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E Costa

Publications and source records attributed to E Costa.

At least 199 records · Page 11Linked to original sources
PubMed1991

gamma-Aminobutyric acidA receptor heterogeneity in rat central nervous system: studies with clonazepam and other benzodiazepine ligands.

The properties of [3H]clonazepam, [3H]diazepam and [3H]zolpidem (N,N,6[trimethyl-2-(4-methyl-phenyl)imidazo[1,2-a]pyridine-3-acetamide hemitratrate) binding to synaptic membranes of cerebellum, cortex, olfactory bulb, striatum and spinal cord of rat were compared to the binding properties of [3H]flunitrazepam, [3H]flumazenil and [3H]midazolam. In the cerebellar, cortical and olfactory bulb membranes, the density of high-affinity binding sites of all these tritiated benzodiazepine (BZ) ligands is almost identical. In contrast, in the striatum, the density of [3H]clonazepam and [3H]zolpidem binding sites is approximately 60 and 30%, respectively, of the density of [3H]diazepam, [3H]flunitrazepam or [3H]flumazenil sites. In spinal cord membranes, the number of high-affinity binding sites of [3H]clonazepam and [3H]zolpidem is less than 20% of the number of binding sites for [3H]diazepam, [3H]flunitrazepam, [3H]flumazenil and [3H]midazolam. Moreover, the displacement of [3H]flunitrazepam from spinal cord membranes by clonazepam and zolpidem was characterized by high IC50 values and Hill slopes significantly less than 1. Because [3H]BZ ligand binding in the spinal cord is enhanced by gamma-aminobutyric acid (GABA), these data suggest that different regions of the rat central nervous system may contain different GABA-BZ receptor subtypes. The different pharmacological properties of clonazepam, diazepam and zolpidem (i.e., regarding their ability to enhance bicuculline seizure threshold, to decrease locomotor activity, to induce ataxia or to elicit anticonflict action) further support the concept that in the rat central nervous system preferential occupancy of heterogeneous GABAA receptors by these drugs can be related to their effects on behavior.

Animals↗
PubMed1991

Mechanism of nerve growth factor mRNA regulation by interleukin-1 and basic fibroblast growth factor in primary cultures of rat astrocytes.

Neonatal rat cortical astrocytes in primary culture synthesize and secrete nerve growth factor (NGF). Interleukin-1 beta(IL-1) and basic fibroblast growth factor (bFGF) treatment of astrocytes increased NGF mRNA content by about 2-fold. The effect of these two factors was specific, because other growth factors, such as tumor necrosis factor-alpha, insulin-like growth factor-1, and epidermal growth factor, failed to change NGF mRNA content. The concentrations of IL-1 and bFGF causing half-maximal stimulation were 1 unit/ml and 1 ng/ml, respectively. The increase in NGF mRNA elicited by IL-1 and bFGF was maximal at 3 hr of incubation. In the presence of IL-1 this increase persisted for 36 hr, whereas in the presence of bFGF the initial increase in NGF mRNA was followed by a decrease to 50% of control levels after 24 hr of incubation. Readdition of bFGF after 24 hr of treatment gave a similar increase in NGF mRNA content, suggesting that the decrease at 24 hr was not due to receptor desensitization. The effect of IL-1 was reversible, because removal of IL-1 after 3 hr of incubation resulted in a decrease of NGF mRNA content to control levels by 6 hr, whereas a readdition of IL-1 at this time led to a 2-3-fold increase in NGF mRNA content after an additional 3 hr of treatment. This second increase in NGF mRNA was also maintained for several hours. The combined treatment of astrocytes with maximally effective doses of IL-1 and bFGF produced an additive increase in NGF mRNA content, suggesting that different mechanisms are operative. Treatment of astrocytes with cycloheximide increased (about 6-fold) NGF mRNA content, and this content failed to increase further with IL-1 or bFGF treatment. Experiments using actinomycin D indicated that IL-1 increased the stability of the NGF mRNA. bFGF treatment failed to change this parameter. Thus, IL-1 increases NGF mRNA content in astrocytes, at least in part, by stabilizing mRNA, whereas bFGF does not affect mRNA stability but may act at the level of NGF gene transcription.

Animals↗
PubMed1991

Stimulation of nerve growth factor biosynthesis in developing rat brain by reserpine: steroids as potential mediators.

