Dopaminergic and serotonergic activities of imidazoquinolinones and related compounds

The synthesis of 5-(dipropylamino)-5,6-dihydro-4H-imidazo[4,5,1-ij] quinolin-2(1H)-one (5), a potent dopamine D2 agonist showing high dopamine/serotonin (5HT1A) selectivity, is described. Dopaminergic activity is associated with the (R)-enantiomer of 5; the (S)-enantiomer shows no dopaminergic activity. A series of analogues where the imidazolone ring was modified to various 5- or 6-membered heterocyclic rings were prepared. Some of these compounds showed a combination of dopaminergic and serotonergic activity, while one compound, 6-(dipropylamino)-1,2,6,7-tetrahydro-3H,5H-pyrido[3,2,1- ij]quinazolin-3-one (24), was a selective serotonergic agonist. Various analogues of 5 where the dipropylamine substituent was modified were prepared. Most of these showed reduced dopaminergic activity, while several were as potent as 5 at the serotonin 5HT1A receptor. Orientations for the new compounds at dopamine and serotonin receptors are proposed and compared with those of other tricyclic ligands known to have high affinity at these receptors.

Reboxetine: a pharmacologically potent, selective, and specific norepinephrine reuptake inhibitor

BACKGROUND

Reboxetine is a potent antidepressant, with efficacy comparable to that of imipramine, desipramine, and fluoxetine, and has improved side-effect profile. The basis of its efficacy and improved tolerability is sought through studies of reboxetine in a number of pharmacological models of depression.

METHODS

Pharmacological selectivity for uptake systems was defined by uptake and binding assays for the three monoamine uptake sites. Specificity was determined in 39 different receptor and 6 enzyme assays. In vivo selectivity was defined by measurement of neuronal firing rates in the locus coeruleus, dorsal raphe, and substantia nigra. Reserpine-induced blepharospasm and hypothermia, clonidine-induced hypothermia, defined reboxetine's in vivo pharmacology. Reboxetine's antidepressant potential was evaluated behaviorally by the tail-suspension test, forced swimming, and the DRL72 operant responding test.

RESULTS

Reboxetine is a potent, selective, and specific norepinephrine reuptake inhibitor (selective NRI) as determined by both in vitro and in vivo measurements. Unlike desipramine or imipramine, reboxetine has weak affinity (Ki > 1,000 nmol/L)for muscarinic, histaminergic H1, adrenergic alpha1, and dopaminergic D2 receptors. In vivo action of reboxetine is entirely consistent with the pharmacological action of an antidepressant with preferential action at the norepinephrine reuptake site. Reboxetine showed an antidepressant profile in all tests of antidepressant activity used. Significant decreases in immobility were observed in the tail suspension test and behavioral despair test. Increased efficiency in responding was observed in the DRL72 test.

CONCLUSIONS

Reboxetine is a potent, selective, and specific noradrenergic reuptake inhibitor. It has a superior pharmacological selectivity to existing tricyclic antidepressants and selective serotonin reuptake inhibitors when tested in a large number of in vitro and in vivo systems. Given the pharmacological profile, reboxetine is expected to be a selective and potent tool for psychopharmacological research. The use of reboxetine in the clinic will also help clarify the role norepinephrine plays in depression.

The effects of (+)-UH232 and (-)-DS121 on local cerebral glucose utilization in rats

Although (+)-UH232 (cis-(+)-5-methoxy-1-methyl-2-(n-dipropylamino)tetralin) and (-)-DS121 (S(-)-3-(3-(cyanophenyl)-N-n-propylpiperidine) are both preferential dopamine autoreceptor antagonists, (-)-DS121 is a more effective behavioral stimulant and dopamine releasing agent. To further compare these two agents, Sokoloff's 2-deoxyglucose autoradiography method was used to study the effects of (+)-UH232 and (-)-DS121 on regional brain energy metabolism. (+)-UH232, 30 mg/kg i.p., depressed metabolism in 37 of 65 brain regions and antagonized the stimulant effects of amphetamine. (-)-DS121, 30 mg/kg i.p., exhibited a strong, nonsignificant trend towards an increase in regional brain energy metabolism by itself and enhanced the stimulant effects of amphetamine. The data demonstrate dramatic differences in the effects of two autoreceptor antagonists on regional brain energy metabolism. It is concluded that, compared to (+)-UH232, (-)-DS121 is a more effective stimulant of brain energy metabolism and autoreceptor antagonist owing to its greater ability to increase DA release.

Neurochemical and behavioral evidence supporting (+)-AJ 76 as a potential pharmacotherapy for cocaine abuse

In vivo microvoltammetry was used to detect synaptic concentrations of dopamine (DA) and serotonin (5-HT) from nucleus accumbens (NAcc) in awake, freely moving, male, Sprague Dawley laboratory rats, while their locomotor behavior was monitored, simultaneously, in an open-field paradigm; the purpose was to evaluate the pharmacology of the D3-preferring, dopamine (DA) autoreceptor antagonist, (+)-AJ 76 [cis-(+)-1S, 2R-5-methoxy-1-methyl-2-(n-propylamino)-tetralin HCL] and its potential use as a pharmacotherapy for cocaine abuse. Results showed that (1). (+)-AJ 76 significantly increased synaptic concentration of DA above baseline (p < 0.001); a small but significant decrease in synaptic concentration of 5-HT was seen (p < 0.001), although a significant increase occurred during the time course, at the 20 minute mark (p < 0.05). Analysis of the two hour data also showed that both locomotor and central locomotor activity were not affected; however, temporally related increases in both behaviors were significant at 10, 20 and 30 minutes (p < 0.05). In a second and separate study, (2). cocaine increased synaptic concentrations of DA (p < 0.001) and 5-HT (p < 0.001), and locomotor activity (p < 0.001) above baseline, but central locomotion was not affected, except for specific temporal enhancements at 10, 20, 30, 50, 60 and 90 min. (p < 0.05). In a third and separate study, (3). an (+)-AJ 76/cocaine study, (+)-AJ 76 was administered five minutes before cocaine. The results showed that synaptic DA concentration was significantly increased over baseline values (p < 0.001) but that synaptic DA was lower than cocaine-induced synaptic DA (p < 0.001). No significant difference in synaptic 5-HT occurred after (+)-AJ 76/cocaine treatment, but temporally related increases over baseline occurred from 10 to 40 min. (p < 0.05). Synaptic 5-HT concentrations after (+)-AJ 76/cocaine were not significantly different from those induced by cocaine per se. (+)-AJ 76/cocaine treatment significantly increased locomotor activity (p < 0.001); central locomotor behavior was not affected, however, time course data showed significant increases at 10, 20, 40, 50 and 80 min. (p < 0.05). The major finding from the present studies, is that +(-) AJ 76/cocaine treatment produced synaptic concentrations of DA from NAcc which were lower than those due to cocaine per se, while no differential effect on synaptic 5-HT concentration, locomotor or central locomotor behavior occurred. Therefore, these data support the hypothesis that (+)-AJ 76 may be useful for the treatment of cocaine addiction or abuse.

Pramipexole--a new dopamine agonist for the treatment of Parkinson's disease

Although L-DOPA is the current 'gold standard' for treatment of Parkinson's disease, its effectiveness fades rapidly and its use results in serious motor fluctuations (on-off, wearing off, freezing, involuntary movements) for most patients with Parkinson's disease. Pramipexole is an aminothiazole dopamine agonist with selective actions at dopamine receptors belonging to the D2 subfamily, where it possesses full activity similar to dopamine itself. Pramipexole's preferential affinity for the D3 receptor subtype could contribute to efficacy in the treatment of both the motor and psychiatric symptoms of Parkinson's disease. Both in vitro and in vivo studies in animals suggest that pramipexole possesses numerous neuroprotective properties, including dopamine autoreceptor agonist properties, antioxidant properties, ability to block the mitochondrial permeability transition pore and the ability to stimulate the release of trophic factors. Clinical studies have demonstrated that pramipexole has excellent pharmacokinetic properties and that it is an effective monotherapy in treating early Parkinson's disease and an effective adjunctive therapy with L-DOPA in treating late Parkinson's disease. In addition, pramipexole has demonstrated efficacy in a clinical trial for the treatment of major depression. In the early disease studies, pramipexole was able to retard the need for L-DOPA treatment for several years. Thus, a new 'L-DOPA-sparing' paradigm for treating Parkinson's disease may now be possible, whereby patients are initially treated with pramipexole and L-DOPA is added only as necessary.

