[Maturation of sexual behavior in laboratory male mice: a role of genotype]

Sexual behaviour and testosterone output in response to a receptive female were investigated in male mice of three inbred strains BALB/cLac, CBA/Lac and PT at puberty (45 days of age) and in adulthood (90 days of age). The animals were exposed for 10 min to a receptive female separated by a plastic grill, which would not allow contact between male and female. Male and female behaviour was recorded by measuring the time the male or female spent at the grill and the number of approaches to it (sexual motivation). The grill was then removed and the number of mounts and chemoinvestigatory behavior towards a female (nasal and anogenital sniffing) was recorded for each male. An increase in serum concentration and testicular content of testosterone was used as an endocrine index of the sensitivity to female pheromones. It has been shown the significant genotype and developmental effects on sexual behaviour and the hormonal response to sexual stimuli. The pubertal BALB/cLac males were characterised by the adult pattern of sexual motivation, chemoinvestigatory behaviour and the evident testosterone respond to a female. Males of the strain PT showed the lowest sexual motivation, chemoinvestigatory behavior towards a receptive female and no testosterone responses at both ages. This is a very different situation with the CBA/Lac's who showed the developmental increase in the sexual motivation, sniffing behaviour and the endocrine reflex, and the highest level of sexual behaviour but the moderate testosterone respond to a female at adulthood. The data obtained suggest genotype related asynchrony in maturation of the olfactory system, pituitary-gonadal axis and neural circuits of sexual behavior, and their independent genetic control. So, the set of mice strains investigated represents a useful tool for genetic and endocrine study of sexual behavior and the chemosensory control of testicular steroidogenesis.

[Competition for limited environmental resources on the social dominance model in laboratory mice]

Asymmetry of social rank in the competition for food and female was studied using the social dominance model with only two male mice. Marking activity was recorded as a useful indicator of the social status. Social rank was determined by asymmetry in aggressive behavior. A food test was presented for 10 min daily within 5 days of the experiment, whereas a sexual test was performed only on the 5th day for 30 min. Marking behavior was estimated twice: before the first interaction and on the 4th day of the experiment. The competition for food was accompanied by active attacks, escapes, vertical defense postures, and sniffing. The level of aggression, sniffing, and food activity was higher in dominant than submissive males. Time course of aggressive, defensive, and sniffing behaviors was characterized by maximum scores in the period of formation of social hierarchy; however, the rate of food activity in this period was low and increased only to the 4th day. Introduction of a receptive female into the male group with the stable social hierarchy stimulated the intermale aggression, defensive and sniffing behaviors. Dominant males were characterized by a greater number of victories over and sniffing contacts with both male and female. Marking activity was also more intense in dominants. Thus, significant unidirectional rank differences in agonistic, sniffing, food, sexual, and marking behaviors were shown on the social dominance model with the minimum number of partners.

[The experimental model of establishment and maintenance of social hierarchy in laboratory mice]

The goal of the investigation is to establish a new experimental model of social hierarchy in laboratory mice. The important feature of the model is a group of two males only placed into the special experimental cage. The cage consists of two nestling chambers and central chamber. Observations were made 3 times per day (20 min each) throughout 5 days. Aggression, defence and sniffing behaviours of both partners were recorded during each observation period using video camera. Social rank was detected by asymmetry in aggressive behaviour. It was shown that social hierarchy was established during the first four tests limited by the first 24 h after pairing. After this period aggression and defence behaviours were greatly decreased. After the first 5 tests a stabilization in aggression (number of wins, active attacks and not direct aggression) and defence (number of vertical defensive postures and escapes) as well as sniffing behaviours took place. But a strong asymmetry in mentioned here behaviours in males of different ranks (dominants and subordinates) was kept up. Thus we offer a new experimental model of minimal society, which entirely reproduces a pattern of establishment and maintenance of social hierarchy. Our model demonstrates significant differences in agonistic, defence and sniffing behaviours between males of different social rank.

