Commissural NTS lesions enhance the pressor response to central cholinergic and adrenergic activation

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ContentslistsavailableatSciVerseScienceDirect

Neuroscience

Letters

j o ur na l ho me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / n e u l e t

Commissural

NTS

lesions

enhance

the

pressor

response

to

central

cholinergic

and

adrenergic

activation

Alexandre

A. Vieira,

Laurival

A. De

Luca

Jr,

Eduardo

Colombari,

Debora

S.A.

Colombari,

José

V. Menani

∗ DepartmentofPhysiologyandPathology,DentistrySchool,SãoPauloStateUniversity(UNESP),Araraquara,SP,Brazil

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◮_Lesions_of_the_commNTS_enhance_the_pressor_responses_to_i.c.v._injection_of_carbachol.

◮_commNTS_inhibitory_mechanisms_are_involved_in_the_modulation_of_the_pressor_responses.

◮_commNTS_lesions_impair_sympathetic_activation_produced_by_peripheral_{chemoreceptor.}

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Articlehistory: Received10March2012

Receivedinrevisedform3May2012 Accepted15May2012

Keywords: Sympathetic Vasopressin Hypertension CommissuralNTS Bloodpressure

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Electrolyticlesionsofthecommissuralnucleusofthesolitarytract(commNTS)inratsenhancethe

pressorresponsetobilateralcarotidocclusionortointravenousinfusionofhypertonicNaClwithout

changingbaroreflexresponses.Inanoppositedirection,commNTSlesionsabolishthepressorresponses

toperipheralchemoreflex activation.Theseopposite effectsof commNTSlesionsapparentlyresult

fromanimpairmentofsympatheticactivationinonecaseandinafacilitationofvasopressin

secre-tionintheothers.Inthepresentstudy,weinvestigatedtheeffectsoftheelectrolyticlesionsofthe

commNTSinthepressorresponsesthatdependonsympatheticactivationandvasopressinsecretion

producedbycentralcholinergicoradrenergicactivationwithintracerebroventricular(i.c.v.)injections

ofcarbacholornoradrenaline,respectively,inunanesthetizedrats.Male Holtzmanrats(280–320g,

n=8–15/group)withacute(1day)orchronic(21days)shamorcommNTSlesions(1mA×10s)and

astainlesssteelcannulaimplantedinthelateralventriclewereused.AcutecommNTSlesionsincreased

thepressorresponsetoi.c.v.injectionofcarbachol(0.5nmol/1␮1)(52±2,vs.sham:37±2mmHg)or

noradrenaline(80nmol/1␮l)(45±6,vs.sham:30±3mmHg),whereaschroniccommNTSlesionsdid

notaffectthepressorresponsestothesametreatments.LesionsofthecommNTSimpairedchemoreflex

responsesproducedbyintravenousKCN,withoutchangingbaroreflexresponses.Theresultssuggest

thatcommNTS-dependentinhibitorysignalsareinvolvedinthemodulationofthepressorresponsesto

centralcholinergicandadrenergicactivation,probablylimitingvasopressinsecretion.

1. Introduction

Signals from peripheralbaro and chemoreceptors reachthe nucleusofthesolitarytract(NTS)beforeascendingtoothercentral sitesthatcontroltheautonomicandhormonalresponsesinvolved inthecardiovascularregulation[24].

Inunanesthetizedrats,theelectrolyticlesionsofthemostcaudal portionoftheNTS,thecommissuralNTS(commNTS),reducethe pressorandbradycardicresponsesproducedbychemoreflex acti-vationwithintravenous(i.v.)injectionofpotassiumcyanide(KCN)

∗Correspondingauthorat:DepartamentodeFisiologiaePatologia,Faculdadede OdontologiadeAraraquara,UNESP,RuaHumaitá,1680,Araraquara,14801903,SP, Brazil.Tel.:+551633016486;fax:+551633016488.

