Neurosteroids: biosynthesis and function of these novel neuromodulators

Effect of neurosteroid modulation on global ischaemia-reperfusion-induced cerebral injury in mice

The present study was designed to investigate the putative effect of neurosteroid modulation on global ischaemia-reperfusion-induced cerebral injury in mice. Bilateral carotid artery occlusion followed by reperfusion, produced a significant rise in cerebral infarct size along with impairment of grip strength and motor coordination in Swiss albino mice. Administration of carbamazepine (16 mg/kg, i.p.) before global cerebral ischaemia significantly attenuated cerebral infarct size and improved the motor performance. However, administration of indomethacin (100 mg/kg, i.p.) attenuated the neuroprotective effect of carbamazepine. Mexiletine (50 mg/kg, i.p.) did not produce significant neuroprotective effect. It may be concluded that the neuroprotective effect of carbamazepine may be due to increase in synthesis of neurosteroids perhaps by activating enzyme (3α HSD) as indomethacin attenuated the neuroprotective effect of carbamazepine. The sodium channel blocking effect of carbamazepine may not be involved in neuroprotection as mexiletine, a sodium channel blocker, did not produce significant neuroprotective effect.

Modulatory role of androgenic and estrogenic neurosteroids in determining the direction of synaptic plasticity in the CA1 hippocampal region of male rats

Estrogenic and androgenic neurosteroids can rapidly modulate synaptic plasticity in the brain through interaction with membrane receptors for estrogens (ERs) and androgens (ARs). We used electrophysiological recordings in slices of young and adolescent male rats to explore the influence of sex neurosteroids on synaptic plasticity in the CA1 hippocampal region, by blocking ARs or ERs during induction of long‐term depression (LTD) and depotentiation (DP) by low‐frequency stimulation (LFS) and long‐term potentiation (LTP) by high‐frequency stimulation (HFS). We found that LTD and DP depend on ARs, while LTP on ERs in both age groups. Accordingly, the AR blocker flutamide affected induction of LTD reverting it into LTP, and prevented DP, while having no effect on HFS‐dependent LTP. Conversely, ER blockade with ICI 182,780 (ICI) markedly reduced LTP, but did not influence LTD and DP. However, the receptor blockade did not affect the maintenance of either LTD or LTP. Moreover, we found that similar to LTP and LTD induced in control condition, the LTP unveiled by flutamide during LFS and residual LTP induced by HFS under ICI depended on N‐methyl‐d aspartate receptor (NMDAR) activation. Furthermore, as the synaptic paired‐pulse facilitation (PPF) was not affected by either AR or ER blockade, we suggest that sex neurosteroids act primarily at a postsynaptic level. This study demonstrates for the first time the crucial role of estrogenic and androgenic neurosteroids in determining the sign of hippocampal synaptic plasticity in male rat and the activity‐dependent recruitment of androgenic and estrogenic pathways leading to LTD and LTP, respectively.

This study shows a crucial and opposite role of estrogenic and androgenic neurosteroids in guiding the direction of synaptic plasticity in the hippocampus CA1 region of male rat, through activation of their specific receptors. In fact, by using selective antagonists for estrogen receptors (ICI 182,730) or androgen receptors (flutamide), we show that long‐term potentiation (LTP) induced by high‐frequency stimulation (HFS) depends on estrogenic signals, while long‐term depression (LTD) and depotentiation induced by low‐frequency stimulation (LFS) require activation of androgenic pathway. We suggest that different stimulation frequencies may lead to LTD or LTP depending on activation of specific neurosteroid pathway.

Synaptic long-term potentiation and depression in the rat medial vestibular nuclei depend on neural activation of estrogenic and androgenic signals

Estrogenic and androgenic steroids can be synthesised in the brain and rapidly modulate synaptic transmission and plasticity through direct interaction with membrane receptors for estrogens (ERs) and androgens (ARs). We used whole cell patch clamp recordings in brainstem slices of male rats to explore the influence of ER and AR activation and local synthesis of 17β-estradiol (E2) and 5α-dihydrotestosterone (DHT) on the long-term synaptic changes induced in the neurons of the medial vestibular nucleus (MVN). Long-term depression (LTD) and long-term potentiation (LTP) caused by different patterns of high frequency stimulation (HFS) of the primary vestibular afferents were assayed under the blockade of ARs and ERs or in the presence of inhibitors for enzymes synthesizing DHT (5α-reductase) and E2 (P450-aromatase) from testosterone (T). We found that LTD is mediated by interaction of locally produced androgens with ARs and LTP by interaction of locally synthesized E2 with ERs. In fact, the AR block with flutamide prevented LTD while did not affect LTP, and the blockade of ERs with ICI 182,780 abolished LTP without influencing LTD. Moreover, the block of P450-aromatase with letrozole not only prevented the LTP induction, but inverted LTP into LTD. This LTD is likely due to the local activation of androgens, since it was abolished under blockade of ARs. Conversely, LTD was still induced in the presence of finasteride the inhibitor of 5α-reductase demonstrating that T is able to activate ARs and induce LTD even when DHT is not synthesized. This study demonstrates a key and opposite role of sex neurosteroids in the long-term synaptic changes of the MVN with a specific role of T-DHT for LTD and of E2 for LTP. Moreover, it suggests that different stimulation patterns can lead to LTD or LTP by specifically activating the enzymes involved in the synthesis of androgenic or estrogenic neurosteroids.

Neurosteroid interactions with synaptic and extrasynaptic GABA(A) receptors: regulation of subunit plasticity, phasic and tonic inhibition, and neuronal network excitability

RATIONALE

Neurosteroids are steroids synthesized within the brain with rapid effects on neuronal excitability. Allopregnanolone, allotetrahydrodeoxycorticosterone, and androstanediol are three widely explored prototype endogenous neurosteroids. They have very different targets and functions compared to conventional steroid hormones. Neuronal γ-aminobutyric acid (GABA) type A (GABA(A)) receptors are one of the prime molecular targets of neurosteroids.

OBJECTIVE

This review provides a critical appraisal of recent advances in the pharmacology of endogenous neurosteroids that interact with GABA(A) receptors in the brain. Neurosteroids possess distinct, characteristic effects on the membrane potential and current conductance of the neuron, mainly via potentiation of GABA(A) receptors at low concentrations and direct activation of receptor chloride channel at higher concentrations. The GABA(A) receptor mediates two types of inhibition, now characterized as synaptic (phasic) and extrasynaptic (tonic) inhibition. Synaptic release of GABA results in the activation of low-affinity γ2-containing synaptic receptors, while high-affinity δ-containing extrasynaptic receptors are persistently activated by the ambient GABA present in the extracellular fluid. Neurosteroids are potent positive allosteric modulators of synaptic and extrasynaptic GABA(A) receptors and therefore enhance both phasic and tonic inhibition. Tonic inhibition is specifically more sensitive to neurosteroids. The resulting tonic conductance generates a form of shunting inhibition that controls neuronal network excitability, seizure susceptibility, and behavior.

CONCLUSION

The growing understanding of the mechanisms of neurosteroid regulation of the structure and function of the synaptic and extrasynaptic GABA(A) receptors provides many opportunities to create improved therapies for sleep, anxiety, stress, epilepsy, and other neuropsychiatric conditions.

Biogenesis and transport of membrane domains-potential implications in brain pathologies

Lipids in biological membranes show astonishing chemical diversity, but they also show some key conserved structures in different organisms. In addition, some of their biophysical properties have been related to specific functions. In this review, we aim to discuss the role of sphingolipids- and cholesterol-rich micro- and nano-membrane domains (MD) and highlight their pivotal role in lipid-protein clustering processes, vesicle biogenesis and membrane fusion. We further review potential connections between human pathologies and defects in MD biosynthesis, recycling and homeostasis. Brain, which is second only to the adipose tissues in term of lipid abundance, is particularly affected by MD defects which are linked to neurodegenerative disorders. Finally we propose a potential connection between MD and several nutrient-related processes and envision how diet and autophagy could bring insights towards understanding the impact of global lipid homeostasis on human health and disease.

