Effects of hormones and lactation on gerbils that seldom scent mark spontaneously

Mongolian gerbils scent mark by rubbing low-lying objects with a ventral scent gland. In males and females that regularly scent mark, the behavior is regulated by gonadal steroid hormones, but the influence of hormones on the scent marking behavior of low- or zero-marking gerbils was unclear. The studies reported here demonstrate that injections of testosterone or of estrogen plus progesterone can stimulate scent marking in some low-marking females but fail to do so in others. Lactation was much more effective for inducing scent marking, but again not all females responded. Although most low- or zero-marking females regularly scent marked while lactating, lactation exaggerated premating differences in marking levels. Very few zero-marking male gerbils exhibited scent marking when castrated and treated with testosterone. In both sexes, scent gland size responded to hormone stimulation even when marking behavior did not.     

Short photoperiods increase ultrasonic vocalization rates among male Syrian hamsters

Two experiments investigated the effects of daylength on the emission of 35 kHz ultrasonic (US) calls among male hamsters. In Experiment 1, castrated males received Silastic implants subcutaneously that contained either low doses of testosterone in oil or oil alone; US calls were recorded when these males were paired with receptive females. Males exposed to eight hours of light per day (short photoperiod) called more often than males exposed to fourteen hours of light per day (long photoperiod). This was true whether or not they received testosterone. In Experiment 2, a similar testing and photoperiod exposure paradigm was used, but the subjects were gonadally intact. Among males exposed to short photoperiods, US call rates increased while endogenous testosterone levels decreased. In contrast, hamsters exposed to long photoperiods maintained stable calling rates and testosterone levels. These findings are related to recent studies concerning the neural mechanisms that regulate ultrasonic vocalizations and to the possible role of photoperiod in modulating conspecific aggression.     

Dominant-subordinate relationships in castrated male mice bearing testosterone implants

This study tested the hypothesis that subordination in male mice is directly related to reduced levels of circulating testosterone. Several measures of aggressiveness and submissiveness were quantified during or after daily encounters between pairs of intact males, castrated males, or castrated males bearing testosterone implants that were designed to maintain plasma testosterone titers at levels slightly above those of intact males. Behavioral measures included the total amount of fighting that resulted from daily pairing, the tendency for subordinates to fight back, and the relative frequency of urine marking. In all these regards, pairs of testosterone-implanted, castrated males formed dominant-subordinate relationships that involved apparently normal submissive behavior (compared to intact control pairs). Thus we found no evidence that submissive behavior was directly related to a reduction in circulating testosterone titers.     

Influence of neonatal androgen on the display of territorial marking behavior in the gerbil.

The effect of the presence or absence of androgen during the neonatal period on territorial marking behavior in the Mongolian gerbil was studied. Scent marking frequency was 20-40 fold greater in males than in females. Gonadectomy depressed marking in males but not in females. Testosterone propionate (TP) therapy completely restored marking in male but increased marking in intact and ovariectomized females to only one fourth that in males. Genetic males castrated within 2 days postpartum did not mark more frequently than TP-treated females after TP treatment in adulthood. Genetic females given a single TP injection within 6 days postpartum marked at male levels after TP treatment in adulthood. Males castrated after Day 2 and females given TP after Day 6 displayed marking frequencies intermediate between normal male and female levels after TP treatment in adulthood. This study suggests that sexual dimorphism in territorial marking behavior is due to a sex difference in the competency to respond to androgen, and it appears that development of this competency occurs during the neonatal period and is regulated, at least in part, by androgen. The onset of this differentiation process occurs earlier in the male than in the female.     

Conspecific urine marking in male-female pairs of laboratory rats

Male-female pairs of rats were observed during social interactions for conspecific markings where an animal deposits urine on the body of a second animal. Injections of sodium fluorescein were used to change urinary color and provide a visible mark on the back of a conspecific. The general hypothesis tested in the three experiments was that a female would mark males differently dependent upon her hormonal status and upon the relative hormonal integrity of the males. Results of Experiment 1 were that males marked females more frequently than vice versa and female marking decreased during her estrus. Moreover, a diestrous female marked an aggressive male more than she marked a non-aggressive male (Experiment 2), and a diestrous female marked a castrated male receiving 800 micrograms testosterone propionate (TP) injections more copiously than she marked a castrated male receiving 200 micrograms TP injections (Experiment 3). Finally, aggressive and non-aggressive males marked females similarly, though the 800 micrograms TP males marked females more than the 200 micrograms TP males. These data were compared with findings from research on environmental marking in rodents, and an hypothesis was suggested that female rats use conspecific marking to identify and select males with preferred behavioral and endocrine characteristics.     

