Divergent mechanisms for trophic actions of estrogens in the brain and peripheral tissues.

17ß-estradiol (E(2)) can enhance reproductive, cognitive, and affective functions; however, the mechanisms by which E(2) has these effects need to be better understood. Pleiotrophic effects of E(2) can occur via traditional and novel actions at various forms of estrogen receptors (ERs). In the central nervous system, trophic effects of E(2) may be related to beneficial effects of hormone replacement therapy (HRT). However, in peripheral reproductive tissues, E(2)'s capacity to evoke growth can increase risk of cancers. This review focuses on investigations aimed at elucidating divergent mechanisms of steroids to promote trophic effects in the brain, independent of effects on peripheral reproductive tissues. First, actions of estrogens via ERα or ERß for peripheral growth (carcinogen-induced tumors, uterine growth) and hippocampus-dependent behaviors (affect, cognition) are described. Second, factors that influence these effects of estrogens are described (e.g. experience, timing/critical windows, non-ER mechanisms). Third, effects of estrogens at ERß related to actions of progestogens, such as 5α-pregnan-3α-ol-20-one (3α,5α-THP) are described. In summary, effects of E(2) may occur via multiple mechanisms, which may underlie favorable effects in the brain with minimal peripheral trophic effects.

Fluoxetine-induced decrements in sexual responses of female rats and hamsters are reversed by 3α,5α-THP.

INTRODUCTION: Sexual dysfunction, as a result of selective-serotonin reuptake inhibitor (SSRI) treatment among women, is relatively common and is a factor in medication compliance. The mechanisms that underlie these side-effects of SSRIs are not well-understood. SSRIs can alter activity of catabolic enzymes that are involved in progesterone's conversion to 5 α-pregnan-3 α-ol-20-one (3 α,5 α-THP). 3 α,5 α-THP plays a key role in female reproductive physiology and behavior. AIMS: This study aimed to determine whether 3 α,5 α-THP, in the midbrain ventral tegmental area (VTA) may be a potential mechanism for fluoxetine's reduction in sexual responding of female rodents. We hypothesized that if fluoxetine induces decrements in sexual responding in part through actions of 3 α,5 α-THP, then fluoxetine will inhibit sexual receptivity concomitant with reducing 3 α,5 α-THP levels, effects which can be reversed by 3 α,5 α-THP administration. METHODS: Experiment 1 investigated effects of acute systemic fluoxetine [20 mg/kg intraperitoneal (IP)] and/or 3 α,5 α-THP [500 µg, subcutaneous (SC)] administration on sexual responding of ovariectomized, hormone-primed rats. Experiment 2 examined effects of 3 α,5 α-THP administration to the midbrain VTA (100 ng) on fluoxetine-induced decrements in lordosis of ovariectomized, hormone-primed rats and hamsters. MAIN OUTCOME MEASURES: Sexual responding was determined in rats and hamsters. For rats, the percentage of times that the lordosis response occurred following mounting by a sexually-vigorous male (lordosis quotients) was utilized. For hamsters, lateral displacement, the pelvic movement that females will make to facilitate intromissions by a male hamster, was utilized. RESULTS: Fluoxetine significantly reduced lordosis, and this was reversed SC 3 α,5 α-THP. Intra-VTA 3 α,5 α-THP attenuated fluoxetine's detrimental effects on lordosis quotients and lateral displacement of rats and hamsters, respectively. CONCLUSIONS: Thus, fluoxetine's effects to disrupt female sexual responses may involve its effects on progestogens in the midbrain VTA.

6-hydroxydopamine lesions enhance progesterone-facilitated lordosis of rats and hamsters, independent of effects on motor behavior.