Clozapine, haloperidol, and the D4 antagonist PNU-101387G: in vivo effects on mesocortical, mesolimbic, and nigrostriatal dopamine and serotonin release

With in vivo microvoltammetry, the dopamine (DA) receptor antagonists, clozapine (D4/D2), haloperidol (D2) and the selective D4 antagonist, PNU-101387G, were evaluated for their effects on DA and serotonin (5-HT) release within A10 neuronal terminal fields [mesocortical, prefrontal cortex (PFC), mesolimbic, nucleus accumbens, (NAcc)] and within A9 neuronal terminal fields [nigrostriatal, caudate putamen (CPU)], in chloral hydrate anesthetized rats. Clozapine, which also has 5-HT2 receptor antagonist properties, significantly (p < 0.001) increased DA release within A10 terminal fields, PFC and NAcc; DA release was not increased by clozapine within A9 terminals, CPU. Serotonin release was significantly (p < 0.001) increased by clozapine within A10 and A9 terminal fields. Haloperidol significantly (p < 0.001) increased DA release within PFC, dramatically and significantly (p < 0.001) increased DA release within CPU, but not within NAcc; haloperidol had a small but statistically significant (p < 0.05) increase on 5-HT release within PFC [only at the highest dose studied (2.5 mg/kg)] and within CPU [only at the lowest dose studied 1.0 mg/kg) (p < 0.05)]. The selective D4 antagonist, PNU-101387G dramatically and significantly (p < 0.001) increased DA release within PFC, modestly, but significantly (p < 0.001) increased DA release within CPU, did not alter DA release within NAcc at the lowest dose studied (1.0 mg/kg) and significantly (p < 0.05) decreased DA release within NAcc at the highest dose studied (1.0 mg/kg). The selective D4 antagonist did not affect 5-HT release within either A10 or A9 terminal fields. The present data are discussed in terms of the neurochemistry, antipsychotic activity, and side effect profiles of clozapine and haloperidol, in order to provide comparative profiles for a selective D4 antagonist, PNU-101387G.

Pharmacology of pramipexole, a dopamine D3-preferring agonist useful in treating Parkinson's disease

Pramipexole is a clinically effective nonergot dopamine agonist. Pramipexole's receptor interactions differ from ergot agonists in several ways. First, it has high selectivity for interacting with dopamine D2 subfamily receptors (D2, D3, and D4 receptor subtypes) and has little interaction with adrenergic or serotonergic receptors. Second, within the D2 subfamily, it has preferential affinity for the D3 receptor subtype, which, according to preclinical studies, could contribute additional efficacy for treatment of both motor and psychiatric syndromes in Parkinson's disease. Third, it has full intrinsic activity at dopamine D2 subfamily receptors. In addition to pramipexole's unusual receptor profile, whole-animal and cell culture studies suggest that pramipexole might provide neuroprotective effects through depression of dopamine metabolism, antioxidant effects, and stimulation of trophic activity. Pramipexole's demonstrated clinical efficacy for successful treatment in early disease for several years in the absence of L-dopa and as adjunctive therapy with L-dopa in late disease suggests a potential new paradigm for treatment of Parkinson's disease whereby new patients are initiated with pramipexole therapy and L-dopa is added only as necessary.

Excitation of type II anterior caudate neurons by stimulation of dopamine D3 receptors

Previous studies have demonstrated that both direct- and indirect-acting dopamine (DA) receptor agonists excite type II neurons in the anterior caudate (CN) by stimulation of DA receptors belonging to the D2 receptor subfamily (D2, D3, D4 receptor subtypes). In the present study, pramipexole, a D3-preferring DA agonist effective in treating Parkinson's disease, excited type II anterior CN neurons. As with other direct-acting agonists, excitation of the CN neurons occurred only at doses above those that silenced DA neurons in the substantia nigra pars compacta (SNPC). Although more potent than pramipexole in inhibiting SNPC cells, PNU-91356A, a D2-preferring agonist, did not excite type II CN cells. The D3-preferring antagonist (+)-AJ76 was weaker than haloperidol, a D2-preferring antagonist, in reversing the effects of amphetamine on firing rates in dopaminergic neurons in both the SNPC and the CN. However, in relationship to its potency in the SNPC, (+)-AJ76 was more potent than haloperidol in the CN. PNU-101387, a selective D4 antagonist, did not alter amphetamine-induced stimulation of type II CN neurons. We conclude that DA agonists may excite type II anterior CN neurons via D3 receptor activation. The stimulation of these neurons may contribute to the anti-parkinsonian effects of pramipexole.

Synthesis and biological activities of (R)-5,6-dihydro-N,N-dimethyl-4H-imidazo[4,5,1-ij]quinolin-5-amine and its metabolites

The imidazoquinoline (R)-5,6-Dihydro-N,N-dimethyl-4H-imidazo[4,5,1-ij]quinolin-5-amine [(R)-3] is a potent dopamine agonist when tested in animals but surprisingly shows very low affinity in in vitro binding assays. When incubated with mouse or monkey liver S9 microsomes, (R)-3 is metabolized by N-demethylation and oxidation to (R)-5,6-dihydro-5-(methylamino)-4H-imidazo[4,5,1-ij]quinolin-2(1H) -one [(R)-6], intermediate metabolites, where N-demethylation to the imidazoquinoline (R)-4 and where oxidation to the imidazoquinolinone (R)-5 has taken place, are also observed in these incubates. A cross-species study on the metabolism of (R)-3 in vitro has shown large variations in the extent of metabolism from species to species. Imidazoquinolinones (R)-5 and (R)-6 have comparable activity to (R)-3 in animals and also show good dopaminergic (D2) and serotonergic (5HT1A) activities in binding assays. It is probable that these metabolites account at least in part for the in vivo activity found for (R)-3. Efficient syntheses for compounds 3-6 as single enantiomers from quinoline are presented together with information on the biological activities and metabolic stabilities of these compounds.

Interactions between cocaine and (-)-DS 121: studies with 2-deoxyglucose autoradiography and microdialysis in the rat brain

(-)-DS 121 [S-(-)-3-(3-cyanophenyl)-N-n-propyl piperidine], a dopamine autoreceptor preferring antagonist, has been shown to stimulate locomotor activity and induce conditioned place preference. However, the drug fails to facilitate intracranial self-stimulation or substitute for cocaine in cueing experiments, and it blocks cocaine self-administration. In the present study using 2-deoxyglucose autoradiography, (-)-DS 121 (at 50 but not 15 mg/kg i.p.) significantly and selectively increased local cerebral glucose utilization in the olfactory cortex, medial and lateral septum, hippocampal areas, substantia nigra pars reticulata, caudate, and mammillary body. Local cerebral glucose utilization was depressed in caudal areas of the cortex. Interestingly, however, both doses of (-)-DS 121 blocked the increases in local cerebral glucose utilization produced by 5 mg/kg i.v. cocaine. The present study also evaluated the effects of (-)-DS 121 of extracellular striatal dopamine levels using microdialysis in freely moving rats. By itself, 15 mg/kg of (-)-DS 121 increased extracellular striatal dopamine levels to approximately 300% of controls. Cocaine (5 mg/kg i.v.) produced a 370% increase in striatal dopamine levels. When rats were pretreated with (-)-DS 121, a subsequent dose of cocaine augmented the increase in extracellular striatal dopamine to 870% of controls. The results support the contention that (-)-DS 121 possesses weak cocaine-mimetic effects and that its antagonism of cocaine's subjective effects are due to interactions with dopamine at postsynaptic sites. It is hypothesized that, like other preferential autoreceptor antagonists, (-)-DS 121 may be useful as a pharmacotherapy in drug addiction.

Pharmacology of U-91356A, an agonist for the dopamine D2 receptor subtype

U-91356A [(R)-5,6-dihydro-5-(propylamino)4H-imidazo[4,5,1-ij]quinolin -2-(1H)-one, monohydrochloride], bound with highest affinity to the dopamine D2 receptor subtype, although it also bound with somewhat lower affinities to the dopamine D3 and D4, as well as the 5-HT1A receptor subtypes. In addition to depressing dopamine synthesis and turnover, injection of U-91356A increased striatal acetylcholine concentrations. U-91356A also depressed firing rates of dopamine neurons. In mice, this compound stimulated cage climbing and locomotor activity in reserpinized animals; it also antagonized D-amphetamine-stimulated locomotor activity. It produced contralateral turning in rats with unilateral lesions of the substantia nigra. These data are consistent with roles for the dopamine D2 receptor subtype as a dopamine autoreceptor and as a stimulatory, postsynaptic dopamine receptor.

