Kinetic Modulation by GABAergic Agents of High- and Low-Affinity Binding of [3H]Methyl β-Carboline-3-Carboxylate

The kinetics of dissociation of [3H]methyl beta-carboline-3-carboxylate (beta-CCM) binding was studied in a synaptosomal membrane preparation of rat cerebral cortex. Dissociation was biphasic: a faster phase (10-30% contribution) was followed by a slower phase. Picrotoxin pretreatment at 22 degrees C enhanced the equilibrium binding of [3H]beta-CCM. The half-life of the slower phase of beta-CCM dissociation (t1/2II) was increased by 60 muM picrotoxin from 1.7 min to 3.3 min. The dissociation of [3H]beta-CCM was identical when initiated by an excess of either diazepam or beta-CCM. Quasi-equilibrium Scatchard analysis of [3H]beta-CCM binding was performed by a kinetic separation of the rapid and slow phases of dissociation. The slow and rapid phases represented beta-CCM binding sites of high and low affinity, respectively. The dissociation of [3H]beta-CCM (control t1/2II = 2.0 min) was decelerated by the gamma-aminobutyric acid (GABA) antagonist 3-alpha-hydroxy-16-imino-5 beta-17-aza-androstan-11-one (R 5135) (t1/2II = 2.5 min) and accelerated by GABA (t1/2II = 1.6 min). GABA inhibited both high- and low-affinity beta-CCM bindings.     

Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake

Bethlenfalvay, G. J., Brown, M. S., Ames, R. N. and Thomas, R. S. 1988. Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake. - Physiol. Plant. 72: 565–571.
Soybean [ Glycine max (L.) Merr.] plants were grown in pot cultures and inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe or provided with P fertilizer (non-VAM plants). After an initial growth period (21 days), plants were exposed to cycles of severe, moderate or no drought stress over a subsequent 28-day period by rewatering at soil water potentials of -1.0, -0.3 or -0.05 MPa. Dry weights of VAM plants were greater at severe stress and smaller at no stress than those of non-VAM plants. Phosphorus fertilization was applied to produce VAM and non-VAM plants of the same size at moderate stress. Root and leaf P concentrations were higher in non-VAM plants at all stress levels. All plants were stressed to permanent wilting prior to harvest. VAM plants had lower soil moisture content at harvest than non-VAM plants. Colonization of roots by G. mosseae did not vary with stress, but the biomass and length of the extraradical mycelium was greater in severely stressed than in non-stressed plants. Growth enhancement of VAM plants relative to P-fertilized non-VAM plants under severe stress was attributed to increased uptake of water as well as to more efficient P uptake. The ability of VAM plants to deplete soil water to a greater extent than non-VAM plants suggests lower permanent wilting potentials for the former.     

Nutrient transfer between the root zones of soybean and maize plants connected by a common mycorrhizal mycelium

The objective of the study was to determine whether nutrient fluxes mediated by hyphae of vesicular-arbuscular mycorrhizal (VAM) fungi between the root zones of grass and legume plants differ with the legume's mode of N nutrition. The plants, nodulating or nonnodulating isolines of soybean [ Glycine max (L.) Merr.], were grown in association with a dwarf maize ( Zea mays L.) cultivar in containers which interposed a 6-cm-wide root-free soil bridge between legume and grass container compartments. The bridge was delimited by screens (44 μm) which permitted the passage of hyphae, but not of roots and minimized non VAM interactions between the plants. All plants were colonized by the VAM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. The effects of N input to N-sufficient soybean plants through N₂-fixation or N-fertilization on associated maize-plant growth and nutrition were compared to those of an N-deficient (nonnodulating, unfertilized) soybean control. Maize, when associated with the N-fertilized soybean, increased 19% in biomass, 67% in N content and 77% in leaf N concentration relative to the maize plants of the N-deficient association. When maize was grown with nodulated soybean, maize N content increased by 22%, biomass did not change, but P content declined by 16%. Spore production by the VAM fungus was greatest in the soils of both plants of the N-fertilized treatment. The patterns of N and P distribution, as well as those of the other essential elements, indicated that association with the N-fertilized soybean plants was more advantageous to maize than was association with the N₂-fixing ones.     

Diversity of coding strategies in influenza viruses.

Influenza viruses have exploited a variety of strategies to increase their genome coding capacities. These include unspliced, spliced, alternatively spliced and bicistronic mRNAs, translation from overlapping reading frames and a coupled stop-start translation of tandem cistrons.     

Effects of selective cholecystokinin antagonists L364,718 and L365,260 on food intake in rats

The selective type A and B cholecystokinin (CCK) receptor antagonists L364,718 and L365,260 were used to identify the receptor subtype that mediates the satiety effect of endogenous CCK. Male rats (n = 12–13/group), fed ground rat chow ad lib, received L364,718 (0, 1, 10, 100, or 1000 μg/kg IP) or L365,260 (0, 0.1, 1, 10, 100, 1000, or 10,000 μg/kg IP) 2 h after lights off, and food intake was measured 1.5, 3.5, and 5.5 h later. L364,718 significantly stimulated 1.5-h food intake by more than 40% at 10 μg/kg and higher doses; cumulative intake at 3.5 and 5.5 h remained elevated by about 20% at 1000 and 100 μg/kg of L364,718, respectively. In contrast, L365,260 had no significant stimulatory effect on feeding at any dose. The potency of L365,260 for antagonizing gastrin-stimulated gastric acid secretion was examined in unanesthetized rats. Male rats (n = 14), prepared with gastric and jugular vein cannulas, received doubling doses of gastrin (G-17I) (0.16–5 nmol/kg/h IV), each dose for 30 min, and gastric juice was collected for each 30-min period. G-17I stimulated gastric acid output dose dependently; the minimal effective dose was 0.16 nmol/kg/h, while maximal output (5-fold above basal) occurred at 5 nmol/kg/h. L365,260 (0, 1, 10, 100, 1000, or 10,000 μg/kg IV), administered 30 min before continuous infusion of G-17I (1.25 or 5 nmol/kg/h), significantly inhibited acid output only at 10,000 μg/kg; cumulative 60-min output was decreased by 60%. These results suggest that CCK acts at CCK-A receptors to produce satiety during the dark period in ad lib-feeding rats.     

