Personality assessment in snow leopards (Uncia uncia)

Knowledge of individual personality is a useful tool in animal husbandry and can be used effectively to improve welfare. This study assessed personality in snow leopards (Uncia uncia) by examining their reactions to six novel objects and comparing them to personality assessments based on a survey completed by zookeepers. The objectives were to determine whether these methods could detect differences in personality, including age and sex differences, and to assess whether the two methods yielded comparable results. Both keeper assessments and novel object tests identified age, sex, and individual differences in snow leopards. Five dimensions of personality were found based on keepers' ratings: Active/Vigilant, Curious/Playful, Calm/Self-Assured, Timid/Anxious, and Friendly to Humans. The dimension Active/Vigilant was significantly positively correlated with the number of visits to the object, time spent locomoting, and time spent in exploratory behaviors. Curious/Playful was significantly positively correlated with the number of visits to the object, time spent locomoting, and time spent in exploratory behaviors. However, other dimensions (Calm/Self-Assured, Friendly to Humans, and Timid/Anxious) did not correlate with novel-object test variables and possible explanations for this are discussed. Thus, some of the traits and behaviors were correlated between assessment methods, showing the novel-object test to be useful in assessing an animal's personality should a keeper be unable to, or to support a keeper's assessment.     

Interrelationships of serum testosterone and free testosterone index with FFM and strength in aging men

Muscle mass and strength losses during aging may be associated with declining levels of serum testosterone (T) in men. Few studies have shown a direct relationship between T and muscle mass and strength. Subjects were 262 men, aged 24-90 yr, from the Baltimore Longitudinal Study of Aging, who had T and sex hormone-binding globulin sex hormone-binding globulin (SHBG) measurements, from which the free T index (FTI) was calculated (T/SHBG) from serum samples collected longitudinally since 1963, total body fat mass and arm and leg fat-free mass (FFM) by dual-energy X-ray absorptiometry and arm and leg strength by dynanomometry. Mixed-effects models estimated T and FTI at the time of mass and strength measurements. Age, total body fat, arm and leg FFM, T, and FTI were significantly associated with concentric and eccentric strength. FTI, not T, was modestly, but directly, related to arm and leg strength after fat, arm and leg FFM, height, and age were accounted for and indirectly through body mass. FTI is a better predictor of arm and leg strength than T in aging men.     

Genetic determinants of aggression and impulsivity in humans

Human aggression/impulsivity-related traits have a complex background that is greatly influenced by genetic and non-genetic factors. The relationship between aggression and anxiety is regulated by highly conserved brain regions including amygdala, which controls neural circuits triggering defensive, aggressive, or avoidant behavioral models. The dysfunction of neural circuits responsible for emotional control was shown to represent an etiological factor of violent behavior. In addition to the amygdala, these circuits also involve the anterior cingulated cortex and regions of the prefrontal cortex. Excessive reactivity in the amygdala coupled with inadequate prefrontal regulation serves to increase the likelihood of aggressive behavior. Developmental alterations in prefrontal-subcortical circuitry as well as neuromodulatory and hormonal abnormality appear to play a role. Imbalance in testosterone/serotonin and testosterone/cortisol ratios (e.g., increased testosterone levels and reduced cortisol levels) increases the propensity toward aggression because of reduced activation of the neural circuitry of impulse control and self-regulation. Serotonin facilitates prefrontal inhibition, and thus insufficient serotonergic activity can enhance aggression. Genetic predisposition to aggression appears to be deeply affected by the polymorphic genetic variants of the serotoninergic system that influences serotonin levels in the central and peripheral nervous system, biological effects of this hormone, and rate of serotonin production, synaptic release and degradation. Among these variants, functional polymorphisms in the monoamine oxidase A (MAOA) and serotonin transporter (5-HTT) may be of particular importance due to the relationship between these polymorphic variants and anatomical changes in the limbic system of aggressive people. Furthermore, functional variants of MAOA and 5-HTT are capable of mediating the influence of environmental factors on aggression-related traits. In this review, we consider genetic determinants of human aggression, with special emphasis on genes involved in serotonin and dopamine metabolism and function.     

