Pharmacology in vivo of the phenylindan derivative, Lu 19-005, a new potent inhibitor of dopamine, noradrenaline and 5-hydroxytryptamine uptake in rat brain

Synthesis of anti-depressant molecules via metal-catalyzed reactions: a review

Depression is one of the most mutilating conditions in the world today. It has been difficult to make advancements toward better, more effective therapies since the introduction of antidepressant medicines in the late 1950s. One important field of medicinal chemistry is the synthesis of antidepressant molecules through metal-catalyzed procedures. The important role that different transition metals, including iron, nickel, ruthenium, and others, serve as catalysts in the synthesis of antidepressants is examined in this review. Key structural motifs included in antidepressant drugs such as tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and others can be synthesized in a variety of effective ways using metal-catalyzed steps. This review examines current developments in the catalytic synthesis of antidepressants and their potential application over the previous thirteen years.

Predict New Therapeutic Drugs for Hepatocellular Carcinoma Based on Gene Mutation and Expression

Hepatocellular carcinoma (HCC) is the fourth most common primary liver tumor and is an important medical problem worldwide. However, the use of current therapies for HCC is no possible to be cured, and despite numerous attempts and clinical trials, there are not so many approved targeted treatments for HCC. So, it is necessary to identify additional treatment strategies to prevent the growth of HCC tumors. We are looking for a systematic drug repositioning bioinformatics method to identify new drug candidates for the treatment of HCC, which considers not only aberrant genomic information, but also the changes of transcriptional landscapes. First, we screen the collection of HCC feature genes, i.e., kernel genes, which frequently mutated in most samples of HCC based on human mutation data. Then, the gene expression data of HCC in TCGA are combined to classify the kernel genes of HCC. Finally, the therapeutic score (TS) of each drug is calculated based on the kolmogorov-smirnov statistical method. Using this strategy, we identify five drugs that associated with HCC, including three drugs that could treat HCC and two drugs that might have side-effect on HCC. In addition, we also make Connectivity Map (CMap) profiles similarity analysis and KEGG enrichment analysis on drug targets. All these findings suggest that our approach is effective for accurate predicting novel therapeutic options for HCC and easily to be extended to other tumors.

Antinociceptive activity of the new triple reuptake inhibitor NS18283 in a mouse model of chemotherapy-induced neuropathic pain

BACKGROUND

Chronic neuropathic pain can lead to anxiety and depression. Drugs that block reuptake of serotonin, norepinephrine and/or dopamine are widely used to treat depression, and have emerged as useful drugs in the treatment of neuropathic pain. This study compared the acute antinociceptive effects of NS18283, a novel triple monoamine reuptake inhibitor (MRI) with indatraline, venlafaxine and escitalopram in a mouse model of neuropathic pain.

METHOD

Neuropathic pain-like behaviours were induced in mice by repeated injections of oxaliplatin (OXA), and assessed using the von Frey hair test, the cold plate test and the thermal preference plate test. Anxio/depressive phenotype and antidepressant-like properties of compounds were assessed by the novelty suppressed feeding test and the tail suspension test, respectively.

RESULTS

In vivo microdialysis experiments showed that each MRI increased extracellular serotonin, norepinephrine and/or dopamine levels in the cingulate cortex, in agreement with their in vitro reuptake inhibitory properties. Indatraline (3 mg/kg) reversed the full repertoire of OXA-induced neuropathic hypersensitivity. NS18283 (10 mg/kg) reversed OXA-induced mechano-hypersensitivity and cold allodynia. Venlafaxine (16 mg/kg) and escitalopram (4 mg/kg) only reversed cold allodynia and mechano-hypersensitivity, respectively. All MRIs produced antidepressant-like activity in anxio/depressive phenotype of OXA mice.

CONCLUSIONS

Acute administration of drugs that enhance the activity of serotonin, norepinephrine and dopamine neurotransmission within nociceptive pathways may provide a broader spectrum of antinociception than dual or selective reuptake inhibitors in animal models of neuropathic pain. Whether similar observations would occur after repeated administration of such compounds in an attempt to simulate dosing in humans, or be compromised by dopaminergic-mediated adverse effects warrants further investigation.

