Pregnenolone sulfate increases hippocampal acetylcholine release and spatial recognition

Neurosteroids: A potential target for neuropsychiatric disorders

Neurosteroids are steroids produced by endocrine glands and subsequently entering the brain, and also include steroids synthesis in the brain. It has been widely known that neurosteroids influence many neurological functions, including neuronal signaling, synaptic adaptations, and neuroprotective effects. In addition, abnormality in the synthesis and function of neurosteroids has been closely linked to neuropsychiatric disorders, such as Alzheimer's disease (AD), schizophrenia (SZ), and epilepsy. Given their important role in brain pathophysiology and disorders, neurosteroids offer potential therapeutic targets for a variety of neuropsychiatric diseases, and that therapeutic strategies targeting neurosteroids probably exert beneficial effects. We therefore summarized the role of neurosteroids in brain physiology and neuropsychiatric disorders, and introduced the recent findings of synthetic neurosteroid analogues for potential treatment of neuropsychiatric disorders, thereby providing insights for further research in the future.

Modulation of Muscarinic Signalling in the Central Nervous System by Steroid Hormones and Neurosteroids

Muscarinic acetylcholine receptors expressed in the central nervous system mediate various functions, including cognition, memory, or reward. Therefore, muscarinic receptors represent potential pharmacological targets for various diseases and conditions, such as Alzheimer's disease, schizophrenia, addiction, epilepsy, or depression. Muscarinic receptors are allosterically modulated by neurosteroids and steroid hormones at physiologically relevant concentrations. In this review, we focus on the modulation of muscarinic receptors by neurosteroids and steroid hormones in the context of diseases and disorders of the central nervous system. Further, we propose the potential use of neuroactive steroids in the development of pharmacotherapeutics for these diseases and conditions.

Allosteric Modulation of Muscarinic Receptors by Cholesterol, Neurosteroids and Neuroactive Steroids

Muscarinic acetylcholine receptors are membrane receptors involved in many physiological processes. Malfunction of muscarinic signaling is a cause of various internal diseases, as well as psychiatric and neurologic conditions. Cholesterol, neurosteroids, neuroactive steroids, and steroid hormones are molecules of steroid origin that, besides having well-known genomic effects, also modulate membrane proteins including muscarinic acetylcholine receptors. Here, we review current knowledge on the allosteric modulation of muscarinic receptors by these steroids. We give a perspective on the research on the non-genomic effects of steroidal compounds on muscarinic receptors and drug development, with an aim to ultimately exploit such knowledge.

Neurosteroids and steroid hormones are allosteric modulators of muscarinic receptors

The membrane cholesterol was found to bind and modulate the function of several G-protein coupled receptors including muscarinic acetylcholine receptors. We investigated the binding of 20 steroidal compounds including neurosteroids and steroid hormones to muscarinic receptors. Corticosterone, progesterone and some neurosteroids bound to muscarinic receptors with the affinity of 100 nM or greater. We established a structure-activity relationship for steroid-based allosteric modulators of muscarinic receptors. Further, we show that corticosterone and progesterone allosterically modulate the functional response of muscarinic receptors to acetylcholine at physiologically relevant concentrations. It can play a role in stress control or in pregnancy, conditions where levels of these hormones dramatically oscillate. Allosteric modulation of muscarinic receptors via the cholesterol-binding site represents a new pharmacological approach at diseases associated with altered cholinergic signalling.

Intranasal pregnenolone increases acetylcholine in frontal cortex, hippocampus, and amygdala-Preferentially in the hemisphere ipsilateral to the injected nostril

This study determined the effects of intranasal pregnenolone (IN-PREG) on acetylcholine (ACh) levels in selected areas of the rat brain, using in vivo microdialysis. Previous studies showed that PREG rapidly reaches the rodent brain after intranasal administration and that direct infusion of PREG and PREG-S into the basal forebrain modulates ACh release in frontal cortex, amygdala, and hippocampus. In the present study, we investigated the effects of IN-PREG on the cholinergic system in the rat brain. In the first experiment, IN-PREG (5.6 and 11.2 mg/ml) or vehicle was applied bilaterally, and we hypothesized that IN-PREG would increase ACh levels in amygdala, hippocampus, and frontal cortex, relative to baseline and vehicle. Dialysate was collected for 100 min, based on pilot data of duration of effect. Bilateral IN-PREG (5.6 and 11.2 mg/ml) increased frontal cortex and hippocampal ACh relative to both baseline and vehicle. Moreover, 11.2 mg/ml PREG increased ACh in the amygdala relative to baseline, the lower dose, and vehicle. Therefore, in the second experiment, IN-PREG (11.2 mg/ml) was applied only into one nostril, with vehicle applied into the other nostril, in order to determine whether ACh is predominantly increased in the ipsilateral relative to the contralateral amygdala. Unilateral application of IN-PREG increased ACh in the ipsilateral amygdala, whereas no effect was observed on the contralateral side, suggesting that PREG was transported from the nostrils to the brain via the olfactory epithelial pathway, but not by circulation. The present data provide additional information on IN-PREG action in the cholinergic system of frontal cortex, amygdala, and hippocampus. This may be relevant for therapeutic IN application of PREG in neurogenerative and neuropsychiatric disorders.

Neurosteroid Actions in Memory and Neurologic/Neuropsychiatric Disorders

Memory dysfunction is a symptomatic feature of many neurologic and neuropsychiatric disorders; however, the basic underlying mechanisms of memory and altered states of circuitry function associated with disorders of memory remain a vast unexplored territory. The initial discovery of endogenous neurosteroids triggered a quest to elucidate their role as neuromodulators in normal and diseased brain function. In this review, based on the perspective of our own research, the advances leading to the discovery of positive and negative neurosteroid allosteric modulators of GABA type-A (GABA_A), NMDA, and non-NMDA type glutamate receptors are brought together in a historical and conceptual framework. We extend the analysis toward a state-of-the art view of how neurosteroid modulation of neural circuitry function may affect memory and memory deficits. By aggregating the results from multiple laboratories using both animal models for disease and human clinical research on neuropsychiatric and age-related neurodegenerative disorders, elements of a circuitry level view begins to emerge. Lastly, the effects of both endogenously active and exogenously administered neurosteroids on neural networks across the life span of women and men point to a possible underlying pharmacological connectome by which these neuromodulators might act to modulate memory across diverse altered states of mind.

Neurosteroid pregnenolone sulfate, alone, and as augmentation of lurasidone or tandospirone, rescues phencyclidine-induced deficits in cognitive function and social interaction

BACKGROUND

Pregnenolone sulfate (PregS), an endogenous neurosteroid, which negatively and positively modulates gamma amino butyric acid subunit A (GABA_A) and N-methyl D-aspartate (NMDA) receptors (R) respectively, among other potential neuroplastic changes on synaptic processes, has shown some beneficial effects on treating cognitive impairment associated with schizophrenia (CIAS) and negative symptoms. Lurasidone (Lur), an atypical antipsychotic drug (AAPD), and tandospirone (Tan), a 5-HT_1A R partial agonist, have also been reported to improve cognitive or negative symptoms, or both, in some schizophrenia patients.

METHODS

We tested whether PregS, by itself, and in combination with Lur or Tan could rescue persistent deficits produced by subchronic treatment with the NMDAR antagonist, phencyclidine (PCP)-in episodic memory, executive functioning, and social behavior, using novel object recognition (NOR), operant reversal learning (ORL), and social interaction (SI) tasks, in male C57BL/6 J mice.

