Progesterone and 3 alpha-androstanediol conjugated to bovine serum albumin affects estrous behavior when applied to the MBH and POA

Effects of non-contingent cocaine on 3 alpha-androstanediol. II. Disruption of lordosis of proestrous rats

Drug use influences sexual behavior, performance, and can be associated with increased sexual risk-taking. Our prior results using an animal model indicate that progestogens contribute to hormonally-mediated changes in sexual behavior of female rodents during acute cocaine exposure. Androgens, such as testosterone, and its metabolite 3ɑ-androstanediol (3α-diol), and estradiol, are known to influence male sexual behavior, but can also alter the expression of sexual behavior of female rodents. As such, we investigated the influence of endogenous androgen and estradiol fluctuations on cocaine-mediated changes in motor behavior and sexual receptivity of rats during diestrous or proestrous phases of the estrous cycle. Female rats were administered saline or cocaine (5, 10, or 20mg/kg, i.p.). Motor behavior was observed in the first 30min following drug administration, and then sexual responding was assessed for 15min. Cocaine decreased aggressive behavior in response to attempted mounts by a male among non-receptive (diestrous) rats and inhibited sexual behavior among sexually receptive (proestrous) rats. Cocaine dose-dependently altered concentrations of testosterone metabolites (estradiol and 3α-diol), but not testosterone, which correlated to motor and sexual behaviors of diestrous and proestrous rats, respectively. These data suggest that actions of 3α-diol may be involved in female sexual and motor behavior in response to cocaine, in a cycle-dependent manner.

3alpha-androstanediol, but not testosterone, attenuates age-related decrements in cognitive, anxiety, and depressive behavior of male rats

Some hippocampally-influenced affective and/or cognitive processes decline with aging. The role of androgens in this process is of interest. Testosterone (T) is aromatized to estrogen, and reduced to dihydrotestosterone (DHT), which is converted to 5α-androstane, 3α, 17α-diol (3α-diol). To determine the extent to which some age-related decline in hippocampally-influenced behaviors may be due to androgens, we examined the effects of variation in androgen levels due to age, gonadectomy, and androgen replacement on cognitive (inhibitory avoidance, Morris water maze) and affective (defensive freezing, forced swim) behavior among young (4 months), middle-aged (13 months), and aged (24 months) male rats. Plasma and hippocampal levels of androgens were determined. In experiment 1, comparisons were made between 4-, 13-, and 24-month-old rats that were intact or gonadectomized (GDX) and administered a T-filled or empty silastic capsule. There was age-related decline in performance of the inhibitory avoidance, water maze, defensive freezing, and forced swim tasks, and hippocampal 3α-diol levels. Chronic, long-term (1–4 weeks) T-replacement reversed the effects of GDX in 4- and 13-month-old, but not 24-month-old, rats in the inhibitory avoidance task. Experiments 2 and 3 assessed whether acute subcutaneous T or 3α-diol, respectively, could reverse age-associated decline in performance. 3α-diol, but not T, compared to vehicle, improved performance in the inhibitory avoidance, water maze, forced swim, and defensive freezing tasks, irrespective of age. Thus, age is associated with a decrease in 3α-diol production and 3α-diol administration reinstates cognitive and affective performance of aged male rats.

Activation of progestin receptors in female reproductive behavior: Interactions with neurotransmitters

The steroid hormone, progesterone (P), modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and reproductive behavior in female mammals. A wide body of evidence indicates that these neural effects of P are predominantly mediated via their intracellular progestin receptors (PRs) functioning as "ligand-dependent" transcription factors in the steroid-sensitive neurons regulating genes and genomic networks. In addition to P, intracellular PRs can be activated by neurotransmitters, growth factors and cyclic nucleotides in a ligand-independent manner via crosstalk and convergence of pathways. Furthermore, recent studies indicate that rapid signaling events associated with membrane PRs and/or extra-nuclear, cytoplasmic PRs converge with classical PR activated pathways in neuroendocrine regulation of female reproductive behavior. The molecular mechanisms, by which multiple signaling pathways converge on PRs to modulate PR-dependent female reproductive behavior, are discussed in this review.

Oxytocin and/or steroid hormone binding globulin infused into the ventral tegmental area modulates progestogen-mediated lordosis

Estradiol (E(2)) and progesterone (P(4)) have classical, steroid receptor-mediated actions in the ventral medial hypothalamus to initiate lordosis of female rodents. P(4) and the P(4) metabolite and neurosteroid, 5 alpha-pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP), have non-classical actions in the midbrain ventral tegmental area (VTA) to modulate lordosis. We investigated the role of steroid hormone binding globulin (SHBG) and oxytocin in the VTA as mechanisms for these effects. Rats were ovariectomized and surgically implanted with bilateral guide cannulae aimed at the VTA. Rats were E(2)-primed (10 microg/0.2 ml) at hour 0, and administered 100 (Experiments 1 and 2), 500 (Experiment 3), or 0 (Experiment 1 and 4) microg/0.2 ml P(4) at hour 44. At hour 47.5, rats received bilateral infusions to the VTA, and were tested for lordosis 30 min post-infusion. Experiment 1: rats were infused with sterile saline vehicle or SHBG (4.5 pg/microl) to the VTA. SHBG, compared to vehicle, to the midbrain VTA significantly increased lordosis in E(2)- and P(4)-primed, but not E(2)-primed, rats. Experiment 2: rats were infused with bilateral infusions of sterile saline or oxytocin (1.0 pg/microl). Compared to vehicle, oxytocin to the VTA increased lordosis. Experiment 3: rats were administered bilateral intra-VTA infusions of saline or an oxytocin receptor antagonist, d(CH(2))(5),[TYr(ME)(2),Thr(4),Tyr-NH(9,2)] (1.2 pg/microl). Compared to vehicle, the oxytocin receptor antagonist to the VTA attenuated lordosis of E(2)- and P(4)-primed rats. Experiment 4: rats were E(2)-primed and infused with vehicle, oxytocin, or oxytocin antagonist. There were no effects of these manipulations in E(2)-primed rats. Thus, SHBG and/or oxytocin may have actions in the VTA for progestogen-facilitated lordosis.

Infusions of bicuculline to the ventral tegmental area attenuates sexual, exploratory, and anti-anxiety behavior of proestrous rats

Actions of 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), in the midbrain ventral tegmental area (VTA) modulate sexual receptivity of female rats. Actions of 3alpha,5alpha-THP at GABAergic substrates in the VTA are known to modulate consummatory aspects of sexual behavior among rodents, such as lordosis. However, the extent to which GABA(A) receptors in the VTA are important for appetitive (exploratory, anti-anxiety, social) aspects of sexual receptivity is not well-understood. Proestrous rats were bilaterally-infused with saline or bicuculline (100 ng), a GABA(A) receptor antagonist, to the VTA or missed control sites. Rats were assessed for exploratory/anti-anxiety (open field/elevated plus maze), social (social interaction), and sexual (paced-mating) behavior. Compared to saline or missed site controls, intra-VTA bicuculline significantly reduced the number of central entries in an open field, time spent on the open arms of an elevated plus maze, frequency and intensity of lordosis, anti-aggression towards a male, pacing of sexual contacts, and 3alpha,5alpha-THP concentrations in midbrain and hippocampus. Bicuculline-infused rats also displayed less affiliation with a novel conspecific, fewer sexual solicitations, and had lower 3alpha,5alpha-THP concentrations in diencephalon and cortex, albeit these were not significant differences. Thus, actions at GABA(A) receptors in the midbrain VTA are essential for appetitive and consummatory aspects of sexual receptivity among rats.

