nevertheless, the short- and long-term consequences of LC dysfunction remain unclear. The LC is among the brain structures first affected in patients suffering from neurodegenerative diseases such as Parkinson's disease and Alzheimer's Disease, hinting that LC dysfunction may play a central role in disease development and progression. Animal models with modified or disrupted LC function are essential to further our understanding of LC function in the normal brain, the consequences of LC dysfunction, and its putative roles in disease development. For this, well-characterized animal models of LC dysfunction are needed. Here, we establish the optimal dose of selective neurotoxin N-(2-chloroethyl)-N-ethyl-bromo-benzylamine (DSP-4) for LC ablation. Using histology and stereology, we compare LC volume and neuron number in LC ablated (LCA) mice and controls to assess the efficacy of LC ablation with different numbers of DSP-4 injections. All LCA groups show a consistent decrease in LC cell count and LC volume. We then proceed to characterize the behavior of LCA mice using a light-dark box test, Barnes maze test, and non-invasive sleep-wakefulness monitoring. Behaviorally, LCA mice differ subtly from control mice, with LCA mice generally being more curious and less anxious compared to controls consistent with known LC function and projections. We note an interesting contrast in that control mice have varying LC size and neuron count but consistent behavior whereas LCA mice (as expected) have consistently sized LC but erratic behavior. Our study provides a thorough characterization of an LC ablation model, firmly consolidating it as a valid model system for the study of LC dysfunction.

Fewer pigmented locus coeruleus neurons in suicide victims: Preliminary results

BackgroundEarly‐onset Alzheimer’s Disease presentations (EOAD, under 65) frequently present with atypical phenotypes and a more aggressive disease course with a higher burden of neuropsychiatric symptoms than late‐onset AD (LOAD). Current treatments for sleep and behavioral disturbances are still non‐specific, causing side effects (e.g., sedation, falls). Identifying the underlying changes driving behavioral differences between EOAD and LOAD is crucial to developing tailored treatment avenues. The noradrenergic locus coeruleus (LC), one of the first sites of tau deposition in AD, has been implicated in sleep‐wake patterns and mood regulation. We aim to test the hypothesis that the LC is more affected in EOAD than LOAD by comparing LC volume (neuromelanin‐sensitive MRI) and sleep‐behavioral symptoms in biomarker‐confirmed EOAD and LOAD cohorts.MethodFifty‐four subjects with AD biomarker‐based diagnosis (20 EOAD, 34 LOAD) were recruited at the Hospital Clínic de Barcelona. All participants and informants completed the Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), and Neuropsychiatric Inventory (NPI) questionnaires to assess the severity of sleep‐wake alterations and neuropsychiatric symptoms. In addition, they underwent a 3T turbospin‐echo MRI to measure LC volume. We compared mean values of LC volume, ESS, PSQI, and NPI between EOAD and LOAD. Furthermore, linear regression models controlling by cognitive status (MMSE) were performed.ResultEOAD and LOAD had similar cognition (MMSE 21.3±5 vs. 22.6±4, respectively), functional status (CDR 0.92±0.1 vs. 0.68±0.1), and prevalence of amnestic phenotype (57 vs. 70%). EOAD compared to LOAD, trended towards higher scores for ESS (7.4±1 vs. 5.1±1, respectively), PSQI (7.3±2 vs. 5.6±1), NPI (21.6±8 vs. 14.6±8), and caregiver distress (9.4±3 vs. 4.7±3). LC volume was lower in EOAD according to preliminary MRI data [n=18, 9 EOAD (21.8±3 mm3), 9 LOAD (29.5±3 mm3)]. Linear regression models showed that MMSE did not influence the EOAD/LOAD effect on LC volume (coef. 7.7, p=0.032).ConclusionThe current preliminary study suggests that LC degeneration is greater in EOAD than LOAD. This difference may explain the EOAD‐associated worse sleep‐wake dysfunction and neuropsychiatric symptoms. Deep phenotyping/comparison of EOAD and LOAD can inform tailored treatment strategies for these behavioral symptoms.