RESULTS

PregS (10, but not 3 mg/kg) significantly rescued subchronic PCP-induced NOR and SI deficits. Co-administration of sub-effective doses (SEDs) of PregS (3 mg/kg) + Lur (0.1 mg/kg) or Tan (0.03 mg/kg) rescued scPCP-induced NOR and SI deficits. Further, PregS (30, but not 10 mg/kg) rescued PCP-induced ORL deficit, as did the combination of SED PregS (10 mg/kg) +SED Lur (1 mg/kg) or Tan (1 mg/kg).

CONCLUSION

PregS was effective alone and as adjunctive treatment for treating two types of cognitive impairments and negative symptoms in this schizophrenia model. Further study of the mechanisms by which PregS alone and in combination with AAPDs and 5-HT_1A R partial agonists, rescues the deficits in cognition and SI in this preclinical model is indicated.

The effects of intra-dorsal hippocampus infusion of pregnenolone sulfate on memory function and hippocampal BDNF mRNA expression of biliary cirrhosis-induced memory impairment in rats

Learning and memory impairment is one of the most challenging complications of cirrhosis and present treatments are unsatisfactory. The exact mechanism of cirrhosis cognitive dysfunction is unknown. Pregnenolone sulfate (PREGS) is an excitatory neurosteroid that acts as a N-methyl-D-aspartate (NMDA) receptor agonist and GABAA receptor antagonist. In this study we evaluated the effect of intra CA1 infusion of PREGS on cirrhotic rats' memory function using the Y-maze test. Hippocampal brain-derived neurotrophic factor (BDNF) mRNA expression was also evaluated. Three weeks after bile duct ligation (BDL) surgery, rats were under stereotaxic surgery for insertion of two guide cannulas in the CA1 region of the hippocampus. After 1-week of recovery, PREGS was administered through CA1 cannulas in cirrhotic rats, while control or sham groups received vehicle. For evaluation of NMDA receptor role in memory-enhancing effects of PREGS, DL-2-Amino-5-phosphonopentanoic acid (AP5) which is a potent and competitive antagonist of NMDA receptor, co-administered with PREGS and for assessment of hippocampal BDNF mRNA expression, quantitative Real-time reverse transcriptase-PCR (RT-PCR) was used. Results showed that 28 days after BDL, cirrhotic animals' memory significantly decreased in comparison with control and sham groups, while PREGS infusion could restore memory impairment (P<0.05). PREGS effects on memory of cirrhotic rats were antagonized by DAP5. RT-PCR findings have shown that hippocampal relative BDNF mRNA expression was up-regulated in PREGS-treated groups in comparison with the BDL group (P<0.001). Our findings suggest that PREGS has a memory-enhancing effect in cirrhosis memory deficit in acute therapy and this effect may be through NMDA (glutamate) receptor involvement and BDNF mRNA expression.

Sigma receptors [σRs]: biology in normal and diseased states

This review compares the biological and physiological function of Sigma receptors [σRs] and their potential therapeutic roles. Sigma receptors are widespread in the central nervous system and across multiple peripheral tissues. σRs consist of sigma receptor one (σ₁R) and sigma receptor two (σ₂R) and are expressed in numerous regions of the brain. The sigma receptor was originally proposed as a subtype of opioid receptors and was suggested to contribute to the delusions and psychoses induced by benzomorphans such as SKF-10047 and pentazocine. Later studies confirmed that σRs are non-opioid receptors (not an µ opioid receptor) and play a more diverse role in intracellular signaling, apoptosis and metabolic regulation. σ₁Rs are intracellular receptors acting as chaperone proteins that modulate Ca²⁺ signaling through the IP₃ receptor. They dynamically translocate inside cells, hence are transmembrane proteins. The σ₁R receptor, at the mitochondrial-associated endoplasmic reticulum membrane, is responsible for mitochondrial metabolic regulation and promotes mitochondrial energy depletion and apoptosis. Studies have demonstrated that they play a role as a modulator of ion channels (K⁺ channels; N-methyl-d-aspartate receptors [NMDAR]; inositol 1,3,5 triphosphate receptors) and regulate lipid transport and metabolism, neuritogenesis, cellular differentiation and myelination in the brain. σ₁R modulation of Ca²⁺ release, modulation of cardiac myocyte contractility and may have links to G-proteins. It has been proposed that σ₁Rs are intracellular signal transduction amplifiers. This review of the literature examines the mechanism of action of the σRs, their interaction with neurotransmitters, pharmacology, location and adverse effects mediated through them.

Validated LC-MS/MS simultaneous assay of five sex steroid/neurosteroid-related sulfates in human serum

Conventionally, the concentration of steroidal sulfates was estimated by indirect or immuno‑based assays before the use of liquid-chromatography tandem mass spectrometry (LC-MS/MS). In the present study, a validated LC-MS/MS method is described for the simultaneous quantification of dehydroepiandrosterone sulfate (DHEA-S), estrone sulfate (E1‑S), androsterone sulfate (ADT‑S), pregnenolone sulfate (Preg‑S) and allopregnanolone sulfate (Allopreg‑S). E1‑S binding to serum proteins was observed, especially for the high concentration quality control serum samples, leading to -10 to -15% bias using a polymer-based SPE. This protein binding can be efficiently eliminated using a Waters Oasis™ WAX following the same extraction procedure. Most likely, the E1‑S binding elimination on Oasis™ WAX can be attributed to its different sorbent structure, where the benzeno group of E1-S can interact with the benzene of the backbone of Oasis™ WAX. With this improvement, the method has been fully validated according to the FDA guidelines. The low quantification limits (LLOQs) are 40ng/mL, 40pg/mL, 5ng/mL, 1.5ng/mL and 0.25ng/mL for DHEA‑S, E1-S, ADT‑S, Preg‑S and Allopreg-S, respectively. A good linearity is obtained with R>0.99 for all compounds within the appropriate calibration range. Accuracies of all levels of QCs are within the range of 10% for DHEA-S, E1‑S, ADT‑S and Preg‑S while for Allopreg‑S, the accuracy is within the 15% range. The interday coefficient variance is 5.5-9.5% for the low limits of quantification of all five compounds while values of 1.3-9.9% are found for higher levels of QCs of all five compounds. Recovery of the five compounds in stripped serum is equivalent to that in unstripped serum. The average recovery difference is less than 5% between stripped and unstripped serum for each compound. All results of other test parameters such as matrix, hemolysis and lipemic effects as well as stabilities meet the acceptance criteria of EndoCeutics SOPs and FDA guidelines.

Choline acetyltransferase in the hippocampus is associated with learning strategy preference in adult male rats

One principle of the multiple memory systems hypothesis posits that the hippocampus-based and striatum-based memory systems compete for control over learning. Consistent with this notion, previous research indicates that the cholinergic system of the hippocampus plays a role in modulating the preference for a hippocampus-based place learning strategy over a striatum-based stimulus--response learning strategy. Interestingly, in the hippocampus, greater activity and higher protein levels of choline acetyltransferase (ChAT), the enzyme that synthesizes acetylcholine, are associated with better performance on hippocampus-based learning and memory tasks. With this in mind, the primary aim of the current study was to determine if higher levels of ChAT and the high-affinity choline uptake transporter (CHT) in the hippocampus were associated with a preference for a hippocampus-based place learning strategy on a task that also could be solved by relying on a striatum-based stimulus--response learning strategy. Results confirmed that levels of ChAT in the dorsal region of the hippocampus were associated with a preference for a place learning strategy on a water maze task that could also be solved by adopting a stimulus-response learning strategy. Consistent with previous studies, the current results support the hypothesis that the cholinergic system of the hippocampus plays a role in balancing competition between memory systems that modulate learning strategy preference.