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. Here we describe the pharmacological effects of a selective D4 antagonist, U-101387. U-101387 displayed moderately high affinity (Ki = 10 nM) and selectivity for the dopamine D4.2 receptor expressed in clonal cell lines. It lacked measurable affinity for not only other dopamine receptors but also noradrenalin, serotonin and histamine receptor families (Ki > 2000 nM). It fully and dose-dependently antagonized quinpirole-induced cAMP inhibition (without producing any effect by itself) in stably transfected cells. U-101387 also displayed excellent oral bioavailability, brain penetration and other pharmacokinetic characteristics. Unlike classical neuroleptics (e.g., haloperidol), U-101387 neither blocked acute behavioral effects of amphetamine or apomorphine nor did it alter spontaneous locomotion by itself. Additionally, U-101387 was without effect in behavioral and biochemical tests predictive of extrapyramidal and neuroendocrine side effects. Consistent with the lack of autoreceptor function of D4, acute administration of U-101387 failed to alter dopamine neuronal firing by itself or reverse the inhibition produced by dopamine agonists and to affect monoamine turnover in areas innervated by the mesencephalic or hypothalamic dopamine neurons. However, U-101387 potently induced c-fos mRNA expression in the infralimbic/ventral prelimbic cortex to a level similar to that produced by the atypical antipsychotic, clozapine. This is consistent with the predominantly cortical distribution of the D4 receptor. Taken together, these results demonstrate that the D4-selective antagonist, U-101387, produces effects that are distinct from those of the nonselective D2 antagonists as well as D3-preferring agents. U-101387 offers a unique tool to understand the role of dopamine D4 receptors in diseases involving central dopamine systems.

High affinity binding for pramipexole, a dopamine D3 receptor ligand, in rat striatum

Quantitative autoradiography of rat brain slices was carried out with eight concentrations of [3H]pramipexole, a dopamine D3 receptor-preferring ligand. Saturation analysis revealed high affinity pramipexole binding (Kd = 0.2-0.4 nM) in the islets of Calleja, nucleus accumbens, olfactory tubercle, and anterior caudate. Since these affinities resemble pramipexole's affinity for the high affinity state of the rat dopamine D3, but not D2 receptors, it is possible that dopamine D3 receptors have greater presence in caudate than has heretofore been appreciated.

Inhibition of dopamine neuron firing by pramipexole, a dopamine D3 receptor-preferring agonist: comparison to other dopamine receptor agonists

Pramipexole, an amino-benzathiazole [(S)-4,5,6,7-tetrahydro-N-6-propyl-2, 6-benzothiazolediamine dihydrochloride monohydrate] direct-acting dopamine receptor agonist effective in treating Parkinson's disease, bound selectively and with high affinity to dopamine D2-like receptors, with highest affinity at dopamine D3 receptors. Ergot dopamine receptor agonists (bromocriptine, lisuride, pergolide) bound to both dopamine and non-dopamine receptors. Although all agonists depressed dopamine neuron firing, only pramipexole and quinpirole completely silenced firing when administered in slowly-accumulating doses. High-dose pergolide, but not other ergots, completely suppressed firing when given by a prompt bolus i.v. injection, suggesting efficacy limitations may have involved receptor desensitization for pergolide, but not for bromocriptine and lisuride. We conclude that pramipexole differs from ergot dopamine receptor agonists currently used in the treatment of Parkinson's disease by virtue of its selectivity for dopamine receptors, its preferential affinity for the dopamine D3 receptor subtype, and its greater efficacy for stimulating dopamine receptors, as indicated in these electrophysiology assays.

Antagonism of cocaine's stimulant effects on local cerebral glucose utilization by the preferential autoreceptor antagonist (+)-AJ 76

(+)-AJ 76 is a stimulant dopamine (DA) antagonist, which has a putative preferential action at DA nerve terminal autoreceptors. Because it is both a mild stimulant and a DA antagonist, it has previously been suggested that (+)-AJ 76 might antagonize both the euphoria and craving associated with cocaine abuse and withdrawal, respectively. To evaluate this hypothesis further, (+)-AJ 76 was evaluated for its ability to affect cocaine-induced changes in regional brain energy metabolism. Using Sokoloff's 2-deoxyglucose autoradiographic technique, (+)-AJ 76 antagonized the stimulant effect of cocaine. Although classical DA antagonists are known to depress regional brain energy metabolism, (+)-AJ 76 by itself had no effect. It is concluded that the results are consistent with the previously stated hypothesis that (+)-AJ 76 might be useful as a pharmacotherapy for treatment of cocaine abuse.

Excitation of type II caudate neurons by systemic administration of dopamine agonists

Using chloral hydrate anesthetized rats, dopamine (DA) agonists were evaluated for their systemic effects on firing rates of DA neurons in rat substantia nigra pars compacta (SNPC) and postsynaptic type II neurons in the anterior caudate nucleus (CN), the major projection area for SNPC DA neurons. Intravenous injections of the indirect DA agonist D-amphetamine, but not L-amphetamine, excited spontaneously active CN neurons by a haloperidol-sensitive mechanism. Doses to achieve CN excitation were similar to those required to inhibit SNPC firing. This data is consistent with the theory that D-amphetamine inhibition of SNPC DA neurons is dependent upon neuronal negative feedback pathways originating in CN. Intravenous injections of direct agonists apomorphine, which stimulates all DA receptor subtypes, and quinpirole, which only stimulates D2 receptor subtypes, increased firing rates of spontaneously active CN neurons, but only at doses above those inhibiting firing rates of SNPC neurons. SKF 38393, a selective D1 agonist, had little or no effect on the firing rates of DA neurons in SNPC, on type II anterior CN neurons, or on the effects of quinpirole on anterior CN neurons. It is concluded that excitation of type II anterior CN neurons is mediated via receptors of the D2 subfamily. These results are compared to those reported elsewhere for type I CN neurons, and the possible relevance of these results for the role of DA in motor function is discussed.

Rat brain binding sites for pramipexole, a clinically useful D3-preferring dopamine agonist

Pramipexole (PPX) is currently being evaluated for treatment of schizophrenia and Parkinson's disease. In studies with cloned subtypes of the dopamine (DA) D2 receptor subfamily, PPX has higher affinity for the D3 compared to the D2 and D4 subtypes; unlike 7-[3H]hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT), it does not bind to sigma sites. Receptor binding autoradiography with [3H]PPX (5 nM, 62 Ci/mmol) was used to evaluate the distribution of PPX binding sites within the rat brain. Consistent with its preference for D3-binding sites, the highest concentrations of [3H]PPX binding sites were found in the islets of Calleja (ICj), previously reported to contain D3 but not D2 or D4 mRNA. [3H]PPX binding was also high in other mesolimbic areas such as the nucleus accumbens (N. accum), olfactory tubercle, and amygdala. [3H]PPX binding was also high in caudate (Cd), although slightly less than in mesolimbic areas. Less [3H]PPX binding sites were found in ventral tegmental area (VTA) and substantia nigra, areas rich in cell bodies for DA neurons. Thus, although PPX most potently stimulates DA autoreceptors, PPX binding sites have their highest concentrations in projection areas containing both DA terminal and postsynaptic receptors. Because of PPX's preferential affinity for the D3 receptor subtype and its resultant high mesolimbic binding, it could have a unique therapeutic profile for treatment of psychiatric and/or neurological diseases.

Levodopa or D2 agonist induced dyskinesia in MPTP monkeys: correlation with changes in dopamine and GABAA receptors in the striatopallidal complex

Dopamine D1 and D2 receptors as well as the GABA/benzodiazepine receptor complex in the striatum and the globus pallidus (internal: GPi and external: GPe) were studied by autoradiography using [3H]SCH 23390, [3H]spiperone, and [3H]flunitrazepam ([3H]FNZ) respectively, in five groups of cynomolgus monkeys. These included (i) untreated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-monkeys; (ii) MPTP monkeys treated chronically with levodopa injections; (iii) MPTP monkeys treated chronically with injections of the novel D2 agonist U91356A; (iv) MPTP monkeys treated chronically with U91356A delivered through an osmotic mini-pump; and (5) naive controls. Animals treated in a pulsatile mode with U91356A or levodopa injections showed progressive sensitization to their respective drug and developed choreic dyskinesia. In contrast, animals treated in a continuous mode with U91356A showed behavioral tolerance but did not develop dyskinesia. A trend for a down-regulation of putaminal D2 receptors was observed following D2 agonist stimulation with U913356A. Striatal [3H]FNZ binding was significantly decreased only in animals treated in a continuous mode with U91356A. The dopamine receptor decrease in the striatum could be implicated with the development of tolerance but cannot explain the appearance of dyskinesia. Denervation by MPTP was associated with a decrease of the GPe/GPi [3H]FNZ binding ratio which reflects an imbalance of striatal output pathways; this ratio was not reversed by any of the treatments although changes were observed in the GPe and GPi. Indeed, pulsatile U91356A treatment restored the decreased [3H]FNZ binding in the GPe near control values and levodopa showed a similar tendency. A significant increase of [3H]FNZ binding in the GPi only of dyskinetic monkeys, namely those treated with pulsatile U91356A or levodopa was seen compared to untreated MPTP or naive controls. This GABAA receptor up-regulation might lead to a supersensitive state of the GPi to gabaergic input which may be involved in the mechanism underlying the development of dopaminomimetic-induced dyskinesia.

