Brain state and plasticity: an integration of the reciprocal interaction model of sleep cycle oscillation with attentional models of hippocampal function

The present paper relates the reciprocal interaction model for sleep cycle oscillation (McCarley and Hobson, ref. 29) to an attentional model of hippocampal function (Schmajuk and Moore, ref. 44). We consider mechanisms by which the interaction between gigantocellular tegmental field (FTG) cells and locus coeruleus (LC) activity proposed by the sleep cycle model may differentially modulate the information processing carried out in the hippocampus as described by the attentional model. Our fundamental assumption is that learning about the relevancy of different stimuli is proportional to the level of LC activation. If the environment becomes unpredictable during waking, the FTG and LC are activated and the LC facilitates hippocampal learning about stimulus relevancy. In a predictable situation during waking, FTG cells discharge rarely because no novelty is detected, and LC neurons are moderately active. If the predictable situation lasts, LC cells also decrease their activity, and a sleep period might start. At sleep onset, LC inhibition decreases and FTG activity is low leading to slow sleep. As FTG activity increases and LC activity reaches its low point, REM sleep starts. Because LC activity is low during REM sleep, values of stimulus relevancy remain unchanged. Since during sleep the threshold for external stimuli is high, only internally generated novel stimuli (subjectively perceived as dream mentation) may activate the LC. LC renewed inhibitory influence on the FTG ends REM sleep.     

Evidence for concerted kinetic oxidation of progesterone by purified rat hepatic cytochrome P-450g

Purified cytochrome P-450g, a male-specific rat hepatic isozyme, was observed to metabolize progesterone to two primary metabolites (6 beta-hydroxyprogesterone and 16 alpha-hydroxyprogesterone), two secondary metabolites (6 beta,16 alpha-dihydroxyprogesterone and 6-ketoprogesterone), and one tertiary metabolite (6-keto-16 alpha-hydroxyprogesterone). The Km,app for the formation of these products from progesterone was determined to be approximately 0.5 microM, while the Km,app for metabolism of 6 beta- and 16 alpha-hydroxyprogesterone was found to be 5-10 microM. The ratio of primary to secondary metabolites did not change significantly at progesterone concentrations from 6 to 150 microM, and a lag in formation of secondary metabolites was not observed in 1-min incubations. Concerted oxidation of progesterone to secondary products without the intermediate products leaving the active site was suggested by these results and confirmed by isotopic dilution experiments in which little or no dilution of metabolically formed 6 beta,16 alpha-dihydroxyprogesterone and 6-keto-16 alpha-hydroxyprogesterone was observed in incubations containing a mixture of radiolabeled progesterone and unlabeled 6 beta-hydroxyprogesterone or 16 alpha-hydroxyprogesterone. Incubation of 6 beta-hydroxyprogesterone with a reconstituted system in an atmosphere of 18O2 resulted in greater than 90% incorporation of 18O in the 16 alpha-position of 6 beta,16 alpha-dihydroxyprogesterone but no incorporation of 18O into 6-ketoprogesterone, even though the reaction was dependent upon enzyme and O2, and not inhibited by mannitol, catalase, or superoxide dismutase. Factors which characterize the metabolism of progesterone by cytochrome P-450g in terms of active-site constraints and the catalytic competence of the enzyme in microsomes were also explored.     

Mechanism of androstenedione formation from testosterone and epitestosterone catalyzed by purified cytochrome P-450b