A comparative review of escitalopram, paroxetine, and sertraline: Are they all alike?

It is known that newer antidepressants, such as the selective serotonin reuptake inhibitors (SSRIs), provide advantages in tolerability over antidepressants such as the tricyclics. However, even within the SSRI class, differences in efficacy or tolerability exist between the individual drugs. Among the three most widely prescribed SSRIs are paroxetine, sertraline, and escitalopram. Escitalopram is commonly referred to as an SSRI, but also has well-documented allosteric properties, and thus can be further classed as an allosteric serotonin reuptake inhibitor. All three antidepressants are efficacious compared with placebo, but there is evidence that escitalopram is more effective than a range of other antidepressants. There are no direct data to regard either paroxetine or sertraline as a superior antidepressant. Escitalopram is superior compared with paroxetine, which has a less favorable tolerability profile. Paroxetine is associated with cholinergic muscarinic antagonism and potent inhibition of CYP2D6, and sertraline has moderate drug interaction issues in comparison with escitalopram. Overall, as an allosteric serotonin reuptake inhibitor that is somewhat different from classical SSRIs, escitalopram is the first choice judged by combined efficacy and tolerability, and nonclinical data have offered possible mechanisms through which escitalopram could be more efficacious, based on its interaction with orthosteric and allosteric binding sites at the serotonin transporter.

Triple monoamine uptake inhibitors

Agents interfering with the reuptake of catecholamines and tryptamines are well-known drugs capable of treating serious illnesses, including depression, pain and dependence. Further therapeutic applications and use have been tested and an increase in the variety of the chemical templates has been achieved in the last few years. This review attempts to give an organic overview of molecules capable of simultaneously interfering with the reuptake of all the three major monoamine neurotransmitters (dopamine, norepinephrine/noradrenaline and serotonin).

Visualizing dopamine transporter integrity with iodine-123-FP-CIT SPECT in combination with high resolution MRI in the brain of the common marmoset monkey

Considerable progress has been made in small animal single photon emission computed tomography (SPECT) imaging in the field of Parkinson's disease. In preclinical research, there is an increasing demand for in vivo imaging techniques to apply to animal models. Here, we report the first protocol for dopamine transporter (DAT) SPECT in common marmosets using the radioligand ¹²³I-N-ω-fluoropropyl-2β-carbomethoxy-3β-{4-iodophenyl}nortropane (¹²³I-FP-CIT). Serial SPECT images were obtained on an upgraded clinical scanner to determine the distribution kinetics of ¹²³I-FP-CIT in the marmoset brain. After intravenous injection of approximately 60 MBq of the radiotracer ¹²³I-FP-CIT, stable and specific striatal uptake was observed for at least 4h. Analysis of plasma samples showed rapid disappearance of the radiotracer from blood plasma within a few minutes after application, with activity declining to 4.1% of the administered activity. Structural magnetic resonance imaging (MRI) at 400 μm resolution provided the details of the underlying anatomy. In a marmoset model of Parkinson's disease, which was generated by unilateral injections of 6-hydroxydopamine (6-OHDA) into the nigro-striatal projection pathway, complete loss of striatal DAT binding in combination with behavioral deficits was observed. The presented study demonstrates that ¹²³I-FP-CIT SPECT is a suitable tool to investigate DAT integrity in preclinical studies on common marmosets.

Monoaminergic Antidepressants in the Relief of Pain: Potential Therapeutic Utility of Triple Reuptake Inhibitors (TRIs)