The stimulation of beta-adrenergic receptors by isoproterenol increases nerve growth factor (NGF) biosynthesis in C6 rat glioma cells, suggesting that norepinephrine may regulate NGF biosynthesis in vivo. We have tested this hypothesis in 21-day-old rats by depleting catecholamine stores with reserpine. Northern blot analysis of NGF mRNA, in combination with a two-site enzyme immunoassay for NGF, showed that depletion of catecholamines was associated with a 3-fold increase in NGF mRNA, which was followed by a significant increase in the NGF content of cerebral cortex. The increase in NGF mRNA was most marked 9 hr after reserpine administration (2 mg/kg, subcutaneously) and was no longer apparent 24 hr after drug administration, when brain monoamine stores were still depleted. Moreover, the lowest dose of reserpine that significantly increased NGF mRNA levels induced only a small change in the content of cortical catecholamines. These results suggest that reserpine mediates the increase in NGF production by a mechanism other than monoamine depletion. Because reserpine increases plasma glucocorticoid concentrations through the pituitary-adrenal axis, we investigated whether adrenal steroids could be responsible for the induction of NGF biosynthesis. The effect of reserpine on NGF biosynthesis was abolished in adrenalectomized rats. Moreover, dexamethasone, a synthetic glucocorticoid, given at a dose of 0.5 mg/kg, subcutaneously, increased the amount of NGF mRNA and NGF in cerebral cortex. NGF biosynthesis in the central nervous system may, thus, be regulated by adrenocortical hormonal secretion.

Adrenal Cortex Hormones↗
PubMed1990

Regulation of nerve growth factor receptor mRNA content by dexamethasone: in vitro and in vivo studies.

Northern blot hybridization analysis was used to study regulation of nerve growth factor receptor (NGFR) mRNA content by glucocorticoids. Treatment for 6 h with dexamethasone (1 microM) caused a 40% decrease of NGFR mRNA content in PC12 cells and a 60% decrease in C6-2B glioma cells which was time and dose dependent. Dexamethasone (1 microM/kg) administered s.c. for two days to 21-day-old rats, elicits a 60% decrease in NGFR mRNA content in septum. These results suggest that the expression of NGFR gene in the brain could be inhibited by endogenous glucocorticoids. Whether dexamethasone inhibits NGFR gene expression by directly affecting cis-regulatory elements in the promoter regions of the gene remains to be elucidated.

Adrenal Gland Neoplasms↗
PubMed1990

The peripheral-type benzodiazepine receptor is functionally linked to Leydig cell steroidogenesis.

Testicular mitochondria were previously shown to contain an abundance of peripheral-type benzodiazepine recognition site(s)/receptor(s) (PBR). We have previously purified, cloned, and expressed an Mr 18,000 PBR protein (Antkiewicz-Michaluk, Mukhin, A. G., Guidotti, A., and Krueger, K. E. (1988) J. Biol. Chem. 263, 17317-17321; (Sprengel, R., Werner, P., Seeburg, P. H., Mukhin, A. G., Santi, M. R., Grayson, D. R., Guidotti, A., and Krueger, K. E. (1989) J. Biol. Chem. 264, 20415-20421); and in this report, we present evidence that PBR are functionally linked to Leydig cell steroid biosynthesis. A spectrum of nine different ligands covering a range of over 4 orders of magnitude in their affinities for PBR were tested for their potencies to modulate steroidogenesis in the MA-10 mouse Leydig tumor cell line. The Ki for inhibition of [3H]1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide binding and the EC50 for steroid biosynthesis for this series of compounds showed a correlation coefficient of r = 0.95. The most potent ligands stimulated steroid production by approximately 4-fold in these cells. This stimulation was not inhibited by cycloheximide, unlike human chorionic gonadotropin- or cyclic AMP-activated steroidogenesis. The action of PBR ligands was not additive to stimulation by human chorionic gonadotropin or cyclic AMP, but was additive to that of epidermal growth factor, another regulator of MA-10 Leydig cell steroidogenesis. Moreover, PBR ligands stimulated, in a dose-dependent manner, pregnenolone biosynthesis by isolated mitochondria when supplied with exogenous cholesterol. This effect was not observed with mitoplasts (mitochondria devoid of the outer membrane). Cytochrome P-450 side chain cleavage activity, as measured by metabolism of (22R)-hydroxycholesterol, was not affected by PBR ligands in intact cells. Similar results were also obtained with purified rat Leydig cells. In conclusion, PBR are implicated in the acute stimulation of Leydig cell steroidogenesis possibly by mediating the entry, distribution, and/or availability of cholesterol within mitochondria.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

[3H]D-serine labels strychnine-insensitive glycine recognition sites of rat central nervous system.

