The length of heat in the albino rat as determined by the copulatory response.код для вставкиСкачать
T H E LENGTH O F HEAT I N T H E ALBINO RAT AS DETERMINED BY T H E COPULATORY RESPONSE RICHARD J. BLANDAU, JOHN L. BOLING AND WILLIAM C. YOUNG Arnold Biological Laboratory, Brown Univer.Pity, Providence, Rho& Island, and Laboratories of Primute Biology, Yale University School of Medicine, New Haeen. Connecticut ONE FIGURE The length of heat in the rat, a s in the guinea pig, is a measure of reproductive normality which has not been widely used. I n most morphological investigations the vaginal condition has served as the end-point and in most studies of behavior (Hemmingsen, ’33; Ball, ’34, ’36, ’37 and ’40) reliance has been placed on the intensity of the copulatory response. Nevertheless, the course of heat can easily and accurately be followed and once its length has been ascertained a very satisfactory basis has been established for determining and studying individual differences and f o r investigating factors involved in the induction and control of mating behavior (Boling and Blandau, ’39). As matters stood, however, there was a need f o r new determinations because no two of the earlier estimates were the same. Tshii ( ’22) gives the length as 4 to 8 hours, Long and Evans ( ’22) as 3 to 1 2 lioui-s, and Ball (’37) as 3 t o 21 hours. There were other reasons for an interest in the problem. When Ball (’37) was studying the rat with much the same purpose we have had, she was troubled by the tendency of animals tested a t frequent intervals to develop a “disturbed endocrine balance” which prolonged the cycle and period of comification and modified the behavioral picture. She states that discontinuance of the practice of making vaginal smears This investigation was supported by a grant f r o m the Committee f o r Research in Problrms of Sex, National Research Council. 453 454 RICHARD J. BLANDAU A N D OTHERS at 6-hour intervals terminated the condition, but many of the data she presents appear t o have been collected before this change in technique was effected. Consequently, the extent to which frequent reference can be made to the behavioral end-points without disturbing the basic physiological rhythm mas not known from any substantial body of data. Over and above an interest in the length of heat as a standard of reference was the desire to obtain information with respect to the factors involved in the induction of mating behavior and in the regulation of its character. I n the guinea pig the existence of a “constitutional” factor was suggested by the consistency of behavior displayed from cycle t o cycle by intact animals (Young, Dempsey, Hagquist and Boling, ’39) and from injection period to injection period by spayed animals (Young and Rundlett, ’39). Inasmucli as the length of heat during consecutive estrous periods provides a measure of consistency or variation as the case may be, advantage was taken of the opportunity to ascertain whether or not the existence of a similar factor is indicated for the rat. MATERIALS A N D METHODS The data were obtained from 145 female rats which were between 3 and 4 months old when the observations were begun. The animals were kept in square wire mesh cages with removable tops which facilitated handling. They were maintained on a ration of Purina fox chow checkers supplemented by green vegetables once a week. Tests of sexual responsiveness were made at hourly intervals, day and night, beginning the second day after the end of the preceding heat period. I n order to minimize the disturbance of constant illumination ( Bromman, ’37 ; Hemrniiigsen and Krarup, ’37), the lights were turned out a t night during the interval between hourly observations. I n addition, during the first 2 days of the cycle when no observations were being made, the animals were kept in an ordinary room in which there. was the normal alternation of daylight and