Membrane receptor-mediated electrophysiological effects of glucocorticoid on mammalian neurons

Glucocorticoids, metabolism and brain activity

The review integrates different experimental approaches including biochemistry, c-Fos expression, microdialysis (glutamate, GABA, noradrenaline and serotonin), electrophysiology and fMRI to better understand the effect of elevated level of glucocorticoids on the brain activity and metabolism. The available data indicate that glucocorticoids alter the dynamics of neuronal activity leading to context-specific changes including both excitation and inhibition and these effects are expected to support the task-related responses. Glucocorticoids also lead to diversification of available sources of energy due to elevated levels of glucose, lactate, pyruvate, mannose and hydroxybutyrate (ketone bodies), which can be used to fuel brain, and facilitate storage and utilization of brain carbohydrate reserves formed by glycogen. However, the mismatch between carbohydrate supply and utilization that is most likely to occur in situations not requiring energy-consuming activities lead to metabolic stress due to elevated brain levels of glucose. Excessive doses of glucocorticoids also impair the production of energy (ATP) and mitochondrial oxidation. Therefore, glucocorticoids have both adaptive and maladaptive effects consistently with the concept of allostatic load and overload.

Nongenomic glucocorticoid effects and their mechanisms of action in vertebrates

Glucocorticoids (GC) act on multiple organ systems to regulate a variety of physiological processes in vertebrates. Due to their immunosuppressive and anti-inflammatory actions, glucocorticoids are an attractive target for pharmaceutical development. Accordingly, they are one of the most widely prescribed classes of therapeutics. Through the classical mechanism of steroid action, glucocorticoids are thought to mainly affect gene transcription, both in a stimulatory and suppressive fashion, regulating de novo protein synthesis that subsequently leads to the physiological response. However, over the past three decades multiple lines of evidence demonstrate that glucocorticoids may work through rapid, nonclassical mechanisms that do not require alterations in gene transcription or translation. This review assimilates evidence across the vertebrate taxa on the diversity of nongenomic actions of glucocorticoids and the membrane-associated cellular mechanisms that may underlie rapid glucocorticoid responses to include potential binding sites characterized to date.

Novel zebrafish behavioral assay to identify modifiers of the rapid, nongenomic stress response

When vertebrates face acute stressors, their bodies rapidly undergo a repertoire of physiological and behavioral adaptations, which is termed the stress response. Rapid changes in heart rate and blood glucose levels occur via the interaction of glucocorticoids and their cognate receptors following hypothalamic-pituitary-adrenal axis activation. These physiological changes are observed within minutes of encountering a stressor and the rapid time domain rules out genomic responses that require gene expression changes. Although behavioral changes corresponding to physiological changes are commonly observed, it is not clearly understood to what extent hypothalamic-pituitary-adrenal axis activation dictates adaptive behavior. We hypothesized that rapid locomotor response to acute stressors in zebrafish requires hypothalamic-pituitary-interrenal (HPI) axis activation. In teleost fish, interrenal cells are functionally homologous to the adrenocortical layer. We derived eight frameshift mutants in genes involved in HPI axis function: two mutants in exon 2 of mc2r (adrenocorticotropic hormone receptor), five in exon 2 or 5 of nr3c1 (glucocorticoid receptor [GR]) and two in exon 2 of nr3c2 (mineralocorticoid receptor [MR]). Exposing larval zebrafish to mild environmental stressors, acute changes in salinity or light illumination, results in a rapid locomotor response. We show that this locomotor response requires a functioning HPI axis via the action of mc2r and the canonical GR encoded by nr3c1 gene, but not MR (nr3c2). Our rapid behavioral assay paradigm based on HPI axis biology can be used to screen for genetic and environmental modifiers of the hypothalamic-pituitary-adrenal axis and to investigate the effects of corticosteroids and their cognate receptor interactions on behavior.

Cellular Mechanisms of Cortisol-Induced Changes in Mauthner-Cell Excitability in the Startle Circuit of Goldfish

Predator pressure and olfactory cues (alarm substance) have been shown to modulate Mauthner cell (M-cell) initiated startle escape responses (C-starts) in teleost fish. The regulation of such adaptive responses to potential threats is thought to involve the release of steroid hormones such as cortisol. However, the mechanism by which cortisol may regulate M-cell excitability is not known. Here, we used intrasomatic, in vivo recordings to elucidate the acute effects of cortisol on M-cell membrane properties and sound evoked post-synaptic potentials (PSPs). Cortisol tonically decreased threshold current in the M-cell within 10 min before trending towards baseline excitability over an hour later, which may indicate the involvement of non-genomic mechanisms. Consistently, current ramp injection experiments showed that cortisol increased M-cell input resistance in the depolarizing membrane, i.e., by a voltage-dependent postsynaptic mechanism. Cortisol also increases the magnitude of sound-evoked M-cell PSPs by reducing the efficacy of local feedforward inhibition (FFI). Interestingly, another pre-synaptic inhibitory network mediating prepulse inhibition (PPI) remained unaffected. Together, our results suggest that cortisol rapidly increases M-cell excitability via a post-synaptic effector mechanism, likely a chloride conductance, which, in combination with its dampening effect on FFI, will modulate information processing to reach threshold. Given the central role of the M-cell in initiating startle, these results are consistent with a role of cortisol in mediating the expression of a vital behavior.

Chronic glucocorticoid exposure activates BK-NLRP1 signal involving in hippocampal neuron damage

BACKGROUND

Neuroinflammation mediated by NLRP1 (nucleotide-binding oligomerization domain (NOD)-like receptor protein 1) inflammasome plays an important role in many neurological diseases such as Parkinson's disease (PD) and Alzheimer's disease (AD). Our previous studies showed that chronic glucocorticoid (GC) exposure increased brain inflammation via NLRP1 inflammasome and induce neurodegeneration. However, little is known about the mechanism of chronic GC exposure on NLRP1 inflammasome activation in hippocampal neurons.

METHODS

Hippocampal neurons damage was assessed by LDH kit and Hoechst 33258 staining. The expression of microtubule-associated protein 2 (MAP2), inflammasome complex protein (NLRP1, ASC and caspase-1), inflammatory cytokines (IL-1β), and large-conductance Ca²⁺ and voltage-activated K⁺ channel (BK channels) protein was detected by Western blot. The inflammatory cytokines (IL-1β and IL-18) were examined by ELISA kit. The mRNA levels of NLRP1, IL-1β, and BK were detected by real-time PCR. BK channel currents were recorded by whole-cell patch-clamp technology. Measurement of [K⁺]_i was performed by ion-selective electrode (ISE) technology.

RESULTS

Chronic dexamethasone (DEX) treatment significantly increased LDH release and neuronal apoptosis and decreased expression of MAP2. The mechanistic studies revealed that chronic DEX exposure significantly increased the expression of NLRP1, ASC, caspase-1, IL-1β, L-18, and BK protein and NLRP1, IL-1β and BK mRNA levels in hippocampal neurons. Further studies showed that DEX exposure results in the increase of BK channel currents, with the subsequent K⁺ efflux and a low concentration of intracellular K⁺, which involved in activation of NLRP1 inflammasome. Moreover, these effects of chronic DEX exposure could be blocked by specific BK channel inhibitor iberiotoxin (IbTx).

CONCLUSION

Our findings suggest that chronic GC exposure may increase neuroinflammation via activation of BK-NLRP1 signal pathway and promote hippocampal neurons damage, which may be involved in the development and progression of AD.

Ultrasound-Guided Intra-articular Injection of the Radio-ulnar and Radio-humeral Joints and Ultrasound-Guided Dry Needling of the Affected Limb Muscles to Relieve Fixed Pronation Deformity and Myofascial Issues around the Shoulder, in a Case of Complex Regional Pain Syndrome Type 1

BACKGROUND

Complex regional pain syndrome (CRPS) occurs due to different pathophysiological mechanisms. Presently there is no description of definitive treatment that can resolve the especially recalcitrant motor issues of disability in CRPS type 1 (CRPS-1).