The influence of stress at puberty on mood and learning: role of the α4βδ GABAA receptor

It is well-known that the onset of puberty is associated with changes in mood as well as cognition. Stress can have an impact on these outcomes, which in many cases, can be more influential in females, suggesting that gender differences exist. The adolescent period is a vulnerable time for the onset of certain psychopathologies, including anxiety disorders, depression and eating disorders, which are also more prevalent in females. One factor which may contribute to stress-triggered anxiety at puberty is the GABAA receptor (GABAR), which is known to play a pivotal role in anxiety. Expression of α4βδ GABARs increases on the dendrites of CA1 pyramidal cells at the onset of puberty in the hippocampus, part of the limbic circuitry which governs emotion. This receptor is a sensitive target for the stress steroid 3α-OH-5[α]β-pregnan-20-one or [allo]pregnanolone, which paradoxically reduces inhibition and increases anxiety during the pubertal period (post-natal day ∼35-44) of female mice in contrast to its usual effect to enhance inhibition and reduce anxiety. Spatial learning and synaptic plasticity are also adversely impacted at puberty, likely a result of increased expression of α4βδ GABARs on the dendritic spines of CA1 hippocampal pyramidal cells, which are essential for consolidation of memory. This review will focus on the role of these receptors in mediating behavioral changes at puberty. Stress-mediated changes in mood and cognition in early adolescence may have relevance for the expression of psychopathologies in adulthood.

The influence of age and season on fecal dehydroepiandrosterone-sulfate (DHEAS) concentrations in Japanese macaques (Macaca fuscata)

Dehydroepiandrosterone (DHEA) and its sulfate, DHEAS, are the most abundant steroid hormones in primates, providing a large reservoir of precursors for the production of androgens. DHEAS levels decline with age in adult humans and nonhuman primates, prompting its consideration as a biomarker of senescence. However, the mechanisms responsible for this age-related decrease and its relationship to reproduction remain elusive. This research investigated DHEAS concentrations in fecal samples in order to determine age-related changes in captive Japanese macaques, as well as to assess the possible influence of seasonality. The subjects were 25 female Japanese macaques (2weeks to 14years-old) housed outdoors in social groups at the Primate Research Institute. We collected three fecal samples from each animal during the breeding season (October to December) and three additional samples from adult females during the non-breeding season (May to June). The hormonal concentrations were determined using enzyme immunoassay. DHEAS concentration was negatively correlated with age, but we did not find a significant difference between breeding and non-breeding seasons. Neonatal macaques had the highest DHEAS concentrations of all age groups. We suggest that elevated neonatal DHEAS is possibly a residue from fetal adrenal secretion and that, as in humans, it might assist in neurobiological development.

Interactive effects of dehydroepiandrosterone and testosterone on cortical thickness during early brain development

Humans and the great apes are the only species demonstrated to exhibit adrenarche, a key endocrine event associated with prepubertal increases in the adrenal production of androgens, most significantly dehydroepiandrosterone (DHEA) and to a certain degree testosterone. Adrenarche also coincides with the emergence of the prosocial and neurobehavioral skills of middle childhood and may therefore represent a human-specific stage of development. Both DHEA and testosterone have been reported in animal and in vitro studies to enhance neuronal survival and programmed cell death depending on the timing, dose, and hormonal context involved, and to potentially compete for the same signaling pathways. Yet no extant brain-hormone studies have examined the interaction between DHEA- and testosterone-related cortical maturation in humans. Here, we used linear mixed models to examine changes in cortical thickness associated with salivary DHEA and testosterone levels in a longitudinal sample of developmentally healthy children and adolescents 4-22 years old. DHEA levels were associated with increases in cortical thickness of the left dorsolateral prefrontal cortex, right temporoparietal junction, right premotor and right entorhinal cortex between the ages of 4-13 years, a period marked by the androgenic changes of adrenarche. There was also an interaction between DHEA and testosterone on cortical thickness of the right cingulate cortex and occipital pole that was most significant in prepubertal subjects. DHEA and testosterone appear to interact and modulate the complex process of cortical maturation during middle childhood, consistent with evidence at the molecular level of fast/nongenomic and slow/genomic or conversion-based mechanisms underlying androgen-related brain development.

α4βδ GABAA receptors and tonic inhibitory current during adolescence: effects on mood and synaptic plasticity

The onset of puberty is associated with alterations in mood as well as changes in cognitive function, which can be more pronounced in females. Puberty onset in female mice is associated with increased expression of α4βδ γ-amino-butyric acid-A (GABAA) receptors (GABARs) in CA1 hippocampus. These receptors, which normally have low expression in this central nervous system (CNS) site, emerge along the apical dendrites as well as on the dendritic spines of pyramidal neurons, adjacent to excitatory synapses where they underlie a tonic inhibition that shunts excitatory current and impairs activation of N-methyl-D-aspartate (NMDA) receptors, the trigger for synaptic plasticity. As would be expected, α4βδ expression at puberty also prevents long-term potentiation (LTP), an in vitro model of learning which is a function of network activity, induced by theta burst stimulation of the Schaffer collaterals to the CA1 hippocampus. The expression of these receptors also impairs spatial learning in a hippocampal-dependent task. These impairments are not seen in δ knock-out (-/-) mice, implicating α4βδ GABARs. α4βδ GABARs are also a sensitive target for steroids such as THP ([allo]pregnanolone or 3α-OH-5α[β]-pregnan-20-one), which are dependent upon the polarity of GABAergic current. It is well-known that THP can increase depolarizing current gated by α4βδ GABARs, but more recent data suggest that THP can reduce hyperpolarizing current by accelerating receptor desensitization. At puberty, THP reduces the hyperpolarizing GABAergic current, which removes the shunting inhibition that impairs synaptic plasticity and learning at this time. However, THP, a stress steroid, also increases anxiety, via its action at α4βδ GABARs because it is not seen in δ(-/-) mice. These findings will be discussed as well as their relevance to changes in mood and cognition at puberty, which can be a critical period for certain types of learning and when anxiety disorders and mood swings can emerge.

A stress steroid triggers anxiety via increased expression of α4βδ GABAA receptors in methamphetamine dependence

Methamphetamine (METH) is an addictive stimulant drug. In addition to drug craving and lethargy, METH withdrawal is associated with stress-triggered anxiety. However, the cellular basis for this stress-triggered anxiety is not understood. The present results suggest that during METH withdrawal (24h) following chronic exposure (3mg/kg, i.p. for 3-5weeks) of adult, male mice, the effect of one neurosteroid released by stress, 3α,5α-THP (3α-OH-5α-pregnan-20-one), and its 3α,5β isomer reverse to trigger anxiety assessed by the acoustic startle response (ASR), in contrast to their usual anti-anxiety effects. This novel effect of 3α,5β-THP was due to increased (three-fold) hippocampal expression of α4βδ GABAA receptors (GABARs) during METH withdrawal (24h-4weeks) because anxiogenic effects of 3α,5β-THP were not seen in α4-/- mice. 3α,5β-THP reduces current at these receptors when it is hyperpolarizing, as observed during METH withdrawal. As a result, 3α,5β-THP (30nM) increased neuronal excitability, assessed with current clamp and cell-attached recordings in CA1hippocampus, one CNS site which regulates anxiety. α4βδ GABARs were first increased 1h after METH exposure and recovered 6weeks after METH withdrawal. Similar increases in α4βδ GABARs and anxiogenic effects of 3α,5β-THP were noted in rats during METH withdrawal (24h). In contrast, the ASR was increased by chronic METH treatment in the absence of 3α,5β-THP administration due to its stimulant effect. Although α4βδ GABARs were increased by chronic METH treatment, the GABAergic current recorded from hippocampal neurons at this time was a depolarizing, shunting inhibition, which was potentiated by 3α,5β-THP. This steroid reduced neuronal excitability and anxiety during chronic METH treatment, consistent with its typical effect. Flumazenil (10mg/kg, i.p., 3×) reduced α4βδ expression and prevented the anxiogenic effect of 3α,5β-THP after METH withdrawal. Our findings suggest a novel mechanism underlying stress-triggered anxiety after METH withdrawal mediated by α4βδ GABARs.

