Epidermal growth factor and basic fibroblast growth factor protect dopaminergic neurons from glutamate toxicity in culture

In this report we characterize the toxicity of the excitatory amino acid L-glutamate with respect to dopaminergic neurons cultured from embryonic rat mesencephalon. We also demonstrate that two growth factors, epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), can protect these neurons from damage. Micromolar concentrations of L-glutamate, as well as agonists that specifically activate N-methyl-D-aspartate (NMDA) and non-NMDA receptors, are all toxic to dopamine neurons in a concentration-dependent manner, as reflected by decreases in high-affinity dopamine uptake and confirmed by decreases in numbers of tyrosine hydroxylase-immunoreactive neurons. Although the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione could attenuate the effects of quisqualate, treatment with this antagonist could not eliminate the effects of glutamate itself. Similarly, (+/-)-2-amino-5-phosphonopentanoic acid was effective against NMDA toxicity but could not protect cells from quisqualate toxicity. Thus, each type of receptor could mediate neurotoxicity independently of the other. The presence of EGF or bFGF in the culture medium conferred a relative resistance of dopaminergic neurons to glutamate and quisqualate neurotoxicity by increased glutamate transport. However, treatment of the cultures with L-trans-pyrrolidine-2,4-dicarboxylic acid, an inhibitor of glutamate transport, attenuated but did not eliminate the protective effects of both growth factors against glutamate toxicity. When cultures were incubated with conditioned medium from growth factor-treated cultures, neuroprotection was also achieved. These results suggest that both EGF and bFGF can protect neurons from neurotoxicity in culture by increasing the capacity of the culture for glutamate uptake as well as by the secretion of soluble factors into the medium.

Glutamate regulation of GDNF gene expression in the striatum and primary striatal astrocytes

The aim of this study was to investigate the regulation of glial cell line-derived neurotrophic factor (GDNF) mRNA by activation of glutamate receptors in the rat striatum. We observed an increase in GDNF mRNA levels in the adult rat striatum after administration of subseizure doses of N-methyl-D,L-aspartic acid (NMA) and kainic acid. Since it is unclear whether the upregulation of GDNF occurred in neurons or astrocytes within the striatum, we further investigated whether GDNF gene expression in primary striatal astrocytes in culture could be regulated by glutamate receptor activation. We found that treatment of the cultures with NMA and kainic acid similarly upregulated GDNF gene expression as observed in vivo, suggesting that striatal astrocytes express functional glutamate receptors. Immunocytochemical and nuclease protection analysis revealed that striatal astrocytes expressed the NMDA-R1 subunit. These findings suggest the regulation of GDNF mRNA in the striatum may be mediated by excitation of glutamate receptors via glutamatergic cortical afferents.

Oral administration of L-arginine and captopril in rats prevents chronic renal failure by nitric oxide production

The effect of oral supplementation of L-arginine, the substrate of nitric oxide, (1.25 g/liter water) and captopril (15 mg/liter water) was studied in 5/6 nephrectomized rats for a period of three months. N-omega-nitro L-arginine, a nitric oxide synthase inhibitor, was given orally (70 mg/liter water) with or without L-arginine or captopril. The urinary excretion of nitrite (NO2) + nitrate (NO3), the known metabolites of nitric oxide, was taken as an index of nitric oxide production. Chronic renal failure rats were characterized by a low creatinine clearance, high FENa%, proteinuria, hypertension and a low urinary excretion of NO2 + NO3; 0.152 +/- 0.06 (P < 0.001) nmol/micrograms creatinine compared with 0.481 +/- 0.004 (P < 0.001) in normal rats and 0.479 +/- 0.11 (P < 0.001) in untreated sham-operated rats. Both L-arginine and captopril were effective in the normalization of all these parameters. The combination of L-arginine and captopril had no additive effects. The nitric oxide synthase inhibitor significantly diminished the captopril beneficial effect. It is concluded that chronic renal failure in rats is a low nitric oxide production state. The supplementation of L-arginine is shown to overcome this condition. It is suggested that the beneficial effect of captopril on chronic renal failure is through a specific L-arginine--nitric oxide synthase--nitric oxide pathway.