CASE REPORT

We have herein described the successful management of motor disability with a multimodal approach in a patient with CRPS-1 that occurred as a result of a fracture sustained in the lower end of the radius. Sensory/sudomotor/vasomotor symptoms were relieved completely by medications and stellate ganglion block in 2 weeks. Ultrasound-guided dry needling secured near-complete improvement of shoulder and hand movements in 45 days. Ultrasound guided intra-articular (radio-ulnar and radio-humeral joint) injections with steroid reduced residual pain and improved forearm movements by 50% initially. The patient continued to receive regular sessions of dry needling, physiotherapy, and cognitive behavioral therapy. By the end of 1 year, the functions of the limb improved remarkably, as did the functional outcome scores.

CONCLUSION

In this patient with CRPS-1, intra-articular injections with steroid reduced nociception in the affected local structures and sensitization in the nervous system; dry needling resolved the myofascial issues; sustained physiotherapy maintained the motor recovery; and behavioral therapy techniques addressed the cognitive and life stress issues. It was concluded that the presenting symptoms in this case were a consequence of interactions between humoral, nervous, and myofascial systems.

Further evidence for a membrane receptor that binds glucocorticoids in the rodent hypothalamus

In parallel with their well-characterized delayed genomic effects, steroid hormones exhibit rapid, non-genomic effects at molecular, cellular and behavioral levels. We have proposed a model of rapid, non-genomic glucocorticoid inhibition of hypothalamic neuroendocrine cells through a putative membrane-associated glucocorticoid receptor (GR). Here we tested for plasma membrane GR immunoreactivity and binding in the hypothalamic supraoptic and paraventricular nuclei. Selective cross-linking of membrane proteins with membrane-impermeant BS³ and subsequent Western blot analysis with a monoclonal GR antibody revealed a reduction in the intensities of a ∼98kDa immunoreactive band and a ∼64kDa band in the rat paraventricular and supraoptic nuclei, and of a 64kDa band in hippocampal tissue, which suggested that these proteins are associated with the membrane. Saturation binding of [³H]-corticosterone and [³H]-dexamethasone in rat and mouse hypothalamic tissue revealed a K_d 4-24-fold lower and a B_max 4-7-fold lower for the membrane-associated GR compared to the intracellular GR, suggesting a lower affinity and abundance of the glucocorticoid binding sites in the membrane than in the cytosol. Together, these findings suggest the presence of a low-affinity, low-abundance membrane-associated GR in the hypothalamus that shares homology with the intracellular GR, and are consistent with physiological evidence of rapid, non-genomic glucocorticoid actions in hypothalamic neuroendocrine cells that are GR dependent.

A scoping review of perineural steroids for the treatment of chronic postoperative inguinal pain

PURPOSE

To review the literature on the efficacy and safety of perineural steroid injections around the ilioinguinal, iliohypogastric, and genitofemoral nerves for chronic postoperative inguinal pain (CPIP).

METHODS

A scoping review was performed to find all relevant case reports, case series, prospective or retrospective cohort studies, case-control studies, and randomized controlled trials (RCTs) where a steroid was used for perineural procedures around ilioinguinal, iliohypogastric, and/or genitofemoral nerves for CPIP. Databases searched included Ovid MEDLINE, EMBASE, CINHAL, Cochrane CENTRAL, and Google Scholar.

RESULTS

A total of five publications were found-three studies were prospective case series, one a retrospective cohort study, and one a RCT. The most common steroids used were methylprednisolone and triamcinolone. The average methylprednisolone-equivalent dose used per procedure was 46 mg (SD 21.9). Procedural guidance included anatomic landmarks (three studies), nerve stimulation and ultrasound (one study), and computed tomography guidance (one study). Four studies reported analgesic benefit in 55-75 % of included patients, with one study documenting an effect up to 50 months later after steroid perineural injections. The RCT demonstrated no benefit of adding steroid to a local anesthetic in the perioperative setting but it did not enroll patients with existing neuropathic pain. No adverse outcomes of perineural steroids were documented within reviewed studies.

CONCLUSIONS

The paucity of data, heterogeneity and lack of appropriate control groups in the available literature precludes firm conclusions on the efficacy and safety of perineural steroids for CPIP. Future adequately powered, high-quality, placebo-controlled studies are needed.

The effect of pre-operative methylprednisolone on the incidence of delayed graft function in renal transplantation

Introduction:

This study explores the effect of different corticosteroid administration timings on the incidence of slow/delayed graft function.

Methods:

One hundred and twelve kidney transplants from January 2011 to March 2014 were retrospectively analysed. Thirty-six cases were excluded because they were donor-specific antibody positive ( n=16), received thymoglobulin/plasma exchange ( n=11), were ABO-incompatible ( n=6) or suffered graft loss from vascular thrombosis within the first week post-transplant ( n=3). The study period straddled three eras of corticosteroid administration, from intra-operative intravenous (IV) hydrocortisone (Era 1; n=26), to intra-operative IV methylprednisolone (Era 2; n=38) and pre-operative IV methylprednisolone (Era 3; n=12). The primary endpoint was the incidence of slow/delayed graft function. Secondary outcomes included estimated glomerular filtration rate at discharge and 120 and 365 days, rejection (acute and one-year), wound complications, post-transplant diabetes, increase in low-density lipoprotein or body mass index, and cytomegalovirus or BK viraemia within one year.

Results:

On univariate analysis, pre-operative methylprednisolone was associated with lower incidence of slow/delayed graft function (17%, 55%, 58% in Eras 3, 2, 1 respectively; p=0.041), superior estimated glomerular filtration rate at discharge (median 56, 37 and 43 ml/min for Eras 3, 2, 1 respectively; p=0.033) and at 120 days (median 60, 52, and 46 ml/min for Eras 3, 2, 1 respectively; p=0.017). On multivariate analysis, pre-operative IV methylprednisolone ( vs. Eras 1 and 2 combined; odds ratio 4.79 (90% confidence interval 1.16–19.80); p=0.07) and living donor type ( vs. deceased; odds ratio 5.56 (90% confidence interval 2.25–13.77); p=0.002) were associated with lower incidence of slow/delayed graft function.

Conclusion:

Pre-operative methylprednisolone was associated with reduced slow/delayed graft function and improved early estimated glomerular filtration.

Rapid Nongenomic Glucocorticoid Actions in Male Mouse Hypothalamic Neuroendocrine Cells Are Dependent on the Nuclear Glucocorticoid Receptor

Corticosteroids act classically via cognate nuclear receptors to regulate gene transcription; however, increasing evidence supports rapid, nontranscriptional corticosteroid actions via activation of membrane receptors. Using whole-cell patch clamp recordings in hypothalamic slices from male mouse genetic models, we tested for nongenomic glucocorticoid actions at glutamate and gamma aminobutyric acid (GABA) synapses in hypothalamic neuroendocrine cells, and for their dependence on the nuclear glucocorticoid receptor (GR). In enhanced green fluorescent protein-expressing CRH neurons of the paraventricular nucleus (PVN) and in magnocellular neurons of the PVN and supraoptic nucleus (SON), dexamethasone activated postsynaptic membrane-associated receptors and G protein signaling to elicit a rapid suppression of excitatory postsynaptic inputs, which was blocked by genetic deletion of type I cannabinoid receptors and a type I cannabinoid receptor antagonist. In magnocellular neurons, dexamethasone also elicited a rapid nitric oxide-dependent increase in inhibitory postsynaptic inputs. These data indicate a rapid, synapse-specific glucocorticoid-induced retrograde endocannabinoid signaling at glutamate synapses and nitric oxide signaling at GABA synapses. Unexpectedly, the rapid glucocorticoid effects on both excitatory and inhibitory synaptic transmission were lost with conditional deletion of GR in the PVN and SON in slices from a single minded-1-cre-directed conditional GR knockout mouse. Thus, the nongenomic glucocorticoid actions at glutamate and GABA synapses on PVN and SON neuroendocrine cells are dependent on the nuclear GR. The nuclear GR, therefore, is responsible for transducing the rapid steroid response at the membrane, or is either a critical component in the signaling cascade or regulates a critical component of the signaling cascade of a distinct membrane GR.