Hormonal influences on seizures: basic neurobiology

There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.

Androgens with activity at estrogen receptor beta have anxiolytic and cognitive-enhancing effects in male rats and mice

Testosterone (T) and its metabolites may underlie some beneficial effects for anxiety and cognition, but the mechanisms for these effects are unclear. T is reduced to dihydrotestosterone (DHT), which can be converted to 5alpha-androstane,3alpha,17beta-diol (3alpha-diol) and/or 5alpha-androstane-3beta,17beta-diol (3beta-diol). Additionally, T can be converted to androstenedione, and then to androsterone. These metabolites bind with varying affinity to androgen receptors (ARs; T and DHT), estrogen receptors (ERbeta; 3alpha-diol, 3beta-diol), or GABA(A)/benzodiazepine receptors (GBRs; 3alpha-diol, androsterone). Three experiments were performed to investigate the hypothesis that reduced anxiety-like and enhanced cognitive performance may be due in part to actions of T metabolites at ERbeta. Experiment 1: Gonadectomized (GDX) wildtype and ERbeta knockout mice (betaERKO) were subcutaneously (SC) administered 3alpha-diol, 3beta-diol, androsterone, or oil vehicle at weekly intervals, and tested in anxiety tasks (open field, elevated plus maze, light-dark transition) or for cognitive performance in the object recognition task. Experiment 2: GDX rats were administered SC 3alpha-diol, 3beta-diol, androsterone, or oil vehicle, and tested in the same tasks. Experiment 3: GDX rats were androsterone- or vehicle-primed and administered an antagonist of ARs (flutamide), ERs (tamoxifen), or GBRs (flumazenil), or vehicle and then tested in the elevated plus maze. Both rats and wildtype mice, but not betaERKO mice, consistently had reduced anxiety and improved performance in the object recognition task. Androsterone was only effective at reducing anxiety-like behavior in the elevated plus maze and this effect was modestly reduced by flumazenil administration. Thus, actions at ERbeta may be required for T's anxiety-reducing and cognitive-enhancing effects.

Exploratory, anti-anxiety, social, and sexual behaviors of rats in behavioral estrus is attenuated with inhibition of 3alpha,5alpha-THP formation in the midbrain ventral tegmental area

The progesterone (P(4)) metabolite and neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) acts in the midbrain ventral tegmental area (VTA) to modulate lordosis of female rats. 3alpha,5alpha-THP also mediates exploratory, affective, and social behaviors; whether actions of 3alpha,5alpha-THP in the VTA mediate these behaviors is of interest. To elucidate the role of the VTA in mediating exploratory, affective, and social behaviors, the present study examined effects of inhibiting 3alpha,5alpha-THP formation in the VTA. Rats received intra-VTA infusions of either PK11195 (400ng/mul, which inhibits de novo 3alpha,5alpha-THP production), indomethacin (10mug/mul, which blocks metabolism of P(4) to 3alpha,5alpha-THP), PK11195 and indomethacin together, or beta-cyclodextrin vehicle and tested on a battery of anxiety (open field and elevated plus maze), social (partner preference and social interaction), and sexual (paced mating) tasks. Compared to rats infused with vehicle to the VTA, rats infused with inhibitor(s) demonstrated significant reductions in central entries in the open field, time on open arms of an elevated plus maze, time spent interacting with a conspecific, initiation and intensity of lordosis, sexual solicitations, and midbrain 3alpha,5alpha-THP levels. These findings suggest that actions of 3alpha,5alpha-THP in the VTA are important for mediating aspects of exploration, anxiety, and social behavior related to mating.

Non-genomic actions of androgens

Previous work in the endocrine and neuroendocrine fields has viewed the androgen receptor (AR) as a transcription factor activated by testosterone or one of its many metabolites. The bound AR acts as transcription regulatory element by binding to specific DNA response elements in target gene promoters, causing activation or repression of transcription and subsequently protein synthesis. Over the past two decades evidence at the cellular and organismal level has accumulated to implicate rapid responses to androgens, dependent or independent of the AR. Androgen's rapid time course of action; its effects in the absence or inhibition of the cellular machinery necessary for transcription/translation; and in the absence of translocation to the nucleus suggest a method of androgen action not initially dependent on genomic mechanisms (i.e. non-genomic in nature). In the present paper, the non-genomic effects of androgens are reviewed, along with a discussion of the possible role non-genomic androgen actions have on animal physiology and behavior.

Androgen administration to aged male mice increases anti-anxiety behavior and enhances cognitive performance

Although androgen secretion is reduced with aging, and may underlie decrements in cognitive and affective performance, the effects and mechanisms of androgens to mediate these behaviors are not well understood. Testosterone (T), the primary male androgen, is aromatized to estrogen (E(2)), and reduced to dihydrotestosterone (DHT), which is converted to 5alpha-androstane, 3alpha, 17beta-diol (3alpha-diol). To ascertain whether actions of the neuroactive metabolite of T, 3alpha-diol, mediates cognitive and affective behaviors, intact, aged male C57/B6 mice (24 month old) as well as young, intact and gonadectomized (GDX; 12 week old) mice were administered s.c. T, 3alpha-diol, E(2), or sesame oil vehicle (1 mg/kg; n=4-5/group) at weekly intervals and 1 h later mice were tested in the activity box, roto-rod, open field, elevated plus maze, zero maze, mirror maze, dark-light transition, forced swim, or Vogel tasks. Mice were trained in the inhibitory avoidance or conditioned contextual fear and were administered hormones following training and then were tested. After the last test occasion, tissues were collected for evaluation of hormone levels and effects on gamma-aminobutyric acid (GABA)-stimulated chloride flux. T, 3alpha-diol, or E(2) increased anti-anxiety and antidepressant behavior of aged, intact mice in the open field, light-dark transition, mirror maze, and forced swim tasks. T or 3alpha-diol, but not E(2), enhanced anti-anxiety behavior in the elevated plus maze, zero maze, and the Vogel task, and increased motor behavior in the activity monitor, latency to fall in the Roto-rod task, and cognitive performance in the hippocampally-mediated, but not the amygdala-mediated, portion of the conditioned fear task and in the inhibitory avoidance task. Anti-anxiety and enhanced cognitive performance was associated with regimen that increased plasma and hippocampal 3alpha-diol levels and GABA-stimulated chloride flux. Similar patterns were seen among young, adult GDX but not in intact mice. Thus, 3alpha-diol can enhance affective and cognitive behavior of male mice.

Steroid modulation of GABAA receptor-mediated transmission in the hypothalamus: effects on reproductive function

The hypothalamus, the seat of neuroendocrine control, is exquisitely sensitive to gonadal steroids. For decades it has been known that androgens, estrogens and progestins, acting through nuclear hormone receptors, elicit both organizational and activational effects in the hypothalamus and basal forebrain that are essential for reproductive function. While changes in gene expression mediated by these classical hormone pathways are paramount in governing both sexual differentiation and the neural control of reproduction, it is also clear that steroids impart critical control of neuroendocrine functions through non-genomic mechanisms. Specifically, endogenous neurosteroid derivatives of deoxycorticosterone, progesterone and testosterone, as well and synthetic anabolic androgenic steroids that are self-administered as drugs of abuse, elicit acute effects via allosteric modulation of gamma-aminobutyric acid type A receptors. GABAergic transmission within the hypothalamus and basal forebrain is a key regulator of pubertal onset, the expression of sexual behaviors, pregnancy and parturition. Summarized here are the known actions of steroid modulators on GABAergic transmission within the hypothalamus/basal forebrain, with a focus on the medial preoptic area and the supraoptic/paraventricular nuclei that are known to be central players in the control of reproduction.

