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D O Calligaro

Publications and source records attributed to D O Calligaro.

46 records · Page 3Linked to original sources
PubMed1992

DL-tetrazol-5-ylglycine, a highly potent NMDA agonist: its synthesis and NMDA receptor efficacy.

At physiological pH, the spatial arrangement of the three charges of DL-tetrazol-5-ylglycine (5) could be viewed as similar to those found in certain conformations of the two excitatory amino acids (EAAs)--aspartic and glutamic acids. Given significant binding to one or more EAA receptors, 5 would offer unique modeling and perhaps biological opportunities. We have previously shown it to be the most potent NMDA agonist known, with a unique and marked in vitro neutrotoxicity at depolarizing concentrations. Now we report the details required for its synthesis, together with its potency and efficacy in two assays of functional activation of the NMDA receptor, namely agonist-influenced [3H]MK801 binding and agonist-induced release of the neurotransmitter [3H]-norepinephrine from brain slices. In both these assays DL-tetrazol-5-ylglycine proved to be more potent and efficacious than NMDA and cis-methanoglutamate. It was more potent than, and equally efficacious to, L-glutamate in [3H]MK801 binding. The structural features of 5 may well reflect optimal agonist interaction at the NMDA receptor site. (We considered the possibility that some decarboxylation of DL-tetrazol-5-ylglycine may have occurred during testing. This would give 5-(aminomethyl)tetrazole (13), the tetrazole acid analog of glycine; and glycine is involved in NMDA receptor activation. Compound 13 does not affect [3H]glycine binding at the strychnine-insensitive glycine binding site, and [3H]MK801 binding studies showed that the (aminomethyl)-tetrazole, even if is formed, would probably have no effect on the activity of tetrazol-5-ylglycine at the NMDA receptor.

Animals↗
PubMed1992

Synthesis and excitatory amino acid pharmacology of a series of heterocyclic-fused quinoxalinones and quinazolinones.

As part of our program aimed at the development of potent excitatory amino acid antagonists, we synthesized and evaluated a series of substituted 1,2,4-triazolo[4,3-a]quinoxalin-4(5H)-ones, 4, tetrazolo[1,5-a]quinoxalin-4(5H)-ones, 5, and pyrazolo[1,5-c]quinazolin-5(6H)-ones, 6, and an imidazo[1,2-a]quinoxalin-4(5H)-one, 7. In general, the same heterocycles which demonstrated the best affinity for the AMPA receptor also demonstrated the best affinity for the glycine site on the NMDA receptor complex. 1-Propyl-7,8-dichloro-1,2,4-triazolo[4,3-a]quinoxalin-4(5H)-one, 4d, was found to bind with the greatest affinity to the AMPA receptor with an IC50 of 0.83 microM and antagonized 40 microM AMPA-induced depolarization in the cortical slice preparation with an IC50 of 44 microM. 7,8-Dichloro-1,2,4-triazolo[4,3-a]quinoxalin-4(5H)-one, 4a, and 7,8-dichloroimidazo[1,2-a]quinoxalin-4(5H)-one, 7, possessed the best affinity for the glycine site with IC50 values of 0.63 and 1.26 microM, respectively. It is noteworthy that the SAR for the heterocyclic compounds did not directly parallel that of known quinoxalinediones (e.g. DNQX, 2, and DCQX, 15) at the AMPA receptor nor that of the kynurenic acids at the glycine site on the NMDA receptor complex.

Animals↗
PubMed1992

Preclinical studies on LY237733, a potent and selective serotonergic antagonist.

8B-N-cyclohexyl-6-methyl-1(1-methylethyl)ergoline-8-carboxamide (LY237733) is an ergoline with potent and highly selective 5-hydroxytryptamine (5-HT) antagonist activity. The in vitro radioligand displacement studies showed that LY237733 has a preferential affinity for 5-HT1c and 5-HT2 receptors compared to other monoaminergic receptors. This characteristic is shared with other previously described ergoline 5-HT antagonists, such as LY53857 and sergolexole. In parallel ligand displacement assays, LY237733 had a similar potency to sergolexole. LY237733 was equipotent to sergolexole, but slightly less potent than LY53857 in the antagonism of 5-HT-induced elevation in blood pressure and quipazine-induced elevation in corticosterone levels, which are considered to be measures of 5-HT2 and possibly 5-HT1c antagonist activity. LY237733 failed to antagonize pergolide or 8-hydroxy-2-(di-n-propylamino)tetralin-induced elevations in serum corticosterone levels, indicating selectivity for the 5-HT1c/2 receptor, relative to 5-HT1a and D2 dopaminergic receptors. The only in vivo response that could be detected after administration of LY237733 alone in doses less than 1 mg/kg was the amplification of male rat sexual behavior. LY237733 was 10 to 100 times more potent than LY53857 or sergolexole in augmenting sexual responses of male rats with different levels of sexual response capacity. LY237733 has a much longer serum half-life than sergolexole. These studies have provided the pre-clinical rationale to evaluate the effects of this compound in the treatment of sexual disorders such as psychogenic erectile dysfunction, and other therapeutic indications for a 5-HT2 antagonist, including depression, anxiety, schizophrenia and migraine.

