Competitive Type Of Interaction Research Articles

The biotic and abiotic contexts of ecological selection mediate the dominance of distinct dispersal strategies in competitive metacommunities.

While the influence of dispersal on ecological selection is the subject of intense research, we still lack a thorough understanding of how ecological selection operates to favour distinct dispersal strategies in metacommunities. To address this issue, we developed a model framework in which species with distinct quantitative dispersal traits that govern the three stages of dispersal-departure, movement and settlement-compete under different ecological contexts. The model identified three primary dispersal strategies (referred to as nomadic, homebody and habitat-sorting) that consistently dominated metacommunities owing to the interplay of spatiotemporal environmental variation and different types of competitive interactions. We outlined the key characteristics of each strategy and formulated theoretical predictions regarding the abiotic and biotic conditions under which each strategy is more likely to prevail in metacommunities. By presenting our results as relationships between dispersal traits and well-known ecological gradients (e.g. seasonality), we were able to contrast our theoretical findings with previous empirical research. Our model demonstrates how landscape environmental characteristics and competitive interactions at the intra- and interspecific levels can interact to favour distinct multivariate and context-dependent dispersal strategies in metacommunities. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Competition through ritualized aggressive interactions between sympatric colonies in solitary foraging neotropical ants.

Understanding the structure of food competition between conspecifics in their natural settings is paramount to addressing more complex questions in ecology, evolution, and conservation. While much research on ants focuses on aggressive food competition between large and foraging trail-using societies, we lack a thorough understanding of inter-colony competition in socially less derived, solitarily foraging species. To fill this gap, we explored the activity of ten neighbouring colonies of the giant ant Dinoponera quadriceps, monitoring 2513 foraging trips of hundreds of workers and all its inter-individual interactions. We found that, on encountering, workers from different colonies rarely engaged in aggressive fights but instead avoided each other or performed ritualised agonistic bouts. We discovered that during foraging trips, a few workers within each colony repeatedly rubbed their gaster on the substrate, a behaviour not observed in the field before. We propose that workers use this behaviour to mark the foraging area and mark more frequently in its periphery. Only 25% of the individuals specialised in this behaviour, and we hypothesise that the specialisation results from the history of interactions and experience of individual foragers. Our study suggests that workers of contiguous D. quadriceps colonies engage in low-risk conflict, mainly displaying ritualised behaviours. As these small societies mainly rely on tiny, unpredictably scattered, albeit abundant in the environment, arthropod prey, and not on persistent food sources, they do not aggressively defend exclusive foraging territories. On the other hand, colonies rely on large overlapping foraging areas to sustain their survival and growth, most often tolerating foragers from nearby colonies. We discuss whether this type of competitive interaction is expected in all solitary foraging species.

Bioprospection and molecular phylogeny of culturable endophytic fungi associated with yellow passion fruit

Endophytic microorganisms live inside the plants without causing any damage to their hosts. In the agricultural field, these endophytes might be a strategy of biological control for phytopathogens. We aimed to isolate endophytic fungi from yellow passion fruit (Passiflora edulis) leaves, evaluating its biocontrol capacity by in vitro antagonism against phytopathogen Colletotrichum sp. CNPU378. We also carried out greenhouse experiments in bean seedlings. A high colonization frequency was obtained (89%), and the molecular identification based on DNA sequencing attested Colletotrichum as the most frequent genus and minor occurrence of Curvularia endophytes. The endophytes tested showed different types of competitive interactions in in vitro antagonism inhibition rate ranging from 28.8 to 48.8%. There were 10 promising antagonists tested for their antagonist activity of crude extracts of secondary metabolites, in which strain PE-36 (20.8%) stood out among the other strains evaluated. In the greenhouse assay, plants inoculated only with endophyte Colletotrichum sp. PE-36 was symptomless and suggest that the endophyte strengthened the growth promotion in common bean plants, especially in the root length and number of leaves when compared to control plants and other treatments. Despite many fungi of Colletotrichum genus being described as causative agents of anthracnose, in this study, the plant sampled was colonized predominantly by Colletotrichum endophytes living in asymptomatic relationship. By the way, we come across a Colletotrichum sp. endophyte able to antagonize a Colletotrichum sp. pathogen.

