Search PubMed⌕ Search

Biomedical subjects

E Costa

Publications and source records attributed to E Costa.

At least 325 records · Page 18Linked to original sources
PubMed1985

Phasic and tonic components in 5-HT2 receptor-mediated rat aorta contraction: participation of Ca++ channels and phospholipase C.

The mechanisms of 5-hydroxytryptamine (5-HT)-induced contraction of rat aorta were investigated in vitro. The 5-HT-induced contraction could be analyzed into two distinct components (phasic and tonic) by the use of appropriate inhibitors; nifedipine, an inhibitor of voltage-dependent Ca++ channels, inhibited only the phasic component of 5-HT-induced contraction while totally blocking the KCl-induced contraction. 2-Nitro-4-carboxyphenyl-N,N-diphenylcarbamate, an inhibitor of phospholipase C, inhibited the tonic components of 5-HT-induced contraction as well as the 5-HT-induced stimulation of phosphoinositide hydrolysis in rat aorta. This component of contraction was mimicked by a protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate. These results suggest that 5-HT2 receptors differentially regulate a voltage-dependent Ca++ channel and phospholipase C activity; the voltage-dependent Ca++ channel is involved in the phasic component of contraction whereas the phosphoinositide hydrolysis that results in the activation of protein kinase C and calcium mobilization by inositol triphosphate plays a physiologically important role in the tonic component of the aortic contraction.

Animals↗
PubMed1985

On the brain endocoid for benzodiazepine recognition sites.

Human and rat brain contain a neuropeptide with 105 amino acid residues which inhibits the binding of 3H-diazepam and other specific benzodiazepine recognition site ligands to crude brain synaptic membranes. DBI injected intracerebroventricularly in thirsty rats which are subjected to a conflict test (Corda et al., 1983), lowers the threshold for behavioral suppression by punishment. In this test DBI acts like an anxiogenic endocoid for the benzodiazepine recognition sites. The large abundance of lysine and arginine residues in the DBI molecule suggest that this polypeptide functions as a precursor of a putative endocoid which regulates anxiety levels. This endocoid acts as an agonist for the benzodiazepine recognition site. Because of the anxiogenic properties of this endocoid, it is proposed that anxiolytic benzodiazepine should be classified as an antagonist and beta-carboline as an agonist at the receptor level.

Amino Acid Sequence↗
PubMed1985

Are Phe-Met-Arg-Phe-NH2 immunoreactive peptides endacoids modulating opiate antinociception?

Phe-Met-Arg-Phe-NH2 (FMRF-NH2) was initially isolated from the macrocallista nimbosa clam and subsequently existence of FMRF-NH2-like immunoreactivity (FMRF-NH2-IR) was detected in mammalian CNS. Due to the structural similarity between FMRF-NH2 and the C-terminal extended form of met5-enkephalin, met5-enkephalin-arg6-phe7 (YGGFMRF), a possible interaction between these two peptides was explored. FMRF-NH2 injected intrathecally decreases the antinociceptive action of YGGFMRF or morphine. However, the FMRF-NH2-IR present in rat and bovine brains differs from FMRF-NH2. Intrathecally injected FMRF-NH2-IR partially purified from bovine brain reduces YGGFMRF antinociception. The antagonism elicited by FMRF-NH2 can be reversed by proglumide, which was reported to act as a CCK antagonist. In order to characterize the biological profile of FMRF-NH2-IR, the effect of proglumide and of the FMRF-NH2 antibody on morphine analgesia was tested. Both the IgG isolated from FMRF-NH2 antiserum and proglumide were found to potentiate the morphine analgesia. The results taken together suggest that endogenous FMRF-NH2-IR modulates opioid antinociception; perhaps by acting as an endogenous naloxone.

Animals↗
PubMed1985

Vasoactive intestinal peptide which coexists with acetylcholine decreases acetylcholine turnover in mouse salivary glands.