Membrane glucocorticoid receptors are localised in the extracellular matrix and signal through the MAPK pathway in mammalian skeletal muscle fibres

KEY POINTS

Many studies have previously suggested the existence of stress hormone receptors on the cell membrane of many cell types, including skeletal muscle fibres; however, the exact localisation of these receptors and how they signal to the rest of the cell is poorly understood. In this study, we investigated the localisation and the mechanism(s) underlying the physiological functions of these receptors in mouse skeletal muscle cells. We found that the receptors were present throughout muscle development and that, in adult muscle fibres, they were localised in the extracellular matrix, satellite cells (muscle stem cells) and close to mitochondria. We also found that they signalled to the rest of the cell by activating enzymes called mitogen-activated protein kinases. From these results we suggest that, at physiological concentrations, stress hormones may be important in skeletal muscle differentiation, repair and regeneration.

ABSTRACT

A number of studies have previously proposed the existence of glucocorticoid receptors on the plasma membrane of many cell types, including skeletal muscle fibres. However, their exact localisation and the cellular signalling pathway(s) they utilise to communicate with the rest of the cell are still poorly understood. In this study, we investigated the localisation and the mechanism(s) underlying the non-genomic physiological functions of these receptors in mouse skeletal muscle cells. The results show that the receptors were localised in the cytoplasm in myoblasts, in the nucleus in myotubes, in the extracellular matrix, in satellite cells and in the proximity of mitochondria in adult muscle fibres. Also, they bound laminin in a glucocorticoid-dependent manner. Treating small skeletal muscle fibre bundles with the synthetic glucocorticoid beclomethasone dipropionate increased the phosphorylation (= activation) of extracellular signal-regulated kinases 1 and 2, c-Jun N-terminal kinase and p38 mitogen-activated protein kinase. This occurred within 5 min and depended on the fibre type and the duration of the treatment. It was also abolished by the glucocorticoid receptor inhibitor, mifepristone, and a monoclonal antibody against the receptor. From these results we conclude that the non-genomic/non-canonical physiological functions of glucocorticoids, in adult skeletal muscle fibres, are mediated by a glucocorticoid receptor localised in the extracellular matrix, in satellite cells and close to mitochondria, and involve activation of the mitogen-activated protein kinase pathway.

G protein-coupled receptors: extranuclear mediators for the non-genomic actions of steroids

Steroids hormones possess two distinct actions, a delayed genomic effect and a rapid non-genomic effect. Rapid steroid-triggered signaling is mediated by specific receptors localized most often to the plasma membrane. The nature of these receptors is of great interest and accumulated data suggest that G protein-coupled receptors (GPCRs) are appealing candidates. Increasing evidence regarding the interaction between steroids and specific membrane proteins, as well as the involvement of G protein and corresponding downstream signaling, have led to identification of physiologically relevant GPCRs as steroid extranuclear receptors. Examples include G protein-coupled receptor 30 (GPR30) for estrogen, membrane progestin receptor for progesterone, G protein-coupled receptor family C group 6 member A (GPRC6A) and zinc transporter member 9 (ZIP9) for androgen, and trace amine associated receptor 1 (TAAR1) for thyroid hormone. These receptor-mediated biological effects have been extended to reproductive development, cardiovascular function, neuroendocrinology and cancer pathophysiology. However, although great progress have been achieved, there are still important questions that need to be answered, including the identities of GPCRs responsible for the remaining steroids (e.g., glucocorticoid), the structural basis of steroids and GPCRs' interaction and the integration of extranuclear and nuclear signaling to the final physiological function. Here, we reviewed the several significant developments in this field and highlighted a hypothesis that attempts to explain the general interaction between steroids and GPCRs.

A membrane glucocorticoid receptor mediates the rapid/non-genomic actions of glucocorticoids in mammalian skeletal muscle fibres

Glucocorticoids (GCs) are steroid hormones released from the adrenal gland in response to stress. They are also some of the most potent anti-inflammatory and immunosuppressive drugs currently in clinical use. They exert most of their physiological and pharmacological actions through the classical/genomic pathway. However, they also have rapid/non-genomic actions whose physiological and pharmacological functions are still poorly understood. Therefore, the primary aim of this study was to investigate the rapid/non-genomic effects of two widely prescribed glucocorticoids, beclomethasone dipropionate (BDP) and prednisolone acetate (PDNA), on force production in isolated, intact, mouse skeletal muscle fibre bundles. The results show that the effects of both GCs on maximum isometric force (Po) were fibre-type dependent. Thus, they increased Po in the slow-twitch fibre bundles without significantly affecting that of the fast-twitch fibre bundles. The increase in Po occurred within 10 min and was insensitive to the transcriptional inhibitor actinomycin D. Also, it was maximal at ∼250 nM and was blocked by the glucocorticoid receptor (GCR) inhibitor RU486 and a monoclonal anti-GCR, suggesting that it was mediated by a membrane (m) GCR. Both muscle fibre types expressed a cytosolic GCR. However, a mGCR was present only in the slow-twitch fibres. The receptor was more abundant in oxidative than in glycolytic fibres and was confined mainly to the periphery of the fibres where it co-localised with laminin. From these findings we conclude that the rapid/non-genomic actions of GCs are mediated by a mGCR and that they are physiologically/therapeutically beneficial, especially in slow-twitch muscle fibres.

Expression and dexamethasone-induced nuclear translocation of glucocorticoid and mineralocorticoid receptors in guinea pig cochlear cells

Glucocorticoids (GC) are powerful anti-inflammatory agents frequently used to protect the auditory organ against damage associated with a variety of conditions, including noise exposure and ototoxic drugs as well as bacterial and viral infections. In addition to glucocorticoid receptors (GC-R), natural and synthetic GC are known to bind mineralocorticoid receptors (MC-R) with great affinity. We used light and laser scanning confocal microscopy to investigate the expression of GC-R and MC-R in different cell populations of the guinea pig cochlea, and their translocation to different cell compartments after treatment with the synthetic GC dexamethasone. We found expression of both types of receptors in the cytoplasm and nucleus of sensory inner and outer hair cells as well as pillar, Hensen and Deiters cells in the organ of Corti, inner and outer sulcus cells, spiral ganglion neurons and several types of spiral ligament and spiral limbus cells; stria vascularis cells expressed mostly MC-R whereas fibrocytes type IV were positive for GC-R only. GC-R and MC-R were also localized at or near the plasma membrane of pillar cells and outer hair cells, whereas GC-R were found at or near the plasma membrane of Hensen cells only. We investigated the relative levels of receptor expression in the cytoplasm and the nucleus of Hensen cells treated with dexamethasone, and found they varied in a way suggestive of dose-induced translocation. These results suggest that the oto-protective effects of GC could be associated with the concerted activation of genomic and non-genomic, GC-R and MC-R mediated signaling pathways in different regions of the cochlea.

Inhaled corticosteroids inhibit substance P receptor expression in asthmatic rat airway smooth muscle cells

Background

Neurokinins (NKs) participate in asthmatic airway inflammation, but the effects of NKs on airway smooth muscle cells (ASMCs) and those of corticosteroids on NKs are unknown.

Methods

To investigate the effect of budesonide on substance P (NK-1) receptor (NK-1R) expression in the lung and ASMCs, 45 Wistar rats were randomly divided into three groups: control, asthmatic, and budesonide treatment. Aerosolized ovalbumin was used to generate the asthmatic rat model, and budesonide was administered after ovalbumin inhalation. On day 21, bronchial responsiveness tests, bronchoalveolar lavage, and cell counting were conducted. NK-1R protein expression in the lung was investigated by immunohistochemistry and image analysis. Primary rat ASMC cultures were established, and purified ASMCs of the fourth passage were collected for mRNA and protein studies via real-time RT-PCR, immunocytochemistry, and image analysis.

Results

NK-1R mRNA and protein expression in the budesonide treatment group rat’s lung and ASMCs were less than that in the asthmatic group but greater than that in the control group.

Conclusions

NK-1R is involved in the pathogenesis of asthma and that budesonide may downregulate the expression of NK-1R in the ASMCs and airways of asthmatic rats, which may alleviate neurogenic airway inflammation.

