Steroid hormones use non-genomic mechanisms to control brain functions and behaviors: a review of evidence

Central mechanisms of stress integration: hierarchical circuitry controlling hypothalamo-pituitary-adrenocortical responsiveness

Appropriate regulatory control of the hypothalamo-pituitary-adrenocortical stress axis is essential to health and survival. The following review documents the principle extrinsic and intrinsic mechanisms responsible for regulating stress-responsive CRH neurons of the hypothalamic paraventricular nucleus, which summate excitatory and inhibitory inputs into a net secretory signal at the pituitary gland. Regions that directly innervate these neurons are primed to relay sensory information, including visceral afferents, nociceptors and circumventricular organs, thereby promoting 'reactive' corticosteroid responses to emergent homeostatic challenges. Indirect inputs from the limbic-associated structures are capable of activating these same cells in the absence of frank physiological challenges; such 'anticipatory' signals regulate glucocorticoid release under conditions in which physical challenges may be predicted, either by innate programs or conditioned stimuli. Importantly, 'anticipatory' circuits are integrated with neural pathways subserving 'reactive' responses at multiple levels. The resultant hierarchical organization of stress-responsive neurocircuitries is capable of comparing information from multiple limbic sources with internally generated and peripherally sensed information, thereby tuning the relative activity of the adrenal cortex. Imbalances among these limbic pathways and homeostatic sensors are likely to underlie hypothalamo-pituitary-adrenocortical dysfunction associated with numerous disease processes.

Gonadal steroid hormone modulation of nociception, morphine antinociception and reproductive indices in male and female rats

The purpose of this study was to examine how gonadal steroid hormones modulate basal nociception and morphine antinociception relative to regulating reproduction in the adult rat. Male and female Sprague-Dawley rats were either gonadectomized (GDX) or sham-gonadectomized (sham); GDX males were implanted subcutaneously with capsules containing testosterone (T), estradiol (E2), dihydrotestosterone (DHT), E2 and DHT, or nothing (0). GDX females received E2, T, or empty (0) capsules immediately after surgery, and vehicle or progesterone (P4) injections at 4-day intervals. Basal nociception and morphine antinociception were tested 28 days after surgery on 50 degrees C and 54 degrees C hotplate tests, and reproductive behavior and physiology were assessed shortly thereafter. There were no significant differences in baseline hotplate latencies among the male treatment groups, but morphine was significantly more potent in sham and GDX+T males than in GDX+0 males. The ability of T to increase morphine's potency was approximated by its major metabolites E2 and DHT, given together but not alone. Baseline hotplate latencies were higher in sham females tested during diestrus than in those tested during estrus. Morphine was significantly more potent in sham females tested during proestrus and diestrus than in those tested during estrus. Baseline hotplate latencies were significantly higher, and morphine was significantly less potent in GDX+E2, GDX+E2/P4 and GDX+T females than in GDX+0 females. All group differences in basal nociception and morphine antinociception observed on the 50 degrees C hotplate test were smaller and generally non-significant on the 54 degrees C hotplate test. Steroid manipulations produced the expected changes in reproductive behaviors and steroid-sensitive organs. These results demonstrate that in adult rats, gonadal steroid manipulations, that are physiologically relevant, modulate (1) basal nociception in females but not males, and (2) morphine's antinociceptive potency in both males and females.

Glucocorticoid regulation of diverse cognitive functions in normal and pathological emotional states

The glucocorticoid hormone cortisol is essential for many forms of regulatory physiology and for cognitive appraisal. Cortisol, while associated with fear and stress response, is also the hormone of energy metabolism and it coordinates behavioral adaptation to the environmental and internal conditions through the regulation of many neurotransmitters and neural circuits. Cortisol has diverse effects on many neuropeptide and neurotransmitter systems thus affecting functional brain systems. As a result, cortisol affects numerous cognitive domains including attention, perception, memory, and emotional processing. When certain pathological emotional states are present, cortisol may have a role in differential activation of brain regions, particularly suppression of hippocampal activation, enhancement of amygdala activity, and dendritic reshaping in these regions as well as in the ventral prefrontal cortex. The coordinated actions of glucocorticoid regulation on various brain systems such as those implicated in emotional processing can lead to perceptual and cognitive adaptations and distortions of events that may be relevant for understanding mood disorders.

