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Testosterone levels in plasma and testes of neonatal mice
J. s~eroidBiochem.Vol. 31, No. 3, pp. 283-286, 1988 Printedin Great Britain.All rightsreserved
0022-4731/88 $3.00 + 0.00 Copyright 0 1988 PergamonPressplc
TESTOSTERONE LEVELS IN PLASMA TESTES OF NEONATAL MICE I.
MOTELICA-HEINO*,
M. CASTANIER~, P. CORBIER, D. A. EDWARDS~
Laboratoire d’Endocrinologie,
AND
and J.
ROFFI
Universite Paris XI, 91405 Orsay Cedex, France
(Received 20 November 1987) Summary-Newborn female and male C57BL6 mice were decapitated at birth or at different times during the first 24 h after birth and testosterone was determined by radioimmunoassay in plasma and testes. In newborn females, plasma testosterone is low and does not significantly change over the first 24 h after birth. In contrast, in newborn males, plasma testosterone more than
doubles during the first 2 h after birth and then falls rapidly to remain relatively low for the remainder of the 24 h period after birth. The increase in plasma testosterone is of almost certain testicular origin since it follows a decrease in testicular testosterone content. It seems likely that the increase in plasma testosterone in male mice which reaches its peak at 2 h after birth is involved in an essential way in the development of well-documented sex differences in gonadotropin secretion and behavior.
INTRODUCIION
EXPERIMENTAL
In the newborn male rat, a rise in serum gonadotropin is followed by a rapid increase in serum testosterone which peaks about 2 h after birth [l, 21. The increase in serum testosterone is clearly of testicular origin since it is not seen in females or males castrated at birth [3]. Male rats castrated at birth are completely feminized with respect to positive feedback and feminine sexual behavior [4,5] and show some deficits in male sexual behavior as well [6]. This research makes it clear that gonadal hormonal stimulation during the first several hours after birth plays a particularly important role in the sexual differentiation of the rat. While a number of studies suggest that gonadal hormonal stimulation during the perinatal period is important in the sexual differentiation of other rodent species [7], there is little or no information available about the pattern of androgen secretion during the first few hours after birth in these species. We choose to study the mouse because perinatal stimulation by testicular hormones has been demonstrated to play an essential role in the processes of defeminization and masculinization [8] and we here describe how androgen levels in testes and plasma change during the first 24 h of postnatal life.
Present Addresses: ‘CNRS, UA 594, Laboratoire de Pharmacologic, Universite Paris-XI, 92290 ChltenayMalabry, France. YFondation de Recherche en Hormonologie, 67, boulevard Pasteur, 94268 Fresnes Cedex, France. IDepartment of Psychology, Emory University, Atlanta, GA 30322, U.S.A.
Animals and preparation of samples for assay
Adult male and female C57BL6 mice were housed in our temperature controlled (2425°C) colony room maintained on a 1410 h light-dark cycle (lights on between 1800 h-0800 h). Food and water were supplied ad libitum. Females were housed 6 per cage and once a week a single adult male was introduced into each cage for an 8 h period (0900 to 1700 h). The next day was counted as “day 1” of gestation and pregnant females were identified on day 16 and caged individually until delivery of the pups. Under these conditions, most females deliver their pups during the dark period on day 19 of gestation. Some pups were delivered by Caesarian section (C-newborns) between 1400 and 1800 h on day 19 of gestation. To do this, pregnant females were killed by cervical dislocation and fetuses were quickly removed from each uterine horn. Some of these pups (Cnewborns) were decapitated at once (0 h) and others were kept at 35°C for either 30 min, 1 or 2 h before decapitation and blood collection. Spontaneously born animals on day 19 of gestation (S-newborns) were either decapitated at birth (0 h) or left with their mother and decapitated at different times during the first 24 h. After decapitation, the trunk blood for a pup was collected in an individually marked heparinized 50 p 1 capillary tube and the sex of the pup was determined by laparotomy. Blood from 14 to 25 pups of the same age and sex was pooled to make up one sample for assay. Samples were formed across litters in order to control inter-litter variability. Samples were kept refrigerated overnight at 4°C and centrifuged under
