Hormonal regulation of adult sympathetic neurons: the effects of castration on neuropeptide Y, norepinephrine, and tyrosine hydroxylase activity

Previous studies utilizing the hypogastric ganglia (HG) have indicated that gonadal steroids exert organizational and activational effects on noradrenergic biochemistry. Bilateral castration of male rodents at birth prevents the normal maturation of tyrosine hydroxylase (T-OH) activity in the HG; castration during adulthood results in a progressive decline in T-OH activity. Testosterone replacement corrects both the ontogenetic and adult functional alterations in the neurotransmitter-synthesizing enzyme. The present studies in adult male rats extend these previous observations and asked the question whether gonadal steroids regulate the neurotransmitters neuropeptide Y (NPY) and norepinephrine (NE) in the HG. Adult rodents were castrated and ganglia T-OH, NPY, and NE were examined at various time points after surgery. All three indices of sympathetic neuron biochemistry declined following castration, but they exhibited different profiles. It appears that hormones may affect enzyme activity and neurotransmitter pools differently within neurons. Testosterone replacement therapy fully restored T-OH activity, and NPY and NE levels in the HG. These studies extend the activational role of testosterone in regulating sympathetic neuron neurotransmitter and neuropeptide levels as well as neurotransmitter-synthesizing enzymes.     

Hormone-dependent regulation of GABAA receptor gamma subunit mRNAs in sexually dimorphic regions of the rat brain.

Transmission mediated by gamma-aminobutyric acid type A (GABAA) receptors expressed within the medial preoptic area (mPOA) and the ventromedial nucleus (VMN) of the hypothalamus is known to play critical, but contrasting, roles in regulating steroid-dependent sexual behaviours in rats. Previous studies have demonstrated a striking dichotomy in receptor composition between the two regions with regard to gamma, but not alpha or beta, subunit expression. To test if gonadal steroids regulate the expression of the gamma subunit genes within the mPOA and the VMN, in situ hybridization analysis for messenger RNAs encoding the gamma 1, gamma 2Short (gamma 2S) and gamma 2Long (gamma 2L) subunits was done in gonadectomized male and female rats and in gonadally intact females over the oestrous cycle. No significant differences in the expression of the gamma subunit mRNAs were observed in gonadectomized male versus female rats. Significant effects of gonadal state in female rats were observed for gamma 1 mRNA levels in the mPOA and gamma 2L levels in the VMN. These data demonstrate that gonadal hormones exert activational control of expression of GABAA receptor gamma subunit mRNAs and suggest that differences in receptor structure may contribute to the functional modulation of female sexual behaviours mediated by GABAergic transmission in these regions.     

Testicular hormones modulate circadian rhythms of the diurnal rodent, Octodon degus

Sex differences have been identified in a variety of circadian rhythms, including free-running rhythms, light-induced phase shifts, sleep patterns, hormonal fluctuations, and rates of reentrainment. In the precocial, diurnal rodent Octodon degus, sex differences have been found in length of free-running rhythm (tau), phase response curves, rates of reentrainment, and in the use of social cues to facilitate reentrainment. Although gonadal hormones primarily organize circadian rhythms during early development, adult gonadal hormones have activational properties on various aspects of circadian rhythms in a number of species examined. Gonadectomy of adult female O. degus did not influence tau, phase angle of entrainment, or activity patterns in previous experiments. The present experiment examined the role of gonadal hormones in adult male degus' circadian wheel-running rhythms. We predicted that male gonadal hormones would have an activational effect on some aspects of circadian rhythms, particularly those in which we see sex differences. Phase angles of entrainment, tau, length of the active period (alpha), maximum and mean activity levels, and activity amplitude were examined for intact and castrated males housed in LD 12:12. Responses to light pulses while housed in constant darkness (DD) were also compared. Castration had no significant effect on tau or light-induced phase shifts. However, castration significantly increased phase angle of entrainment and decreased activity levels. The data indicate that adult gonadal steroids are not responsible for the sex differences in endogenous circadian mechanisms of O. degus (tau, PRC), although they influence activity level and phase angle of entrainment. This is most likely due to masking properties of testosterone, similar to the activity-increasing effects of estrogen during estrus in O. degus females.     