Over 75% of depressed patients suffer from painful symptoms predicting a greater severity and a less favorable outcome of depression. Imaging, anatomical and functional studies have demonstrated the existence of common brain structures, neuronal pathways and neurotransmitters in depression and pain. In particular, the ascending serotonergic and noradrenergic pathways originating from the raphe nuclei and the locus coeruleus; respectively, send projections to the limbic system. Such pathways control many of the psychological functions that are disturbed in depression and in the perception of pain. On the other hand, the descending pathways, from monoaminergic nuclei to the spinal cord, are specifically implicated in the inhibition of nociception providing rationale for the use of serotonin (5-HT) and/or norepinephrine (NE) reuptake inhibitors (SSRIs, NRIs, SNRIs), in the relief of pain. Compelling evidence suggests that dopamine (DA) is also involved in the pathophysiology and treatment of depression. Indeed, recent insights have demonstrated a central role for DA in analgesia through an action at both the spinal and suprasinal levels including brain regions such as the periaqueductal grey (PAG), the thalamus, the basal ganglia and the limbic system. In this context, dopaminergic antidepressants (i.e., containing dopaminergic activity), such as bupropion, nomifensine and more recently triple reuptake inhibitors (TRIs), might represent new promising therapeutic tools in the treatment of painful symptoms with depression. Nevertheless, whether the addition of the dopaminergic component produces more robust effects than single- or dual-acting agents, has yet to be demonstrated. This article reviews the main pathways regulating pain transmission in relation with the monoaminergic systems. It then focuses on the current knowledge regarding the in vivo pharmacological properties and mechanism of action of monoaminergic antidepressants including SSRIs, NRIs, SNRIs and TRIs. Finally, a synthesis of the preclinical studies supporting the efficacy of these antidepressants in analgesia is also addressed in order to highlight the relative contribution of 5-HT, NE and DA to nociception.

Non-amine-based dopamine transporter (reuptake) inhibitors retain properties of amine-based progenitors

Without exception, therapeutic and addictive drugs that produce their primary effects by blocking monoamine transporters in brain contain an amine nitrogen in their structure. This fundamental canon of drug design was based on a prevailing premise that an amine nitrogen is required to mimic the structures of monoamine neurotransmitters and other natural products. Non-amines, a novel class of compounds that contain no amine nitrogen, block monoamine transporters in the nM range and display markedly high selectivity for monoamine transporters, but not for receptors. Non-amines retain the spectrum of biochemical and pharmacological properties characteristic of amine-bearing counterparts. These novel drugs compel a revision of current concepts of drug-monoamine transporter complex formation and open avenues for discovery of a new generation of therapeutic drugs.

Influence of fluoxetine on the ability of bupropion to modulate extracellular dopamine and norepinephrine concentrations in three mesocorticolimbic areas of rats

The finding that serotonin (5-HT) can modulate dopamine (DA) and norepinephrine (NE) release in the brain has led us to hypothesize that fluoxetine, a selective 5-HT reuptake inhibitor, may influence the ability of bupropion, a preferential DA and NE dual reuptake inhibitor, to modulate extracellular DA and NE concentrations in some brain areas. The present study was designed to evaluate this hypothesis by assessing the effects of fluoxetine on bupropion-induced changes in extracellular monoamine concentrations by means of in vivo microdialysis. Three mesocorticolimbic areas including hypothalamus (Ht), prefrontal cortex (Pfc) and nucleus accumbens (Acb) were selected based on their relevance to depression and antidepressant actions. In the Ht of untreated rats, bupropion dose-dependently (s.c.) increased extracellular DA and NE concentrations either in single injection study or in sequential injection study. Thus, 10 mg/kg of bupropion had no effect on the DA and NE concentrations, while 30 mg/kg of bupropion induced transient but significant increases (about 240% of the baselines), and 100 mg/kg of bupropion induced marked and persistent increases (over 600% of the baselines) in the DA and NE concentrations. In the rats pre-treated with fluoxetine (10 mg/kg, s.c., 90 min interval), the threshold dose of bupropion (10 mg/kg) significantly increased the DA and NE concentrations to more than 350% of the baselines, and 30 mg/kg of bupropion markedly increased the DA and NE concentrations to more than 570% of the baselines in the Ht. The fluoxetine pre-treatment also potentiated the DA increases induced by 10 mg/kg of bupropion in the Pfc (260% for bupropion alone vs 357% for the combination) and in the Acb (224% vs 645%). The bupropion-induced NE increases were potentiated by fluoxetine mainly in the Ht. Bupropion did not significantly affect the extracellular 5-HT concentrations in all the 3 brain areas tested. In summary, the present study demonstrated that bupropion can increase extracellular DA and NE concentrations in several mesocorticolimbic areas, which may have an impact on bupropion's antidepressant actions. Furthermore, fluoxetine can potentiate the bupropion-induced DA and NE increases, which may produce more effective and rapid antidepressant actions.

