Corticosterone-responsive mRNAs in primary rat astrocytes

Glutamine synthetase regulation by dexamethasone, RU486, and compound A in astrocytes derived from aged mouse cerebral hemispheres is mediated via glucocorticoid receptor

Glucocorticoids (GCs) regulate astrocyte function, while glutamine synthetase (GS), an enzyme highly expressed in astrocytes, is one of the most remarkable GCs-induced genes. GCs mediate their effects through their cognate glucocorticoid receptor (GRα and GRβ isoforms); however, the mechanism via which these isoforms regulate GS activity in astrocytes remains unknown. We used dexamethasone (DEX), a classical GRα/GRβ agonist, RU486, which is a specific GRβ ligand, and Compound A, a known "dissociated" ligand, to delineate the mechanism via which GR modulates GS activity. Aged Mouse Cerebral Hemisphere astrocytes were treated with DEX (1 μM), RU486 (1 nM-1 μM) or compound A (10 μM), alone or in combination with DEX. GS activity and expression, GR isoforms (mRNA and protein levels), and GRα subcellular trafficking were measured. DEX increased GS activity in parallel with GRα nuclear translocation. RU486 increased GS activity in absence of GRα nuclear translocation implicating thus a role of GRβ-mediated mechanism compound A had no effect on GS activity implicating a GRα-GRE-mediated mechanism. None of the compounds affected whole-cell GRα protein content. DEX reduced GRα and GRβ mRNA levels, while RU486 increased GRβ gene expression. We provide evidence that GS activity, in astrocytes, is regulated via GRα- and GRβ-mediated pathways with important implications in pathological conditions in which astrocytes are involved.

Astrocyte Clocks and Glucose Homeostasis

The endogenous timekeeping system evolved to anticipate the time of the day through the 24 hours cycle of the Earth's rotation. In mammals, the circadian clock governs rhythmic physiological and behavioral processes, including the daily oscillation in glucose metabolism, food intake, energy expenditure, and whole-body insulin sensitivity. The results from a series of studies have demonstrated that environmental or genetic alterations of the circadian cycle in humans and rodents are strongly associated with metabolic diseases such as obesity and type 2 diabetes. Emerging evidence suggests that astrocyte clocks have a crucial role in regulating molecular, physiological, and behavioral circadian rhythms such as glucose metabolism and insulin sensitivity. Given the concurrent high prevalence of type 2 diabetes and circadian disruption, understanding the mechanisms underlying glucose homeostasis regulation by the circadian clock and its dysregulation may improve glycemic control. In this review, we summarize the current knowledge on the tight interconnection between the timekeeping system, glucose homeostasis, and insulin sensitivity. We focus specifically on the involvement of astrocyte clocks, at the organism, cellular, and molecular levels, in the regulation of glucose metabolism.

Urea transporter and glutamine synthetase regulation and localization in gulf toadfish gill

The goal of the present study was to investigate the role of circulating cortisol and urea in the transcriptional regulation of branchial glutamine synthetase (GS), which incorporates NH(3) into glutamate to form glutamine, and the toadfish urea transporter, tUT, which is involved in urea excretion across the gill of the gulf toadfish. GS (of which there are two isoforms, LGS and GGS) and tUT mRNA expression and activity were measured in toadfish exposed to treatments that would induce variable stress responses. In addition, the role of circulating urea in tUT regulation was investigated by infusing toadfish with urea alone or in combination with intraperitoneal injection of RU486, a corticosteroid type II receptor antagonist. There was a 4.8-fold upregulation in the mRNA expression of the gill-specific GS isoform (GGS) in response to cortisol infusion and a similar upregulation in the more ubiquitous isoform (LGS). Furthermore, there was a significant 1.9-fold and 3.3-fold upregulation in the mRNA expression of the toadfish urea transporter, tUT, in response to stress through crowding or exogenous cortisol loading through infusion, respectively. In addition, tUT was found to have a urea-sensitive component to transcriptional regulation that was independent of circulating cortisol concentrations. However, the changes measured in mRNA expression of GGS, LGS and tUT did not correspond with changes in protein activity. To determine the cell type(s) involved in glutamine production and urea excretion, we attempted to localize GGS, LGS and tUT using in situ hybridization. This study is the first to show that GGS and tUT expression appear to occur in gill mitochondria-rich cells of toadfish, suggesting that these cells play a combined glutamine production and urea excretion role, which may have implications for predator avoidance.

