Immunohistochemical localization of keratin in bull,goat, and sheep anterior pituitary glands

Summary Immunohistochemical localization of keratin, an intermediate filament protein, was studied in bull, goat, and sheep anterior pituitary glands, i.e., in animals of the order Artiodactyla. Strong immunoreactivity was detected in the cells of the marginal layer of bull and goat, as well as in cysts or large follicles in the anterior lobe of all 3 species. In addition, a number of stellateshape cells were immunoreactive for keratin and were distributed throughout the anterior lobe. The localization of keratin-positive cells in light-microscopic preparations correlated precisely with the localization of folliculo-stellate cells in adjacent ultrathin sections. In ultrastructural studies, many slender and elliptical membranous components which were different from smooth endoplasmic reticulum were observed in the cytoplasm of the some keratin-positive cells. Some of the folliculostellate cells in the 3 species were also immunoreactive for the subunit of S-100 protein, which exists in some epithelial cells. On the other hand, immunolocalization of glial fibrillary acidic protein, a glial cell marker, could not be demonstrated in the anterior pituitary glands of the 3 species studied. These results suggest that keratin-positive folliculo-stellate cells express epithelial-like characteristics.     

Transition time control analysis of a glycolytic system under different glucose concentrations. Control of transition time versus control of flux

Control and Response Coefficients of transition time have been determined in a rat liver glycolytic system under different glucose concentrations. Results have been compared with the Flux Control and Flux Response Coefficients measured in the same conditions, showing that transition time and flux are different responses of the system, subject to different regulation and control. Control Coefficients of flux and transition time show a very different profile in each condition of glucose concentration assayed. Ratio of Flux Control coefficients of glucokinase over phosphofructokinase at 5 and 20 mM glucose concentration changes from 3.2 to 0.5, while the same ratio in the case of Transition Time Control Coefficients moves from 0.6 to 0.93. Moreover, the absolute values of Transition Time Control Coefficients in glycolytic conditions are one order of magnitude bigger than in gluconeogenic conditions. Values of Response Coefficients also show that the transition time has a bigger sensitivity to changes in glucose concentration than the flux in all conditions assayed, but particularly in glycolytic ones.     

Protonmotive force in freshwater sulfate-reducing bacteria,and its role in sulfate accumulation in Desulfobulbus propionicus

The protonmotive force in several sulfate-reducing bacteria has been determined by means of radiolabelled membrane-permeant probes (tetraphenyl-phosphonium cation, TPP⁺, for , and benzoate for pH). In six of ten freshwater strains tested only the pH gradient could be determine, while the membrane potential was not accessible due to nonspecific binding of TPP⁺. The protonmotive force of the other four strains was between –110 and –155 mV, composed of a membrane potential of –80 to –140 mV and a pH gradient between 0.25 and 0.8 (inside alkaline) at pH_out=7. In Desulfobulbus propionicus the pH gradient decreased with rising external pH values. This decrease, however, was compensated by an increasing membrane potential. Sulfate, which can be highly accumulated by the cells, did not affect the protonmotive force, if added in concentrations of up to 4 mM. The highest sulfate accumulation observed (2500-fold), which occurred at external sulfate concentrations below 5 M, could be explained by a symport of three protons per sulfate, if equilibrium with the protonmotive force was assumed. At higher sulfate concentrations the accumulation decreased and suggested an electroneutral symport of two protons per sulfate. At sulfate concentrations above 500 M, the cells stopped sulfate uptake before reaching an equilibrium with the protonmotive force.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - MOPS morpholinopropanesulfonic acid - TPP⁺ tetraphenylphosphonium cation - EDTA ethylenediaminetetraacetic acid - pH transmembrane pH gradient (pH_in-pH_out) - transmembrane electrical potential difference     

The time and egg budget of Leptopilina clavipes, a parasitoid of larval Drosophila

Abstract.

