@article{4170, abstract = {We identified 6 genes that are essential for specifying ventral regions of the early zebrafish embryo, Mutations in these genes cause an expansion of structures normally derived from dorsal-lateral regions of the blastula at the expense of ventrally derived structures, A series of phenotypes of varied strengths is observed with different alleles of these mutants, The weakest phenotype is a reduction in the ventral tail fin, observed as a dominant phenotype of swirl, piggytail, and somitabun and a recessive phenotype of min fin, lost-a-fin and some piggytail alleles, With increasing phenotypic strength, the blood and pronephric anlagen are also reduced or absent, while the paraxial mesoderm and anterior neuroectoderm is progressively expanded, In the strong phenotypes, displayed by homozygous embryos of snailhouse, swirl and somitabun, the somites circle around the embryo and the midbrain region is expanded laterally, Several mutations in this group of genes are semidominant as well as recessive indicating a strong dosage sensitivity of the processes involved, Mutations in the piggytail gene display an unusual dominance that depends on both a maternal and zygotic heterozygous genotype, while somitabun is a fully penetrant dominant maternal-effect mutation, The similar and overlapping phenotypes of mutants of the 6 genes identified suggest that they function in a common pathway, which begins in oogenesis, but also depends on factors provided after the onset of zygotic transcription, presumably during blastula stages, This pathway provides ventral positional information, counteracting the dorsalizing instructions of the organizer, which is localized in the dorsal shield.}, author = {Mullins, Mary and Hammerschmidt, Matthias and Kane, Donald and Odenthal, Jörg and Brand, Michael and Van Eeden, Fredericus and Furutani Seiki, Makoto and Granato, Michael and Haffter, Pascal and Heisenberg, Carl-Philipp J and Jiang, Yunjin and Kelsh, Robert and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, number = {1}, pages = {81 -- 93}, publisher = {Company of Biologists}, title = {{Genes establishing dorsoventral pattern formation in the zebrafish embryo: The ventral specifying genes}}, doi = {10.1242/dev.123.1.81}, volume = {123}, year = {1996}, } @article{4189, abstract = {This report describes mutants of the zebrafish having phenotypes causing a general arrest in early morphogenesis. These mutants identify a group of loci making up about 20% of the loci identified by mutants with visible morphological phenotypes within the first day of development. There are 12 Class I mutants, which fall into 5 complementation groups and have cells that lyse before morphological defects are observed. Mutants at three loci, speed bump, ogre and zombie, display abnormal nuclei. The 8 Class II mutants, which fall into 6 complementation groups, arrest development before cell lysis is observed. These mutants seemingly stop development in the late segmentation stages, and maintain a body shape similar to a 20 hour embryo. Mutations in speed bump, ogre, zombie, specter, poltergeist and troll were tested for cell lethality by transplanting mutant cells into wild-type hosts. With poltergeist, transplanted mutant cells all survive. The remainder of the mutants tested were autonomously but conditionally lethal: mutant cells, most of which lyse, sometimes survive to become notochord, muscles, or, in rare cases, large neurons, all cell types which become postmitotic in the gastrula. Some of the genes of the early arrest group may be necessary for progression though the cell cycle; if so, the survival of early differentiating cells may be based on having their terminal mitosis before the zygotic requirement for these genes.}, author = {Kane, Donald and Maischein, Hans and Brand, Michael and Van Eeden, Fredericus and Furutani Seiki, Makoto and Granato, Michael and Haffter, Pascal and Hammerschmidt, Matthias and Heisenberg, Carl-Philipp J and Jiang, Yunjin and Kelsh, Robert and Mullins, Mary and Odenthal, Jörg and Warga, Rachel and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, number = {1}, pages = {57 -- 66}, publisher = {Company of Biologists}, title = {{The zebrafish early arrest mutants}}, doi = {10.1242/dev.123.1.57 }, volume = {123}, year = {1996}, } @article{4191, abstract = {In a screen for embryonic mutants in the zebrafish a large number of mutants were isolated with abnormal brain morphology, We describe here 26 mutants in 13 complementation groups