TurkJBiol 25(2001)301-321 ©TÜB‹TAK EffectsofPhotoperiodandMelatoninInfusionson BodyWeightinPinealectomizedJuvenileSiberian Hamsters(Phodopussungorus) BülentGÜNDÜZ,AlperKARAKAfi DepartmentofBiology,FacultyofArtsandSciences,Abant‹zzetBaysalUniversity, 14280Bolu-TURKEY Received:25.02.2000 Abstract: Weexaminedtheeffectsofdailymelatonin(Mel)infusionsinpinealectomizedprepubertal maleSiberianhamstersinthreedifferentconditions.Inonestudyweinvestigatedthebodyweight maturationresponsetoonehourdailyinfusionsof10ng,25ng,or50ngofMelinpinealectomized hamsters.Animalsreceived,atday15oflife,programmedsubcutaneousinfusionsofMelorvehicle atoneoffivetimepoints(1900-2000,2000-2100,2100-2200,2400-0100,and0300-0400 hours)for30days.Inlong-day-born(16L)animals,Melinfusionrightafterlightsoff(2000-2100 hours)significantlyinhibitedbodygrowth;thisdosewasineffectiveatothertimes.Dosesof10ng and25ngMelwereineffectiveatalltimepoints.Inasecondstudy,hamstersreceivedeither4-or 8-hinfusionsofMel(either50ng/hor50ng/day)atvarioustimesthroughoutthedayandnightof a16Lor10Lphotoperiod.Daily4-h,50ng/h,Melinfusionsat1700-2100hoursinhibitedbody weightgrowthin16Landdaily4-hMelinfusions(either50ng/hor50ng/day)inhibitedbodyweight growthat1700-2100hoursin10L.Inallcases,daily8-hinfusionssuppressedbodyweight development.Inathirdstudy,long-day-bornpinealectomizedhamsterswereinfusedwithtwo signalsoffourhoursseparatedbyanintervaloftwohours.Melinfusedgroupshadsignificantly inhibitedbodygrowthcomparedtovehicleinfusedanimals.Bodyweightdevelopmentwasmaximally inhibitedonlyinthosegroupsinwhichtheperiodofMelsensitivitywasidentifiedinthefirststudy (2000-2100hours)overlappedorimmediatelyfollowedaperiodofMelinfusionTheseresultsshow thatthephotoperiodicbodyweightresponseinjuvenileSiberianhamstersisregulatedbythe coincidenceintimeofexogenouslyadministeredMelwithanintrinsicrhythmofsensitivitytoMel, andthedurationoftheMelsignalalonecannotexplaintheresults. KeyWords: Bodyweight,Infusion,Melatonin,Photoperiod,Pinealectomy,Hamster PinealektomiliJuvenilSibiryaHamsterlerinde(Phodopussungorus) FotoperiyotveMelatonin‹nfüzyonlar›n›nVücutA¤›rl›¤›ÜzerineEtkileri Özet: Pinealektomili,püberteöncesierkekSibiryahamsterlerindegünlükmelatonin(Mel) infüzyonlar›n›netkileriniüçayr›çal›flmadainceledik.Birinciçal›flmadahamsterlerinvücuta¤›rl›k geliflimlerinin,10ng,25ngve50ng,günlükbirsaatMelinfüzyonlar›naverdi¤icevab›araflt›rd›k. Hayvanlar15günlükikenpinealbezlerial›n›pbeflgrubaayr›ld›.30günsüreboyuncahergrubafarkl› zamanlarda(19:00-20:00,20:00-21:00,21:00-22:00,24:00-01:00ve03:00-04:00saat)olmak 301 EffectsofPhotoperiodandMelatoninInfusionsonBodyWeightinPinealectomizedJuvenileSiberianHamsters (Phodopussungorus) üzerederialt›naprogramlanm›flinfüzyonileMelyadaarac›s›verildi.Uzungün(16L)do¤umlu hayvanlarda,›fl›klarkapand›ktanhemensonra(20:00-21:00saat)yap›lanMelinfüzyonu,vücut a¤›rl›klar›n›nart›fl›n›inhibeetti;budozdi¤ergruplardaetkilide¤ildi.10ngve25ngMeldozlar›test edilentümgruplardaetkiliolmad›.‹kinciçal›flmadahamsterlere16Lyada10Lfotoperiyodunda, de¤iflikzamanlarda4yada8saatMelinfüzyonuyap›ld›.16L’degünlük4saat,17:00-21:00saatleri aras›ndaki50ng/saatMelinfüzyonu,10L’deise17:00-2100saatleriaras›ndagünlük4saat uygulanangerek50ng/saat,gerekse50ng/günMelinfüzyonuvücuta¤›rl›kgelifliminibask›lad›. Bütündurumlardagünlük8saatMelinfüzyonlar›vücuta¤›rl›kgeliflimleriniinhibeetti.