Effects of gonadal steroids during pubertal development on androgen and estrogen receptor‐α immunoreactivity in the hypothalamus and amygdala

Perinatal development is often viewed as the major window of time for organization of steroid‐sensitive neural circuits by steroid hormones. Behavioral and neuroendocrine responses to steroids are dramatically different before and after puberty, suggesting that puberty is another window of time during which gonadal steroids affect neural development. In the present study, we investigated whether the presence of gonadal hormones during pubertal development affects the number of androgen receptor and estrogen receptor α‐immunoreactive (AR‐ir and ERα‐ir, respectively) cells in limbic regions. Male Syrian hamsters were castrated either before or after pubertal development, and 4 weeks later they received a single injection of testosterone or oil vehicle 4 h prior to tissue collection. Immunocytochemistry for AR and ERα was performed on brain sections from testosterone‐treated and oil‐treated males, respectively. Adult males that had been castrated before puberty had a greater number of AR‐ir cells in the medial preoptic nucleus than adult males that had been castrated after puberty. There were no significant differences in ERα‐ir cell number in any of the brain regions examined. The demonstration that exposure to gonadal hormones during pubertal development is associated with reduced AR‐ir in the medial preoptic nucleus indicates that puberty is a period of neural development during which hormones shape steroid‐sensitive neural circuits. © 2000 John Wiley & Sons, Inc. J Neurobiol 44: 361–368, 2000     

Region-specific regulation of cytochrome P450 aromatase messenger ribonucleic acid by androgen in brains of male rhesus monkeys

We demonstrated previously that testosterone regulates aromatase activity in the anterior/dorsolateral hypothalamus of male rhesus macaques. To determine the level of the androgen effect, we developed a ribonuclease protection assay to study the effects of testosterone or dihydrotestosterone (DHT) on aromatase (P450(AROM)) mRNA in selected brain areas. Adult male rhesus monkeys were treated with testosterone or DHT. Steroids in serum were quantified by RIA. Fourteen brain regions were analyzed for P450(AROM) mRNA. Significant elevations of its message over controls (P<0.05) were found in the medial preoptic area/anterior hypothalamus of both androgen treatment groups and the medial basal hypothalamus of the testosterone-treated males. Other brain areas were not affected by androgen treatment. We conclude that testosterone and DHT regulate P450(AROM) mRNA in brain regions that mediate reproductive behaviors and gonadotropin release. The P450(AROM) mRNA of other brain areas is not androgen dependent. Brain-derived estrogens may also be important for maintaining neural circuitry in brain areas not related to reproduction. The control of P450(AROM) mRNA in these areas may differ from what we report here, but it is equally important to understand the function of in situ estrogen formation in these areas.     

Effects of gonadal steroids during pubertal development on androgen and estrogen receptor-alpha immunoreactivity in the hypothalamus and amygdala

Perinatal development is often viewed as the major window of time for organization of steroid-sensitive neural circuits by steroid hormones. Behavioral and neuroendocrine responses to steroids are dramatically different before and after puberty, suggesting that puberty is another window of time during which gonadal steroids affect neural development. In the present study, we investigated whether the presence of gonadal hormones during pubertal development affects the number of androgen receptor and estrogen receptor alpha-immunoreactive (AR-ir and ER alpha-ir, respectively) cells in limbic regions. Male Syrian hamsters were castrated either before or after pubertal development, and 4 weeks later they received a single injection of testosterone or oil vehicle 4 h prior to tissue collection. Immunocytochemistry for AR and ER alpha was performed on brain sections from testosterone-treated and oil-treated males, respectively. Adult males that had been castrated before puberty had a greater number of AR-ir cells in the medial preoptic nucleus than adult males that had been castrated after puberty. There were no significant differences in ER alpha-ir cell number in any of the brain regions examined. The demonstration that exposure to gonadal hormones during pubertal development is associated with reduced AR-ir in the medial preoptic nucleus indicates that puberty is a period of neural development during which hormones shape steroid-sensitive neural circuits.     

Control of masculinization of the brain and behavior

Sex steroid hormones exert a profound influence on the sexual differentiation and function of the neural circuits that mediate dimorphic behaviors. Both estrogen and testosterone are essential for male typical behaviors in many species. Recent studies with genetically modified mice provide important new insights into the logic whereby these two hormones coordinate the display of sexually dimorphic behaviors: estrogen sets up the masculine repertoire of sexual and territorial behaviors and testosterone controls the extent of these male displays.     

