Identification and characterization of a pregnane steroid recognition site that is functionally coupled to an expressed GABAA receptor

Forty Years Searching for Neurosteroid Binding Sites on GABAA Receptors

Brain inhibition is a vital process for controlling and sculpting the excitability of the central nervous system in healthy individuals. This level of control is provided over several timescales and involves the neurotransmitter GABA acting at inhibitory synapses to: rapidly inhibit neurons by activating the GABAA receptor; over a slower timescale, to tonically activate extrasynaptic GABAA receptors to provide a low level of background inhibition; and finally, to activate G-protein coupled GABAB receptors to control transmitter release by inhibiting presynaptic Ca2+ channels whilst providing postsynaptic inhibition via K+ channel activation. From this plethora of roles for GABA and its receptors, the GABAA receptor isoform is of major interest due to its dynamic functional plasticity, which in part, is due to being targeted by modulatory brain neurosteroids derived from sex and stress hormones. This family of neurosteroids can, depending on their structure, potentiate, activate and also inhibit the activity of GABAA receptors to affect brain inhibition. This review tracks the methods that have been deployed in probing GABAA receptors, and charts the sterling efforts made by several groups to locate the key neurosteroid binding sites that affect these important receptors. Increasing our knowledge of these binding sites will greatly facilitate our understanding of the physiological roles of neurosteroids and will help to advance their use as novel therapeutics to combat debilitating brain diseases.

Effects of inhibitory GABA-active neurosteroids on cocaine seeking and cocaine taking in rats

RATIONALE

Several compounds that potentiate GABA-induced inhibitory currents also decrease stress, anxiety and addiction-related behaviors. Because of the well-established connection between stress and addiction, compounds that reduce stress-induced responses might be efficacious in treating addiction. Since endogenous neurosteroids such as allopregnanolone may function in a manner similar to benzodiazepines to reduce HPA axis activation and anxiety following stressful stimuli, we hypothesized that exogenously applied neurosteroids would reduce cocaine reinforcement in two animal models.

METHODS

Male Wistar rats were trained to self-administer cocaine and food under a concurrent alternating operant schedule of reinforcement. Two separate groups of rats were trained to self-administer cocaine or food pellets and were then exposed to similar cue-induced reinstatement paradigms. Both groups of rats were pretreated with various doses of neurosteroids.

RESULTS

Allopregnanolone and 3α-hydroxy-3β-methyl-17β-nitro-5α-androstane (R6305-7, a synthetic neurosteroid) were ineffective in selectively decreasing cocaine relative to food self-administration. On the other hand, both allopregnanolone and R6305-7 significantly decreased the cue-induced reinstatement of extinguished cocaine seeking, confirmed by one-way ANOVA.

CONCLUSIONS

These results suggest that neurosteroids may be effective in reducing the relapse to cocaine use without affecting ongoing cocaine self-administration.

Membrane progesterone receptor expression in mammalian tissues: a review of regulation and physiological implications

The recent discovery of a novel, membrane localized progestin receptor (mPR) unrelated to the classical progesterone receptor (PR) in fishes and its subsequent identification in mammals suggests a potential mediator of non-traditional progestin actions, particularly in tissues where PR is absent. While early studies on mPR focused on final oocyte maturation in fishes, more current studies have examined mPRs in multiple mammalian systems in both reproductive and non-reproductive tissues as well as in diseased tissues. Here we review the current data on mPR in mammalian systems including male and female reproductive tracts, liver, neuroendocrine tissues, the immune system and breast and ovarian cancer. We also provide new data demonstrating mPR expression in the RAW 264.7 immune cell line and bone marrow-derived macrophages as well as mPR expression and downstream gene regulation in ovarian cancer cells.

Delineation of downstream signalling components during acrosome reaction mediated by heat solubilized human zona pellucida

BACKGROUND

Human egg is enveloped by a glycoproteinaceous matrix, zona pellucida (ZP), responsible for binding of the human spermatozoa to the egg and induction of acrosomal exocytosis in the spermatozoon bound to ZP. In the present manuscript, attempts have been made to delineate the downstream signalling components employed by human ZP to induce acrosome reaction.

METHODS

Heat-solubilized human ZP (SIZP) was used to study the induction of acrosome reaction in capacitated human spermatozoa using tetramethylrhodamine isothiocyanate conjugated Pisum sativum agglutinin (TRITC-PSA) in absence or presence of various pharmacological inhibitors. In addition, intracellular calcium ([Ca2+]i) levels in sperm using Fluo-3 acetoxymethyl ester as fluorescent probe were also estimated in response to SIZP.

RESULTS

SIZP induces acrosomal exocytosis in capacitated human sperm in a dose dependent manner accompanied by an increase in [Ca2+]i. Human SIZP mediated induction of acrosome reaction depends on extracellular Ca2+ and involves activation of Gi protein-coupled receptor, tyrosine kinase, protein kinases A & C and phosphoinositide 3 (PI3)- kinase. In addition, T-type voltage operated calcium channels and GABA-A receptor associated chloride (Cl-) channels play an important role in SIZP mediated induction of acrosome reaction.

CONCLUSIONS

Results described in the present study provide a comprehensive account of the various downstream signalling components associated with human ZP mediated acrosome reaction.

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.