that show abnormal development of large regions of the brain, Early neurogenesis is affected in white tail (wit), During segmentation stages, homozygous wit embryos display an irregularly formed neural keel, particularly in the hindbrain, Using a variety of molecular markers, a severe increase in the number of various early differentiating neurons can be demonstrated, In contrast, late differentiating neurons, radial glial cells and some nonneural cell types, such as the neural crest-derived melanoblasts, are much reduced, Somitogenesis appears delayed, In addition, very reduced numbers of melanophores are present posterior to the mid-trunk, The wit phenotype is reminiscent of neurogenic mutants in Drosophila, such as Notch or Delta, In mutant parachute (pac) embryos the general organization of the hindbrain is disturbed and many rounded cells accumulate loosely in the hindbrain and midbrain ventricles, Mutants in a group of 6 genes, snakehead(snk), natter (nat), otter (ott) fullbrain (ful) viper (vip) and white snake (wis) develop collapsed brain ventricles, before showing signs of general degeneration, atlantis (atl), big head (bid), wicked brain (win), scabland (sbd) and eisspalte (ele) mutants have different malformation of the brain folds, Some of them have transient phenotypes, and mutant individuals may grow up to adults.}, author = {Jiang, Yunjin and Brand, Michael and Heisenberg, Carl-Philipp J and Beuchle, Dirk and Furutani Seiki, Makoto and Kelsh, Robert and Warga, Rachel and Granato, Michael and Haffter, Pascal and Hammerschmidt, Matthias and Kane, Donald and Mullins, Mary and Odenthal, Jörg and Van Eeden, Fredericus and Nüsslein Volhard, Christiane}, issn = {0950-1991}, journal = {Development}, number = {1}, pages = {205 -- 216}, publisher = {Company of Biologists}, title = {{Mutations affecting neurogenesis and brain morphology in the zebrafish, Danio rerio}}, doi = {10.1242/dev.123.1.205}, 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{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}, } @inbook{3454, abstract = {The study of gene expression and regulation in the central nervous system (CNS) is a daunting task because of the diversity of neuronal phenotypes and the complexity of many protein classes. Molecular cloning revealed the presence of a large number of different protein families in the CNS, each comprising several members. Ligand-gated ion channels may serve as an example to illustrate this point (for review, see Unwin, 1993). Heterologous expression combined with electrophysiological analysis suggests that ligand-gated channels are multimeric proteins with functional properties depending on the subunit composition. Very little is known, however, about how the functional properties of the recombinant and native receptors relate to each other. Thus, it is of eminent importance to elucidate the subunit expression profile in different types of neurons in the CNS and to correlate this with the functional properties of the native receptors.}, author = {Monyer, Hannah and Jonas, Peter M}, booktitle = {Single-channel recording}, editor = {Sakmann, Bert and Neher, Erwin}, isbn = {978-0-306-44870-6}, pages = {357 -- 373}, publisher = {Plenum}, title = {{Polymerase chain reaction analysis of ion channel expression in single neurons of brain slices}}, doi = {10.1007/978-1-4419-1229-9_16}, year = {1995}, } @inbook{3455, abstract = {At a synapse, the transmitter is stored in synaptic vesicles and is released into the synaptic cleft almost instantaneously upon fusion of these vesicles with the presynaptic membrane. Subsequently, the transmitter diffuses to ligand-gated ion channels in the postsynaptic density, binds to them, and thereby causes channel activation. Unfortunately, we have estimates neither of the exact amount of transmitter in the synaptic vesicle nor of the concentration in the synaptic cleft reaching the postsynaptic receptors, and in some cases even the identity of the transmitter is unknown. These questions may be addressed by modeling of release and diffusion. Such a theoretical approach, however, is based on several assumptions, some of which lack experimental evidence.