Continuous administration decreases and pulsatile administration increases behavioral sensitivity to a novel dopamine D2 agonist (U-91356A) in MPTP-exposed monkeys

We compared the behavioral effects of a novel and highly selective dopamine D2 receptor agonist, U-91356A, administered to 6 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-exposed parkinsonian monkeys for 27 days following an intermittent (n = 3) or continuous (n = 3) schedule, using subcutaneous osmotic minipumps for the latter group. Each group received equivalent amount of drug daily. Dopamine D1 and D2 receptor binding assays were performed on striatal tissue homogenates with tritiated selective antagonists and were compared with those of 3 healthy control animals and 3 MPTP-exposed monkeys treated in parallel with daily doses of levodopa and 2 additional MPTP-exposed monkeys otherwise untreated. U-91356A quickly relieved all parkinsonian features and greatly stimulated locomotion in all animals. The pulsatile administration group showed progressive sensitization to the drug, and all 3 animals developed chorea during the first week of treatment that subsequently increased in intensity. The same pattern was seen in the levodopa-treated animals. In contrast, an apparent, incomplete tachyphylaxis were observed in 2 of 3 animals in the continuous infusion group during the first 10 days of treatment. Only 1 of these animals developed minimal and transient choreic dyskinesia. An apparent decrease of D2 receptor binding was observed. No upregulation of dopamine receptors occurred in the dyskinetic monkeys of the pulsatile group, but a tendency toward upregulation of putaminal D1 receptors was observed in the levodopa-treated, dyskinetic animals. These results confirm that the mode of administration of dopaminergic agents may result in a markedly different clinical outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of U-92016A as a selective, orally active, high intrinsic activity 5-hydroxytryptamine1A agonist

The purpose of the present study was to characterize U-92016A [(+)-R)-2-cyano-N,N-dipropyl-8-amino-6,7,8,9-tetrahydro-3H-benz[e] indole] as a 5-hydroxytryptamine (5-HT)1A receptor agonist and to compare its activity with that of standard 5-HT1A receptor agonists. U-92016A binds with high affinity to human 5-HT1A receptors expressed in Chinese hamster ovary cells (Ki = 0.2 nM). Radioligand binding studies also indicate that U-92016A is selective for the 5-HT1A receptor over other biogenic amine receptors. In Chinese hamster ovary cells expressing the human 5HT1A receptor, U-92016A decreased the forskolin-induced increase in cyclic AMP synthesis and had an intrinsic activity of 0.82 relative to 5-HT. U-92016A potently decreased rectal temperature in mice. The maximum temperature decrease was significantly greater than that observed for 8-hydroxy-di-n-propyl aminotetralin, buspirone, gepirone, ipsapirone or flesinoxan. U-92016A also elicited the 5-HT-mediated syndrome in rats and resulted in a dose-related decrease in 5-hydroxytryptophan accumulation. The compound also decreased arterial blood pressure in spontaneously hypertensive rats and inhibited sympathetic nerve activity in cats. In these assays U-92016A displayed excellent potency and a long duration of action. U-92016A also inhibited the firing of dorsal raphe 5-HT neurons and was active in two social interaction assays. The p.o. bioavailability of U-92016A was calculated to be 45%. Taken together, these data indicate that U-92016A is a metabolically stable, p.o. active 5-HT1A receptor agonist with an exceptionally high degree of intrinsic activity.

Metabolic effects of scopolamine and physostigmine in human brain measured by positron emission tomography

Two of the more consistent findings in Alzheimer's disease are depressions in frontal and temporoparietal glucose metabolism and a loss of cholinergic neurons in the nucleus basalis of Meynert. Nonetheless, cholinergic replacement strategies have had only minimal therapeutic successes. Whether this situation reflects the limited contribution of cholinergic deafferentation to the intellectual decline or the meager ability of the pharmaceuticals tested to exert their intended pharmacologic action remains unclear. To address this question, the distribution of cerebral abnormalities found in untreated Alzheimer patients, as revealed by positron emission tomography following 18F-fluorodeoxyglucose, were compared with the pattern of functional changes produced by drugs that block or stimulate cholinergic function. Physostigmine was administered to 6 Alzheimer patients to increase brain cholinergic neurotransmission. The anticholinergic scopolamine, given to normal volunteers, was administered to 6 age-matched controls. These data were compared to those obtained from the same subjects while receiving placebo. Amnestic doses of the anticholinergic, scopolamine increased glucose metabolism by up to 20% (p < 0.001) in all brain regions studied, except thalamus. This response contrasted with the metabolic reductions of up to 17% (p < 0.01), especially in parietal and frontal association cortices, occurring in unmedicated Alzheimer patients. Maximum tolerated doses of the anti-cholinesterase, physostigmine, rather than tending to normalize abnormalities in these patients, further reduced cerebral metabolism (p < 0.01) and increased metabolism in thalamus in a pattern inversely correlated (p < 0.001) with that produced by scopolamine. These results fail to support a cholinergic basis for the abnormal metabolic pattern in Alzheimer's disease.

Excitation of noradrenergic cell firing by 5-hydroxytryptamine1A agonists correlates with dopamine antagonist properties

The 5-HT1A receptor agonists buspirone, 8-hydroxy-N,N-dipropyl-2-aminotetralin, gepirone and ipsapirone were evaluated for their receptor binding profiles and their effects on firing rates of 5-HT, dopamine (DA) and noradrenaline (NA) neurons in the dorsal raphe, substantia nigra pars compacta and the locus ceruleus, respectively. All agents bound to 5-HT1A receptors with high affinities. All agents also bound to dopamine D2 receptors but, with the exception of buspirone, affinities were usually much lower than for 5-HT1A receptors. All agents depressed 5-HT neurons, with 8-hydroxy-N,N-dipropyl-2-aminotetralin having a potency about 8 to 12 times those for the other three. All agents also antagonized the inhibition of DA neurons by amphetamine, an index of DA antagonist properties. Buspirone reversed amphetamine's effects with doses similar to those for depressing 5-HT neurons, but the remaining three required much higher doses to affect DA neuron function. All four 5-HT1A agonists excited NA neurons. In each case, doses required for excitation of NA cells were similar to those reversing amphetamine's effects on DA cells, but not to those for depressing 5-HT cells. Haloperidol also stimulated NA cells. It is concluded that excitation of NA neurons by 5-HT1A agonists may be due to interactions with dopaminergic, rather than serotonergic, receptors.

Pharmacology of a mixed 5-hydroxytryptamine1A/dopamine agonist

U-67413B (4-hydroxydipropylaminodihydrophenalene) bound with high affinity to both 5-hydroxytryptamine (HT)1A and D2-dopamine (DA) receptor sites. U-67413B depressed 5-HT and DA cell firing rates and depressed synthesis of both neurotransmitters. The drug depressed mouse body temperatures by an amount similar to that for buspirone, gepirone and ipsapirone, but less than that for 8-hydroxy-N,N-dipropyl-2-aminotetralin. In rats, it produced the 5-HT1A behavioral syndrome. In contrast to 5-HT1A agonists having DA antagonist effects, U-67413B mildly depressed rather than stimulated firing rates of noradrenaline (NA) neurons in the locus ceruleus by a non-alpha-2 receptor mechanism. In behavioral tests designed to measure anxiolytic activities, U-67413B was a slightly more effective anxiolytic than standard 5-HT1A anxiolytics (buspirone, gepirone and ipsapirone). The data are consistent with the hypothesis that effects of 5-HT1A agonists on NA neuron activity are mediated through effects on dopaminergic mechanisms, and that effects on NA neurons could modulate anxiolytic activities of 5-HT1A agonists.

Comparison of cholinergic drug effects on regional brain glucose consumption in rats and humans by means of autoradiography and position emission tomography

Cholinergic mechanisms have been extensively studied in animals and have been implicated in the pathogenesis of human disorders such as Alzheimer's disease. However, few investigations have directly evaluated the validity of extrapolating the results of animal studies to humans. As a component of a continuing examination of the contribution of cholinergic deficits to the alterations in brain metabolism that occur in Alzheimer's disease, we have compared the effects of scopolamine and physostigmine on regional brain energy metabolism in both rats and humans, using a common region of interest atlas. In Alzheimer's patients and in rodents, physostigmine increased glucose metabolism in several regions (e.g. thalamus) and decreased it in others. Overall, there was a significant positive correlation for the effects of physostigmine in the nineteen brain regions studied in both species (r = 0.51, P < 0.05). In normal humans, scopolamine induced a metabolic increase in most brain regions except in the thalamus. Outside this structure, the regional effects of scopolamine were significantly and negatively correlated (r = 0.58, P < 0.01) between rat and human. These results suggest that: (1) cholinergic mechanisms have a similar anatomic distribution in both species, (2) muscarinic receptor-mediated cholinergic effects could predominate outside the thalamus, (3) muscarinic mechanisms are inhibitory in humans but are more complex and possibly excitatory in rats, (4) nicotinic stimulatory effects are found in the thalamus of both species, and (5) physostigmine, but not scopolamine, alters glucose consumption similarly in both species.

