@article{3756, abstract = {In many eukaryotic cells going through M-phase, a bipolar spindle is formed by microtubules nucleated from centrosomes. These microtubules, in addition to being `'captured” by kinetochores, may be stabilized by chromatin in two different ways: short-range stabilization effects may affect microtubules in close contact with the chromatin, while long-range stabilization effects may `'guide” microtubule growth towards the chromatin (e.g., by introducing a diffusive gradient of an enzymatic activity that affects microtubule assembly). Here, we use both meiotic and mitotic extracts from Xenopus laevis eggs to study microtubule aster formation and microtubule dynamics in the presence of chromatin. In `'low-speed” meiotic extracts, in the presence of salmon sperm chromatin, we find that short-range stabilization effects lead to a strong anisotropy of the microtubule asters. Analysis of the dynamic parameters of microtubule growth shows that this anisotropy arises from a decrease in the catastrophe frequency, an increase in the rescue frequency and a decrease in the growth velocity. In this system we also find evidence for long-range `'guidance” effects, which lead to a weak anisotropy of the asters. Statistically relevant results on these long-range effects are obtained in `'high-speed” mitotic extracts in the presence of artificially constructed chromatin stripes. We find that aster anisotropy is biased in the direction of the chromatin and that the catastrophe frequency is reduced in its vicinity. In this system we also find a surprising dependence of the catastrophe and the rescue frequencies on the length of microtubules nucleated from centrosomes: the catastrophe frequency increases and the rescue frequency decreases with microtubule length.}, author = {Dogterom, Marileen and Felix, M. and Guet, Calin C and Leibler, Stanislas}, issn = {0021-9525}, journal = {Journal of Cell Biology}, number = {1}, pages = {125 -- 140}, publisher = {Rockefeller University Press}, title = {{Influence of M-phase chromatin on the anisotropy of microtubule asters}}, doi = {doi: 10.1083/jcb.133.1.125 }, volume = {133}, year = {1996}, } @article{4025, abstract = {Questions of chemical reactivity can often be cast as questions of molecular geometry. Common geometric models for proteins and other molecules are the space-filling diagram, the solvent accessible surface and the molecular surface. In this paper we present a new approach to triangulating the surface of a molecule under the three models, which is fast, robust, and results in topologically correct triangulations. Our computations are based on a simplicial complex dual to the molecule models. All proposed algorithms are parallelizable.}, author = {Akkiraju, Nataraj and Edelsbrunner, Herbert}, issn = {0166-218X}, journal = {Discrete Applied Mathematics}, number = {1-3}, pages = {5 -- 22}, publisher = {Elsevier}, title = {{Triangulating the surface of a molecule}}, doi = {10.1016/S0166-218X(96)00054-6}, volume = {71}, year = {1996}, } @misc{4030, author = {Liang, Jie and Edelsbrunner, Herbert and Subramaniam, Shankar}, booktitle = {Fortieth Annual Meeting}, number = {2, Part 2}, pages = {A224 -- A224}, publisher = {Cell Press}, title = {{Effects of molecular shape representations on boundary element method for protein electrostatics computations}}, doi = {10.1016/S0006-3495(96)79664-9}, volume = {70}, year = {1996}, } @misc{4031, author = {Liang, Jie and Edelsbrunner, Herbert and Pamidghantam, Sudhakar and Subramaniam, Shankar}, booktitle = {Fortieth Annual Meeting}, number = {2, Part 2}, pages = {A377 -- A377}, publisher = {Cell Press}, title = {{Analytical method for molecular shapes: Area, volume, cavities, interface and pockets}}, doi = {10.1016/S0006-3495(96)79670-4}, volume = {70}, year = {1996}, } @article{4166, abstract = {In a large scale screen for mutants with defects in the embryonic development of the zebrafish we identified mutations in four genes, floating head (flh), memo (mom), no tail (ntl), and dec, that are required for early notochord formation. Mutations in flh and ntl have been described previously, while mom and doe are newly identified genes. Mutant mom embryos lack a notochord in the trunk, and trunk somites from the right and left side of the embryo fuse underneath the neural tube. In this respect morn appears similar to flh. In contrast, notochord precursor cells are present in both ntl and doc embryos. In order to gain a greater understanding of the phenotypes, we have analysed the expression of several axial mesoderm markers in mutant embryos of all four genes. In flh and mom, Ntl expression is normal in the germ ring and tailbud, while the expression of Nd and other notochord markers in the axial mesodermal region is disrupted. Nd expression is normal in doc embryos until early semitic stages, when there is a reduction in expression which is first