E-mailaddress:menani@foar.unesp.br(J.V.Menani).

andthepressorresponsestol_-glutamate_injected_into_the_lateral portionoftheintermediateNTS,withoutchangingtheresponsesto baroreflexactivation[13].AlthoughcommNTSlesionsdonotaffect baselinemeanarterialpressure(MAP)innormotensiverats,these lesionsreduceMAPtonormotensivelevels,foratleastfivedays, inspontaneouslyhypertensiverats(SHR)[23,30].Thereductionof baselineMAPinSHRorthepressorresponsestoi.v.KCNby comm-NTSlesionssuggeststhatthecommNTSispartofthehindbrain mechanismsinvolvedinsympatheticactivation.

On the other hand, commNTS lesions enhance the pressor

responsestobilateralcommoncarotid occlusionorto intragas-tric (i.g.)gavage of 2M NaCl [4,29], suggesting that commNTS

inhibitory mechanisms may oppose the action of the pressor

mechanisms activatedin theseconditions. The enhanced pres-sor responses to bilateral common carotid occlusion or to i.g. gavage of 2M NaCl was abolished in rats pre-treated with a

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32 A.A.Vieiraetal./NeuroscienceLetters521 (2012) 31–36

vasopressin antagonist, suggesting that vasopressin secretion inducedbyhyperosmolarityor bycommoncarotidocclusion is inhibitedbycommNTSmechanisms[4,29].Therefore,studieshave suggestedthatcommNTSmayhaveoppositerolesinthecontrol ofsympatheticactivationandvasopressinrelease whichresults in opposite effects of the commNTS lesions on cardiovascular responsesdependingontheconditiontested[4,13,23,27,30].The reasonsforthesedifferencesoncardiovascularregulationarenot clearyet.

Exceptforthepressorresponsestoglutamateinjectionintothe intermediateNTS,alltheothercardiovascularresponsestestedin thecommNTS-lesionedratswereproduced bytheactivationof peripheralmechanismsoramixofcentralandperipheral mecha-nismsalmostexclusivelyintegratedinthehindbrain.Itwasnot tested yet the effects of the commNTS lesions in the pressor responsesproducedbytheactivationofforebrainmechanismsthat increasesympatheticactivityand/orvasopressinreleaselikethe pressorresponsestoforebraincholinergicoradrenergicactivation ([1,8,6,17,19,31]).Consideringthatpreviousstudieshave shown thatcommNTSlesionsmayaffectsympatheticactivationand vaso-pressinsecretioninoppositedirections,inthepresentstudy,we testedtheeffectsofthecommNTSlesionsinthepressorresponses producedbycentralcholinergicoradrenergicactivationwiththe injectionofcarbacholornoradrenaline,respectively,intothe lat-eralventricle(LV).

2. Materialsandmethods

2.1. Animals

MaleHoltzmanratsweighing280–320gwereused.The ani-malswerehousedindividuallyinstainlesssteelcagesinaroom withcontrolledtemperature(23±2◦_C)_and_humidity₍₅₅_±_10%). Lightswereonfrom7:00amto7:00pm.StandardPurinachow andtapwaterwereavailableadlibitum.TheEthicalCommittee for Animal Careand Use from Dentistry School of Araraquara-UNESPapprovedtheexperimentalprotocolsusedinthepresent study.

2.2. LesionofthecommNTS

Ratsanesthetizedwithhalothane werefixedtoastereotaxic frame(model900,DavidKopfInstruments).Thedorsalsurfaceof thebrainstemwasexposed.Atungstenwireelectrode(0.2mm ofdiameter)wasintroducedintothebrainstem0.0and0.5mm caudaltocalamusscriptorius, inmidlineand0.5mmbelowthe dorsalsurfaceofthebrain.Lesionswereperformedusingcathodal current(1mA×10sineachpointsoftheelectrodeintroduction).

