Alterations in the properties and isoforms of sciatic nerve Na(+), K(+)-ATPase in methylcyclopentadienyl manganese tricarbonyl-treated mice

Methylcyclopentadienyl Manganese Tricarbonyl Alter Behavior and Cause Ultrastructural Changes in the Substantia Nigra of Rats: Comparison with Inorganic Manganese Chloride

The antiknock additive methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic manganese(Mn) compound. Mn neurotoxicity caused by occupational Mn exposure (mostly inorganic MnCl₂) is associated with motor and cognitive disturbances, referred to as Manganism. However, the impact of environmentally relevant Mn exposure on MMT-induced Manganism is poorly understood. In this investigation, we studied the effects of MMT on motor function and brain structure, and compared its effects with those of inorganic MnCl₂. After adaptive feeding for 7 days, male and female Sprague-Dawley (SD) rats in the MMT-treated groups and positive control group were treated for 8 weeks with MMT (1, 2 and 4 mg/kg/i.g.) or MnCl₂·4H₂O (200 mg/kg/i.g.). Mn content in blood, liver, spleen and distinct brain regions was determined by inductively coupled plasma-mass spectrometer (ICP-MS). We found that MMT and MnCl₂ exposure led to slower body-weight-gain in female rats, impaired motor and balance function and spatial learning and memory both in male and female rats. HE staining showed that MMT and MnCl₂ led to altered structure of the substantia nigra pars compacta (SNpc), and Nissl staining corroborated MMT's propensity to damage the SNpc both in male and female rat. In addition, Immunostaining of the SNpc showed decreased TH-positive neurons in MMT- and MnCl₂-treated rats, concomitant with Iba1 activation in microglia. Moreover, no statistically significant difference was noted between the rats in the H-MMT and MnCl₂ groups. In summary, these findings suggest that MMT and MnCl₂ exposure cause ultrastructural changes in the SNpc neurons culminating in altered motor behavior and cognition, suggesting that altered SNpc structure and function may underline the motor and cognitive deficits inherent to Manganism, and accounting for MMT and MnCl₂'s manifestations of atypical parkinsonism.

Alterations of motor nerve functions in animals exposed to motorcycle exhaust

The effect of motorcycle exhaust (ME) on the motor nerve was studied using animals exposed to the exhaust by inhalation, intratracheal, or intraperitoneal administration of ME particulate (MEP). A 4-wk ME inhalation and intratracheal instillation of MEP for 1 d in rats or intraperitoneal administration of MEP (0.5 g/kg/d for 1 d and 0.1 g/kg/d for 2 d) in mice significantly decreased both rota-rod performance and motor nerve conduction velocity. The effect of some polycyclic aromatic hydrocarbons on the motor nerve was also investigated. Treatment with benzo[a]pyrene (0.05 and 0.1 g/kg/d for 3 d), but not pyrene (0.1 g/kg/d for 3 d), resulted in significant decrease of motor nerve conduction velocity in mice. Moreover, the Na(+),K(+)-ATPase activities of sciatic nerves isolated from ME-, MEP-, or benzo[a]pyrene-exposed animals were decreased. Treatment with pyrene did not markedly affect the Na(+),K(+)-ATPase activity of sciatic nerve. The rats exposed to ME for 4 wk showed increases in blood and sciatic nerve manganese levels. Results indicate that motorcycle exhaust produces adverse effects on the motor nerve, which is associated with a fall in nerve Na(+),K(+)-ATPase activity.