Evidence that estrogen receptor alpha, but not beta, mediates seasonal changes in the response of the ovine retrochiasmatic area to estradiol

In ewes, anestrus results from a reduction in LH pulsatility due to an increased sensitivity of the hypothalamic estradiol negative feedback system. Considerable evidence has implicated the A15 group of dopaminergic neurons in the retrochiasmatic area in this seasonally dependent estradiol effect. Moreover, estradiol administered to the retrochiasmatic area in ovariectomized anestrous ewes inhibits LH secretion. However, A15 neurons do not appear to contain the classical estrogen receptors (ERalpha). Therefore, we tested the hypothesis that beta-estrogen receptors mediate the action of estradiol in the retrochiasmatic area by comparing the effects of estradiol and genistein, a selective ERbeta agonist. We also examined whether there are seasonal changes in response of the retrochiasmatic area to these agonists and if these effects are mediated by dopamine. To test these hypotheses, ovariectomized ewes were implanted with bilateral guide cannulae targeting the retrochiasmatic area. Crystalline agonists were administered via microimplants inserted down the cannulae. Blood samples taken before and 4 days after microimplant insertion were analyzed for LH concentrations, pulse frequency, and amplitude. Genistein treatment produced no significant change in LH levels in either season. Estradiol treatment decreased both mean LH concentrations and pulse frequency in anestrous but not breeding-season ewes. Administration of the dopamine antagonist sulpiride to ovariectomized ewes with estradiol microimplants in the retrochiasmatic area returned LH pulse frequency to levels indistinguishable from controls. From these data, we hypothesize that estradiol acts on local ERalpha-containing neurons in this area to stimulate a dopaminergic pathway that inhibits LH secretion during anestrus.

Testosterone suppresses circadian responsiveness to social cues in the diurnal rodent Octodon degus

The diurnal, social rodent Octodon degus displays a robust sex difference in the ability to use social cues to facilitate reentrainment following a phase advance of the light cycle. Adult females housed with a female social cue donor reentrained 25% to 40% faster than did females reentraining alone. However, reentrainment rates of males were unaffected by exposure to female social cues during reentrainment. The authors hypothesized that males were less sensitive to the reentrainment-enhancing effects of social cues and that their higher threshold to the stimuli could be overcome if the social cues were either increased in strength or salience. Housing a male with two females significantly shortened the time to reentrain following a 9-h phase advance (p = 0.002). Housing with a sister had no effect on reentrainment. Therefore, male degus are able to respond to social cues but require the stimulus to be stronger than that for females. The effect of testosterone was tested by comparing reentrainment rates of castrated males before and after testosterone replacement both with and without a female social cue donor. Castrated males responded to a single female social cue donor, reentraining 35% faster than when housed alone (p = 0.006), whereas the time to reentrainment of intact males and males with testosterone capsule implants did not differ. Intact females were also implanted with testosterone and phase shifted with and without donors. Testosterone treatment eliminated the increase in reentrainment rates in the presence of social cues. The authors conclude that the rate of recovery from odor-enhanced phase shifts is modulated by activational effects of testosterone in male degus. Testosterone is also effective in suppressing social cue responsiveness in females, suggesting that testosterone's effects on responsiveness are not sexually dimorphic. This hormonal effect likely occurs by altering sensory system functions or CNS response to sensory information.

17beta-estradiol effect on the extracellular concentration of amino acids in the glutamate excitotoxicity model in the rat

Estrogen has demonstrated a neuroprotective role in a rat model of glutamate excitotoxicity and other neurodegenerative disorders. We studied the effect of 17beta-estradiol on glutamate-induced increases in amino acids levels (aspartate, histidine, taurine and GABA) in the rat cortex. Local perfusion of glutamate produced a transient increase of aspartate, histidine, taurine and GABA in the extracellular fluid. Pretreatment with 17beta-estradiol significantly reduced the increases of taurine and moderately attenuated that of histidine, whereas aspartate and GABA releases were not modified. The effect of 17beta-estradiol on histidine release was reversed by the antiestrogen tamoxifen, suggesting a receptor-dependent mechanism. Good correlations between the volumes of the glutamate-induced lesions and the extracellular concentrations of taurine and aspartate were observed. These findings suggest that the attenuation of the glutamate-induced release of taurine by 17beta-estradiol may participate in the neuroprotective effects of 17beta-estradiol and that increased levels of aspartate and taurine are markers for the severity of the glutamate-induced cortical lesions.

