Parkinson's Disease (PD) is a neurodegenerative disease characterized by loss of the dopamine-containing neurons in the substantia nigra pars conpacta (SNpc). Although the cause of neuronal death remains unclear, increasing evidence points to the role of chronic inflammatory processes. In order to explore the possibility that microglial activation causes dopaminergic cell death, we injected lipopolysaccharide (LPS) into the SNpc. The LPS injection not only induced microglial activation, but also resulted in a dose-dependent, selective loss of dopaminergic neurons by apoptosis in the SNpc. We therfore hypothesize that an environmental toxin, such as LPS may activate microglia in the substantia nigra (SN), resulting in the release of cytotoxic agents. These agents may, in turn, activate signal transduction pathways that may cause neuronal degeneration of the dopaminergic neurons in the SN. To test this hypothesis, we propose the following specific aims: 1) To determine if the dopaminergic neurons of the SN are specifically susceptible to inflammatory processes, we swill inject LPS into three discrete brain areas, SN, striatum and hippocampus. Activation of microglia will be characterized by morphological changes and measured by OX-42 immunostaining. Survival of dopaminergic neurons as well as other neuronal populations, such as GABAergic and serotonergic neurons, in the SN will be determined by immunocytochemistry. Neuronal survival in other area of the brain will be examined using specific neuronal markers. 2) To elucidate the molecular mechanisms underlying neuronal degeneration induced by LPS, we will measure the activation of three signal transduction factors, NPkB, P38 MAP kinase, and c-jun N-terminal kinase. In addition, the expression of inflammatory cytokines and apoptosis-related genes will be determined by RNase protection assay. 3) To protect dopaminergic neurons from LPS toxicity, we will inject IL-4, a cytokine that inhibits microglial activation, the microphage inhibitory factor, or the opiate antagonist naloxone. The long-term goal of this study is to validate LPS treatment as a new animal model of PD that can be used to elucidate the etiology and molecular mechanisms underlying PD and to develop novel therapeutic treatments for this and other neurodegenerative diseases.
