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

Progesterone's role in neuroprotection, a review of the evidence

The sex hormone progesterone has been shown to improve outcomes in animal models of a number of neurologic diseases, including traumatic brain injury, ischemia, spinal cord injury, peripheral nerve injury, demyelinating disease, neuromuscular disorders, and seizures. Evidence suggests it exerts its neuroprotective effects through several pathways, including reducing edema, improving neuronal survival, and modulating inflammation and apoptosis. In this review, we summarize the functional outcomes and pathophysiologic mechanisms attributed to progesterone treatment in neurologic disease. We then comment on the breadth of evidence for the use of progesterone in each neurologic disease family. Finally, we provide support for further human studies using progesterone to treat several neurologic diseases.

Local changes in neurosteroid levels in the substantia nigra reticulata and the ventral tegmental area alter chronic ethanol withdrawal severity in male withdrawal seizure-prone mice

BACKGROUND

Allopregnanolone (ALLO) is a potent positive modulator of γ-aminobutyric acidA receptors (GABAA Rs) that affects ethanol (EtOH) withdrawal. Finasteride (FIN), a 5α-reductase inhibitor that blocks the formation of ALLO and other GABAergic neurosteroids, alters EtOH sensitivity. Recently, we found that Withdrawal Seizure-Prone mice from the first genetic replicate (WSP-1) exhibited behavioral tolerance to the anticonvulsant effect of intrahippocampal ALLO during EtOH withdrawal and that intrahippocampal FIN significantly increased EtOH withdrawal severity. The purpose of this study was to determine whether neurosteroid manipulations in the substantia nigra reticulata (SNR) and ventral tegmental area (VTA) produced effects during EtOH withdrawal comparable to those seen with intrahippocampal ALLO and FIN.

METHODS

Male WSP-1 mice were surgically implanted with bilateral guide cannulae aimed at the SNR or VTA at 2 weeks prior to EtOH vapor or air exposure for 72 hours. Initial studies examined the anticonvulsant effect of a single ALLO infusion (0, 100, or 400 ng/side) at a time corresponding to peak withdrawal in the air- and EtOH-exposed mice. Separate studies examined the effect of 4 FIN infusions (0 or 10 μg/side/d) during the development of physical dependence on the expression of EtOH withdrawal.

RESULTS

ALLO infusion exerted a potent anticonvulsant effect in EtOH-naïve mice, but a diminished anticonvulsant effect during EtOH withdrawal. Administration of FIN into the SNR exerted a delayed proconvulsant effect in EtOH-naïve mice, whereas infusion into the VTA increased EtOH withdrawal duration.

CONCLUSIONS

Activation of local GABAA Rs in the SNR and VTA via ALLO infusion is sufficient to exert an anticonvulsant effect in naïve mice and to produce behavioral tolerance to the anticonvulsant effect of ALLO infusion during EtOH withdrawal. Thus, EtOH withdrawal reduced sensitivity of GABAA Rs to GABAergic neurosteroids in 2 neuroanatomical substrates within the basal ganglia in WSP-1 male mice.

Localization of brain 5α-reductase messenger RNA in mice selectively bred for high chronic alcohol withdrawal severity

Several lines of evidence suggest that fluctuations in endogenous levels of the γ-aminobutyric acid (GABA)ergic neurosteroid allopregnanolone (ALLO) represent one mechanism for regulation of GABAergic inhibitory tone in the brain, with an ultimate impact on behavior. Consistent with this idea, there was an inverse relationship between ALLO levels and symptoms of anxiety and depression in humans and convulsive activity in rodents during alcohol withdrawal. Our recent studies examined the activity and expression of 5α-reductase (Srd5a1), the rate-limiting enzyme in the biosynthesis of ALLO, during alcohol withdrawal in mice selectively bred for high chronic alcohol withdrawal (Withdrawal Seizure-Prone [WSP]) and found that Srd5a1 was downregulated in the cortex and hippocampus over the time course of dependence and withdrawal. The purpose of the present studies was to extend these findings and more discretely map the regions of Srd5a1 expression in mouse brain using radioactive in situ hybridization in WSP mice that were ethanol naïve, following exposure to 72h ethanol vapor (dependent) or during peak withdrawal. In naïve animals, expression of Srd5a1 was widely distributed throughout the mouse brain, with highest expression in specific regions of the cerebral cortex, hippocampus, thalamus, hypothalamus, and amygdala. In dependent animals and during withdrawal, there was no change in Srd5a1 expression in cortex or hippocampus, which differed from our recent findings in dissected tissues. These results suggest that local Srd5a1 mRNA expression in WSP brain may not change in parallel with local ALLO content or withdrawal severity.

