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R A Reis

Publications and source records attributed to R A Reis.

9 recordsLinked to original sources
PubMed2001

Dopaminergic retinal cell differentiation in culture: modulation by forskolin and dopamine.

We examined the effects of dopamine and cAMP on the differentiation of dopaminergic retinal cells in the chick retina, using an in vitro system and tyrosine hydroxylase immunocytochemistry. Tyrosine hydroxylase-positive cells were detected in cultures prepared from embryonic day 10 retinas. These increased in number as a function of time in vitro and by treatment for 4 days with forskolin. Besides causing a 3.4-fold increase in the tyrosine hydroxylase-positive population, forskolin also caused these cells to developed morphogenetic features of more mature cells. As opposed to forskolin, cultures treated with dopamine exhibited a 55% reduction of the tyrosine hydroxylase-positive cell population, as compared to untreated cultures. Quinpirole was able to mimic the dopamine effect. This dopamine effect could only be blocked by clozapine, whereas raclopride and eticlopride were ineffective. Our results suggest the existence of a narrow window during development when undifferentiated dopaminergic cells are capable of being influenced by specific signals, possibly via cAMP production. The data also indicate that dopamine may act as a regulatory factor limiting the tyrosine hydroxylase-positive population in the retina.

Animals↗
PubMed2001

Inhibition of choline acetyltransferase by excitatory amino acids as a possible mechanism for cholinergic dysfunction in the central nervous system.

Choline acetyltransferase (ChAT) activity was reduced by more than 85% in cultured retina cells after 16 h treatment with 150 microM kainate (T(1/2) : 3.5 h). Glutamate, AMPA and quisqualate also inhibited the enzyme in equivalent proportion. Cell lesion measured by lactate dehydrogenase (LDH) release, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide - thiazolyl blue (MTT) reduction and microscopic observation was not detected even after 48 h with kainate. Other retina neurochemical markers were not affected by kainate and full recovery of the enzyme was achieved 9 days after kainate removal. Moreover, hemicolinium-3 sensitive choline uptake and hemicolinium-3 binding sites were maintained intact after kainate treatment. The immunoblot and immunohistochemical analysis of the enzyme revealed that ChAT molecules were maintained in cholinergic neurons. The use of antagonists showed that ionotropic and group 1 metabotropic receptors mediated the effect of glutamate on ChAT inhibition, in a calcium dependent manner. The quisqualate mediated ChAT inhibition and part of the kainate effect (30%) was prevented by 5 mM N(G)-nitro-L-arginine methyl ester (L-NAME). Veratridine (3 microM) also reduced ChAT by a Ca(2+) dependent, but glutamate independent mechanism and was prevented by 1 microM tetrodotoxin.

Animals↗
PubMed1998

Convulxin induces platelet activation by a tyrosine-kinase-dependent pathway and stimulates tyrosine phosphorylation of platelet proteins, including PLC gamma 2, independently of integrin alpha IIb beta 3.

1Convulxin (Cvx) is a well-characterized platelet aggregating glycoprotein isolated from Crotalus durissus terrificus and C. d. cascavella venoms. In the present report we show that Cvx induces tyrosine phosphorylation of human platelet proteins, including phospholipase C-gamma 2 (PLC gamma 2), and also stimulates [3H]arachidonic acid ([3H]AA) mobilization, pleckstrin phosphorylation, and an increase in the cytosolic Ca2+ concentration ([Ca2+]in) due to both Ca2+ entry and internal Ca2+ mobilization. Staurosporine, a potent protein kinase inhibitor, and genistein, a specific inhibitor of protein tyrosine kinases (PTK), were used to evaluate the role of protein tyrosine phosphorylation (PTP) in the signal transduction evoked by Cvx. Staurosporine and genistein inhibited in a dose-dependent manner platelet aggregation induced by Cvx. Both inhibitors significantly blocked to near basal levels breakdown of phosphatidylinositol 4,5-bisphosphate from [myo-2-3H]inositol-labeled platelets and the production of [3H]AA metabolites from [3H]AA-labeled platelets after challenge with Cvx. Cvx provokes an increase in [Ca2+]in in Fura-2-loaded platelets that was abolished by concentrations of staurosporine which also inhibited Cvx-induced platelet aggregation. In addition, Cvx stimulates a rapid increase in tyrosine phosphorylation of human platelets proteins with molecular masses of 40, 72/74, 78/80, 105, 120, and 145 kDa, followed by dephosphorylation. Furthermore, Cvx stimulates a rapid tyrosyl phosphorylation of a 145-kDa molecular mass protein that was identified as PLC gamma 2. PTP induced by Cvx was not inhibited when platelets were stimulated in the presence of indomethacin, apyrase, EDTA, or RGDS peptide. These results indicate that PTP is chronologically proximal to Cvx binding to platelets, and is independent of aggregation or fibrinogen binding to the integrin alpha IIb beta 3. On the other hand, the dephosphorylation step is inhibited by RGDS peptide or EDTA, suggesting that integrin alpha IIb beta 3 is envolved in this step. The profile obtained with Cvx resembles that obtained in platelets adherent to an immobilized ligand, such as immobilized collagen, in which PTP is independent on integrin alpha IIb beta 3. Thus, we suggest that Cvx is an example of a protein with adhesion molecule-like properties; i.e., it is an adhesin. In conclusion, our results show that Cvx induces multiple signaling pathways in platelets via a PTK-dependent pathway involving PLC gamma 2 tyrosyl phosphorylation, with the subsequent platelet responses. Cvx is unique among platelet soluble agonists because under test tube stirring conditions it induces a PTP profile independently of integrin alpha IIb beta 3.

