Although immunosuppressant immunophilin ligands promote neurite outgrowth in vitro, their neurotrophic activities are clearly independent of their immunosuppressive activity. In the present report, a novel nonimmunosuppressive immunophilin ligand, GPI-1046 (3-(3-pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate) is described. In vitro, GPI-1046 bound to FK506 binding protein-12 and elicited neurite outgrowth from sensory neuronal cultures with picomolar potency with maximal effects comparable to nerve growth factor. In vivo, GPI-1046 stimulated the regeneration of lesioned sciatic nerve axons and myelin levels. In the central nervous system, GPI-1046 promoted protection and͞or sprouting of serotonincontaining nerve fibers in somatosensory cortex following parachloroamphetamine treatment. GPI-1046 also induced regenerative sprouting from spared nigrostriatal dopaminergic neurons following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity in mice or 6-hydroxydopamine (6-OHDA) toxicity in rats. The rotational abnormality in 6-OHDA treated rats was alleviated by GPI-1046. These neurotrophic actions in multiple models suggest therapeutic utility for GPI-1046 in neurodegenerative diseases.

Ethanol, at pharmacologically relevant concentrations of 20 to 100 mM, stimulates gamma-aminobutyric (GABA) receptor-mediated uptake of 36Cl-labeled chlorine into isolated brain vesicles. One drug that acts at GABA-benzodiazepine receptors, the imidazobenzodiazepine Ro15-4513, has been found to be a potent antagonist of ethanol-stimulated 36Cl- uptake into brain vesicles, but it fails to antagonize either pentobarbital- or muscimol-stimulated 36Cl- uptake. Pretreatment of rats with Ro15-4513 blocks the anticonflict activity of low doses of ethanol (but not pentobarbital) as well as the behavioral intoxication observed with higher doses of ethanol. The effects of Ro15-4513 in antagonizing ethanol-stimulated 36Cl- uptake and behavior are completely blocked by benzodiazepine receptor antagonists. However, other benzodiazepine receptor inverse agonists fail to antagonize the actions of ethanol in vitro or in vivo, suggesting a novel interaction of Ro15-4513 with the GABA receptor-coupled chloride ion channel complex. The identification of a selective benzodiazepine antagonist of ethanol-stimulated 36Cl- uptake in vitro that blocks the anxiolytic and intoxicating actions of ethanol suggests that many of the neuropharmacologic actions of ethanol may be mediated via central GABA receptors.

The effects of ethanol on Cl-uptake were studied using a cell-free subcellular preparation from brain that contains a y-aminobutyric acid (GABA)/barbiturate receptor-sensitive Cl transport system. In isolated vesicles prepared from rat cerebral cortex, ethanol, at concentrations that are present during acute intoxication (20-50 mM), stimulated 36CI-uptake in a concentration-dependent and biphasic manner. The ethanol-stimulated uptake of 36CI-was markedly inhibited by the GABA antagonists picrotoxin and bicuculline but not by a variety of other neurotransmitter receptor antagonists. The effects of ethanol in stimulating 36CI-uptake in isolated brain vesicles were qualitatively and quantitatively similar to that of pentobarbital. Ethanol also markedly potentiated both muscimol-and pentobarbital-stimulated 36CI-uptake at concentrations below those that directly stimulate Cl-uptake. Under our incubation conditions, ethanol did not release GABA, suggesting that it interacts with the postsynaptic GABA/barbiturate receptor complex. The ability of ethanol to stimulate GABA/barbiturate receptor-mediated Cl-transport may explain many of its pharmacological properties and provides a mechanism for the common psychopharmacological actions of ethanol, barbiturates, and benzodiazepines.Ethanol is one of the oldest and most commonly used of all psychotropic drugs (1). Repeated exposure to ethanol produces both psychological and physical dependence and its abuse potential constitutes a major public health problem (2). The neurochemical mechanism(s) underlying the depressant effects of ethanol on the central nervous system (CNS) is poorly understood (3) despite numerous studies demonstrating effects of ethanol on several neurotransmitter systems (4, 5). Ethanol shares many pharmacologic actions with both barbiturates and benzodiazepines. For example, ethanol, like barbiturates and benzodiazepines, possesses anxiolytic and sedative/hypnotic activity in both laboratory animals (6, 7) and humans (8). Moreover, previous studies have documented the development of behavioral cross-tolerance between ethanol, barbiturates, and benzodiazepines (9, 10). Benzodiazepines and barbiturates, which also show crossdependence with each other, are effective in alleviating the withdrawal symptoms that occur after chronic ethanol administration, suggesting that all three drugs may share a common mechanism of action (11).It is now generally accepted that both benzodiazepines and barbiturates produce their major pharmacological effects by augmenting the actions of the principal inhibitory neurotransmitter of brain, y-aminobutyric acid (GABA) (12)(13)(14)(15) ly associated with the Cl-channel in both rat and mouse brain membranes (25,26). Unfortunately, the concentrations of ethanol used in many of these receptor binding studies exceed those observed during acute intoxication (>30 mM) and are, in fact, many times above the lethal concentration (>100 mM) (27,28).Recently, we have reported the use of the "synaptoneurosome," a subcellular brain pre...

We review the neurochemical and behavioral profile of the selective gamma-aminobutyric acid (GABA) uptake inhibitor, (R)-N-(4,4-di-(3-methylthien-2-yl)but-3-enyl) nipecotic acid hydrochloride [tiagabine (TGB), previously termed NNC 05-0328, NO 05-0328, and NO-328], which is currently in phase III clinical trials for epilepsy. TGB is a potent, and specific GABA uptake inhibitor. TGB lacks significant affinity for other neurotransmitter receptor binding sites and/or uptake sites. In electrophysiological experiments in hippocampal slices in culture, TGB prolonged the inhibitory postsynaptic potentials (IPSP) and inhibitory postsynaptic currents (IPSC) in the CA1 and CA3 produced by the addition of exogenous GABA. In vivo microdialysis shows that TGB also increases extracellular GABA overflow in a dose-dependent manner. Together these biochemical data suggest that the in vitro and in vivo mechanism of action of TGB is to inhibit GABA uptake specifically, resulting in an increase in GABAergic mediated inhibition in the brain. TGB is a potent anticonvulsant agent against methyl-6,7-dimethyoxy-4-ethyl-B-carboline-3-carboxylate (DMCM)-induced clonic convulsions (mice), subcutaneous pentylenetetrazol (PTZ)-induced tonic convulsions (mice and rats), sound-induced convulsions in DBA/2 mice and genetically epilepsy-prone rats (GEPR), and electrically induced convulsions in kindled rats. TGB is partially efficacious, against subcutaneous PTZ-induced clonic convulsions, and photically induced myoclonus in Papio papio. TGB is weakly efficacious in the intravenous PTZ seizure threshold test and the maximal electroshock seizure (MES) test and produces only partial protection against bicuculline (BIC)-induced convulsions in rats. The overall biochemical and anticonvulsant profile of TGB suggests potential utility in the treatment of chronic seizure disorders such as generalized clonic-tonic epilepsy (GTCS), photomyoclonic seizures, myoclonic petit mal epilepsy, and complex partial epilepsy.