Evidence for specific phases in the development of human neuromelanin

A combined MRI, histological and immunohistochemical rendering of the rhesus macaque locus coeruleus (LC) enables the differentiation of three distinct LC subcompartments

Locus coeruleus (LC) neurons send their noradrenergic axons across multiple brain regions, including neocortex, subcortical regions, and spinal cord. Many aspects of cognition are known to be dependent on the noradrenergic system, and it has been suggested that dysfunction in this system may play central roles in cognitive decline associated with both normative aging and neurodegenerative disease. While basic anatomical and biochemical features of the LC have been examined in many species, detailed characterizations of the structure and function of the LC across the lifespan are not currently available. This includes the rhesus macaque, which is an important model of human brain function because of their striking similarities in brain architecture and behavioral capacities. In the present study, we describe a method to combine structural MRI, Nissl, and immunofluorescent histology from individual monkeys to reconstruct, in 3 dimensions, the entire macaque LC nucleus. Using these combined methods, a standardized volume of the LC was determined, and high-resolution confocal images of tyrosine hydroxylase-positive neurons were mapped into this volume. This detailed representation of the LC allows definitions to be proposed for three distinct subnuclei, including a medial region and a lateral region (based on location with respect to the central gray, inside or outside, respectively), and a compact region (defined by densely packed neurons within the medial compartment). This enabled the volume to be estimated and cell density to be calculated independently in each LC subnucleus for the first time. This combination of methods should allow precise characterization of the LC and has the potential to do the same for other nuclei with distinct molecular features.

Probing midbrain dopamine function in pediatric obsessive-compulsive disorder via neuromelanin-sensitive magnetic resonance imaging

Obsessive-compulsive disorder (OCD) is an impairing psychiatric condition, which often onsets in childhood. Growing research highlights dopaminergic alterations in adult OCD, yet pediatric studies are limited by methodological constraints. This is the first study to utilize neuromelanin-sensitive MRI as a proxy for dopaminergic function among children with OCD. N = 135 youth (6-14-year-olds) completed high-resolution neuromelanin-sensitive MRI across two sites; n = 64 had an OCD diagnosis. N = 47 children with OCD completed a second scan after cognitive-behavioral therapy. Voxel-wise analyses identified that neuromelanin-MRI signal was higher among children with OCD compared to those without (483 voxels, permutation-corrected p = 0.018). Effects were significant within both the substania nigra pars compacta (p = 0.004, Cohen's d = 0.51) and ventral tegmental area (p = 0.006, d = 0.50). Follow-up analyses indicated that more severe lifetime symptoms (t = -2.72, p = 0.009) and longer illness duration (t = -2.22, p = 0.03) related to lower neuromelanin-MRI signal. Despite significant symptom reduction with therapy (p < 0.001, d = 1.44), neither baseline nor change in neuromelanin-MRI signal associated with symptom improvement. Current results provide the first demonstration of the utility of neuromelanin-MRI in pediatric psychiatry, specifically highlighting in vivo evidence for midbrain dopamine alterations in treatment-seeking youth with OCD. Neuromelanin-MRI likely indexes accumulating alterations over time, herein, implicating dopamine hyperactivity in OCD. Given evidence of increased neuromelanin signal in pediatric OCD but negative association with symptom severity, additional work is needed to parse potential longitudinal or compensatory mechanisms. Future studies should explore the utility of neuromelanin-MRI biomarkers to identify early risk prior to onset, parse OCD subtypes or symptom heterogeneity, and explore prediction of pharmacotherapy response.

Metabolic set points of mammalian neurodevelopment

The human nervous system matures over a protracted developmental time frame relative to other species. What sets the pace of maturation has remained a mystery. In a recent publication in Science, Iwata et al. unearth critical contributions of mitochondrial metabolism in setting the pace of species-specific corticogenesis.