A purified rat hepatic monooxygenase system containing cytochrome P-450b oxidizes testosterone to androstenedione and 16 alpha- and 16 beta-hydroxytestosterone at approximately equal rates. The metabolism of epitestosterone by the same system is characterized by a marked stereoselectivity in favor of 16 beta-hydroxylation (4- to 5-fold relative to 16 alpha-hydroxylation), formation of 15 alpha-hydroxyepitestosterone, and a rate of androstenedione formation which is three to five times higher than that observed with testosterone. Apparent Km values for 16 alpha- and 16 beta-hydroxylation and androstenedione formation are 20-30 microM with either substrate. Mass spectral analysis of the androstenedione formed from [16,16-2H2]testosterone and [16,16-2H2] epitestosterone indicates essentially complete retention of deuterium, thereby ruling out a mechanism of androstenedione formation via C-16 hydroxylation followed by loss of water and rearrangement. Mass spectral analysis of the C-16 hydroxylation products from incubations of testosterone or epitestosterone in 18O2 shows essentially complete incorporation of 18O (greater than 95%). Androstenedione formed from testosterone is enriched in 18O only 2-fold (5-8%) over background, while the androstenedione formed from epitestosterone shows 84% enrichment. Kinetic experiments utilizing [17-2H]testosterone and [17-2H]epitestosterone as substrates indicate that cleavage of the C-17 carbon-hydrogen bond is involved in a rate-limiting step in the formation of androstenedione from both substrates. Taken together, our results indicate that androstenedione formation from epitestosterone proceeds exclusively through the gem-diol pathway, while androstenedione formation from testosterone may proceed through a combination of gem-diol and dual hydrogen abstraction pathways.     

Evidence that isoniazid and ethanol induce the same microsomal cytochrome P-450 in rat liver, an isozyme homologous to rabbit liver cytochrome P-450 isozyme 3a

Cytochrome P-450j has been purified to electrophoretic homogeneity from hepatic microsomes of adult male rats administered ethanol and compared to the corresponding enzyme from isoniazid-treated rats. The enzymes isolated from ethanol- and isoniazid-treated rats have identical chromatographic properties, minimum molecular weights, spectral properties, peptide maps, NH2-terminal sequences, immunochemical reactivities, and substrate selectivities. Both preparations of cytochrome P-450j have high catalytic activity in aniline hydroxylation, butanol oxidation, and N-nitrosodimethylamine demethylation with turnover numbers of 17-18, 37-46, and 15 nmol product/min/nmol of P-450, respectively. A single immunoprecipitin band exhibiting complete identity was observed when the two preparations were tested by double diffusion analysis with antibody to isoniazid-inducible cytochrome P-450j. Ethanol- and isoniazid-inducible rat liver cytochrome P-450j preparations have also been compared and contrasted with cytochrome P-450 isozyme 3a, the major ethanol-inducible isozyme from rabbit liver. The rat and rabbit liver enzymes have slightly different minimum molecular weights and somewhat different peptide maps but similar spectral, catalytic, and immunological properties, as well as significant homology in their NH2-terminal sequences. Antibody to either the rat or rabbit isozyme cross-reacts with the heterologous enzyme, showing a strong reaction of partial identity. Antibody against isozyme 3a specifically recognizes cytochrome P-450j in immunoblots of induced rat liver microsomes. Aniline hydroxylation catalyzed by the reconstituted system containing cytochrome P-450j is markedly inhibited (greater than 90%) by antibody to the rabbit protein. Furthermore, greater than 85% of butanol or aniline metabolism catalyzed by hepatic microsomes from ethanol- or isoniazid-treated rats is inhibited by antibody against isozyme 3a. Results of antibody inhibition studies suggest that cytochrome P-450j is induced four- to sixfold by ethanol or isoniazid treatment of rats. All of the evidence presented in this study indicates that the identical cytochrome P-450, P-450j, is induced in rat liver by either isoniazid or ethanol, and that this isozyme is closely related to rabbit cytochrome P-450 isozyme 3a.     

The low affinity 40,000 Fc gamma receptor and the transferrin receptor can be alternative or simultaneous target structures on cells sensitive for natural killing