The choice between two distinct T cell determinants within a 23-amino acid region of lysozyme depends on their structural context

The specificity of C57BL/6 T cells reactive to peptide aa 74-96 of hen egg-white lysozyme (HEL) was analyzed by using a panel of synthetic peptides of varying lengths from this region. It was found that peptide 74-96-reactive T cells induced by native HEL (aa 1-129) or its denatured fragment L2 (aa 13-105) recognized two distinct but overlapping determinants contained within aa 74-90 or aa 81-96, respectively. Peptide 74-96 itself induced both peptide 74-90-and peptide 81-96-specific T cells. Thus, a choice was made between these two potential T cell determinants on peptide 74-96, depending on which immunogen was used. Interestingly, the ability of both peptide determinants aa 74-90 and aa 81-96 to stimulate peptide 74-96-reactive T cells was partly dependent on the presence of residues within the overlap region (aa 81-90), suggesting that this region may play an important role in Iab-restricted T cell activation. This was further supported by the poor immunogenicity of shorter peptides 74-86 or 85-96, lacking residues from the overlap region in B6 mice. These two short peptides were nevertheless capable of eliciting T cell responses in B10.A mice, suggesting that the importance of this overlap region in obtaining a response to peptide 74-96 is related to the MHC haplotype.     

SALT REGULATION AND LEAF SENESCENCE IN AGING LEAVES OF JAUMEA CARNOSA (LESS.) GRAY (ASTERACEAE), A SALT MARSH SPECIES EXPOSED TO NaCl STRESS

The effects of increasing salt stress on leaf senescence and salt regulation were investigated in the halophyte Jaumea carnosa in hydroponic culture experiments. The plants were grown in Hoagland's nutrient solution plus additional NaCl salt (0, 300, 400, 500 mm NaCl). Decreases in nucleic acids, protein, and chlorophyll were used as indicators of leaf senescence. The results indicated no definitive pattern of acceleration in leaf senescence with increasing salt stress. Salt regulation was also unaffected as leaves aged under increasing NaCl concentrations. The results are consistent with those of previous studies of the halophyte which indicated that the species was very tolerant of high NaCl concentrations.     

The relationship between first and second chromosome segregation ratios from Drosophila melanogaster males bearing Segregation Distorter

Summary Drosophila melanogaster males heterozygous for the second chromosome locus Segregation Distorter preferentially transmit this chromosome to their progeny due to a dysfunctioning of SD ⁺-bearing sperm. SD males with a normal sex chromosome constitution produce more females than males among SD ⁺ progeny. This report shows that this unequal recovery of sexes is enhanced from XY/Y; SD/SD ⁺ males and enhanced still further from XY/O; SD/SD ⁺ males. It is argued that the probability that a SD ⁺-bearing sperm will dysfunction is related to its sex chromsome complement, with the relative probabilities of dysfunction ranked O> Y> X> XY. It is shown that a modified probit analysis accounts for the relationship between sex ratio and second chromosome segregation frequency for all paternal genotypes. Finally, SD/SD ⁺ males show no increase in sex chromosome nondisjunction with respect to a control.R. E. Denell was supported by U.S.P.H.S. Training Grant No. GM00337 and by a U.S.P.H.S. Postdoctoral Fellowship; George L. Gabor Miklos was supported by A.E.C. Contract No. AT (04-3)-34 PA150.     

Age,smoking habits,heat stress,and their interactive effects with carbon monoxide and peroxyacetylnitrate on man's aerobic power

Metabolic, body temperature, and cardiorespiratory responses of 16 healthy middle-aged (40–57 years) men, 9 nonsmokers and 7 smokers, were obtained during tests of maximal aerobic power at ambient environmental temperatures of 25 ± 0.5 and 35 ± 0.5°C and 20% relative humidity under four conditions: (a) filtered air, FA; (b) 50 ppm carbon monoxide in filtered air, CO; (c) 0.27 ppm peroxyacetylnitrate in filtered air, PAN; and (d) a combination of all three mixtures, PANCO. There was no significant change in maximum aerobic power \(\left( {\dot VO2max} \right)\) related to the presence of air pollutants, although total working time was lowered in the 25°C environment while breathing CO. Older nonsmokers did have a decrement in \(\left( {\dot VO2max} \right)\) while breathing 50 ppm CO, while older smokers failed to show any change. This difference was related to the initial COHb levels of the smokers, who, when breathing this level of ambient CO, had only a 14% increase in COHb over their initial levels in contrast to the 200% increase in the nonsmokers. Smoking habits were the most influential factor affecting the cardiorespiratory responses of these older men to maximal exercise. Regardless of ambient conditions, smokers had a significantly lower (27%) aerobic power than nonsmokers, were breathing closer to their maximal breathing capacities throughout the walk, and had a higher respiratory exchange ratio. While the \(\left( {\dot VO2max} \right)\) of nonsmokers was only 6% less than that of younger nonsmoking males ( \(\bar x\) age = 25 years) working under similar conditions, the aerobic power of the older smokers was 26% lower than that of young smokers ( \(\bar x\) age = 24 years).