Desarrollo Reproductivo en Hamster

7/27/2019 Desarrollo Reproductivo en Hamster

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B IOLOGY O F R EP RO DU CT IO N 2, 223-229 (1970)

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R e p ro d u c tiv e D e v e lo p m e n t in th e F e m a le G o ld e nH a m s te r in R e la tio n to S p o n ta n e o u s E s tru sM ILTON D IAMOND AN D RYUZO YANAG IM ACH I

D epar tm en t o f A n a tom y ,M ed ic a l S cho o l,

U n iv ers ity o f H aw aii ,H on o lu lu , H awa ii 968 22

Rece ived N ovem ber 26 , 196 9

P ub erta l m atura tion o f the rep rod uctive-sex ual beh av ior system in 2 2 fem ale h am ste rsw as stud ied w ith prim ary o rie n tat ion tow a rd th e m anifesta tio n of e stru s. S po ntaneo usestrus w a s d em ons tra ted as ea rly as 2 6 day s of age , v ag inal op en ing w as seen by 5-10days, an d ovulat ion occurred as e arly a s D ay 29 . D epen dab le co ord ina tio n be tw een es tru s,ov u la tion , and other reprodu ctive fac to rs n ece ssa ry for su cce ssfu l pregn ancy w as no tco nsis ten tly se en , how ev er, un til 35 d ays of age . P rio r to th is ag e, a nov ula to ry estrus ,an estra l o vu latio n , an d nonp rod uct ive fert ile m ating s m ay b e seen . W hile the h am ste r isthu s rev ealed as a spe cie s capab le of ex trem e ly ea rly and rap id sexua l d eve lopm ent, dur ingdevelo pm en t a p eriod of ado lescen t steril ity of ap pro x im ate ly 9 day s ex ists d urin g w h ichtim e coo rd inat ion o f the m any-face ted feature s of rep rod uct ion occurs .

In th e study of sexu al deve lopm en t, tw olife stages m ay be co nsid ered of p rim e co nce rn :the pe riod of p rena tal o r neona ta l sexua ld iffe ren tiatio n and pube rty . T he fo rm er s tag eis consid e red c ruc ial fo r th e o rg an iza tion o fbehav io ra l and p hy sio log ica l rep rod uc tivepa tterns seen in th e ad u lt. T h e la tte r is c ruc ia lfo r th e activ atio n of th ese pa tte rn s o r theb ring in g o f th ese pa tte rn s to ex press ion . T h isis a s true fo r hum ans as it is fo r o the r sp ec ie s(D iam ond , 19 65 ; 19 68). In the fem ale , recen tstud ie s o f sexu al d iffe ren tia tion h av e co ncen -tra ted o n the m a lleab ility o f the neural tissuesas soc ia ted w ith m a ting behav io r and th ehypo tha lam ic -p itu ita ry -g onada l ax is in rep ro -duc tion (e .g ., P h oen ix , G oy , G era ll, andY oung , 1 959 ; B arrac lou gh and G o rsk i, 1 962 ),w h ile the stud ie s o f p ube rty seem to co ncen -tra te o n the in itia tion o f ov u la tion and theab ility to p ro du ce young (e.g ., G reenw a ld andP epp le r , 1 968 ) o r p robe th e gene ral qu estio no f ad o le scen t ste rility (H artm an , 19 31). Someexpe rim en ta l s tud ie s h av e attem pted to in ducepube rty (e .g ., R am irez and S aw yer, 1 965 ) and

from them extrapo la te m echan ism s of th eneural-endo crine in f luence o n pube rty andrep roduc t ion . A sid e from the s in gu la r w o rk ofB lan dau and M oney (1943) in the ra t, fewstud ies are know n , how ev er , w h ich have si-m ultaneou sly inv estig a ted the in teg ra tion ofsex b ehav io r p ro cesse s an d rep rodu c tive ab il-ities a lon g th e spec trum of pa ram ete rs d u rin gpuberta l deve lopm en t. T h is is so desp ite th efac t th at successfu l rep rodu ctio n is dep en den tupo n th e p rope r coord in atio n of sexua l be -hav io r a s w e ll as o the r ph ysio lo g ical pa ram -eters .

