Age-specific survivorship analysis ofHeliothis spp. Populations on cotton

Population dynamics of Heliothis virescens (F.) and Heliothis zea (Boddie ) (Lepidoptera: Noctuidae) eggs and larvae were studied for two years in a small plot of cotton, Gossypium hirsutum (L.). Due to morphological and ecological similarities, the pooled Heliothis population was considered for most of the analyses. Two generations of Heliothis eggs and larvae were completed during each year. Stage recruitment was estimated for the eggs and larval instars 2–6, and recruitment variances were estimated by a Monte Carlo method. A modified form of the Weibull distribution was developed and used as a model to characterize survivorship curves for each of the four Heliothis generations. A Type I survivorship curve (mortality rate increasing with age) was inferred for both Generation 1 (early season) data sets, whereas a Type II survivorship curve (mortality rate constant and thus independent of age) was inferred for both Generation 2 (late season) data sets. The shapes of the survivorship curves for the individual H. virescens and H. zea populations were inferred to be the same as those for the pooled populations. Analysis of the contributions of various factors to Heliothis stage-specific mortality indicated that natural enemies (predators and parasites) and the availability of food for larvae were responsible for between-generation differences in survivorship patterns.     

Reduced lipogenesis in cafeteria-fed rats exhibiting diet-induced thermogenesis

Fatty-acid synthesis has been measured in vivo with³H₂O in cafeteria-fed rats exhibiting diet-induced thermogenesis. Synthesis was decreased in brown adipose tissue, the liver, white adipose tissue, and the carcass of the cafeteria-fed animals compared to rats fed the normal stock diet. Whole-body synthesis was also decreased in the cafeteria-fed group. Diet-induced thermogenesis, in contrast to cold-induced non-shivering thermogenesis does not lead to increased fatty-acid synthesis and this is presumably due to the inhibitory effects on lipogenesis of the high dietary fat intake characteristic of cafeteria diets. The results also indicate that the energy cost of body fat deposition in cafeteria-fed rats is lower than in animals fed a low-fat/high-carbohydrate stock diet.     

Development and characterization of monoclonal antibodies to human type III procollagen

Hybridomas which secrete monoclonal antibodies against human type III procollagen have been developed. By an enzyme-linked immunosorbent assay, three of the monoclonal antibodies have been determined to be against non-helical extensions of the molecules while two of the antibodies are against helical portion of the molecules which is sensitive to bacterial collagenase action. These findings have been further confirmed by carrying out immuno-reaction of the pro α-chains transferred on nitrocellulose paper from sodium dodecyl sulfate polyacrylamide gels. These monoclonal antibodies have been found to be suitable reagents for immunohistochemical studies as well as for immunoassays of type III procollagen and collagen.     

Fibronectin in osteoarthritic canine articular cartilage

A large non-collagenous protein was extracted from degenerated cartilage of osteoarthritic canine joints. Evidence was presented that this protein is fibronectin. It had a molecular weight identical to that of fibronectin isolated from canine serum, required the presence of heparin and urea in the extraction buffer for solubilization, reacted with both polyclonal and monoclonal antibodies to fibronectin in an enzyme-linked immunosorbent assay (ELISA), and exhibited gelatin binding properties. Fibronectin was detected in normal cartilage as well, although in lesser amounts than observed in osteoarthritic cartilage.     