Substituted 3-phenylpiperidines: new centrally acting dopamine autoreceptor antagonists

The (+)-and (-)-enantiomer of compounds 4 and 5 were synthesized and tested for central dopamine (DA) receptor stimulating activity, using biochemical and behavioral tests in rats. Based on the available data the (-)-enantiomers of 4 and 5 are characterized as centrally acting DA autoreceptor antagonists with oral activity. They display a similar pharmacological profile as the prototype DA autoreceptor antagonists (+)-1 and (+)-2 and show a certain preference for the D3 DA receptor antagonist binding site.

Antagonism of cocaine self-administration by the preferential dopamine autoreceptor antagonist, (+)-AJ 76

(+)-AJ 76 is a presumed preferential dopamine (DA) autoreceptor antagonist which, in previous behavioral investigations, has displayed properties characteristic of both DA agonists and DA antagonists. In an attempt to test the hypothesis that (+)-AJ 76 might be an effective cocaine pharmacotherapy, the present experiments evaluated (+)-AJ 76's behavioral profile in 3 standard reinforcement paradigms. In the first experiment, (+)-AJ 76 paralleled a DA antagonist in that it failed to support self-administration behavior at all doses (0.1, 0.32, and 1.0 mg/kg/inj) tested. In the second experiment, (+)-AJ 76 (0.9, 3.5, and 14.0 mg/kg) closely resembled the DA agonist D-amphetamine (0.25, 1.0, and 4.0 mg/kg) in producing a clear dose-dependent conditioned place preference. In the third experiment, (+)-AJ 76 (1.88, 3.75, 7.5, 15.0, and 30.0 mg/kg) significantly reduced breaking points (BPs), increased rates of responding, and delayed the onset of responding for cocaine. While (+)-AJ 76 mimics a typical DA antagonist in its ability to reduce BPs and augment rates of responding for cocaine, recent evidence suggests that it more closely resembles a DA agonist in its ability to delay the onset of responding for cocaine. In summary, the present investigations have shown that (+)-AJ 76's profile in 3 reinforcement paradigms is unusual and not exclusively representative of either DA agonists or DA antagonists. The potential utility for such an agent in treating cocaine abuse is discussed.

Evaluation of the reinforcing and discriminative stimulus effects of cocaine in combination with (+)-AJ76 or clozapine

Because self-administration and discrimination of a drug by animals correlate with its abuse and subjective effects in humans, interventions that modify the reinforcing and discriminative stimulus effects of the drug may be useful in the treatment of its abuse. The present study was designed to evaluate the effects of the putative dopamine autoreceptor antagonist (+)-AJ76 (AJ) or the atypical antipsychotic clozapine (CLZ) on the reinforcing and discriminative stimulus effects of cocaine in monkeys. One group of rhesus monkeys (n = 6) was allowed to self-administer cocaine (0.03 or 0.1 mg/kg/injection i.v. fixed-ratio 10, 2 hr/day). A second group of monkeys (n = 5) was trained to discriminate cocaine (0.2 or 0.4 mg/kg i.m., 10 min presession) from saline in a two lever, food-reinforced, drug discrimination paradigm. When behavior was stable, AJ or CLZ was administered i.m., 15 or 30 min presession. Intermediate doses of both compounds (1.0-3.0 mg/kg of AJ; 0.3-1.0 mg/kg of CLZ) increased cocaine self-administration, while responding remained evenly distributed over the session. A higher dose of CLZ decreased cocaine self-administration in an apparently nonspecific manner. When combined with saline, partial substitution for cocaine was seen in one of three monkeys with AJ and in none with CLZ. In combination with the training dose of cocaine in the discrimination experiment, both AJ and CLZ decreased drug appropriate responding by at least 50% in two of four monkeys, but had little or no effect in the other monkeys up to doses that completely suppressed lever pressing (6.4 mg/kg of AJ; 3.2 mg/kg of CLZ). Taken together, the present findings suggest that any blockade of the reinforcing and discriminative stimulus effects of cocaine by AJ and CLZ was, at best, partial. Furthermore, the stimulant effects of AJ observed in rats were not prominent in monkeys.

Synthesis and biological activity of cis-(3aR)-(-)-2,3,3a,4,5,9b-hexahydro- 3-propyl-1H-benz[e]indole-9-carboxamide: a potent and selective 5-HT1A receptor agonist with good oral availability

The synthesis and biological activity of cis-(3aR)-(-)-2,3,3a,4,5,9b- hexahydro-3-propyl-1H-benz[e]indole-9-carboxamide ((-)-3a), U93385, is described. The cis racemate and its enantiomer as well as the corresponding trans enantiomers were also synthesized and evaluated. The synthesis of these analogs was achieved via either a four-step conversion of the 9-hydroxy precursor into 9-carboxamide or an alternative synthesis using the (R)-alpha-methylbenzyl group as the chiral auxiliary. The cis racemate (+/-)-3a, was found to be a selective and potent 5-HT1A receptor agonist with the activity residing in the cis-(3aR)-enantiomer, (-)-3a. The cis-(3aS)-enantiomer (+)-3a and trans-(3aR)-enantiomer (-)-3b displayed partial 5-HT1A agonist activity whereas the other trans-(3aS)-enantiomer (+)-3b showed no activity. The enantiomer (-)-3a was found to be selective in both in vitro and in vivo biochemical/behavioral assays. This compound potently reduced rectal temperature in mice, decreased the firing rate of rat midbrain serotonergic neurons, and suppressed rat brain 5-HT synthesis. This compound also reduced sympathetic nerve discharge and blood pressure in the anesthetized cat and showed activity in the forced swim assay in mice. It exhibited good oral activity in behavioral and biochemical assays and, in fact, had a 46% oral availability in the rat when comparing blood levels of parent drug after iv and po administration. This compound has demonstrated a potential for anxiolytic and antidepressant activity and is currently undergoing clinical evaluation.

Novel 2-substituted tetrahydro-3H-benz[e]indolamines: highly potent and selective agonists acting at the 5-HT1A receptor as possible anxiolytics and antidepressants

The synthesis of (+)-(R)-2-cyano-N,N-dipropyl-8-amino-6,7,8,9-tetrahydro-3H- benz[e]indole [(R)-14, U92016A], a potent 5-HT1A agonist, and related analogs is described. In vitro binding studies show that the (R)-enantiomers of this series possess the highest potency for the 5-HT1A receptor. In vivo hypothermia correlates with this, with the (R)-enantiomers causing a greater temperature drop than the (S)-enantiomers. The most active compound in 5-HT1A binding and in the in vivo models was (R)-14, which was found to be highly potent as an agonist in single cell firing studies, as well as potent and of very high intrinsic activity in mouse hypothermia and the sympathetic nerve discharge (SND) models. An in vivo duration of action study, following SND, showed (R)-14 to possess a long duration of action. The synthesis via a nitrene insertion, determination of absolute configuration, and biological activities of this series is described.

Centrally acting serotonergic and dopaminergic agents. 1. Synthesis and structure-activity relationships of 2,3,3a,4,5,9b-hexahydro-1H-benz[e]indole derivatives

The synthesis and structure-activity relationships (SAR) of 2,3,3a,4,5,9b-hexahydro-1H-benz[e]indole derivatives (3) are described. These compounds are conformationally restricted, angular tricyclic analogs of 2-aminotetralin. The synthesis was achieved in several steps from the corresponding 2-tetralones. The enantiomers of the cis analogs were obtained from either fractional recrystallizations of the diastereomeric salts of di-p-toluoyl-L-(or D)-tartaric acid or an asymmetric synthesis using chiral (R)-alpha-methylbenzylamine. All analogs were evaluated in the in vitro 5-HT1A and D2 binding assays and selected analogs were investigated further in biochemical and behavioral tests. Analogs with 9-methoxy substitution (R1 in 3) showed mixed 5-HT1A agonist and dopamine antagonist activities whereas the corresponding 9-hydroxy analogs displayed selective 5-HT1A agonist activity. The cis analogs were found to be more potent than the corresponding trans analogs and in the cis series, the (3aR)-(-)-enantiomers displayed higher potency. Nitrogen substitution (R2 in 3) with either an n-propyl or an allyl group produced similar activities whereas replacement with a bulky alpha-methylbenzyl group resulted in loss of activity. Analogs without aromatic substitution (R1 = H in 3) still showed good 5-HT1A agonist activity, although less potent than the 9-methoxy series. In this case, the trans analogs possessed equal or higher in vitro 5-HT1A affinity than the corresponding cis analogs. Analogs with either 6-methoxy or 6-hydroxy substitution (R1 in 3) were found to display dopamine antagonist properties. However, only N-allyl analogs showed this activity. In the 6-methoxy-N-allyl series, the cis analog was found to be more potent than the trans analog. Again, between the pair of cis enantiomers, the (3aR)-(-)-enantiomer showed higher potency. Incorporation of an additional methyl group into 9-methoxy cis analogs at C-2 resulted in retention of potent 5-HT1A agonist activity.