Effects of pregnenolone intervention on the cholinergic system and synaptic protein 1 in aged rats

OBJECTIVE

To observe the effect of pregnenolone (PREG) intervention on the cholinergic system function and the synaptic protein 1 (SYP1) expression in different brain regions of aged rats.

METHOD

Twenty-four-month-old male Sprague Dawley rats intraperitoneally injected every other day for one month were divided into blank control group, solvent control group, PREG (0.5 mg/kg) intervention group and PREG (2.0 mg/kg) intervention group. The rats were sacrificed 2 d after the intervention and the corresponding regions of brain tissue were separated and cryopreserved. Western blot analysis was used to detect the expression level of choline acetyltransferase (ChAT), SYP1, serum PREG and the activity of ChAT and acetylcholinesterase (AChE) in different brain regions. In addition, the semiquantitative changes in the expression level of ChAT and SYP1 in frontal lobe and hippocampus were tested by immunohistochemistry.

RESULT

Western blot and immunohistochemistry analysis showed that PREG (2.0 mg/kg) administration led to a significant increase of ChAT and SYP1 expressions in frontal lobe, temporal lobe, and hippocampus regions (p < 0.05). The result of enzyme-linked immunosorbent assay showed that PREG (2.0 mg/kg) administration significantly increased ChAT activity and serum PREG levels and caused a decrease in AChE activity (p < 0.05); while PREG (0.5 mg/kg) only elevated levels of serum PREG.

CONCLUSION

PREG significantly improved the synaptic plasticity of memory-related brain areas of aged rats, significantly increased brain cholinergic activity and thus helps to improve learning and memory in aged rats.

Pregnenolone sulphate enhances spatial orientation and object discrimination in adult male rats: evidence from a behavioural and electrophysiological study

Neurosteroids can alter neuronal excitability interacting with specific neurotransmitter receptors, thus affecting several functions such as cognition and emotionality. In this study we investigated, in adult male rats, the effects of the acute administration of pregnenolone-sulfate (PREGS) (10mg/kg, s.c.) on cognitive processes using the Can test, a non aversive spatial/visual task which allows the assessment of both spatial orientation-acquisition and object discrimination in a simple and in a complex version of the visual task. Electrophysiological recordings were also performed in vivo, after acute PREGS systemic administration in order to investigate on the neuronal activation in the hippocampus and the perirhinal cortex. Our results indicate that, PREGS induces an improvement in spatial orientation-acquisition and in object discrimination in the simple and in the complex visual task; the behavioural responses were also confirmed by electrophysiological recordings showing a potentiation in the neuronal activity of the hippocampus and the perirhinal cortex. In conclusion, this study demonstrates that PREGS systemic administration in rats exerts cognitive enhancing properties which involve both the acquisition and utilization of spatial information, and object discrimination memory, and also correlates the behavioural potentiation observed to an increase in the neuronal firing of discrete cerebral areas critical for spatial learning and object recognition. This provides further evidence in support of the role of PREGS in exerting a protective and enhancing role on human memory.

The role of pregnenolone sulphate in spatial orientation-acquisition and retention: an interplay between cognitive potentiation and mood regulation

Neurosteroids can alter neuronal excitability interacting with specific neurotransmitter receptors, thus affecting several functions such as cognition and emotionality. In this study, we investigated, in adult male rats, the effects of the acute administration of pregnenolone-sulfate (PREGS) (10 mg/Kg, s.c.) on cognitive processes using the Can test, a non aversive spatial/visual task which allows the assessment of spatial information-acquisition during the baseline training, and of memory retention in the longitudinal study. Furthermore, on the basis of PREGS pharmacological profile, the modulation of depressive-like behaviour was also evaluated in the forced swim test (FST). Our results indicate that acute PREGS induces: an improvement in spatial orientation-acquisition and in reference memory, during the baseline training; a strengthening effect on reference and working memory during the longitudinal study. A decrease in immobility time in the FST has also been recorded. In conclusion, PREGS exerts enhancing properties on acquisition, consolidation and retrieval of spatial information, probably due of improved hippocampal-dependent memory processes. The additional antidepressant effect observed in the FST can provide further evidence in support of the potential of PREGS as a therapeutic tool for the treatment of cognitive deficits associated with mood disorders. This article is part of a Special Issue entitled: insert SI title.

Slc10A4 - what do we know about the function of this "secret ligand carrier" protein?

This commentary discusses the possible functions of a relatively newly described solute carrier protein, Slc10a4, in regards to a recent article by Zelano et al. (2013) published in the January issue of Experimental Neurology, 239, 73-81. Slc10a4 belongs to the sodium-bile acid cotransporter family (Slc10), but does not show plasma membrane transport activity of bile acids and related molecules. It is co-localized with synaptic vesicle transporters for acetylcholine and dopamine. In Slc10a4 lacking mice, Zelano et al. found increased excitability in hippocampal slices and in vivo responses to pilocarpine, but not kainate. These findings are critically examined here. This author speculates on the possible function of Slc10a4, but remains partial about "specific effects of Slc10a4 in cholinergic systems". It is hoped that approaches targeting human SLC10A4 can be discovered for potential clinical use in neurological disorders, such as Alzheimer's and Parkinson's disease, schizophrenia and addiction. Conversely, some side effects are expected due to peripheral Slc10a4 localization in sympathetic and parasympathetic nerves, as well as mast cells.

Pregnenolone rescues schizophrenia-like behavior in dopamine transporter knockout mice

Pregnenolone belongs to a class of endogenous neurosteroids in the central nervous system (CNS), which has been suggested to enhance cognitive functions through GABA(A) receptor signaling by its metabolites. It has been shown that the level of pregnenolone is altered in certain brain areas of schizophrenic patients, and clozapine enhances pregnenolone in the CNS in rats, suggesting that pregnenolone could be used to treat certain symptoms of schizophrenia. In addition, early phase proof-of-concept clinical trials have indicated that pregnenolone is effective in reducing the negative symptoms and cognitive deficits of schizophrenia patients. Here, we evaluate the actions of pregnenolone on a mouse model for schizophrenia, the dopamine transporter knockout mouse (DAT KO). DAT KO mice mirror certain symptoms evident in patients with schizophrenia, such as the psychomotor agitation, stereotypy, deficits of prepulse inhibition and cognitive impairments. Following acute treatment, pregnenolone was found to reduce the hyperlocomotion, stereotypic bouts and pre-pulse inhibition (PPI) deficits in DAT KO mice in a dose-dependent manner. At 60 mg/kg of pregnenolone, there were no significant differences in locomotor activities and stereotypy between wild-type and DAT KO mice. Similarly, acute treatment of 60 mg/kg of pregnenolone fully rescued PPI deficits of DAT KO mice. Following chronic treatment with pregnenolone at 60 mg/kg, the cognitive deficits of DAT KO mice were rescued in the paradigms of novel object recognition test and social transmission of food preference test. Pregnenolone thus holds promise as a therapeutic candidate in schizophrenia.

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.