seen in anterior regions of the embryo. This suggests a function for doc in the maintenance of ntl expression. Other notochord markers such as twist, sonic hedgehog and axial are not expressed in the axial mesoderm of ntl embryos, their expression parallels the expression of ntl in the axial mesoderm of mutant doc,flh and mom embryos, indicating that ntl is required for the expression of these markers. The role of doc in the expression of the notochord markers appears indirect via ntl. Floor plate formation is disrupted in most regions in flh and mom mutant embryos but is present in mutant ntl and doc embryos. In mutant embryos with strong ntl alleles the band of cells expressing floor plate markers is broadened. A similar broadening is also observed in the axial mesoderm underlying the floor plate of ntl embryos, suggesting a direct involvement of the notochord precursor cells in floor plate induction. Mutations in al of these four genes result in embryos lacking a horizontal myoseptum and muscle pioneer cells, both of which are thought to be induced by the notochord. These somite defects can be traced back to an impairment of the specification of the adaxial cells during early stages of development. Transplantation of wild-type cells into mutant doc embryos reveals that wild-type notochord cells are sufficient to induce horizontal myoseptum formation in the flanking mutant tissue. Thus dec, like flh and ntl, acts cell autonomously in the notochord. In addition to the four mutants with defects in early notochord formation, we have isolated 84 mutants, defining at least 15 genes, with defects in later stages of notochord development. These are listed in an appendix to this study.}, author = {Odenthal, Jörg and Haffter, Pascal and Vogelsang, Elisabeth and Brand, Michael and Van Eeden, Fredericus and Furutani Seiki, Makoto and Granato, Michael and Hammerschmidt, Matthias and Heisenberg, Carl-Philipp J and Jiang, Yunjin and Kane, Donald and Kelsh, Robert and Mullins, Mary and Warga, Rachel and Allende, Miguel and Weinberg, Eric and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, number = {1}, pages = {103 -- 115}, publisher = {Company of Biologists}, title = {{Mutations affecting the formation of the notochord in the zebrafish, Danio rerio}}, doi = {10.1242/dev.123.1.103}, volume = {123}, year = {1996}, } @article{4215, abstract = {In a screen for early developmental mutants of the zebrafish, we have identified mutations specifically affecting the internal organs, We identified 53 mutations affecting the cardiovascular system, Nine of them affect specific landmarks of heart morphogenesis. Mutations in four genes cause a failure in the fusion of the bilateral heart primordia, resulting in cardia bifida. In lonely atrium, no heart venticle is visible and the atrium is directly fused to the outflow tract. In the overlooped mutant, the relative position of the two heart chambers is distorted, The heart is enormously enlarged in the santa mutant, In two mutants, scotch tape and superglue, the cardiac jelly between the two layers of the heart is significantly reduced, We also identified a number of mutations affecting the function of the heart, The mutations affecting heart function can be subdivided into two groups, one affecting heart contraction and another affecting the rhythm of the heart beat. Among the contractility group of mutants are 5 with no heart beat at all and 15 with a reduced heart beat of one or both chambers, 6 mutations are in the rhythmicity group and specifically affect the beating pattern of the heart, Mutations in two genes, bypass and kurzschluss, cause specific defects in the circulatory system, In addition to the heart mutants, we identified 23 mutations affecting the integrity of the liver, the intestine or the kidney, In this report, we demonstrate that it is feasible to screen for genes specific for the patterning or function of certain internal organs in the zebrafish, The mutations presented here could serve as an entrypoint to the establishment of a genetic hierarchy underlying organogenesis.}, author = {Chen, Jaunian and Haffter, Pascal and Odenthal, Jörg and Vogelsang, Elisabeth and Brand, Michael and Van Eeden, Fredericus and Furutani Seiki, Makoto and Granato, Michael and Hammerschmidt, Matthias and Heisenberg, Carl-Philipp J and Jiang, Yunjin and Kane, Donald and Kelsh, Robert and Mullins, Mary and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, pages = {293 -- 302}, publisher = {Company of Biologists}, title = {{Mutations affecting the cardiovascular system and other internal organs in zebrafish}}, doi = {10.1242/dev.123.1.293}, volume = {123}, year = {1996}, } @article{4216, abstract = {Tissues of the dorsal midline of vertebrate embryos, such as notochord and floor plate, have been implicated in inductive interactions that pattern the neural tube and somites. In our screen for embryonic visible