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E Costa

Publications and source records attributed to E Costa.

At least 271 records · Page 15Linked to original sources
PubMed1987

Activation of specific glutamate receptor subtypes increases C-fos proto-oncogene expression in primary cultures of neonatal rat cerebellar granule cells.

In primary cultures of rat cerebellar granule cells the activation of excitatory amino acid receptors by 1-glutamate enhances the steady state level of c-fos proto-oncogene messenger RNA. This effect is blocked by magnesium (1mM) as well as by the glutamate receptor antagonist 2-amino-5-phosphono-valerate (APV). Among the other excitatory amino acid agonists N-methyl-D-Aspartate (NMDA) and quisqualate also increased c-fos mRNA content, the latter however to a significantly lesser extent, while kainate failed to modify the basal level of c-fos expression. The addition of the muscarinic agonist carbachol or of the inhibitory neurotransmitter GABA did not affect the basal level of c-fos mRNA. This data demonstrate for the first time that activation of signal transduction at a specific excitatory amino acid receptor subtype can increase the steady state level of c-fos proto-oncogene mRNA in primary culture of cerebellar neurons.

Animals↗
PubMed1987

Beta-adrenergic receptor regulation of NGF-mRNA content in rat C6-2B glioma cells.

In C6-2B astrocytoma cells the Beta NGF content and secretion rate are increased by isoproterenol activation of beta-adrenergic receptors (Schwartz and Costa, 1977). Utilizing poly (A+) RNA hybridization analysis with a cRNA probe for mouse Beta NGF it was found that isoproterenol activation of C6-2B cells produces also a 4 fold increase of the content of messenger RNA encoding Beta NGF. This increase is specifically antagonized by 1-propanolol, but not by phentolamine. Furthermore, addition of dibutyryl-cAMP induces an increase of Beta NGF mRNA content similar to that obtained with isoproterenol. These results are consistent with the hypothesis that regulation of Beta NGF synthesis in neuroglial cells may be modulated by beta-adrenergic receptor activation.

Animals↗
PubMed1987

Phencyclidine is a negative allosteric modulator of signal transduction at two subclasses of excitatory amino acid receptors.

Phencyclidine (PCP) and some of its pharmacological congeners inhibit the signal transduction at specific excitatory amino acid receptors of cerebellar granule cells in primary cultures. These drugs do not bind to the transmitter recognition sites, and affinity of this specific binding site is increased by the presence of the transmitter bound to its recognition sites. PCP inhibits phosphatidylinositol phosphate hydrolysis mediated by Mg2+-sensitive glutamate receptors (GP1) but not that mediated by Mg2+-insensitive glutamate receptors (GP2). In addition, PCP inhibits Ca2+ influx and cGMP formation mediated by the activation of Mg2+-sensitive glutamate receptors (GC1) but not that mediated by Mg2+-insensitive glutamate receptors (GC2). In this cell culture the activation of phosphatidylinositol phosphate hydrolysis by muscarinic receptor agonists is not affected by PCP. Since PCP inhibits noncompetitively GP1 and GC1 signal transduction it may act as a negative allosteric modulator of signal transduction at both receptors. The pharmacological profile of PCP and its congeners delimits a class of drugs modulating allosterically the action of the primary transmitter at GP1 and GC1 receptors. These drugs need the presence of the transmitter to act and they cannot be termed inverse agonists because they are devoid of activity in the absence of the transmitter; moreover, they do not bind to the transmitter recognition site nor do they prevent the transmitter binding to its recognition sites.

Allosteric Regulation↗
PubMed1987

Ganglioside inhibition of glutamate-mediated protein kinase C translocation in primary cultures of cerebellar neurons.

In primary cultures of cerebellar granule cells, protein kinase C (PKC) translocation and activation can be triggered by the stimulation of excitatory amino acid neurotransmitter receptors. Glutamate evokes a dose-related translocation of 4-beta-[3H]phorbol 12,13-dibutyrate ([3H]-P(BtO)2) binding sites from the cytosol to the neuronal membrane and stimulates the incorporation of 32P into a number of membrane proteins, particularly protein bands in the range of 80, 50, and 40 kDa. The glutamate-evoked PKC translocation is Mg2+ sensitive, is prevented by 2-amino-5-phosphonovalerate and phencyclidine, is not inhibited by nitrendipine (a voltage-dependent Ca2+-channel blocker) but is abolished by the removal of Ca2+ from the incubation medium, suggesting that glutamate-mediated Ca2+ influx is operative in the redistribution of PKC. Exposure of granule cells to the gangliosides trisialosylgangliotetraglycosylceramide (GT1b) or monosialosylgangliotetraglycosylceramide (GM1) inhibits the translocation and activation of PKC evoked by glutamate. These glycosphingolipids fail to interfere with glutamate binding to its high-affinity recognition site or with the [3H]P(BtO)2 binding, nor do they affect the Ca2+ influx. These gangliosides may prevent PKC translocation by interfering with the PKC binding to the neuronal membrane phosphatidylserine.