Behavioral neuroendocrinology of vasotocin and vasopressin and the sensorimotor processing hypothesis

Vasotocin (AVT) and vasopressin (AVP) are potent modulators of social behaviors in diverse species of vertebrates. This review addresses questions about how and where AVT and AVP act to modulate social behaviors, focusing on research with an amphibian model (Taricha granulosa). In general, the behaviorally important AVT and AVP neurons occur in the forebrain and project to sites throughout the brain. Social behaviors are modulated by AVT and AVP acting at multiple sites in the brain and at multiple levels in the behavioral sequence. This review proposes that AVT and AVP can act on sensory pathways to modulate the responsiveness of neurons to behaviorally relevant sensory stimuli and also can act on motor pathways in the brainstem and spinal cord to modulate the neuronal output to behavior-specific pattern generators. This neurobehavioral model, in which AVT and AVP are thought to modulate social behaviors by affecting sensorimotor processing, warrants further research.

Effects of cortisol on aggression and locomotor activity in rainbow trout

Noninvasive administration of cortisol through the diet resulted in relatively rapid (<1.5 h) and highly reproducible increases in plasma cortisol in rainbow trout, comparable to changes seen in fish subjected to substantial stress. Juvenile rainbow trout were reared in isolation for 1 week, before their daily food ration was replaced by a meal of cortisol-treated food corresponding to 6 mg cortisol kg(-1). All fish were observed for 30 min, beginning at 1 or 48 h following the introduction of cortisol-treated food. Additional cortisol (75% of the original dose on Day 2, and 50% on Day 3) was administered to the long-term cortisol-treated group. The resulting blood plasma concentrations of cortisol were similar in short- and long-term treated fish, and corresponded to those previously seen in stressed rainbow trout. Controls were fed similar food without cortisol. Half of the fish from each treatment group (controls and short- and long-term cortisol) were subjected to an intruder test (a smaller conspecific introduced into the aquarium), while half of the fish were observed in isolation. In fish challenged by a conspecific intruder, short-term cortisol treatment stimulated locomotor activity, while long-term treatment inhibited locomotion. Aggressive behavior was also inhibited by long-term cortisol treatment, but not by short-term exposure to cortisol. Cortisol treatment had no effect on locomotor activity in undisturbed fish, indicating that the behavioral effects of cortisol were mediated through interaction with other signal systems activated during the simulated territorial intrusion test. This study demonstrates for the first time that cortisol has time- and context-dependent effects on behavior in teleost fish.

Non-genomic steroid receptors in the bovine ovary

Over the last few years, rapid and physiologically important non-genomic actions of all classes of steroid hormones have been described in many cell types. A putative non-genomic membrane progesterone receptor (NGPR) was the first, and so far the only, non-genomic steroid receptor cloned. Two homologous NGPR proteins have been identified in the human, and a similar protein in the bovine and rat. Various detection methods have been used to identify putative NGPRs in a range of tissues: however, different methods often yield quite different molecular weights, and probably detect distinct moieties. We describe some properties of the specific cell-surface membrane binding sites for [3H]-progesterone in enriched cell membrane preparations of bovine luteal and follicular cells. Similar binding sites were also detected in cell-membranes of some (but not all) bovine tissues. Western blots of detergent extracts of bovine luteal membranes identified a protein (85kDa) that reacted with an antiserum to the N-terminal peptide of porcine NGPR. Activity was low in native non-denatured extracts, but increased dramatically in a dose-dependent manner following pretreatment with the cholesterol-complexing agent, digitonin. This protein was co-precipitated by antisera to caveolin. In contrast, a specific monoclonal antibody to the ligand binding domain of the genomic progesterone receptor (Mab C262) detected two proteins (M(r), 55 and 60kDa) in luteal membrane detergent extracts. Immunostaining of these proteins by Mab C262 was abolished by digitonin concentration-dependent manner in non-denatured extracts. However, both proteins were unaffected by digitonin in fully denatured detergent extracts, suggesting that digitonin induced a conformational change in the native protein that prevented binding of Mab C262 to its epitope. Our data suggest the presence of a complex of two or more distinct membrane-associated progesterone-binding proteins in bovine luteal membranes. Moreover, their conformations are specifically affected by removal of bound cholesterol.

