Noradrenergic pathways of locus coeruleus in Parkinson's and Alzheimer's pathology

Advancements in Genetic and Biochemical Insights: Unraveling the Etiopathogenesis of Neurodegeneration in Parkinson's Disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative movement disorder worldwide, which is primarily characterized by motor impairments. Even though multiple hypotheses have been proposed over the decades that explain the pathogenesis of PD, presently, there are no cures or promising preventive therapies for PD. This could be attributed to the intricate pathophysiology of PD and the poorly understood molecular mechanism. To address these challenges comprehensively, a thorough disease model is imperative for a nuanced understanding of PD's underlying pathogenic mechanisms. This review offers a detailed analysis of the current state of knowledge regarding the molecular mechanisms underlying the pathogenesis of PD, with a particular emphasis on the roles played by gene-based factors in the disease's development and progression. This study includes an extensive discussion of the proteins and mutations of primary genes that are linked to PD, including α-synuclein, GBA1, LRRK2, VPS35, PINK1, DJ-1, and Parkin. Further, this review explores plausible mechanisms for DAergic neural loss, non-motor and non-dopaminergic pathologies, and the risk factors associated with PD. The present study will encourage the related research fields to understand better and analyze the current status of the biochemical mechanisms of PD, which might contribute to the design and development of efficacious and safe treatment strategies for PD in future endeavors.

Is alumina suitable for solid phase extraction of catecholamines from brain tissue?

Occupational and environmental toxicology specialists find catecholamine fluctuations in brain tissue relevant for research of neurotoxicity, such as that induced by manganese or zinc, pesticides, industrial solvents, plastic, air pollution, or irradiation. Considering that catecholamine tissue concentrations are generally very low, their extraction requires a reliable and optimal method that will achieve maximum recovery and minimise other interferences. This study aimed to evaluate whether the aluminium (III) oxide (Al2O3, alumina) based cartridges designed for catecholamine isolation from plasma could be used for solid-phase extraction (SPE) of catecholamine from the brain tissue. To do that, we homogenised Wistar rat brain tissue with perchloric acid and compared three extraction techniques: SPE, the routine filtration through a 0.22 µm membrane filter, and their combination. In the extracts, we compared relative chromatographic catecholamine mobility measured with high performance liquid chromatography with electrochemical detection. Chromatographic patterns for norepinephrine and epinephrine were similar regardless of the extraction technique, which indicates that the alumina cartridge is good enough to isolate them from brain tissue. However, the dopamine pattern was unsatisfactory, and further experiments are needed to identify the issue and optimise the protocol.

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.

Locus coeruleus ablation in mice: protocol optimization, stereology and behavioral impact

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.

The Neurodegenerative Elderly Syndrome (NES) hypothesis: Alzheimer and Parkinson are two faces of the same disease

Increasing evidence suggests that Alzheimer's disease (AD) and Parkinson's disease (PD) share monoamine and alpha-synuclein (αSyn) dysfunctions, often beginning years before clinical manifestations onset. The triggers for these impairments and the causes leading these early neurodegenerative processes to become AD or PD remain unclear. We address these issues by proposing a radically new perspective to frame AD and PD: they are different manifestations of one only disease we call "Neurodegenerative Elderly Syndrome (NES)". NES goes through three phases. The seeding stage, which starts years before clinical signs, and where the part of the brain-body affected by the initial αSyn and monoamine dysfunctions, influences the future possible progression of NES towards PD or AD. The compensatory stage, where the clinical symptoms are still silent thanks to compensatory mechanisms keeping monoamine concentrations homeostasis. The bifurcation stage, where NES becomes AD or PD. We present recent literature supporting NES and discuss how this hypothesis could radically change the comprehension of AD and PD comorbidities and the design of novel system-level diagnostic and therapeutic actions.

The role of neurotransmitter systems in mediating deep brain stimulation effects in Parkinson’s disease

Deep brain stimulation (DBS) is among the most successful paradigms in both translational and reverse translational neuroscience. DBS has developed into a standard treatment for movement disorders such as Parkinson’s disease (PD) in recent decades, however, specific mechanisms behind DBS’s efficacy and side effects remain unrevealed. Several hypotheses have been proposed, including neuronal firing rate and pattern theories that emphasize the impact of DBS on local circuitry but detail distant electrophysiological readouts to a lesser extent. Furthermore, ample preclinical and clinical evidence indicates that DBS influences neurotransmitter dynamics in PD, particularly the effects of subthalamic nucleus (STN) DBS on striatal dopaminergic and glutamatergic systems; pallidum DBS on striatal dopaminergic and GABAergic systems; pedunculopontine nucleus DBS on cholinergic systems; and STN-DBS on locus coeruleus (LC) noradrenergic system. DBS has additionally been associated with mood-related side effects within brainstem serotoninergic systems in response to STN-DBS. Still, addressing the mechanisms of DBS on neurotransmitters’ dynamics is commonly overlooked due to its practical difficulties in monitoring real-time changes in remote areas. Given that electrical stimulation alters neurotransmitter release in local and remote regions, it eventually exhibits changes in specific neuronal functions. Consequently, such changes lead to further modulation, synthesis, and release of neurotransmitters. This narrative review discusses the main neurotransmitter dynamics in PD and their role in mediating DBS effects from preclinical and clinical data.

REM sleep behavior and olfactory dysfunction: improving the utility and translation of animal models in the search for neuroprotective therapies for Parkinson's disease

Parkinson's disease (PD) is a heterogeneous neurodegenerative disease that belongs to the family of synucleiopathies, varying in age, symptoms and progression. Hallmark of the disease is the accumulation of misfolded α-synuclein protein (α-Syn) in neuronal and non-neuronal brain cells. In past decades, diagnosis and treatment of PD has focused on motor deficits, which for the clinical endpoint, have contributed to the prevalence of deficits in the nigrostriatal dopaminergic system and animal models related to motor behavior to study disease. However, clinical trials have failed to translate results from animal models into effective treatments. PD as a multisystem disorder therefore requires additional assessment of motor and non-motor symptoms. Braak's staging revealed early α-Syn pathology in pontine brainstem and olfactory circuits controlling rapid eye movement sleep behavior disorder (RBD) and olfaction, respectively. Recent converging evidence from multicenter clinical studies supports that RBD is the most important risk factor for prodromal PD and the conduct of neuroprotective therapeutic trials in RBD-enriched cohorts has been recommended. Animal models of RBD and olfaction dysfunction can aid to fill the gap in translational research.