Estrogenic contributions to sexual differentiation in the female guinea pig: influences of diethylstilbestrol and tamoxifen on neural, behavioral, and ovarian development

We administered the synthetic estrogen, diethylstilbestrol (DES), or the antiestrogen, tamoxifen, to pregnant guinea pigs and observed the consequences for sexual differentiation of their female offspring. Hormones were administered during the period when treatment of fetuses with testosterone influences the development of sex-related traits (approximately Days 30 to 65 of gestation). Ovarian function, masculine and feminine sexual behavior, and the structure of a sexually dimorphic neural region in the preoptic area were assessed in adulthood in hormone-exposed animals and in oil-treated and untreated controls. Prenatal exposure to DES dipropionate (DESDP) caused masculinization and defeminization. DESDP-treated females mounted more than control females, both without hormonal stimulation and when given testosterone propionate (TP) as adults. The sexually dimorphic neural region was also masculinized in these females. In regard to defeminization, they showed delayed vaginal opening, impaired progesterone (P) production, an absence of corpora lutea, and impaired lordosis and mounting responses to estradiol benzoate (EB) and P. Prenatal treatment with tamoxifen produced a complicated pattern of results. Tamoxifen-exposed females evidenced less masculine-typical behavior, showing diminished mounting without hormonal stimulation and in response to TP. However, they also showed delayed vaginal opening, enhanced P production, and impaired mounting in response to EB and P. Their lordosis behavior and the volume of the sexually dimorphic neural region were unaffected. These results suggest that estrogens play a substantial role in sexual differentiation in the guinea pig. High levels of estrogen promote masculine-typical development, and unusually low levels may impair some aspects of both masculine-typical and feminine-typical development.     

Leaf economics and hydraulic traits are decoupled in five species‐rich tropical‐subtropical forests

Leaf economics and hydraulic traits are critical to leaf photosynthesis, yet it is debated whether these two sets of traits vary in a fully coordinated manner or there is room for independent variation. Here, we tested the relationship between leaf economics traits, including leaf nitrogen concentration and leaf dry mass per area, and leaf hydraulic traits including stomatal density and vein density in five tropical‐subtropical forests. Surprisingly, these two suites of traits were statistically decoupled. This decoupling suggests that independent trait dimensions exist within a leaf, with leaf economics dimension corresponding to light capture and tissue longevity, and the hydraulic dimension to water‐use and leaf temperature maintenance. Clearly, leaf economics and hydraulic traits can vary independently, thus allowing for more possible plant trait combinations. Compared with a single trait dimension, multiple trait dimensions may better enable species adaptations to multifarious niche dimensions, promote diverse plant strategies and facilitate species coexistence.     

Aromatase activity in the rat brain: Hormonal regulation and sex differences

The intracellular conversion of testosterone to estradiol by the aromatase enzyme complex is an important step in many of the central actions of testosterone. In rats, estrogen given alone, or in combination with dihydrotestosterone, mimics most of the behavioral effects of testosterone, whereas treatment with antiestrogens or aromatase inhibitors block facilitation of copulatory behavior by testosterone. We used a highly sensitive in vitro radiometric assay to analyze the distribution and regulation of brain aromatase activity. Studies using micropunch dissections revealed that the highest levels of aromatase activity are found in an interconnected group of sexually dimorphic nuclei which constitutes a neural circuit important in the control of male sexual behavior. Androgen regulated aromatase activity in many diencephalic nucleic, including the medial preoptic nucleus, but not in the medial and cortical nuclei of the amygdala. Additional genetic evidence for both androgen-dependent and -independent control of brain AA was obtained by studies of androgen-insensitive testicular-feminized rats. These observations suggest that critical differences in enzyme responsiveness are present in different brain areas. Within several nuclei, sex differences in aromatase induction correlated with differences in nuclear androgen receptor concentrations suggesting that neural responsiveness to testosterone is sexually differentiated. Estradiol and dihydrotestosterone acted synergistically to regulate aromatase activity in the preoptic area. In addition, time-course studies showed that estrogen treatment increased the duration of nuclear androgen receptor occupation in the preoptic area of male rats treated with dihydrotestosterone. These results suggest possible ways that estrogens and androgens may interact at the cellular level to regulate neural function and behavior.     

The influence of androgenic and estrogenic hormones on sexual behavior in castrated adult male pigs

The objectives of these studies were to evaluate the influence of testosterone propionate (TP), estradiol cypionate (EC), dihydrotestosterone propionate (DHTP), EC + TP, EC + DHTP, and TP + DHTP on traits of masculine sexual behavior in castrated adult male pigs of different breeds. Masculine sexual behavior was restored and maintained by TP, whereas EC initially activated sexual behavior, including copulation and ejaculation, but was unable to sustain copulatory behavior for the 8- to 18-week periods that were evaluated. Treatment with DHTP was ineffective for stimulation of sexual behavior; thus, it is suggested that testosterone promotes some aspects of masculine sexual behavior in male pigs via aromatization to estrogen, but both androgen and estrogen are required for maintenance of the full complement of masculine sexual behavior traits.     