T he presen t investig atio n is an attem p t tom ore fu lly and com ple te ly an aly ze pu be rta lm atura tion in a mos t rap id ly deve lop ingspec ie s and to a llow a m ore com ple te an d com -preh en sive com parison b etw een com ponen tso f th e sexua l b eh av io r-rep ro duc tive sy stem ofth e fem ale during dev elo pm en t. Fu rth erm o re ,an attem p t is m ade to m ore c lose ly co rre la tethe pu be rta l f ind ings o f sexua l behav io r w itho th er deve lopm en ta l p aram e ters , pa rticu la rlyin reg ard to th e qu es tio n o f ado le scen t ste rility .


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22 4 D IAMO ND AND YANAG IM ACH I

For th is w ork a rap id ly m atu ring laborato ryspec ies , th e go ld en ham s ter , w as chosen .

T h is study investig ated the spon taneousan d s im u ltaneou s deve lopm ent o f rep ro duc tiv efea tu re s in c lud in g firs t ap pea rance o f e stru s,o vu la tion , vag in al o pen ing , vag ina l cyc licity ,fe rtiliz ab ility o f o va , and ab ility to bea r andd eliv er v iab le yo ung .

M A TER IA LS AND M ETHOD SF em ale g o lden h am ste rs b red in ou r ow n lab-

orato ry an d left w ith litte rm ate s un til w ean ing w ereused . Tw enty-tw o an im a ls from seven li tters w e rew ean ed at D ay 17 or 18 and kept in gro ups of th re eor four . T hey w e re ho used in o paq ue , w hite p las ticcages , 1 0 X 12 X 6V 2 inch es u n ti l tem pora ry rem ov alfo r b ehav io ral tests o r sep ara tion in bre ed ing cag es.A ll an im a ls w ere w e igh ed pr io r to ea ch b ehav io raltes t. The lig h t schedule w as ad jus ted to p rov ide a6 :00 P .M . to 6 :00 AM . dark cyc le .

O n th e day of b ir th (eq uals D ay 0) and aga in o nD ays 5 , 10 , an d then d aily , 14 of th e 22 in ta ct fem a lesw ere ex am ined un til th e firs t app earanc e o f a p aten tvag in al o rifice w a s seen . S tar ting a t 17 d ays of ag eal l fem ale s w ere w eig hed and exam ined d aily fo r thefirs t d isp lay o f beh av iora l and vag ina l e strus, ovu la-tio n , a nd the ab il ity to con ceiv e, be ar, an d pa rtu rate .B ehav ioral tests fo r estrus w ere in it ia lly co ndu ctedbe tween 9:00 PM and 11:00 PM and co n sis ted o fpla cin g the fem ale to be tested in to an ob serv ationcag e w ith an ex pe rien ced adu lt m ale for 5 mm .O bse rva tion s w ere co nducted u nd er red l igh t. B e-hav io ral re cep tiv i ty w as q uantita tiv ely ev alua ted b yre cord in g the num ber of 15 -sec in terv als (qu art iles )du rin g w hich the fem ale ex hib ite d lord osis in respon seto the in ves tig atin g-s tim ula tin g m ale . A m axim umscore w ould thu s be 20 (4 qu arti les X S mm ). F e-m ale s m anife stin g vag in al e stru s w ith ou t sh ow ing alo rdo sis respon se o n th eir firs t test o r if sh ow ing 10or less re spo nse q uar tile s w ere retested betw een11 :00 pa t and 1:0 0 AM the sam e even ing .

A ll fem a les show in g vagin al es tru s, a nd a ll th eseexh ib it ing lordos is w ere le ft ov ern igh t w ith m alesand ch ecked for vag in al spe rm the n ex t m orn ing .