Competition for grooming partners and interference in affiliation among female mandrills

AbstractGrooming is the most common primate affiliative behaviour, and primates compete for accessing grooming partners. We studied a captive group of mandrills (Mandrillus sphinx) to evaluate the role of different types of competitive interactions in shaping the distribution of grooming among females. Mandrill females preferentially groomed high‐ranking individuals, but low‐ranking females were less able to do so. Interference in others’ grooming and a (consequent) reluctance of low‐ranking females to access dominant group mates occurred frequently and contributed to the observed pattern of grooming distribution, while takeovers of grooming partners was relatively rare. Interference in others’ affiliation was possibly used to prevent the formation of revolutionary alliances. Difficulties in accessing individuals already engaged in grooming exerted a strong but rank‐independent effect on grooming interactions. These results highlight the role of competition in determining access to preferred social partners.

МОДЕЛЮВАННЯ ОБСЯГУ ПРОДУКЦІЇ ДЛЯ ЗАДОВОЛЕННЯ ПОПИТУ ЗА ДОПОМОГОЮ ДИНАМІЧНОЇ МОДЕЛІ ЧАСТКИ РИНКУ ТА ІНТЕРВАЛЬНОЇ МОДЕЛІ РОЗМІРУ РИНКУ

The mathematical model for analysis and forecasting company market share, the interval model for market size and company product volume estimation in view of the product utility function and the type of competitive interaction is described in the research paper. The model of the dependence of the market share dynamics on the company product utility change with time and the products of its main competitors determination of company product value, probability market size model is examined and transferred to interval model which allows to consider oscillatory nature of prices. It is shown that the proposed model allows to study and to analyse the dynamic of development and various strategies of the companies’ behaviour in the market. Analysis and modelling on historical data prove that the model gives sufficiently accurate results and an acceptable deviation. As a result, on the basis of the proposed model, the boundaries in which the size of the market will fluctuate were determined, and the company development dynamics are analysed in accordance with competitors’ development. It is important to note that the data considered take into account possible price fluctuations in a certain interval, as well as possible change in the competitive positions in the market. Based on the market share dynamics and the total market size, an interval was established for determining the volume of products that would satisfy the demand for the goods of all companies. An outstanding forecast volume of products that each enterprise must supply to the market to meet demand. For the scenario under consideration, an assumptions were made about a further strategy for the company's behaviour to preserve, as well as strengthen its competitive positions in the market. Thus, the work shows how, based on the dynamic model of the market share and the interval model of market size, which takes into account the fluctuating nature of prices and the possible change in the competitive position, the company can determine the direction of the commodity and marketing policy, using the utility function of the product, market share and interval estimation of market size.

The interactive effect of cobalt enrichment in Artemia on the survival and larval growth of barramundi, Lates calcarifer

Cobalt is a naturally occurring element in the aquatic environment and is essential for many living functions of vertebrates. The role, retention and interactions of cobalt with other trace elements in the marine fish nutrition have been poorly documented. In this study the accumulation and effect of cobalt was investigated on the survival and larval growth of barramundi, Lates calcarifer, when fed individually and combined with zinc and manganese through a nourishment organism. Barramundi larvae from 14 to 30dph were fed with Artemia nauplii in nine treatments (n=3): without enrichment (control), enriched with 50mgL−1 and 100mgL−1 CoCl2 (Co-1 and Co-2), MnCl2 (Mn-1 and Mn-2), CoCl2 along with MnCl2 (CoMn-1 and CoMn-2) as well as CoCl2 along with ZnSO4 (CoZn-1 and CoZn-2) respectively. All treatments had significant effect on the cobalt, manganese and zinc level of Artemia. The concentration of these elements increased in parallel with the dose of supplementations. Our results show that a significantly higher growth performance of barramundi larvae can be achieved when cobalt and manganese supplementation is applied. No interaction occurred between the retention of zinc and cobalt, but a competitive type of interaction is assumed between the deposition of cobalt and manganese in barramundi larvae. Combined treatments of cobalt and manganese increased cannibalism and mortality significantly, while other treatments had no significant effect on the survival of barramundi. Redundancy analysis showed a strong correlation between the cobalt and manganese concentration of Artemia and barramundi larvae, as well as a total agreement between the zinc concentration of the zooplankton and the larvae.