Non-genomic effect of glucocorticoids on cardiovascular system

Glucocorticoids (GCs) are essential steroid hormones for homeostasis, development, metabolism, and cognition and possess anti-inflammatory and immunosuppressive actions. Since glucocorticoid receptor II (GR) is nearly ubiquitous, chronic activation or depletion of GCs leads to dysfunction of diverse organs, including the heart and blood vessels, resulting predominantly from changes in gene expression. Most studies, therefore, have focused on the genomic effects of GC to understand its related pathophysiological manifestations. The nongenomic effects of GCs clearly differ from well-known genomic effects, with the former responding within several minutes without the need for protein synthesis. There is increasing evidence that the nongenomic actions of GCs influence various physiological functions. To develop a GC-mediated therapeutic target for the treatment of cardiovascular disease, understanding the genomic and nongenomic effects of GC on the cardiovascular system is needed. This article reviews our current understanding of the underlying mechanisms of GCs on cardiovascular diseases and stress, as well as how nongenomic GC signaling contributes to these conditions. We suggest that manipulation of GC action based on both GC and GR metabolism, mitochondrial impact, and the action of serum- and glucocorticoid-dependent kinase 1 may provide new information with which to treat cardiovascular diseases.

A novel strategy for development of glucocorticoids through non-genomic mechanism

Glucocorticoids (GCs) are routinely believed to take effect through genomic mechanisms, which are also largely responsible for GCs' side effects. Beneficial non-genomic effects of GCs have been reported as being independent of the genomic pathway. Here, we synthesized a new type of GCs, which took effect mainly via non-genomic mechanisms. Hydrocortisone was conjugated with glycine, lysine and phenylalanine to get a bigger molecular structure, which could hardly go through the cell membrane. Evaluation of the anti-inflammatory efficacy showed that hydrocortisone-conjugated glycine (HG) and lysine could inhibit neutrophil degranulation within 15 min. HG could inhibit IgE-mediated histamine release from mast cells via a non-genomic pathway, and rapidly alleviate allergic reaction. Luciferase reporter assay showed that HG would not activate the glucocorticoid response element within 30 min, which verified the rapid effects independent of the genomic pathway. The work proposes a novel insight into the development of novel GCs, and provides new tools for experimental study on non-genomic mechanisms.

Rapid glucocorticoid receptor-mediated inhibition of hypothalamic-pituitary-adrenal ultradian activity in healthy males

A complex dynamic ultradian rhythm underlies the hypothalamic-pituitary-adrenal (HPA) circadian rhythm. We have investigated in normal human male subjects the importance, site of action, and receptor-mediated processes involved in rapid basal corticosteroid feedback and its interaction with corticotrophin releasing hormone (CRH) drive. Pro-opiomelanocortin (POMC), ACTH, and cortisol were measured every 10 min from healthy males during the awakening period or late afternoon using an automated blood sampling system. Mathematical modeling into discrete pulses of activity revealed that intravenous infusion of the synthetic mixed glucocorticoid/mineralocorticoid agonist prednisolone produced rapid inhibition of ACTH and cortisol pulsatility within 30 min in the morning and afternoon. Any pulse that had commenced at the time of injection was unaffected, and subsequent pulsatility was inhibited. Prednisolone also inhibited ACTH and cortisol secretion in response to exogenous CRH stimulation, inferring rapid feedback inhibition at the anterior pituitary. Circulating POMC peptide concentrations were unaffected, suggesting that the rapid corticosteroid inhibitory effect specifically targeted ACTH secretion from pituitary corticotrophs. Prednisolone fast feedback was only reduced by glucocorticoid receptor antagonist pretreatment and not by mineralocorticoid receptor antagonism, suggesting a glucocorticoid receptor-mediated pathway. The intravenous prednisolone suppression test provides a powerful new tool to investigate HPA abnormalities underlying metabolic and psychiatric disease states.

Inhibition of ATP-induced Ca2+ influx by corticosterone in dorsal root ganglion neurons

In addition to the classic genomic effects, it is well known that glucocorticoids also have rapid, nongenomic effects on neurons. In the present study, the effect of corticosterone (CORT) on ATP-induced Ca(2+) mobilization in cultured dorsal root ganglion (DRG) neurons were detected with confocal laser scanning microscopy using fluo-4/AM as a calcium fluorescent indicator that could monitor real-time alterations of intracellular calcium concentration ([Ca(2+)]i). ATP, an algesic agent, caused [Ca(2+)]i increase in DRG neurons by activation of P2X receptor. Pretreatment with CORT (1 nM-1 microM for 5 min) inhibited ATP-induced [Ca(2+)]i increase in DRG neurons. The rapid inhibition of ATP-induced Ca(2+) response by CORT was concentration-dependent, reversible and could be blocked by glucocorticoid receptor antagonist RU38486 (10 microM). Furthermore, the inhibitory effect of CORT was abolished by protein kinase A inhibitor H89 (10 microM), but was not influenced by protein kinase C inhibitor Chelerythrine chloride (10 microM). On the other hand, membrane-impermeable bovine serum albumin-conjugated corticosterone had no effect on ATP-induced [Ca(2+)]i transients. These observations suggest that a nongenomic pathways may be involved in the effect of CORT on ATP-induced [Ca(2+)]i transients in cultured DRG neurons.

Glucocorticoid rapidly enhances NMDA-evoked neurotoxicity by attenuating the NR2A-containing NMDA receptor-mediated ERK1/2 activation

Glucocorticoid (GC) has been shown to affect the neuronal survival/death through a genomic mechanism, but whether or not it does through a nongenomic mechanism is unknown. Using a previously identified GR-deficient primary hippocampal neuron culture, we show here that a 15-min coexposure of N-methyl-D-aspartate (NMDA) with corticosterone at a stress-induced level significantly enhances neuronal death compared to NMDA alone. This enhancing effect of GC can be mimicked by the BSA-conjugated corticosterone, which is plasma membrane impermeable and cannot be blocked by RU38486 spironolactone. Furthermore, using a calcium-imaging technique, we found that B could increase both the percentage of neurons showing a significant increment of intracellular free calcium ([Ca2+](i)) due to NMDA stimulation and the amplitude of [Ca2+](i) increment in the individual responsive cells. Interestingly, this boosting effect of GC on [Ca2+](i) increment could be blocked by the NMDA receptor subunit 2A (NR2A)-specific antagonist [(R)-[(S)-1-(4-bromo-phenyl)-ethylamino]-(2,3-dioxo-1,2,3,4-tetrahydro-quinoxalin-5-yl)-methyl]-phosphonic acid (NVP-AAM077) but not by the NMDA receptor subunit 2B (NR2B)-specific antagonist Ro25-6981. Moreover, we also found that GC can dramatically attenuate the NMDA-induced activation of ERK1/2 without affecting that of p38; and that the NMDA-induced ERK1/2 activation and its attenuation by GC both can be occluded by the NVP-AAM077 but not by Ro25-6981. Consistently, the enhancing effect of GC on NMDA neurotoxicity can also be blocked by NVP-AAM077 and the ERK1/2 inhibitor PD98059 but not by Ro25-6981 and p38 inhibitor SB203580. Indeed, the NMDA neurotoxicity itself can be blocked by Ro25-6981 or SB203580, whereas it is increased by NVP-AAM077 and PD98059. Therefore, it is probable that NMDA triggers a prodeath signaling through the NR2B-p38 MAPK pathway, and a prosurvival signaling through the NR2A-ERK1/2 MAPK pathway, whereas the latter was negatively regulated by rapid GC action. Taken together, the present data suggest a nongenomic action by GC that enhances NMDA neurotoxicity through facilitating [Ca2+](i) increment and attenuating the NR2A-ERK1/2-mediated neuroprotective signaling, implicating a novel pathway underlying the regulatory effect of GC on neuronal survival/death.

Imaging the immediate non-genomic effects of stress hormone on brain activity

The stress hormones, glucocorticoids, bind to intracellular receptor proteins and act as transcription factors affecting gene activity. These genomic effects occur over hours and even days producing long-term changes in synaptic plasticity and neural transmission. In addition to this classic genomic pathway, there is evidence that stress hormones can have immediate, non-genomic effects on brain function. Using non-invasive functional magnetic resonance imaging, awake, adrenalectomized rats were given intravenous doses of corticosterone mimicking blood levels of hormone achieved with modest and intense stress. The dose of corticosterone mimicking high stress caused a significant increase in functional activity in the hippocampus, forebrain cortex and lateral hypothalamus within minutes of administration. This finding shows that stress hormones can have non-genomic effects on brain activity potentially affecting the immediate cognitive and behavioral response to a highly emotional experience.

