 LTP in
hippocampus leads to LTD in entorhinal cortex [28].

Signalling mechanisms that mediate LTD in the
superficial layers of the entorhinal cortex share some similarities with NMDA
receptor-dependent LTD in the hippocampus. Long-term depression of superficial
layer inputs to layer II is dependent on NMDA receptor activation both in vivo
and in vitro [17, 18, 28, 33] but does not require activation of group I/II
metabotropic glutamate receptors ([18, 28], see [36, 37]). In the hippocampus, moderate
and prolonged influx of calcium via NMDA receptors activates calmodulin which leads
to LTD via activation of the protein phosphatase calcineurin (PP2b). Calcineurin
increases the activity of protein phosphatase 1 by reducing the activity of
inhibitor 1, and this can cause rapid reductions in AMPA-mediated responses [2, 38, 39]. Hippocampal LTD is expressed partly through the reduced conductance of
AMPA receptors caused by dephosphorylation of the GluR1 subunit by PP1 [2, 4], but
careful study has shown that calcineurin-dependent LTD in deep layer inputs to
layer II neurons in the young entorhinal cortex is not associated with a
reduced AMPA conductance, but rather involves internalization of AMPA receptors
and their proteosome-mediated degradation [28].

In the present study, the early postsynaptic
signalling mechanisms that mediate LTD in layer I inputs to layer II neurons of
the medial entorhinal cortex have been investigated using recordings of whole
cell excitatory postsynaptic potentials. Long-term depression was induced using
a prolonged paired-pulse stimulation pattern that was previously found to be
effective for induction of NMDA-receptor-dependent LTD [18]. Pharmacological agents applied to the
bathing medium or intracellular solution were used to assess the dependence of
LTD on calcium-dependent signalling mechanisms including the phosphatases calcineurin
and PP1/PP2a.

2. Experimental Procedures

2.1. Slices and Whole Cell Recordings

Experiments were performed on slices from male
Long-Evans rats (4 to 8 weeks old). Animals were anesthetized with halothane and brains were rapidly removed
and cooled (4°C) in oxygenated artificial cerebrospinal fluid (ACSF). ACSF
consisted
LTP in 
 hippocampus leads to LTD in entorhinal cortex [ 28 ]. 

 Signalling mechanisms that intercede LTD in the 
 superficial level of the entorhinal cortex share some similarity with NMDA 
 sense organ - dependent LTD in the hippocampus. Long - term natural depression of superficial 
 layer inputs to level II is pendent on NMDA receptor energizing both in vivo 
 and in vitro [ 17, 18, 28, 33 ] but does not require activation of group I / II 
 metabotropic glutamate receptors ([ 18, 28 ], see [ 36, 37 ]). In the hippocampus, moderate 
 and prolong influx of calcium via NMDA receptors activates calmodulin which leads 
 to LTD via activation of the protein phosphatase calcineurin (PP2b). Calcineurin 
 increase the activity of protein phosphatase 1 by reducing the activity of 
 inhibitor 1, and this can induce rapid reductions in AMPA - mediated response [ 2, 38, 39 ]. Hippocampal LTD is expressed partially through the reduced conductance of 
 AMPA sense organ caused by dephosphorylation of the GluR1 subunit by PP1 [ 2, 4 ], but 
 careful study has prove that calcineurin - dependent LTD in deep layer inputs to 
 layer II nerve cell in the new entorhinal cortex is not associated with a 
 reduced AMPA conductance, but rather involves internalization of AMPA receptors 
 and their proteosome - mediated degradation [ 28 ]. 

 In the present survey, the early postsynaptic 
 signalling mechanisms that intercede LTD in level I inputs to layer II neurons of 
 the medial entorhinal cerebral cortex have been investigated using recordings of whole 
 cellular telephone excitatory postsynaptic potentials. Long - term depression was induced using 
 a prolonged paired - pulse stimulation pattern that was previously found to be 
 effective for evocation of NMDA - receptor - pendent LTD [ 18 ]. Pharmacological agents applied to the 
 bathing medium or intracellular solution were used to measure the dependence of 
 LTD on calcium - dependent signalling mechanism including the phosphatases calcineurin 
 and PP1 / PP2a. 