}, author = {Jonas, Peter M}, booktitle = {Single-channel recording}, editor = {Sakmann, Bert and Neher, Erwin}, isbn = {978-0-306-44870-6}, pages = {231 -- 243}, publisher = {Plenum}, title = {{Fast application of agonists to isolated membrane patches}}, doi = {10.1007/978-1-4419-1229-9_10}, 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}, } @inproceedings{3551, abstract = {Common geometric models for proteins and other molecules are the space filling diagram, the solvent accessible surface, and the molecular surface. We describe software that computes metric properties of these models, including volume and surface area. It also measures voids or empty space enclosed by the protein, and it keeps track of surface area contributions of individual atoms. The software is based on 3-dimensional alpha complexes and on inclusion-exclusion formulas with terms derived from the simplices in this complex.}, author = {Edelsbrunner, Herbert and Facello, Michael and Fu, Ping and Liang, Jie}, booktitle = {Proceedings of the 28th Annual Hawaii International Conference on System Sciences}, isbn = {0-8186-6930-6}, location = {Wailea, HI, United States of America}, pages = {256 -- 264}, publisher = {IEEE}, title = {{Measuring proteins and voids in proteins}}, doi = {10.1109/HICSS.1995.375331}, year = {1995}, } @article{3640, abstract = {The probability of fixation of a favorable mutation is reduced if selection at other loci causes inherited variation in fitness. A general method for calculating the fixation probability of an allele that can find itself in a variety of genetic backgrounds is applied to find the effect of substitutions, fluctuating polymorphisms, and deleterious mutations in a large population. With loose linkage, r, the effects depend on the additive genetic variance in relative fitness, var(W), and act by reducing effective population size by (N/Ne) = 1 + var(W)/2r2. However, tightly linked loci can have a substantial effect not predictable from Ne. Linked deleterious mutations reduce the fixation probability of weakly favored alleles by exp (-2U/R), where U is the total mutation rate and R is the map length in Morgans. Substitutions can cause a greater reduction: an allele with advantage s < scrit = (pi 2/6) loge (S/s) [var(W)/R] is very unlikely to be fixed. (S is the advantage of the substitution impeding fixation.) Fluctuating polymorphisms at many (n) linked loci can also have a substantial effect, reducing fixation probability by exp [square root of 2Kn var(W)/R] [K = -1/E((u-u)2/uv) depending on the frequencies (u,v) at the selected polymorphisms]. Hitchhiking due to all three kinds of selection may substantially impede adaptation that depends on weakly favored alleles.}, author = {Barton, Nicholas H}, issn = {0016-6731}, journal = {Genetics}, number = {2}, pages = {821 -- 841}, publisher = {Genetics Society of America}, title = {{Linkage and the limits to natural selection}}, doi = { 10.1093/genetics/140.2.821}, volume = {140}, year = {1995}, } @article{2557, abstract = {The distribution of the metabotropic glutamate receptors mGluR2 and mGluR3 was immunohistochemically examined in the rat cerebellar cortex at both light and electron microscope levels. An antibody was raised against a fusion protein containing a C-terminal portion of mGluR2. On immunoblot, the antibody reacted with both mGluR2 and mGluR3 in rat brain. mGluR2/3 immunoreactivity was expressed in cell bodies, dendrites, and axon terminals of Golgi cells, as well as in presumed glial processes. Golgi axon terminals with mGluR2/3 immunoreactivity were often encountered in the vicinity of glutamatergic mossy fiber terminals. The results suggest that transmitter glutamate may exert control influences upon Golgi cells not only through dendritic mGluR2/3, but also through axonal mGluR2/3.}, author = {Ohishi, Hitoshi and Ogawa Meguro, Reiko and Shigemoto, Ryuichi and Kaneko, Takeshi and Nakanishi, Shigetada and Mizuno, Noboru}, issn = {0896-6273}, journal = {Neuron}, number = {1}, pages = {55 -- 66}, publisher = {Elsevier}, title = {{Immunohistochemical localization of metabotropic glutamate receptors, mGluR2 and mGluR3, in rat cerebellar cortex}}, doi = {10.1016/0896-6273(94)90459-6}, volume = {13}, year = {1994}, } @article{3475, abstract = {1. A potassium channel activated by internal Na+ ions (K+Na channel) was identified in peripheral myelinated axons of Xenopus laevis using the cell-attached and excised configurations of the patch clamp technique. 2. The single-channel conductance for the main open state was 88 pS with [K+]o = 105 mM and pS with [K+]o = 2.5 mM ([K+]i = 105 mM). The channel was selectively permeable to K+ over Na+ ions. A characteristic feature of the K+Na channel was the frequent occurrence of subconductance states. 