Hippocampal long-term potentiation is reduced in mature compared to young male rats but not in female rats.

Aging is associated with a decline in cognitive function which could be due to reduced synaptic plasticity. Hippocampal long-term potentiation (LTP) is an activity-dependent form of increased transmission efficacy at synapses that is considered the basis for some forms of learning and memory. We studied the N-methyl-d-aspartic acid (NMDA) receptor-dependent LTP in the CA1 region of hippocampus in young (2 months) and mature (8 months) male and female rats. We have found that in young male rats the tetanus increased the magnitude of excitatory post-synaptic potentials to 204+/-10% of basal while in mature male rats the magnitude of the LTP was significantly lower reaching only 153+/-11% of basal. This decrease did not occur in female rats. Similar changes occurred in the content of the NMDA receptor subunits NR1 and NR2A in hippocampus. The amount of both subunits was reduced significantly (15-16%) in hippocampus of 8-month-old compared with 2-month-old male rats. This decrease was not observed in female rats. Moreover, there is a significant correlation between the content of NR1 subunit and the magnitude of the potentiation. These data suggest that some of the neurobiological changes induced in hippocampus by aging are different in males and females.

Water quality and health status of the Senegal River estuary.

The Senegal River estuary was sampled in May 2002 to get the first data on both the trophic and sanitary status of the water of the main river of the northwest African coast. Several physical, chemical and microbiological variables were measured twice along a transect. Inorganic nutrient concentrations were low while phytoplanktonic abundances (0.58-1.8 x 10(5) cells ml(-1)), bacterial abundances (0.27-8.1 x 10(7) cells ml(-1)), activity (22-474 pmol l(-1) h(-1)), were among the highest recorded in such ecosystems. Microbiological variables revealed a eutrophicated status for this estuary. Largest abundances of fecal contamination bacterial indicators were only detected in localized areas (Saint-Louis city and surrounding areas). The apparent good survival of fecal indicator bacteria in the estuarine waters despite a long residence time (4-5 days) has been evaluated by complementary survival experiments. Exposed to a salinity gradient, a local Escherichia coli strain showed a significantly better survival than those of an E. coli reference strain.

Chronic exposure to 2,5-hexanedione impairs the glutamate-nitric oxide-cyclic GMP pathway in cerebellar neurons in culture and in rat brain in vivo.

2,5-Hexanedione is a neurotoxic metabolite of hexane. The mechanisms of its neurotoxicity remain unclear. We assessed whether chronic exposure to 2,5-hexanedione affects the glutamate-nitric oxide-cGMP pathway in primary cultures of cerebellar neurons and/or in the cerebellum of rats. Chronic exposure of cultured cerebellar neurons to 2,5-hexanedione (200 microM) reduced by approximately 50% NMDA-induced formation of cGMP. Activation of soluble guanylate cyclase by nitric oxide was reduced by 46%. This treatment reduced the content of neuronal nitric oxide synthase and soluble guanylate cyclase in neurons by 23 and 20%, respectively. In the cerebellum of rats chronically exposed to 2,5-hexanedione (in the drinking water) NMDA-induced formation of cGMP was reduced by 55% as determined by in vivo brain microdialysis. Activation of soluble guanylate cyclase by nitric oxide was reduced by 65%. The content of neuronal nitric oxide synthase and of soluble guanylate cyclase was reduced by 25 and 21%, respectively, in the cerebellum of these rats. The effects are the same in both systems, indicating that cultured neurons are a good model to study the mechanisms of neurotoxicity of 2,5-hexanedione. These results indicate that chronic exposure to 2,5-hexanedione affects the glutamate-nitric oxide-cGMP pathway at different steps both in cultured neurons and in cerebellum of the animal in vivo. The alteration of this pathway may contribute to the neurotoxic effects of 2,5-hexanedione.

Aluminium impairs the glutamate-nitric oxide-cGMP pathway in cultured neurons and in rat brain in vivo: molecular mechanisms and implications for neuropathology.

