Synaptic activity protects against AD and FTD-like pathology via autophagic-lysosomal degradation.

Changes in synaptic excitability and reduced brain metabolism are among the earliest detectable alterations associated with the development of Alzheimer's disease (AD). Stimulation of synaptic activity has been shown to be protective in models of AD beta-amyloidosis. Remarkably, deep brain stimulation (DBS) provides beneficial effects in AD patients, and represents an important therapeutic approach against AD and other forms of dementia. While several studies have explored the effect of synaptic activation on beta-amyloid, little is known about Tau protein. In this study, we investigated the effect of synaptic stimulation on Tau pathology and synapses in in vivo and in vitro models of AD and frontotemporal dementia (FTD). We found that chronic DBS or chemically induced synaptic stimulation reduced accumulation of pathological forms of Tau and protected synapses, while chronic inhibition of synaptic activity worsened Tau pathology and caused detrimental effects on pre- and post-synaptic markers, suggesting that synapses are affected. Interestingly, degradation via the proteasomal system was not involved in the reduction of pathological Tau during stimulation. In contrast, chronic synaptic activation promoted clearance of Tau oligomers by autophagosomes and lysosomes. Chronic inhibition of synaptic activity resulted in opposite outcomes, with build-up of Tau oligomers in enlarged auto-lysosomes. Our data indicate that synaptic activity counteracts the negative effects of Tau in AD and FTD by acting on autophagy, providing a rationale for therapeutic use of DBS and synaptic stimulation in tauopathies.

Isomerization and Oligomerization of Truncated and Mutated Tau Forms by FKBP52 are Independent Processes.

The aggregation of the neuronal Tau protein is one molecular hallmark of Alzheimer's disease and other related tauopathies, but the precise molecular mechanisms of the aggregation process remain unclear. The FK506 binding protein FKBP52 is able to induce oligomers in the pathogenic Tau P301L mutant and in a truncated form of the wild-type human Tau protein. Here, we investigate whether FKBP52's capacity to induce Tau oligomers depends on its prolyl cis/trans isomerase activity. We find that FKBP52 indeed can isomerize selected prolyl bonds in the different Tau proteins, and that this activity is carried solely by its first FK506 binding domain. Its capacity to oligomerize Tau is, however, not linked to this peptidyl-prolyl isomerase activity. In addition, we identified a novel molecular interaction implying the PHF6 peptide of Tau and the FK1/FK2 domains of FKBP52 independent of FK506 binding; these data point toward a non-catalytic molecular interaction that might govern the effect of FKBP52 on Tau.

The Prevention of Post-Partum Relapses with Progestin and Estradiol in Multiple Sclerosis (POPART'MUS) trial: rationale, objectives and state of advancement.

Multiple sclerosis (MS) affects 1 in 1000 people in western countries, mainly women in their childbearing years. It is an autoimmune disease of the central nervous system, which results in a chronic focal inflammatory response with subsequent demyelination and axonal loss. It usually begins with acute episodes of neurological dysfunction, the relapses, followed by periods of partial or complete remission. This relapsing-remitting phase is usually followed by a steady, continuous and irreversible worsening of the neurological dysfunction, which characterizes the progressive phase of the disease. Recent prospective studies reported a significant decline by two-third in the rate of relapses during the third trimester of pregnancy and a significant increase by two-third during the first three months post-partum by comparison to the relapse rate observed during the year prior to the pregnancy. These dramatic changes in the relapse rate occur at a time when impregnation of many substances, among which sexual steroids, is at its highest, before a dramatic decline to the pre-pregnancy levels, immediately following delivery. It may be hypothesized that sexual steroids could exert beneficial effects through a modulation of the immune state with a lowering of the pro-inflammatory lymphocyte responses of the Th1 type and an enhancement of anti-inflammatory responses of the Th2 type. They may also play a direct role in remyelination of central nervous system lesions, as they do in the peripheral nervous system, where progesterone increases the extent of myelin sheath formation after a cryolesion of the male mouse sciatic nerve. The POPART'MUS study is a European, multicentre, randomized, placebo-controlled and double-blind clinical trial, which aims to prevent MS relapses related to the post-partum condition, by administrating high doses of progestin, in combination with endometrial protective doses of estradiol. Treatment is given immediately after delivery and continuously during the first three months post-partum. At present, 126 patients have been enrolled and 107 patients have completed the protocol. Assuming the results of the trial to be positive, this new treatment could be considered in the relapsing-remitting phase of the disease in women afar from pregnancy and post-partum. The trial is registered under the reference NTC00127075.

