Effects of anabolic androgenic steroids on the development and expression of running wheel activity and circadian rhythms in male rats

In humans, anabolic androgenic steroid (AAS) use has been associated with hyperactivity and disruption of circadian rhythmicity. We used an animal model to determine the impact of AAS on the development and expression of circadian function. Beginning on day 68 gonadally intact male rats received testosterone, nandrolone, or stanozolol via constant release pellets for 60 days; gonadally intact controls received vehicle pellets. Wheel running was recorded in a 12:12 LD cycle and constant dim red light (RR) before and after AAS implants. Post-AAS implant, circadian activity phase, period and mean level of wheel running wheel activity were compared to baseline measures. Post-AAS phase response to a light pulse at circadian time 15 h was also tested. To determine if AAS differentially affects steroid receptor coactivator (SRC) expression we measured SRC-1 and SRC-2 protein in brain. Running wheel activity was significantly elevated by testosterone, significantly depressed by nandrolone, and unaffected by stanozolol. None of the AAS altered measures of circadian rhythmicity or phase response. While SRC-1 was unaffected by AAS exposure, SRC-2 was decreased by testosterone in the hypothalamus. Activity levels, phase of peak activity and circadian period all changed over the course of development from puberty to adulthood. Development of activity was clearly modified by AAS exposure as testosterone significantly elevated activity levels and nandrolone significantly suppressed activity relative to controls. Thus, AAS exposure differentially affects both the magnitude and direction of developmental changes in activity levels depending in part on the chemical composition of the AAS.     

Impact of anabolic androgenic steroids on adolescent males

Anabolic androgenic steroid (AAS) use increased dramatically among adolescent males. This review focuses on studies using animal models of AAS exposure during adolescence which is a hormonally sensitive developmental period. AAS exposure during this critical period has wide-ranging consequences, including increased dendritic spine density, altered brain serotonin levels and escalated aggression in response to physical provocation. Human data suggest that AAS induces indiscriminate and unprovoked aggression often described as “'roid rage”. However, animal studies indicate that the behavioral impact of AAS is modulated by experiential and social contingencies, a perceived provocation, and the chemical composition of the AAS. The AAS, testosterone increases aggression in juvenile and adult male rats when physically provoked. In contrast, stanzolol, inhibits aggression in both juvenile and adult male rats, even when physically provoked. Nandrolone has minimal effects on aggression, unless preceded by attack training. Exposure to AAS during adolescence may have a host of unintended bio-behavioral consequences. Yet, the perception of harmlessness surrounds AAS use. The perception of harmlessness is promoted by the availability of AAS especially through internet pharmacies. The perception of acceptability is reflected in current cultural ethics that no longer condemn cheating to obtain personal achievement or success. A prevailing conviction is that although AAS are illegal they are not really bad. Reduction of the availability of AAS to adolescents requires ardent legislative and legal intervention. The problem of acceptability can be addressed by educating adolescents about the short-term and long-term effects of AAS on brain and behavior, to increase awareness of the potential consequences of AAS use that apply directly to them.     

Organizational role for pubertal androgens on adult hypothalamic-pituitary-adrenal sensitivity to testosterone in the male rat

The inhibitory effect of androgens on the hypothalamic-pituitary-adrenal (HPA) axis in basal and stress conditions in adult male rats is well documented. Major sex-related neuroendocrine changes take place during puberty. There is a robust rise in production and secretion of gonadal steroids, which is thought to underlie numerous neural and behavioural changes brought on after puberty. The present study investigated the effect of the pubertal rise in gonadal steroid levels on the subsequent adult corticosterone profile, particularly the sensitivity of the adult HPA axis to testosterone. Animals were castrated either prepubertally (28 days) or in adulthood (11 weeks) and adult animals were subsequently treated with subcutaneous implants containing either testosterone or cholesterol. Using an automated blood sampling system, blood was collected from each freely moving, conscious rat every 10 min (i) over a 24 h period; (ii) in response to 10 min of noise stress, and (iii) following an immunological challenge with lipopolysaccharide (LPS). Analysis revealed that testosterone treatment did not significantly affect overall corticosterone release over the 24 h period in adult animals castrated before puberty in contrast to animals castrated in adulthood in which testosterone significantly suppressed corticosterone secretion. Following either a noise stress or LPS injection, testosterone treatment did not affect the hypothalamic or adrenal stress response in animals castrated prepubertally. Testosterone significantly suppressed the corticotrophin-releasing hormone and arginine vasopressin mRNA as well as the corticosterone response to LPS in castrated animals that had had their testes intact over puberty. These data provide evidence that puberty is a critical organizational period during which rising levels of gonadal steroids programme the sensitivity of the adult HPA axis to gonadal steroids in adulthood.     

