Environmental pesticides including organochlorines and carbamates act as potential risk factors for neurodegeneration of dopamine (DA)-containing neurons in Parkinson's Disease. Damage to DA-containing neurons can occur by either eliciting direct toxicity or by increasing the vulnerability of these neurons to selective detrimental effects of naturally occurring isoquinolines (IsoQ), specifically 1,2,3,4, tetrahydroisoquinoline (TIQ) and salsolinol (SAL). The investigators' preliminary data suggest: 1) heptachlor (HC), TIQ, SAL and MPP-positive have concentration-dependent toxicities to DA-containing neurons; 2) concentrations of HC that are minimally toxic increase the toxicity of MPP-positive; 3) IsoQs induce mitochondrial depolarization and redistribution of cyto C; and, 4) TIQ increases expression of BAX. These findings suggest that in addition to the known disruption of mitochondrial bioenergetics by IsoQs and pesticides, these neurotoxins disrupt mitochondrial physiology and could initiate biochemical cascades that further compromise the viability of DA-containing cells. The investigators hypothesize that the toxicity of two IsoQ compounds, TIQ and SAL and two classes of pesticides, HC as an organochlorine and diethyldithiocarbamate as a dithiocarbamate alone and in combination, is a manifestation of mitochondrial dysfunction, involving opening of mitochondrial permeability transition pore (PTP), mitochondrial membrane potential depolarization, cytochrome c (cyto C) release from mitochondria and caspase activation. Secondly, they hypothesize that pesticides and IsoQ alone and in combination induce p53 and its related target gene BAX in DA-containing neurons. Cigarette smoking is the most consistent negative risk factor for the occurrence of PD. Nicotinic alpha-7 receptors are neuroprotective in various models of neurotoxicity, raising the possibility that activation of these receptors could underlie the neuronal protection associated with cigarette smoking. Thirdly, the investigators hypothesize that activation of cholinergic nicotinic alpha-7 receptors attenuates pesticide and IsoQ toxicities. These hypotheses will be tested in a series of experiments utilizing in vitro viability assays, confocal microscopy coupled with double-labeled immunocytochemistry, Western blots, fluorescent plate reader assays and pharmacological interventions in cultured DA-containing neurons. Collectively, these studies will provide a comprehensive evaluation of the role of mitochondrial PTP, membrane potential, cyto C release and caspase activation in mechanisms of environmental and endogenous risks factors in PD, and the potential benefit derived from nicotinic alpha-7-receptor activation.