In the central nervous system, glycine binds to two recognition sites; one of them (G2), associated with the glutamate receptor, is insensitive to strychnine. Strychnine-insensitive sites were predominant in the forebrain areas and bound D-serine and D-alanine better than the respective L stereoisomers. [3H]D-serine was a more selective radioligand than [3H]glycine for the strychnine-insensitive sites. In the forebrain, the binding of both ligands was inhibited by the putative G2 receptor antagonists, 7-chlorokynurenate and 3-amino-1-hydroxy-2-pyrrolidone, while in pons and in spinal cord only the latter drug was effective. This may indicate the heterogeneity of strychnine-insensitive glycine recognition sites.

Animals↗
PubMed1990

Baclofen inhibits with high affinity an L-type-like voltage-dependent calcium channel in cerebellar granule cell cultures.

In primary cultures of cerebellar granule cells, D,L baclofen (p-chlorophenyl-GABA) inhibited approximately 50% of the calcium-45 influx induced with cell depolarization. The half maximal effective concentration for baclofen was 4 nM. Basal calcium influx was not influenced by baclofen thus suggesting that its inhibitory action could be exerted via a voltage dependent calcium channel (VDCC). Whole-cell recordings by patch-clamp technique showed a calcium current that appeared to be similar to the reported L-type VDCC. Nanomolar concentrations of baclofen also inhibited this calcium current by about 60%. However, in order for baclofen to be active, it needed to be placed into the incubation buffer at least five minutes before patching a cell raising the possibility that baclofen may be acting to inhibit the VDCC via a second messenger system.

Animals↗
PubMed1990

A study of diazepam binding inhibitor (DBI) processing products in human cerebrospinal fluid and in postmortem human brain.

Diazepam binding inhibitor (DBI) is a neuropeptide of 11 kDa molecular size and is unevenly distributed in human and rat brain. It appears to function as a negative allosteric modulator of GABAA receptors. In the present paper, using antibodies directed against several synthetic peptides, which correspond to selective regions of human DBI (DBI 51-70, DBI 37-50, DBI 81-101), it is shown that DBI is processed into at least 6 peptide fragments in both postmortem human brain and in cerebrospinal fluid (CSF). One of these fragments was identified as the synthetic DBI 51-70 fragment (an eikosaneuropeptide, ENP) by combined chromatographic procedures. Immunoblotting analysis of the other fragments, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE), revealed an apparent molecular size, ranging from 3-4 kDa for four of them and a larger molecular form of 8 kDa. On the basis of the immunological properties, a tentative amino acid sequence was deduced.

Acetates↗
PubMed1990

CSF diazepam-binding inhibitor in alcoholics and normal controls.

Diazepam-binding-inhibitor (DBI) and gamma-aminobutyric acid (GABA) are colocalized in neurons in the brain. This system has been implicated in anxiety and in the regulation of corticotropin-releasing hormone (CRH) secretion. Alcohol has direct and indirect effects on the functioning of GABAA receptors. Abstinent alcoholics are, on the average, more anxious than controls. In tests of animal behavior, DBI has anxiogenic, and alcohol has anxiolytic potency. Therefore, we compared alcoholic patients and healthy controls for cerebrospinal fluid (CSF) levels of DBI, and looked for a correlation between CSF levels of DBI and CRH. There was no significant difference in CSF concentrations of DBI between the two groups and no significant correlation between CSF DBI and our measure of anxiety. However, there was a significant positive correlation between CSF levels of DBI and CRH in both the alcoholic and control groups.

Adult↗
PubMed1990

Neurosteroids act on recombinant human GABAA receptors.

The endogenous steroid metabolites 3 alpha,21dihydroxy-5 alpha-pregnan-20-one and 3 alpha-hydroxy-5 alpha-pregnan-20-one potentiate GABA-activated Cl- currents recorded from a human cell line transfected with the beta 1, alpha 1 beta 1, and alpha 1 beta 1 gamma 2 combinations of human GABAA receptor subunits. These steroids are active at nanomolar concentrations in potentiating GABA-activated Cl- currents and directly elicit bicuculline-sensitive Cl- currents when applied at micromolar concentrations. The potentiating and direct actions of both steroids were expressed with every combination of subunits tested. However, an examination of single-channel currents recorded from outside-out patches excised from these transfected cells suggests that despite the common minimal structural requirements for expressing steroid and barbiturate actions, the mechanism of GABAA receptor modulation by these pregnane steroids may differ from that of barbiturates.