BackgroundIncreasing evidence suggests that neurodegeneration of the locus coeruleus (LC) is an early pathological feature of Alzheimer’s Disease (AD). However, assessment of the LC in‐vivo is hampered by its small size. Here we test the feasibility of characterizing LC’s integrity in‐vivo using ultra‐high field MRI.MethodEight young controls (age: 23+3y, education: 17+2y) and 9 elderly subjects from the Geneva memory clinic cohort (age: 74+7y, education: 16+3y; MMSE: 26+2; diagnosis: 1 cognitively normal, 7 cognitively impaired; biomarker profile: 63% A+, 14% T+) underwent MRI on a 7T Siemens Magnetom scanner, including magnetization transfer (MT; voxel: 0.43x0.43x0.5mm) and diffusion tensor imaging (DTI; voxel: 1.3x1.3x1.4mm). A MT template was generated from all the MT images with the Advanced Normalization Tools software. A LC map was extracted from the template with semi‐automated intensity thresholding. Individual MT and DTI images were warped to the MT template of the LC to measure: LC contrast ratio (CR) on MT; fractional anisotropy (FA) and mean diffusivity (MD) on DTI. These metrics were compared between groups and hemispheres using non‐parametric tests.ResultThe LC volume (MT template) was 62mm3, spanning 15mm rostro‐caudally. Elderly showed higher CR than younger subjects (median [IQR]: 23 [21‐28] vs 15 [12‐19], p=0.008 on Mann Whitney U test). This difference was detected along most of the rostro‐caudal LC axis (significance differences over 77% of the LC axis). In both younger and older subjects, the CR was greater in the left vs. right hemisphere (p=0.018 and p=0.015 respectively, Wilcoxon signed‐rank test). MD was more heterogeneous and overall higher in the LC of elderly compared to younger subjects (median [IQR]: 1.7 [0.7‐2.4] vs 0.94 [0.86‐1.02], p=0.023 on Mann Whitney U test). FA showed neither group nor hemisphere differences.ConclusionThese findings are consistent with previous LC literature at 3T. We confirmed that LC signal increases with age and reported a hemisphere asymmetry in LC signal. Microstructure atrophy with age is suggested by increased diffusivity. Data acquisition is ongoing with the aim to evaluate MT, DTI and fMRI differences across cognitively normal, AD and non‐AD impaired groups. Funding: H2020‐EU.3.1.1 (grant ID:667375), Swiss National Science Foundation (SNF‐320030_169876).

BACKGROUND Cranial radiotherapy is essential in treating pediatric brain tumor patients but also a major contributor to neurocognitive impairments. While hippocampal damage has been extensively studied in this context, radiosensitivity of other cognition-related regions remains largely unexplored. The locus coeruleus (LC), a small brain stem nucleus and the sole source of noradrenaline (NA) to the hippocampus, plays a critical role in modulating synaptic plasticity and memory consolidation. We therefore evaluated the impact of juvenile brain irradiation on the LC-NA system and whether pharmacological modulation of NA could mitigate potential dysfunction. METHODS Juvenile mice received a single 10 Gy cranial irradiation at P22. NA agonists, reboxetine or atipamezole, were administered daily for seven days post-irradiation. Sham-treated controls received sterile saline. One month post-radiation, LC damage was investigated by immunohistochemistry (TH, DBH, MAO-A, and NET). Fiber photometry (GCaMP6s in LC, GRABNE2m in hippocampus) during tail suspension stress evaluated functional responses. Finally, novelty-induced cFOS expression was analyzed 90 min. after Y-maze exposure. RESULTS At one month post-irradiation, we observed a significant reduction in DBH+ cells and increased MAO-A intensity, which was mitigated by atipamezole treatment. In contrast, NET and TH expression, LC volume, and total DAPI+ cell count remained unchanged. Functionally, fiber photometry showed reduced LC activity during tail suspension stress in irradiated animals, while hippocampal NA release remained unaffected. Reduced novelty-induced cFOS expression further supported LC dysfunction, which was partially restored by atipamezole. CONCLUSION This study provides the first evidence of LC damage following irradiation, marked by disrupted NA metabolism and degradation without structural loss. LC vulnerability following irradiation was further supported by fiber photometry recordings, revealing functional deficits in LC activity during tail suspension stress. Altogether, these results underscore the importance of investigating other cognition-related regions beside the hippocampus to better understand and prevent radiation-induced cognitive decline in young cancer survivors.

BackgroundMelanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that projects throughout the central nervous system, including the noradrenergic locus coeruleus (LC). Our previous study suggested that MCH/MCH receptor 1 (MCHR1) in the LC may be involved in the regulation of depression. The present study investigated whether the role of MCH/MCHR1 in the LC in depression-like behaviors is associated with the regulation of norepinephrine.MethodChronic unpredictable stress (CUS) and an acute intra-LC microinjection of MCH induced depression-like behaviors in rats. The MCHR1 antagonist SNAP-94847 was also microinjected in the LC in rats that were suffering CUS or treated with MCH. The sucrose preference, forced swim, and locomotor tests were used for behavioral evaluation. Immunofluorescence staining, enzyme-linked immunosorbent assay, western blot, and high-performance liquid chromatography with electrochemical detection were used to explore the mechanism of MCH/MCHR1 in the regulation of depression-like behaviors.ResultsCUS induced an abnormal elevation of MCH levels and downregulated MCHR1 in the LC, which was highly correlated with the formation of depression-like behaviors. SNAP-94847 exerted antidepressant effects in CUS-exposed rats by normalizing tyrosine hydroxylase, dopamine β hydroxylase, and norepinephrine in the LC. An acute microinjection of MCH induced depression-like behaviors through its action on MCHR1. MCHR1 antagonism in the LC significantly reversed the MCH-induced downregulation of norepinephrine production by normalizing MCHR1-medicated cAMP-PKA signaling.ConclusionsOur study confirmed that the MCH/MCHR1 system in the LC may be involved in depression-like behaviors by downregulating norepinephrine production. These results improve our understanding of the pathogenesis of depression that is related to the MCH/MCHR1 system in the LC.

We aimed to analyze the diagnostic accuracy of an automated segmentation and quantification method of the SNc and locus coeruleus (LC) volumes based on neuromelanin (NM)-sensitive MRI (NM-MRI) in patients with idiopathic (iPD) and monogenic (iPD) Parkinson's disease (PD). Thirty-six patients (23 idiopathic and 13 monogenic PARKIN or LRRK2 mutations) and 37 age-matched healthy controls underwent 3T-NM-MRI. SNc and LC volumetry were performed using fully automated multi-image atlas segmentation. The diagnostic performance to differentiate PD from controls was measured using the area under the curve (AUC) and likelihood ratios based on receiver operating characteristic (ROC) analyses. We found a significant reduction of SNc and LC volumes in patients, when compared to controls. ROC analysis showed better diagnostic accuracy when using SNc volume than LC volume. Significant differences between ipsilateral and contralateral SNc volumes, in relation to the more clinically affected side, were found in patients with iPD (P = 0.007). Contralateral atrophy in the SNc showed the highest power to discriminate PD subjects from controls (AUC, 0.93-0.94; sensitivity, 91%-92%; specificity, 89%; positive likelihood ratio: 8.4-8.5; negative likelihood ratio: 0.09-0.1 at a single cut-off point). Interval likelihood ratios for contralateral SNc volume improved the diagnostic accuracy of volumetric measurements. SNc and LC volumetry based on NM-MRI resulting from the automated segmentation and quantification technique can yield high diagnostic accuracy for differentiating PD from health and might be an unbiased disease biomarker. © 2015 International Parkinson and Movement Disorder Society.

