Increase of GABAA receptor-mediated tonic inhibition in DG c(6)

Z.Mtchedlishvilietal./NeurobiologyofDisease38(2010)464–475469

Fig.2.LossofdiazepamsensitivityinDGCsafterCCI.TypicalexamplesofmIPSCsincontrolandCCIDGCs(averagesfromsingleneurons)andcumulativeprobabilityplotsofpeakamplitudeanddecaytimeconstantsatbaseline(solidline)andinthecontinuouspresenceof300nMdiazepam(dottedline).DGCswerevoltage-clampedto 70mVandrecordedat23°Cinthepresenceof50μMAP-5,20μMDNQX,and1μMTTX.(A)AnaveragedtracefromacontrolDGCatbaseline(black)andafterapplicationof300nMdiazepam(grey).Eachtraceisobtainedfrom～500individualmIPSCsinthisandsubsequenttraces.(B)AnaveragedtracefromaCCIDGCatbaseline(black)andafterapplicationof300nMdiazepam(grey)Notethestrongerpotentiationofpeakamplitudeby300nMdiazepaminthecontrolDGCcomparedtotheCCIDGC.(C,D)CumulativeprobabilityplotsofthepeakamplitudesofmIPSCsrecordedfromthesameneurons(A,B),respectively.NotethelargerrightwardshiftofthecurveinthepresenceofdiazepaminthecontrolDGC(C)comparedtotheCCIDGC(D).(E,F)ForthesameDGCsasin(A)and(B),thepeakamplitudesofmIPSCswerenormalizedtotheamplitudesofthetracesrecordedundercontinuousapplicationof300nMdiazepamtodemonstratetheeffectsofdiazepamondecaytimesincontrolandCCIDGCs.Notethelossofpotentiationofdecaytimeby300nMdiazepaminmIPSCsrecordedintheCCIDGC.(G,H)CumulativeprobabilityplotsofdecaytimesofmIPSCsrecordedfromthesamecontrolandCCIDGCs(E,F)NotethelargerrightwardshiftofthecurveinthepresenceofdiazepaminthecontrolDGC(G)comparedtotheCCIDGC(H).

relative,ratherthantheabsolute,differenceintoniccurrent.Forthesereasons,weconsidereditessentialthatbicucullinewastestedshortlyafterTHIP-inducedcurrentreacheditspeak.

Slowinwardcurrentoccursinresponsetobicucullineapplicationaccompaniedbylossofsynapticcurrentsandreductionofbaselinenoise.Reductionofbaselinenoiseoccursbecausetheclosureofchloridechannelscausesanincreaseofmembraneresistance.SeveralstudieshaveusedtheshiftofholdingcurrentbyGABAARantagoniststomeasuretonicinhibition(Baietal.,2001;Hamannetal.,2002;NusserandMody,2002;ModyandPearce,2004;Manganetal.,2005;MtchedlishviliandKapur,2006).Bicucullineblockedmostsynapticevents,decreasedbaselinenoise,andshiftedholdingcurrentin

both