Search

2614W94 [3-(1-trifluoromethyl)ethoxyphenoxathiin 10,10-dioxide] is a selective, reversible inhibitor of monoamine oxidase-A with a competitive mechanism of inhibition and a Ki value of 1.6 nM with serotonin as substrate. In pretreated rats, the ED50 value after single oral dosing was 1.7 mg/kg, similar to an ED50 value of 1.1 mg/kg estimated in the 5-hydroxytryptophan potentiation test. Maximal inhibition of monoamine oxidase-A (MAO-A) was observed by 0.5 h after dosing, suggesting rapid transport to brain. Inhibition in brain was maintained for several hours, followed by a gradual reversal with a half-time of 7.2 h. Brain levels of parent compound were higher than plasma levels at all times after dosing. No significant inhibition of MAO-B was observed. After preincubation of MAO with 2614W94 at 37°C, the inhibition was reversed by dialysis. Concentrations of serotonin, norepinephrine, and dopamine were clearly elevated in brains of rats after single oral doses, whereas levels of MAO metabolites were decreased. In a rat model designed to show blood pressure elevations in response to a threshold dose of orally administered tyramine, 2614W94 compared well with moclobemide, an MAO-A selective inhibitor that has not been associated with problems relating to dietary tyramine. The two stereoisomers of 2614W94 were both potent MAO-A inhibitors. In vitro and in vivo properties of 2614W94 suggest that this compound and its close analogs are among the most potent MAO-A inhibitors known and that they may have therapeutic potential as safe new antidepressant/anxiolytic agents. Drug Dev. Res. 45:1–9, 1998. © 1998 Wiley-Liss, Inc.

A series of bicyclo analogues of several 2-phenylmorpholines were synthesized and tested for anti-tetrabenazine activity in mice. Most of the target compounds were prepared by reaction of 2-bromopropio-phenone (22) with the appropriate amino alcohol to form 2-phenylmorpholinols. Reduction of the 2-phenyl-morpholinols with sodium borohydride gave amino diols, which were cyclized to morpholines with acid. Alternatively, oxazines 17 and 18 were synthesized by alkylation of phenyl-(2-pyrrolo)carbinol (32a) and phenyl-(2-piperidyl)carbinol (32b) with 2-bromoethanol, followed by cyclization of the resulting amino diols with acid. Only the spirocyclic compounds 8 and 9 had i.p. anti-tetrabenazine activity comparable to the non-cyclic compounds 2a-3b, but 8 and 9 were less active by the oral route of administration.

A series of 6-(alkylamino)-9-alkylpurines was synthesized and evaluated for the property of antagonizing the behavioral effects in animals of the dopamine agonist apomorphine. This model for identifying potential antipsychotic agents is based on the hypothesis that agents that antagonize apomorphine-induced aggressive behavior in rats and apomorphine-induced climbing in mice, but that do not block stereotyped behavior, could have an antipsychotic effect in humans without producing extrapyramidal side effects. The antiaggressive-behavior activity of lead compound 1 (6-(dimethylamino)-9-(3-phenylalaninamidobenzyl)-9H-purine) was improved 48-fold with 6-(cyclopropylamino)-9-(cyclopropylmethyl)-2-(trifluoromethyl)-9H- purine (80) (po ED50 of 2 mg/kg), which was obtained through an iterative sequence of structure--activity relationship studies that encompassed evaluation of the effects of structure variations at the purine 9-, 6-, and 2-positions. Potency was enhanced with a 9-cyclopropyl group, the duration of action was improved with the 6-(cyclopropylamino) substituent, potency was further enhanced with an N-formyl prodrug, and an agent with reduced cardiovascular effect emerged with the 2-trifluoromethyl purine 80. This potential antipsychotic agent was not developed further due to undesirable effects on the stomach.

1192U90 was developed on the assumption that antagonism of 5-HT2 receptors efficacy yields more potently than D2 receptors against positive and negative symptoms of schizophrenia with minimal liability for extrapyramidal side effects (EPSs), and that 5-HT1A agonism further reduces EPSs and provides anxiolytic and antidepressant activity. 1192U90 was submitted to four tests that predict antipsychotic efficacy (antagonism of apomorphine-induced climbing in mouse, antagonism of apomorphine-induced circling in rats with unilateral 6-OHDA lesions, antagonism of amphetamine-induced hyperlocomotion in rat, and inhibition of conditioned avoidance in rat), two tests of 5-HT2 function (antagonism of 5-MeODMT-induced head twitches in mouse and antagonism of 5-HTP-induced wet dog shakes in rat), and three tests that predict EPS liability (antagonism of apomorphine-induced stereotypy in mouse and rat and induction of catalepsy in mouse). ED50s (mg/kg PO) were as follows: climbing 10.1, circling 7.9, hyperlocomotion 6.6, and avoidance 5.7; head twitches 5 and wet dog shakes 4.6; stereotypy in mouse 91.1, stereotypy in rat 133.4, and catalepsy 192.4. The ratio of ED50 for stereotypy antagonism to ED50 for climbing antagonism was 9 (compared to 4, 3, and 4 for clozapine, risperidone, and haloperidol). The ratio of ED50 for catalepsy induction to ED50 for climbing antagonism was 19 (compared to 7, 2, and 17 for clozapine, risperidone, and haloperidol). 1192U90 was also submitted to three tests that predict anxiolysis: It produced only a small increase in punished lever pressing for food in rat (Geller-Seifter conflict test), which is specific for rapid-onset efficacy, but produced large increases in punished key pecking for food in pigeon and cork gnawing in rat, which identify the delayed onset 5-HT1A agonists such as buspirone. The results suggest that 1192U90 would be effective for positive and negative symptoms of schizophrenia, with minimal liability for EPSs, and may also have anxiolytic properties.