Roles of estrogen receptors alpha and beta in differentiation of mouse sexual behavior

Sex differences in brain and behavior are ubiquitous in sexually reproducing species. Developmental differences in circulating concentrations of gonadal steroids underlie many sexual dimorphisms. During the late embryonic and early perinatal periods, the testes produce androgens, thus, male brains are exposed to testosterone, and in situ testosterone is aromatized to estradiol. In contrast, females are not exposed to high concentrations of testosterone or estradiol until puberty. In many species, neural sex differences and sexually dimorphic behaviors in adults are initiated primarily by estradiol exposure during early development. In brain, estradiol activates two independent processes: masculinization of neural circuits and networks that are essential for expression of male-typical adult behaviors, and defeminization, the loss of the ability to display adult female-typical behaviors. Here, data for the roles of each of the known estrogen receptors (estrogen receptor alpha and estrogen receptor beta) in these two processes are reviewed. Based on work done primarily in knockout mouse models, separate roles for the two estrogen receptors are suggested. Estrogen receptor alpha is primarily involved in masculinization, while estrogen receptor beta has a major role in defeminization of sexual behaviors. In sum, estradiol can have selective effects on distinct behavioral processes via selective interactions with its two receptors, estrogen receptor alpha and estrogen receptor beta.     

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.     

Effects of withdrawal from anabolic androgenic steroids on aggression in adult male rats

In gonadally intact male rats, chronic exposure to high levels of testosterone propionate (TP) increases aggression, nandrolone (ND) has little effect and stanozolol (ST) suppresses aggression. The present experiment tested whether the effects of TP, ND and ST on aggression and reproductive tissues are reversed following anabolic androgenic steroid (AAS) withdrawal. Gonadally intact males received TP, ND, ST or vehicle for 12 weeks. Injections were then discontinued. Aggression was tested 3 weeks (short term) and 12 weeks (long term) after withdrawal of AAS treatment, with either a gonadally intact or a castrated opponent in three different environments (home, opponent's and neutral cage). After short-term withdrawal, some parameters of aggression were significantly above control levels in TP males. There were no significant differences between ND or ST males and controls, though ST males showed the lowest levels of aggression. No significant differences between any of the groups were found after long-term withdrawal. Eighteen weeks after AAS withdrawal, serum testosterone (T) and LH levels were comparable to controls in all groups. Testes weights were at control levels in ST males, but significantly higher than controls in TP and ND males. Seminal vesicle weights were significantly elevated in TP males, but similar to controls in both ND and ST males. None of the prostate weights were significantly different from controls. These results suggest that aggression gradually returns to normal following withdrawal from AAS. Some, if not all, hormone levels and tissue weights return to normal, suggesting possible long-lasting effects of chronic AAS exposure.     

Neural androgen receptors and scent marking of male gerbils: modulation by females.

The involvement of brain cytosolic androgen receptors in the female-induced increase in scent-marking behavior of male Mongolian gerbils was studied. Scent-marking activities and serum testosterone concentrations were measured in low-marking control males and in males with increased scent-marking activities, stimulated by the presence of conspecific females in the same room. For every individual male the concentrations and affinities of androgen receptors were determined in four parts of the brain, which contained the hippocampus, septum, corpus striatum, amygdala, stria terminalis, and the hypothalamus. Compared to the basal unstimulated period, the marking activities of male gerbils significantly increased 58% during the presence of female conspecifics in their housing room. The serum testosterone concentrations did not change significantly during female presence. The association constants of the cytosolic androgen receptors were higher in the female-stimulated males compared to isolated control males. In contrast, the cytosolic receptor concentration was reduced. The difference reached significance in one of the brain parts. Individual levels in scent-marking activities could not be explained by correlation with individual androgen receptor parameters. The present results suggest that increased androgen binding in the brain may be involved in the elevation of scent-marking activities in male gerbils, caused by urinary chemical signals of female conspecifics.     