Neonatal allopregnanolone levels alteration: effects on behavior and role of the hippocampus

Several works have pointed out the importance of the neurosteroid allopregnanolone for the maturation of the central nervous system and for adult behavior. The alteration of neonatal allopregnanolone levels in the first weeks of life alters emotional adult behavior and sensory gating processes. Without ruling out brain structures, some of these behavioral alterations seem to be related to a different functioning of the hippocampus in adult age. We focus here on the different behavioral studies that have revealed the importance of neonatal allopregnanolone levels for the adult response to novel environmental stimuli, anxiety-related behaviors and processing of sensory inputs (prepulse inhibition). An increase in neonatal physiological allopregnanolone levels decreases anxiety and increases novelty responses in adult age, thus affecting the individual response to environmental cues. These effects are also accompanied by a decrease in prepulse inhibition, indicating alterations in sensory gating that have been related to that present in disorders, such as schizophrenia. Moreover, behavioral studies have shown that some of these effects are related to a different functioning of the dorsal hippocampus, as the behavioral effects (decrease in anxiety and locomotion or increase in prepulse inhibition) of intrahippocampal allopregnanolone infusions in adult age are not present in those subjects in whom neonatal allopregnanolone levels were altered. Recent data indicated that this hippocampal involvement may be related to alterations in the expression of gamma-aminobutyric-acid receptors containing α4 and δ subunits, molecular alterations that can persist into adult age and that can, in part, explain the reported behavioral disturbances.

Potential role of allopregnanolone for a safe and effective therapy of neuropathic pain

Because the treatment and management of neuropathic pain are extremely complicated, the characterization of novel analgesics and neuroprotectors with safe toxicological profiles is a crucial need to develop efficient therapies. Several investigations revealed that the natural neurosteroid allopregnanolone (AP) exerts analgesic, neuroprotective, antidepressant and anxiolytic effects. These effects result from AP ability to modulate GABA(A), glycine, L- and T-type calcium channels. It has been shown that AP treatment induced beneficial actions in humans and animal models with no toxic side effects. In particular, a multi-parametric analysis revealed that AP efficiently counteracted chemotherapy-evoked neuropathic pain in rats. It has also been demonstrated that the modulation of AP-producing enzyme, 3α-hydroxysteroid oxido-reductase (3α-HSOR), in the spinal cord regulates thermal and mechanical pain thresholds of peripheral nerve injured neuropathic rats. The painful symptoms were exacerbated by intrathecal injections of provera (pharmacological inhibitor of 3α-HSOR) which decreased AP production in the spinal cord. By contrast, the enhancement of AP concentration in the intrathecal space induced analgesia and suppression of neuropathic symptoms. Moreover, in vivo siRNA-knockdown of 3α-HSOR expression in healthy rat dorsal root ganglia increased thermal and mechanical pain perceptions while AP evoked a potent antinociceptive action. In humans, blood levels of AP were inversely associated with low back and chest pain. Furthermore, oral administration of AP analogs induced antinociception. Altogether, these data indicate that AP, which possesses a high therapeutic potential and a good toxicological profile, may be used to develop effective and safe strategies against chronic neuropathic pain.

Brain and pineal 7α-hydroxypregnenolone stimulating locomotor activity: identification, mode of action and regulation of biosynthesis

Biologically active steroids synthesized in the central and peripheral nervous systems are termed neurosteroids. However, the biosynthetic pathways leading to the formation of neurosteroids are still incompletely elucidated. 7α-Hydroxypregnenolone, a novel bioactive neurosteroid stimulating locomotor activity, has been recently identified in the brain of newts and quail. Subsequently, the mode of action and regulation of biosynthesis of 7α-hydroxypregnenolone have been determined. Moreover, recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity in juvenile chickens, connecting light-induced gene expression with locomotion. This review summarizes the advances in our understanding of the identification, mode of action and regulation of biosynthesis of brain and pineal 7α-hydroxypregnenolone, a potent stimulator of locomotor activity.

Neonatal neurosteroid levels are determinant in shaping adult prepulse inhibition response to hippocampal allopregnanolone in rats

Diverse studies indicate that the alteration of the physiological levels of neurosteroids in early neonatal phases provokes alterations in the maturation of certain cerebral structures. Allopregnanolone (ALLO) has important modulatory effects in the hippocampus during the postnatal period where the adult pattern of inhibitory transmission is being established. In order to study whether endogenous neonatal ALLO levels would be a determinant parameter involved in mediating adult hippocampal GABAA system maturation, we investigated the effects of neonatal finasteride (50mg/kg, SC) treatment and ALLO (ALLO; 20mg/kg, SC) supplementation on an animal behavioural model with relevance to neurodevelopmental disorder, such as schizophrenia. Two sets of experiments were conducted. Neonatal treatment (from postnatal day (pnd) 5 to pnd9) was performed in 23 male Wistar rats and steroid quantification was performed in hippocampal homogenates at pnd9. A second group (n=127) underwent neonatal treatment (pnd5-pnd9) and were submitted to hippocampal surgery at 80d. The behavioural response to bilateral intrahippocampal neurosteroid administration (ALLO, 0.2μg/0.5μl per side or pregnenolone sulphate 5ng/0.5μl per side) on novelty-induced exploration activity and prepulse inhibition (PPI) was assessed at 95d. Results showed that neonatal ALLO and finasteride administration decreased novelty directed exploratory behaviour and impaired the prepulse inhibition of the acoustic startle response at 95 days of age. Moreover, intrahippocampal ALLO increased head-dipping behaviour independently of the neonatal treatment, while intrahippocampal ALLO decreased PPI only in finasteride and ALLO groups. The results obtained in the present study indicate the importance of neonatal neurosteroid levels in the development of hippocampal function and their relevance in a behavioural phenotype that some have likened to that present in schizophrenia.

New biosynthesis and biological actions of avian neurosteroids

De novo neurosteroidogenesis from cholesterol occurs in the brain of various avian species. However, the biosynthetic pathways leading to the formation of neurosteroids are still not completely elucidated. We have recently found that the avian brain produces 7α-hydroxypregnenolone, a novel bioactive neurosteroid that stimulates locomotor activity. Until recently, it was believed that neurosteroids are produced in neurons and glial cells in the central and peripheral nervous systems. However, our recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity of juvenile birds, connecting light-induced gene expression with locomotion. The other major pineal neurosteroid allopregnanolone is involved in Purkinje cell survival during development. This paper highlights new aspects of neurosteroid synthesis and actions in birds.

Changes in serum dehydroepiandrosterone, androstenedione, testosterone, and 17β-oestradiol levels associated with disease and surgery in the horse

The aim of this work was to measure serum concentrations of dehydroepiandrosterone, androstenedione, testosterone and 17β-oestradiol in horses with various diseases and after surgery. We hypothesize that diseases and castration could potentially affect concentrations of steroid reproductive hormones. Blood samples were obtained from six groups of horses comprising a total of 119 horses (75 males and 44 females, 5–15 years old) with laminitis, acute abdominal syndrome, acute diseases, chronic diseases, after castration and healthy control. Hormone concentrations in serum were determined for each group using competitive enzyme immunoassay. Significant increases compared to control were found for dehydroepiandrosterone in horses with castration (P < 0.01), acute abdominal syndrome and acute diseases (P < 0.05). Besides, significant increases were observed for androstenedione in horses with laminitis, castration and acute diseases (P < 0.01), and in acute abdominal syndrome and chronic diseases (P < 0.05). Significant increases were also found for testosterone in horses with castration (P < 0.01) and with laminitis, acute abdominal syndrome and chronic diseases (P < 0.05). The lowest values of testosterone were found in the control group. Compared to control, 17b-oestradiol serum concentrations showed significant decreases (P < 0.01) in horses with laminitis, acute abdominal syndrome, acute and chronic diseases. Significant differences (P < 0.05) for the four studied hormones were found between males and females in each group. Our results showed that there were significant differences in steroid reproductive hormone concentrations in diseased horses and in those after surgery, compared to controls.

Changes in neuroactive steroid concentrations after preterm delivery in the Guinea pig

BACKGROUND

Preterm birth is a major cause of neurodevelopmental disorders. Allopregnanolone, a key metabolite of progesterone, has neuroprotective and developmental effects in the brain. The objectives of this study were to measure the neuroactive steroid concentrations following preterm delivery in a neonatal guinea pig model and assess the potential for postnatal progesterone replacement therapy to affect neuroactive steroid brain and plasma concentrations in preterm neonates.

