Immunocytochemical localization of glucocorticoid receptors in the spinal cord: effects of adrenalectomy, glucocorticoid treatment, and spinal cord transection

Long-term effects of the glucocorticoid receptor modulator CORT113176 in murine motoneuron degeneration

The Wobbler mouse spinal cord shows vacuolated motoneurons, glial reaction, inflammation and abnormal glutamatergic parameters. Wobblers also show deficits of motor performance. These conditions resemble amyotrophic lateral sclerosis (ALS). Wobbler mice also show high levels of corticosterone in blood, adrenals and brain plus adrenal hypertrophy, suggesting that chronically elevated glucocorticoids prime spinal cord neuroinflammation. Therefore, we analyzed if treatment of Wobbler mice with the glucocorticoid receptor (GR) antagonist CORT113176 mitigated the mentioned abnormalities. 30 mg/kg CORT113176 given daily for 3 weeks reduced motoneuron vacuolation, decreased astro and microgliosis, lowered the inflammatory mediators high mobility group box 1 protein (HMGB1), toll-like receptor 4, myeloid differentiation primary response 88 (MyD88), p50 subunit of nuclear factor kappa B (NFκB), tumor necrosis factor (TNF) receptor, and interleukin 18 (IL18) compared to untreated Wobblers. CORT113176 increased the survival signal pAKT (serine-threonine kinase) and decreased the death signal phosphorylated Junk-N-terminal kinase (pJNK), symptomatic of antiapoptosis. There was a moderate positive effect on glutamine synthase and astrocyte glutamate transporters, suggesting decreased glutamate excitotoxicity. In this pre-clinical study, Wobblers receiving CORT113176 showed enhanced resistance to fatigue in the rota rod test and lower forelimb atrophy at weeks 2-3. Therefore, long-term treatment with CORT113176 attenuated degeneration and inflammation, increased motor performance and decreased paw deformity. Antagonism of the GR may be of potential therapeutic value for neurodegenerative diseases.

Stress Increases Peripheral Axon Growth and Regeneration through Glucocorticoid Receptor-Dependent Transcriptional Programs

Stress and glucocorticoid (GC) release are common behavioral and hormonal responses to injury or disease. In the brain, stress/GCs can alter neuron structure and function leading to cognitive impairment. Stress and GCs also exacerbate pain, but whether a corresponding change occurs in structural plasticity of sensory neurons is unknown. Here, we show that in female mice (Mus musculus) basal GC receptor (Nr3c1, also known as GR) expression in dorsal root ganglion (DRG) sensory neurons is 15-fold higher than in neurons in canonical stress-responsive brain regions (M. musculus). In response to stress or GCs, adult DRG neurite growth increases through mechanisms involving GR-dependent gene transcription. In vivo, prior exposure to an acute systemic stress increases peripheral nerve regeneration. These data have broad clinical implications and highlight the importance of stress and GCs as novel behavioral and circulating modifiers of neuronal plasticity.

Nuclear expression of PG-21, SRC-1, and pCREB in regions of the lumbosacral spinal cord involved in pelvic innervation in young adult and aged rats

In rats, ageing results in dysfunctional patterns of micturition and diminished sexual reflexes that may reflect degenerative changes within spinal circuitry. In both sexes the dorsal lateral nucleus and the spinal nucleus of the bulbospongiosus, which lie in the L5-S1 spinal segments, contain motor neurons that innervate perineal muscles, and the external anal and urethral sphincters. Neurons in the sacral parasympathetic nucleus of these segments provide autonomic control of the bladder, cervix and penis and other lower urinary tract structures. Interneurons in the dorsal gray commissure and dorsal horn have also been implicated in lower urinary tract function. This study investigates the cellular localisation of PG-21 androgen receptors, steroid receptor co-activator one (SRC-1) and the phosphorylated form of c-AMP response element binding protein (pCREB) within these spinal nuclei. These are components of signalling pathways that mediate cellular responses to steroid hormones and neurotrophins. Nuclear expression of PG-21 androgen receptors, SRC-1 and pCREB in young and aged rats was quantified using immunohistochemistry. There was a reduction in the number of spinal neurons expressing these molecules in the aged males while in aged females, SRC-1 and pCREB expression was largely unchanged. This suggests that the observed age-related changes may be linked to declining testosterone levels. Acute testosterone therapy restored expression of PG-21 androgen receptor in aged and orchidectomised male rats, however levels of re-expression varied within different nuclei suggesting a more prolonged period of hormone replacement may be required for full restoration.