MK-801 infusions to the ventral tegmental area and ventromedial hypothalamus produce opposite effects on lordosis of hormone-primed rats

Progesterone initiates female sexual behavior of rodents (lordosis) through actions at intracellular progestin receptors in the ventromedial hypothalamus. Progesterone's metabolite, 5alpha-pregnan-3alpha-ol-20-one, mediates the intensity and duration of lordosis through its actions at GABA(A) receptors in the ventral tegmental area. Whether progestins can influence sexual behavior through actions that involve N-methyl-D-aspartate receptors (NMDARs) in the ventromedial hypothalamus and ventral tegmental area was investigated. The current study examines the effect of bilateral ventral tegmental area or ventromedial hypothalamus infusions of the non-competitive NMDAR antagonist (+)-MK-801 hydrogen maleate (MK-801; 0, 20, or 200 ng) on lordosis, motor activity, and NMDA R1 subtype (NMDAR1) immunoreactivity in estradiol benzoate (10 microg)+progesterone (50 microg)- and estradiol benzoate+vehicle primed rats. Compared to vehicle infusions, infusions of MK-801 to the ventral tegmental area facilitated lordosis of estradiol benzoate (10 microg)+progesterone (50 microg)- and estradiol benzoate+vehicle primed rats. Infusions of MK-801 to the ventromedial hypothalamus inhibited lordosis of estradiol benzoate (10 microg)+progesterone (50 microg)- and estradiol benzoate+vehicle primed rats, compared to vehicle. There was no effect of MK-801 infusions to the ventral tegmental area or the ventromedial hypothalamus on motor behavior. Immunocytochemistry for NMDAR1 revealed MK-801 (200 ng) infusions to the ventral tegmental area or ventromedial hypothalamus of estradiol benzoate (10 microg)+progesterone (50 microg)- or estradiol benzoate+vehicle primed rats significantly reduced the number of darkly stained NMDAR1-immunoreactive cells, compared to vehicle infusions. These data suggest NMDARs may be important in the mediation of hormonal actions in both the ventral tegmental area and the ventromedial hypothalamus for sexual receptivity of rodents, but in different ways.

Some rewarding effects of androgens may be mediated by actions of its 5alpha-reduced metabolite 3alpha-androstanediol

The abuse of anabolic-androgenic steroids (AS) is a growing problem; however, the effects and mechanisms underlying their addictive effects are not well understood. Research findings regarding androgen abuse in people and hedonic effects of androgens in laboratory rats are reviewed. Androgens, like other steroids, can have traditional actions via cognate intracellular steroid receptors, as well as other substrates. Our recent results indicate that testosterone (T) metabolites may have actions in part via gamma-aminobutyric acid (GABA)(A)/benzodiazepine receptor complexes (GBRs) and/or dopaminergic neurons in the nucleus accumbens, to mediate T's positive hedonic states. This may provide the basis for positive reinforcing effects of androgen seeking and use behavior. Following a comprehensive review of the background literature, our findings are presented that have explored the extent to which metabolites of T mediate euphorogenic effects of androgens by acting in the nucleus accumbens. Then results regarding whether GBRs are necessary substrates for androgens' positive hedonic effects are discussed. Lastly, research that addresses if dopaminergic neurons in the nucleus accumbens are necessary for these effects of androgens are discussed. This review provides a comprehensive examination of the hedonic properties and abuse/addiction potential of androgens and the putative mechanisms underlying these effects.

Progesterone's effects to reduce anxiety behavior of aged mice do not require actions via intracellular progestin receptors

RATIONALE

Aging is associated with reduced secretion of, and down-regulation of receptors for, progesterone (P); yet, P's effects when administered to younger and older animals have not been systematically investigated. Some of P's antianxiety effects may be due to its conversion to 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) and its subsequent actions as a positive modulator at GABAA receptor complexes (GBRs).

OBJECTIVES

We investigated whether P administration can decrease anxiety behavior of progestin receptor (PR) knockout (PRKO) or wild-type control mice.

METHODS

P (10 mg/kg) or vehicle (propylene glycol) were administered subcutaneously to intact, female or male wild-type or PRKO mice that were either 9-12 or 18-24 months of age. Behavior in tasks that assess spontaneous activity (activity monitor and roto-rod), free exploration of a novel environment (open field, elevated plus maze, and elevated zero maze), and conflict behavior (mirror chamber, dark-light transition, and punished drinking) were examined 1 h after injection.

RESULTS

P significantly decreased anxiety behavior of both PRKO and wild-type mice. P did not alter motor behavior but increased central entries in the open field, time in the open quadrants of the elevated zero maze, time in the mirrored chamber, time in the light compartment of the dark-light transition, and punished drinking in young and old mice. P-administered mice had higher levels of hippocampal 3alpha,5alpha-THP and GABA-stimulated chloride flux than did vehicle-administered PRKO or wild-type mice.

CONCLUSIONS

The effects of P to decrease anxiety behavior of younger and older mice do not require classic PRs and may involve actions of 3alpha,5alpha-THP at GBRs.

Lordosis of rats is modified by neurosteroidogenic effects of membrane benzodiazepine receptors in the ventral tegmental area

Progestins modulate lordosis through actions in the ventral tegmental area (VTA). Whether neurosteroidogenesis of 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), involving mitochondrial benzodiazepine receptors (MBR), is important for lordosis was investigated. Ovariectomized (Ovx), hormone-primed rats (experiments 1, 3, 5, 6) and rats in behavioral estrus (experiments 2 and 4) were unilaterally infused via chronic guide cannula to the VTA with a MBR agonist, N,N-dihexyl-2-(4-fluorophenyl) indole-30-acetamide (FGIN 1-27) or antagonist 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboximide (PK-11195). Experiment 1: Estradiol benzoate (EB)-primed (25 microg) rats administered 0 or 25 microg progesterone (P4) SC showed increased lordosis when infused with 5.0 microg FGIN 1-27 to the VTA; those administered 100 or 200 microg P4 SC exhibited greater lordosis when infused with 2.5 or 5.0 microg FGIN, relative to saline-infused rats. Experiment 2: Rats, near the termination of behavioral estrus, infused with 2.5 or 5.0 microg of FGIN 1-27 to the VTA, showed increased lordosis compared to that seen following vehicle administration. Experiment 3: EB-primed rats administered 200 or 500 microg P4 SC showed decreased lordosis when infused with 100, 200, or 400 ng PK-11195, relative to saline-infused rats. Experiment 4: Rats infused at the peak of behavioral estrus with 100, 200, or 400 ng PK-11195 to the VTA exhibited reduced lordosis compared to that seen following vehicle administration. Experiment 5: 3alpha,5alpha-THP (100 ng) infusions to the VTA reinstated lordosis of hormone-primed rats infused with PK-11195 (100 ng) to the VTA. Experiment 6: FGIN 1-27 (5.0 microg) and PK-11195 (100 ng) infusions aimed at the VTA respectively increased and decreased midbrain levels of 3alpha,5alpha-THP compared to vehicle. Notably, the specific effects observed with infusions to the VTA were not seen with infusions to the control site, the substantia nigra. These data suggest that neurosteroidogenesis involving MBRs in the VTA mediates lordosis of hormone-primed or behavioral estrous rats.