METHODS

Preterm (62-63 days) and term (69 days) guinea pig pups were delivered by cesarean section and tissue was collected at 24 hours. Plasma progesterone, cortisol, allopregnanolone, and brain allopregnanolone concentrations were measured by immunoassay. Brain 5α-reductase (5αR) expression was determined by Western blot. Neurodevelopmental maturity of preterm neonates was assessed by immunohistochemistry staining for myelination, glial cells, and neurons.

RESULTS

Brain allopregnanolone concentrations were significantly reduced after birth in both preterm and term neonates. Postnatal progesterone treatment in preterm neonates increased brain and plasma allopregnanolone concentrations. Preterm neonates had reduced myelination, low birth weight, and high mortality compared to term neonates. Brain 5αR expression was also significantly reduced in neonates compared to fetal expression.

CONCLUSIONS

Delivery results in a loss of neuroactive steroid concentrations resulting in a premature reduction in brain allopregnanolone in preterm neonates. Postnatal progesterone therapy reestablished neuroactive steroid levels in preterm brains, a finding that has implications for postnatal growth following preterm birth that occurs at a time of neurodevelopmental immaturity.

Hyperammonemia alters the modulation by different neurosteroids of the glutamate-nitric oxide-cyclic GMP pathway through NMDA- GABAA - or sigma receptors in cerebellum in vivo

Several neurosteroids modulate the glutamate-nitric oxide (NO)-cGMP pathway in cerebellum through modulation of NMDA- GABAA - or sigma receptors. Hyperammonemia alters the concentration of several neurosteroids and impairs the glutamate-NO-cGMP pathway, leading to impaired learning ability. This work aimed to assess whether chronic hyperammonemia alters the modulation by different neurosteroids of GABAA, NMDA, and/or sigma receptors and of the glutamate-NO-cGMP pathway in cerebellum. Neurosteroids were administered through microdialysis probes, and extracellular cGMP and citrulline were measured. Then NMDA was administered to assess the effects on the glutamate-NO-cGMP pathway activation. Hyperammonemia completely modifies the effects of pregnanolone and pregnenolone. Pregnanolone acts as a GABAA receptor agonist in controls, but as an NMDA receptor antagonist in hyperammonemic rats. Pregnenolone does not induce any effect in controls, but acts as a sigma receptor agonist in hyperammonemic rats. Hyperammonemia potentiates the actions of tetrahydrodeoxy-corticosterone (THDOC) as a GABAA receptor agonist, allopregnanolone as an NMDA receptor antagonist, and pregnenolone sulfate as an NMDA receptor activation enhancer. Neurosteroids that reduce the pathway (pregnanolone, THDOC, allopregnanolone, DHEAS) may contribute to cognitive impairment in hyperammonemia and hepatic encephalopathy. Pregnenolone would impair cognitive function in hyperammonemia. Neurosteroids that restore the pathway in hyperammonemia (pregnenolone sulfate) could restore cognitive function in hyperammonemia and encephalopathy.

Regional distribution of 5α-reductase type 2 in the adult rat brain: an immunohistochemical analysis

The enzyme 5α-reductase (5αR) catalyzes the conversion of testosterone and other Δ(4)-3-ketosteroids into their 5α-reduced metabolites. Of the five members of the 5αR family, the type 2 enzyme (5αR2) plays a key role in androgen metabolism, and is abundantly distributed in the urogenital system. Although 5αR2 has been reported to be highly expressed in the brain during early developmental stages, little is currently known on its anatomical and cellular distribution in the adult brain. Thus, the present study was designed to determine the detailed localization of 5αR2 in the adult rat brain, using a highly specific polyclonal antibody against this isoform. Parasagittal and coronal sections revealed 5αR2 immunoreactivity throughout most brain regions, with strong immunolabeling in the layers III and VI of the prefrontal and somatosensory cortex, olfactory bulb, thalamic nuclei, CA3 field of hippocampus, basolateral amygdala and Purkinje cell layer of cerebellum. Lower 5αR2 levels were detected in the hypothalamus and midbrain. Moreover, double labeling fluorescence with confocal laser scanning microscopy (CLSM) revealed that 5αR2 is localized in neurons, but not in glial cells. Specifically, the enzyme was documented in the pyramidal neurons of the cortex by CLSM analysis of simultaneous Golgi-Cox and immunofluorescent staining. Finally, low levels of 5αR2 expression were identified in GABAergic cells across the cortex, hippocampus and striatum. These findings show that, in the adult brain, 5αR2 is distributed in critical regions for behavioral regulation, suggesting that the functional role of this isoform is present throughout the entire lifespan of the individual.

Determination of steroid metabolome as a possible tool for laboratory diagnosis of schizophrenia

Metabolomic studies represent a promising tool for early diagnosis of schizophrenia. The aim of this study was to find differences in the steroid spectrum in patients and controls, and to assess the diagnosis of schizophrenia by building a predictive model based on steroid data. Thirty-nine serum steroids (22 neuroactive steroids and their metabolites and 17 polar conjugates) representing steroid metabolome were measured by gas chromatography-mass spectrometry in 22 drug-naive (first episode) schizophrenia patients (13 men and 9 women) before and after six-month treatment with atypical antipsychotics. The results were compared to the data from healthy subjects (22 males, 25 females). In summary the following significant differences were found: (1) In both sexes higher levels of pregnenolone sulfate and sulfated 5α- as well as 5β-saturated metabolites of C21-steroids in progesterone metabolic pathway were found in patients, pointing to decreased activity of sulfatase. (2) In a few instances decreased levels of the respective 5α-metabolites of C21 steroids were found in patients. (3) As C19 steroids concern, in both sexes there were considerably lowered levels of 5β-reduced metabolites in patients. On the other hand, with only a few exceptions, the treatment did not significantly influence most steroid levels. Further, to assess the relationships between schizophrenia status and steroid levels and to build the predictive model of schizophrenia, multivariate regression with reduction of dimensionality (the method of orthogonal projections to latent structures, OPLS) was applied. Irrespective of the small number of patients, use of this model enabled us to state the diagnosis of schizophrenia with almost 100% sensitivity. Our findings suggest that the assessment of steroid levels may become a valid and accurate laboratory test in psychiatry. A limitation of our study is the absence of subjects with a diagnosis other than schizophrenia, so we cannot conclude whether the results are specific for schizophrenia. On the other hand, steroid metabolome model may be used as a diagnostic tool for further studies.

Characterization, neurosteroid binding and brain distribution of human membrane progesterone receptors δ and {epsilon} (mPRδ and mPR{epsilon}) and mPRδ involvement in neurosteroid inhibition of apoptosis

Three members of the progestin and adipoQ receptor (PAQR) family, PAQR-7, PAQR-8, and PAQR-5 [membrane progesterone (P4) receptor (PR) (mPR)α, mPRβ, and mPRγ], function as plasma mPRs coupled to G proteins in mammalian cells, but the characteristics of two other members, PAQR6 and PAQR9 (mPRδ and mPRε), remain unclear, because they have only been investigated in yeast expression systems. Here, we show that recombinant human mPRδ and mPRε expressed in MDA-MB-231 breast cancer cells display specific, saturable, high-affinity [(3)H]-P4 binding on the plasma membranes of transfected cells with equilibrium dissociation constants (K(d)s) of 2.71 and 2.85 nm, respectively, and low affinity for R5020, characteristics typical of mPRs. P4 treatment increased cAMP production as well as [(35)S]-guanosine 5'-triphosphate (GTP)γS binding to transfected cell membranes, which was immunoprecipitated with a stimulatory G protein antibody, suggesting both mPRδ and mPRε activate a stimulatory G protein (Gs), unlike other mPRs, which activate an inhibitory G protein (Gi). All five mPR mRNAs were detected in different regions of the human brain, but mPRδ showed greatest expression in many regions, including the forebrain, hypothalamus, amygdala, corpus callosum, and spinal cord, whereas mPRε was abundant in the pituitary gland and hypothalamus. Allopregnanolone and other neurosteroids bound to mPRδ and other mPRs and acted as agonists, activating second messengers and decreased starvation-induced cell death and apoptosis in mPRδ-transfected cells and in hippocampal neuronal cells at low nanomolar concentrations. The results suggest that mPRδ and mPRε function as mPRs coupled to G proteins and are potential intermediaries of nonclassical antiapoptotic actions of neurosteroids in the central nervous system.