The Ventral Tegmental Area (VTA) is an important brain area for progesterone (P(4))'s effects to facilitate female sexual behavior of rodents. We investigated the importance of dopaminergic neurons in the VTA, and two dopaminergic projection sites, the Nucleus Accumbens (NAc), and Caudate Nucleus of the Striatum (CN), in modulating P(4)-facilitated sex and motor behavior. Ovariectomized (ovx) rats and hamsters, administered estradiol benzoate (10 microg) and P(4) (0, 50, 100, 200, or 500 microg), were tested for motor behavior in a chamber that automatically records horizontal beam breaks, and for sexual behavior in response to a sexually-experienced male. Animals were tested once a week until each P(4) dosage was received; animals then had bilateral 6-hydroxydopamine (6-OHDA) or sham lesions to the VTA, NAc, or CN and were re-tested at each P(4) dosage on subsequent weeks. Fixed brains were stained with cresyl violet and processed for dopamine transporter (DAT) immunoreactivity. The number of cresyl violet stained cells was significantly lower in all 6-OHDA infusion sites compared to non-6-OHDA infusion sites of rats and hamsters. Also, in rats, the number of DAT-immunoreactive neurons was lower in all 6-OHDA infusion sites compared to non-6-OHDA infusion sites. In rats, 6-OHDA but not sham, lesions to the VTA, NAc, or CN produced P(4)-dependent increases in lordosis quotients and resulted in modest increases in motor behavior. In hamsters, 6-OHDA, but not sham, lesions to the VTA, NAc, or CN produced P(4)-dependent increases in total lordosis durations and produced modest decreases in motor behavior. This suggests that the dopaminergic output neurons of midbrain VTA may play an important role in modulation of P(4)-facilitated sexual lordosis among rodents.

Increasing 3alpha,5alpha-THP following inhibition of neurosteroid biosynthesis in the ventral tegmental area reinstates anti-anxiety, social, and sexual behavior of naturally receptive rats.

The progesterone metabolite and neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), has actions in the midbrain ventral tegmental area (VTA) to modulate lordosis, but its effects on other reproductively relevant behaviors are not well understood. Effects on exploration, anxiety, and social behavior resulting from inhibition of 3alpha,5alpha-THP formation, as well as 3alpha,5alpha-THP enhancement, were investigated in the midbrain VTA. Naturally sexually receptive, female rats (n=8-10/group) received infusions aimed at the midbrain VTA of vehicle, PK11195 (an inhibitor of neurosteroidogenesis), and/or indomethacin (an inhibitor of 3alpha,5alpha-THP formation from prohormones), and were subsequently infused with vehicle or FGIN 1-27 (a neurosteroidogenesis enhancer). The rats were then assessed in a behavioral battery that examined exploration (open field), anxiety (elevated plus maze), social (social interaction), and sexual (paced mating) behavior. Inhibition of 3alpha,5alpha-THP formation decreased exploratory, anti-anxiety, social, and sexual behavior, as well as midbrain 3alpha,5alpha-THP levels. Infusions of FGIN 1-27 following 3alpha,5alpha-THP inhibition restored these behaviors and midbrain 3alpha,5alpha-THP levels to those commensurate with control rats that had not been administered inhibitors. These findings suggest that 3alpha,5alpha-THP formation in the midbrain VTA may influence appetitive, as well as consummatory, aspects of mating behavior.

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.

Infusions of 3alpha,5alpha-THP to the VTA enhance exploratory, anti-anxiety, social, and sexual behavior and increase levels of 3alpha,5alpha-THP in midbrain, hippocampus, diencephalon, and cortex of female rats.

17beta-Estradiol (E2) and progesterone (P4) influence the onset and duration of sexual behavior and are also associated with changes in behaviors that may contribute to mating, such as exploration, anxiety, and social behaviors (socio-sexual behaviors). In the midbrain ventral tegmental area (VTA), the P4 metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), modulates lordosis of E2-primed rodents; 3alpha,5alpha-THP can also influence anxiety and social behaviors. To examine if 3alpha,5alpha-THP in the VTA mediates socio-sexual behaviors, we infused 3alpha,5alpha-THP to the VTA of diestrous and proestrous rats. As expected, proestrous, compared to diestrous, rats showed more exploratory (open field), anxiolytic (elevated plus maze), pro-social (partner preference, social interaction), and sexual (paced mating) behavior and had increased E2, P4, dihydroprogesterone (DHP), and 3alpha,5alpha-THP in serum, midbrain, hippocampus, diencephalon, and cortex. Infusions of 3alpha,5alpha-THP to the VTA, but not control sites, such as the substantia nigra (SN) or central grey (CG), of diestrous rats produced behavioral and endocrine effects akin to that of proestrous rats and increased DHP and 3alpha,5alpha-THP levels in midbrain, hippocampus, and diencephalon. Levels of DHP and 3alpha,5alpha-THP, but neither E2 nor P4 concentrations, in midbrain, hippocampus, diencephalon, and/or cortex were positively correlated with socio-sexual behaviors. Thus, 3alpha,5alpha-THP infusions to the VTA, but not SN or CG, can enhance socio-sexual behaviors and increase levels in midbrain, hippocampus, and diencephalon.

