Upregulation and axonal transport of synaptotagmin-IV in the direct-pathway medium spiny neurons in hemi-parkinsonian rats induced by dopamine D1 receptor stimulation

Neuroinflammation-Induced Upregulation of Glial Cathepsin X Expression and Activity in vivo

Neuroinflammation is an important factor in the pathogenesis of neurodegenerative diseases. Microglia-derived lysosomal cathepsins have been increasingly recognized as important inflammatory mediators that trigger signaling pathways that aggravate neuroinflammation. In vitro, a contribution to neuroinflammation processes has been shown for cathepsin X: however, the expression patterns and functional role of cathepsin X in neuroinflammatory brain pathology remain elusive. In this study we analyzed the expression, activity, regional distribution and cellular localization of cathepsin X in the rat brain with neuroinflammation-induced neurodegeneration. The unilateral injection of lipopolysaccharide (LPS) induced a strong upregulation of cathepsin X expression and its activity in the ipsilateral striatum. In addition to the striatum, cathepsin X overexpression was detected in other brain areas such as the cerebral cortex, corpus callosum, subventricular zone and external globus pallidus, whereas the upregulation was mainly restricted to activated microglia and reactive astrocytes. Continuous administration of the cathepsin X inhibitor AMS36 indicated protective effects against LPS-induced striatal degeneration, as seen by the attenuated LPS-mediated dilation of the lateral ventricles and partial decreased extent of striatal lesion. Taken together, our results indicate that cathepsin X plays a role as a pathogenic factor in neuroinflammation-induced neurodegeneration and represents a potential therapeutic target for neurodegenerative diseases associated with neuroinflammation.

Are the Symptoms of Parkinsonism Cortical in Origin?

We present three reasons to suspect that the major deleterious consequence of dopamine loss from the striatum is a cortical malfunction. We suggest that it is cortex, rather than striatum, that should be considered as the source of the debilitating symptoms of Parkinson's disease (PD) since:1.

Cortical synapses onto striatal dendritic spines are lost in PD.

2.

All known treatments of the symptoms of PD disrupt beta oscillations. Oscillations that are also disrupted following antidromic activation of cortical neurons.

3.

The final output of basal ganglia directly modulates thalamic connections to layer I of frontal cortical areas, regions intimately associated with motor behaviour.

These three reasons combined with evidence that the current summary diagram of the basal ganglia involvement in PD is imprecise at best, suggest that a re-orientation of the treatment strategies towards cortical, rather than striatal malfunction, is overdue.

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Suggested experimental contributions support the proposal of a cortical participation in PD.

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DBS produces antidromic activation of motor cortex and desynchronizes beta oscillations.

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Loss of dopamine decreases dendritic spines in the striatal D2 projection neurons.

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Motor thalamus distributes terminals into frontal cortex layer I.

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Thalamocortical-layer I activity increases with locomotion.