Neurosteroids infusion into the CA1 hippocampal region on exploration, anxiety-like behaviour and aversive learning

Neurosteroids (NS) are substances synthesised de novo in the brain that have rapid modulatory effects on ionotropic receptors. Specifically, NS can act as positive allosteric modulators of GABAA receptors as pregnanolone or allopregnanolone (Allop), or GABAA negative modulators and NMDA positive modulators as pregnenolone (PREG) or dehydroepiandrosterone (DHEA) and their sulphate esters (PREGS and DHEAS). Given this, their role in anxiety and emotional disturbances has been suggested. In addition, NS such as PREGS or DHEAS have demonstrated a promnesic role in several learning tests. The aim of the present work is to highlight the role that the dorsal (CA1) hippocampus plays in the behavioural profile of NS such as Allop and PREGS in tests assessing exploration, anxiety and aversive learning in rats. For this purpose, animals were administered intrahippocampally with Allop (0.2μg/0.5μl), PREGS (5ng/0.5μl) or vehicle in each hippocampus, and tested in the Boissier and elevated plus maze (EPM) tests. For learning test we have chosen the passive avoidance paradigm. Results indicate that intrahippocampal administration of Allop enhances exploration, reflected in an increase in the total and the inner number of head-dips. Allop-injected animals also showed an increase in the percentage of entries into the open arms of the EPM, suggesting an anxiolytic-like profile. In addition, post-acquisition PREGS administration enhanced passive avoidance retention, while post-acquisition Allop administration had no effects on aversive learning retention. These results point out the important role of the dorsal (CA1) hippocampus in several NS behavioural effects, such as exploration, anxiety, learning and memory.

Pregnenolone sulfate and its enantiomer: differential modulation of memory in a spatial discrimination task using forebrain NMDA receptor deficient mice

This study examined the role of forebrain N-methyl-D-aspartate receptors (NMDA-Rs) in the promnesiant effects of natural (+) pregnenolone sulfate (PREGS) and its synthetic (-) enantiomer ent-PREGS in young adult mice. Using the two-trial arm discrimination task in a Y-maze, PREGS and ent-PREGS administration to control mice increased memory performances. In mice with a knock-out of the NR1 subunit of NMDA-Rs in the forebrain, the promnesiant effect of ent-PREGS was maintained whereas the activity of PREGS was lost. Memory enhancement by PREGS involves the NMDA-R activity in the hippocampal CA1 area and possibly in some locations of the cortical layers, whereas ent-PREGS acts independently of NMDA-R function.

Modulatory metaplasticity induced by pregnenolone sulfate in the rat hippocampus: a leftward shift in LTP/LTD-frequency curve

We recently have found that an acute application of the neurosteroid pregnenolone sulfate (PREGS) at 50 muM to rat hippocampal slices induces a long-lasting potentiation (LLP(PREGS)) via a sustained ERK2/CREB activation at perforant-path/granule-cell synapses in the dentate gyrus. This study is a follow up to investigate whether the expression of LLP(PREGS) influences subsequent frequency-dependent synaptic plasticity. Conditioning electric stimuli (CS) at 0.1-200 Hz were given to the perforant-path of rat hippocampal slices expressing LLP(PREGS) to induce long-term potentiation (LTP) and long-term depression (LTD). The largest LTP was induced at about 20 Hz-CS, which is normally a subthreshold frequency, and the largest LTD at 0.5 Hz-CS, resulting in a leftward-shift of the LTP/LTD-frequency curve. Furthermore, the level of LTP at 100 Hz-CS was significantly attenuated to give band-pass filter characteristics of LTP induction with a center frequency of about 20 Hz. The LTP induced by 20 Hz-CS (termed 20 Hz-LTP) was found to be postsynaptic origin and dependent on L-type voltage-gated calcium channel (L-VGCC) but not on N-methyl-D-aspartate receptor (NMDAr). Moreover, the induction of 20 Hz-LTP required a sustained activation of ERK2 that had been triggered by PREGS. In conclusion, the transient elevation of PREGS is suggested to induce a modulatory metaplasticity through a sustained activation of ERK2 in an L-VGCC dependent manner.

Neuroactive steroid pregnenolone sulphate inhibits long-term potentiation via activation of alpha2-adrenoreceptors at excitatory synapses in rat medial prefrontal cortex

Pregnenolone sulphate (PREGS) is one of the most important neuroactive steroids. Previous study showed that PREGS enhanced long-term potentiation (LTP) via activation of post-synaptic NMDA receptors at excitatory synapses in the hippocampus. The present paper studied the effect of PREGS on LTP at excitatory synapses in the pyramidal cells of layers V-VI of the medial prefrontal cortex (mPFC) using whole-cell patch-clamp in slices and made a comparison with that in the hippocampus. We also studied the mechanism of the effect of PREGS in the mPFC. We found that PREGS inhibited induction of LTP in the mPFC and had no influence on NMDA currents, which was different from its effect in the hippocampus. Moreover, the effect of PREGS on LTP in the mPFC was cancelled by alpha2-adrenoreceptor antagonist, alpha2A-adrenoreceptor antagonist, Gi protein inhibitor, adenylate cyclase inhibitor and protein kinase A inhibitor. These results suggest that PREGS inhibits LTP via activation of the alpha2-adrenoreceptor-Gi protein-adenylate cyclase-protein kinase A signalling pathway in the mPFC.

PREGS induces LTP in the hippocampal dentate gyrus of adult rats via the tyrosine phosphorylation of NR2B coupled to ERK/CREB [corrected] signaling

An acute application of neurosteroid pregnenolone sulfate (PREGS) to hippocampal slices from adult rats induced a long-lasting potentiation (LLP PREGS) at the perforant path-granule cell synapse. As a partial mechanism of the LLP PREGS, we previously revealed that PREGS transiently increases the probability of presynaptic glutamate release via a sensitization of alpha7-nicotinic acetylcholine receptor (alpha7nAChR). We herein demonstrate that the LLP PREGS could be separated into two independent processes: the above-mentioned early presynaptic-origin short-term potentiation (STP PREGS) and a delayed postsynaptic N-methyl-d-aspartate receptor (NMDAr)-dependent long-term potentiation termed LTP(PREGS). This study focused on the analysis of the signaling mechanism underlying the LTP PREGS. PREGS increased the tyrosine phosphorylation of NR2B, a subunit of NMDAr, and the NMDAr-mediated Ca2+ influx in the granule cells. The enhanced Ca2+ influx was largely attenuated by the NR2B subunit inhibitor ifenprodil and the Src kinase family inhibitor PP2. PREGS also triggered a persistent phosphorylation of extracellular signal-regulated kinase 2 (ERK2) followed by an ERK-dependent phosphorylation of cAMP-response element-binding protein (CREB), which was crucial for the LTP PREGS induction and was sensitive to ifenprodil. These results suggest that PREGS induces an acute increase in the NR2B tyrosine phosphorylation which enhances the Ca2+ influx through NMDAr, followed by an activation of the ERK/CREB signaling cascade that leads to LTP PREGS.