Verapamil enhances acute stress or glucocorticoid-induced deficits in retrieval of long-term memory in rats

This study was designed to investigate an interaction between acute restraint stress and corticosterone with verapamil, a blocker of L-type voltage-dependent calcium (VDC) channels on retrieval of long-term memory. Young adult male rats were trained in one trial inhibitory avoidance task (0.5 mA, 3 s footshock). On retention test given 48 h after training, the latency to re-enter dark compartment of the apparatus was recorded. In Experiment 1, verapamil pretreatment (5, 10, or 20 mg/kg) enhanced the impairing effects of acute stress (which was applied for 10 min in a Plexiglass tube 30 min before the retention test) on memory retrieval. The applied stress increased circulating corticosterone levels as assessed immediately after the retention test, indicating that stress-induced impairment of memory retrieval is mediated, in part, by increased plasma levels of glucocorticoids. Verapamil did not change this response. In Experiment 2, pretreatment of an intermediate dose of verapamil also enhanced corticosterone-induced impairment of memory retrieval. In Experiments 3 and 4, acute stress or corticosterone did not change motor activity with or without prior treatment of verapamil, suggesting that stress or glucocorticoid-induced impairment of memory retrieval is not due to any gross disturbances in motor performance of animals. These findings indicate that blockade of L-type VDC channels enhances stress or glucocorticoid-induced impairment of memory retrieval, and provide evidence for the existence of an interaction between glucocorticoids and L-type VDC channels on memory retrieval.

Glucocorticoids inhibit degranulation of mast cells in allergic asthma via nongenomic mechanism

BACKGROUND

Glucocorticoids (GCs) are the most potent anti-inflammatory agents available for allergic diseases including asthma, which are routinely believed to need several hours to take effect through regulating gene expression. Our previous report had shown that GCs could inhibit allergic asthma within 10 min, which the classical mechanism could not explain.

OBJECTIVE

To confirm the existence and verify the sites of GCs' rapid action, we investigated nongenomic effects of GCs on degranulation of mast cells in allergic asthma.

METHODS

The GCs' rapid action on airway mast cells deregulations was evaluated in the allergic asthma model of guinea pigs by the computer-assisted morphometry. Using whole-cell patch clamp and fluorometric assay, we examined GCs' nongenomic effect on IgE-mediated exocytosis and histamine release of rat basophilic leukaemia-2H3 mast cells. Employing the flash photolysis technique, we studied the role of Ca(2+) signal in the GCs' nongenomic effect.

RESULTS

Inhaled GCs significantly inhibited airway mast cells degranulation in the allergic asthma model of guinea pigs within 10 min. In vitro, GCs could rapidly inhibit IgE-mediated exocytosis and histamine release of mast cells, and neither GC nuclear receptor antagonist nor protein synthesis inhibitor could block the rapid action. We further demonstrated that GCs' nongenomic effect was not through direct action on secretory machinery, but was mediated by a reduction in the [Ca(2+)](i) elevation.

CONCLUSIONS

The study suggested for the first time that nongenomic pathway was involved in GCs' rapid inhibition on allergic asthma, and raised the possibility of new therapeutic strategies for allergic diseases including asthma.

The effects of non-genomic glucocorticoid mechanisms on bodily functions and the central neural system. A critical evaluation of findings

Mounting evidence suggests that--beyond the well-known genomic effects--glucocorticoids affect cell function via non-genomic mechanisms. Such mechanisms operate in many major systems and organs including the cardiovascular, immune, endocrine and nervous systems, smooth and skeletal muscles, liver, and fat cells. Non-genomic effects are exerted by direct actions on membrane lipids (affecting membrane fluidity), membrane proteins (e.g. ion channels and neurotransmitter receptors), and cytoplasmic proteins (e.g. MAPKs, phospholipases, protein kinases, etc.). These actions are mediated by the glucocorticoids per se or by the proteins dissociated from the liganded glucocorticoid receptor complex. The MR and GR also activate non-genomic mechanisms in certain cases. Some effects of glucocorticoids are shared by a variety of steroids, whereas others are more selective. Moreover, "ultra-selective" effects-mediated by certain glucocorticoids only-were also shown. Disparate findings suggest that non-genomic mechanisms also show "demand-specificity", i.e. require the coincidence of two or more processes. Some of the non-genomic mechanisms activated by glucocorticoids are therapeutically relevant; moreover, the "non-genomic specificity" of certain glucocorticoids raises the possibility of therapeutic applications. Despite the large body of evidence, however, the non-genomic mechanisms of glucocorticoids are still poorly understood. Criteria for differentiating genomic and non-genomic mechanisms are often loosely applied; interactions between various mechanisms are unknown, and non-genomic mechanism-specific pharmacological (potentially therapeutic) agents are lacking. Nevertheless, the discovery of non-genomic mechanisms is a major breakthrough in stress research, and further insights into these mechanisms may open novel approaches for the therapy of various diseases.

Central mineralocorticoid receptors are indispensable for corticosterone-induced impairment of memory retrieval in rats

Previous studies indicated that stress levels of glucocorticoid hormones (cortisol in humans, and corticosterone in rodents) induce impairment of long-term memory retrieval, but the underlying mechanisms (genomic or nongenomic) are not clear. To clarify this issue, we investigated the involvement of brain corticosteroid receptors and protein synthesis in the corticosterone-induced impairment of memory retrieval. Young rats were trained in the water maze task with six trials per day for 6 consecutive days. Retention of the spatial training was assessed 24 h after the last training session with a 60-s probe trial. Experiments included intraventricular injections of anisomycin, a specific protein synthesis inhibitor or specific antagonists for both types of corticocosteroid receptors (mineralocorticoid receptor, MR, and glucocorticoids receptor, GR) before corticosterone administration shortly before retention testing. The results showed that administration of anisomycin did not change the corticosterone response. Administration of the MR, but not GR, antagonist blocked the corticosterone-induced response dose dependently. These findings provide evidence for the view that glucocorticoids impair memory retrieval through nongenomic mechanisms involving an interaction with central MRs.

Effects of repeated prenatal glucocorticoid exposure on long-term potentiation in the juvenile guinea-pig hippocampus

Synthetic glucocorticoids (sGCs) are routinely used to treat women at risk of preterm labour to promote fetal lung maturation. There is now strong evidence that exposure to excess glucocorticoid during periods of rapid brain development has permanent consequences for endocrine function and behaviour in the offspring. Prenatal exposure to sGC alters the expression of N-methyl-D-aspartate receptor (NMDA-R) subunits in the fetal and neonatal hippocampus. Given the integral role of the NMDA-R in synaptic plasticity, we hypothesized that prenatal sGC exposure will have effects on hippocampal long-term potentiation (LTP) after birth. Further, this may occur in either the presence or absence of elevated cortisol concentrations, in vitro. Pregnant guinea-pigs were injected with betamethasone (Beta, 1 mg kg(-1)) or vehicle on gestational days (gd) 40, 41, 50, 51, 60 and 61 (term approximately 70 days), a regimen comparable to that given to pregnant women. On postnatal day 21, LTP was examined at Schaffer collateral synapses in the CA1 region of hippocampal slices prepared from juvenile animals exposed to betamethasone or vehicle, in utero. Subsequently, the acute glucocorticoid receptor (GR)- and mineralocorticoid receptor (MR)-dependent effects of cortisol (0.1-10 microM; bath applied 30 min before LTP induction) were examined. There was no effect of prenatal sGC treatment on LTP under basal conditions. The application of 10 microM cortisol depressed excitatory synaptic transmission in all treatment groups regardless of sex. Similarly, LTP was depressed by 10 microM cortisol in all groups, with the exception of Beta-exposed females, in which LTP was unaltered. Hippocampal MR and GR protein levels were increased in Beta-exposed females, but not in any other prenatal treatment group. This study reveals sex-specific effects of prenatal exposure to sGC on LTP in the presence of elevated cortisol, a situation that would occur in vivo during stress.