Engaging in paced mating, but neither exploratory, anti-anxiety, nor social behavior, increases 5alpha-reduced progestin concentrations in midbrain, hippocampus, striatum, and cortex.

Sequential actions of 17beta-estradiol (E(2)) and progesterone (P(4)) in the hypothalamus and the P(4) metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), in the midbrain ventral tegmental area (VTA) respectively mediate the initiation and intensity of lordosis of female rats and may also modulate anxiety and social behaviors, through actions in these, and/or other brain regions. Biosynthesis of E(2), P(4), and 3alpha,5alpha-THP can also occur in brain, independent of peripheral gland secretion, in response to environmental/behavioral stimuli. The extent to which engaging in tasks related to reproductive behaviors and/or mating increased E(2) or progestin concentrations in brain was investigated. In Experiment 1, proestrous rats were randomly assigned to be tested in individual tasks, including the open field, elevated plus maze, partner preference, social interaction, or no test control, in conjunction with paced mating or no mating. Engaging in paced mating, but not other behaviors, significantly increased dihydroprogesterone (DHP) and 3alpha,5alpha-THP levels in midbrain, hippocampus, striatum, and cortex. In Experiment 2, proestrous rats were tested in the combinations of the above tasks (open field and elevated plus maze, partner preference, and social interaction) with or without paced mating. As in Experiment 1, only engaging in paced mating increased DHP and 3alpha,5alpha-THP concentrations in midbrain, hippocampus, striatum, and cortex. Thus, paced mating enhances concentrations of 5alpha-reduced progestins in brain areas associated with reproduction (midbrain), as well as exploration/anxiety (hippocampus and striatum) and social behavior (cortex).

Estradiol-induced conditioned place preference may require actions at estrogen receptors in the nucleus accumbens.

Intrinsic rewarding effects of estradiol (E(2)) may underlie some of the sex differences that emerge postpuberty for the prevalence of drug use and behavioral responses to drugs, but the effects and mechanisms of E(2) for reward have not been well characterized. Conditioned place preference (CPP), as measured by the time spent on the nonpreferred/drug-associated side of the chamber, was utilized as a functional assay to investigate the effects and mechanisms of E(2) in the nucleus accumbens for reward. To determine whether intracellular estrogen receptors (ERs) are important for E(2)-induced CPP, rats were administered E(2) (10 microg; subcutaneously (s.c.)), which produced CPP in each experiment, and/or ER blockers, such as tamoxifen (Experiment 1), ICI 182,780 (Experiment 2), or antisense oligonucleotides targeted to ERs (Experiment 3). Experiment 1: E(2) significantly increased the time spent on the originally nonpreferred side of the chamber. Coadministration of tamoxifen (10 mg/kg; s.c.) attenuated effects of E(2) to produce a CPP, but tamoxifen alone, increased time spent on the nonpreferred side. Experiment 2: coadministration of ICI 182,780 (10 microg/microl) to the nucleus accumbens attenuated effects of E(2) to enhance CPP and did not produce a CPP when administered alone. Experiment 3: coadministration of s.c. E(2) with ER antisense oligonucleotides to the nucleus accumbens significantly decreased time spent on the nonpreferred side and expression of ERs in the nucleus accumbens compared to scrambled antisense oligonucleotides or saline vehicle administration. Thus, E(2)'s rewarding effects may involve actions at ERs in the nucleus accumbens.

Progestin concentrations are increased following paced mating in midbrain, hippocampus, diencephalon, and cortex of rats in behavioral estrus, but only in midbrain of diestrous rats.