Aluminium (Al) is a neurotoxicant and appears as a possible etiological factor in Alzheimer's disease and other neurological disorders. The mechanisms of Al neurotoxicity are presently unclear but evidence has emerged suggesting that Al accumulation in the brain can alter neuronal signal transduction pathways associated with glutamate receptors. In cerebellar neurons in culture, long term-exposure to Al added 'in vitro' impaired the glutamate-nitric oxide (NO)-cyclic GMP (cGMP) pathway, reducing glutamate-induced activation of NO synthase and NO-induced activation of the cGMP generating enzyme, guanylate cyclase. Prenatal exposure to Al also affected strongly the function of the glutamate-NO-cGMP pathway. In cultured neurons from rats prenatally exposed to Al, we found reduced content of NO synthase and of guanylate cyclase, and a dramatic decrease in the ability of glutamate to increase cGMP formation. Activation of the glutamate-NO-cGMP pathway was also strongly impaired in cerebellum of rats chronically treated with Al, as assessed by in vivo brain microdialysis in freely moving rats. These findings suggest that the impairment of the Glu-NO-cGMP pathway in the brain may be responsible for some of the neurological alterations induced by Al.

Altered content and modulation of soluble guanylate cyclase in the cerebellum of rats with portacaval anastomosis.

It is shown that the glutamate-NO-cGMP pathway is impaired in cerebellum of rats with portacaval anastomosis in vivo as assessed by in vivo brain microdialysis in freely moving rats. NMDA-induced increase in extracellular cGMP in the cerebellum was significantly reduced (by 27%) in rats with portacaval anastomosis. Activation of soluble guanylate cyclase by the NO-generating agent S-nitroso-N-acetyl-penicillamine and by the NO-independent activator YC-1 was also significantly reduced (by 35-40%), indicating that portacaval anastomosis leads to remarkable alterations in the modulation of guanylate cyclase in cerebellum. Moreover, the content of soluble guanylate cyclase was increased ca. two-fold in the cerebellum of rats with portacaval anastomosis. Activation of soluble guanylate cyclase by NO was higher in lymphocytes isolated from rats with portacaval anastomosis (3.3-fold) than in lymphocytes from control rats (2.1-fold). The results reported show that the content and modulation of soluble guanylate cyclase are altered in brain of rats with hepatic failure, resulting in altered function of the glutamate-NO-cGMP pathway in the rat in vivo. This may lead to alterations in cerebral processes such as intercellular communication, circadian rhythms, including the sleep-waking cycle, long-term potentiation, and some forms of learning and memory.

The Responses of a Natural Bacterioplankton Community to Different Levels of Ultraviolet-B Radiation: A Food Web Perspective.

With the continuing increase of ultraviolet-B radiation (UVBR: 280-320 nm) fluxes toward the Earth's surface, there is concern regarding a possible negative impact on heterotrophic bacterioplankton. The effects of enhanced UVBR on a natural bacterioplankton community were studied during a 7-day experiment conducted in mesocosms (1500 L). Four light regimes were tested: natural light, 280 to 313 nm excluded UVBR, and two levels of UVBR enhancement. During the first 3 days of the experiment characterized by high inorganic nutrient concentrations (nitrates > 1 µmol L-1 and ammonium > 0.1 µmol L-l), UVBR had no effect on both bacterial abundances and activities. From day 4 to the end of the experiment, nitrate concentrations remained low (

Role of nitric oxide and cyclic GMP in glutamate-induced neuronal death.

Glutamate is the main excitatory neurotransmitter in mammals. However, excessive activation of glutamate receptors is neurotoxic, leading to neuronal degeneration and death. In many systems, including primary cultures of cerebellar neurons, glutamate neurotoxicity is mainly mediated by excessive activation of NMDA receptors, leading to increased intracellular calcium which binds to calmodulin and activates neuronal nitric oxide synthase (NOS), increasing nitric oxide (NO) which in turn activates guanylate cyclase and increases cGMP. Inhibition of NOS prevents glutamate neurotoxicity, indicating that NO mediates glutamate-induced neuronal death in this system. NO generating agents such as SNAP also induce neuronal death. Compounds that can act as "scavengers" of NO such as Croman 6 (CR-6) prevent glutamate neurotoxicity. The role of cGMP in the mediation of glutamate neurotoxicity remains controversial. Some reports indicate that cGMP mediates glutamate neurotoxicity while others indicate that cGMP is neuroprotective. We have studied the role of cGMP in the mediation of glutamate and NO neurotoxicity in cerebellar neurons. Inhibition of soluble guanylate cyclase prevents glutamate and NO neurotoxicity. There is a good correlation between inhibition of cGMP formation and neuroprotection. Moreover 8-Br-cGMP, a cell permeable analog of cGMP, induced neuronal death. These results indicate that increased intracellular cGMP is involved in the mechanism of neurotoxicity. Inhibitors of phosphodiesterase increased extracellular but not intracellular cGMP and prevented glutamate neurotoxicity. Addition of cGMP to the medium also prevented glutamate neurotoxicity. These results are compatible with a neurotoxic effect of increased intracellular cGMP and a neuroprotective effect of increased extracellular cGMP.