Extracts of Ginkgo biloba leaves produce reversible inhibition of rat brain monoamine (MAO). Both MAO-A and -B types were inhibited to a similar extent. The MAO inhibitory compound(s) were present in dried or fresh Ginkgo biloba leaves as well as in commercially available capsules of Ginkgo biloba and appear to be heat stable with relatively low molecular weight. MAO inhibition by Ginkgo biloba may be a mechanism underlying reported anti-stress and anxiolytic activities of this natural product.

A series of analogues of 2-phenylmorpholines with alkyl substituents at the C-3 position were synthesized for anti-tetrabenazine (anti-TBZ) testing in mice. The target compounds were prepared by reaction of (2-bromoalkyl) phenyl ketones 21a-h with the appropriate aminoalcohol 20a-b to form morpholinols 22a-h. Hydride reduction of the morpholinols gave aminodiols 23a-h which were cyclized to morpholines 6, 8, 10–12, 14–16, 18 and 19 by acid catalaysis. Compounds 7, 9, 13 and 17 were prepared by reductive formylation. The smaller straight chain substituents of 6, 8, 12 and 15, and the beta branching of the iso-butyl group of 16 were well tolerated; anti-tetrabenazine ED50′s were comparable to compounds 2–5. The α-branched, N-methylated, and side chain aryl derivatives were less active.

The imidazo[4,5-d]-1,2,3-triazine and pyrazolo[3,4-d]-1,2,3-triazine analogues of the potent anticonvul-sant purine, BW 78U79 (9-(2-fluorobenzyl)-6-methylamino-9H-purine, 1), were synthesized and tested for anticonvulsant activity. The imidazo[4,5-d]-1,2,3-triazines 11–13 were prepared in four steps from 5-aminoimidazole-4-carboxamide (2) and the pyrazolo[3,4-d]-1,2,3-triazines 18–21 were synthesized starting with 5-amino-1-(2-fluorobenzyl)pyrazole-4-carbonitrile (14). The intermediate 1,2,3-triazin-4-ones 6 and 16 were converted to the 4-substituted targets via the 4-(4-dimethylaminopyridinium) salts 10 and 17. Imidazotriazine 11 had potent anticonvulsant activity against maximal electroshock-induced seizures, but its propensity to cause emesis precluded further development.

A series of novel 4-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)butyl) cyclic amides was prepared and evaluated as potential antipsychotic agents. The target compounds were examined in vitro for their binding affinities to the dopamine D2, serotonin 5-HT2, and serotonin 5-HT1a receptors and in vivo for their ability to antagonize the apomorphine-induced climbing response in mice. Derivatives that exhibited good D2/5-HT2 selectivity in vitro and good potency in vivo were selected for further evaluation in tests designed to assess their potential extrapyramidal side effect liability. Structural modifications discussed herein focus on the bicyclic amide subunit leading to the preparation of a variety of heterocyclic ring systems (i.e., phthalimide, isoindolinone, isoquinolinone, benzazepinone, indazolone, phthalazinone, 4-methyl phthalazinone, benzisothiazolone 1,1-dioxide, benzotriazinone, homophthalimide, benzisothiazolone, phthalazinedione, quinazoline, and saturated phthalazinones). The potency and selectivity within this series was found to be dependent on ring size, nature of the covalent linking unit, relative position of the functional groups, degree of unsaturation, and relative stereochemistry. In general, the cyclic benzamides examined in this investigation exhibited receptor binding activities indicative of potential atypical antipsychotic agents. Several of these derivatives possessed in vivo activities that suggest they would be useful in the treatment of schizophrenia and would have a low propensity to induce extrapyramidal side effects. Two potent analogues were identified and selected for further evaluation: 2-(4-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)butyl)-1-isoind olinone (31) and (+-)-cis-2-(4-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)-butyl)- 4a,5,6,7,8,8a-hexahydro-1(2H)-phthalazinone hydrochloride (52).

Adult and neonatal rats treated with 6-OHDA to reduce NE, DA or both catecholamines have been used to examine the role of brain catecholamines in several behaviours (Table 1). The data implicated DA-containing fibres in the maintenance of several diverse functions including consummatory behaviour, active avoidance responding and self-stimulation of brain. Motor activity and stereotypies induced by amphetamine also appear to be dependent upon brain DA. Table 1 shows that brain NE at this time has been associated only with temperature control. Present findings are consistent with proposals (Everett and Wiegand, 1962; Seiden and Carlsson, 1963) suggesting alternative roles for DA not clearly related to its usual association with extrapyramidal function.

Eleven substituted 8-amino-3-benzyl-1,2,4-triazolo[4,3-a] pyrazines were synthesized and tested for anticonvulsant activity against maximal electroshock-induced seizures (MES) in rats. The compounds were prepared in four stages from the phenylacetonitriles. I. The intermediate (2,2,2-triethoxyethyl)benzenes III were condensed with 2-chloro-3-hydrazinopyrazine (IV) to provide the 3-benzyl-8-chloro-1,2,4-triazolo[4,3-a]pyrazines V. The latter were converted to the 8-amine targets VI with methylamine or ammonia. Several compounds exhibited potent activity against MES; the 3-(2-fluorobenzyl)-8-(methylamino) and 3-(2,6-difluorobenzyl)-8-(methylamino)congeners (4 and 12) exhibited the best anticonvulsant activity with oral ED50S of 3 mg/kg. The 1,2,4-triazolo[4,3-a]pyrazine ring system serves as a bioisostere of the purine ring for anticonvulsant activity; however, these agents exhibit less propensity to cause emesis.