BACKGROUND: The progesterone (P(4)) metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), acts in the midbrain ventral tegmental area (VTA) to modulate the intensity and duration of lordosis. 3alpha,5alpha-THP can also have anti-anxiety and anti-stress effects in part through actions in the hippocampus. Separate reports indicate that manipulating 3alpha,5alpha-THP levels in the VTA or hippocampus respectively can influence lordosis and affective behavior. 3alpha,5alpha-THP levels can also be altered by behavioral experiences, such as mating or swim stress. Whether endogenous levels of 3alpha,5alpha-THP modulate and/or are increased in response to affective and/or reproductively-relevant behaviors was investigated. METHODS: In Experiment 1, rats in behavioral estrus or diestrus were individually tested sequentially in the open field, elevated plus maze, partner preference, social interaction, and paced mating tasks and levels of 17beta-estradiol (E(2)), P(4), dihydroprogesterone (DHP), and 3alpha,5alpha-THP in serum, midbrain, hippocampus, diencephalon, and cortex were examined. In Experiments 2 and 3, rats in behavioral estrus or diestrus, were individually tested in the battery indicated above, with, or without, paced mating and tissues were collected immediately after testing for later assessment of endocrine measures. RESULTS: In Experiment 1, behavioral estrous, compared to diestrous, rats demonstrated more exploratory, anti-anxiety, social, and reproductive behaviors, and had higher levels of E(2) and progestins in serum, midbrain, hippocampus, diencephalon, and cortex. In Experiment 2, in midbrain and hippocampus, levels of 3alpha,5alpha-THP and its precursor DHP were increased among rats in behavioral estrus that were mated. In diencephalon, and cortex, DHP levels were increased by mating. In Experiment 3, in midbrain, levels of 3alpha,5alpha-THP and its precursor DHP were increased among diestrous rats that were tested in the behavioral battery with mating as compared to those tested in the behavioral battery without mating. CONCLUSIONS: Increased levels of 3alpha,5alpha-THP in behavioral estrus versus diestrous rats are associated with enhanced exploratory, anti-anxiety, social, and reproductive behaviors. Rats in behavioral estrus that are mated have further increases in 3alpha,5alpha-THP and/or DHP levels in midbrain, hippocampus, diencephalon, and cortex than do non-mated rats in behavioral estrus, whereas diestrous rats only show 3alpha,5alpha-THP increases in midbrain in response to behavioral testing that included mating.

Ovarian steroids enhance object recognition in naturally cycling and ovariectomized, hormone-primed rats.

Learning and memory processes may be influenced by fluctuations in steroid hormones, such as estrogens and progestins. In this study, we have used an animal model to investigate the effects of endogenous fluctuations in ovarian steroids in intact female rats and effects of administration of ovarian steroids to ovariectomized rats for non-spatial, working memory using the object recognition task. Performance in this task relies on cortical and hippocampal function. As such, serum, cortical, and hippocampal concentrations of estradiol (E2), progesterone (P4), and P4's metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), were measured by radioimmunoassay. Experiment 1: Rats in behavioral estrus, compared to those in diestrus or estrus, spent a greater percentage of time exploring a novel object concomitant with increases in serum E2, P4, and 3alpha,5alpha-THP levels. Regression analyses revealed that there was a significant positive relationship between E2 levels in the hippocampus and 3alpha,5alpha-THP levels in the hippocampus and cortex and performance in this task. Experiment 2: Administration of E2 and/or P4 immediately post-training increased the percentage of time spent exploring the novel object and produced levels of E2, P4, and 3alpha,5alpha-THP akin to that of rats in behavioral estrus. Experiment 3: Post-training administration of selective estrogen receptor modulators, including 17beta-E2, propyl pyrazole triol, and diarylpropionitrile increased the percentage of time spent exploring the novel object compared to vehicle-administration. Experiment 4: Post-training P4 or 3alpha,5alpha-THP administration, compared to vehicle, increased the percentage of time spent exploring the novel object and produced P4 and/or 3alpha,5alpha-THP levels within the physiological range typically observed for rats in behavioral estrus. Experiment 5: If post-training administration of E2 and/or P4 was delayed one hour, no enhancement in object recognition was observed. Together, these results suggest that E2 and progestins can have mnemonic effects through actions in the cortex and/or hippocampus.