Estrogen contributes to seasonal plasticity of the adult avian song control system

Songbirds show dramatic neural plasticity as adults, including large-scale anatomical changes in discrete brain regions ("song control nuclei") controlling the production of singing behavior. The volumes of several song control nuclei are much larger in the breeding season than in the nonbreeding season, and these seasonal neural changes are regulated by plasma testosterone (T) levels. In many cases, the effects of T on the central nervous system are mediated by neural conversion to estradiol (E(2)) by the enzyme aromatase. The forebrain of male songbirds expresses very high levels of aromatase, in some cases adjacent to song control nuclei. We examined the effects of aromatase inhibition and estrogen treatment on song nuclei size using wild male songbirds in both the breeding and nonbreeding seasons. In breeding males, aromatase inhibition caused the volume of a telencephalic song control nucleus (HVC) to decrease, and this effect was partially rescued by concurrent estrogen replacement. In nonbreeding males, estradiol treatment caused HVC to grow to maximal spring size within 2 weeks. Overall, these data suggest that aromatization of T is an important mediator of song control system plasticity, and that estradiol has neurotrophic effects in adult male songbirds. This study demonstrates that estrogen can affect adult neural plasticity on a gross anatomical scale and is the first examination of estrogen effects on the brain of a wild animal.     

Differential regulation of insulin resistance and hypertension by sex hormones in fructose-fed male rats

Differences in gender are in part responsible for the development of insulin resistance (IR) and associated hypertension. Currently, it is unclear whether these differences are dictated by gender itself or by the relative changes in plasma estrogen and/or testosterone. We investigated the interrelationships between testosterone and estrogen in the progression of IR and hypertension in vivo in intact and gonadectomized fructose-fed male rats. Treatment with estrogen significantly reduced the testosterone levels in both normal chow-fed and fructose-fed rats. Interestingly, fructose feeding induced a relative increase in estradiol levels, which did not affect IR in both intact and gonadectomized fructose-fed rats. However, increasing the estrogen levels improved insulin sensitivity in both intact and gonadectomized fructose-fed rats. In intact males, fructose feeding increased the blood pressure (140 +/- 2 mmHg), which was prevented by estrogen treatment. However, the blood pressure in the fructose-fed estrogen rats (125 +/- 1 mmHg) was significantly higher than that of normal chow-fed (113 +/- 1 mmHg) and fructose-fed gonadectomized rats. Estrogen treatment did not affect the blood pressure in gonadectomized fructose-fed rats (105 +/- 2 mmHg). These data suggest the existence of a threshold value for estrogen below which insulin sensitivity is unaffected. The development of hypertension in this model is dictated solely by the presence or absence of testosterone. In summary, the development of IR and hypertension is governed not by gender per se but by the interactions of specific sex hormones such as estrogen and testosterone.     

Effects of gonadal steroids on tuberoinfundibular and tuberohypophysial dopaminergic neuronal activity in male and female rats

The activities of tuberoinfundibular and tuberohypophysial dopamine (DA) neurons were estimated by measuring the turnover of DA in terminals of these neurons in the median eminence and in the neural and intermediate lobes of the pituitary, respectively. The rate of DA turnover (alpha-methyltyrosine-induced decline of DA) in the median eminence was two to three times faster in females than in males, but no sexual differences in DA turnover rates were noted in the neural and intermediate lobes. Two weeks following gonadectomy the rate of DA turnover in the median eminence was increased in the male but decreased in the female. These effects were reversed by testosterone and estrogen replacement in gonadectomized males and females, respectively. Neither gonadectomy nor steroid replacement altered DA turnover in the neural or intermediate lobes of either males or females. These results indicate that estrogen stimulates and testosterone inhibits tuberoinfundibular DA neuronal activity while neither steroid affects tuberohypophysial DA neuronal activity.     

Role for prenatal estrogen in the development of masculine sexual behavior in the male ferret

Previous studies have shown that neonatal exposure to testosterone is essential for coital masculinization in male ferrets. In the present experiments, masculine sexual behavior was diminished in male ferrets by prenatal exposure to drugs which inhibited estrogenic stimulation of the brain. Similarly timed prenatal treatments with testosterone failed to masculinize the behavior of female offspring. We hypothesize that prenatal exposure of the male ferret to estrogen, derived from the neural aromatization of circulating androgen, may sensitize the developing brain to the subsequent masculinizing action of testosterone shortly after birth.     