Fatty Acid Oxidation and Ketogenesis by Astrocytes in Primary Culture

The oxidation of the fatty acids octanoate and palmitate to CO2 and the ketone bodies acetoacetate and D-(-)-3-hydroxybutyrate was examined in astrocytes that were prepared from cortex of 2-day-old rat brain and grown in primary culture to confluence. Accumulation of acetoacetate (by mass) in the culture medium of astrocytes incubated with octanoate (0.3-0.5 mM) was 50-90 nmol C2 units h-1 mg of protein-1. A similar rate was obtained using radiolabeled tracer methodology with [1-14C]octanoate as labeled substrate. The results from the radiolabeled tracer studies using [1-14C]- and [7-14C]octanoate and [1-14C]-, [13-14C]-, and [15-14C]palmitate indicated that a substantial proportion of the omega-terminal four-carbon unit of these fatty acids bypassed the beta-ketothiolase step of the beta-oxidation pathway and the 3-hydroxy-3-methylglutaryl (HMG)-CoA cycle of the classic ketogenic pathway. The [14C]acetoacetate formed from the 1-14C-labeled fatty acids, obligated to pass through the acetyl-CoA pool, contained 50% of the label at carbon 3 and 50% at carbon 1. By contrast, the [14C]acetoacetate formed from (omega-1)-labeled fatty acids contained 90% of the label at carbon 3 and 10% at carbon 1, whereas that formed from the (omega-3)-labeled fatty acid contained 20% of the label at carbon 3 and 80% at carbon 1. These results indicate that acetoacetate is primarily formed either by the action of 3-oxo-acid-CoA transferase (EC 2.8.3.5) or acetoacetyl-CoA deacylase (EC 3.1.2.11) or both on acetoacetyl-CoA and not by the action of the mitochondrial HMG-CoA cycle involving HMG-CoA lyase (EC 4.1.3.4), which was readily detected, and HMG-CoA synthase (EC 4.1.3.5), which was barely measurable.     

Immunoelectron microscopy studies with a monoclonal antibody directed against a receptor recognition site epitope in human α2-macroglobulin

α₂-Macroglobulin (α₂M) is a plasma proteinase inhibitor that binds up to 2 mole of proteinase per mole of inhibitor. Proteinase binding or reaction with small primary amines causes a major conformational change in α₂M. As a result of this conformational change, a new epitope recognized by monoclonal antibody 7H11D6 is exposed. The association of α₂M-proteinase or α₂M-methylamine with α₂M cellular receptors is prevented by 7H11D6. In this investigation, the binding of 7H11D6 to α₂M was studied by electron microscopy. 7H11D6 bound to α₂M-methylamine and α₂M-trypsin but not to native α₂M. The structure of α₂M after conformational change resembled the letter “H.” 7H11D6 epitopes were identified near the apices of the four arms in the α₂M “H” structure. 7H11D6 that was adducted to colloidal gold (7HAu) retained the specificity of the free antibody (binding to α₂M-trypsin but not to native α₂M). α₂M conformational change intermediates prepared by sequential reaction with a protein crosslinker and trypsin also bound 7HAu. These results suggest that a complete α₂M conformational change is not necessary for 7H11D6 epitope exposure and may not be required for receptor recognition. 7HAu was used to isolate a preparation consisting primarily of binary α₂M-trypsin (1 mole trypsin per mole α₂M instead of 2). Structures resembling the letter “H” were most common; however, each field showed some atypical molecules with arms that were compacted instead of thin and elongated. These incompletely transformed structures were similar to the α₂M conformational intermediates described previously (S. L. Gonias and N. L. Figler (1989) J. Biol. Chem. 264, 9565–9570). We propose that lateral arm extension is a critical step in α₂M conformational change. Failure of lateral arm extension is probably a common property of different α₂M conformational intermediates.     

Interaction of leukocyte integrins with ligand is necessary but not sufficient for function