Centrally acting serotonergic and dopaminergic agents. 2. Synthesis and structure-activity relationships of 2,3,3a,4,9,9a-hexahydro-1H-benz[f]indole derivatives

The conformationally restricted linear tricyclic analogs of 5- and 8-hydroxy-2-(di-n-propylamino)-tetralins were investigated for their serotonergic and dopaminergic properties. These cis and trans analogs of 2,3,3a,4,9,9a-hexahydro-1H-benz[f]indole (3), where a five-membered ring is fused between the nitrogen and C-3 carbon of 2-aminotetralin, were synthesized from 5-methoxy- and 8-methoxytetralones. The enantiomers of trans-5-methoxy-N-n-propyl and -N-allyl analogs were obtained via fractional recrystallization of their di-p-toluoyl-L (or D) tartaric acid salts. All analogs were evaluated in the in vitro 5-HT1A and D2 binding assays and selected analogs were investigated further in biochemical and behavioral tests. In the 5-substituted series (R1 in 3), the trans isomers were found to possess higher levels of pharmacological activity then the corresponding cis isomers. The trans-5-methoxy analogs showed selective 5-HT1A receptor activity in vitro but displayed mixed 5-HT1A and D2 agonist properties in vivo. The corresponding trans-5-hydroxy analogs were found to be potent D2 agonists with full intrinsic activity. An examination of nitrogen substitution (R2 in 3) revealed that analogs with either an allyl or an n-propyl group displayed equipotent activities. Substitution with a cyclopropylmethyl or benzyl group resulted in reduced activity. Among the resolved analogs tested, the activity was found to reside exclusively in the (3aS)-(-)-enantiomers. In the 8-substituted series (R1 in 3), only 8-methoxy-N-allyl analogs were synthesized and evaluated. In this case, both cis and trans isomers showed equally weak in vitro 5-HT1A receptor agonist activity devoid of dopaminergic effects. The presence of an additional methyl group at the C-2 position (R3 in 3) of the cis-(+/-)-8-methoxy-N-n-propyl analog resulted in enhancement of in vitro 5-HT1A receptor binding affinity, with the (2 beta,3a alpha,9a alpha)-(+/-)-isomer displaying potency 35 times greater than the (2 alpha,3a alpha,9a alpha)-(+/-)-isomer.

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. Among the 8-OMe or 8-OH C-1,N-disubstituted analogs synthesized, the cis analogs were more potent in the 5-HT1A binding assay than the corresponding trans analogs. However, in the case of 1-(cyclopropylmethyl)-N-n-propyl analogs, the trans isomer has a slightly higher 5-HT1A affinity than its cis counterpart. The order of binding potency for C-1 substitution was found to be allyl > hydroxymethyl > n-propyl > cyclopropylmethyl >> carbomethoxy. Interestingly, the 5-OMe analogs were found to be inactive in both the 5-HT1A and dopamine D2 binding assays. In the C-3 allyl-substituted analogs, 5-HT1A agonist activity was found to be considerably lower. In these examples, the trans analogs showed weak 5-HT1A binding activity whereas the cis analogs were inactive. Analogs with C-1,N,N-trisubstitution also showed a marked decrease in 5-HT1A binding affinity. Overall, the SAR study showed that cis C-1 substitution maintains the 5-HT1A agonist activity of 8-OH-DPAT whereas trans C-1 substitution displays somewhat diminished activity. On the other hand, the trans C-3 substitution shows modest agonist activity whereas cis C-3 substitution removes the activity completely.

Effects of cholinergic agonists on regional brain energy metabolism in the scopolamine-treated rat

The effects of scopolamine, physostigmine, RS86 and U-80816B on regional energy metabolism were studied in rodents by means of the 2-deoxyglucose autoradiographic technique. Scopolamine depressed metabolism in an area of cerebral cortex, focused around the parietal region. Rats treated with cholinergic direct agonists (U-80816B, RS86) as well as with the indirect agonist (physostigmine) all showed decreases in cortical energy metabolism, similar to scopolamine. They also induced an increase in thalamic metabolism. When these drugs were given in conjunction with scopolamine, metabolism tended to change in the opposite direction from the values obtained with the drug alone. These results suggest that there are complex interactions between pre- and post-synaptic muscarinic receptors. Additionally, nicotinic receptors could also be involved in some of the effects of physostigmine.

Intrinsic activity determinations at the dopamine D2 guanine nucleotide-binding protein-coupled receptor: utilization of receptor state binding affinities

Guanine nucleotide-binding protein-coupled receptors have been shown to exist in both a high affinity agonist (HiAg) and a low affinity agonist (LowAg) state. The formation of the HiAg state is promoted by agonists, and the formation of this state of the receptor appears to be a critical factor in the generation of the effector-activating complex G alpha.GTP.Mg2+ and in the production of a stimulus. The magnitude of the difference in the affinity a compound has for the HiAg versus the LowAg state of the receptor has been related to the intrinsic activity of the compound. In this paper the HiAg and LowAg affinities (Ki) of full and partial dopamine agonists of varying levels of intrinsic activity were determined using membranes from Chinese hamster ovary cells stably transfected with the D2i receptor. The HiAg state was defined using the recently described dopamine agonist ligand [3H]U-86170, and the LowAg state was defined using [3H] raclopride plus 600 microM GTP. The LowAg/HiAg ratios for apomorphine (43), HW-165 (12.5), (-)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine [(-)-3-PPP] (4.5), terguride (1.6), SDZ-208-911 (1.2), and SDZ-208-912 (0.3) were found to correlate well with their electrophysiologically derived intrinsic activities (r = 0.92). Using this relationship, the intrinsic activity for compounds such as (+)-3-PPP (112%), quinpirole (104%), U-68553B (102%), and U-86170 (95%) was predicted to be high (greater than 90%); (-)-apomorphine (73%) was of high/moderate intrinsic activity, HW-165 (52%), (+)-apomorphine (51%), and (-)-3-PPP (34%) were in the intermediate range, and terguride (16.5%), SDZ-208-911 (11.7%), and SDZ-208-912 (-12%) were at the lower end of the intrinsic activity spectrum. The receptor state binding-determined intrinsic activity values for quinpirole (100%), U-86170F (94.8%), HW-165 (52.1%), (-)-3-PPP (34.3%), SDZ-208-911 (11.7%), and SDZ-208-912 (-12%) were found to correlate well (r = 0.908) with their maximum response (intrinsic activity), as determined using ATP-mediated increases in arachidonic acid release from CHO-D2i cells. In addition, the maximal effect of several of these compounds on rat striatal homovanillic acid (HVA) levels was determined. The drug-induced changes in tissue HVA levels were found to be consistent with the affinity-derived intrinsic activities of the drugs.(ABSTRACT TRUNCATED AT 400 WORDS)

Antagonism of cocaine's pharmacological effects by the stimulant dopaminergic antagonists, (+)-AJ76 and (+)-UH232

The aminotetralins (+)-AJ76 and (+)-UH232 are stimulant dopaminergic antagonists, which may preferentially antagonize autoreceptors of dopamine nerve terminals. Both agents antagonized cocaine's depressant effects on firing rates of ventral tegmental dopaminergic neurons, but (+)-UH232 was much more potent. When injected simultaneously with cocaine, (+)-UH232 inhibited and (+)-AJ76 enhanced the locomotor stimulation observed during the first 30 min following s.c. cocaine administration. However, (+)-AJ76 antagonized cocaine-induced stereotypies as well as the later more intense cocaine locomotor stimulation. It is suggested that preferential dopamine autoreceptor antagonists may provide a novel approach to a pharmacotherapy for treating cocaine abuse.