Acetylcholine (ACh) and vasoactive intestinal peptide (VIP) probably coexist in cholinergic neurons of rodent salivary glands. In this tissue, cholinergic drugs regulate release of both ACh and VIP from postganglionic cholinergic neurons. In the present study we investigated whether VIP could modulate the metabolism of ACh in mouse submandibular gland cholinergic neurons using ACh turnover rate (TRACh) as a parameter. The TRACh was estimated via measurement of the formation of [3H]ACh during constant rate infusion of [3H]choline. Choline and ACh were separated by reverse phase high-performance liquid chromatography and were detected electrochemically after enzymatic postcolumn reaction. We calculated that the TRACh was about 3 nmol/mg of protein per hr. Pilocarpine, a muscarinic agonist decreased the TRACh about 5-fold whereas atropine methyl Br, a muscarinic antagonist, caused a large increase in turnover. Turnover, therefore, appears to be regulated by a feedback mechanism triggered by occupancy of postsynaptic receptors. VIP infused i.v. (40 micrograms/kg/min) decreased the TRACh by about 50%. Atropine completely prevented the inhibition of the TRACh induced by VIP. These results suggest that, by changing postsynaptic or presynaptic muscarinic receptor function, VIP may participate in the control of ACh metabolism. Parasympathetic decentralization of salivary glands did not prevent the effect of either atropine or VIP on TRACh. This finding suggests that the central afferent input to the ganglionic cells is not required for the regulation of ACh metabolism and, therefore, the feedback loop probably acts via a postganglionic mechanism which is not elucidated by present experiments.

Acetylcholine↗
PubMed1985

Use of mRNA hybridization and radioimmunoassay to study mechanisms of drug-induced accumulation of enkephalins in rat brain structures.

The repeated administration of haloperidol or fenfluramine for several days led to an increase of enkephalin content in specific brain areas. In order to characterize the nature of the dynamic changes underlying this increase, we measured the content of proenkephalin mRNA (PE-mRNA), of high molecular weight (HMW) enkephalin precursors, and of low molecular weight enkephalin peptides (LMW) in various brain areas. To measure PE-mRNA, we hybridized the specific mRNA with a [32P]cDNA probe for human pheochromocytoma PE. HMW and LMW enkephalin content was measured by radioimmunoassay after separation of the immunoreactive peaks by Bio-Gel P-2 column chromatography and enzymatic digestion of the precursors. Haloperidol treatment increased enkephalins, the precursor, and PE-mRNA content in the striatum, suggesting that this drug might increase enkephalin steady state by increasing transcription, translation, or both processes. In contrast, fenfluramine increased hypothalamic and striatal enkephalin content by preferentially reducing neuropeptide utilization or decreasing its catabolism without changing its synthesis.

Animals↗
PubMed1985

Reserpine changes the dynamic state of enkephalin stores in rat striatum and adrenal medulla by different mechanisms.

The administration of reserpine increases enkephalin content in rat striatum and adrenal medulla. In order to investigate the mechanisms operative in this increase, we have studied in vivo the dynamic state of enkephalin stores by determining the content of proenkephalin mRNA, enkephalin precursors, and enkephalins in rats receiving reserpine. We measured proenkephalin mRNA by using a cDNA probe for human proenkephalin mRNA which hybridizes to the same species of mRNA either in the brain or in adrenal medulla. (Met5)-Enkephalin-Arg6-Phe7, as well as the high and low molecular weight forms of the enkephalins separated by Sephadex G-75 column chromatography, were measured by radioimmunoassay. Reserpine (2 mg/kg, i.p., repeated daily for two consecutive days) led 3 to 5 days later to an increase in the striatal content of proenkephalin mRNA as well as high and low molecular weight peptides containing enkephalin. The same treatment produced, in adrenal medulla, a shift from higher molecular weight to lower molecular weight enkephalin-containing peptides, an increase of enkephalin peptides, and a decrease of proenkephalin mRNA content. The results in striatum suggest that reserpine increases enkephalin synthesis by removing a tonic dopaminergic inhibition: those in adrenal medulla indicate that reserpine causes an accumulation of enkephalins by blocking the release and/or increasing the processing which may trigger a feedback-regulatory mechanism leading to a decrease in proenkephalin mRNA content.

Adrenal Medulla↗
PubMed1985

Evidence for an endacoid for the 5HT2 recognition site.

A peptide was partially purified from bovine forebrain which specifically inhibits the binding of [3H]-ketanserin to the 5HT2 recognition site. The peptide has a MW of approximately 6,000 daltons and is partially destroyed by limited proteolysis. We suggest that the peptide is a candidate for an endacoid for the 5HT2 recognition site.

