The role of nitric oxide and NMDA receptors in the development of motor neuron dendrites

Nitric oxide (NO) has been implicated in the establishment of precise synaptic connectivity throughout the neuroaxis in several species. To determine the contribution of NO to NMDA receptor-dependent dendritic growth in motor neurons, we administered the NMDA antagonist MK-801 to wild-type mice and neuronal nitric oxide synthase (nNOS) knock-out mice between postnatal days 7 and 14. Compared to saline-treated wild-type animals the number of dendritic bifurcations was significantly reduced in nNOS knock-out animals and MK-801-treated wild-type animals. There was no significant difference in dendritic bifurcation between MK-801-treated wild-type, MK-801-treated nNOS knock-out, and saline-treated nNOS knock-out animals, suggesting that nNOS knock-out and NMDA receptor block had similar effects. The path of the longest dendrite and the number of primary dendrites was the same in all treatment groups, indicating an effect specific to bifurcation. Sholl analysis revealed that differences in bifurcation numbers occurred between 160 and 320 micrometers from the cell body, the distance at which second, third, and fourth order dendrites are most prevalent. Dendrite order analyses confirmed a significant reduction in numbers, but not lengths, of third and fourth order dendrites in nNOS knock-out and drug-treatment groups. Finally, immunohistochemical examination of the developing spinal cord indicated that NMDA receptors and nNOS are colocalized within interneurons surrounding the motor neuron pool. These results support the view that at least part of NMDA receptor-dependent arborization of motor neuron dendrites is mediated by the local production of NO within the developing spinal cord.     

Effect of cysteine modifications on the activity of the 'small' Clostridium perfringens sialidase

The 'small' (43 kDa) sialidase of Clostridium perfringens is inhibited by low concentrations of mercury ions. For the investigation of possible functional roles of the enzyme's four cysteine residues at the amino acid positions 2, 282, 333 and 349, they were separately altered to serine by site-directed mutagenesis. The four mutant sialidases expressed in E. coli and purified by metal chelate chromatography were markedly reduced in specific activity when compared to the wild-type enzyme but with the exception of C282S exhibited similar K(M)-values indicating an unchanged mode of substrate binding. The substrate specificity was also conserved for C2S, C282S, and C333S. Only the C349S sialidase exhibited a higher relative activity with colominic acid and the alpha2,6-linked sialic acid of sialyllactose compared to the alpha2,3-linked isomer than the other mutants. Chemical modifications with the thiol-blocking reagents N-ethylmaleimide (NEM), p-chloromercuribenzoate (pCMB) and HgCl2 had little effect on the C282S sialidase, e.g., 6% inhibition by 5 mM NEM compared to reductions in activity between 65 and 90% for the wild-type and other mutant enzymes, supporting the idea that among the enzyme's cysteines, Cys-282 has the highest structural or functional significance. The results also explain the higher mercury tolerance of Salmonella typhimurium and Clostridium tertium sialidases, which have the positions equivalent to Cys-282 altered to Val and Thr, respectively, indicating that the thiol group of Cys-282, despite being situated near the active site, is not involved in catalysis.     

A field method for sampling benzene in end-exhaled air

A simple and reliable field method is presented for sampling and analysis of benzene in end-exhaled air. The sample is collected directly on an adsorbent tube while the subject exhales through a sampling device consisting of a modified peak expiratory flow meter. To ensure sampling of end-exhaled air, the temperature of the breath is monitored during expiration. The analytes subsequently are thermally desorbed and analyzed by gas chromatography. No sample preparation before analysis is needed, and therefore sample loss is minimized, shipping is easy, storage is possible, and clean up is unnecessary. All these steps have been major problems in earlier methods for breath analysis. The presented method has been applied to the monitoring of benzene. The separation of benzene from other components of exhaled air was good and the detection limit low (0.5 microgram/m3), and therefore benzene could be monitored in occupationally nonexposed nonsmokers. No carry-over in the sampling device or breakthrough could be detected. The samples were stable for at least a week. The combined precision in sampling and analysis was excellent, with a coefficient of variation of 13%.     

Discovery and evaluation of a series of 3-acylindole imidazopyridine platelet-activating factor antagonists

Studies conducted with the goal of discovering a second-generation platelet-activating factor (PAF) antagonist have identified a novel class of potent and orally active antagonists which have high aqueous solubility and long duration of action in animal models. The compounds arose from the combination of the lipophilic indole portion of Abbott's first-generation PAF antagonist ABT-299 (2) with the methylimidazopyridine heterocycle moiety of British Biotechnology's BB-882 (1) and possess the positive attributes of both of these clinical candidates. Structure-activity relationship (SAR) studies indicated that modification of the indole and benzoyl spacer of lead compound 7b gave analogues that were more potent, longer-lived, and bioavailable and resulted in the identification of 1-(N, N-dimethylcarbamoyl)-4-ethynyl-3-[3-fluoro-4-[(1H-2-methylimidazo[4,5-c] pyrid-1-yl)methyl]benzoyl]indole hydrochloride (ABT-491, 22 m.HCl) which has been evaluated extensively and is currently in clinical development.     

