SUMMARY Recent research, done as part of the parent grant, resulted in the important revelation that e-cigarette (e-cig) operating power may be more relevant for metal exposure and associated brain metal accumulation and neurotoxicity than total aerosol dose (aerosol concentration times exposure duration). Our data show that metal accumulation in e-cig aerosol from an open e-cig device massively and dose-dependently increases with operating power within the range recommended by the manufacturer (30-50 W). Moreover, while our previous 2-month mouse exposure experiment, performed with e-cig aerosol produced at 40 W, revealed significant and dose-dependent metal deposition and dyshomeostasis in mouse brain (Re et al., 2021), our latest data indicates that the lower levels of metals measured in e-cig aerosol generated at 30 W do not cause overt metal deposition in mouse brain even after 6 months of chronic exposure. Yet, this exposure paradigm caused some neurotoxicity, especially in males carrying the Parkinson’s Disease (PD)-linked mutation, as shown by motor deficit and gait impairment, potentially attributable to other aerosol components such as aldehydes. This recent finding leads to the central hypothesis of this diversity supplement, that e-cig operating power may be more relevant for metal exposure and associated brain metal accumulation and neurotoxicity than total aerosol dose. Leveraging the experiments from the parent grant, we will rigorously evaluate the effects of operating power on the levels of neurotoxic metals and aldehydes produced in e-cig aerosol, and the neurotoxic consequences of chronic inhalation exposure to these aerosols. We will expand the aims of the parent grant by: 1) measuring metal and aldehyde mixtures in e-cig aerosol produced at 30, 40 and 50 W, 2) examining cognitive/motor deficit progression and endpoint brain neurotoxicity in mice exposed at 30 or 50 W and contrast these with our previous exposure study performed at 40 W, and finally 3) untangling the modulatory effects of sex and genetic susceptibility to PD on these neurotoxic outcomes. In Aim 1, we will determine metal and aldehyde mixture composition of e-cig aerosols as a function of e-cig operating power by collecting e-cig aerosols from a device operated at three different powers (30, 40 and 50 W). We will also evaluate coil aging effects on aerosol chemical composition, by taking samples for several weeks over consecutive days (to cool down the device between uses). For Aim 2, we will investigate whether operating power is a critical determinant of brain metal accumulation, neurobehavioral toxicity and neuropathology in mice chronically exposed to e-cig aerosol. In Aim 3, we will evaluate whether sex and genetic susceptibility to PD modify the dependence of the aerosol mixture neurotoxicity in mice on e-cig operating power (30-50 W). Our findings could support regulatory interventions (e.g., limiting operating power) ultimately resulting in reduced neur...