Melanin and Neuromelanin: Linking Skin Pigmentation and Parkinson's Disease

Neuromelanin-containing dopaminergic neurons in the substantia nigra pars compacta (SNpc) are the most vulnerable neurons in Parkinson's disease (PD). Recent work suggests that the accumulation of oxidized dopamine and neuromelanin mediate the convergence of mitochondrial and lysosomal dysfunction in patient-derived neurons. In addition, the expression of human tyrosinase in mouse SNpc led to the formation of neuromelanin resulting in the degeneration of nigral dopaminergic neurons, further highlighting the importance of neuromelanin in PD. The potential role of neuromelanin in PD pathogenesis has been supported by epidemiological observations, whereby individuals with lighter pigmentation or cutaneous malignant melanoma exhibit higher incidence of PD. Because neuromelanin and melanin share many functional characteristics and overlapping biosynthetic pathways, it has been postulated that genes involved in skin pigmentation and melanin formation may play a role in the susceptibility of vulnerable midbrain dopaminergic neurons to neurodegeneration. Here, we highlight potential mechanisms that may explain the link between skin pigmentation and PD, focusing on the role of skin pigmentation genes in the pathogenesis of PD. We also discuss the importance of genetic ancestry in assessing the contribution of pigmentation-related genes to risk of PD. © 2022 International Parkinson and Movement Disorder Society.

Chelation Combination-A Strategy to Mitigate the Neurotoxicity of Manganese, Iron, and Copper?

The chelating thiol dimercaptosuccinate (DMSA) and the traditional agent D-penicillamine (PSH) are effective in enhancing the urinary excretion of copper (Cu) and lead (Pb) in poisoned individuals. However, DMSA, PSH, EDTA (ethylenediamine tetraacetate), and deferoxamine (DFOA) are water-soluble agents with limited access to the central nervous system (CNS). Strategies for mobilization of metals such as manganese (Mn), iron (Fe), and Cu from brain deposits may require the combined use of two agents: one water-soluble agent to remove circulating metal into urine, in addition to an adjuvant shuttler to facilitate the brain-to-blood mobilization. The present review discusses the chemical basis of metal chelation and the ligand exchange of metal ions. To obtain increased excretion of Mn, Cu, and Fe, early experiences showed promising results for CaEDTA, PSH, and DFOA, respectively. Recent experiments have indicated that p-amino salicylate (PAS) plus CaEDTA may be a useful combination to remove Mn from binding sites in CNS, while the deferasirox-DFOA and the tetrathiomolybdate-DMSA combinations may be preferable to promote mobilization of Fe and Cu, respectively, from the CNS. Further research is requested to explore benefits of chelator combinations.

Neuromelanin granules of the substantia nigra: proteomic profile provides links to tyrosine hydroxylase, stress granules and lysosomes

Neuromelanin is a black-brownish pigment, present in so-called neuromelanin granules (NMGs) in the cell bodies of dopaminergic neurons in the substantia nigra (SN) pars compacta. These neurons are lost in neurodegenerative diseases, such as Parkinson’s disease and dementia with Lewy bodies. Although it is known that lipids, proteins, and environmental toxins accumulate in NMGs, the function of NMGs has not yet been finally clarified as well as their origin and the synthesis of neuromelanin. We, therefore, isolated NMGs and surrounding SN tissue from control patients by laser microdissection and analyzed the proteomic profile by tandem mass spectrometry. With our improved workflow, we were able to (1) strengthen the regularly reported link between NMGs and lysosomes, (2) detect tyrosine hydroxylase to be highly abundant in NMGs, which may be related to neuromelanin synthesis and (3) indicate a yet undescribed link between stress granules (SGs) and NMGs. Based on our findings, we cautiously hypothesize, that SGs may be the origin of NMGs or form in close proximity to them, potentially due to the oxidative stress caused by neuromelanin-bound metals.