• 1 For the understanding of the influence of natural selection on the persistence of host selection behaviour in populations of Drosophila parasitoids it is important to know whether parasitoids will become time- or egg-limited. We investigated whether the Drosophila parasitoid Leptopilina clavipes (Hartig) meets egg- or time-limited conditions in the field.
• 2 To this end the following aspects of the parasitoid's life were studied: egg load at emergence, travelling velocity between patches, patch residence times, oviposition rates and life expectancy. Together with the results from earlier studies on host and patch distributions, this formed the input of a ‘Monte Carlo’ simulation model, in which the life history of an individual parasitoid can be traced.
• 3 The simulations revealed that under the conditions found in the field 12.9% of the parasitoid population is egg-limited. The model was also run for a number of scenarios which reflect ‘good’ or ‘bad’ circumstances. In most cases a significant proportion of the parasitoid population proved to be egg-limited.
• 4 For the measurement of travelling velocities and patch residence times a marking method, especially applicable to small-sized parasitoids such as L.clavipes, is described. Marking did not affect survival, host habitat location or host detection rate. Parasitoids were found to be attracted to the odour of fruit-bodies of Phallus impudicus, the most important breeding substrate of their hosts.

     

Stimulus-evoked slow potential shifts and changes in [K+]0 of the frog optic tectum

Summary In 17 frogs (Rana esculenta var ridibunda) immobilised with succinyl choline the optic tectal surface was stimulated by trains of electrical pulses or by a flash to the contralateral eye. Sustained potential shifts (SPSs) and changes in extracellular potassium concentration ( [K⁺]₀) were simultaneously recorded.In response to electrical stimulation SPSs of maximal amplitudes (1.19±0.1 mV) were recorded between 50 and 200 m in depth and maximal [K⁺]₀ (0.69 ±0.08 mM) between 100 and 350 m. The changes of SPS and [K⁺]₀ showed a close similarity in experiments with changes in voltage, pulse duration and frequency of stimuli within a train. The induced SPS had a duration of 28±1.54 s, the [K⁺]₀ of 32±1.23 s.The flash stimulus induced an SPS and [K⁺]₀ of maximal amplitudes between 50 and 200 m in depth with values of 0.57±0.1 mV and 0.29±0.03 mM respectively. An additional wave with a latency of ca 1 s and a duration of ca 3 s arose on the background of the SPS to a flash stimulus, associated with an additional increase in [K⁺]₀.It is considered that the accumulation of K⁺ in extra-cellular space, with neuronal activity, results in depolarization of radial processes of ependymal glia. This is reflected in the neuropil of the upper layers of the optic tectum as an SPS.We would like to dedicate this article to the memory of Alexander Roitbak who died as a result of a tragic accident while this paper was in press. He will be remembered fondly especially for his contributions to understanding of the functions of Neuroglia. E.V.O., P.R.L., T.A.R.     

Parameters not influenced by vesamicol: Membrane potential,calcium uptake,and internal calcium concentration of synaptosomes

In our previous study vesamicol, an inhibitor of the acetylcholine transporter of the cholinergic vesicles, inhibited veratridine-evoked external Ca²⁺-dependent acetylcholine release from striatal slices but did not influence acetylcholine release observed in Ca²⁺-free medium (4). Here we examined if the effect of veratridine on membrane potential, Ca²⁺ uptake, and intracellular Ca²⁺ concentration of synaptosomes was altered by vesamicol in parallel with the inhibition of acetylcholine release. The depolarizing effect of 10 M veratridine (from 67±2.3 mV resting membrane potential to 50.7±2.5 mV) was not significantly influenced by vesamicol (1–20 M). Vesamicol (1–20 M) had no effect on either the overall curve of the veratridine-evoked⁴⁵Ca²⁺ uptake or the amount of Ca²⁺ taken up by synaptosomes. Veratridine caused a rise in intrasynaptosomal Ca²⁺ concentration as measured by Fura2 fluorescence, and the same increase both in characteristics and in magnitude was observed in the presence of vesamicol (20 M). The K⁺-evoked (40 mM) increase of Ca²⁺ uptake and of intracellular calcium concentration were also unaltered by vesamicol. In high concentration (50 M) vesamicol inhibited both the fall in membrane potential and the elevated Ca²⁺ uptake by veratridine, indicating a possible nonspecific effect on potential-dependent Na⁺ channels at this concentration. Vesamicol, in lower concentration (20 M) when neither of the above parameters was changed, completely prevented veratridine-evoked increase of [¹⁴C]acetylcholine release. This was observed only when vesamicol was present in the media throughout the experiment after loading the preparation with [¹⁴C]choline. The results suggest that vesamicol does not interfere with veratridine-induced changes in isolated nerve terminals other than with the release of acetylcholine, thus further supporting the involvement of a vesamicol-sensitive vesicular transmitter pool in Ca²⁺-dependent veratridine-elicited acetylcholine release.     