283
284
1. MOTELICA-HEINO et 01.
refrigeration (10,000 g for 20 min at 4°C). Plasma was removed and stored at - 20°C until assay. Testes were rapidly removed from decapitated males, and dissected free of adhering tissue on an ice-cold platform. Testes were then placed in single or multiple pairs in test tubes containing melting ice to a volume of 0.6ml distilled water, the tubes were stored at -20°C until assay. Adult males, ranging in age from 40-70 days, were decapitated between 140&1500 h, and trunk blood from 4 different males/sample was collected in a test tube. The blood was treated and stored until radioimmunoassay as described above. Radioimmunoassay 0.3 ml of a solution of collagenasedipase (3% in distilled water) was added to each tube containing the testes. Digestion was allowed to proceed for 30 min at 37°C in a shaker bath. The androgens were determined in testes and plasma samples by radioimmunoassay after extraction with diethyl ether and chromatography on Celite microcolumns following the method of Roger et al. [9], with slight modifications [lo]. The antisera were raised in rabbits injected with either testosterone-15carboxymethyloxineBSA or androstenedione- 11CL -hemisuccinate-BSA. The antiserum anti-testosterone cross-reacted significantly with 5x-dihydrotestosterone (23.5%), 5c(androstene38, 178 -dial (10.8%) and androstenedione (3.4%). The most important cross-reaction of the antiserum anti-androstenedione was displayed with epitestosterone (4.0%). However all these steroids were not liable to interfere with either testosterone or androstenedione assays since they were not eluted in the same fraction from the Celite microcolumn. The assays of testosterone and androstenedione have been already validated [9]. The mean recovery of tritiated steroids added to plasma was 86.5% for testosterone and 74.9% for androstenedione. The intra-assay coefficients of variation were 8.6% for testosterone and 7.4% for androstenedione. The inter-assay coefficients of variation were 8.0% for the two steroids. Results are expressed in pmol of testosterone or androstenedione per pair of testes or per pmol of testosterone per ml plasma.
cf S-newborns
01234
(I
18
H&s
24
AD
Fig. 1. Plasma testosterone in Caesarian-delivered (0) and spontaneously delivered (0) male mice. Blood from 14 to 25 pups was pooled to make up each sample for testosterone assay. Each point on the graph represents the value for one sample. Different samples were -taken at different times during the 24 h after birth. Details of deliverv are given in the text. The column on the right shows the mean aid SEM for plasma testosterone in adult (AD) male mice, and is based on 28 samples. RESULTS
Serum testosterone in neonatal and adult males A total of 442 pups (246 Caesarian delivered newborns and 196 spontaneously delivered newborns) and 188 adults were used. In both Caesarian delivered and spontaneously delivered newborn males, plasma testosterone more than doubles during the first 2 h after delivery (Fig. l), and then falls rapidly by 3 h to remain relatively low for the remainder of the 24 h period after birth. The mean value for samples taken at l-2 h (mean = 6.84 + 0.94 pmol/ml, Caesarian and spontaneously delivered combined, n = 19) was significantly higher (P < 0.001) than the mean for samples (n = 10) taken 3-24 h after delivery (2.00 f 0.37 pmol/ml). The mean plasma testosterone for adult males was 7.25 f 1.07 pmol/ml (28 assays). Plasma testosterone in neonatal females A total of 428 pups (219 Caesarian and 209 spontaneously delivered females) were used. Testosterone values for Caesarian and spontaneously delivered pups were quite similar (Fig. 2). Testosterone values for females are low and do not significantly change over the first 24 h after delivery. Mean testosterone level for males (Caesarian and spontaneously delivered combined) at 1 h and males
Statistical analysis Peritz’s F-test [l l] is applicable to all comparisons among data set means. It does not require equal sample size, but does require that at least two observations per data set mean be obtained (i.e. that degrees of freedom for each set be >O). The F value is calculated exactly as for analysis of variance but the required significance level is adjusted so as to keep all comparisons experimentwise at P < 0.05. Only differences significant at P < 0.05 are reported.
C-newborns
l
01234
6
.
C-newborns
o
S-newborns
H&s
18
24
Fig. 2. Plasma testosterone in Caesarian-delivered (0) and spontaneously delivered (0) female mice. Each point on the graph represents the value for one sample. See Fig. 1 and the text for additional details.