Neuroanatomical Correlates of Hormone Sensitive Behaviors in Frogs and Birds

In this paper I review some aspects of neural and endocrineinteractions in the control of reproductive behaviors of frogsand song birds. In Xenopus laevis, we have shown that castrationwill eliminate a male sex behavior, clasping, and that thisbehavior can be restored by the administration of exogenoustestosterone or dihydrotestosterone but not by estradiol. Thisdifference in hormone action is paralleled by differences inthe locations of androgen and estrogen concentrating cells inthe CNS of Xenopus. Certain brain regions contain autoradiographicallydemonstrable labelled cells only after the administration oftritiated testosterone; others only after estradiol injection.The possibility that label in a third group of nuclei, whichcontain radioactive steroid after either hormone, is due tometabolism of testosterone to estradiol is discussed. Studiesin other anuran species have demonstrated that regions of hormoneuptake are also involved in neural control of frog sex behavior.The song of oscine birds represents another hormone sensitivereproductive behavior whose neural control is probably inlluencedby the activity of hormone concentrating CNS cells. Some ofthe brain nuclei which comprise the efferent pathway for controlof song in the canary have been shown to concentrate tritiatedandrogen in autoradiographic studies on song birds. The uptakeof androgens by medullary motor neurons involved in the controlof reproductively important vocalizations is common to anuransand oscine song birds. Whether this feature of hormone actionon the CNS represents a special feature of the frog and birdbrain or whether the phenomenon may also be present in othervertebrate groups awaits further investigation.     

Plant phenology,leaf traits and leaf litterfall of contrasting life forms in the arid Patagonian Monte,Argentina

Question: Do coexisting plant life forms differ in overall phenology, leaf traits and patterns of leaf litterfall? Location: Patagonian Monte, Chubut Province, Argentina. Methods: We assessed phenology, traits of green and senesced leaves and the pattern of leaf litterfall in 12 species of coexisting life forms (perennial grasses, deciduous shrubs, evergreen shrubs). Results: We did not identify differences in phenology, leaf traits and patterns of leaf litterfall among life forms but these attributes contrasted among species. Independent of the life form, the maintenance of green leaves or vegetative growth during the dry season was mostly associated with leaves with high leaf mass per area (LMA) and high concentration of secondary compounds. Low LMA species produced low litterfall mass with low concentration of secondary compounds, and high N concentration. High LMA species produced the largest mass of leaf litterfall. Accordingly, species were distributed along two main dimensions of ecological variation, the dimension secondary compounds in leaves ‐ length and timing of the vegetative growth period (SC ‐ VGP) and the dimension leaf mass per area ‐ leaf litterfall mass (LMA ‐ LLM). Conclusions: Phenology, leaf traits and leaf litterfall varied among species and overlapped among life forms. The two dimensions of ecological variation among species (SC ‐ VGP, LMA ‐ LLM) represent distinct combinations of plant traits or strategies related to resource acquisition and drought tolerance which are reflected in the patterns of leaf litterfall.     

Estrogen-responsive neural circuits governing male and female mating behavior in mice

Decades of knockout analyses have highlighted the crucial involvement of estrogen receptors and downstream genes in controlling mating behaviors. More recently, advancements in neural circuit research have unveiled a distributed subcortical network comprising estrogen-receptor or estrogen-synthesis-enzyme-expressing cells that transforms sensory inputs into sex-specific mating actions. This review provides an overview of the latest discoveries on estrogen-responsive neurons in various brain regions and the associated neural circuits that govern different aspects of male and female mating actions in mice. By contextualizing these findings within previous knockout studies of estrogen receptors, we emphasize the emerging field of “circuit genetics”, where identifying mating behavior-related neural circuits may allow for a more precise evaluation of gene functions within these circuits. Such investigations will enable a deeper understanding of how hormone fluctuation, acting through estrogen receptors and downstream genes, influences the connectivity and activity of neural circuits, ultimately impacting the manifestation of innate mating actions.     

Skeletal muscle and bone: effect of sex steroids and aging

Both estrogen and testosterone are present in males and females. Both hormones contribute to the well being of skeletal muscle and bone in men and women, and there is evidence that the loss of sex hormones is associated with the age-related decline in bone and skeletal muscle mass. Hormonal supplementation of older adults to restore estrogen and testosterone levels to those of young men and women is not without penalty.