The nucleus accumbens as a site of action for rewarding properties of testosterone and its 5alpha-reduced metabolites

Testosterone (T)'s positive hedonic effects may be mediated by actions of its metabolites, dihydrotestosterone (DHT) or 3alpha-androstanediol (3alpha-diol), in the nucleus accumbens (NA). In Experiment 1, adult, intact, male rats were systemically administered 1 mg of T, DHT, 3alpha-diol or vehicle, at different time points to examine concentrations of androgens in the NA. Rats administered 3alpha-diol had significantly increased concentrations of 3alpha-diol in the region of the brain encompassing the NA. These data are consistent with previous data from our laboratory demonstrating that 3alpha-diol elicits a conditioned place preference (CPP) more effectively than either T or DHT, when administered systemically. In Experiment 2, rats received implants of T, DHT or 3alpha-diol to the NA immediately prior to placement in the CPP apparatus on conditioning days. Implants of T, DHT or 3alpha-diol, but not vehicle, significantly increased time spent on the non-preferred side of the chamber on the test day. This effect was only produced by androgenic stimulation of the shell of the NA and not the core of the NA. Thus, androgen regimens we have previously found to enhance CPP produced the greatest increases in 3alpha-diol concentrations in the NA region and direct implants of T, DHT or 3alpha-diol to the shell, but not the core, of the NA enhanced CPP. These data are consistent with the hypothesis that the hedonic effects of T may be due to actions of its metabolites in the NA.

Prenatal stress alters reproductive responses of rats in behavioral estrus and paced mating of hormone-primed rats

Adult female offspring of dams exposed to gestational stress (prenatal stress, PNS) may show altered reproductive behavior, exploration in novel environments, and/or social interactions than do their non-PNS counterparts. These behavioral differences may be more readily observed in a seminatural, paced mating paradigm, in which females have greater control of their sexual contacts, than in a standard mating situation. Adult offspring of dams exposed to restraint and lights for 45 min on Gestational Days 14-20 (PNS) were compared with those not subjected to stress (non-PNS, control condition). The motor, reproductive, and sociosexual behaviors of hormone-primed (Experiment 1) or cycling adult offspring in behavioral estrus (Experiment 2) were examined following 20 min of restraint stress under bright lights (postnatal stress). Hormone-primed PNS rats displayed less motor behavior in a novel arena than did non-PNS rats. In a standard mating test, hormone-primed PNS females tended to be more aggressive toward the male than were non-PNS rats. In a seminatural mating situation, hormone-primed PNS females showed increased avoidance behavior, such as longer latencies to the initial intromission, greater return latencies following mounts and intromissions, and more exiting subsequent to mounts and intromissions, than did non-PNS rats. PNS rats in behavioral estrus had decreased incidence and intensity of lordosis, and fewer solicitation behaviors, in both standard or paced mating situations, in which latency to and number of mounts were also increased. Thus, hormone-primed PNS rats exposed to restraint showed more avoidance behaviors in paced mating situations, while cycling PNS rats in behavioral estrus had greater disruption of reproductive responses in standard or paced mating paradigms than did non-PNS control rats.

Sex hormone binding globulin facilitates female sexual receptivity except when coupled to dihydrotestosterone

Sex hormone binding globulin (SHBG) is produced in brain where it is often co-localized with oxytocin. Infusions of SHBG into the medial preoptic area-anterior hypothalamus facilitate female sexual receptivity. SHBG has receptors on plasma membranes of the prostate gland where binding of the 5alpha-reduced androgen dihydrotestosterone (DHT) by SHBG acts as an antagonist on SHBG receptors. This study attempted to determine whether pre-coupling DHT to SHBG would inhibit SHBG-induced facilitation of female sexual receptivity. Ovariectomized rats were injected daily with 0.75 microg estradiol benzoate for 3 days. On the fourth day after a pre-infusion baseline behavioral test animals were infused with 1 microl per side through bilateral cannulae with SHBG (1.77x10(-6) M), SHBG coupled to DHT (SHBG-DHT; 1.66x10(-6) M DHT), with DHT alone or with artificial cerebrospinal fluid vehicle. As before, SHBG significantly increased female sexual receptivity when infused into the medial preoptic area-anterior hypothalamus. Rats infused with SHBG-DHT had significantly lower sexual receptivity. Therefore, whereas SHBG in the medial preoptic area facilitated female sexual behavior, SHBG coupled to DHT did not. DHT itself did not significantly affect sexual receptivity. Pre-coupling DHT to SHBG eliminated the facilitative effect of SHBG on female sexual receptivity just as DHT inhibits SHBG activity at prostate SHBG receptors suggesting that central receptors for SHBG are similar to those demonstrated in the periphery.

Prenatal stress produces deficits in socio-sexual behavior of cycling, but not hormone-primed, Long-Evans rats

Prenatal stress (PNS) alters behavior of adult offspring in novel environments or in social interactions; variable effects of PNS on female reproductive behavior have been reported. Effects of exposure to restraint and lights for 45 min/day on Gestational Days 14-20 were examined on the motor and socio-sexual behavior of adult female offspring. In a novel arena, proestrous PNS rats displayed greater behavioral inhibition as indicated by significantly fewer beam breaks made in the horizontal crossing task compared to that of proestrous non-PNS rats. In a standard mating test, in which females are exposed to males in a relatively small space for a restricted time or number of sexual contacts, PNS females in proestrus were found to have significant decreases in the intensity of lordosis and in the number of solicitation behaviors that they directed towards the male compared to non-PNS rats. In a seminatural mating test, in which females can control the timing of the sexual contacts from the male, PNS females in proestrus engaged in significantly less pacing of their sexual contacts compared to that of the non-PNS females. When additional PNS and non-PNS rats were ovariectomized (ovx) and tested following hormone priming, behavioral differences were abrogated. PNS decreased motor behavior in a novel arena, lordosis intensity, and solicitation behavior in a standard mating paradigm, as well as adaptive, approach-avoidance behavior in a seminatural mating situation of endogenously cycling proestrous rats but not ovx, hormone-primed rats. Thus, hormone priming may override or mask effects of PNS on some aspects of socio-sexual behavior.

Testosterone increases analgesia, anxiolysis, and cognitive performance of male rats

Preliminary evidence suggests that testosterone (T) may have anxiety-reducing and cognitive-enhancing properties in animals and people. Performance in a number of affective and cognitive behavioral tasks was examined in intact, T-depleted, and T-depleted and T-replaced male rats. Rats that were gonadally intact (n = 33), gonadectomized (GDX; n = 30), or GDX with silastic capsules of T implanted (n = 28) were tested through a battery of affective tasks (horizontal crossing, open field, elevated plus-maze, emergence, holeboard, social interaction, tailflick, pawlick, and defensive burying) and in the inhibitory avoidance task for cognitive performance. An additional 6 rats per group had plasma androgen concentrations measured and were determined to be physiological for intact rats, supraphysiological for T-implanted rats, and near the nadir for GDX rats. Testosterone implants produced analgesia as shown by the increased tailflick latencies of the GDX rats with silastic capsules of T implanted, relative to intact or GDX rats. Testosterone also produced anxiolysis. Intact rats spent more time interacting with a conspecific and less time burying an electrified prod than did the GDX or T-implanted rats. Intact rats or GDX rats with T implants also spent more time on the open arms of the elevated plus-maze than did GDX rats. Testosterone also enhanced cognitive performance in the inhibitory avoidance task. Intact rats had longer crossover latencies in the inhibitory avoidance task relative to GDX rats; GDX rats with T implants had longer crossover latencies relative to GDX or intact rats. Together, these data demonstrate that endogenous T or administration of T produced analgesia and enhanced affect and cognitive performance of adult male rats.