Action by and sensitivity to neuroactive steroids in menstrual cycle related CNS disorders

Neuroactive steroids are a large group of substances having effect in the brain and on brain function. The steroids most studied are allopregnanolone (ALLO), tetrahydrodesoxycorticosterone (THDOC), pregnenolone sulfate (PS) dihydroepiandrosteronesulfate (DHEAS), and estradiol (E2). ALLO and THDOC are called gamma-aminobutyric acid (GABA) steroids as they are positive modulators of the GABAA receptor in a similar way as benzodiazepines, barbiturates, and alcohol. GABA steroids not only have similar behavioral effects as benzodiazepines and barbiturates but, possibly, also similar adverse effects as well. This review aims to elucidate the possible role that neuroactive steroids play in the development of mood disorders in women. One of the most clear-cut examples of the interaction between mood, neuroactive steroids, and the GABA system is premenstrual dysphoric disorder (PMDD), which is a cluster of negative mood symptoms occurring during the luteal phase of the menstrual cycle in 2-6% of reproductive women. Furthermore, certain women also experience adverse mood effects during sequential progestin addition to postmenopausal estrogen treatment, which is why the role of neuroactive steroids in postmenopausal women is also addressed in this review.

Pharmacokinetic and behavioral effects of allopregnanolone in healthy women

RATIONALE

The behavioral effects of allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one) in women are not known.

OBJECTIVE

Allopregnanolone, a neuroactive steroid secreted by the mammalian ovary, exerts its anesthetic, anxiolytic, and sedative/hypnotic effects through potentiation of GABAA receptors. The purpose of this study was to evaluate the behavioral effects of allopregnanolone in healthy women.

METHODS

Ten healthy women were given three increasing intravenous doses of allopregnanolone in the follicular phase of the menstrual cycle. Saccadic eye movement parameters and visual analogue scales of sedation were used to evaluate the behavioral response of allopregnanolone. Repeated blood samples for analyses of allopregnanolone were drawn throughout the study day.

RESULTS

Exogenously administered allopregnanolone decreases saccadic eye movement parameters and increases subjective ratings of sedation that correlate with increased serum concentrations of this neuroactive steroid.

CONCLUSION

The behavioral effects of allopregnanolone are similar to that of its 5beta-stereoisomer, pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one). Apart from fatigue and mild nausea, allopregnanolone given in a cumulative dose of 0.09 mg/kg did not have any adverse effects.

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.

Alphaxalone and epiallopregnanolone in rats trained to discriminate ethanol

BACKGROUND

Neurosteroids with a 3 alpha-hydroxy orientation share pharmacological effects with ethanol, increase in brain after ethanol administration, and may mediate ethanol effects. 3beta-hydroxy neurosteroids antagonize in vitro and some, but not all in vivo effects of ethanol and 3 alpha-hydroxy neurosteroids.

METHODS

We assessed the discriminative stimulus and rate altering effects of alphaxalone, a 3 alpha-hydroxy neurosteroid, and epiallopregnanolone, a 3beta-hydroxy neurosteroid, in rats trained to discriminate either 0.8 g/kg or 1.2 g/kg ethanol. The ability of epiallopregnanolone to antagonize the discriminative stimulus or rate-altering effects of ethanol or alphaxalone was also assessed.

RESULTS

Ethanol had similar discriminative ED50s (0.5 g/kg) in both groups; however rats trained with the lower ethanol dose were more sensitive to rate-decreasing effects of ethanol. Alphaxalone occasioned ethanol-appropriate responding in both training groups, although less effectively in rats trained on the lower ethanol dose (maximum 65% versus 80% ethanol-appropriate responding). No difference in sensitivity to the rate-decreasing effects of alphaxalone was present between groups. Epiallopregnanolone did not reliably occasion ethanol-appropriate responding in either training group, and rats trained on the lower ethanol dose were slightly more sensitive to epiallopregnanolone rate decreasing effects. Epiallopregnanolone did not alter any effects of ethanol or alphaxalone.

CONCLUSIONS

Our results agree with previous reports that 3 alpha-hydroxy neurosteroids occasion ethanol-appropriate responding, while 3beta-hydroxy neurosteroids do not; as well as reports showing no antagonism of the discriminative stimulus or rate-suppressant effects of ethanol or 3 alpha-hydroxy neurosteroids by 3beta-hydroxy neurosteroids. Results of the present study demonstrate that ethanol and 3 alpha-hydroxy neurosteroids share discriminative stimulus effects. However, these results are inconsistent with the hypothesis that such neurosteroids mediate the discriminative stimulus of ethanol.

In vitro effect of gamma-aminobutyric acid on bovine spermatozoa capacitation

Sperm capacitation is defined as the maturational changes that render a sperm competent for fertilization and occurs in the female reproductive tract. Identification of the factor/s that regulate sperm capacitation would allow the understanding of these phenomena. Among these factors, gamma-aminobutyric acid (GABA) has recently become as a putative modulator of sperm function. The aim of this study was to explore the presence of a GABAergic regulation of bovine sperm capacitation as well as the possible intracellular mechanisms involved. GABA was detected in fresh semen by a sensitive radioreceptor assay (spermatozoa, 0.064 +/- 0.003 nmoles/10(6) cells; seminal plasma, 23.21 +/- 1.16 nmoles/ml). Scatchard analysis of [(3)H]-muscimol binding to sperm membranes yielded a linear plot consistent with a single population of binding sites (K(d) = 3.87 nM, B(max) = 417 fmol/mg prot.). [(3)H]-muscimol specific binding to sperm membranes was significantly inhibited by the GABA A receptor (GABA A-R) antagonist bicuculline and by the agonists muscimol and isoguvacine. Addition of GABA to the incubation medium resulted in a concentration-dependent increase in the percentage of capacitated spermatozoa (chlortetracycline assay). We observed a significant increment on intracellular calcium and cyclic 3',5' adenosine monophosphate (cAMP) concentrations induced by GABA, being the cation influx abolished when the cell suspensions were coincubated with the antagonists bicuculline or picrotoxin. It is concluded that GABA induces sperm capacitation through an intracellular mechanism dependent on calcium influx and cAMP accumulation mediated by a specific GABA A-R.