Animals↗
PubMed1998

Atypical effect of dopamine in modulating the functional inhibition of NMDA receptors of cultured retina cells.

Cultured retina cells released accumulated [3H]GABA (gamma-aminobutyric acid) when stimulated by L-glutamate, N-methyl-D-aspartate (NMDA) and kainate. In the absence of Mg2+, dopamine at 200 microM (IC50 60 microM), inhibited in more than 50% the release of [3H]GABA induced by L-glutamate and NMDA, but not by kainate. This effect was not blocked by the D1-like dopamine receptor antagonist, R-(+)-7-chloro-8-hydroxy-3-methyl- -phenyl-2,3,4,5-tetrahydro- H-3-benzazepine hydrochloride (SCH 23390), neither by haloperidol nor spiroperidol (dopamine D2-like receptor antagonists). The dopamine D1-like receptor agonist R(+)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,diol hydrochloride (SKF 38393) at 50 microM, but not its enantiomer, also inhibited the release of [3H]GABA induced by NMDA, but not by kainate; an effect that was not prevented by the antagonists mentioned above. (+/-)-6-Chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepin e hydrobromide (SKF 812497) had no effect. Neither 8BrcAMP (5 mM) nor forskolin (10 microM) inhibited the release of [3H]GABA. Our results suggest that dopamine and (+)-SKF 38393 inhibit the glutamate and NMDA-evoked [3H]GABA release through mechanisms that seem not to involve known dopaminergic receptor systems.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1995

Transient coupling of NMDA receptor with ip3 production in cultured cells of the avian retina.

The mobilization of inositol triphosphate ip3 by N-methyl D-aspartate (NMDA) and kainate, two excitatory amino acid EAA receptor agonists, was studied in cultured chick retina cells as a function of culture differentiation. Kainate (EC50 = 30 microM) stimulated from 6 to 9-fold the production of [3H]ip3 between E8C3 (embryonic day 8 plus 3 days in vitro) and E8C13. The kainate response was blocked by CNQX (100 microM) by more than 80% until stage E8C9. MK-801, however, was totally ineffective in preventing the kainate induced ip3 generation. [3H]ip3 production evoked by NMDA was increased 4-fold above basal levels at E8C3. As cultures differentiated, [3H]ip3 production promoted by NMDA decreased to 2.5-fold at E8C6 to 1.6-fold the basal levels in cultures at later stages of differentiation. The removal of Mg2+ from the incubating medium at E8C3 increased the NMDA mediated [3H]ip3 production by 80%. However, at more differentiated stages of the cultures, when cells were not responsive to NMDA, removal of Mg2+ plus the addition of 1 mM glycine did not change the pattern of the response. Although NMDA mediated ip3 production is almost absent in more differentiated cultures, NMDA is able to induce [3H]GABA release in E8C3 and E8C13 cultures with characteristics that reflect typical NMDA receptor activation: it is highly potentiated by the absence of Mg2+ and by the presence of glycine. The NMDA induced production of [3H]ip3 at E8C3 was entirely blocked by MK-801 (100 microM) and APV (100 microM) but not by CNQX.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1995

Domoic acid induces neurotoxicity and ip3 mobilization in cultured cells of embryonic chick retina.

Domoic acid (DOM), 1 to 50 microM, a glutamate agonist responsible for several neurological effects such as loss of memory and confusion, induced the death of cultured neurons of chick embryonic retina, in a concentration- and Ca(2+)-dependent manner. This effect was blocked by 100 microM CNQX, a competitive antagonist of the non-NMDA receptor, but not by 10 microM MK-801, a non-competitive antagonist of the NMDA receptor. DOM also induced inositol triphosphate (ip3) accumulation 4 to 7 times above basal levels. This effect was also dependent on external Ca2+ and was entirely blocked by 100 microM CNQX, but not by 10 microM MK-801. These results suggest that DOM interaction with non-NMDA glutamate receptors mediates signal transduction with ip3 accumulation and cell death.

Animals↗