DHEA decreases HIF-1alpha accumulation under hypoxia in human pulmonary artery cells: potential role in the treatment of pulmonary arterial hypertension.

Previous work showed that dehydroepiandrosterone (DHEA) prevents and reverses chronic hypoxic pulmonary artery hypertension in rat via targeting smooth muscle cells. In our study, DHEA was tested on human pulmonary arterial smooth muscle cells (HPASMC) to identify its mechanism of action under hypoxia in vitro. We show that DHEA decreased HIF-1alpha accumulation under both "chemical hypoxia" with treatment by the iron chelator deferroxamin and gas hypoxia (1% O2). The mRNA levels of HIF-1alpha were unchanged whether or not DHEA was applied under chemical and gas hypoxia, as compared to controls in normoxia, suggesting a post-transcriptional effect of the steroid. Protein levels of prolyl hydroxylases responsible for HIF-1alpha degradation were not modified by DHEA treatment. In addition, a synthetic derivative of DHEA, 3beta-methyl-Delta5-androsten-17-one (which cannot be metabolized), was as active as DHEA on HIF-1alpha accumulation, as well as testosterone and 17beta-estradiol (E2). In HPASMC cultures under normoxia and both types of hypoxia, DHEA gave rise to Delta5-androstene-3beta,17beta-diol (ADIOL) and DHEA-sulfate (DHEA-S). Neither testosterone, nor E2 were found. In addition, ADIOL, DHEA-S, 7alpha-hydroxy-DHEA and Delta4-androstene-3,17-dione were ineffective on HIF-1alpha accumulation. The effect of DHEA per se reducing HIF-1alpha accumulation may be relevant to reduced hypoxia effects in pulmonary arterial hypertension.

Neuroprotective effect of mifepristone involves neuron depolarization.

In several regions of the developing nervous system, neurons undergo programmed cell death. In the rat cerebellum, Purkinje cell apoptosis is exacerbated when cerebellar slices are cultured during the first postnatal week. To understand the mechanism of this developmental apoptosis, we took advantage of its inhibition by the steroid analog mifepristone. This effect did not involve the classical steroid nuclear receptors. Microarray analysis revealed that mifepristone down-regulated mRNA levels of the Na+/K+-ATPase alpha3 subunit more than three times. Consistent with the down-regulation of the Na+/K+-ATPase, mifepristone caused Purkinje cell membrane depolarization. Depolarizing agents like ouabain (1 microM), tetraethylammonium (2 mM), and veratridine (2 microM) protected Purkinje cells from apoptosis. These results suggest a role of excitatory inputs in Purkinje cell survival during early postnatal development. Indeed, coculturing cerebellar slices with glutamatergic inferior olivary neuron preparations allowed rescue of Purkinje cells. These findings reveal a new neuroprotective mechanism of mifepristone and support a pivotal role for excitatory inputs in the survival of Purkinje neurons. Mifepristone may be a useful lead compound in the development of novel therapeutic approaches for maintaining the resting potential of neurons at values favorable for their survival under neuropathological conditions.

Progesterone increases oligodendroglial cell proliferation in rat cerebellar slice cultures.

We have previously demonstrated that progesterone significantly increases the rate of myelination in organotypic slice cultures of 7-day-old rat and mouse cerebellum. Here, we show that progesterone (20microM) stimulates the proliferation of oligodendrocyte precursors in cultured cerebellar slices of 7-day-old rats. The steroid increased the number of pre-oligodendrocytes (NG2(+), O4(+)) and to some extent of oligodendrocyte precursors, corresponding to an earlier developmental stage (nestin(+), PDGFalphaR(+), NG2(+), O4(-)). Progesterone stimulated the proliferation of both NG2(+) and O4(+) cells as shown by increased double-immunolabeling with the cell proliferation marker Ki67. The mitogenic effect of progesterone was inhibited by the progesterone receptor antagonist mifepristone (10microM) and could not be mimicked by its GABA-active metabolite 3alpha,5alpha-tetrahydroprogesterone (allopregnanolone), even at the high concentration of 50microM. Results indicate that progesterone first strongly and transiently stimulates the proliferation of oligodendrocyte precursors, and that it may thereafter accelerate their maturation into myelinating oligodendrocytes. Although oligodendrocyte precursors may be a direct target for the actions of progesterone, their number may also be indirectly influenced by the effects of the steroid on neurons and microglial cells, since treatment of the cerebellar slices with progesterone enhanced staining of the neuronal cytoskeleton marker microtubule-associated protein-2 and increased the number of OX-42(+) microglia. A small percentage (about 0.1%) of the NG2(+) cells transiently became OX-42(+) in response to progesterone. These results point to novel mechanisms by which progesterone may promote myelination in the CNS, specifically by stimulating the proliferation and maturation of oligodendrocyte precursors into myelinating oligodendrocytes.

