Dentate gyrus NMDA receptors mediate rapid pattern separation in the hippocampal network     

McHugh TJ  Jones MW  Quinn JJ  Balthasar N  Coppari R  Elmquist JK  Lowell BB  Fanselow MS  Wilson MA  Tonegawa S 《Science (New York, N.Y.)》2007,317(5834):94-99

Forming distinct representations of multiple contexts, places, and episodes is a crucial function of the hippocampus. The dentate gyrus subregion has been suggested to fulfill this role. We have tested this hypothesis by generating and analyzing a mouse strain that lacks the gene encoding the essential subunit of the N-methyl-d-aspartate (NMDA) receptor NR1, specifically in dentate gyrus granule cells. The mutant mice performed normally in contextual fear conditioning, but were impaired in the ability to distinguish two similar contexts. A significant reduction in the context-specific modulation of firing rate was observed in the CA3 pyramidal cells when the mutant mice were transferred from one context to another. These results provide evidence that NMDA receptors in the granule cells of the dentate gyrus play a crucial role in the process of pattern separation.  相似文献   

Black farmers/farms: The search for equity     

Joel Schor 《Agriculture and Human Values》1996,13(3):48-63

Black farmers are still Black farmers, yet now are considered a part of minority or small or limited resource farmers/ranchers (SLRF/R) by the Department of Agriculture. Except for a few Southern states, their numbers have fallen from a remnant to a fragment in recent years. They continue to leave agriculture at a faster rate than whites. What few programs the Department has for this category of producers (SLRF/R) show genuine promise, provided they are pursued diligently by the Congress and the Department. Also vigorous enforcement of civil rights laws and directives of the Secretary and the new initiatives by the Office of Civil Rights Enforcement (OCRE) have to be sustained.  相似文献   

Discovery of pulsed OH maser emission stimulated by a pulsar     

Weisberg JM  Johnston S  Koribalski B  Stanimirovic S 《Science (New York, N.Y.)》2005,309(5731):106-110

Stimulated emission of radiation has not been directly observed in astrophysical situations up to this time. Here we demonstrate that photons from pulsar B1641-45 stimulate pulses of excess 1720-megahertz line emission in an interstellar hydroxyl (OH) cloud. As this stimulated emission is driven by the pulsar, it varies on a few-millisecond time scale, which is orders of magnitude shorter than the quickest OH maser variations previously detected. Our 1612-megahertz spectra are inverted copies of the 1720-megahertz spectra. This "conjugate line" phenomenon enables us to constrain the properties of the interstellar OH line-producing gas. We also show that pulsar signals undergo significantly deeper OH absorption than do other background sources, which confirms earlier tentative findings that OH clouds are clumpier on small scales than are neutral hydrogen clouds.  相似文献   

Pattern in escalations in insurgent and terrorist activity     

Johnson N  Carran S  Botner J  Fontaine K  Laxague N  Nuetzel P  Turnley J  Tivnan B 《Science (New York, N.Y.)》2011,333(6038):81-84

In military planning, it is important to be able to estimate not only the number of fatalities but how often attacks that result in fatalities will take place. We uncovered a simple dynamical pattern that may be used to estimate the escalation rate and timing of fatal attacks. The time difference between fatal attacks by insurgent groups within individual provinces in both Afghanistan and Iraq, and by terrorist groups operating worldwide, gives a potent indicator of the later pace of lethal activity.  相似文献   

Race disparity in grants: empirical solutions vital     

Voss JL 《Science (New York, N.Y.)》2011,334(6058):899; author reply 899-899; author reply 901

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Chemistry. Beyond Born-Oppenheimer     

Bowman JM 《Science (New York, N.Y.)》2008,319(5859):40-41

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Book reviews     

Christopher Vecsey  Lawrence Busch  Robert E. Mazur  S. 'Tunji Titilola  Joel Schor  Don F. Hadwiger  E. Wesley F. Peterson  Lorraine Garkovich  Scott R. Collard  Tony Smith 《Agriculture and Human Values》1990,7(3-4):107-131

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From the editors     

Paul B. Thompson  Keith M. Moore  William M. Rivera  Gary P. Green  Joel Schor  et al. 《Agriculture and Human Values》1991,8(3):1-2

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Activation of integrin alphaIIbbeta3 by modulation of transmembrane helix associations     

Li R  Mitra N  Gratkowski H  Vilaire G  Litvinov R  Nagasami C  Weisel JW  Lear JD  DeGrado WF  Bennett JS 《Science (New York, N.Y.)》2003,300(5620):795-798

Transmembrane helices of integrin alpha and beta subunits have been implicated in the regulation of integrin activity. Two mutations, glycine-708 to asparagine-708 (G708N)and methionine-701 to asparagine-701, in the transmembrane helix of the beta3 subunit enabled integrin alphaIIbbeta3 to constitutively bind soluble fibrinogen. Further characterization of the G708N mutant revealed that it induced alphaIIbbeta3 clustering and constitutive phosphorylation of focal adhesion kinase. This mutation also enhanced the tendency of the transmembrane helix to form homotrimers. These results suggest that homomeric associations involving transmembrane domains provide a driving force for integrin activation. They also suggest a structural basis for the coincidence of integrin activation and clustering.  相似文献   

Graphoepitaxy of self-assembled block copolymers on two-dimensional periodic patterned templates     

Bita I  Yang JK  Jung YS  Ross CA  Thomas EL  Berggren KK 《Science (New York, N.Y.)》2008,321(5891):939-943

Self-assembling materials are the building blocks of bottom-up nanofabrication processes, but they need to be templated to impose long-range order and eliminate defects. In this work, the self-assembly of a thin film of a spherical-morphology block copolymer is templated using an array of nanoscale topographical elements that act as surrogates for the minority domains of the block copolymer. The orientation and periodicity of the resulting array of spherical microdomains are governed by the commensurability between the block copolymer period and the template period and is accurately described by a free-energy model. This method, which forms high-spatial-frequency arrays using a lower-spatial-frequency template, will be useful in nanolithography applications such as the formation of high-density microelectronic structures.  相似文献