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1、Untilaboutfiveyearsago,theveryideathatpeptidehormonesmightbemadeanywhereinthebrainbesidesthehypothalamuswasastounding.Peptidehormones,scientiststhought,weremadebyendocrineglandsandthehypothalamuswasthoughttobethebrains’onlyendocrinegland.Whatismore,b
2、ecausepeptidehormonescannotcrosstheblood-brainbarrier,researchersbelievedthattheynevergottoanypartofthebrainotherthanthehypothalamus,wheretheyweresimplyproducedandthenreleasedintothebloodstream. Butthesebeliefsaboutpeptidehormoneswerequestionedaslab
3、oratoryafterlaboratoryfoundthatantiserumstopeptidehormones,wheninjectedintothebrain,bindinplacesotherthanthehypothalamus,indicatingthateitherthehormonesorsubstancesthatcross-reactwiththeantiserumsarepresent.Theimmunologicalmethodofdetectingpeptidehor
4、monesbymeansofantiserums,however,isimprecise.Cross-reactionsarepossibleandthismethodcannotdeterminewhetherthesubstancesdetectedbytheantiserumsreallyarethehormones,ormerelycloserelatives.Furthermore,thismethodcannotbeusedtodeterminethelocationinthebod
5、ywherethedetectedsubstancesareactuallyproduced. Newtechniquesofmolecularbiology,however,provideawaytoanswerthesequestions.ItispossibletomakespecificcomplementaryDNA’s(cDNA’s)thatcanserveasmolecularprobesseekoutthemessengerRNA’s(mRNA’s)ofthepeptideho
6、rmones.Ifbraincellsaremakingthehormones,thecellswillcontainthesemRNA’s.Iftheproductsthebraincellsmakeresemblethehormonesbutarenotidenticaltothem,thenthecDNA’sshouldstillbindtothesemRNA’s,butshouldnotbindastightlyastheywouldtomRNA’sforthetruehormones.
7、ThecellscontainingthesemRNA’scanthenbeisolatedandtheirmRNA’sdecodedtodeterminejustwhattheirproteinproductsareandhowcloselytheproductsresemblethetruepeptidehormones. ThemolecularapproachtodetectingpeptidehormonesusingcDNAprobesshouldalsobemuchfastert
8、hantheimmunologicalmethodbecauseitcantakeyearsoftediouspurificationstoisolatepeptidehormonesandthendevelopantiserumstothem.Roberts,expressingthesentimentofmanyresearchers,states:“Iwastrainedasanendocrinologist.Butitbecamecleartomethatthefieldofendocr