Systemic progesterone administration results in a partial reversal of the age-associated decline in CNS remyelination following toxin-induced demyelination in male rats.

In order to establish the effects of systemically administered progesterone on central nervous system (CNS) remyelination, a toxin-induced model of CNS demyelination was used in which the rate of remyelination is age-dependent. The rapid remyelination in young adult rats allowed an assessment of potential adverse effects of progesterone while the slow remyelination in older adult rats allowed an assessment of its potentially beneficial effects. There was no significant difference in the rate of remyelination between young control and treated animals. However, a modest but significant increase in the extent of oligodendrocyte remyelination in response to progesterone (and a comparable significant decrease in the proportion of axons that remained demyelinated) was observed in older rats 5 weeks after lesion induction. We also found a significant increase in the proportion of Schwann cell remyelinated axons between 3 and 5 weeks after lesion induction that was not apparent in the control animals. These results indicate that progesterone does not inhibit CNS remyelination and that it has a positive modulating effect on oligodendrocyte remyelination in circumstances where it is occurring sub-optimally.

Steroid hormones and neurosteroids in normal and pathological aging of the nervous system.

Without medical progress, dementing diseases such as Alzheimer's disease will become one of the main causes of disability. Preventing or delaying them has thus become a real challenge for biomedical research. Steroids offer interesting therapeutical opportunities for promoting successful aging because of their pleiotropic effects in the nervous system: they regulate main neurotransmitter systems, promote the viability of neurons, play an important role in myelination and influence cognitive processes, in particular learning and memory. Preclinical research has provided evidence that the normally aging nervous system maintains some capacity for regeneration and that age-dependent changes in the nervous system and cognitive dysfunctions can be reversed to some extent by the administration of steroids. The aging nervous system also remains sensitive to the neuroprotective effects of steroids. In contrast to the large number of studies documenting beneficial effects of steroids on the nervous system in young and aged animals, the results from hormone replacement studies in the elderly are so far not conclusive. There is also little information concerning changes of steroid levels in the aging human brain. As steroids present in nervous tissues originate from the endocrine glands (steroid hormones) and from local synthesis (neurosteroids), changes in blood levels of steroids with age do not necessarily reflect changes in their brain levels. There is indeed strong evidence that neurosteroids are also synthesized in human brain and peripheral nerves. The development of a very sensitive and precise method for the analysis of steroids by gas chromatography/mass spectrometry (GC/MS) offers new possibilities for the study of neurosteroids. The concentrations of a range of neurosteroids have recently been measured in various brain regions of aged Alzheimer's disease patients and aged non-demented controls by GC/MS, providing reference values. In Alzheimer's patients, there was a general trend toward lower levels of neurosteroids in different brain regions, and neurosteroid levels were negatively correlated with two biochemical markers of Alzheimer's disease, the phosphorylated tau protein and the beta-amyloid peptides. The metabolism of dehydroepiandrosterone has also been analyzed for the first time in the aging brain from Alzheimer patients and non-demented controls. The conversion of dehydroepiandrosterone to Delta5-androstene-3beta,17beta-diol and to 7alpha-OH-dehydroepiandrosterone occurred in frontal cortex, hippocampus, amygdala, cerebellum and striatum of both Alzheimer's patients and controls. The formation of these metabolites within distinct brain regions negatively correlated with the density of beta-amyloid deposits.

Steroids and the reversal of age-associated changes in myelination and remyelination.