Modulation of glutamatergic transmission by sulfated steroids: role in fetal alcohol spectrum disorder

It is well established that sulfated steroids regulate synaptic transmission by altering the function of postsynaptic neurotransmitter receptors. In recent years, evidence from several laboratories indicates that these agents also regulate glutamatergic synaptic transmission at the presynaptic level in an age-dependent manner. In developing neurons, pregnenolone sulfate (PREGS) increases the probability of glutamate release, as evidenced by an increase in the frequency of AMPA receptor-mediated miniature excitatory postsynaptic currents and a decrease in paired-pulse facilitation. In hippocampal slices from postnatal day 3-5 rats, this effect is mediated by an increase in Ca(2+) levels in the axonal terminal that depends on presynaptic NMDA receptors. This is followed by delayed potentiation of postsynaptic AMPA receptor currents. Importantly, depolarization of postsynaptic neurons, inhibition of hydroxysteroid sulfatase activity and acute exposure to ethanol mimics the effect of exogenous PREGS application. This developmental form of synaptic plasticity cannot be observed in slices from rats older than postnatal day 6, when presynaptic NMDA receptors are no longer expressed in CA1 hippocampal region. Both in the CA1 hippocampal region and the dentate gyrus of more mature rats, PREGS, dehydroepiandrosterone sulfate and hydroxysteroid sulfatase inhibitors increase paired-pulse facilitation, without affecting basal glutamate release probability. This effect depends on activation of sigma(1)-like receptors and G(i/o) and involves a target in the release machinery that is downstream of residual Ca(2+). These presynaptic actions of sulfated steroids could play important roles in physiological processes ranging from synapse maturation to learning and memory, as well as pathophysiological conditions such as fetal alcohol spectrum disorder.

Neurosteroid pregnenolone sulfate enhances glutamatergic synaptic transmission by facilitating presynaptic calcium currents at the calyx of Held of immature rats

Pregnenolone sulfate (PREGS) is an endogenous neurosteroid widely released from neurons in the brain, and is thought to play a memory-enhancing role. At excitatory synapses PREGS facilitates transmitter release, but the underlying mechanism is not known. We addressed this issue at the calyx of Held in rat brainstem slices, where direct whole-cell recordings from giant nerve terminals are feasible. PREGS potentiated nerve-evoked excitatory postsynaptic currents (EPSCs) without affecting the amplitude of miniature EPSCs, suggesting that its site of action is presynaptic. In whole-cell recordings from calyceal nerve terminals, PREGS facilitated Ca2+ currents, by accelerating their activation kinetics and shifting the half-activation voltage toward negative potentials. PREGS had no effect on presynaptic K+ currents, resting conductance or action potential waveforms. In simultaneous pre- and postsynaptic recordings, PREGS did not change the relationship between presynaptic Ca2+ influx and EPSCs, suggesting that exocytotic machinery downstream of Ca2+ influx is not involved in its effect. PREGS facilitated Ba2+ currents recorded from nerve terminals and also from HEK 293 cells expressed with recombinant N- or P/Q-type Ca2+ channels, suggesting that PREGS-induced facilitation of voltage-gated Ca2+ channels (VGCCs) is neither Ca2+ dependent nor VGCC-type specific. The PREGS-induced VGCC facilitation was blocked by the PREGS scavenger (2-hydroxypropyl)-beta-cyclodextrin applied from outside, but not from inside, of nerve terminals. We conclude that PREGS facilitates VGCCs in presynaptic terminals by acting from outside, thereby enhancing transmitter release. We propose that PREGS may directly modulate VGCCs acting on their extracellular domain.

Neurosteroid-induced enhancement of short-term facilitation involves a component downstream from presynaptic calcium in hippocampal slices

We used Magnesium Green AM to measure Ca(2+) transients in Schaffer collateral presynaptic terminals simultaneously with postsynaptic field potentials (fEPSPs) to investigate the mechanism of neurosteroid enhancement of short-term synaptic facilitation. Measurement of [Ca(2+)](i), isolated to presynaptic events, using the fluorescence ratio (DeltaF/F(0)) demonstrated that at a constant stimulus intensity there was no change in the excitability of presynaptic fibres between paired stimuli or between ACSF and 1 mum pregnenolone sulphate (PREGS). Paired-pulse facilitation (PPF) was correlated with residual Ca(2+) ([Ca(2+)](res)), and there was an additional increase in the integralDeltaF/F(0) for the [Ca(2+)](res)-subtracted response to the second of paired stimuli, resulting primarily from a slowing of the decay time constant. In addition to the role of presynaptic [Ca(2+)](res) in PPF, we observed a decrease in EC(50) and a greater maximum for Hill function fits to fEPSP versus DeltaF/F(0) during the second of paired responses. The enhancement of fEPSP PPF by PREGS did not result from an increase of DeltaF/F(0). The data presented here support a PREGS-induced increase in presynaptic glutamate release from the second, but not the first, of a pair of stimuli for a given presynaptic [Ca(2+)] because: (a) there is actually a decrease in the integralDeltaF/F(0) of the [Ca(2+)](res)-subtracted second response over that seen in ACSF; (b) PREGS causes no change in presynaptic Ca(2+) buffering; and (c) there is a decrease in EC(50) and an increase of y(max) in the Hill function fits to DeltaF/F(0) versus fEPSP data. We hypothesize that PREGS enhances short-term facilitation by acting on the Ca(2+)-dependent vesicle release machinery and that this mechanism plays a role in the cognitive effects of this sulphated neurosteroid.

Neurosteroids and cholinergic systems: implications for sleep and cognitive processes and potential role of age-related changes

RATIONALE

The neurosteroids pregnenolone sulfate (PREGS), dehydroepiandrosterone sulfate (DHEAS) and allopregnanolone (3alpha,5alpha THPROG) have been implicated as powerful modulators of memory processes and sleep states in young and aged subjects with memory impairment. As these processes depend on the integrity of cholinergic systems, a specific effect of neurosteroids on these systems may account for their effects on sleep and memory.

OBJECTIVE

To review the evidence for a specific and differential effect of neurosteroids on cholinergic systems.

METHODS

We carried out keyword searches in "Medline" to identify articles concerning (1) the effects of neurosteroids on cholinergic systems, sleep and memory processes, and (2) changes in neurosteroid concentrations during aging. Few results are available for humans. Most data concerned rodents.

RESULTS

Peripheral and central administrations of PREGS, DHEAS, and 3alpha,5alpha THPROG modulate the basal forebrain and brainstem projection cholinergic neurons but not striatal cholinergic interneurons. Local administration of neurosteroids to the basal forebrain and brainstem cholinergic neurons alters sleep and memory in rodents. There are a few conflicting reports concerning the effects of aging on neurosteroid concentrations in normal and pathological conditions.

CONCLUSIONS

The specific modulation of basal forebrain and brainstem cholinergic systems by neurosteroids may account for the effects of these compounds on sleep and memory processes. To improve our understanding of the role of neurosteroids in cholinergic systems during normal and pathological aging, we need to determine whether there is specific regionalization of neurosteroids, and we need to investigate the relationship between neurosteroid concentrations in cholinergic nuclei and age-related sleep and memory impairments.

The Sigma1 Protein as a Target for the Non-genomic Effects of Neuro(active)steroids: Molecular, Physiological, and Behavioral Aspects

Steroids synthesized in the periphery or de novo in the brain, so called 'neurosteroids', exert both genomic and nongenomic actions on neurotransmission systems. Through rapid modulatory effects on neurotransmitter receptors, they influence inhibitory and excitatory neurotransmission. In particular, progesterone derivatives like 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) are positive allosteric modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor and therefore act as inhibitory steroids, while pregnenolone sulphate (PREGS) and dehydroepiandrosterone sulphate (DHEAS) are negative modulators of the GABA(A) receptor and positive modulators of the N-methyl-D-aspartate (NMDA) receptor, therefore acting as excitatory neurosteroids. Some steroids also interact with atypical proteins, the sigma (sigma) receptors. Recent studies particularly demonstrated that the sigma1 receptor contributes effectively to their pharmacological actions. The present article will review the data demonstrating that the sigma1 receptor binds neurosteroids in physiological conditions. The physiological relevance of this interaction will be analyzed and the impact on physiopathological outcomes in memory and drug addiction will be illustrated. We will particularly highlight, first, the importance of the sigma1-receptor activation by PREGS and DHEAS which may contribute to their modulatory effect on calcium homeostasis and, second, the importance of the steroid tonus in the pharmacological development of selective sigma1 drugs.