Animals↗
PubMed1991

General pharmacology of a new potent 5-hydroxytryptamine antagonist.

The potential of the investigational 5-hydroxytryptamine (5HT3) antagonist, LY277359, to alter cardiovascular, central nervous system (CNS), smooth muscle, and gastrointestinal functions at multiples of pharmacologically active doses, was examined to provide a profile of possible secondary pharmacological effects. In the anesthetized dog, significant cardiovascular effects were observed at doses 100-1000 and 4-15 times those found to be pharmacologically active at 5HT3 receptors in vivo in rats and dogs, respectively. These effects were limited to decreased heart rate (approximately 20%) at intravenous doses of 1.75 and 3.5 mg/kg and prolonged Q-Tc intervals (approximately 20 to 50%) at doses of 0.438 to 3.5 mg/kg. At an oral dose of 135 mg/kg (representing 1500-4500 times the pharmacologically active dose in rats), LY277359 induced hypoactive behavior and reduced body temperature in mice. Seizure activity was potentiated at high oral doses of LY277359 (45 and 135 mg/kg). A single oral dose of 135 mg/kg increased hexobarbital-induced sleep time. In smooth and cardiac muscle tissue studies in vitro, LY277359 was essentially inactive: it did not alter contractile activity or receptor function of the guinea pig ileum, rat vas deferens, rat uterus, or guinea pig atria at concentrations of 10(-5) to 10(-10) mol/l. At a concentration 50,000 times the 5HT3 antagonistic level in vitro (10(-4) mol/l), LY277359 inhibited the response of the ileum to field stimulation, acetylcholine and angiotensin I, and suppressed the rate of the spontaneously beating guinea pig atria in a noncompetitive manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

5,7-Dichlorokynurenic acid, a potent and selective competitive antagonist of the glycine site on NMDA receptors.

Fourteen substituted derivatives of kynurenic acid were compared for their ability to block ionic currents evoked by N-methyl-D-aspartate (NMDA) plus glycine, or kainate, in voltage-clamped Xenopus oocytes injected with rat brain messenger RNA. Among these analogues there was an excellent correlation between the Ki for displacing [3H]glycine binding to rat brain membranes, and the ability to inhibit ionic currents evoked by glycine/NMDA in Xenopus oocytes. In the oocyte 5,7-dichlorokynurenic acid (5,7-DCK) was a competitive blocker of the glycine recognition site on NMDA receptors, and was more potent (KB 65 nM in Schild analysis) and selective (509-fold more potent vs glycine than kainate) than the prototype glycine antagonist, 7-chlorokynurenic acid, 5,7-DCK also reduced NMDA-induced neuron injury in rat cortical cell cultures.

Animals↗
PubMed1988

High affinity binding of [3H] cocaine to rat liver microsomes.

[3H]Cocaine bound reversibly, with high affinity (KD 2.3 +/- 1.1 nM) and stereospecificity to rat liver microsomes. Little binding was detected in the lysosomal, mitochondrial and nuclear fractions. The binding kinetics were slow (T1/2 for association, 6 min and for dissociation 17 min), and the kinetically calculated KD was 2 nM. Induction of mixed function oxidases by phenobarbital did not produce significant change in [3H]cocaine binding. On the other hand, chronic administration of cocaine reduced [3H]cocaine binding drastically. Neither treatment affected the affinity of the liver binding protein for cocaine. Microsomes from mouse and human livers had less cocaine-binding protein and lower affinity for cocaine than those from rat liver. Binding of [3H]cocaine to rat liver microsomes was insensitive to monovalent cations and greater than 10 fold less sensitive to biogenic amines than the cocaine receptor in rat striatum. However, the liver protein had higher affinity for cocaine and metabolites except for norcocaine. Amine uptake inhibitors displaced [3H]cocaine binding to liver with a different rank order of potency than their displacement of [3H]cocaine binding to striatum. This high affinity [3H]cocaine binding protein in liver is not likely to be a monooxygenase, but may have a role in cocaine-induced hepatotoxicity.

Amines↗
PubMed1987

Central and peripheral cocaine receptors.

