Abstract
Dystonia pathophysiology has been partly linked to downregulation and dysfunction of dopamine D2 receptors in striatum. We aimed to investigate the possible morpho-structural correlates of D2 receptor downregulation in the striatum of a DYT1 Tor1a mouse model. Adult control Tor1a+/+ and mutant Tor1a+/− mice were used. The brains were perfused and free-floating sections of basal ganglia were incubated with polyclonal anti-D2 antibody, followed by secondary immune-fluorescent antibody. Confocal microscopy was used to detect immune-fluorescent signals. The same primary antibody was used to evaluate D2 receptor expression by western blot. The D2 receptor immune-fluorescence appeared circumscribed in small disks (~0.3–0.5 µm diameter), likely representing D2 synapse aggregates, densely distributed in the striatum of Tor1a+/+ mice. In the Tor1a+/− mice the D2 aggregates were significantly smaller (µm2 2.4 ± SE 0.16, compared to µm2 6.73 ± SE 3.41 in Tor1a+/+) and sparse, with ~30% less number per microscopic field, value correspondent to the amount of reduced D2 expression in western blotting analysis. In DYT1 mutant mice the sparse and small D2 synapses in the striatum may be insufficient to “gate” the amount of presynaptic dopamine release diffusing in peri-synaptic space, and this consequently may result in a timing and spatially larger nonselective sphere of influence of dopamine action.
Highlights
Dystonia is a disorder of movement characterized by disturbed agonist-antagonist muscle activation [1], with particular difficulty switching between sequential muscles involved in a complex task, either voluntary or involuntary [2]
In DYT1 mutant mice the sparse and small D2 synapses in the striatum may be insufficient to “gate” the amount of presynaptic dopamine release diffusing in peri-synaptic space, and this may result in a timing and spatially larger nonselective sphere of influence of dopamine action
We first quantified the levels of D2 receptors on proteins extracted from the striatum
Summary
Dystonia is a disorder of movement characterized by disturbed agonist-antagonist muscle activation [1], with particular difficulty switching between sequential muscles involved in a complex task, either voluntary or involuntary [2]. Symptomatic dystonia can be observed in various neurological disorders, including cerebrovascular diseases, Parkinson’s disease, and Wilson’s disease [3]. No pathologic correlate is still known for many dystonic disorders categorized as idiopathic dystonia, and further divided into generalized, focal, and segmental dystonia [4]. Various dystonic forms were often interpreted in psychological or psychiatric terms until the late 19th century [3,5], when the descriptions of familial forms of generalized primary torsion dystonia suggested that it is an organic disease [6,7]. The identification of genetic mutations in some families in the late 20th century established an organic framework for idiopathic dystonia (see 3). The most common and severe form of genetic dystonia is caused by a 3 bp deletion (GAG) in the coding region of the TOR1A (DYT1) gene, which results in a defective protein called torsinA [8]
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