3alpha,5alpha-THP in the midbrain ventral tegmental area of rats and hamsters is increased in exogenous hormonal states associated with estrous cyclicity and sexual receptivity

Steroid Transport, Local Synthesis, and Signaling within the Brain: Roles in Neurogenesis, Neuroprotection, and Sexual Behaviors

Sex steroid hormones are synthesized from cholesterol and exert pleiotropic effects notably in the central nervous system. Pioneering studies from Baulieu and colleagues have suggested that steroids are also locally-synthesized in the brain. Such steroids, called neurosteroids, can rapidly modulate neuronal excitability and functions, brain plasticity, and behavior. Accumulating data obtained on a wide variety of species demonstrate that neurosteroidogenesis is an evolutionary conserved feature across fish, birds, and mammals. In this review, we will first document neurosteroidogenesis and steroid signaling for estrogens, progestagens, and androgens in the brain of teleost fish, birds, and mammals. We will next consider the effects of sex steroids in homeostatic and regenerative neurogenesis, in neuroprotection, and in sexual behaviors. In a last part, we will discuss the transport of steroids and lipoproteins from the periphery within the brain (and vice-versa) and document their effects on the blood-brain barrier (BBB) permeability and on neuroprotection. We will emphasize the potential interaction between lipoproteins and sex steroids, addressing the beneficial effects of steroids and lipoproteins, particularly HDL-cholesterol, against the breakdown of the BBB reported to occur during brain ischemic stroke. We will consequently highlight the potential anti-inflammatory, anti-oxidant, and neuroprotective properties of sex steroid and lipoproteins, these latest improving cholesterol and steroid ester transport within the brain after insults.

Novel receptor targets for production and action of allopregnanolone in the central nervous system: a focus on pregnane xenobiotic receptor

Neurosteroids are cholesterol-based hormones that can be produced in the brain, independent of secretion from peripheral endocrine glands, such as the gonads and adrenals. A focus in our laboratory for over 25 years has been how production of the pregnane neurosteroid, allopregnanolone, is regulated and the novel (i.e., non steroid receptor) targets for steroid action for behavior. One endpoint of interest has been lordosis, the mating posture of female rodents. Allopregnanolone is necessary and sufficient for lordosis, and the brain circuitry underlying it, such as actions in the midbrain ventral tegmental area (VTA), has been well-characterized. Published and recent findings supporting a dynamic role of allopregnanolone are included in this review. First, contributions of ovarian and adrenal sources of precursors of allopregnanolone, and the requisite enzymatic actions for de novo production in the central nervous system will be discussed. Second, how allopregnanolone produced in the brain has actions on behavioral processes that are independent of binding to steroid receptors, but instead involve rapid modulatory actions via neurotransmitter targets (e.g., γ-amino butyric acid-GABA, N-methyl-D-aspartate- NMDA) will be reviewed. Third, a recent focus on characterizing the role of a promiscuous nuclear receptor, pregnane xenobiotic receptor (PXR), involved in cholesterol metabolism and expressed in the VTA, as a target for allopregnanolone and how this relates to both actions and production of allopregnanolone will be addressed. For example, allopregnanolone can bind PXR and knocking down expression of PXR in the midbrain VTA attenuates actions of allopregnanolone via NMDA and/or GABA_A for lordosis. Our understanding of allopregnanolone’s actions in the VTA for lordosis has been extended to reveal the role of allopregnanolone for broader, clinically-relevant questions, such as neurodevelopmental processes, neuropsychiatric disorders, epilepsy, and aging.