Identification, classification, and partial characterization of genes in humans and other vertebrates homologous to a fish membrane progestin receptor

Recently we discovered a previously uncharacterized gene with the characteristics of a membrane progestin receptor (mPR) in a fish model, spotted seatrout. Here, we report the identification, cloning, and characteristics of other members of this hitherto unknown family of putative mPRs from several vertebrate species, including human, mouse, pig, Xenopus, zebrafish, and Fugu, with highly conserved nucleotide and deduced amino acid sequences and similar structures to the spotted seatrout mPR. The 13 vertebrate genes identified seem to belong to an unknown gene family. Phylogenetic analysis indicates these cDNAs comprise three distinct groups (named alpha, beta, and gamma) within this gene family. Structural analyses of the translated cDNAs suggest they encode membrane proteins with seven transmembrane domains. The transcript sizes of the human alpha, beta, and gamma putative mPR mRNAs varied from 2.8 to 5.8 kb and showed distinct distributions in reproductive, neural, kidney and intestinal tissues, respectively. Recombinant human alpha, gamma, and mouse beta proteins produced in an Escherichia coli expression system demonstrated high affinity (K(d) = 20-30 nM) saturable binding for progesterone. Further analysis of binding to the gamma-subtype revealed binding was specific for progestins and was displaceable, with rapid rates of association and dissociation (t(1/2) = 2-8 min). These results suggest this is a new family of steroid receptors unrelated to nuclear steroid receptors, but instead having characteristics of G protein-coupled receptors.

Preclinical development of neurosteroids as neuroprotective agents for the treatment of neurodegenerative diseases

Recent literature has emphasized the unique role that the neurosteroid subclass of steroids, which includes dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS), play in the developing and adult central nervous system (CNS). Both DHEA and DHEAS are found in abundance in the CNS (Majewska, 1995), and both can be synthesized and metabolized in the brain of many species (Baulieu, 1981, 1998; Corpéchot et al., 1981, 1983; Zwain and Yen, 1999). DHEA and DHEAS have been implicated as potential signaling molecules for neocortical organization during neuronal development, suggesting that they have trophic factor-like activity (neurotrophic or neurotropic) or can interact with various neurotransmitter systems to promote neuronal remodeling (Compagnone and Mellon, 1998; Mao and Barger, 1998). Consistent with a neurotrophic role for these steroids, studies have shown that DHEAS protects certain neuronal populations against neurotoxic insults inflicted by the excitatory amino acid glutamate (Kimonides et al., 1998; Mao and Barger, 1998). This finding suggests that DHEAS may be useful in treating neurodegenerative diseases in which excitotoxicity is believed to be the underlying cause or a major contributor to cell death. Moreover, because DHEA and DHEAS are multifunctional and exhibit a variety of properties in the CNS, including memory consolidation, neuroprotection, and reduction of neurodegeneration (Majewska, 1992, 1995; Lapchak et al., 2000), their potential therapeutic benefits may be extended to include the treatment of other neurodegenerative diseases not directly linked to excitotoxicity.

Membrane-bound progesterone receptors contain a cytochrome b5-like ligand-binding domain

BACKGROUND

Membrane-associated progesterone receptors (MAPRs) are thought to mediate a number of rapid cellular effects not involving changes in gene expression. They do not show sequence similarity to any of the classical steroid receptors. We were interested in identifying distant homologs of MAPR better to understand their biological roles.

RESULTS

We have identified MAPRs as distant homologs of cytochrome b5. We have also found regions homologous to cytochrome b5 in the mammalian HERC2 ubiquitin transferase proteins and a number of fungal chitin synthases.

CONCLUSIONS

In view of these findings, we propose that the heme-binding cytochrome b5 domain served as a template for the evolution of membrane-associated binding pockets for non-heme ligands.

The inhibitory effects of allopregnanolone and pregnanolone on the population spike, evoked in the rat hippocampal CA1 stratum pyramidale in vitro, can be blocked selectively by epiallopregnanolone

The progesterone metabolites allopregnanolone (Allo, 3alpha-hydroxy-5alpha-pregnan-20-one) and pregnanolone (Preg, 3alpha-hydroxy-5beta-pregnan-20-one) enhance the gamma-aminobutyric acid (GABA) action through a distinct site on the GABAA-receptor. Their 3beta-isomers epiallopregnanolone (Epiallo, 3beta-hydroxy-5alpha-pregnan-20-one) and epipregnanolone (Epipreg, 3beta-hydroxy-5beta-pregnan-20-one), do not have these effects on GABAA-receptors. We have studied the interaction between Allo/Preg and their 3beta-isomers on action potentials in rat hippocampal slices in vitro. The Schaffer collaterals were stimulated electrically in CA1 striatum radiatum and the population spike (POPSP) was recorded in stratum pyramidale. A 0.5-nL droplet of drug was applied locally onto stratum oriens-pyramidale via a pressure pipett. Muscimol (Mus) (12.5 fmol), Allo and Preg (6.25 fmol) caused a reversible inhibition of POPSP. On the other hand, 6.25 fmol Epiallo had no significant effect on POPSP compared with the vehicle control. Combined Epiallo and Allo application caused a dose-dependent reduction of the Allo inhibition of POPSP. A full blockage was seen at a molar ratio of 1:1. Epiallo also blocked the Preg inhibition of POPSP, when the two drugs were combined in a molar ratio of 1:1. Epiallo did not block the Mus inhibition of POPSP, when the two drugs were combined at a molar ratio of 1:2. Bath perfusion of 12.5 microM Epiallo blocked the inhibition of 6.25 fmol Allo on POPSP, but not the inhibition caused by 12.5 fmol Mus. Epipreg did not block the inhibition of Allo and Preg on POPSP, when it was combined with the two latter drugs at a molar ratio of 1:1. Our data suggest that the steroid modulation of the GABAA transmitted inhibition of the CA1 pyramidal neurones is selectively and dose dependently blocked by Epiallo, the 3beta-hydroxy-isomer of Allo, but not by Epipreg, the 3beta-hydroxy-isomer of Preg.