mutations in the zebrafish we found 113 mutations in more than 27 genes with altered body shape, often with additional defects in CNS development. We concentrated on a subgroup of mutations in ten genes (the midline-group) that cause defective development of the floor plate. By using floor plate markers, such as the signaling molecule sonic hedgehog, we show that the schmalspur (sur) gene is needed for early floor plate development, similar to one-eyed-pinhead (oep) and the previously described cyclops (eye) gene. In contrast to oep and cyc, sur embryos show deletions of ventral CNS tissue restricted to the mid- and hindbrain, whereas the forebrain appears largely unaffected. In the underlying mesendodermal tissue of the head, sur is needed only for development of the posterior prechordal plate, whereas oep and eye are required for both anterior and posterior prechordal plate development. Our analysis of sur mutants suggests that defects within the posterior prechordal plate may cause aberrant development of ventral CNS structures in the mid- and hindbrain. Later development of the floor plate is affected in mutant chameleon, you-too, sonic-you, iguana, detour, schmalkars and monorail embryos; these mutants often show additional defects in tissues that are known to depend on signals from notochord and floor plate, For example, sur, con, and yot mutants show reduction of motor neurons; median deletions of brain tissue are seen in sur, con and yot embryos; and eye, con, yet, igu and dtr mutants often show no or abnormal formation of the optic chiasm. We also find fusions of the ventral neurocranium for all midline mutants tested, which may reveal a hitherto unrecognized function of the midline in influencing differentiation of neural crest cells at their destination. As a working hypothesis, we propose that midline-group genes may act to maintain proper structure and inductive function of zebrafish midline tissues.}, author = {Brand, Michael and Heisenberg, Carl-Philipp J and Warga, Rachel and Pelegri, Francisco and Karlstrom, Rolf and Beuchle, Dirk and Picker, Alexander and Jiang, Yunjin and Furutani Seiki, Makoto and Van Eeden, Fredericus and Granato, Michael and Haffter, Pascal and Hammerschmidt, Matthias and Kane, Donald and Kelsh, Robert and Mullins, Mary and Odenthal, Jörg and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, number = {1}, pages = {129 -- 142}, publisher = {Company of Biologists}, title = {{Mutations affecting development of the midline and general body shape during zebrafish embryogenesis}}, doi = {10.1242/dev.123.1.129 }, volume = {123}, year = {1996}, } @article{4219, abstract = {Mutations in two genes affect the formation of the boundary between midbrain and hindbrain (MHB): no isthmus (noi) and acerebellar (ace), noi mutant embryos lack the MHB constriction, the cerebellum and optic tectum, as well as the pronephric duct. Analysis of noi mutant embryos with neuron-specific antibodies shows that the MHB region and the dorsal and ventral midbrain are absent or abnormal, but that the rostral hindbrain is unaffected with the exception of the cerebellum, Using markers that are expressed during its formation (eng, wnt1 and pax-b), we find that the MHB region is already misspecified in noi mutant embryos during late gastrulation. The tectum is initially present and later degenerates, The defect in ace mutant embryos is more restricted: MHB and cerebellum are absent, but a tectum is formed, Molecular organisation of the tectum and tegmentum is disturbed, however, since eng, wntl and pax-b marker gene expression is not maintained, We propose that noi and ace are required for development of the MHB region and of the adjacent mid- and hindbrain, which are thought to be patterned by the MHB region, Presence of pax-b RNA, and absence of pax-b protein, together with the observation of genetic linkage and the occurrence of a point mutation, show that noi mutations are located in the pax-b gene, pax-b is a vertebrate orthologue of the Drosophila gene paired, which is involved in a pathway of cellular interactions at the posterior compartment boundary in Drosophila, Our results confirm and extend a previous report, and show that at least one member of this conserved signalling pathway is required for formation of the boundary between midbrain and hindbrain in the zebrafish.