Animals↗
PubMed1987

Protracted treatment with diazepam increases the turnover of putative endogenous ligands for the benzodiazepine/beta-carboline recognition site.

DBI (diazepam-binding inhibitor) is a putative neuromodulatory peptide isolated from rat brain that acts on gamma-aminobutyric acid-benzodiazepine-Cl- ionophore receptor complex inducing beta-carboline-like effects. We used a cDNA probe complementary to DBI mRNA and a specific antibody for rat DBI to study in rat brain how the dynamic state of DBI can be affected after protracted (three times a day for 10 days) treatment with diazepam and chlordiazepoxide by oral gavage. Both the content of DBI and DBI mRNA increased in the cerebellum and cerebral cortex but failed to change in the hippocampus and striatum of rats receiving this protracted benzodiazepine treatment. Acute treatment with diazepam did not affect the dynamic state of brain DBI. An antibody was raised against a biologically active octadecaneuropeptide (Gln-Ala-Thr-Val-Gly-Asp-Val-Asn-Thr-Asp-Arg-Pro-Gly-Leu-Leu-Asp-Leu-Lys ) derived from the tryptic digestion of DBI. The combined HPLC/RIA analysis of rat cerebellar extracts carried out with this antibody showed that multiple molecular forms of the octadecaneuropeptide-like reactivity are present and all of them are increased in rats receiving repeated daily injections of diazepam. It is inferred that tolerance to benzodiazepines is associated with an increase in the turnover rate of DBI, which may be responsible for the gamma-aminobutyric acid receptor desensitization that occurs after protracted benzodiazepine administration.

Animals↗
PubMed1987

Opioid peptide biosynthesis: enzymatic selectivity and regulatory mechanisms.

Certain general principles determine the biosynthesis of most biologically active peptides, including the opioid peptides, from large protein precursors. In almost all instances, the active peptide is embedded in the precursor flanked on both sides by pairs of basic amino acids. The first step in processing involves a trypsinlike enzyme, cleaving to the carboxyl terminus of basic amino acids, and leaving the active peptide with a basic amino acid on the carboxyl terminus. A carboxy-peptidase peptidase B-like enzyme then removes the remaining basic amino acid. It has been unclear whether any endopeptidases with trypsinlike activity are selective for one or another basic amino acid. Recently a soluble endopeptidase has been identified that can cleave to both the carboxyl and amino termini of basic amino acids. Enkephalin convertase (carboxypeptidase E, H) (EC 3.4.17.10) has considerable selectivity, and appears to be physiologically associated with the biosynthesis of enkephalin as well as a limited number of other neuropeptides. The turnover of opioid peptides and other neuropeptides is most effectively ascertained by measuring levels of mRNA either biochemically or by in situ hybridization. Striking dynamic alterations include a pronounced increase in levels of proenkephalin mRNA in the corpus striatum after blockade of dopamine receptors, but changes in opioid peptide mRNA after opiate addiction are less clear.

Animals↗
PubMed1987

Magnesium ions inhibit the stimulation of inositol phospholipid hydrolysis by endogenous excitatory amino acids in primary cultures of cerebellar granule cells.

