Researchers funded by NIEHS reported that inhalation of the widely used pesticide paraquat reduced the sense of smell in male mice for several months after exposure. Moreover, the chemical entered the brain and other tissues. These results underscore the importance of studying the effects of inhalation of neurotoxicants, to protect public health.
Loss of sense of smell, or olfactory impairment, is an early sign of Parkinson's disease. The findings, published Dec. 29, 2020, in the journal Toxicological Sciences, suggest paraquat may contribute to such neurodegenerative diseases.
Researchers at the University of Rochester modeled an inhalation of low concentrations of paraquat. Using the university's Inhalation Core facility, they exposed mice to aerosolized paraquat. The team then measured levels of the pesticide in lung, kidney, and four regions of the brain — olfactory bulb, striatum, midbrain, and cerebellum.
"Inhalation can provide a direct route of entry to the brain," explained first author Timothy Anderson. "If you inhale something and it goes into your nose, it can actually enter the neurons responsible for sense of smell, and travel into the brain." Anderson is a graduate student at the University of Rochester lab of Deborah Cory-Slechta, Ph.D.,where the study was conducted. Cory-Slechta is deputy director of the university's NIEHS-funded Environmental Health Sciences Center.
Co-author Kevin Welle measured the highest brain levels in the olfactory bulb, suggesting paraquat entered the brain through nasal-olfactory neurons.
"The sex-dependent olfactory impairment observed after paraquat [PQ] inhalation exposure is intriguing and parallels important features of Parkinson's disease [PD], including early loss of sense of smell and greater prevalence in males," said Jonathan Hollander, Ph.D.,health scientist administrator in the NIEHS Genes, Environment, and Health Branch. Hollander oversees research grants for neurodegenerative diseases and other areas.
"Given that paraquat is a known risk factor for PD, and inhalation is a prevalent source of exposure, this study may lead to a more useful animal model of PQ-induced neurodegeneration," he added.