A series of (fluorobenzyl)triazolo[4,5-c]pyridines was synthesized and tested for activity against maximal electroshock-induced seizures in rodents. The most promising compound, 14 (BW 534U87), which is a carbon-nitrogen isoster of a purine anticonvulsant, has a profile in rodents that suggests 14 will be free of emesis and useful in the treatment of seizure disorders for which phenytoin is presently indicated.

The 3H-imidazo[4,5-c]pyridazine, 1H-imidazo[4,5-d]pyridazine, and 1H-benzimidazole analogues of the potent anticonvulsant purine 9-(2-fluorobenzyl)-6-methylamino-9H-purine (1, 78U79) were synthesized and tested for anticonvulsant activity. The 3H-imidazo[4,5-c]pyridazines 8 and 9 were prepared in five stages from 3,4,5-trichloropyridazine (2). The 1H-imidazolo[4,5-d]pyridazine 15 was synthesized in four stages from 5-[(benzyloxy)methyl]-1,5-dihydro-4H-imidazo[4,5-d] pyridazin-4-one (10a). The benz-imidazole analogues 18 and 20 were prepared from 2,6-dinitroaniline in three stages. These compounds were one-tenth or less as active as 1 in protecting rats against maximal electroshock-induced seizures.

Analogues of 9-(2-fluorobenzyl)-6-(methylamino)-9H-purine (1) containing isosteric replacements of the imidazole ring atoms were synthesized and tested for anticonvulsant activity. The pyrrolo[2,3-d]-, pyrazolo[3,4-d]-, and triazolo[4,5-d]pyrimidines were less active than 1 against maximal electroshock-induced seizures (MES) in rats when given po. The differences in anti-MES activity for these analogues was not explained by differences in pKa or lipophilicity. However, the four classes of heterocycles have distinctly different calculated electrostatic isopotential maps, which may be related to optimum anticonvulsant activity.

Systemic administration of ritanserin elicited rapid changes in dopamine (DA) and serotonin (5-HT) levels in both dialysate and neuronal tissue extracts. These effects occurred in both a site-selective and a dose-related manner. Increases in extracellular levels of DA and 5-HT in the nucleus accumbens were maximal at 120–140 min after treatment. A dose of 0.63 mgJ.kg of ritanserin elicited larger and more prolonged increases in extracellular DA and 5-HT levels than did the 0.3 mgJ.kg dose. By contrast, 0.63 mgJ.kg of ritanserin elicited no changes in either DA or 5-HT levels with dialysate collected from the striatum. Ritanserin also induced dose-related decreases in tissue levels of DA and 5-HT from the nucleus accumbens. The site specificity of action was again noted in that there were no dose-dependent decreases in tissue levels of DA or 5-HT measured from the striatum. Ritanserin exerted little effect on metabolite levels from either dialysate or tissue extracts. Taken together, these findings show that selective 5-HT2 receptor antagonism modulates DA and 5-HT neurotrans-mission in a specific manner. These actions appear to involve increased release of DA and 5-HT rather than significant changes in metabolism. These findings add further weight to the importance of 5-HT2 receptor interactions as an important component of antipsychotic activity.

Monoamine oxidase (MAO) inhibitors increase brain concentrations of biogenic amines and decrease concentrations of the acidic metabolites of biogenic amines. It has been suggested that the magnitude of these effects is an indicator of MAO inhibition. Oral doses of BW 1370U87, moclobemide, and brofaromine were given to rats at doses previously shown to induce brain MAO-A inhibition by at least 80%. The effects on brain biogenic amines and their metabolites were quantified 2 and 4 hr after oral dosing using HPLC with electrochemical detection. Moclobemide and BW 1370U87 induced larger increases in 5HT, NE, and DA and larger decreases in DOPAC, 5HIAA, and HVA than did brofaromine at the doses tested. At 8 hr post-dose the effects of BW 1370U87 on 5HT, NE, DOPAC, and HVA were still significant (P≤0.05), and the time course was similar to that seen following moclobemide and brofaromine treatment. Only BW 1370U87 increased brain concentrations of biogenic amines at a dose that does not significantly potentiate pressor effects of orally administered tyramine.

We employed broken cell liver preparations in order to investigate potential species-specific differences in the metabolism of BW 1370U87, a new selective and reversible MAO-A inhibitor. The drug metabolizing capacity of crude liver homogenates from rat, dog, cat, monkey, and man was assessed based on the utilization of BW 1370U87 and the appearance of suspected metabolites. When incubated with liver homogenates (37° C) in the presence of a cofactor preparation designed to generate TPNH, BW 1370U87 (1 or 10 μM) was metabolized in a species and time dependent manner. The rate of disappearence of BW 1370U87 was more rapid in dog and cat preparations than those of rat, monkey and man. The appearance of metabolites coincided with the disappearance of BW 1370U87. Three metabolites, identified and synthesized as BW 183U88, BW 380U88, and BW 330U88 appeared in all five species. These metabolites were also found to be selective MAO-A inhibitors both in vitro and ex vivo and may contribute to the overall activity exhibited by the parent molecule.