Modulatory role of locus coeruleus and estradiol on the stress response of female rats

The activity of the hypothalamic-pituitary-adrenal axis is modulated by the norepinephrinergic system and, in females, also by the ovarian hormones. We investigated the role of ovarian steroids and the locus coeruleus (LC) on stress-induced corticosterone secretion in female rats. Ovariectomized rats without hormonal replacement (OVX) or treated with estradiol (OVE) or estradiol plus progesterone (OVEP) were subjected to jugular cannulation. Immediately after that, each hormonal treatment group was subjected to LC lesion or sham surgery or no brain surgery. After 24 h, blood samples of all 9 groups were collected before and after ether inhalation. Other four groups (OVX control, sham and lesioned, and OVE) were perfused for glucocorticoid receptor (GR) immunocytochemistry in hippocampal CA1 neurons and paraventricular nucleus (PVN). Estradiol replacement decreased while LC lesions increased stress-induced corticosterone secretion. The effect of LC lesion was potentiated with the removal of ovarian steroids. Since GR expression of lesioned animals decreased in the hippocampus, but not in PVN, we suggest that the effect of LC lesion on corticosterone secretion could be due to a reduction in the efficiency of the negative feedback system in the CA1 neurons. However, this mechanism is not involved in the estradiol modulation on corticosteroid secretion, as no change in GR expression was observed in estradiol-treated animals.

Effects of injury and progesterone treatment on progesterone receptor and progesterone binding protein 25-Dx expression in the rat spinal cord

Progesterone provides neuroprotection after spinal cord injury, but the molecular mechanisms involved in this effect are not completely understood. In this work, expression of two binding proteins for progesterone was studied in intact and injured rat spinal cord: the classical intracellular progesterone receptor (PR) and 25-Dx, a recently discovered progesterone membrane binding site. RT-PCR was employed to determine their relative mRNA levels, whereas cellular localization and relative protein levels were investigated by immunocytochemistry. We observed that spinal cord PR mRNA was not up-regulated by estrogen in contrast to what is observed in many brain areas and in the uterus, but was abundant as it amounted to a third of that measured in the estradiol-stimulated uterus. In male rats with complete spinal cord transection, levels of PR mRNA were significantly decreased, while those of 25-Dx mRNA remained unchanged with respect to control animals. When spinal cord-injured animals received progesterone treatment during 72 h, PR mRNA levels were not affected and remained low, whereas 25-Dx mRNA levels were significantly increased. Immunostaining of PR showed its intracellular localization in both neurons and glial cells, whereas 25-Dx immunoreactivity was localized to cell membranes of dorsal horn and central canal neurons. As the two binding proteins for progesterone differ with respect to their response to lesion, their regulation by progesterone, their cellular and subcellular localizations, their functions may differ under normal and pathological conditions. These observations point to a novel and potentially important role of the progesterone binding protein 25-Dx after injury of the nervous system and suggest that the neuroprotective effects of progesterone may not necessarily be mediated by the classical progesterone receptor but may involve distinct membrane binding sites.

SRC-1 localisation in lumbosacral spinal cord of male and female Wistar rats

Nuclear receptor co-activators play an important role in enhancing transcriptional activity of steroid hormone receptors, however there is currently little information concerning their distribution within the spinal cord. In this study, the distribution of steroid receptor co-activator-1 (SRC-1) was examined with immunocytochemistry, in the lumbosacral cord of Wistar rats of both sexes. In all rats, regardless of sex, SRC-1 was predominant in neurons of the superficial laminae of the dorsal horn and within motorneurons of lamina IX. Sexually dimorphic nuclei exhibited robust SRC-1 immunoreactivity in young rats, including orchidectomised animals, but this appeared to decline in aged rats. Dorsal horn labelling appeared similarly reduced suggesting a possible age-related down-regulation of the transcription mediated by steroid receptors in some spinal neurons.