darkness. L E N G T H OF HEAT 455 Tlie time of lieat was ascertainrd by the res1)onse to manual maiiipulation. Thc mcthod is iI modification of that uscd by Jlcmniingscln ( ’ 3 3 ) and Ball ( ’3). Tlic tliuml-,and riug finger ai’e placecl anterior to tltc iliac c i ~ s t sand tlie second and third fingers a r e placed 011 opposite sides of tlie tail in such a way that tltc tips lie in the vulvar region (fig. l a ) . Animals Fig. 1 a. Method of stiiiiulnting tlic display of the copulatory responsc o r lordosis. b. Female rat disp1:rying lortlosis imiiiedi;ctely after inaiiual stimulation. at the hciglit of cstrous i-espond quickly with a typical l o d o s i s in prc1)aration f o r coitus (fig. 11)). The reaction may or may not be accompwnicd by car quivering, depending on tlic strain used (Hemmirigsen; Ball). If the estrus is of low intensity, o r when the animal is fingrued near the end of heat, several seconds’ stimulation may be reqnircd. Associated heliavior siich as darting and hopping ai-e helpful in iclentifyirig animals wliich a r e about to come into heat its 456 ItICITARI) J. BLANI)AU 4NI) OTHEIlS o r arc in a state of low excitability. Animals not in lieat resist tlie manual stimnlation more or less vigorously by kic:king, snapping or ruiiiiiiig away. Tlic willingness to copulate wlien this i*esponseis given mas tcstcd during an earlier study (Boliiig and Blandau, ’39) by introducing a vigorwns male into the cage. Tnasmuch as tlic copulatory response could be obtained from all animals whicli would mate, elici tat ioii of the i~esponsc by nianual manipulation in this study was consicic~~ccl adequate evidence for the existence of heat. Tlic length of heat, tlic length of tlie c y l c a i i d the time of day lieat loegins arc t ~ y a i d e das measures of normalit? and \vcrc rccoi-decl for a11 aiiimnls observed during tlie iiivestigatioii. Tlic ability of tlw rat to withstand prolongcd observation w a s tested hy esamiiiing thii-ty-seveii aiiimals throughout 7 or 8 consecutive lieat periods. J h t a bcai,irig on the extent to whicli consistency of hellarioi. is displayed were obtained f iwm tlic animals obsei*ved during 7 01. 8 coiisccutivc lieat peiaiods. 11iscellaiicous information hearing o n the occurrciice of the “split ” estrus (Young, Dcmpsey, Hagquist and Eoling, ’39) and the effect of copulation on thc Icrigtli of heat, w a s obtained from the cn tire colony. OBSERVATIONS Tlic length of 609 heat periods observed in 114 animals averaged 13.7 hours, range 1 to 28 Iioiivs, standard deviation 4.55. This cornpaws favorably with tlie determination madr by Ball, but is longer than Tsliii’s (’22) cstimatc of 4 to 8 hours and Long and Evans’ (’22) estimate of 3 to 12 hours. When observations ~vei’emade thi*ougliont seven or cight consecutive estrous periods the mean length of lieat did not vary significantly (table 1 ) . The time of day estrus began was not affected by frequent ohservatioii. Analysis of 653 records is made in table 2. I n the thirty-seven aiiimals observed during seven or cight consccutivc heat periods the bcginiiing of heat TWS also most 457 LENGTH O F HEAT TABLE 1 The lrngth of heat in liours in rats observed over consrcutive heat periods. When estrus was antermittent ( " ) the length of the final part only is shown in the table - - ANTMAT. 17 27 28 31 37 45 61 68 77 81 83 111,s 112 113 131 137 142 162 167 168 181 184 183 187 190 194 19t 11 >9 >9 >16 9 >I2 15 17 15 20 20 13 19 7 14 13 >I0 >15 17 11 14 13 If: 197 200 19A 50A 52A ilA 125A 156A 161A 182A 16 11 13 16 16 24 22 18 15 19 13 12 20 20 hle:111 14.01 196 2nd 3rd 10 12 13 22 8 20 16 I6 10 11 15* 14 22 15 15 12 18 17 16 5* 5 14 16 16 9 13 7 3 2 19 18 16 19 12 9 17 18 5 13 12 13 10 13 18 14 1.5 12 24 10 10 15 15 11 12 14 17 6 10 18 11 11 9 13 6 21 17 8 2 19 16 14 17 17 13* "3" 13.51 12.72 12.89 - - 11 7 - - 4th 8 12 9 22 14 13 8 15* 11 12 18 11 14 12 11 17 14 11 17 10 10 9 21 12 12 13 8 10' 9 10 10 12 9 20 A th MIRAN 8 17 18 19 5th (ill1 11 14 5% 1.i 17 13 1.T 19 1ti 23 12 13 17 13 16 9 17 17 12 17 17 7 8 11 8 .. 