Glucocorticoids-potent modulators of astrocytic calcium signaling

Glucocorticoids are the first line of choice in the treatment of cerebral edema associated with brain tumors. High-dose glucocorticoids reduce the extent of edema within hours, often relieving critical increases in intracranial pressure, but the mechanisms by which glucocorticoids modulate brain water content are not well-understood. A possible target of action may be glucocorticoid receptor-expressing astrocytes, which are the primary regulators of interstitial ion homeostasis in brain. In this study, we demonstrate that two glucocorticoids, methylprednisolone and dexamethasone, potentiate astrocytic signaling, via long-range calcium waves. Glucocorticoid treatment increased both resting cytosolic calcium (Ca2+i) level and the extent and amplitude of Ca2+ wave propagation two-fold, compared to matched controls. RU-486, a potent steroid receptor antagonist, inhibited the effects of methylprednisolone. The glucocorticoid-associated potentiation of Ca2+ signaling may result from upregulation of the cellular ability to mobilize Ca2+ and release ATP, because both agonist-induced Ca2+i increments (via ATP and bradykinin) and ATP release were proportionally enhanced by glucocorticoids. In contrast, neither gap junction expression (as manifested connexin 43 immunoreactivity) nor functional coupling was significantly affected by methylprednisolone. Confocal microscopy revealed both the expression of glucocorticoid receptors and nuclear translocation of these receptors when exposed to methylprednisolone. We postulate that the edemolytic effects of glucocorticoids may result from enhanced astrocytic calcium signaling.

Influence of progesterone and GABAA receptor on calcium mobilization during human sperm acrosome reaction

At fertilization, mammalian sperm has to undergo morphological changes of acrosome, namely acrosome reaction (AR), during which a dramatic increase of cytosolic calcium in consequence of extracellular calcium influx induces acrosomal exocytosis. It has been reported that progesterone is capable of inducing mammalian sperm AR. Several authors insisted that the agent, which was so far understood to bind with intracellular receptor, might act as an agonist against cell surface r-aminobutyric acid with type A (GABAA) receptor. The mode of action is, however, still in controversy. To investigate whether progesterone-induced AR is mediated by GABAA receptor, the present study examined pharmacologically the actions of progesterone on the morphological changes of acrosome and calcium mobilization during human sperm AR. Progesterone (15 microM) stimulated AR and increased cytosolic calcium, and the AR rate was further promoted by the coexistence of GABA (15 microM). Then these phenomena were suppressed by an antagonist of GABAA receptor (bicuculline, 10 microM), a blocker of GABAA receptor-coupled chloride channel (picrotoxin, 200 microM) and an antagonist of receptor-operated calcium channel (Lantan, 250 microM), respectively. These results indicated that the complex work of GABAA receptor-chloride channel and receptor operated calcium channel might participate in progesterone-induced AR and the transient increase of cytosolic calcium.

Gamma-aminobutyric acid (GABA) A and B receptors mediate the stimulatory effects of GABA on the human sperm acrosome reaction: interaction with progesterone

OBJECTIVE

To evaluate which gamma-aminobutyric acid (GABA) receptor mediates the stimulatory effects of this neurotransmitter on the human sperm acrosome reaction, and to examine the interaction of progesterone, a physiologic inducer of the acrosome reaction, with the GABA(A) receptor.

DESIGN

Prospective study.

SETTING

A university clinic of andrology.

PATIENT(S)

Men with normal sperm analysis parameters.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The acrosome reaction of motile spermatozoa.

RESULT(S)

The acrosome reaction was stimulated by GABA in a dose-dependent manner. This effect was inhibited completely by bicuculline, a GABA(A) receptor antagonist, and only partially by saclofen, a GABA(B) receptor antagonist. Accordingly, muscimol, a GABA(A) receptor agonist, stimulated the acrosome reaction to the same extent as GABA, whereas baclofen, a GABA(B) receptor agonist, was less effective. Preincubation with progesterone followed by the addition of GABA resulted in a significant increase in the percentage of acrosome-reacted spermatozoa compared with progesterone alone. However, this increase was less than a simple addition of effects, suggesting that GABA and progesterone act through the same receptor and/or use the same mechanism of action. To test this hypothesis, the ability of progesterone to induce acrosome reaction was tested in the presence of bicuculline, which suppressed the stimulatory effects of progesterone. Given that the GABA(A) receptor is linked to the chloride channel, we tested whether picrotoxin, a blocker of this channel, could modulate the effects of progesterone or GABA. Picrotoxin completely suppressed the acrosome reaction induced by progesterone and only partially suppressed that caused by GABA.