Sex, stress, and mood disorders: at the intersection of adrenal and gonadal hormones

The risk for neuropsychiatric illnesses has a strong sex bias, and for major depressive disorder (MDD), females show a more than 2-fold greater risk compared to males. Such mood disorders are commonly associated with a dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis. Thus, sex differences in the incidence of MDD may be related with the levels of gonadal steroid hormone in adulthood or during early development as well as with the sex differences in HPA axis function. In rodents, organizational and activational effects of gonadal steroid hormones have been described for the regulation of HPA axis function and, if consistent with humans, this may underlie the increased risk of mood disorders in women. Other developmental factors, such as prenatal stress and prenatal overexposure to glucocorticoids can also impact behaviors and neuroendocrine responses to stress in adulthood and these effects are also reported to occur with sex differences. Similarly, in humans, the clinical benefits of antidepressants are associated with the normalization of the dysregulated HPA axis, and genetic polymorphisms have been found in some genes involved in controlling the stress response. This review examines some potential factors contributing to the sex difference in the risk of affective disorders with a focus on adrenal and gonadal hormones as potential modulators. Genetic and environmental factors that contribute to individual risk for affective disorders are also described. Ultimately, future treatment strategies for depression should consider all of these biological elements in their design.     

Female-specific target sites for both oestrogen and androgen in the teleost brain

To dissect the molecular and cellular basis of sexual differentiation of the teleost brain, which maintains marked sexual plasticity throughout life, we examined sex differences in neural expression of all subtypes of nuclear oestrogen and androgen receptors (ER and AR) in medaka. All receptors were differentially expressed between the sexes in specific nuclei in the forebrain. The most pronounced sex differences were found in several nuclei in the ventral telencephalic and preoptic areas, where ER and AR expression were prominent in females but almost completely absent in males, indicating that these nuclei represent female-specific target sites for both oestrogen and androgen in the brain. Subsequent analyses revealed that the female-specific expression of ER and AR is not under the direct control of sex-linked genes but is instead regulated positively by oestrogen and negatively by androgen in a transient and reversible manner. Taken together, the present study demonstrates that sex-specific target sites for both oestrogen and androgen occur in the brain as a result of the activational effects of gonadal steroids. The consequent sex-specific but reversible steroid sensitivity of the adult brain probably contributes substantially to the process of sexual differentiation and the persistent sexual plasticity of the teleost brain.     

Gonadal hormones and sex differences in nonreproductive behaviors in rodents: organizational and activational influences

Sex differences in many nonreproductive behaviors have been described in rodents. Among the behaviors that are sexually dimorphic in the rat are activity, aggression, pain, and taste sensitivity, food intake and body weight regulation, the learning and retention of certain kinds of mazes, avoidance responses, taste aversion, and performance on certain schedules of reinforcement. Gonadal hormones seem to be responsible, in part, for sex differences in these behaviors, but their contribution varies greatly with the behavior in question. Frequently, these sexually dimorphic behaviors are influenced both by organizational and activational actions of sex hormones. In other instances (e.g., maze learning and the acquisition of shuttle-box avoidance responses) organizational influences predominate. And while there is no sexually dimorphic behavior surveyed that can be shown to be influenced only by activational effects, wheel-running activity is clearly more strongly subject to activational than to organizational effects of the gonadal hormones. In general, only rudimentary information exists regarding the temporal limits of the period in development when organizational influences on nonsexual behaviors occur. The suggestion can be made that organizational influences often occur outside of the critical period for differentiation of the neuroendocrine system regulating cyclic release of gonadotrophins. Even for behaviors where organizational effects usually occur during a roughly delimited period of development, data for other behavioral systems suggest that the time limits during which organizational effects can occur are not rigidly fixed. Very little information exists regarding biochemical or neural mechanisms by which organizational or activational effects on sexually dimorphic nonreproductive behaviors are expressed. It is important to recognize for many of the sexually dimorphic behaviors in the rat that differences between the sexes are neither large nor absolute. This is especially true of several kinds of learning situations where groups of males and females typically differ in average levels of performance. Ostensibly minor variations in test procedure can abolish or accentuate the average difference in performance between the sexes. We are a long way from an adequate understanding of what factors are important, but such information could be quite helpful in estimating whether sex differences in certain laboratory learning tasks have any adaptive significance.Sex differences in nonreproductive behaviors may be influenced by many factors other than hormonal status. This greatly complicates a comparative analysis, but such an analysis will ultimately be necessary. What limited data exist on rodents suggest that: (1) Sexually dimorphic responses in the rat are often not similarly differentiated in the hamster, the gerbil, or the mouse; and (2) major differences exist among rodent species in hormonal effects on such responses.Over the last decade it has become clear that the behavioral effects of deliberate neurological insult are not necessarily the same in male and female rats (or in one case, in rhesus monkeys). Sex differences in the behavioral effects of ventromedial hypothalamic, lateral hypothalamic, septal, and striatal lesions in the rat and of orbital prefrontal cortex lesions in the monkey have been described. While information regarding hormonal modulation of these differences in response to brain damage is very limited, available data suggest both organizational and activational effects of sex hormones may be involved. It is too early to tell where this line of research may ultimately lead, but rather striking sex differences in the incidence of certain neurological disorders in humans suggest that further research may have both practical and theoretical significance.     