Üçüncü çal›flmadauzungündo¤umlu,pinealektomilihamsterlere2saatarailekesintiyeu¤ram›fl,4saatlikiki sinyalileinfüzyonyap›ld›.MelinfüzedilmiflgruplarMelarac›s›ileinfüzedilmiflgruplaragöredaha azvücuta¤›rl›kart›fl›gösterdiler.Vücuta¤›rl›kgelifliminininfüzedilenMel’egösterdi¤icevapsadece Mel’inhassasoldu¤uperiyot(20:00-21:00saat)ileüstüstegeldi¤indeyadaMelinfüzyonperiyodunu hementakipetti¤inoktadagerçekleflmifltir.SonuçolarakjuvenilSibiryahamsterlerindafotoperiyodik vücuta¤›rl›¤›cevab›,melatonineolaniçselritmiled›flar›danverilenmelatonininrastlant›salolarak karfl›laflmas›ilegerçekleflmifltirvetekbafl›naMelsüresinyalibusonuçlar›aç›klayamamaktad›r. AnahtarSözcükler: VücutA¤›rl›¤›,‹nfüzyon,Melatonin,Fotoperiyod,PinealBez,Hamster Introduction Inmanysmallrodents,suchasSiberianhamsters( Phodopussungorus),annualchangesin photoperiodareinvolvedinseasonalcyclesofbodymass,reproductiveactivity(adults)and reproductivedevelopment(juveniles),pelagecolorandthermoregulation.Inthelaboratory, longphotoperiods(16hlight/day)stimulaterapidgrowthandtheearlyonsetofsexual maturation,whileshortphotoperiods(8hlight/day)inhibitgrowthanddelaytheonsetof sexualmaturation(1-3). ThereisampleevidencethatMelsynthesizedwithinthepinealglandisamajorfactorinthis photoperiodicresponse(4-6).Melsynthesisandreleaseshowacircadianrhythmwith depressedlevelsduringthedaylighthours,increasingatabouttwohoursafterlightsoffand remainingelevatedthroughoutthedarkuntilatorjustbeforelightson(7).Pinealectomy rendersjuvenileSiberianhamstersincapableofperceivingphotoperiodicchangeandthebody massandthegonadsaremaintainedaccordingtopreviousphotoperiodicinput(8-10). Daylengthistransducedintoaneuroendocrinesignalviaphoticregulationofthecircadian rhythmofMelproduction.AlthoughthereisstrongevidenceoftheimportanceoftheMel rhythminencodingdaylengthinformation,controversyexistsintheliteratureconcerningwhich parametersoftheMelrhythmarethemostimportantinthisphenomenon(11,12). TwohypotheseshavebeenproposedtoexplainthemechanismbywhichMelactsto transducephotoperiodicinformation.ThefirstproposesthatthedurationofMelproduction andsecretionsignalsdaylengthfortheorganism,andthedurationofMelproductionis proportionaltothedurationofthedarkphase;thelongerthenight,thelongerthedurationof Melproductionandsecretion.Inaseriesofexperiments,CarterandGoldman(8,9)attempted 302 B.GÜNDÜZ,A.KARAKAfi toidentifywhichcharacteristicsofthenocturnalMelsecretionprofilearemostimportantfor mediatingphotoperiod-inducedchangesinreproductivestatusandbodyweightinjuvenile Siberianhamsters.Whenjuvenilepinealectomizedhamstersatday18oflifewereinfusedwith 10ngMel/dayfor12days,infusionsof12hours’durationinhibitedbodygrowth,whereas4- houror6-hourinfusionsfailedtoexhibitanyinhibitoryeffect.Theeffectsoflongduration(12 h)andshortduration(4hor6h)infusionswereindependentofthetimeofdayatwhich infusionswereadministered.TheinvestigatorsconcludedthatthegrowthactionsofMelare dependentonthedurationoftheMelsignal.Theyalsoconcludedthatreproductivechangesare correlatedcloselywithbodyweightresponse.Inanothersetofexperiments,18-day-old