The leukocyte integrins (CD11/CD18 or beta 2-type integrins) are expressed exclusively on leukocytes and participate in many adhesion- dependent functions (Arnaout, M.A. 1990. Blood. 75:1037-1050; Springer, T. A. 1990. Nature. (Lond.) 346:425-434; Dustin, M. L., and T. S. Springer. 1991. Annu. Rev. Immunol. 9:27-66). The avidity of leukocyte integrin binding to their ligands or counter-receptors is dependent upon response to intracellular signals (Wright, S. D., and B. C. Meyer. 1986. J. Immunol. 136:1759-1764; Dustin, M. A., and T. S. Springer. 1989. Nature (Lond.). 341:619-624). We have investigated the effects of a novel mAb (mAb 24) which defines a leukocyte integrin alpha subunit epitope that is Mg(2+)-dependent and may be used as a "reporter" of the activation state of these receptors (Dransfield, I., and N. Hogg. 1989. EMBO (Eur. Mol. Biol. Organ) J. 8:3759-3765; Dransfield, I., A.-M. Buckle, and N. Hogg. 1990. Immunol. Rev. 114:29-44; Dransfield, I., C. Cabanas, A. Craig, and N. Hogg. 1992. J. Cell Biol.) Data is presented to show that this mAb inhibits monocyte-dependent, antigen-specific T cell proliferation and IL-2-activated natural killer cell assays which are both dependent on lymphocyte function-associated antigen-1 (LFA-1), and complement receptor type 3 (CR3)-mediated neutrophil chemotaxis to f-Met-Leu-Phe. This inhibitory effect is not caused by the prevention of receptor/ligand binding because LFA-1/ICAM-1, LFA-1/ICAM-2,3 and CR3/iC3b interactions are, under activating conditions, promoted rather than blocked by mAb 24. As it does not interfere with mitogen- stimulated T cell proliferation, it is unlikely that mAb 24 transduces a "negative" or antiproliferative signal to the T cells to which it is bound. Using a model system of transient activation of LFA-1, we have found that mAb 24 prevents "deadhesion" of receptor/ligand pairs, possibly locking leukocyte integrins in an "active" conformation. It is speculated that inhibition of leukocyte integrin function by this mAb reflects the necessity for dynamic leukocyte integrin/ligand interactions.     

Comparison of Rates of Local Cerebral Glucose Utilization Determined with Deoxy[l-14C]glucose and Deoxy[6-14C]glucose

The activity of the pentose phosphate shunt pathway in brain is thought to be linked to neurotransmitter metabolism, glutathione reduction, and synthetic pathways requiring NADPH. There is currently no method available to assess flux of glucose through the pentose phosphate pathway in localized regions of the brain of conscious animals in vivo. Because metabolites of deoxy[1-14C]glucose are lost from brain when the experimental period of the deoxy[14C]glucose method exceeds 45 min, the possibility was considered that the loss reflected activity of this shunt pathway and that this hexose might be used to assay regional pentose phosphate shunt pathway activity in brain. Decarboxylation of deoxy[1-14C]glucose by brain extracts was detected in vitro, and small quantities of 14C were recovered in the 6-phosphodeoxygluconate fraction when deoxy[14C]glucose metabolites were isolated from freeze-blown brains and separated by HPLC. Local rates of glucose utilization determined with deoxy[1-14C]glucose and deoxy[6-14C]glucose were, however, similar in 20 brain structures at 45, 60, 90, and 120 min after the pulse, indicating that the rate of loss of 14CO2 from deoxy[1-14C]glucose-6-phosphate in normal adult rat brain is too low to permit assay pentose phosphate shunt activity in vivo. Further metabolism of deoxy[1-14]glucose-6-phosphate via this pathway does not interfere during routine use of the deoxyglucose method or explain the progressive decrease in calculated metabolic rate when the experimental period exceeds 45 min.     

Foraging behavior of specialist and generalist caterpillars on plantain (Plantago lanceolata) altered by predatory stinkbugs

Summary To examine the effects of predators and plant genotype on the behavior, patterns of herbivory, growth and survivorship of caterpillars, we used an experimental garden in which we contrasted two hostplant genotypes of plantain (Plantago lanceolata), two kinds of herbivores (specialist Junonia coenia vs. generalist Pyrrharctia isabella) and two levels of caterpillar predation (with and without Podisus maculiventris stinkbugs). Each of the replicate plots per treatment contained two plants of the same genotype. The stinkbugs reduced the survivorship of the specialist caterpillars but not that of the generalists, which reflects the differences in predatoravoidance behaviors of these species. Nonetheless, the stinkbugs influenced the behavior of both caterpillar species. When stinkbugs were present, both specialist and generalist caterpillars were less likely to be found on the plant upon which they were initially placed (=initial plant), and they were more likely to be off both plants within the plot than larvae in the absence of predators. Consequently in the presence of the stinkbug predators, the proportion of the initial plants consumed was less than in the absence of the predators. Plant genotype influenced plant size and the proportion of individual plants eaten, but it did not affect larval location on the plots. Neither presence of predators nor plant genotype had an effect on relative growth rate of the caterpillars.