BW 1370U87 is a potent, reversible, selective inhibitor of rat and human brain MAO-A with a competitive mechanism of action. The ED50 of BW 1370U87 for inhibition of MAO-A in rat brain is 8 mg/kg after oral administration, and the duration of action exceeds 7 hr. The ED80 dose for inhibition of MAO-A (20 mg/kg) elevates NE, DA, and 5-HT levels in brains of rats without significantly potentiating the blood pressure effects of a 15 mg/kg oral dose of tyramine. This dose of tyramine, extrapolated to man, exceeds the amount that could be consumed at one time from dietary sources. No inhibition of MAO-B has been observed with BW 1370U87 either in vitro or ex vivo. BW 1370U87 was effective in the 5-hydroxytryptophan potentiation test over the dose range that produced MAO-A inhibition in brain in both rats and mice, and it reduced swim stress induced immobility in the Porsolt test. The compound has positive effects on abnormal social behavior produced by early social deprivation in the rhesus monkey. BW 1370U87 had no adverse cardiovascular effects in dogs or rats. It also had no significant pharmacological effects on various isolated tissue preparations and did not cause changes in the neuronal transport or the receptor systems which mediate the antidepressant effects or side effects of the tricyclic antidepressants. An acute oral dose 100 times that which produced an 80% inhibition of brain MAO-A exhibited no signs of toxicity. BW 137OU87 appears to be a safe reversible MAO-A inhibitor with potential for treating depression, anxiety conditions, panic, phobias, obsessive compulsive behaviors, and borderline personality disorders.

The design of rigid cyclic analogues derived from cinnamamide 1, (E)-N-cyclopropyl-3-(3-fluorophenyl)prop-2-enamide, and beta-methylcinnamamide 2, (E)-N-cyclopropyl-3-(3-fluorophenyl)but-2-enamide, has led to the discovery of the potent, centrally acting muscle relaxant (E)-2-(4,6-difluoro-1-indanylidene)acetamide, 17. Compound 17 also possesses potent antiinflammatory and analgesic activity. This paper describes the synthesis and the muscle relaxant, antiinflammatory, and analgesic structure-activity relationships of 17 and 67 of its analogues. Compound 17 has been taken into phase I clinical trials.

Extension of the structure-activity relationship studies that led to the discovery of the nonsedating potent muscle relaxant, antiinflammatory, and analgesic agent (E)-2-(4,6-difluoro-1-indanylidene)acetamide, 1, has given rise to (E)-2-(4-chloro-6-fluoro-1-indanylidene)-N-methylacetamide, 2. Compound 2 is a potent antiinflammatory and analgesic agent without centrally acting muscle relaxant activity.

11192U90 was submitted to receptor binding and monoamine uptake assays. It bound potently at serotonin 5-HT2, dopaminergic D2, serotonin 5-HT1A, and adrenergic alpha 1 and alpha 2 receptors. It also bound to dopaminergic D1, serotonin 5-HT3, serotonin 5-HT4, and sigma sites, albeit with lower affinity. It was essentially inactive at 22 other sites, including those for cholinergic M1 and M2. It weakly inhibited uptake of 3H-norepinephrine, 3H-serotonin and 3H-dopamine. Acute doses of 1192U90 (5 and 20 mg/kg P.O.) increased whole-brain levels of dopamine metabolites but did not affect levels of norepinephrine, dopamine, and serotonin. Subcutaneous injection of 1192U90 (0.8 mg/kg/day) and clozapine (20 mg/kg/day) for 28 days preferentially decreased the number of spontaneously active dopamine cells in the ventral tegmental area (VTA) but not the substantia nigra (SN) of rats, as measured by population sampling. This outcome is characteristics of atypical antipsychotics like clozapine. Acute injections of 1192U90 reversed the rate-inhibiting effects of microiontophoretically applied dopamine and intravenously injected apomorphine and d-amphetamine on dopamine cell firing. Intravenous injection or iontophoretic application of 1192U90 or the 5-HT1A agonist (+/-)8-OH-DPAT inhibited the firing rates of dorsal raphe nucleus (DRN) neurons in rats, and the effects of both compounds were blocked by iontophoretically applied S(-) propranolol, a 5-HT1A antagonist. The results suggest that 1192U90 is a preferential dopamine D2 antagonist as well as a 5-HT1A agonist that may prove to be an atypical antipsychotic.

Over the last few decades it has become clear that depression can be effectively treated by elevating serotonergic and/or noradrenergic function in the brain. The close interplay between the ascending serotonergic pathways from the raphe and the ascending noradrenergic pathways from the locus coeruleus at both somatic and presynaptic sites makes it likely that both of these monoaminergic pathways will be altered by drugs acting selectively at enzymes or receptors of either one of these pathways. The role of 5-HT in the amelioration of unipolar depression has gained recent support with the introduction of the clinically effective selective serotonin reuptake inhibitors (SSRIs). However, a problem still unsolved by the introduction of the SSRIs is the slow onset of therapeutic effectiveness of all antidepressants of several weeks. Several lines of evidence suggest that this slow onset of action, particularly for the SSRIs, may be due to an inhibitory autoregulation of the serotonergic pathway after an elevation of synaptic 5-HT caused by activation of the somatodendritic 5-HT1A autoreceptor (Artigas et al.,1994; see Blier and Montigny, 1994). Larger increases in 5-HT than those achieved by the SSRIs may overcome some of the consequences of this inhibitory autoregulation and may therefore hasten the onset of therapeutic effect.