Striatal TGF-alpha: postnatal developmental expression and evidence for a role in the proliferation of subependymal cells

Transforming growth factor alpha (TGF-alpha) is expressed in the brain and affects cells by binding to the epidermal growth factor receptor (EGF-R). Using a ribonuclease protection assay, we found that TGF-alpha steady state mRNA levels in the mouse striatum peak during the first week of postnatal life. Temporally this peak correlates with the height of gliogenesis in the subependymal layer (SEL), which lies along the striatal border of the lateral ventricle. In vitro studies demonstrate that TGF-alpha can stimulate the proliferation of astrocytes, so glial fibrillary acidic protein (GFAP) mRNA levels were measured as well and it was observed that the peak of GFAP expression followed that of TGF-alpha by 1 week. Furthermore, in a TGF-alpha deficient mouse, waved-1 (wa-1), a significant reduction of GFAP mRNA levels and immunostaining for GFAP was found in the striatum. Bromodeoxyuridine labeling combined with immunohistochemistry of normal postnatal day 6 brain showed that the proliferating cells in the SEL are EGF-R immunoreactive. In the waved-1 SEL, there were fewer BrdU positive cells and there was a reduced level of [3H]thymidine incorporation. EGF-R immunoreactive cells were found in the SEL of the adult mouse brain. Taken together, our data suggest that the TGF-alpha/EGF-R signaling pathway is involved in postnatal mitogenic events in the brain.

Prenatal corticosterone increases spontaneous and d-amphetamine induced locomotor activity and brain dopamine metabolism in prepubertal male and female rats

Recently, both glucocorticoid receptor immunoreactivity and glucocorticoid receptor messenger RNA levels were found in multiple brain areas, especially in the neuroepithelium during the late prenatal development of the rat brain. To better understand the potential influence of stress on fetal brain development by release of maternal adrenocortical steroids, we have investigated the effects of corticosterone administration to pregnant rats on the locomotor activity of their prepubertal offspring. On day 16 of pregnancy female rats were implanted with either placebo or corticosterone pellets (release of 2.4 mg/day for seven days). After birth their offspring were nursed by foster mothers to avoid any postnatal effects of the corticosterone pellets. At three weeks of age, the offspring were tested for spontaneous motor behaviours. Both male and female offspring from corticosterone treated mothers showed significantly increased spontaneous ambulation, motility and rearing compared to placebo treated groups. No significant sex differences were found in locomotor activity between male and female offspring from placebo groups. Following d-amphetamine (1.5 mg/kg) treatment, a preferential dopamine releasing agent, we observed a significant increase in ambulation, motility and rearing activity in the male offspring treated with corticosterone. In the female offspring, only the rearing activity was significantly higher after d-amphetamine treatment in the prenatal corticosterone group compared with the placebo treated group. Basal dopamine metabolism (dihydroxyphenylacetic acid/dopamine ratio) was increased in the dorsal striatum and ventral striatum of male and female offspring from corticosterone-treated dams. In the male offspring, corticosterone treatment was associated with a disappearance of the right side dominance of dopamine metabolism in the dorsal striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Perinatal asphyxia increases bFGF mRNA levels and DA cell body number in the mesencephalon of rats

The present investigation was undertaken in order to study the long-term effects of perinatal asphyxia on basic fibroblast growth factor (bFGF) gene expression and the number of dopamine nerve cell bodies in the mesencephalon of the rat. Asphyxia was induced during birth for 19-20 min. A 30% increase in the number of tyrosine-hydroxylase immunoreactive (TH-IR) nerve cell bodies (i.e. dopamine-containing neurones) as well as a 50% increase in bFGF gene expression following asphyxia was found in the substantia nigra/ventral tegmental area 4 weeks after birth. The increase in bFGF mRNA levels may underlie the increase found in the number of dopamine cell bodies. The present results indicate that asphyxia during birth can prime the long-term development of the central nervous system.