Hyperspectral and Physiological Analyses of Coral-Algal Interactions

Space limitation leads to competition between benthic, sessile organisms on coral reefs. As a primary example, reef-building corals are in direct contact with each other and many different species and functional groups of algae. Here we characterize interactions between three coral genera and three algal functional groups using a combination of hyperspectral imaging and oxygen microprofiling. We also performed in situ interaction transects to quantify the relative occurrence of these interaction on coral reefs. These studies were conducted in the Southern Line Islands, home to some of the most remote and near-pristine reefs in the world. Our goal was to determine if different types of coral-coral and coral-algal interactions were characterized by unique fine-scale physiological signatures. This is the first report using hyperspectral imaging for characterization of marine benthic organisms at the micron scale and proved to be a valuable tool for discriminating among different photosynthetic organisms. Consistent patterns emerged in physiology across different types of competitive interactions. In cases where corals were in direct contact with turf or macroalgae, there was a zone of hypoxia and altered pigmentation on the coral. In contrast, interaction zones between corals and crustose coralline algae (CCA) were not hypoxic and the coral tissue was consistent across the colony. Our results suggest that at least two main characteristic coral interaction phenotypes exist: 1) hypoxia and coral tissue disruption, seen with interactions between corals and fleshy turf and/or some species of macroalgae, and 2) no hypoxia or tissue disruption, seen with interactions between corals and some species of CCA. Hyperspectral imaging in combination with oxygen profiling provided useful information on competitive interactions between benthic reef organisms, and demonstrated that some turf and fleshy macroalgae can be a constant source of stress for corals, while CCA are not.

The Impact of Capital Market Imperfections on the Relationship Between Competition and Corporate Performance

This paper explores the relationship between product market competition and firm performance under different levels of information-related capital market imperfections. We show empirically, on a sample of listed as well as unlisted firms, that for companies suffering from financing constraints, increasing competition leads to a decrease in both productivity and profitability while the opposite holds for non (less) constrained firms. This result is robust to alternative measures of competition and can be explained by differences in access to external financing and its impact on investment behavior. Combining the logic of option theory with the literature on competition, we argue that the value of postponing investment is influenced by both the intensity and the type of competitive interaction. Intense and aggressive competition pressures firms to exercise investment options early. For firms with limited access to external financing this pressure to invest exacerbates financing constraints, forcing them to leave valuable investment options unexercised. Overall, our results suggest that competition is not necessarily beneficial for firm performance and that the positive relation that is usually found in the recent corporate governance literature, can be due to restricting the sample to listed firms, i.e., companies that suffer least from capital market imperfections.

The effect of colonization and competition processes on the relation between disturbance and diversity in plant communities

Many theoretical and field studies have emphasized the impact of disturbance in the dynamics and diversity of sessile organism communities. This view is best reflected by the Intermediate Disturbance Hypothesis (IDH), which states that a maximum of diversity is found in ecosystems or communities experiencing intermediate disturbance regimes or at an intermediate stage of development since the last major disturbance event. Although theoretical models based on competitive interactions tend to validate this hypothesis, a recent meta-analysis of field experiments revealed that the mono-modal relationship between disturbance and diversity might not be a general pattern. In this article, we investigate the relationship between disturbance and diversity through the study of patch models, combining two types of competitive interactions: with or without competitive hierarchy, with two mechanisms influencing colonization: negative frequency dependence in colonization rates and immigration. These combinations led to various disturbance–diversity patterns. In the model without competitive hierarchy (founder effect model), a decreasing relationship appeared to be the rule as mentioned in previous studies. In the model with competitive hierarchy, the IDH pattern was obtained for low frequency dependence and low immigration. Nevertheless, high negative frequency dependence in colonization rates led to a decreasing relationship between disturbance and diversity. In contrast, high immigration led to an increasing relationship. The coexistence window (the range of disturbance intensity allowing coexistence) was the widest for intermediate immigration rates. For random species assemblages, patterns with multiple peaks were also possible. These results highlight the fact that the mono-modal IDH pattern should not be considered a rule. Competition and colonization mechanisms have a profound impact on the relationship between disturbance and diversity.