A series of (fluorobenzyl)triazolo[4,5-c]pyridines was synthesized and tested for activity against maximal electroshock-induced seizures in rodents. The most promising compound, 14 (BW 534U87), which is a carbon-nitrogen isoster of a purine anticonvulsant, has a profile in rodents that suggests 14 will be free of emesis and useful in the treatment of seizure disorders for which phenytoin is presently indicated.

Eleven substituted 8-amino-3-benzyl-1,2,4-triazolo[4,3-a] pyrazines were synthesized and tested for anticonvulsant activity against maximal electroshock-induced seizures (MES) in rats. The compounds were prepared in four stages from the phenylacetonitriles. I. The intermediate (2,2,2-triethoxyethyl)benzenes III were condensed with 2-chloro-3-hydrazinopyrazine (IV) to provide the 3-benzyl-8-chloro-1,2,4-triazolo[4,3-a]pyrazines V. The latter were converted to the 8-amine targets VI with methylamine or ammonia. Several compounds exhibited potent activity against MES; the 3-(2-fluorobenzyl)-8-(methylamino) and 3-(2,6-difluorobenzyl)-8-(methylamino)congeners (4 and 12) exhibited the best anticonvulsant activity with oral ED50S of 3 mg/kg. The 1,2,4-triazolo[4,3-a]pyrazine ring system serves as a bioisostere of the purine ring for anticonvulsant activity; however, these agents exhibit less propensity to cause emesis.

Background and Purpose Elevated glutamate levels are thought to be a primary cause of neuronal death after global cerebral ischemia. The purpose of this study was to investigate the potential neuroprotective effects of lamotrigine, a novel antiepileptic drug that inhibits the release of glutamate in vitro, with both behavioral and histological measures of global ischemia in gerbils. Methods The common carotid arteries of gerbils were occluded for either 5, 10, or 15 minutes. Twenty-one days after reperfusion, gerbils were tested for impairments in a spatial memory task (Morris water maze). After water maze testing the animals were killed, and damage to hippocampal pyramidal cells was assessed. The effect of lamotrigine on the behavioral and histological outcome of either 5 or 15 minutes of global ischemia was evaluated. Results Bilateral occlusion of the common carotid arteries for 5 minutes resulted in severe degeneration of hippocampal CA1 and CA2 pyramidal cells. Lamotrigine significantly prevented loss of hippocampal CA1 neurons when administered acutely (100 mg/kg PO) immediately after reperfusion or when administered in two equal doses of 30 or 50 mg/kg 2 hours before and immediately after reperfusion. Gerbils subjected to 5 minutes of ischemic insult were not impaired in their ability to solve a spatial memory task 21 days after cerebral ischemia. However, gerbils subjected to 10 and 15 minutes of carotid artery occlusion showed significant impairment in their ability to solve a water maze task. Lamotrigine significantly protected against the cognitive deficits associated with 15 minutes of cerebral ischemia. Histologically, increased durations of cerebral ischemia resulted in a progressive loss of CA1, CA2, and CA3 pyramidal cells. Lamotrigine completely protected gerbils exposed to 15 minutes of cerebral ischemia against CA3 cell loss and greatly reduced damage to the CA1 and CA2 cell tracts of the hippocampus. Lamotrigine also reduced the mortality associated with 15 minutes of ischemia. Conclusions Lamotrigine had neuroprotective effects in a gerbil model of global cerebral ischemia. Lamotrigine protected gerbils against behavioral deficits resulting from 15 minutes of carotid occlusion and also prevented histological damage resulting from 5 and 15 minutes of global cerebral ischemia.

The effects of a novel inhibitor 680C91 ((E)-6-fluoro-3-[2-(3-pyridyl)vinyl]-1H-indole) of the key enzyme of tryptophan catabolism tryptophan 2,3-dioxygenase (TDO), and a novel inhibitor 709W92 ((E)-6-fluoro-3-[2-(4-pyridyl)vinyl]-1H-indole), of both TDO and 5-hydroxytryptamine (5-HT) reuptake, were examined on tryptophan catabolism, cerebrospinal fluid (CSF) concentrations of tryptophan and 5-HT and serotonergic-mediated physiology and behaviour in the rat. The catabolism of L-[ring-2-14C]tryptophan in vivo was completely inhibited by prior administration of 709W92. 709W92, but not 680C91, potentiated head-twitch produced by 5-hydroxytryptophan, prevented head-twitch and whole brain 5-HT depletion produced by p-chloroamphetamine and rapidly decreased dorsal raphe firing. Both 709W92 and 680C91 elevated CSF tryptophan by up to 260% of basal concentration. A maximally effective dose of 680C91 elevated a global measure of brain extracellular 5-HT (CSF 5-HT) to concentrations similar to those seen maximally after exogenous tryptophan administration (approx 170% of basal). Maximally effective doses of 709W92 increased CSF 5-HT to concentrations comparable to those seen after tryptophan and 5-HT reuptake inhibitor coadministration (approx 900% of basal) and to concentrations greater than those achieved maximally with serotonergically active antidepressant monotherapy (approx 500% of basal). 709W92 did not elevate CSF 5-HT to concentrations associated with the serotonin syndrome (approx 3000% of basal). The combined TDO inhibitor/5-HT reuptake inhibitor, 709W92, showed anxiolytic activity in the rat-pup vocalization model of anxiety. These results show that 709W92 (a novel inhibitor of both TDO and 5-HT reuptake), can produce an elevation of CSF 5-HT similar to that achieved with a serotonin reuptake inhibitor/tryptophan combination therapy but with a more sustained timecourse; such compounds may therefore have superior antidepressant efficacy in the clinic.