Biosynthesis and biological actions of pineal neurosteroids in domestic birds

The central and peripheral nervous systems have the capacity of synthesizing steroids de novo from cholesterol, the so-called 'neurosteroids'. De novo synthesis of neurosteroids from cholesterol appears to be a conserved property across the subphylum vertebrata. Until recently, it was generally believed that neurosteroids are produced in neurons and glial cells in the central and peripheral nervous systems. However, our recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity of juvenile birds, connecting light-induced gene expression with locomotion. The other major pineal neurosteroid allopregnanolone is involved in Purkinje cell survival by suppressing the activity of caspase-3, a crucial mediator of apoptosis during cerebellar development. This review is an updated summary of the biosynthesis and biological actions of pineal neurosteroids.

Alteration of neonatal Allopregnanolone levels affects exploration, anxiety, aversive learning and adult behavioural response to intrahippocampal neurosteroids

Neurosteroids (NS) are well known to exert modulatory effects on ionotropic receptors. Recent findings indicate that NS could also act as important factors during development. In this sense, neonatal modifications of Allopregnanolone (Allop) levels during critical periods have been demonstrate to alter the morphology of the hippocampus but also other brain structures. The aim of the present work is to screen whether the alterations of Allop levels modify adult CA1 hippocampal response to NS administration. For this purpose, pups were injected with Allop (20 mg/kg s.c.), Finasteride (5α-reductase inhibitor that impedes Allop synthesis) (50 mg/kg s.c.) or Vehicle from postnatal day 5 (P5) to postnatal day 9 (P9). NS levels were tested at P5. To test the behavioural hippocampal response to NS in adulthood, animals were implanted with a bilateral cannula into the CA1 hippocampus at 80 days old and injected with Allop (0.2 μg/0.5 μl), Pregnenolone sulphate (5 ng/0.5 μl) or Vehicle in each hippocampus. After injections animals were tested in the Boisser test to assess exploratory behaviour, the elevated plus maze to assess anxiety and the passive avoidance to test aversive learning. Results indicate that alteration of neonatal Allop or pregnenolone levels (by Allop and Finasteride administration, respectively) suppressed intrahippocampal Allop anxiolytic effect in the EPM. Moreover our results also indicate that manipulation of neonatal Allop levels (Allop and Finast administration) alters exploratory and anxiety-like behaviour and impairs aversive learning in the adulthood. These data point out the role of Allop in the maturation of hippocampal function and behaviour.

Possible role of pineal allopregnanolone in Purkinje cell survival

It is believed that neurosteroids are produced in the brain and other nervous systems. Here, we show that allopregnanolone (ALLO), a neurosteroid, is exceedingly produced in the pineal gland compared with the brain and that pineal ALLO acts on the Purkinje cell, a principal cerebellar neuron, to prevent apoptosis in the juvenile quail. We first demonstrated that the pineal gland is a major organ of neurosteroidogenesis. A series of experiments using molecular and biochemical techniques has further demonstrated that the pineal gland produces a variety of neurosteroids de novo from cholesterol in the juvenile quail. Importantly, ALLO was far more actively produced in the pineal gland than in the brain. Pinealectomy (Px) decreased ALLO concentration in the cerebellum and induced apoptosis of Purkinje cells, whereas administration of ALLO to Px quail chicks prevented apoptosis of Purkinje cells. We further found that Px significantly increased the number of Purkinje cells that expressed active caspase-3, a key protease in apoptotic pathway, and daily injection of ALLO to Px quail chicks decreased the number of Purkinje cells expressing active caspase-3. These results indicate that the neuroprotective effect of pineal ALLO is associated with the decrease in caspase-3 activity during the early stage of neuronal development. We thus provide evidence that the pineal gland is an important neurosteroidogenic organ and that pineal ALLO may be involved in Purkinje cell survival during development. This is an important function of the pineal gland in the formation of neuronal circuits in the developing cerebellum.

RU486 blocks effects of allopregnanolone on the response to restraint stress

These experiments were designed to provide information about the potential involvement of progesterone receptors in the ability of allopregnanolone (3α-hydroxy-5α-pregnan-20-one) to reduce the lordosis-inhibiting effects of restraint stress. Ovariectomized Fischer rats were hormonally primed with 10 μg estradiol benzoate and 4 mg/kg allopregnanolone or vehicle. One hour before allopregnanolone, rats were injected with the progesterone receptor antagonist, RU486 (11β-(4-dimethylamino)phenyl-17β-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one), or vehicle. Four hours after allopregnanolone or vehicle, sexual behavior was examined before and after a 5-min restraint stress. Lordosis behavior of rats primed only with estradiol benzoate declined after the 5 min of restraint while allopregnanolone prevented this decline. RU486 attenuated the ability of allopregnanolone to prevent the restraint-induced decline in lordosis behavior. These findings are consistent with earlier suggestions that progesterone receptors are involved in allopregnanolone's ability to reduce the effects of restraint stress.

Sex and estradiol influence glial pro-inflammatory responses to lipopolysaccharide in rats

There is a greater prevalence of neuroinflammatory diseases in females than males. Microglia, the major immunocompetent cells of the central nervous system, play a key role in neuroinflammation. We aimed to determine if inherent differences in toll-like receptor 4 mediated pro-inflammatory response in glia could possibly contribute to the skewed female prevalence of neuroinflammatory disorders. In addition, in order to identify if estradiol (E2), the major female sex steroid contributes to a heightened pro-inflammatory response, estradiol was added both in vivo and in vitro. Microglia and astrocytes were isolated from neonatal pups and stimulated with lipopolysaccharide (LPS) in the presence and absence of E2. Hippocampal microglia were isolated from adult male and female rats and stimulated ex vivo with LPS. Male neonatal microglia and astrocytes produced greater IL-1β mRNA than females. However, when co-incubated with varying doses of estradiol (E2), the E2 produced anti-inflammatory effects in the male microglia but a pro-inflammatory effect in female microglia. LPS-induced IL-1β mRNA was attenuated by E2 in female but not male adult hippocampal microglia. However, females supplemented with E2 in vivo produced a potentiated IL-1β mRNA response. TLR4 mRNA was decreased by LPS in both microglia and astrocytes but was not affected by sex or E2. CD14 mRNA was increased by LPS and may be elevated more in females than males in microglia but not astrocytes. Therefore, sexual dimorphic differences do occur in both neonatal and adult microglia though maturity of the microglia at the time of isolation influences the pro-inflammatory response.

The biology of fear- and anxiety-related behaviors

Anxiety is a psychological, physiological, and behavioral state induced in animals and humans by a threat to well-being or survival, either actual or potential. It is characterized by increased arousal, expectancy, autonomic and neuroendocrine activation, and specific behavior patterns. The function of these changes is to facilitate coping with an adverse or unexpected situation. Pathological anxiety interferes with the ability to cope successfully with life challenges. Vulnerability to psychopathology appears to be a consequence of predisposing factors (or traits), which result from numerous gene-environment interactions during development (particularly during the perinatal period) and experience (life events), in this review, the biology of fear and anxiety will be examined from systemic (brain-behavior relationships, neuronal circuitry, and functional neuroanatomy) and cellular/molecular (neurotransmitters, hormones, and other biochemical factors) points of view, with particular reference to animal models. These models have been instrumental in establishing the biological correlates of fear and anxiety, although the recent development of noninvasive investigation methods in humans, such as the various neuroimaging techniques, certainly opens new avenues of research in this field. Our current knowledge of the biological bases of fear and anxiety is already impressive, and further progress toward models or theories integrating contributions from the medical, biological, and psychological sciences can be expected.