Bacterial dynamics in first year sea ice and underlying seawater of Saroma-ko Lagoon (Sea of Okhotsk, Japan) and resolute passage (High Canadian Arctic): inhibitory effects of ice algae on bacterial dynamics.

The seasonal development of bacterial abundance in first year bottom ice and underlying seawater were studied at Saroma-ko Lagoon in Hokkaido, Japan, and at Resolute Passage in the High Canadian Arctic during the algal bloom in spring 1992. The aim of this study was to evaluate whether the high algal concentrations reached during the bloom of ice algae have inhibitory effects on bacterial dynamics. Bacterial abundance (measured as total cell count and colony-forming units CFU) increased with the increase of the algal biomass up to 500 micrograms Chla.L-1 in both locations. Culturable fraction (measured as the percentage of CFU counts versus the total cell counts) was between 7% and 22% at Saroma-ko, and approximately 0.08% at Resolute Passage. When algal biomass exceeded 500 micrograms of Chla.L-1, both bacterial abundance and culturable fraction decreased significantly. There was a maximum threshold of algal biomass (between 500 and 800 micrograms of Chla.L-1) after which bacterial dynamics become negatively coupled to the algal biomass. These results suggest that bactericidal and/or bacteriostatic compounds from these extremely high algal concentrations could explain the decrease in bacterial abundance and culturability in bottom ice observed after the ice algae bloom.

Metallothionein-III prevents glutamate and nitric oxide neurotoxicity in primary cultures of cerebellar neurons.

Metallothionein (MT)-III, a member of the MT family of metal-binding proteins, is mainly expressed in the CNS and is abundant in glutamatergic neurons. Results in genetically altered mice indicate that MT-III may play neuroprotective roles in the brain, but the mechanisms through which this protein functions have not been elucidated. The aim of this work was to assess whether MT-III is able to prevent glutamate neurotoxicity and to identify the step of the neurotoxic process interfered with by MT-III. Glutamate neurotoxicity in cerebellar neurons in culture is mediated by excessive activation of glutamate receptors, increased intracellular calcium, and increased nitric oxide. It is shown that MT-III prevented glutamate- and nitric oxide-induced neurotoxicity in a dose-dependent manner, with nearly complete protection at 0.3-1 microgram/ml. MT-III did not prevent the glutamate-induced rise of intracellular calcium level but reduced significantly the nitric oxide-induced formation of cyclic GMP. Circular dichroism analysis revealed that nitric oxide triggers the release of the metals coordinated to the cysteine residues of MT-III, indicative of the S(Cys)-nitrosylation of the protein. Therefore, the present results indicate that MT-III can quench pathological levels of nitric oxide, thus preventing glutamate and nitric oxide neurotoxicity.

Hyperammonemia impairs NMDA receptor-dependent long-term potentiation in the CA1 of rat hippocampus in vitro.

Hyperammonemia is considered the main factor responsible for the neurological and cognitive alterations found in hepatic encephalopathy and in patients with congenital deficiencies of the urea cycle enzymes. The underlying mechanisms remain unclear. Chronic moderate hyperammonemia reduces nitric oxide-induced activation of soluble guanylate cyclase and glutamate-induced formation of cGMP. NMDA receptor-associated transduction pathways, including activation of soluble guanylate cyclase, are involved in the induction of long-term potentiation (LTP), a phenomenon that is considered to be the molecular basis for some forms of memory and learning. Using an animal model we show that chronic hyperammonemia significantly reduces the degree of long-term potentiation induced in the CA1 of hippocampus slices (200% increase in control and 50% increase in slices of hyperammonemic animals). Also, addition of 1 mM ammonia impaired the maintenance of non-decremental LTP. The LTP impairment could be involved in the intellectual impairment present in chronic hepatocerebral disorders associated with hyperammonemia.

Activation of N-methyl-D-aspartate receptors in rat brain in vivo following acute ammonia intoxication: characterization by in vivo brain microdialysis.

