Metal deposition and functional neurotoxicity in rats after 3-6 weeks nasal exposure by two physicochemical forms of manganese.

Airborne manganese represents a major risk of nervous system damage first of all in industrial settings. The resulting effects may depend on the dose and physicochemical form of Mn. To compare the effect of soluble and nanoparticulate Mn, adult male rats received daily instillation of MnCl(2) solution or MnO(2) nanoparticle suspension (dose: 2.53mg Mn per rat) into the nasal cavity for 3 and 6 weeks. At the end of treatment, spontaneous open field motility was tested, electrophysiological recording was done in anesthesia, and brain tissue Mn level was determined. Metal level increase in the rats' brain, body weight gain reduction, and decrease of open field motility was significant in the MnCl(2), but not nano-Mn, treated rats. Most evoked cortical activity parameters were significantly altered in both groups, but spontaneous cortical activity spectrum only in the rats receiving MnCl(2). There was fair correlation between brain Mn levels and certain neuro-functional parameters, underlining the causal relationship. Electrophysiological tests might be more sensitive to the effects of Mn than general toxicological or neurobehavioral tests.