Perinatal exposure to genistein alters reproductive development and aggressive behavior in male mice

Exposure to endocrine disrupting chemicals adversely affects reproductive development and behavior in males. The goal of this study was to determine if exposure to genistein, an isoflavone found in soy, during early periods of sex differentiation alters reproductive development and behavior in male mice. Female C57BL/6 mice were fed a phytoestrogen-free diet supplemented with 0, 5 or 300 mg/kg of genistein throughout gestation and lactation. Anogenital distance (AGD) and body mass of male offspring was measured weekly from postnatal days 2-21, timing of preputial separation was assessed at puberty, and in adulthood, reproductive organ masses, sperm and testosterone production, and reproductive and aggressive behaviors were assessed. Exposure to genistein resulted in smaller AGD are reduced body mass, with the low-dose diet exerting a greater effect. Timing of preputial separation, adult reproductive behavior, sperm concentrations and testosterone production were not influenced by genistein treatment at either dose. Aggressive behaviors were decreased, whereas defensive behaviors were increased, in males that received the low-dose genistein diet. Exposure to genistein during critical periods of sex differentiation results in concurrent and persistent demasculinization in male mice. Phenotypic and behavioral abnormalities induced by genistein showed a non-monotonic response, where treatment with a low dose exerted a greater effect than treatment with a high dose of genistein. Given the popularity of soy infant formulas, the influence isoflavone exposure on reproductive and behavioral health in boys and men should be considered.     

Effects of chronic exposure to an anabolic androgenic steroid cocktail on α5-receptor-mediated GABAergic transmission and neural signaling in the forebrain of female mice

Anabolic androgenic steroids (AAS) are synthetic derivatives of testosterone that are illicitly self-administered for enhancement of performance and body image, but which also have significant effects on the brain and on behavior. While the stereotypical AAS user is an adult male, AAS abuse in women is rapidly increasing, yet few studies have examined AAS effects in female subjects. We have assessed the effects in female mice of a combination of commonly abused AAS on neuronal activity and neurotransmission mediated by GABA type A (GABA_A) receptors in the medial preoptic nucleus (MPN); a nexus in the circuits of the hypothalamus and forebrain that are critical for the expression of social behaviors known to be altered in AAS abuse. Our data indicate that chronic exposure to AAS resulted in androgen receptor (AR)–dependent upregulation of α₅, β₃ and δ subunit mRNAs. Acute application of the α₅ subunit-selective inverse agonist, L-655,708 (L6), indicated that a significant fraction of the synaptic current is carried by α₅-containing receptors and that AAS treatment may enhance expression of α₅-containing receptors contributing to synaptic, but not tonic, currents in the MPN. AAS treatment also resulted in a significant decrease in action potential frequency in MPN neurons that was also correlated with an increased sensitivity to L-655,708. Our data demonstrate that chronic exposure to multiple AAS elicits significant changes in GABAergic transmission and neuronal activity that are likely to reflect changes in the expression of α₅-containing synaptic receptors within the MPN.     

Estradiol facilitates mounting behavior in male green anole lizards

Steroid hormones activate sexual behaviors across vertebrate species. In green anole lizards, testosterone is particularly important for the display of courtship and copulation by adult males. However, unlike a variety of other species, the role of its metabolite, estradiol, has been unclear. To evaluate its function and potential interaction with testosterone in the facilitation of reproductive behaviors, adult males were gonadectomized and given two treatments. The first consisted of either estradiol or its vehicle, and the second testosterone or a blank control. Parallel manipulations were done in the breeding and non-breeding seasons. Courtship and copulatory behaviors were more readily facilitated during the breeding than non-breeding season. As predicted based on previous experiments, testosterone increased the display of sexual behaviors. In addition, estradiol increased mount attempts. While this hormone did not influence the effects of subsequent testosterone exposure, the present data are consistent with the idea that it facilitates a component of reproduction in the green anole, as in species from other taxa.     