Presynaptic modulation of synaptic transmission by pregnenolone sulfate as studied by optical recordings

The effects of pregnenolone sulfate (PREGS), a putative neurosteroid, on the transmission of perforant path-granule cell synapses were investigated with an optical recording technique in rat hippocampal slices stained with voltage-sensitive dyes. Application of PREGS to the bath solution resulted in an acute augmentation of EPSP in a dose-dependent manner. The PREGS effect was dependent on the extracellular Ca(2+) concentration ([Ca(2+)](o)), but independent of NMDA receptor activation. PREGS caused a decrease in paired-pulse facilitation, which implies that PREGS positively modulates presynaptic neurotransmitter releases. Firmer support for this mechanism was that PREGS augmented the synaptically induced glial depolarization (SIGD) that reflects the activity of electrogenic glutamate transporters in glial cells during the uptake of released glutamate. The selective alpha7nAChR antagonist alpha-BGT or MLA prevented the SIGD increase by PREGS. Furthermore DMXB, a selective alpha7nAChR agonist, mimicked the PREGS effect on SIGD and antagonized the effect of PREGS. The presynaptic effect of PREGS was partially attenuated by the L-type Ca(2+) channel (VGCC) blocker nifedipine. Based on these findings, we proposed a novel mechanism underlying the facilitated synaptic transmission by PREGS: this neurosteroid sensitizes presynaptic alpha7nAChR that is followed by an activation of L-type VGCC to increase the presynaptic glutamate release.

The effects of the neurosteroids: pregnenolone, progesterone and dehydroepiandrosterone on muscarinic receptor-induced responses in Xenopus oocytes expressing M1 and M3 receptors

The neurosteroids pregnenolone, progesterone, and dehydroepiandrosterone (DHEA) occur naturally in the nervous system. They act on neural tissues, participate in neuronal signaling, and are reported to alter neuronal excitability via nongenomic mechanisms. Muscarinic receptors have important roles in neuronal functions in the brain and autonomic nervous system. In this study, we investigated the effects of pregnenolone, progesterone, and DHEA on M(1) and M(3) muscarinic receptors using the Xenopus oocyte expression system. Pregnenolone and progesterone inhibited the acetylcholine (ACh)-mediated responses of M(1) and M(3) receptors expressed in Xenopus oocytes, whereas DHEA did not. The half-maximal inhibitory concentrations (IC(50)) for pregnenolone inhibition of M(1) receptor- and M(3) receptor-mediated currents were 11.4 and 6.0 microM respectively; the IC(50) values for progesterone inhibition of M(1) receptor- and M(3) receptor-mediated currents were 2.5 and 3.0 microM respectively. The selective protein kinase C (PKC) inhibitor GF109203X had little effect on the pregnenolone or progesterone inhibition of the ACh-induced currents in Xenopus oocytes expressing M(1) or M(3) receptors. The inhibitory effects of pregnenolone and progesterone were overcome at higher concentrations of ACh. Pregnenolone and progesterone inhibited the [(3)H]quinuclidinyl benzilate (QNB) binding to M(1) and M(3) receptor expressed in Xenopus oocytes, and Scatchard plot analysis of [(3)H]QNB binding revealed that pregnenolone and progesterone altered the K(d) value and the B(max), indicating noncompetitive inhibition. In conclusion, pregnenolone and progesterone inhibited M(1) and M(3) receptor functions noncompetitively by the mechanism independent of PKC and by interfering with ACh binding to the receptors.

Neurosteroid paradoxical enhancement of paired-pulse inhibition through paired-pulse facilitation of inhibitory circuits in dentate granule cells

Neurosteroids are produced in the brain independently of peripheral endocrine glands to act locally in the nervous system. They exert potent promnesic effects and play significant roles in mental health-related disorders. In part, neurosteroids act by affecting ligand-gated ion channels and metabotropic receptors through rapid non-genomic processes. We have previously demonstrated that neurosteroids also affect synaptic transmission presynaptically in the CA1 region of the hippocampus. Here we describe the effects of the most abundant neurosteroid in the rodent brain, pregnenolone sulfate (PregS), on signal processing in the dentate subfield of the hippocampus. We show that PregS acts presynaptically at low concentrations (300 nM) to enhance paired-pulse facilitation (PPF) in perforant pathway terminals on dentate granule cells. Similar effects were found with two steroid sulfatase inhibitors demonstrating a potential contribution of endogenous steroids to dentate synaptic plasticity. This enhanced presynaptic facilitation paradoxically increases paired-pulse inhibition (PPI) at short interpulse intervals. Based on these data, a model of dentate gyrus circuit interactions is proposed for the presynaptic action of PregS on the filtering dynamics of the dentate subfield at frequencies similar to those of the endogenous signals from the entorhinal cortex. These modeling studies are consistent with experimental measurements demonstrating positive modulation by PregS at low frequencies and negative modulation at high frequencies. These studies show an important role for the presynaptic action of neurosteroids in modulating input signals to the hippocampus.

Pregnenolone sulfate enhances neurogenesis and PSA-NCAM in young and aged hippocampus

Age-dependent cognitive impairments have been correlated with functional and structural modifications in the hippocampal formation. In particular, the brain endogenous steroid pregnenolone-sulfate (Preg-S) is a cognitive enhancer whose hippocampal levels have been linked physiologically to cognitive performance in senescent animals. However, the mechanism of its actions remains unknown. Because neurogenesis is sensitive to hormonal influences, we examined the effect of Preg-S on neurogenesis, a novel form of plasticity, in young and old rats. We demonstrate that in vivo infusion of Preg-S stimulates neurogenesis and the expression of the polysialylated forms of NCAM, PSA-NCAM, in the dentate gyrus of 3- and 20-month-old rats. These influences on hippocampal plasticity are mediated by the modulation of the gamma-aminobutyric acid receptor complex A (GABA(A)) receptors present on hippocampal neuroblasts. In vitro, Preg-S stimulates the division of adult-derived spheres suggesting a direct influence on progenitors. These data provide evidence that neurosteroids represent one of the local secreted signals controlling hippocampal neurogenesis. Thus, therapies which stimulate neurosteroidogenesis could preserve hippocampal plasticity and prevent the appearance of age-related cognitive disturbances.

A steroid modulatory domain on NR2B controls N-methyl-D-aspartate receptor proton sensitivity

N-methyl-D-aspartate (NMDA) receptor function is modulated by several endogenous molecules, including zinc, polyamines, protons, and sulfated neurosteroids. Zinc, polyamines, and phenylethanolamines exert their respective modulatory effects by exacerbating or relieving tonic proton inhibition. Here, we report that pregnenolone sulfate (PS) uses a unique mechanism for enhancement of NMDA receptor function that is independent of the proton sensor. We identify a steroid modulatory domain, SMD1, on the NMDA receptor NR2B subunit that is critical for both PS enhancement and proton sensitivity. This domain includes the J/K helices in the S2 region of the glutamate recognition site and the fourth membrane transmembrane region (M4). A molecular model based on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor structure suggests that steroid modulatory domain 1 contributes residues to a hydrophobic pocket that is capable of accommodating PS. The results demonstrate that the J/K helices and the fourth membrane transmembrane region participate in transducing allosteric interactions induced by steroid and proton binding to their respective sites.