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.

Progesterone, administered before kainic acid, prevents decrements in cognitive performance in the Morris Water Maze

The nature of progesterone (P₄)'s neuroprotective effects is of interest. We investigated effects of P₄ when administered before, or after, kainic acid, which produces ictal activity and damage to the hippocampus, to mediate effects on spatial performance. The hypothesis was that P₄, compared with vehicle, would reduce decrements in Morris Water Maze performance induced by kainic acid. Experiment 1: We examined the effects of kainic acid on plasma stress hormone, corticosterone, and progestogen (P₄ and its metabolites) levels in plasma and the hippocampus after subcutaneous (s.c.) P₄ administration to ovariectomized rats. Rats administered kainic acid had the highest corticosterone levels immediately following injection. P₄ is 5α-reduced to dihydroprogesterone (DHP) and subsequently metabolized to 5α-pregnan-3α-ol-20-one (3α,5α-THP) by 3α-hydroxysteroid dehydrogenase. The regimen of P₄ used produced circulating and hippocampal levels of P₄, DHP, and 3α,5α-THP within a physiological range, which declined at 14 hours postinjection and were not altered by kainic acid. Experiment 2: The physiological P₄ regimen was administered to rats before, or after, kainic acid-induced seizures, and later effects on water maze performance were compared with that of rats administered vehicle. Rats administered kainic acid had significantly poorer performance in the water maze (i.e., increased latencies and distances to the hidden platform) than did rats administered vehicle. Administration of P₄ before, but not after, kainic acid prevented these performance deficits. Thus, these data suggest that a physiological regimen of P₄ can prevent some of the deficits in water maze performance produced by kainic acid.

Effect of flutamide and two novel synthetic steroids on GABA, glutamine and some oxidative stress markers in rat brain and prostate

Flutamide is a steroid used to treat androgen-dependent disorders and as antiepileptic, but it induces a number of non-desirable side effects. This work was aimed at assaying the effect of flutamide and two novel synthetic steroids on the levels of GABA, glutamine and oxidative stress markers. Male Wistar rats (weight 180 g) received a single diazepam dose (5 mg/kg) 30 min prior to sacrifice (group A). Group B, flutamide; group C, 16β-methyl-17α-benzoyloxypregnen-4-en-3,20-dione; group D, estrone-3-hemisuccinate; group E, testosterone; group F, progesterone; all administered intraperitoneally at 10 mg/kg, daily for 3 days. Brain and prostate were obtained to assess lipid peroxidation (TBARS), Na(+) , K(+) ATPase activity, reduced glutathione (GSH), γ-amino butiric acid (GABA), glutamine and serotonin (5-HT) concentrations through spectrophotometry, fluorescence and HPLC. GABA levels increased and glutamine decreased in group A (P < 0.05). Total ATPase activity increased in group F and TBARS decreased in group B (P < 0.05). GSH decreased in A, B and C groups. 5-HT increased in group A and the prostate weight was increased in group E. The conclusion is that 16β-methyl-17α-benzoyloxypregnen-4-en-3,20-dione may be considered novel and promising to treat androgen-dependent diseases and epilepsy, since it showed an antioxidant effect and seemed to impair the GABAergic and serotonergic metabolism.

Neuroprotective actions of neurosteroids

Neurosteroids were initially defined as steroid hormones locally synthesized within the nervous tissue. Subsequently, they were described as steroid hormone derivatives that devoid hormonal action but still affect neuronal excitability through modulation of ionotropic receptors. Neurosteroids are further subdivided into natural (produced in the brain) and synthetic. Some authors distinguish between hormonal and regular neurosteroids in the group of natural ones. The latter group, including hormone metabolites like allopregnanolone or tetrahydrodeoxycorticosterone, is devoid of hormonal activity. Both hormones and their derivatives share, however, most of the physiological functions. It is usually very difficult to distinguish the effects of hormones and their metabolites. All these substances may influence seizure phenomena and exhibit neuroprotective effects. Neuroprotection offered by steroid hormones may be realized in both genomic and non-genomic mechanisms and involve regulation of the pro- and anti-apoptotic factors expression, intracellular signaling pathways, neurotransmission, oxidative, and inflammatory processes. Since regular neurosteroids show no affinity for steroid receptors, they may act only in a non-genomic mode. Multiple studies have been conducted so far to show efficacy of neurosteroids in the treatment of the central and peripheral nervous system injury, ischemia, neurodegenerative diseases, or seizures. In this review we focused primarily on neurosteroid mechanisms of action and their role in the process of neurodegeneration. Most of the data refers to results obtained in experimental studies. However, it should be realized that knowledge about neuroactive steroids remains still incomplete and requires confirmation in clinical conditions.