Cellular basis for progesterone neuroprotection in the injured spinal cord

Progesterone (PROG) exerts beneficial and neuroprotective effects in the injured central and peripheral nervous system. In the present work, we examine PROG effects on three measures of neuronal function under negative regulation (choline acetyltransferase [ChAT] and Na,K-ATPase) or stimulated (growth-associated protein [GAP-43]) after acute spinal cord transection injury in rats. As expected, spinal cord injury reduced ChAT immunostaining intensity of ventral horn neurons. A 3-day course of intensive PROG treatment of transected rats restored ChAT immunoreactivity, as assessed by frequency histograms that recorded shifts from predominantly light neuronal staining to medium, dark or intense staining typical of control rats. Transection also reduced the expression of the mRNA for the alpha3 catalytic and beta1 regulatory subunits of neuronal Na,K-ATPase, whereas PROG treatment restored both subunit mRNA to normal levels. Additionally, the upregulation observed for GAP-43 mRNA in ventral horn neurons in spinal cord-transected rats, was further enhanced by PROG administration. In no case did PROG modify ChAT immunoreactivity, Na,K-ATPase subunit mRNA or GAP-43 mRNA in control, sham-operated rats. Further, the PROG-mediated effects on these three markers were observed in large, presumably Lamina IX motoneurons, as well as in smaller neurons measuring approximately <500 micro2. Overall, the stimulatory effects of PROG on ChAT appears to replenish acetylcholine, with its stimulatory effects on Na,K-ATPase seems capable of restoring membrane potential, ion transport and nutrient uptake. PROG effects on GAP-43 also appear to accelerate reparative responses to injury. As the cellular basis for PROG neuroprotection becomes better understood it may prove of therapeutic benefit to spinal cord injury patients.

Glucocorticoid effects on Fos immunoreactivity and NADPH-diaphorase histochemical staining following spinal cord injury

Glucocorticoids (GC) provide neuroprotection and early recovery after spinal cord injury (SCI). While several mechanisms were proposed to account for these effects, limited information exists regarding GC actions in sensory areas of the spinal cord. Presently, we studied the time course of Fos expression, and reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemical staining to monitor neuronal responses to SCI with or without GC treatment. Rats with sham-operation or transection at the thoracic level (T7-T8) received vehicle or 5 mg/kg of the GC dexamethasone (DEX) at 5 min post-lesion and were sacrificed 2 or 4 h after surgery. Another group of SCI rats received vehicle or intensive DEX treatment (5 min, 6 h, 18 h and 46 h post-lesion) and were sacrificed 48 h after surgery. The number of NADPH-d positive neurons or Fos immunoreactive nuclei was studied by computer-assisted image analysis in superficial dorsal horn (Laminae I-III) and central canal area (Lamina X) below the lesion. While constitutive Fos immunoreactive nuclei were sparse in controls, SCI increased Fos expression at 2 and 4 h after injury. DEX treatment significantly enhanced the number of Fos positive nuclei in Laminae I-III by 4 h after transection, although the response was not maintained by intensive steroid treatment when tested at 48 h after SCI. NADPH-d positive neurons in Laminae I-III increased at 2 and 4 h after SCI while a delayed increased was found in central canal area (Lamina X). DEX treatment decreased NADPH-d positive neurons to sham-operated levels at all time points examined. Thus, while GC stimulation of Fos suggests activation of neurons involved in sympathetic outflow and/or pain, down-regulation of NADPH-d indicates attenuation of nociceptive outflow, considering the role of enzyme-derived nitric oxide in pain-related mechanisms. Differential hormonal effects on these molecules agree with their localization in different cell populations.

Immunocytochemical evidence for a progesterone receptor in neurons and glial cells of the rat spinal cord

Using the KC 146 monoclonal antibody recognizing the B-form of the progesterone receptor (PR) and immunocytochemical techniques, we investigated if PR-immunoreactive cells are present in the rat spinal cord. Neurons from ventral horn Lamina IX, glial cells in gray and white matter and ependymal cells were PR-positive. Evidence for estrogen-inducibility of PR in ovariectomized rats was not observed. There were no significant gender differences in neuronal PR immunostaining intensity in the spinal cord, measured by computerized image analysis. In pituitary and uterus from estrogenized female rats, PR showed a strict nuclear localization, whereas in neurons and glial cells of the spinal cord, PR localized in cytoplasm and/or nucleus and in some cell processes. This receptor may be implicated in some of the biological effects of progesterone described in the spinal cord.

