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1、EuropeanJournalofNeuroscience,Vol.12,pp.155±164,2000ãEuropeanNeuroscienceAssociationSpontaneousandlocomotor-relatedGABAergicinputonto
primaryafferentsintheneonatalratSilviaFellippa-Marques,LaurentVinayandFrancËoisClaracCNRS,UPRNeurobiologieetMouvements(UPR901
2、1),31cheminJosephAiguier,13402MarseilleCx20,FranceKeywords:antidromicdischarges,bicuculline,presynapticinhibition,spinalcordAbstractTheinvitrobrainstem±spinalcordpreparationofneonatalrats(0±5daysold)wasusedtoexaminethecontributionofGABAA(g-
aminobutyricacid)r
3、eceptorstothespontaneousandlocomotor-relatedantidromic®ringinthedorsalrootsofneonatalrats.
Spontaneousburstsofantidromicdischargesweregeneratedbytheunderlyingafferentterminaldepolarizationsreachingspiking
threshold.Thenumberofantidromicactionpotentialsincreas
4、edsigni®cantlyinsalinesolutionwithCl±concentrationreducedto50%ofcontrol.BathapplicationoftheGABAAreceptorantagonistbicuculline,atlowconcentrations(1±2mM),orpicrotoxinblockedtheantidromicdischargesinthedorsalrootsalmostcompletely.TheincreaseinCl±conductancewas
5、thereforemediatedbyanactivationofGABAAreceptors.Increasingtheconcentrationofbicucullineto10±20mMneverblockedthesedischargesfurther.Onthecontrary,inhalfofthepreparations,thenumberofantidromicactionpotentialswashigherinthepresenceofhighconcentrationsofbicuculli
6、ne(10±20mM)thaninthepresenceofpicrotoxinorlowconcentrationsofbicuculline.Thissuggeststhatbicuculline,athigh
concentrations,mayhaveothereffects,inadditiontoblockingGABAAreceptors.Dorsalroot®ringwasobservedduring®ctive
locomotioninducedbybathapplicationofexcita
7、toryaminoacidsandserotonin.Arhythmicalpatternwasoftendemonstrated.
Bicucullineatlowconcentrationscausedadecreaseoftheantidromicdischargewhereas,athighconcentrations,burstsof
dischargesappeared.Adouble-bathwithabarrierbuiltattheL3levelwasthenusedtoseparatethem
8、echanismswhichgenerate
locomotionfromthosemediatingprimaryafferentdepolarizations.Excitatoryaminoacidsandserotoninwereperfusedintherostral
poolonly.Decreasingtheconcentrationofchlorideint