The role of neurosteroids and non-genomic effects of progestins and androgens in mediating sexual receptivity of rodents

Progestins and androgens modulate sexual receptivity in rodents, in part through mechanisms independent of traditional intracellular steroid receptors. Progesterone (PROG) in the ventromedial hypothalamus (VMH) and ventral tegmental (VTA) facilitates lordosis but has different actions in these brain areas. Primarily using lordosis in rodents as an in vivo experimental model, we have examined the effects that progestins exert in the midbrain and hypothalamus. Localization and blocker studies indicate that PROG's actions in the VMH require intracellular progestin receptors (PRs) but in the VTA they do not. Progestins that have rapid, membrane effects, and/or are devoid of affinity for PRs, facilitate lordosis when applied to the VTA. Manipulation of GABA and/or GABA(A)/benzodiazepine receptor complexes (GBRs) in the VTA alters lordosis, which suggests that progestins may interact with GBRs to facilitate receptivity by enhancing the function of GABAergic neurons. Interfering with PROG's metabolism to, or the biosynthesis of, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG or allopregnanolone), the most effective endogenous GBR agonist, in the VTA attenuates female sexual behavior in rodents. Stimulation of mitochondrial benzodiazepine receptors (MBRs), which enhances neurosteroid production, by infusions of an MBR agonist to the VTA enhances lordosis. 3alpha,5alpha-TH PROG is increased in the midbrain of mated>proestrous>diestrous rodents. These data suggest that in the VTA, PROG may facilitate lordosis following metabolism to and/or biosynthesis of 3alpha,5alpha-TH PROG, which may have subsequent actions at GBRs and/or MBRs to acutely modulate female sexual behavior in rodents. The 3alpha-hydroxysteroid oxidoreduced metabolite of dihydrotestosterone (DHT), 5alpha-androstane-3alpha,17beta-diol (3alpha-androstanediol), is important for termination of sexual receptivity in rodents and has these effects in the absence of functional intracellular androgens receptors. As well, altering GBR function in the hypothalamus can influence 3alpha-androstanediol's inhibition of sexual receptivity. Through actions in the hypothalamus that are independent of intracellular androgen receptors but involving GBRs, 3alpha-androstanediol inhibits lordosis. These findings suggest that the PROG metabolite and pregnane neurosteroid, 3alpha,5alpha-TH PROG, and the testosterone metabolite and androstane neurosteroid, 3alpha-androstanediol, can have proximate influences on lordosis that is via nonclassical actions at intracellular steroid receptors.

The testosterone metabolite and neurosteroid 3alpha-androstanediol may mediate the effects of testosterone on conditioned place preference

Testosterone (T) and pregnane neurosteroids can enhance conditioned place preference (CPP). The present experiment examined CPP produced by T and its androgenic metabolite dihydrotestosterone (DHT) and 3alpha-Androstanediol (3alpha-diol; an androstane neurosteroid). Administration of 3alpha-diol (>DHT>T) to intact male Long-Evans rats, 1.0 mg daily for six days, 30 min prior to exposure to the non-preferred side of the CPP chamber significantly increased preference for the non-preferred side of the chamber compared to that seen in home cage controls. Levels of circulating 3alpha-diol were increased significantly in 3alpha-diol>DHT>T-administered rats, compared to rats that had vehicle administered or androgen-administration discontinued. Androgen administration decreased seminal vesicle weight and intrahypothalamic androgen receptor (AR) binding compared to that seen in rats that had vehicle administered or androgen-administration discontinued. Testosterone, DHT, and 3alpha-diol decreased GABA-stimulated chloride influx in cortical synaptoneurosomes, and muscimol binding in the hippocampus compared to that seen in rats with vehicle administered or that had androgen-administration discontinued. These data indicate that administration of 3alpha-diol is more effective at enhancing CPP and increasing circulating 3alpha-diol levels than is DHT or T administration, and that all of the androgen regimens employed decreased peripheral and hypothalamic androgen receptor binding and cortical and hippocampal GABA(A) receptor function. Hence, whether the effects of 3 alpha-diol on CPP are mediated by differential actions at ARs or GABA(A) receptors in particular brain regions needs to be determined.

Posttraining androgens' enhancement of cognitive performance is temporally distinct from androgens' increases in affective behavior

Steroid hormone-induced variations in spatial learning and memory tasks have been reported. In this study, androgens' effects in various cognitive and affective tasks were investigated in order to determine whether any observed differences in cognitive performance could be due to affective changes produced by the hormones. Ovariectomized rats (N = 72) received 0.0, 3.0, or 7.5 mg/kg subcutaneously, of testosterone (T), dihydrotestosterone (DHT), or 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-Diol) suspended in 10% ethanol/sesame oil v/v. For the cognitive tasks (Y maze, inhibitory avoidance, and object recognition), subjects were injected after training trials. For the affective tasks (open field, elevated plus maze, and tailflick), subjects were injected 1 or 24 h before testing. Posttraining injections that produced physiological concentrations of androgens--T, DHT, and 3 alpha-Diol--1 h later increased the percentage of correct choices in the Y maze, the latencies to cross to the shock-associated side of the inhibitory avoidance chamber, and percentage of time exploring novel objects 24 h later, when androgen levels were no longer increased. Administration of T, DHT, and 3 alpha-Diol also increased the number of entries into the center squares of a brightly lit open field, open-arm time in the elevated plus maze, and tailflick latencies 1 but not 24 h following administration. These findings suggest that these androgens, when administered following training, can enhance cognitive performance in the tasks investigated 24 h later when androgen levels nadir, but overt changes in the affective behaviors examined occurred at the time of physiological concentrations 1 h but not 24 h following androgen administration. These findings suggest posttraining androgens can enhance consolidation and cognitive performance, independent of their anxiolytic actions.

Deficits in progesterone-facilitated sexual behaviors and forebrain estrogen and progestin receptors in obese female Zucker rats

Obese female Zucker rats (fa/fa) are sterile. Among their reproductive abnormalities is hyporesponsiveness to the stimulatory effects of ovarian steroid hormones on sexual behaviors. This study was designed to test the hypothesis that obese Zucker females are deficient in hypothalamic/preoptic area estrogen receptors (ERs) and/or estradiol-induced progestin receptors (PRs). Ovariectomized (OVX) lean and obese Zucker rats were tested for the display of sexual behaviors following injection of estradiol benzoate (EB, 15 or 100 microg/kg) plus progesterone (P, 2 mg/kg). As expected, obese females showed significantly lower lordosis quotients and lordosis ratings than lean animals after injection of the lower, physiological dose of EB followed by P. In contrast, obese and lean females receiving the higher EB dose, prior to P, showed similar levels of sexual receptivity. Two weeks later, these OVX lean and obese females received injections of vehicle, 15 or 100 microg/kg EB, prior to perfusion and tissue processing for PR immunocytochemistry (ICC). Additional groups of OVX virgin females of both genotypes were perfused and tissue from the preoptic area and hypothalamus was processed for ER alpha ICC. No genotypic differences in the number of cells containing ER alpha-immunoreactivity (-IR) in the medial preoptic area (MPOA), ventromedial hypothalamus (VMH) or arcuate nucleus (ARC) were noted, but obese females had significantly fewer ER alpha-IR cells in the anteroventral periventricular nucleus (AVPV) than lean rats. In both genotypes, the number of PR-IR cells in the AVPV, MPOA and VMH was significantly higher following injection of EB (either dose) as compared to vehicle, demonstrating estradiol induction of PRs. Only in the MPOA was there a significant difference between fat and lean females in estradiol-induced PR-IR. Obese females receiving 15 microg/kg EB had fewer PR-IR cells in the MPOA than comparably-treated lean animals. No such genotypic difference was observed following injection of the vehicle or higher dose (100 microg/kg) of EB. These data are consistent with the hypothesis that deficiencies in ER alpha in the AVPV and/or PRs in the MPOA may contribute to obese Zucker females' poor responsiveness to ovarian steroid hormones.

