Piperazine imidazo[1,5-a]quinoxaline ureas as high-affinity GABAA ligands of dual functionality.

A series of imidazo[1,5-a]quinoxaline piperazine ureas appended with a tert-butyl ester side chain at the 3-position was developed. Analogues within this series have high affinity for the gamma-aminobutyric acid A (GABAA)/benzodiazepine receptor complex with efficacies ranging from inverse agonists to full agonists. Many analogues were found to be partial agonists as indicated by [35S]TBPS and Cl- current ratios.

Pharmacological approaches to counter the toxicity of Dopa.

Dopa and related catecholamines and their degradation products have been demonstrated to have neurotoxic potential in a number of cellular and in vivo experiments. Several mechanisms have been hypothesized to be involved including generation of prooxidant products that subsequently oxidize membrane lipids and exposed macromolecules. We have utilized a neuronal culture of cerebellar granule cells to study the toxicity of Dopa and the ability of various neuroprotective and antiparkinsonian compounds to offer protection therefrom.

Two imidazoquinoxaline ligands for the benzodiazepine site sharing a second low affinity site on rat GABA(A) receptors but with the opposite functionality.

1. Imidazoquinoxaline PNU-97775 and imidazoquinoline PNU-101017 are benzodiazepine site ligands with a second low affinity binding site on GABA(A) receptors, the occupancy of which at high drug concentrations reverses their positive allosteric activity via the benzodiazepine site, and may potentially minimize abuse liability and physical dependence. 2.

Azulenyl nitrones: colorimetric detection of oxyradical end products and neuroprotection in the gerbil transient forebrain ischemia/reperfusion model.

We present analytical and neuroprotective data on a unique spin trapping agent derived from a novel chemical class known as an azulenyl nitrone (AZN). Based on Colorimetric properties, AZN was used to assess the formation of free radicals in a bilateral carotid occlusion (BCO) model in gerbils by monitoring the conversion of the nitrone to the aldehyde in affected tissue. In addition, AZN was tested as a neuroprotectant in this model regarding the preservation of CA1 pyramidal cells of the hippocampus following transient ischemia/reperfusion.

PNU-107484A with alpha isoform-dependent functional changes in alpha(x)beta2gamma2 subtypes of rat recombinant GABA(A) receptors.

1. We discovered a novel gamma-aminobutyric acidA (GABA(A)) receptor ligand displaying seemingly opposite functionalities, depending on the alpha isoform of the alpha(x)beta2gamma2 subtypes. PNU-107484A enhanced GABA-induced Cl- currents in the alpha1beta2gamma2 subtype, but inhibited the currents in the alpha3beta2gamma2 and alpha6beta2gamma2 subtypes, and its half-maximal concentrations in the subtypes were 3.

Pyrrolopyrimidines: novel brain-penetrating antioxidants with neuroprotective activity in brain injury and ischemia models.

A novel group of antioxidant compounds, the pyrrolopyrimidines, has been discovered recently. Many of these possess significantly improved oral bioavailability (56-70% in rats), increased efficacy and potency in protecting cultured neurons against iron-induced lipid peroxidative injury and as much as a 5-fold increase in brain uptake compared with the 21-aminosteroid antioxidant compound, tirilazad mesylate (U-74006F), described earlier. They appear to quench lipid peroxidation reactions by electron-donating and/or radical-trapping mechanisms.

D1 dopamine receptor activity of anti-parkinsonian drugs.

Clinical and preclinical investigations suggest that stimulation of D1 dopamine receptors may be responsible for dyskinesias induced by dopamine agonist treatment of Parkinson's Disease (PD), and that these dyskinesias may be decreased by treatment with a D1 antagonist (clozapine). Therefore, the effects of dopamine agonists and antagonists have been investigated in a primary cerebellar granule cell model of cAMP formation that seems to be highly responsive to the D1 receptors. SKF 38393, lisuride, apomorphine, pergolide, dopamine, bromocriptine and 7-OH-DPAT showed concentration-dependent increases in cAMP formation, with EC50s (in microM) of 0.

Effects of lazaroids and a peroxynitrite scavenger in a cell model of peroxynitrite toxicity.

We developed a cerebellar granule cell model of peroxynitrite toxicity and showed that certain sulfhydryl-containing compounds (e.g., penicillamine) present as concurrent treatments could inhibit this toxicity.

Neuroprotective effects of the dopamine D2/D3 agonist pramipexole against postischemic or methamphetamine-induced degeneration of nigrostriatal neurons.