}, author = {Brand, Michael and Heisenberg, Carl-Philipp J and Jiang, Yunjin and Beuchle, Dirk and Lun, Klaus and Furutani Seiki, Makoto and Granato, Michael and Haffter, Pascal and Hammerschmidt, Matthias and Kane, Donald and Kelsh, Robert and Mullins, Mary and Odenthal, Jörg and Van Eeden, Fredericus and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, number = {1}, pages = {179 -- 190}, publisher = {Company of Biologists}, title = {{Mutations in zebrafish genes affecting the formation of the boundary between midbrain and hindbrain}}, doi = {10.1242/dev.123.1.179 }, volume = {123}, year = {1996}, } @article{4220, abstract = {In the zebrafish, Danio rerio, a caudal and pectoral fin fold develop during embryogenesis. At larval stages the caudal fin fold is replaced by four different fins, the unpaired anal, dorsal and tail fins. In addition the paired pelvic fins are formed, We have identified a total of 118 mutations affecting larval fin formation, Mutations in 11 genes lead to abnormal morphology or degeneration of both caudal and pectoral fin folds, Most mutants survive to adulthood and form a surprisingly normal complement of adult fins, Mutations in nine genes result in an increased or reduced size of the pectoral fins, Interestingly, in mutants of one of these genes, dackel (dak), pectoral fin buds form initially, but later the fin epithelium fails to expand, Expression of sonic hedgehog mRNA in the posterior mesenchyme of the pectoral fin bud is initiated in dak embryos, but not maintained, Mutations in five other genes affect adult fin but not larval fin development, Two mutants, longfin (lof) and another longfin (alf) have generally longer fins. Stein und bein (sub) has reduced dorsal and pelvic fins, whereas finless (fls) and wanda (wan) mutants affect all adult fins, Finally, mutations in four genes causing defects in embryonic skin formation will be briefly reported.}, author = {Van Eeden, Fredericus and Granato, Michael and Schach, Ursula and Brand, Michael and Furutani Seiki, Makoto and Haffter, Pascal and Hammerschmidt, Matthias and Heisenberg, Carl-Philipp J and Jiang, Yunjin and Kane, Donald and Kelsh, Robert and Mullins, Mary and Odenthal, Jörg and Warga, Rachel and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, number = {1}, pages = {255 -- 262}, publisher = {Company of Biologists}, title = {{Genetic analysis of fin formation in the zebrafish, Danio rerio}}, doi = {10.1242/dev.123.1.255 }, volume = {123}, year = {1996}, } @article{4222, abstract = {Somitogenesis is the basis of segmentation of the mesoderm in the trunk and tail of vertebrate embryos, Two groups of mutants with defects in this patterning process have been isolated in our screen for zygotic mutations affecting the embryonic development of the zebrafish (Danio rerio), In mutants of the first group, boundaries between individual somites are invisible early on, although the paraxial mesoderm is present, Later, irregular boundaries between somites are present, Mutations infused somites (fss) and beamter (bea) affect all somites, whereas mutations in deadly seven (des), after eight (aei) and white tail (wit) only affect the more posterior somites, Mutants of all genes but wit are homozygous viable and fertile, Skeletal stainings and the expression pattern of myoD and snail1 suggest that anteroposterior patterning within individual somites is abnormal, In the second group of mutants, formation of the horizontal myoseptum, which separates the dorsal and ventral part of the myotome, is reduced, Six genes have been defined in this group (you-type genes), yea-too mutants show the most severe phenotype; in these the adaxial cells, muscle pioneers and the primary motoneurons are affected, in addition to the horizontal myoseptum. The horizontal myoseptum is also missing in mutants that lack a notochord. The similarity of the somite phenotype in mutants lacking the notochord and in the you-type mutants suggests that the genes mutated in these two groups are involved in a signaling pathway from the notochord, important for patterning of the somites.}, author = {Van Eeden, Fredericus and Granato, Michael and Schach, Ursula and Brand, Michael and Furutani Seiki, Makoto and Haffter, Pascal and Hammerschmidt, Matthias and Heisenberg, Carl-Philipp J and Jiang, Yunjin and Kane, Donald and Kelsh, Robert and Mullins, Mary and Odenthal, Jörg and Warga, Rachel and Allende, Miguel and Weinberg, Eric and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, number = {1}, pages = {153 -- 164}, publisher = {Company of Biologists}, title = {{Mutations affecting somite formation and patterning in the zebrafish, Danio rerio}}, doi = {10.1242/dev.123.1.153}, volume = {123}, year = {1996}, } @inbook{4295, abstract = {Genetic studies are beginning to provide insights into the evolutionary processes that reduce the fitness of hybrids between recently diverged species. However, the deleterious gene interactions responsible for this fitness reduction are still poorly understood.