The effect of intra-nucleus accumbens administration of allopregnanolone on δ and γ2 GABA(A) receptor subunit mRNA expression in the hippocampus and on depressive-like and grooming behaviors in rats

Alterations in GABA(A) receptor expression have been associated with the allopregnanolone (3α-hydroxy-5α-pregnan-20-one; 3α,5α-THP) antidepressant-like effect in rats. The present study aimed to verify the effect of bilateral, intra-nucleus accumbens core (intra-AcbC) administration of the neurosteroid allopregnanolone on behaviors in the forced swim and grooming microstructure tests and in the δ and γ2 GABA(A) receptor subunit mRNA expression in right and left hippocampus of rats. The results of this study showed that bilateral, intra-AcbC allopregnanolone administration (5μg/rat) presented antidepressant-like activity in the forced swim test concomitant with an increase in climbing. Allopregnanolone at doses of 1.25 and 5μg/rat also decreased the percentage of correct transitions in the grooming microstructure test. Both δ and γ2 GABA(A) subunit expressions increased in the rat hippocampus after allopregnanolone intra-AcbC treatment. Our findings point to asymmetrical GABA(A) receptor expression changes in the hippocampus of animals treated with allopregnanolone. Further investigation should evaluate the antidepressant-like effect of allopregnanolone not only in other directly infused regions but also with respect to changes in other brain areas of the limbic system to understand allopregnanolone's mechanism of action.

Involvement of the neurosteroid 7α-hydroxypregnenolone in the courtship behavior of the male newt Cynops pyrrhogaster

Reproductive behavior in amphibians, as in other vertebrate animals, is controlled by multiple hormones. A neurosteroid, 7α-hydroxypregnenolone, has recently been found to enhance locomotor activity in the male newt, Cynops pyrrhogaster. Here, we show that this neurosteroid is also involved in enhancing the expression of courtship behavior. Intracerebroventricular (ICV) injection of 7α-hydroxypregnenolone enhanced courtship behavior dose-dependently in the sexually undeveloped males that had been pretreated with prolactin and gonadotropin, which is known to bring the males to a sexually developed state. But, unlike the case in the locomotion activity, 7α-hydroxypregnenolone did not elicit the behavior in males receiving no prior injections of these hormones. ICV administration of ketoconazole, an inhibitor of the steroidogenic enzyme cytochrome P450s, suppressed the spontaneously occurring courtship behavior in sexually active males. Supplementation with 7α-hydroxypregnenolone reversed the effect of ketoconazole in these animals. It was also demonstrated that the effect of the neurosteroid on the courtship behavior was blocked by a dopamine D2-like, but not by a D1-like, receptor antagonist. These results indicate that endogenous 7α-hydroxypregnenolone enhances the expression of the male courtship behavior through a dopaminergic system mediated by a D2-like receptor in the brain.

3α5β-Pregnanolone glutamate, a use-dependent NMDA antagonist, reversed spatial learning deficit in an animal model of schizophrenia

Neuroactive steroids modulate receptors for neurotransmitters in the brain and thus might be efficacious in the treatment of various diseases of the central nervous system such as schizophrenia. We have designed and synthetized a novel use-dependent NMDA receptor antagonist 3α5β-pregnanolone glutamate (3α5β-P-Glu). In this study, we evaluate procognitive properties of 3α5β-P-Glu in an animal model of schizophrenia induced by systemic application of MK-801. The procognitive properties were evaluated using active place avoidance on a rotating arena (Carousel maze). We evaluated effects of 3α5β-P-Glu on the avoidance, on locomotor activity, and anxiety. 3α5β-P-Glu alone altered neither spatial learning nor locomotor activity in control animals. In the model animals, 3α5β-P-Glu reversed the MK-801-induced cognitive deficit without reducing hyperlocomotion. The highest dose of 3α5β-P-Glu also showed anxiolytic properties. Taken together, 3α5β-P-Glu may participate in the restoration of normal brain functioning and these results may facilitate the development of new promising drugs improving cognitive functioning in schizophrenia.

Mild exercise increases dihydrotestosterone in hippocampus providing evidence for androgenic mediation of neurogenesis

Mild exercise activates hippocampal neurons through the glutamatergic pathway and also promotes adult hippocampal neurogenesis (AHN). We hypothesized that such exercise could enhance local androgen synthesis and cause AHN because hippocampal steroid synthesis is facilitated by activated neurons via N-methyl-D-aspartate receptors. Here we addressed this question using a mild-intense treadmill running model that has been shown to be a potent AHN stimulator. A mass-spectrometric analysis demonstrated that hippocampal dihydrotestosterone increased significantly, whereas testosterone levels did not increase significantly after 2 wk of treadmill running in both orchidectomized (ORX) and sham castrated (Sham) male rats. Furthermore, analysis of mRNA expression for the two isoforms of 5α-reductases (srd5a1, srd5a2) and for androgen receptor (AR) revealed that both increased in the hippocampus after exercise, even in ORX rats. All rats were injected twice with 5'-bromo-2'deoxyuridine (50 mg/kg body weight, i.p.) on the day before training. Mild exercise significantly increased AHN in both ORX and Sham rats. Moreover, the increase of doublecortin or 5'-bromo-2'deoxyuridine/NeuN-positive cells in ORX rats was blocked by s.c. flutamide, an AR antagonist. It was also found that application of an estrogen receptor antagonist, tamoxifen, did not suppress exercise-induced AHN. These results support the hypothesis that, in male animals, mild exercise enhances hippocampal synthesis of dihydrotestosterone and increases AHN via androgenenic mediation.

Vitamin D(3) enhances ATRA-mediated neurosteroid biosynthesis in human glioma GI-1 cells

Emerging evidence indicates that vitamin D (VD) is an important modulator of brain development and function. To investigate whether VD modulates neurosteroid biosynthesis in neural cells, we investigated the effect of VD(3) on steroidogenic gene expression in human glioma GI-1 cells. We found that VD(3) enhanced CYP11A1 and 3β-hydroxysteroid dehydrogenase gene expression. The induction of CYP11A1 gene expression by VD(3) was dose- and incubation time-dependent. Calcipotriol, a VD(3) receptor (VDR) agonist, also induced CYP11A1 gene expression in GI-1 cells, indicating that VDR is involved in this induction. The induction of progesterone (PROG) de novo synthesis was observed along with the induction of steroidogenic genes by VD(3). Furthermore, VD(3) enhanced all-trans retinoic acid (ATRA)-induced CYP11A1 gene expression and PROG production. This suggests cooperative regulation of steroidogenic gene expression by the two fat-soluble vitamins, A and D. In addition, a mixed culture of neuronal IMR-32 cells and GI-1 cells treated with ATRA and VD(3) resulted in the induction of PROG-responsive gene expression in the IMR-32 cells. This result shows a paracrine action of PROG that is induced in and released by the GI-1 cells. The relationship between neurological dysfunction associated with VD deficiency and neurosteroid induction by VD is discussed.

Regulation of the surface expression of α4β2δ GABAA receptors by high efficacy states

α4βδ GABA(A) receptors (GABARs) have low CNS expression, but their expression is increased by 48h exposure to the neurosteroid THP (3α-OH-5α[β]-pregnan-20-one). THP also increases the efficacy of δ-containing GABARs acutely, where GABA is a partial agonist. Thus, we examined effects of THP (100 nM) and full GABA agonists at α4β2δ (gaboxadol, 10 μM, and β-alanine, 10 μM-1mM), on surface expression of α4β2δ. To this end, we used an α4 construct tagged with a 3XFLAG (F) epitope or measured expression of native α4 and δ. HEK-293 cells or cultured hippocampal neurons were transfected with α4Fβ2δ and treated 24h later with GABA agonists, THP, GABA plus THP or vehicle (0.01% DMSO) for 0.5 h-48 h. Immunocytochemistry was performed under both non-permeabilized and permeabilized conditions to detect surface and intracellular labeling, respectively, using confocal microscopy. The high efficacy agonists and GABA (1 or 10 μM) plus THP increased α4β2δ surface expression up to 3-fold after 48h, an effect first seen by 0.5h. This effect was not dependent upon the polarity of GABAergic current, although expression was increased by KCC2. Intracellular labeling was decreased while functional expression was confirmed by whole cell patch clamp recordings of responses to GABA agonists. GABA plus THP treatment did not alter the rate of receptor removal from the surface membrane, suggesting that THP-induced α4β2δ expression is likely via receptor insertion. Surface expression of α4β2δ was decreased by rottlerin (10 μM), suggesting a role for PKC-δ. These results suggest that trafficking of α4β2δ GABARs is regulated by high efficacy states.