Organization of territorial marking behavior by testosterone during puberty in male tree shrews

According to current hypotheses, in mammals male-specific behavior is organized perinatally, and activated in adulthood by male gonadal hormones. However, this strict differentiation between early organizational and late activational hormone effects has been criticized recently. Around puberty the testosterone levels of male mammals rise far above adult levels. In this study we examined the relevance of this pubertal testosterone peak on marking behavior of adult tree shrews (Tupaia belangeri). Male tree shrews were castrated before puberty and treated with testosterone either around puberty or in adulthood. Several months later, the marking behavior of the castrated adult animals was examined in standard tests in different scent conditions before and after a second testosterone treatment. Males castrated as adults as well as fertile females were used as controls. The testosterone peak during puberty did not influence male marking behavior in the absence of scent from conspecifics (familiarization marking) or in the presence of female scent (sexual marking). However, testosterone during puberty determined both the male-specific reaction patterns to male scent (territorial marking) and the male-specific regulation of this behavior by testosterone. These results indicate that testosterone during puberty specifically organizes male territorial-marking behavior. To our knowledge, these are the first results demonstrating organizational effects of testosterone during puberty on male behavior.     

Ovarian influences on the development of sexual behavior in neonatally androgenized rats

Female sexual behavior was studied in male and female rats. Males were castrated on the day of birth (Day 1); some received ovarian implants at that time; others were injected on Day 3 with oil, 5 μg testosterone propionate (TP), or 50 μg TP. Females were ovariectomized at birth, 20, or 60 days of age; on Day 3 all were injected with oil, 5 μg, TP, or 50 μg TP. Prepuberal ovarian tenancy in females tended to counteract the effects on sexual receptivity of TP administered during neonatal life. In males ovarian implants facilitated female sexual behavior at adulthood in oil-injected animals, but did not significantly influence the effect on neonatally injected TP.     

Social and hormonal influences on scent marking in the mongolian gerbil

Marking with the ventral scent gland by the male Mongolian gerbil is abolished after castration. Testosterone implants (25 mg) raised the blood level of testosterone to higher than normal and restored the weight of the scent gland and seminal vesicles. The frequency of marking in castrates bearing implants was raised to the same level as in intact controls, but testosterone implants in intact gerbils did not further stimulate marking. Marking is inhibited in adult sons caged with their father. The normal size of the scent gland and seminal vesicles is evidence that testosterone secretion is not suppressed. Additional testosterone (via implants) did not stimulate marking. Social factors thus seem to control marking behaviour in the male gerbil, provided that a basal level of testosterone is present.     

Testosterone and its metabolites in male cynomolgus monkeys (Macaca fascicularis): behavior and biochemistry

To extend our previous study on the behavioral effects of testosterone propionate (TP) and dihydrotestosterone propionate (DHTP) to a dose-range producing supra-physiological plasma androgen levels, 4 castrated cynomolgus monkeys were tested with the same 4 females during successive 4-week treatment periods while receiving 800 micrograms, 1.6 mg, 3.2 mg, 6.4 mg and 12.8 mg of TP or DHTP SC/day in counterbalanced order (16 pairs, 828 1-hr tests). Both androgens increased male sexual activity, but DHTP was less effective than TP in increasing the numbers of ejaculations per test and failed to restore ejaculations to intact levels. Giving androgen-treated males single injections of 50 micrograms and 100 micrograms estradiol benzoate (EB) was without any additional effect on behavior (16 pairs, 256 tests). To examine hormonal effects in the brain, castrated males were given either 3H-T or 3H-DHT, and tissues were examined by high performance liquid chromatography (hplc). After 3H-T, 3H-E2 and unchanged 3H-T were the major forms of radioactivity in nuclei from hypothalamus, preoptic area and amygdala. After 3H-DHT, unchanged 3H-DHT predominated. The lower behavioral effectiveness of DHT could not be ascribed to its failure to enter the brain. The data suggested a role for unchanged T in the regulation of ejaculatory behavior in a male primate.     