Blocking effects of intra-hippocampal naltrexone microinjections on glucocorticoid-induced impairment of spatial memory retrieval in rats

Previous studies have indicated that stress levels of glucocorticoid hormones induce impairment of long-term memory retrieval. In a recent study, we have found that peripheral injections of naloxone blocked stress or glucocorticoid-induced deficit in memory retrieval, but the anatomical sites of such an interaction were not known. The present study examined whether the opioid receptors in the hippocampus interact with glucocorticoid effects on memory retrieval in a water maze (WM). Young rats carrying bilateral cannulae aimed at the hippocampus were trained in a WM task with six trials per day for six consecutive days. Retention of the spatial training was assessed 24h after the last training session with a 60-s probe trial. Corticosterone (1mg/kg) was injected 30 min before retention testing with or without prior bilateral intra-hippocampal injections of naltrexone (5, 10 or 20 microg/mul per site) as a classical opioid antagonist. The results show that corticosterone-induced impairment of memory retrieval was blocked by intra-hippocampal infusions of naltrexone in a dose-dependent manner. Moreover, even a higher dose of corticosterone (3 mg/kg) was ineffective in impairing memory retrieval in the animals that received 20 microg of naltrexone. These findings provide evidence for the view that glucocorticoids interact with the hippocampal opioid receptors in influencing long-term memory retrieval.

Actions of glucocorticoids at a seasonal baseline as compared to stress-related levels in the regulation of periodic life processes

For decades, demands associated with the predictable life-history cycle have been considered stressful and have not been distinguished from stress that occurs in association with unpredictable and life-threatening perturbations in the environment. The recent emergence of the concept of allostasis distinguishes behavioral and physiological responses to predictable routines as opposed to unpredictable perturbations, and allows for their comparison within one theoretical framework. Glucocorticosteroids (GCs) have been proposed as important mediators of allostasis, as they allow for rapid readjustment and support of behavior and physiology in response to predictable and unpredictable demands (allostatic load). Much work has already been done in defining GC action at the high concentrations that accompany life-threatening perturbations. However, less is known about the role of GCs in relation to daily and seasonal life processes. In this review, we summarize the known behavioral and physiological effects of GCs relating to the predictable life-history cycle, paying particular attention to feeding behavior, locomotor activity and energy metabolism. Although we utilize a comparative approach, emphasis is placed on birds. In addition, we briefly review effects of GCs at stress-related concentrations to test the hypothesis that different levels of GCs play specific and distinct roles in the regulation of life processes and, thus, participate in the promotion of different physiological states. We also examine the receptor types through which GC action may be mediated and suggest mechanisms whereby different GC concentrations may exert their actions. In conclusion, we argue that biological actions of GCs at "non-stress" seasonal concentrations play a critical role in the adjustment of responses that accompany predictable variability in the environment and demand more careful consideration in future studies.

Involvement of the coeliac ganglion in the luteotrophic effect of androstenedione in late pregnant rats

Using the ex vivo coeliac ganglion-superior ovarian nerve-ovary system at the end of pregnancy when luteal regression starts, we investigated whether, when administered systemically or when added directly to the ganglion compartment, androstenedione (A2) can reverse such regression, and whether the neural (noradrenaline (NA)) and endocrine (A2) joint action modifies the release of ovarian progesterone. The experimental groups were as follows: group 1 – A2 injected systemically 48 h before incubation of the system (A2)s; group 2 – A2 directly added to the ganglion compartment (A2)g; group 3 – A2 injected 48 h before incubation of the system with NA in the ganglion compartment (A2 + NA); group 4 – A2 plus NA added to the ganglion compartment (NA + A2)g. The controls were ex vivo systems without treatment (control), and with the addition of NA alone in the ganglion compartment (NA). The results were as follows. For (A2)s versus control, progesterone increased on days 19 and 21 of pregnancy at all the studied times and only at 180 min on day 20. For (A2 + NA) versus (A2)s, progesterone increased on days 19 and 21. For (A2 + NA) versus NA, progesterone increased at all the studied times on days 19 and 21 and at 180 min on day 20. For (A2)g versus control, progesterone significantly increased every pregnancy day. For (NA + A2)g versus (A2)g, progesterone decreased at 120 and 180 min on day 19. For (NA + A2)g versus NA, progesterone increased on days 20 and 21. We can conclude that A2 can reverse the functional regression of the corpus luteum either systemically or, what is more surprising, when directly added to the coeliac ganglion, whose action on the ovary is exerted via superior ovarian nerve.

Glucocorticoids stimulate the activity of large-conductance Ca2+ -activated K+ channels in pituitary GH3 and AtT-20 cells via a non-genomic mechanism

The effects of glucocorticoids on ion currents were investigated in pituitary GH3 and AtT-20 cells. In whole-cell configuration, dexamethasone, a synthetic glucocorticoid, reversibly increased the density of Ca2+ -activated K+ current (IK(Ca)) with an EC50 value of 21 +/- 5 microM. Dexamethasone-induced increase in IK(Ca) density was suppressed by paxilline (1 microM), yet not by glibenclamide (10 microM), pandinotoxin-Kalpha (1 microM) or mifepristone (10 microM). Paxilline is a blocker of large-conductance Ca2+ -activated K+ (BKCa) channels, while glibenclamide and pandinotoxin-Kalpha are blockers of ATP-sensitive and A-type K+ channels, respectively. Mifepristone can block cytosolic glucocorticoid receptors. In inside-out configuration, the application of dexamethasone (30 microM) into the intracellular surface caused no change in single-channel conductance; however, it did increase BKCa -channel activity. Its effect was associated with a negative shift of the activation curve. However, no Ca2+ -sensitiviy of these channels was altered by dexamethasone. Dexamethasone-stimulated channel activity involves an increase in mean open time and a decrease in mean closed time. Under current-clamp configuration, dexamethasone decreased the firing frequency of action potentials. In pituitary AtT-20 cells, dexamethasone (30 microM) also increased BKCa -channel activity. Dexamethasone-mediated stimulation of IK(Ca) presented here that is likely pharmacological, seems to be not linked to a genomic mechanism. The non-genomic, channel-stimulating properties of dexamethasone may partly contribute to the underlying mechanisms by which glucocorticoids affect neuroendocrine function.

Rapid inhibitory effect of glucocorticoids on airway smooth muscle contractions in guinea pigs

The common disease asthma is characterized by the obstruction, inflammation and increased sensitivity of the airways. Glucocorticoids (GCs) are one of the most potent anti-inflammatory agents available for treating allergic disease. In this study, we report that the GC budesonide (BUD) can rapidly inhibit the histamine-induced contractions of airway smooth muscle in a process mediated by non-genomic mechanisms. The tracheas of albino Hartley guinea pigs were used. We measured the effects of BUD on the increased isometric tension of trachea segment rings and the shrinking of single airway smooth muscle cells (ASMCs) induced by histamine. With the application of each reagent, the changes in the isometric tension of the segment rings upon maximum contraction and at four time points were recorded. We found that BUD significantly suppressed the increase in isometric tension induced by histamine in guinea pigs within 15 min. We also observed that BUD can reduce the histamine-induced shrinking of single ASMCs in an even shorter time. Mifepristone (RU486) and actidione did not depress the inhibitory effect of BUD. The results preclude action via genomic-mediated responses that usually take several hours to occur. We conclude therefore that GCs have a rapid non-genomic inhibitory effect on guinea pig airway smooth muscle contractions, and provide a new way to investigate this non-genomic mechanism. Further study can provide theoretical evidence for the clinical application of GCs in asthma and other allergic diseases.

Beta2 and beta4 subunits of BK channels confer differential sensitivity to acute modulation by steroid hormones

Membrane-associated receptors for rapid, steroidal neuromodulation remain elusive. Estradiol has been reported to facilitate activation of voltage- and Ca(2+)-dependent BK potassium channels encoded by Slo, if associated with beta1 subunits. We show here that 1) multiple members of the beta family confer sensitivity to multiple steroids on BK channels, 2) that beta subunits differentiate between steroids, and 3) that different betas have distinct relative preferences for particular steroids. Expressed in HEK 293 cells, inside-out patches with channels composed of Slo-alpha alone showed no steroid sensitivity. Cells expressing alphabeta4 exhibited potent, rapid, reversible, and dose-dependent potentiation by corticosterone (CORT; a glucocorticoid), and were potentiated to a lesser degree by other sex and stress steroids. In contrast, alphabeta2 channels were potentiated more strongly by dehydroepiandrosterone (DHEA; an enigmatic, stress-related adrenal androgen), and to a lesser extent by CORT, estradiol, testosterone, and DHEA-S. Cholesterol had no effect on any BK channel compositions tested. Conductance-voltage plots of channels composed of alpha plus beta2 or beta4 subunits were shifted in the negative direction by steroids, indicating greater activation at negative voltages. Thus our results argue that the variety of Slo-beta subunit coexpression patterns occurring in vivo expands the repertoire of Slo channel gating in yet another dimension not fully appreciated, rendering BK gating responsive to dynamic fluctuations in a multiple of steroid hormones.

