No abstract

The neurotoxic effects of inorganic lead are known to include peripheral neuropathy in adults and encephalopathy in children. The purpose of this study was to determine the effect of inorganic lead (PbCl2) administration on norepinephrinergic neurons of the locus ceruleus in neonatal rats by immunocytochemical and electron microscopic analyses. Lead chloride solutions, 0.05%, 0.1% and 0.2% in concentrations, were prepared in distilled water and administered orally via drinking water. After 4, 8, or 12 weeks of continuous administration, the rats were sacrificed and brains were immunostained with the tyrosine hydroxylase antibody. The number of immunoreactive cell bodies in the locus ceruleus was estimated. Densitometric analysis of immunoreactive profiles visualized by electron microscopy was performed using an image analyzer. The numbers of immunoreactive neurons in the locus ceruleus were increased statistically by lead administration. The intensity of the immunoreaction, both under the light and electron microscopes was also increased. Degenerative changes, including intra-axonal vacuole formation and widening of the extracellular spaces, were found by electron microscopy in and around the tyrosine hydroxylase immunoreactive axons. Increased tyrosine hydroxylase immunoreactivity may correlate with the hyper-reactivity of lead intoxicated children. Degenerative changes may account for the reported deficits in intellectual attainment and achievement in lead intoxicated children.

In this paper, the feasibility of dynamic impedance matching for noise reduction in a cylindrical waveguide is demonstrated. An active acoustic coating, inserted parallel to the direction of wave propagation, is assumed to dynamically match the acoustic impedance of the incoming wave. The active coating appears as an acoustic branch containing the same fluid, and therefore part of the incoming wave can be diverted to and dissipated in the coating. The performance of the active coating is evaluated using a finite element analysis, where the coating is modeled as a dynamic impedance matching boundary. Simulations reveal that significant reductions in the downstream acoustic pressure can be achieved. Unlike the conventional active techniques that employ phase cancellation, dynamic impedance matching has a number of advantages such as a relatively low power requirement.