285
Testosterone in neonatal mice
cl
EtbI,
OfPS4
,
6
16
24
H&s
Fig. 3. Testosterone (a) and androstenedione (0) content of the testes from neonatal male mice taken at different times after birth. The numbers in parentheses represent the numbers of assays for each stage. The vertical line through each point shows the standard error of the mean for the samples assayed at that time period.
at 2 h were significantty higher than for the eomparable groups of females (P = O.OI and 0.002 respectively). Contrary to males, no significant differences were found between plasma testosterone values in females collected at l-2 h and at 3-24 h respectively.
m&e mice rarely show lordosis following injection of fernate sex hormones in adulthood f17f. There is no doubt that these differences arise from differences in perinatal stimulation by testicular hormones [ 16, 171. In the present study, we show that the essential hormonal difference between males and females during the first day after birth lies in an elevated plasma testosterone level for males which peaks about 2 h after birth. Aithough the period of susceptibility to the masculinizing and defeminizing effects of perinatal hormonal stimulation may be quite prolonged [3], our results suggest that the increase in plasma testosterone in male mice which reaches its peak at 2 h after birth may initiate processes of differentiation for mechanisms which will ultimately govern gonadotropin secretion and the control of adult sexual and aggressive behaviors. REFERENCES 1. Roth J., Corbier P. and Kerdelhut II.: Stimulation de la
2.
The testosterone and androstenedione content of testes taken from 201 spontaneously delivered newborn males is shown in Pig. 3. Testicular testosterone falls rapidly during the first hour after birth and remains low from 6 to 24 h after birth. Androstenedione in testes is highest at 2 h after birth, and falls gradually from that point over the first 24h after birth. Testicular a&roster&one is ~gni~cantly higher at 0 h than at aI1 other stages (P < 0.001).
3.
4.
5. DISCUSSION
fn newborn male mice, whether Caesarian or spontaneously delivered, plasma testosterone peaks during the first 2 h after delivery to a level which, in some cases, exceeds that for an adult male. Plasma testosterone then decreases so that by 6 h after delivery, plasma testosterone for the neonatal male is not significantly different from that for a comparable neonatal female. The increase in plasma testosterone follows a decrease in testicular testosterone content, and it seems certain that the relatively high level of testosterone seen in blood at 2 h is derived from the testes. In this regard, our results for the mouse are quite similar to ones reported for the rat [3,12-IS], a closely related species with a similar gestation period. Similarly, the presence of androstenedione in the testes of the newborn mouse is in agreement with previous data reported for the rat [13]. In mice, sex differences in aggressive behavior and sexual behavior are well-documented. Male mice are more responsive to the aggression promoting effects of testosterone than females [16]> and female mice given ovarian hormones are quite receptive while
6.
7.
8.
secretion de LH et de FSH et augmentation du poids testiculaire a la naissance, chez le Rat. C. P. hebd. Acad. Skanc,, Sci, Paris, 284 (1977) 13131316. Corbier P., Kerdelhue B., Picon R. and Roffi 3.: Changes in testicular weight and serum gonadotropin and testosterone levels b=efore, during and after birth in the perinatal rat. E~docr~~~o~y 103 (1978) 1985-1991. Corbier P., RofIi J., Rhoda J. and KerdeIhue 8.: Increased activity of the hypothalamo-pituitarvtesticular axis in -the rat at birth: implication in the sexual differentiation of the brain? In Sexual Differentiation: Basic and Clinical Aspects (Edited by MT Serio ef al.). Raven Press, New York (1984) pp. 133-148. Corbier P.: Sexual differentiation of positive feedback: effect of hour of castration at birth on estra~al-undue luteinizing hormone secretion in immature male rats. End~r~~oio~v I16 (I 985) f42-147. Corbier P,,-“Roffi J. and Rhoda J,: Female sexual behavior in male rats: effect of hour af castration at birth. Phvsial. Behav. 30 11983) 613616. Roffi J., Chami F., Corbikr P. and Edwards D.: Testicular hormones during the first few hours after birth augment the tendency of adult male rats to mount receptive female. Physiof. Behao. 39 (1987) 625-628. Gorski R. A.: Sexual di~erent~a~on of brain structure in rodents. In Sexual ~~~re~~ia~~o~: Basic and C&&al Aspects (Edited by M. S&o et ai.). Raven Press, New York (1984) pp, 65-77. Edwards D. A.: Post-neonatal androgeniration and adult aggressive behavior in female mice. Physioi. Behav. 5 (1970) 465-467.
