Hormonal control of precopulatory sebaceous scent marking and ultrasonic mating vocalizations in male rats

The effects of testosterone (T) and its major metabolites, estradiol (E2) and dihydrotestosterone (DHT), on the restoration of sebaceous scent marking and 50-kHz ultrasonic vocalizations in male rats were measured in two studies (Experiments 1 and 2) employing different hormone levels. Silastic capsule administration of high and low doses of T (10 and 20 mm) or E2 (5%; 5 and 10 mm) completely restored marking to precastration levels. Both doses of DHT (30 and 40 mm) or no hormone replacement were without effect when tested in presence of estrous odor cues. In our testing paradigm, males appeared to mark glass objects with a sebaceous secretion rather than urine. Only the high dose of T (20 mm) restored vocalizations to intact levels, while animals receiving the high or low dose of E2 or DHT showed no restoration of behavior. In Experiment 3, habituation to estrous odor cues over weekly tests was not observed for marking or vocalizations. These results are discussed with respect to similarities and differences in the hormonal control of signaling behaviors by androgen metabolites in male rodents.     

The role of scent marking in Lemur catta agonistic behavior

Certain forms of marking behavior in Lemur catta have been considered to be aggressive in nature but had not been analyzed specifically in this respect. This study examines the relationship between the occurrence of all forms of marking behavior displayed by a captive group of lemurs and their physical and nonphysical aggressive interactions. All forms of marking behavior, especially males' tail mark and tail wave displays, were found to correlate with aggressive behavior including female-instigated agonism. In comparison, allogrooming, a behavior thought not to have an agonistic component, was not significantly correlated with any marking nor agonistic category. The data suggest that in intersexual interactions male marking behavior is an aggressive but nonphysical substitute for physical aggression toward females who have generally been regarded as dominant to males in this species.     

Prolactin levels and maternal behavior induced by ultrasonic vocalizations of the rat pup.

The relationship among ultrasonic vocalization (USV), prolactin and maternal behavior was investigated in lactating rat mothers and their pups. The lactating mother had a cannula inserted into the external jugular vein, and was exposed to USVs emitted from a pup immediately. Changes of prolactin and maternal behavior were determined. Prolactin increased dramatically during exposure to USVs, when maternal search, retrieving and nest building behavior appeared significantly. These results suggested that the relationship among USV, prolactin and maternal behavior was included in communication between lactating mother and pup.     

Structure of rat ultrasonic vocalizations and its relevance to behavior

Rats are known to emit ultrasonic vocalizations (USVs). These USVs have been hypothesized to hold biological meaning, and the relationship between USVs and behavior has been extensively studied. However, most of these studies looked at specific conditions, such as fear-inducing situations and sexual encounters. In the present experiment, the USVs of pairs of rats in ordinary housing conditions were recorded and their features were examined. Three clusters of USVs in the 25-, 40-, and 60-kHz range were detected, which roughly corresponded to fighting, feeding, and moving, respectively. We analyzed sequential combinations of two or more clusters using a state transition model. The results revealed a more specific correspondence between the USVs and behaviors, suggesting that rat USV may work as a type of communication tool.     

Sexual behavior and scent marking in male gerbils: comparison of changes after castration and testosterone replacement

This study compared changes in sexual behavior of male gerbils with changes in scent-marking frequency following castration and exposure to various doses of testosterone. Castration eliminated sexual activity in male gerbils. Injections of testosterone propionate (75 μg twice weekly) prevented this decrease. Larger (600 μg) injections of testosterone propionate or implantation of Silastic capsules of testosterone reinstated mating behavior. Sexual behavior showed a different pattern of changes than scent marking. Sexual behavior was maintained more effectively than scent marking by hormone injections, but scent marking was reinstated more readily than sexual behavior by the tonic hormone levels produced by Silastic implants.     