Repeated treatment with the selective kappa opioid agonist U-69593 produces a marked depletion of dopamine D2 receptors

U-69593, the selective K-opioid agonist, was repeatedly administered in single daily injections (0.32 mg/kg) to male, Sprague-Dawley rats. Two or ten days later, the rats were euthanized and dopamine D1 and D2 receptors were measured using (3H]SCH 23390 or [3H]sulpiride, respectively, in caudate putamen and nucleus accumbens. Two days after the last of three injections, dopamine D2 receptors in the caudate putamen were decreased by approximately 40%, with no change in D1 receptors. Dopamine D2 receptor number had returned to normal by 10 days posttreatment. In contrast, in the nucleus accumbens there was a small, nonsignificant decrease in dopamine D2 receptors 2 days after treatment, but a large increase (65%) after 10 days. In agreement with the changes in D2 receptors, there was a significant downward shift in the locomotor activity curve for the D2 agonist quinpirole after a 2-day withdrawal. There were no differences in either the total amount of dopamine taken up or in the IC50 for cocaine to inhibit dopamine uptake following this treatment, suggesting that the dopamine transporter and presynaptic terminals were intact. The results of these studies demonstrate that repeated administration of a selective K-opioid agonist induces long-term alterations in dopamine D2 receptors. Furthermore, the finding that these changes in receptor number require both repeated injections and a withdrawal time greater than 1 day suggests that these alterations are compensatory in nature.

Prolonged dopamine and serotonin transporter inhibition after exposure to tropanes

Cocaine and tropane analogs are known to interact with biogenic monoamine transporters by inhibiting amine uptake. Previous in vivo studies have demonstrated that some of these tropanes produce a longer lasting behavioral effect compared with cocaine. We have previously examined several tropane analogs and found a difference in their relative affinities for dopamine (DA) and serotonin (5-HT) transporters. The purpose of this study was to determine the recovery time of transporter function in vitro and in vivo comparing cocaine with the tropane analogs WF-11 (PTT, selective for DA transporters), WF-31 (selective for 5-HT transporters) and WF-23 (highly potent at both DA and 5-HT transporters). In vitro, using primary rat brain cultures of either midbrain or raphe regions, the recovery of the ability to transport either [3H]dopamine or [3H]serotonin, respectively was evaluated at 0, 3, 24, 48, 120 and 240 h after a 1 h exposure to cocaine and tropane analogs. The tropanes exhibited clearance half-lives ranging from 12 to 69 h, while cocaine, on the other hand, exhibited a clearance half-life of approximately 6 h. In studies utilizing [125I]RTI-55 binding, intraperitoneal injections of cocaine and WF-23 into the rat resulted in striatal clearance half-lives ex vivo that were almost identical to those obtained in vitro. These data suggest that the tropanes bind to and reduce transporter function for prolonged periods of time (up to 10-fold longer than cocaine) and those compounds with the highest affinity may produce a pseudo-irreversible inhibition of transporter function.

Perseveration and strategy in a novel spatial self-ordered sequencing task for nonhuman primates: effects of excitotoxic lesions and dopamine depletions of the prefrontal cortex

Damage to the prefrontal cortex disrupts the performance of self-ordered sequencing tasks, although the precise mechanisms by which this effect occurs is unclear. Active working memory, inhibitory control, and the ability to generate and perform a sequence of responses are all putative cognitive abilities that may be responsible for the impaired performance that results from disruption of prefrontal processing. In addition, the neurochemical substrates underlying prefrontal cognitive function are not well understood, although active working memory appears to depend upon an intact mesocortical dopamine system. The present experiments were therefore designed to evaluate explicitly the contribution of each of these abilities to successful performance of a novel spatial self-ordered sequencing task and to examine the contribution of the prefrontal cortex and its dopamine innervation to each ability in turn. Excitotoxic lesions of the prefrontal cortex of the common marmoset profoundly impaired the performance of the self-ordered sequencing task and induced robust perseverative responding. Task manipulations that precluded perseveration ameliorated the effect of this lesion and revealed that the ability to generate and perform sequences of responses was unaffected by excitotoxic damage to prefrontal cortex. In contrast, large dopamine and noradrenaline depletions within the same areas of prefrontal cortex had no effect on any aspect of the self-ordered task but did impair the acquisition of an active working memory task, spatial delayed response, to the same degree as the excitotoxic lesion. These results demonstrate that a lesion of the ascending monoamine projections to the prefrontal cortex is not always synonymous with a lesion of the prefrontal cortex itself and thereby challenge existing concepts concerning the neuromodulation of prefrontal cognitive function.

