Enhancement of NMDA-mediated responses by cyanide

The effect of cyanide on NMDA-activated ion current and MK801 binding was studied in cultured rat hippocampal neurons. In microfluorometric analysis using fura-2, removal of extracellular Mg²⁺ resulted in a five-fold increase in NMDA-induced peak of [Ca²⁺]_i. One mM NaCN enhanced the peak NMDA responses in the presence, but not in the absence of extracellular Mg²⁺. Cyanide enhanced the immediate rise in [Ca²⁺]_i produced by NMDA, followed over a 1–5 min period by a gradual increase of [Ca²⁺]_i. Similar results were obtained in whole-cell patch clamp recordings from hippocampal neurons. One mM KCN enhanced the NMDA-activated current in the presence, but not in the absence of extracellular Mg²⁺. This effect was independent of cyanide-mediated metabolic inhibition since the recording pipette contained ATP (2 mM). In binding assays NaCN (1 mM) increased the binding affinity of [³H]MK-801 to rat forebrain membranes in the presence of Mg²⁺, whereas in the absence of Mg²⁺, NaCN did not influence binding. These results indicate that cyanide enhances NMDA-mediated Ca²⁺ influx and inward current by interacting with the Mg²⁺ block of the NMDA receptor. The effect of cyanide can be explained by an initial interaction with the Mg²⁺ block of the NMDA receptor/ionophore which appears to be energy-independent, followed by a gradual increase in Ca²⁺ influx resulting from cellular energy reserve depletion.Abbreviations NMDA N-Methyl-D-Aspartate - EAA excitatory amino acid - MK-801 (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohept-5,10-imine maleate     

Studies on the striatal dopamine uptake system of weaver mutant mice and effects of ventral mesencephalic grafts

The dopamine (DA) uptake system was investigated in the mesostriatal system of normal and weaver mutant mice, which lose mesencephalic DA neurons, as well as in weaver mutants with ventral mesencephalic grafts to the striatum. Assays of [³H]DA uptake in striatal synaptosomal fractions in vitro and autoradiography of [³H]mazindol binding in brain sections were carried out in wild-type mice (+/+) and in the two hemispheres of homozygous weaver mutants (wv/wv) that had received unilateral grafts of mesencephalic cell suspensions to the right side. Net [³H]DA uptake, expressed as pmol/mg-protein/2-min, was on the average 50.6 in the striatum of wild-type mice, 7.9 in the non-grafted, and 10.1 in the transplanted striatum of weaver mutants. [³]DA uptake in wild-type mice differed significantly from both the grafted and non-grafted weaver striata (P<0.001). Paired comparisons for [³H]DA uptake between right and left sides of recipient weaver mice showed a significant side effect (P<0.02), the right side being 28–38% higher than the left side [mean of all individual (R-L)/L values]. The results of amphetamine-induced turning behavior tests were compared with the biochemical findings. Mice with grafts to the right side rotated an average of 22 turns to the left and 7 turns to the right during the five one-minute sessions; the mean value L/(L+R) was 64%. A plot of (L-R) rotations against (R-L) [³H]DA uptake gave a correlation coefficient of 0.552 (P<0.05), indicating that animals with a strong rotational bias to the left tended to have higher [³H]DA on the right. Similarly, the animals that were used for [³H]mazindol binding autoradiographic studies displayed on the average 72% rotations to the left side. In the [³H]mazindol binding data, non-grafted weaver mutants showed the severest depletion relative to wild-type in the dorsomedial and dorsolateral caudate-putamen (86% and 87%, respectively). Mice with unilateral grafts to the right side showed an increase in [³H]mazindol binding signal in the transplanted side of 40–64% (depending on dorsoventral topography) over the contralateral, non-grafted side. These findings attest to the functional effects of the grafts at the anatomical, biochemical, and behavioral levels. The parallel measurements of motor performance and DA uptake in the same animals offers an index of behavioral recovery as a function of transmitter-related activity. Furthermore, by conducting measurements of the synaptosomal DA uptake in vitro and of the binding characteristics of mazindol in brain slices by autoradiography, one has the advantage of combining the anatomical resolution of uptake site visualization with a dynamic indicator of function for DA uptake in the nerve terminal.Special issue dedicated to Professor Sidney Ochs     