The neuroactive steroid 3-alpha-ol-5-beta-pregnan-20-one hemisuccinate, a selective NMDA receptor antagonist improves behavioral performance following spinal cord ischemia

The initial response to an ischemic event is the rapid release of excitatory amino acid's followed by the activation of the "ischemic cascade". It has been suggested that neurosteroids, which act as negative modulators of excitatory amino acid receptors, may improve behavioral functions and promote neuronal survival following ischemia. The present study evaluated the pharmacological effects of 3-alpha-ol-5-beta-pregnan-20-one hemisuccinate (ABHS), a neurosteroid that inhibits excitatory amino acid receptor function, in a rabbit reversible spinal cord ischemia model (RSCIM). ABHS was administered (25 mg/kg) intravenously (i.v.) 5 or 30 min following the start of occlusion to groups of rabbits exposed to ischemia induced by temporary occlusion of the infrarenal aorta. The group P50 represents the duration of ischemia (min) associated with a 50% probability of resultant permanent paraplegia. Quantal analysis indicated that the P50 of the control group was 23.44 +/- 4.32 min. Using the RSCIM, neuroprotection is observed if a drug significantly prolongs the P50 compared to the control group. Treatment with ABHS (25 mg/kg) 5 min post-occlusion significantly (p < 0.05) prolonged the P50 of the group to 49.18 +/- 10.44 min, an increase of 110%. The effect of ABHS was not durable following a single injection since a significant difference between the control and ABHS-treated groups was not measurable at 48 h. However, if ABHS was injected 5 min following the start of ischemia and again 24 h after ischemia, there was a persistent effect of the drug at 48 h. Moreover, ABHS also increased the tolerance to ischemia if administered 30 min following the start of occlusion. Our results suggest that neuroactive steroids such as ABHS, which are selective NMDA receptor antagonists, may have substantial therapeutic benefit for the treatment of ischemic injuries including spinal cord neurodegeneration and stroke.

A capillary gas chromatography/mass spectrometric method for the quantification of hydroxysteroids in human plasma

A specific and sensitive methodology for the quantitative determination of hydroxysteroids dehydroepiandrosterone and pregnenolone and their main metabolites in human plasma is described. Hydroxysteroids were extracted using methanol and steroids were further separated by reverse-phase high-performance liquid chromatography, allowing for minimization of the possible chromatographic interferences. Eluted fractions were collected, pooled, and analyzed by gas chromatography-mass spectrometry as trimethylsilyl ether derivatives. The quantification was performed with single-ion monitoring of the highly abundant m/z 129 or m/z 358 fragments. The combination of the chromatographic characteristics to the specific fragments ensured the selectivity and specificity of the method. Under these conditions the method was linear (typical R2 is superior to 0.98 for all hydroxysteroids studied) over the concentration range of 2 x 10(-9) to 10(-6)M with good precision and accuracy.

Sleep-wake states and cortical synchronization control by pregnenolone sulfate into the pedunculopontine nucleus

Cholinergic neurons of the pedunculopontine tegmentum nucleus (PPT) are crucial for initiation and maintenance of electroencephalographic (EEG) desynchronization states like paradoxical sleep and wakefulness. These neurons are regulated by classical neurotransmitter systems from the pontomesencephalic reticular formation and basal ganglia. In addition to this regulation, PPT neuron activity could be modulated by endogenous neurosteroids and particularly by pregnenolone sulfate (PREG-S) because synthesis enzymes of this neurosteroid are present in this area and peripheral administrations of PREG-S affect sleep-wakefulness states. To test this hypothesis, we studied the effects of different doses of PREG-S infusion into the PPT on sleep-wakefulness states in rats. Our results show dose-dependent effects of PREG-S on sleep-wakefulness states. Low concentration of PREG-S (5 ng) increased the amount of paradoxical sleep without any modification of slow wave sleep and wakefulness. High level of PREG-S (10 and 20 ng) increased paradoxical sleep and slow wave sleep together with an increase of delta power and a decrease of theta power during wakefulness. Dependent on the doses used, PREG-S thus can promote paradoxical sleep alone or the global propensity to fall asleep, impairing the quality of wakefulness. These results unveil a new regulation pathway for PPT neurons and strengthen the role of PREG-S in sleep-wakefulness regulation.

Neurosteroids in the Retina

Steroids may have a powerful role in neuronal degeneration. Recent research has revealed that steroids may influence the onset and progression of some retinal disorders as well as neurodegenerative diseases and, as in brain, they accumulate in the retina via a local synthesis (neurosteroids) and metabolism of blood-circulating steroid hormones. Their crucial role as neurodegenerative and neuroprotective agents has been also upheld in a retinal excitotoxic paradigm. These findings are reviewed especially from the emerging perspective that after an insult local changes in steroidogenic responses and consequent neurosteroid availability might turn out to be offensive or defensive cellular adaptations for the potentiation or prevention of neuronal death.

Individual differences in cognitive aging: implication of pregnenolone sulfate

In humans and animals, individual differences in aging of cognitive functions are classically reported. Some old individuals exhibit performances similar to those of young subjects while others are severely impaired. In senescent animals, we have previously demonstrated a significant correlation between the cognitive performance and the cerebral concentration of a neurosteroid, the pregnenolone sulfate (PREG-S). Neurotransmitter systems modulated by this neurosteroid were unknown until our recent report of an enhancement of acetylcholine (ACh) release in basolateral amygdala, cortex and hippocampus induced by intracerebroventricular (i.c.v.) or intracerebral administrations of PREG-S. Central ACh neurotransmission is known to be involved in the regulation of memory processes and is affected in normal aging and severely altered in human neurodegenerative pathologies like Alzheimer's disease. In the central nervous system, ACh neurotransmission is also involved in the modulation of sleep-wakefulness cycle, and particularly the paradoxical sleep (PS). Relationships between paradoxical sleep and memory are documented in the literature in old animals in which the spatial memory performance positively correlates with the basal amounts of paradoxical sleep. PREG-S infused at the level of ACh cell bodies (nucleus basalis magnocellularis, NBM, or pedunculopontine nucleus, PPT) increases paradoxical sleep in young animals.Finally, aging related cognitive dysfunctions, particularly those observed in Alzheimer's disease, have also been related to alterations of mechanisms underlying cerebral plasticity. Amongst these mechanisms, neurogenesis has been extensively studied recently. Our data demonstrate that PREG-S central infusions dramatically increase neurogenesis, this effect could be related to the negative modulator properties of this steroid at the GABA(A) receptor level. Taken together these data suggest that neurosteroids can influence cognitive processes, particularly in senescent subjects, through a modulation of ACh neurotransmission associated with paradoxical sleep modifications; furthermore, our recent data suggest a critical role for neurosteroids in the modulation of cerebral plasticity, mainly on hippocampal neurogenesis.

Neurosteroid modulation of glutamate release in hippocampal neurons: lack of an effect of a chronic prenatal ethanol exposure paradigm

BACKGROUND

Pregnenolone sulfate (PREGS) is a promnesic neurosteroid that is abundantly expressed in the hippocampus of rodents. Studies have shown that the modulation of postsynaptic ligand-gated ion channels by this neurosteroid is impaired in preparations from the brains of fetal ethanol-exposed animals. In this study, we examined whether the presynaptic actions of PREGS also are affected by exposure to ethanol in utero.