Behavioral effects of clozapine and dopamine receptor subtypes

The atypical neuroleptic clozapine (CLZ) is an extremely effective antipsychotic that produces relatively few motoric side effects. However, CLZ displays limited antagonism at the dopamine (DA) D2 receptor, the receptor commonly thought to mediate the antipsychotic activity of neuroleptics. The mechanism of action behind the efficacy of CLZ remains to be determined. Miller, Wickens and Beninger [Progr. Neurobiol., 34, 143-184 (1990)] propose a "D1 hypothesis of antipsychotic action" that may explain the antipsychotic effects of CLZ. This hypothesis is built on the interactions between D2, cholinergic and D1 mechanisms in the striatum. These authors assert that although typical neuroleptics block D2 receptors, it is through an indirect action on D1 receptors that their antipsychotic action is manifest. The extra-pyramidal side effects produced by typical neuroleptics are hypothesized to be due to an indirect action on cholinergic receptors. It is argued that the anticholinergic properties of CLZ negate the D2 (motor side effects) action of CLZ, allowing CLZ to diminish psychotic symptoms through a direct action on D1 receptors. Thus, CLZ may function as a D1 receptor antagonist in behavioral paradigms. The current paper reviews and compares the behavioral profile of CLZ to those produced by D2- and D1-selective antagonists with specific reference to unconditioned and conditioned behaviors in order to more fully evaluate the "D1 hypothesis of CLZ action". Although the actions of CLZ remain unique, they do share some striking similarities with D1 receptor antagonists especially in tests of unconditioned behavior, possibly implicating the D1 receptor in the action of this antipsychotic drug.

Stereoselective behavioral effects of Lu 19-005 in monkeys: relation to binding at cocaine recognition sites

The effects of the monoamine uptake inhibitor Lu 19-005 ((+/-)-trans-3-(3,4-dichlorophenyl)-N-methyl-1-indanamine) and its (+) and (-) enantiomers, Lu 20-042 and Lu 20-043, were compared with those of cocaine and the selective dopamine uptake inhibitor GBR 12909 (1-(2-[bis(4-fluorophenyl)methoxy]ethyl)-4-(3-phenylpropyl)piperazine) in behavioral and radioligand binding experiments. Behavioral experiments were conducted in groups of squirrel monkeys trained under fixed-interval schedules of reinforcement in which responding was maintained either by presentation of food or by termination of a visual stimulus associated with mild electric shock. Radioligand binding studies were conducted using [3H]CFT and [3H]GBR 12935 to label elements of the dopamine uptake system in caudate-putamen membranes of cynomolgus monkeys. All drugs produced dose-related increases in response rate under the fixed-interval schedules. Lu 19-005, Lu 20-042, and Lu 20-043 had relatively slow onsets (approximately 2 h) and relatively long durations of action, with effects persisting for two or more days following administration. Stereoselectivity was evident in the behavioral effects of the enantiomers of Lu 19-005, with Lu 20-042 being approximately 14 times more potent than Lu 20-043. In radioligand binding experiments, Lu 19-005 and its enantiomers were potent inhibitors of specifically bound [3H]CFT and [3H]GBR 12935. As in behavioral experiments, Lu 20-042 was more potent than Lu 20-043. The degree of stereoselectivity, however, varied with the temperature of the assay medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic localization of cocaine binding sites by [3H]CFT ([3H]WIN 35,428) in the monkey brain