Keratinocytes as depository of ammonium-inducible glutamine synthetase: age- and anatomy-dependent distribution in human and rat skin

In inner organs, glutamine contributes to proliferation, detoxification and establishment of a mechanical barrier, i.e., functions essential for skin, as well. However, the age-dependent and regional peculiarities of distribution of glutamine synthetase (GS), an enzyme responsible for generation of glutamine, and factors regulating its enzymatic activity in mammalian skin remain undisclosed. To explore this, GS localization was investigated using immunohistochemistry and double-labeling of young and adult human and rat skin sections as well as skin cells in culture. In human and rat skin GS was almost completely co-localized with astrocyte-specific proteins (e.g. GFAP). While GS staining was pronounced in all layers of the epidermis of young human skin, staining was reduced and more differentiated among different layers with age. In stratum basale and in stratum spinosum GS was co-localized with the adherens junction component beta-catenin. Inhibition of, glycogen synthase kinase 3beta in cultured keratinocytes and HaCaT cells, however, did not support a direct role of beta-catenin in regulation of GS. Enzymatic and reverse transcriptase polymerase chain reaction studies revealed an unusual mode of regulation of this enzyme in keratinocytes, i.e., GS activity, but not expression, was enhanced about 8-10 fold when the cells were exposed to ammonium ions. Prominent posttranscriptional up-regulation of GS activity in keratinocytes by ammonium ions in conjunction with widespread distribution of GS immunoreactivity throughout the epidermis allows considering the skin as a large reservoir of latent GS. Such a depository of glutamine-generating enzyme seems essential for continuous renewal of epidermal permeability barrier and during pathological processes accompanied by hyperammonemia.

The neurobiology of glia in the context of water and ion homeostasis

Astrocytes are highly complex cells that respond to a variety of external stimulations. One of the chief functions of astrocytes is to optimize the interstitial space for synaptic transmission by tight control of water and ionic homeostasis. Several lines of work have, over the past decade, expanded the role of astrocytes and it is now clear that astrocytes are active participants in the tri-partite synapse and modulate synaptic activity in hippocampus, cortex, and hypothalamus. Thus, the emerging concept of astrocytes includes both supportive functions as well as active modulation of neuronal output. Glutamate plays a central role in astrocytic-neuronal interactions. This excitatory amino acid is cleared from the neuronal synapses by astrocytes via glutamate transporters, and is converted into glutamine, which is released and in turn taken up by neurons. Furthermore, metabotropic glutamate receptor activation on astrocytes triggers via increases in cytosolic Ca(2+) a variety of responses. For example, calcium-dependent glutamate release from the astrocytes modulates the activity of both excitatory and inhibitory synapses. In vivo studies have identified the astrocytic end-foot processes enveloping the vessel walls as the center for astrocytic Ca(2+) signaling and it is possible that Ca(2+) signaling events in the cellular component of the blood-brain barrier are instrumental in modulation of local blood flow as well as substrate transport. The hormonal regulation of water and ionic homeostasis is achieved by the opposing effects of vasopressin and atrial natriuretic peptide on astroglial water and chloride uptake. In conjuncture, the brain appears to have a distinct astrocytic perivascular system, involving several potassium channels as well as aquaporin 4, a membrane water channel, which has been localized to astrocytic endfeet and mediate water fluxes within the brain. The multitask functions of astrocytes are essential for higher brain function. One of the major challenges for future studies is to link receptor-mediated signaling events in astrocytes to their roles in metabolism, ion, and water homeostasis.

Glutamine synthetase in tilapia gastrointestinal tract: zonation, cDNA and induction by cortisol