11 10 21 21 9 10 17 14 13 12 22 17 17 21 13 19 12 - 7th - - 23 15 6 16 17 I0 18 16 1'7 11 6 14 20 18 11 19 16 17 9 22 16 16 15 12 16 21 20 13" 18 7 11 14 13 25 T T 21 13 22 18 13 16 18 11 20 20 17 20 26 18 14 11 12 13 >I3 23 11 22 20 10.63 12.38 12.25 18.88 12.00 15.63 14.13 14.14 12.00 13.75 18.00 11.57 14.38 11.25 15.57 16.88 13.57 12.38 15.38 11.43 12.63 14.88 li.25 15.38 11.28 15.00 9.71 13.50 13.25 20.43 17.63 12.00 12.75 13.57 12.26 16.00 20.38 14.64 15.45 15.29 5.12 14.28 - li 11 17 .. 21 12 .. 10 13 .. I .. 17* 14 24 10 19 18 15 23 23 19 11 17 5 19 .. .. Ii 21 7 1.6 .. .. .. 18 19 .. 16 4 18 .. - - 45 8 RICHARD J. BLANDAU A N D OTHERS TABLE 2 Hourly record of the time of day at wkich heat begins NO. TIME O F DAY T I M E O F DAY OF CASES 3 2 14 15 24 53 89 84 - NO. OF T I X E OF DAY CASKS - 11 A.M. t o 12 N. 1 z N . to 1 P . M . 1 P.M. t o 2 P . M . 2 P . N . t o 3 P.M. 3 P . N . to 4 P.M. 4 P.N. t o 5 P.M. 5 P.M. to 6 P.M. 6 P.M. t o 7 P . M . NO. OF CASES 7 P . M . t o 8 P.M. 8 P.M. to 9 P . N . 9 P.N. to i n P.N. 10 P.M. to 11 P.M. 11 P.M. to 12 P.M. 12 P . M . to 1 A . N . 1 A.M. t o 2 -4.51. 2 A . N . to 3 A . X . 102 71 91 33 34 17 8 8 - 3 A.M. t o 4 A . N . 4 A.M. to 5 A.M. 5 A.hf. t o 6 A.M. 6 A.M. to 7 A.M. 7 A.M. t o 8 A.M. 8 A . N . t o 9 A.M. 9 A . N . to 10 A . N . 10 A.N. t o 11 A.M. 2 0 n 1 2 0 0 0 frequent between 4 P.M. and 10 P.M. at each of tlie periods of observation. The length of 567 cycles varied from 2 to 19 days, a variation which is not essentially different from that recorded by Long and Evans and Ball. Eighty-seven per cent were from 4 to 6 days in length, average 4.4 days or 105.3 hours. By an application of Brandt's test for homogeneity of variance (Snedecor, '38)t o data sumarized in table 3 it was determined TABLE 3 T h e mean length of consecutive reproductive cycles CYCLE 1st 2nd 3rd 4th 5th Ni&IBE3E$ I MEAN LENGTH INHOURR 104.1 Gtli 105.2 m.3 102.3 99.3 7th 100.3 37 I STANDARD DEVIATION in.2 15.8 24.8 23.7 20.8 14.4 14.6 I 90 to 122 47 t o 125 68 to 196 68 to 162 7 1 to 167 68 to 145 91 t o 118 that at no time during the six to seven cycles when the animals mere being observed continuously was any significant variation shown in the length of the cycle. The data contained in table 1 were used in an effort to ascertain whether or not consistency in the character of behavior as determined by the length of heat tends to be shown LENGTH O F HEAT 459 by individual animals. When they were analyzed by the “F” method of Snedecor, F equalled 3.3582. The probability, therefore, that the smaller variance within animals is due to chance is much less than one in a hundred and a considerable consistency of behavior is shown. Similar analyses of data bearing on the length of the cycle and on the time of day heat begins indicate an individual consistency in these features of reproductive behavior. An abnormal type of heat previously observed in the guinca pig (Young, Dempsey and Myers, ’35 ; Young, Dempsey, Hagquist and Doling, ’39) and horse (Satoh and Hoshi, ’33; AlcKenzie and Andrews, ’37; Day, ’39) and referred to by Young, Dempsey and Myers as a “split” estrus has been scen in the rats observed during this study. Our information is not as complete as that for the guinea pig because proof cannot be given that in the rat the split, or perhaps better, “intermittent” estrus, is associated with delayed ovulation. I n every respect, however, in which comparison is possible the intermittent estrus is identical with that seen in some guinea pigs. The first part or parts tend to be shorter than the final part with which ovulation is assumed to be associated. I n sixteen cases the average length of the first part was 4.3 liours, range 1 t o 16 hours, whereas the average length of the second p a r t was 9.1 hours, range 2 to 17 hours. When a