Pregnane xenobiotic receptors and membrane progestin receptors: role in neurosteroid-mediated motivated behaviours

Progestogens have actions in the midbrain ventral tegmental area (VTA) to mediate motivated behaviours, such as those involved in reproductive processes, among female rodents. In the VTA, the formation and actions of one progestogen, 5α-pregnan-3α-ol-20-one (3α,5α-THP), are necessary and sufficient to facilitate sexual responding (measured by lordosis) of female rodents. Although 3α,5α-THP can be produced after metabolism of ovarian progesterone, 3α,5α-THP is also a neurosteroid produced de novo in brain regions, such as the VTA. There can be dynamic changes in 3α,5α-THP production associated with behavioural experience, such as mating. Questions of interest are the sources and targets of 3α,5α-THP. Regarding sources, the pregnane xenobiotic receptor (PXR) may be a novel factor involved in 3α,5α-THP metabolism in the VTA (as well as a direct target of 3α,5α-THP). We have identified PXR in the midbrain of female rats, and manipulating PXR in this region reduces 3α,5α-THP synthesis and alters lordosis, as well as affective and social behaviours. Regarding targets, recent studies have focused on the role of membrane progestin receptors (mPRs). We have analysed the expression of two of the common forms of these receptors (mPRα/paqr7 and mPRβ/paqr8) in female rats. The expression of mPRα was observed in peripheral tissues and brain areas, including the hypothalamus and midbrain. The expression of mPRβ was only observed in brain tissues and was abundant in the midbrain and hypothalamus. To our knowledge, studies of these receptors in mammalian models have been limited to expression and regulation, instead of function. One question that was addressed was the functional effects of progestogens via mPRα and mPRβ in the midbrain of hormone-primed rats for lordosis. Studies to date suggest that mPRβ may be an important target of progestogens in the VTA for lordosis. Taken together, the result of these studies demonstrate that PXR is involved in the production of 3α,5α-THP in the midbrain VTA. Moreover, mPRs may be a target for the actions of progestogens in the VTA for lordosis.

Progestogens influence cognitive processes in aging

Steroid hormones may alter mnemonic processes. The majority of investigations have focused on the effects of 17β-estradiol (E(2)) to mediate learning. However, progesterone (P(4)), which varies across endogenous hormonal milieu with E(2), may also have effects on cognitive processes. P(4) may have effects in the hippocampus, prefrontal cortex (PFC) and/or striatum to enhance cognitive performance. Cognitive performance/learning has been assessed using tasks that are mediated by the hippocampus (water maze), PFC (object recognition) and striatum (conditioning). Our findings suggest that progestogens can have pervasive effects to enhance cognitive performance and learning in tasks mediated by the hippocampus, PFC and striatum and that these effects may be in part independent of actions at intracellular progestin receptors. Progestogens may therefore influence cognitive processes.

I. Levels of 5α-reduced progesterone metabolite in the midbrain account for variability in reproductive behavior of middle-aged female rats

At middle-age, the reproductive capacity of female rats begins to decline. Whether there are consequences for social and reproductive behaviors related to changes in estradiol (E(2)), progesterone (P(4)) and its 5α-reduced metabolites, dihydroprogesterone (DHP) and 5α-pregnan-3α-ol-20-one (3α,5α-THP), is of interest. In Experiment 1, 1-year-old female breeder rats that had "maintained their reproductive status" (having 4-5 days estrous cycles, > 60% successful pregnancies after mating, > 10 pups/litter) or their age-matched counterparts with "declining reproductive status" were assessed in social interaction, standard mating, and paced mating when in proestrus. Rats that maintained reproductive status tended to have higher levels of proceptivity, and significantly reduced aggression, towards males, compared to rats with declining reproductive status. Basal midbrain E(2) and DHP levels accounted for a significant proportion of variance in lordosis. In Experiment 2, 1-year-old, age-matched, female breeders that had maintained reproductive status or were in reproductive decline were compared to three-month old, nulliparous females that had regular (4-5 days) or irregular estrous cycles. Age did not influence paced mating but younger rats had greater diencephalon E(2) than did middle-aged rats. After mating, rats with declining/irregular reproductive status had higher P(4) and DHP levels in midbrain than did rats with maintaining/regular reproductive status, albeit differences in midbrain 3α,5α-THP were not seen. Middle-aged rats that maintained reproductive function had greater 3α,5α-THP formation in diencephalon compared to other groups. Thus, age-related changes in central progestogen formation in midbrain or diencephalon may contribute to some variability in expression of reproductive behaviors.