[Effect of prenatal stress on the pituitary-adrenal axis in blue foxes]

Handling is a source of stress for farm bred blue foxes. The influence of handling during the late gestation period on the pituitary--adrenal axis was studied in 10-day old male and female blue foxes. Cortisol and progesterone were measured by radioimmunoassay in the plasma, adrenal homogenates, and in vitro incubates from animals of both sexes. Adrenals were incubated in vitro in the absence or presence of ACTH. In addition, the adrenal weight and plasma concentration of ACTH were assessed. In cubs of both sexes, the adrenal weight was decreased after prenatal stress. The plasma concentration of progesterone and the adrenal cortisol in vitro production were elevated in the prenatally stressed female cubs, as compared to the control, along with the adrenal progesterone in vitro production in prenatally stressed male cubs. The adrenal cortisol and progesterone content and plasma ACTH and cortisol concentrations were not affected by prenatal stress. In conclusion, the results of this study suggest that the prenatal stress induced by handling pregnant vixens can affect the pituitary--adrenal axis in neonatal offspring, this effect being more pronounced in female cubs.

[Sex-related differences in blood and gonad levels of testosterone in silver fox fetuses]

The mass of silver fox fetuses of both sexes, their gonads, and adrenals, and the levels of testosterone in blood serum and in gonads and adrenals were determined from day 31 of gestation and every five days thereafter until its termination. Marked sex-related differences were revealed: the blood and gonad levels of testosterone in male fetuses were much higher than those in female fetuses. The fetal adrenals contained significantly less testosterone than the gonads. No sex-related differences in the content of testosterone in the fetal adrenals were found. No differences were found in the body and adrenal mass in female and male fetuses at all the developmental stages studied, while the mass of ovaries exceeded that of testes from day 45 of gestation. The data obtained suggest sex dimorphism in the production of testosterone by gonads in silver foxes appears after day 35 and appears to correspond to the period of morphological differentiation of gonads.

Handling during pregnancy in the blue fox (Alopex lagopus): the influence on the fetal pituitary-adrenal axis

Previous studies revealed that handling is a stressor for farmed blue foxes. The present study was designed to examine the effects of a 1-min daily handling stress applied to pregnant blue fox vixens on the function of the fetal pituitary-adrenal system. Plasma concentrations of adrenocorticotropin hormone (ACTH), cortisol, and progesterone, adrenal content of cortisol and progesterone, in vitro adrenal production of these steroids and response to ACTH, and adrenal weights were measured in control (C; n = 73) and stressed (S; n = 58) fetuses. The ACTH levels were lower in stressed fetuses than in the controls (C: males, 128.6 +/- 6.1 pg/ml; females, 165.9 +/- 6.1 pg/ml; S: males, 122.3 +/- 5.4 pg/ml; females, 145.0 +/- 8.1 pg/ml; P < 0.05). In contrast, increased plasma cortisol concentrations in both sexes were demonstrated in stressed compared with control fetuses (C: males, 9.2 +/- 0.4 ng/ml; females, 9.2 +/- 0.4 ng/ml; S: males, 11.8 +/- 0.7 ng/ml; females, 13.2 +/- 0.7 ng/ml; P < 0.00001). The same difference was observed in plasma progesterone concentrations (C: males, 1.54 +/- 0.07 ng/ml; females, 1.49 +/- 0.10 ng/ml; S: males, 1.86 +/- 0.11 ng/ml; females, 1.74 +/- 0.10 ng/ml; P < 0.01). Prenatal stress did not change the baseline adrenal production of cortisol but prevented the cortisol response to ACTH in female fetuses and decreased the progesterone production in both sexes. Additionally, prenatally stressed fetuses of both sexes had significantly lower adrenal weights than controls (C: males, 9.4 +/- 0.3 mg; females, 9.5 +/- 0.4 mg; S: males, 8.1 +/- 0.3 mg; females, 8.2 +/- 0.4 mg; P < 0.001). These results indicate that prenatal handling stress induces a dysregulation of the pituitary-adrenal axis in the fetus and suggest that increased plasma glucocorticoids in the stressed dam can cross the placenta and influence the fetal hypothalamicpituitary-adrenal axis.