High-affinity binding sites for [3H]cocaine (levo-[benzoyl-3,4-3H(N)]) were detected in membrane preparations from rat brain and liver. Analysis of binding to rat whole brain membranes revealed a high-affinity site (Kd = 16 nM) present at 0.65 pmol/mg of protein and a lower affinity site of (Kd = 660 nM) present at 5.1 pmol/mg of protein. The striatum had a much higher density of [3H]cocaine binding sites than either the frontal or occipital cortices. Also, the ratio of high/low affinity sites was highest for striatum, lower for cortices and lowest for whole brain. Scatchard analysis of cocaine binding to striatum and cortex suggested that, in addition to the high affinity binding (Kd = 16 nM), there were two or more lower affinity sites. Liver membranes bound [3H]cocaine with a single high affinity (Kd = 1.7 nM) present at high concentrations (Bmax = 66 pmol/mg of protein). Binding of cocaine to both brain and liver membranes was sensitive to proteases, reduced by high Na+ concentrations (30-100 mM), eliminated by denaturing temperatures (i.e., 95 degrees C for 5 min) and optimal at pH 7.4. Binding of [3H]cocaine to the striatal and cortical synaptic membranes was inhibited by cocaine and analogs in the following decreasing rank order: (-)-cocaine greater than (-)-norcocaine greater than (-)-cinnamoylcocaine greater than (+)-pseudococaine but (-)-ecgonine had no effect. The effective analogs also inhibited [3H]norepinephrine (levo[7-3H(N)]) and [3H]dopamine (dihydroxyphenylethylamine, 3,4-[7-3H]) uptake into cortical and striatal synaptosomes, respectively, with similar rank order.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

High affinity stereospecific binding of [3H] cocaine in striatum and its relationship to the dopamine transporter.

A high affinity (KD 35 nM) binding site for [3H]cocaine is detected in rat brain striatum present at 2-3 pmol/mg protein of synaptic membranes. This binding is displaced by cocaine analogues with the same rank order as their inhibition of [3H]dopamine ([3H]DA) uptake into striatal synaptosomes (r = 0.99), paralleling the order of their central stimulant activity. The potent DA uptake inhibitors nomifensine, mazindol, and benztropine are more potent inhibitors of this high affinity [3H]cocaine binding than desipramine and imipramine. Cathinone and amphetamine, which are more potent central stimulants than cocaine, displace the high affinity [3H]cocaine binding stereospecifically, but with lower potency (IC50 approximately equal to 1 microM) than does cocaine. It is suggested that the DA transporter in striatum is the putative "cocaine receptor." Binding of [3H]cocaine, measured in 10 mM Na2HPO4-0.32 M sucrose, pH 7.4 buffer, is inhibited by physiologic concentrations of Na+ and K+ and by biogenic amines. DA and Na+ reduce the affinity of the putative "cocaine receptor" for [3H]cocaine without changing the Bmax, suggesting that inhibition may be competitive. However, TRIS reduces [3H]cocaine binding noncompetitively while Na+ potentiates it in TRIS buffer. Binding of [3H]mazindol is inhibited competitively by cocaine. In phosphate-sucrose buffer, cocaine and mazindol are equally potent in inhibiting [3H]mazindol binding, but in TRIS-NaCl buffer cocaine has 10 times lower potency. It is suggested that the cocaine receptor in the striatum may be an allosteric protein with mazindol and cocaine binding to overlapping sites, while Na+ and DA are allosteric modulators, which stabilize a lower affinity state for cocaine.

Alkaloids↗
PubMedDate not supplied

Allosteric regulation by sodium of the binding of [3H]cocaine and [3H]GBR 12935 to rat and bovine striata.

Sodium regulation of ligand binding to the dopamine transporter of rat and/or bovine striata was investigated using a filtration binding assay. In low Na+ phosphate or bicarbonate-buffered sucrose (300 mOsm), the tissue exhibited high affinity for [3H]cocaine which was reduced by the addition of Na+ in a dose-dependent manner. However, [3H]GBR 12935 binding was insensitive to Na+ in these physiological buffers. Although binding of [3H]GBR 12935 was displaced by cocaine in a manner consistent with competitive displacement, a non-linear affinity shift of the displacement of [3H]GBR 12935 by cocaine suggests that the two ligands bind to distinct sites. Binding of both radioligands was suppressed when measured in sodium-free 50 nM Tris-sucrose and increased with the addition of Na+. Scatchard analysis indicated that Bmax for [3H]cocaine binding in Tris plus 120 mM NaCl reached the same level as in the physiological buffers. In Krebs-Ringer buffer with phosphate, bicarbonate or Tris, which contained 120 nM NaCl, both [3H]cocaine and [3H]WIN 35428 binding exhibited lower affinities than in Na(+)-deficient phosphate buffer. It is suggested that the cation form of Tris binds to the dopamine transporter and that the Tris-receptor complex does not bind [3H]cocaine or [3H]GBR 12935. Na+ displaces Tris, forming a Na(+)-receptor complex which binds these ligands. Thus, it is suggested that the Na(+)-dependent binding of cocaine to the dopamine transporter is observed only in Tris.

Allosteric Regulation↗