A ny fem ale exh ib it ing lord os is dur ing the tes t per iodw as laparo tom iz ed th e nex t m orn ing and the lef to vary and ovid uct rem oved an d exam in ed fo r ev idenceof o vu lation . In c ase o f do ub t th e ov arie s w ere p re-pa red for h isto lo g ica l insp ec tion . Th e o vid ucts w ereflush ed w ith 0 .9% NaC I so lu tion in search of ov a.W hen ferti lized eg gs (in th e pro nu clea r sta ge) w e refoun d in the oviduc t, th e fem a le w as sepa rate d in anind iv id ua l c ag e an d obse rved fo r a lea st 18 ad dit ion ald ays (n orm al adu lt ge sta t ion = 16 d ay s). F or tho se

fem a les n o t be aring or pa rtu ratin g y oung from th isf irst pa irin g , m atin g w as ag ain in itia ted a t th e nex tavai lab le estrus and the se an im als w ere ag ain fo l low edfor the ir ab ili ty to be ar and p artu ra te . A ny fem a leexh ib it in g th e sequ en tia l vag in a l se cr etory cond ition styp ical o f es tru s fo llow ed th e nex t m orn in g by apo sto vu lato ry co ndition w ere la paro tom ized an d in-sp ected for tu bal o va and the p resenc e o f corporalu tea even if estrou s b eh av io r w as not d isp la yed .

V aginal es trus an d cy clic ity w a s determ ined byu til iz in g th e ca teg ories o f vag ina l sec retion en um era tedb y O rsin i (1 96 1). E ssen tia lly , a clea r, t ran slu cen t andstr ing y m ucou s secretion is a sso cia ted w ith a pre -o vu lato ry cond ition (o ur la te D ay 4 ); an op aqu e,w hite , th ick , o d ifero us m uco id m ass is as soc iated w itha p ostovu lato ry con dition (ou r D ay 1) ; a nd anopaque , w axy , ye llow ish p lug is a sso ciated w ithd ies tru s (D ay 2 ). V ag inal sec retions are u sua lly absen to n the se con d die strus day (D ay 3) an d ear ly o nD ay 4 .

T hro ughou t the ex pe rim ent al l a n im als w e re kep tin air-co nd itio ned qu arte rs at a tem pe ratu re o f 6 8-75#{176}. D ie t co nsisted of stan da rd ra t/ham s ter chowsupplem ented w ith dog chow and w ate r ad lib itu m.

RESULTST he m ost ob v iou s re su lt is tha t fu ll rep ro -

duc tiv e m a tu rity and in teg ra tion of a ll thev a riou s com pon en ts inv o lved in successfu lpregnan cy m ay b e sa id to o ccu r by th e age o f35 days in th e fem a le go lden h am ste r. T heva rio us face ts , h ow ev er , ap pear to deve lop ina re la ted b u t in dependen t m anne r. A ll resu ltsa re lis ted in T ab le 1 .

A pp a ren tly , th e earlie st rep rodu ctiv e fea -tu re to deve lop is v ag ina l pa ten cy . B etw een5 an d 10 days of age , 11 of th e 14 fem a leham s ters in spec ted sh ow ed vag in a l pa tency ,a ll 14 vag inae w ere o pened by 15 d ay s o f age .

T he firs t e stru s occu rred in on e fem a le a t2 6 days o f ag e . Tw elv e add itio na l fem ale scam e in to f irs t hea t be tw een 28 and 35 dayso f age . Typ ica lly , th is firs t b eh av io ral heatw as p receded by a c lea r m u cous v ag ina le strous co nd itio n fo llow ed by ovu latio n andfe rtiliz atio n . F or tw o fem a le s, e stru s w as ne i-ther preceded by vag ina l m ucous ty p ica l o festru s nor fo llow ed by ovu latio n . O ne fem ale(L 3-10) d id no t com e in to heat du rin g theex tend ed obse rv a tion pe riod ; w h ile sh e d idsh ow cyc lic v ag ina l changes and ovu la tion .