CONCLUSION(S)

gamma-Aminobutyric acid stimulated the acrosome reaction in human spermatozoa, acting mainly through the GABA(A) receptor and to a lesser extent through the GABA(B) receptor. Progesterone interacted with the GABA(A) receptor to induce the acrosome reaction, and the functional integrity of the chloride channel was vital for this effect.

Sexual differentiation modifies the allopregnanolone anxiolytic actions in rats

The administration of progesterone (0.0, 1.0 and 2.0 mg/rat, s.c.) and allopregnanolone (5 alpha, 3 alpha dihydroprogesterone) (0.0, 0.5 and 1.0 mg/rat, s.c.) to both, males and females, produced a similar reduction in burying behavior. Only allopregnanolone showed a gender-dependent effect on burying behavior latency. Allopregnanolone actions were established in five groups of animals according to their neonatal hormonal manipulation: intact males and females, neonatally-testosterone propionate-treated female rats (TP, 30 and 120 micrograms/rat, s.c. at day 5) and neonatally (4-12 h after delivery) castrated males. Males and females showed a reduction in anxiety after treatment with allopregnanolone. Both neonatally-androgenized-females and -castrated males were completely insensitive to allopregnanolone anxiolytic action tested in both burying behavior and plus-maze paradigm. The virilizing action of neonatally administered TP was demonstrated by dose-dependent delayed vaginal opening, a persistent estrus in their vaginal smears and the presence of polifollicular ovaries. Results are discussed on the bases of the differences and similarities between males, females, androgenized females and neonatally castrated males to anxiolytic steroids and the underlying possible processes.

Resistance of the hippocampus in the lactating rat to N-methyl-D-aspartate (NMDA)-mediated excitation is not due to a nonfunctional receptor system

The lactating rat has been shown to lack a behavioral response and immediate early gene expression (cFos) in the hippocampus (Hipc) following intravenous or intracerebroventricular administration of an N-methyl-d-aspartate (NMDA) receptor agonist. The purpose of this study is to determine whether neurons in the Hipc have an intact postsynaptic NMDA receptor system. The presence of NMDA receptor protein was determined by Western blot analysis for the NR1, NR2A, and NR2B subunits. The presence of functional NMDA receptors in the Hipc was determined by behavioral responses and the expression of cFos immunoreactivity (-ir) in response to microinjection of an NMDA receptor agonist into the hilus of the dentate gyrus. No difference in NR1 and NR2A subunit protein in the Hipc was detected between the lactating and nonlactating rats. However, there was a 26% decrease in NR2B subunit protein in this region in the lactating rat. Lactating rats receiving NMA injections displayed hyperactive behavior, similar to that observed in the nonlactating animals receiving the same treatment. The lactating rat and the nonlactating rat also displayed equivalent bilateral cFos-ir in the dentate gyrus (DG), CA1 and CA3 regions of the Hipc in response to unilateral NMA injections into the Hipc. These data indicate that the lactating rat has an intact postsynaptic NMDA receptor system. Thus, Hipc refractoriness to peripheral and third ventricular injections of an NMDA receptor agonist may reflect inhibition of presynaptic input and glutamate release.

A-ring reduced derivatives of two synthetic progestins induce anxiolytic effects in ovariectomized rats

The putative anxiolytic action of the synthetic progestins, norethisterone (NET), levonorgestrel (LNG) and their respective 5 alpha-reduced metabolites, (5 alpha-NET), (3 alpha,5 alpha-NET), (3 beta,5 alpha-NET), (5 alpha-LNG), (3 alpha,5 alpha-LNG) and (3 beta,5 alpha-LNG), were studied in the burying behavior paradigm. From these compounds only 3 alpha,5 alpha-NET and 3 beta,5 alpha-LNG reduced burying behavior without modifying other parameters. Burying behavior latency was prolonged after administration of the highest dose (1.0 mg/rat) of NET and 5 alpha-NET. As a positive control 3 alpha,5 alpha-pregnanolone (allopregnanolone) was included at the same doses used for synthetic steroids. This steroid produced a clear dose-dependent reduction in burying behavior without affecting latency. No steroid with anxiolytic properties affected the general ambulatory behavior. All synthetic steroids with anxiolytic activity proved to be less potent than allopregnanolone. Results are discussed on the basis of the chemical structure requirements necessary to induce tranquilizing effects.

Prenatal alcohol exposure influences the effects of neuroactive steroids on separation-induced ultrasonic vocalizations in rat pups

Fetal alcohol exposure has been reported to be associated with hyper-responsiveness to stress. Using a maternal separation paradigm, this study examined whether prenatal alcohol exposure affected sensitivity to neurosteroid modulation of stress. We have shown that the neuroactive steroid allopregnanolone reduces ultrasonic vocalizations (USVs) after brief maternal separation in week-old rat pups. Prenatal alcohol exposure, however, resulted in reduced sensitivity to this neurosteroid. In this study's first experiment, the behavioral effects of pregnenolone sulfate, a neurosteroid with reportedly opposite modulatory effects on the GABAA receptor, were characterized. Pregnenolone sulfate had a triphasic effect on the production of ultrasonic vocalizations and on open field activity. Blockade of conversion of pregnenolone sulfate to allopregnanolone via the 5 alpha-reductase inhibitor 4-MA also blocked the drug-related reduction in USVs, but not the higher-dose augmentation. The enzyme inhibitor alone had no significant effects on USV production, nor did progesterone. These results suggest that the neuroactive steroid pregnenolone sulfate may play an independent role in the stress response after maternal separation as well as being a precursor for the anxiolytic neurosteroid allopregnanolone. In the second experiment, prenatal alcohol exposure was found to eliminate both the low dose USV-reducing effect and the higher dose USV-increasing effect. These results support previous results demonstrating that prenatal alcohol exposure may cause an altered sensitivity to the neuromodulatory effects of neurosteroids.