Maturational and maintenance effects of testosterone on terminal axon density and neuropeptide expression in the rat vas deferens

Testosterone causes growth of many pelvic ganglion cells at puberty and their maintenance during adulthood. Here we have focused on two populations of pelvic ganglion cells that project to the rat vas deferens: noradrenergic neurons that innervate the smooth muscle and synthesize neuropeptide Y, and cholinergic neurons that primarily innervate the mucosa and contain vasoactive intestinal peptide. We have assessed the muscle innervation after pre- or postpubertal castration, using immunohistochemistry to determine axon density and radioimmunoassay to quantify levels of neuropeptides in tissue extracts.Our results show that androgen deprivation in each period causes substantial effects. Noradrenergic axons in the muscle increase in density after castration, partly due to organ size being smaller than age-matched controls. However, when corrected for target size, there is an overall decrease in total number of axons. This implies that androgen exposure at puberty has a direct effect on neurons to ensure that the adult pattern of innervation is attained, and that this is not simply by matching terminal field to target size. Similar effects of pre- and postpubertal castration imply that continued exposure to testosterone is necessary to maintain normal target innervation. Castration in both time periods increased the density of axons containing vasoactive intestinal peptide, however the effects of castration on the total number of these axons in the muscle were more variable. The concentration of vasoactive intestinal peptide increased substantially following either pre- or postpubertal castration although absolute amounts per vas deferens were decreased. Effects on neuropeptide Y concentration were less pronounced but the total amount per vas deferens was decreased after pre- or postpubertal castration.Our study shows that the action of testosterone (or a metabolite) on a pelvic ganglion cell soma is likely to reflect a change in its terminal field, but that these effects are not mediated simply by testosterone influencing the size of its target organ.     

Anabolic androgenic steroids and forebrain GABAergic transmission

Anabolic androgenic steroids are synthetic derivatives of testosterone designed for therapeutic purposes, but now taken predominantly as drugs of abuse. The most common behavioral effects associated with anabolic androgenic steroid use are changes in anxiety, aggression and reproductive behaviors, including the onset of puberty and sexual receptivity. GABAergic circuits in the forebrain underlie these behaviors and are regulated by gonadal steroids. Work from our laboratories has shown that the expression and function of GABA(A) receptors in the rat and mouse forebrain varies between the sexes and across the estrous cycle. We have also shown that there are significant changes in GABA(A) receptor expression that occur with the progression through puberty to adulthood. Because GABAergic systems are both steroid-sensitive and critical for the expression of behaviors altered with anabolic androgenic steroid use, forebrain GABA(A) receptors are an attractive candidate to assess how molecular actions of anabolic androgenic steroids may be translated to known behavioral outcomes. Our studies demonstrate that anabolic androgenic steroids elicit both acute modulation of GABA(A) receptor-mediated currents, as well as chronic regulation of GABA(A) receptor expression and forebrain GABAergic transmission. Because anabolic androgenic steroid use has now become prevalent not only among adolescent boys, but in an increasing number of adolescent girls, we have also been particularly interested in determining age- and sex-specific effects of anabolic androgenic steroids. Our data show that the effects of chronic anabolic androgenic steroid exposure can be greater for adolescent than adult animals and are more marked in females than in males. These data have particularly important implications with respect to studies we have done demonstrating that chronic anabolic androgenic steroid exposure alters the onset of puberty, estrous cyclicity and sexual receptivity.     

Ethanol exposure during development reduces resident aggression and testosterone in rats

Ethanol exposure during development has been shown to alter social behaviors in people, but the range of deficits is not clear. Using an animal model of Fetal Alcohol Spectrum Disorders, inter-male aggression and testosterone levels were examined in adult rats. Rats were exposed to ethanol during the entire prenatal period and from postnatal day 2 through 10. Ethanol was administered via intragastric intubation. Two other groups consisted of a nontreated control and an intubated control group that was exposed to the administration procedures but not ethanol. Both offensive and defensive aggression were examined in experimental residents and intruders under three different housing conditions for the resident males: (1) with another male, (2) with a pregnant female, and (3) with a female and litter fathered by the experimental animal. When housed with a female and litter, ethanol-exposed rats displayed reduced offensive aggression compared to control groups under the same condition. Defensive aggression in the non-experimental intruders was reduced in this same condition. There were no differences in duration of non-aggressive social behaviors among the groups in any of the housing conditions. Testosterone levels were reduced in ethanol-exposed rats compared to controls. In summary, ethanol exposure over the combined prenatal and postnatal periods reduces aggressive behavior in a condition where aggressive behavior is normally seen. This reduction may be related to lower testosterone levels.     