Animals↗
PubMed1984

A reduction of the tone of 5-hydroxytryptamine neurons decreases utilization rates of striatal and hypothalamic enkephalins.

The administration of drugs such as fenfluramine, p-chlorophenylalanine or 5,7-dihydroxytryptamine, which lower brain 5-hydroxytryptamine content, increases the enkephalin content of hypothalamus and striatum. None of these treatments changes proenkephalin mRNA content. On the basis of these results, we propose that 5-hydroxytryptamine does not increase the biosynthesis of enkephalin, but might increase the content of the neuropeptide by reducing peptide utilization.

5,7-Dihydroxytryptamine↗
PubMed1984

Age-related and diurnal changes in Met5-Enk-Arg6-Phe7 and Met5-enkephalin contents of pituitary and rat brain structures.

The beta-endorphin, met5-enkephalin-arg6-phe7 (MEAP) and met5-enkephalin (ME) changes related to age and diurnal rhythms were studied in various regions of rat brain and in the pituitary by specific radioimmunoassays. The contents of MEAP, met5-enkephalin and beta-endorphin were higher in the pituitary of old rats (18 months old) than that of young rats (23 days old) while the content of these opioid peptides was higher in the hypothalamus of young rats than in that of old rats. Beta-endorphin was also higher in the striatum of 23 days old rats, but no age-associated changes were observed in the hippocampus, brain stem or cortex. In the diurnal rhythm study, it was found that in the hypothalamus and striatum of the adult rat (2-3 months old), both MEAP and ME contents were higher at mid-dark than at mid-light and that in the intermediate posterior lobe of the pituitary, the ME content was also higher at mid-dark.

Age Factors↗
PubMed1984

Isolation, purification and partial sequence of a neuropeptide (diazepam-binding inhibitor) precursor of an anxiogenic putative ligand for benzodiazepine recognition site.

Diazepam binding inhibitor (DBI), a brain neuropeptide putative ligand for benzodiazepine binding sites, has been isolated and purified to homogeneity. This compound, like the anxiogenic beta-carbolines, injected intracerebroventricularly facilitates shock-induced suppression of drinking in thirsty rats. Cyanogen bromide (CNBr) cleavage of DBI produces three peptide fragments: the carboxy terminal fragment (F3 approximately equal to 1800 mol.wt.) and an intermediate fragment (F2 approximately equal to 3200 mol.wt.) are inactive, whereas the fragment that contains the amino terminus (F1 approximately equal to 6500 mol. wt.) facilitates punishment inhibition of operant behavior in rat. These data suggest that the F1 peptide contains the active sequence. The latter might be the natural effector of benzodiazepine recognition sites while DBI could be a polyprotein functioning as the precursor of the putative endogenous ligand of the benzodiazepine recognition site.

Amino Acid Sequence↗
PubMed1984

On the neurotoxicity of chlordecone: a role for gamma-aminobutyric acid and serotonin.

Rats receiving the chlorinated insecticide, chlordecone (80 mg/kg i.p.), exhibit hyperexcitability, exaggerated startle response and tremors within a few hours after the injection. Since the chlordecone-elicited tremors are relieved by injections of muscarinic receptor blockers, acetylcholine has been implicated indirectly in the mechanism of chlordecone toxicity. Our studies on acetylcholine steady-state levels and turnover in several brain structures failed to detect evidence for an involvement of cholinergic presynaptic mechanisms in the chlordecone toxicity. We then investigated whether GABA is involved by measuring the rate of its accumulation following intraventricular injection of gabaculine. Chlordecone reduced the rate of GABA accumulation in striatum, but not in cerebellum, brainstem or hippocampus. Such inhibition appeared 4 h after drug injection thereby preceding the onset of tremors. Since tremors elicited by chlordecone are attenuated by the administration of serotonin receptor blockers and since chlordecone increases serotonin (5-HT) turnover, we studied whether 5-HT recognition sites are modified following chlordecone administration. We have found a reduction of the Bmax of 5-HT1 receptors in striatum and hippocampus without any modification in the kinetic characteristics of 5-HT2 receptors. We have also shown that the temporal relationship between down regulation of 5-HT1 recognition sites, reduction of striatal GABA turnover and tremors caused by chlordecone allows one to consider these 3 phenomena as reciprocally dependent. In conclusion our results favor the possibility that tremors may result from a decrease in the striatal GABergic tone which probably is elicited by an increase of serotonergic activity caused by chlordecone by a yet unknown mechanism.