Omission of Mg2+ from the incubation buffer results in a six- to eightfold increase in [3H]inositol-1-phosphate ([3H]Ins-1-P) accumulation in primary cultures of cerebellar granule cells at 7-9 days in vitro. This increase is reversed by low concentrations of 2-amino-5-phosphono-valerate (APV), a result indicating that the absence of Mg2+ facilitates the activation of a specific receptor by the endogenous excitatory amino acids (presumably L-glutamate and L-aspartate) released from the granule cells. The absence of Mg2+ also potentiates the action of exogenously applied N-methyl-D-aspartate (NMDA), L-glutamate, L-aspartate, and kainate. In contrast, the action of quisqualate is virtually unaffected by Mg2+ and is resistant to APV inhibition. Addition of the depolarizing agent veratridine enhances the accumulation of [3H]Ins-1-P also in Mg2+-containing buffer. The action of veratridine is antagonized by APV, a result suggesting that, under depolarized conditions, the NMDA receptor can be activated by the endogenously released excitatory amino acids, despite the presence of Mg2+. Accordingly, in the presence of Mg2+, veratridine potentiates the action of exogenously applied NMDA but does not facilitate the action of quisqualate.

2-Amino-5-phosphonovalerate↗
PubMed1987

Subcellular location and neuronal release of diazepam binding inhibitor.

Diazepam binding inhibitor (DBI), a peptide located in CNS neurons, blocks the binding of benzodiazepines and beta-carbolines to the allosteric modulatory sites of gamma-aminobutyric acid (GABAA) receptors. Subcellular fractionation studies of rat brain indicate that DBI is compartmentalized. DBI-like immunoreactivity is highly enriched in synaptosomes obtained by differential centrifugation in isotonic sucrose followed by a Percoll gradient. In synaptosomal lysate, DBI-like immunoreactivity is primarily associated with synaptic vesicles partially purified by differential centrifugation and continuous sucrose gradient. Depolarization induced by high K+ levels (50 mM) or veratridine (50 microM) released DBI stored in neurons of superfused slices of hypothalamus, hippocampus, striatum, and cerebral cortex. The high K+ level-induced release is Ca2+ dependent, and the release induced by veratridine is blocked by 1.7 microM tetrodotoxin. Depolarization released GABA and Met5-enkephalin-Arg6-Phe7 together with DBI. DBI is also released by veratridine depolarization, in a tetrodotoxin-sensitive fashion, from primary cultures of cerebral cortical neurons, but not from cortical astrocytes. Depolarization fails to release DBI from slices of liver and other peripheral organs. These data support the view that DBI may be released as a putative neuromodulatory substance from rat brain neurons.

Animals↗
PubMed1987

Changes of cholinergic, noradrenergic and serotonergic synaptic transmission indices elicited by ethylcholine aziridinium ion (AF64A) infused intraventricularly.

Bilateral (3 nmol/side) i.c.v. infusion of ethylcholine aziridinium ion (AF64A) causes a 70% decrease of hippocampal acetylcholine content lasting for longer than 30 days without changing the density of hippocampal recognition sites for muscarinic ligands. In hippocampal slices prepared from rats receiving i.c.v. AF64A, the activation of phosphoinositide turnover or the inhibition of cyclic AMP accumulation elicited by muscarinic receptor agonists is facilitated. This AF64A treatment also causes a long-lasting decrease of hippocampal norepinephrine and serotonin (5-HT) content. Even a smaller dose of AF64A (1.5 nmol/side) reduces the hippocampal 5-HT content. The number of alpha-1 adrenoceptor recognition sites is slightly increased by 3 nmol/side of AF64A and the stimulation of phosphoinositide turnover by norepinephrine is facilitated. In contrast the decrease of hippocampal 5-HT concentration elicited by AF64A fails to change the 5-HT receptor indices that were measured. These results indicate that in rat hippocampus muscarinic receptors and alpha-1 adrenoceptors are denervated by AF64A and that this denervation promotes a receptor supersensitivity. These results also suggest that we could not find appropriate conditions to express a complete specificity of AF64A in destroying cholinergic axons and therefore this drug cannot be used readily to induce a selective deficiency of central cholinergic transmission.

Acetylcholine↗
PubMed1987

Actions of benzodiazepine and beta-carboline derivatives on gamma-aminobutyric acid-activated Cl- channels recorded from membrane patches of neonatal rat cortical neurons in culture.

Using the patch-clamp, single-channel recording technique, the authors determined conductance and kinetics of gamma-aminobutyric acid-activated Cl- channels recorded from membrane patches excised from neonatal rat cortical neurons in primary culture. The anxiolytic benzodiazepine flunitrazepam increased the channel opening frequency, but it did not change conductance or channel opening burst duration. The anxiogenic compound methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate decreased gamma-aminobutyric acid-activated Cl- channel opening frequency without changing conductance or opening duration. An increase and decrease in the number of channel bursts were elicited by flunitrazepam and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, respectively. The effects of both drugs were antagonized by ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5][1,4] -benzodiazepine-3-carboxylate (flumazenil), a benzodiazepine antagonist, which per se failed to modify Cl- channel kinetics and conductance.