3. The open probability of the channel was strongly dependent on the concentration of Na+ ions at the inner side of the membrane. The half-maximal activating Na+ concentration and the Hill coefficient were 33 mM and 2.9, respectively. The open probability of the channel showed only weak potential dependence. 4. The K+Na channel was relatively insensitive to external tetraethylammonium (TEA+) in comparison with voltage-dependent axonal K+ channels; the half-maximal inhibitory concentration (IC50) was 21.3 mM (at -90 mV). In contrast, the channel was blocked by low concentrations of external Ba2+ and Cs+ ions, with IC50 values of 0.7 and 1.1 mM, respectively (at -90 mV). The block by Ba2+ and Cs+ was more pronounced at negative than at positive membrane potentials. 5. A comparison of the number of K+Na channels in nodal and paranodal patches from the same axon revealed that the channel density was about 10-fold higher at the node of Ranvier than at the paranode. Moreover, a correlation between the number of K+Na channels and voltage-dependent Na+ channels in the same patches was found, suggesting co-localization of both channel types. 6. As weakly potential-dependent ('leakage') channels, axonal K+Na channels may be involved in setting the resting potential of vertebrate axons. Simulations of Na+ ion diffusion suggest two possible mechanisms of activation of K+Na channels: the local increase of Na+ concentration in a cluster of Na+ channels during a single action potential or the accumulation in the intracellular axonal compartment during a train of action potentials.}, author = {Koh, Duk and Jonas, Peter M and Vogel, Werner}, issn = {0022-3751}, journal = {Journal of Physiology}, pages = {183 -- 197}, publisher = {Wiley-Blackwell}, title = {{Na+-activated K+ channels localized in the nodal region of myelinated axons of Xenopus}}, doi = {10.1113/jphysiol.1994.sp020287}, volume = {479}, year = {1994}, } @article{3641, abstract = {The probability of fixation of a mutation with selective advantage s will be reduced by substitutions at other loci. The effect of a single substitution, with selective advantage S0016672300032857inline1, can be approximated as a sudden reduction in the frequency of the favourable allele, by a fraction w = 1 −(s/S)r/s (where r is the recombination rate). An expression for the effect of a given sequence of such catastrophes is derived. This also applies to the ecological prxoblem of finding the probability that a small population will survive, despite occasional disasters. It is shown that if substitutions occur at a rate Δ, and are scattered randomly over a genetic map of length R, then an allele is unlikely to be fixed if its advantage is less than a critical value, Scrit = (π2/6)(2ΔS/(Rlog(S/s))). This threshold depends primarily on the variance in fitness per unit map length dueto substitutions, var(W)/R = 2ΔS/R. With no recombination, the fixation probability can be calculated for a finite population. If Δ > s, it is of the same order as for a neutral allele ( ≈ Δ/(2N(Δ−s))), whilst if S0016672300032857inline2, fixation probability is much higher than for a neutral allele, but much lower than in the absence of hitch-hiking S0016672300032857inline3. These results suggest that hitch-hiking may substantially impede the accumulation of weakly favoured adaptations.}, author = {Barton, Nicholas H}, issn = {0016-6723}, journal = {Genetical Research}, number = {3}, pages = {199 -- 208}, publisher = {Cambridge University Press}, title = {{The reduction in fixation probability caused by substitutions at linked loci}}, doi = {10.1017/S0016672300032857 }, volume = {64}, year = {1994}, } @article{3474, abstract = {1. Excitatory postsynaptic currents (EPSCs) were recorded in CA3 pyramidal cells of hippocampal slices of 15- to 24-day-old rats (22 degrees C) using the whole-cell configuration of the patch clamp technique. 2. Composite EPSCs were evoked by extracellular stimulation of the mossy fibre tract. Using the selective blockers 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and D-2-amino-5-phosphonopentanoic acid (APV), a major alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptor-mediated component and a minor NMDA receptor-mediated component with slower time course were distinguished. For the AMPA/kainate receptor-mediated component, the peak current-voltage (I-V) relation was linear, with a reversal potential close to 0 mV. The half-maximal blocking concentration of CNQX was 353 nM. 3. Unitary EPSCs of the mossy fibre terminal (MF)-CA3 pyramidal cell synapse were evoked at membrane potentials of -70 to -90 mV by low-intensity extracellular stimulation of granule cell somata using fine-tipped pipettes. The EPSC peak amplitude as a function of stimulus intensity showed all-or-none behaviour. The region of low threshold was restricted to a few micrometres. This suggests that extracellular stimulation was focal, and that the stimulus-evoked EPSCs were unitary. 