Sexual interactions between estrous female rats and castrated male rats treated with testosterone propionate or estradiol benzoate

Estrous female rats display 'precopulatory behaviors' such as ear wiggling and hopping/darting when castrated males treated with testosterone propionate (TP) are placed in their vicinity and before copulatory interactions have taken place. Castrated males treated with estradiol benzoate (EB) do not elicit these precopulatory behaviors in advance of copulatory interactions. It therefore seemed of interest to study females' sexual behavior with castrated males treated with TP or EB when males or females had primary control over the temporal patterning of the behavior. Unrestrained sexual behavior (= male control) with EB-treated males was characterized by large numbers of intromissions and long periods of time preceding ejaculation, as compared with interactions with TP-treated males. The temporal pattern of sexual behavior did not change importantly when the males were tethered (= sexual behavior controlled by females). When given a choice between two sexually active castrated and tethered males, one treated with TP and the other with EB, estrous females 'preferred' EB-treated animals in various respects. Fewer interactions occurred with, and less time was spent in the vicinity of, TP-treated males over prolonged observation periods (115-135 min). The preference for EB-treated males disappeared, and TP- and EB-treated animals became equally attractive, when the vaginal opening of the female animals was covered with adhesive tape to prevent the occurrence of penile intromissions during mounting. It is concluded that female control over copulatory behavior does not necessarily change the females' sexual behavior.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chin-marking behavior in male and female New Zealand rabbits: onset, development, and activation by steroids.

Chin marking (chinning) frequency was determined daily in 25 male and 24 female New Zealand rabbits aged 31-150 days. Chinning appeared earlier in females (mean +/- SD = 41 +/- 16 days) than in males (47 +/- 13 days). Between days 30-50, females displayed chinning more frequently than males. Thereafter, chinning increased steadily in both sexes up to day 100. Chinning curves levelled on days 100 and 140 in males and females, respectively. Profile analysis of male and female chinning curves showed significant differences in their slopes and in their population means (p < 0.001). At 7 months of age (days 210-224), both sexes displayed adult chinning frequencies: mean of means +/- SD = 103 +/- 18 and 79 +/- 14 marks/10 min in males (n = 8) and females (n = 8), respectively. The administration of testosterone propionate (TP, 1 mg/day) or estradiol benzoate (EB, 1 microgram/day) to males and females, respectively, from days 31-50, stimulated higher chinning frequencies than those displayed by untreated animals. Results suggest that chinning frequency increases throughout development largely as a consequence of a concomitant increase in sex steroid secretion.     

Sexual imprinting in male japanese quail: The effects of castration at hatching

This study investigated whether gonadal hormones are required for sexual imprinting in male Japanese quail during the period of exposure to the imprinting stimulus. Brown males were either castrated or laparotomized on the day of hatching. Between Days 10 and 30 of age castrated males (N = 15) and intact laparotomized males (N = 10) were exposed individually to white females. A 2nd group of intact laparotomized males (N = 13) were exposed to brown females. When adult (Day 54), 7 of the castrated males were treated with testosterone propionate (TP): the remaining 8 castrated males and intact groups received saline. All males were given choices between novel white and novel brown females starting on Day 62. The TP-treated castrated males behaved like intact white-exposed males, preferring to approach and copulate with white females significantly more readily than did intact brown-exposed males. The untreated castrated males showed no sexual behavior. The results indicate that gonadal hormones are not required during the period of exposure to an imprinting stimulus in male Japanese quail.     

Lack of an inhibitory effect of hyperprolactinemia on androgen-dependent marking.

An experiment was performed to determine if hyperprolactinemia (chronically elevated serum prolactin levels), which inhibits testosterone-activated male sexual activity, also affects other androgen-dependent behaviors. Thus defecation and urine marking in response to a novel environment were examined in sham-operated and pituitary-grafted (hyperprolactinemic) male rats that had been castrated or castrated and given subcutaneous testosterone implants. Both castration and pituitary grafting significantly inhibited defecation, with the inhibitory effects of hyperprolactinemia being most pronounced in the castrated non-testosterone-treated animals. In contrast, castration significantly reduced the amount of urine marking observed, but pituitary grafting was without effect on this behavior. Thus, although hyperprolactinemia may inhibit sexual activity through an antagonism of the activational effects of testosterone, these results suggest that this effect is specific to sexual behavior and does not involve a more generalized inhibition of the effects of testosterone on androgen-dependent behaviors.     