9. Roger M., Nahoul K., Toublanc J. I?., Castanier M., Canlorbe P. and Job J. C.: Les androgenes plasmatiques chez le garqon de la naissance B l’adolescence. Ann. Pkdiat, 26 (1979) 239-245.
10. Nahoul K. and Scholler R.: Comparison of saliva and plasma 17-hydrox~rogesterone time-course response to hCG administration in normal men. J. steroid Biochem. 26 (1987) 251-257. 11. Harper J. II.: Peritz’ F test: basic program of a robust multiple comparison test for statistical analysis of all differences among group means, Camp. Biol. Med. 14 (1984) 437-445. 12. Lieberburg I., Krey L. C. and McEwen B, S.: Sex differences in serum testosterone and in exchangeable brain cell nuclear estradiol during the neonatal period in rats. Bra% Res. 178 (1979) 207-212.
286
I. MOTELICA-HEINO et al.
13. Pang S. F., Caggiula A. R., Gay V. L., Goodman R. L. and Pang C. S. F.: Difference between serum testosterone levels of male and female neonatal rats during the critical period of neural sexual differentiation. Neurosci. Abstr. 2 (1976) 679. 14. Resko J. A., Feder H. H. and Goy R. W.: Androgen
concentrations in plasma and testis of developing _ - rats. J. Endocr. 40 (1968) 485491. 15. Slob A. K., Ooms M. P. and Wreeburg J. T. M.: Prenatal and early postnatal sex differences in plasma
and gonadal testosterone and plasma luteinizing hormone in female and male rats. J. Endocr. 87 (1980) 81-87. 16. Edwards D. A.: Early androgen stimulation and aggressive behavior in male and female mice. Pbpiol. Be/mu. 4 (1969) 333-338. 17. Edwards D. A. and Burge K. G.: Early androgen treatment and male and female sexual behavior in mice. Horm. Behav. 2 (1971) 49-58.
0022-4731/88 $3.00 + 0.00 Copyright 0 1988 PergamonPressplc
TESTOSTERONE LEVELS IN PLASMA TESTES OF NEONATAL MICE I.
MOTELICA-HEINO*,
M. CASTANIER~, P. CORBIER, D. A. EDWARDS~
Laboratoire d’Endocrinologie,
AND
and J.
ROFFI
Universite Paris XI, 91405 Orsay Cedex, France
(Received 20 November 1987) Summary-Newborn female and male C57BL6 mice were decapitated at birth or at different times during the first 24 h after birth and testosterone was determined by radioimmunoassay in plasma and testes. In newborn females, plasma testosterone is low and does not significantly change over the first 24 h after birth. In contrast, in newborn males, plasma testosterone more than
doubles during the first 2 h after birth and then falls rapidly to remain relatively low for the remainder of the 24 h period after birth. The increase in plasma testosterone is of almost certain testicular origin since it follows a decrease in testicular testosterone content. It seems likely that the increase in plasma testosterone in male mice which reaches its peak at 2 h after birth is involved in an essential way in the development of well-documented sex differences in gonadotropin secretion and behavior.
INTRODUCIION
EXPERIMENTAL
In the newborn male rat, a rise in serum gonadotropin is followed by a rapid increase in serum testosterone which peaks about 2 h after birth [l, 21. The increase in serum testosterone is clearly of testicular origin since it is not seen in females or males castrated at birth [3]. Male rats castrated at birth are completely feminized with respect to positive feedback and feminine sexual behavior [4,5] and show some deficits in male sexual behavior as well [6]. This research makes it clear that gonadal hormonal stimulation during the first several hours after birth plays a particularly important role in the sexual differentiation of the rat. While a number of studies suggest that gonadal hormonal stimulation during the perinatal period is important in the sexual differentiation of other rodent species [7], there is little or no information available about the pattern of androgen secretion during the first few hours after birth in these species. We choose to study the mouse because perinatal stimulation by testicular hormones has been demonstrated to play an essential role in the processes of defeminization and masculinization [8] and we here describe how androgen levels in testes and plasma change during the first 24 h of postnatal life.