4. Latency and rise time histograms of EPSCs evoked by granule cell stimulation showed narrow unimodal distributions within each experiment. The mean latency was 4.2 +/- 1.0 ms, and the mean 20-80% rise time was 0.6 +/- 0.1 ms (23 cells). When fitted within the range 0.7 ms to 20 ms after the peak, the decay of the EPSCs with the fastest rise (rise time 0.5 ms or less) could be described by a single exponential function; the mean time constant was in the range 3.0-6.6 ms with a mean of 4.8 ms (8 cells). 5. Peak amplitudes of the EPSCs evoked by suprathreshold granule cell stimulation fluctuated between trials. The apparent EPSC peak conductance in normal extracellular solution (2 mM Ca2+, 1 mM Mg2+), excluding failures, was 1 nS. Reducing the Ca2+ concentration and increasing the Mg2+ concentration reduced the mean peak amplitude in a concentration-dependent manner. 6. Peaks in EPSC peak amplitude distributions were apparent in low Ca2+ and high Mg2+. Using the criteria of equidistance and the presence of peaks and dips in the autocorrelation function, five of nine EPSC peak amplitude distributions were judged to be quantal.}, author = {Jonas, Peter M and Major, Guy and Sakmann, Bert}, issn = {0022-3751}, journal = {Journal of Physiology}, pages = {615 -- 663}, publisher = {Wiley-Blackwell}, title = {{Quantal components of unitary EPSCs at the mossy fibre synapse on CA3 pyramidal cells of rat hippocampus}}, doi = {10.1113/jphysiol.1993.sp019965}, volume = {472}, year = {1993}, } @article{2532, abstract = {In the present study, we have investigated the expression of both the erythrocyte-type (GLUT1) and the brain-type (GLUT3) glucose transporter isoforms in primary human brain tumors. In situ hybridization made it possible to localize and semiquantify both GLUT1 and GLUT3 mRNAs of individual cells in all 18 samples examined. More signals for GLUT3 mRNA than for GLUT1 mRNA were found over astrocytoma cells, while the reverse was the case in all 6 meningiomas. In astrocytomas, for both mRNAs, the density of silver grains over tumor cells was well correlated with the malignancy of the cells. This correlation was, as was also confirmed by Northern blot analysis, more marked with GLUT3 mRNA than with GLUT1 mRNA. In 2 of 5 anaplastic astrocytomas and in all 3 glioblastomas, numerous tumor cells with large amounts of both mRNAs tended to surround the perivascular regions. 'Tumor vessels' with endothelial proliferation, an almost pathognomonic feature of glioblastomas, expressed much GLUT3 mRNA but no significant GLUT1 mRNA, while a single- or a few-layered capillary endothelium expressed much GLUT1 mRNA. The distribution of both mRNAs was in good accordance with that of both proteins. Our results suggest that the expression of both glucose transporter isoforms may contribute to the maintenance of human brain tumors and that the expression of the GLUT3 isoform may be closely related to the malignant change of astrocytomas and particularly related to the aberrant neovascularization which accompanies glioblastomas.}, author = {Nishioka, Tatsuya and Oda, Yoshifumi and Seino, Yutaka and Yamamoto, Taizo and Inagaki, Nobuya and Yano, Hideki and Imura, Hiroo and Shigemoto, Ryuichi and Kikuchi, Haruhiko}, issn = {0008-5472}, journal = {Cancer Research}, number = {14}, pages = {3972 -- 3979}, publisher = {American Association for Cancer Research}, title = {{Distribution of the glucose transporters in human brain tumors}}, volume = {52}, year = {1992}, } @article{3470, abstract = {Currents activated by glutamate receptor (GluR) agonists were recorded from outside-out patches isolated from the soma of visually identified pyramidal neurones of the (CA3 and CA1 region of rat hippocampal slices. α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). L-glutamate (L-Glu), and kainate (KA) were delivered either by bath application through perfusion of the recording chamber or by rapid application via a piezo-driven two-barrelled fast application system. 