pinealectomizedSiberianhamstersreceiveddaily10ngMelinfusionsofseveraldurations. Durationswerecenteredatthemidpointofthedarkphaseofthelight/darkcycle.After12days oftreatment,malesreceiving8,10,or12hourMelinfusionsfailedtoshowtesticularandbody weightdevelopment,whereasinfusionsof4or6hoursdurationpromotedrapidtesticular developmentandincreaseinbodyweight.Theseinfusiondurationsaresimilartonaturally occurringdurationsofnocturnallyelevatedpinealMelsynthesisinjuvenilehamstershoused understimulatoryandinhibitoryphotoperiods(13).Thus,theauthorsconcludedthatthe resultsmimictheresponsesofpineal-intacthamsterstransferredfromlongtoshortdays(8). Thesecondhypothesis,the"coincidencehypothesis",proposesthatreproductiveresponses occurwhenMelcoincidesintimewiththesensitivityoftheMeltargetorgan(s).Supportfor thishypothesisderivesfromexperimentsinvolvingtimeddailyinjectionsofMelinintactadult Syrianhamsters( Mesocricetusauratus)(14),Turkishhamsters( Mesocricetusbrandti)(15), andSiberianhamsters(16)andpinealectomizedadultSyrianhamsters(17,18).Theresponse ofgonadsandbodyweightsareoftendependentuponthetimeofdayMelisadministrated (19).Therefore,intheseexperimentsboththephotoperiodandthetimeofdayoftheMel injectionwereimportant,andsomeaspectofthetemporalpatternofpinealMelsecretionwas importanttoelicitphotoperiodicresponses. Theaimoftheresearchdescribedhereinwastoexaminetheeffectsofvariousdurationsof MelinfusionsonbodyweightdevelopmentinjuvenileSiberianhamsters.Weperformeda detailedstudyoftimedMelinfusionstotestthevalidityofthedurationandcoincidence hypotheseswithasingleMeladministration;weusedinfusiontechniquestosearchfora sensitivephaseofMelinteractionwithitstargettissuesensitivity. MaterialsandMethods AnimalsandHousing:JuvenileSiberianhamsters( Phodopussungorus)wereusedinthis experiment.Allhamsterswereborneitherunderalongphotoperiod(LD16:8=16L;lightson from0400to2000)orashortphotoperiod(LD10:14=10L;lightsonfrom1000to2000). Breedingpairswerehousedonpineshavingbeddinginplasticcages.Hamstersweredesignated 303 EffectsofPhotoperiodandMelatoninInfusionsonBodyWeightinPinealectomizedJuvenileSiberianHamsters (Phodopussungorus) 1dayofageontheirdayofbirth.Pupswerekeptwiththeirmothersinplasticcagesuntil15 daysofage.Litterswereweanedat15daysofageandhamstersweighing11-16gfrom differentmotherswererandomlydistributedthroughoutallexperimentalgroups.Experimental treatmentbeganwithhamstersat15daysofage.Hamstersreceivedtapwaterandfoodad libitum.Roomtemperaturewasmaintainedat22±1ºCandalllightingwasprovidedbycool- whitefluorescenttubes;lightintensitiesattheanimal’seyelevelexceeded200lux.Before surgery,hamsterswereanesthetizedintraperitoneallywithpentobarbitol(32.5mg/kgBW)and subcutaneouslywithketamine(20mg/kgBW;SigmaChemicalCompany,St.Louis,MO,USA). Pinealectomy: Pinealectomyof15-day-oldhamsterswasperformedaccordingtothe methodofHoffmanandReiter(20). Cannulation: Cannulationoftheanimalsforinfusionwasperformedfollowingthe techniqueusedbyCarterandGoldman(8,9)usinga60cmlengthofpolyethylenetubing. Infusions: Infusedanimalswerehousedsinglyinplasticcages.Theproximalendofthe cannulawasplacedintoaplasticvial,whichwassecuredtoaswivelfixedtoabarhungonthe topofthecage.Asmallholewasdrilledinthisvialthroughwhichthecannulawaspassedand