Anti-sense oligonucleotides, for progestin receptors in the VMH and glutamic acid decarboxylase in the VTA, attenuate progesterone-induced lordosis in hamsters and rats

Immunocytochemical (ICC) staining for progesterone (P) receptors (PRs) and glutamic acid decarboxylase (GAD), the enzyme responsible for GABA production, reveal that there are many PRs in the ventral medial hypothalamus (VMH) and many GAD containing neurons in the ventral tegmental area (VTA). To investigate P's action on lordosis in the VMH and VTA, anti-sense oligos specific to PRs and GAD(65&67) were intracerebrally infused into the VMH and VTA of 24 ovariectomized hamsters and 40 ovariectomized rats. Estradiol benzoate (2 microg) primed hamsters and rats were infused to the VMH and the VTA with either PR (250 ng/1.0 microl infusion) or GAD (500 ng/1.0 microl infusion) anti-sense oligos, their scramble controls, or saline vehicle at hour 0 and again at hour 24. At hr 44, rodents were subcutaneously injected with P (500 microg) and were tested for sexual receptivity with a male 4 h later. There were significant reductions in lordosis of hamsters and rats following PR anti-sense infusions to the VMH compared to scrambled or vehicle control infusions. Effects of PR anti-sense to the VMH were not different from combined VMH and VTA PR anti-sense infusions; however, VMH infusions reduced lordosis compared to VTA-only anti-sense infusions. GAD anti-sense infusions reduced lordosis when infused into the VTA, compared to scrambled or saline vehicle infusions. Lordosis responsiveness following VTA GAD anti-sense infusions was not different from combined VMH and VTA infusions, but VTA infusions of GAD anti-sense reduced lordosis compared to VMH-only anti-sense infusions. These data suggest that in the VMH, PRs are important for P-facilitated lordosis, whereas in the VTA, GABAergic neurons may be an important substrate for mediating P's actions on lordosis of rodents.

Androgens are neuroprotective in the dentate gyrus of adrenalectomized female rats

Neuroprotective effects of androgens have not been well-characterized, but there is evidence that 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) has anti-seizure effects. To further examine androgens' neuroprotective effects, testosterone (T), dihydrotestosterone (DHT), 3 alpha-diol (1.0 mg/kg SC daily), or sesame oil vehicle was administered to adrenalectomized or sham-operated, young, female Long Evans rats (N = 52). After seven days, animals were perfused and trunk blood was collected for radioimmunoassay of plasma corticosterone and androgens. No pyknotic cells were seen in the dentate of the sham-operated animals or those animals that had incomplete adrenalectomies (n = 20); however, cresyl violet and TUNEL stains revealed pyknotic cells in the granule layer of the dentate gyrus of adrenalectomized rats (n = 28). Testosterone, DHT, or 3 alpha-diol significantly reduced the number of pyknotic cells in the dentate gyrus compared to vehicle administered, adrenalectomized rats. Steroid-administered animals had levels of T, DHT, or 3 alpha-diol within physiological concentrations. These findings suggest that T, DHT, or 3 alpha-diol may have neuroprotective effects via a common mechanism of action.

Metabolism of androgens in rat pituitary gland and hypothalamus: catabolism of dihydrotestosterone or transformation of androgen signal?

The role of androgen metabolism and individual androgen metabolites in rat pituitary gland and hypothalamus is discussed on the basis of published data and results of our experiments. It is proposed that metabolism of androgens in these structures is aimed at the formation of not only true sex steroids estradiol-17 beta and 5 alpha-dihydrotestosterone, but also of androgens contributing to the regulation of cell processes, i.e. represents modification (transformation) of androgen signal (testosterone) in target pituitary and hypothalamic cells.

The neurosteroid, 3alpha-androstanediol, prevents inhibitory avoidance deficits and pyknotic cells in the granule layer of the dentate gyrus induced by adrenalectomy in rats

Testosterone (T), dihydrotestosterone (DHT), 3alpha-diol (5alpha-androstane-3alpha,17beta-diol), or vehicle was administered daily to gonadectomized, adrenalectomized male Long-Evans rats. Four days after adrenalectomy (ADX), animals were tested for inhibitory avoidance. Vehicle-treated rats had shorter latencies than 3alpha-diol-treated rats and non-corticosterone-depleted rats. All three androgens significantly reduced the number of pyknotic cells in corticosterone-depleted rats. Neurosteroids may mediate androgens' functional and morphological neuroprotective effects.

Mating stimuli influence endogenous variations in the neurosteroids 3alpha,5alpha-THP and 3alpha-Diol

Progesterone facilitates and 5alpha-dihydrotestosterone (DHT) inhibits female sexual behaviour in rodents; their metabolites, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) and 5alpha-androstane-3alpha-17beta-Diol (3alpha-Diol), may influence the onset and termination of lordosis. Changes in these and related steroids in hormonal states associated with differences in receptivity were investigated. Rats were assigned to oestrus, metoestrus, dioestrus, pro-oestrus, mated, gestational days 5-7, 12-14, 18-20, or post-partum conditions; rats 9+ months of age were considered older. Pro-oestrus rats were exposed to the mating arena, sight and smell of a male with no tactile contact, artificial vaginocervical stimulation, standard mating, or no mating. Progesterone, 5alpha-pregnane-3,20-dione, 3alpha,5alpha-THP, oestradiol, testosterone, DHT, 3alpha-Diol, dehydroepiandrosterone, and corticosterone were measured in plasma and whole brain, midbrain, hypothalamus, cortex, amygdala, hippocampus. 3alpha,5alpha-THP and 3alpha-Diol changed with reproductive state and mating stimuli. Plasma and whole brain 3alpha,5alpha-THP and 3alpha-Diol were significantly increased in pro-oestrus versus dioestrus rats; plasma 3alpha,5alpha-THP was decreased and 3alpha-Diol increased in mated versus pro-oestrus rats. The midbrain and hypothalamus had the most evident changes in 3alpha,5alpha-THP and 3alpha-Diol between dioestrus versus pro-oestrus and pro-oestrus versus mated rats. 3alpha,5alpha-THP and 3alpha-Diol were altered differently in response to mating stimuli. 3alpha,5alpha-THP was greater in the midbrain of mated versus pro-oestrus rats; other mating-relevant stimuli decreased 3alpha,5alpha-THP. Midbrain 3alpha-Diol was increased with exposure to a male <VCS< mating. 3alpha,5alpha-THP was increased and 3alpha-Diol was decreased in the hypothalamus of mated versus pro-oestrus rats; exposure to the various mating stimuli decreased 3alpha,5alpha-THP and 3alpha-Diol. The neurosteroids, 3alpha,5alpha-THP and 3alpha-Diol, vary with mating in the hypothalamus and midbrain of rats.