Differential modulation of the GYKI 53784-induced inhibition of AMPA currents by various AMPA-positive modulators in cerebellar Purkinje cells

The effects of various ( S)-α-amino-3-hydroxy-5-methyl-4-izoxazole-propionate (AMPA) receptor modulators on AMPA-induced whole-cell currents were compared in isolated rat cerebellar Purkinje cells. The positive modulators, aniracetam, cyclothiazide, 1-(1,3-benzodioxol-5-ylcarbonyl)-piperidine (1-BCP), and 1-(quinoxaline-6-ylcarbonyl)-piperidine (BDP-12), dose-dependently potentiated the steady-state component of AMPA currents. The negative modulator, (−)1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-4,5-dihydro-3-methylcarbamoyl-2,3-benzodiazepine (GYKI 53784), dose-dependently suppressed AMPA responses. Its concentration–response curve was shifted to the right in a parallel fashion by all positive modulators, indicating a competitive type of interaction. However, the relative potencies of the positive modulators were different with regard to the enhancement of AMPA responses and the reversal of GYKI 53784-induced inhibition, respectively. It is supposed that positive modulators act at multiple allosteric sites and that they interact with GYKI 53784 at only one of these sites.

Kinetics of waterborne strontium uptake in the common carp, Cyprinus carpio, at different calcium levels

AbstractThe uptake kinetics of strontium in the commoncarp(Cyprinus carpio) were characterized in vivo, exposing preac‐climated fish to a wide range of Sr2+ (0.27 μM–10.0 mM) and Ca2+ (10 μM–10 mM) concentrations in water; 85Sr, 45Ca, and 47Ca were used as tracers in determining the uptake, and the possibility of adsorption of the tracers to the exterior of the fish were verified. The uptake rates were determined in the whole body, gills, and blood of the fish after an exposure period of 3 h and were analyzed as a function of the free‐ion activity of strontium and calcium in water. With the increase of Sr2+ concentration in the exposure water, Sr2+ uptake did not increase linearly but displayed Michaelis–Menten saturation kinetics, and with the increase of Ca2+ concentration, Sr2+ uptake decreased significantly in the whole body, gills, and blood. The competitive inhibition model fitted to the pooled data for whole‐body uptake explains about 94% of the variation in Sr2+ uptake and 71% in Ca2+ uptake, indicating a competitive type of interaction during the transport of these metal ions across the biological interfaces. The maximum uptake rate of Sr2+ (JmaxSr) was estimated to be 243.0 μmol/kg/h and that of Ca2+ (JmaxCa) 119.4 μmol/kg/h. The apparent Km for Sr2+ uptake increased greatly with the increase of Ca2+ concentration in water (186, 789, and 5,515 μM for 35, 348, and 3,480 μM Ca2+, respectively). Estimation of the true Km for Sr2+ uptake (KmSr) and its inhibitor constant for Ca2+ (KiCa) yielded the values of 96.3 and 28.5 μM, respectively. These values are very close to those obtained for Ca2+ uptake (KmCa = 24.9 and KiSr = 100.9 μM). This model provides a mechanistic description of the effect of calcium on strontium uptake from water and, vice versa, in carp.

KINETICS OF WATERBORNE STRONTIUM UPTAKE IN THE COMMON CARP, CYPRINUS CARPIO, AT DIFFERENT CALCIUM LEVELS

The uptake kinetics of strontium in the common carp (Cyprinus carpio) were characterized in vivo, exposing preacclimated fish to a wide range of Sr{sup 2+} and Ca{sup 2+} concentrations in water; {sup 85}Sr, {sup 45}Ca, and {sup 47}Ca were used as tracers in determining the uptake, and the possibility of adsorption of the tracers to the exterior of the fish were verified. The uptake rates were determined in the whole body, gills, and blood of the fish after an exposure period of 3 h and were analyzed as a function of the free-ion activity of strontium and calcium in water. With the increase of Sr{sup 2+} concentration in the exposure water, Sr{sup 2+} uptake did not increase linearly but displayed Michaelis-Menten saturation kinetics, and with the increase of Ca{sup 2+} concentration, Sr{sup 2+} uptake decreased significantly in the whole body, gills, and blood. The competitive inhibition model fitted to the pooled data for whole-body uptake explains about 94% of the variation in Sr{sup 2+} uptake and 71% in Ca{sup 2+} uptake, indicating a competitive type of interaction during the transport of these metal ions across the biological interfaces. The maximum uptake rate of Sr{sup 2+} (J{sub maxSr}) was estimated tomore » be 243.0 {micro}mol/kg/h and that of Ca{sup 2+} (J{sub maxCa}) 119.4 {micro}mol/kg/h. The apparent K{sub m} for Sr{sup 2+} uptake increased greatly with the increase of Ca{sup 2+} concentration in water. Estimation of the true K{sub m} for Sr{sup 2+} uptake (K{sub mSr}) and its inhibitor constant for Ca{sup 2+} (K{sub iCa}) yielded the values of 96.3 and 28.5 {micro}M, respectively. These values are very close to those obtained for Ca{sup 2+} uptake. This model provides a mechanistic description of the effect of calcium on strontium uptake from water and, vice versa, in carp.« less

