Dopamine (DA) replacement therapy of Parkinson's Disease (PD) often becomes ineffective late in disease progression due to development of drug resistance and dyskinesias. We hypothesize that this is due to altered morphology of striatal medium spiny neurons arising from changes in expression andlor function of dendritic proteins. Preliminary Studies exploit a rat model of PD generated by unilateral injection of 6-hydroxyzopamine (6-OHDA) into substantia nigra. Total CaMKIIa levels in lesioned striaturn were decreased by 30% relative to contralateral control striaturn 9 months after 6-OHDA-injection; several other proteins were unchanged. CaMKII is critical for hippocampal synaTtic plasticity: NMDA receptor activation induces Thr 286 autophosphorylation, generating a Ca2+- independent form of CaMKII that translocates to postsynaptic densities, phsphorylates AMPA receptors (GluRl) and is required for long term potentiation. Although striatal CaMKII functions remain obscure, preliminary data indicate that Thr 286 autophosphorylation of CaMKII is increased in 6-OHDA lesioned striatum. Together, these exciting findings suggest the specific hypothesis that chronic dopamine deficiency in PD or induced by 6 OHDA perturbs normal physiological regulation of the key CaMKII signaling pathway, which will be tested using three Aims. 1. Characterize CaMKII expression in 6-OHDA-lesioned striaturn. CaMKII expression/localization in 6-OHDA lesioned striaturn will be compared to control striatum from the contralateral hemisphere and from vehicle-injected animals. Possible amelioration of changes by I-DOPA, or glutamate-receptor blockers will be investigated. 2. Determine role(s) of DA in acute regulation of CaMKII in normal striaturn. Isolated striatal slices will be used to investigate roles of D1 and D2 DA receptors in regulating basal and glutamate-stimulated CaMKII autophosphorylation as well as phosphorylation of upstream (DARPP32) and downstream (GluRl, %) components of this signaling pathway. 3. Define effect(s) of chronic DA depletion on CaMKII signaling. Effects of striatal 6-OHDA lesion or chronic administration of D1/D2 DA receptor antagonists on basal CaMKII autophosphorylation and phosphorylation of DARPP32, GluRl and NR2B will be determined. Pathological defects in acute DA signaling will be determined by comparing CaMKII regulation in acutely isolated slices from 6-OHDA lesioned and control striaturn. All data will be correlated with plasticity of spine morphology and synaptic transmission determined in Projects 1 and 3 of this PPG. Chronic disruption of DA signaling is predicted to substantially impact CaMKIi signaling, which may contribute to complications of late-phase PD. These insights may help develop improved PD treatment strategies.
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