[The effect of prenatal stress on steroidogenesis in the gonads of Arctic foxes (Alopex lagopus)]

Handling is a source of stress for farm-bred blue foxes. The influence of handling during the late gestational period was investigated in 10-day old male and female blue foxes. Testosterone and estradiol were measured by RIA in the plasma, gonadal homogenates and in vitro incubates from blue foxes of both sexes. The gonads were incubated in vitro without or with human chorionic gonadotropin. In cubs of both sexes, the gonad weights and ovarian estradiol production were decreased by stress. The testicular testosterone and ovarian estradiol contents were increased in prenatally stressed cubs as compared to the controls. The testicular content and baseline in vitro production of testosterone were not affected by prenatal stress, but the testicular response to human chorionic gonadotropin was higher in the stressed group. This study suggests that prenatal stress induced by handling pregnant vixens may influence gonadal steroidogenesis and this effect was more pronounced in female cubs.

Effect of restricted food intake on production, catabolism, and effects of IGF-I and cyclic nucleotides in cultured ovarian tissue of domestic nutria (Myocastor coypus)

The aims of these in vitro experiments were to examine the effects of short-term food restriction on ovarian secretory activity and the role of IGF-I and cAMP- and cGMP-dependent intracellular mechanisms in the control of ovarian function in domestic nutria. Slices of ovary from sexually mature animals kept under conditions of normal and restricted ((1/2) of standard ration) feeding were cultured with or without IGF-I (50 ng/ml), cAMP analogues (dbcAMP and Rp-cAMPS), and cGMP analogues (8-pCPT-cGMP and Rp-8-Br-PET-cGMPS; all at 100 nM). In nonovarian cells dbcAMP activates and Rp-cAMPS inhibits protein kinase A, while 8-p-CPT-cGMP activates and RP-8-Br-PET-cGMPS inhibits protein kinase G and cGMP-gated ion channels. IGF-I release and catabolism, as well as the release of progesterone (P), estradiol (E), and cAMP by the cultures, were evaluated using RIA. IGF-I did not affect cAMP release, while each of the cAMP and cGMP analogues inhibited IGF-I release in both control and experimental groups. Fasting did not affect cAMP or IGF-I release. It partially prevented the effect of Rp-cAMPS, but not of other cyclic nucleotides, on IGF-I release and inhibited IGF-I catabolism. The Rp-cAMPS and Rp-8-Br-PET-cGMPS also inhibited IGF-I catabolism and the effects were greater with tissue from food-restricted than control animals. Ovaries from the underfed nutria secreted significantly more P and less E than those from normally fed animals. IGF-I and both cAMP analogues, given alone, did not affect P release whereas a combination of IGF-I and Rp-cAMPS increased P output in control, but not in the experimental group. The 8-pCPT-cGMP had no effect P release. Rp-8-Br-PET-cGMPS, given alone or in combination with IGF-I, dramatically increased P secretion by tissue from control but not underfed animals. Estradiol secretion by tissue from underfed animals was stimulated by IGF-I, dbcAMP, Rp-cAMPS, 8-pCPT-cGMP, and Rp-8-Br-PET-cGMPS as well as by combinations of IGF-I and Rp-cAMPS or Rp-8-Br-PET-cGMPS; these effects were not seen with control tissue. The results demonstrate that: (1) ovaries of domestic nutria secrete IGF-I, P, E, and cAMP; (2) cAMP and cGMP can influence IGF-I release and catabolism; (3) the cyclic nucleotides may have an IGF-I-mediated effect on P and E output; (4) IGF-I and cyclic nucleotides can prevent the effect of undernutrition on E, but not on P release; (5) effects of cAMP and cGMP on P and E are probably not mediated by protein kinase A, protein kinase G, or cGMP-gated ion channels; and (6) food restriction can influence ovarian IGF-I catabolism, P, and E release and modulate the effects of cyclic nucleotides and IGF-I on steroidogenesis. It is concluded that ovarian secretory activity may be regulated separately by nutrition and the cyclic nucleotide-IGF-I system, and there may be functional interrelationships between these mechanisms.