Novel indolodioxanes with antihypertensive effects: potent ligands for the 5-HT1A receptor

The synthesis and biological evaluation of a new family of tricyclic indolodioxanes is described. These compounds all contain the 2,3-dihydro-7H-1,4-dioxino[2,3-e]indole nucleus and bear substituents at the 2 and/or 8 positions. Thirteen members of this class were prepared and shown to be potent ligands for the 5-HT1A receptor, with several compounds displaying subnanomolar inhibition constants. These compounds also bind to the dopamine D-2 receptor, but generally with higher inhibition constants than those for 5-HT1A. Certain members of this novel structural class show in vivo activity in the mouse hypothermia assay. One of these compounds, U-86192A, has been shown to have antihypertensive effects in the cat, completely eliminating sympathetic nerve discharge at 1 mg/kg iv and lowering mean arterial pressure to 50% pretreatment levels. These effects can be reversed by the administration of spiperone, indicating that U-86192A is acting via a central serotonergic mechanism.

Effects of the putative dopamine autoreceptor antagonists (+)-AJ 76 and (+)-UH 232 on the discriminative stimulus properties of cocaine

Recent evidence suggests that the putative dopamine (DA) autoreceptor antagonists, (+)-AJ 76 and (+)-UH 232, share some neurochemical and behavioral effects with both psychostimulants and neuroleptics. The ability of (+)-AJ 76 and (+)-UH 232 to mimic or antagonize the stimulus effects of cocaine was investigated in rats trained to discriminate 5 mg/kg (N = 8) or 10 mg/kg (N = 8) of cocaine from saline in a two-lever, water-reinforced, drug discrimination task. In the cocaine (10 mg/kg) group, administration of (+)-AJ 76 (2.5-20 mg/kg) engendered only a partial substitution for cocaine (maximum 60% cocaine-lever responses). Given in combination with cocaine (10 mg/kg), (+)-AJ 76 (2.5-40 mg/kg) did not significantly attenuate the cocaine cue. A fixed dose of (+)-AJ 76 (2.5 or 10 mg/kg) plus various doses of cocaine (1.25-5 mg/kg) did not alter the cocaine dose-response curve. (+)-UH 232 (2-16 mg/kg) produced primarily saline-appropriate responding in rats trained to discriminate 5 mg/kg of cocaine and was unable to block the interoceptive cocaine state when given in combination with cocaine (5 mg/kg). (+)-UH 232 (2 or 8 mg/kg) also did not alter the cocaine dose-response curve. These results suggest that (+)-AJ 76 and (+)-UH 232 elicit only weak or no cocaine-like stimulus effects and, unlike neuroleptics, do not attenuate the cocaine cue.

Effect of the anticonvulsant U-54494A on cortical neuron excitability: Comparison to the kappa agonist U-50488H

U-54494A, a 1,2-diamine anticonvulsant, and U-50488H, a structurally related agonist for opiate kappa receptors, were tested for effects on spontaneous and glutamate-evoked firing rates in cerebral cortex of urethane-anesthetized male Sprague-Dawley rats. Iontophoretic application of 1,2-diamines, glutamate diethyl ether (GDEE), or procaine depressed spontaneous and amino acid-induced firing of cortical neurones. With continued ejection of 1,2-diamines or procaine, firing was silenced completely, but GDEE could maintain a partial suppression. A rapid rebound of excitation followed cessation of procaine ejections, but not of other agents. Procaine, but not U-54494A, blocked axonal conduction of rabbit sciatic nerve. Intravenous U-54494A and U-50488H significantly depressed spontaneous firing rates of cortical neurones, but only the U-50488H effects were antagonized by naloxone. It is concluded that U-54494A inhibits neuronal excitability by a mechanism independent of the analgesic kappa receptor. Biochemical and physiological studies have demonstrated that U-54494A and the kappa opioid agonist U-50488H (a structurally related diamine) (1) have anticonvulsant activity (2, 3). U-54494A lacks kappa analgesic and sedative properties, and it has been suggested that the mechanism of action of this compound may be mediated by a subtype of kappa opioid receptor (3). The effects of kappa analgesics on neuronal firing in nociceptive pathways have been described (4, 5). However, no previous electrophysiological studies on U-54494A have been done. Since U-54494A antagonizes amino acid-induced seizures (3), the interactions of this compound with glutamate are of interest. In the present study, the antagonist efficacies of U-54494A and U-50488H for inhibiting spontaneous and 1-glutamate stimulated neurons of the rat prefrontal cerebral cortex were assessed after i.v. and microiontophoretic administration of the compounds. Effects observed with these routes of administration allow the observation of neuronal changes occurring immediately after administration and take advantage of the high temporal resolution provided by the electrophysiological recording techniques of single cells. A preliminary account of portions of this work have been previously disclosed (6).

Regional cerebral glucose metabolism compared in rodents and humans

In order to compare regional brain glucose metabolism in rats and humans, this parameter was measured using Sokoloff's deoxyglucose method in rats, and positron emission tomography with magnetic resonance imaging in humans. An atlas of cerebral regions of interest common to both species was developed to facilitate the evaluation of the relationship in regional values. We found among the regions studied a significant positive correlation in their metabolic values (r = 0.72, P less than 0.001) and coefficients of variation (r = 0.59, P less than 0.01) suggesting that regional brain glucose consumption is comparable between rat and human. Results of this study support the view that rat and human brain may be phylogenetically linked functionally as well as anatomically.

5-HT1A agonists uncouple noradrenergic somatodendritic impulse flow and terminal release

Both noradrenergic (NE) and serotonergic (5-HT) systems have been implicated in anxiety and depression, as well as in the therapeutic actions of drugs treating these conditions. We have used microelectrode recordings of nerve cell impulse frequencies and in vivo voltammetric recordings of monoamine release to evaluate effects of the arylpiperazine 5-HT1A anxiolytics, buspirone and ipsapirone. Both buspirone and ipsapirone significantly depressed 5-HT neuronal firing rates in dorsal raphe (DR), but significantly increased NE neuronal firing rates in locus coeruleus (LC). In CA1 region of hippocampus, both buspirone and ipsapirone significantly depressed NE release with potencies greater than those required for the significant depression of 5-HT release. It is concluded that, contrary to the belief that the 5-HT1A arylpiperazines act primarily through 5-HT mechanisms, alterations in NE function may be critically important for their therapeutic effects, just as is the case for the benzodiazepine anxiolytics and the tricyclic antidepressants.

Effects of the partial dopamine receptor agonists SDZ 208-911, SDZ 208-912 and terguride on central monoamine receptors. A behavioral, biochemical and electrophysiological study

The partial dopamine receptor agonists SDZ 208-911 (N-[(8-alpha)-2,6-dimethylergoline-8-yl]-2,2-dimethylpropanamid e), SDZ 208-912 (N-[8-alpha)-2-chloro-6-methylergoline-8-yl]-2,2- dimethylpropanamide) and terguride (transdihydrolisuride; TDHL) were tested in biochemical, behavioral (locomotor activity) and electrophysiological assays in male rats. In reserpine-pretreated rats, SDZ 208-911 and terguride dose-dependently reduced striatal DOPA formation (NSD 1015 treatment) with similar efficacy (-80%) and potency as the selective D2 receptor agonist quinpirole (LY 171555). SDZ 208-912 only produced a partial reduction (-32%) at the highest dose tested. SDZ 208-911 and terguride partially reversed (by approximately 50%) the gamma-butyrolactone (GBL)-induced increase in striatal DOPA accumulation. Quinpirole produced a 100% reversal while SDZ208-912, per se, was inactive. While quinpirole decreased DOPA accumulation, all three partial agonists elevated striatal DOPA accumulation in non-pretreated rats with SDZ 208-912 being as potent and efficacious as haloperidol. The three partial agonists displayed comparatively high affinities in vitro for the dopamine D2 (3H-spiperone) receptor site and somewhat lower affinity for the 5-HT1A (3H-8-OH-DPAT) receptor site. SDZ 208-911 and SDZ 208-912 also showed high affinities for central alpha 2 (3H-idazoxane) receptors. In line with these findings, the partial ergoline agonists dose-dependently elevated the DOPA accumulation in the noradrenaline-rich cortical brain region and decreased the 5-HT synthesis rate (5-HTP accumulation) in the limbic brain region. Furthermore, high doses of SDZ 208-911 and terguride produced weak signs of the 5-HT behavioral syndrome (flat body posture) in reserpinized rats. In the locomotor activity studies in non-pretreated rats, SDZ 208-911, SDZ 208-912 and terguride reduced the activity to 10-20% of controls with SDZ 208-912 being approximately ten times less potent than the other two compounds. Weak postsynaptic dopamine receptor agonist effects of the partial agonists were demonstrated only in reserpine-pretreated rats; all three partial agonists tested produced occasional forward locomotion and the so-called "jerking" behavior. Extracellular single unit recordings were carried out in chloral hydrate-anesthetized rats to investigate the effects on firing rates of dopamine neurons located in the substantia nigra pars compacta. Intravenous administration of SDZ 208-911 and terguride depressed the firing rate by 42 and 53%, respectively, while apomorphine completely inhibited the cells. SDZ 208-912 only reduced the firing by 16% and some cells displayed a biphasic response with a weak depression at low doses that disappeared at high doses.(ABSTRACT TRUNCATED AT 400 WORDS)

The hypnotics triazolam and zolpidem have identical metabolic effects throughout the brain: implications for benzodiazepine receptor subtypes

Using Sokoloff's 2-deoxyglucose autoradiography procedure, the effects of trizolam, a classical benzodiazepine (BZ) hypnotic, were compared to those of zolpidem, which preferentially binds to BZ1 receptor subtypes. Triazolam depressed metabolism in 40 of the more than 60 brain regions evaluated. Zolpidem depressed metabolism in all of these areas, including the spinal cord, an area where the BZ1 receptor subtype is not supposed to exist. Zolpidem and triazolam also depressed metabolism in the molecular layer of the dentate gyrus, an area low in BZ1 receptors. Neither drug affected metabolism in 21 areas, including the regions most specific for the BZ1 subtype (cerebellum, inferior colliculus, globus pallidus, and substantia nigra pars reticularis). It is concluded that: (i) zolpidem and triazolam depress energy metabolism of the same areas of the brain, (ii) zolpidem's effects may not be mediated solely through the BZ1 receptor subtype, and (iii) the BZ2 receptor may be functionally more significant than the BZ1 receptor.