Corticosteroid and neurosteroid dysregulation in an animal model of autism, BTBR mice

Autism spectrum disorders (ASD) are a constellation of neurodevelopmental disorders associated with disruptions in social, cognitive, and/or motor behaviors. ASD are more prevalent among males than females and characterized by aberrant social and language development, and a dysregulation in stress-responding. Levels of progesterone (P(4)) and its metabolite 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) are higher and more variable in females compared to males. 3alpha,5alpha-THP is also a neurosteroid, which can be rapidly produced de novo in the brain, independent of peripheral gland secretion, and can exert homeostatic effects to modulate stress-responding. An inbred mouse strain that has demonstrated an ASD-like behavioral and neuroendocrine phenotype is BTBR T +tf/J (BTBR). BTBR mice have deficits in cognitive and social behaviors and have high circulating levels of the stress hormone, corticosterone. We hypothesized that central 3alpha,5alpha-THP levels would be different among BTBR mice compared to mice on a similar background C57BL/6J (C57/J) and 129S1/SvlmJ (129S1). Tissues were collected from BTBR, C57/J and 129S1 male mice and levels of corticosterone, P(4), and 3alpha,5alpha-THP in plasma and in the hypothalamus, midbrain, hippocampus, and cerebellum were measured by radioimmunoassay. Circulating levels of corticosterone, P(4), and 3alpha,5alpha-THP were significantly higher among BTBR, than C57/J and 129S1, mice. Levels of P(4) in the cerebellum were significantly higher than other brain regions among all mouse strains. Levels of 3alpha,5alpha-THP in the hypothalamus of BTBR mice were significantly higher compared to C57/J and 129S1 mice. These findings suggest that neuroendocrine dysregulation among BTBR mice extends to 3alpha,5alpha-THP.

Neurosteroids' effects and mechanisms for social, cognitive, emotional, and physical functions

Hormones are trophic factors that integrate central and peripheral nervous system functions, and can influence social, cognitive, emotional and physical (SCEP) processes. Greater understanding of behavioral and neurobiological underpinnings of mental, cognitive, and/or physical changes with maturation is becoming increasingly important as the world's population ages. There are individual differences in how people age, but the factors that influence these differences are not well understood. Social supports are one factor that may influence the trajectory of age-related processes. The loss of close relationships, especially among older persons, is one of the greatest risk factors for mental and physical decline. Progesterone, secreted by the ovaries, or produced de novo in the brain, is readily converted centrally to 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), and can influence SCEP, through rapid, non-classical steroid-mediated actions. Our hypothesis is that 3alpha,5alpha-THP is a key trophic factor in SCEP and development. Our research has demonstrated that 3alpha,5alpha-THP facilitates social and sexual behavior of rodents, which evokes further increases in 3alpha,5alpha-THP in midbrain and hippocampus, brain areas involved in SCEP. The role of 3alpha,5alpha-THP to influence social and/or sexual experience, and thereby SCEP, is discussed in this review. Further understanding of these neurobiological and/or behavioral factors may lead to findings that ultimately can promote health and prevent disease.

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).

Cellular distribution of the GABAA receptor-modulating 3alpha-hydroxy, 5alpha-reduced pregnane steroids in the adult rat brain

