Fluorescence imaging study of extracellular zinc at the hippocampal mossy fiber synapse.

Although synaptically released, vesicular Zn(2+) has been proposed to play a neuromodulatory or neuronal signaling role at the mossy fiber-CA3 synapse, Zn(2+) release remains controversial, especially when detected using fluorescent imaging. In the present study, we investigated synaptically released Zn(2+) at the mossy fiber (MF) synapse in rat hippocampal slices using three chemically distinct, fluorescent Zn(2+) indicators. The indicators employed for this study were cell membrane impermeable (or extracellular) Newport Green [K(DZn2+) approximatelly 1 microM] , Zinpyr-4 K(DZn2+) approximately 1 nM and FluoZin-3 K(DZn2+) approximately 15 nM, chosen, in part, for their distinct dissociation constants. Among the three indicators, FluoZin-3 was also sensitive to Ca(2+) K(DCa2+) approximately 200-300 microM which was present in the extracellular medium ([Ca(2+)](o)>2mM). Hippocampal slices loaded with either Newport Green or FluoZin-3 showed increases in fluorescence after electrical stimulation of the mossy fiber pathway. These results are consistent with previous studies suggesting the presence of synaptically released Zn(2+) in the extracellular space during neuronal activities; however, the rise in FluoZin-3 fluorescence observed was complicated by the data that the addition of exogenous Zn(2+) onto FluoZin-3 loaded slices gave little change in fluorescence. In the slices loaded with the high-affinity indicator Zinpyr-4, there was little change in fluorescence after mossy fiber activation by electrical stimulation. Further study revealed that the sensitivity of Zinpyr-4 was mitigated by saturation with Zn(2+) contamination from the slice. These data suggest that the sensitivity and selectivity of a probe may affect individual outcomes in a given experimental system.

32P-postlabelling in studies of polycyclic aromatic hydrocarbon activation.

Polycyclic aromatic hydrocarbons (PAHs) undergo metabolic activation reactions to yield intermediates that react with DNA to form covalent adducts. PAH administration leads to the formation of various types of DNA adducts that may differ between species, strains and tissues due to differences in metabolic activation and repair. The structures of PAH-DNA adducts can be identified by three approaches: co-chromatography with synthetic mononucleotide adduct standards; examining the adducts resulting from metabolism of pathway intermediates; or chemically blocking metabolic activation at specific sites on the PAH. Administration of putative metabolic intermediates of a PAH leads to enhanced formation of DNA adducts resulting from further activation along that pathway. Conversely, chemically blocking a bond or position on a PAH prevents adducts arising from activation at that site. By comparing the DNA adduct spectra generated by metabolites, blocked forms, and parent PAH administration, the pathways important in the metabolic activation of the PAH in each tissue may be deduced. Partial identification of these adducts may also be made by co-chromatography with the products of reactions between synthetic reactive intermediates and defined polydeoxynucleotides, and more thorough identification by using synthetic DNA adduct standards. These approaches have all been successfully applied to studies of PAH activation, and are reviewed here.

[Analysis of organic and inorganic components of Diesel engine exhaust absorbed on ore-mine aerosol particles]. / Issledovanie sorbirovannykh na chastitsakh rudnichnogo aérozolia organicheskikh i neorganicheskikh komponentov vykhlopa dizel'nykh dvigatelei.

The article proposes results of research into exhausts' major components absorption in accumulated and floating dusts in ore mines in which self-propelled diesel vehicles are predominantly used. It was established that ore-mine aerosol particles had a large specific surface and contained a high percentage of carbon-black (1,1-35.1%). Different results were received for both organic and non-organic substances' sorption indices. In the samples, in addition to 3,4-benzapyrene, 11 more polycyclic aromatic hydrocarbons were identified, with concentrations 10-15 times higher than those of 3,4-benzapyrene.

A pragmatic approach to standard setting--the example of coal tar products and asphalt.

This article will outline a pragmatic approach directed to incorporating key elements of a scientific review of the literature and derive a proposal for an occupational exposure standard for coal tar, coal tar pitch, creosote, petroleum pitch, bitumen and asphalt, six substances which contain polynuclear aromatic hydrocarbons. Five approaches to the standard setting process are reviewed and their strengths and weaknesses discussed. Unfortunately there does not exist an acceptable epidemiological data set, other than the coke oven emission studies, on which to base a valid and reliable risk assessment model. Based on comparative potency experiments of complex mixtures, consideration of the state-of-the-art sampling and analytical methods, prevention of acute human health effects, and current existing standards for these substances throughout the world, a set of recommended exposure standards are derived for health policy makers.