2.3. ImplantofcannulasintotheLV

Rats were anesthetized with ketamine (80mg/kg of body

weight) combinedwith xylazine(7mg/kg of body weight) and placedinastereotaxicframe(model900,DavidKopfInstruments). A stainlesssteel 23-gauge cannula wasimplanted into the lat-eralcerebralventricle(LV)usingthecoordinates0.3mmcaudal tobregma,1.5mmlateraltomidlineand3.5mmbelowtodura mater.Thecannulaswerefixedtothecraniumusingdentalacrylic resinandjewelerscrews.Theratsreceivedaprophylacticdoseof penicillin(30,000IU)givenintramuscularlypost-surgically.

InratsusedtotesttheeffectsofacutecommNTSlesions,the stainlesssteelcannulawasimplantedintotheLV5daysbefore thelesionandinratsusedtotesttheeffectsofchroniccommNTS lesions,thecannulawasimplanted15daysafterthelesion.

2.4. Arterialpressureandheartraterecording

Meanarterialpressure(MAP)andheartrate(HR)wererecorded inunanesthetized rats.Onedaybeforerecording,theratswere anesthetizedwithketamine(80mg/kgofbodyweight)+xylazine (7mg/kg of body weight), a polyethylene tubing (PE-10 con-nectedtoaPE-50)wasinsertedintotheabdominalaortathrough thefemoralarteryfor arterialpressure recordingand a second polyethylenetubingwasinsertedintothefemoralveinfordrug administration.Arterialandvenouscathetersweretunneled sub-cutaneouslyandexposedonthebackoftherattoallowaccessin unrestrained,freelymovingrats.Torecordpulsatilearterial pres-sure,MAPandHR,thearterialcatheterwasconnectedtoaStathan Gould (P23 Db)pressure transducercoupledto a pre-amplifier (modelETH-200 BridgeBio Amplifier)that wasconnected toa Powerlabcomputerdataacquisitionsystem(modelPowerlab16SP, ADInstruments).

2.5. InjectionsintotheLV

InjectionsintotheLVwereperformedusingaHamiltonsyringe connectedtoaninjector needle(2mmlongerthanthecannula fixedtotheanimal’shead)byaPE-10polyethylenetubing.

2.6. Drugs

Carbachol(0.5nmol/1␮l)ornoradrenaline(80nmol/1␮l)was injectedintotheLV.Phenylephrine(5␮g/kgofbodyweight)and sodiumnitroprusside(30␮g/kgofbodyweight)wereinjectedi.v. fortestingbaroreflex.Potassiumcyanide(KCN,40␮g/0.1ml/rat) wasinjectedi.v. forchemoreflextest.Alldrugswerepurchased fromSigmaChem.Co.,St.Louis,MO,USA.Thedosesofcarbachol andnoradrenalinewereadaptedfromthepreviousstudiesthat testedtheeffectsofnoradrenalineandcarbacholinjectedintothe LVonarterialpressure[22,10].

2.7. Histology

Attheendoftheexperiments,ratsweredeeplyanesthetized with sodium thiopental (70mg/kg of body weight, ip). Saline

followed by 10% buffered formalin was perfused through the

heart. The brains were frozen, cut coronally (50␮m sections), stainedwithGiemsastainand analyzedbylight microscopyto confirmthesite of injectionintothe LV andthe lesionsinthe commNTS.

2.8. Statisticalanalysis

Theresultsarereportedasmeans±standarderrorsofmeans

(SEM).OnewayANOVAcombinedwithaStudentNewmanKeuls

testswereusedforcomparisons.Differenceswereconsidered sig-nificantatp<0.05.

2.9. Experimentalprotocol

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Fig.1.(A–C)Schematicdiagramsand(D)photomicrographshowing(A)thelocalizationofthecommNTSwithinthemedullaoblongataand(B–D)thelesioncorrectlyplaced inthecommNTS(darkinBandCandindicatedbythearrowinD).AP,areapostrema;cc,centralcanal;XII,hypoglossalnucleus;Gr,gracilenucleus;py,pyramidaltract.