}, author = {Barton, Nicholas H}, booktitle = {Current Biology}, issn = {0960-9822}, pages = {1244 -- 1246}, publisher = {Cell Press}, title = {{Speciation: more than the sum of its parts}}, doi = {10.1016/S0960-9822(02)70707-0}, volume = {6}, year = {1996}, } @article{2559, abstract = {Taking advantage of the restricted expression of metabotropic glutamate receptor subtype 6 (mGIuR6) in retinal ON bipolar cells, we generated knockout mice lacking mGIuR6 expression. The homozygous mutant mice showed a loss of ON responses but unchanged OFF responses to light. The mutant mice displayed no obvious changes in retinal cell organization nor in the projection of optic fibers to the brain. Furthermore, the mGIuR6-deficient mice showed visual behavioral responses to light stimulation as examined by shuttle box avoidance behavior experiments using light exposure as a conditioned stimulus. The results demonstrate that mGIuR6 is essential in synaptic transmission to the ON bipolar cell and that the OFF response provides an important means for transmitting visual information.}, author = {Masu, Masayuki and Iwakabe, Hideki and Tagawa, Yoshiaki and Miyoshi, Tomomitsu and Yamashita, Masayuki and Fukuda, Yutaka and Sasaki, Hitoshi and Hiroi, Kano and Nakamura, Yasuhisa and Shigemoto, Ryuichi and Takada, Masahiko and Nakamura, Kenji and Nakao, Kazuki and Katsuki, Motoya and Nakanishi, Shigetada}, issn = {0092-8674}, journal = {Cell}, number = {5}, pages = {757 -- 765}, publisher = {Cell Press}, title = {{Specific deficit of the ON response in visual transmission by targeted disruption of the mGIuR6 gene}}, doi = {10.1016/0092-8674(95)90354-2}, volume = {80}, year = {1995}, } @article{1943, abstract = {Transhydrogenase from beef-heart mitochondria was solubilised with Triton X-100 and purified by column chromatography. The detergent-dispersed enzyme catalysed the reduction of acetylpyridine adenine dinucleotide (AcPdAD+) by NADH, but only in the presence of NADP+. Experiments showed that this reaction was cyclic; NADP(H), whilst remaining bound to the enzyme, was alternately reduced by NADH and oxidised by AcPdAD+. A period of incubation of the enzyme with NADPH at pH 6.0 led to inhibition of the simple transhydrogenation reaction between AcPdAD+ and NADPH. However, after such treatment, transhydrogenase acquired the ability to catalyse the (NADPH-dependent) reduction of AcPdAD+ by NADH. It is suggested that this is a similar cycle to the one described above. Evidently, the binding affinity for NADP+ increases as a consequence of the inhibition process resulting from prolonged incubation with NADPH. The pH dependences of simple and cyclic transhydrogenation reactions are described. Though more complex than those in Escherichia coli transhydrogenase, they are consistent with the view [Hutton, M., Day, J.M., Bizouarn, T. and Jackson, J.B. (1994) Eur. J. Biochem. 219, 1041–10511] that, also in the mitochondrial enzyme, binding the release of NADP+ and NADP are accompanied by binding and release of a proton. The enzyme was successfully reconstituted into liposomes by a cholate dilution procedure. The proteoliposomes catalysed cyclic NADPH-dependent reduction of AcPdAD+ by NADH only when they were tightly coupled. However, they catalysed cyclic NADP+-dependent reduction of AcPdAD+ by NADH only when they were uncoupled eg. by addition of carbonylcyanide-p-trifluoromethoxyphenyl hydrazone. These observations are evidence that the proton binding and release which accompany NADP+ binding and release, respectively, take place on the inside of the vesicle, and that they are components of the electrogenic processes of the enzyme.}, author = {Sazanov, Leonid A and Jackson, Baz}, issn = {0005-2728}, journal = {Biochimica et Biophysica Acta - Bioenergetics}, number = {3}, pages = {304 -- 312}, publisher = {Elsevier}, title = {{Cyclic reactions catalysed by detergent-dispersed and reconstituted transhydrogenase from beef heart mitochondria; implications for the mechanism of proton translocation}}, doi = {10.1016/0005-2728(95)00096-2}, volume = {1231}, year = {1995}, } @inproceedings{11928, abstract = {We present a model with restricted randomness for edge updates in dynamic graph algorithms and a general technique for analyzing the expected running time of an update operation. This model is able to capture the average case in many applications, since (1) it allows restrictions on the set of edges which can be used for insertions and (2) the type (insertion or deletion) of each update operation is arbitrary, i.e., not random. We use our technique to analyze existing and new dynamic algorithms for maximum cardinality matching, minimum spanning forest, connectivity, 2-edge connectivity, k-edge connectivity, k-vertex connectivity, and bipartiteness. Given a random graph G with mo edges and n vertices and a sequence of 1 update operations such that the graph contains rni edges after operation i, the expected time for performing the updates for any 1 is O(1 logn + n xi=, l/fii) in the case of minimum spanning forests, connectivity, 2- edge connectivity, and bipartiteness. The expected time per update operation is O(n) in the case of maximum matching. For k-edge and k-vertex connectivity we also give improved bounds. Additionally we give an insertions-only algorithm for maximum cardinality matching with worst-case