Cerebral Iron Deposition in Neurodegeneration

Disruption of cerebral iron regulation appears to have a role in aging and in the pathogenesis of various neurodegenerative disorders. Possible unfavorable impacts of iron accumulation include reactive oxygen species generation, induction of ferroptosis, and acceleration of inflammatory changes. Whole-brain iron-sensitive magnetic resonance imaging (MRI) techniques allow the examination of macroscopic patterns of brain iron deposits in vivo, while modern analytical methods ex vivo enable the determination of metal-specific content inside individual cell-types, sometimes also within specific cellular compartments. The present review summarizes the whole brain, cellular, and subcellular patterns of iron accumulation in neurodegenerative diseases of genetic and sporadic origin. We also provide an update on mechanisms, biomarkers, and effects of brain iron accumulation in these disorders, focusing on recent publications. In Parkinson’s disease, Friedreich’s disease, and several disorders within the neurodegeneration with brain iron accumulation group, there is a focal siderosis, typically in regions with the most pronounced neuropathological changes. The second group of disorders including multiple sclerosis, Alzheimer’s disease, and amyotrophic lateral sclerosis shows iron accumulation in the globus pallidus, caudate, and putamen, and in specific cortical regions. Yet, other disorders such as aceruloplasminemia, neuroferritinopathy, or Wilson disease manifest with diffuse iron accumulation in the deep gray matter in a pattern comparable to or even more extensive than that observed during normal aging. On the microscopic level, brain iron deposits are present mostly in dystrophic microglia variably accompanied by iron-laden macrophages and in astrocytes, implicating a role of inflammatory changes and blood–brain barrier disturbance in iron accumulation. Options and potential benefits of iron reducing strategies in neurodegeneration are discussed. Future research investigating whether genetic predispositions play a role in brain Fe accumulation is necessary. If confirmed, the prevention of further brain Fe uptake in individuals at risk may be key for preventing neurodegenerative disorders.

Estimates of locus coeruleus function with functional magnetic resonance imaging are influenced by localization approaches and the use of multi-echo data

The locus coeruleus (LC) plays a central role in regulating human cognition, arousal, and autonomic states. Efforts to characterize the LC’s function in humans using functional magnetic resonance imaging have been hampered by its small size and location near a large source of noise, the fourth ventricle. We tested whether the ability to characterize LC function is improved by employing neuromelanin-T1 weighted images (nmT1) for LC localization and multi-echo functional magnetic resonance imaging (ME-fMRI) for estimating intrinsic functional connectivity (iFC). Analyses indicated that, relative to a probabilistic atlas, utilizing nmT1 images to individually localize the LC increases the specificity of seed time series and clusters in the iFC maps. When combined with independent components analysis (ME-ICA), ME-fMRI data provided significant improvements in the temporal signal to noise ratio and DVARS relative to denoised single echo data (1E-fMRI). The effects of acquiring nmT1 images and ME-fMRI data did not appear to only reflect increases in power: iFC maps for each approach overlapped only moderately. This is consistent with findings that ME-fMRI offers substantial advantages over 1E-fMRI acquisition and denoising. It also suggests that individually identifying LC with nmT1 scans is likely to reduce the influence of other nearby brainstem regions on estimates of LC function.

Lower Locus Coeruleus MRI intensity in patients with late-life major depression

Background

The locus coeruleus (LC) is the major noradrenergic source in the central nervous system. Structural alterations in the LC contribute to the pathophysiology of different neuropsychiatric disorders, which may increase to a variable extent the likelihood of developing neurodegenerative conditions. The characterization of such alterations may therefore help to predict progression to neurodegenerative disorders. Despite the LC cannot be visualized with conventional magnetic resonance imaging (MRI), specific MRI sequences have been developed to infer its structural integrity.

Methods

We quantified LC signal Contrast Ratios (LCCRs) in late-life major depressive disorder (MDD) (n = 37, 9 with comorbid aMCI), amnestic Mild Cognitive Impairment (aMCI) (n = 21, without comorbid MDD), and healthy controls (HCs) (n = 31), and also assessed the putative modulatory effects of comorbidities and other clinical variables.

Results

LCCRs were lower in MDD compared to aMCI and HCs. While no effects of aMCI comorbidity were observed, lower LCCRs were specifically observed in patients taking serotonin/norepinephrine reuptake inhibitors (SNRIs).

Conclusion

Our results do not support the hypothesis that lower LCCRs characterize the different clinical groups that may eventually develop a neurodegenerative disorder. Conversely, our results were specifically observed in patients with late-life MDD taking SNRIs. Further research with larger samples is warranted to ascertain whether medication or particular clinical features of patients taking SNRIs are associated with changes in LC neurons.