InothergroupsofratswithshamorcommNTSlesions(1and 21days)thesameprotocolwastested,exceptthatnoradrenaline (80nmol/1␮l)insteadofcarbacholwasinjectedintotheLV.

3. Results

3.1. Histologicalanalysis

Fig. 1 presents schematic diagrams and a photomicrograph showingthesiteofthelesioncorrectlyplaced inthecommNTS. ThecommNTSlesionswerelocatedinthemidline,abovethe cen-tralcanalandextendedfromtheleveloftheobextoaround1mm caudaltotheobex.LesionswererestrictedtothecommNTS,and

didnotinvolvethelateralportionsoftheNTS,hypoglossalnucleus ortheareapostrema,aspreviouslyshown[4,13,28,29].

3.2. Pressorresponsestoi.c.v.carbacholornoradrenalinein commNTS-lesionedrats

Acute(1day)commNTSlesionsenhancedthepressorresponses to i.c.v. injection of carbacol (0.5nmol/1␮l) (52±2mmHg, vs. sham rats: 37±2mmHg) [F(1, 29)=50.22; p<0.001] (Fig. 2A) or noradrenaline (80nmol/1␮l) (45±6mmHg, vs. sham rats: 30±3mmHg)[F(1,22)=10.23;p<0.05](Fig.2B).Chronic(21days) commNTSlesionsdidnot modifythepressor responsestoi.c.v. carbachol(43±4mmHg,vs.shamrats:39±4mmHg)(Fig.2A)or noradrenaline(34±4mmHg,vs.sham:32±4mmHg)(Fig.2B).

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Fig.3. IncreasesinMAPandreductionsinHRproducedbyi.v.injectionsofKCN(40␮g/0.1ml/rat)inshamorcommNTS-lesionedrats(1or21days)ofthegroupsofrats thatreceived(A)carbacholor(B)noradrenalinei.c.v.Theresultsarerepresentedbymeans±SEM.Thenumberofratsisindicatedinparenthesisaboveorbeloweachbar.

AcuteorchroniccommNTSlesionsdidnotaffectthechanges in HRproduced by i.c.v. injectionof carbachol (Fig.2C). Acute commNTS lesions reduced the bradycardia to i.c.v. injection of noradrenaline (−28±12bpm, vs. sham rats: −60±6bpm) [F(1,22)=10.13;p<0.05],whereaschroniccommNTSlesiondid not modify the bradycardia to i.c.v. injection of noradrenaline (−52±13bpm,vs.shamrats:−80±6bpm)(Fig.2D).

AcuteorchroniccommNTSlesionsdidnotaffectthebaseline MAP(104±3and 108±3mmHg,respectively) orHR (340±11 and356±13mmHg,respectively)comparedtothebaselineMAP (110±3and 116±1mmHg,respectively)and HR(387±15 and 386±17mmHg,respectively)ofshamrats.

3.3. BaroreflexandchemoreflexresponsesincommNTS-lesioned rats

Intheratstestedfortheeffectsofi.c.v.carbachol,acute(1day) commNTSlesionsreducedthepressor [F(1,23)=10.05;p<0.05] andbradycardicresponses[F(1,23)=19.66;p<0.001]toi.v. injec-tionofKCN(40␮g/0.1ml/rat),whereaschronic(21days)commNTS lesionsdidnotreducethepressor[F(1,17)=0.79;p>0.05]or brady-cardic[F(1, 17)=1.34; p>0.05] responses to i.v. KCN (Fig. 3A). Acuteor chronic commNTSlesions didnot modifythe pressor andbradycardicresponsetoi.v.injectionofphenylephrineorthe hypotension to i.v. infusion of sodium nitroprusside, however, acutecommNTSlesionsreducedthetachycardicresponsestoi.v. sodiumnitroprusside(60±6bpm,vs.shamrats:91±7bpm)[F(1, 23)=12.67;p<0.005].