The 3alpha-hydroxy,5alpha-reduced pregnane steroids, allopregnanolone and allotetrahydrodeoxycorticosterone, are the most potent endogenous positive modulators of GABA(A) receptor-mediated inhibition. This study presents the first immunohistochemical examination of the cellular distribution of 3alpha-hydroxy,5alpha-reduced pregnane steroids across the brain. We found a widespread distribution in the adult rat, with dense immunolabelling in the olfactory bulb, striatum and cerebral cortex, and lower density labelling in the brainstem reticular formation. In general terms, this distribution accords with the regional concentrations of 3alpha-hydroxy,5alpha-reduced steroids determined, in other laboratories, by brain region sampling and either gas chromatography-mass fragmentography or radioimmunoassay. However, immunohistochemistry allowed for a more detailed examination of regional distribution and cellular specificity. All immunoreactivity was confined to the cell bodies and thick dendrites of neurones; no identifiable glia were labelled. In most brain areas, the location and morphology of labelled cells identified them as excitatory neurones. In addition, cell populations known to be projecting GABAergic neurones (e.g. cerebellar Purkinje cells) were immunoreactive, whereas local inhibitory neurones generally were not. The cellular distribution of 3alpha-hydroxy,5alpha-reduced steroids suggests that sensory, motor, limbic and homeostatic systems can be influenced by neurosteroids at multiple stages of processing.

Progestins influence motivation, reward, conditioning, stress, and/or response to drugs of abuse

Progesterone (pregn-4-ene-3,20-dione; P) and its metabolite 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) are secreted by ovaries, adrenals, and glial cells. 3alpha,5alpha-THP in the midbrain ventral tegmental area mediates sexual receptivity of rodents through its actions at GABA(A), NMDA, and/or D(1) receptors. The extent to which 3alpha,5alpha-THP may influence anti-anxiety/anti-stress effects, conditioning and/or reward through these substrates and/or by altering hypothalamic pituitary adrenal axis function is discussed. Biosynthesis of 3alpha,5alpha-THP occurs in responses to mating and may underlie some of the rewarding aspects of sexual behavior. Recent findings from our laboratory which demonstrate that progestins can enhance approach to novel stimuli, conditioning, and reinforcement are reviewed. How progestins' effects on these processes may underlie response to drugs of abuse is considered and new findings which demonstrate interactions between progestins and cocaine are presented.

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.

Inhibiting 5alpha-reductase in the amygdala attenuates antianxiety and antidepressive behavior of naturally receptive and hormone-primed ovariectomized rats

RATIONALE

Greater incidence of anxiety and depressive disorders of women compared to men may be due in part to progesterone (P) and its neuroactive metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), acting in limbic regions, such as the amygdala.

OBJECTIVE

If P's metabolism via 5alpha-reduction to 3alpha,5alpha-THP in the amygdala is critical for antianxiety and antidepressive behavior, then blocking 5alpha-reductase in the amygdala of female rats is likely to attenuate the antianxiety and antidepressive effects of high progestin levels from both endogenous and exogenous sources.

METHODS

Naturally receptive female rats with high endogenous estrogen (E2) and P and ovariectomized (ovx) rats administered E2 (10 microg) and P (500 microg) subcutaneously were administered finasteride (10 microg/microl), a Type II 5alpha-reductase inhibitor, or vehicle to the amygdala. Anxiety behavior (open field, elevated plus maze, defensive freezing) and depressive behavior (Porsolt forced swim test) were assessed.

RESULTS

There were similar effects of finasteride administration to the amygdala to attenuate antianxiety behavior in naturally receptive and ovx, hormone-primed rats. Finasteride administration significantly decreased central entries in the open field, decreased open arm time in the elevated plus maze, increased defensive freezing in response to footshock, and increased time spent immobile compared to vehicle.

CONCLUSIONS

Thus, formation and subsequent actions of 3alpha,5alpha-THP in the amygdala may be important for antianxiety and antidepressive effects.

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.