Ammonia is considered the main agent responsible for the neurological alterations in hepatic encephalopathy. It was suggested that ammonia toxicity is mediated by activation of N-methyl-D-aspartate (NMDA) receptors. The aim of this work was to assess, by in vivo brain microdialysis in freely moving rats, whether acute ammonia intoxication leads to activation of NMDA receptors in the cerebellum of the rat in vivo. We measured the effects of ammonia intoxication on the neuronal glutamate-nitric oxide-cyclic guanosine monophosphate (cGMP) pathway, by measuring the ammonia-induced increase of extracellular cGMP. Ammonia intoxication increases extracellular cGMP, and this increase is prevented by (5R,10S)-5-methyl-10,11-dihydro-5H-dibenzo[a, d]cyclohepten-5,10-imine hydrogen maleate (MK-801). There is a good correlation between the increase in cGMP and the seriousness of the neurological symptoms elicited by different doses of ammonia. Ammonia doses inducing coma did not affect extracellular glutamate, while doses leading to death increased it by 349%. The time courses of ammonia-induced increases in extracellular ammonia, cGMP, and glutamate indicate that NMDA receptor activation occurs before the increase in extracellular glutamate. Ammonia-induced increase in glutamate is prevented by MK-801. These results indicate that ammonia intoxication leads to activation of NMDA receptors in the animal in vivo, and that this activation is not caused by increased extracellular glutamate. The possible underlying mechanism is discussed.

Inhibitors of phospholipase C prevent glutamate neurotoxicity in primary cultures of cerebellar neurons.

The role of phospholipase C in the molecular mechanism of glutamate neurotoxicity was assessed in primary cultures of cerebellar neurons. It is shown that 1-[6-[[(17b)-3-methoxyestra-1,3, 5(10)-trien-17-yl]amino] hexyl]-1H-pyrrole-2,5-dione (U-73122) and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphorylcholine (Et-18-OCH(3)), two agents that inhibit phospholipase C, prevent glutamate and N-methyl-D-aspartic acid (NMDA) neurotoxicity. It is shown that both compounds prevent glutamate neurotoxicity at concentrations lower than those required to inhibit carbachol-induced hydrolysis of inositol phospholipids. In contrast, it was a good correlation between the concentrations of U-73122 and Et-18-OCH(3) required to inhibit NMDA-induced hydrolysis of phospholipids and those required to prevent glutamate and NMDA neurotoxicity. NMDA-induced hydrolysis of phospholipids is inhibited by nitroarginine, an inhibitor of nitric-oxide synthase, and is mimicked by the nitric oxide-generating agent S-nitroso-N-acetylpenicillamine. The results reported indicate that glutamate neurotoxicity would be mediated by activation of NMDA receptors, leading to activation of nitric-oxide synthase and increased formation of nitric oxide, which results in increased activity of phospholipase C. Inhibition of phospholipase C by U-73122 or Et-18-OCH(3) prevents glutamate-induced neuronal death.

Stability of methacholine chloride in isotonic sodium chloride using a capillary electrophoresis assay.

OBJECTIVE: To investigate the stability of methacholine chloride in 0.9% sodium chloride solutions. METHOD: Methacholine powder was mixed with diluent to a final concentration of 5 and 10 mg/ml. Duplicates of each admixture were divided and stored in glass vials at 25 degrees C, 4 degrees C and -20 degrees C for 12 months. At appropriate times intervals, samples were removed from solutions and analysed. Methacholine concentrations were measured using a high performance capillary electrophoresis assay. RESULTS: No colour or other visual changes were seen in any sample. However, an additional peak was observed in some samples. CONCLUSION: Methacholine chloride solutions 5 mg/ml were stable in isotonic sodium chloride after refrigeration or freezing over a period of one year; methacholine chloride solutions 10 mg/ml were stable for one year after freezing. The solutions stored at ambient temperature were stable for 35 days and for less than 14 days, respectively, for the 5 and the 10 mg/ml solutions.

Listeria innocua and Salmonella panama in mussels: a comparative study.

Bivalve molluscs are exposed to a wide range of contamination by pathogenic bacteria and viruses. Therefore, the behavior of bacterial pathogens in bivalves after harvesting is important in terms of food safety. Mussels were artificially contaminated with Listeria innocua and Salmonella panama, held under different conditions, and then examined for Listeria and Salmonella viable counts. In a simplified depuration system, L. innocua levels were lower than those observed for S. panama in mussels during the same period and under the same conditions. This result may be related to the rapid die-off reported for Listeria in seawater. In mussels stored in air, the two pathogens presented similar behaviors: levels of both pathogens remained constant in mussels during the storage period in air. However, in shucked mussels Listeria innocua counts increased with the duration of storage, whereas Salmonella panama showed a slight decrease.