Present Addresses: ‘CNRS, UA 594, Laboratoire de Pharmacologic, Universite Paris-XI, 92290 ChltenayMalabry, France. YFondation de Recherche en Hormonologie, 67, boulevard Pasteur, 94268 Fresnes Cedex, France. IDepartment of Psychology, Emory University, Atlanta, GA 30322, U.S.A.
Animals and preparation of samples for assay
Adult male and female C57BL6 mice were housed in our temperature controlled (2425°C) colony room maintained on a 1410 h light-dark cycle (lights on between 1800 h-0800 h). Food and water were supplied ad libitum. Females were housed 6 per cage and once a week a single adult male was introduced into each cage for an 8 h period (0900 to 1700 h). The next day was counted as “day 1” of gestation and pregnant females were identified on day 16 and caged individually until delivery of the pups. Under these conditions, most females deliver their pups during the dark period on day 19 of gestation. Some pups were delivered by Caesarian section (C-newborns) between 1400 and 1800 h on day 19 of gestation. To do this, pregnant females were killed by cervical dislocation and fetuses were quickly removed from each uterine horn. Some of these pups (Cnewborns) were decapitated at once (0 h) and others were kept at 35°C for either 30 min, 1 or 2 h before decapitation and blood collection. Spontaneously born animals on day 19 of gestation (S-newborns) were either decapitated at birth (0 h) or left with their mother and decapitated at different times during the first 24 h. After decapitation, the trunk blood for a pup was collected in an individually marked heparinized 50 p 1 capillary tube and the sex of the pup was determined by laparotomy. Blood from 14 to 25 pups of the same age and sex was pooled to make up one sample for assay. Samples were formed across litters in order to control inter-litter variability. Samples were kept refrigerated overnight at 4°C and centrifuged under
283
284
1. MOTELICA-HEINO et 01.
refrigeration (10,000 g for 20 min at 4°C). Plasma was removed and stored at - 20°C until assay. Testes were rapidly removed from decapitated males, and dissected free of adhering tissue on an ice-cold platform. Testes were then placed in single or multiple pairs in test tubes containing melting ice to a volume of 0.6ml distilled water, the tubes were stored at -20°C until assay. Adult males, ranging in age from 40-70 days, were decapitated between 140&1500 h, and trunk blood from 4 different males/sample was collected in a test tube. The blood was treated and stored until radioimmunoassay as described above. Radioimmunoassay 0.3 ml of a solution of collagenasedipase (3% in distilled water) was added to each tube containing the testes. Digestion was allowed to proceed for 30 min at 37°C in a shaker bath. The androgens were determined in testes and plasma samples by radioimmunoassay after extraction with diethyl ether and chromatography on Celite microcolumns following the method of Roger et al. [9], with slight modifications [lo]. The antisera were raised in rabbits injected with either testosterone-15carboxymethyloxineBSA or androstenedione- 11CL -hemisuccinate-BSA. The antiserum anti-testosterone cross-reacted significantly with 5x-dihydrotestosterone (23.5%), 5c(androstene38, 178 -dial (10.8%) and androstenedione (3.4%). The most important cross-reaction of the antiserum anti-androstenedione was displayed with epitestosterone (4.0%). However all these steroids were not liable to interfere with either testosterone or androstenedione assays since they were not eluted in the same fraction from the Celite microcolumn. The assays of testosterone and androstenedione have been already validated [9]. The mean recovery of tritiated steroids added to plasma was 86.5% for testosterone and 74.9% for androstenedione. The intra-assay coefficients of variation were 8.6% for testosterone and 7.4% for androstenedione. The inter-assay coefficients of variation were 8.0% for the two steroids. Results are expressed in pmol of testosterone or androstenedione per pair of testes or per pmol of testosterone per ml plasma.