Signal transduction mechanisms mediating rapid, nongenomic effects of cortisol on prolactin release

While the mechanisms governing genomically mediated glucocorticoid actions are becoming increasingly understood, relatively little is known with regard to the cell signaling pathways that transduce rapid glucocorticoid actions. Studies of the cultured tilapia rostral pars distalis (RPD), a naturally segregated region of the fish pituitary gland that contains a 95-99% pure population of prolactin (PRL) cells and is easily dissected and maintained in a completely defined, serum-free media, indicate that physiological concentrations of cortisol rapidly inhibit PRL release. The attenuative action of cortisol on PRL release occurs within 10-20 min, is insensitive to the protein synthesis inhibitor, cycloheximide, and mimicked by its membrane impermeable analog, cortisol-21 hemisuccinate-conjugated bovine serum albumin (BSA). Cortisol and somatostatin, a peptide known to work through membrane receptors to inhibit PRL release, rapidly and reversibly reduces intracellular free Ca(2+) (Ca(i)(2+)), and inhibits 45Ca(2+) influx and BAYK-8644 induced PRL release. Preliminary investigations show cortisol, but not somatostatin, suppresses phospholipase C (PLC) activity in PRL cell membrane preparations. In addition, cortisol and somatostatin reduce intracellular cAMP and membrane adenylyl cyclase activity. These findings indicate that the acute inhibitory effects of cortisol on PRL release occur through a nongenomic mechanism involving interactions with the plasma membrane and inhibition of both the Ca(2+) and cAMP signal transduction pathways. Cortisol may reduce Ca(i)(2+) by inhibiting influx through L-type voltage-gated channels and possibly release through a PLC/inositol triphosphate sensitive intracellular Ca(2+) pool. In addition, it is also likely the steroid inhibits adenylyl cyclase activity in events leading to reduced cAMP production and the subsequent release of PRL.

Implicit power motivation predicts men's testosterone changes and implicit learning in a contest situation

This study tested the hypothesis that implicit power motivation moderates men's testosterone responses to victory or defeat in a contest situation. It also explored to what extent postvictory testosterone increases are associated with enhanced implicit learning of behavior instrumental for winning a contest. Salivary testosterone levels were assessed in 66 male adults several times before and after a contest whose outcome (winning or losing against a competitor on an implicit learning task) was varied experimentally. Among participants low in activity inhibition, a measure of impulse control, the power motive was a significant positive predictor of testosterone increases (15 min postcontest; r = 0.71, P = 0.01) and implicit learning (r = 0.68, P < 0.05) after a victory, whereas it was a significant negative predictor of implicit learning (r = -0.58, P = 0.01) but not of testosterone increases (r = -0.08, ns) after a defeat. Moreover, among participants low in activity inhibition testosterone increases were associated with enhanced implicit learning (r = 0.38, P < 0.05) and there was statistical evidence that in winners testosterone increases mediated the effect of power motivation on implicit learning. Participants high in activity inhibition did not display this pattern of results.

Differences in behaviour between rainbow trout selected for high- and low-stress responsiveness

Two F1 lines of rainbow trout Oncorhynchus mykiss, divergent for plasma cortisol responsiveness, were generated by individual selection for post-stress cortisol values within the F0 generation. Adult females of the F1 generation were transferred to rearing in social isolation in observation tanks. After 6 days, locomotor activity in high-responding (HR) and low-responding (LR) individuals was quantified as time spent moving during a 20 min observation period. Behavioural observations were repeated the next day with a smaller conspecific intruder present in each observation tank. Differential hypothalamus–pituitary–interrenal axis activity in the two lines was subsequently confirmed by a standardised confinement stress test, which resulted in significantly higher plasma cortisol concentrations in HR than LR fish. HR fish displayed higher levels of locomotor activity than LR fish in the presence of an intruder, but not when in isolation. Aggressive behaviour towards the intruder was not seen, suggesting either a state-dependent lack of territorial aggression, or chronic stress in the experimental fish. A significantly higher incidence of feed intake was seen in LR trout when held in observation tanks (40 % versus 0 % of the fish took food when in isolation), suggesting that these fish acclimated more successfully to the experimental conditions than HR fish did. These results suggest that selection for stress responsiveness in salmonid fish leads to behavioural alterations, which are of potential importance to the performance of these fish in aquaculture rearing operations.