Insertional inactivation of a gene which controls expression of vancomycin resistance on plasmid pHKK100

Expression of inducible high level vancomycin resistance (Vmr) in enterococci appears to require other plasmid-encoded genes in addition to the previously described structural genes vanA and vanH. Tn917 mutagenesis was used to identify such a region in the Vmr plasmid pHKK100. Insertional inactivation of a 693-bp open reading frame upstream from vanH resulted in complete loss of Vmr. This putative 26,642-Da protein has been designated VanR.     

Molecular modeling of the amphipathic helices of the plasma apolipoproteins.

In this paper we propose a classification of the amphipathic helical repeats occurring in the plasma apolipoprotein sequences. It is based upon the calculation of the molecular hydrophobicity potential around the helical segments. The repeats were identified using a new autocorrelation matrix, based upon similarities of hydrophobic and hydrophilic properties of the amino acid residues within the apolipoprotein sequences. The helices were constructed by molecular modeling, the molecular hydrophobicity potential was calculated, and isopotential contour lines drawn around the helices yielded a three-dimensional visualization of the hydrophobicity potential. Two classes of apolipoproteins could be differentiated by comparing the hydrophobic angles obtained by projection of the isopotential contour lines on a plane perpendicular to the long axis of the helix. The isopotential contour lines around apo AI, AIV, and E are more hydrophilic than hydrophobic, whereas they are of similar intensity for apo AII, CI, and CIII. In both cases discoidal lipid-protein complexes are generated, with the amphipathic helices around the edge of the lipid core. The long axis of the helices is oriented parallel to the phospholipid acyl chains and the hydrophilic side of the helix toward the aqueous phase. As a result of the differences in hydrophobicity potential, the contact between the hydrophobic side of the helices and the phospholipid acyl chains is larger for apo AII, CI, and CIII than for the other apolipoproteins. This might account for the greater stability of the discoidal complexes generated between phospholipids and these apoproteins.     

Queen succession in the primitively eusocial tropical waspRopalidia marginata (Lep.) (Hymenoptera: Vespidae)

Females of the primitively eusocial wasp Ropalidia marginata can be classified into three behavioral groups: Sitters, Fighters, and Foragers. It has been speculated that both Sitters and Fighters may be hopeful queens and that the Foragers may have little or no opportunities for direct reproduction. Here we show that in 9 of 12 queen-removal experiments where such a behavioral differentiation could be discerned, the individual that became a queen (the potential queen) was a Sitter in 6 cases, a Fighter in 2 cases, and a Forager in only 1 case. Although potential queens spent significantly more time absent from the nest and showed significantly higher rates of dominance behavior compared to the mean values for nonqueens in their colonies, they were intermediate with respect to all behaviors and age when compared to the range of values for nonqueens in their colonies. Potential queens were not necessarily the highest-ranking individuals among the nonqueens. The pattern of queen succession in this species appears to be quite different from the temperate pattern, where an old and active forager of high dominance rank is the potential queen. Although somewhat similar to the tropical pattern of a relatively younger female that has performed relatively little foraging being the potential queen, it is perhaps more accurate to describe the potential queens of R. marginata as unspecialized intermediates.     

The parasitoidOoencyrtus nezarae (Hymenoptera: Encyrtidae) prefers hosts parasitized by conspecifics over unparasitized hosts

Summary Two laboratory experiments were conducted to examine the ovipositional preferences of the egg parasitoidOoencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) for parasitized and unparasitizedMegacopta punctatissimum Montandon (Hemiptera: Plataspidae). Females that had never oviposited or that had not oviposite for 3 days preferred recently parasitized hosts more than unparasitized hosts. The preference for recently parasitized hosts appeared to be mediated by the punctures in already parasitized hosts made by the ovipositor of the first female. Survival of the parasitoid progeny was lower in recently parasitized hosts than in unparasitized hosts. However, handling time of parasitized hosts was extremely short relative to that of unparasitized hosts, because the superparasitizing female could use the punctures made by the previous females. It is concluded that the females preferred the parasitized hosts over unparasitized hosts because the benefit of saving time and energy for drilling was more than the cost of progeny survival.