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REPRODUCT IV E DEVELOPM ENT IN HAMSTER 22 5

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22 6 D IAM OND AND YANAG IIIIX ACH I

W hile f irs t e stru s o ccu rred am ong th ean im als over a span o f 17 days (2 6 -4 3 days) ,w ith in each litte r the span w as m uch na rrow er,usua l ly 3- 5 days, and never m o re than 6 .

D uring th e firs t es tru s o f eve ry fem a le ob -se rv ed , the typ ica l firm lo rdos is s tance wa sseen . T he in tensity o f th is f irs t spon tan eo usestrus, how eve r , as m easured by du ra tio n oflo rdo sis d isp lay w as genera lly w eaker in theseyoung an im als than in an im als o lde r than 35day s. A pp ro x im a te ly 25% of younge r fem a lesd id n o t re sp ond to the stim u latin g m a le s a tthe in itial 9 :0 0 PM te s t, bu t d id so a t thesub sequen t te sting b etw een 11 :00 PM an d1 :00 AM . Those fem a les firs t re sp ond ing afte r35 days o f age d id so o n the in itia l 9 -11 PMtest.

W hen th e y oung fem a le is n o t sexu allyrecep tive , in co n tra st to the typ ica l ag gre ssiv epa tte rn and fig h ting d isp layed b y an adu ltfem a le, the ado lescen t tr ie s to avo id con tac t,c lim b th e w a ll o f th e te st enc losu re , ro lls o nhe r back or as sum es a stand ing box ing po seto pa rry th e m oun ts o f the m a le. N o d irec tagg re ssive con tac t resu lting in an y bod ilydam age to eithe r the m ale or fem ale wa s seen .

V agina l secre tions typ ica l o f the estrou scyc le w ere consis ten tly th e ea rlie st p recu rso ro f behav io ra l e stru s; usu ally a c lear s t r ingym uco id sec re tion b u t occasiona lly o f m ilkyco lo r . T h e firs t v ag ina l sec re tion in seve ralf ema l e s was waxy.

Ovula tion , a s d ete rm ined by lapa ro tom y af-te r vag in al es tru s and a posto vu la to ry v ag ina lsec re tion w as n o t a lw ay s p reced ed by estrus.F ive fem a le s from th ree litte rs d isp layedanestro us ovu latio ns ( silen t h ea t ); o nefem a le d id th is tw ice on sub seq uen t cyc les .S tro ng lo rd osis behav io r wa s seen d urin g thesu bsequ en t cyc les o f the rem a in in g fou r fe -m a le s. T hese fem ale s w ere sac rif iced a fte r thetw o hem icas tra tion s needed fo r the de te rm i-na tion of ovu la tion .

Ovulat ion wa s no t ev idenced by tu ba l ovaor ova rian co rpora on D ay 27 in th e fem a led isp lay in g the earlie st e stru s o r in ano th erfem a le o n D ay 34 . Th e firs t ovu latio n w as

de tec ted on D ay 29 . Th is wa s no t p receded byvag ina l sig ns o f e stru s a ltho ugh a stron g be -hav io ra l respon se (1 8 qua rtiles ) w as seen .Sta rting a t 3 2 days of ag e all fem a le s typ ica llyovu lated a fte r vag ina l and b eh av io ral estru s ,an d fe rtiliz a tion re su lted from a ll b u t on ema t i n g .

D esp ite th e norm a l appea ran ce o f fe r tilizedova in the m a ted fem a le s, on in itial con cep tio no n ly th ree o f n in e tha t o ccu rred b efo re th efem a le w as 34 days o f age te rm ina ted su c-cessfu lly , w h ile a fte r 35 days o f age th ree o ff ive de live red y oung . S ubsequ en t pa irin gs re -su lted in fru itfu l p regn ancy and p artu r itionin all ca se s. In th ese p regn an cie s g esta tionleng th w as b etw een 15 an d 16 days. L itte rsfrom the y ounge r m oth ers w ere usua llysm a ller than from o lde r m o the rs . A ll m o the rsrega rd les s o f ag e successfu lly nursed and ca redfo r th eir you ng . N o can n iba lism w as seen (a sin deed is ra re in our co lo ny ).