The role of the low avidity 40,000 dalton receptor for IgG (Fc gamma R) present on K562 and U937 cells in sensitivity to natural killing (NK) was studied by using a murine monoclonal antibody (mAb) specific for the 40,000 dalton Fc gamma R (alpha Fc gamma R mAb). Pretreatment of K562 target cells with intact alpha Fc gamma R mAb or its Fab fragment or anti-transferrin receptor (alpha TFR) mAb partially blocked in a dose-dependent manner, NK activity to K562 cells. However, combined pretreatment with alpha Fc gamma R and alpha TFR mAb completely blocked NK activity against K562 targets. As compared with K562 cells, lower levels of NK were elicited against Molt-4, U937, HL-60, and Daudi targets. Although NK activity to Molt-4 targets was not affected by alpha Fc gamma R mAb, it was fully prevented by pretreatment with alpha TFR mAb. In contrast, NK to U937 cells was not influenced by alpha TFR mAb, but it was strongly inhibited by alpha Fc gamma R mAb. The resistance of 3H-TdR-prelabeled adherent HEp-2 cells to natural cell-mediated cytotoxicity was not affected by either mAb. Lectin-dependent cell-mediated cytotoxicity (LDCC) against HEp-2 cells due to the presence of concanavalin A, and was completely abrogated by pretreatment of the targets with alpha TFR mAb, but was unaffected by alpha Fc gamma R mAb. By use of the flow cytometer, a significant correlation was detected between the relative expression of 40,000 dalton Fc gamma R and the susceptibility to NK, whereas the expression of TFR was discordant from NK sensitivity. As determined in the single cell cytotoxicity assay alpha Fc gamma R mAb reduced the frequency of target binding effector cells without affecting the number of dead bound targets. This pattern of inhibition was found against both K562 and U937 targets. Alternatively, alpha TFR mAb inhibited both binding and killing of K562 and Molt-4 targets. Because pretreatment of HEp-2 cells with alpha TFR mAb did not influence conjugate formation, the blocking of LDCC to HEp-2 cells by alpha TFR mAb can be related to post-binding events. These data show that although both the 40,000 dalton Fc gamma R and the TFR can be target structures for NK cell recognition, the TFR may also play an important role in the post-binding events.     

Changes in lipoprotein composition during larval-pupal metamorphosis of an insect, Manduca sexta

During the transition from the last feeding larval stage to the pupal stage of the tobacco hornworm, Manduca sexta, significant changes occur in the properties of lipophorin, the major hemolymph lipoprotein. Within the first 24 h after cessation of feeding, the larval lipophorin (HDLp-L) is first converted to a higher density form (HDLp-W2) and then HDLp-W2 is converted to a lower density form (HDLp-W1). HDLp-W1 remains in the hemolymph until pupation, when another form, HDLp-P, with a density between HDLp-W1 and HDLp-L, is present. Although all the lipophorins contain identical apoproteins, they differ in lipid content and composition; the differences in density being primarily related to diacylglycerol content. The conversion of HDLp-L to HDLp-W1 is accompanied by a loss of hydrocarbon and uptake of carotenes. These latter changes in lipophorin composition reflect alterations in cuticular lipid composition. HDLp-L was radiolabeled in the apoproteins by injecting animals with 3H-amino acids early in the last larval stage. Subsequently HDLp-L was isolated at the end of the larval stage, HDLp-W2 and HDLp-W1 were isolated during the wandering stage, and HDLp-P was isolated after pupation. The specific activity of the apoproteins in the four lipophorins was not significantly different, suggesting that the observed alterations in lipophorin properties do not require synthesis of new apoproteins but result from retailoring the lipid composition of preexisting molecules. Examination of the hemolymph of individual animals during these transitions showed that only one species of lipoprotein was present, never a mixture of two or more species. These observations suggest that the lipoprotein conversions are precisely timed and that lipoprotein metabolism during larval development and pupation cannot be considered a static process. The unique finding of these studies was that synthesis of lipophorin apoproteins proceeds actively during the first part of the fifth instar but then ceases and does not recommence during the wandering or early pupal stages.     

Lipoprotein interconversions in an insect, Manduca sexta. Evidence for a lipid transfer factor in the hemolymph