Anatomical and biochemical evidence for the synthesis of unconjugated and sulfated neurosteroids in amphibians

Various studies have shown that, in mammals, neurons and glial cells are capable of synthesizing bioactive steroids, or neurosteroids, which regulate the activity of the central nervous system (CNS). However, although steroid hormones are involved in the regulation of behavioral and neuroendocrine processes in amphibians, neurosteroid biosynthesis has never been studied in the CNS of non-mammalian vertebrates. Reviewed here are several data sets concerning the production of unconjugated and sulfated neurosteroids in amphibians. These data were obtained by investigating the immunohistochemical localization and activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and hydroxysteroid sulfotransferase (HST), in the frog brain. Numerous 3beta-HSD-immunoreactive neurons were detected in the anterior preoptic area, nucleus of the periventricular organ, posterior tuberculum, ventral and dorsal hypothalamic nuclei. 17beta-HSD-like immunoreactivity was found in ependymal gliocytes bordering the lateral ventricles of the telencephalon. Two populations of HST-immunoreactive neurons were localized in the anterior preoptic area and the dorsal magnocellular nucleus of the hypothalamus. High amounts of progesterone (PROG), 17-hydroxyprogesterone (17OH-PROG), testosterone (T) and dehydroepiandrosterone sulfate (DHEAS) were measured in the frog brain by combining HPLC analysis of tissue extracts with radioimmunoassay detection. Incubation of telencephalic or hypothalamic explants with tritiated pregnenolone ([3H]PREG) yielded the synthesis of various metabolites including PROG, 17OH-PROG, DHEA and T. Incorporation of [35S]3'-phosphoadenosine 5'-phosphosulfate ([35S]PAPS) and [3H]PREG or [3H]DHEA into frog brain homogenates led to the formation of [3H,35S]pregnenolone sulfate ([3H,35S]PREGS) or [3H,35S]DHEAS, respectively. Altogether, these results demonstrate that the process of neurosteroid biosynthesis occurs in amphibians as previously seen in mammals.

The classical progesterone receptor associates with p42 MAPK and is involved in phosphatidylinositol 3-kinase signaling in Xenopus oocytes

The induction of Xenopus laevis oocyte maturation by progesterone is a striking example of a steroid hormone-mediated event that does not require transcription. Here we have investigated the role of the classical progesterone receptor in this nongenomic signaling. The Xenopus progesterone receptor (XPR) was predominantly cytoplasmic; however, a significant fraction ( approximately 5%) of one form of the receptor (p82 XPR) was associated with the plasma membrane-containing P-10,000 fraction, compatible with the observation that membrane-impermeant derivatives of progesterone can induce maturation. XPR co-precipitated with active phosphatidylinositol 3-kinase. The phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin delayed progesterone-induced maturation and completely blocked the insulin-dependent maturation, indicating that the association of XPR with PI3-K could be functionally important. We also examined whether the nongenomic signaling properties of XPR can account for the ability of glucocorticoids and the progesterone antagonist RU486 to induce maturation. We found that none of these steroids cause XPR to become associated with active PI3-K; thus, association of XPR with active PI3-K is progesterone-specific. Finally, we showed that p42 mitogen-activated protein kinase (MAPK) associates with XPR after progesterone-induced germinal vesicle breakdown and that active recombinant MAPK is able to phosphorylate p110 XPR in vitro. These findings demonstrate that the classical progesterone receptor is involved in progesterone-induced nongenomic signaling in Xenopus oocytes and provide evidence that p42 MAPK and PI3-K activity are directly associated with the classical progesterone receptor.