Progestins' rapid facilitation of lordosis when applied to the ventral tegmentum corresponds to efficacy at enhancing GABA(A)receptor activity

Progestins may have actions in the midbrain though gamma-aminobutyric acid (GABA)A/benzodiazepine receptor complexes (GBRs) that are relevant for sexual receptivity. The efficacy and time course of various progestins to enhance lordosis when applied to the ventral tegmental area (VTA), following progesterone to the ventral medial hypothalamus (VMH) was investigated. Ovariectomized, oestrogen-primed rats and hamsters with contralateral VMH/VTA cannulae were tested for lordosis before and after implants of P to the VMH and progestins to the VTA. The progestins were P, 5alpha-pregnan-3,20-dione (DHP), 5alpha-pregnan-3alpha-ol-20-one(3alpha,5alpha-TH P), 5alpha-pregnan-3alpha,21-diol-20-one (THDOC), 5beta-pregnan-3alpha-ol-20-one(3alpha,5beta-THP) , 17alpha-ol-6-methyl-4,6-pregnadiene-3,20-dione-17-acetate (megestrol acetate, MA), and 6-chloro-17-ol-4,6-pregnadiene-3, 20-dione-17-acetate (chlormadinone acetate, CA). Progestins' effects on GABA-mediated chloride influx and SR 95531 binding in cortical and midbrain tissue, respectively, were examined in rats and hamsters. 3alpha,5alpha-THP and THDOC implants to the VTA were the most effective at immediately facilitating lordosis of rats and hamsters. Two hours later all other progestins, except MA and CA, increased lordosis in rats; only P, 3alpha,5alpha-THP, and THDOC were effective in hamsters. The progestins' effectiveness at facilitating lordosis were similar to their effects on GABA-stimulated chloride influx and SR 95531 receptor binding (3alpha,5alpha-THP and THDOC>P>DHP>3alpha, 5beta-THP>MA and CA). These findings suggest that progesterone lordosis enhancing effects in the rodent VTA may be via GBRs.

Endogenous levels of 5 alpha-reduced progestins and androgens in fetal vs. adult rat brains

5 Alpha-reduced metabolites of certain steroids have been shown to have important functions in adult brains and may play a role in brain development. To assess which 5 alpha-reduced steroid metabolites may have an impact during development, endogenous levels of 5 alpha-reduced androgens and progestins and their parent hormones were measured in male and female fetal brains over the last 5 days of gestation. These levels were compared to levels measured in adult male and female brains (evaluated at different stages of the estrous cycle). Neither the brain levels of parent hormones nor of their 5 alpha-reduced metabolites varied as a function of fetal sex or of gestational age. Therefore, the data from the two sexes were combined. In fetal brains, the levels of the progesterone reduced metabolites were 20-fold higher than levels of progesterone itself whereas levels of testosterone reduced metabolites were 10-fold lower than testosterone levels. In contrast to fetal brain, conversion of progesterone to reduced metabolites was much lower in adult brain, but the level of 5 alpha-reduced androgens was 3-10-fold higher than the level of testosterone in all adult tissue, indicating more conversion of androgen to 5 alpha-reduced metabolites in adult than in fetal brains. These results imply that the reduction of progesterone to reduced metabolites may play a critical role in brain development.

Radioligand assays for oestradiol and progesterone conjugated to protein reveal evidence for a common membrane binding site in the medial preoptic area-anterior hypothalamus and differential modulation by cholera toxin and GTPgammaS

In this study membrane oestradiol (E) binding sites in the medial preoptic area-anterior hypothalamus (MPOA-AH) of ovariectomized (OVX) rats were characterized using standard radioligand binding techniques employing E conjugated to bovine serum albumin (BSA) at position 6 and radiolabeled with 125I (E-6-[125I-BSA]). In previous studies binding of a radioactive conjugate of progesterone (P) and BSA (P-3-[125I-BSA]) was examined using the same membrane preparation. E-6-[125I-BSA] binding was linear across a tissue concentration range of 0.005-0.02 mg protein/0.1 ml of membrane suspension. An association T1/2 of 9.5 min and a dissociation T1/2 of 52.1 min for E-6-[125I-BSA] were derived from kinetic experiments. Competition binding experiments revealed high (Ki=0.63+/-(0.50 nM) and low (Ki=161.5(96.5 nM) affinity binding sites for E-6-[125I-BSA], demonstrating different binding parameters than shown in our previous work for P-3-[125I-BSA] binding. Further studies on MPOA-AH membranes treated with cholera toxin (CTX) and GTPgammaS suggested that E-6-BSA binding sites are associated with G proteins. E-6-[125I-BSA] binding demonstrated both high-and low-affinity sites. GTPgammaS added to the assay reduced both E-6-[125I-BSA] and P-3-[125I-BSA] binding suggesting that G proteins are associated with both binding sites. Extensive analysis of both E-6-[125I-BSA] and P-3-[125I-BSA] binding sites demonstrated a reciprocal relationship such that high-affinity E-6-[125I-BSA] binding sites exhibit low affinity for P-3-[125I-BSA] and low-affinity E-6-[125I-BSA] binding sites exhibit high affinity for P-3-[125I-BSA]. Preincubating membranes with CTX or GTPgammaS reduced high-affinity E-6-[125I-BSA] binding and enhanced high-affinity P-3-[125I-BSA] binding. These results suggest that, in the MPOA-AH, membrane steroid binding sites exist in two interconvertible conformations that preferentially bind either E-6-BSA or P-3-BSA, depending on their association with a G protein. Additional studies with free steroids revealed that: (1) oestrogens (17beta-oestradiol, diethylstilbestrol) as well as synthetic oestrogen antagonists tamoxifen and ICI 182 780 displaced P-3-[125I-BSA] further suggesting a relationship between membrane binding sites for E and P-3-[125I-BSA] binding sites; and (2) treatment of OVX rats with E decreased displacement by P-3-BSA and increased displacement by ICI 182,780 and tamoxifen suggesting these antagonists affect membrane P-3-[125I-BSA] binding sites after in-vivo E treatment. The membrane binding sites for E and P demonstrate interrelationships not demonstrated by their nuclear receptors.

The importance of being dehydroepiandrosterone sulfate (in the blood of primates): a longer and healthier life?

The general aging sequence in tissues of healthy human beings is proposed to be: capillary endothelial cell damage --> arteriosclerosis --> decreased blood flow --> metabolic dysregulation --> secondary tissue damage. Molecular O2 is an obligatory substrate for the successive syntheses of 17alpha-OH pregnenolone and dehydroepiandrosterone (DHEA) by cytochrome P450c17 in the zona reticularis of the adrenal cortex, in which it is suggested that arteriosclerosis --> decreased blood flow --> O2 and glucose deficit --> decreased O2-requiring synthesis of DHEA --> eventual decrease in number of DHEA-synthesizing cells. Aging changes in the zona reticularis synergize with those in the hypothalamo-hypophyseal machinery that controls it neurally and hormonally, with ACTH-evoked pulsatile floods of cortisol coming from the adrenal zona fasciculata, with the onslaught of free radicals generated by the metabolism of catecholamines released from interdigitating cells of the adrenal medulla, and with age-correlated disabilities of erythrocytes to bind and release O2 to decrease the viability of the DHEA and dehydroepiandrosterone sulfate (DHEAS)-forming cells. One of the chief functions of serum DHEAS in the male may be to act as an allosteric facilitator of the binding of testosterone (T) to serum albumin, thereby helping target T to specific receptors and to allosteric sites for rapid and efficient action at the cellular level. There is reason to consider combining O2 therapy with appropriate administration of DHEA and T to optimize steroid functionality in the healthy aging male, and thus, possibly, to alleviate some of the age-related cognitive and physical decrements that occur.