The effects of social experience and gonadal hormones on retrieving behavior of mice and their responses to pup ultrasonic vocalizations

Pup ultrasonic vocalizations (USVs) are emitted from maternally separated pups and are thought to be a trigger for eliciting maternal behavior in mice. We investigated the effects of social experience and gonadectomy on the retrieving behavior of mice and their responses to pup USVs produced by a nanocrystalline silicon thermo-acoustic emitter. In each experiment, virgin, gonadectomized, sham-operated, sexually experienced, and parenting mice of both sexes were used, and the effects of these manipulations were compared in each sex. The retrieving behavior of both sexes increased with social experience or gonadectomy. In particular, mothers showed the highest retrieving activity among female groups, while castrated male mice showed the highest retrieving activity among male groups. All groups of female mice responded to pup USVs, with the responsiveness of sexually experienced female mice being the most enhanced. Unlike the females, virgin male mice did not respond to pup USVs, although socially experienced or castrated males showed this response; fathers exhibited the highest responsiveness. These results suggest that not only parenting experience, but also mating experience, may enhance retrieving activity and response to pup USVs in mice of both sexes. Nevertheless, the degree to which parenting experience contributed to the enhancement of both activities differed between the sexes. Furthermore, gonadectomy enhanced both activities in both sexes, although its effect was more prominent in males. Overall, our findings suggest that alteration in responsiveness of mice to pup USVs might be one of the changes in parental behavior caused by social experiences or gonadal hormones.     

The hormonal control of scent marking and precopulatory behavior in male gray short-tailed opossums (Monodelphis domestica)

Little is known about the hormonal control of behavior in marsupials. In the present study, the effects of castration and of testosterone or estradiol replacement therapy on scent marking and precopulatory behavior in male gray short-tailed oppossums (Monodelphis domestica) were examined. It was found that castration resulted in decreases in chest and flank/hip marking displayed by male gray opossums. Testosterone but not estradiol stimulated chest marking in castrates. Males treated with either estradiol or testosterone displayed more flank/hip marking than control males. Highest levels of female aggression toward males were seen when the males had received testosterone treatment. These findings are discussed with respect to similarities and differences between marsupials and eutherians in the neural metabolism of testosterone and the hormonal control of scent marking behavior.     

Interleukin-1beta deficiency results in reduced NF-kappaB levels in pregnant mice

To determine the role of the renal nerves on renin secretion and expression in the mature ovine fetus, we performed bilateral renal denervation on eight fetuses of time-dated pregnant ewes (126.8 +/- 0.6 days gestation) and compared renin in them to seven fetuses that underwent sham denervation (126.7 +/- 0.6 days gestation). Fetal arterial and venous catheters were implanted, and after 5-7 days of recovery isoproterenol was infused. Plasma active renin was lower in denervated animals than in intact animals under basal conditions and at each dose of isoproterenol. Plasma prorenin levels were lower in denervated fetuses but unaffected by isoproterenol. Denervation did not change renal renin, prorenin, or renin mRNA, but it did block isoproterenol-induced increases in renin mRNA in renocortical cells in vitro. We conclude that the renal nerves are required for renin secretory mechanisms and responsiveness of renin mRNA to beta-adrenergic stimulation but not for the expression of renin in the fetal kidney. We propose that one or more of the factors that maintain renin expression in the perinatal period may be absent or may be replaced by the renal nerves in the adult.     

Age-related changes on marking, marking-like behavior and the scent gland in adult Mongolian gerbils (Meriones unguiculatus).

Marking behavior, marking-like behavior [3], and changes of the scent glands were observed in aged Mongolian gerbils. In Experiment 1, changes in the marking and marking-like behavior with aging were evaluated in adult male and female Mongolian gerbils of an inbred strain aged 6 to 36 months. The frequency of marking behavior in males was significantly higher than females throughout the observation period except at 36 months of age. On the other hand, frequency of marking-like behavior in males, but not in females decreased with aging, significantly. In Experiment 2, changes of the scent gland in adult males and females aged 6 to 36 months were morphologically evaluated. Macroscopic examination revealed an increase in the size length and width of the glands of males aged 12 months and females aged 6 months. Histologically the glands of all the males and females aged 6 months developed moderately or well. Some of the 12-month-old males and females showed acinar atrophy of the glands, and all the females aged 18 months or more had highly atrophied scent glands. From these results, we concluded that there is no relationship between the changes of marking behavior and those of the scent glands in aged male Mongolian gerbils, and assume that marking behavior in aged animals does not have an important meaning as marking. In Experiment 3, marking and marking-like behavior in castrated adult Mongolian gerbils aged 16 weeks were observed. The result showed that marking behavior, not marking-like behavior was inhibited after castration. From these findings, we consider that generally marking behavior in Mongolian gerbils consists of androgen-dependent marking behavior and androgen-independent marking behavior (marking-like behavior).     