Postprandial intestinal-derived chylomicron and chylomicron remnants in essential hypertensive patients before and after prolonged captopril therapy

The metabolism of the postprandial intestinal-derived lipoproteins, chylomicron and chylomicron remnants, is not known in patients with essential hypertension. After a fat meal, using the vitamin A test as a marker, retinyl palmitate was measured in the total plasma, chylomicron, and chylomicron remnant fractions in 14 untreated nondiabetic essential hypertensive patients with normal fasting lipids and lipoproteins. The vitamin A fat loading test was repeated in eight hypertensive patients after 3 months of captopril therapy. Fifteen matched normotensive subjects were used as controls. The untreated essential hypertensive patients had significantly higher chylomicron fraction concentration curves (AUC 17,469 +/- 2553 micrograms/L/h) P < .001 compared with the control group (AUC 13,208 +/- 1245 micrograms/L/h), by two-way analysis of variance with repeated measurements. After 3 months of captopril therapy, the chylomicron fraction (AUC 9701 +/- 1566 micrograms/L/h), and chylomicron remnants fraction (AUC 3487 +/- 580 micrograms/L/h) were much lower (P < .001) than before captopril therapy. Oral glucose tolerance tests were borderline in five of the eight hypertensives before captopril treatment but returned to normal after 3 months of therapy. In summary, postprandial intestinal-derived lipoprotein metabolism is altered in essential hypertensive patients. Captopril therapy caused significant improvement in the postprandial chylomicron metabolism.

Role of nitric oxide (EDRF) in radiocontrast acute renal failure in rats

This study was undertaken to examine the possible role of endothelium-derived relaxing factor (EDRF), identified as nitric oxide (NO), in the pathogenesis of radiocontrast-induced acute renal failure in rats. Normal and salt-depleted rats were monitored for 60 min or 24 h after radiocontrast administration. The administration of L-arginine to normal rats abolished the immediate decrease in p-aminohippurate clearance (CPAH) and attenuated the decrease in inulin clearance (CIn). The administration of NO synthase inhibitor to the salt-depleted animals resulted in a significantly more pronounced decrease in CPAH compared with both the control and the L-arginine-treated animals. The recovery of CIn 24 h after radiocontrast administration to the salt-depleted rats was significantly better in the L-arginine-treated rats than in either the control or inhibitor-treated groups. The administration of radiocontrast material resulted in a significant decrease in urinary guanosine 3',5'-cyclic monophosphate as well as NO2 + NO3 excretion. This decrease was significantly attenuated by L-arginine. Our results 1) suggest that NO plays a major role in the pathogenesis of radiocontrast-induced acute renal failure and 2) suggest a novel therapeutic approach, i.e., the use of L-arginine in this form of acute renal failure.

Deletion of T lymphocytes in human CD4 transgenic mice induced by HIV-gp120 and gp120-specific antibodies from AIDS patients

CD4, a T cell receptor for major histocompatibility complex class II antigen, is a key regulator of immunological reactivities. When engaged together with the T cell antigen receptor, CD4 enhances immune reactions, whereas when ligated independently of the antigen receptor CD4 inhibits the activation of T cells or initiates their deletion. CD4 serves also as a receptor for the human immunodeficiency virus (HIV), which binds the receptor with high avidity through its envelope molecule, gp120. Studies in tissue culture have shown that its affinity to CD4 gives the virus opportunities to utilize CD4-mediated signaling and to manipulate immunocytes. We show here in human CD4 transgenic mice that appropriately cross-linked HIV envelope protein causes massive deletion of HIV-reactive T cells in vivo.

Epidermal growth factor and basic fibroblast growth factor have independent actions on mesencephalic dopamine neurons in culture

Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) are both trophic for dopamine neurons in cultures of dissociated embryonic rat mesencephalon, but the significance of this apparent overlap in neurotrophic activity is not yet known. In this study, we investigated the mechanisms of action of these two growth factors and the potential relationship between them. Using a nuclease protection assay, we determined that bFGF mRNA was expressed in the cultures. Double-label immunocytochemistry revealed that bFGF immunoreactive material could be detected in tyrosine hydroxylase immunoreactive neurons and glial fibrillary acidic protein immunoreactive astrocytes. EGF treatment increased bFGF mRNA content per culture dish. As we have previously demonstrated that EGF exerts its dopaminergic neurotrophic activity via an intermediate cell type, studies were designed to address whether the pathway by which EGF acts on dopaminergic neurons is mediated by the release of bFGF. However, the trophic action of EGF on dopamine neurons, represented by high-affinity neuronal dopamine uptake, could not be blocked by immunoneutralization of bFGF, suggesting that the actions of EGF were not mediated by bFGF release. The time course of the effects of EGF and bFGF on dopamine uptake were similar, with significant increases detectable only after 5 days in culture. Both growth factors were active in the picomolar-to-nanomolar range with maximal trophic activity between 0.4 and 2.5 nM. EGF, however, was the more potent mitogen under these conditions. When cultures were simultaneously incubated with maximal concentrations of EGF and bFGF, the effect on dopamine uptake was significantly greater than with either growth factor alone and, in fact, approximated the sum of the individual effects. On the basis of these results we conclude that these growth factors have independent effects on dopamine neurons of the mesencephalon.