Sex and sodium intake in the rat.

Female rats drink more 3% NaCl solution than do males, both when they need sodium (need-induced sodium intake or sodium appetite) and when they do not (need-free sodium intake). The sexual dimorphism of sodium intake is a secondary sexual characteristic because after castration at 1 day of age male rats drank 3% NaCl in adulthood in a manner similar to that of females in both the need-free and need-induced state, and females given long-term, neonatal testosterone drank low, malelike volumes of 3% NaCl on a daily need-free basis, but their response to sodium depletion was unchanged. This sexual dimorphism of sodium intake seems to be governed by testosterone that has been converted in the brain to estrogen because treatment of Day 1 castrated females with a nonaromatizable androgen, dihydrotestosterone, did not change either their need-free or their need-induced 3% NaCl intake. Castration in adulthood of male and female rats did not change their sodium consumption. However, when castrated adults received testosterone, need-free intakes of NaCl were suppressed in both sexes, but the suppression of 3% NaCl intake occurred only while the steroid was present. Exogenous testosterone also lowered the need-induced sodium intake of adult castrated females. Thus, in castrated adults, need-free intake was actively suppressed by exogenous testosterone in both sexes, whereas need-induced intake of NaCl was suppressed only in females. These data indicate that sodium intake in the rat is a sexually dimorphic behavior that is organized neonatally and can be actively suppressed in adulthood by testosterone.     

Neonatal hormone experience and adult lordosis and fighting in the golden hamster.

Androgenization by testicular secretions or exogenous testosterone propionate (TP treatments administered 24-48 hr post partum) suppressed sexual receptivity in the golden hamster. In response to prolonged adult estradiol benzoate (EB) treatment, gonadectomized normal females and neonatally castrated males exhibited significantly longer total lordosis durations than normal male or neonatally TP-treated (20 mug or 200 mug) females. These results suggest that one aspect of androgen-induced masculinization in the hamster involves reduced estrogen sensitivity. Responses to sequential EB followed by progesterone treatment were also lower in the androgenized groups. Neonatally castrated males did not differ significantly from normal females in their lordosis behavior. Irrespective of adult hormone treatment, androgenized animals fought more than normal females or neonatally castrated males. A genital mask was used to reduce sex differences in peripheral stimulation during testing.     

Temporal boundary of the sensitive period for hormonal organization of social play in juvenile rats

The play-fighting of juvenile rats is a sexually dimorphic behavior which is influenced by the organizational actions of testosterone and dihydrotestosterone but is not dependent on activational influences of these testicular hormones. To delimit more precisely the temporal period in early development when these organizational effects are expressed, male rats were castrated 1, 6, 10 or 20 days after birth and their play behavior was compared to that of intact males and females. Daily observations were made of groups of 6–7 animals from 31–40 days of age. Intact males engaged in rough play more frequently than females and also initiated more play bouts. Castration at day 10 or 20 did not affect play in males, but castration on day 1 or 6 reduced male play to levels that were not reliably different from females. The development of social play depends on the presence of testicular androgens for at least 6 days after birth.     

Aggression by a female rat cohabitating with a sterile male: termination of pseudopregnancy does not abolish aggression.

At the end of that time, each female was assessed for aggressiveness toward an unfamiliar female intruder once each week for 3 weeks. Those females displaying a high level of aggression had their male cagemate changed. For half of the females, the new male cagemate was a castrated male with a testosterone implant. For the other half, the new cagemate was a castrated male without a testosterone implant. Replacement males had been subjected to surgery 9 weeks previously. There were no differences in the aggressiveness of females of the two groups on any of 3 subsequent weekly tests of aggression. In a 3-h evaluation of male sexual behavior, none of the 9 castrated males without testosterone replacement displayed sexual activity with an estrogen/progesterone primed ovariectomized female, but 6 of 9 males with testosterone replacement did. Reanalysis of the aggression data comparing the females whose males had no testosterone replacement and females housed with the 6 males that were sexually active also revealed no differences in aggression over the 21-day test period. Since pseudopregnancy is known to last 13 days, these results indicate that the continuous presence of pseudopregnancy is not required for maintenance of aggression by a female cohabiting with a sterile male.     