The cocaine analog [3H]2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane ([3H]CFT or [3H]WIN 35,428 binds with high affinity and selectivity to cocaine receptors in the monkey caudate-putamen. [3H]CFT was used to map the regional distribution of cocaine binding sites in slide-mounted sections of monkey brains using autoradiographic techniques. Hemicoronal brain sections were incubated with [3H]CFT (3 nM) alone or in the presence of excess (-)-cocaine (30 microM) to mask the binding sites. High densities of [3H]CFT binding sites were detected in the caudate nucleus, putamen, and nucleus accumbens. In all three regions, binding was markedly reduced by coincubation with unlabeled (-)-cocaine, indicating low levels of nonspecific binding. Little or no binding was observed in the cortex, thalamus, globus pallidus, or white matter tracts at the levels studied. In order to characterize binding sites for [3H]CFT in tissue sections, competition experiments were conducted using a fixed concentration of [3H]CFT (3 nM) and a range of concentrations of (-)-cocaine, (+)-cocaine, CFT, Lu 19-005, GBR 12909, bupropion, and citalopram. The IC50 values for the drugs in tissue sections corresponded closely with their reported IC50 values in monkey caudate-putamen membranes (r = 0.99, p less than 0.001), suggesting that [3H]CFT binding is similar in the two preparations. These findings support the view that cocaine receptors labeled by [3H]CFT are localized predominantly in dopamine-rich brain regions implicated in the behavioral effects and abuse of cocaine.

In vivo neurochemical profile of dopamine uptake inhibitors and releasers in rat caudate-putamen

The in vivo neurochemical profile of recently synthesized dopamine (DA) uptake inhibitors (Lu 19-005, Lu 17-133 and GBR 12.921) is described. The antidepressant, nomifensine, as well as another typical DA uptake inhibitor, methylphenidate, was also tested with the microdialysis technique. Most of the new DA uptake inhibitors induced a gradual dose- and time-dependent accumulation of extracellular DA with a weak influence on DA metabolites, similar to that of methylphenidate. Nomifensine, however, caused a DA overflow during the first hour after injection. This was distinguishable from the effect of other uptake inhibitors but comparable to amphetamine. The moderate increase of DOPAC induced by nomifensine compared to the marked decrease produced by amphetamine corroborates reports that the DA 'release' induced by these drugs is mediated by different mechanisms, originating from different intracellular storage pools of DA. The fact that nomifensine can be distinguished from other uptake inhibitors shows clearly that evaluation of dynamic changes in transmitter overflow provides information pertinent to the overall neurochemical characterization of a drug.

Ca2+ dependence of the amphetamine, nomifensine, and Lu 19-005 effect on in vivo dopamine transmission

The present in vivo microdialysis study examined the role of vesicular- and carrier-mediated mechanisms underlying dopamine (DA) release, uptake and metabolism in halothane-anaesthetized rats. Omission of calcium (Ca2+) from the dialysis perfusing medium, thereby reducing the concentration of Ca2+ in the striatal microenvironment necessary for vesicular DA release, attenuated the elevation of DA normally induced by the potent DA uptake inhibitors, nomifensine and Lu 19-005. Consistent with the results of in vitro studies, amphetamine release DA in a Ca2+-independent manner. The release of DA induced by amphetamine could be effectively blocked by nomifensine and Lu 19-005, demonstrating that the in vivo movement of amines occurred via a transport carried-mediated mechanism. Additionally, the inhibition of DA metabolism produced by amphetamine could be reversed or blocked by prior or delayed treatment with DA uptake inhibitors. The results support a bidirectional in vivo capability of the amine transport carrier.

Cocaine: an in vivo microdialysis evaluation of its acute action on dopamine transmission in rat striatum