Early postnatal stimulation alters pregnane neurosteroids in the hippocampus.

RATIONALE: The progesterone metabolite 5alpha-pregnane-3alpha-ol-20-one (3alpha,5alpha-THP) is an important modulator of the hypothalamic-pituitary-adrenal axis and stress-induced corticosterone response. Typically, 3alpha,5alpha-THP levels are increased in response to acute stress, which may then reduce corticosterone release from the adrenals. Early postnatal stimulation is a developmental stressor that can produce pervasive endocrine effects. OBJECTIVES: The present studies investigated the effects of early postnatal stimulation on plasma progestin and corticosterone levels and hippocampal progestin levels of rats. METHODS: On postnatal days 9 and 10, rats were either left in their home cage undisturbed or injected intraperitoneally as a means of early stimulation (ES). Tissues were collected on either postnatal day 10 (6 h after last handling experience) or adulthood. Plasma corticosterone, progesterone, and 3alpha,5alpha-THP and hippocampal progesterone and 3alpha,5alpha-THP were measured by radioimmunoassay. RESULTS: On postnatal day 10, plasma, but not hippocampal, levels of progesterone and 3alpha,5alpha-THP were significantly lower among rats exposed to ES than control rats. These effects occurred concomitant with a tendency for plasma corticosterone to be higher among ES compared to control rats. In adulthood, hippocampal 3alpha,5alpha-THP was significantly lower among ES vs control rats. CONCLUSIONS: Together, these data suggest that ES may influence immediate secretion of 3alpha,5alpha-THP and corticosterone and have pervasive effects in adulthood on the biosynthesis and/or metabolism of progestins in the hippocampus.

Administration of estrogen to ovariectomized rats promotes conditioned place preference and produces moderate levels of estrogen in the nucleus accumbens.

Estrogen (E2) can modulate a variety of functional processes, including conditioning. However, the precise relationship between E2 and these processes is not entirely understood. Indeed, the nature of E2's effects on conditioning may depend upon several factors, including, but not limited to, the task examined, route of E2 administration, bioavailability of E2 administered, and/or duration of E2 exposure. The present studies examined the effects of E2 on conditioned place preference (CPP), and E2 levels produced in plasma and the nucleus accumbens. In Experiment 1, ovariectomized, Long-Evans rats were subcutaneously (SC) administered sesame oil vehicle (n = 12), 10 microg (n = 12), or 1 mg (n = 10), E2 immediately prior to placement in the CPP apparatus on conditioning days. Only rats administered 10 microg E2 exhibited a CPP. This regimen of E2 (n = 5/group) also produced moderate levels of E2 in the nucleus accumbens (significantly greater than vehicle and less than 1 mg E2). In Experiment 2, ovariectomized rats were SC administered propylene glycol vehicle (n = 11), 10 microg (n = 13), or 1 mg (n = 14), E2 immediately prior to conditioning. Administration of 1 mg E2 in propylene glycol produced a CPP. Notably, 1 mg E2 in propylene glycol produced moderate levels of E2 in the nucleus accumbens (significantly greater than vehicle or 10 microg E2) that were similar to those produced by 10 microg E2 in sesame oil (n = 5/group). Together, these data suggest that regimen of E2 that can produce a CPP result in moderate levels of E2 in the nucleus accumbens.

ERbeta-selective SERMs produce mnemonic-enhancing effects in the inhibitory avoidance and water maze tasks.