17beta-Estradiol reduces cortical lesion size in the glutamate excitotoxicity model by enhancing extracellular lactate: a new neuroprotective pathway

Estrogens play an important role in neuronal function and in protecting neurones in the cerebral cortex against pathological conditions. An in vivo model of glutamate excitotoxicity in which glutamate is applied to the cortex of rats through a microdialysis probe has been used to investigate the neuroprotective processes initiated by 17beta-estradiol. Rats were pre-treated with 17beta-estradiol (i.v.) before local application of 100 mM glutamate into the cortex through a microdialysis probe. Pre-treatment with 17beta-estradiol significantly reduced the size of the glutamate-induced cortical lesion. In the cortical microdialysates collected from the probe, a peak of lactate was observed immediately after glutamate application. After 17beta-estradiol pre-treatment this peak of lactate was significantly higher with estradiol than without 120 min after glutamate application, reaching 700% basal level at the end of measurement. The level of extracellular glucose was markedly decreased with and without 17beta-estradiol pre-treatment. Local blockage of neuronal lactate transporters with alpha-cyano-4-hydroxycinnamate (4-CIN) completely abolished the neuroprotective effect of 17beta-estradiol and induced a larger cortical lesion. An accumulation of extracellular lactate was observed after inhibition of the lactate transporters suggesting that transport of lactate into neurones is necessary for the neuroprotective effect of 17beta-estradiol. The anti-estrogen tamoxifen also abolished the neuroprotective effect of 17beta-estradiol on the lesion size and inhibited the production of lactate. These results suggest a new neuroprotective mechanism of 17beta-estradiol by activating glutamate-stimulated lactate production, which is estrogen receptor-dependent.

Mice with targeted mutations of glucocorticoid and mineralocorticoid receptors: models for depression and anxiety?

Impaired corticosteroid receptor signaling is a key mechanism in the pathogenesis of stress-related psychiatric disorders such as depression and anxiety. Since in vivo expression and functional studies of corticosteroid receptors are not feasible in the human central nervous system, such analyses have to be done in animal models. Transgenic mice with mutations of corticosteroid receptors are promising tools, which allow us to investigate the role of these proteins in the pathogenesis of symptoms characteristic for depression and anxiety. This review summarizes the neuroendocrinological and behavioral findings that have been obtained in six different mouse strains with specific mutations that influence the expression or the function of the glucocorticoid or the mineralocorticoid receptor (MR). The analyses of these mice helped to define molecular concepts of how corticosteroid receptors regulate the activity of the hypothalamic-pituitary-adrenal (HPA) system. Furthermore, some of these mutant mice exhibited characteristic alterations in behavioral tests for anxiety and despair. However, so far, none of the mouse strains described here can be viewed as an animal model of a specific psychiatric disease defined by common diagnostic criteria. Using high throughput technologies for the identification of genes regulated by glucocorticoid receptor (GR) and MR in brain areas responsible for specific symptoms of stress-related disorders will yield potential new drug targets for the treatment of depression and anxiety.

Cortisol suppresses prolactin release through a non-genomic mechanism involving interactions with the plasma membrane

In the classical theory of steroid hormone action, steroids diffuse through the membrane and alter transcription of specific genes resulting in synthesis of proteins important for modulating cell function. Most often, steroids work solely through the genome to exert their physiological actions in a process that normally takes hours or days to occur. In tilapia (Oreochromis mossambicus), cortisol inhibits prolactin (PRL) release within 10-20 min in vitro. This action is accompanied by similarly rapid reductions in cellular Ca(2+) and cAMP levels, second messengers known to transduce the membrane effects of peptide hormones. We further examined whether cortisol might inhibit PRL release through a non-genomic, membrane-associated mechanism using the protein synthesis inhibitor, cycloheximide, and a membrane impermeant form of cortisol, cortisol-21 hemisuccinate BSA (HEF/BSA). Cycloheximide (2 and 10 microg/ml) was ineffective in overcoming PRL release induced by hyposmotic medium or that inhibited by cortisol over 4 h static incubations. These dosages reduced protein synthesis as measured by amino acid incorporation in pituitaries by 75 and 99%, respectively. During 4-h incubation, HEF/BSA and HEF significantly reduced PRL release in a dose-dependent fashion. These studies suggest that cortisol inhibits PRL release through a plasma membrane-associated, protein-synthesis independent (non-genomic) pathway.

Sex steroids and human behavior: implications for developmental psychopathology

In a variety of mammalian species, prenatal androgens organize brain structures and functions that are later activated by steroid hormones in postnatal life. In humans, studies of individuals with typical and atypical development suggest that sex differences in reproductive and nonreproductive behavior derive in part from similar prenatal and postnatal steroid effects on brain development. This paper provides a summary of research investigating hormonal influences on human behavior and describes how sex differences in the prevalences and natural histories of developmental psychopathologies may be consistent with these steroid effects. An association between patterns of sexual differentiation and specific forms of psychopathology suggests novel avenues for assessing the effects of sex steroids on brain structure and function, which may in turn improve our understanding of typical and atypical development in women and men.