The Neuromelanin Paradox and Its Dual Role in Oxidative Stress and Neurodegeneration

Aging is associated with an increasing dysfunction of key brain homeostasis mechanisms and represents the main risk factor across most neurodegenerative disorders. However, the degree of dysregulation and the affectation of specific pathways set apart normal aging from neurodegenerative disorders. In particular, the neuronal metabolism of catecholaminergic neurotransmitters appears to be a specifically sensitive pathway that is affected in different neurodegenerations. In humans, catecholaminergic neurons are characterized by an age-related accumulation of neuromelanin (NM), rendering the soma of the neurons black. This intracellular NM appears to serve as a very efficient quencher for toxic molecules. However, when a neuron degenerates, NM is released together with its load (many undegraded cellular components, transition metals, lipids, xenobiotics) contributing to initiate and worsen an eventual immune response, exacerbating the oxidative stress, ultimately leading to the neurodegenerative process. This review focuses on the analysis of the role of NM in normal aging and neurodegeneration related to its capabilities as an antioxidant and scavenging of harmful molecules, versus its involvement in oxidative stress and aberrant immune response, depending on NM saturation state and its extracellular release.

The Locus Coeruleus in Aging and Alzheimer's Disease: A Postmortem and Brain Imaging Review

The locus coeruleus (LC), a tiny nucleus in the brainstem and the principal site of noradrenaline synthesis, has a major role in regulating autonomic function, arousal, attention, and neuroinflammation. LC dysfunction has been linked to a range of disorders; however particular interest is given to the role it plays in Alzheimer's disease (AD). The LC undergoes significant neuronal loss in AD, thought to occur early in the disease process. While neuronal loss in the LC has also been suggested to occur in aging, this relationship is less clear as the findings have been contradictory. LC density has been suggested to be indicative of cognitive reserve and the evidence for these claims will be discussed. Recent imaging techniques allowing visualization of the LC in vivo using neuromelanin-sensitive MRI are developing our understanding of the role of LC in aging and AD. Tau pathology within the LC is evident at an early age in most individuals; however, the relationship between tau accumulation and neuronal loss and why some individuals then develop AD is not understood. Neuromelanin pigment accumulates within LC cells with age and is proposed to be toxic and inflammatory when released into the extracellular environment. This review will explore our current knowledge of the LC changes in both aging and AD from postmortem, imaging, and experimental studies. We will discuss the reasons behind the susceptibility of the LC to neuronal loss, with a focus on the role of extracellular neuromelanin and neuroinflammation caused by the dysfunction of the LC-noradrenaline pathway.

Evidence for altered excitatory and inhibitory tone in the post-mortem substantia nigra in schizophrenia

Objectives: The substantia nigra (SN) receives glutamatergic and GABAergic inputs that regulate dopaminergic neuronal activity. Imaging studies have shown hyperactivity of the SN in schizophrenia (SZ) patients. We examined neurochemically defined inputs to the SN, synaptic density, and neuromelanin content that might contribute to or reflect this hyperexcitability.Methods: Glutamatergic axon terminals were identified by the immunohistochemical localisation of vGLUT1 and vGLUT2; GABA inputs were identified by the immunohistochemical localisation of GAD67. Neuromelanin granules are visible in unstained sections and thus were assessed in unstained sections. Optical densitometry was measured to assess the density of vGLUT1, vGLUT2 or GAD67 immunolabelled axon terminals and neuromelanin granules. Electron microscopy was used to quantify synaptic and mitochondrial density.Results: Compared to controls, SZ subjects had nonsignificant trends toward a decrease in vGLUT1, and an increase in both vGLUT2 and GAD67. vGLUT1 was negatively correlated with GAD67 in normal controls (NCs) and positively correlated in SZ subjects. A correlation of coefficient analysis showed a significant difference between the negative correlation in NCs and the positive correlation in SZ subjects. Frequency histograms showed the distribution of neuromelanin density was different in SZ subjects compared to NCs. Synaptic density data showed a decrease in inhibitory synapses in SZ subjects. Mitochondrial density was normal in SZ subjects.Conclusions: Synaptic density alterations and the lack of a positive correlation between GAD67 and vGLUT1 could contribute to hyperactivity in the SN.