How do cryptogenic and symptomatic infantile spasms differ? Review of biochemical studies in Finnish patients

Infants with cryptogenic infantile spasms seem to differ from those with symptomatic spasms in having a higher cerebrospinal fluid corticotropin content, different levels of corticotropin release after exogenous vasopressin, higher serum levels of progesterone, higher dehydroepiandrosterone: androstenedione ratio (during corticotropin therapy), a higher cerebrospinal fluid gamma-aminobutyric acid content, and higher cerebrospinal fluid nerve growth factor concentrations. It remains to be seen whether the biochemical differences between the two groups are specific or only happen to correlate with the early brain damage. However, these differences would explain many pathophysiologic features of infantile spasms.

Benzodiazepine binding varies with stage of estrous cycle in unwashed membranes from mouse brain

The influence of the stage of the estrous cycle on binding of [3H]diazepam was examined in membranes from brains of female mice. In order to conserve endogenous factors such as progesterone, other steroids, or GABA, the assay was performed without the extensive washing procedures typically employed in measurements of benzodiazepine binding. Significant variations in the apparent maximal numbers of binding sites (Bmax) were noted during the estrous cycle in both hypothalamus and cortex. The Bmax measured in membranes from proestrus female mice was significantly higher than in membranes from mice at other stages in the estrous cycle. Variations in apparent equilibrium binding dissociation constants (Kd) were not statistically significant by stage of the estrous cycle. The demonstrated variations in binding suggest the existence of a factor which varies with the estrous cycle in female mice and modulates the activity of the GABAA receptor complex.

Specific subunit mRNAs of the GABAA receptor are regulated by progesterone in subfields of the hippocampus

The ability of ovarian steroids to regulate the excitability of hippocampal neurons may be mediated by alterations in the inhibitory activity of GABA. We assessed the ability of estradiol, progesterone, and 3 alpha-OH-5 alpha-pregnan-20-one (3 alpha-OH-DHP; a metabolite of progesterone) to regulate gene expression of selected GABAA receptor subunits (alpha 1, alpha 2, beta 1, beta 2, and gamma 2). Using in situ hybridization, we found that progesterone, or 3 alpha-OH-DHP, suppressed mRNA levels for the alpha 1 subunit in the CA2, CA3, and the dentate gyrus subfields of the hippocampus in animals that were pretreated with estradiol. Progesterone had a more limited effect on the alpha 2 subunit, suppressing mRNA levels in estradiol-primed animals only in the CA3 region. In contrast, progesterone increased mRNA levels for the gamma 2 subunit in the CA1, CA2, and CA3 regions of the hippocampus, but only in animals that were not estradiol-primed. Estradiol alone had no significant effect on the expression of any subunit examined. Beta 1 and beta 2 subunit mRNA levels were not altered by any of the hormones tested. These data support the conclusion that progesterone and its metabolites may regulate excitability of the hippocampus by modulating the GABAA receptor gene expression; these effects of progesterone are dependent upon the circulating levels of estradiol. Alterations in the gene expression of selective subunits may lead to changes in the density of GABAA receptor protein or to changes in receptor subunit composition which might alter receptor sensitivity to activation by GABA or modulators such as the benzodiazepines and convulsants.

Nongenomic actions of progesterone on human spermatozoa

Progesterone's (P) stimulatory actions on human spermatozoa have been known for many years. P indeed appears to be the main sperm stimulator present in women's biological fluids, particularly the follicular fluid. The nongenomic nature of the biological effects of P on human spermatozoa has been demonstrated only recently. P and 17-alpha-hydroxy P have been shown to increase sperm intracellular calcium, phosphatidylinositide hydrolysis, and tyrosine phosphorylation of proteins, and to induce the acrosome reaction (AR), through a rapid, nongenomic mechanism. The effect on calcium is due to influx of the ion from the extracellular medium, as it is inhibited by the calcium chelator EGTA and appears to be mediated by P-binding sites present on the sperm surface, particularly at the head level. The nature of such binding sites has not been addressed so far, but the lack of inhibition of P action by the potent antiprogestin RU486 strongly suggests a biochemical difference from the genomic ones. Evidence exists for involvement of the phospholipid platelet-activating factor (PAF), polyamines, tyrosine kinase activation, proteases, and other factors in P-mediated calcium increase and acrosome reaction. Recent studies suggest the possibility that the sperm's response to P may be functionally related to their fertilizing ability, thus opening new perspectives in the possible development of a predictive test in the assisted reproductive techniques.