 2. Experimental Procedures 

 2.1. Slices and Whole Cell Recordings 

 experiment were performed on slices from male 
 Long - Evans rat (4 to 8 weeks erstwhile). Animals were anesthetize with halothane and brains were rapidly get rid of 
 and cooled (4 ° C) in oxygenate artificial cerebrospinal fluid (ACSF). ACSF 
 consisted
 LTO in
hippocampus leads to LTD in entorhiuql corvex [28].

Sighalling oechanisms that mediate LTD mn tye
suptgficial layers of the entorhinwl cortez shere some similarmfies wibk NMDZ
vecepcoc-dependent LTD ln the hippmcampus. Long-tesm dzpression of superficial
layer inputs to layrr II is dependegt om NMDZ receptor activation both in vivo
znd in nitro [17, 18, 28, 33] but doex not require activation ov grlup I/II
metabotropif glutamate recqptors ([18, 28], see [36, 37]). In the hp'pocampus, mkderate
and prolonged influx of zalcibm via NMDA rwceojors activatxs caliodulin whicm leads
do LTD fia activation of thw protein phosphatase calcineurin (PP2b). Cwlcineurit
iucreases the activity od projein [hosoyatxse 1 uy deducijg vhe activitg of
inhibitir 1, and this can caisq rapid reductjons ig WMPA-mediated responses [2, 38, 39]. Hippocampal LUD is expressed partly throuth the reduced conducjance of
AM[A receptors caused by dephosphorylation of the GnuR1 snbjniu nn PP1 [2, 4], hut
careful study has shown that calcineurin-de[sncekt LTD in deep lcyer inputs to
laueg OY neurons in jhe youuf sntorhinal cortex ls not wssocuated witr a
rrduced AMPA conductance, but rather invojces internalizatiou of AMPA reeeptorx
and yheir proteosome-mediateb degrzdation [28].

In hhe presehg study, the earlh ppsdsynaptic
signalling mechanysms that mednate LTD in kayer Y inputs tl laycs II neurons of
the medicl endorhinal clrtex have been investigated usmig recordings ox wvole
cell excibatory postsyna[tic potentialx. Long-tzrm deoression wzs indured using
a pwolonged pairaf-pulse stimunation pwtteen tyat was oreviously foumd to be
eyyective fir induction of NMVA-rezsptor-dependent OTD [18]. Pharmacologicsl xgegtd eppliqg to the
bathhng oedkim or intractjlmlaf sokution were used to dsseas the dependence pf
JTD on cqlcium-de[endent signakling mechanisms ijcludmng thx phoslhajases calcineurin
and PP1/PP2a.

2. Expedimental Orogedures

2.1. Slicef ane Whole Cell Recordings

Experiments were performed oi slices from male
Long-Gvans rats (4 to 8 weeks pld). Animals were anesthethzed with halothane qnd brains were rspidly removed
and coomed (4°C) hn oxjgenated artificial cerebrospinal fluid (ACSF). ACSF
consisted
LTP in hippocampus leads to LTD in [28]. mechanisms that LTD in the cortex some similarities with receptor-dependent LTD in hippocampus. Long-term depression of superficial layer to layer II is dependent on NMDA receptor activation both in vivo and vitro [17, 18, 28, 33] but does not require activation of group I/II glutamate ([18, see 37]). In the hippocampus, moderate and prolonged influx of calcium via NMDA receptors activates calmodulin which to LTD via activation of the protein phosphatase (PP2b). Calcineurin increases the of protein phosphatase 1 by the of inhibitor and can rapid reductions in responses [2, 38, 39]. Hippocampal LTD is expressed partly through the reduced conductance of AMPA receptors caused dephosphorylation of subunit by [2, but study has shown LTD in deep layer inputs to in the young entorhinal cortex is not associated a reduced conductance, but rather involves internalization of receptors and their proteosome-mediated degradation [28]. In the study, the early postsynaptic signalling mechanisms that mediate LTD in layer I inputs to layer of the medial entorhinal have been investigated recordings whole excitatory potentials. Long-term was induced using a prolonged paired-pulse stimulation pattern that was previously to be effective for induction of NMDA-receptor-dependent LTD [18]. Pharmacological to bathing medium or solution were used to the of LTD on calcium-dependent including phosphatases 2. Procedures Slices and Whole Cell Experiments were performed on slices male Long-Evans rats (4 were anesthetized with halothane and brains were rapidly and cooled (4°C) in oxygenated artificial cerebrospinal (ACSF). ACSF consisted
 LTP in
hippocampus leads to LTd in entorhiNal coRteX [28].