Bupropion (BW 323U66) has been considered a dopaminergic antidepressant based on its ability to inhibit the uptake of dopamine (DA) somewhat more selectively than it inhibits uptake of norepinephrine (NE) or serotonin (5-HT). This report describes new evidence that bupropion selectively inhibits firing rates of NE cells in the locus coeruleus (LC) at doses significantly lower than those that inhibit activity of midbrain DA cells or dorsal raphe 5-HT cells. The IC50 dose (13 mg/kg i.p.) for inhibition of LC firing produced plasma concentrations that were not significantly different from those generated by the ED50 in the Porsolt test (10 mg/kg i.p.). The fourfold higher dose needed to inhibit DA cell firing (IC50 = 42 mg/kg i.p.) was similar to the dose associated with locomotor stimulation in freely moving rats. Bupropion did not change the firing rates of 5-HT cells in the dorsal raphe nucleus at any dose. In both in vitro and in vivo tests, the metabolite 306U73 (hydroxybupropion), a weak inhibitor of NE uptake, was approximately equipotent to bupropion with regard to inhibition of LC cells. Another metabolite, 494U73, had no effect on LC firing rates over a wide range of doses. Because of species variation in metabolism, 306U73 was not detected in plasma of rats after i.v. doses of bupropion that inhibited LC firing. Only trace amounts of 306U73 were detected after bupropion dosing for the Porsolt test. Pretreatment with reserpine markedly depleted catecholamines and reduced (by 30-fold) the potency of bupropion to inhibit LC firing.(ABSTRACT TRUNCATED AT 250 WORDS)

Rats were made dependent upon alcohol by oral intubation and tested for either audiogenic Scizure susceptibility, the effects of GABA-ergic drugs on audiogenic Scizure susceptibility, or changes in GABA levels. Audiogenic Scizures occurred during a period of 12–36 hrs after ethanol withdrawal with a peak at 18–24 hrs. Intracisternal injection of GABA or GABA agonists antagonized Scizures as did treatment with GABA-T inhibitors. GABA levels in brain stem (but not whole brain) were decreased significantly by 18 hrs after withdrawal. This decrease was not seen if “dependent” rats received alcohol prior to sacrifice. A depletion of brain stem GABA with dl-C-allylglycine also resulted in audiogenic Scizure susceptibility. Results suggest that GABA may play a role in Scizure susceptibility during withdrawal from alcohol.

Intracisternal injections of the selective GABA-T inhibitor, ethanolamine-O-sulfate (EOS) resulted in the blockade of apomorphine-stimulated locomotor activity and stereotyped behavior which was compared to haloperidol. Unlike haloperidol, EOS did not elevate measures of dopamine synthesis. EOS also did not affect the reduction of dopamine synthesis produced by apomorphine at doses which completely blocked the behavioral effects of apomorphine. While other studies showed that no evidence could be obtained that EOS blocked dopamine receptors in vitro , prior EOS treatment antagonized accumulation of 3 H-spiroperidol in striatum in vivo . Since this effect was seen 24 hrs after EOS but not 1 hr after EOS, it appears that EOS treatment results in the accumulation of a substance which may produce effects similar to neuroleptic drugs. GABA would be one likely candidate for this action.

Thyrotropin releasing hormone (TRH) antagonizes the behavioral and temperature reducing effects of pentobarbital in rodents. The hormone is effective whether given before or after the barbiturate. This antagonism by TRH of the effects of pentobarbital probably does not depend upon thyroid hormone release as L-triiodothyronine administration is ineffective.

Bupropion is a novel antidepressant agent. In the present study, an attempt was made to gain some insight into the mechanism of the drug's antidepressant activity. In vitro studies revealed that bupropion was a weak, competitive inhibitor of norepinephrine (NE) uptake into rat hypothalamic synaptosomes and of dopamine (DM) uptake into rat striatal synaptosomes, having IC50 values of 6.5 ± 0.6 × 10−6 M and 3.4 ± 0.4 × 10−6 M, respectively. At 1 × 10−5 M, the drug produced a 20 ± 3% inhibition of serotonin (5-HT) uptake into rat hypothalamic synaptosomes. The drug was also a weak inhibitor of the ATP-Mg+2 stimulated uptake of NE and DM into synaptic vesicles of whole rat brain, having IC50 values of 3.3 × 10−5 M and 6.0 × 10−5 M, respectively. Bupropion had no dose-dependent effect on the spontaneous release of NE, DM, and 5-HT from these synaptosomal preparations in concentrations as high as 1 × 10−4 M. Brain monoamine oxidase (MAO) activity in vitro was not affected by concentrations of the drug ranging from 10−7 M to 10−5 M. Bupropion was also without effect on brain MAO, 1 hr after i.p. doses in rats as high as 100 mg/kg. The ED50 value for bupropion necessary to inhibit the uptake of 3H-catecholamines by 50% into synaptosomes incubated in the serum from rats treated with the drug was 40 mg/kg i.p., while its ED50 value for antidepressant activity, as judged by the ability of bupropion to reverse the immobile posture of “helpless” rats, was 8 mg/kg i.p. These neurochemical properties of bupropion on uptake of biogenic amines and on MAO activity serve to distinguish it from other antidepressant drugs of the tricyclic and MAO inhibitor classes.