Animals↗
PubMed1987

Effect of a protracted antidepressant treatment on signal transduction and [3H](-)-baclofen binding at GABAB receptors.

In membranes prepared from frontal cortex of rats receiving desmethylimipramine (10 mg/kg i.p. twice daily) or imipramine (7.5 mg/kg i.p. twice daily) for 3 weeks, the density of high-affinity gamma-aminobutyric acid (GABA)B recognition sites is increased when measured by [3H]GABA binding in the presence of an excess of bicuculline, but it is unchanged when measured by [3H](-)-baclofen binding. When the atypical antidepressant maprotiline was administered (10 mg/kg i.p. twice daily for 3 weeks), no change in the density of GABAB recognition sites was observed using either [3H]GABA or [3H](-)-baclofen as ligands. In addition, a protracted treatment with imipramine, desmethylimipramine and maprotiline failed to change GABAB receptor-coupled signal transduction as monitored by the ability of (-)-baclofen to inhibit the forskolin-stimulated adenylate cyclase activity in membranes prepared from frontal cortex and hippocampus or the cyclic AMP formation in slices from frontal cortex. Hence, after protracted antidepressant treatment, the increase of [3H]GABA binding may not reflect changes in the characteristics of the recognition sites of the GABAB receptors subclass coupled to the adenylate cyclase through a guanine nucleotide binding protein inhibitory (Ni).

Adenylyl Cyclases↗
PubMed1987

Excitatory amino acid receptors coupled with guanylate cyclase in primary cultures of cerebellar granule cells.

Primary cultures of cerebellar granule cells have been used in pharmacologically and functionally characterizing excitatory amino acid recognition sites coupled with guanylate cyclase. When granule cells were incubated in physiological culture conditions (Locke's solution, pH 7.4), only kainate and, to a lesser extent, L-glutamate increased cyclic GMP (cGMP) levels. Under these conditions, L-aspartate, N-methyl-D-aspartate (NMDA), and quisqualate were inactive. When granule cells were incubated in the absence of extracellular Mg2+ or in the presence of the depolarizing agent veratrine, L-glutamate, L-aspartate, and NMDA became as effective as kainate in enhancing cGMP formation. The action of kainate was preferentially antagonized by 2,3-cis-piperidindicarboxylate, whereas the action of L-glutamate was preferentially antagonized by (+/-)2-amino-5-phosphonovalerate. These data suggest that 2 different excitatory amino acid recognition sites (activated by kainate or by L-glutamate, L-aspartate, and NMDA, respectively) are coupled with guanylate cyclase in primary cultures of cerebellar granule cells: While the coupling of the recognition site for kainate with guanylate cyclase operates under resting conditions and in the presence of Mg2+, the coupling of the recognition site for L-glutamate, L-aspartate, and NMDA with guanylate cyclase requires depolarizing conditions or the absence of extracellular Mg2+.

Amino Acids↗
PubMed1987

In rat hippocampus, somatostatin 14 and muscarinic receptor ligands modulate an adenylate cyclase belonging to a common domain of the receptor.

In hippocampal slices, somatostatin 14 and its stable analog L363 [cyclo(Phe-Pro-Phe-D-Trp-Lys-Thr)] fail to modify muscarinic signal transduction mediated by stimulation of phosphoinositide breakdown, whereas somatostatin 14 mimics oxotremorine in inhibiting adenylate cyclase activity of hippocampal membranes. The simultaneous addition of somatostatin 14 and oxotremorine elicits a nonadditive convergent inhibition of adenylate cyclase activity. Both L363 and oxotremorine nonadditively stimulate a high-affinity guanosine 5'-triphosphatase activity of hippocampal membranes. This stimulation could be operative in mediating the convergent inhibition of adenylate cyclase activity elicited by the binding of specific ligands to somatostatin and muscarinic recognition sites present in hippocampal membranes. Because L363 competitively displaces muscarinic agonists fand antagonists from their specific recognition sites, one might infer that the two recognition sites interact functionally; that is, somatostatin reduces the efficacy of oxotremorine and/or vice versa.

