A serotonergic system in the brain of the Antarctic fish, Trematomus bernacchii

The immunohistochemical distribution of serotonin-containing nerve fibres and cells has been described in the brain of the Antarctic fish, Trematomus bernacchii. The largest serotonergic system was associated with the diencephalic and rhombencephalic ventricles. In particular, serotonin-positive cells have been found in the lateral recess and neuropile zone of the diencephalic ventricle, where we have identified the serotonergic portion of the paraventricular organ. Numerous serotonin cells were localized in the dorsal nucleus of the raphe, the dorsal tegmental nucleus and the central gray. Two large cell groups, arranged in a pair of well-defined columns and connecting the central gray with the dorsal reticular formation, were immunostained in the region of the trigeminal nuclei. In addition, few positive cells have been found in the preoptic area and the cerebellar valvula, and few serotonergic nerve fibres, probably belonging to the lateral lemniscus, have been identified. The distribution of serotonin elements in the brain of T. bernacchii has been compared with that described in other fish, where it showed some modifications in the immunoreactive pattern. Finally, the lack of a serotonergic system at the level of the reticular superior formation has been reported; however, it was not possible to rule out a phylogenetic or environmental explanation.     

Neuronal Basis of Innate Olfactory Attraction to Ethanol in Drosophila

The decision to move towards a mating partner or a food source is essential for life. The mechanisms underlying these behaviors are not well understood. Here, we investigated the role of octopamine – the invertebrate analogue of noradrenaline – in innate olfactory attraction to ethanol. We confirmed that preference is caused via an olfactory stimulus by dissecting the function of the olfactory co-receptor Orco (formally known as OR83b). Orco function is not required for ethanol recognition per se, however it plays a role in context dependent recognition of ethanol. Odor-evoked ethanol preference requires the function of Tbh (Tyramine β hydroxalyse), the rate-limiting enzyme of octopamine synthesis. In addition, neuronal activity in a subset of octopaminergic neurons is necessary for olfactory ethanol preference. Notably, a specific neuronal activation pattern of tyraminergic/octopaminergic neurons elicit preference and is therefore sufficient to induce preference. In contrast, dopamine dependent increase in locomotor activity is not sufficient for olfactory ethanol preference. Consistent with the role of noradrenaline in mammalian drug induced rewards, we provide evidence that in adult Drosophila the octopaminergic neurotransmitter functions as a reinforcer and that the molecular dissection of the innate attraction to ethanol uncovers the basic properties of a response selection system.     

Effect of nickel on oxygen free radical metabolism

The effect of nickel on superoxide dismutase activity (SOD), as well as on rate of hydroxydopamine oxidation, was studied in vitro since lipid peroxidation has been implicated in cell damage by nickel, whose toxicity and carcinogenicity are well established. Nickel strongly inhibits SOD activity. The degree of inhibition is directly proportion to the nickel concentration (tested range 0.066 to 0.33 microgram/mL in the reaction mixture); to the substrate concentration (tested range 0.4 x 10 4M to 1.1 x 10 4M 6-hydroxydopamine); and to reaction mixture. Autoxidation of 6-hydroxydopamine was increased by nickel concentrations higher than 15 micrograms/mL. The combination of excessive oxygen free radical production and inhibition of their elimination by inhibition of SOD activity may contribute to the nickel toxicity that has been reported in industrial accidents, as well as to the high incidence of cancer occurring in nickel workers. It may also contribute to many complications in uremic patients, in whom increased serum nickel levels were reported to be in a similar range to those inhibiting SOD.     

Natural antibodies to interferon-gamma

Natural antibodies to interferon (IFN)-γ were detected in the serum of virus-infected patients and also, at a low titre, in the serum of healthy subjects. The increased titre of antibodies to IFN-γ in the sera of virus-infected patients, and its decrease with clinical resolution, indicate that these antibodies are related to viral infection and probably reflect IFN-γ production as a result of antigenic stimulationin vivo. Natural antibodies to IFN-γ were affinity purified and studied for their capability to interferein vitro with the multiple activities of the lymphokine. Data obtained show that these human anti-IFN-γ antibodies have no inhibitory effect on the antiviral and antiproliferative activity of IFN-γ and do not interfere with the binding of the lymphokine to its specific cell receptor. Instead, they can inhibit the expression of HLA-DR antigens induced by IFN-γ on U937 cells and interfere, in mixed lymphocyte culture, with the proliferation of lymphocytes and the generation of cytotoxic lymphocytes. Experiments in animal models suggest that natural antibodies to IFN-γ may have a role in the immunoregulatory process limiting the intensity and/or duration of immune response. As they can interfere only with the immunomodulating activities of IFN-γ, these antibodies might open up new therapeutic approaches to diseases with evidence of activated cell-mediated immunity.     

Gas exchange studies in two Portuguese grapevine cultivars

Gas exchange characteristics of leaves of Vitis vinifera L. cvs Tinta Amarela and Periquita, two grapevine cultivars grown in distinct climatic regions of Portugal, were studied under natural and controlled conditions. Daily time courses of gas exchange were measured on both a hot, sunny day and a cooler, partly cloudy day. Responses of net photosynthesis to irradiance and internal partial pressure of CO₂, were also obtained. A strong correlation between net photosynthesis (P_N) and leaf conductance (g_s) was found during the diurnal time courses of gas exchange, as well as a relatively constant internal partial pressure of CO₂ (P_i), even under non-steady-state conditions. On the cloudless day, both P_N and g_s were lower in the afternoon than in the morning, despite similar conditions of leaf temperature, air to leaf water vapor deficit and irradiance. The response curves of net photosynthesis to internal CO₂ showed linearity up to p_i values of 50 Pa, possibly indicating a substantial excess of photosynthetic capacity. When measured at low partial pressures of O₂ (1 kPa), P_N became inhibited at high CO₂ levels. Inhibition of P_N at high CO₂ was absent under normal levels of O₂ (21 kPa). Significant differences in gas exchange characteristics were found between the two cultivars, with T. Amarela having higher rates under similar measurement conditions. In particular, the superior performance of T. Amarela at high temperatures may represent adaptation to the warmer conditions at its place of origin.     