O(n) amortized time per insertion. }, author = {Alberts, David and Henzinger, Monika H}, booktitle = {6th Annual ACM-SIAM Symposium on Discrete Algorithms}, isbn = {0898713498}, location = {San Francisco, CA, United States}, pages = {312--321}, publisher = {Society for Industrial and Applied Mathematics}, title = {{Average case analysis of dynamic graph algorithms}}, year = {1995}, } @article{3461, author = {Jonas, Peter M and Burnashev, Nail}, issn = {0896-6273}, journal = {Neuron}, number = {5}, pages = {987 -- 990}, publisher = {Elsevier}, title = {{Molecular mechanisms controlling calcium entry through AMPA-type glutamate receptor channels}}, doi = {10.1016/0896-6273(95)90087-X}, volume = {15}, year = {1995}, } @article{3478, abstract = {1. Properties of dendritic glutamate receptor (GluR) channels were investigated using fast application of glutamate to outside-out membrane patches isolated from the apical dendrites of CA3 and CA1 pyramidal neurons in rat hippocampal slices. CA3 patches were formed (15-76 μm from the soma) in the region of messy fibre (MF) synapses, and CA1 patches (25-174 μm from the soma) in the region of Schaffer collateral (SC) innervation. 2. Dual-component responses consisting of a rapidly rising and decaying component followed by a second, substantially slower, component were elicited by 1 ms pulses of 1 mM glutamate in the presence of 10 μM glycine and absence of external Mg2+. The fast component was selectively blocked by 2-5 μM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and the slow component by 30 μM D-2-amino-5-phosphonopentanoic acid (D-AP5), suggesting that the fast and slow components were mediated by the GluR channels of the L-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and NMDA type, respectively. The peak amplitude ratio of the NMDA to AMPA receptor-mediated components varied between 0.03 and 0.62 in patches from both CA3 and CA1 dendrites. Patches lacking either component were rarely observed. 3. The peak current-voltage (I-V) relationship of the fast component was almost linear, whereas the I-V relationship of the slow component showed a region of negative slope in the presence of 1 mM external Mg2+. The reversal potential for both components was close to 0 mV. 4. Kainate-preferring GluR channels did not contribute appreciably to the response to glutamate. The responses to 100 ms pulses of 1 mM glutamate were mimicked by application of 1 mM AMPA, whereas 1 mM kainate produced much smaller, weakly desensitizing currents. This suggests that the fast component is primarily mediated by the action of glutamate on AMPA-preferring receptors. 5. The mean elementary conductance of AMPA receptor channels was about 10 pS, as estimated by non-stationary fluctuation analysis. The permeability of these channels to Ca2+ was low (~5% of the permeability to Cs+). 6. The elementary conductance of NMDA receptor channels was larger, with a main conductance state of about 45 pS. These channels were 3.6 times more permeable to Ca2+ than to Cs+. 7. AMPA receptor-mediated currents activated rapidly in response to 1 ms pulses of 1 mM glutamate and deactivated with a predominant, fast time constant and a smaller, slower component (τ1≃2 ms, τ2≃8 ms, contributing ~80 and ~20% to the total decay amplitude, respectively). Desensitization of the current during a 100 ms pulse was best fitted by two time constants (τ1≃10 ms, ~60%; τ2≃34 ms, ~40%). 8. NMDA receptor-mediated currents in response to 1 ms pulses of 1 mM glutamate activated and deactivated much more slowly than AMPA receptor-mediated currents. The time course could be described by a single exponential rising phase (τ≃7 ms) followed by a double exponential decay (τ1≃200 ms, ~80%; τ2≃1-3 s, ~20%). 9. Mg2+ blocked the NMDA component in a voltage-dependent manner, with a half-maximal inhibitory concentration (IC50) of 21 μM at -80 mV. At physiological Mg2+ concentrations, block of the NMDA component could be rapidly relieved with voltage jumps from negative to positive potentials. Block of the current upon return to negative potentials occurred almost instantaneously. 10. Zn2+ also selectively-blocked the NMDA receptor-mediated current with an IC50 of 22 μM, but this block differed from that of Mg2+ in that it showed little voltage dependence. Rapid application of Zn2+ together with glutamate produced partial block of the current. More block was observed if Zn2+ and glutamate were co-applied when NMDA receptor channels were already open. 11. The functional properties of dendritic GluRs were similar to those found at the soma. Knowledge of these properties facilitated simulations investigating the contribution of coactivated AMPA and NMDA receptors to synaptic depolarization and Ca2+ entry into dendritic spines. Because of its slow deactivation, the NMDA receptor-mediated current contributes substantially to depolarization and Ca2+ entry and is susceptible to modulation over a period of seconds, either by backpropagating action potentials or by the release of Zn2+ from presynaptic boutons.