Locus Coeruleus (LC)-noradrenaline system plays important roles in many brain functions, including decision making, arousal, emotion, antinociception and sleep-wake cycle. The previous data of our group showed that the spontaneous firing rate (SFR) of LC neurons is regulated by GABAB receptors (GABABRs) in a tonic inhibition manner. However, the mechanism of this GABABR regulation is still unknown. The metabotropic GABAB receptor (GABABR) plays important roles in regulating neuronal excitability in the brain. GABABR is well known to exert both pre- and postsynaptic inhibition through inhibiting voltage-gated Ca2+ channel and activating K+ (GIRK) channel, respectively. Beside these effects, here we found that GABABR activation caused an increase in phosphorylated extracellular signal- regulated kinase 1/2 (pERK1/2) level in LC, which consists of noradrenergic neurons and play divers roles in behavior. Our work applies whole cell patch-clamp and cell-attachment electrophysiology, cellular immunohistochemistry staining and western blot to study the GABABR-pERK1/2 signaling pathway mechanism on LC neurons in rats. Morphological results show that pERK1/2 signal in LC neurons exhibits circadian cycle which is similar to ambient GABA level, opposite to LC activity. Using western-blot analysis, LC tissues isolated from brainstem slices bathed in baclofen, a GABABR agonist, showed an increase in pERK1 and pERK2 compared to tissue from slices bathed in normal medium. Furthermore, this effect was specific to GABABR activation as it was not observed in LC tissue from slices bathed with baclofen and CGP54626, a GABABR antagonist. More interestingly, in whole cell recording, bath application of baclofen for 15 min induced a CGP54626 sensitive baclofen-induced current in LC neuron (Vm -70 mV) that underwent slow and partial desensitization. In slices pretreated with ERK1/2 blockers, U0126 or FR180204, but not in ERK1 blocker, PD98059, baclofen-induced current showed a faster and more prominent desensitization. Besides to desensitization, balance of GPCR trafficking is also important for controlling the GABAB receptor functions. Using cell-attachment recording, we found that ERK1/2 activity is involved in restoration of GABAB receptor on cell surface of LC neurons, and further affects the average firing rate of LC neurons. Together, the above results show that GABABR activation recruits ERK1/2-signaling pathway for an autoregulation that prevents GABABR from quick desensitization and restores cell surface GABABR of LC neurons, therefore maintains tonic inhibition, an important mechanism for tuning FR of LC neurons.

The locus coeruleus (LC) is a nucleus in the brain stem producing noradrenaline. While cognitive decline in Alzheimer's disease (AD) has primarily been related to cholinergic depletion, evidence indicates extensive LC degeneration as its earliest pathological marker. The current study aimed to systematically evaluate current evidence investigating the role of the LC in the pathogenesis of AD. A systematic search of the literature was performed on electronic databases including PubMed and Web of Science. Twelve animal, human post mortem, and human imaging studies were included in this review. Screening, data extraction, and quality assessment were undertaken following Preferred Reporting Items for Systematic Reviews and Meta‐Analyses guidelines for preferred reporting of systematic reviews. Significant associations were identified between LC changes and cognitive decline. Significant reductions in fiber density, neuronal number, and LC volume were seen to correlate with other pathological degenerative markers. Current evidence indicates an important role of the LC in pathogenesis of AD and suggests its potential in both diagnosis and treatment of AD. This systematic review advances our understanding of the role of the LC in AD by synthesizing available evidence, identifying research gaps, highlighting methodological challenges, and making recommendations for future work.

The purpose of this study was to assess the reproducibility of substantia nigra pars compacta (SNpc) and locus coeruleus (LC) delineation and measurement with neuromelanin-sensitive MRI. Eleven subjects underwent two neuromelanin-sensitive MRI scans. SNpc and LC volumes were extracted for each scan. Reproducibility of volume and magnetization transfer contrast measurements in SNpc and LC was assessed using intraclass correlation coefficients (ICC) and dice similarity coefficients (DSC). SNpc and LC volume measurements showed excellent reproducibility (SNpc-ICC: 0.94, p<0.001; LC-ICC: 0.96, p<0.001). SNpc and LC were accurately delineated between scans (SNpc-DSC: 0.80±0.03; LC-DSC: 0.63±0.07). Neuromelanin-sensitive MRI can consistently delineate SNpc and LC.

Locus coeruleus volume and cell population changes during Alzheimer's disease progression: A stereological study in human postmortem brains with potential implication for early-stage biomarker discovery