Abrogation of the alternative complement pathway by targeted deletion of murine factor B

To investigate the role of complement protein factor B (Bf) and alternative pathway activity in vivo, and to test the hypothesized potential genetic lethal effect of Bf deficiency, the murine Bf gene was interrupted by exchange of exon 3 through exon 7 (including the factor D cleaving site) with the neor gene. Mice heterozygous for the targeted Bf allele were interbred, yielding Bf-deficient offspring after the F1 generation at a frequency suggesting that Bf deficiency alone has no major effect on fertility or fetal development. However, in the context of one or more genes derived from the 129 mouse strain, offspring homozygous for Bf deficiency were generated at less than expected numbers (P = 0.012). Bf-deficient mice showed no gross phenotypic difference from wild-type littermates. Sera from Bf-deficient mice lacked detectable alternative complement pathway activity; purified mouse Bf overcame the deficit. Classical pathway-dependent total hemolytic activity was lower in Bf-deficient than wild-type mice, possibly reflecting loss of the alternative pathway amplification loop. Lymphoid organ structure and IgG1 antibody response to a T-dependent antigen appeared normal in Bf-deficient mice. Sensitivity to lethal endotoxic shock was not significantly altered in Bf-deficient mice. Thus, deficiency of Bf and alternative complement activation pathway led to a less dramatic phenotype than expected. Nevertheless, these mice provide an excellent model for the assessment of the role of Bf and the alternative pathway in host defense and other functions in vivo.

Plasticity of the cochleotopic (frequency) map in specialized and nonspecialized auditory cortices

Auditory conditioning (associative learning) causes reorganization of the cochleotopic (frequency) maps of the primary auditory cortex (AI) and the inferior colliculus. Focal electric stimulation of the AI also evokes basically the same cortical and collicular reorganization as that caused by conditioning. Therefore, part of the neural mechanism for the plasticity of the central auditory system caused by conditioning can be explored by focal electric stimulation of the AI. The reorganization is due to shifts in best frequencies (BFs) together with shifts in frequency-tuning curves of single neurons. In the AI of the Mongolian gerbil (Meriones unguiculatus) and the posterior division of the AI of the mustached bat (Pteronotus parnellii), focal electric stimulation evokes BF shifts of cortical auditory neurons located within a 0.7-mm distance along the frequency axis. The amount and direction of BF shift differ depending on the relationship in BF between stimulated and recorded neurons, and between the gerbil and mustached bat. Comparison in BF shift between different mammalian species and between different cortical areas of a single species indicates that BF shift toward the BF of electrically stimulated cortical neurons (centripetal BF shift) is common in the AI, whereas BF shift away from the BF of electrically stimulated cortical neurons (centrifugal BF shift) is special. Therefore, we propose a hypothesis that reorganization, and accordingly organization, of cortical auditory areas caused by associative learning can be quite different between specialized and nonspecialized (ordinary) areas of the auditory cortex.

Induction of cytochrome P4501A1 by 2,3,7,8-tetrachlorodibenzo-p-dioxin or indolo(3,2-b)carbazole is associated with oxidative DNA damage.

Induction of cytochrome P4501A1 (CYP1A1) in the hepatoma Hepa1c1c7 cell line results in an elevation in the excretion rate of 8-oxoguanine (oxo8Gua), a biomarker of oxidative DNA damage and the major repair product of 8-oxo-2'-deoxyguanosine (oxo8dG) residues in DNA. Treatment of this cell line with 2,3,7,8-tetrachloro-p-dibenzodioxin (TCDD), a nonmetabolized environmental contaminant, and indolo(3,2-b)carbazole (ICZ), a metabolite of a natural pesticide found in cruciferous vegetables, is shown to both induce CYP1A1 activity and elevate the excretion rate of oxo8Gua; 7,8-benzoflavone (7,8-BF or alpha-naphthoflavone), an inhibitor of CYP1A1 activity and an antagonist of the aryl hydrocarbon (Ah) receptor, reduced the excretion rate of oxo8Gua. The essential role of Ah-receptor, which mediates the induction of CYP1A1, is shown by the inability of TCDD to induce CYP1A1 and to increase excretion of oxo8Gua in Ah receptor-defective c4 mutant cells. While there was a significant 7.0-fold increase over 2 days in the excretion rate of oxo8Gua into the growth medium of TCDD-treated Hepa1c1c7 cells compared to control, no significant increase was detected in the steady-state level of oxo8dG in the DNA presumably due to efficient DNA repair. Thus, the induction of CYP1A1 appears to lead to a leak of oxygen radicals and consequent oxidative DNA damage that could lead to mutation and cancer.