Abundance and diversity of planktonic rotifers in the Po River

Zooplankton samples from the middle reach of the Po River were collected daily from 27 July to 24 August 1988 from a station located near Viadana. Changes in the biocoenosis structure were analyzed in relation to variations in flow rate. Rotifers accounted for more than 99% of the total zooplankton (protozoans excluded) in every sample. The dominant species were Brachionus calyciflorus, Brachionus bennini, Brachionus budapestinensis and Epiphanes macrourus. Under scanty flow conditions, the taxocoenosis showed marked stability. An increase in flow rate acts as a disturbance factor leading to a significant decrease in both total density and dominance.     

Evidence for the lateral intraparietal area as the parietal eye field.

It has long been appreciated that the posterior parietal cortex plays a role in the processing of saccadic eye movements. Only recently has it been discovered that a small cortical area, the lateral intraparietal area, within this much larger area appears to be specialized for saccadic eye movements. Unlike other cortical areas in the posterior parietal cortex, the lateral intraparietal area has strong anatomical connections to other saccade centers, and its cells have saccade-related responses that begin before the saccades. The lateral intraparietal area appears to be neither a strictly visual nor strictly motor structure; rather it performs visuomotor integration functions including determining the spatial location of saccade targets and forming plans to make eye movements.     

Observations sur la spécificité de la coloration aux acides phosphotungstique et phosphomolybdique

Résumé Les Auteurs ont démontré que, en conditions histochimiques sur du matériel fixé au formol, les acides phosphotungstique et phosphomolybdique ont une double action: 1. une action oxydative à la charge des radicaux PAS-positifs (vic-glycols et éthyleniques) en milieu aqueux, et à la charge des radicaux aminiques en milieu anhydre; cette action entraine la transformation de ces radicaux en aldéhydes; 2. la formation d'une liaison chimique entre les aldéhydes et les molécules des acides phosphomolybdique et phosphotungstique. — La coloration du collagène, au contraire, n'est pas due ni aux radicaux aminiques ni vic-glycols et implique un mécanisme encore inconnu.

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Observations about the specificity of staining of phosphotungstic and phosphomolybdic acid

Summary The authors demonstrated that phosphotungstic and phosphomolybdic acid applied to formol-fixed tissues explete two following actions: 1. An oxidative action on the PAS-positive radicals (double bonds, vic-glycols groups) if in water solution and on aminogroups if in anhydrous solution. This oxidation results in a production of aldehydic radicals 2. The formation of chemical bonds between the aldehydic new-formed groups and the molecules of phosphotungstic or phosphomolybdicacid.— However, the above mentioned mechanism of action is not applicable to the collagen staining for which a different explanation has to be supposed.

     

Kinetics of tert-[35S]Butylbicyclophosphorothionate Binding in the Cerebral Cortex of Newborn and Adult Rats: Effects of GABA and Receptor Desensitization

Abstract: The effects of GABA on the kinetics of tert -[³⁵S]butylbicyclophosphorothionate ([³⁵S]TBPS) binding to the convulsant site of GABA_A receptors were studied in membrane suspensions from the cerebral cortex of newborn (1-day-old) and adult (90-day-old) rats. TBPS dissociation was biphasic in neonates and adults, indicating that more than one interconvertible state of [³⁵S]TBPS binding sites may be present in the cerebral cortex. In the absence of GABA, the fast ( t _1/2, 11 min) and slow ( t _1/2, 77 min) components of TBPS dissociation in newborn rats were approximately fourfold slower than in adults. The acceleration of the dissociation rates caused by 2 µ M GABA, however, was more robust in neonates than in adults (six- to ninefold vs. twofold increase, respectively). Moreover, the dissociation rates of TBPS in membranes preincubated with 2 µ M GABA (dissociation started by adding 40 µ M picrotoxin) were two- to fourfold slower than in membranes preincubated without GABA (dissociation started by adding 40 µ M picrotoxin plus 2 µ M GABA). Taken together, these results suggest that (1) the closed state of GABA_A receptors is associated with a more effective steric barrier for the binding of TBPS in neonates compared with adults, (2) GABA produces a larger acceleration of the binding kinetics of TBPS in neonates than in adults, and (3) long incubations with GABA may cause receptor desensitization, which in turn slows down the dissociation rates of TBPS.     

Identification of P-glycoprotein at the membrane of mast cell secretory granules. An immunofluorescence and protein A-gold electron microscopical investigation

The presence of P-glycoprotein has been investigated in rat peritoneal mast cells by means of immunofluorescence and immunogold electron microscopy, using the specific monoclonal antibody JSB-1. Immunofluorescence studi es showed that the glycoprotein is primarily concentrated in mast cell granules, and little is localized at the plasma membrane. Electron microscope observations revealed a marked accumulation of colloidal gold particles at the granule-coating membranes, whereas decoration of the plasma membrane is much less intense. When mast cells are stimulated to exocytate with compound 48/80, both immunofluorescence and electron microscopy showed concentration of P-glycoprotein reactivity at the plasma membrane level. Indeed, fusion of the granule with the plasma membrane allowed transfer of immunoreactive P-glycoprotein material from the granule-coating membrane to the cell surface membrane. These findings confirmed the presence of P-glycoprotein in mast cells; it is predominantly localized in the granules and is exposed on the cell surface only after exocytosis, suggesting, therefore, a possible physiological role for P-glycoprotein in the secretion of certain mediators. This revised version was published online in November 2006 with corrections to the Cover Date.     