Incidence of Listeria spp. in Breton live shellfish.

Live shellfish samples (120) were collected from nine littoral sites in Brittany (western France). They were screened for Listeria spp. and a count of faecal coliforms was carried out. Analysis of the results revealed Listeria spp. in 55% of samples, a much higher rate than the previous, infrequent, recorded data. Furthermore, the study demonstrated that the frequency of Listeria spp. in winter was more important than in summer (P < 0.001), and underlined a significant relationship between the occurrence of these bacteria and the concentration of faecal coliforms (P < 0.001). Finally, comparison of the official and Gen-Probe methods revealed the limits of the standardized technique in the search for L. monocytogenes in shellfish.

In vivo functional discrimination between plant thioredoxins by heterologous expression in the yeast Saccharomyces cerevisiae.

Whereas vertebrates possess only two thioredoxin genes, higher plants present a much greater diversity of thioredoxins. For example, Arabidopsis thaliana has five cytoplasmic thioredoxins (type h) and at least as many chloroplastic thioredoxins. The abundance of plant thioredoxins leads to the question whether the various plant thioredoxins play a similar role or have specific functions. Because most of these proteins display very similar activities on artificial or biological substrates in vitro, we developed an in vivo approach to answer this question. The disruption of both of the two Saccharomyces cerevisiae thioredoxin genes leads to pleiotropic effects including methionine auxotrophy, H2O2 hypersensitivity, altered cell cycle characteristics, and a limited ability to use methionine sulfoxide as source of methionine. We expressed eight plant thioredoxins (six cytoplasmic and two chloroplastic) in yeast trx1, trx2 double mutant cells and analyzed the different phenotypes. Arabidopsis type h thioredoxin 2 efficiently restored sulfate assimilation whereas Arabidopsis type h thioredoxin 3 conferred H2O2 tolerance. All thioredoxins tested could complement for reduction of methionine sulfoxide, whereas only type h thioredoxins were able to complement the cell cycle defect. These findings clearly indicate that specific interactions between plant thioredoxins and their targets occur in vivo.

Fatal disease mimicking leptospirosis in a dog, caused by Aeromonas hydrophila.

A dog was treated for leptospirosis on clinical and epidemiological arguments. The amoxicillin treatment was not successful. Pure culture of Aeromonas hydrophila was then obtained from liver and kidney, indicating that the septicemia was due to this bacteria commonly found in waters.

Effects of environmental factors present in the St. Lawrence Estuary (Quebec, Canada) on experimental survival of Salmonella salamae as determined by flow cytometry.

Survival of Salmonella salamae in the St. Lawrence Estuary was studied experimentally during an oceanographic cruise using in situ exposure diffusion chambers. The abundance distribution (colony-forming units) of culturable S. salamae on media was compared with the distribution of cells enumerated by flow cytometry. Flow cytometry was also used to characterize the size distribution and DNA content of cells exposed to various environmental factors. Solar radiation, starvation, and a gradual increase in salinity led to an abrupt loss of the ability of S. salamae cells to form cultures and to a gradual reduction in the cell size and DNA content. Conversely, starvation combined with a gradual increase in salinity in the absence of sunlight led to a gradual loss of the cells' ability to form cultures and an abrupt reduction in cell size and DNA content (i.e., a rapid increase in cell damage). Mortality (i.e., a decrease in total cell count) of S. salamae placed in darkness began at a lower salinity (11.4/1000) than did the mortality of cells exposed to sunlight (23.1/1000). Therefore, the S. salamae cells exposed to sunlight seemed to be more resistant to gradual salinity stress than the cells that were not subjected to sunlight.

Comparison of flow cytometry and epifluorescence microscopy for counting bacteria in aquatic ecosystems.

Flow cytometry was used to count bacterial cells from diverse origins: one strain of E. coli, one sample of lake water, and 18 samples of estuary water. To verify the accuracy and the precision of this technique, total bacteria counts made by flow cytometry were compared with counts by direct observation using epifluorescence microscopy. The results of this study showed that flow cytometry was a reliable technique for counting a mixture of bacteria in samples from aquatic ecosystems.