cf S-newborns
01234
(I
18
H&s
24
AD
Fig. 1. Plasma testosterone in Caesarian-delivered (0) and spontaneously delivered (0) male mice. Blood from 14 to 25 pups was pooled to make up each sample for testosterone assay. Each point on the graph represents the value for one sample. Different samples were -taken at different times during the 24 h after birth. Details of deliverv are given in the text. The column on the right shows the mean aid SEM for plasma testosterone in adult (AD) male mice, and is based on 28 samples. RESULTS
Serum testosterone in neonatal and adult males A total of 442 pups (246 Caesarian delivered newborns and 196 spontaneously delivered newborns) and 188 adults were used. In both Caesarian delivered and spontaneously delivered newborn males, plasma testosterone more than doubles during the first 2 h after delivery (Fig. l), and then falls rapidly by 3 h to remain relatively low for the remainder of the 24 h period after birth. The mean value for samples taken at l-2 h (mean = 6.84 + 0.94 pmol/ml, Caesarian and spontaneously delivered combined, n = 19) was significantly higher (P < 0.001) than the mean for samples (n = 10) taken 3-24 h after delivery (2.00 f 0.37 pmol/ml). The mean plasma testosterone for adult males was 7.25 f 1.07 pmol/ml (28 assays). Plasma testosterone in neonatal females A total of 428 pups (219 Caesarian and 209 spontaneously delivered females) were used. Testosterone values for Caesarian and spontaneously delivered pups were quite similar (Fig. 2). Testosterone values for females are low and do not significantly change over the first 24 h after delivery. Mean testosterone level for males (Caesarian and spontaneously delivered combined) at 1 h and males
Statistical analysis Peritz’s F-test [l l] is applicable to all comparisons among data set means. It does not require equal sample size, but does require that at least two observations per data set mean be obtained (i.e. that degrees of freedom for each set be >O). The F value is calculated exactly as for analysis of variance but the required significance level is adjusted so as to keep all comparisons experimentwise at P < 0.05. Only differences significant at P < 0.05 are reported.
C-newborns
l
01234
6
.
C-newborns
o
S-newborns
H&s
18
24
Fig. 2. Plasma testosterone in Caesarian-delivered (0) and spontaneously delivered (0) female mice. Each point on the graph represents the value for one sample. See Fig. 1 and the text for additional details.
285
Testosterone in neonatal mice
cl
EtbI,
OfPS4
,
6
16
24
H&s
Fig. 3. Testosterone (a) and androstenedione (0) content of the testes from neonatal male mice taken at different times after birth. The numbers in parentheses represent the numbers of assays for each stage. The vertical line through each point shows the standard error of the mean for the samples assayed at that time period.
at 2 h were significantty higher than for the eomparable groups of females (P = O.OI and 0.002 respectively). Contrary to males, no significant differences were found between plasma testosterone values in females collected at l-2 h and at 3-24 h respectively.
m&e mice rarely show lordosis following injection of fernate sex hormones in adulthood f17f. There is no doubt that these differences arise from differences in perinatal stimulation by testicular hormones [ 16, 171. In the present study, we show that the essential hormonal difference between males and females during the first day after birth lies in an elevated plasma testosterone level for males which peaks about 2 h after birth. Aithough the period of susceptibility to the masculinizing and defeminizing effects of perinatal hormonal stimulation may be quite prolonged [3], our results suggest that the increase in plasma testosterone in male mice which reaches its peak at 2 h after birth may initiate processes of differentiation for mechanisms which will ultimately govern gonadotropin secretion and the control of adult sexual and aggressive behaviors. REFERENCES 1. Roth J., Corbier P. and Kerdelhut II.: Stimulation de la
2.
The testosterone and androstenedione content of testes taken from 201 spontaneously delivered newborn males is shown in Pig. 3. Testicular testosterone falls rapidly during the first hour after birth and remains low from 6 to 24 h after birth. Androstenedione in testes is highest at 2 h after birth, and falls gradually from that point over the first 24h after birth. Testicular a&roster&one is ~gni~cantly higher at 0 h than at aI1 other stages (P < 0.001).
3.
4.
