Glutamic acid decarboxylase of embryonic avian retina cells in culture: Regulation byγ-aminobutyric acid (GABA)

1. Retina-cell aggregate cultures expressed glutamate decarboxylase activity (L-glutamate 1-carboxylase; EC 4.1.1.15) as a function of culture differentiation. 2. Glutamic acid decarboxylase (GAD) activity was low in the initial phases of culture and increased eight-fold until culture day 7, remaining high up to day 13 (last stage studied). 3. The addition of GABA to the culture medium 24 h after cell seeding almost totally prevented the expression of GAD activity. 4. In association with decreased enzyme activity, aggregates exposed to GABA did not display immunoreactivity for GAD, suggesting that GAD molecules were either lost from GABAergic neurons or significantly altered with GABA treatment. 5. Control, untreated aggregates showed intense GAD immunoreactivity in neurons. Positive cell bodies were characterized by a thin rim of labeled cytoplasm with thickest labeling at the emergence of the main neurite. 6. Heavily labeled patches were also observed throughout the aggregates, possibly reflecting regions enriched in neurites. 7. The GABA-mediated reduction of GAD immunoreactivity was a reversible phenomenon and could be prevented by picrotoxin.     

Identification of neuroendocrine cells producing a diuretic hormone in the tobacco hornworm moth,Manduca sexta

Summary Separate antisera were raised to the N- and C-terminal half of the diuretic hormone from Manduca sexta. Antisera against the two halves of this peptide recognized the same cells in M. sexta, and preabsorption of the antisera with the peptides used as antigens abolished the immunoreactivity, confirming their specificity. The antisera reacted with two median neurosecretory cells on each side of the protocerebral groove in larvae, and with a group of about 80 small median neurosecretory cells in the adult, as well as their axons to, and their axon terminals in, the corpora cardiaca. During the early pupal stages, small cells, which are possibly derived from a common neuroblast, differentiate into immunoreactive neurosecretory cells, which explains the large increase in cell numbers in the adult. In the sleepy sulphur butterfly, Eurema nicippe, homologous median neurosecretory cells in the adult were immunoreactive with both antisera.     

Induction of lymphokine-activated killer activity in rat splenocyte cultures: The importance of 2-mercaptoethanol and indomethacin

Summary The role of 2-mercaptoethanol and indomethacin in the induction of lymphokine-activated killer (LAK) activity by interleukin-2 (IL-2) in rat splenocyte cultures was investigated. Spleens from 4-month-old male rats of five different strains were tested. Splenocytes were cultured for 3–5 days in the presence of IL-2 (1000 U/ml) and LAK activity was assessed by 4-h⁵¹Cr release assays with P815 and YAC-1 cells as targets. LAK activity could be induced by IL-2 in splenocytes from all rat strains, but only when 2-mercaptoethanol was present in the culture medium. Optimal LAK activity was induced when the 2-mercaptoethanol concentration in splenocyte cultures was at least 5 µM. Different rat strains showed differences in levels of in vitro induction of LAK activity. In the presence of 2-mercaptoethanol the level of LAK activity induced by IL-2 was high in BN and Lewis rats, intermediate in Wistar and Wag rats, and low in DZB rats. In the absence of 2-mercaptoethanol no or minimal LAK activity was induced. Furthermore we observed that addition of 50 µm indomethacin to the culture medium in the presence of 2-mercaptoethanol augmented the induction of LAK activity to some extent. In the absence of 2-mercaptoethanol, addition of indomethacin resulted only in low levels or no induction of LAK activity. We conclude that for optimal induction of LAK activity by IL-2 in rat splenocyte cultures 2-mercaptoethanol is essential, while indomethacin can only marginally further improve this induction.     

Cowpea aphid performance and behaviour on two resistant cowpea lines

In a series of laboratory and climate chamber tests we compared the growth and behaviour of Aphis craccivora on one susceptible (ICV-1) and two aphid-resistant (ICV-11 and ICV-12) cowpea lines. The aphids' growth rates were much lower on the resistant cowpea lines than on the susceptible one, indicating strong antibiosis. In addition, the aphids invariably settled in higher numbers on the susceptible line than on either of the resistant. Compared to ICV-1, damaged leaves of the resistant line ICV-12 were settled upon to a higher degree than undamaged leaves, and leaf discs from the same line were even less resistant.On resistant lines individual aphids waited a significantly longer time before making their first test probe. Total probing time as well as the time preceding a decision to stay or leave was also longer.These results are discussed in relation to the possible mechanisms involved, and we also consider the effects of previous leaf feeding on the expression of resistance in the field.

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Résumé Au cours d'expériences au laboratoire et en chambres climatisées nous avons comparé la croissance et le comportement de A. craccivora sur une lignée sensible (ICV-1) et deux lignées résistantes (ICV-11 et ICV-12) de V. unguiculata. Les vitesses de croissance des pucerons ont été beaucoup plus lentes sur les lignées résistantes que sur la lignée sensible, ce qui révèle une forte antibiose. De plus, les pucerons atterrissent invariablement en plus grand nombre sur la variété sensible. Par comparaison avec ICV-1, les atterrissages sur lignée résistante ICV-12 étaient plus nombreux sur les feuilles endommagées que sur les feuilles intactes; les disques de feuilles de cette même lignée étaient encore moins résistants.Les pucerons ont séjourné individuellement un temps plus long sur les lignées résistantes avant de faire leur premier sondage. Le temps consacré aux sondages ainsi que le temps précédant de choix entre départ ou maintien sur la feuille étaient plus longs avec les lignées résistantes.Ces résultats ont été discutés en fonction des mécanismes impliqués. Nous avons aussi examiné les effets de la consommation antérieure sur les manifestations de la résistance dans la nature.

