gre考试阅读真题解析(A)
<p> <span word="Much">Much</span> <span word="of">of</span> <span word="the">the</span> <span word="research">research</span> <span word="on">on</span> <span word="hallucinogenic">hallucinogenic</span> <span word="drugs">drugs</span> <span word="such">such</span> <span word="as">as</span> <span word="LSD">LSD</span> <span word="has">has</span> <span word="focused">focused</span> <span word="on">on</span> <span word="the">the</span> <span word="neurotransmitter">neurotransmitter</span> <span word="serotonin">serotonin</span>, <span word="a">a</span> <span word="chemical">chemical</span> <span word="that">that</span> <span word="when">when</span> <span word="released">released</span> <span word="from">from</span> <span word="a">a</span> <span word="presynaptic">presynaptic</span> <span word="serotonin">serotonin</span>-<span word="secreting">secreting</span> <span word="neuron">neuron</span> <span word="causes">causes</span> <span word="the">the</span> <span word="transmission">transmission</span> <span word="of">of</span> <span word="a">a</span> <span word="nerve">nerve</span> <span word="impulse">impulse</span> <span word="across">across</span> <span word="a">a</span> <span word="synapse">synapse</span> <span word="to">to</span> <span word="an">an</span> <span word="adjacent">adjacent</span> <span word="postsynaptic">postsynaptic</span>, <span word="or">or</span> <span word="target">target</span>, <span word="neuron">neuron</span>. <span word="There">There</span> <span word="are">are</span> <span word="two">two</span> <span word="major">major</span> <span word="reasons">reasons</span> <span word="for">for</span> <span word="this">this</span> <span word="emphasis">emphasis</span>. <span word="First">First</span>, <span word="it">it</span> <span word="was">was</span> <span word="discovered">discovered</span> <span word="early">early</span> <span word="on">on</span> <span word="that">that</span> <span word="many">many</span> <span word="of">of</span> <span word="the">the</span> <span word="major">major</span> <span word="hallucinogens">hallucinogens</span> <span word="have">have</span> <span word="a">a</span> <span word="molecular">molecular</span> <span word="structure">structure</span> <span word="similar">similar</span> <span word="to">to</span> <span word="that">that</span> <span word="of">of</span> <span word="serotonin">serotonin</span>. <span word="In">In</span> <span word="addition">addition</span>, <span word="animal">animal</span> <span word="studies">studies</span> <span word="of">of</span> <span word="brain">brain</span> <span word="neurochemistry">neurochemistry</span> <span word="following">following</span> <span word="administration">administration</span> <span word="of">of</span> <span word="hallucinogens">hallucinogens</span> <span word="invariably">invariably</span> <span word="reported">reported</span> <span word="changes">changes</span> <span word="in">in</span> <span word="serotonin">serotonin</span> <span word="levels">levels</span>.</p><p> <span word="Early">Early</span> <span word="investigators">investigators</span> <span word="correctly">correctly</span> <span word="reasoned">reasoned</span> <span word="that">that</span> <span word="the">the</span> <span word="structural">structural</span> <span word="similarity">similarity</span> <span word="to">to</span> <span word="the">the</span> <span word="serotonin">serotonin</span> <span word="molecule">molecule</span> <span word="might">might</span> <span word="imply">imply</span> <span word="that">that</span> <span word="LSDs">LSDs</span> <span word="effects">effects</span> <span word="are">are</span> <span word="brought">brought</span> <span word="about">about</span> <span word="by">by</span> <span word="an">an</span> <span word="action">action</span> <span word="on">on</span> <span word="the">the</span> <span word="neurotransmission">neurotransmission</span> <span word="of">of</span> <span word="serotonin">serotonin</span> <span word="in">in</span> <span word="the">the</span> <span word="brain">brain</span>. <span word="Unfortunately">Unfortunately</span>, <span word="the">the</span> <span word="level">level</span> <span word="of">of</span> <span word="technical">technical</span> <span word="expertise">expertise</span> <span word="in">in</span> <span word="the">the</span> <span word="field">field</span> <span word="of">of</span> <span word="brain">brain</span> <span word="research">research</span> <span word="was">was</span> <span word="such">such</span> <span word="that">that</span> <span word="this">this</span> <span word="hypothesis">hypothesis</span> <span word="had">had</span> <span word="to">to</span> <span word="be">be</span> <span word="tested">tested</span> <span word="on">on</span> <span word="peripheral">peripheral</span> <span word="tissue">tissue</span> . <span word="Two">Two</span> <span word="different">different</span> <span word="groups">groups</span> <span word="of">of</span> <span word="scientists">scientists</span> <span word="reported">reported</span> <span