The organizational–activational hypothesis as the foundation for a unified theory of sexual differentiation of all mammalian tissues

The 1959 publication of the paper by Phoenix et al. was a major turning point in the study of sexual differentiation of the brain. That study showed that sex differences in behavior, and by extension in the brain, were permanently sexually differentiated by testosterone, a testicular secretion, during an early critical period of development. The study placed the brain together in a class with other major sexually dimorphic tissues (external genitalia and genital tracts), and proposed an integrated hormonal theory of sexual differentiation for all of these non-gonadal tissues. Since 1959, the organizational–activational theory has been amended but survives as a central concept that explains many sex differences in phenotype, in diverse tissues and at all levels of analysis from the molecular to the behavioral. In the last two decades, however, sex differences have been found that are not explained by such gonadal hormonal effects, but rather because of the primary action of genes encoded on the sex chromosomes. To integrate the classic organizational and activational effects with the more recently discovered sex chromosome effects, we propose a unified theory of sexual differentiation that applies to all mammalian tissues.     

Intracerebral Sex Differences in the Vasotocin System in Birds: Possible Implication in Behavioral and Autonomic Functions

The brain vasotocinergic system demonstrates clear sexual dimorphism in birds investigated so far. This paper examines the evidence obtained in studies on gallinaceous (domestic fowl, Japanese quail) and passerine (canary, junco, zebra finch) birds. Vasotocin (VT)-immunoreactive parvocellular neurons are present in the nucleus of stria terminalis of males, but they are less abundant or absent in the corresponding structure of females. A similar difference has been observed in the dorsal paraventricular area of domestic fowl. Sex-related differences in VT-gene expression have been confirmed byin situhybridization. Moreover, overall brain content of VT mRNA in cockerels is about twice that of hens, suggesting that VT synthesis may also be sexually dimorphic in other brain areas where morphological sex differences have not yet been revealed. The vasotocinergic system in birds is implicated in body fluid homeostasis, and during ontogeny it starts to respond to osmotic challenges in a sexually dimorphic way. Photoperiod, aging, or castration—all associated with changes in circulating testosterone levels—affect sexually dimorphic VT pathways and cell clusters. Sexually dimorphic vasotocinergic circuits are distributed in regions containing steroid-concentrating cells and are closely intermingled with aromatase-containing neurons that may mediate activational effects of gonadal steroids on this peptidergic system. However, it remains undetermined whether the observed neuroanatomical sex differences are related to sexually dimorphic autonomic and behavioral effects induced by VT. Most likely, VT in birds has a modulatory rather than a specific regulatory function in control of male sexual behavior and vocalization.     

Metabolic and hormonal control of the desire for food and sex: implications for obesity and eating disorders

During evolution, the ability to overeat and store the extra energy as glycogen and lipids in specialized tissues must have conferred a reproductive advantage by releasing animals from the need to eat constantly, enabling them to engage in behaviors that improved reproductive success. Mechanisms that inhibited ingestive behavior might have been most adaptive when they caused individuals to stop foraging, hoarding and eating in order to find and court potential mates. Conversely, the ability to abstain from reproductive activities to engage in foraging and eating was probably critical for individual survival during severe energetic challenges because reproductive processes are energetically costly and can be delayed until the energetic conditions improve. The mechanisms that control ingestive behavior most likely evolved under conditions in which both food and mates were available, and thus, our understanding might be limited by our narrow focus on food intake in animals isolated from potential mates, and reproductive behaviors in the absence of food. Our understanding of obesity and eating disorders will be enriched by the study of the choice between ingestive and reproductive behaviors and by a renewed attention to "reproductive" hormones such as gonadal steroids and hypothalamic releasing hormones. Furthermore, leptin and reproductive hormones have both organizational and activational effects on the energy balancing system including those mechanisms that control appetite, body fat content and body fat distribution. Understanding these organizational and activational effects on body fat distribution might lead to a better understanding of sex differences in the propensity to develop obesity, type II diabetes and eating disorders.     