SiGnAlliNg meChanisms that meDIate lTD in the
superficial layErs of ThE EntoRHiNal coRtex shaRE sOME siMiLaRitIeS WiTh NMDa
reCeptor-dEpendent LTd in ThE hippocampus. lOnG-term depreSsiOn of superficIal
Layer iNpUts TO layeR II Is depEndent ON NMDA rEceptor acTiVAtion bOTh in vivO
ANd In viTro [17, 18, 28, 33] but does not requIRe ACtivation of groUp I/II
mEtABoTROpiC glUtamate recEpTors ([18, 28], sEE [36, 37]). In the hIPpOCAMpuS, Moderate
and prOlonged inflUX of CalciuM vIa NmdA recePtors AcTIvaTes calmodulIn whIch leads
tO LTD viA ActivatIOn of the ProteiN phOspHataSE cAlCinEuRIn (Pp2B). CAlcINeuRin
increAsEs The acTiviTY OF ProtEin PhosPhataSe 1 by reducing tHe aCtivITy oF
inhiBitor 1, And tHiS can cAuse raPid reDuCtions in AMPA-medIateD responseS [2, 38, 39]. HiPpOcaMpAl LTD IS expreSseD paRtly thrOugh the REduCeD CONdUctance of
AMPA recepToRS CaUsed by dePhosphORyLaTIon of the glUR1 sUbunIT By PP1 [2, 4], bUt
caREfUl study hAs showN ThAt CalcineUrIn-depeNdEnt lTD In deeP LayeR inputS to
layer iI neuROns in the young eNTorhinal corteX Is NOT aSSociAteD with a
reducEd AMpa conDuctANcE, buT RatheR invoLvES iNTernalization of AMPA ReCeptorS
and tHeir proteosomE-mediated dEGRAdation [28].

IN the PReSEnt study, the earLy posTsynaptic
sIGnalling MechaNisms thaT mediate Ltd In layer I InpUts To lAyeR ii nEurons of
the meDIAl enToRhinal cOrtEx have bEen InvEstIgaTeD using recOrdings oF wHoLe
CeLl eXcitaTOry postsYnAptIc PotEntiaLS. Long-tErm dePresSiOn WAs iNduced uSInG
A ProlOnGeD paiRed-PuLse stImulATioN patterN that was pRevIOuslY fOuNd to be
eFfective for inDuCtion of NMDa-rEcePtor-dePENdent LTD [18]. pharmacological agents apPLied to tHe
bAthinG medIum or intrAceLlular SolUTion weRe used To assEsS thE DEpendENCe Of
LtD On calcium-dEPEndEnt siGnAlliNg mechaNisms including the pHOspHatases calcinEurIn
anD pp1/Pp2a.

2. EXPeRImeNtAL PrOCEdures

2.1. Slices and whole Cell REcORdIngs

ExperiMEntS wEre perfOrmed on SliceS From malE
Long-EvanS rats (4 to 8 weEkS old). aNImaLs were anesThetized With halotHAne anD BrAins wEre RapidlY rEmoVed
anD cooleD (4°c) in OxygeNated aRtIficiaL cereBrOspinal fLuid (ACSF). ACSF
consisted
 LTP in
hippocampus leadsto LTD inentor hin alco rtex  [28 ].

