Basal Ganglia Circuits: What's Now and Next?

The current model of the basal ganglia was introduced two decades ago and has become the basis for most of our current understanding of basal ganglia function and dysfunction. Extensive research efforts have been carried out in recent years leading to unprecedented levels of understanding of the main operational principles underlying the pathophysiology of the basal ganglia. Although somewhat obsolete, the “classical ” basal ganglia model developed in the mid 1980s by the “founding fathers ” (Penney and Young, 1986; Crossman, 1987; Albin et al., 1989; DeLong, 1990) still maintains a remarkable appeal. This model was shaped mainly by the preponderance of anatomical and physiological data available at the time. In the past few years, the development of a whole range of new technical breakthroughs has boosted the availability of data with paramount importance at a breath-taking speed, and thus incorporating these recent advances to further enrich the classical model has becom

On the relationships between the caudal intralaminar nuclei of the thalamus and the basal ganglia : implications for the pathophysiology of Parkinson’s disease

Besides corticostriatal projections, the thalamic intralaminar nuclei are a major source of glutamatergic afferents reaching the basal ganglia input nuclei. Although the thalamostriatal system is already well characterized from the anatomical point of view, the role to be played by this pathway within basal ganglia function (both in normal and pathological conditions) remains poorly understood. On one hand, neurode- generation phenomena restricted to the caudal intralaminar nuclei have been described in several neurodegenerative disorders such as Parkinson’s disease, progressive supranuclear palsy and Huntington’s disease. On the other hand, after unilateral dopaminergic depletion in rodents the caudal intralaminar nuclei are highly hyperactive. Indeed, the chemical ablation of the caudal intralaminar nuclei prevents the increase of the activity observed in both the basal ganglia output nuclei and the subthalamic nucleus (STN) after unilateral dopaminergic depletion. These findings suggest that the caudal intralaminar nuclei might be responsible (at least partially) for the changes in activity of the STN and basal ganglia output nuclei typically seen under circumstances of dopamine removal. These results paved the way for the implementation of pioneer clinical experiences focused on targeting the caudal intralaminar nuclei with a deep brain stimulation electrode in patients suffering from advanced Parkinson’s disease. This approach resulted in the alleviation of cardinal symptoms of the disease such as resting tremor, druginduced dyskinesias and chronic pain.peer-reviewe

Angiotensin Type 1 Receptor Antagonists Protect Against Alpha-Synuclein-Induced Neuroinflammation and Dopaminergic Neuron Death

Altres ajuts: This study received funding from the Centro de Investigación Biomédica en Red Enfermedades Neurodegenerativas' intramural program (2014/01 and 2017/02), Galician Government (Xunta de Galicia, Consellería de Educación; GRC2014/002), Navarra Government (Departamento de Salud; 046-2017), and Fondo Europeo de Desarrollo Regional (Regional European Development Fund).The loss of dopaminergic neurons and α-synuclein accumulation are major hallmarks of Parkinson's disease (PD), and it has been suggested that a major mechanism of α-synuclein toxicity is microglial activation. The lack of animal models that properly reproduce PD, and particularly the underlying synucleinopathy, has hampered the clarification of PD mechanisms and the development of effective therapies. Here, we used neurospecific adeno-associated viral vectors serotype 9 coding for either the wild-type or mutated forms of human alpha-synuclein (WT and SynA53T, respectively) under the control of a synapsin promoter to further induce a marked dopaminergic neuron loss together with an important microglial neuroinflammatory response. Overexpression of neuronal alpha-synuclein led to increased expression of angiotensin type 1 receptors and NADPH oxidase activity, together with a marked increase in the number of OX-6-positive microglial cells and expression of markers of phagocytic activity (CD68) and classical pro-inflammatory/M1 microglial phenotype markers such as inducible nitric oxide synthase, tumor necrosis factor alpha, interleukin-1β, and IL-6. Moreover, a significant decrease in the expression of markers of immunoregulatory/M2 microglial phenotype such as the enzyme arginase-1 was constantly observed. Interestingly, alpha-synuclein-induced changes in microglial phenotype markers and dopaminergic neuron death were inhibited by simultaneous treatment with the angiotensin type 1 blockers candesartan or telmisartan. Our results suggest the repurposing of candesartan and telmisartan as a neuroprotective strategy for PD

Differential organization of cortical inputs to striatal projection neurons of the matrix compartment in rats

