Age-related vulnerability to nigral dopaminergic degeneration in rats via Zn 2+ -permeable GluR2-lacking AMPA receptor activation

On the basis of the evidence that extracellular Zn influx induced with AMPA causes Parkinson's syndrome in rats that apomorphine-induced movement disorder emerges, here we used a low dose of AMPA, which does not increase intracellular Zn level in the substantia nigra pars compacta (SNpc) of young adult rats, and tested whether intracellular Zn dysregulation induced with AMPA is accelerated in the SNpc of aged rats, resulting in age-related vulnerability to Parkinson's syndrome. When AMPA (1 mM) was injected at the rate of 0.05 μl/min for 20 min into the SNpc, intracellular Zn level was increased in the SNpc of aged rats followed by increase in turning behavior in response to apomorphine and nigral dopaminergic degeneration. In contrast, young adult rats do not show movement disorder and nigral dopaminergic degeneration, in addition to no increase in intracellular Zn . In aged rats, movement disorder and nigral dopaminergic degeneration were rescued by co-injection of either extracellular (CaEDTA) or intracellular (ZnAF-2DA) Zn chelators. 1-Naphthyl acetyl spermine (NASPM), a selective blocker of Ca - and Zn -permeable GluR2-lacking AMPA receptors blocked increase in intracellular Zn in the SNpc of aged rats followed by rescuing nigral dopaminergic degeneration. The present study indicates that intracellular Zn dysregulation is accelerated by Ca - and Zn -permeable GluR2-lacking AMPA receptor activation in the SNpc of aged rats, resulting in age-related vulnerability to Parkinson's syndrome.