We have examined the neuroprotective efficacy of the selective dopamine (DA) D2/D3 receptor agonist pramipexole in two models of nigrostriatal (NS) degeneration. The first involves the delayed (28-day) postischemic retrograde NS degeneration that takes place in gerbils following a 10-min episode of bilateral carotid arterial occlusion-induced forebrain ischemia. In vehicle (40% hydroxypropyl cyclodextrin)-treated male gerbils, there was a 40-45% loss of NS cell bodies in the pars compacta and pars reticulata (TH immunohistochemistry and Cresyl violet histochemistry) by 28 days after ischemia/reperfusion.

Pharmacological characterization of U-101387, a dopamine D4 receptor selective antagonist.

Dopamine D2-like receptors play an important role in the pharmacotherapy of psychotic disorders. Molecular and cellular techniques have identified distinct gene products (D2-long, D2-short, D3 and D4) displaying the D2 receptor pharmacology. However, the contribution of each subtype in antipsychotic effects of or their physiological role remain unclear.

3-Phenyl-substituted imidazo[1,5-alpha]quinoxalin-4-ones and imidazo[1,5-alpha]quinoxaline ureas that have high affinity at the GABAA/benzodiazepine receptor complex.

A series of imidazo[1,5-alpha]quinoxalin-4-ones and imidazo[1,5-alpha]quinoxaline ureas containing substituted phenyl groups at the 3-position was developed. Compounds within the imidazo[1,5-alpha]quinoxaline urea series had high affinity for the GABAA/benzodiazepine receptor complex with varying in vitro efficacy, although most analogs were partial agonists as indicated by [35S]TBPS and Cl- current ratios. Interestingly, a subseries of piperazine ureas was identified which had biphasic efficacy, becoming more antagonistic with increasing concentration.

Thyroid hormonal modulation of the binding and activity of the GABAA receptor complex of brain.

Thyroid hormones, which are known to act by genomic mechanisms in peripheral tissues, were found to influence the binding and function of the GABAA receptor complex in brain membranes. Submicromolar concentrations of triiodothyronine and thyroxine stereospecifically stimulated the binding of [35S]t-butylbicyclophosphorothionate (a convulsant ligand for the GABAA receptor complex) to highly washed rat brain membranes, while higher concentrations of the hormones inhibited radioligand binding. GABA-stimulated 36Cl-flux in isolated brain membrane sacs was inhibited by L-triiodothyronine with a half-maximally inhibitory concentration (IC50) of 10(-7) M.

High-affinity partial agonist imidazo[1,5-a]quinoxaline amides, carbamates, and ureas at the gamma-aminobutyric acid A/benzodiazepine receptor complex.

A series of imidazo[1,5-a]quinoxaline amides, carbamates, and ureas which have high affinity for the gamma-aminobutyric acid A/benzodiazepine receptor complex was developed. Compounds within this class have varying efficacies ranging from antagonists to full agonists. However, most analogs were found to be partial agonists as indicated by [35S]TBPS and Cl- current ratios.

U-90042, a sedative/hypnotic compound that interacts differentially with the GABAA receptor subtypes.

U-90042 is a structurally novel compound that has comparable affinities for binding to three recombinant subtypes of the gamma-aminobutyric acidA receptor: alpha 1 beta 2 gamma 2, alpha 3 beta 2 gamma 2 and alpha 6 beta 2 gamma 2. The relatively high affinity for the alpha 6 beta 2 gamma 2 subtype is similar to the benzodiazepine (BZ) partial inverse agonist Ro 15-4513 and different from BZ sedative/hypnotics such as diazepam and zolpidem. In the present study, U-90042 (3 mg/kg i.

Antibody transformation by peroxynitrite as determined using capillary electrophoresis: a feasibility study.

Peroxynitrite may be a physiologically relevant endogenous neurotoxin that forms following CNS trauma when excessive levels of NO and .O2 accumulate. Recently, peroxynitrite was found to inactivate the polyclonal antibody to cAMP.

Structure activity relationships of peroxynitrite scavengers an approach to nitric oxide neurotoxicity.

Nitric oxide (NO) is made by NO synthase during the conversion of arginine to citrulline. Researchers have found that they can block the actions of excitotoxins by inhibiting NO synthase. Released from excitable cells during trauma, NO may react with superoxide to form peroxynitrite.

The use of salicylate hydroxylation to detect hydroxyl radical generation in ischemic and traumatic brain injury. Reversal by tirilazad mesylate (U-74006F).