2. Bath application of each of the three agonists activated inward currents in all patches (n = 134) at holding potentials of -50 or -60 mV. The current amplitude increased in size between 3 to 30 μM-AMPA and 100 μM to 1 mM-KA. With this slow mode of bath application, the responses showed no apparent desensitization even at saturating concentrations of AMPA (30 μM) and KA (1 mM). 3. The ratio of currents activated by 30 μM-AMPA and 300 μM-KA showed a characteristic difference between CA3 and CA1 neurones. The ratio was 0.242 ± 0.028 (mean ± S.E.M., n = 16) for CA3 cell patches and 0.097 ± 0.012 (n = 8) for CA1 cell patches indicating that GluRs in the two cell populations are different. 4. The steady-state current-voltage relations (I-Vs) for AMPA- and KA-activated currents showed pronounced outward rectification for both cell types (when the main cations are Na+ in the bath and Cs+ in the pipette solution). The current reversed close to 0 mV and the ratio of chord conductances 80 mV on either side of the reversal potential was 2.66 for KA-activated currents in CA3 cell patches and 2.60 in CA1 cell patches. AMPA-activated currents showed a time-dependent increase after steps to positive membrane potentials and a decrease after steps to negative voltages, indicating that a gating process is responsible for outward rectification of the steady-state I-IV. 5. The permeability (P) of GluR channels was high for Na+ as compared to Cs+ for both cell types (P(Na)/P(Cs) = 0.88 and 0.84). The permeability was low for N-methyl-D-glucamine+ (P(NMG)/P(Cs) ≤ 0.03) and Ca2+ (P(Ca)/P(Cs) ≤0.05). 6. The current noise level increased during application of AMPA or KA. Apparent single-channel conductances obtained from fluctuation analysis were higher for AMPA than for KA, but similar for both cell types. In CA3 cell patches, AMPA activated channels with an apparent chord conductance of 7.2 pS, KA of 3.0 pS conductance. 7. Fast agonist application revealed desensitization of GluR channels which was dependent on the type of agonist, currents activated by AMPA and L-Glu rose rapidly to a peak and then desensitized to a steady-state current. In contrast, currents activated by fast application of KA rose to a plateau and did not desensitize. The steady state current expressed as a percentage of the peak current was higher for L-Glu than for AMPA and slightly higher for CA3 than for CA1 cell patches. For CA3 cell patches, this fraction amounted to 6.2 %, with 300 μM-L-Glu and 2.8%, with 300 μM-AMPA. For CA1 cell patches, corresponding values were 3.6 and 1.9 % 8. The dose response relations for the peak current activated by AMPA and L-Glu and the steady-state current activated by KA were similar for CA3 and CA1 cell patches. The order of potency was AMPA > L-Glu ≃ KA for both cell types EC50 values 189, 342 and 344 μM for CA3 cell patches and 183, 424 and 474 μM for CA1 cell patches). In all cases, the Hill coefficients ranged between 12 and 1.7. 8. The rise of AMPA and L-Glu-activated currents became faster with increasing agonist concentration for both cell types. With L-Glu, rise times decreased from about 3 ms at 100 μM to 500 μs at 3 mM. The delay for agonist concentrations ≥ 300 μM was described by the sum of two exponential functions. The time constant of the predominant fast component was slightly concentration dependent and decreased from about 12 ms at 300 μM to 8 ms at 3 mM-L-Glu. 10. The current voltage relations of the peak currents activated by 300 μM-AMPA were linear for both cell types with a reversal potential close to OmV. 11. It is concluded that the GluR channels in pyramidal cells of hippocampal CA3 and CA1 regions are distinet but share many pharmacological and functional properties. Comparison of the properties of native and recombinant GluRs suggests that in both CA3 and CA1 regions GluR channels are hetero-oligomers containing the GluR-B subunit.}, author = {Jonas, Peter M and Sakmann, Bert}, issn = {0022-3751}, journal = {Journal of Physiology}, pages = {143 -- 171}, publisher = {Wiley-Blackwell}, title = {{Glutamate receptor channels in isolated patches from CA1 and CA3 pyramidal cells of rat hippocampal slices}}, doi = {10.1113/jphysiol.1992.sp019294 }, volume = {455}, year = {1992}, } @article{3471, abstract = {1. Outside-out patches were isolated from granule cells of dentate gyrus and pyramidal cells of CA3 and CA1 regions of rat hippocampal slices. Patches were exposed briefly to L-glutamate using a piezo-driven double-barrelled application pipette. 2. Applications of glutamate (1 mM) of 1 ms duration activated patch currents which rose and decayed rapidly. The 20-80% rise time of these glutamate receptor (GluR)-mediated currents was usually 0.2-0.6 ms. At -50 mV the peak current varied from 10 to 500 pA in different patches. 