Neuroactive steroids induce changes in fetal sheep behavior during normoxic and asphyxic states

Allopregnanolone and related steroids are potent γ-aminobutyric acid receptor-A receptor agonistic allosteric modulators that suppress central nervous system (CNS) activity; in some species, these neurosteroids regulate normal CNS activity before birth. The aims of this study were to determine the effect of suppressing allopregnanolone production on behavioral responses to transient asphyxia in late gestation fetal sheep using the 5α-reductase (R)-2 inhibitor, finasteride. Specificity of the effects of finasteride was assessed by co-infusion of alfaxalone, a synthetic analog of allopregnanolone. Fetal catheters and electrodes for measurement of the electrocorticogram (ECoG) and nuchal electromyogram were implanted at 125 days of gestation, and an inflatable occluder was placed to allow umbilical cord occlusion (UCO). At approximately 130 days of gestation, fetuses received carotid arterial infusion of vehicle (2-hydroxypropyl-β-cyclodextrin; 40% w/vol), finasteride (40 mg/kg/h), alfaxalone (5 mg/kg/h), or finasteride + alfaxalone. A further three groups of fetuses were subjected to 5 min UCO at 30 min after the start of each infusion regime. Finasteride treatment alone increased the incidence of arousal-like activity; this was reduced by co-infusion of alfaxalone. After UCO, finasteride treatment caused a prolongation of sub-low voltage (LV) ECoG activity and increase in aberrant ECoG spike activity when compared to vehicle-treated UCO fetuses. After UCO, alfaxalone treatment reduced the incidence of sub-LV, reduced the number of aberrant EEG spikes, and restored ECoG activity to the pattern observed after UCO in vehicle-treated fetuses. These results confirm that neurosteroids significantly modulate normal CNS activity in the late gestation fetus, modify, and limit the effects of asphyxia on the brain.

Estrogen increases latencies to seizures and levels of 5alpha-pregnan-3alpha-ol-20-one in hippocampus of wild-type, but not 5alpha-reductase knockout, mice

Sex steroids can influence seizures. Estrogen (E(2)), progesterone (P(4)), and its metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), in particular, have received much attention for exerting these effects. Typically, it is thought that E(2) precipitates seizures, and progestogens, such as P(4) and 3alpha,5alpha-THP, attenuate seizures. However, E(2) may also have antiseizure effects, perhaps in part through its enhancement of the formation of 3alpha,5alpha-THP, which has GABA(A)/benzodiazepine receptor agonist-like actions. To test this hypothesis, male and female, castrated or ovariectomized, wild-type and 5alpha-reductase knockout mice were implanted with Silastic capsules of E(2) or vehicle and then administered pentylenetetrazol (85 mg/kg, ip). Wild-type, but not 5alpha-reductase knockout, mice administered E(2) had significantly longer latencies to myoclonus and increased levels of 3alpha,5alpha-THP in the hippocampus. Thus, some of the anticonvulsive effects of E(2) may involve formation of 3alpha,5alpha-THP in the hippocampus.

The neurosteroid environment in the hippocampus exerts bi-directional effects on seizure susceptibility in mice

The progesterone derivative allopregnanolone (ALLO) rapidly potentiates gamma-aminobutyric acid(A) (GABA(A)) receptor mediated inhibition. The present studies determined whether specific manipulation of neurosteroid levels in the hippocampus would alter seizure susceptibility in an animal model genetically susceptible to severe ethanol (EtOH) withdrawal, Withdrawal Seizure-Prone (WSP) mice. Male WSP mice were surgically implanted with bilateral guide cannulae aimed at the CA1 region of the hippocampus one week prior to measuring seizure susceptibility to the convulsant pentylenetetrazol (PTZ), given via timed tail vein infusion. Bilateral intra-hippocampal infusion of ALLO (0.1 microg/side) was anticonvulsant, increasing the threshold dose of PTZ for onset to myoclonic twitch and face and forelimb clonus by 2- to 3-fold. In contrast, infusion of the 5 alpha-reductase inhibitor finasteride (FIN; 2 microg/side), which decreases endogenous ALLO levels, exhibited a proconvulsant effect. During withdrawal from chronic EtOH exposure, WSP mice were tolerant to the anticonvulsant effect of intra-hippocampal ALLO infusion, consistent with published results following systemic injection. Finally, administration of intra-hippocampal FIN given only during the development of physical dependence significantly increased EtOH withdrawal severity, measured by handling-induced convulsions. These findings are the first demonstration that bi-directional manipulation of hippocampal ALLO levels produces opposite behavioral consequences that are consistent with alterations in GABAergic inhibitory tone in drug-naive mice. Importantly, EtOH withdrawal rendered WSP mice less sensitive to ALLO's anticonvulsant effect and more sensitive to FIN's proconvulsant effect, suggesting an alteration in the sensitivity of hippocampal GABA(A) receptors in response to fluctuations in GABAergic neurosteroids during ethanol withdrawal.