Rats bred for high versus low anxiety responses neonatally demonstrate increases in lordosis, pacing behavior, and midbrain 3α,5α-THP levels as adults

Duration and intensity of lordosis is mediated by actions of the progesterone (P) metabolite, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-THP) at GABA-sub(A) receptors in the midbrain ventral tegmental area. Because rats selectively bred for infantile vocalizations may differ in endogenous 3 alpha,5 alpha-THP secretion, their sexual behavior, midbrain, and plasma 3 alpha,5 alpha-THP levels as adult rats in behavioral estrus was examined. Rats bred for high rates of infantile vocalizations had shorter latencies and intervals between intromissions and ejaculation, higher lordosis quotients and ratings, more pacing of their sexual contacts, and had higher P and 3 alpha,5 alpha-THP levels in plasma and midbrain than did rats bred for low rats of infantile vocalizations. Thus, levels of 3 alpha,5 alpha-THP in the midbrain are associated with differences in sexual behavior of these rats.

Inhibiting biosynthesis and/or metabolism of progestins in the ventral tegmental area attenuates lordosis of rats in behavioural oestrus

In the ventral tegmental area (VTA), lordosis of rats is facilitated by 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). Central 3alpha,5alpha-THP results from metabolism of peripheral progesterone, from the ovaries and/or adrenals, by sequential enzymatic activity of 5alpha-reductase and 3alpha-hydroxysteroid oxidoreductase (3alpha-HSOR). In addition, in glial cells, cholesterol is converted into pregnenolone by the P450 side-chain cleavage enzyme (P450scc), which is then metabolized to progesterone by 3beta-hydroxysteroid dehydrogenase, and subsequently reduced to 3alpha,5alpha-THP. We hypothesize that, in the VTA, formation of 3alpha,5alpha-THP by both metabolism and biosynthesis is necessary for facilitation of lordosis of female rats. In Experiment 1, naturally-receptive rats received bilateral VTA infusions of a P450scc inhibitor, digitoxin (1 microg/side); a 5alpha-reductase inhibitor, finasteride (10 microg/side); digitoxin (1 microg/side)+finasteride (10 microg/side); or vehicle and were tested 3 h later for lordosis. In Experiment 2, the effects of VTA infusions of digitoxin, finasteride, digitoxin+finasteride, or vehicle on lordosis and midbrain and plasma 3alpha,5alpha-THP levels were examined. In Experiment 3, we investigated whether infusions of 3alpha,5alpha-THP to the VTA reinstated lordosis and midbrain 3alpha,5alpha-THP levels following administration of inhibitors. VTA infusions of digitoxin, finasteride, or digitoxin+finasteride, significantly and similarly reduced lordosis and midbrain, but not plasma 3alpha,5alpha-THP levels, compared to vehicle. Following receipt of inhibitor infusions, 3alpha,5alpha-THP to the VTA restored lordosis and midbrain 3alpha,5alpha-THP levels. These data suggest that, in the VTA, both central biosynthesis of progesterone and metabolism of progesterone (from central and/or peripheral sources) to 3alpha,5alpha-THP are important for mediating lordosis of rats.

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.

Progesterone's 5α-reduced metabolite, 3α,5α-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.

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.

Estrogen and/or progesterone administered systemically or to the amygdala can have anxiety-, fear-, and pain-reducing effects in ovariectomized rats

Estrogen (E2) and/or progesterone (P) in the amygdala may influence anxiety, fear, and pain behaviors. Ovariectomized rats were administered subcutaneous or intra-amygdala vehicle, E2, P, or E2 + P: Effects on open field, elevated plus-maze, defensive freezing, and hot-plate task performance were observed. Subcutaneous E2 + P or intra-amygdala E2, P, or E2 + P increased open field central entries and open arm time in the plus-maze compared with vehicle. Subcutaneous or intra-amygdala E2, P, or E2 + P decreased time spent freezing postshock compared with vehicle. Subcutaneous or intra-amygdala E2 + P increased latencies to lick paws compared with vehicle. Thus, E2 and P may have effects in the amygdala to decrease anxiety, fear, and/or pain responses.