A narrow hybrid zone between two crayfish species from a Mexican cave

In Northern Chiapas (Mexico), two newly discovered species of Procambarus crayfish inhabit a subterranean stream. These species can be morphologically distinguished only by comparing extreme phenotypes (dark, thick-eyed, surface dwelling-like individuals vs light, elongated, microphtalmic, cave dwelling-like individuals). Individuals with intermediate phenotypes co-occur with those exhibiting extreme phenotypes. Crayfish were assayed electrophoretically and individual patterns at 23 gene loci were obtained. Unusually high levels of heterozygosity in both species and a clear discrimination between the two gene pools were revealed. The relationships between individuals were investigated by means of multivariate analysis on individual multilocus genotype profiles. Results showed the occurrence of individuals genetically intermediate between the two major clusters, which shared allozymic variants with both species. Due to the occurrence of alternative alleles in the two gene pools, we could quantify patterns of introgression, which revealed asymmetric gene flow between the two species. Moreover, differential levels of introgression in subsamples within the surface-like species were found: most introgressed individuals came from the inner section of the cave, where the two species were greatly mixed. These results are also discussed in reference to the morphometric results from a companion paper. A possible evolutionary pathway, leading to the situation in this cave, and possibly in neighbouring cave systems, is outlined. The hypothesis of a past history of allopatric divergence from a common ancestor and a subsequent secondary contact between these two Procambarus species is supported by geological studies. Crayfish sympatry and competitive exclusion are also discussed.     

Amiloride-sensitive Na+ pathways in capillary endothelial cell swelling during hemorrhagic shock.

We recently discovered that the endothelium of skeletal muscle capillaries swells in the low-flow ischemia induced by hemorrhagic shock. The present study was undertaken to determine the Na+ transmembrane pathways involved in this swelling, since hypoxic cell swelling is attributed to an influx of Na+ and water. In an initial series of experiments, amiloride (5 mg/kg body wt), which blocks multiple Na+ pathways, was infused intravenously into anesthetized rabbits 30 min prior to shock (40% single-withdrawal hemorrhage). Intravital microscopy of treated capillaries in the rabbit tenuissimus muscle showed that after a 1-h shock period, there was no endothelial cell swelling, as evidenced by no measurable change in the width of red blood cells traversing the capillary. In contrast, the swollen endothelium of untreated capillaries reduced the luminal diameter by 20-25% with a preserved stationary abluminal membrane. The specific effects of amiloride on Na+ transport were investigated with amiloride analogues. Animal pretreatment with 5-(N,N-hexamethylene)amiloride, a selective inhibitor of Na(+)-H+ activity, in a dose of 0.5 mg/kg did not significantly mitigate shock-induced swelling; however, a dose of 1 mg/kg completely prevented it. Phenamil, a selective inhibitor of Na+ channel conductance, even at a potent dosage of 0.5 mg/kg, did not affect swelling. These results suggest a primary role for Na(+)-H+ exchange in endothelial cell swelling during hemorrhagic shock, possibly as a means to regulate cellular pH, which may become acidic during ischemia. Narrowed capillaries with elevated hydraulic resistances could delay and diminish resumption of microcirculatory flow on shock resuscitation.     

Effect of Kainic Acid, Glutamate, and Aspartate on CO2 Production by Goldfish Tectal Slices

For a study of the excitatory effect of kainate, glutamate, and aspartate in the goldfish optic tectum, these substances were tested on the production of CO2 from radioactive glucose in tectal slices incubated in Krebs-Ringer medium for fish. Kainate increased the rate of CO2 production for up to 30 min in a dose-related manner, the effect being maximum at 0.1 mM concentration and decreasing at higher doses. The effect was blocked by ouabain (1 mM) as well as by the substitution of choline for Na+ in the incubation medium. Glutamate and aspartate exerted a less pronounced excitatory effect on CO2 production at higher concentration than kainate. This effect was also abolished by ouabain. Glutamate, added to the medium at a concentration at least 100-fold higher than kainate, partially reversed the increase in CO2 production induced by kainic acid. No similar effect was noticed for aspartate. The supposed glutamate antagonists glutamic acid diethylester (1 mM) and proline (5 mM) did not affect the excitatory action of kainic acid or exert an antagonistic effect towards glutamate. At higher concentration (10 mM) glutamic acid diethylester increased CO2 production, an effect that was, however, ouabain insensitive. Methyltetrahydrofolic acid (1 mM), a substance reported to compete for the kainate receptor, did not inhibit the effect of kainic acid or increase CO2 production.     

Recognition of human minor alloantigen(s) by cytotoxic lymphocytes in vitro

Lymphocytes from an extensively transfused patient with aplastic anemia were induced to cytotoxicity against target cells from several HLA-matched siblings by in vitro stimulation with allogeneic cells. Effective stimulating cells shared HLA-B7 with the patient, but not all B7 individuals were effective. An additional factor, which was found to segregate in both the patient's and an unrelated sibship, was also necessary. Segregation of this minor alloantigen, W, was also revealed among the patient's HLA-matched sibs by differential susceptibility to lysis by effectors from the patient. The ratio of six positive to four negative siblings suggests that the antigen difference might be coded by a single locus. Lymphocytes from a normal sib, who like the patient is lacking the minor antigen, could not be induced to cytotoxicity against positive targets. Thus in vivo sensitization of the donor of the responding cells appears to be necessary for the demonstration of the cytotoxic response to the minor antigen in vitro. No correlation was observed between the segregation pattern of W and of known blood group antigens, and no cytotoxic antibody to W was detected in the patient's serum in several trials.Abbreviations used in this paper MHC major histocompatibility complex - Tc thymus dependent cells capable of mediating cytotoxicity in the absence of Immoral antibody - GVHD graft versus host disease - CML cell mediated lympholysis - MLC unidirectional mixed lymphocyte culture - ADCC antibody-dependent cell mediated cytotoxicity