Inhibition of progesterone metabolism mimics the effect of progesterone withdrawal on forced swim test immobility

Withdrawal from high levels of progesterone in rodents has been proposed as a model for premenstrual syndrome or postpartum depression. Forced swim test (FST) immobility, used to model depression, was assessed in intact female DBA/2J mice following progesterone withdrawal (PWD) or treatment with the 5alpha-reductase inhibitor finasteride. Following 5 daily progesterone injections (5 mg/kg IP) FST immobility increased only in mice withdrawn for 3 days (p<.05). In another experiment, 3 days of PWD significantly decreased levels of progesterone compared to 0 days of withdrawal, but progesterone levels at 3 days of PWD did not differ from vehicle-treated controls. In a final study, mice received daily injections of progesterone (5 mg/kg IP) for 8 days, with 0 mg/kg, 50 mg/kg, or 100 mg/kg finasteride co-administered for the last three days. Mice that received 100 mg/kg finasteride, but not 50 mg/kg finasteride, displayed increased FST immobility. PWD and finasteride treatment, both of which reduce allopregnanolone levels, were associated with increased FST immobility in female DBA/2J mice. These findings suggest that decreased levels of the GABAergic neurosteroid allopregnanolone contribute to symptoms of PWD. Future studies of PWD may provide information about human conditions that are associated with hormone changes such as premenstrual syndrome or postpartum depression.

Hypothalamic-pituitary-adrenal axis modulation of GABAergic neuroactive steroids influences ethanol sensitivity and drinking behavior

Activation of the hypothalamic-pituitary-adrenal (HPA) axis leads to elevations in gamma-aminobutyric acid (GABA)-ergic neuroactive steroids that enhance GABA neurotransmission and restore homeostasis following stress. This regulation of the HPA axis maintains healthy brain function and protects against neuropsychiatric disease. Ethanol sensitivity is influenced by elevations in neuroactive steroids that enhance the GABAergic effects of ethanol, and may prevent excessive drinking in rodents and humans. Low ethanol sensitivity is associated with greater alcohol consumption and increased risk of alcoholism. Indeed, ethanol-dependent rats show blunted neurosteroid responses to ethanol administration that may contribute to ethanol tolerance and the propensity to drink greater amounts of ethanol. The review presents evidence to support the hypothesis that neurosteroids contribute to ethanol actions and prevent excessive drinking, while the lack of neurosteroid responses to ethanol may underlie innate or chronic tolerance and increased risk of excessive drinking. Neurosteroids may have therapeutic use in alcohol withdrawal or for relapse prevention.

A new look at the 5alpha-reductase inhibitor finasteride

Finasteride is the first 5alpha-reductase inhibitor that received clinical approval for the treatment of human benign prostatic hyperplasia (BPH) and androgenetic alopecia (male pattern hair loss). These clinical applications are based on the ability of finasteride to inhibit the Type II isoform of the 5alpha-reductase enzyme, which is the predominant form in human prostate and hair follicles, and the concomitant reduction of testosterone to dihydrotestosterone (DHT). In addition to catalyzing the rate-limiting step in the reduction of testosterone, both isoforms of the 5alpha-reductase enzyme are responsible for the reduction of progesterone and deoxycorticosterone to dihydroprogesterone (DHP) and dihydrodeoxycorticosterone (DHDOC), respectively. Recent preclinical data indicate that the subsequent 3alpha-reduction of DHT, DHP and DHDOC produces steroid metabolites with rapid non-genomic effects on brain function and behavior, primarily via an enhancement of gamma-aminobutyric acid (GABA)ergic inhibitory neurotransmission. Consistent with their ability to enhance the action of GABA at GABA(A) receptors, these steroid derivatives (termed neuroactive steroids) possess anticonvulsant, antidepressant and anxiolytic effects in addition to altering aspects of sexual- and alcohol-related behaviors. Thus, finasteride, which inhibits both isoforms of 5alpha-reductase in rodents, has been used as a tool to manipulate neuroactive steroid levels and determine the impact on behavior. Results of some preclinical studies and clinical observations with finasteride are described in this review article. The data suggest that endogenous neuroactive steroid levels may be inversely related to symptoms of premenstrual and postpartum dysphoric disorder, catamenial epilepsy, depression, and alcohol withdrawal.

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

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

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

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