Fast glucocorticoid actions on brain: back to the future

Rapid, non-transcriptionally mediated, effects of glucocorticoids affect many behaviors as well as inhibition of function in the hypothalamo-pituitary-adrenal axis. In this short review, it is argued that the fast glucocorticoid actions which are mediated by membrane receptors are an ancient type of sterol/steroid-mediated effect, and that these may be the primordial glucocorticoid receptors. Although the fast feedback actions of the glucocorticoids enjoyed study in the middle of the last century, new results and the availability of new techniques suggest that it is again time for a concerted effort to be made to understand the mechanism(s) of these rapid effects.

Cultured embryonic hippocampal neurons deficient in glucocorticoid (GC) receptor: a novel model for studying nongenomic effects of GC in the neural system

Glucocorticoid (GC) acts through both genomic and nongenomic mechanisms. It affects the structure and function of the central nervous system, especially the hippocampus. Here we report an in vitro culture system that can yield embryonic hippocampal neurons deficient in the expression of GC receptor as demonstrated by immunoblotting, immunocytochemistry, and RT-PCR. Owing to this unique feature, those neuron preparations can serve as an ideal model for studying the nongenomic actions of GC on neural cells. In this study, we found that the Erk1/2, c-Jun N-terminal kinase (JNK), and p38 MAPKs were activated in these neurons by BSA-conjugated corticosterone within 15 min of treatment. This activation was not blocked by RU38486, spironolactone, or cycloheximide. Therefore, it is concluded that the activation of MAPKs observed here was due to the nongenomic action of GC. Furthermore, a 24-h incubation with corticosterone at concentrations ranged from 10(-11)-10(-5) M did not have an effect on the viability of GC receptor-deficient neurons.

Rapid activation of JNK and p38 by glucocorticoids in primary cultured hippocampal cells

Rapid activation of JNK and p38 and their translocation to the cell nucleus by glucocorticoids, corticosterone (Cort), and bovine serum-conjugated corticosterone (Cort-BSA) were studied in primary cultured hippocampal cells by using immunoblotting and immunofluorescence confocal microscopy. The rapid activation occurred 5 min after stimulation and was maintained at plateau for as long as 2-4 hr; i.e., the response persisted for 2 hr after washing out the 15-min application of Cort-BSA. The activation occurred at a minimal concentration of 10(-9) M for Cort and 10(-8) M for Cort-BSA. GDPbetaS blocked the activation, but RU38486, a nuclear glucocorticoid receptor antagonist, could not block the activation, indicating the involvement of the membrane-delineated receptor in this reaction. The protein kinase C (PKC) inhibitor Go6976 blocked the response, whereas the protein kinase A inhibitor H89 could not, implying the involvement of PKC in the intracellular signal transduction pathway. The nongenomic nature of the responses and the transduction pathway and the significance of persistent action and biological significance are discussed.

Rapid, hierarchical modulation of vocal patterning by steroid hormones

Vocal control systems have been identified in all major groups of jawed vertebrates. Although steroid hormones are instrumental in the long-term development and maintenance of neural structures underlying vocalization, it is unknown whether steroids rapidly modulate the neural activity of vocal motor systems. The midshipman fish generates advertisement and agonistic calls that mainly differ in duration. A descending midbrain pathway activates a hindbrain-spinal vocal circuit that directly establishes the discharge frequency and duration of the rhythmic vocal motor volley. This vocal motor output, which can be monitored from occipital nerve roots, directly determines the rate and duration of contraction of a pair of sonic muscles and, in turn, the fundamental frequency and duration of vocalizations. Here, we demonstrate that the duration of the vocal motor volley, or fictive vocalization, is rapidly responsive to steroid hormones, including androgens, estrogens, and glucocorticoids. These responses are consistent, in part, with a nongenomic mechanism and are steroid specific at the receptor level, suggesting the possibility of multiple membrane-bound receptor populations. We also show, using intact and semi-intact preparations, that steroids hierarchically modulate fictive vocalizations; whereas the hindbrain-spinal region is both necessary and sufficient for rapid (within 5 min) effects on duration, descending midbrain input is necessary for maintenance (up to 120 min) of these effects. The conserved nature of vertebrate vocal motor systems suggests that the neuroendocrine principles outlined in this study may be a fundamental feature of all vocal vertebrates.

The effects of acute restraint stress and dexamethasone on retrieval of long-term memory in rats: an interaction with opiate system

This study investigated whether application of acute restraint stress or dexamethasone, as a glucocorticoid receptor agonist, impaired retrieval of long-term memory and if pretreatment with opiate antagonist naloxone blocked their effects on memory retrieval. Young adult male rats were trained in one trial inhibitory avoidance task (1 mA, 1.5 s footshock). On retention test given 48 h after training, the latency to re-enter dark compartment of the apparatus was recorded. Thirty minutes before retention test, the rats were exposed to a 10 min of restraint stress in a Plexiglass tube or were injected with dexamethasone (1 mg/kg) with or without prior treatment of naloxone (1 or 2 mg/kg). The results showed that both acute restraint stress and dexamethasone impaired retention performance. Both doses of naloxone were effective in blocking the impairing effect of stress, but only higher dose of naloxone blocked dexamethasone-induced impairment. The applied stress increased circulating corticosterone levels as assessed immediately after the retention test, indicating that stress-induced impairment of memory retrieval is mediated, in part, by increased plasma levels of glucocorticoids. These findings further indicate that acute restraint stress and glucocorticoids impair retrieval of long-term memory, and provide evidence for the existence of an interaction between glucocortioids and opiate system on this process.

Cortisol rapidly suppresses intracellular calcium and voltage-gated calcium channel activity in prolactin cells of the tilapia (Oreochromis mossambicus)

Cortisol was previously shown to rapidly (10-20 min) reduce the release of prolactin (PRL) from pituitary glands of tilapia (Oreochromis mossambicus). This inhibition of PRL release by cortisol is accompanied by rapid reductions in (45)Ca(2+) and cAMP accumulation. Cortisol's early actions occur through a protein synthesis-independent pathway and are mimicked by a membrane-impermeable analog. The signaling pathway that mediates rapid, nongenomic membrane effects of glucocorticoids is poorly understood. Using the advantageous characteristics of the teleost pituitary gland from which a nearly pure population of PRL cells can be isolated and incubated in defined medium, we examined whether cortisol rapidly reduces intracellular free calcium (Ca(i)(2+)) and suppresses L-type voltage-gated ion channel activity in events that lead to reduced PRL release. Microspectrofluorometry, used in combination with the Ca(2+)-sensitive dye fura 2 revealed that cortisol reversibly reduces basal and hyposmotically induced Ca(i)(2+) within seconds (P < 0.001) in dispersed pituitary cells. Somatostatin, a peptide known to inhibit PRL release through a membrane receptor-coupled mechanism, similarly reduces Ca(i)(2+). Under depolarizing [K(+)], the L-type calcium channel agonist BAY K 8644, a factor known to delay the closing of L-type Ca(2+) channels, stimulates PRL release in a concentration-dependent fashion (P < 0.01). Cortisol (and somatostatin) blocks BAY K 8644-induced PRL release (P < 0.01; 30 min), well within the time course over which its actions occur, independent of protein synthesis and at the level of the plasma membrane. Results indicate that cortisol inhibits tilapia PRL release through rapid reductions in Ca(i)(2+) that likely involve an attenuation of Ca(2+) entry through L-type voltage-gated Ca(2+) channels. These results provide further evidence that glucocorticoids rapidly modulate hormone secretion via a membrane-associated mechanism similar to that observed with the fast effects of peptides and neurotransmitters.