Glucocorticoid regulation of motoneuronal parameters in rats with spinal cord injury

1. Glucocorticoids exert beneficial effects after acute CNS injury in humans and experimental animals. To elucidate potential mechanisms of glucocorticoid action in the lesioned spinal cord, we have studied if treatment with dexamethasone (DEX) modulated the neurotrophin binding receptor p75 (p75NTR) and choline acetyltransferase (ChAT), a marker of neuronal functional viability. 2. Rats with a sham operation or with spinal cord transection at the thoracic level received vehicle or DEX several times postlesion and were sacrificed 48 hr after surgery. The lumbar region caudal to the lesion was processed for p75NTR and ChAT immunoreactivity (IR) using quantitative densitometric analysis. 3. We observed that p75NTR-IR was absent from ventral horn motoneurons of sham-operated rats, in contrast to strong staining of neuronal perikaryon in TRX rats. Administration of DEX to TRX rats had no effect on the number of neuronal cell bodies expressing p75NTR-IR but significantly increased the number and length of immunostained neuronal processes. 4. Furthermore, spinal cord transection reduced ChAT immunostaining of motoneurons by 50%, whereas DEX treatment reverted this pattern to cells with a strong immunoreaction intensity in perikaryon and cell processes. 5. It is hypothesized that increased expression of p75NTR in cell processes and of ChAT in motoneurons may be part of a mechanism by which glucocorticoids afford neuroprotection, in addition to their known antiinflammatory effects.

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.

Distribution of adrenocorticoid receptors in the rat CNS measured by competitive PCR and cytosolic binding

Combined quantitative polymerase chain reaction (PCR) and cytosolic binding assay techniques are used to measure mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) mRNA, Kd, and Bmax in various rat central nervous system (CNS) regions, namely amygdala, hypothalamus, hippocampus, cortex, pituitary, and cervical, thoracic, and lumbar spinal cord. Two internal standards (i.s.) cDNA were cloned for quantitative PCR purposes. The i.s. templates differed from the respective wild-type (wt) templates for a single base-pair mutation introduced by PCR that generated a unique restriction site, thus allowing amplification products arising from coamplification of wt and i.s. to be distinguished. Results show that cerebellum, which displayed average Bmax values for both receptors, contained the highest level of MR and GR mRNA. Hippocampus also had a high level of MR mRNA. Low mRNA content was found in the hypothalamus for MR and GR as well as in the cortex for GR. High Bmax values for both MR and GR were found in the lumbar spinal cord, despite a modest mRNA content. The lowest Bmax values were found in the cortex for both receptors. It is, therefore, concluded that mRNA content and Bmax are not closely correlated in the rat CNS. These data suggest a differential regulation of various adrenocorticoid receptor isoforms. Moreover, this quantitative PCR method is very sensitive and can be used to assay small amounts of material in order to obtain absolute measurements of mRNA expression.

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.

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.

Time-dependent effects of dexamethasone on glutamate binding, ornithine decarboxylase activity and polyamine levels in the transected spinal cord

Evidence exists that the spinal cord is a glucocorticoid-responsive tissue, and glucocorticoids have beneficial effects in cases of spinal cord injury. Using sham-operated rats, spinal cord transected (TRX) rats, and TRX animals receiving dexamethasone (DEX) 5 min or 24 h post-lesion, we have examined the following GC-sensitive parameters 6 h after DEX treatment: (1) binding of glutamate to NMDA-sensitive receptors; (2) the activity of ornithine decarboxylase (ODC); and (3) levels of polyamines. We found that glutamate binding in the dorsal horn (Laminae 1-2) and central canal were upregulated in TRX rats, whereas DEX had an additional stimulatory effect. 24 h post-lesion, glutamate binding was unmodified in TRX or TRX+DEX rats. ODC activity was increased 10-fold in rats killed on the day of transection but only 2-fold 24 h post-lesion. DEX reduced ODC activity on transection day but highly increased it when given 24 h after surgery. The content of the polyamines spermidine and spermine were unchanged after TRX or DEX treatment, in contrast to putrescine which increased in TRX rats and further increased in TRX+DEX rats when measured the day post-lesion. Thus, parallel increases in ODC and putrescine 1 day after the lesion, suggest that glucocorticoid effects on growth responses due to polyamines may develop at a late period. The changes of glutamate binding in the dorsal horn and central canal due to early glucocorticoid treatment, further suggest hormonal modulation of neurotransmission in sensitive areas of the deafferented spinal cord.