Fluoxetine may influence lordosis of rats through effects on midbrain 3 alpha,5 alpha-THP concentrations

5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) in the ventral tegmental area (VTA) mediates lordosis of rodents. If fluoxetine's effects on lordosis are mediated in part by midbrain 3alpha,5alpha-THP, then fluoxetine regimens that decrease and increase lordosis would be expected to respectively lower and elevate midbrain 3alpha,5-THP levels. Experiment 1: Ovariectomized (ovx) rats received estradiol benzoate (EB; 5 micro g, SC) at 0 and 24 h and fluoxetine (20 mg/kg, IP) or vehicle 30 min before sex testing and tissue collection. Other rats received fluoxetine (10 mg/kg, IP) or vehicle for 15 days followed by EB-priming and testing. Systemic acute or chronic fluoxetine significantly decreased lordosis and midbrain 3alpha,5alpha-THP levels compared to vehicle. Experiment 2: Ovx rats with unilateral cannula to the VTA were primed with EB (5 micro g; 0, 24 h) and/or progesterone (0 or 100 micro g; 44 h, SC). At 47.5 h, fluoxetine (3.6 mM) or vehicle was infused to the VTA. At 48 h, rats were tested. Administering fluoxetine to the VTA significantly increased lordosis and midbrain 3alpha,5alpha-THP levels compared to vehicle infusions. Experiment 3: Ovx EB-primed rats were tested prior to, and 30 min after, treatmemt with acute fluoxetine (20 mg/kg, IP). Rats were then infused with 3alpha,5alpha-THP (100 ng) or vehicle to the VTA and were retested. 3alpha,5alpha-THP, but not vehicle, to the VTA reversed acute fluoxetine's inhibitory effects on lordosis. Together, these data suggest fluoxetine may alter lordosis in part through actions of 3alpha-THP in the midbrain.

Effects of olanzapine infusions to the ventral tegmental area on lordosis and midbrain 3alpha,5alpha-THP concentrations in rats

RATIONALE

The progesterone metabolite and neurosteroid 5alpha-pregnane-3alpha-ol-20-one (3alpha,5alpha-THP) facilitates sexual behavior of estradiol-primed rodents through its actions in the ventral tegmental area (VTA). Olanzapine, an atypical antipsychotic, may exert some of its actions by increasing 3alpha,5alpha-THP levels.

OBJECTIVE

If olanzapine has effects by increasing 3alpha,5alpha-THP levels, then olanzapine administration to the VTA should facilitate feminine sexual behavior of estradiol-primed rodents concomitant with increasing midbrain levels of 3alpha,5alpha-THP. METHODS. In experiment 1, ovariectomized rats with bilateral cannulae to the VTA were primed with estradiol at 0 h, infused with olanzapine (10 or 20 microg) or vehicle at 47 h, and tested for sexual behavior at 47.5 h. In experiment 2, estradiol-primed ovariectomized rats were infused with olanzapine (10 microg) or vehicle, tested for sexual behavior, then tissues were collected for measurement of midbrain progesterone and 3alpha,5alpha-THP, and plasma corticosterone, progesterone, and 3alpha,5alpha-THP. In experiment 3, estradiol-primed, ovariectomized rats were administered progesterone (500 microg, SC), tested for sexual behavior, then tissues were collected for midbrain and plasma progesterone and 3alpha,5alpha-THP levels.

RESULTS

Infusions of 10 or 20 microg olanzapine to the VTA significantly increased the incidence and intensity of lordosis, and the occurrence of proceptive and aggressive behaviors. Rats infused with olanzapine to the VTA had significantly greater levels of midbrain 3alpha,5alpha-THP than did vehicle-administered rats. Olanzapine did not increase progesterone or corticosterone levels.

CONCLUSIONS

Olanzapine increases lordosis and midbrain 3alpha,5alpha-THP when infused to the VTA which suggest that olanzapine's behavioral effects may result, in part, through actions of 3alpha,5alpha-THP, independent of progesterone or corticosterone.