Estradiol (17beta-E2) can have mnemonic-enhancing effects; however, its mechanisms for these effects are not well-understood. The present studies examined effects of 17beta-E2 and selective estrogen receptor modulators (SERMs) on emotional and spatial memory of female, Long-Evans rats. First, whether or not 17beta-E2 has dose-dependent effects on inhibitory avoidance memory was investigated. Only the highest concentration of 17beta-E2 examined (10 microg), which produces physiological concentrations of E2, was effective at enhancing inhibitory avoidance memory (Experiment 1). Further studies were designed to elucidate whether SERMs may produce mnemonic effects similar to those of 17beta-E2. Compounds utilized were, the ERalpha-selective SERMs, propyl pyrazole triol (PPT) or 17alpha-E2, the ERbeta-specific SERMs, diarylpropionitrile (DPN) or 7,12-dihydrocoumestan (coumestrol), or vehicle (oil). Post-training administration of 10 microg 17beta-E2 or coumestrol enhanced memory in the inhibitory avoidance task compared to vehicle (Experiment 2). Memory in the water maze was enhanced by post-training administration of 17beta-E2, coumestrol, or DPN, compared to vehicle (Experiment 3). Co-administration of 17alpha-E2&DPN enhanced inhibitory avoidance memory similar to that seen following 17beta-E2 or coumestrol (Experiment 4). Administration of E2 2 h post-training was not effective at enhancing memory in the inhibitory avoidance or water maze tasks (Experiment 5). Lordosis of rats was enhanced by 17beta-E2, 17alpha-E2, or PPT, compared to vehicle (Experiment 6). These data suggest that: E2's actions at ERbeta, rather than ERalpha, may enhance spatial memory, E2's actions at ERalpha can facilitate sexual behavior, and that E2's actions involving both ERalpha and ERbeta may be important for emotional memory.

Estrogen-priming can enhance progesterone's anti-seizure effects in part by increasing hippocampal levels of allopregnanolone.

Estrogen can be proconvulsant, while progesterone and its metabolite allopregnanolone typically have anti-seizure effects. We investigated whether estrogen-priming also has anti-seizure effects by altering progesterone's metabolism to allopregnanolone, or levels of brain-derived neurotrophic factor (BDNF), in the hippocampus. Two experiments investigated effects of different estrogen-priming regimen (Experiment 1--10 microg; Experiment 2--2 microg) on pentylenetetrazole (PTZ)-induced seizures and levels of estrogen, progesterone and allopregnanolone in plasma and hippocampus. In Experiment 1, ovariectomized (ovx) rats were administered sesame oil vehicle or 10 microg 17beta-estrogen at hour 0. Forty-four hours later, progesterone (500 microg; s.c.) or vehicle was administered. At hour 47, PTZ (70 mg/kg i.p.) was administered. For Experiment 2, a similar protocol was used except that ovx rats were administered vehicle or 2 microg 17beta-estradiol at hours 0 and 24. Progesterone, alone or in conjunction with either 10 or 2 microg estrogen-priming, tended to increase the latency to, and significantly reduced the number of, tonic seizures and elevated levels of progestins in hippocampus and plasma. Two, but not 10, micrograms of estrogen alone had anti-seizure effects and increased levels of allopregnanolone in the hippocampus. BDNF levels in the hippocampus were increased by estrogen-priming, but reduced by progesterone administration. Thus, estrogen may have anti-seizure effects by enhancing formation of allopregnanolone.

Ketogenic diet decreases circulating concentrations of neuroactive steroids of female rats.

Ketogenic diet (KD) is used to manage intractable epilepsy; however, the mechanisms underlying its therapeutic effects are not known. Steroid hormones, such as progesterone and testosterone, are derived from cholesterol, and are readily 5alpha-reduced to dihydroprogesterone and dihydrotestosterone, which are subsequently converted to 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) and 3alpha-androstanediol, neuroactive steroids that can influence seizures. The present study examined the effects of the KD on circulating concentrations of these neuroactive steroids, and their precursors, in intact female rats. Thirty-six, 22-day-old female Sprague-Dawley rats (weaned at 21 days) were fasted for 8 hours prior to placement on one of three dietary regimens for 6 weeks: ad libitum chow, calorie-restricted chow, or KD. After 6 weeks of the diet, when six rats in each dietary condition were in diestrus and six were in behavioral estrus, all rats were administered pentylenetetrazole (PTZ, 70 mg/kg, i.p.). The latency and incidence of seizures were recorded by an observer who was uninformed of the estrous cycle and dietary treatment conditions of the rats. Immediately after each test, trunk blood was obtained for later measurement of pregnane (progesterone, dihydroprogesterone, 3alpha,5alpha-THP) and androstane (testosterone, dihydrotestosterone, 3alpha-androstanediol) neuroactive steroid concentrations in plasma by radioimmunoassay. KD tended to lengthen the latency to, and significantly reduced the number of, PTZ-induced barrel roll seizures. KD also significantly reduced plasma levels of the pregnane (dihydroprogesterone, 3alpha,5alpha-THP) and androstane (dihydrotestosterone, 3alpha-androstanediol) 5alpha-reduced metabolites. These data suggest that levels of pregnane and androstane neuroactive steroids, or their precursors, may underlie some of the antiseizure effects of KD.