Role of mineralocorticoid action in the brain in salt-sensitive hypertension

1. The mechanisms by which excessive salt causes hypertension involve more than retention of sodium and water by the kidneys and are far from clear. Mineralocorticoids act centrally to increase salt appetite, sympathetic drive and vasopressin release, resulting in hypertension that is prevented by the central infusion of mineralocorticoid receptor (MR) antagonists. The MR has similar affinity for aldosterone and the glucocorticoids corticosterone or cortisol. Specificity is conferred in transport epithelia by the colocalization of the MR with 11β-hydroxysteroid dehydrogenase Type 2. Coexpression also occurs in some neurons, notably those of the nucleus tractus solitarius that are activated by sodium depletion and aldosterone and mediate salt-seeking behaviour. 2. The salt-induced hypertension of the Dahl salt-sensitive rat is mitigated by the central infusion of a mineralocorticoid antagonist even though circulating aldosterone is normal or reduced in salt-sensitive (SS). Contrary to reports that salt appetite in the Dahl salt-sensitive rat is depressed, we found that it is increased compared with that in Spraque-Dawley rats. 3. Extra-adrenal aldosterone synthesis in the brain occurs in minute amounts that could only be relevant locally. Expression of aldosterone synthase mRNA and aldosterone concentrations in the brain of Dahl salt-sensitive rats are increased compared with Spraque-Dawley rats. The central infusion of inhibitors of aldosterone synthesis lowers salt-induced hypertension in the Dahl salt-sensitive rat, suggesting a role for excessive Dahl salt-sensitive synthesis in the brain. Brain MR, particularly those in the paraventricular nuclei, regulate inflammatory processes that are exacerbated by sodium and lead to cardiovascular dysfunction.

7α-Hydroxypregnenolone, a new key regulator of amphibian locomotion: discovery, progress and prospect

Seasonally-breeding amphibians have served as excellent animal models to investigate the biosynthesis and biological actions of neurosteroids. Previous studies have demonstrated that the brain of amphibians possesses key steroidogenic enzymes and produces pregnenolone, a precursor of steroid hormones, and other various neurosteroids. We recently found that the brain of seasonally-breeding newts actively produces 7α-hydroxypregnenolone, a previously undescribed amphibian neurosteroid. This novel amphibian neurosteroid acts as a neuronal modulator to stimulate locomotor activity in newts. Subsequently, the mode of action of 7α-hydroxypregnenolone has been demonstrated in the newt brain. 7α-Hydroxypregnenolone stimulates locomotor activity through activation of the dopaminergic system. To understand the functional significance of 7α-hydroxypregnenolone in the regulation of locomotor activity, diurnal and seasonal changes in synthesis of 7α-hydroxypregnenolone have also been demonstrated in the newt brain. Melatonin derived from the pineal gland and eyes regulates 7α-hydroxypregnenolone synthesis in the brain, thus inducing diurnal locomotor changes. Prolactin, an adenohypophyseal hormone, regulates 7α-hydroxypregnenolone synthesis in the brain, and also induces seasonal locomotor changes. In addition, 7α-hydroxypregnenolone mediates corticosterone action to increase locomotor activity under stress. This review summarizes the discovery, progress and prospect of 7α-hydroxypregnenolone, a new key regulator of amphibian locomotion.

Allopregnanolone and induction of endogenous opioid inhibition of oxytocin responses to immune stress in pregnant rats

In virgin rats, systemic administration of interleukin (IL)-1β (i.e. to mimic infection), increases oxytocin secretion and the firing rate of oxytocin neurones in the supraoptic nucleus (SON). However, in late pregnancy, stimulated oxytocin secretion is inhibited by an endogenous opioid mechanism, preserving the expanded neurohypophysial oxytocin stores for parturition and minimising the risk of preterm labour. Central levels of the neuroactive metabolite of progesterone, allopregnanolone, increase during pregnancy and allopregnanolone acting on GABA(A) receptors on oxytocin neurones enhances inhibitory transmission. In the present study, we tested whether allopregnanolone induces opioid inhibition of the oxytocin system in response to IL-1β in late pregnancy. Inhibition of 5α-reductase (an allopregnanolone-synthesising enzyme) with finasteride potentiated IL-1β-evoked oxytocin secretion in late pregnant rats, whereas allopregnanolone reduced the oxytocin response in virgin rats. IL-1β increased the number of magnocellular neurones in the SON and paraventricular nucleus (PVN) expressing Fos (an indicator of neuronal activation) in virgin but not pregnant rats. In immunoreactive oxytocin neurones in the SON and PVN, finasteride increased IL-1β-induced Fos expression in pregnant rats. Conversely, allopregnanolone reduced the number of magnocellular oxytocin neurones activated by IL-1β in virgin rats. Treatment with naloxone (an opioid antagonist) greatly enhanced the oxytocin response to IL-1β in pregnancy, and finasteride did not enhance this effect, indicating that allopregnanolone and the endogenous opioid mechanisms do not act independently. Indeed, allopregnanolone induced opioid inhibition over oxytocin responses to IL-1β in virgin rats. Thus, in late pregnancy, allopregnanolone induces opioid inhibition over magnocellular oxytocin neurones and hence on oxytocin secretion in response to immune challenge. This mechanism will minimise the risk of preterm labour and prevent the depletion of neurohypophysial oxytocin stores, which are required for parturition.

HIV associated dementia: role for neurosteroids

HIV associated dementia (HAD), is a neuronal complication of HIV infection and causes cognitive and motor impairment. The cognitive decline in HAD is due to widespread synaptic loss than neuronal loss. The neurotoxicity in HAD is caused by activation of NMDA receptors by HIV-proteins but the exact mechanism of the synaptic loss is yet to be determined. This article explores a novel pathomechanism for the observed synaptic loss. The HIV-proteins augment NMDA mediated increase of intracellular Ca(2+) in neurons which activates nNOs for Nitric Oxide (NO) synthesis. The NO activates MAPK and phosphorylates Microtubule-associated protein-2(MAP2) at specific sites causing conformational changes, microtubular disassembly and promote MAP2 degradation by the ubiquitin-proteosome pathway. Under physiological conditions Ca(2+) signaling increases cholesterol transport into mitochondria for steroidogenesis by the CYP11A1. The neurosteroid pregnenolone binds to MAP2 and causes inhibition of phosphorylation, increase in microtubule assembly and decrease MAP2 degradation. The NO can inhibits CYP11A1 in a concentration dependent manner and reduces steroidogeneisis. There is a upregulation of NO production in HAD from HIV infected microglia and astrocytes which cross neuronal membrane and increase intracellular NO. This can cause profound inhibition of steroidogenesis in the brain, increase MAP2 degradation and synaptic loss in presence of HIV-proteins.

Novel actions of progesterone: what we know today and what will be the scenario in the future?

Objectives

This article is aimed to review the novel actions of progesterone, which otherwise is considered as a female reproductive hormone. The article focuses on its important physiological actions in males too and gives an overview of its novel perspectives in disorders of central and peripheral nervous system.

Key findings

Progesterone may have a potential benefit in treatment of traumatic brain injury, various neurological disorders and male related diseases like benign prostatic hypertrophy (BPH), prostate cancer and osteoporosis. Norethisterone (NETA), a progesterone derivative, decreases bone mineral loss in male castrated mice suggesting its role in osteoporosis. In the future, progesterone may find use as a male contraceptive too, but still needs confirmatory trials for safety, tolerability and acceptability. Megestrol acetate, a progesterone derivative is preferred in prostatic cancer. Further, it may find utility in nicotine addiction, traumatic brain injury (recently entered Phase III trial) and Alzheimer's disease, diabetic neuropathy and crush injuries. Studies also suggest role of progesterone in stroke, for which further clinical trials are needed. The non genomic actions of progesterone may be in part responsible for these novel actions.

Summary

Although progesterone has shown promising role in various non-hormonal benefits, further clinical studies are needed to prove its usefulness in conditions like stroke, traumatic brain injury, neuropathy and crush injury. In male related illnesses like BPH and prostatic Ca, it may prove a boon in near future. New era of hormonal male contraception may be initiated by use of progesterone along with testosterone.