Th e rela tion sh ip be tw een w e igh t and dayo f firs t es tru s w as com pu ted . N o sign if ican tco rrela tion w as seen (r , = .35 ) .

D ISCUSS IONIn con tras t to the ra t, in w h ich vag ina l

p aten cy usua lly deve lop s abou t a w eek prio rto th e f irs t e stru s and m ay even fo llow it(B landau and M oney , 1 943 ), in th e h am ste rthe v ag ina op ens qu ite soon a fte r b ir th inde -p en den tly and w ith ou t re latio n to ovu latio nor e stru s. O ur fin d ing s o f ea r ly o pen ing cor-respon d to those o f K upp erm an , G reenb latt,and H a ir (19 44), B ond (19 45), B run ne r andW itsch i (1 946 ), an d O rtiz (19 47), but d ifferfrom repo rts o f la te open in g (D ay 27-35 )g iv en by Sheehan an d B ru nne r (1 945 ).R easo ns fo r the appa ren t w ide d isp arity a reno t c lea r.

N o rm al e stru s in 26 - and 28-day-o ld fe -m a le s is pe rhap s th e ea rlie st kn ow n o ccurren ceo f spo n taneou s sexu a l recep tiv ity repo rted fo rany m amm al. T h is , cou p led w ith our f ind in gstha t the rem a in ing fem a les w ill m ate b y 43days o f age is com parab le to th e find ings o fS e lle (1 945 ), G reenw a ld an d P epp le r (196 8),


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R EPRODUC TIV E D EV ELO PM ENT IN HAM STER 22 7

and Peczen ik (194 2) . R eed an d R eed (1946) ,h ow ev er , repor t the firs t m a ting in the ir co lo nyo ccu rred a t 46 day s o f ag e. I t m ay b e no te -w orthy to co nsid er tha t th e s tim u li su r-roun d ing de te rm ina tion of e stru s v ariedcon side rab ly am ong these stu d ie s . S elle (194 5)ob se rv ed h is fem ale s w ith seven m a les fo r anhour each n igh t w h ile in th e G reenw a ld andP epp le r study (19 68 ) the fem ale s an d m a le sw ere pe rm anen tly caged toge the r and m a tingde te rm ined by subseq uen t spe rm check s. Inour te st s itu atio n , the fem ale w as expo sed toa m a le on ly fo r th e 5 -mm obse rva tion p e riod sduring the activ e n oc tu rna l h ours .

T he fin d ing s tha t fem ale s w ith in the sam elitter tend to com e in to firs t es tru s and ovu la teat ages m o re like the ir s ib s than o th e r ag em a tes and find ings o f an estra l ov u la tions con-cen tra ting in the sam e litters a re p ro voca tive .It m ay ind ica te a g en etic facto r need be con-side red in pu be rta l deve lopm en t.

In gen era l, the in itia l e stru s fo llow s appro -p ria te vag ina l ch an ges and precedes ov u la tion .O u r fin d ing s o f anovu la to ry estrus and itscoun terpa rt anestro us ov u la tion , how eve r , a resim ila r to f ind in gs seen in th e deve lop ing ra t(B land au an d M oney , 19 43) in w hich ovu-latio n and estru s m ay in dependen tly m an ife stthem se lves. A lso in ag reem en t a re ou r fin d ing sin rega rd to the on se t o f e stru s in w h ich m orem atu re fem a le s com e in to estrus ea r lie r in th eeven in g th en do le ss m a tu re ones. H arvey ,Y anag im ach i, and C h ang (1961) rep orted100% o f 100 m a tu re fem a le ham s ters d is -p lay ed es trus by 11 :00 PM ; 23% of ou r 22d id no t sh ow hea t un til a f te r 1 1 :00 PM onthe ir f irs t e stru s. In th e ham ste r the in tensityo f th e lo rd osis resp onse is les s stro ng on th isf irs t h ea t th an subsequ en tly . Th is has beenreported a lso in th e ra t (B lan dau and M oney ,1943) .Few an im a ls m a ting p rio r to 34 day s o f agew ere ab le to com ple te a succes sfu l p regn ancy .S e lle (1 943 ) an d B ond (1945) rep ort copu la -tion s as early as 30 days o f age bu t firs tlitte r ing no t occu rr ing u n til m uch la te r.D ean esly (19 38) fou nd th e earlie st p regn an-