Actions at GABA(A) receptors in the hippocampus may mediate some antiseizure effects of progestins.

Progestins can have antiseizure effects; however, the mechanisms and sites of action of these effects are not well-understood. Whether progesterone's actions at GABA(A) receptors in the hippocampus are important for its antiseizure effects was investigated. In Experiment 1, ovariectomized rats were administered sesame oil vehicle or a regimen of progesterone (500 microg sc, which produces physiological concentrations in plasma and the hippocampus), followed 2.5 hours later by administration of saline vehicle or a regimen of bicuculline (1 mg/kg, sc), a GABA(A) receptor antagonist, which does not produce any intrinsic effects on seizures. Progesterone, compared with vehicle, significantly increased the latency to, and decreased the number of, pentylenetetrazole-induced tonic seizures and increased GABA-stimulated chloride flux. Co-administration of bicuculline attenuated progesterone's antiseizure effects and decreased GABA-stimulated chloride flux in the hippocampus. Bicuculline did not alter ictal behavior compared with vehicle. In Experiment 2, ovariectomized rats were subcutaneously administered sesame oil or progesterone (500 microg), followed 2.5 hours later by bilateral infusions of bicuculline (100 ng) or vehicle (saline) into the hippocampus. Infusion of bicuculline into the hippocampus of progesterone-primed rats significantly increased ictal activity, compared with that induced by progesterone administration alone, but alone did not alter seizures compared with that produced by saline infusions into the hippocampus. These data suggest that actions of progesterone at GABA(A) receptors in the hippocampus are important for progesterone's antiseizure effects.

Progesterone's 5 alpha-reduced metabolite, 3 alpha,5 alpha-THP, mediates lateral displacement of hamsters.

5 alpha-Pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP), progesterone (P4)'s 5 alpha-reduced, 3 alpha-hydroxysteroid oxidoreduced product, facilitates lordosis of rodents in part via agonist-like actions at GABA(A)/benzodiazepine receptor complexes in the ventral tegmental area (VTA). Whether 3 alpha,5 alpha-THP influences another reproductively-relevant behavior, lateral displacement, of hamsters was investigated. Lateral displacement is the movement that female hamsters make with their perineum towards male-like tactile stimulation. This behavior facilitates, and is essential for, successful mating. Hamsters in behavioral estrus had greater lateral displacement responses when endogenous progestin levels were elevated compared to when progestin levels were lower. Administration of P4, a prohormone for 3 alpha,5 alpha-THP, dose-dependently (500 > 200 > 100, 50, or 0 microg) enhanced lateral displacement of ovariectomized hamsters that had been primed with SC estradiol benzoate (5 or 10 microg). Inhibiting P4's metabolism to 3 alpha,5 alpha-THP by co-administering finasteride, a 5 alpha-reductase inhibitor, or indomethacin, a 3 alpha-hydroxysteroid oxidoreductase inhibitor, either systemically or to the VTA, significantly decreased lateral displacement and midbrain progestin levels of naturally receptive or hormone-primed hamsters compared to controls. These data suggest that lateral displacement is progestin-sensitive and requires the formation of 3 alpha,5 alpha-THP in the midbrain VTA.

Attenuating 5alpha-pregnane-3alpha-ol-20-one formation in the hippocampus of female rats increases pentylenetetrazole-induced seizures.