Interaction between l-DOPA and 3- O-methyl- l-DOPA for transport in immortalised rat capillary cerebral endothelial cells

The present study aimed to determine the kinetics of l-3,4-dihydroxyphenylalanine ( l-DOPA) uptake in an immortalised cell line of rat capillary cerebral endothelial cells (clones RBE 4 and RBE 4B), to define the type of interaction with 3- O-methyl- l-DOPA (3-OM- l-DOPA), sensitivity to 2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid (BHC), N-(methylamino)-isobutyric acid (MeAIB) and sodium. Non-linear analysis of the saturation curves for l-DOPA and 3-OM- l-DOPA revealed in RBE 4 cells K m values (in μM) of 72 (53, 91) and 40 (25, 57) and in RBE 4B cells K m values (in μM) of 60 (46, 74) and 44 (13, 75), respectively. IC 50 values for 3-OM- l-DOPA (RBE 4, 642 [542, 759] μM; RBE 4B, 482 [475, 489] μM) obtained in the presence of a nearly saturating (250 μM) concentration of l-DOPA were greater than the corresponding K i values (RBE 4, 143 [121, 170] μM; RBE 4B, 93 [92, 95] μM) obtained in the presence of a nearly saturating (250 μM) concentration of 3-OM- l-DOPA; this is compatible with a competitive type of interaction between l-DOPA and 3-OM- l-DOPA. Uptake of both l-DOPA and 3-OM- l-DOPA in RBE 4 and RBE 4B cells was sensitive to BHC with similar IC 50 values. MeAIB (up to 2.5 mM) was found not to interfere with the uptake of both l-DOPA and 3-OM- l-DOPA. Uptake of (250 μM) l-DOPA and 3-OM- l-DOPA in the absence of sodium in the incubation medium was similar to that observed in the presence of increasing concentrations of sodium (20–140 mM). Homogenates of both cell lines were endowed with considerable COMT activity. Incubation of RBE 4 and RBE 4B cells with l-DOPA (25 μM) in the presence of a methyl donor ( S-adenosyl- l-methionine) resulted in the formation of 3-OM- l-DOPA; this was abolished by 1 μM tolcapone. The fractional outflow of intracellular l-DOPA through the luminal and abluminal cell side was not affected by the presence of intracellular 3-OM- l-DOPA. The fractional outflow of exogenous 3-OM- l-DOPA applied from the luminal cell border was similar to that observed for 3-OM- l-DOPA with origin in l-DOPA. It is concluded that RBE 4 and RBE 4B cells are endowed with the l-type amino acid transporter through which l-DOPA and 3-OM- l-DOPA can be taken up, and 3-OM- l-DOPA behaves as a competitive inhibitor for the uptake of l-DOPA. This, however, only occurs for luminal cell inward movement but not for abluminal cell outward movement of the substrates.

The Many Faces of Competition

Despite a great deal of theoretical research on competition, there has been limited empirical work assessing the type of competitive interaction that actually exists in the marketplace. The empirical work that has been conducted has suggested that there is significant variation in the type of competitive interaction across categories and across marketing instruments. Consequently, the central objective of this paper is descriptive in nature—what does competition look like? Focusing on the competition that exists across strategic groups (Porter 1985), we categorize competitive interaction between private labels and national brands for each of 58 categories and four marketing instruments. Specifically, we look at five types of competitive interaction. Three, cooperative, non-cooperative, and independent (Nash) are symmetric in nature, while two, leader-follower (Stackelberg) and dominant/fringe-firm, are asymmetric. The empirical results suggest that general comments or assumptions about competitive interaction can produce very misleading conclusions. There is no consistent pattern of competition that exists between private labels and national brands across categories. Further, the pattern of interaction is quite complex, while there is likely to be a significant variation across instruments within a category. National brand leadership is the most common form of interaction for each marketing mix variable. However, it characterizes only 19 out of 58 categories for regular price, and 16, 19, and 15 out of 58 categories for temporary price reduction, feature and display, respectively. Further, the interaction is idiosyncratic to the category, depending heavily upon the demand and competitive characteristics of the category. Implications for both game theorists and for managers are explored.