Second messenger regulation of mouse gonadotropin-releasing hormone gene expression in immortalized mouse hypothalamic GT1-3 cells

Using a transgenic mouse derived GnRH expressing neuronal cell line, GT1-3, we studied the effects of activation of cAMP, Ca2+ and protein kinase C pathways by forskolin, ionomycin and the phorbol ester phorbol 12-myristate 13-acetate (PMA), respectively, upon gonadotropin-releasing hormone (GnRH) secretion, cellular peptide content, mRNA and RNA primary transcript levels. Forskolin, ionomycin and phorbol ester all caused an increase in GnRH secretion in GT1-3 cells in a time and dose-dependent manner during a short-term (1 h) static incubation. Prolonged treatment with forskolin (10 microM), ionomycin (1 microM) and PMA (10 nM) for 12 or 24 h resulted in significant decreases in GnRH mRNA levels. Time-course studies showed that the increases in GnRH secretion stimulated by forskolin, ionomycin and PMA were gradually attenuated over time in parallel with the decreases in mRNA expression. In contrast, there were only small and variable changes in the GnRH cellular content. Studies using a GnRH antagonist (100 microM) suggested that the released GnRH has a negative feedback effect on its own secretion. However, co-incubation with the GnRH antagonist did not alter the inhibitory effects on GnRH mRNA levels by the secretagogues. Further studies on the transcriptional effects of forskolin, ionomycin and PMA on GnRH gene expression in GT1-3 cells revealed that all three secretagogues suppressed GnRH RNA primary transcript levels, with forskolin having a slower time course of action. Thus, the inhibition of cytoplasmic GnRH mRNA, and presumably its synthesis, after 12-24 h of secretagogue treatment may be due at least in part to a suppression of GnRH gene transcription.(ABSTRACT TRUNCATED AT 250 WORDS)

[Cerebral tuberous sclerosis and Coats disease]

A 10-year-old boy with known tuberous sclerosis since early childhood suffered from unilateral Coats' disease. Initially his parents noticed a divergent squint. On examination, well-advanced Coats' disease involving almost the entire retina including the macula was found. Visual acuity had decreased to 20/300. Intrascleral diathermy was successfully performed, and after painful secondary glaucoma, cryotherapy of the ciliary body became necessary. Coats' disease has been reported in a number of genetic diseases, most of them quite variable in their clinical manifestations. To the best of our knowledge this is the first description of Coats' disease associated with tuberous sclerosis, which is known to be of genetic origin. Although in Coats' disease no genetic predisposition has been proven to date, the growing list of genetic diseases associated with Coats' disease should be considered in patients presenting with this retinopathy.

Molecular cloning of the human homeobox gene goosecoid (GSC) and mapping of the gene to human chromosome 14q32.1

Goosecoid is a homeobox gene first isolated from a Xenopus dorsal lip cDNA library. Homologous genes have been isolated from mouse, zebrafish, and chick. In all species examined, the gene is expressed and plays an important role during the process of gastrulation in early embryonic development. We report here the cloning of the human goosecoid gene (GSC) from a genomic library and the sequence of its encoded protein. The genomic organization and protein sequence of the human gene are highly conserved with respect to those of its Xenopus and mouse counterparts: all three genes consist of three exons, with conserved exon-intron boundaries; the sequence of the homeodomain is 100% conserved in most vertebrates. Using somatic cell hybrid and chromosomal in situ hybridization, the gene was mapped to chromosome 14q32.1.