Neuromelanin, aging, and neuronal vulnerability in Parkinson's disease

Neuromelanin, a dark brown intracellular pigment, has long been associated with Parkinson's disease (PD). In PD, neuromelanin-containing neurons preferentially degenerate, tell-tale neuropathological inclusions form in close association with this pigment, and neuroinflammation is restricted to neuromelanin-containing areas. In humans, neuromelanin accumulates with age, which in turn is the main risk factor for PD. The potential contribution of neuromelanin to PD pathogenesis remains unknown because, in contrast to humans, common laboratory animals lack neuromelanin. The recent introduction of a rodent model exhibiting an age-dependent production of human-like neuromelanin has allowed, for the first time, for the consequences of progressive neuromelanin accumulation-up to levels reached in elderly human brains-to be assessed in vivo. In these animals, intracellular neuromelanin accumulation above a specific threshold compromises neuronal function and triggers a PD-like pathology. As neuromelanin levels reach this threshold in PD patients and presymptomatic PD patients, the modulation of neuromelanin accumulation could provide a therapeutic benefit for PD patients and delay brain aging. © 2019 The Author. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Malassezia and Parkinson's Disease

Parkinson's disease (PD) is a common debilitating neurodegenerative disease caused by a loss of dopamine neurons in the substantia nigra within the central nervous system (CNS). The process leading to this neuronal loss is poorly understood. Seborrheic dermatitis (SD) is a common benign inflammatory condition of the skin which mainly affects lipid-rich regions of the head and trunk. SD is caused by over proliferation of the lipophilic fungus Malassezia. PD and SD are strongly associated. The increased PD risk following an SD diagnosis (OR = 1.69, 95% CI 1.36, 2.1; p < 0.001) reported by Tanner and colleagues remains unexplained. Malassezia were historically considered commensals confined to the skin. However, many recent studies report finding Malassezia in internal organs, including the CNS. This raises the possibility that Malassezia might be directly contributing to PD. Several lines of evidence support this hypothesis. AIDS is causally associated with both parkinsonism and SD, suggesting that weak T cell-mediated control of commensal microbes such as Malassezia might contribute to both. Genetic polymorphisms associated with PD (LRRK2, GBA, PINK1, SPG11, SNCA) increase availability of lipids within human cells, providing a suitable environment for Malassezia. Four LRRK2 polymorphisms which increase PD risk also increase Crohn's disease risk; Crohn's disease is strongly associated with an immune response against fungi, particularly Malassezia. Finally, Malassezia hypha formation and melanin synthesis are stimulated by L-DOPA, which could promote Malassezia invasiveness of dopamine neurons, and contribute to the accumulation of melanin in these neurons. Although Malassezia's presence in the substantia nigra remains to be confirmed, if Malassezia play a role in PD etiology, antifungal drugs should be tested as a possible therapeutic intervention.

Brain tyrosinase overexpression implicates age-dependent neuromelanin production in Parkinson's disease pathogenesis

In Parkinson's disease (PD) there is a selective degeneration of neuromelanin-containing neurons, especially substantia nigra dopaminergic neurons. In humans, neuromelanin accumulates with age, the latter being the main risk factor for PD. The contribution of neuromelanin to PD pathogenesis remains unknown because, unlike humans, common laboratory animals lack neuromelanin. Synthesis of peripheral melanins is mediated by tyrosinase, an enzyme also present at low levels in the brain. Here we report that overexpression of human tyrosinase in rat substantia nigra results in age-dependent production of human-like neuromelanin within nigral dopaminergic neurons, up to levels reached in elderly humans. In these animals, intracellular neuromelanin accumulation above a specific threshold is associated to an age-dependent PD phenotype, including hypokinesia, Lewy body-like formation and nigrostriatal neurodegeneration. Enhancing lysosomal proteostasis reduces intracellular neuromelanin and prevents neurodegeneration in tyrosinase-overexpressing animals. Our results suggest that intracellular neuromelanin levels may set the threshold for the initiation of PD.

Brain tyrosinase overexpression implicates age-dependent neuromelanin production in Parkinson's disease pathogenesis

In Parkinson's disease (PD) there is a selective degeneration of neuromelanin-containing neurons, especially substantia nigra dopaminergic neurons. In humans, neuromelanin accumulates with age, the latter being the main risk factor for PD. The contribution of neuromelanin to PD pathogenesis remains unknown because, unlike humans, common laboratory animals lack neuromelanin. Synthesis of peripheral melanins is mediated by tyrosinase, an enzyme also present at low levels in the brain. Here we report that overexpression of human tyrosinase in rat substantia nigra results in age-dependent production of human-like neuromelanin within nigral dopaminergic neurons, up to levels reached in elderly humans. In these animals, intracellular neuromelanin accumulation above a specific threshold is associated to an age-dependent PD phenotype, including hypokinesia, Lewy body-like formation and nigrostriatal neurodegeneration. Enhancing lysosomal proteostasis reduces intracellular neuromelanin and prevents neurodegeneration in tyrosinase-overexpressing animals. Our results suggest that intracellular neuromelanin levels may set the threshold for the initiation of PD.