Acetylcholine↗
PubMed1984

Comparative distribution of bombesin/GRP- and substance-P-like immunoreactivities in rat hypothalamus.

Immunohistochemical localization of bombesin/gastrin-releasing peptide ( GRP )-like immunoreactivity (BN/ GRP -LI) and substance P-like immunoreactivity (SP-LI) in consecutive sections of rat hypothalamus was studied. Bombesin/ GRP -like immunoreactivity in the hypothalamus was partially characterized by gel filtration chromatography followed by radioimmunoassay. In the hypothalamus, SP-LI was more widely distributed than BN/ GRP -LI. Only the anterior and medial parvocellular parts of the nucleus paraventricularis and the nucleus suprachiasmaticus contained numerous cell bodies which exhibited BN/ GRP -LI. Neurons in these areas did not exhibit SP-LI. In contrast, cell bodies exhibiting SP-LI were numerous in the nucleus preopticus medialis and lateralis, nucleus anterior, nucleus ventromedialis and dorsomedialis, nucleus lateralis, nucleus arcuatus, and nucleus premamillaris ventralis and dorsalis. Only occasional cell bodies in these areas exhibited BN/ GRP -LI. It is concluded that the neuronal systems in the hypothalamus containing BN/ GRP -LI and SP-LI are separate, though the terminal fields in many areas overlap. Two peaks of BN/ GRP -LI were detected after gel filtration chromatography from extracts of the rat nucleus paraventricularis. The high molecular weight form coeluted with synthetic GRP (1-27), and the small molecular weight form eluted after synthetic bombesin. Thus, the endogenous BN/ GRP -LI is probably not authentic bombesin.

Animals↗
PubMed1984

The (-)-deprenyl actions on beta-adrenergic receptors require the integrity of brain serotonergic axon terminals.

In rats receiving (-)-deprenyl (1 mumol/kg, s.c.) twice daily for 3 weeks, the Bmax of imipramine binding sites located in crude synaptic membranes prepared from frontal cortex increases while the NE stimulation of cAMP accumulation in minces prepared from frontal cortex is attenuated. The presence of intact 5HT axon terminals is an absolute requirement for the down-regulation of the beta-adrenergic receptor function by repeated injections of (-)-deprenyl. These and other lines of evidence suggest that the increase in the Bmax of [3H]imipramine binding sites and the attenuation of beta-adrenergic receptor function elicited by (-)-deprenyl might be causally related.

5,7-Dihydroxytryptamine↗
PubMed1984

An immunohistochemical study on the location of GABAergic neurons in rat septum.

Antisera against L-glutamate decarboxylase (GAD), the synthesizing enzyme of gamma-aminobutyric acid (GABA) were used to locate GABAergic neurons and nerve terminals in the septal complex of the rat by using the peroxidase-antiperoxidase method. Varying densities of immunoreactive terminals were observed in saline-treated rats but nerve cell bodies were only demonstrated after interventricular or intraseptal injections of colchicine. Small and medium-sized GAD-positive neurons were found in lateral septal nuclei, the largest number of these cells being in the pars dorsalis, and in the bed nucleus of the stria terminalis. Several GAD-immunoreactive neurons were located in the medial septal nucleus and the nucleus of the diagonal band of Broca (DB), where the cells were larger in the ventral than dorsal parts of the region. In the medial septal nucleus and in DB the GAD-positive cell bodies were distributed similarly to cholinergic neurons. Large GAD-positive neurons were also found in the septofimbrial nucleus. Intense immunoreactivity in nerve terminals was observed in the lateral septal nucleus, around the island of Calleja magna, between the DB and nucleus accumbens, and in the septofimbrial and triangular septal nuclei. In contrast, the medial septal nucleus, the DB, and the bed nucleus of the stria terminalis only showed weak to moderate immunoreactivity. These results provide direct morphological evidence for the presence of neurons capable of synthesizing GABA in septal nuclei. We suggest that there are two different GABAergic neuronal systems operating in the septum: a population of small cells in the lateral septal nucleus and a group of large cells in the medial septum and DB.

Animals↗