Progesterone synthesis in the nervous system: implications for myelination and myelin repair

Progesterone is well known as a female reproductive hormone and in particular for its role in uterine receptivity, implantation, and the maintenance of pregnancy. However, neuroendocrine research over the past decades has established that progesterone has multiple functions beyond reproduction. Within the nervous system, its neuromodulatory and neuroprotective effects are much studied. Although progesterone has been shown to also promote myelin repair, its influence and that of other steroids on myelination and remyelination is relatively neglected. Reasons for this are that hormonal influences are still not considered as a central problem by most myelin biologists, and that neuroendocrinologists are not sufficiently concerned with the importance of myelin in neuron functions and viability. The effects of progesterone in the nervous system involve a variety of signaling mechanisms. The identification of the classical intracellular progesterone receptors as therapeutic targets for myelin repair suggests new health benefits for synthetic progestins, specifically designed for contraceptive use and hormone replacement therapies. There are also major advantages to use natural progesterone in neuroprotective and myelin repair strategies, because progesterone is converted to biologically active metabolites in nervous tissues and interacts with multiple target proteins. The delivery of progesterone however represents a challenge because of its first-pass metabolism in digestive tract and liver. Recently, the intranasal route of progesterone administration has received attention for easy and efficient targeting of the brain. Progesterone in the brain is derived from the steroidogenic endocrine glands or from local synthesis by neural cells. Stimulating the formation of endogenous progesterone is currently explored as an alternative strategy for neuroprotection, axonal regeneration, and myelin repair.

Steroid sulfatase-deficient mice exhibit endophenotypes relevant to attention deficit hyperactivity disorder

Attention Deficit Hyperactivity Disorder (ADHD) is a common neurodevelopmental condition characterised by inattention, impulsivity and hyperactivity; it is frequently co-morbid with anxiety and conduct disorders, sleep perturbation and abnormal consummatory behaviours. Recent studies have implicated the neurosteroid-modulating enzyme steroid sulfatase (STS) as a modulator of ADHD-related endophenotypes. The effects of steroid sulfatase deficiency on homecage activity, feeding/drinking behaviours, anxiety-related behaviours (assayed in light-dark box and open field paradigms), social dominance and serum steroid hormone levels were determined by comparing 40,XY and 39,X(Y*)O mice. Subsequently, mice administered the steroid sulfatase inhibitor COUMATE acutely were compared to vehicle-treated mice on behavioural tasks sensitive to enzyme deficiency to dissociate between its developmental and ongoing effects. 39,X(Y*)O mice exhibited heightened reactivity to a novel environment, hyperactivity in the active phase, and increased water (but not food) consumption relative to 40,XY mice during a 24h period; the former group also demonstrated evidence for heightened emotional reactivity. There was no difference in social dominance between the 40,XY and 39,X(Y*)O mice. COUMATE administration had no effect on homecage activity, water consumption or anxiety measures in the open field. 39,X(Y*)O mice exhibited significantly lower dehydroepiandrosterone (DHEA) serum levels than 40,XY mice, but equivalent corticosterone levels. Together with previous data, the present results suggest that steroid sulfatase may influence core and associated ADHD behavioural endophenotypes via both developmental and ongoing mechanisms, and that the 39,X(Y*)O model may represent a useful tool for elucidating the neurobiological basis of these endophenotypes.

Integration of transient receptor potential canonical channels with lipids

Transient receptor potential canonical (TRPC) channels are the canonical (C) subset of the TRP proteins, which are widely expressed in mammalian cells. They are thought to be primarily involved in determining calcium and sodium entry and have wide-ranging functions that include regulation of cell proliferation, motility and contraction. The channels are modulated by a multiplicity of factors, putatively existing as integrators in the plasma membrane. This review considers the sensitivities of TRPC channels to lipids that include diacylglycerols, phosphatidylinositol bisphosphate, lysophospholipids, oxidized phospholipids, arachidonic acid and its metabolites, sphingosine-1-phosphate, cholesterol and some steroidal derivatives and other lipid factors such as gangliosides. Promiscuous and selective lipid sensing have been detected. There appear to be close working relationships with lipids of the phospholipase C and A₂ enzyme systems, which may enable integration with receptor signalling and membrane stretch. There are differences in the properties of each TRPC channel that are further complicated by TRPC heteromultimerization. The lipids modulate activity of the channels or insertion in the plasma membrane. Lipid microenvironments and intermediate sensing proteins have been described that include caveolae, G protein signalling, SEC14-like and spectrin-type domains 1 (SESTD1) and podocin. The data suggest that lipid sensing is an important aspect of TRPC channel biology enabling integration with other signalling systems.

Acute stress increases the synthesis of 7α-hydroxypregnenolone, a new key neurosteroid stimulating locomotor activity, through corticosterone action in newts

7α-Hydroxypregnenolone (7α-OH PREG) is a newly identified bioactive neurosteroid stimulating locomotor activity in the brain of newt, a wild animal, which serves as an excellent model to investigate the biosynthesis and biological action of neurosteroids. Here, we show that acute stress increases 7α-OH PREG synthesis in the dorsomedial hypothalamus (DMH) through corticosterone (CORT) action in newts. A 30-min restraint stress increased 7α-OH PREG synthesis in the brain tissue concomitant with the increase in plasma CORT concentrations. A 30-min restraint stress also increased the expression of cytochrome P450(7α) (CYP7B), the steroidogenic enzyme of 7α-OH PREG formation, in the DMH. Decreasing plasma CORT concentrations by hypophysectomy or trilostane administration decreased 7α-OH PREG synthesis in the diencephalon, whereas administration of CORT to these animals increased 7α-OH PREG synthesis. Glucocorticoid receptor was present in DMH neurons expressing CYP7B. Thus, CORT appears to act directly on DMH neurons to increase 7α-OH PREG synthesis. We further investigated the biological action of 7α-OH PREG in the brain under stress. A 30-min restraint stress or central administration of 7α-OH PREG increased serotonin concentrations in the diencephalon. Double immunolabeling further showed colocalization of CYP7B and serotonin in the DMH. These results indicate that acute stress increases the synthesis of 7α-OH PREG via CORT action in the DMH, and 7α-OH PREG activates serotonergic neurons in the DMH that may coordinate behavioral responses to stress. This is the first demonstration of neurosteroid biosynthesis regulated by peripheral steroid hormone and of neurosteroid action in the brain under stress in any vertebrate class.

Effects and Mechanisms of 3α,5α,-THP on Emotion, Motivation, and Reward Functions Involving Pregnane Xenobiotic Receptor

Progestogens [progesterone (P(4)) and its products] play fundamental roles in the development and/or function of the central nervous system during pregnancy. We, and others, have investigated the role of pregnane neurosteroids for a plethora of functional effects beyond their pro-gestational processes. Emerging findings regarding the effects, mechanisms, and sources of neurosteroids have challenged traditional dogma about steroid action. How the P(4) metabolite and neurosteroid, 3α-hydroxy-5α-pregnan-20-one (3α,5α-THP), influences cellular functions and behavioral processes involved in emotion/affect, motivation, and reward, is the focus of the present review. To further understand these processes, we have utilized an animal model assessing the effects, mechanisms, and sources of 3α,5α-THP. In the ventral tegmental area (VTA), 3α,5α-THP has actions to facilitate affective, and motivated, social behaviors through non-traditional targets, such as GABA, glutamate, and dopamine receptors. 3α,5α-THP levels in the midbrain VTA both facilitate, and/or are enhanced by, affective and social behavior. The pregnane xenobiotic receptor (PXR) mediates the production of, and/or metabolism to, various neurobiological factors. PXR is localized to the midbrain VTA of rats. The role of PXR to influence 3α,5α-THP production from central biosynthesis, and/or metabolism of peripheral P(4), in the VTA, as well as its role to facilitate, or be increased by, affective/social behaviors is under investigation. Investigating novel behavioral functions of 3α,5α-THP extends our knowledge of the neurobiology of progestogens, relevant for affective/social behaviors, and their connections to systems that regulate affect and motivated processes, such as those important for stress regulation and neuropsychiatric disorders (anxiety, depression, schizophrenia, drug dependence). Thus, further understanding of 3α,5α-THP's role and mechanisms to enhance affective and motivated processes is essential.