When the parameters of taste aversion conditioning and testing have been appropriately adjusted, benzodiazepines and barbiturates will markedly antagonize the expression of moderate taste aversions in rats. We call this the taste aversion conflict model of anxiety. In the present study, we investigate whether buspirone HCl (buspirone; p.o. and i.p.) is active in the taste aversion conflict model and whether buspirone will also increase unsuppressed saccharin (SACC) intake. We also investigated the effects of imipramine, desipramine, phenelzine sulfate, chlorpromazine, scopolamine and d-amphetamine sulfate in the taste aversion conflict model. To assess the possible effects of buspirone on the GABA-benzodiazepine supramolecular receptor complex, we compared buspirone with certain benzodiazepines, meprobamate and sodium phenobarbital on the antagonism of pentylenetetrazol-induced lethality in mice. Unlike benzodiazepines, meprobamate and phenobarbital, buspirone did not antagonize pentylenetetrazol-induced lethality. However, like those other anxiolytics, buspirone markedly antagonized the expression of conditioned taste aversion. All nonanxiolytic drugs tested had either no effect or very slight effects on the expression of conditioned taste aversion. These results suggest that the taste aversion conflict model is sensitive to novel anxiolytics and that it is selective for drugs clinically effective in the treatment of generalized anxiety disorders in man.

Thyrotropin releasing hormone (TRH) produced a rapid dose related elevation of muscle tonus accompanied by tremor and shivering-like movements in cats. This stimulant action of TRH also occurred in decerebrate cats and cats which had undergone spinal cord transection at the level of the first cervical vertebra. Recordings froir spinal cord ventral roots indicated that TRH induced a pronounced increase in spontaneous motor neuron action potentials. No such stimulation of muscle activity was produced by injections of thyrotropin (TSH), triiodothyronine (T3), deamidated TRH, or the constituent amino acids of TRH, pyroglutamic acid, histidine, and proline amide. Results suggest that TRH can act directly on the spinal cord to stimulate muscle activity via a nonendocrine mechanism.

Both thyrotropin-releasing hormone (TRH) and amphetamine antagonize pentobarbital. They are more effective in the day than at night. This is true for TRH even when the dose of pentobarbital is increased at night to prolong sedation. Under this condition the day-night difference is lost for amphetamine. Both substances are more effective in cold ambient temperatures (18 degrees C) and less effective in warm temperatures, but their activity at warmer temperatures (37 degrees C) is still substantial. In contrast, somatotropin release-inhibiting factor (SRIF) augments the effects of pentobarbital at room temperature. This action is unaffected by time of day. However, the increase in sleeping time is lost in both a warm environment and in a cold environment.

Rats learned to avoid a saccharin solution if their initial consumption of it was followed by intraperitoneal (IP) administration of 25 mg/kg l-5-hydroxytryptophan (l-5-HTP); this taste aversion learning did not occur in rats pretreated with 50 mg/kg (IP) of the aromatic l-amino acid decarboxylase inhibitor RO 4-4602 (benserazide). RO 4-4602 antagonized the l-5-HTP-induced elevation of 5-hydroxytryptamine (5-HT) in the mesentery but significantly increased the l-5-HTP-induced elevation of 5-HT in the brain. These results indicate that l-5-HTP-induced taste aversion is correlated with peripheral, but not central, elevation of 5-HT.

Summary Intracisternal administration of 200 μg of 5,7-dihydroxytrptamine (5,7-DHT) caused a prolonged reduction of brain serotonin which was accompanied by a depletion of brain norepinephrine. The depletion of norepinephrine was found to be antagonized by agents that inhibit uptake of norepinephrine as well as by several monoamine oxidase inhibitors. Intracisternal injections of 5,7-DHT (75 or 100 μg) to 7-day-old neonatal rats reduced brain serotonin and norepinephrine and produced a significant reduction of adult body weight. As in adults, pretreatment of neonatal rats with pargyline or desipramine prevented 5,7-DHT induced depletion of norepinephrine without affecting depletion of serotonin. Behaviorally, treatment of adult rats with 5,7-DHT facilitated acquisition of an active avoidance task and enhanced muricidal behavior. 5,7-DHT treatment was also found to enhance the depressant effects of 5-hydroxytryptophan on a fixed-ratio barpress response, suggesting that 5,7-DHT treated rats are supersensitive to serotonin in the central nervous system.

The anorectic effects of ( + )-amphetamine, mephentermine, methylphenidate, amantα-dine, or fenfluramine were examined in animals pretreated intracisternally with either 6-hydroxydopamine or 5,7-dihydroxytryptamine. Destruction of brain dopamine systems antagonized the anorectic effect of ( +)-amphetamine and mephentermine, but did not block the anorectic effects of fenfluramine. Neither destruction of brain norepinephrine systems nor depletion of norepinephrine with the dopamine-β-hydroxylase inhibitor, U-14,624, antagonized the anorectic response to ( + )-amphetamine. While destruction of brain serotonin-containing systems did not alter the anorectic response to ( + )-amphetamine, it significantly enhanced the anorectic potency of fenfluramine.