Sex differences in opioid analgesia, hyperalgesia, tolerance and withdrawal: Central mechanisms of action and roles of gonadal hormones

This article reviews sex differences in opiate analgesic and related processes as part of a Special Issue in Hormones and Behavior. The research findings on sex differences are organized in the following manner: (a) systemic opioid analgesia across mu, delta and kappa opioid receptor subtypes and drug efficacy at their respective receptors, (b) effects of the activational and organizational roles of gonadal steroid hormones and estrus phase on systemic analgesic responses, (c) sex differences in spinal opioid analgesia, (d) sex differences in supraspinal opioid analgesia and gonadal hormone effects, (e) the contribution of genetic variance to analgesic sex differences, (f) sex differences in opioid-induced hyperalgesia, (g) sex differences in tolerance and withdrawal-dependence effects, and (h) implications for clinical therapies.     

Sexually dimorphic effects of morphine and MK-801: sex steroid-dependent and -independent mechanisms.

Rats show gender differences in responses to morphine and the N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801); the role of sex steroids in mediating these differences is unclear. We tested the overall hypothesis that circulating gonadal steroids determine the gender differences in morphine- and MK-801-induced behavior and c-Fos expression. Morphine caused a greater expression of c-Fos in the striatum of intact males than of that females, which was independent of sex steroids. MK-801 completely inhibited morphine-induced c-Fos in intact females but only caused partial inhibition in intact males; castrated males showed complete inhibition, which was reversed by testosterone, but gonadal steroids had no effect on this response in females. In thalamus, there was a large sex difference in the response to MK-801 that was independent of gonadal steroids. Behavioral responses to morphine were greater in males, but responses to MK-801 were greater in females; both were sex steroid independent. These findings show significant sex differences in response to morphine and MK-801 that are mediated by sex steroid-dependent and -independent mechanisms, which may be important in treatment outcomes of drug addiction.     

Do Sex Differences in the Brain Explain Sex Differences in the Hormonal Induction of Reproductive Behavior? What 25 Years of Research on the Japanese Quail Tells Us

Early workers interested in the mechanisms mediating sex differences in morphology and behavior assumed that differences in behavior that are commonly observed between males and females result from the sex specificity of androgens and estrogens. Androgens were thought to facilitate male-typical traits, and estrogens were thought to facilitate female-typical traits. By the mid-20th century, however, it was apparent that administering androgens to females or estrogens to males was not always effective in sex-reversing behavior and that in some cases a “female” hormone such as an estrogen could produce male-typical behavior and an androgen could induce female-typical behavior. These conceptual difficulties were resolved to a large extent by the seminal paper of C. H. Phoenix, R. W. Goy, A. A. Gerall, and W. C. Young in (1959,Endocrinology65, 369–382) that illustrated that several aspects of sexual behavior are different between males and females because the sexes have been exposed during their perinatal life to a different endocrine milieu that has irreversibly modified their response to steroids in adulthood. Phoenixet al.(1959) therefore formalized a clear dichotomy between the organizational and activational effects of sex steroid hormones. Since this paper, a substantial amount of research has been carried out in an attempt to identify the aspects of brain morphology or neurochemistry that differentiate under the embryonic/neonatal effects of steroids and are responsible for the different behavioral response of males and females to the activation by steroids in adulthood. During the past 25 years, research in behavioral neuroendocrinology has identified many sex differences in brain morphology or neurochemistry; however many of these sex differences disappear when male and female subjects are placed in similar endocrine conditions (e.g., are gonadectomized and treated with the same amount of steroids) so that these differences appear to be of an activational nature and cannot therefore explain sex differences in behavior that are still present in gonadectomized steroid-treated adults. This research has also revealed many aspects of brain morphology and chemistry that are markedly affected by steroids in adulthood and are thought to mediate the activation of behavior at the central level. It has been explicitly, or in some cases, implicitly assumed that the sexual differentiation of brain and behavior driven by early exposure to steroids concerns primarily those neuroanatomical/neurochemical characteristics that are altered by steroids in adulthood and presumably mediate the activation of behavior. Extensive efforts to identify these sexually differentiated brain characteristics over the past 20 years has only met with limited success, however. As regards reproductive behavior, in all model species that have been studied it is still impossible to identify satisfactorily brain characteristics that differentiate under early steroid action and explain the sex differences in behavioral activating effects of steroids. This problem is illustrated by research conducted on Japanese quail (Coturnix japonica), an avian model system that displays prominent sex differences in the sexual behavioral response to testosterone, and in which the endocrine mechanisms that control sexual differentiation of behavior have been clearly identified so that subjects with a fully sex-reversed behavioral phenotype can be easily produced. In this species, studies of sex differences in the neural substrate mediating the action of steroids in the brain, including the activity of the enzymes that metabolize steroids such as aromatase and the distribution of steroid hormone receptors as well as related neurotransmitter systems, did not result in a satisfactory explanation of sex differences in the behavioral effectiveness of testosterone. Possible explanations for the relative failure to identify the organized brain characteristics responsible for behavioral sex differences in the responsiveness to steroids are presented. It is argued that novel research strategies may have to be employed to successfully attack the fundamental question of the hormonal mechanisms regulating sex differences in behavior.     