Benzodiazepines↗
PubMed1990

Gangliosides normalize distorted single-cell intracellular free Ca2+ dynamics after toxic doses of glutamate in cerebellar granule cells.

Glutamate-induced delayed neurotoxicity after abusive and paroxismal activation of its receptors has been proposed to depend upon a sustained increase in intracellular free Ca2+ [( Ca2+]i). To elucidate the temporal and causal relationship between glutamate-induced changes in [Ca2+]i and neuronal death, we simultaneously studied the dynamics of [Ca2+]i changes in single neurons with the acetoxymethyl ester of fura-2 and the cell viability by imaging the nuclear penetration of propidium iodide. The main difference between toxic (50 microM) and nontoxic (5 microM) doses of glutamate is the lack of regulation in [Ca2+]i 20 min after glutamate is removed. This protracted rise in [Ca2+]i in a single cell is correlated with (r = 0.87, P less than 0.01, Spearman's test), and consequently predictive of, the time of appearance of neuronal death, as measured by propidium iodide fluorescence. In addition, the glutamate receptor antagonists dibenzocyclohepteneimine (MK-801) and 3,3-(2-carboxypiperazine-4-yl)propyl 1-phosphate reduce the acute increase of [Ca2+]i induced by glutamate but fail to revert the protracted increase of [Ca2+]i, elicited by toxic doses of glutamate. In contrast, the ganglioside GM1 and the semisynthetic lysoGM1 with N-acetylsphingosine (LIGA-4) and lysoGM1 with N-dichloroacetylsphingosine (LIGA-20) failed to change the immediate rise of [Ca2+]i elicited by glutamate but prevented the protracted increase in [Ca2+]i after toxic doses of glutamate. Voltage-dependent Ca2+ channel blockers (nifedipine, etc.) did not change the initial or protracted responses to glutamate.

Animals↗
PubMed1990

Serum and depolarizing agents cause acute neurotoxicity in cultured cerebellar granule cells: role of the glutamate receptor responsive to N-methyl-D-aspartate.

The life span of neonatal rat cerebellar granule cells, grown in basal minimal Eagle's medium containing 10% (vol/vol) fetal calf serum, was extended to 21-30 days by weekly supplementation with glucose. Addition of 1% fetal calf serum to the culture at 14 days killed 85% of the cells within 1 hr. This lethal effect could be prevented by the N-methyl-D-aspartate (NMDA) receptor antagonists dibenzocyclohepteneimine (MK-801) and 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP). These findings suggested that the glutamate in the serum caused the dramatic neuronal death through action on the NMDA receptor. Indeed, a 5-min incubation in a Locke physiological salt solution containing 20 microM glutamate and 5 microM glycine killed 55-90% of the cells. This acute toxicity could be prevented by a lyso-GM1 ganglioside with N-acetylated sphingosine. The relatively low glutamate content of the sera analyzed suggests that factors in addition to glycine potentiate serum neurotoxicity. The above noted antagonists of the NMDA receptor also greatly reduced the lethal effect of depolarization by 90 mM KCl or 10 microM veratridine. Therefore, it is likely that the toxicity of the depolarizing agents is mediated by glutamate released from the cells. It is concluded that survival of cerebellar neurons in primary culture may be strongly affected by unsuspected neurotoxic phenomena elicited by brief action of a rather low glutamate concentration.

Animals↗
PubMed1990

Down-regulation of protein kinase C protects cerebellar granule neurons in primary culture from glutamate-induced neuronal death.

Exposing primary cultures of cerebellar granule neurons to 100 nM phorbol 12-myristate 13-acetate (PMA) for 24 hr decreases the Ca2+/phosphatidylserine/diolein-dependent protein kinase C (PKC; ATP:protein phosphotransferase, EC 2.7.1.37) by approximately 90% in the 100,000 x g supernatant and pellet fractions of neuronal culture homogenates. Immunoblot analysis of the homogenates with polyclonal antibodies raised against either the beta-type PKC peptide or total rat brain PKC reveals a virtual loss of 78-kDa PKC immunoreactivity in the supernatant and a marked decrease of PKC immunoreactivity in the pellet. Exposure of the cultures to 50 microM glutamate for 15 min (no Mg2+) induces the translocation of supernatant PKC immunoreactivity to the pellet. Such translocation persists after glutamate withdrawal and is followed by a progressive increase in neuronal death, which begins 2 hr later. Neuronal death approaches completion in about 24 hr. PMA-induced down-regulation of PKC decreases glutamate-elicited neurotoxicity. Yet, the culture exposure to 100 nM PMA fails to decrease the high-affinity binding of [3H]glutamate to neuronal membranes and does not reduce glutamate-induced activation of ionotropic or metabolotropic receptors (assayed as total membrane current measured in whole-cell voltage-clamped neurons, 45Ca2+ uptake in intact monolayers, inositolphospholipid hydrolysis, and transcriptional activation and translation of c-fos mRNA). Moreover, the immediate cell-body swelling and activation of spectrin proteolysis elicited by glutamate remain unchanged. On the other hand, PMA-induced PKC down-regulation reduces any increase in 45Ca2+ uptake or Ca2(+)-dependent proteolysis (measured as spectrin degradation) after glutamate withdrawal. These results support the view that PKC translocation is operative in glutamate-induced destabilization of cytosolic ionized Ca2+ homeostasis and neuronal death.