Brain choline-containing compounds are elevated in HIV-positive patients before the onset of AIDS dementia complex: A proton magnetic resonance spectroscopic study

The CNS is frequently involved in human immunodeficiency virus (HIV) infection. In recent studies using proton magnetic resonance spectroscopy, investigators found a significant reduction in N-acetyl aspartate, a metabolic marker of neurons, in late stages of dementia. To further understand the relationship between proton magnetic resonance spectroscopy changes and clinical disease and dementia, we compared 20 HIV-infected patients presenting at varying stages of acquired immunodeficiency syndrome (AIDS) dementia complex and infection to 10 age-matched controls. We found a significant reduction in N-acetyl aspartate/creatine only in patients who had advanced dementia and CD4 counts less that 200/microliter. By contrast, a significant elevation in compounds containing choline was present in patients in the early stages of HIV infection of who had CD4 counts greater than 200/microliter, in patients with normal MRI scans, and in all AIDS dementia complex groups, including subjects with no or minimal cognitive impairment. An elevated choline level also occurred in later stages of HIV infection (CD4 < 200/microliter). Our results suggest that an increase in choline occurs before N-acetyl aspartate decrements, MRI abnormalities, and the onset of dementia, and may therefore provide a useful marker for early detection of brain injury associated with HIV infection.     

Role of the negative charges in the cytosolic domain of TOM22 in the import of precursor proteins into mitochondria

TOM22 is an essential mitochondrial outer membrane protein required for the import of precursor proteins into the organelles. The amino-terminal 84 amino acids of TOM22 extend into the cytosol and include 19 negatively and 6 positively charged residues. This region of the protein is thought to interact with positively charged presequences on mitochondrial preproteins, presumably via electrostatic interactions. We constructed a series of mutant derivatives of TOM22 in which 2 to 15 of the negatively charged residues in the cytosolic domain were changed to their corresponding amido forms. The mutant constructs were transformed into a sheltered Neurospora crassa heterokaryon bearing a tom22::hygromycin R disruption in one nucleus. All constructs restored viability to the disruption-carrying nucleus and gave rise to homokaryotic strains containing mutant tom22 alleles. Isolated mitochondria from three representative mutant strains, including the mutant carrying 15 neutralized residues (strain 861), imported precursor proteins at efficiencies comparable to those for wild-type organelles. Precursor binding studies with mitochondrial outer membrane vesicles from several of the mutant strains, including strain 861, revealed only slight differences from binding to wild-type vesicles. Deletion mutants lacking portions of the negatively charged region of TOM22 can also restore viability to the disruption-containing nucleus, but mutants lacking the entire region cannot. Taken together, these data suggest that an abundance of negative charges in the cytosolic domain of TOM22 is not essential for the binding or import of mitochondrial precursor proteins; however, other features in the domain are required.     

Effects of postmortem storage on the ultrastructure of the endomysium and myofibrils in normal and callipyge longissimus

These experiments were conducted to examine ultrastructural changes in longissimus from normal and callipyge lamb during 14 d of postmortem storage at 4 degrees C. Six crossbred ewe lambs (1/2 Dorset x 1/2 Romanov) were grain-fed and slaughtered at approximately 250 d of age. Leg conformation score was the basis for classifying carcasses into normal and callipyge. The normal and callipyge longissimus had mean Warner-Bratzler shear force of 2.8 (2.7, 2.4, and 3.4) and 9.0 (12.2, 6.9, and 7.9) kg, respectively, after 14 d of postmortem storage. The results of transmission electron microscopy demonstrated ultrastructural changes, including sarcolemma detachment, loss of myofibril lateral attachments, and I-band breaks in normal longissimus. Detachment of sarcolemma from myofibrils occurred in both phenotypes, but it was delayed by several days in callipyge longissimus. Thus, the sarcolemma detachment seems not to contribute significantly to postmortem tenderization. The endomysium of both phenotypes did not change with postmortem storage. In normal longissimus, the percentage of fractured I-bands increased from 0% at d 1 to 11% at d 3 (P<.05) and did not change between 3 and 14 d (15%) postmortem (P>.05). However, postmortem storage did not affect (0 to 3%) the frequency of the I-band breaks in the callipyge longissimus (P>.05). Therefore, the break in the I-band region in postmortem muscle is a change that is associated with postmortem tenderization. We conclude that the major factor responsible for the toughness of meat from callipyge longissimus is the postmortem stability of myofibrils.