c ies success fu l a t 50-7 0 days o f ag e. A ccord ingto our o bse rva tions, th e ova p rod uced on th esein itia l o vu la tion s (D ay 29 to D ay 44) ap -pea red to h av e been successfu lly and no rm a llyfe r tilized . Th e lack of succes sfu l sub seq uen tp regnancy in d icate s tha t som e o th er h ypo -tha lam ic (u ter ine? ) p roces ses rem ain todev elo p . Th e hem ispay ed young h am ste rseem s no less capab le o f b ea ring an d pa rtu -ra tin g than the in tact adu lt fem a le. T he num -be r o f-pu ps bo rn to o ur young fem a le s andtho se from Se lle s in tact fem a les a re com para-b le to th ese rep orted bo rn to 1 - and 2-m on th -o ld fem a les b y Sod e rw a ll e t a l. (1960) . T hegesta tion len g th o f all ou r f irs t- te rm preg nan-cies w as be tw een 15 and 16 days. T h is too isin keep ing w ith the find in gs o f Sode rw a ll etal . th at un til 5 m on ths o f age th e ave ragegesta tion leng th is le ss th an 16 fu ll days. Thesim ila r ities ind ica te tha t h em icastra tion d idno t s eem to sign if ican tly a ffect the n um ber o fyo ung bo rn and the abso lu te num ber o f fu nc -tion in g co rp ora lu tea , if a t le as t fou r a rep re sen t, is n o t c ru cia l fo r successfu l g estatio n .I t m ay b e sign if ican t tha t re so rp tio n is n o tu ncomm on in the ham ster and u sua lly o ccu rsaf te r D ay 9 of gesta tion (P urdy an d H il-Iem ann , 195 0). W ith our sm a lle r num ber o fin itia l em b ry os re so rp tion m ig h t h av e b eenm in ima l .

T he w eig h t o f the ham ste r a t f irs t e stru s o rf irs t o vu latio n does no t co rre la te w ith the ag eof th ese even ts . F rom the p re sen t s tudy inco ncert w ith d ata ran g ing from ra t (L ong andEv an s, 192 2 ; B landau and M oney , 1 943 ) toh um an (D onov an an d v an de r W erif tenB osch , 19 65) w e su gg est p ube rty be cons id -ered as no t depen den t up on any sing le faceto f rep ro duc tion an d sexu al m atu rity , bu tra the r re flec t the m any proces se s invo lved .Thu s w e w ou ld de fine p ube rty , fo r fem ale s o fan y specie s , a s tha t per i od during w hich adu lt-lik e sexu al b eh av io r and physio log ica l rep ro -duc tive p ro cesses becom e ac tiva ted andnorm a lly becom e coo rd in ated . O rgan iza tio n ofth ese rep ro duc tive param ete rs m ay b e sa id tooccu r ove r a rela tive ly sh ort pe r iod . C oo rd i-


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22 8 D IAMO ND AND YANAG IM ACH I

na ted ac tiva tion o ccurs ove r a m ore p ro trac tedd uratio n . C om ponen t o r co ord ina ted ac tiva -tion m ay n ev er o ccu r; ad u lt fem a le s s ter ilefo r one reason or ano th e r m ay m ate b u t neve rbecom e pregnan t o r m ay ovu la te an d neve rm ate . Th ey , hav ing passed th rou gh the per i odduring w hich pube rty norm a lly o ccu rs , w ou ldbe cons ide red rep ro duc tiv ely po stpub erta l andmatu re.