Prenatal exposure to a low-frequency electromagnetic field demasculinizes adult scent marking behavior and increases accessory sex organ weights in rats

Pregnant Sprague-Dawley dams were exposed to a low-level, low-frequency pulsed electromagnetic (EM) field (15 Hz, 0.3 msec duration, peak intensity 8 gauss) for 15 min twice a day from day 15 through day 20 of gestation, a period in development that is critical for sexual differentiation of the male rat brain. No differences in litter size, number of stillborns, or body weight were observed in offspring from field-exposed dams. At 120 days of age, field-exposed male offspring exhibited significantly less scent marking behavior than controls. Accessory sex organ weights, including epididymis, seminal vesicles, and prostate, were significantly higher in field-exposed subjects at this age. However, circulating levels of testosterone, luteinizing hormone, and follicle-stimulating hormone, as well as epididymal sperm counts, were normal. These data indicate that brief, intermittent exposure to low-frequency EM fields during the critical prenatal period for neurobehavioral sex differentiation can demasculinize male scent marking behavior and increase accessory sex organ weights in adulthood.     

The effect of social environment on estrogen excretion,scent marking,and sociosexual behavior in tamarins (Saguinus oedipus)

The influence of various social environments on estrogen excretion, scent marking, and the expression of sociosexual behavior was examined in cotton-top tamarins (Sanguinus o. oedipus). Behavioral observations and urine collections were conducted on five females while first housed in their natal family group or in the presence of another cycling adult female and then while housed with an unrelated adult male in a separate cage. Behavioral observations only were conducted on males in natal family groups and while housed with an unrelated adult female. Levels of urinary estrone and estradiol for females were measured by specific radioimmunoassays. Females housed in family groups or in the presence of an adult cycling female showed low and noncyclic patterns of estrogen excretion. Removal from these environments resulted in a rapid increase in urinary estrone and estradiol and three of five females demonstrated cyclic patterns of estrone excretion. Rates of anogenital marking in females were elevated after the social change, and sexual interactions, virtually absent in the original environments, were observed in all five females. In males, similar manipulations of the social environment affected the expression of sexual behavior, but not scent marking. The social environment, therefore has a profound impact on fertility and sociosexual behavior in cotton-top tamarin groups, with implications for callitrichid social structure and behavior.     

The effects of gonadal hormones on scent marking and related behavior and morphology in female gray short-tailed opossums (Monodelphis domestica)

The hormonal control of scent marking and related behavior and morphology was examined in female gray short-tailed opossums. Females rarely scent marked when intact or following ovariectomy. Testosterone (T) but not estradiol (E) treatment stimulated chest marking while either hormone stimulated head marking in ovariectomized females tested alone. When the same females were tested with males, T-treated females showed little scent marking of any type; E-treated females showed hip marking in significantly more tests than females in the other treatment groups. Suprasternal scent glands (absent in intact females) and phalluses of females that received T were significantly larger than those of animals that received E or control animals. These findings are discussed with respect to similarities and differences between marsupial and eutherian females and between male and female gray opossums in the hormonal control of sexually dimorphic behavior and morphology.     

Effects of androgen on scent marking and aggressive behavior of neonatally bulbectomized female Mongolian gerbils (Meriones unguiculatus)

Female gerbils were bilaterally bulbectomized, unilaterally bulbectomized or sham-operated at 2 days of age (Birth DAY = 0). As adults, the occurrence of scent marking and aggressive behavior was measured prior to and following administration of either testosterone propionate (TP) or oil. TP-treated sham operates showed increased scent marking; bilaterally bulbectomized and unilaterally bulbectomized females treated with TP did not. The display of aggressiveness increased for all females following TP. Neonatally bulbectomized animals treated with TP, however, were the most aggressive. Although androgen augments these species-typical response patterns, it seems dependent upon the integrity of the olfactory bulbs.     