3. The peak current-voltage relation for brief pulses of 1 mM glutamate was virtually linear in normal extracellular solution for patches from the three cell types (-100 to 60 mV). 4. The permeability of GluR channels activated at the peak to Ca2+, relative to K+, was less than 0.1 for all three cell types (under bi-ionic conditions with Ca2+ on the extracellular side and K+ on the intracellular side of the membrane). 5. The offset decay time constant of the current following 1 ms pulses of 1 mM glutamate was brief, with mean values of 3.0 +/- 0.8, 2.5 +/- 0.7, and 2.3 +/- 0.7 ms for dentate, CA3 and CA1 cell patches, respectively. Offset time constants were independent of membrane potential and independent of glutamate concentration (200 microM and 1 mM) for the three cell types. 6. Applications of 1 mM glutamate of 100 ms duration showed that glutamate responses desensitized rapidly. The time constants for desensitization were 9.4 +/- 2.7, 11.3 +/- 2.8, and 9.3 +/- 2.8 ms for patches from dentate, CA3 and CA1 cells respectively. Desensitization time constants were only weakly dependent on glutamate concentration (200 microM and 1 mM) for the three cell types. Thus offset time constants are about four times faster than desensitization time constants for both glutamate concentrations. 7. Double pulse application of glutamate indicated that even a 1 ms pulse of 1 mM glutamate causes partial (about 60%) desensitization of GluR channels. The time course of recovery from desensitization was slower in dentate gyrus granule cell patches than in CA3 or CA1 pyramidal cell patches. 8. Desensitization was studied at equilibrium by exposing patches to low glutamate concentrations for at least 15 s before a 1 ms test pulse of 1 mM glutamate.}, author = {Colquhoun, D. and Jonas, Peter M and Sakmann, Bert}, issn = {0022-3751}, journal = {Journal of Physiology}, pages = {261 -- 287}, publisher = {Wiley-Blackwell}, title = {{Action of brief pulses of glutamate on AMPA/kainate receptors in patches from different neurones of rat hippocampal slices}}, doi = {10.1113/jphysiol.1992.sp019417}, volume = {458}, year = {1992}, } @article{3645, abstract = {Three components of mating call (pulse duration, cycle length, and fundamental frequency) were measured and six diagnostic enzyme loci scored across the hybrid zone between the toads Bombina bombina and B. variegata. All three call components differ significantly, but only cycle length is diagnostic. The clines in call coincide with those for enzymes, and have similar widths. This suggests that there is no strong selection on any of these characters. There are significant correlations between electrophoretic markers and call components, but these are no stronger than would be expected if the electrophoretic loci and the genes causing mating call were neutral. The selection differential on the call is no greater than 6% of the difference in mean cycle length between the two taxa. There is a substantial increase in the variance of cycle length in the center of the zone, suggesting that a small number of loci are involved (≈ three). Recombination between these loci will hinder the evolution of reinforcement and may partly be responsible for the lack of premating isolation between B. bombina and B. variegata.}, author = {Sanderson, Neil and Szymura, Jacek and Barton, Nicholas H}, issn = {0014-3820}, journal = {Evolution}, number = {3}, pages = {595 -- 607}, publisher = {Wiley-Blackwell}, title = {{Variation in mating call across the hybrid zone between the fire-bellied toads Bombina bombina and B. variegata}}, doi = {10.1111/j.1558-5646.1992.tb02068.x}, volume = {46}, year = {1992}, } @article{4065, abstract = {We prove that given n⩾3 convex, compact, and pairwise disjoint sets in the plane, they may be covered with n non-overlapping convex polygons with a total of not more than 6n−9 sides, and with not more than 3n−6 distinct slopes. Furthermore, we construct sets that require 6n−9 sides and 3n−6 slopes for n⩾3. The upper bound on the number of slopes implies a new bound on a recently studied transversal problem.}, author = {Edelsbrunner, Herbert and Robison, Arch and Shen, Xiao}, issn = {1872-681X}, journal = {Discrete Mathematics}, number = {2}, pages = {153 -- 164}, publisher = {Elsevier}, title = {{Covering convex sets with non-overlapping polygons}}, doi = {10.1016/0012-365X(90)90147-A}, volume = {81}, year = {1990}, }