Effects of MDMA ('ecstasy') on firing rates of serotonergic, dopaminergic, and noradrenergic neurons in the rat

3,4-Methylenedioxymethamphetamine (MDMA), a non-hallucinogenic drug of abuse, potently depressed firing rates of a subpopulation of serotonin neurons in the dorsal and median raphe. High neurotoxic doses depressed those serotonin neurons unresponsive to low doses. Noradrenaline neurons in the locus coeruleus were also depressed by moderate doses. Dopamine neurons were unaffected. It is concluded that MDMA's unique psychological effects are mediated through a subpopulation of serotonergic and noradrenergic neurons, presumably through effects on release mechanisms.

Electrophysiological effects of dopamine autoreceptor antagonists, (+)-AJ 76 and (+)-UH 232

The weak aminotetralin stimulants, (+)-AJ 76, cis-(+)-5-methoxy-1-methyl-2-(n-propylamino)tetralin and (+)-UH 232, cis-(+)-5-methoxy-1-methyl-2-(di-n-propylamino)tetralin, were tested for their effects on firing rates of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNPC). (+)-AJ 76 and (+)-UH 232 antagonized the depression of DA neuron firing rates following autoreceptor stimulation by apomorphine. Thus, just as they antagonize DA autoreceptors on presynaptic terminals, these aminotetralins also antagonize the somatodendritic DA autoreceptor. However, in contrast to terminal autoreceptors where (+)-AJ 76 is the most potent antagonist, (+)-UH 232 is the most potent on cell body autoreceptors. (+)-AJ 76 and (+)-UH 232 also reversed the depression of DA neurons arising from activation of negative feedback pathways by amphetamine-induced DA release in postynaptic areas. Based on potencies to reverse amphetamine and apomorphine, respectively, the postsynaptic/presynaptic potency ratios for (+)-AJ 76, (+)-UH 232, and haloperidol were all near unity. It is concluded that (+)-AJ 76 and (+)-UH 232 antagonize both postsynaptic and somatodendritic sites with equal potencies, and that their weak stimulant properties may be due to a preferential antagonism of nerve terminal autoreceptors.

Spinal analgesic actions of kappa receptor agonists, U-50488H and spiradoline (U-62066)

Administered i.p. to mice, the selective kappa receptor agonists U-50488H and spiradoline (U-62066) were more potent on the tail-flick than on the hot-plate analgesic assay. Both were more potent after i.s. rather than i.c. administration, a result consistent with earlier demonstrations that tail-flick analgesia is generally dependent upon spinal mechanisms. Intraspinal U-50488H was not effective in elevating rat tail-flick latencies. Both drugs increased the thresholds for cat spinal cord nociceptive neurons to respond to a noxious heat stimulus. However, maximal responses of spinal cord neurons to nociceptive stimuli were not altered. It is concluded that although spinal cord sites may be critical to kappa receptor analgesic mechanisms, the effects are quite distinct from spinal cord effects observed previously with classical narcotic analgesics.

Autoradiographic identification of prolactin binding sites in rat median eminence

Binding sites for prolactin were localized and quantified in the female rat brain by in vitro autoradiographic analysis with iodine-125-labeled ovine prolactin. Following incubation, labeled prolactin bound preferentially to the median eminence and choroid plexus of the lateral and third ventricles. The addition of excess unlabeled ovine prolactin blocked binding of the labeled hormone in the choroid plexus, and attenuated prolactin binding in the median eminence. These results provide evidence for median eminence. These results provide evidence for prolactin-specific recognition sites in the median eminence, a region intimately involved in the hypothalamic regulation of prolactin secretion.

Animal behavioral and neurochemical effects of the CNS toxic amino acid antitumor agent, acivicin

The investigational amino acid antitumor agent, acivicin, has been reported to cause dose-related and reversible CNS toxicity in humans characterized by sedation, ataxia, hallucinations, personality changes, and other symptoms. In a series of studies aimed at characterizing this toxicity, we investigated several species as potential animal models, determined the effects of acivicin on neuronal action potentials, and measured drug effects on the brain content of several putative amino acid neurotransmitters. In mice, we were unable to demonstrate any effects of acivicin in a battery of tests used in identifying and classifying CNS-active agents of potential therapeutic utility. In rats, unlike phencyclidine and certain other psychotomimetic drugs, acivicin produced no impairment of shock avoidance or brightness discrimination in animals trained on an automated Y-maze. In contrast to the rodent species, acivicin effects were perceived as resembling those of cyclazocine by rhesus monkeys trained to discriminate between psychoactive drugs and saline by food reinforcement. Cats treated with acivicin exhibited dose-related symptoms of sedation, somnolence, and ataxia. Iontophoretically applied acivicin was shown to have no effect on the spontaneous firing rate of dorsal horn interneurones in spinal cats. At the time of peak CNS symptoms in cats treated with 100 mg/kg acivicin, content of gamma-aminobutyric acid (GABA; nmoles/mg protein) was elevated from 57-140% in cerebellum, diencephalon, midbrain, and corpus callosum compared to control animals. Brain contents of glutamate, glutamine, and aspartate were not altered in cats experiencing neurotoxicity. These studies have shown that some symptoms of acivicin CNS toxicity are shared by humans and higher non-human species such as the cat and the monkey but not by rodents. Acivicin itself is apparently not a CNS excitant or depressant, but metabolites of the drug could be. Acivicin may also cause increases in the GABA content of localized regions of brain.

Electrophysiological evidence that spiperone is an antagonist of 5-HT1A receptors in the dorsal raphe nucleus

The neuroleptic spiperone, which binds to 5-HT1A, 5-HT2 and dopamine (DA) receptors, was studied for its effects on serotonin (5-HT) and DA neurons in dorsal raphe nucleus and substantia nigra pars compacta, respectively. We found that 1 mg/kg i.v. spiperone, but not LY53837 (a 5-HT2 antagonist), antagonized the inhibition induced by 5-HT1A agonists 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) and buspirone in the dorsal raphe nucleus. Lower spiperone doses blocked DA receptors in substantia nigra pars compacta, but did not affect 5-HT neurons. Doses of 8-OH-DPAT completely silencing dorsal raphe neurons were ineffective in substantia nigra pars compacta. However, buspirone antagonized DA receptors in substantia nigra pars compacta with doses similar to those depressing dorsal raphe neurons. It is concluded that spiperone is an antagonist of 5-HT1A receptors in the dorsal raphe nucleus.

Dramatic limbic and cortical effects mediated by high affinity PCP receptors

Using Sokoloff's 2-deoxyglucose (2-DG) autoradiographic technique, the psychotomimetic drug, phencyclidine (PCP, "angel dust") dramatically increased metabolism in diencephalic and telencephalic brain regions known to be rich in high affinity PCP receptors. These effects were greatest in the limbic circuit described in 1937 by the neurologist James Papez (mammillary bodies, anterior thalamus, cingulate gyrus, entorhinal cortex, hippocampus, fornix) and the terminal zones of dopaminergic projections. Caudal to the prefrontal cortex, the cerebral cortex developed an anterior-posterior metabolic gradient somewhat similar to that reported in schizophrenia. Brainstem areas were generally unaffected. These data 1) provide functional data to support Papez' assertion that his central limbic circuit may be important in emotional expression, 2) reaffirm the potential importance of dopaminergic function in psychotic-like behaviors, 3) provide an animal model for schizophrenia, and 4) establish that PCP uses high affinity PCP receptor binding sites to express its psychobiological effects.