Nongenomic membrane actions of glucocorticoids in vertebrates

For decades, it was widely assumed that glucocorticoids (GCs) work solely through changes in gene expression to exert their physiological actions, a process that normally takes several hours to occur. However, recent evidence indicates that GCs might also act at the membrane through specific receptors to exert multiple rapid effects on various tissues and cells. GCs modulate hormone secretion, neuronal excitability, behavior, cell morphology, carbohydrate metabolism and other processes within seconds or minutes. These early actions occur independent of the genome and are transduced by the same biochemical effector pathways responsible for mediating rapid responses to neurotransmitters. The biological significance of most rapid GC effects are not well understood, but many might be related to the important functions that this hormone plays in modulating stress responses.

Dynamic exercise discloses different time-related responses in stress hormones

OBJECTIVE

Responses to stressful events are generally regarded as reactions of the organism to accommodate to or compensate for stress. This reaction is classically described as an activation of the sympathoadrenal system and the hypothalamic-pituitary-adrenocortical (HPA) axis. Activation of the release of growth hormone and prolactin in blood also occurs during various types of stress. Assuming that the stress response is a neuroendocrine mechanism that occurs in anticipation of physical exercise, we investigated whether an incremental exercise protocol can be used as a model stressor to disclose a distinct pattern of activation in these hormonal systems, which would support the notion that these systems have different roles in preparing the organism for physical activity and recovery. Moreover, such a model may help improve our understanding of the endocrine expressions of psychological stress.

METHODS

After an overnight fast, 8 healthy men (age, 19-26 years) cycled at 40, 60, 80, and 100% of the power output at VO2max in successive time blocks of 10 minutes each up to exhaustion. Venous blood was sampled immediately before exercise, at the end of each block, and during the recovery phase 5 and 30 minutes after exercise. Plasma adrenalin and noradrenalin were measured by high-performance liquid chromatography; plasma adrenocorticotropic hormone, beta-endorphin, cortisol, growth hormone, and prolactin were measured by specific immunoassays. Heart rate and levels of blood lactate and adrenalin were measured as markers of workload-related responses.

RESULTS

Results showed that increases in heart rate, lactate, adrenalin, noradrenalin, and growth hormone reflected the relative workload, in contrast to increases in adrenocorticotropic hormone, beta endorphin, and prolactin, which were observed only after exercise reached an intensity of 80% VO2max. Increases in cortisol were found just after exhaustion. The delayed response of cortisol may be initiated by a drop in blood glucose levels but may also be considered preparatory to vigorous muscular effort and protective against tissue damage.

CONCLUSIONS

Measurement of the cumulative response to exercise shows that activation of stress hormones occurs at different time points, supporting the notion that these hormones have different roles in preparing the organism for physical activity and recovery: ie, workload- and effort-related adaptation on one hand and protection against disturbed homeostasis on the other. The delayed response of the HPA axis during incremental exercise contrasts with the nondelayed HPA axis response observed during psychological stress and points to involvement of different neurobiological and cognitive emotional mechanisms.

The orthodox view of brain sexual differentiation

The standard view of sexual differentiation of the brain, derived primarily from work with mammals, is that the same steroidal signal which permanently masculinizes the body early in life, androgen, also permanently masculinizes the nervous system. This oversimplified view overlooks the rich diversity of mechanisms produced by natural selection. We review the mechanisms underlying sexual differentiation of what may be the simplest mammalian model, the spinal nucleus of the bulbocavernosus (SNB), a system that is intimately associated with sexual differentiation of the periphery. Indeed, in many instances, early androgen can permanently masculinize the SNB system but, surprisingly, these early influences may depend to some extent on social mediating factors. Furthermore, in adulthood, androgen continues to affect the SNB system in diverse ways, acting on several different loci, indicating a life-long plasticity in even this simple system. Finally, there is evidence that adult androgens interact with social experience in order to affect the SNB system. Thus the SNB system displays a far richer array of interactions than the standard view of sexual differentiation would predict. Examination of other systems and other species, as depicted in the following reports, reveals a far more complicated, and far more interesting perspective on how the brains and behaviors of males and females diverge.

