Comparative effects of organic and inorganic mercury on in vivo dopamine release in freely moving rats

The present study was carried out in order to compare the effects of administration of organic (methylmercury, MeHg) and inorganic (mercury chloride, HgCl 2 ) forms of mercury on in vivo dopamine (DA) release from rat striatum. Experiments were performed in conscious and freely moving female adult Sprague-Dawley (230-280 g) rats using brain microdialysis coupled to HPLC with electrochemical detection. Perfusion of different concentrations of MeHg or HgCl 2 (2 muL/min for 1 h, N = 5-7/group) into the striatum produced significant increases in the levels of DA. Infusion of 40 muM, 400 muM, or 4 mM MeHg increased DA levels to 907 ± 31, 2324 ± 156, and 9032 ± 70 percent of basal levels, respectively. The same concentrations of HgCl 2 increased DA levels to 1240 ± 66, 2500 ± 424, and 2658 ± 337 percent of basal levels, respectively. These increases were associated with significant decreases in levels of dihydroxyphenylacetic acid and homovallinic acid. Intrastriatal administration of MeHg induced a sharp concentration-dependent increase in DA levels with a peak 30 min after injection, whereas HgCl 2 induced a gradual, lower (for 4 mM) and delayed increase in DA levels (75 min after the beginning of perfusion). Comparing the neurochemical profile of the two mercury derivatives to induce increases in DA levels, we observed that the time-course of these increases induced by both mercurials was different and the effect produced by HgCl 2 was not concentration-dependent (the effect was the same for the concentrations of 400 muM and 4 mM HgCl 2 ). These results indicate that HgCl 2 produces increases in extracellular DA levels by a mechanism differing from that of MeHg.

Localization of NADPH diaphorase activity in the human visual cortex

The present report describes the activity of NADPH-diaphorase (NADPHd) in area 17 of autopsied normal human visual cortex. Four human brains from autopsy tissue (4-8 h postmortem) were fixed by immersion in 4 per cent paraformaldehyde in 0.1 M sodium phosphate buffer, pH 7.2-7.4, or in 10 per cent formalin for 24 h. NADPHd histochemistry was done using the malic enzyme indirect method. The neurpile pattern of enzyme activity presented a clear six layer appearance. Cell morphology and the laminar distribution of 73 NADPHd-positive neurons are descrived. All neurons found in area 17 of human cortex were sparsely spiny or smooth cells, located in all cortical layers exept layer 4c. Quantitative analysis of the branching pattern of the dendritic tree was carried out. A symmetrical pattern was observed with no particular dendritic bias except for a few white matter and layer 1 cells. Larger dendritic fields were found in white matter cells when compared to the other corical layers. Comparison of cell densities for gray and white matters showed that 85 per cent of the NADPHd-positive neurons were located in the white matter. NADPH was colocalized with nitric oxide synthase which produces nitric oxide, a short-life neuromediator implicated in synaptic plasticity, neuroprotection, and neurotoxicity. thus, the spatial distribution of the NADPHd cells is important for posterior functional studies of the neuromediators in the brain