It is obv ious the re rem a ins m uch to beelu cid a ted reg ard in g those facto rs w h ich ac -tu ally beg in to coo rd ina te th e adu lt sexbehav io r-rep rod uc tive system . S tud ies re -cen tly com p leted in d icate th a t th e neuraltissues m ed ia ting sexua l b eh av io r ac tiva tiona re no t th e lim itin g fac to rs . W e can indu ce,w ith estro gen an d prog este rone , e stru s incas tra ted an d in tac t fem a le s as yo ung as 1 9days of age and in al l cases b y 28 days of age(D iam ond and Y anag im ach i, 1 97 0). Th isind ica te s th at th e p rop er act ivat ion o f co -o rd ina ted m a ting and rep rodu ctiv e activ itie sprob ab ly depend s upon those cruc ia l hyp o-tha lam ic-p itu itary -ova rian p ro cesse s o rg a-n ized p re - o r n eo na ta lly .

ACKNOWLEDGMENTSAppre ciat ion for as sistanc e in th e execu tion of th is

research is ex tend ed to M r. A lfo nso L la cun a and M rs.E . B arb ara Zegar t. Th is re sea rch w as su ppo rte d inp art by P ublic H ea lth Serv ic e G ran ts H D 03394 , andHD 02066 , o f th e N ationa l Ins titu te of C hild H ea lthand Hum an D ev elo pm ent o f th e N a tio nal Ins titu teso f H ea lth , a nd in par t by fund s f rom the F ordF oun dation . T he sen ior au thor is s jppor ted in par tby a L ed erle M ed ica l Facu lty Aw ard .

R E FER ENCESBA RRAC LOUGH , C . A ., AND GOR SK I, R . A . (1962).

S tud ies o n m ating behav ior in th e and rog en-ster -ilized fem ale rat in re la t ion to the hypoth alam icregulation of sexual behavior. I . E ndo crino l . 25 ,175-182 .

BLA NDAU , R. J. , AND MONEY , W . L . (19 43) . Th eatta inm en t o f sexu a l m atu rity in th e fem a le a lb in ora t a s determ in ed by the cop ula to ry resp onse. Ana t .R e c . 86 , 197-215 .

B OND , C . R . (1 94 5). T he go lden h am ste r (C ric etu sau ratu s): care , b reed in g , a nd g row th . Physiol .Zoo l . 18 , 52 - 59 .

B R UNNER , J. A ., A ND W IT scH I, E . (194 6) . T estoste r-one -in duced m odific atio ns o f sex dev elo pm en t infem ale ham ste rs. Am er . J . A n a t. 79 , 293-320 .

DEANESLY , R . ( 1938). The reproductive cycle of thego lden h am s ter (C rice tus aura tus ). P roc . Zo o l. S oc .Se r . A , 31 -37 .

D I AMOND , M . (1965) . A crit ica l eva lua tio n of theon tog en y of h um an sexu al behav ior. Q ua rt. R ev .B i o l . 40 , 147-175 .

DIAMOND , M . (1968) . G ene tic-end ocr ine in te rac -t io n s and h um an p sy chosexua lity . In Perspect ivesin R ep roductio n a nd Sexua l B eha v ior , pp . 417-443 , Ind iana Univ . P ress, B loom ing ton , Ind iana .

D I AMOND , M ., A ND Y AN AG IM A cH I, R . (19 70). Repro -d u ctive d eve lopm en t in th e fem a le go ld en ham steri n relation to ind uced estrus. H orm . B ehav . Inprepara t ion.

DONOVAN , B . T . (19 63). T he tim ing of puberty. Sci .B asis M ed . 53-75 .