Glutamine synthetase, an enzyme generally associated with ammonia detoxication in the vertebrate brain and with hepatic nitrogen turnover in mammals, shows substantial activities in the gastrointestinal tract of teleostean fishes. Enzyme activity is highest in the central area of the stomach and reveals a distinct distribution pattern in stomach and along the intestine of tilapia (Oreochromis niloticus), rainbow trout (Oncorhynchus mykiss) and copper rockfish (Sebastes caurinus). In all three species, intestinal activity peaks in the distal region of the intestine. The brain contains the highest titre of the enzyme (46 U g(-1) in tilapia brain versus 15 U g(-1) in tilapia stomach), but because of the relative mass of the stomach, the largest glutamine synthetase pool in tilapia body appears to be localized in the stomach. Activities in white and red muscle are very modest at 0.1% of the brain. Independent of distribution, peak activities of glutamine synthetase in selected areas of tilapia stomach and intestine are significantly (two- to fourfold) increased after a 5-day treatment with an intraperitoneal cortisol deposit. Cortisol also increases glutamine synthetase activity in tilapia liver, white and red muscle, while activities in brain remain unaffected. We cloned and sequenced the predominant transcript of tilapia stomach glutamine synthetase (about 1.9 kb), encoding a 371-amino acid peptide. The open reading frame shows considerable identity with glutamine synthetase in toadfish (92% at peptide level, 87% at nucleotide level), but possesses a longer 3'-untranslated region than the toadfish. The tilapia glutamine synthetase mRNA contains a remnant of a putative mitochondrial leader sequence, but without a conserved second site for initiation of translation. We also find evidence for additional transcripts of glutamine synthetase in tilapia, suggesting multiple genes. Finally, we present evidence for similar abundance of glutamine synthetase transcripts in all regions of rockfish intestine. The physiological significance of the presence of glutamine synthetase in teleostean intestine is discussed.

Repeated prenatal corticosteroids reduce glial fibrillary acidic protein in the ovine central nervous system

INTRODUCTION

A single course of corticosteroid reduces intracranial hemorrhage in preterm infants. The mechanism of protection is unclear. Glial fibrillary acidic protein (GFAP), expressed by astrocytes, is regulated by glucosteroids and is an important component of the cells forming the blood brain barrier. We have evaluated the effect of prenatal corticosteroid upon ovine GFAP.

METHODS

Date-mated ewes were studied in two protocols and lambs delivered on day 125 or 145 (term = 150). In the maternal injection protocol (n = 36) ewes were administered saline, single or repeated injections of corticosteroid. In the fetal injection protocol (n = 48) direct ultrasound-guided fetal injections of saline, single or repeated corticosteroid were administered, and an additional control group did not receive fetal injections. Optic nerve GFAP immunohistochemistry was performed and quantified.

RESULTS

At 125 days, repeated, but not single, administration of corticosteroid, by either maternal or fetal route, was associated with a significant reduction in GFAP (both p < 0.002); by 145 days, the deficit had recovered (both p > 0.05). The process of performing repeated fetal injections had an independent effect upon GFAP at 145 days (p = 0.002).

CONCLUSION

Repeated administration of corticosteroid results in a reduction in GFAP in the developing ovine optic nerve, with recovery demonstrated by 145 days.

Reversed effects of RU486 and anisomycin on memory retention of light exposure or corticosterone facilitation in the dark-incubated chicks

Memory formation for a weak passive avoidance task in the dark-incubated chicks is facilitated by light exposure or corticosterone administration at optimally pre-hatch time points. To explore the potential mechanisms underlying activation of brain memory function development by light or corticosterone exposure during late embryo, steroid receptor antagonist RU486, or protein synthetic inhibitor anisomycin, was administered intraembryonically to the embryos of either only 24-h light-exposure or complete dark-hatched on embryonic day 20 (E20). The results showed that RU486 and anisomycin significantly retarded the facilitated retention both by light and corticosterone exposure in the dark-incubated chicks. They also suggest that the act of corticosterone or light exposure on the development of brain memory function is mediated by the effect of steroid receptor, or afterward on related protein syntheses that is involved in memory formation of post-hatched performance of day-old chicks.

Cellular signaling by neural cell adhesion molecules of the immunoglobulin superfamily