[The effect of the photoperiod on steroid hormone secretion, on seasonal reproductive rhythms and on fertility in female silver foxes]

The silver fox is a strictly seasonal breeder and photoperiod is a main factor that regulates reproduction in this species. The aim of the present work was to study the effects of different skeleton photoperiods on the induction of early estrus, hormonal activity of gonads and fertility in anestrous silver foxes. Adult females (n = 48) were exposed to short days (9.5L:14.5D) from September until March. Females (n = 12) kept under the natural daylight conditions served as the control. The experimental groups received illumination in two fractions: 7- and 2.5-hour long. The 7-hour period comprised natural daylight from 10:00 to 17:00 and an additional light pulse at night (00-02:30, group 1), in the morning (06:00-08:30, group 2) and in the evening (17:30-20:00, group 3). There are three types of response in group 1. A half of animals showed signs of estrus in November-December, 2.5-3.0 months before the natural reproductive season. The second part displayed no changes until the end of the experiment indicating photorefractoriness. The third part had estrus during the natural reproductive season. Photoperiod 2 and 3 did not affect the temporal pattern of reproductive rhythm. All artificial photoperiods increased the estradiol level and decreased the progesterone, cortisol and testosterone levels during the anestrous phase and suppressed the ovarian hormonal activity during the follicular and luteal phases but photoperiod 1 had the most pronounced effects. Fertility was decreased in all experimental groups. Our results suggest that the photoperiod with a light pulse at night can induce early estrus and ovarian hormonal activity in anestrous females. The data obtained suggest that decreased fertility under these conditions could be due to altered ovarian hormonal secretion.

[Biosynthesis of testosterone in the gonads in silver fox embryos after long-term selection for domesticated behavior]

Fetal gonad weight and testosterone content in serum and gonads were analyzed in silver fox every five days from the 35th day of pregnancy until delivery. Fetal testicles were also tested for testosterone production induced by chorionic gonadotropin (CG) in vitro. Pregnant females were sampled from an experimental population subjected to selection for domesticated behavior and a commercial population (control). Fetal gonad weight was significantly lower in domesticated animals than in controls. No differences were revealed in the testosterone contents in their serum and gonads and in the basal production of testosterone in fetal testicles. CG-induced production of testosterone was detectable from the 40th day of fetal development in domesticated animals and from the 50th day in controls. The results obtained suggest that domestication results in the hetero-chronic fetal development of the hypophysial-testicular complex in silver fox.

[Effect of long-term selection for behavior on progesterone level in blood and its level in adrenal glands of silver fox embryos]

The level of progesterone in blood serum and its concentration in adrenals and gonads have been assayed in male and female silver fox embryos, starting from day 35 of pregnancy for every five days. Pregnant females from an experimental population, selected for the domestic type of behavior and, as a control group, females from a commercial population, were used. At the end of prenatal development (days 45-50) the concentration of progesterone in adrenals was show to be significantly lower in embryos from mothers of the selected population, than in the unselected control group. On the contrary, the domesticated and wild animals did not differ in the level of progesterone in blood. The results suggest that selection of animals for domestic behavior decreases the synthesis of progesterone by embryonic adrenal glands.

[Phenogenetic analysis of prenatal development of the glucocorticoid function of the adrenals in silver foxes after long-term selection for domesticated behavior]

The level of cortisol in serum and adrenals and its production by adrenals in vitro was studied by the radioimmune method in male and female silver fox embryos, starting from day 30 of pregnancy every five days. Pregnant females from a commercial population and an experimental population, which had been selected for domestic behavior, was used. It was shown that, at the end of the prenatal developmental stage, all investigated parameters of the glucocorticoid function of adrenals were significantly lower in embryos from selected mothers as compared to the unselected control group. The addition of adrenocorticotropic hormone into the incubation medium increased cortisol biosynthesis at all embryogenesis stages, but in the selected population the increase was less than that in the control group.

