Dystonia is a neurological disorder characterized by involuntary twisting movements or abnormal postures that are caused by excessive activation of specific muscles or co-activation of agonist and antagonist muscle groups. Though there are many different types and causes for human dystonia, in most cases the pathogenesis is poorly understood and treatment strategies are limited. Recently, two lines of evidence have suggested that dystonia may be associated with abnormal calcium metabolism in the brain. First, + Bay K 8644 and FPL 64176, two structurally distinct and specific L-type calcium channel agonists can provoke dystonia in normal C57L/6J mice. Second, dystonia is a prominent feature of several strains of mice carrying mutations in genes encoding calcium channel proteins or related regulatory proteins. The overall goal of this proposal is to assess the pathogenesis of dystonia in mouse models of dystonia associated with abnormal calcium channel function. Our hypothesis is that aberrant calcium function in regions involved in motor control are responsible for dystonia.
Specific aim 1 addresses the neuroanatomic and neuropharmacologic basis of dystonia in a mouse model induced by administration of L-type calcium channel agonists. We will use functional mapping techniques, 2-deoxyglucose autoradiography and immediate early gene induction, to define regions of abnormal brain activity followed by regional microinjection studies to determine which of these regions is most responsible for dystonia in this model. To define the neuropharmacologic basis of dystonia in this model, we will examine the ability of several drugs selective towards specific neurotransmitter systems to modify dystonia caused by the L-type calcium channel agonists.
Aim 2 involved the use of functional mapping in strains of mice with mutations in genes encoding calcium channel proteins to define regions of abnormal brain activity that appear normal in standard histopathologic studies. We will focus on three mutants, tottering, lethargic, and leaner, that have either generalized or inducible dystonia.
In aim 3, we will develop electromyographic criteria to characterize dystonia in the pharmacologic and genetic models, and determine if they can be applied to other mouse mutants with abnormal motor behavior that is otherwise difficult to classify. Since preliminary animal work suggests that L-type calcium channel antagonists might be useful in the treatment of human dystonia, we will conduct a pilot double-blinded crossover trial of nifedipine in patients with three easily-defined subtypes of dystonia. These studies have direct relevance for advancing our understanding of the pathogenesis and treatment of dystonia.
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