Anti-nociception following exposure to trimethylthiazoline, peripheral or intra-amygdala estrogen and/or progesterone

Estradiol (E(2)) and/or progesterone (P) to the amygdala may influence stress-induced analgesia following predator odor, trimethylthiazoline (TMT), exposure. Ovariectomized (ovx) rats were administered subcutaneous (SC) or intra-amygdala vehicle, E(2), P, or E(2)+P. The effects on performance in a test of pain sensitivity, the tailflick task, was observed in animals that experienced an acute exposure to TMT or no odor (control) in a small chamber. Rats that were exposed to TMT had increased tailflick latencies compared to rats not exposed to TMT, this was partially attenuated by the opiate antagonist naloxone. Systemic E(2), P, or E(2)+P increased tailflick latencies compared to vehicle administration to ovx rats. Ovx rats administered E(2)+P to the amygdala had increased tailflick latencies compared to control rats. These data suggest that following exposure to predator odor, pain sensitivity in the tailflick task is decreased and that E(2) and/or P may have actions in the amygdala to produce similar anti-nociceptive effects.

Mitochondrial benzodiazepine receptors in the ventral tegmental area modulate sexual behaviour of cycling or hormone-primed hamsters

Hamsters are highly dependent upon the central actions of progesterone (P4) for facilitation of sexual behaviour. In the ventral tegmental area (VTA), P4 has actions through its neurosteroid metabolite 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). The effects of enhancing or inhibiting neurosteroidogenesis (and thereby 3alpha,5alpha-THP concentrations), through manipulations of mitochondrial benzodiazepine receptors, in the VTA on socio-sexual behaviour of female hamsters were examined. Intact, naturally receptive hamsters and ovariectomized (OVX), hormone-primed hamsters were unilaterally infused via chronic guide cannula to the VTA with the mitochondrial benzodiazepine receptor antagonist 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboximide (PK-11195) or the mitochondrial benzodiazepine receptor agonist, N,N-dihexyl-2-(4-fluorophenyl)indole-30-acetamide (FGIN 1-27) and tested for sexual responsiveness and lordosis. PK-11195 (5.6, 11.2 or 22.4 nm) to the VTA attenuated sexual responsiveness of naturally receptive or oestradiol benzoate (EB) + P4-primed hamsters compared to vehicle. In addition, FGIN 1-27 (11.4 nm) infusions to the VTA increased sexual responsiveness and lordosis of cycling or OVX, EB + P4-primed hamsters, compared to vehicle infusions. In OVX, EB + P4-primed hamsters, decrements in sexual responsiveness produced by VTA infusions of PK-11195 (5.6 nm) were attenuated by VTA infusions of 3alpha,5alpha-THP. VTA infusions of PK-11195 (5.6 nm) or FGIN 1-27 (11.4 nm), respectively, decreased and increased midbrain levels of 3alpha,5alpha-THP compared to each other. Together, these findings indicate that manipulating actions of mitochondrial benzodiazepine receptors in the VTA can augment and inhibit neurosteroidogenesis and sexual responsiveness of hormone-primed and naturally receptive hamsters.

Ventral tegmental area infusions of inhibitors of the biosynthesis and metabolism of 3alpha,5alpha-THP attenuate lordosis of hormone-primed and behavioural oestrous rats and hamsters

The importance of progesterone biosynthesis and metabolism to 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), which exerts its effects via GABAA/benzodiazepine receptor complexes (GBRs) rather than intracellular progestin receptors (PRs), was investigated for its effects on sexual receptivity. Epostane, a 3beta-hydroxysteroid dehydrogenase inhibitor, blocks progesterone and 3alpha,5alpha-THP biosynthesis. Finasteride, a 5alpha-reductase inhibitor, blocks the metabolism of progesterone to dihydroprogesterone (DHP), which is subsequently metabolized to 3alpha,5alpha-THP. Indomethacin, a 3alpha-hydroxysteroid oxidoreductase inhibitor, blocks DHP's metabolism to 3alpha,5alpha-THP, and its oxidation to DHP. Epostane, finasteride, indomethacin or vehicle were infused intracranially in the ventral tegmental area (VTA) of hormone-primed or naturally receptive rats and hamsters and sexual behaviour was recorded. Epostane, finasteride and indomethacin to the VTA significantly reduced lordosis, compared to vehicle infusions, in hormone-primed and behavioural oestrous rats and hamsters. Radioimmunoassay revealed that concentrations of midbrain 3alpha,5alpha-THP were reduced following epostane, finasteride or indomethacin infusions that significantly decreased lordosis. Immunocytochemistry for 3alpha,5alpha-THP revealed the number of immunoreactive cells were significantly reduced in the VTA following epostane, finasteride or indomethacin infusion to the VTA, but not other midbrain sites. These data suggest that biosynthesis of progestins, and the metabolism of progesterone to 3alpha,5alpha-THP in the VTA, are important for progestin-facilitated sexual receptivity of rats and hamsters.