Effects of Ca(II) ions on Mn(II) dynamics in chick glia and rat astrocytes: Potential regulation of glutamine synthetase

Previous studies have demonstrated that in glia and astrocytes Mn(II) is distributed with ca. 30–40% in the cytoplasm, 60–70% in mitochondria. Ca(II) ions were observed to alter both the flux rates and distribution of Mn(II) ions in primary cultues of chick glia and rat astrocytes. External (influxing) Ca(II) ions had the greatest effect on Mn(II) uptake and efflux, compared to internal (effluxing) or internal-external equilibrated Ca(II) ions. External (influxing) Ca(II) ions inhibited the net rate and extent of Mn(II) uptake but enhanced Mn(II) efflux from mitochondria. These observations differ from Ca(II)–Mn(II) effects previously reported with brain (neuronal) mitochondria. Overall, increased cytoplasmic Ca(II) acts to block Mn(II) uptake and enhance Mn(II) release by mitochondria, which serve to increase the cytoplasmic concentration of free Mn(II). A hypothesis is presented involving external L-glutamate acting through membrane receptors to mobilize cell Ca(II), which in turn causes mitochondrial Mn(II) to be released. Because the concentration of free cytoplasmic Mn(II) is poised near the K_d for Mn(II) with glutamine synthetase, a slight increase in cytoplasmic Mn(II) will directly enhance the activity of glutamine synthetase, which catalyzes removal of neurotoxic glutamate and ammonia.     

Regulation of N-Methyl-d-aspartate receptor-mediated calcium transport and norepinephrine release in rat hippocampus synaptosomes by polyamines

The role of polyamines (PA) synthesis in NMDA receptor-mediated⁴⁵Ca²⁺ fluxes and norepinephrine release was studied in rat hippocampal synaptosomes. NMDA (50M) caused a sharp (>2-fold) transient increase in PA synthesis regulating enzyme, ornithine decarboxylase (ODC) activity with concomitant elevation in PA levels in the order putrescine>spermidine>spermine. ODC inhibitor, -difluoromethylornithine (DFMO), and NMDA antagonist, 2-amino-5-phosphonovaleric acid (D-AP5), both blocked increases in ODC activity and PA levels. Activation of NMDA receptors induced a sharp (3 to 4-fold) and quick (15 seconds) increase in⁴⁵Ca²⁺ uptake by synaptosomes within 15 seconds of exposure at 37°C. The efflux of⁴⁵Ca²⁺ and³H-norepinephrine (NE) release at 22°C from pre-loaded synaptosomes was also significantly (2 to 4-fold) enhanced by NMDA within 15 seconds. These NMDA receptor-mediated effects on calcium fluxes and NE release were blocked by NMDA receptor-antagonists (DAP-5 and MK-801) and PA synthesis inhibitor, DFMO and the DFMO inhibition nullified by exogenous putrescine. These observations establish that ODC/PA cascade play an important role in transduction of excitatory amino acid mediated signals at NMDA receptors.Special issue dedicated to Dr. Sidney Ochs.     

Effect of temperature and growth phase on fatty acid composition of the psychrophilic Vibrio sp. strain no. 5710

Abstract The cellular fatty acid composition of the psychrophilic Vibrio sp. strain No. 5710 isolated from a deep-sea sediment sample was analyzed. The presence of docosahexaenoic acid (22:6) was demonstrated as found previously in other deep-sea bacteria, and the relative amount of 22:6 decreased as the growth temperature increased. A temperature shift from 10°C to 0°C resulted in a relative increase of 22:6, and an opposite shift led to a decrease. In addition, hexadecanoic acid (16:0) was found to increase as the growth temperature increased. Therefore, it is suggested that the adaptation of 5710 to the growth temperature was carried out by the changes in the relative amounts of 22:6 and 16:0. When 5710 was grown at low temperature, it increased the relative amount of 22:6 presumably to maintain membrane fluidity at that temperature. In contrast, 5710 grown at high temperature probably maintained the membrane fluidity by increasing the amount of a saturated fatty acid, 16:0. Furthermore, observation of the fatty acid compositions at mid-exponential phase and early stationary phase revealed the proportions of several fatty acids, including a major fatty acid, 9- cis -hexadecenoic acid (16:1c, palmitoleic acid), were affected by the growth phase which may be due to the physiological difference between the growth phases.     

