Optogenetic and Morphological Assessment of Paraquat-Induced Dopaminergic Damage in Caenorhabditis elegans

Paraquat (PQ) is a herbicide that disrupts the glutathione redox cycle, induces mitochondrial dysfunction, and damages dopaminergic neurons, leading to a Parkinsonian phenotype. The antioxidant N-acetylcysteine (NAC) has been proposed to mitigate PQ-induced toxicity. In this study, we evaluated dopaminergic function using an optogenetic approach and dopaminergic neuronal morphology in Caenorhabditis elegans exposed to sublethal PQ concentrations. Synchronized ZX909 (pdat-1::ChR2(H134R)::mCherry) L4 worms expressing Channelrhodopsin-2 in dopaminergic neurons were exposed to 5 mM PQ and/or 0.5 mM NAC for 24 h. Under blue-light stimulation, PQ significantly reduced locomotor activity, in terms of distance and speed. Dopaminergic integrity was analyzed in the UA44 strain (Pdat-1::α-syn, Pdat-1::GFP) by confocal microscopy in young adults and aged worms. Control and NAC-only animals of both ages displayed normal neuronal morphology. Only ~15% of young adults exposed to PQ or PQ+NAC showed low-severity degeneration of dopaminergic projections, whereas ~50% of aged worms exhibited medium-severity damage. Overall, PQ induced dopaminergic dysfunction and neurodegeneration, while NAC provided little protection in these endpoints. The greater neuronal damage observed in PQ-exposed-aged worms highlights aging as a critical factor that enhances susceptibility to dopaminergic degeneration, providing further insight into the environmental basis of neurodegenerative diseases.