The effects of cocaine on dopamine (DA) neurotransmission were evaluated by in vivo microdialysis in the striatum of halothane-anesthetized rats. Intravenous cocaine produced a dose-dependent, transient increase of the extracellular concentration of DA, with a peak response within 10 min and a return to control level by 30 min. The sharp DA response pattern was abolished in a calcium-free environment, indicating that DA release enhanced by cocaine originates from a vesicular storage pool. Continuous administration of cocaine (via the perfusion medium) directly into the nigrostriatal terminal region also produced a dose-dependent increase in DA release. Low concentrations (10(-5) M and 10(-6) M) of cocaine maintained DA at a constant stable level, consistent with the effects observed after potent DA uptake inhibitory agents (e.g., nomifensine and Lu19005). However, continuous exposure to high concentrations (greater than or equal to 10(-4) M) induced a transient elevation of DA within 20 min, following which DA decreased to a stable but high level; this decrease might reflect tolerance to the effect of cocaine. Administration of cocaine (10(-3) M) into the substantia nigra did not change striatal DA release. The local striatal action of cocaine was less potent than amphetamine in elevating DA overflow and in its effect on DA metabolism. These findings suggest that the fast transient enhancement of DA by intravenous cocaine is most likely a consequence of the transient presence of cocaine in the terminal region, correlating with the well-known rapid pharmacokinetic and behavioral aspects of the drug.

Influence of a carrier transport process on in vivo release and metabolism of dopamine: dependence on extracellular Na+

In vivo microdialysis was utilized to evaluate the role of extracellular Na+ in regulating dopamine (DA) neurotransmission in the caudate-putamen of halothane-anaesthetized rats. Reduction of the extracellular Na+ concentration by introduction of a perfusion media containing 50mM Na+ (with choline replacement) produced an excessive release of DA that could be effectively blocked by nomifensine and Lu 19-005, potent inhibitors of an amine transport carrier. These results substantiate reports of a carrier-mediated efflux of DA from presynaptic terminals. Pretreatment with amphetamine, considered both a DA uptake inhibitor and releaser, did not, however, influence the efflux of DA induced by the low extracellular Na+ environment. Although the release of DA from an apparent non-granular cytosolic pool was greatly enhanced by the low extracellular Na+ environment, 3,4-dihydrophenylacetic acid (DOPAC) levels, which supposedly reflect metabolism of non-vesicular DA, were minimally effected. In contrast, homovanillic acid (HVA) was sensitive to extracellular Na+ and not directly related to extracellular levels of either DA or DOPAC, suggesting the possibility of a Na+-sensitive (carrier-mediated?) process involved in the formation of HVA. Overall, the results of this paper cannot be completely reconciled with the traditional concept of intracellular organization of DA pools and suggests the possibility of various non-granular pools being differentially sensitive to efflux and metabolism.

The stereoselectivity of the 'single drug binding site' of human alpha 1-acid glycoprotein (orosomucoid)

The stereoselective binding of six pairs of basic, one pair of acidic drug enantiomers, and one pair of diastereomers for human alpha 1-acid glycoprotein was investigated by means of competition experiments against [3H]propranolol- or [14C]nicardipine-labelled binding sites using equilibrium dialysis to separate free from bound marker ligand. The affinity constants (Ka) for association of [3H]propranolol and [14C]nicardipine with alpha 1-AGP were 1.2 +/- 0.6 X 10(5) M-1 and 3.4 +/- 1.4 X 10(5) M-1, respectively, and control binding amounted to 57 +/- 7 and 91 +/- 2%, respectively. The following selectivity factors, calculated as the ratio of the higher over the lower enantiomer concentrations displacing 15% of control radiomarker binding (IC15-value), were obtained against propranolol and nicardipine: (-)/(+) propranolol: 1.9 and 1.7.; (+)-/(-)-disopyramide: 2.8 and 1.4; (+)-/(-)-verapamil: 1.6 and 1.9; (+)-(S)-/(-)-(R)-202-791, a dihydropyridine derivative: 2.6 and 2.0; (-)-/(+)-asocainol: 1.7 and 3.0; (+)-/(-)-tilidine: 1.1 and approximately equal to 2; (-)-(S)-/(+)-(R)- warfarin: 1.6 and 2.4; (+/-)-cis/(+/-)-trans-trans-tilidine: 1.7 and 1.8. When the calculation of radioligand-free fractions is also taken into account, it is apparent that only the tilidine isomers show no selectivity at propranolol-marked, and the disopyramide isomers at nicardipine-marked alpha 1-AGP-binding sites, in all other cases, a weak selectivity is detectable, which is, however, far below the values obtained for most neurotransmitter receptors. It is concluded that the single drug binding site of alpha 1-AGP is only slightly stereoselective and that the stereoselective binding of the drugs investigated is probably of no clinical consequence.