Reproduction in the North Atlantic oceanic ichthyofauna and the relationship between fecundity and species' sizes

Synopsis The pelagic (589 spp.) and demersal (505 spp.) oceanic ichthyofaunas of the North Atlantic Basin have very different compositions at ordinal and family level. Yet the pattern of relationships between species' maximum size and maximum fecundity from data available (10% of the pelagic, 19% of the demersal species) was similar. A positive relationship between fecundity and weight was confirmed among most teleosts, but was not followed by the elasmobranchs represented. Species' reproductive styles are reviewed in ordinal groupings within a framework of the overall body size/fecundity distribution. Species size (maximum weight) spectra were synthesized for both pelagic and demersal assemblages to assess the allocation of potential reproductive effort throughout the North Atlantic oceanic ichthyofauna. The only available examples of species size spectra and biomass spectra from the pelagic and demersal ichthyofauna in this ocean basin imply geographic and bathymetric variation in overall reproductive effort among fishes whose fecundity is size dependent. Further implications concerning reproductive effort are discussed in the light of food availability.     

USE OF BIOELECTRICAL IMPEDANCE ANALYSIS TO ASSESS BODY COMPOSITION OF SEALS

Abstract: Bioelectrical impedance analysis (BIA) measures resistance and reactance of a current as it passes through an organism. The validity of using BIA as a tool to measure body water content, and hence body composition and condition, was tested on harp and ringed seals. The resistance and reactance readings from BIA were compared to estimates of total body water (TBW) determined via tritiated water dilution. The relationship between resistance and TBW (% of body mass) was linear after logarithmic transformation and the two variables were highly correlated. We describe the electrode configuration and placements which provide reliable results in these seals. Our findings indicate that BIA has considerable potential as an inexpensive, rapid, and reliable technique for estimating body composition of phocid seals.     

PrP in pathology and pathogenesis in scrapie-infected mice

PrP accumulation in the brains of mice infected with scrapie takes several different forms: amyloid plaques, widespread accumulation in neuropile, and perineuronal deposits. PrP is also sometimes detected within microglia and in or around astrocytes. There are dramatic and reproducible differences between scrapie strains in the relative prominence of these changes and their distribution in the brain. Depending on the scrapie strain, PrP pathology is targeted precisely to particular brain areas, often showing a clear association with identifiable groups of neurons. These results suggest that PrP changes are primarily associated with neurons, and that different scrapie strains recognize and selectively replicate in different populations of neurons. Immunostaining at the ultrastructural level demonstrates an association of PrP with neurite plasmalemma, around amyloid plaques, and in areas of widespread neuropile and perineuronal accumulation. It is probable that PrP is encoded by theSinc gene, which controls the incubation period of scrapie in mice. Studies using the intraocular infection route show that theSinc gene controls the onset rather than the rate of replication, suggesting that PrP may be involved in cell-to-cell spread of infection. The accumulation of PrP at the surface of neurons is consistent with such a role.     

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.Author for correspondence     

Guanine nucleotide regulatory protein alterations in young Milan hypertensive strain rats

Vascular smooth muscle cell membranes from prehypertensive rats of the Milan hypertensive strain (MHS) were used to examine adenylyl cyclase activity and its regulation by guanine nucleotide regulatory proteins (G-proteins). Basal adenylyl cyclase activity was similar in MHS and Milan normontensive strain (MNS) membranes. Forsokolin (10^?4 M) produced a significantly greater stimulatory response in MHS membranes, but this was not observed with NaF (10^?2 M). Isoporterenol (10^?4 M) caused a significantly decreased stimulation of adenylyl cyclase activity in MHS membranes, while prostaglandin E₁ (10^?5 M) produced similar responses in the two strains. G_i function and GTP responses, as observed by biphasic effects of GTP on isoproterenol-stimulated membranes, were similar in both strains. The levels of G_i2α and G_qα/G₁₁α were similar in the two strains, while the levels of G_sα (44 and 42 kDa forms) and the β-subunit were significantly reduced by ～20% in MHS membranes. The α-subunit of G_i3 was dramatically reduced by ～80% in MHS membranes. The affinities of β-adrenergic receptors for the antagonist, cyanophindolol, were similar in the two strains; however, the number of β-adrenoceptors was substantially reduced in MHS membranes. These findings may be of relevance to altered vascular reactivity and transmembrane ion distribution observed in the MHS.