Metal-containing airborne particles represent an important occupational and environmental health hazard including nervous system effects. In this work, adult male Wistar rats were treated with MnO₂ nanoparticles of ca. 23 nm nominal particle diameter, instilled into the trachea for 3, 6 and 9 weeks in daily doses of 2.63 and 5.26 mg Mn/kg. The animals' body weight was checked weekly. At the end of treatment, the rats' spontaneous motility was tested in an open field box. Then, spontaneous and stimulus-evoked cortical activity and action potential of the tail nerve were recorded in urethane anesthesia. The rats were finally dissected, organs weights were measured, and Mn level in blood and brain samples was determined by ICP-MS.

Control rats had normal weight gain but the body weights of the treated rats showed no growth from the 6^th week on. In the electrocorticogram of the treated rats, high-frequency activity increased and low frequency, decreased. The latency of the evoked potentials was lengthened, and the conduction velocity of the tail nerve decreased. In the open field these rats showed less ambulation and rearing, and more local activity and immobility. These changes developed in a dose- and time dependent way.

Mn level in the treated rats' blood and brain samples was significantly higher than in the controls and there was some parallelism between the behavioral and electrophysiological alterations and the amount of Mn deposited in the brain.

According to these results the Mn content of instilled nanoparticles had access from the airways to the brain and affected functions at several levels. Such experiments may thus be suitable for modeling the neurological damage seen in humans exposed to airborne Mn.