The myelin sheaths that surround all but the smallest diameter axons within the mammalian central nervous system (CNS) must maintain their structural integrity for many years. Like many tissues, however, this function is prone to the effects of ageing, and various structural anomalies become apparent in the aged CNS. Similarly, the regenerative process by which myelin sheaths, lost as a consequence of exposure to a demyelinating insult, are restored (remyelination) is also affected by age. As animals grow older, the efficiency of remyelination progressively declines. In this article, we review both phenomena and describe how both can be partially reversed by steroid hormones and their derivatives.

Progesterone and its metabolites increase myelin basic protein expression in organotypic slice cultures of rat cerebellum.

We have previously shown that progesterone (PROG) is synthesized by Schwann cells and promotes myelin formation in the peripheral nervous system (PNS). We now report that this neurosteroid also stimulates myelination in organotypic slice cultures of 7-day-old (P7) rat and mouse cerebellum. Myelination was evaluated by immunofluorescence analysis of the myelin basic protein (MBP). After 7 days in culture (7DIV), we found that adding PROG (2(-5) x 10(-5) M) to the culture medium caused a fourfold increase in MBP expression when compared to control slices. The effect of PROG on MBP expression involves the classical intracellular PROG receptor (PR): the selective PR agonist R5020 significantly increased MBP expression and the PR antagonist mifepristone (RU486) completely abolished the effect of PROG on this MBP expression. Moreover, treatment of P7-cerebellar slice cultures from PR knockout (PRKO) mice with PROG had no significant effect on MBP expression. PROG was metabolized in the cerebellar slices to 5alpha-dihydroprogesterone (5alpha-DHP) and to the GABAA receptor-active metabolite 3alpha,5alpha-tetrahydroprogesterone (3alpha,5alpha-THP, allopregnanolone). The 5alpha-reductase inhibitor L685-273 partially inhibited the effect of PROG, and 3alpha,5alpha-THP (2(-5) x 10(-5) M) significantly stimulated the MBP expression, although to a lesser extent than PROG. The increase in MBP expression by 3alpha,5alpha-THP involved GABAA receptors, as it could be inhibited by the selective GABAA receptor antagonist bicuculline. These findings suggest that progestins stimulate MBP expression and consequently suggest an increase in CNS myelination via two signalling systems, the intracellular PR and membrane GABAA receptors, and they confirm a new role of GABAA receptors in myelination.

Mifepristone (RU486) protects Purkinje cells from cell death in organotypic slice cultures of postnatal rat and mouse cerebellum.

Mifepristone (RU486), which binds with high affinity to both progesterone and glucocorticosteroid receptors (PR and GR), is well known for its use in the termination of unwanted pregnancy, but other activities including neuroprotection have been suggested. Cerebellar organotypic cultures from 3 to 7 postnatal day rat (P3-P7) were studied to examine the neuroprotective potential of RU486. In such cultures, Purkinje cells enter a process of apoptosis with a maximum at P3. This study shows that RU486 (20 microM) can protect Purkinje cells from this apoptotic process. The neuroprotective effect did involve neither PR nor GR, because it could not be mimicked or inhibited by other ligands of these receptors, and because it still took place in PR mutant (PR-KO) mice and in brain-specific GR mutant mice (GRNes/Cre). Potent antioxidant agents did not prevent Purkinje cells from this developmental cell death. The neuroprotective effect of RU486 could also be observed in pathological Purkinje cell death. Indeed, this steroid is able to prevent Purkinje cells from death in organotypic cultures of cerebellar slices from Purkinje cell degeneration (pcd) mutant mice, a murine model of hereditary neurodegenerative ataxia. In P0 cerebellar slices treated with RU486 for 6 days and further kept in culture up to 21 days, the synthetic steroid increased by 16.2-fold the survival of pcd/pcd Purkinje cells. Our results show that RU486 may act through a new mechanism, not yet elucidated, to protect Purkinje cells from death.

Expression of steroidogenic acute regulatory protein in cultured Schwann cells and its regulation by cAMP.

In steroidogenic cells the steroidogenic acute regulatory (StAR) protein plays a key role in the transport of cholesterol to the inner mitochondrial membrane, where the first step of steroidogenesis, the conversion of cholesterol to pregnenolone, takes place. cAMP is a known positive regulator of StAR gene expression and steroid biosynthesis in steroidogenic cells. As some steroids, such as progesterone, can also be synthesized de novo in the central and peripheral nervous systems and display neuroprotective and neurotrophic effects, we decided to verify the effect of cAMP on StAR gene expression in cultured Schwann cells. We observed that (1) in the presence of serum, forskolin, an agent known to elevate intracellular cAMP, induced both a morphological change and proliferation of cultured Schwann cells; (2) StAR mRNA and protein were expressed in Schwann cells; (3) unexpectedly, forskolin and 8 Br-cAMP, a cell-permeant analogue of cAMP, extinguishcd StAR gene expression; and (4) this response was similar in the presence or absence of serum.