Neural cell adhesion molecules (CAMs) of the immunoglobulin superfamily nucleate and maintain groups of cells at key sites during early development and in the adult. In addition to their adhesive properties, binding of CAMs can affect intracellular signaling. Their ability to influence developmental events, including cell migration, proliferation, and differentiation can therefore result both from their adhesive as well as their signaling properties. This review focuses on the two CAMs for which the most information is known, the neural CAM, N-CAM, and L1. N-CAM was the first CAM to be characterized and, therefore, has been studied extensively. The binding of N-CAM to cells leads to a number of signaling events, some of which result in changes in gene expression. Interest in L1 derives from the fact that mutations in its gene lead to human genetic diseases including mental retardation. Much is known about modifications of the L1 cytoplasmic domain and its interaction with cytoskeletal molecules. The study of CAM signaling mechanisms has been assay-dependent rather than molecule-dependent, with particular emphasis on assays of neurite outgrowth and gene expression, an emphasis that is maintained throughout the review. The signals generated following CAM binding that lead to alterations in cell morphology and gene expression have been linked directly in only a few cases. We also review information on other CAMs, giving special consideration to those that are anchored in the membrane by a phospholipid anchor. These proteins, including a form of N-CAM, are presumed to be localized in lipid rafts, membrane substructures that include distinctive subsets of cytoplasmic signaling molecules such as members of the src-family of nonreceptor protein tyrosine kinases. In the end, these studies may reveal that what CAMs do after they bind cells together may have as profound consequences for the cells as the adhesive interactions themselves. This area will therefore remain a rich ground for future studies.

Glucocorticoids up-regulate the expression of glial fibrillary acidic protein in the rat suprachiasmatic nucleus

Immunoreactivity against glial fibrillary acidic protein (GFAP) was used as a dynamic index in adrenalectomized rats subjected or not to corticosterone replacement to investigate whether glucocorticoids may interact with astrocytes in the suprachiasmatic nucleus (SCN), the master component of the central circadian clock. GFAP staining in the SCN was significantly higher in rats having received implants that restored physiological plasma levels of corticosterone within diurnal or nocturnal limits than in non-normalized rats. The effects of corticosterone were similar in the parvocellular portion of the paraventricular nucleus but were opposite in the hippocampus, another major site of negative feed-back regulation of the hypothalamic-pituitary-adrenal axis, where a decreased GFAP staining was observed in discrete regions of the dentate gyrus. This indicates that glucocorticoids may positively or negatively regulate GFAP, depending on the target brain structure. In the SCN, that contains only few if any glucocorticoid receptors, indirect mechanisms that may involve serotoninergic neurons are probably responsible for the effects of corticosterone level. It is proposed that the corticosterone-induced increase in GFAP staining in that nucleus accounts for dynamic changes in neurone-astrocyte interactions that might occur in relation with natural fluctuations of glucocorticoids over the 24 h period.

Glucocorticoid control of glial gene expression

The glucocorticoid signaling pathway is responsive to a considerable number of internal and external signals and can therefore establish diverse patterns of gene expression. A glial-specific pattern, for example, is shown by the glucocorticoid-inducible gene glutamine synthetase. The enzyme is expressed at a particularly high level in glial cells, where it catalyzes the recycling of the neurotransmitter glutamate, and at a low level in most other cells, for housekeeping duties. Glial specificity of glutamine synthetase induction is achieved by the use of positive and negative regulatory elements, a glucocorticoid response element and a neural restrictive silencer element. Though not glial specific by themselves, these elements may establish a glial-specific pattern of expression through their mutual activity and their combined effect. The inductive activity of glucocorticoids is markedly repressed by the c-Jun protein, which is expressed at relatively high levels in proliferating glial cells. The signaling pathway of c-Jun is activated by the disruption of glia-neuron cell contacts, by transformation with v-src, and in proliferating retinal cells of early embryonic ages. The c-Jun protein inhibits the transcriptional activity of the glucocorticoid receptor and thus represses glutamine synthetase expression. This repressive mechanism might also affect the ability of glial cells to cope with glutamate neurotoxicity in injured tissues.

Regulation of the spatiotemporal pattern of expression of the glutamine synthetase gene

Glutamine synthetase, the enzyme that catalyzes the ATP-dependent conversion of glutamate and ammonia into glutamine, is expressed in a tissue-specific and developmentally controlled manner. The first part of this review focuses on its spatiotemporal pattern of expression, the factors that regulate its levels under (patho)physiological conditions, and its role in glutamine, glutamate, and ammonia metabolism in mammals. Glutamine synthetase protein stability is more than 10-fold reduced by its product glutamine and by covalent modifications. During late fetal development, translational efficiency increases more than 10-fold. Glutamine synthetase mRNA stability is negatively affected by cAMP, whereas glucocorticoids, growth hormone, insulin (all positive), and cAMP (negative) regulate its rate of transcription. The signal transduction pathways by which these factors may regulate the expression of glutamine synthetase are briefly discussed. The second part of the review focuses on the evolution, structure, and transcriptional regulation of the glutamine synthetase gene in rat and chicken. Two enhancers (at -6.5 and -2.5 kb) were identified in the upstream region and two enhancers (between +156 and +857 bp) in the first intron of the rat glutamine synthetase gene. In addition, sequence analysis suggests a regulatory role for regions in the 3' untranslated region of the gene. The immediate-upstream region of the chicken glutamine synthetase gene is responsible for its cell-specific expression, whereas the glucocorticoid-induced developmental appearance in the neural retina is governed by its far-upstream region.