Recovery of lordotic activity by dorsal deafferentation of the preoptic area in male and androgenized female rats

Lordotic activity was examined in male and neonatally androgenized female rats following dorsal deafferentation of the preoptic area (POA). Female pups were injected with various doses (100, 250, 500, or 1000 micrograms) of testosterone propionate (TP) on day 3 postpartum. Ten weeks after birth, all animals were castrated, then half of the castrated males and females in each group were subjected to dorsal deafferentation of the POA (anterior roof deafferentation: ARD) by using an L-shaped Halász knife in order to transect the dorsal forebrain efferents which are thought to exert an inhibitory influence on the lordosis mediating mechanism. Animals were implanted subcutaneously with Silastic tubes containing estradiol-17 beta (E2). Observations of lordosis behavior were carried out 5, 10, and 15 days after implantation of E2. Three to six hours before each behavioral test, all rats were injected with 0.5 mg progesterone. Regardless of the dose of TP given neonatally, androgenized females, as well as males, showed low levels of lordotic behavior. In contrast, males with ARD and androgenized females with ARD displayed lordosis more frequently than males without ARD, and androgenized females without ARD. Lordotic activity in the androgenized females with ARD was negatively correlated with the dose of TP given neonatally. The ARD females injected with a large dose (1000 micrograms) of TP neonatally were significantly less receptive than those injected with lower doses of TP and ARD males. These results suggest that a large dose of neonatal TP may cause permanent changes in not only the neural substrates for lordosis inhibition affected by ARD but also other structures involved in lordosis facilitation.     

Sex differences in the response to neonatal steroid treatment in the Mongolian gerbil

The present study examines whether genetic male and female gerbils differ in response to neonatal steroid treatment as evidenced by the display of sexually dimorphic territorial marking behavior in adulthood. The advantage of this behavioral endpoint is that male and female marking differs only in frequency, permitting direct between-sex comparison of neonatal treatment effects. Females and day-2 castrated males received a single SC injection of 10 to 100 μg testosterone propionate (TP) or estradiol benzoate (EB) between birth and day-14 postpartum. Between 7 and 9 months of age, the territorial marking behavior response to exogenous TP was determined in all animals. Based on marking frequency, the time of greatest sensitivity to TP administered during the critical neonatal period occurred earlier in the male (days 3–5) than in the female (days 5–7). In addition females consistently showed greater sensitivity to given dose of either TP or EB than did males. EB was more effective than TP at the 10 μg dose in both sexes. These results indicate that sex differences exist in timing and steroid sensitivity in the sexual differentiation of the neural substrate regulating territorial marking behavior.     

Effect of flutamide (an antiandrogen) and diethylstilbestrol on the reproductive behavior of Japanese quail

Three experiments were conducted in order to investigate the role of brain androgen and estrogen receptors in sex hormone activated male reproductive behavior in Japanese quail. In Experiment 1, castrated male quail were injected with oil, testosterone propionate (TP), flutamide (FLUT), an androgen antagonist, or TP+FLUT. Males given TP+FLUT, compared with birds receiving TP alone, strutted much less and had smaller proctodeal (foam) glands. Copulation was reduced by FLUT only on the last test day and only on one measure (number of head grabs + mounts). These results suggest that binding of testosterone or one of its metabolites to an androgen receptor is part of the mechanism of TP activated strutting, and therefore that central nervous system androgen receptors are involved in a male reproductive behavior pattern. In Experiment 2, castrated male quail were injected with oil, with 50 micrograms estradiol benzoate (EB), or with 25, 50 or 100 micrograms diethylstilbestrol (DES), a synthetic estrogen that does not bind to androgen receptors. EB but not DES activated copulation to a significant extent. In Experiment 3 male and female quail with photically regressed gonads were given intraperitoneal Silastic implants of DES, estradiol (E) or cholesterol. DES was highly effective at activating male-typical copulation in males and receptivity in both sexes. Thus hormonal interaction with estrogen receptors alone is sufficient for the activation of male-typical as well as female-typical copulatory behavior in this species.