Independent influences of sex steroids of systemic and central origin in a rat model of Parkinson's disease: A contribution to sex-specific neuroprotection by estrogens

This review considers evidence which reveals considerable complexity and sex differences in the response of the nigrostriatal dopaminergic (NSDA) system to hormonal influences. This pathway degenerates in Parkinson's disease (PD) and sex hormones contribute to sex differences in PD, where men fare worse than women. Here we discuss evidence from animal studies which allows us to hypothesize that, contrary to expectations, the acclaimed neuroprotective property of physiological concentrations of estradiol arises not by promoting NSDA neuron survival, but by targeting powerful adaptive responses in the surviving neurons, which restore striatal DA functionality until over 60% of neurons are lost. Estrogen generated locally in the NSDA region appears to promote these adaptive mechanisms in females and males to preserve striatal DA levels in the partially injured NSDA pathway. However, responses to systemic steroids differ between the sexes. In females there is general agreement that gonadal steroids and exogenous estradiol promote striatal adaptation in the partially injured NSDA pathway to protect against striatal DA loss. In contrast, the balance of evidence suggests that in males gonadal factors and exogenous estradiol have negligible or even harmful effects. Sex differences in the organization of NSDA-related circuitry may well account for these differences. Compensatory mechanisms and sexually dimorphic hard-wiring are therefore likely to represent important biological substrates for sex dimorphisms. As these processes may be targeted differentially by systemic steroids in males and females, further understanding of the underlying processes would provide valuable insights into the potential for hormone-based therapies in PD, which would need to be sex-specific. Alternatively, evidence that estrogen generated locally is protective in the injured male NSDA pathway indicates the great therapeutic potential of harnessing central steroid synthesis to ameliorate neurodegenerative disorders. A clearer understanding of the relative contributions and inter-relationships of central and systemic steroids within the NSDA system is an important goal for future studies.     

Organizational and activational effects of sex steroids on brain and behavior: A reanalysis

The actions of sex steroids on brain and behavior traditionally have been divided into organizational and activational effects. Organizational effects are permanent and occur early in development; activational effects are transient and occur throughout life. Over the past decade, experimental results have accumulated which do not fit such a simple two-process theory. Specifically, the characteristics said to distinguish organizational and activational effects on behavior are sometimes mixed, as when permanent effects occur in adulthood. Attempts to determine whether specific cellular processes are uniquely associated with either organizational or activational effects are unsuccessful. These considerations blur the organizational-activational distinction sufficiently to suggest that a rigid dichotomy is no longer tenable.     

Androgenic regulation of the central glia response following nerve damage.