Subclassification of α1‐adrenoceptor recognition sites by urapidil derivatives and other selective antagonists

1. The affinities of urapidil derivatives and other antagonists for alpha 1-adrenoceptors labelled by [3H]-prazosin were determined on membranes of six different rat tissues. 2. Urapidil and its 5-acetyl-, 5-formyl- and 5-methyl-derivative displaced [3H]-prazosin from alpha 1-adrenoceptor binding sites in a concentration-dependent manner which varied with tissue. IC50 values were lower in vas deferens, hippocampus and cerebral cortex than in heart, liver and spleen. For 5-methyl-urapidil, binding to two distinct sites could be demonstrated with mean K1 values of about 0.6 and 45 nM. Saturation binding studies with [3H]-prazosin in the presence of 5-methyl-urapidil indicated a competitive type of interaction between 5-methyl-urapidil and [3H]-prazosin. 3. The proportion of [3H]-prazosin binding sites with high affinity for 5-methyl-urapidil was 58% in vas deferens, 69% in hippocampus, 41% in cerebral cortex and 23% in myocardium. In liver and spleen virtually no high affinity sites were found. These values were in good agreement with the percentages of binding sites with high affinities for WB-4101 and phentolamine, indicating that all these antagonists bind to the same subtype of alpha 1-recognition sites, whereas other alpha-antagonists like BE 2254, yohimbine and unlabelled prazosin did not discriminate between two binding sites. 4. Preincubating membranes of the cerebral cortex with chloroethylclonidine preferentially inactivated [3H]-prazosin binding sites with low affinity for 5-methyl-urapidil. 5. The antagonist potencies of 5-methyl-urapidil and WB-4101 against alpha 1- adrenoceptor-mediated contractile responses were higher in vas deferens than in myocardium. The alpha 1-mediated effects in vas deferens but not in the heart were highly susceptible to nitrendipine. 6. Using 5-methyl-urapidil, the existence of two distinct alpha 1-adrenoceptor recognition sites could be demonstrated which correspond to the proposed alpha 1A- and alpha 1B-subtypes. Since 5-methyl-urapidil is one of the ligands with most selectivity between these subtypes in binding studies it may serve as a valuable tool for such investigations.

Quinoxalinediones selectively block quisqualate and kainate receptors and synaptic events in rat neocortex and hippocampus and frog spinal cord in vitro.

1. Two quinozalinediones, FG9041 and FG9065, which had previously been shown to displace binding to the quisqualate receptor, were tested on rat neocortex and frog spinal cord in vitro against depolarizations induced by quisqualate, kainate and N-methyl-D-aspartate (NMDA). In both preparations effects of quisqualate were reduced the most and those of NMDA the least. 2. The near unitary slopes of the Schild plots were consistent with a competitive type of interaction. pA2 values for FG9041 were estimated to be 6.6, 6.1 and 5.1 in frog cord and 5.9, 5.3 and and about 4 in the rat neocortex for quisqualate, kainate and NMDA antagonism, respectively. FG9065 gave equivalent pA2 values of 6.2, 5.6 and 4.5. 3. At concentrations, which were without effect on depolarizations induced by NMDA, FG9041 and FG9065 reduced or blocked synaptically-evoked field potentials in hippocampal and neocortical slices superfused with normal magnesium-containing medium. Since these synaptic components are also insensitive to NMDA antagonists, these results are consistent with their mediation by postsynaptic receptors of the quisqualate (or kainate) type. 4. By contrast, quinoxalinediones had only limited effects on spontaneous epileptiform activity seen in both neocortical and hippocampal preparations when superfused with magnesium-free medium. These burst discharges were, however, abolished by NMDA antagonists. 5. In the frog spinal cord the early component of the dorsal root to ventral root reflexes was selectively reduced by FG9041 whereas NMDA antagonists reduced the longer latency components. 6. Our results suggest that the quinoxalinediones are likely to be useful pharmacological probes for elucidating the role of non-NMDA receptors in the vertebrate central nervous system.