Prenatal exposure to testosterone and its precursors influences morphology and later behavioral responsiveness to testosterone of female mice.

Prenatal exposure to testosterone (T), dehydroepiandrosterone or progesterone significantly increased ano-genital distance of female mice. In addition, prenatal exposure to T or pregnenolone significantly reduced the duration of T exposure during adult life required to induce intraspecific fighting behavior. However, the most masculinized females, those exposed to T prenatally, still had significantly shorter ano-genital distances and required a longer exposure period to T in order to establish fighting than did prenatally oil-exposed male mice. Additional experiments revealed that pregnenolone augments later responsiveness to the aggression-promoting property of T only if it is administered during the prenatal period of development.     

The effect of the ovarian cycle on the sexual behaviour of the common marmoset (Callithrix jacchus)

The sexual behaviour of 7 pairs of marmosets was observed during 30 minute tests for 44-68 days and blood samples were collected from females for measurement of plasma progesterone, testosterone and oestrone. Copulations occurred throughout the ovarian cycle of 24-30 days. Females used a "tongue-flicking" display both as an invitational behaviour (proceptive tongue-flicks) and during copulation (receptive tongue-flicks) most frequently during the peri-ovulatory period. Frequencies of proceptivity were correlated positively with high mean levels of testosterone and oestrone during the cycle and with a short follicular phase. Males showed significant increases in tongue-flicks, mounts and ejaculations during the peri-ovulatory phase, together with a shortened post-ejaculatory interval and increased duration of penile erection after ejaculation. A retrospective analysis showed that these changes in the males' behaviour occurred only during tests where females were proceptive and not during other tests in the peri-ovulatory period. Females refused significantly more of the males' mounting attempts during the luteal phase and a corresponding reduction in mount frequency occurred at this time. Grooming, scent-marking, olfactory inspections and some other behaviours did not alter significantly in either sex during the ovarian cycle.     

Pubertal exposure to anabolic androgenic steroids increases spine densities on neurons in the limbic system of male rats

Human studies show that the number of teenagers abusing anabolic androgenic steroids (AAS) is increasing. During adolescence, brain development is altered by androgen exposure, which suggests that AAS may potentially alter central nervous system (CNS) development. The goal of the present study was to determine whether pubertal AAS exposure increased dendritic spine densities on neurons within the medial amygdala and the dorsal hippocampus. Pubertal gonadally intact male rats received the AAS testosterone propionate (5 mg/kg) or vehicle for 5 days/week for 4 weeks. To determine the long-term implications of pubertal AAS use, another set of males received the same AAS treatment and was then withdrawn from AAS exposure for 4 weeks. Results showed that pubertal AAS exposure significantly increased spine densities on neurons in the anterior medial amygdala, posterodorsal medial amygdala, and the cornu ammonis region 1 (CA1) of the hippocampus compared with gonadally intact control males. Spine densities returned to control levels within the anterior medial amygdala and the posterodorsal medial amygdala 4 weeks after withdrawal. However, spine densities remained significantly elevated after AAS withdrawal in the CA1 region of the hippocampus, suggesting that pubertal AAS exposure may have a long-lasting impact on CA1 hippocampal neuroanatomy. Since pubertal AAS exposure increased spine densities and most excitatory synapses in the CNS occur on dendritic spines, AAS may increase neuronal excitation. It is proposed that this increase in excitation may underlie the behavioral responses seen in pubertal AAS-treated male rats.     

Modulation of affect after chronic exposure to the anabolic steroid 17alpha-methyltestosterone in adult mice

A battery of behavioral tasks in C57BL/6J mice was used to assess changes in affective components of behavior after systemic exposure to the anabolic-androgenic steroid (AAS) 17alpha-methyltestosterone (7.5 mg/kg). Gonadal weight in both sexes was reduced after 16 days of AAS exposure. Changes in discrete components of social behaviors were observed. No changes were recorded in the elevated plus-maze, the light-dark transition, and defensive behavior tests on exposure to 17alpha-methyltestosterone. When compared with controls, AAS-exposed females received a greater number of shocks, and AAS-exposed males displayed a shorter recovery time to consume water after a negative reinforcer in the modified Vogel conflict test. Results show that systemic exposure to a single AAS modified social behaviors, whereas minimal effects on anxiety-related behaviors were observed according to sex.     

