Direct and indirect climate forcing in a multi-species marine system

Interactions within and between species complicate quantification of climate effects, by causing indirect, often delayed, effects of climate fluctuations and compensation of mortality. Here we identify direct and indirect climate effects by analysing unique Russian time-series data from the Norwegian Sea–Barents Sea ecosystem on the first life stages of cod, capelin, herring and haddock, their predators, competitors and zooplanktonic prey. By analysing growth and survival from one life stage to the next (eggs–larvae–juveniles–recruits), we find evidence for both bottom-up, direct and top-down effects of climate. Ambient zooplankton biomass predicts survival of all species, whereas ambient temperature mainly affects survival through effects on growth. In warm years, all species experienced improved growth and feeding conditions. Cohorts born following a warm year will, however, experience increased predation and competition because of increased densities of subadult cod and herring, leading to delayed climate effects. While climate thus affects early growth and survival through several mechanisms, only some of the identified mechanisms were found to be significant predictors of population growth. In particular, our findings exemplify that climate impacts are barely propagated to later life stages when density dependence is strong.     

Validation of organotypical hippocampal slice cultures as an ex vivo model of brain ischemia: different roles of NMDA receptors in cell death signalling after exposure to NMDA or oxygen and glucose deprivation

N-Methyl-D-aspartate receptors (NMDARs) are essential mediators of synaptic plasticity under normal physiological conditions. During brain ischemia, these receptors are excessively activated due to glutamate overflow and mediate excitotoxic cell death. Although organotypical hippocampal slice cultures are widely used to study brain ischemia in vitro by induction of oxygen and glucose deprivation (OGD), there is scant data regarding expression and functionality of NMDARs in such slice cultures. Here, we have evaluated the contribution of NMDARs in mediating excitotoxic cell death after exposure to NMDA or OGD in organotypical hippocampal slice cultures after 14 days in vitro (DIV14). We found that all NMDAR subunits were expressed at DIV14. The NMDARs were functional and contributed to cell death, as evidenced by use of the NMDAR antagonist MK-801 (dizocilpine). Excitotoxic cell death induced by NMDA could be fully antagonized by 10 μM MK-801, a dose that offered only partial protection against OGD-induced cell death. Very high concentrations of MK-801 (50–100 μM) were required to counteract cell death at long delays (48–72 h) after OGD. The relative high dose of MK-801 needed for long-term protection after OGD could not be attributed to down-regulation of NMDARs at the gene expression level. Our data indicate that NMDAR signaling is just one of several mechanisms underlying ischemic cell death and that prospective cytoprotective therapies must be directed to multiple targets.     

Beta-dystroglycan as a target for MMP-9, in response to enhanced neuronal activity

Matrix metalloproteinase-9 has recently emerged as an important molecule in control of extracellular proteolysis in the synaptic plasticity. However, no synaptic targets for its enzymatic activity had been identified before. In this report, we show that beta-dystroglycan comprises such a neuronal activity-driven target for matrix metalloproteinase-9. This notion is based on the following observations. (i) Recombinant, autoactivating matrix metalloproteinase-9 produces limited proteolytic cleavage of beta-dystroglycan. (ii) In neuronal cultures, beta-dystroglycan proteolysis occurs in response to stimulation with either glutamate or bicuculline and is blocked by tissue inhibitor of metalloproteinases-1, a metalloproteinase inhibitor. (iii) Beta-dystroglycan degradation is also observed in the hippocampus in vivo in response to seizures but not in the matrix metalloproteinase-9 knock-out mice. (iv) Beta-dystroglycan cleavage correlates in time with increased matrix metalloproteinase-9 activity. (v) Finally, beta-dystroglycan and matrix metalloproteinase-9 colocalize in postsynaptic elements in the hippocampus. In conclusion, our data identify the beta-dystroglycan as a first matrix metalloproteinase-9 substrate digested in response to enhanced synaptic activity. This demonstration may help to understand the possible role of both proteins in neuronal functions, especially in synaptic plasticity, learning, and memory.     

Neurotransmission in the vestibular endorgans--glutamatergic transmission in the afferent synapses of hair cells.

In the sensory pathways the first synapse is that between hair cells and primary afferent neurons and its most likely neurotransmitter candidate has long been thought to be glutamate. A number of pharmacological and electrophysiological studies have lent credence to this theory (reviewed by Bledsoe et al. 1988, Bobbin 1979, Ehrenberger and Felix 1991, Puel et al. 1991; Puel 1995) as has recent neurochemical and immunocytochemical work (reviewed by Ottersen et al. 1998; Usami et al. 2000). These recent studies reveal that the afferent hair cell synapse resembles the central glutamate synapses in many ways. Of the proteins confirmed to be involved in signal transduction and transmitter metabolism at most central synapses, many are also seen in the afferent hair cell synapse, and have an analogous compartmentation. On the other hand, there are also important differences, especially those related to the molecular mechanisms that underlie transmitter release.     