Animals↗
PubMed1990

Abusive stimulation of excitatory amino acid receptors: a strategy to limit neurotoxicity.

Glutamate is an important excitatory amino acid at many central nervous system synapses. After its release from presynaptic nerve terminals, glutamate transiently binds to specific neuronal membrane receptors, which transduce its signal by the generation of intracellular second messengers before being rapidly cleared from the synapse. However, during ischemia, the glutamate concentration at synapses surrounding the focal lesion can be increased for sustained periods of time, resulting in abusive stimulation of glutamate receptors that can eventually be neurotoxic. To develop drugs capable of selectively blocking the pathological effects of glutamate in neurons surrounding ischemic lesions while leaving the physiological actions of glutamate in nonlesioned areas of the brain unaffected, it is essential to delineate glutamate-induced intracellular events that are specific to receptor abuse. This article describes the intracellular sequelae of physiological and pathological glutamate receptor activation and suggests potential targets for such receptor abuse-dependent antagonists (RADAs).

Animals↗
PubMed1990

N-methyl-D-aspartate-sensitive glutamate receptors induce calcium-mediated arachidonic acid release in primary cultures of cerebellar granule cells.

In primary cultures of cerebellar granule cells, glutamate, aspartate, and N-methyl-D-aspartate (NMDA) induced a dose-dependent release of [3H]arachidonic acid ([3H]AA) which was selective for these agonists and was inhibited by NMDA receptor antagonists. The agonist-induced [3H]AA release was reduced by quinacrine at concentrations that inhibited phospholipase A2 (PLA2) but affected neither the activity of phospholipase C (PLC) nor the hydrolysis of phosphoinositides induced by glutamate or quisqualate. Thus, the increased formation of AA was due to the receptor-mediated activation of PLA2 rather than to the action of PLC followed by diacylglycerol lipase. The receptor-mediated [3H]AA release was dependent on the presence of extracellular Ca2+ and was mimicked by the Ca2+ ionophore ionomycin. Pretreatment of granule cells with either pertussis or cholera toxin failed to inhibit the receptor-mediated [3H]AA release. Hence, in cerebellar granule cells, the stimulation of NMDA-sensitive glutamate receptors leads to the activation of PLA2 that is mediated by Ca2+ ions entering through the cationic channels functioning as effectors of NMDA receptors. A coupling through a toxin-sensitive GTP-binding protein can be excluded.

Animals↗
PubMed1990

Endogenous benzodiazepine receptor ligands in human and animal hepatic encephalopathy.

The role of endogenous benzodiazepine receptor ligands in the pathogenesis of hepatic encephalopathy was studied in humans and in rat models of hepatic encephalopathy. Endogenous benzodiazepine ligands were extracted from rat brain and human CSF by acid treatment and purification by HPLC. Detection and partial characterization of these endogenous benzodiazepine ligands were carried out using both radioreceptor binding assays and radioimmunoassays with anti-benzodiazepine antibodies. Four different benzodiazepine receptor ligands were identified in human and rat tissue, two of which may be diazepam and desmethyldiazepam, based on elution profiles and anti-benzo-diazepine antibody reactivity. Human CSF and serum from patients with hepatic encephalopathy contained approximately 10 times more endogenous benzodiazepine receptor ligand than CSF from controls or nonencephalopathic patients with liver disease. The levels of brain benzodiazepine receptor ligand compounds were also increased approximately 10-fold in rats suffering from fulminant hepatic failure, but not in rats with portacaval shunts, a model of chronic hepatic disease. The increased concentrations of these substances could be behaviorally significant and may contribute to the pathogenesis of hepatic encephalopathy.

Adult↗