Further evaluation of the mechanism by which amphetamine reduces striatal dopamine metabolism: a brain dialysis study

An intracerebral dialysis method was used in the halothane-anaesthetized rat to further clarify the site which mediates the amphetamine-induced decrease of the striatal dopamine (DA) metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). Following subcutaneous injection of amphetamine (0.1-5.0 mg/kg), DOPAC and HVA in striatal perfusates decreased over the 2 h time course, with 0.5 mg/kg of the drug having maximal effect. In comparison, amphetamine (0.1-5.0 mg/kg) caused a strictly dose-dependent increase of DA in striatal perfusates. Following low (0.1-5.0 mg/kg) but not high (2.0-5.0 mg/kg) doses of amphetamine there was a negative correlation between the increase of DA and decrease of DOPAC in the striatum. Amphetamine (0.5 mg/kg) caused a reduction in DA metabolism in the ibotenic acid-lesioned striatum. Intranigral injection of 10 micrograms, but not of 1 microgram amphetamine, decreased DOPAC (-27%) in the striatal perfusates. However, injection of 1 microgram amphetamine into the striatum caused a strong decrease in striatal DOPAC (-46%) and HVA (-22%). The possible mechanisms of action of amphetamine are discussed in the light of these data.

Dopamine-like activities of an aminopyridazine derivative, CM 30366: a behavioural study

The behavioural effects of CM 30366, an aminopyridazine derivative, on dopamine-mediated neurotransmissions, have been studied in mice and rats. CM 30366 induced stereotyped behaviour and antagonized haloperidol-induced catalepsy in rats, after parenteral and oral administration. In 6-hydroxy dopamine (6-OHDA)-lesioned mice, CM 30366 induced contralateral rotations and, when injected before 6-OHDA, protected mice against its neurotoxicity. CM 30366 also provoked contralateral rotations when injected directly into the mouse right striatum. After parenteral injection, CM 30366 slightly increased motility in mice, at least at low doses. The stereotypies and rotations (after intrastriatal injection) induced by CM 30366 were antagonized by haloperidol, alpha-methyl-p-tyrosine and reserpine. The effects of CM 30366 were compared to those of direct and indirect dopamine-like drugs. Bromocriptine induced a behavioural profile, which in most aspects, was qualitatively and quantitatively similar to that of CM 30366. Apomorphine was found slightly more potent than CM 30366, but in contrast to the latter, apomorphine-induced stereotypies were insensitive to alpha-methyl-p-tyrosine or reserpine. (+)-Amphetamine and nomifensine were less potent than CM 30366, and unlike CM 30366, induced ipsilateral rotations in 6-OHDA-lesioned mice. These results indicate that CM 30366 is a potent atypical dopamine-like drug of potential therapeutic usefulness.

Down-regulation of dopamine D-2, 5-HT2 receptors and beta-adrenoceptors in rat brain after prolonged treatment with a new potential antidepressant, Lu 19-005

Lu 19-005 is a new phenylindan derivative with strong and equipotent inhibitory effect on dopamine (DA), noradrenaline (NA) and serotonin (5-HT) uptake. The adaptive effects of 2 weeks treatment with Lu 19-005, on receptor binding in vitro and on d-amphetamine responsiveness in vivo have been investigated in rats. One or 3 days after the final dose the number of beta-adrenoceptors and of 5-HT2 and DA D-2 receptors was decreased by 20-30%, whereas alpha 1-adrenoceptor number was slightly decreased only 1 day after withdrawal. The DA D-2 receptor number remained decreased at 7 days withdrawal, but returned to normal after another 3 days. The brain levels of DA, NA and 5-HT were not changed by 2 weeks' Lu 19-005 treatment. The down-regulation of DA D-2 receptors was accompanied by tolerance to d-amphetamine-induced hypermotility (after low doses) and stereotyped licking or biting (after a high dose). The tolerance to d-amphetamine-induced hypermotility was maximal at 3-5 days withdrawal time, and remained significant also 15 days after the last dose. An acute dose of Lu 19-005 did not modify the effects of d-amphetamine. The results are discussed in relation to the effect of prolonged treatment with other antidepressant drugs.