Life span pigmentation changes of the substantia nigra detected by neuromelanin-sensitive MRI

Background: Neuromelanin is a pigment with strong iron‐chelating properties preferentially found in dopaminergic neurons of the substantia nigra pars compacta (SNpc). Parkinson's disease is characterized by pronounced, MRI‐detectable neuromelanin loss, but the neuroprotective or neurotoxic role of neuromelanin remains debated. Histological studies have demonstrated neuromelanin increases with age, but this has not been confirmed in vivo, and there is uncertainty whether neuromelanin declines, stabilizes, or increases from middle age.

Methods: This study aimed to establish physiological changes of pigmentation of the SNpc using a pooled data set of neuromelanin‐sensitive 3T MRI from 134 healthy individuals aged 5‐83 years. Neuromelanin‐related brightness (regional contrast to ratio) and calibrated hyperintense volumes were analyzed using linear and nonlinear regression models to characterize age effects. Laterality, sex, and subregional effects were also assessed.

Results: For brightness, age effects were best described as a quadratic trajectory explaining 81.5% of the observed variance in the SNpc showing a strong increase from childhood to adolescence, with plateauing in middle age and a decline in older age. Similar but less pronounced effects were seen in hyperintense volumes. We also show an anterior‐posterior gradient in SNpc contrast, larger normalized neuromelanin‐rich volume in women > 47 years old, but no laterality effect.

Conclusions: Using optimized neuromelanin MRI in a life span sample, we demonstrate a strong age effect with inverted U‐shaped SNpc pigmentation‐related contrast from childhood to old age. This age trajectory of physiological SNpc pigmentation needs to be taken into account for diagnostic applications of depigmentation. The study also paves the way for systematic investigations of the mechanisms of neuromelanin in healthy and pathological brain development and aging. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Proteomic characterization of neuromelanin granules isolated from human substantia nigra by laser-microdissection

Neuromelanin is a complex polymer pigment found primarily in the dopaminergic neurons of human substantia nigra. Neuromelanin pigment is stored in granules including a protein matrix and lipid droplets. Neuromelanin granules are yet only partially characterised regarding their structure and function. To clarify the exact function of neuromelanin granules in humans, their enrichment and in-depth characterization from human substantia nigra is necessary. Previously published global proteome studies of neuromelanin granules in human substantia nigra required high tissue amounts. Due to the limited availability of human brain tissue we established a new method based on laser microdissection combined with mass spectrometry for the isolation and analysis of neuromelanin granules. With this method it is possible for the first time to isolate a sufficient amount of neuromelanin granules for global proteomics analysis from ten 10 μm tissue sections. In total 1,000 proteins were identified associated with neuromelanin granules. More than 68% of those proteins were also identified in previously performed studies. Our results confirm and further extend previously described findings, supporting the connection of neuromelanin granules to iron homeostasis and lysosomes or endosomes. Hence, this method is suitable for the donor specific enrichment and proteomic analysis of neuromelanin granules.

Parkinson's disease as a result of aging

It is generally considered that Parkinson's disease is induced by specific agents that degenerate a clearly defined population of dopaminergic neurons. Data commented in this review suggest that this assumption is not as clear as is often thought and that aging may be critical for Parkinson's disease. Neurons degenerating in Parkinson's disease also degenerate in normal aging, and the different agents involved in the etiology of this illness are also involved in aging. Senescence is a wider phenomenon affecting cells all over the body, whereas Parkinson's disease seems to be restricted to certain brain centers and cell populations. However, reviewed data suggest that Parkinson's disease may be a local expression of aging on cell populations which, by their characteristics (high number of synaptic terminals and mitochondria, unmyelinated axons, etc.), are highly vulnerable to the agents promoting aging. The development of new knowledge about Parkinson's disease could be accelerated if the research on aging and Parkinson's disease were planned together, and the perspective provided by gerontology gains relevance in this field.