Intheratstestedfortheeffectsofi.c.v.noradrenaline,acute[F(1, 22)=17.87;p<0.001]orchronic[F(1,15)=4.75;p<0.05] comm-NTSlesionsreducedthepressorresponsetoi.v.injectionofKCN (40␮g/0.1ml/rat)(Fig.3B).AcutecommNTSlesionsalsoreduced thebradycardicresponses[F(1,22)=10.07;p<0.05]producedby i.v.injectionofKCN(40␮g/0.1ml/rat).AcuteorchroniccommNTS lesionsdidnotmodifythepressorandbradycardicresponsesto i.v.injectionofphenylephrineorthedepressor andtachycardic responsestoi.v.sodiumnitroprusside.

4. Discussion

Thepresentresultsshowthatacute(1day)electrolyticlesions of the commNTSenhance the pressor responses toi.c.v. injec-tion of carbachol or noradrenaline, suggesting that commNTS inhibitorymechanismsareinvolvedinthemodulationofthe pres-sorresponsestocentralcholinergicoradrenergicactivation.The bradycardiatoi.c.v. injectionofcarbachol wasnotmodified by thecommNTSlesions,however,thebradycardiatoi.c.v.injection ofnoradrenalinewasreducedincommNTS-lesionedrats,which may also facilitate the pressor responses. The same commNTS lesionsthatfacilitatedthepressorresponsestoi.c.v.carbacholor noradrenalinereducedthepressorandbradycardicresponsesto peripheralchemoreflexactivationwithi.v.KCNanddidnotaffect thechangesinHRproducedbybaroreflexactivation.Theseresults suggestthattheinhibitorymechanismsdeactivatedbycommNTS lesionsarenotthesameinvolvedinthebaroreflexmodulationof autonomic responsesinvolved incardiovascular regulation.The facilitationof the pressor responsesto i.c.v. injectionof carba-cholornoradrenalinebycommNTSlesionsissimilartotheresults ofpreviousstudiesthatshowedenhanced pressorresponsesto bilateralcommoncarotidocclusionortoi.g.gavageof2MNaCl incommNTS-lesioned rats[4,29].Therefore, thepresent results extend the conclusion of the previous studies suggesting that thecommNTSinhibitorymechanismsalsomodulatethepressor responsestoforebraincholinergicoradrenergicactivation.

Differently from acute commNTS lesions, chronic (21 days) commNTS lesionsdid not affect the pressor responses to i.c.v. carbacholornoradrenaline,resultssimilartothoseofthe previ-ousstudy[28]thatshowednodifferenceinthepressorresponse produced by bilateral carotid occlusion in chronic commNTS-lesionedrats.Therecoveryoftheinhibitoryfunctioninchronic commNTS-lesionedratsisprobablyrelatedtotheneural plastic-ity,amechanismthatallowsareasnotdamagedbythelesion,like remainingportionsoftheNTS,toreplacethefunctionimpaired bythecommNTSlesions.Although theelectrolyticlesionsmay

also damage the fibers of passage, a previous study showed

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dopamine-beta-hydroxylase-containingneuronsinthecommNTS aresimilar,suggestingthattheeffectsofthecommNTSlesionswere notduetothedestructionofthefibersofpassage[14].

