Experimental analyses of competition between two species of bumble bees (Hymenoptera: apidae)

Summary Dynamical aspects of flower usage and forager body size in sympatric and experimentally-induced allopatric populations of Bombus flaviforns and Bombus rufocinctus were studied in 10 discrete subalpine meadows and over the last half of one summer. Results indicate that there is a high degree of asymmetry in the competitive effects and that B. flavifrons is the clear competitive and numerical dominant. When occurring alone, B. rufocinctus used the same spectrum of flowers in similar frequencies to that of B. flavifrons whose flower use was invariant over all meadows and treatments. When sympatric with B. flavifrons, B. rufocinctus was relegated to secondary, less preferred flowers. Shifts in flower use by B. rufocinctus were accompanied by changes in forager body-size: body weights were greater in allopatric populations of B. rufocinctus and smaller in those sympatric with B. flavifrons. Competitive dominance may be related to differences in species phenologies. Bombus flavifrons initiated colonies in the spring three weeks before B. rufocinctus and maintained higher densities over the summer; by virtue of greater numbers of foragers, it may control exploitation of the most profitable flowers.     

Relation of precipitation and temperature with yield of herbaceous plants in eastern Oregon

Eighteen years of herbage yields of range grasses and concomitant precipitation and temperature fluctuations were examined with correlation and regression techniques. Antecedent precipitation was the dominant factor influencing yield of perennial herbaceous species, while both temperature and precipitation were important for prediction of yield of downy bromegrass, a winter annual. Total yield of the herbaceous community was closely correlated with precipitation received during the September to June period (r = 0.92); however, September to March precipitation was also highly correlated (r = 0.89). These correlations provide timely and useful estimates of native range production on eastern Oregon ranges. Sixty to 92% of yield variation was accounted for by the regression models for 9 of the 12 species or species groups examined.     

Stimulation of phagocytic function by factors inhibiting leukocyte and macrophage migration in humans

Fractions containing macrophage migration inhibition factor (MIF) and leucocyte migration inhibition factor (LIF) were obtained using Sephadex G-200 filtration from supernatant fluids of human lymphocyte cultures stimulated by PHA. The fractions were tested for the ability to affect migration and phagocytic activity of target cells. Peripheral blood leucocyte migration capacity was inhibited by the fraction with the molecular mass of 60,000-70,000 D (LIF), while migration activity of mouse peritoneal exudate cells was suppressed by the fraction with the molecular mass of 20,000-30,000 D (MIF). MIF- and LIF-containing fractions increased almost three-fold Fc-receptor-mediated phagocytic activity of neutrophils.     

The role of surface charge and hydrophilic groups on liposome clearance in vivo.

The effect of negative surface charge and hydrophilic groups on liposome clearance from blood was investigated in mice using liposome-entrapped 67gallium-deferoxamine as a label. The presence of negatively-charged lipids may retard or accelerate liposome clearance. Physicochemical features contributing to optimal retardation of liposome clearance include a hydrophilic carbohydrate moiety and a sterically hindered negatively-charged group. The relevance of the negative charge steric effect is suggested by the finding that phosphatidylinositol phosphate (PIP) and trisialoganglioside (GT1) are less effective than phosphatidylinositol (PI) and monosialoganglioside (GM1), respectively, in retarding liposome clearance. The need for negative charge in addition to the carbohydrate group for optimal effect on retardation of clearance is indicated by the observation that asialoganglioside (AGM1) is less effective than GM1 in this respect. The negative charge effect is observed with liposome bilayers having both low and high temperature phase-transitions. Increasing the molar fraction of negatively-charged lipid (hydrogenated PI derived from soya) from 23 to 41% resulted in a dramatic acceleration of liposome clearance. The clearance-accelerating effect of the high negative charge was specifically directed to the liver with selective reduction of spleen uptake. Increasing liposome size also had an accelerating effect on clearance but in this case it was accompanied by a non-specific concomitant increase of both liver and spleen uptake.     

Alveolar macrophages in pulmonary immune responses. I. Role in the initiation of primary immune responses and in the selective recruitment of T lymphocytes to the lung

Antigen inoculated intratracheally (IT) into animals can induce primary immune responses and selectively recruit specific T cells to the lung. In the current study, the role of alveolar macrophages (AM) in these two responses was investigated. Antigen-pulsed bronchoalveolar cells (BAC) inoculated IT into guinea pigs generated a population of immune T cells that proliferated in vitro on reexposure to antigen-pulsed macrophages (M?). The possibility that antigen-pulsed donor BAC shed antigen that was subsequently processed and presented by host M? was ruled out by genetic experiments. Thus, peritoneal exudate lymphocytes (PEL) from (2 X 13)F1 guinea pigs primed with antigen-pulsed BAC from strain 2 animals responded preferentially to antigen-pulsed strain 2 M? rather than to antigen-pulsed strain 13 M?. In a second set of studies, antigen-pulsed BAC inoculated IT into guinea pigs selectively recruited antigen-specific T cells to the lung. Genetic experiments verified that inoculated BAC were the source of the antigen-presenting cells responsible for selective recruitment. Thus, antigen-pulsed strain 2 BAC inoculated IT recruited a greater proportion of (2 X 13)F1 T cells that recognized antigen in the context of strain 2 M? than F1 T cells that recognized antigen on strain 13 M?. Taken together, these studies suggest that AM contribute to the regulation of pulmonary immunity by both inducing T lymphocyte immunity and selectively recruiting specific T cells to the lung.     