third part occurred, a s it did in three animals, the length averaged 16 hours, range 10 to 23 hours. The length of the interval between the parts of this abnormal estrus varied from 2 to 23 hours. I n the guinea pig the length of the normal heat periods of animals which displayed an intermittent estrus tended t o be longer than the average for the colony. I n the rat this may or may not be true. The length of seventy-eight “normal ” heat periods displayed by fourteen animals which had also displayed at least one intermittent estrus averaged 14.9 hours. The length of 468 heat periods displayed by seventythree aninials in which there was no record of an intermittent estrus averaged 13.2 hours. The “t ” test for the sicgnificancc 460 R I C H A R D J. B L A N D A U A N D OTHERS of differences (Snedecor, ’38) was applied to the data. The value obtained for “ t ” was near the 5% level of significance but was not conclusive. The effect of mating at the beginning of estrus on the length of that estrous period was studied in twelve animals. The average length of seventy-six heat periods displayed by these animals prior to that during which mating occurred was 14.4 hours. The average length of heat when mating was permitted at the beginning was 11.6 hours. When the “t” test of Snedecor was applied t o the data, the value obtained for “ t ” was greater than that shown in the table for the 1% level; consequently the data for the twelve animals indicate that the difference between the length of heat in the absence of mating and when it occurs is significant. Endoubtedly, however, it would be desirable to have more experiments. I n addition, the possibility should be explored that a quantitative relationship exists between the amount of stimulation and the continuation of heat which is similar to that between tlie amount of stimulation and the production of pseudopregnancy (Ball, ’34). DISCUSSION An objective in this investigation has been the development of a method whereby periodic changes in the estrous cycle of the rat can be followed at close intervals without disturbing their normality. Providing the precautions described above are taken, this can be accomplished by direct observations of behavior. Throughout a period of as many as eight consecutive estrous periods, the length of heat, the time of day it began, and the length of the cycle were not affected by the procedure that was used. The direct observation of behavior has the additional advantage that it permits determination of the beginning and end of heat and therefore of its length. The usefulness of the length of heat as a measure of reproductive normality should be considerable. It has already been employed in this study and elsewhere (Young, Dempsep, Hagquist and Boling, LENGTH O F HEAT 461 '39) in an effort to ascertain something about the extent to which individual differences are found. The fact that the length of the induced estrogen-progesterone heat in spayed rats was similar to that of heat in normal animals did much to convince us that we were dealing with the combination of ovarian hormones which is normally responsible for the display of this behavior (Boling and Blandau, '39). Determination of the length of heat has furthered the comparison of the guinea pig and rat. Despite the rat's shorter cycle, the period of heat is longer. I t s average length of 13 to 14 hours exceeds that in the guinea pig by approximately 5 hours. I n other respects, however, similarities are seen. The facility with which the behavioral responses can be elicited is about the same in the two species. Individuals of both species show a considerable consistency of heat length from cycle to cycle. Lastly, the abnormal heat referred to as the intermittent estrus is displayed by both species. It should be emphasized that the length of heat is not considered superior to the intensity of the estrous responses (Hemmingsen, '33 ; Ball, '37) as a