Histologic validation of locus coeruleus MRI contrast in post-mortem tissue

The locus coeruleus (LC) noradrenergic system regulates arousal and modulates attention through its extensive projections across the brain. LC dysfunction has been implicated in a broad range of neurodevelopmental, neurodegenerative and psychiatric disorders, as well as in the cognitive changes observed during normal aging. Magnetic resonance imaging (MRI) has been used to characterize the human LC (elevated contrast relative to surrounding structures), but there is limited understanding of the factors underlying putative LC contrast that are critical to successful biomarker development and confidence in localizing nucleus LC. We used ultra-high-field 7 T magnetic resonance imaging (MRI) to acquire T1-weighted microscopy resolution images (78 μm in-plane resolution) of the LC from post-mortem tissue samples. Histological analyses were performed to characterize the distribution of tyrosine hydroxylase (TH) and neuromelanin in the scanned tissue, which allowed for direct comparison with MR microscopy images. Our results indicate that LC-MRI contrast corresponds to the location of neuromelanin cells in LC; these also correspond to norepinephrine neurons. Thus, neuromelanin appears to serve as a natural contrast agent for nucleus LC that can be used to localize nucleus LC and may have the potential to characterize neurodegenerative disease.

Inflaming the diseased brain: a role for tainted melanins

Inflammation plays a crucial role in neurodegenerative diseases, but the irritants responsible for this response remain largely unknown. This report addressed the hypothesis that hypochlorous acid reacts with dopamine to produce melanic precipitates that promote cerebral inflammation. Spectrophotometric studies demonstrated that nM amounts of HOCl and dopamine react within seconds. A second-order rate constant for the reaction of HOCl and dopamine of 2.5 × 10(4)M(-1)s(-1) was obtained by measuring loss of dopaminergic fluorescence due to HOCl. Gravimetric measurements, electron microscopy, elemental analysis, and a novel use of flow cytometry confirmed that the major product of this reaction is a precipitate with an average diameter of 1.5 μm. Flow cytometry was also used to demonstrate the preferential reaction of HOCl with dopamine rather than albumin. Engulfment of the chlorodopamine particulates by phagocytes in vitro caused these cells to release TNFα and die. Intrastriatal administration of 10(6) particles also increased the content of TNFα in the brain and led to a 50% loss of the dopaminergic neurons in the nigra. These studies indicate that HOCl and dopamine react quickly and preferentially with each other to produce particles that promote inflammation and neuronal death in the brain.

Neuromelanin of the human substantia nigra: an update

Dopaminergic neurons of the substantia nigra selectively degenerate over the course of Parkinson's disease. These neurons are also the most heavily pigmented cells of the brain, accumulating the dark pigment neuromelanin over a lifetime. The massive presence of neuromelanin in these brain areas has long been suspected as a key factor involved in the selective vulnerability of neurons. The high concentration of neuromelanin in substantia nigra neurons seems to be linked to the presence of considerable amounts of cytosolic dopamine that have not been sequestered into synaptic vesicles. Over the past few years, studies have uncovered a dual nature of neuromelanin. Intraneuronal neuromelanin can be a protective factor, shielding the cells from toxic effects of redox active metals, toxins, and excess of cytosolic catecholamines. In contrast, neuromelanin released by dying neurons can contribute to the activation of neuroglia triggering the neuroinflammation that characterizes Parkinson's disease. This article reviews recent studies on the molecular aspects of neuromelanin of the human substantia nigra.