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 role of neurosteroids and nongenomic effects of progestins in the ventral tegmental area in mediating sexual receptivity of rodents

Progesterone (P(4)) in the ventromedial hypothalamus (VMH) and ventral tegmental (VTA) is important for facilitation of lordosis; however, P(4)'s actions in these brain areas are different. Using lordosis in rodents as in vivo experimental models, we have examined the effects progestins exert in the midbrain and hypothalamus. Localization and blocker studies indicate that P(4)'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 alter lordosis, which suggests that progestins may interact with GBRs to facilitate receptivity by enhancing the function of GABAergic neurons. Interfering with P(4)'s metabolism to 5 alpha-pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP), the most effective endogenous positive modulator of GBRs, or the biosynthesis of the neurosteroid 3 alpha,5 alpha-THP in the VTA attenuates female sexual behavior in rodents. Stimulation of mitochondrial benzodiazepine receptors (MBRs), which enhance neurosteroid production, by infusions of a MBR agonist to the VTA enhances lordosis. 3 alpha,5 alpha-THP is increased in the midbrain of mated > proestrous > diestrous rodents. These data suggest that 3 alpha,5 alpha-THP has a proximate modulatory role on lordosis. In summary, the actions of P(4) in the VTA are different from those in the VMH that involve PRs. In the VTA, P(4) may facilitate lordosis following metabolism to and/or biosynthesis of 3 alpha,5 alpha-THP, which may have subsequent actions at GBRs and/or MBRs to acutely modulate female sexual behavior in rodents.

Inhibiting progesterone metabolism in the hippocampus of rats in behavioral estrus decreases anxiolytic behaviors and enhances exploratory and antinociceptive behaviors

Blocking progesterone's metabolism to 5 alpha-pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP) with finasteride, a 5 alpha-reductase inhibitor, and effects on anxiolytic, exploratory, and antinociceptive behaviors of rats in behavioral estrus were examined. Rats in behavioral estrus received finasteride systemically (SC), to the hippocampus, or to control implant sites, the nucleus accumbens (NA) or ventral tegmental area (VTA), and were tested in horizontal crossing, open-field, elevated plus-maze, emergence, holeboard, social interaction, tailflick, pawlick, and defensive freezing tasks. Finasteride, SC or intrahippocampally, reduced 3 alpha,5 alpha-THP in the hippocampus relative to vehicle implants or finasteride to the NA or VTA. Systemic or intrahippocampal finasteride decreased central entries in the open field and open-arm time on the elevated plus-maze and increased freezing in response to shock relative to vehicle. Finasteride to the hippocampus decreased emergence latencies and increased social interaction, pawlick, and tailflick latencies relative to all other groups. Finasteride to the hippocampus of rats in behavioral estrous decreased anxiolysis and enhanced exploration and analgesia. In summary, these data demonstrate that decreases in anxiolytic behavior of behavioral estrous rats can be produced by reductions in 3 alpha,5 alpha-THP in the hippocampus, which suggest that elevations in 3 alpha,5 alpha-THP in the hippocampus may give rise to anxiolysis seen during behavioral estrus.