Acetylcholine↗
PubMed1987

Regulation of striatal enkephalin turnover in rats receiving antagonists of specific dopamine receptor subtypes.

The hypothesis that striatal dopamine regulates enkephalin (ENK) synthesis is supported by the increase of striatal proenkephalin mRNA and ENK after intranigral injection of 6-hydroxydopamine. In order to elucidate which dopamine receptor subtype is operative in the regulation of the dynamic state of ENK, the effect of drugs that block D-1 or D-2 receptor selectively was studied. Daily administration of 140 mumol/kg s.c. of the D-2 antagonist I-sulpiride twice daily for 2 weeks produces a 30% decrease in the content of striatal proenkephalin mRNA and ENK. In contrast, a 50% increase was observed after 2 weeks of treatment with the D-1 antagonist SCH 23390 at 74 nmol/kg s.c. three times a day. Hence, it can be inferred that the endogenous activation of D-1 tonically decreases striatal ENK synthesis. Removal of this neurally mediated regulation either by a specific pharmacologic blockage of D-1 or by lesioning with 6-hydroxydopamine increases the biosynthesis of ENK. The increase of ENK biosynthesis elicited by denervation with 6-hydroxydopamine cannot be due to the endogenous activation of D-2 receptors and must be due to the inactivation of the tonic inhibition exerted by D-1 receptors.

Animals↗
PubMed1986

A diazepam binding inhibitor (DBI)-like neuropeptide is detected in human brain.

Diazepam binding inhibitor (DBI), a 11,000 MW neuropeptide, which coexists with GABA and elicits proconflict responses in the rat, has been purified and partially sequenced from rat brain. We now report purification and characterization of a DBI-like neuropeptide from human brain. Its molecular weight and pharmacological profile is identical to that of rat DBI but differs in the amino acid composition and immunologically. The tryptic fragments of human DBI differ from rat DBI in the HPLC elution profile and in the amino acid sequence. Using high affinity specific human DBI antibodies, the distribution of DBI-like immunoreactivity in bioptic samples of human brain appeared to be similar to that of DBI found in rat brain. DBI-like immunoreactivity was also found in spinal fluid of human volunteers. The cerebrospinal fluid content of this peptide might be used as a probe to study whether spinal fluid DBI content changes in neuropsychiatric disorders.

Amino Acid Sequence↗
PubMed1986

Kindling enhances the stimulation of inositol phospholipid hydrolysis elicited by ibotenic acid in rat hippocampal slices.

The increment of inositol phospholipid hydrolysis elicited by ibotenic acid (IBO) is greater in hippocampal slices prepared from brain of rats receiving single or repeated hippocampal electrical stimulation or electrically induced amygdala kindling. In the latter group of rats, a potentiation of IBO stimulation of inositol phospholipid hydrolysis was associated with stage 3-4 of kindling according to Racine's scale. This increment returned to normal within one month after withdrawal from electrical stimulations. In both control and stimulated animals, 2-amino-4-phosphonobutyric acid antagonized the increment of inositol phospholipid metabolism elicited by IBO. The stimulation of inositol phospholipid hydrolysis elicited by carbamylcholine and norepinephrine was virtually unaffected by amygdala kindling.

Amygdala↗
PubMed1986

[3H]imipramine displacement and 5HT uptake inhibition by tryptoline derivatives: in rat brain 5-methoxytryptoline is not the autacoid for [3H]imipramine recognition sites.

A putative endacoid capable of displacing [3H]imipramine from its high affinity binding site and of inhibiting [3H]serotonin (5HT) uptake has been partially purified from rat brain tissue. It appears to be unevenly distributed in various rat brain structures following a pattern that only partially matches the extent of the serotonergic innervation in the rat brain structures investigated. The highest amounts have been recovered in striatum followed by hippocampus, cerebral cortex, brain stem and less in diencephalon, cerebellum, hypothalamus, olfactory bulb. Virtually no inhibitory activity on [3H]imipramine binding or on [3H]5HT uptake in addition to 5HT has been found in rat pineal extracts. Its absence in the pineal and various chemicophysical properties discussed in this report suggest that the rat brain endacoid for the imipramine binding site is not 5-methoxytryptoline, a compound previous proposed as the candidate for the role of endogenous ligand of [3H]imipramine recognition site. Moreover, the study of a series of tryptoline derivatives indirectly supports these conclusions.

Animals↗