DONOVAN , B . T ., AND VAN DER WER FF TEN B OSC H , J.J. (19 65) . Phy sio log y o f P ube rty . W illiam s &W ilk ins , B a ltim o re, M ary land .

GREENWALD , G . S ., AND PEPPLER , R . D . (1968 ).Prepu ber ta l an d pub erta l chang es in th e h am sterova ry . Ana t. R ec . 161, 447-458 .

HAR TMAN , C . G . (1 931 ). O n the rela t ive s ter ility o fth e ado le scen t org an ism . S cien ce 7 4 , 226-227.

HARV EY , E . B ., YANAGIMAC I I I , R . AND CHANG , M . C .(19 61). O n se t of estrus and o vu la tion in th e go ld enhamste r . J . E xf.. Zo o l. 146, 231-235 .

KU P P ERMAN , H . S ., GR EEN BLA TT , R . B ., AN D HA IR ,L. Q. (19 44) . Th e sex ua l cy cle an d reprodu ctionin the golden hamster (Crice tus auratus). Ana t .R e c . 88 , 441-4 42 (abstr.).

LONG , J. A ., AND EVAN S, H . M . (19 22). T he oestrouscy cle in the rat and its associa ted ph enom ena .M em . U n iv . C a lif . 6, 1-148 .

OR s IN I , M . W . (19 61) . T he ex te rna l v ag inal phe -nom ena ch arac ter iz in g the sta ges of the estrou scycle, pregnancy, p seudopregnancy , lactation, in thean estrou s h am ste r, M eso cricetus aura tus W ate r-house. P ro c . A n im a l C a re Pa nel 11 , 193-206.

ORTI z , E. (1947). The postn ata l deve lopm en t of ther ep ro ductiv e sys tem of th e go ld en h am ste r (C r ice tu sau ratus) and its r ea ct iv it y t o h or mo ne s. Phy s i o l .Zoo l . 2 0, 45-66 .

PA cZEN IK , 0. (1 942 ). A c tio ns o f sex horm ones onoe str ou s cycle and rep rodu ction of th e g o ld enhamster . J . E n do cr in o l. 3, 157-167.

PHOENLX , C . H ., G oy , R . W ., GERA LL , A . A ., AN DYOUNG , W . C . (195 9). O rg an izin g a ctio n o f pre -na tal ly adm in iste red tes tos tero ne prop iona te on th et issues media ting mating behavior in the famalegu inea pig. Endoc r i no l ogy 65 , 369-382.


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PURDY , D. M ., A ND H IL LE MA NN , H . H . (19 50). P re -na tal m o rtal ity in the go lden h am ste r (C ric etusauratus) . Ana t. R ec . 103 , 5 77-583 .

RAMIREZ , V . D ., A ND SA WY ER , C . F l. (1 965 ). A dvan ce -m en t o f pube rty in the fem a le ra t by es trog en .Endoc r i no l ogy 76 , 1158-1168 .

RE ED , C . A ., AND R EED , R . (194 6). T he copula t orybehav ior of the g o ld en h am ster . J . C om p . P sych o l.3 9, 7 -1 2.

S ELLE , R . M . (1945 ). Ham ster sexu ally m a ture attwen ty-eight days of age. Sc i e nc e 1 02 , 4 85 -4 86 .

SHE EHAN , J. F. , m BR UNN ER , J. A . (19 45) . Thecare , bre eding habi ts, and vagina l sm ear cycle ofth e labo rato ry h am ster (C rice tus aura tus ). Tur t oxN e w s 23 , 65-68 .

SOD ERWALL , A . L ., KENT , H . A ., J R., T UR BY FI LL , C . L .A ND B RIT EN BA KE R, A . L . (1 960). Va ria tio n in ge sta -tion len g th an d litte r size of the go lden ham ste r,M es oc ri ce tu s a ur at us . J . G er on to l. 15 , 246-248.

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Desarrollo Reproductivo en Hamster