Regulation of gene expression by corticoid hormones in the brain and spinal cord

Glucocorticoids (GC) and mineralocorticoids (MC) have profound regulatory effects upon the central nervous system (CNS). Hormonal regulation affects several molecules essential to CNS function. First, evidences are presented that mRNA expression of the alpha3 and beta1-subunits of the Na,K-ATPase are increased by GC and physiological doses of MC in a region-dependent manner. Instead, high MC doses reduce the beta1 isoform and enzyme activity in amygdaloid and hypothalamic nuclei, an effect which may be related to MC control of salt appetite. The alpha3-subunit mRNA of the Na,K-ATPase is also stimulated by GC in motoneurons of the injured spinal cord, suggesting a role for the enzyme in GC neuroprotection. Second, we provide evidences for hormonal effects on the expression of mRNA for the neuropeptide arginine vasopressin (AVP). Our data show that GC inhibition of AVP mRNA levels in the paraventricular nucleus is sex-hormone dependent. This sexual dimorphism may explain sex differences in the hypothalamic-pituitary-adrenal axis function between female and male rats. Third, steroid effects on the astrocyte marker glial fibrillary acidic protein (GFAP) points to a complex regulatory mechanism. In an animal model of neurodegeneration (the Wobbler mouse) showing pronounced astrogliosis of the spinal cord, in vivo GC treatment down-regulated GFAP immunoreactivity, whereas the membrane-active steroid antioxidant U-74389F up-regulated this protein. It is likely that variations in GFAP protein expression affect spinal cord neurodegeneration in Wobbler mice. Fourth, an interaction between neurotrophins and GC is shown in the injured rat spinal cord. In this model, intensive GC treatment increases immunoreactive low affinity nerve growth factor (NGF) receptor in motoneuron processes. Because GC also increases immunoreactive NGF, this mechanism would support trophism and regeneration in damaged tissues. In conclusion, evidences show that some molecules regulated by adrenal steroids in neurons and glial cells are not only involved in physiological control, but additionally, may play important roles in neuropathology.

Glucocorticoid receptor pathways are involved in the inhibition of astrocyte proliferation

In earlier studies, the neural cell adhesion molecule, N-CAM, was found to inhibit the proliferation of rat astrocytes both in vitro and in vivo. To identify the gene targets involved, we used subtractive hybridization to examine changes in gene expression that occur after astrocytes are exposed to N-CAM in vitro. While the mRNA levels for N-CAM decreased after such treatment, the levels of mRNAs for glutamine synthetase and calreticulin increased. Since glutamine synthetase and calreticulin are known to be involved in glucocorticoid receptor pathways, we tested a number of steroids for their effects on astrocyte proliferation. Dexamethasone, corticosterone, and aldosterone were all found to inhibit rat cortical astrocyte proliferation in culture in a dose-dependent manner. RU-486, a potent glucocorticoid antagonist, reversed the inhibitory effects of dexamethasone. These observations prompted the hypothesis that the inhibition of proliferation by N-CAM might be mediated through the glucocorticoid receptor pathway. Consistent with this hypothesis, the inhibition of astrocyte proliferation by N-CAM was reversed in part by a number of glucocorticoid antagonists, including RU-486, dehydroepiandrosterone, and progesterone. In transfection experiments with cultured astrocytes, N-CAM treatment increased the expression of a luciferase reporter gene under the control of a minimal promoter linked to a glucocorticoid response element. The enhanced activity of this construct stimulated by N-CAM was abolished in the presence of RU-486. The combined data suggest that astrocyte proliferation is in part regulated by alterations in glucocorticoid receptor pathways.