Transport of l(-)malic acid and other dicarboxylic acids in the yeast Candida sphaerica

Summary dl-Malic acid grown cells of Candida sphaerica (anamorph of Kluyveromyces marxianus) formed a saturable transport system that mediated accumulative transport of l(-)malic acid with the following kinetic parameters at pH 5.0: V _max, 0.44 nmol l(-)malate·s^-1 per milligram dry weight; K _m ,0.1 mM l(-)malate. Initial uptake of the acid was accompanied by disappearance of extracellular protons, the rates of which followed Michaelis-Menten kinetics as a function of the acid concentration. Variation with extracellular pH of the K _m values, calculated either as the concentrations of anions or of undissociated acid, pointed to anions as the transported form. Furthermore, accumulated free acid suffered rapid efflux after the addition of the protonophore carbonylcyanide-M-chlorophenyl-hydrazone (CCCP). These results suggested that the transport system was a dicarboxylate-proton symporter. The system was inducible and was subject to glucose repression. Succinic, fumaric, -ketoglutaric, oxaloacetic and d-malic acid, but not maleic, malonic, oxalic nor l(+)-tartaric acid, apparently used the same transport system since they acted as competitive inhibitors of l(-)malic acid transport and induced proton movements that followed Michaelis-Menten kinetics. Experiments with glucose-repressed cells showed that undissociated dicarboxylic acid (measured with labelled succinic acid) entered the cells slowly by simple diffusion. The permeability of the cells for undissociated acid increased exponentially with pH, the diffusion constant increasing 100-fold between pH 3.5 and 6.0.     

Structure and function of hemoglobin in antarctic fishes and evolutionary implications

Summary The hematological features of cold-adapted, red-blooded Antarctic teleosts has prompted this study on the relationship between hemoglobin molecular structure and oxygen-binding properties. The hemolysates from 21 species of 5 families contained one component (Hb 1), often accompanied by an additional, minor one (Hb 2, 5%–10% of total). On the other hand, 3 species of Zoarcidae, a non-endemic family, had 4–5 components. All purified hemoglobins from the former group, but only 1–2 of the 4–5 hemoglobins of Zoarcidae, showed a strong Root effect (pH regulation of oxygen binding). Globins from each hemoglobin have been purified and characterised with respect to molecular structure in several species. The similarity between the complete amino acid sequence of one -chain and those of non-Antarctic -chains is lower than that among the latter sequences, suggesting independent pathways of evolution.Presented at the 5th SCAR Symposium on Antarctic Biology, Hobart, Australia (August 29th-September 3rd, 1988)     

Linkage data suggesting allelic heterogeneity for paramyotonia congenita and hyperkalemic periodic paralysis on chromosome 17

Summary Paramyotonia congenita (PC), an autosomal dominant non-progressive muscle disorder, is characterised by cold-induced stiffness followed by muscle weakness. The weakness is caused by a dysfunction of the sodium channel in muscle fibre. Parts of the gene coding for the -subunit of the sodium channel of the adult human skeletal muscle (SCN4A) have been localised on chromosome 17. To investigate the role of this gene in the etiology of PC, a linkage analysis in 17 well-defined families was carried out. The results (z=20.61, =0.001) show that the mutant gene responsible for the disorder is indeed tightly linked to the SCN4A gene. The mutation causing hyperkalemic periodic paralysis (HyperPP) with myotonia has previously been mapped to this gene locus by the same candidate gene approach. Thus, our data suggest that PC and HyperPP are caused by allelic mutations at a single locus on chromosome 17.Dedicated to Professor P. E. Becker on the occasion of his 83rd birthday.     

Human erythrocyte glucose-6-phosphate dehydrogenase. Identification of a reactive lysyl residue labelled with pyridoxal 5'-phosphate

Human erythrocyte glucose-6-phosphate dehydrogenase contains a reactive lysyl residue, which can be labelled with pyridoxal 5'-phosphate. The binding of one mole of pyridoxal 5'-phosphate per mole of enzyme subunit produces substantial inactivation. The substrate glucose-6-phosphate prevents the loss of activity, suggesting that the reaction site is close to the substrate-binding site. A tryptic peptide containing the pyridoxal-5'-phosphate-binding lysyl residue has been isolated and characterised. The reactive lysyl residue has been identified in the glucose-6-phosphate dehydrogenase amino acid sequence. Comparison with glucose-6-phosphate dehydrogenase from other sources shows a high homology with a peptide containing a reactive lysyl residue, isolated from the enzyme from Saccharomyces cerevisiae; glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides also contains a region highly homologous with the sequence around the reactive lysyl residue in the human enzyme. The results of this communication provide the first direct evidence for the association of an essential catalytic function with a specific region of the molecule of human erythrocyte glucose-6-phosphate dehydrogenase.