A subset of kappa opioid ligands bind to the membrane glucocorticoid receptor in an amphibian brain

Previous studies demonstrated that a membrane receptor for glucocorticoids (mGR) exists in neuronal membranes from the roughskin newt (Taricha granulosa) and that this receptor appears to be a G protein-coupled receptor (GPCR). The present study investigated the question of whether this mGR recognizes nonsteroid ligands that bind to cognate receptors in the GPCR superfamily. To address this question, ligand-binding competition studies evaluated the potencies of various ligands to displace [3H]corticosterone (CORT) binding to neuronal membranes. Initial screening studies tested 21 different competitors and found that [3H]CORT binding was displaced only by dynorphin 1-13 amide (an endogenous kappa-selective opioid peptide), U50,488 (a synthetic kappa-specific agonist) and naloxone (a nonselective opioid antagonist). Follow-up studies revealed that the kappa agonists bremazocine (BRE) and ethylketocyclazocine (EKC) also displaced [3H]CORT binding to neuronal membranes, but that U69,593 (a kappa specific agonist) and nor-BNI (a kappa specific antagonist) were ineffective. The Ki values measured for the opioid competitors were in the subnanomolar to low micromolar range and had the following rank-order: dynorphin > U50,488 > naloxone > BRE > EKC. Because these ligands displaced, at most, only 70% of [3H]CORT specific binding, it appears that some [3H]CORT binding sites are opioid insensitive. Kinetic analysis of [3H]CORT off-rates in the presence of U50,488 and/or CORT revealed no differences in dissociation rate constants, suggesting that there is a direct, rather than allosteric, interaction with the [3H]CORT binding site. In summary, these results are consistent with the hypothesis that the high-affinity membrane binding site for [3H] CORT is located on a kappa opioid-like receptor.

Lack of glucocorticoids attenuates the self-stimulation-induced increase in the in vivo synthesis rate of dopamine but not serotonin in the rat nucleus accumbens

Our previous study demonstrated that intracranial self-stimulation of the medial forebrain bundle can increase the in vivo synthesis turnover rate of dopamine (DA) and serotonin (5-HT) in the nucleus accumbens of adrenal-intact rats. The present study examined using microdialysis whether such increases in DA and 5-HT syntheses are influenced by adrenal hormones, which are also activated following intracranial self-stimulation. A decarboxylase inhibitor, NSD-1015, was perfused through reversed microdialysis which enabled the simultaneous measurement of 3,4-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) as an index of the in vivo turnover rate of DA and 5-HT syntheses. Adrenalectomy (ADX) attenuated significantly the self-stimulation-induced increase in dialysate levels of DOPA but not 5-HTP. Corticosterone (Cort) replacement reversed the attenuation in DOPA levels in adrenalectomized rats. The finding indicates that activation of DA synthesis in vivo in the nucleus accumbens during intracranial self-stimulation is dependent on, whereas that of 5-HT synthesis is independent of glucocorticoid modulation.

Partial purification and biochemical characterization of a membrane glucocorticoid receptor from an amphibian brain

A membrane receptor for corticosterone (mGR) in the brain of the roughskin newt (Taricha granulosa) has been previously identified. This manuscript reports the evaluation of several chromatographic resins for enrichment of the newt mGR solubilized from neuronal membranes. A protein with an apparent molecular weight of 63 kDa was purified to near homogeneity following sequential purification using ammonium sulfate fractionation, wheat germ agglutinin (WGA)-agarose chromatography, hydroxylapatite chromatography, and an immobilized ligand affinity resin (Corticosterone-Sepharose). Other studies employed a novel protein differential display strategy and a photoaffinity labeling strategy to visualize candidate receptor proteins following SDS-PAGE. Both of these techniques also identified a 63 kDa protein, agreeing with the estimation of molecular weight from the purification data. Furthermore, the use of 2D SDS-PAGE following the photolabeling procedure showed the candidate 63 kDa protein to have a pI of approximately 5.0. Taken together these data suggest that the newt mGR is an acidic glycoprotein with an apparent molecular weight of 63 kDa. Because these characteristics of newt mGR are inconsistent with the characteristics of intracellular glucocorticoid receptors, these two receptor proteins are apparently distinct.