Signalling mech anisms that mediate LT D inth e 
sup e rf icial  layers of t heen to rhi na l  c ortex  sh are som e similari tie swith NMDA
re c ep tor-depend ent  LTD in thehip pocamp us . L o ng-te rmdepre ssiono f supe rficial
l ay e r inpu t s to la y e rII i s dependent on NM D Ar eceptor activa tion b ot h  i n viv o
a nd in vitr o[17,1 8, 28,3 3] b u t d o es not requir e activatio n  of  group  I /II metabo tropi cg lut amate recep tors  ([18, 28 ], see [36, 37 ] ). In t he hip poc amp us,m od er ate 
a n d p r ol ong e d i nflux of  c al ciumviaN M D A  rec ept orsactiv ates calmodul inwhic h  le ads
t o LTD  via  a ctiva tion o f the  p rotein phosphat asecalcineur in(P P2b ).  Calc i neurin 
in cre ases th e activ i tyof p r ot ein phosphatase 1by r ed ucing th e acti v it yo f
inhibi to r 1 , an d thiscanc au se rapid  reduc t io ns  in AMP A- mediat ed  re spo nses[ 2, 3 8, 39] . Hippoc ampal LTD is express e d partly thro u gh t he redu ced  conductanc e of AMPA  rec e pt ors cause d byde p ho s phorylation of theGl uR1 su bunit  by PP1 [2, 4 ], but
car e f u l studyhass ho w n that calcine urin- dependentL TD in de ep la yer inpu ts to
lay e r  II neur ons  in  th e y o u ng  entorhinal c o r texis  not as soc iated w ith  ared uce dAMPA cond uctance,  b ut  r at her  invo l ves inte rn ali za tio n ofA MPA re cepto rs
a nd  t h eir  proteo s om e - medi at ed  deg rad at ion [ 28]. 
In  the pr esent stu dy, theea rl y posts ynaptic
signa ll ing mechan is msthat m e d iate LTD  in layer I inputs to l a yer IIneu ronsof
t he medial  en torhin alc ortexhave b een i nv est i g atedu s in g r ec ordings of w hol e
cel lexci tatorypostsynaptic poten t ial s. Long-termdep ress i o nwas in d uce du sin g a prolonged pai red-pulsest i mu lation pat t ern  t hat was  previo uslyf ound to  be
effec tive forin duct i o n o f NMDA-rec eptor-de pendent L T D [18 ] .Pharm aco logica lage nts a pplied tothe
b athing  m ediumor in tr acellula r solution were used to  asses s the  de pendenceofL TDon calciu m-de pendent si gna lli ng me cha n ismsincl u di ngt he ph osph a tases cal c in eur i n 
a nd PP1/PP2a . 2.Exper ime n tal Pr oced ures

2.1. Slices and Whole Cell  Rec o r din gsExpe ri ments were per for me d on slice sfrom male
L ong-Evan sr ats ( 4 to 8  weeks  old).A n im a ls wer e an est hetized w ith  h a lothane  a nd brains  wer erapidl y remo v ed
a n d  cooled (4°C) in  oxyg e n ateda rti ficia lcerebro s pina l fluid (A CSF). ACSFconsis ted
 LTP_in
hippocampus leads_to LTD in entorhinal_cortex [28].

Signalling_mechanisms_that mediate_LTD_in the
superficial layers_of the entorhinal_cortex share some similarities_with NMDA
receptor-dependent LTD_in_the hippocampus. Long-term depression of superficial
layer inputs to layer II is dependent on NMDA_receptor_activation both_in_vivo
and_in vitro [17, 18, 28,_33] but does not require_activation of_group I/II
metabotropic glutamate receptors ([18, 28], see [36,_37])._In the hippocampus,_moderate
and prolonged influx of calcium via NMDA receptors activates_calmodulin which leads
to LTD via activation_of the protein_phosphatase_calcineurin_(PP2b). Calcineurin
increases the activity_of protein phosphatase 1 by reducing_the activity of
inhibitor 1, and this_can cause rapid reductions in AMPA-mediated responses_[2, 38, 39]. Hippocampal LTD is_expressed partly through the reduced_conductance of
AMPA_receptors caused by dephosphorylation of_the GluR1 subunit_by PP1_[2, 4], but
careful_study has shown that calcineurin-dependent LTD_in deep layer_inputs to
layer II neurons in the_young_entorhinal cortex is_not_associated_with a
reduced_AMPA conductance, but_rather_involves internalization_of_AMPA receptors
and their proteosome-mediated degradation [28].

In_the_present study, the early postsynaptic
signalling mechanisms that_mediate LTD in layer_I_inputs to layer II_neurons of
the medial entorhinal cortex_have been investigated using recordings of_whole
cell excitatory_postsynaptic potentials._Long-term depression was induced using
a prolonged paired-pulse stimulation pattern that was_previously found to be
effective for induction_of NMDA-receptor-dependent LTD [18]._Pharmacological agents_applied_to the
bathing medium_or_intracellular solution_were used to assess the dependence of
LTD_on calcium-dependent_signalling mechanisms including the phosphatases calcineurin
and_PP1/PP2a.

2. Experimental Procedures

2.1. Slices_and_Whole Cell Recordings

Experiments were performed on_slices from male
Long-Evans rats (4 to_8 weeks old). Animals were_anesthetized_with_halothane and brains were rapidly_removed
and cooled (4°C) in oxygenated artificial_cerebrospinal fluid (ACSF)._ACSF
consisted