[Sexual activity and anomalous spermatogenesis in young male silver foxes]

The total number of spermatozoa in ejaculate of males with normal sexual activity was 165,647,5 million and the mean percentage of morphologically abnormal spermatozoa was 21,64,4%. The percentage of morphologically defective spermatozoa in sexually inactive males was significantly lower than in sexually active ones.

Cortisol production in fetal adrenals of the silver fox

The present study was designed to examine cortisol production by the silver fox fetal adrenals and their response to ACTH at different periods of prenatal life. Serum levels of cortisol were determined on days 35, 40, 45 and 50 of gestation (term on day 52) in embryos of both sexes. Cortisol content in adrenal tissue homogenates and its in vitro adrenal production were also investigated at the same time points. Hormones were measured by RIA. The levels of cortisol changed slightly during embryonic life. The adrenal content and the in vitro production of cortisol increased sharply and progressively (by 4-10 times from days 35 to 50 of gestation). The rises in cortisol content and in vitro production were associated with a rapid growth of the fetal adrenals. There were no sex differences in cortisol level and its adrenal content. ACTH (50 mIU per sample) increased the in vitro cortisol production by the adrenals in the two sexes on all the studied days (by 3-4 times on day 35 and by 1.4-1.7 times on day 50). These results indicate that 1) silver fox fetal adrenals are capable of synthesising cortisol; 2) ACTH is a potent activator of the in vitro cortisol production during embryonic life in this species.

[Spermatogenesis and the testosterone level in young male silver foxes in their reproductive period]

15.7% of spermatozoa were found to be abnormal in silver fox males during their first reproductive season. The total number of spermatozoa and the abnormal spermatogenesis remained unchanged during mating season. Sexual stimulation increased the testosterone level only at the beginning of the mating season.

[The biosynthesis of cortisol and its regulation by the adrenocorticotropic hormone in the adrenals of silver fox embryos]

We studied the cortisol level in blood serum and adrenal homogenates, as well as the in vitro production of cortisol in adrenals of silver fox embryos of both sexes in response to exogenous adrenocorticotropic hormone (ACTH) stimulation. The level of cortisol in blood serum did not show any significant changes during the embryo development, while its level in adrenals and production by adrenals in vitro increased progressively from Day 35 to Day 50 of prenatal life. We found that ACTH is capable of stimulating cortisol biosynthesis and production in vitro during all studied periods of embryogenesis.

[The role of steroid hormones in the sexual and agonistic behaviors of male silver foxes]

Silver fox males were tested for sexual and agonistic behaviour after introduction of a female at different stages of the reproductive cycle. The high level of aggressive interactions between male and female and no mountings were observed out of the reproductive season. During the reproductive season, the introduction of anoestrus female did not affect the aggressive behaviour but increased the number of mountings while introduction of a receptive female reduced aggressive contacts and augmented sexual behaviour in pairs independently of mating. Considerable variations in testosterone and oestradiol but not cortisol plasma levels were observed between different stages of sexual activity. At the beginning of the reproductive season, silver fox males responded to anoestrus females with significant increase in their blood levels of testosterone and oestradiol. Contents of these two hormones did not change in males during the reproductive season when they encountered a receptive female. A female did not elicit any cortisol response in a male during different periods of the reproductive cycle. The data obtained suggest that the sexual behaviour in silver fox males can be facilitated by testosterone and oestradiol while aggressive interactions between male and female occur independently of these hormones.

[Circadian changes in the levels of sex and glucocorticoid hormones in the peripheral blood plasma of female silver foxes]

Domesticated and wild silver fox vixens were shown to differ in their diurnal contents of cortisol and progesterone in the blood plasma. The data obtained reveal that domestication of silver fox vixens modifies their diurnal rhythms of the adrenocortical steroid activity.