Rabies virus quasispecies: implications for pathogenesis

Passage of the mouse-adapted rabies virus strain CVS-24 (where CVS is challenge virus standard) in BHK cells results in the rapid selection of a dominant variant designated CVS-B2c that differs genotypically and phenotypically from the dominant variant CVS-N2c present in mouse-brain- or neuroblastoma-cell-passaged CVS-24. The glycoprotein of CVS-B2c has 10 amino acid substitutions compared with that of CVS-N2c. Because CVS-B2c can be reproducibly selected in BHK cells, it is likely to be a conserved minor subpopulation of CVS-24. CVS-N2c is more neurotropic in vitro and in vivo than CVS-B2c, which replicates more readily in nonneuronal cells in vitro and in vivo. These characteristics appear to be relevant to the pathogenicity of the two variants. CVS-N2c is more pathogenic for adult mice than CVS-B2c. In contrast, CVS-B2c is more pathogenic for neonatal mice. These differences in pathogenicity are reflected in the selection pattern when mixtures of CVS-N2c and CVS-B2c were used to infect neonatal and adult mice. Although CVS-N2c was highly selected in adult mice, no selection for either variant was seen in neonates, suggesting that certain aspects of development, such as maturation of the nervous and immune systems, may contribute to the selection process. We speculate that the existence of different variants within a rabies virus strain may facilitate the virus in overcoming barriers to its spread, both within the host and between species.     

DNA polymerase fidelity: from genetics toward a biochemical understanding

This review summarizes mutagenesis studies, emphasizing the use of bacteriophage T4 mutator and antimutator strains. Early genetic studies on T4 identified mutator and antimutator variants of DNA polymerase that, in turn, stimulated the development of model systems for the study of DNA polymerase fidelity in vitro. Later enzymatic studies using purified T4 mutator and antimutator polymerases were essential in elucidating mechanisms of base selection and exonuclease proofreading. In both cases, the base analogue 2-aminopurine (2AP) proved tremendously useful-first as a mutagen in vivo and then as a probe of DNA polymerase fidelity in vitro. Investigations into mechanisms of DNA polymerase fidelity inspired theoretical models that, in turn, called for kinetic and thermodynamic analyses. Thus, the field of DNA synthesis fidelity has grown from many directions: genetics, enzymology, kinetics, physical biochemistry, and thermodynamics, and today the interplay continues. The relative contributions of hydrogen bonding and base stacking to the accuracy of DNA synthesis are beginning to be deciphered. For the future, the main challenges lie in understanding the origins of mutational hot and cold spots.     

Effects of central and peripheral administration of kynurenic acid on hippocampal evoked responses in vivo and in vitro

Kynurenic acid is an excitatory amino acid antagonist with preferential activity at the N-methyl-D-aspartate subtype of glutamate receptors. It is produced endogenously in the brain, but is synthesized more effectively in the periphery. The influence of peripheral kynurenic acid on brain function is unclear because kynurenic acid is likely to penetrate the blood-brain barrier poorly. To determine the potential central effects of peripheral kynurenic acid, we compared its effects in the hippocampus after peripheral or direct administration. The hippocampus of the rat was chosen as a test system because this region receives glutamatergic inputs, and because responses to stimulation of these inputs can be compared after peripheral drug administration in vivo, and after direct administration of drugs in vitro. Peripherally-administered kynurenic acid was injected via a catheter in the jugular vein. Bath-application to hippocampal slices was used to test effects of direct administration. Area CA1 pyramidal cells and dentate gyrus granule cells were examined by extracellular recording and stimulation of area CA3 or the perforant path, respectively. Pairs of identical stimuli were used to assess paired-pulse inhibition and paired-pulse facilitation. Kynurenic acid decreased evoked responses in area CA1 and the dentate gyrus, both in vivo and in vitro. Effective concentrations were in the low micromolar range, and therefore were likely to be mediated by antagonism of N-methyl-D-aspartate receptors. In both preparations, area CA1 was more sensitive than the dentate gyrus, and paired-pulse facilitation was affected, but not paired-pulse inhibition. Control solutions had no effect. We conclude that kynurenic acid can enter the brain after peripheral administration, and that peripheral and direct effects in the hippocampus are qualitatively similar. Therefore, we predict that effects of endogenous kynurenic acid that was synthesized peripherally or centrally would be similar. Furthermore, the results suggest that modulation of the glycine site of the N-methyl-D-aspartate receptor, for example by kynurenic acid, may vary considerably among different brain areas.     

Statins and the kidney

In this paper an attempt is described to estimate the incidence and frequency of neurologic and otologic symptoms among patients two years after TBE. We examined 43 persons of both sexes aged 17-58. The most frequent complaints were: headache--34.9%, equilibrium problems--37.2%, buzzing in the ears--27.9%, hearing problems--23.3%, memory problems--25.6%. Decrease of throat reflexes was stated in 3 (7%) and pseudobulbaris symptoms in 2 (4.6%), weakness of muscles in 4 (9.3%). In audiometric examination decrease of hearing was stated in 8 persons (18.5%). We registered nystagmus: spontaneous--4.6-7%, gaze--13.9-18.6%, positional-T, mainly Nylen I and III type-18.6-25.6%. Pathologic recording in the eye-tracking pattern test was shown in 7 (16.3%) persons. Asymmetry of optokinetic nystagmus was stated in 6 (13.9%) examined persons. Asymmetry in caloric test was proved in 25.5% of examined persons.