Differential behavioral effects of the neuroactive steroid allopregnanolone on neonatal rats prenatally exposed to alcohol

The effects of prenatal alcohol exposure on the behavioral response to the neuroactive steroid allopregnanolone (3 alpha-hydroxy-5 alpha-pregnan-20-one) were investigated in neonatal rats. Two behaviors were assessed: retention of an odor conditioning task and production of ultrasonic vocalizations after brief maternal separation. Subjects from one of the three prenatal conditions (lab chow, alcohol, or pair-fed) received either no injection or an ICV injection of vehicle or one of three doses (1.25-5.0 micrograms) of allopregnanolone either 20 min prior to or immediately after training in an appetitive odor association paradigm. Retention was assessed 1 h later in a two-choice odor preference chamber. Posttraining injections of allopregnanolone caused a dose-dependent impairment in retention in the odor task, but there was no differential sensitivity to allopregnanolone in the alcohol-exposed offspring. All pretraining injections, including the vehicle, resulted in impairments in retention on the task, suggesting an impairment due to stress but not due to allopregnanolone. Allopregnanolone also reduced ultrasonic vocalizations after brief maternal separation in all subjects in a second experiment, but alcohol-exposed offspring displayed a dose-dependent shift to the right in their anxiolytic response to this neurosteroid. This decreased sensitivity suggests that prenatal alcohol exposure may cause a decrease in the density or affinity of the GABA receptors involved in stress response, but not cognitive processes, at this age.

Anti-anxiety effects of progesterone and some of its reduced metabolites: an evaluation using the burying behavior test

In this study, pregnenolone sulfate, progesterone and some of its main reduced metabolites were tested for anxiolytic properties in rats using the burying behavior paradigm. All steroids were subcutaneously injected. Progesterone (0.5, 1.0, 2.0 and 4.0 mg/rat) and its 3 alpha-5 alpha-reduced metabolite (0.125, 0.250, 0.5 and 1.0 mg/rat) produced a clear dose-dependent anxiolytic response, without affecting the spontaneous ambulatory behavior. 5 alpha-Pregnanedione decreased burying behavior only at the highest dose (4.0 mg/rat). Pregnenolone sulfate (1.0, 2.0 and 4.0 mg/rat), 5 beta-pregnanedione and 3 beta- or 5 beta-pregnenolones were devoid of effects. The 3 beta-5 beta-reduced metabolite of progesterone (2.0 and 4.0 mg/rat) decreased motor activity, without altering the burying behavior. These results demonstrate that the 3 alpha-5 alpha metabolite of progesterone shows the highest anxiolytic potency in the burying behavior test, when compared with all steroids evaluated. The data are discussed in terms of the close structure-activity relationship requirements of steroids to stimulate the GABA/benzodiazepine receptor-chloride ionophore complex.

The cell surface progesterone receptor which stimulates calcium influx in human sperm is unlike the A ring reduced steroid site on the GABAA receptor/chloride channel

Progesterone elicits a rapid, transient calcium influx in sperm that is a prerequisite for the progesterone-induced acrosome reaction. The possibility that the GABAA receptor/chloride channel was the receptor that mediated the progesterone-induced calcium influx in human sperm was examined. A-ring reduced 3 alpha-hydroxy pregnane steroids (e.g. alfaxalone, allopregnanolone, pregnanolone), which are active on the GABAA receptor/chloride channel, were found to be much weaker than progesterone at stimulating Ca2+ influx in sperm. The effects of a variety of progesterone metabolites and analogs and other steroids were compared for their ability to (i) stimulate GABA-induced 36Cl- uptake in synaptoneurosomes, (ii) stimulate GABA-induced Cl- currents in HEK-293 cells transfected with alpha 1, beta 2, and gamma 2 subunits of the GABAA receptor/chloride complex, and (iii) elicit a rapid Ca2+ influx in sperm. No correlation was observed between the ability of a given steroid to stimulate Ca2+ influx and efficacy in eliciting either 36Cl- uptake or chloride currents. Importantly, the action of progesterone to stimulate Ca2+ influx was not modified by GABA, diazepam, picrotoxin and pentobarbitol (known regulators of the GABAA receptor/chloride channel). It is concluded from these studies that the cell surface progesterone binding site on human sperm that mediates progesterone-induced changes in [Ca2+]i is unlike the steroid binding site on the GABAA receptor/chloride channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroid modulation of GABAA receptors in an amphibian brain

Steroids can modulate gamma-aminobutyric acid (GABAA) receptor function in rat brains, but the physiological relevance of this mechanism is still unclear. To determine whether this phenomenon is widespread among vertebrates, we investigated steroid modulation of GABAA receptors in amphibian brain tissue. Equilibrium binding parameters for t-butylbicyclophosphorothionate ([35S]TBPS) and [3H]flunitrazepam were similar in Taricha granulosa and mammalian brains, as was the allosteric regulation of [35S]TBPS and [3H]flunitrazepam binding by GABA. The rank order and absolute potencies of steroids to inhibit [35S]TBPS binding and enhance [3H]flunitrazepam binding were also similar in Taricha and rat brains. As in mammalian studies, physiological concentrations of corticosterone had no effect on ligand binding or GABA-stimulated Cl- uptake. In autoradiographic studies, 3 alpha-hydroxy-5 alpha-pregnan-20-one inhibited [35S]TBPS binding sites in all brain regions examined, whereas corticosterone had no effect on [35S]TBPS binding. These studies suggest that the steroid recognition sites on GABAA receptors have been highly conserved through vertebrate evolution and thus portend physiologically important functions. However, the pharmacological profiles for the GABAA receptor and the high-affinity corticosteroid receptor are apparently different, suggesting there are multiple types of steroid recognition sites on neuronal membranes.

