Restoration of Noradrenergic Function in Parkinson's Disease Model Mice

Noradrenergic alterations in Parkinson's disease: a combined 11C-yohimbine PET/neuromelanin MRI study

Degeneration of the noradrenergic system is now considered a pathological hallmark of Parkinson's disease, but little is known about its consequences in terms of parkinsonian manifestations. Here, we evaluated two aspects of the noradrenergic system using multimodal in vivo imaging in patients with Parkinson's disease and healthy controls: the pigmented cell bodies of the locus coeruleus with neuromelanin sensitive MRI; and the density of α2-adrenergic receptors (ARs) with PET using 11C-yohimbine. Thirty patients with Parkinson's disease and 30 age- and sex-matched healthy control subjects were included. The characteristics of the patients' symptoms were assessed using the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS). Patients showed reduced neuromelanin signal intensity in the locus coeruleus compared with controls and diminished 11C-yohimbine binding in widespread cortical regions, including the motor cortex, as well as in the insula, thalamus and putamen. Clinically, locus coeruleus neuronal loss was correlated with motor (bradykinesia, motor fluctuations, tremor) and non-motor (fatigue, apathy, constipation) symptoms. A reduction of α2-AR availability in the thalamus was associated with tremor, while a reduction in the putamen, the insula and the superior temporal gyrus was associated with anxiety. These results highlight a multifaceted alteration of the noradrenergic system in Parkinson's disease since locus coeruleus and α2-AR degeneration were found to be partly uncoupled. These findings raise important issues about noradrenergic dysfunction that may encourage the search for new drugs targeting this system, including α2-ARs, for the treatment of Parkinson's disease.

Distribution of α2-Adrenergic Receptors in the Living Human Brain Using [11C]yohimbine PET

The neurofunctional basis of the noradrenergic (NA) system and its associated disorders is still very incomplete because in vivo imaging tools in humans have been missing up to now. Here, for the first time, we use [¹¹C]yohimbine in a large sample of subjects (46 healthy volunteers, 23 females, 23 males; aged 20-50) to perform direct quantification of regional alpha 2 adrenergic receptors' (α₂-ARs) availability in the living human brain. The global map shows the highest [¹¹C]yohimbine binding in the hippocampus, the occipital lobe, the cingulate gyrus, and the frontal lobe. Moderate binding was found in the parietal lobe, thalamus, parahippocampus, insula, and temporal lobe. Low levels of binding were found in the basal ganglia, the amygdala, the cerebellum, and the raphe nucleus. Parcellation of the brain into anatomical subregions revealed important variations in [¹¹C]yohimbine binding within most structures. Strong heterogeneity was found in the occipital lobe, the frontal lobe, and the basal ganglia, with substantial gender effects. Mapping the distribution of α₂-ARs in the living human brain may prove useful not only for understanding the role of the NA system in many brain functions, but also for understanding neurodegenerative diseases in which altered NA transmission with specific loss of α₂-ARs is suspected.

The noradrenergic subtype of Parkinson disease: from animal models to clinical practice

Many advances in understanding the pathophysiology of Parkinson disease (PD) have been based on research addressing its motor symptoms and phenotypes. Various data-driven clinical phenotyping studies supported by neuropathological and in vivo neuroimaging data suggest the existence of distinct non-motor endophenotypes of PD even at diagnosis, a concept further strengthened by the predominantly non-motor spectrum of symptoms in prodromal PD. Preclinical and clinical studies support early dysfunction of noradrenergic transmission in both the CNS and peripheral nervous system circuits in patients with PD that results in a specific cluster of non-motor symptoms, including rapid eye movement sleep behaviour disorder, pain, anxiety and dysautonomia (particularly orthostatic hypotension and urinary dysfunction). Cluster analyses of large independent cohorts of patients with PD and phenotype-focused studies have confirmed the existence of a noradrenergic subtype of PD, which had been previously postulated but not fully characterized. This Review discusses the translational work that unravelled the clinical and neuropathological processes underpinning the noradrenergic PD subtype. Although some overlap with other PD subtypes is inevitable as the disease progresses, recognition of noradrenergic PD as a distinct early disease subtype represents an important advance towards the delivery of personalized medicine for patients with PD.

Two-photon fluorescence imaging and specifically biosensing of norepinephrine on a 100-ms timescale

Norepinephrine (NE) is a key neurotransmitter in the central nervous system of organisms; however, specifically tracking the transient NE dynamics with high spatiotemporal resolution in living systems remains a great challenge. Herein, we develop a small molecular fluorescent probe that can precisely anchor on neuronal cytomembranes and specifically respond to NE on a 100-ms timescale. A unique dual acceleration mechanism of molecular-folding and water-bridging is disclosed, which boosts the reaction kinetics by ˃10⁵ and ˃10³ times, respectively. Benefiting from its excellent spatiotemporal resolution, the probe is applied to monitor NE dynamics at the single-neuron level, thereby, successfully snapshotting the fast fluctuation of NE levels at neuronal cytomembranes within 2 s. Moreover, two-photon fluorescence imaging of acute brain tissue slices reveals a close correlation between downregulated NE levels and Alzheimer's disease pathology as well as antioxidant therapy.

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.

Carving the senescent phenotype by the chemical reactivity of catecholamines: An integrative review

Macromolecules damaged by covalent modifications produced by chemically reactive metabolites accumulate in the slowly renewable components of living bodies and compromise their functions. Among such metabolites, catecholamines (CA) are unique, compared with the ubiquitous oxygen, ROS, glucose and methylglyoxal, in that their high chemical reactivity is confined to a limited set of cell types, including the dopaminergic and noradrenergic neurons and their direct targets, which suffer from CA propensities for autoxidation yielding toxic quinones, and for Pictet-Spengler reactions with carbonyl-containing compounds, which yield mitochondrial toxins. The functions progressively compromised because of that include motor performance, cognition, reward-driven behaviors, emotional tuning, and the neuroendocrine control of reproduction. The phenotypic manifestations of the resulting disorders culminate in such conditions as Parkinson's and Alzheimer's diseases, hypertension, sarcopenia, and menopause. The reasons to suspect that CA play some special role in aging accumulated since early 1970-ies. Published reviews address the role of CA hazardousness in the development of specific aging-associated diseases. The present integrative review explores how the bizarre discrepancy between CA hazardousness and biological importance could have emerged in evolution, how much does the chemical reactivity of CA contribute to the senescent phenotype in mammals, and what can be done with it.