Reinforcing aspects of androgens

Are androgens reinforcing? Androgenic-anabolic steroids (AAS) are drugs of abuse. They are taken in large quantities by athletes and others to increase performance, often with negative long-term health consequences. As a result, in 1991, testosterone was declared a controlled substance. Recently, Brower [K.J. Brower, Anabolic steroid abuse and dependence. Curr. Psychiatry Rep. 4 (2002) 377-387.] proposed a two-stage model of AAS dependence. Users initiate steroid use for their anabolic effects on muscle growth. With continued exposure, dependence on the psychoactive effects of AAS develops. However, it is difficult in humans to separate direct psychoactive effects of AAS from the user's psychological dependence on the anabolic effects of AAS. Thus, studies in laboratory animals are useful to explore androgen reinforcement. Testosterone induces a conditioned place preference in rats and mice, and is voluntarily consumed through oral, intravenous, and intracerebroventricular self-administration in hamsters. Active, gonad-intact male and female hamsters will deliver 1 microg/microl testosterone into the lateral ventricles. Indeed, some individuals self-administer testosterone intracerebroventricularly to the point of death. Male rats develop a conditioned place preference to testosterone injections into the nucleus accumbens, an effect blocked by dopamine receptor antagonists. These data suggest that androgen reinforcement is mediated by the brain. Moreover, testosterone appears to act through the mesolimbic dopamine system, a common substrate for drugs of abuse. Nonetheless, androgen reinforcement is not comparable to that of cocaine or heroin. Instead, testosterone resembles other mild reinforcers, such as caffeine, nicotine, or benzodiazepines. The potential for androgen addiction remains to be determined.     

Androgens and the evolution of male-gender identity among male pseudohermaphrodites with 5alpha-reductase deficiency.

To determine the contribution of androgens to the formation of male-gender identity, we studied male pseudohermaphrodites who had decreased dihydrotestosterone production due to 5 alpha-reductase deficiency. These subjects were born with female-appearing external genitalia and were raised as girls. They have plasma testosterone levels in the high normal range, show an excellent response to testosterone and are unique models for evaluating the effect of testosterone, as compared with a female upbringing, in determining gender identity. Eighteen of 38 affected subjects were unambiguously raised as girls, yet during or after puberty, 17 of 18 changed to a male-gender identity and 16 of 18 to a male-gender role. Thus, exposure of the brain to normal levels of testosterone in utero, neonatally and at puberty appears to contribute substantially to the formation of male-gender identity. These subjects demonstrate that in the absence of sociocultural factors that could interrupt the natural sequence of events, the effect of testosterone predominates, over-riding the effect of rearing as girls.     

Preliminary evidence that gonadal hormones organize and activate disordered eating

OBJECTIVE: Eating disorders are more common in females than in males. Gender differences may be due to organizational (i.e. prenatal) and activational (i.e. post-natal) gonadal hormone effects that influence sex differences in behavior. This preliminary set of studies examined these effects by investigating relationships between eating disorder symptoms, prenatal testosterone exposure, and adult levels of estrogen in women. METHOD: We examined organizational associations by investigating relationships between disordered eating and finger-length ratios, which are known to be somatic markers of prenatal testosterone exposure. Participants included 113 adult female twins drawn from the community. Disordered eating was assessed with the total score from the Minnesota Eating Behavior Survey (MEBS). Finger lengths were hand scored using a ruler and photocopies of both hands. We also investigated activational influences by examining associations between circulating levels of estradiol and disordered eating symptoms. Two independent samples of adult females (n's = 24 and 25) drawn from the community were used for this study. Disordered eating was again assessed with the MEBS total score, while saliva samples were used for assessing estradiol. RESULTS: Positive associations were found between disordered eating and both finger-length ratios and circulating estradiol levels. CONCLUSIONS: Findings suggest that lower levels of prenatal testosterone exposure and higher adult levels of estradiol are associated with increased eating disorder symptoms. We hypothesize that the relatively low level of testosterone before birth in females permits their brains to respond to estrogens at puberty, when the hormones activate the genes contributing to disordered eating in vulnerable girls.