Observation of marking-like behavior, marking behavior, and growth of the scent gland in young Mongolian gerbils (Meriones unguiculatus) of an inbred strain.

A marking-like behavior (defined by authors), a marking behavior, and growth of the scent glands were observed in young Mongolian gerbils of an inbred strain. In males and females, a marking-like behavior, in which animals rub their abdominal scent glands on the floor, began to be seen at the age of 19 days and could be seen in almost all the gerbils at 22 days of age during the suckling period. The frequency of this behavior was highest at 60 days of age (males: 17.9/10 min, females: 15.4/10 min) and there was no sex difference. Marking behavior, in which animals rub their abdominal scent glands on small protruding objects, began to be seen at the age of 40 days in males and 50 days in females. The frequency of this behavior tended to increase until 90 days of age in males (13.7/10 min), but the levels were low (2.5-5.0/10 min) in females. The values in the male group therefore tended to be higher than that in the female group. Macroscopic scent gland pads were clearly observed at the age of 30 days in males, but not until 45 days of age in females. At the age of 45-90 days, the length of the scent gland pad in males and females was 2.1-2.8 and 1.6-1.7 cm, respectively and the width was 0.3-0.5 in males and 0.2-0.3 cm in females. During this period, the length and depth of the pads in males were significantly greater than those in females (p < 0.05). Histological examination of the structure of the scent glands after the age of 45 days showed that the development of clusters of acinar cells in females occurred much later than that in males, but the basic structure of these glands was similar in both sexes. These results suggest that the marking-like behavior was manifested although during the period when the scent glands had not yet developed, whereas true marking behavior first occurred when the glands were moderately well developed.     

Altered TNSALP expression and phosphate regulation contribute to reduced mineralization in mice lacking androgen receptor

While androgen receptor (AR)-deficient mice developed osteopenia in endochondral bones due to the high bone turnover with increased bone resorption by osteoclasts, little is known about the mechanism of intramembranous bone loss contributed by AR in osteoblasts. Here, we discovered a dramatic decrease in the area of calcification, new bone, and the number of osteocytes in calvaria from AR-deficient mice related to a reduction in mineralization caused, in part, by the diminished activity of AR-deficient osteoblasts. Enforced AR expression in differentiated osteoblasts boosts mineralization while knockdown of AR expression prevents androgen-induced mineralization. We identified the tissue-nonspecific alkaline phosphatase (TNSALP) and several members of small integrin binding ligand N-linked glycoprotein (SIBLING) gene family as androgen target genes required for AR-mediated bone formation. We show that inorganic phosphate (P(i)) levels and TNSALP activity increased in response to androgen/AR and P(i) signals increase the expression and translocation of AR. The ectopic expression of TNSALP or P(i) partially rescued the bone loss due to AR deficiency. Thus, androgen/AR signaling plays an essential role in bone formation by coordinating the expression of genes associated with phosphate regulation.     

Fertility status,dominance, and scent marking behavior of family-housed female cotton-top tamarins (Saguinus oedipus) in absence of their mothers

The effect of the mother's absence on the fertility status and expression of scent marking behavior was examined in 12 sexually mature female cotton-top tamarins (Saguinus oedipus) living in four motherless families. Behavioral data and urine samples were collected on an average of five times per week and levels of estrone-glucuronide (E1G) were quantified directly by radioimmunoassay to establish whether the females showed ovarian cyclicity. Of the 12 females investigated only the dominant female in each motherless group exhibited regular E1G cycles. By contrast, low and acyclic hormonal profiles were found for subordinate sisters. In addition to differences in the patterns and levels of E1G, scent gland morphology and rates of scent marking differed between females: dominant, cycling females had elaborate glands and significantly higher rates of scent marking than subordinates. These results indicate that the presence of the mother (breeding female) is one important factor regulating ovarian function in cotton-top tamarin daughters. The findings also show that dominance status is a vital determinant of each female's subsequent physiological reproductive competence, with only the dominant female obtaining complete fertility and probably inhibiting ovulatory activity in her subordinate sisters. Scent marking behavior seems to be involved in the regulation of this phenomenon of intrasexual reproductive competition.     

