BIPN 144 Week 10 Notes (part 2)

BIPN 144 Week 10 Notes (part 2) - BIPN144Week10Notes(Part2)

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Unformatted text preview: BIPN144Week10Notes(Part2) Note:ThishasnotbeenreviewedbyDr.Bierandmayhaveerrors.Always trusttheprofessoroverthesenotes. Todaywasallaboutlongtermpotentiation(LTP)!Aswelearnedattheendoflast lecture,therearethreecriteriafordefiningLTP. 1) cooperative(morethanoneinputrequired) 2) Associative(requiressimultaneousfiringofinputs) 3) Specific(onlytheactivepathwaysarepotentiated). HealsointroducedthetermHebbianCorrelationDetectionwithitsassociated principles 1) Asynchronousfiringinputscompeteanddisplaceeachother 2) Correlatedfiringofcellssuppressescompetitionbetweennervefibers Thisiswhatwehavebeendiscussinguptothispointwiththemotorneuronsand musclesaswellasoculardominancecolumns,etc ButbacktoLTP. ThemostbasicLTPexperimentistheobservationthatafterusingelectrodesto deliveratetanus(alotofrapidhighpowerstimulation)toaneuronitincreasesits responsiveness.Thisincreasedresponsivenesslastsforweeks. Dr.BierthenbegandiscussingtheNMDAreceptor NMDAisatypeofglutamatereceptor,whichactsasacoincidencedetector.Anerve fiberhasanumberoftheselittleboutons,theabovepictureisacloseupofone boutonandthepresynapticneuronthatspraysglutamateonit.Asyoucansee, thereisabigredMagnesiumIonblockingtheNMDAreceptorfromallowingCa++to enter.NexttotheNMDAreceptorisaNa+channel/glutamatereceptor.Glutamate alonecanopenthischannelandletinsomeNa+,butthisdepolarizationisnot sufficienttounblocktheNMDAreceptor.InordertounblocktheNMDAreceptor, multipleboutonsmustbestimulatedsimultaneously.What'smore,theMg++ion willonlybeliberatedfromNMDAreceptorsthatareinvolvedinthissimultaneous firing.(InshortitrequirescoincidentalfiringtoopentheNMDAreceptorchannels). PeoplehavedoneexperimentstodeterminetheeffectsonLTPofeliminating coincidencedetectorsinseaslugs,fliesandmice.Themostfamousisprobablythe milk/platformtest.Inthistestamouseistossedintoabucketofmilkywater,witha flagstickingoutofaplatform,whichisjustbarelysubmergedundertheopaque liquid.Allmicecanfindtheplatform.Afterdoingthisafewtimes,theytaketheflag away.Normalmiceuseothercuesembeddedintheirmemoriestoquicklylocatethe platform.Mutantmicecan'tdothis. AnotherinterestingphenomenoninvolvingLTPoccurswhenamousewith electrodesinitsheadisputintoabox.Asthemouseexploresandbecomesfamiliar withthebox,"placecells"begintofirewhenthemousesitsinacertainquadrant. Forexample,ifamousesitsinquadrantA,placeCellAfires,etc.Attheendofthe daythemouseisremovedfromthebox.Thenextday,themouseisputbackinthe box,andplacecellsagainbegintoassignthemselvestodifferentquadrantsofthe box,butnotthesameorganizationaslasttime.(Forexample,placecellAfrom yesterday,maybeassignedtoquadrantBtoday).However,ifyoumakearicher environmentthananondescriptbox,byaddingafoodsoure,awatersource,shelter, etc.themousewillformandmaintainamorepermanentinternalmap(thesame placecellswillbeassociatedwiththesamelocationsdayafterday). Dr.BierthenbegantotalkaboutCAMKinaseII(CK2).CK2actsasaswitch.Itis madeup0fmultiplesubunits.Ouroldfriendcalmodulin,whenactive(fullof calcium)likestophosphorylatethesubunitsofCK2.SmallamountsofCalmodulin canphosporylateonlyafewsubunitsofCK2atatime,whichlaterare dephosphorylatedbyaphosphatase.HoweverifthereisatonofCa++thisactivates atonofcalmodulin,whichphosphorylatesalloftheCK2subunitsatoncewhich allowsittostayactiveintheabsenceofpersistentCa++!Seetheonlineclassnotes forcoolillustrations. AnotherswitchisCPEBP(cytoplasmicpolyadenylationelementbindingprotein).It isatranslationfactorthatbindstothepolyAtailofmRNA's,increasingtheir translationefficiency.CPEBPhasaprionlikedomain.Itexistsintwoforms:a partiallyactivemonomericformandahighlyactivedimericform.Synaptic reinforcementcantransformCPEBintotheactiveformwhichcanthen persistentlytransformotherCPEBmoleculesintoactivestate(likePrion proteindoes). Othercoolstuff:HMwasapatientwhounderwentbilateralhypocampalremovalto combatsevereepilepsy(Ithink).Sincethesurgeryhehasbeenunabletoforma singlenewlongtermmemorydespitehavinganotherwisenormalbrain. CliveWaring,afamousmusicalconductor,hasasimilarcondition.Goodluckonthe final,brngpensandbluebooks. ...
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