Characterization of parvalbumin cDNA clones and gene expression in normal and dystrophic mice of strain 129 ReJ

Parvalbumin is a calcium-binding protein found in fast-twitch skeletal muscles and selected cells in the brain. In several dystrophic mutants in the mouse, the parvalbumin content of skeletal muscles and brain is reduced and this deficiency appears to correlate with the inability of these mice to handle enhanced calcium uptake associated with the dystrophic process. In this study, two overlapping cDNA clones of 392 and 1268 base pairs were isolated from a mouse cDNA library in lambda gt11, characterized, and used as probes to study the involvement of the parvalbumin gene and its expression in various tissues of dystrophic mice of strain 129 ReJ. Southern blot analyses of restriction fragments of genomic DNA from normal and dystrophic mice indicate the same number and size of parvalbumin-specific gene fragments observed by other researchers, suggesting that the size of the Pva gene is the same in both normal and dystrophic mice of strain 129 ReJ. Northern blot analyses of total RNA from hind-limb muscles using cloned parvalbumin cDNA as probes revealed an abundant 800-nucleotide mRNA with lesser amounts of a 1000-nucleotide mRNA transcript in both normal and dystrophic mice of strain 129 ReJ. The amount of these mRNAs was reduced by 65-77% in dystrophic muscles preparations and was similar to the levels of beta-actin mRNA in these animals. These results suggest that parvalbumin gene expression is not down regulated in dystrophic mice of strain 129 ReJ.

Flow-cytometric determination of dehydrogenase activities in primary human gastrointestinal tumor cell lines

The activities of 6 dehydrogenases, lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G6PDH), isocitrate dehydrogenase (ICDH), glycerol-3-phosphate dehydrogenase (GDH), succinate dehydrogenase (SDH) and glutamate dehydrogenase (GLDH), determined by means of flow cytometry in 13 primary human gastrointestinal tumour cell lines, including 10 esophageal carcinomas, one gastric cancer, and 2 pancreatic cancers. Two-parametric measurements of specific dehydrogenase activities in single cells were performed with DAPI as fluorochrome for the nuclear DNA and with the fluorescent redox system of 5-cyano-2,3-ditolyl-tetrazolium chloride (CTC) which forms brilliant red formazan crystals upon reduction by cellular redox enzymes. Furthermore, with the aid of the calibration procedure reported previously [18] the enzyme activities were expressed as biochemical units. This application of tetrazolium salt technique for demonstrating dehydrogenase activities in human tumour cells by flow cytometry offers an alternative tool to characterize malignant tumors.

Mechanism of pepsin-catalyzed aminotranspeptidation reactions

1. The tetrapeptide Ala2-Nph2 (where Nph = p-nitrophenylalanyl) is treated by porcine pepsin to study the mechanism of aminotranspeptidation reactions. 2. The major initial product is Ala2-Nph and the major transpeptidation products are Nph2 and Nph3 accompanied by some Nph, a little Nph4, Ala2-Nph3 and Ala2-Nph4. 3. Oligomers of Nph greater than tetramers are formed near the end of the reaction. 4. In presence of [3H]Nph, no incorporation of Nph into the transpeptidation products is observed. 5. 18O-labeling shows extensive incorporation of 18O atoms from [18O]water in the carbonyl oxygens of Nph residues.

Effect of chronic cholesterol loading in the development of acute ischemic renal failure in rats

The effect of chronic cholesterol loading and lovastatin administration in renal artery clamping acute renal failure in rats is not known. Acute renal failure was induced by 60-min left renal artery clamping immediately after right nephrectomy. The changes in renal function after renal artery clamping in the hyperlipidemic rats were unexpected. The acute renal failure in the cholesterol-loaded groups was less severe than in the nonhyperlipidemic rats. The lovastatin administration had some favorable effect on renal function after ischemia; however, this effect was not additive to the high dietary cholesterol administration. Our results seems to favor the concept that in this special form of experimental renal ischemic acute renal failure, serum cholesterol levels, elevated through diet, may have protective effects with respect to renal tubular lesions during or following the acute ischemic insult.

Characterization of porcine bone sialoprotein: primary structure and cellular expression

Bone sialoprotein (BSP) is a highly glycosylated and sulphated phosphoprotein that is a major non-collagenous protein of bone. To further characterize the porcine protein and to study its expression during bone formation BSP cDNA clones were isolated from a porcine bone cDNA library. The primary sequence of the protein was derived from the nucleotide sequence of the largest cDNA insert and from the amino-terminal amino acid sequence determined by the automated Edman degradation procedure. When compared with sequences obtained from the human and rat BSPs 74% and 64% of the amino acids, respectively, were identical and a further 11% and 17%, respectively, were conservative replacements. Moreover, 60% of the amino acids in a concensus sequence derived from the primary sequences of mammalian BSPs were conserved with 16% conservative replacements. The two stretches of polyglutamic acid, through which the protein is capable of binding to hydroxyapatite, and an RGD motif that mediates cell attachment are retained in conserved sequences as are a number of potential sites of serine, threonine and tyrosine phosphorylation, glycosylation and tyrosine sulphation. Secondary structure prediction and hydrophilicity analysis indicate that the nascent BSP has an open flexible structure with the potential to form significant amounts of alpha-helix and some beta-sheet. In situ hybridization of fetal porcine bone with cRNA probes to porcine BSP mRNA shows that BSP is specifically expressed in differentiated osteoblasts on the surface of newly-forming bone trabeculae with especially high levels of hybridization at sites of de novo bone formation. The highly conserved features of BSP and its restricted distribution indicate an important role for this sialoprotein in the formation of bone.