Productivity in the Barents Sea - Response to Recent Climate Variability

The temporal and spatial dynamics of primary and secondary biomass/production in the Barents Sea since the late 1990s are examined using remote sensing data, observations and a coupled physical-biological model. Field observations of mesozooplankton biomass, and chlorophyll a data from transects (different seasons) and large-scale surveys (autumn) were used for validation of the remote sensing products and modeling results. The validation showed that satellite data are well suited to study temporal and spatial dynamics of chlorophyll a in the Barents Sea and that the model is an essential tool for secondary production estimates. Temperature, open water area, chlorophyll a, and zooplankton biomass show large interannual variations in the Barents Sea. The climatic variability is strongest in the northern and eastern parts. The moderate increase in net primary production evident in this study is likely an ecosystem response to changes in climate during the same period. Increased open water area and duration of open water season, which are related to elevated temperatures, appear to be the key drivers of the changes in annual net primary production that has occurred in the northern and eastern areas of this ecosystem. The temporal and spatial variability in zooplankton biomass appears to be controlled largely by predation pressure. In the southeastern Barents Sea, statistically significant linkages were observed between chlorophyll a and zooplankton biomass, as well as between net primary production and fish biomass, indicating bottom-up trophic interactions in this region.     

High-resolution immunogold cytochemistry indicates that AQP4 is concentrated along the basal membrane of parietal cell in rat stomach.

Gastric parietal cells secrete hydrochloric acid in stomach. Because the secreted HCl solution is isotonic with the plasma fluid, it should accompany the water transport across the membranes of parietal cells. Aquaporins (AQPs) are water channel proteins that play the central role in the cellular handling of water in various mammalian tissues. Using immunocytochemistry, we found that AQP4 was expressed only in parietal cells of rat gastric mucosa. Immunogold electron microscopy study further demonstrated that AQP4 was mostly localized at the basal membrane of parietal cells. In the basal membrane, AQP4 was prominently enriched on the portion contacting with the basement membrane surrounding gastric glands. These results suggest that the contact between basement membrane and basal membrane may generate the signal involved in the targeting of AQP4 in gastric parietal cells.     

Review article. Studying climate effects on ecology through the use of climate indices: the North Atlantic Oscillation, El Niño Southern Oscillation and beyond

Whereas the El Niño Southern Oscillation (ENSO) affects weather and climate variability worldwide, the North Atlantic Oscillation (NAO) represents the dominant climate pattern in the North Atlantic region. Both climate systems have been demonstrated to considerably influence ecological processes. Several other large-scale climate patterns also exist. Although less well known outside the field of climatology, these patterns are also likely to be of ecological interest. We provide an overview of these climate patterns within the context of the ecological effects of climate variability. The application of climate indices by definition reduces complex space and time variability into simple measures, ''packages of weather''. The disadvantages of using global climate indices are all related to the fact that another level of problems are added to the ecology-climate interface, namely the link between global climate indices and local climate. We identify issues related to: (i) spatial variation; (ii) seasonality; (iii) non-stationarity; (iv) nonlinearity; and (v) lack of correlation in the relationship between global and local climate. The main advantages of using global climate indices are: (i) biological effects may be related more strongly to global indices than to any single local climate variable; (ii) it helps to avoid problems of model selection; (iii) it opens the possibility for ecologists to make predictions; and (iv) they are typically readily available on Internet.     

The morphology and distribution of 'Kolmer-Agduhr cells', a class of cerebrospinal-fluid-contacting neurons revealed in the frog embryo spinal cord by GABA immunocytochemistry

An immunocytochemical method that localizes GABA in glutaraldehyde-fixed tissue has been applied to the study of the Xenopus embryo spinal cord. This procedure stained an anatomical class of neuron, which had somata forming two more or less continuous rows, one on either side of the central canal, in the ventral part of the spinal cord. The total number of stained neurons in the stage 37-38 embryo spinal cord was about 300. The medial surface on the soma protruded into the central canal and had a brush border which electron microscope studies showed to consist of many microvilli or stereocilia and one or two cilia. The external end of the neuron soma had an ipsilateral ascending axon. The axon of many of these neurons had a growth cone which was also clearly stained. We propose calling these neurons 'Kolmer-Agduhr cells' after W. Kolmer and E. Agduhr who described them in the spinal cords of many vertebrate classes. Their early embryonic origin, GABA-like immunoreactivity, axonal projections and distribution as a whole population have not previously been known.     

Evaluation of the immunocytochemical method for amino acids

Free amino acids can be coupled to proteins by glutaraldehyde. Rabbits immunised with a bovine serum albumin-glutaraldehyde-amino acid conjugate form antibodies that recognise similar conjugates with brain proteins in glutaraldehyde-fixed tissue. Antisera raised against conjugated GABA (gamma-aminobutyrate), glutamate, aspartate, taurine, glutamine, or glycine were tested against a variety of small molecular compounds that had been fixed by glutaraldehyde to brain protein and immobilised on cellulose ester filters for processing together with the brain sections. This system permitted closely similar conditions for testing and immunocytochemistry. After removing antibodies against the carrier used for immunisation and against cross reacting amino acid conjugates the antisera showed a high specificity. The specific nature of the antisera was corroborated by solid phase adsorption to the homologous antigens and by inhibition experiments with free amino acids and amino acid-glutaraldehyde fixation complexes. After transection of the striatonigral pathway the ipsilateral substantia nigra was almost depleted of GABA-like immunoreactivity; this observation lends additional support to the selectivity of the GABA antiserum. A semiquantitative relation was established between the concentration of amino acid before fixation in a model system and the subsequent intensity of immunostaining. Similar model experiments suggested that the conjugation of an amino acid to brain protein with glutaraldehyde, and the immunoreactivity of the conjugates, may be significantly inhibited in the presence of high concentrations of other amino compounds.