Ethanolamine-O-sulfate (EOS) is an irreversible selective inhibitor of GABA-transaminase. Intracisternal injections of EOS (100–400 μg/brain) produced dose-related inhibition of food-motivated operant behavior, decreases in food consumption and body weight, inhibition of GABA-transaminase, and increases in brain GABA levels. The time course of the changes in brain GABA correlated with the alterations in food-related behaviors. EOS over the same dose range did not produce observable changes in behavior, changes in operant behavior not motivated by food, or produce a conditioned taste aversion. Although EOS crosses the blood-brain barrier poorly, repeated intraperitoneal injections of 250 and 500 mg/kg produced decreases in body weight and increases in brain GABA levels. Confirmation of a role for GABA was obtained in experiments using aminooxyacetic acid, another GABA transaminase inhibitor, and muscimol, a GABA receptor agonist. These results suggest that a prominent pharmacological effect of GABA receptor stimulation and elevation of whole brain GABA is anorexia indicating that this putative neurotransmitter has a function in regulating hunger (or satiety) in the rat.

Thyrotropin releasing hormone (TRH) antagonizes pentobarbital sedation and hypothermia; somatotropin release inhibiting factor amplifies them. Other hypothalamic polypeptide releasing factors, Substance P and a variety of amino acids are ineffective. Three congeners of TRH antagonize pentobarbital; one amplifies it. The potencies of congeners as pentobarbital antagonists are unrelated to their potencies as pituitary thyrotropin releasers.

The effects of blockade of CA and 5-HT synthesis upon electrically-rewarded behavior were evaluated with two behavioral techniques. Comparison of free-operant responding and a rate-free measure suggests that interference with CA synthesis has a minimal effect on specific task performance, the effects being preponderantly exerted on an adrenergic motivational substrate. Interference with 5-HT synthesis produced no effect on performance or motivation in this study.

Present data support the proposal that dopaminergic fibers play an important role in the maintenance of intracranial self-stimulation. In addition, amphetamine-induced motor activity as well as the sterotypies produced by this drug were also found to be dependent upon intact dopaminergic fibers. Evidence was also presented that serotonin fibers may modulate the behavioral actions of amphetamine by acting as an inhibitory transmitter.

Changes in electrical self-stimulation responding were examined in rats with electrodes implanted in the lateral hypothalamus following 6-hydroxydopamine treatments which depleted brain dopamine, norepinephrine or both of these catecholamines. Acute depression of self-stimulation occurred after treatments which reduced brain dopamine, but did not occur in rats treated to deplete just brain norepinephrine. A chronic deficit in self-stimulation responding occurred in rats treated with 6-hydroxydopamine in combination with pargyline to reduce both brain amines, while responding of animals in which brain dopamine was reduced returned to levels observed prior to 6-hydroxydopamine treatment. A dose of α-methyl-tyrosine (25 mg/kg), which did not affect responding of control rats, caused a significant reduction in responding of rats depleted of brain dopamine. This treatment did not affect responding of rats depleted of brain norepinephrine. Administration of the dopamine-Β-hydroxylase inhibitor, U-14624, failed to affect self-stimulation in spite of an additional 70% reduction of brain norepinephrine content. The response to a dose of d-amphetamine (0.25 mg/kg), that increased self-stimulation of control rats, was significantly reduced in rats with brain dopamine selectively depleted. Rats in which norepinephrine was depleted responded to d-amphetamine like the control group. α-Methyltyrosine antagonized the increased self-stimulation responding following administration of d-amphetamine (1 mg/kg) to reserpinized rats, while U-14624 did not. Results support the hypothesis that central dopaminergic fibers have an important involvement in the maintenance of self-stimulation of brain.

Rats treated intracisternally with multiple doses of 6-hydroxydopamine (2 × 200 μg) in combination with pargyline, which depleted both brain norepinephrine and dopamine, showed no evidence of acquisition of an avoidance response in the shuttle box. Mean intertrial interval (ITI) crosses were not significantly different from control. Treatment with 2 × 250 μg of 6-hydroxydopamine without pargyline also retarded acquisition of avoidance, but to a lesser extent. ITI crosses for this latter group were significantly increased. Preferential depletion of norepinephrine facilitated acquistion of avoidance and increased the number of ITI crosses. The rate of acquisiton of the avoidance response by rats in which dopamine was preferentially reduced was not significantly different from control animals even though ITI crossing was significantly increased. These results are discussed in relation to views concerning the role of brain catecholamines in avoidance responding.

1-(n-decyl)-3-Pyrazolidinone (BW357U) is a potent, selective inhibitor of gamma-aminobutyrate aminotransferase (GABA-T) in vitro and in vivo. After acute or chronic, oral or intraperitoneal administration of BW357U to rats, brain GABA levels were elevated in a dose-dependent manner. When inhibition of brain GABA-T exceeded 50%, whole brain GABA levels were elevated approximately threefold, and an anorectic effect was observed in the absence of other symptoms. This compound, because of its potency and selectivity, may be useful in studies relating to the function of GABA-containing neurons in appetite regulation.

The effects of magnesium pemoline, tricyanoaminopropene, and d-amphetamine on the acquisition of a discriminated avoidance response were compared in 30-, 50-, and 100-day-old naive rats. The rats were placed in an automated shuttlebox immediately after drug treatment. The number of avoidance responses in a series of 100 trials was measured. Ten days after the initial acquisition session, the rats were retrained on the same task. The 30-day group was inferior to the 50- and 100-day groups in the training session, but no differences occurred in retraining. The drug-treated groups showed improved performance in the initial training session but were not different from the controls in the retraining session. No Drug by Age interaction was significant.