5. DISCUSSION
fn newborn male mice, whether Caesarian or spontaneously delivered, plasma testosterone peaks during the first 2 h after delivery to a level which, in some cases, exceeds that for an adult male. Plasma testosterone then decreases so that by 6 h after delivery, plasma testosterone for the neonatal male is not significantly different from that for a comparable neonatal female. The increase in plasma testosterone follows a decrease in testicular testosterone content, and it seems certain that the relatively high level of testosterone seen in blood at 2 h is derived from the testes. In this regard, our results for the mouse are quite similar to ones reported for the rat [3,12-IS], a closely related species with a similar gestation period. Similarly, the presence of androstenedione in the testes of the newborn mouse is in agreement with previous data reported for the rat [13]. In mice, sex differences in aggressive behavior and sexual behavior are well-documented. Male mice are more responsive to the aggression promoting effects of testosterone than females [16]> and female mice given ovarian hormones are quite receptive while
6.
7.
8.
secretion de LH et de FSH et augmentation du poids testiculaire a la naissance, chez le Rat. C. P. hebd. Acad. Skanc,, Sci, Paris, 284 (1977) 13131316. Corbier P., Kerdelhue B., Picon R. and Roffi 3.: Changes in testicular weight and serum gonadotropin and testosterone levels b=efore, during and after birth in the perinatal rat. E~docr~~~o~y 103 (1978) 1985-1991. Corbier P., RofIi J., Rhoda J. and KerdeIhue 8.: Increased activity of the hypothalamo-pituitarvtesticular axis in -the rat at birth: implication in the sexual differentiation of the brain? In Sexual Differentiation: Basic and Clinical Aspects (Edited by MT Serio ef al.). Raven Press, New York (1984) pp. 133-148. Corbier P.: Sexual differentiation of positive feedback: effect of hour of castration at birth on estra~al-undue luteinizing hormone secretion in immature male rats. End~r~~oio~v I16 (I 985) f42-147. Corbier P,,-“Roffi J. and Rhoda J,: Female sexual behavior in male rats: effect of hour af castration at birth. Phvsial. Behav. 30 11983) 613616. Roffi J., Chami F., Corbikr P. and Edwards D.: Testicular hormones during the first few hours after birth augment the tendency of adult male rats to mount receptive female. Physiof. Behao. 39 (1987) 625-628. Gorski R. A.: Sexual di~erent~a~on of brain structure in rodents. In Sexual ~~~re~~ia~~o~: Basic and C&&al Aspects (Edited by M. S&o et ai.). Raven Press, New York (1984) pp, 65-77. Edwards D. A.: Post-neonatal androgeniration and adult aggressive behavior in female mice. Physioi. Behav. 5 (1970) 465-467.
9. Roger M., Nahoul K., Toublanc J. I?., Castanier M., Canlorbe P. and Job J. C.: Les androgenes plasmatiques chez le garqon de la naissance B l’adolescence. Ann. Pkdiat, 26 (1979) 239-245.
10. Nahoul K. and Scholler R.: Comparison of saliva and plasma 17-hydrox~rogesterone time-course response to hCG administration in normal men. J. steroid Biochem. 26 (1987) 251-257. 11. Harper J. II.: Peritz’ F test: basic program of a robust multiple comparison test for statistical analysis of all differences among group means, Camp. Biol. Med. 14 (1984) 437-445. 12. Lieberburg I., Krey L. C. and McEwen B, S.: Sex differences in serum testosterone and in exchangeable brain cell nuclear estradiol during the neonatal period in rats. Bra% Res. 178 (1979) 207-212.
286
I. MOTELICA-HEINO et al.
13. Pang S. F., Caggiula A. R., Gay V. L., Goodman R. L. and Pang C. S. F.: Difference between serum testosterone levels of male and female neonatal rats during the critical period of neural sexual differentiation. Neurosci. Abstr. 2 (1976) 679. 14. Resko J. A., Feder H. H. and Goy R. W.: Androgen
concentrations in plasma and testis of developing _ - rats. J. Endocr. 40 (1968) 485491. 15. Slob A. K., Ooms M. P. and Wreeburg J. T. M.: Prenatal and early postnatal sex differences in plasma
and gonadal testosterone and plasma luteinizing hormone in female and male rats. J. Endocr. 87 (1980) 81-87. 16. Edwards D. A.: Early androgen stimulation and aggressive behavior in male and female mice. Pbpiol. Be/mu. 4 (1969) 333-338. 17. Edwards D. A. and Burge K. G.: Early androgen treatment and male and female sexual behavior in mice. Horm. Behav. 2 (1971) 49-58.