Hemolymph lipoproteins (lipophorins) of adult Manduca sexta are disinct from larval forms in density, lipid content, composition, and the presence of a third, low molecular weight apoprotein. Generally, only one lipoprotein species exists in M. sexta hemolymph during any given life stage. Progression through the life cycle results in alterations of existing lipoproteins to produce new forms, without new protein synthesis. The observed alterations in lipoprotein density could result from facilitated lipid transfer in insect hemolymph. An in vitro assay of facilitated lipid transfer was developed which employs a high density lipophorin from the wandering larva (density = 1.18 g/ml) as acceptor and adult low density lipophorin (density = 1.03 g/ml) as donor. Adult lipophorin-deficient hemolymph was shown to catalyze a time-dependent equilibration of the starting lipoproteins to produce a new intermediate lipophorin, Lp-I. Hydrodynamic experiments on the donor, acceptor, and product lipoproteins excluded fusion as the mechanism whereby Lp-I is produced. Thus, it is concluded that Lp-I results from facilitated net lipid transfer from low to high density lipoprotein. Furthermore, experiments conducted with radioiodinated donor and radioiodinated acceptor lipoproteins demonstrated that apoprotein exchange does not occur during the lipid transfer reaction. When donor lipoprotein was labeled in the lipid moiety with carbon-14, evidence of diacylglycerol and phospholipid exchange was obtained. Partial characterization of the lipid transfer factor revealed a relationship between incubation time, donor concentration, acceptor concentration, lipophorin-deficient hemolymph concentration, and transfer activity, as measured by Lp-I production. It is concluded that lipophorin-deficient hemolymph contains one or more factor(s) that catalyze net lipid transfer as well as diacylglycerol and phospholipid exchange between lipophorins to produce a single form at equilibrium.     

Mechanism of inactivation of rat liver microsomal cytochrome P-450c by 2-bromo-4'-nitroacetophenone

The mechanism by which 2-bromo-4'-nitroacetophenone (BrNAP) inactivates cytochrome P-450c, which involves alkylation primarily at Cys-292, is shown in the present study to involve an uncoupling of NADPH utilization and oxygen consumption from product formation. Alkylation of cytochrome P-450c with BrNAP markedly stimulated (approximately 30-fold) its rate of anaerobic reduction by NADPH-cytochrome P-450 reductase, as determined by stopped flow spectroscopy. This marked stimulation in reduction rate is highly unusual in that Cys-292 is apparently not part of the heme- or substrate-binding site, and its alkylation by BrNAP does not cause a low spin to high spin state transition in cytochrome P-450c. Under aerobic conditions the rapid oxidation of NADPH catalyzed by alkylated cytochrome P-450c was associated with rapid reduction of molecular oxygen to hydrogen peroxide via superoxide anion. The intermediacy of superoxide anion, formed by the one-electron reduction of molecular oxygen, established that alkylation of cytochrome P-450c with BrNAP uncouples the catalytic cycle prior to introduction of the second electron. The generation of superoxide anion by decomposition of the Fe2+ X O2 complex was consistent with the observations that, in contrast to native cytochrome P-450c, alkylated cytochrome P-450c failed to form a 430 nm absorbing chromophore during the metabolism of 7-ethoxycoumarin. Alkylation of cytochrome P-450c with BrNAP did not completely uncouple the catalytic cycle such that 5-20% of the catalytic activity remained for the alkylated cytochrome compared to the native protein depending on the substrate assayed. The uncoupling effect was, however, highly specific for cytochrome P-450c. Alkylation of nine other rat liver microsomal cytochrome P-450 isozymes with BrNAP caused little or no increase in hydrogen peroxide formation in the presence of NADPH-cytochrome P-450 reductase and NADPH.     

Properties of a cellulolytic Sporolactobacillus and some non-sporing cellulolytic rods, presumptive clostridia, from an anaerobic digester

Anaerobic digesters contain a wide variety of anaerobic cellulolytic bacteria. Many of these are sporing rods. Some isolates from a mesophilic cattle waste anaerobic digester were classified as Sporolactobacillus spp. A further group of bacteria could not be induced to sporulate. In some respects they resembled Eubacterium , but considering all the properties it is suggested that they should be classified as a species of Clostridium.     

Absolute configuration of the 5,6-oxide formed from 7,12-dimethylbenz[a]anthracene by cytochrome P450c

The absolute configurations of the enantiomeric 5,6-arene oxides of 7,12-dimethylbenz[a]anthracene (DMBA) were recently assigned such that the late eluting enantiomer from a chiral HPLC column has 5R,6S absolute configuration. [Mushtaq et al. (1984) BBRC 125, 539]. The authors further concluded that the 5R,6S-enantiomer predominates on metabolism of DMBA by cytochrome P450c in liver microsomes from 3-methylcholanthrene-treated rats. Their chemical assignment of absolute configuration is incorrect. Thus, metabolism of DMBA by these microsomes as well as by homogeneous cytochrome P450c produces 5,6-oxide highly enriched (95%) in the 5S,6R-enantiomer in accord with theoretical predictions.