Current research on the effects of gonadal steroids on the brain and spinal cord indicates that these agents have profound trophic effects on many aspects of neuronal functioning, including cell survival, growth and metabolism, elaboration of processes, synaptogenesis, and neurotransmission (Jones et al., 1985; Luine, 1985; Nordeen et al., 1985; Matsumoto et al., 1988a,b; Gould et al., 1990). Since many of the aspects of normal neuronal functioning altered by gonadal steroids are affected by injury to the nervous system, we initiated a series of experiments designed to exploit the trophic capabilities of steroids as therapeutic agents in neuronal injury and repair (Kujawa et al., 1989, 1991; Kujawa and Jones, 1990). Three steroid-sensitive model systems were used for these studies: the hamster facial motoneuron, the rat sciatic motoneuron, and the hamster rubrospinal motoneuron. The results of our initial series of experiments suggest that androgens, and possibly estrogens, act either directly or indirectly on the injured motoneuron and enhance elements of the neuronal reparative response that are critical to successful recovery of function. Recently, we discovered that gonadal steroids may also modulate the central glia response to nerve damage. In this review, a summary of our data identifying a therapeutic role for androgens in enhancing the reparative response of motoneurons to injury is presented. This is followed by a discussion of the effects of androgens on the glial response to injury.     

Dysregulation of neonatal hippocampal cell genesis in the androgen insensitive Tfm rat

The first two weeks of life are a critical period for hippocampal development. At this time gonadal steroid exposure organizes sex differences in hippocampal sensitivity to activational effects of steroids, hippocampal cell morphology and hippocampus dependent behaviors. Our laboratory has characterized a robust sex difference in neonatal neurogenesis in the hippocampus that is mediated by estradiol. Here, we extend our knowledge of this sex difference by comparing the male and female hippocampus to the androgen insensitive testicular feminized mutant (Tfm) rat. In the neonatal Tfm rat hippocampus, fewer newly generated cells survive compared to males or females. This deficit in cell genesis is partially recovered with the potent androgen DHT, but is more completely recovered following estradiol administration. Tfm rats do not differ from males or females in the level of endogenous estradiol in the neonatal hippocampus, suggesting other mechanisms mediate a differential sensitivity to estradiol in male, female and Tfm hippocampus. We also demonstrate disrupted performance on a hippocampal-dependent contextual fear discrimination task. Tfm rats generalize fear across contexts, and do not exhibit significant loss of fear during extinction exposure. These results extend prior reports of exaggerated response to stress in Tfm rats, and following gonadectomy in normal male rats.     

Endogenous testosterone levels, mental rotation performance, and constituent abilities in middle-to-older aged men

Evidence from both human and animal studies suggests that gonadal steroids, such as testosterone, exert activational effects on adult spatial behavior. Endogenous testosterone levels decline gradually but variably as men age; it remains to be shown whether these decreases are associated with age-related declines in visuo-spatial performance or constituent abilities indicative of generalized age-related cognitive decline. Ninety-six healthy, community dwelling men aged between 38 and 69 years completed the Vandenberg and Kuse Mental Rotation Test (MRT) together with a battery of tests including processing speed, executive function, perceptual discrimination, working memory, and reaction time measures. Significant main effects of tertiles of calculated free testosterone levels (cEFT) were found on composite measures of processing speed, executive function, and perceptual discrimination ability in a subset of men aged over 50 years in age and crystallized intelligence controlled analyses; higher cEFT levels were associated with poorer performance. Hierarchical multiple regression and path analyses on the whole data set showed that cEFT levels negatively moderated processing speed performance, which in turn predicted both working memory and MRT performance with aging. Together these data suggest that age-related declines in endogenous testosterone levels in healthy middle-to-older aged men are not associated with generalized age-related cognitive decline.     

Gonadal steroids regulate the expression of aggrecanases in human endometrial stromal cells in vitro

The human endometrium undergoes cyclic change during each menstrual cycle in response to gonadal steroids. Proteolysis of endometrial extracellular matrix (ECM) is necessary to prepare this dynamic tissue for pregnancy. Proteolytic enzymes such as matrix metalloproteinase (MMP) and closely related a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) have been assigned key roles in the highly regulated cyclic remodelling of the endometrial ECM. We have previously shown that ADAMTS‐1 undergoes spatiotemporal changes in human endometrial stromal cells under the regulation of gonadal steroids. This suggests that other ADAMTS subtypes, known as aggrecanases, may contribute to the ECM remodelling events that occur in female physiological cycles and in preparation for pregnancy. To determine whether progesterone (P4), 17β‐estradiol (E2), or dihydrotestosterone (DHT), alone or in combination, are capable of regulating ADAMTS‐4, ‐5, ‐8 or ‐9 expression in human endometrial stromal cells in vitro. Real‐time quantitative PCR and Western blot analysis were used to measure ADAMTSs mRNA and protein levels in primary cultures of human endometrial stromal cells (n = 12). P4, DHT but not E2 have regulatory effects on ADAMTS‐8, ‐9 and ‐5 expression. Combined treatment with gonadal steroids did not show any synergistic or antagonistic effects. However, the synthetic steroid antagonists RU486 and hydroxyflutamide specifically inhibited the P4‐ or DHT‐mediated regulatory effects on ADAMTS expression. These studies provide evidence that the regulation of aggrecanases by gonadal steroids in human endometrial stromal cells may play an important role during decidualization.     