Stoichiometry of microsomal oxidation reactions. Distribution of redox-equivalents in monooxygenase and oxidase reactions catalyzed by cytochrome P-450

The stoichiometry of NADPH oxidation in rabbit liver microsomes was studied. It was shown that in uncoupled reactions cytochrome P-450, besides O2- generation catalyzes direct two- and four-electron reduction of O2 to produce H2O2 and water, respectively. With an increase in pH and ionic strength, the amount of O2 reduced via an one-electron route increases at the expense of the two-electron reaction. In parallel, with a rise in pH the steady-state concentration of the oxy-complex of cytochrome P-450 increases, while the synergism of NADPH and NADH action in the H2O2 formation reaction is replaced by competition. The four-electron reduction is markedly accelerated and becomes the main pathway of O2 reduction in the presence of a pseudo-substrate--perfluorohexane. Treatment of rabbit with phenobarbital, which induces the cytochrome P-450 isozyme specific to benzphetamine results in a 2-fold increase in the degree of coupling of NADPH and benzphetamine oxidation. The experimental results suggest that the ratio of reactions of one- and two-electron reduction of O2 is controlled by the ratio of rates of one- and two-electron reduction of cytochrome P-450. In the presence of pseudo-substrates cytochrome P-450 acts predominantly as a four-electron oxidase; one of possible reasons for the uncoupling of microsomal monooxygenase reactions is the multiplicity of cytochrome P-450 isozymes.     

In vivo cellular responses to electrophoretically applied dynorphin in the rat hippocampus

Recent immunohistochemical and radioimmunochemical observations have demonstrated a differential distribution of immunoreactive dynorphin (DYN) in rat brain. The presence of DYN immunoreactivity in a major intrinsic fiber pathway within the rat hippocampus (the mossy fiber system) has led us to evaluate the possible role of DYN and other closely related peptides in this structure. Single cell activity and hippocampal field potentials have been recorded from the CA1-CA3 cellular fields in halothane or urethane anesthetized rats. DYN, DYN1-13, DYN1-8, and alpha-neo-endorphin had an excitatory effect on most CA1-CA3 neurons encountered as has been previously observed for opiates and other opioid peptides. This response could be blocked by naloxone or by co-administration of Mg++ ion suggesting an indirect (synaptic) mechanism of excitation similar to that hypothetized for enkephalin. A significant number of CA3 neurons, however, exhibited a non-naloxone sensitive inhibitory response to DYN, related opioid peptides, and the kappa agonist WIN 35-197 (ethylketocyclazocine). Field potential analysis of CA1-CA3 neuronal responses to mossy fiber activation also indicated an excitatory, Mg++ reversible, action of iontophoretically applied DYN. These observations support our cytochemical and assay studies indicating diverse opioid systems within the rat hippocampus. In addition, these functional studies are congruent with other evidence suggesting multiple opioid mechanisms in this structure.     

Radiation inactivation target size of rat adipocyte glucose transporters in the plasma membrane and intracellular pools

The in situ assembly states of the glucose transport carrier protein in the plasma membrane and in the intracellular (microsomal) storage pool of rat adipocytes were assessed by studying radiation-induced inactivation of the D-glucose-sensitive cytochalasin B binding activities. High energy radiation inactivated the glucose-sensitive cytochalasin B binding of each of these membrane preparations by reducing the total number of the binding sites without affecting the dissociation constant. The reduction in total number of binding sites was analyzed as a function of radiation dose based on target theory, from which a radiation-sensitive mass (target size) was calculated. When the plasma membranes of insulin-treated adipocytes were used, a target size of approximately 58,000 daltons was obtained. For adipocyte microsomal membranes, we obtained target sizes of approximately 112,000 and 109,000 daltons prior to and after insulin treatment, respectively. In the case of microsomal membranes, however, inactivation data showed anomalously low radiation sensitivities at low radiation doses, which may be interpreted as indicating the presence of a radiation-sensitive inhibitor. These results suggest that the adipocyte glucose transporter occurs as a monomer in the plasma membrane while existing in the intracellular reserve pool either as a homodimer or as a stoichiometric complex with a protein of an approximately equal size.