Reduction of rat pup ultrasonic vocalizations by the neuroactive steroid allopregnanolone

Several of the recently characterized neuroactive steroids have been proposed to have anxiolytic effects in behavioral models when subjects were tested as adults. In this experiment, the effects on infant subjects were examined using the isolation distress model of anxiety. The production of ultrasonic vocalizations in week-old rat pups after maternal separation was assessed after ICV injections of vehicle or allopregnanolone (1.25-5 micrograms), or sham injections. Subjects were also observed for activity and behavioral responses and tested on three measures of sedation. Allopregnanolone caused a dose-dependent decrease in ultrasonic vocalizations, with increasing motor incoordination, ataxia, and turning at the higher doses. Sex differences were not observed for any measure. These results suggest the GABAA receptor binding site for neuroactive steroids is behaviorally active in neonates as well as in adults, and that the anxiolytic effects of the neuroactive steroids at this site may be dissociable from their sedative effects at low doses.

Characteristics of a membrane-associated antilactogen binding site for tamoxifen

The antilactogen binding site (ALBS) is a membrane associated protein to which tamoxifen (TAM) and related non-steroidal antiestrogens, but not estrogen, bind. It is through this site that TAM inhibits lactogen binding to the prolactin (Prl) receptor and subsequent Prl induced growth and differentiation in target tissues. Binding of lactogens to the Prl receptor is inhibited by TAM or 4-hydroxy-TAM at 4 degrees C as well as room temperature, thus suggesting that the ALBS is not an enzyme. TAM acts by inhibiting the binding of lactogens to the receptor rather than promoting dissociation of the hormone-receptor complex. Lactogens bind to mammary gland membranes with an Kd of 4.3-8.2 x 10(-10) M. In the presence of 10(-7) M TAM the affinity decreased to a Kd of 0.8-1.6 x 10(-9) M. Binding of 3H-TAM to mammary gland membranes was effectively inhibited by an anti-Prl receptor antibody, thus suggesting a close relationship between the Prl receptor and the ALBS. Separate affinity purification of the ALBS and the Prl receptor resulted in peak fractions demonstrating specific binding activity for both TAM and lactogenic hormones. Re-isolation of the affinity purified Prl receptor on a TAM-Sepharose affinity resin again resulted in co-elution of both binding activities. The isolates from both affinity resins contained primarily a single band with an apparent molecular mass of 90 kDa. This band was precipitated with the anti-Prl receptor antibody and specifically bound the affinity label ring-3H-TAM aziridine.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional and interspecies differences in brain progesterone metabolism

Metabolites of [3H]progesterone were studied in slices prepared from different brain regions of male rat, mouse, and monkey. The major metabolites were 5 alpha-dihydroprogesterone (5 alpha-DHP) and 3 alpha,5 alpha-tetrahydroprogesterone (3 alpha,5 alpha-THP) in rat brain slices, 5 alpha-DHP and 20 alpha-dihydroprogesterone (20 alpha-DHP) in mouse brain slices, and 20 alpha-DHP in monkey brain slices. In rat olfactory bulb slices, 5 alpha-DHP represented 25.2 +/- 3.3% of total radioactivity and 3 alpha,5 alpha-THP 17.5 +/- 2.8%, whereas in rat medulla oblongata slices, 5 alpha-DHP was 31.3 +/- 3.5% and 3 alpha,5 alpha-THP 5.4 +/- 1.5% of total radioactivity. In slices from other rat brain regions, both metabolites represented 12-20% of total radioactivity. The highest metabolite content in mouse brain was also detected in olfactory bulb slices, where 5 alpha-DHP represented 16.6 +/- 4.6% and 20 alpha-DHP 9.5 +/- 2.3% of total radioactivity. In cortical and corpus callosum slices of monkey brain, 26.8 +/- 4.4% and 2.4 +/- 0.5% of total radioactivity, respectively, were converted to 20 alpha-DHP, and less than 3% of total radioactivity could be attributed to any of the other metabolites detected. The 3 alpha, 5 alpha-THP content in both rat and monkey brain was below 1 nM, but increased in rat brain to 6.7 +/- 2.5 nM after electroshock. Endogenous 3 alpha,5 alpha-THP might play an important role in the regulation of rat behavior through the modulation of GABA action on the GABAA receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Anxiolytic activity of the progesterone metabolite 5 alpha-pregnan-3 alpha-o1-20-one

3 alpha-hydroxylated pregnane steroids have been shown to possess anesthetic, hypnotic, anticonvulsant and anxiolytic properties. In this study, metabolites of progesterone and deoxycorticosterone, 5 alpha-pregnan-3 alpha-o1-20-one (3 alpha-OH-DHP) and 5 alpha-pregnan-3 alpha,21-diol-20-one (5 alpha-THDOC), respectively, were tested for anxiolytic effects in N.I.H. Swiss-Webster mice using the light/dark transition, open-field and lick-suppression tests. Similar to the benzodiazepine (BZ) diazepam, 3 alpha-OH-DHP (5-40 mg/kg) and 5 alpha-THDOC (5-40 mg/kg) significantly increased the number of light/dark transitions. 3 alpha-OH-DHP's effects were stereospecific as its diasteriomer, 3 beta-OH-DHP was devoid of activity. The benzodiazepine antagonist CGS-8216 (10 mg/kg) blocked diazepam's (1.0 mg/kg) anxiolytic effects, but did not have any effect against 3 alpha-OH-DHP (20 mg/kg). The data indicate that the pregnane steroids produce their anxiolytic effects through a separate mechanism than the BZs. 3 alpha-OH-DHP (20 mg/kg), 5 alpha-THDOC (20 mg/kg) and diazepam (1.0 mg/kg) increased activity in a open-field test. 3 beta-OH-DHP had no effect in the open-field test. Furthermore, 3 alpha-OH-DHP produced a 235% increase in punished responding in a lick-suppression test. These results demonstrate that the endogenous pregnane steroids possess anxiolytic effects that may be clinically relevant.