Reproductive Hormone-Dependent and -Independent Contributions to Developmental Changes in Kisspeptin in GnRH-Deficient Hypogonadal Mice

Kisspeptin is a potent activator of GnRH-induced gonadotropin secretion and is a proposed central regulator of pubertal onset. In mice, there is a neuroanatomical separation of two discrete kisspeptin neuronal populations, which are sexually dimorphic and are believed to make distinct contributions to reproductive physiology. Within these kisspeptin neuron populations, Kiss1 expression is directly regulated by sex hormones, thereby confounding the roles of sex differences and early activational events that drive the establishment of kisspeptin neurons. In order to better understand sex steroid hormone-dependent and -independent effects on the maturation of kisspeptin neurons, hypogonadal (hpg) mice deficient in GnRH and its downstream effectors were used to determine changes in the developmental kisspeptin expression. In hpg mice, sex differences in Kiss1 mRNA levels and kisspeptin immunoreactivity, typically present at 30 days of age, were absent in the anteroventral periventricular nucleus (AVPV). Although immunoreactive kisspeptin increased from 10 to 30 days of age to levels intermediate between wild type (WT) females and males, corresponding increases in Kiss1 mRNA were not detected. In contrast, the hpg arcuate nucleus (ARC) demonstrated a 10-fold increase in Kiss1 mRNA between 10 and 30 days in both females and males, suggesting that the ARC is a significant center for sex steroid-independent pubertal kisspeptin expression. Interestingly, the normal positive feedback response of AVPV kisspeptin neurons to estrogen observed in WT mice was lost in hpg females, suggesting that exposure to reproductive hormones during development may contribute to the establishment of the ovulatory gonadotropin surge mechanism. Overall, these studies suggest that the onset of pubertal kisspeptin expression is not dependent on reproductive hormones, but that gonadal sex steroids critically shape the hypothalamic kisspeptin neuronal subpopulations to make distinct contributions to the activation and control of the reproductive hormone cascade at the time of puberty.     

Evidence for a hyporesponsive limbic-hypothalamic-pituitary-adrenal axis following early-life repetitive hypoglycemia in adult male rats

The developing limbic-hypothalamic-pituitary-adrenal (LHPA) axis is highly vulnerable to programming by early-life environmental factors, including exposure to synthetic glucocorticoids and nutrient deficiencies. Early-life repetitive hypoglycemia (RHG) is a common complication of insulin therapy for type-1 diabetes that may have long-term consequences in adulthood. Recent observations in a rat model of early RHG suggest persistent changes in LHPA axis function, including changes in relevant hormones and affective behaviors, which support a hyperresponsive LHPA axis. Thus, we hypothesized that early RHG would alter the expression of key genes regulating LHPA axis function in adulthood. The present study employed a rat model of insulin-induced RHG spanning postnatal days (P)24-28, a neurodevelopmental equivalent of early childhood in humans, to assess the long-term effects on mRNA levels for proteins relevant to the LHPA function and the corticosterone responses to ACTH stimulation of dispersed adrenocortical cells in vitro and restraint stress in vivo at adulthood. This early RHG model resulted in a hyporesponsive LHPA axis characterized by impaired corticosterone response, increased hippocampal glucocorticoid and mineralocorticoid receptor (GR and MR), decreased hypothalamic corticotropin-releasing hormone, increased adrenal steroidogenic-acute-regulatory protein and GR, and decreased adrenal MR, melanocortin-type-2 receptor and low-density lipoprotein receptor expression. Our findings highlight a complex environmental-gene interaction between RHG and LHPA axis during development that influences regulation of this axis in adulthood. The findings are consistent with the developmental origins of disease and underscore the influences of early-life events on the programming of a major regulatory system.