Progesterone and the oligodendroglial lineage: stage-dependent biosynthesis and metabolism.

Evidence has been accumulated showing that neurosteroids, particularly progesterone (PROG) and its metabolites, may participate in myelination and remyelination in the peripheral nervous system, but very few studies have been undertaken in the central nervous system (CNS). The aim of this work was to investigate the capacities of synthesis and metabolism of PROG at three important stages of the oligodendroglial lineage: oligodendrocyte pre-progenitors (OPP), oligodendrocyte progenitors (OP), and fully differentiated oligodendrocytes (OL). Experiments have been conducted in vitro using highly purified primary cell cultures from rat brain. Cells were incubated with (3)H-pregnenolone ((3)H-PREG), the immediate precursor of PROG, or with (3)H-PROG, and steroids metabolites were then identified by thin layer chromatography and high-performance liquid chromatography (HPLC). mRNA expression of key steroidogenic enzymes was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). The results showed that only OPP and OP, but not OL, expressed 3 beta-hydroxysteroid dehydrogenase/Delta 5-Delta 4 isomerase mRNA and were able to synthesize PROG from PREG. In the three cell types studied, PROG was metabolized by the type 1 isoform of 5 alpha-reductase into 5 alpha-dihydroprogesterone (5 alpha-DHPROG). This enzyme exhibited a 5-fold higher activity in OL than in OPP and OP. 5 alpha-DHPROG was further transformed either into 3 alpha,5 alpha-tetrahydroprogesterone (3 alpha,5 alpha-THPROG), known as a positive allosteric modulator of the GABA(A) receptor, or into the 3 beta-isomer. The 3 alpha,5 alpha-THPROG synthesis was 10 times higher in OPP than in the other cell studied, while the 3 beta,5 alpha-THPROG production did not change with cell differentiation. PROG synthesis and metabolism and the dramatic changes in neurosteroidogenesis observed during the oligodendroglial differentiation may contribute to oligodendrocyte development or the myelination process.

Neurosteroids: recent findings.

The term neurosteroid applies to those steroids that are synthesized in the nervous system, from cholesterol or other blood-borne steroidal precursors, and that accumulate in the nervous system to levels that are at least in part independent from steroidogenic gland secretion. Both glial cells and neurons participate in neurosteroid biosynthesis and metabolism. Several neurosteroids are involved in auto/paracrine mechanisms involving regulation of target gene expression and/or effects on membrane receptors (particularly those for neurotransmitters). An additional unexpected mechanism of steroid action is reported here: pregnenolone binds to neural microtubule-associated protein of type 2 (MAP2) and increases both the rate and extent of tubulin polymerization, forming microtubules of normal electron microscopic appearance. This novel mechanism may play a role in regulating microtubule formation and dynamics and thus neuronal plasticity and function.

Progesterone synthesis and myelin formation in peripheral nerves.

Progesterone is synthesized in the nervous system by neurons and glial cells. Because of their simple structure, plasticity and capacity of regeneration, peripheral nerves are particularly well suited for studying the biosynthesis, mechanisms of action and effects of the hormone. Schwann cells, the myelinating glial cells in the peripheral nervous system, synthesize progesterone in response to a diffusible neuronal signal. In peripheral nerves, the local synthesis of progesterone plays an important role in the formation of myelin sheaths. This has been shown in vivo, after cryolesion of the mouse sciatic nerve, and in vitro, in cocultures of Schwann cells and sensory neurons. Schwann cells also express an intracellular receptor for progesterone, which thus functions as an autocrine signalling molecule. Progesterone may promote myelination by activating the expression of genes coding for transcription factors (Krox-20) and/or for myelin proteins (P0, PMP22). Recently, it has been proposed that progesterone may indirectly regulate myelin formation by influencing gene expression in neurons. Steroid hormones also influence the proliferation of Schwann cells: estradiol becomes a potent mitogen for Schwann cells when levels of cAMP are elevated and glucocorticosteroids have been shown to increase the mitogenic effects of peptide growth factors.