}, author = {Spruston, Nelson and Jonas, Peter M and Sakmann, Bert}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {Pt 2}, pages = {325 -- 352}, publisher = {Wiley-Blackwell}, title = {{Dendritic glutamate receptor channels in rat hippocampal CA3 and CA1 pyramidal neurons}}, doi = {10.1113/jphysiol.1995.sp020521}, volume = {482}, year = {1995}, } @article{3479, abstract = {1. Glutamate receptor (GluR) channels were studied in basket cells in the dentate gyrus of rat hippocampal slices. Basket cells were identified by their location, dendritic morphology and high frequency of action potentials generated during sustained current injection. 2. Dual-component currents were activated by fast application of glutamate to outside-out membrane patches isolated from basket cell somata (10 μM glycine, no external Mg2+). The fast component was selectively blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), the slow component by D-2-amino-5-phosphonopentanoic acid (D-AP5). This suggests that the two components were mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor (AMPAR)/kainate receptor and N-methyl-D-aspartate receptor (NMDAR) channels, respectively. The mean ratio of the peak current of the NMDAR component to that of the AMPAR/kainate receptor component was 0.22 (1 ms pulses of 10 mM glutamate). 3. The AMPAR/kainate receptor component, which was studied in isolation in the presence of D-AP5, was identified as AMPAR mediated on the basis of the preferential activation by AMPA as compared with kainate, the weak desensitization of kainate-activated currents, the cross-desensitization between AMPA and kainate, and the reduction of desensitization by cyclothiazide. 4. Deactivation of basket cell AMPARs following 1 ms pulses of glutamate occurred with a time constant (τ) of 1.2 ± 0.1 ms (mean ± S.E.M.). During 100 ms glutamate pulses, AMPARs desensitized with a τ of 3.7 ± 0.2 ms. 5. The peak current-voltage (I-V) relation of AMPAR-mediated currents in Na+-rich extracellular solution showed a reversal potential of -4.0 ± 2.6 mV and was characterized by a doubly rectifying shape. The conductance of single AMPAR channels was estimated as 22.6 ± 1.6 pS using non-stationary fluctuation analysis. AMPARs expressed in hippocampal basket cells mere highly Ca2+ permeable (P(Ca)/P(K) = 1.79). 6. NMDARs in hippocampal basket cells were studied in isolation in the presence of CNQX. Deactivation of NMDARs activated by glutamate pulses occurred bi-exponentially with mean τ values of 266 ± 23 ms (76%) and 2620 ± 383 ms (24%). 7. The peak I-V relation of the NMDAR-mediated component in Na+-rich extracellular solution showed a reversal potential of 1.5 ± 0.6 mV and a region of negative slope at negative membrane potentials in the presence of external Mg2+, due to voltage-dependent block by these ions. The conductance of single NMDAR channels in the main open state was 50.2 ± 1.8 pS. NMDARs in hippocampal basket cells were highly permeable to Ca2+ (P(Ca)/P(K) = 6.68). 8. AMPARs in hippocampal basket cells are characterized by about threefold faster kinetics and twentyfold higher Ca2+ permeability than AMPARs in hippocampal granule or pyramidal cells. Simulations show that the Ca2+ influx through basket cell AMPARs is comparable to that through NMDARs at negative membrane potentials with physiological concentrations of Ca2+ and Mg2+. This suggests a dual pathway of synaptically mediated Ca2+ entry into interneurones.}, author = {Koh, Duk and Geiger, Jörg and Jonas, Peter M and Sakmann, Bert}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {Pt 2}, pages = {383 -- 402}, publisher = {Wiley-Blackwell}, title = {{Ca(2+)-permeable AMPA and NMDA receptor channels in basket cells of rat hippocampal dentate gyrus}}, doi = {10.1113/jphysiol.1995.sp020737}, volume = {485}, year = {1995}, } @article{3480, abstract = {Recording of glutamate-activated currents in membrane patches was combine with RT-PCR-mediated AMPA receptor (AMPAR) subunit mRNA analysis in single identified cells of rat brain slices. Analysis of AMPARs in principal neurons end interneurons of hippocampus and neocortex and in auditory relay neurons and Bergmann glial cells indicates that the GluR-B subunit in its flip version determines formation of receptors with relatively slow gating, whereas the GluR-D subunit promotes assembly of more rapidly gated receptors. The relation between Ca 2+ permeability of AMPAR channels and the relative GluR-B mRNA abundance is consistent with the dominance of this subunit in determining the Ca 2+ permeability of native receptors. The results suggest that differential expression of GluR-B and GluR-D subunit genes, as well as splicing end editing of their mRNAs, account for the differences in gating and Ca 2+ permeability of native AMPAR channels.