Melanin affinity and its possible role in neurodegeneration

Certain drugs with melanin affinity are known to have caused pigmentary lesions in the eye and skin. This was the basis for the hypothesis that compounds with melanin affinity may cause damage also in other melanin-bearing tissues such as the substantia nigra. The heterogeneity of compounds that binds to melanin is large. Toxins, drugs, and several other compounds have melanin affinity. Compounds showing the highest affinity are mainly organic amines and metal ions. The binding of toxicants to melanin probably protects the cells initially. However, the binding is normally, slowly reversible and melanin may accumulate the toxicant and gradually release it into the cytosol. Several studies indicate that neuromelanin may play a significant role both in the initiation and in the progression of neurodegeneration. MPTP/MPP(+) that has been causally linked with Parkinsonism has high affinity for neuromelanin, and the induced dopaminergic denervation correlates with the neuromelanin content in the cells. This shows that the toxicological implications of the accumulation of toxicants in pigmented neurons and its possible role in neurodegeneration should not be neglected. Extracellular neuromelanin has been reported to activate dendritic cells and microglia. An initial neuronal damage induced by a neurotoxicant that leaks neuromelanin from the cells may therefore lead to a vicious cycle of neuroinflammation and further neurodegeneration. Although there are many clues to the particular vulnerability of dopaminergic neurons of substantia nigra in Parkinson's disease, the critical factors are not known. Further studies to determine the importance of neuromelanin in neurodegeneration and Parkinson's disease are warranted.

Age-related appearance of dendritic inclusions in catecholaminergic brainstem neurons

We identified p62-immunoreactive inclusions in dendrites of catecholaminergic brainstem projection neurons using antibodies against p62, ubiquitin, α-synuclein, hyperphosphorylated tau, and tyrosine hydroxylase in 100-μm sections through the brainstem dorsal vagal area, locus coeruleus, and substantia nigra of 149 autopsy cases staged for intraneuronal Alzheimer's and Parkinson's disease-associated lesions. The inclusions resembled Marinesco bodies within cell nuclei of catecholaminergic neurons as well as the dot-like structures previously described by Dickson in specific neuropil areas in humans. The p62-positive inclusions were confined to dendrites of catecholaminergic neurons, lacked neuromelanin granules, and were tau- and α-synuclein-negative. Their immunoreactivity for ubiquitin varied and their prevalence significantly increased with advancing age. The presence or absence of Alzheimer's and/or Parkinson's disease-associated pathology did not influence their existence. There was a strong association between the presence of p62-positive inclusions and Marinesco bodies (p < 0.0001). Our results reveal a hitherto unknown alteration within specific neuronal types of the human brainstem that may be independent of the sequestosome-ubiquitin-proteasomal pathway and unrelated to proteinaceous aggregate-formation of neurodegenerative diseases.

A case of melanotic desmoplastic ganglioglioma

We describe a case of desmoplastic infantile ganglioglioma (DIG) in a 9-month-old boy located in the temporal lobe. Grossly the tumor was brown and superficially located. Histologically the tumor contained pigment in numerous neoplastic cells, shown to be melanosomal melanin by ultrastructural examination. Pigmented neoplasms have been reported at various sites in the central and peripheral nervous system. Previous reports on pigmented neuroepithelial tumors include neoplasms containing melanin, while others have contained neuromelanin and or lipofuscin. This case represents the first description of pigmented neoplastic cells in DIG, enlarging the spectrum of pigmented primary CNS tumors.

The importance of brain banks for molecular neuropathological research: The New South Wales Tissue Resource Centre experience

New developments in molecular neuropathology have evoked increased demands for postmortem human brain tissue. The New South Wales Tissue Resource Centre (TRC) at The University of Sydney has grown from a small tissue collection into one of the leading international brain banking facilities, which operates with best practice and quality control protocols. The focus of this tissue collection is on schizophrenia and allied disorders, alcohol use disorders and controls. This review highlights changes in TRC operational procedures dictated by modern neuroscience, and provides examples of applications of modern molecular techniques to study the neuropathogenesis of many different brain disorders.

Tyrosinase is not detected in human catecholaminergic neurons by immunohistochemistry and Western blot analysis

Catecholaminergic neurons of the primate substantia nigra (SN) pars compacta (SNc) and the locus coeruleus contain neuromelanin (NM) granules as characteristic structures underlying the pigmentation of these brain areas. Due to a phylogenetic appearance NM granules are absent in the rodent brain, but gradually become present in primates until they reach a maximal expression in humans. Although a possible mechanism of pigment formation may be autoxidation of the NM precursors dopamine or noradrenalin, several groups have suggested an enzymatic formation of NM mediated by tyrosinase or a related enzyme. Since tyrosinase mRNA is suggested to be expressed in the SN of mice and humans, we reinvestigated the expression of tyrosinase in the human SNc and the locus coeruleus at the protein level by immunohistochemistry and Western blot analysis, but could not detect tyrosinase in these brain regions.