METHODS

Rat dams were exposed to one of the following diets during pregnancy: (1) 5% ethanol liquid diet, (2) 0% ethanol liquid diet with pair-feeding, and (3) ad libitum controls. We then studied the presynaptic actions of PREGS on (1) alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-mediated miniature excitatory postsynaptic currents (mEPSCs) recorded from cultured hippocampal neurons in the whole-cell patch-clamp configuration and (2) paired-pulse facilitation of NMDA receptor-dependent excitatory postsynaptic potentials that were intracellularly recorded from CA1 pyramidal neurons in hippocampal slices from adult rats.

RESULTS

Chronic prenatal ethanol exposure affected neither basal mEPSC frequency nor its potentiation by PREGS. Basal paired-pulse facilitation (i.e., in the absence of PREGS) was unaffected by fetal ethanol exposure. Chronic prenatal ethanol exposure did not affect the PREGS-induced potentiation of paired-pulse facilitation.

CONCLUSIONS

Chronic prenatal ethanol exposure does not affect the basal probability of glutamate release in immature or mature hippocampal neurons. Moreover, the presynaptic actions of the neurosteroid PREGS also are unaffected by this exposure. Given that modulation of glutamate release could have a role in the mechanism of the promnesic actions of this neurosteroid, future studies are warranted to determine whether PREGS can ameliorate learning and memory deficits in fetal ethanol-exposed animals.

Neuroactive steroids: new biomarkers of cognitive aging

Intensive studies in animals established that neuroactive steroids display neuronal actions and influence behavioral functions. We describe here investigations on the role of neuroactive steroids in learning and memory processes during aging and suggest their role as biomarkers of cognitive aging. Our work demonstrated the role of the steroid pregnenolone (PREG) sulfate as a factor underlying an individual's age-related cognitive decline in animals. As new perspectives of research we argue that knowing whether neuroactive steroids exist as endogenous neuromodulators and modulate physiologically behavioral functions is essential. To this end, a new approach using the sensitive, specific, and accurate quantitative determination of neuroactive steroids by mass spectrometry seems to have potential for examining the role of each steroid in discrete brain areas in learning and memory alterations, as observed during aging.

Cooperation between memory systems: acetylcholine release in the amygdala correlates positively with performance on a hippocampus-dependent task

The present experiment examined the relationship between release of acetylcholine (ACh) in the amygdala and performance on a hippocampus-dependent spatial working memory task. Using in vivo microdialysis, the authors measured ACh release in rats during testing on a spontaneous alternation task. Amygdala ACh release was positively correlated with performance on the hippocampus-dependent task. These findings suggest that activation of the amygdala promotes processing in other neural systems important for learning and memory.

Inhibition by pregnenolone sulfate of nicotinic acetylcholine response in adrenal chromaffin cells

To evaluate whether pregnenolone sulfate, an abundant neurosteroid in the brain, modulates nicotinic receptor-mediated responses, the effect of pregnenolone sulfate on acetylcholine-induced catecholamine secretion was investigated in cultured bovine adrenal chromaffin cells. Pregnenolone sulfate inhibited acetylcholine-induced catecholamine secretion (IC(50): 27 microM). In addition, pregnenolone sulfate inhibited acetylcholine-induced Na(+) (IC(50): 12 microM) and Ca(2+) (IC(50): 20 microM) influxes. However, pregnenolone sulfate did not inhibit either catecholamine secretion or Ca(2+) influx stimulated by high K(+). Binding of [3H]nicotine to nicotinic receptors was not altered by pregnenolone sulfate. The inhibitory effect on the acetylcholine-induced secretion was insurmountable by increasing acetylcholine concentrations, but was enhanced by decreasing external Na(+) concentrations. These results suggest strongly that pregnenolone sulfate noncompetitively inhibits nicotinic receptor-operated ion channels, thereby suppressing Na(+) influx through the channels and, consequently, attenuates both Ca(2+) influx and catecholamine secretion. Our results further indicate that pregnenolone sulfate may modulate nicotinic receptor-mediated responses in the brain.

The neurosteroid pregnenolone sulfate infused into the medial septum nucleus increases hippocampal acetylcholine and spatial memory in rats

The effects of an infusion of the neurosteroid pregnenolone sulfate into the medial septum on acetylcholine release in the hippocampus and on spatial memory were evaluated in two experiments. Results show that pregnenolone sulfate enhanced acetylcholine release by more than 50% of baseline and improved recognition memory of a familiar environment. Therefore, our results suggest that the septo-hippocampal pathway could be involved in the promnesic properties of this neurosteroid.

Sulfonation and molecular action

The sulfonation of endogenous molecules is a pervasive biological phenomenon that is not always easily understood, and although it is increasingly recognized as a function of fundamental importance, there remain areas in which significant cognizance is still lacking or at most minimal. This is particularly true in the field of endocrinology, in which the sulfoconjugation of hormones is a widespread occurrence that is only partially, if at all, appreciated. In the realm of steroid/sterol sulfoconjugation, the discovery of a novel gene that utilizes an alternative exon 1 to encode for two sulfotransferase isoforms, one of which sulfonates cholesterol and the other pregnenolone, has been an important advance. This is significant because cholesterol sulfate plays a crucial role in physiological systems such as keratinocyte differentiation and development of the skin barrier, and pregnenolone sulfate is now acknowledged as an important neurosteroid. The sulfonation of thyroglobulin and thyroid hormones has been extensively investigated and, although this transformation is better understood, there remain areas of incomplete comprehension. The sulfonation of catecholamines is a prevalent modification that has been extensively studied but, unfortunately, remains poorly understood. The sulfonation of pituitary glycoprotein hormones, especially LH and TSH, does not affect binding to their cognate receptors; however, sulfonation does play an important role in their plasma clearance, which indirectly has a significant effect on biological activity. On the other hand, the sulfonation of distinct neuroendocrine peptides does have a profound influence on receptor binding and, thus, a direct effect on biological activity. The sulfonation of specific extracellular structures plays an essential role in the binding and signaling of a large family of extracellular growth factors. In summary, sulfonation is a ubiquitous posttranslational modification of hormones and extracellular components that can lead to dramatic structural changes in affected molecules, the biological significance of which is now beginning to be appreciated.

Neurosteroids enhance spontaneous glutamate release in hippocampal neurons. Possible role of metabotropic sigma1-like receptors

Pregnenolone sulfate (PREGS), one of the most abundantly produced neurosteroids in the mammalian brain, improves cognitive performance in rodents. The mechanism of this effect has been attributed to its allosteric modulatory actions on glutamate- and gamma-aminobutyric acid-gated ion channels. Here we report a novel effect of PREGS that could also mediate some of its actions in the nervous system. We found that PREGS induces a robust potentiation of the frequency but not the amplitude of miniature excitatory postsynaptic currents (mEPSCs) mediated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors in cultured hippocampal neurons. PREGS also decreased paired pulse facilitation of autaptic EPSCs evoked by depolarization, indicating that it modulates glutamate release probability presynaptically. PREGS potentiation of mEPSCs was mimicked by dehydroepiandrosterone sulfate and (+)-pentazocine but not by (-)-pentazocine, the synthetic (-)-enantiomer of PREGS or the inactive steroid isopregnanolone. The sigma receptor antagonists, haloperidol and BD-1063, blocked the effect of PREGS on mEPSCs, as did pertussis toxin and the membrane-permeable Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetoxymethyl) ester. These results suggest that PREGS increases spontaneous glutamate release via activation of a presynaptic G(i/o)-coupled sigma receptor and an elevation in intracellular Ca2+ levels. We postulate that presynaptic actions of neurosteroids have a role in the maturation and/or maintenance of synaptic networks and the processing of information in the central nervous system.