Progesterone has antiseizure effects, which may be due to the actions of its 5alpha-reduced metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). Whether metabolism of progesterone to 3alpha,5alpha-THP in the hippocampus is essential for its antiseizure effects was investigated. In Experiment 1, ovariectomized rats were administered subcutaneous progesterone (500 microg) or vehicle (sesame oil), followed 1 hour later by subcutaneous administration of an inhibitor of the 5alpha-reductase enzyme, finasteride (50 mg/kg), or vehicle (90% sesame oil, 10% ethanol). Administration of progesterone increased the latency to, and decreased the number of, tonic seizures and increased hippocampal 3alpha,5alpha-THP levels, compared with vehicle. Administration of finasteride with progesterone attenuated progesterone's antiseizure effects and decreased levels of 3alpha,5alpha-THP in the hippocampus. Finasteride administration alone did not alter ictal behavior or 3alpha,5alpha-THP levels compared with vehicle. In Experiment 2, ovariectomized rats were administered subcutaneous progesterone (500 microg) or vehicle (sesame oil), followed 1 hour later by bilateral infusions of finasteride (10 microg) or vehicle (beta-cyclodextran) into the hippocampus. Administration of finasteride to the hippocampus of progesterone-primed rats significantly increased ictal activity and decreased hippocampal 3alpha,5alpha-THP levels, compared with progesterone administration alone. These data suggest that formation of 3alpha,5alpha-THP in the hippocampus is important for progesterone's antiseizure effects.

Estradiol to aged female or male mice improves learning in inhibitory avoidance and water maze tasks.

Although 17beta-Estradiol (E2) improves cognitive performance of aged female mice, its mnemonic effects when administered post-training to aged male mice have not been examined. E2 (10 microg, SC) or oil vehicle was administered to intact, 24-month-old female or male congenic (primarily C57BL/6 background) mice immediately after training in the inhibitory avoidance or water maze tasks. Following behavioral testing, effects of 1 or 24 h of E2 exposure on hippocampal levels of E2 and brain-derived neurotrophic factor (BDNF) were examined. Female and male mice administered E2 showed significantly better performance in the inhibitory avoidance task than did vehicle-administered mice. When tested 24 h after training, mice that received E2 had significantly longer latencies to cross-over to the shock-associated side of the chamber than did vehicle-administered mice. Female or male mice administered E2 showed significantly better performance in the reference memory aspect of the spatial water maze task. When tested 30 min after training, mice administered E2 had shorter latencies to, and spent longer swimming in, the quadrant that the hidden platform had previously been located in. E2 administration produced physiological levels of E2 in the hippocampus 1 and 24 h after E2. BDNF levels in the hippocampus were decreased following 1 h of E2 exposure compared to vehicle. These findings suggest that E2 to female and male mice may overcome age-related deficits in reference memory in an emotional or spatial learning task.

Progestins in the hippocampus of female rats have antiseizure effects in a pentylenetetrazole seizure model.

PURPOSE: Progestins can have profound effects on seizure processes. However, the effects and mechanisms of progestins to modulate seizures have not been systematically investigated. The present studies were designed to characterize the effects of progestins to modulate pentylenetetrazole (PTZ)-induced seizures in female rats. METHODS: In Experiment 1, ictal activity and plasma and hippocampal progesterone (P) and 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) levels of proestrous rats were compared with those of diestrous and ovariectomized (ovx) rats. Experiments 2 and 3 examined effects of ovx and replacement with vehicle, P, or 3alpha,5alpha-THP, systemically (Experiment 2) or to the hippocampus (Experiment 3) on seizures and plasma and hippocampal P and 3alpha,5alpha-THP concentrations. RESULTS: Proestrous rats had reduced ictal activity and increased levels of P and 3alpha,5alpha-THP in plasma and hippocampus compared with diestrous or ovx rats (Experiment 1). Rats administered systemic P or 3alpha,5alpha-THP had significantly reduced ictal activity and increased plasma and hippocampal P and 3alpha,5alpha-THP levels compared with vehicle-administered rats (Experiment 2). Administration of P or 3alpha,5alpha-THP to the hippocampus of ovx rats significantly reduced seizure activity and increased hippocampal, but not plasma, levels of P and 3alpha,5alpha-THP compared with vehicle administration (Experiment 3). CONCLUSIONS: Together, these data suggest that P can have antiseizure effects, and these effects may be due in part to actions of its metabolite, 3alpha,5alpha-THP, in the hippocampus.