}, author = {Geiger, Jörg and Melcher, Thorsten and Koh, Duk and Sakmann, Bert and Seeburg, Peter and Jonas, Peter M and Monyer, Hannah}, issn = {0896-6273}, journal = {Neuron}, number = {1}, pages = {193 -- 204}, publisher = {Elsevier}, title = {{Relative abundance of subunit mRNAs determines gating and Ca(2+) permeability of AMPA receptors in principal neurons and interneurons in rat CNS}}, doi = {10.1016/0896-6273(95)90076-4}, volume = {15}, year = {1995}, } @article{3481, abstract = {1. The influence of intracellular factors on current rectification of different subtypes of native α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) was studied in rat brain slices by combining fast application of glutamate with patch pipette perfusion. 2. The peak current-voltage (I-V) relation of the AMPARs expressed in Bergmann glial cells of cerebellum and dentate gyrus (DG) basket cells of hippocampus was weakly rectifying in outside-out patches and nystatin-perforated vesicles, but showed a doubly rectifying shape with a region of reduced slope between 0 and +40 mV in nucleated patches. The I-V relation of AMPARs expressed in hippocampal CA3 pyramidal neurones was linear in all recording configurations. 3. Intracellular application of 2.5 μM spermine, a naturally occurring polyamine, blocked outward currents in outside-oat patches from Bergmann glial cells and DG basket cells in a voltage-dependent manner, generating I-V relations with a doubly rectifying shape which were similar to those recorded in nucleated patches. AMPARs in CA3 pyramidal cell patches were unaffected by 25 μM spermine. 4. The half-maximal blocking concentration of spermine at +40 mV was 0.3 μM in Bergmann glial cell patches and 1.5 μM in DG basket cell patches, whereas it was much higher (≥ 100 μM) for CA3 pyramidal. cell patches. Spermidine also affected current rectification, but with lower affinity. The block of outward current by polyamines following voltage jumps developed within < 0.5 ms. 5. We conclude that current rectification, rather than being an intrinsic property of the Ca2+ permeable AMPAR channel, is generated by polyamine block.}, author = {Koh, Duk and Burnashev, Nail and Jonas, Peter M}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {Pt 2}, pages = {305 -- 312}, publisher = {Wiley-Blackwell}, title = {{Block of native Ca(2+)-permeable AMPA receptors in rat brain by intracellular polyamines generates double rectification}}, doi = {10.1113/jphysiol.1995.sp020813}, volume = {486}, year = {1995}, } @article{3636, abstract = {Observations on the means, variances, and covariances of quantitative traits across hybrid zones can give information similar to that from Mendelian markers. In addition, they can identify particular traits through which the cline is maintained. We describe a survey of six traits across the hybrid zone between Bombina bombina and Bombina variegata (Amphibia: Discoglossidae) near Pescenica in Croatia. We obtained laboratory measuments of the belly pattern, skin thickness, mating call, skeletal form, egg size, and the developmental time of tadpoles. Although offspring from hybrid populations showed no evidence of reduced viability, a third of the F1 families failed completely, irrespective of the direction of the cross. All traits differed significantly between the taxa. Clines in belly pattern, skin thickness, mating call, and skeletal form were closely concordant with clines in four diagnostic enzyme loci. However, the cline in developmental time was displaced towards bombina, and the cline in egg size was displaced towards variegata. This discordance could be because the traits are not inherited additively or because they are subject to different selection pressures. We favor the latter explanation in the case of developmental time. We show that moderate selection acting directly on a trait suffices to shift its position; rather stronger selection is needed to change its width appreciably. Within hybrid populations, there are significant associations among quantitative traits, and between traits and enzymes. Phenotypic variances also increase in hybrid populations. These observations can be explained by linkage disequilibria among the underlying loci. However, the average magnitude of the covariance between traits is about half that expected from the linkage disequilibria between enzyme loci. The discrepancy is not readily explained by nonadditive gene action. This puzzle is now unresolved and calls for further investigation.}, author = {Nürnberger, Beate and Barton, Nicholas H and Maccallum, Catriona and Gilchrist, Jason and Appleby, Michael}, issn = {0014-3820}, journal = {Evolution}, number = {6}, pages = {1224 -- 1238}, publisher = {Wiley-Blackwell}, title = {{Natural selection on quantitative traits in the Bombina hybrid zone}}, doi = {10.1111/j.1558-5646.1995.tb04449.x}, volume = {49}, year = {1995}, }