word="that">that</span> <span word="LSD">LSD</span> <span word="powerfully">powerfully</span> <span word="blockaded">blockaded</span> <span word="serotonins">serotonins</span> <span word="action">action</span>. <span word="Their">Their</span> <span word="conclusions">conclusions</span> <span word="were">were</span> <span word="quickly">quickly</span> <span word="challenged">challenged</span>, <span word="however">however</span>. <span word="We">We</span> <span word="now">now</span> <span word="know">know</span> <span word="that">that</span> <span word="the">the</span> <span word="action">action</span> <span word="of">of</span> <span word="a">a</span> <span word="drug">drug</span> <span word="at">at</span> <span word="one">one</span> <span word="site">site</span> <span word="in">in</span> <span word="the">the</span> <span word="body">body</span> <span word="does">does</span> <span word="not">not</span> <span word="necessarily">necessarily</span> <span word="correspond">correspond</span> <span word="to">to</span> <span word="the">the</span> <span word="drugs">drugs</span> <span word="action">action</span> <span word="at">at</span> <span word="another">another</span> <span word="site">site</span>, <span word="especially">especially</span> <span word="when">when</span> <span word="one">one</span> <span word="site">site</span> <span word="is">is</span> <span word="in">in</span> <span word="the">the</span> <span word="brain">brain</span> <span word="and">and</span> <span word="the">the</span> <span word="other">other</span> <span word="is">is</span> <span word="not">not</span>.</p><p> <span word="By">By</span> <span word="the">the</span> 1960<span word="s">s</span>, <span word="technical">technical</span> <span word="advances">advances</span> <span word="permitted">permitted</span> <span word="the">the</span> <span word="direct">direct</span> <span word="testing">testing</span> <span word="of">of</span> <span word="the">the</span> <span word="hypothesis">hypothesis</span> <span word="that">that</span> <span word="LSD">LSD</span> <span word="and">and</span> <span word="related">related</span> <span word="hallucinogens">hallucinogens</span> <span word="act">act</span> <span word="by">by</span> <span word="directly">directly</span> <span word="suppressing">suppressing</span> <span word="the">the</span> <span word="activity">activity</span> <span word="of">of</span> <span word="serotonin">serotonin</span>-<span word="secreting">secreting</span> <span word="neurons">neurons</span> <span word="themselvesthe">themselvesthe</span> <span word="so">so</span>-<span word="called">called</span> <span word="presynaptic">presynaptic</span> <span word="hypothesis">hypothesis</span>. <span word="Researchers">Researchers</span> <span word="reasoned">reasoned</span> <span word="that">that</span> <span word="if">if</span> <span word="the">the</span> <span word="hallucinogenic">hallucinogenic</span> <span word="drugs">drugs</span> <span word="act">act</span> <span word="by">by</span> <span word="suppressing">suppressing</span> <span word="the">the</span> <span word="activity">activity</span> <span word="of">of</span> <span word="serotonin">serotonin</span>-<span word="secreting">secreting</span> <span word="neurons">neurons</span>, <span word="then">then</span> <span word="drugs">drugs</span> <span word="administered">administered</span> <span word="after">after</span> <span word="these">these</span> <span word="neurons">neurons</span> <span word="had">had</span> <span word="been">been</span> <span word="destroyed">destroyed</span> <span word="should">should</span> <span word="have">have</span> <span word="no">no</span> <span word="effect">effect</span> <span word="on">on</span> <span word="behavior">behavior</span>, <span word="because">because</span> <span word="the">the</span> <span word="system">system</span> <span word="would">would</span> <span word="already">already</span> <span word="be">be</span> <span word="maximally">maximally</span> <span word="suppressed">suppressed</span>. <span word="Contrary">Contrary</span> <span word="to">to</span> <span word="their">their</span> <span word="expectations">expectations</span>, <span word="neuron">neuron</span> <span word="destruction">destruction</span> <span word="enhanced">enhanced</span> <span word="the">the</span> <span word="effect">effect</span> <span word="of">of</span> <span word="LSD">LSD</span> <span word="and">and</span> <span word="related">related</span> <span word="hallucinogens">hallucinogens</span> <span word="on">on</span> <span word="behavior">behavior</span>. <span word="Thus">Thus</span>, <span word="hallucinogenic">hallucinogenic</span> <span word="drugs">drugs</span> <span word="apparently">apparently</span> <span word="do">do</span> <span word="not">not</span> <span word="act">act</span> <span word="directly">directly</span> <span word="on">on</span> <span word="serotonin">serotonin</span>-<span word="secreting">secreting</span> <span word="neurons">neurons</span>.</p>
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