Nongenomic glucocorticoid inhibition via endocannabinoid release in the hypothalamus: a fast feedback mechanism

Glucocorticoid negative feedback in the brain controls stress, feeding, and neural-immune interactions by regulating the hypothalamic-pituitary-adrenal axis, but the mechanisms of inhibition of hypothalamic neurosecretory cells have never been elucidated. Using whole-cell patch-clamp recordings in an acute hypothalamic slice preparation, we demonstrate a rapid suppression of excitatory glutamatergic synaptic inputs to parvocellular neurosecretory neurons of the hypothalamic paraventricular nucleus (PVN) by the glucocorticoids dexamethasone and corticosterone. The effect was maintained with dexamethasone conjugated to bovine serum albumin and was not seen with direct intracellular glucocorticoid perfusion via the patch pipette, suggesting actions at a membrane receptor. The presynaptic inhibition of glutamate release by glucocorticoids was blocked by postsynaptic inhibition of G-protein activity with intracellular GDP-beta-S application, implicating a postsynaptic G-protein-coupled receptor and the release of a retrograde messenger. The glucocorticoid effect was not blocked by the nitric oxide synthesis antagonist N(G)-nitro-L-arginine methyl ester hydrochloride or by hemoglobin but was blocked completely by the CB1 cannabinoid receptor antagonists AM251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] and AM281 [1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide] and mimicked and occluded by the cannabinoid receptor agonist WIN55,212-2 [(beta)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate], indicating that it was mediated by retrograde endocannabinoid release. Several peptidergic subtypes of parvocellular neuron, identified by single-cell reverse transcripton-PCR analysis, were subject to rapid inhibitory glucocorticoid regulation, including corticotropin-releasing hormone-, thyrotropin-releasing hormone-, vasopressin-, and oxytocin-expressing neurons. Therefore, our findings reveal a mechanism of rapid glucocorticoid feedback inhibition of hypothalamic hormone secretion via endocannabinoid release in the PVN and provide a link between the actions of glucocorticoids and cannabinoids in the hypothalamus that regulate stress and energy homeostasis.

Nongenomic steroid action: controversies, questions, and answers

Steroids may exert their action in living cells by several ways: 1). the well-known genomic pathway, involving hormone binding to cytosolic (classic) receptors and subsequent modulation of gene expression followed by protein synthesis. 2). Alternatively, pathways are operating that do not act on the genome, therefore indicating nongenomic action. Although it is comparatively easy to confirm the nongenomic nature of a particular phenomenon observed, e.g., by using inhibitors of transcription or translation, considerable controversy exists about the identity of receptors that mediate these responses. Many different approaches have been employed to answer this question, including pharmacology, knock-out animals, and numerous biochemical studies. Evidence is presented for and against both the participation of classic receptors, or proteins closely related to them, as well as for the involvement of yet poorly understood, novel membrane steroid receptors. In addition, clinical implications for a wide array of nongenomic steroid actions are outlined.

Rapid inhibitory effects of corticosterone on calcium influx in rat dorsal root ganglion neurons

Corticosterone may nongenomically affect cell functions in addition to its well-characterized effects on gene expression. The purpose of this study is to examine if corticosterone has a rapid nongenomic effect on excitability of dorsal root ganglion neurons by using patch-clamp and single-cell Ca(2+) microfluometry techniques. The results show that corticosterone has a dose-dependent rapid inhibitory effect on the voltage-dependent calcium currents in dorsal root ganglion neurons. Moreover, corticosterone inhibits [Ca(2+)](i) elevation induced by 50 mM high K(+) within just 3 s. The inhibitory effects of corticosterone on the voltage-dependent calcium current and high K(+)-induced calcium influx diminish after adding protein kinase C inhibitor or pretreatment with pertussis toxin for 24 h. Our results demonstrate an nongenomic effect of corticosterone on the excitability of dorsal root ganglion neurons and the effect is mediated through a putative pertussis toxin-sensitive G-protein-coupled receptor and activation of protein kinase C.

Nongenomic mechanism of glucocorticoid inhibition of bradykinin-induced calcium influx in PC12 cells: possible involvement of protein kinase C

Many stimulants, including bradykinin (BK), can induce increase in [Ca(2+)](i) in PC12 cells. Bradykinin induces an increase in [Ca(2+)](i) via intracellular Ca(2+) release and extracellular Ca(2+) influx through the transduction of G protein, but not through voltage-sensitive calcium channels. In this experiment, We analyzed how corticosterone (Cort) influences BK-induced intracellular Ca(2+) release and extracellular Ca(2+) influx, and further studied the mechanism of glucocorticoid's action. To dissociate the intracellular Ca(2+) release and extracellular Ca(2+) influx induced by BK, the Ca(2+)-free/Ca(2+)- reintroduction protocol was used. The results were as follows: (1) The Ca(2+) influx induced by BK could be rapidly inhibited by Cort, but intracellular Ca(2+) release could not be affected significantly. (2) The inhibitory effect of Cort-BSA (BSA -conjugated Cort) on Ca(2+) influx induced by BK was the same as the effect of free Cort. (3) Protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate) could mimic and PKC inhibitor Gö6976 could reverse the inhibitory effect of Cort. (4) There was no inhibitory effect of Cort on Ca(2+) influx induced by BK when pretreated with pertussis toxin. The results suggested, for the first time, that Cort might act via a putative membrane receptor and inhibit the Ca(2+) influx induced by BK through the pertussis toxin -sensitive G protein-PKC pathway.

Evaluation of pituitary and thyroid hormones in patients with subarachnoid hemorrhage due to ruptured intracranial aneurysm

It is well known that the central nervous system (CNS) influences the pituitary hormone secretions and that diseases of CNS are frequently associated with an altered endocrine function. The aim of this study has been the evaluation of the serum concentrations of the pituitary and thyroid hormones in a series of patients with subarachnoid hemorrhage due to a ruptured cerebral aneurysm. Thirty-five patients (23 females and 12 males), aged 51.9 +/- 13.3 years on the mean were admitted. They were evaluated to assess the clinical severity of the subarachnoid hemorrhage by Hunt & Hess scale: nine patients were in the grade I, 14 in the grade II, and 12 in the grade III. Blood samples were obtained between 8:00 and 9:00 a.m. and serum hormones were measured by commercial kits (IRMA or MEIA methods). Cortisol serum levels (normal range (NR) = 5 to 18 micro g/dL) were increased in all the patients (mean +/- standard deviation = 31.4 +/- 12.4 micro g/dL). Mean prolactin levels (NR < 20 ng/mL) were 18.6 +/- 17.1 ng/mL and five patients (14.2%) had levels higher than normal. FSH and LH levels were normal according to age and sex: men: FSH = 4 +/- 2.9 mUI/mL (NR = 1 to 10.5 mUI/mL); LH = 6.1 +/- 6.3 mUI/mL (NR = 2 to 12 mUI/mL); premenopausa women: FSH = 2.5 +/- 1.5 mUI/mL (NR = 2.4 to 9.3 mUI/mL); LH 3.9 +/- 5.1 mUI/mL (NR =2 to 15 mUI/mL); post- menopausal women: FSH = 48.3 +/- 18.5 mUI/mL (NR =31 to 134 mUI/mL); LH = 29 +/- 13.8 mUI/mL (NR =16 to 64 mUI/mL). Mean TSH levels were 3.9 +/- 5.2 micro UI/mL (NR =0.5 to 4.7 micro UI/mL) and five patients (14.2%) had levels higher than normal. Mean triiodothyronine levels (T3) were 66.4 +/- 18.7 ng/dL (NR = 45 to 137 ng/dL) and five patients (14.2%) had levels lower than normal (33.8 +/- 9 ng/dL). Mean thyroxine levels (T4) (NR= 4.5 to 12.5 micro g/dL) were 7.4 +/- 1.7 micro g/dL and two patients (5.6%) had levels lower than normal. Thyroglobulin and microsomal antibodies were not detectable.

CONCLUSIONS

In the first 24 hours following ictus, the hormonal changes may be due to the stress produced by the intracranial bleeding; thyroid hormone alterations suggest that patients with subarachnoid hemorrhage might have an euthyroid sick syndrome.