Conjugated estradiol increases female sexual receptivity in response to oxytocin infused into the medial preoptic area and medial basal hypothalamus

The ovarian steroid estradiol (E) has been found to increase both receptor affinity and release of the neuropeptide oxytocin (OT) in plasma membrane preparations. Therefore, we hypothesized that E conjugated to bovine serum albumin at position 6 (E-6-BSA) would increase behavioral responsiveness to OT. Preliminary results showed that 200 ng/microl of E-6-BSA increased sexual receptivity slightly, but not significantly. Therefore, this dose was used as a subthreshold dose to test whether it would increase sexual responsiveness when infused in combination with 100 ng/microl OT. After recovery from cannula implantation surgery animals were injected with 0.5 microg E benzoate daily for 3 days before testing. On the fourth day, after a baseline preinfusion test rats were infused bilaterally with E-6-BSA alone or with OT, OT with BSA, or conjugated progesterone, luteinizing hormone-releasing hormone equimolar to OT alone, or with E-6-BSA or conjugated progesterone alone. When infused into either the medial preoptic area-anterior hypothalamus or the medial basal hypothalamus the combination of OT and E-6-BSA significantly increased sexual receptivity over receptivity after artificial cerebrospinal fluid control infusions. Neither bilateral infusions of OT in combination with conjugated progesterone nor E-6-BSA in combination with luteinizing hormone-releasing hormone enhanced sexual receptivity. Results presented here strongly support the conclusion that some of the effects that E has in sensitizing brain systems to the facilitating effects of OT occur at the membrane level in the medial preoptic area-anterior hypothalamus and medial basal hypothalamus.

Progesterone has rapid and membrane effects in the facilitation of female mouse sexual behavior

Ovariectomized (ovx) mice require both estradiol (E2) and progesterone (P) administration to reinstate feminine sexual behavior (lordosis). The importance of P's actions at E2-induced intracellular progestin receptors (PRs) to facilitate lordosis was investigated in PR knockout (PRKO) mice, PRKO's wild type littermates (C57X129), and wild type C57BL/6J (C57) mice. Subjects were ovx, E2-primed (0.5 microg) and tested following intravenous (i. v.) and intercereberal P. Intravenous P (200 microg) significantly increased lordosis of all mice within 10 min of P, but vehicle infusion did not (Experiment 1). Intravenous P significantly increased the amount and duration and reduced the latency of lordosis, over that seen with vehicle infusion, in PRKO and wild type mice. Whole brain concentrations of P and its 5alpha-reduced metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), which has low affinity for intracellular PRs, were also increased following P compared to vehicle infusion. Progesterone, but not vehicle infusions, significantly increased the number of PR-immunoreactive (PR-IR) cells in the ventromedial hypothalamus (VMH) of C57 and C57X129 mice and increased number of 3alpha, 5alpha-THP-immunoreactive (3alpha,5alpha-THP-IR) cells in the ventral tegmental area (VTA) of all mice. In Experiment 2, P conjugated to bovine serum albumin (P:BSA) increased lordosis when applied bilaterally to both the VMH and VTA of E2-primed mice more than BSA implants. Progesterone implants increased the number of PR-IR cells in the VMH of C57 and C57X129 mice and the number of 3alpha,5alpha-THP-IR cells in the VTA of all mice. The rapid facilitation of lordosis with i.v. P infusion and increases in lordosis when P's effects are relegated to the membrane in the VMH and VTA of PRKO and wild type mice suggest that P may facilitate lordosis through actions at substrates other than intracellular PRs. The present findings suggest a role of 3alpha,5alpha-THP.

Inhibition of estrogen-induced sexual receptivity by androgens: role of the androgen receptor

Both naturally occurring and synthetic androgens have been shown to inhibit estrogen-induced sexual receptivity when administered to ovariectomized (OVX) rats. The mechanisms by which androgens exert these effects, however, remain unclear. Experiments were conducted to determine the role of the androgen receptor in the inhibition of estrogen-induced sexual receptivity in OVX rats by using flutamide, an androgen receptor antagonist. In each experiment, OVX Long-Evans rats received 6 consecutive days of estradiol benzoate (EB; 2.0 microg/day) followed by 15 days of EB concurrent with flutamide (10. 0 mg/kg; twice daily) or the vehicle and one of the following androgens or the vehicle: dihydrotestosterone propionate (7.5 mg/kg), 3alpha-androstanediol (3.75 mg/kg), 17alpha-methyltestosterone (7.5 mg/kg), stanozolol (7.5 mg/kg), or nandrolone decanoate (7.5 mg/kg). On Day 15, all female rats received progesterone (P; 1.0 mg/rat) 4 h before testing. Tests for sexual receptivity were conducted on Days 3, 6, 14, and 15 of androgen/flutamide treatment. Each androgen inhibited sexual receptivity as expected, and concurrent treatment with flutamide reversed the inhibitory effects of all androgens on sexual receptivity on all test days. High levels of sexual receptivity were displayed in response to P on Day 15, regardless of experimental treatment. These results suggest that naturally occurring and synthetic androgens act at the androgen receptor to inhibit estrogen-induced sexual receptivity in OVX rats.

Androgenic neurosteroids: anti-seizure effects in an animal model of epilepsy

These studies investigate whether the neurosteroid and 5 alpha-reduced metabolite of testosterone (T), 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-Diol), has anti-seizure effects similar to its parent compound. In experiment 1, ovariectomized (ovx) Long-Evans rats (n = 20) were subcutaneously (s.c.) administered 32 mg/kg kainic acid or saline vehicle 10 min following 0.0, 3.0, or 7.5 mg/kg 3 alpha-Diol in 10% ethanol, propylene glycol vehicle (veh). During 2 h of observation of ictal activity, 3 alpha-Diol (3.0 and 7.5 mg/kg) prior to kainic acid significantly decreased the number and duration of partial and full seizures compared to the 0.0 3 alpha-Diol conditions and produced ictal activity that was comparable to 0.0 mg/kg 3 alpha-Diol no kainic acid controls (procedure controls). Animals that received 7.5 mg/kg 3 alpha-Diol prior to kainic acid had shorter latencies and distances to the hidden platform in a Morris Water Maze task than those that received 0.0 3 alpha-Diol, 1 week following ictal activity. Administration of 3 alpha-Diol (3.0 or 7.5 mg/kg) prior to kainic acid stimulation resulted in a greater number of identifiable neurons in the hilar region of the hippocampus, compared to 0.0 3 alpha-Diol condition. Experiment 2 was conducted to ascertain whether 3 alpha-Diol's anti-seizure effects were comparable to T and possibly a result of metabolism from T. Ovx rats (n = 36) were stereotaxically implanted with bipolar electrodes into the perforant pathway. One hour prior to perforant pathway stimulation, six rats were s.c. injected with either T (7.5 mg/kg), 3 alpha-Diol (7.5 mg/kg), 7.5 mg/kg T + 4MA (a 5 alpha-reductase inhibitor, 17 beta-N,N-diethylcarbamoyl-4-methyl-4aza,5 alpha-androstan-3-one), 4MA alone, 10% propylene glycol vehicle (veh) with perforant pathway stimulation, or veh without perforant pathway stimulation. 3 alpha-Diol and T produced similar seizure activity, water maze performance, and neuronal integrity in the hilar region of the hippocampus that were comparable to unstimulated controls. Because the T and 3 alpha-Diol groups were not different from T + 4MA but tended to be different from 4MA alone on these measures, this suggests that 3 alpha-Diol and T can have similar anti-seizure effects which may be due to actions of neurosteroids.