Glucocorticoid receptors and actions in the spinal cord of the Wobbler mouse, a model for neurodegenerative diseases

We have studied glucocorticoid receptors (GR) and actions in the spinal cord of the Wobbler mouse, a model for amyotrophic lateral sclerosis and infantile spinal muscular atrophy. Basal and stress levels of circulating corticosterone (CORT) were increased in Wobbler mice. Single point binding assays showed that cytosolic type II GR in the spinal cord of Wobbler mice of both sexes were slightly reduced compared with normal littermates. Saturation analysis further demonstrated a non-significant reduction in Bmax with increased Kd. In the hippocampus, however, we found down-regulation of GR, a probable response to increased CORT levels. We also found that the basal activity of ornithine decarboxylase (ODC), a rate-limiting enzyme of polyamine biosynthesis, was higher in Wobbler mice than in control animals. Both groups showed a two-fold stimulation of ODC activity after treatment with dexamethasone (DEX). Additionally, Wobbler mice presented with an intense proliferation of astrocytes immunoreactive (ir) for glial fibrillary acidic protein (GFAP) in grey and white matter of the spinal cord. The enhanced GFAP-ir was attenuated after four days of treatment with a corticosterone (CORT) pellet implant, producing a pharmacological increase in peripheral circulating CORT. Taking into consideration the content of GR and the changes in ODC activity and GFAP-ir brought about by glucocorticoids, we suggest that Wobbler mice are hormone responsive. Further elucidation of glucocorticoid effects in this model may be relevant for understanding the possible use of hormones in human neurodegenerative diseases.

Monoamine oxidase B expression is selectively regulated by dexamethasone in cultured rat astrocytes

The influence of dexamethasone on monoamine oxidase (MAO) A and B expression and activity was investigated in primary cultures of rat type 1 astrocytes cultured under serum free, defined conditions. Dexamethasone treatment resulted in a dose- and time-dependent induction of MAO-B, but not of MAO-A, activity. The selective MAO-B increase was substantially reduced by the antagonist RU 486, thus suggesting a glucocorticoid receptor-mediated action of the hormone. Kinetic analysis showed an increase in Vmax of MAO-B with no change in apparent K(m). The dexamethasone-induced selective rise in MAO-B activity appeared to be due to enhanced enzyme synthesis, since MAO-B mRNA was markedly increased by dexamethasone treatment and the recovery of MAO-B activity after its irreversible inhibition by deprenyl was more pronounced in the presence than in the absence of the hormone. Furthermore, the dexamethasone effect was abolished by the protein synthesis inhibitors actinomycin D or cycloheximide. The present study demonstrates that dexamethasone is able to selectively induce MAO-B in type 1 astrocytes and leads to speculation of a possible role for glucocorticoids in the increase in brain MAO-B associated with neurodegenerative disorders, such as Parkinson's and Alzheimer's diseases.

The 21-aminosteroid U-74389F increases the number of glial fibrillary acidic protein-expressing astrocytes in the spinal cord of control and Wobbler mice

1. Wobbler mice suffer an autosomal recessive mutation producing severe motoneuron degeneration and dense astrogliosis, with increased levels of glial fibrillary acidic protein (GFAP) in the spinal cord and brain stem. They have been considered animal models of amyotrophic lateral sclerosis and infantile spinal muscular atrophy. 2. Using Wobbler mice and normal littermates, we investigated the effects of the membrane-active steroid Lazaroid U-74389F on the number of GFAP-expressing astrocytes and glucocorticoid receptors (GR). Lazaroids are inhibitors of oxygen radical-induced lipid peroxidation, and proved beneficial in cases of CNS injury and ischemia. 3. Four days after pellet implantation of U-74389F into Wobbler mice, hyperplasia and hypertophy of GFAP-expressing astrocytes were apparent in the spinal cord ventral and dorsal horn, areas showing already intense astrogliosis in untreated Wobbler mice. In control mice, U-74389F also produced astrocyte hyperplasia and hypertophy in the dorsal horn and hyperplasia in the ventral-lateral funiculi of the cord. 4. Given in vivo U-74389F did not change GR in spinal cord of Wobbler or control mice, in line with the concept that it is active in membranes but does not bind to GR. Besides, U-74390F did not compete for [3H]dexamethasone binding when added in vitro. 5. The results suggest that stimulation of proliferation and size of GFAP-expressing astrocytes by U-74389F may be a novel mechanism of action of this compound. The Wobbler mouse may be a valuable animal model for further pharmacological testing of glucocorticoid and nonglucocorticoid steroids in neurodegenerative diseases.