Oxygen free radicals have been implicated as a causal factor in posttraumatic neuronal cell loss following cerebral ischemia and head injury. The conversion of salicylate to dihydroxybenzoic acid (DHBA) in vivo was employed to study the formation of hydroxyl radical (.OH) following central nervous system (CNS) injury.

Differential affinity of dihydroimidazoquinoxalines and diimidazoquinazolines to the alpha 1 beta 2 gamma 2 and alpha 6 beta 2 gamma 2 subtypes of cloned GABAA receptors.

1. In this study, we compared two series of newly discovered ligands for their selectivity to benzodiazepine sites in the alpha 1 beta 2 gamma 2 and the alpha 6 beta 2 gamma 2 subtypes of cloned gamma-aminobutyric acidA (GABAA) receptors, the latter being unique in not interacting with classical benzodiazepines. 2.

Anticonvulsant and related effects of U-54494A in various seizure tests.

The anticonvulsant activity of (+-)-cis-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benz am ide monohydrochloride (U-54494A), a benzamide derivative chemically related to kappa opioid receptor agonists, was investigated in three selected seizure models of experimental epilepsy. In the maximal electroshock seizure test in mice, U-54494A (ED50 28 mg/kg i.p.

Potentiation of gamma-aminobutyric acid-induced chloride currents by various benzodiazepine site agonists with the alpha 1 gamma 2, beta 2 gamma 2 and alpha 1 beta 2 gamma 2 subtypes of cloned gamma-aminobutyric acid type A receptors.

Previous studies with cloned gamma-aminobutyric acid type A receptors expressed in human embryonic kidney cells have indicated that the alpha 1 beta 2 gamma 2 and alpha 1 gamma 2 (but not alpha 1 beta 2) subtypes have benzodiazepine sites. We found in this study that even the beta 2 gamma 2 subtype displays gamma-aminobutyric acid-induced Cl- currents that are potentiated by triazolam (a triazolobenzodiazepine). The maximal efficacy of the drug among the subtypes was highest with the alpha 1 beta 2 gamma 2 subtype, followed by the alpha 1 gamma 2 and beta 2 gamma 2 subtypes.

Triazolobenzodiazepines: a new class of stimulators of tissue-type plasminogen activator synthesis in human endothelial cells.

In our search for compounds that can stimulate endogenous fibrinolysis, we have found that certain triazolobenzodiazepines enhance the production of tissue-type plasminogen activator (t-PA) by vascular endothelial cells maintained in vitro, with no or even a lowering effect on plasminogen activator inhibitor type-1 (PAI-1) production. The most active compounds tested, U-34599, U-46195 and U-51477, were studied in more detail and showed a time- and dose-dependent increase in the production of t-PA by human umbilical vein endothelial cells. At optimal stimulatory concentrations (about 10 microM), the three compounds stimulated t-PA expression about 2-fold after 24 hr and maximally about 4-fold after 48 hr of incubation; this maximal increase in t-PA synthesis was sustained at prolonged incubations of 72 or 96 hr.

Centrally acting serotonergic agents. Synthesis and structure-activity relationships of C-1- or C-3-substituted derivatives of 8-hydroxy-2-(di-n-propylamino)tetralin.

The synthesis and structure-activity relationships (SAR) of C-1- or C-3-substituted derivatives of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) are described. These analogs were synthesized via alkylation of the tetralone derivatives followed by reductive amination. All of the analogs were inactive at the dopamine D2 receptor.

Competitive irreversible inhibition of dopamine uptake by 6-hydroxydopamine.

We examined the effects of 6-hydroxydopamine (6-OHDA) treatment on the human neuroblastoma cell line SK-N-SH-SY5Y (SY5Y) and the rat pheochromocytoma cell line, PC12. Structural and metabolic integrity was tested by measuring the ability of cells to transport the non-metabolizable amino acid analogue [3H]-alpha-aminoisobutyric acid (AIB). We determined that treatment with 6-OHDA at concentrations of 49 microM and 62 microM inhibited 50% of the AIB uptake in SY5Y and PC12 cells, respectively.

Hydroxyl radical production and lipid peroxidation parallels selective post-ischemic vulnerability in gerbil brain.

The salicylate trapping method was used to investigate the changes in hydroxyl radical (.OH) levels in the selectively vulnerable hippocampus compared to the cerebral cortex of gerbils subjected to a 10 min period of near complete forebrain ischemia. Salicylate-derived 2,5-dihydroxybenzoic acid (2,5-DHBA) was measured in sham-operated animals and at 1, 5, and 15 min of reperfusion.