     

The use of periphyton communities for nutrient removal from polluted streams

The results of experiments on the efficiency of periphyton communities for nutrient removal from polluted streams in a continuous flow-through are given. The artifical stream (5 m × 0.7 m × 0.5 m) was made of wood, with silon (a kind of nylon) screens, as a substratum for periphyton growth. The elimination of nutrients was monitored by ammonium, nitrite, nitrate and orthophosphate analyses. In addition, the elimination of organics and the decrease in trophic state were determined. During two field experiments a marked elimination of nitrogen and phosphorus was demonstrated. The maximum efficiency of ammonium and orthophosphate removal was 80% and 70%, respectively. Organic removal reached 35% (C.O.D._Mn-Kubel) and 54% (B.O.D.₅). Inorganic and organic nutrient elimination caused significant changes in periphyton community structure in the outflow portion of the through, evaluated by the saprobic index and the similarity coefficient. The experiments confirmed that periphyton communities are a useful means of nutrient removal from polluted streams.     

Copepods associated with reef corals: a comparison between the Atlantic and the Pacific

Endoparasitic copepods are very numerous in Indo-West Pacific corals. In West Indian corals they were thought to be absent, but recent studies have shown that a varied endoparasitic copepod fauna exists as well. Striking is the taxonomic composition of the coral-inhabiting copepods:In the Indo-West Pacific Lichomolgidae and Xarifiidae are the dominant families, both are absent in the West Indies. On the other hand, Corallovexiidae and Asterocheridae dominate in the West Indies; the former family is absent and the latter is apparently rare and not very diversified in the Indo-West Pacific.     

Combined Oxygen and Nitrous Oxide Microsensor for Denitrification Studies

The construction of a microsensor which can be used to measure O₂ and N₂O simultaneously is described. The microsensor exhibited a linear response to both O₂ and N₂O, and the response to N₂O was independent of the O₂ concentration and vice versa. The N₂O detection limit of a microsensor with a tip diameter of 20 μm was around 1 μmol liter⁻¹. The signals for O₂ and N₂O were affected by hydrogen sulfide, but other interfering agents were not observed in the biofilms and sediments analyzed. Microprofiles of O₂ and N₂O were measured in a biofilm which was exposed to acetylene to block the N₂O reductase activity of denitrifying bacteria. O₂ penetrated about 0.5 mm into the biofilm and was not affected by acetylene, but the N₂O concentration at 1.4 mm depth increased from 32 to 411 μmol liter⁻¹ after the addition of the inhibitor. The shape of the N₂O profile after the addition of acetylene showed that denitrification (denitrifying activity) was detectable in all anoxic layers of the biofilm.     

Linear dichroism and orientational studies of carotenoid Langmuir-Blodgett films

The linear dichroism of single monolayers of lutein, zeaxanthin and a mixture of lutein and synthetic phosphatidylcholine has been measured. The angle of orientation of the carotenoid molecules was found to lie between 45° and 51° relative to the plane of the solid support. Although the adsorbed monolayers were mostly in a monomeric state, microscopic observations, as well as the II-A isotherms, indicated the existence of crystalline islets. The results have been interpreted in connection with Haidinger's polarization brushes.     

Pathogenesis of the delayed phase of Rauscher virus-induced thrombocytopenia

BALB/c (H-2d) mice infected with Rauscher murine leukemia virus (RMuLV) developed two phases of thrombocytopenia: an acute phase, probably due to direct virus-platelet interactions, and a delayed phase, starting 2 to 3 wk after virus injection, which was associated with the infection of megakaryocytes by RMuLV and with the expression of RMuLV gp70 and p30 antigens on platelet membranes. This study was concerned with the pathogenesis of this second phase of thrombocytopenia. During this period, the number of marrow megakaryocytes was increased. A peripheral platelet destruction was further indicated by reduced platelet life span. It was shown that radiolabeled platelets, either normal or infected, were submitted to a more rapid clearance in infected recipients than in normal recipients. This might be due to the splenomegaly observed in infected recipients. However, the immediate clearance of gp70+ platelets was more accelerated in infected recipients with high titers of serum anti-gp70 antibodies than in infected recipients without detectable serum anti-gp70 antibodies. In addition, the passive transfer of anti-RMuLV serum to normal BALB/c mice induced a rapid and specific clearance of previously injected radiolabeled platelets expressing RMuLV antigens. In H-2d mice, viral gp70 antigen expression on platelets correlated with the development of delayed thrombocytopenia; but H-2k strains of mice, although susceptible to RMuLV and expressing RMuLV-related antigens on their platelets, did not develop any anti-RMuLV antibodies nor any delayed thrombocytopenia. These results suggest that specific clearance of gp70+ platelets in the presence of significant amounts of serum antiviral antibodies and nonspecific hypersplenism play a role in the development of delayed thrombocytopenia in RMuLV-infected mice.