measure of reproductive normality. Ideally, both should be recorded, especially when the central interest is in mating behavior. For other purposes which require frequent examinations of the animals, it is probable that either would be as satisfactory as the other, depending on its convenience to the investigator. SUMMARY AND CONCLUSIONS The development of a procedure was sought whereby tests of the estrous condition of the female rat can be made at frequent intervals over a considerable period of time mithout disturbing the normality of the cycle. Reference to the mating behavior displayed at the time of heat served this purpose. 1. Provided proper precautions are taken, hourly tests for sexual receptivity can be made over at least eight consecutive estrous periods without affecting the length of heat, the time of day animals come into heat or the length of the cycle. 462 KICIIABD J. BLANDAU AND OTHERS 2. The length of lieat is a n excellent standard of reference for many studies of ovarian hormone action. I11 this study it averaged 13.7 hours. 3. Individual animals tend to show a consistency in the character of cyclic behavior as measured by the length of heat, the length of the cycle and the time of day a t which heat begins. 4. A ‘(split” or intermittent estrus similar to that displayed abnormally by the guinea pig and horse is occasionally displayed by the rat. 5 . The average length of heat in twelve animals mated a t the beginning of estrus was slightly, but nevertheless significantly shorter than in the controls. LITERATURE C I T E D BALL,J. 1934 Sex behavior of tlic ]at after removal of tlie uterus and vagina. J. Comp. Psychol., vol. 18, pp. 419-422. 1936 Further evidence on hormonal basis of “heat” behavior. Proc. Soc. Exp. Riol., vol. 35, pp. 4 1 6 4 1 8 . 1937 A test for measuring sexual excitability in the fcmale rat. C‘omp. Psychol. Monog., vol. 14, no. 1, pp. 1-37. ___- 1940 The effect of testosterone on the sex I-diavior of female rats. J. Conip. Psychol., vol. 29, pp. 151-165. 1939 The estrogen-progesteroiie induction of BOLING,J. I,., A N D R. J. BLANDAU niating responses in the spajed feniale rat. Endocrinol., vol. 25, pp. 359-364. BROWNAN, L. G. 1937 Light in its relation to activity and estrous rhythms in the albino rat. J. Exp. Zool., vol. 7.5, pp. 375-388. DAY, F. T. 1939 The oestrous cycic of the mare following removal of the foetus a t tarious stages of pregiiaiicy. J. Agric. Sei., vol. 29, pp. 470-455. HEYNINGSEN, A. M. 1933 Studies on the oestrus-producing hormone (oestrin). Skand. Arch. Physiol., rol. 63, pp. 97-250. A. M., AND N. E. KRARVP 1937 Rhythmic diuriial varifitions i n tlie ocstrous pheuoineiia of the rat and their susceptibility to light and dark. I<. Ilanslie Vidensknb. Selskab. Biol. hfeddelel., vol. 13, 110. 7, pp. 1-61. HEiflIINGSEN, ISHII,0. 1922 Observations on the sexual cycle of the white rat. Anat. Rec., v01. 23, pp. 311-314. LONG,J. A., AND H. M. EVANS 1922 The oestrous cycle in the rat a i d its associ:itcd pliciiomrna. Mem. Vniv. Calif., 1-01. 6, pp. 3-148. LENGTH O F HEAT 463 MCICENZIE,F. F., AND F. N. ANDREWS 1937 Estrus and ovulation in the mare. Proc. Am. SOC.Animal Prod., vol. 30, pp. 64-70. SATOH, S., AND S. HOSHI 1933 A study of reproduction in the mare. 11. The study on the oestrus. J . Jap. Soe. Vet. Sci., vol. 12, pp. 200-223. SNEDECOR, G. W. 1938 Statistical methods applied to experiments in agriculture and biology. Collegiate Press, Ine., Ames, Iowa. YOUNG,W. C., 3:. W. DEMPSEY,C. W. HAGQUIST, AND J . L. BOLING 1939 Sexual behavior and sexual receptivity in the female guinea pig. J . Comp. Psycho]., V O ~ . 27, pp. 49-68. YOUNG,W. C., E. W. DEMPSEY,AND H. I. MYERS 1935 Cyclic reproductive behavior in the female guiuea pig. J. Comp. Pspchol., vol. 19, pp. 313-335. YOUNG, W. c., AND B. RUNDLETT 1939 Tlic hormonal induction of llomosexual behavior in the spayed female guinea pig. Psychosomatic Med., vol. 1, pp. 449-460.