Cloning of Rhizobium leguminosarum genes for competitive nodulation blocking on peas.

One type of competitive interaction among rhizobia is that between nonnodulating and nodulating strains of Rhizobium leguminosarum on primitive pea genotypes. Pisum sativum cv. Afghanistan nodulates effectively with R. leguminosarum TOM, and this can be blocked in mixed inoculations by R. leguminosarum PF2, which does not nodulate this cultivar. We termed this PF2 phenotype Cnb+, for competitive nodulation blocking. Strain PF2 contains three large plasmids including a 250-kilobase-pair symbiotic (Sym) plasmid. Transfer of this plasmid, pSymPF2, to nonblocking rhizobia conferred the Cnb+ phenotype on recipients in mixed inoculations on cultivar Afghanistan with TOM. A library of the PF2 genome constructed in the vector pMMB33 was used to isolate two cosmid clones which hybridize to pSymPF2. These cosmids, pDD50 and pDD58, overlapped to the extent of 23 kilobase pairs and conferred a Cnb+ phenotype on recipient Cnb- rhizobia, as did pSD1, a subclone from the common region.

Competitive interaction of pirenzepine with rat brain muscarinic acetylcholine receptors

In the present work, we studied the details of the interaction of the nonclassical muscarinic receptor antagonist pirenzepine with [ 3H]quinuclidinyl benzilate binding sites in rat brain homogenates. Pirenzepine showed biphasic competition curves with a Hill coefficient lower than unity, and these curves were better described according to a two-site receptor model. The affinities and the relative preponderance of these sites were constant at different ligand concentrations, in accordance with a competitive type of interaction. Similarly, pirenzepine did not influence the rate of dissociation of the [ 3H]quinuclidinyl benzilate-receptor complex, even at relatively high concentrations. However, although low concentrations of pirenzepine decreased the affinity of [ 3H]quinuclidinyl benzilate for the receptor without affecting the density of the binding sites, higher concentrations of the antagonist decreased the receptor number in a reversible fashion. Schild plots of these data indicated an apparent deviation from simple competition in this experimental design, an observation which can be attributed to the selectivity of pirenzepine for different receptor subtypes. Furthermore, pirenzepine, at concentrations high enough to saturate both its high- and low-affinity sites protected [ 3H]quiniclidinyl benzilate binding sites in the brain against irreversible alkylation by propylbenzilylcholine mustard. Therefore, our data support a competitive nature of interaction of pirenzepine with rat brain muscarinic receptors.

Interaction of 4-aminopyridine with [ 3H]phencyclidine receptors in rat brain homogenates

The effect of 4-aminopyridine and its analogs on the specific binding of [ 3H]phencyclidine was investigated in rat brain homogenates. 4-Aminopyridine (4-AP) and 3,4-diaminopyridine displaced [ 3H]phencyclidine binding, while 3-aminopyridine was without effect. The concentrations of 4-AP required for inhibition of binding increased with increasing the ligand concentration, and the resultant Dixon plots indicated a competitive type of interaction. However, 4-AP also accelerated the dissociation rate of the ligand-receptor complex, suggesting that the effect of 4-AP on phencyclidine receptors in the brain might not be purely competitive.

Bacterial peptides with C-terminal similarities to bovine neurotensin

Using radioimmunoassay, peptides resembling the C-terminal region of bovine neurotensin (NT) have been demonstrated in acid/acetone extracts of Rhodopseudomonas palustris, Escherichia coli, and Caulaobacter crescentus. The NT-like bacterial components were shown to behave as peptides of small molecular weight (less than 2000) which were stable to acid and heat but labile to proteolytic digestion. In the radioimmunoassay toward NT they displayed dose-response curves parallel to standard and gave results indicating a competitive type of interaction with NT binding sites on antibody. The bacterial extracts did not register in a control radioimmunoassay toward rat luteinizing hormone. Some of the NT-like immunoreactivity could also be bound to an retrieved from anti-NT-antibody-Sepharose preparations. Since the C-terminal region of NT constitutes its biologically active core, these results suggest that presence of biologically important congeners of NT in bacteria.