LesionsofthecommNTSincreaseosmotic-inducedactivation of the paraventricular and supraoptic hypothalamic nuclei and plasmavasopressinlevels([5]andunpublishedresultsfromour laboratory).Theenhanced pressor responsetoani.g. gavageof 2MNaClortocommoncarotidocclusionincommNTS-lesioned ratswasabolishedbythepre-treatmentwithvasopressin antag-onist[4,29]. Therefore, the suggestion is that the commNTS is partofacentralcircuitrythatinhibitsvasopressinsecretion.The pressorresponsetoforebraincholinergicoradrenergicactivation aremediatedbyincreasesinsympatheticactivityandvasopressin release [1,8,6,17,19,31].Therefore, similartotheincreaseof i.g. 2MNaCl-orcarotidocclusion-inducedpressorresponses[4,29], theincreasedpressorresponsetocentralcholinergicoradrenergic activationincommNTS-lesionedratsmightbeduetoanincrease invasopressinsecretion.Althoughitisnotpossibletocompletely discardanincreasedsympatheticactivationtoi.c.v.carbacholor noradrenalineincommNTS-lesionedrats,theevidenceofprevious studies[13]suggestingthatcommNTSlesionsimpairsympathetic activationproducedbyperipheralchemoreceptoractivationorby glutamateinjectedintotheintermediateNTSsignalsinanopposite direction.

TheintermediateandcommNTSareanatomicallyconnectedto thelateralparabrachialnucleus(LPBN),theregionsurroundingthe anteroventralpartofthirdventricle(AV3Vregion),the paraventric-ular(PVN)andthesupraopticnuclei(SON)ofthehypothalamus [16,25,26,32]. These connections may convey signals from the peripheralcardiovascularreceptorsthatascendtoforebrainareas involved in the control of fluid-electrolytebalance and cardio-vascularregulation likethoseinvolved intheinhibitorycontrol ofvasopressinsecretion.Withoutexcludingotherreceptors, arte-rialbaroreceptorsarethemainsourceofinhibitorysignalsthat limitthepressorresponsesbyfacilitatingparasympatheticactivity andinhibitingsympatheticactivityandvasopressinsecretion.The commNTSreceivesmainlytheprimaryafferentprojectionsfrom theperipheralchemoreceptors,whereasmorerostralpartsofthe NTS,liketheintermediateNTSreceivesmainlytheprimaryafferent projectionsfromarterialbaroreceptors[24].AlthoughcommNTS isnotthemainsiteofthefirstsynapseofbaroreceptorafferents, itmightreceivebaroreceptorsignalsfromtheintermediateNTS, beforetheycouldreachforebrainareasinvolved in thecontrol ofvasopressinsecretion.However,differentlyfromthecontrolof vasopressinsecretion,theautonomiccontrolofthe cardiovascu-larsystembybaroreceptorsignalsseemstobeindependentfrom thecommNTS.ThismightexplainwhycommNTSlesionsstrongly affectthebaroreceptormodulationofvasopressinsecretionand onlyslightlyinfluenceautonomicresponsesmediatedby sympa-theticandparasympathetic mechanisms.On theotherhand,an increaseinvasopressinsecretiontocentralcholinergicor adrener-gicactivationbycommNTSlesionsissupportedbypreviousstudies thatproposedtheimportanceofchemoreceptorreflexinthe con-troloffluid-electrolytebalance[18].Theexpositionofmammals tolowoxygenpressure(moderatehigh-altitudehypoxia)results indiuresis,whichmightbeaconsequenceofreducedvasopressin secretionduetoaninhibitoryactionofperipheralchemoreceptor. ThelesionsofthecommNTSmayremovetheinhibitory mecha-nismsactivatedbyperipheralchemoreflexincreasingvasopressin secretionby stimuli like central cholinergicor adrenergic acti-vation.Therefore, thepresentand previousresultssuggest that the control of neural/autonomic and/or humoral responses to peripheralbaroreceptororchemoreceptoractivationmayinvolve

opposite mechanisms in the commNTS and the result can be

oppositecardiovascularresponsesdependingonwhichisthe pre-dominantmechanismactivated.

Acknowledgments

WethankSilasPereiraBarbosa,ReginaldodaConceic¸ãoQueiróz andSilviaFógliaforexperttechnicalassistance,SilvanaA.D. Mala-voltaforsecretarialassistance,andAnaV.deOliveiraforanimal care.ThisresearchwassupportedbypublicfundingfromFundac¸ão

de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and

Conselho NacionaldeDesenvolvimento CientíficoeTecnológico (CNPq).

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