In prior studies, we described the differential organization of corticostriatal and thalamostriatal inputs to the spines of direct pathway (dSPNs) and indirect pathway striatal projection neurons (iSPNs) of the matrix compartment. In the present electron microscopic (EM) analysis, we have refined understanding of the relative amounts of cortical axospinous versus axodendritic input to the two types of SPNs. Of note, we found that individual dSPNs receive about twice as many axospinous synaptic terminals from IT-type (intratelencephalically projecting) cortical neurons as they do from PT-type (pyramidal tract projecting) cortical neurons. We also found that PT-type axospinous synaptic terminals were about 1.5 times as common on individual iSPNs as IT-type axospinous synaptic terminals. Overall, a higher percentage of IT-type terminals contacted dSPN than iSPN spines, while a higher percentage of PT-type terminals contacted iSPN than dSPN spines. Notably, IT-type axospinous synaptic terminals were significantly larger on iSPN spines than on dSPN spines. By contrast to axospinous input, the axodendritic PT-type input to dSPNs was more substantial than that to iSPNs, and the axodendritic IT-type input appeared to be meager and comparable for both SPN types. The prominent axodendritic PT-type input to dSPNs may accentuate their PT-type responsiveness, and the large size of axospinous IT-type terminals on iSPNs may accentuate their IT-type responsiveness. Using transneuronal labeling with rabies virus to selectively label the cortical neurons with direct input to the dSPNs projecting to the substantia nigra pars reticulata, we found that the input predominantly arose from neurons in the upper layers of motor cortices, in which IT-type perikarya predominate. The differential cortical input to SPNs is likely to play key roles in motor control and motor learning

Goal-directed and habitual control in the basal ganglia: implications for Parkinson's disease

Progressive loss of the ascending dopaminergic projection in the basal ganglia is a fundamental pathological feature of Parkinson's disease. Studies in animals and humans have identified spatially segregated functional territories in the basal ganglia for the control of goal-directed and habitual actions. In patients with Parkinson's disease the loss of dopamine is predominantly in the posterior putamen, a region of the basal ganglia associated with the control of habitual behaviour. These patients may therefore be forced into a progressive reliance on the goal-directed mode of action control that is mediated by comparatively preserved processing in the rostromedial striatum. Thus, many of their behavioural difficulties may reflect a loss of normal automatic control owing to distorting output signals from habitual control circuits, which impede the expression of goal-directed action. © 2010 Macmillan Publishers Limited. All rights reserved

Parkinson's Disease Cell Vulnerability and Disease Progression

Parkinson's disease is a neurodegenerative disorder that affects 1.5% of the global population over 65 years of age. The hallmark feature of this disease is the degeneration of dopamine neurons in the substantia nigra pars compacta and a consequent striatal dopamine deficiency. The pathogenesis of Parkinson's Disease remains unclear. Despite tremendous growth in recent years in our knowledge of the molecular basis of Parkinson's Disease and the molecular pathways of cell death important questions remain regarding why are substantia nigra cells especially vulnerable, which mechanisms underlie progressive cell loss or what do Lewy bodies or alpha-synuclein reveal about disease progression. Understanding the different vulnerability of the dopaminergic neurons from midbrain regions and the mechanisms whereby pathology becomes widespread are primary objectives of basic and clinical research in Parkinson's Disease. This e-Book discusses the etiopathogenesis of Parkinson's Disease, presenting a series of papers that provide up-to-date, state-of-the-art information on molecular and cellular mechanisms involved in the neurodegeneration process in the disease, the role of activation of functional anatomical organization of the basal ganglia and in particular habitual vs goal directed systems as a factor of neuronal vulnerability, the possibility that Parkinson's Disease coulb be a prion disease and how genetic factors linked to familial and sporadic forms of PD. We hope that this e-Book will stimulate the continuing efforts to understand the cell and physiological mechanisms underlying the origin of Parkinson's Disease

Neuroanatomical tract-tracing techniques that did go viral

Neuroanatomical tracing methods remain fundamental for elucidating the complexity of brain circuits. During the past decades, the technical arsenal at our disposal has been greatly enriched, with a steady supply of fresh arrivals. This paper provides a landscape view of classical and modern tools for tract-tracing purposes. Focus is placed on methods that have gone viral, i.e., became most widespread used and fully reliable. To keep an historical perspective, we start by reviewing one-dimensional, standalone transport-tracing tools; these including today’s two most favorite anterograde neuroanatomical tracers such as Phaseolus vulgaris-leucoagglutinin and biotinylated dextran amine. Next, emphasis is placed on several classical tools widely used for retrograde neuroanatomical tracing purposes, where Fluoro-Gold in our opinion represents the best example. Furthermore, it is worth noting that multi-dimensional paradigms can be designed by combining different tracers or by applying a given tracer together with detecting one or more neurochemical substances, as illustrated here with several examples. Finally, it is without any doubt that we are currently witnessing the unstoppable and spectacular rise of modern molecular-genetic techniques based on the use of modified viruses as delivery vehicles for genetic material, therefore, pushing the tract-tracing field forward into a new era. In summary, here, we aim to provide neuroscientists with the advice and background required when facing a choice on which neuroanatomical tracer—or combination thereof—might be best suited for addressing a given experimental design