Normal thyroid thermogenesis but reduced viability and adiposity in mice lacking the mitochondrial glycerol phosphate dehydrogenase

The mitochondrial glycerol phosphate dehydrogenase (mGPD) is important for metabolism of glycerol phosphate for gluconeogenesis or energy production and has been implicated in thermogenesis induced by cold and thyroid hormone treatment. mGPD in combination with the cytosolic glycerol phosphate dehydrogenase (cGPD) is proposed to form the glycerol phosphate shuttle, catalyzing the interconversion of dihydroxyacetone phosphate and glycerol phosphate with net oxidation of cytosolic NADH. We made a targeted deletion in Gdm1 and produced mice lacking mGPD. On a C57BL/6J background these mice showed a 50% reduction in viability compared with wild-type littermates. Uncoupling protein-1 mRNA levels in brown adipose tissue did not differ between mGPD knockout and control pups, suggesting normal thermogenesis. Pups lacking mGPD had decreased liver ATP and slightly increased liver glycerol phosphate. In contrast, liver and muscle metabolites were normal in adult animals. Adult mGPD knockout animals had a normal cold tolerance, normal circadian rhythm in body temperature, and demonstrated a normal temperature increase in response to thyroid hormone. However, they were found to have a lower body mass index, a 40% reduction in the weight of white adipose tissue, and a slightly lower fasting blood glucose than controls. The phenotype may be secondary to consequences of the obligatory production of cytosolic NADH from glycerol metabolism in the mGPD knockout animal. We conclude that, although mGPD is not essential for thyroid thermogenesis, variations in its function affect viability and adiposity in mice.     

The scent of senescence: sexual signalling and female preference in house mice

Sexual signals are expected to be costly to produce and maintain, thus ensuring that only males in good condition can sustain their expression at high levels. When males reach senescence they lose physiological function and condition, which could constrain their ability to invest in costly sexual signals, decreasing their attractiveness to mates. Furthermore, females may have evolved mating preferences that cause avoidance of senesced males to enhance fertilization success and viability of offspring. Among mammals, the size of antlers and other weapons can decrease with senescence, but changes in olfactory sexual signals have been largely unexplored. We examined changes in olfactory signals with senescence in house mice (Mus musculus domesticus), where males excrete volatile and involatile molecules in scent marks that elicit behavioural and priming responses in females. Compared to middle-aged males, the urine of senesced males contained a lower concentration of involatile signalling proteins (major urinary proteins or MUPs), and associated volatiles that bind to these proteins. The reduced intensity of male scent will affect the longevity of scent signals deposited in the environment and, accordingly, females were less attracted to urine from senesced males deposited 12 h previously. Females also discriminated against senesced males encountered behind a mesh barrier. These results reveal that investment in olfactory signalling is reduced during senescence and suggest that senesced males and their scent may be less attractive to females.     

Decreased renal NO excretion and reduced glomerular tuft area in mice lacking the bradykinin B2 receptor

Bradykinin B(2) receptor knockout mice (B(2)-/-) have been useful to study the role of bradykinin under pathological conditions. With the use of these mice, it was shown that bradykinin plays an important role in angiogenesis, heart failure, salt-induced hypertension, and kidney fibrosis. Data on the role of the bradykinin B(2) receptor under physiological conditions using these mice are controversial and scarce, because these mice have no typical phenotype. For this reason, we have studied, under physiological conditions, renal hemodynamics as well as a number of morphometric glomerular parameters of B(2)-/- mice on a homogenized genetic background and on mice bred in a pathogen-free environment. Backcrossed B(2)-/- mice had normal blood pressure and normal apparent renal hemodynamics and morphology. However, reduced renal nitrite excretion and glomerular cGMP content were found, which was associated with a reduced glomerular capillary surface area. These differences had, however, no detectable effects on renal hemodynamics. These differences between B(2)-/- and wild-type mice might become important under pathological conditions as shown by a number of studies using these bradykinin B(2) receptor knockout mice.