Effect of sympathetic block demonstrated by triple-phase bone scan

The triple-phase bone scan is frequently used in the diagnosis of reflex sympathetic dystrophy although the etiology of the abnormal findings is not well established. This study evaluated the effect of increased blood flow secondary to sympathetic block on the triple-phase bone scan. In 15 reflex sympathetic dystrophy patients, all of whom had significant relief with sympathetic block, baseline and postsympathetic block bone scans were analyzed. There was a significant linear relationship between change in counts from baseline to postsympathetic block on the blood pool image and bone uptake image. As the blood pool and bone uptake counts increased, the likelihood of typical reflex sympathetic dystrophy findings on visual inspection also increased. These results strongly support the concept of increased vascular flow as the cause of increased periarticular uptake.

[Traumatic cataracts. Surgical methods and results in 106 patients]

Eyes with traumatic cataracts comprise a very heterogeneous group with respect to morphological and functional changes in the anterior and posterior segments. In the current study, data on 106 eyes with traumatic cataracts were analyzed. All eyes had undergone surgery at the Department of Ophthalmology at the University of Heidelberg between 1987 and 1991. There was a total of 55 blunt (group A) and 51 perforating (group 2) injuries. The male-to-female ratio was 2:1; the mean age was 54.8 (+/- 15.2) years in group 1 and 43.7 (+/- 19.1) years in group 2. In 91.4% of the eyes in group A without zonular defects (A1, n = 35) and 65% with zonular defects (A2, n = 20) a posterior chamber IOL was implanted. This value was 66.7% following perforating injuries (B, n = 51). Mean visual acuity was 0.68 +/- 0.29 for group A1, 0.56 +/- 0.35 for group A2, and 0.52 +/- 0.30 for group B. In 7.5% of all eyes additional surgery was required because of delayed complications. Overall, relatively good visual acuity was obtained, but results largely depended on the severity of traumatic damage to the eye and the status of the zonular/capsular apparatus.

Glucocorticoid receptor function in rat pituitary intermediate lobe is inhibited by an endogenous protein

Though glucocorticoids inhibit proopiomelanocortin (POMC) gene expression and POMC-derived peptide release from corticotroph cells of the anterior pituitary, the regulation of this gene by glucocorticoids is less clear in the melanotroph cell of the pituitary intermediate lobe. To examine the difference between glucocorticoid sensitivity of the anterior lobe (AL) and intermediate lobe (IL) of the pituitary we have examined glucocorticoid receptor (GR) status of these two tissues and the role glucocorticoids play in regulating IL POMC gene expression. The rate of in vivo GR gene transcription, measured by nuclear run-on assay was consistently higher in the pituitary neurointermediate lobe (NIL) compared with the AL of the same animals. On a concentration basis, cytoplasmic GR mRNA in the NIL was similar to that found in the AL, and GR binding using [3H]dexamethasone (DEX) as ligand demonstrated similar concentrations of specific [3H]DEX binding in acutely isolated AL and NIL tissues. The specific Type II corticosteroid receptor ligand RU28362 displaced [3H]DEX binding to levels equivalent to non-specific binding, thus indicating that DEX was binding only to Type II corticosteroid receptors. To assess the direct action of glucocorticoids on POMC gene expression, NIL cells were cultured for 7 days and then treated with DEX. One hour DEX treatment of NIL primary cultures had no effect on levels of POMC heteronuclear RNA levels; in contrast, DEX induced a rapid and potent inhibition of POMC heteronuclear RNA levels in cells treated with the protein synthesis inhibitor puromycin.(ABSTRACT TRUNCATED AT 250 WORDS)