The synthetic enantiomer of pregnenolone sulfate is very active on memory in rats and mice, even more so than its physiological neurosteroid counterpart: distinct mechanisms?

The demonstration that the neurosteroid pregnenolone sulfate (PREGS) is active on memory function at both the physiological and pharmacological levels led to us examining in detail the effects of the steroid on spatial working memory by using a two-trial recognition task in a Y-maze, a paradigm based on the natural drive in rodents to explore a novel environment. Dose-response studies in young male adult Sprague-Dawley rats and Swiss mice, after the postacquisition intracerebroventricular injection of steroid, showed an U-inverted curve for memory performance and indicated a greater responsiveness in rats compared with mice. Remarkably, the synthetic (-) enantiomer of PREGS not only also displayed promnesiant activity, but its potency was 10 times higher than that of the natural steroid. Intracerebroventricular coadministration experiments with DL-2-amino-5-phosphonovaleric acid, a competitive selective antagonist of the N-methyl-D-aspartate receptor, abolished the memory-enhancing effect of PREGS, but not that of the PREGS enantiomer, evoking enantiomeric selectivity at the N-methyl-d-aspartate receptor and/or different mechanisms for the promnestic function of the two enantiomers.

Double-blind placebo-controlled trial of oral dehydroepiandrosterone in patients with advanced HIV disease.

OBJECTIVE: Plasma levels of dehydroepiandrosterone sulphate (DHEA-S) decrease with the progression of HIV disease. Here, we report on the efficacy and safety of the oral administration of DHEA as replacement therapy, in patients with advanced HIV disease, in a trial that was primarily aimed at assessing quality of life. DESIGN: The trial was randomized and double-blind. Thirty-two patients were allocated to either DHEA 50 mg per day for 4 months (n = 14) or a matching placebo (n = 18). Clinical data, virological and immunological surrogate markers of HIV infection, plasma levels of DHEA-S and the Medical Outcomes Study HIV Health Survey (MOS-HIV) quality of life scale were recorded every month. RESULTS: The mean age of the patients was 40 +/- 11 years. The mean CD4 cell count at baseline was 32.5 +/- 32.4 x 10(6)/l. The mean DHEA-S plasma level at baseline was 5.23 +/- 0.76 micromol/l. No side-effects related to DHEA occurred during the study. A statistically significant increase in the levels of DHEA-S was observed in the treated group throughout the study (P < 0.01). A significant improvement in the Mental Health and Health Distress dimension of MOS-HIV was observed in the DHEA treated group; P = 0.001 and 0.004, respectively. No change in CD4 cell counts was seen during follow-up. CONCLUSIONS: The administration of DHEA in patients with advanced HIV infection results in improved mental function scores as assessed by the MOS-HIV quality of life scale.

Neurosteroids: beginning of the story.

Neurosteroids are synthetisized in the central and the peripheral nervous system, in glial cells, and also in neurons, from cholesterol or steroidal precursors imported from peripheral sources. They include 3 beta-hydroxy-delta 5-compounds, such as pregnenolone (PREG) and dehydroepiandrosterone, their sulfate esters, and compounds known as reduced metabolites of steroid hormones, such as the tetrahydroderivative of progesterone 3 alpha-hydroxy-5 alpha-pregnan-20-one. These neurosteroids can act as modulators of neurotransmitter receptors, such as GABAA, NMDA, and sigma 1 receptors. Progesterone itself is also a neurosteroid, and a progesterone receptor has been detected in peripheral and central glial cells. At different sites in the brain, neurosteroid concentrations vary according to environmental and behavioral circumstances, such as stress, sex recognition, or aggressiveness. A physiological function of neurosteroids in the central nervous system is strongly suggested by the role of hippocampal PREGS with respect to memory performance, observed in aging rats. In the peripheral nervous system, a role for PROG synthesized in Schwann cells has been demonstrated in remyelination after cryolesion of the sciatic nerve in vivo and in cultures of dorsal root ganglia. A new mechanism of PREG action discovered in the brain involves specific steroid binding to microtubule associated protein and increased tubulin polymerization for assembling microtubules. It may be important to study the effects of abnormal neurosteroid concentration/metabolism in view of the possible treatment of functional and trophic disturbances of the nervous system.