benztropine and vanoxerine

The discovery and development of medications to treat addiction and notably, cocaine addiction, have been frustrated by both the complexity of the disorder and the lack of target validation in human subjects. The dopamine transporter has historically been a primary target for cocaine abuse medication development, but addictive liability and other confounds of such inhibitors of dopamine uptake have limited clinical evaluation and validation. Herein we describe efforts to develop analogues of the dopamine uptake inhibitors GBR 12909 and benztropine that show promising profiles in animal models of cocaine abuse that contrast to that of cocaine. Their unique pharmacological profiles have provided important insights into the reinforcing actions of cocaine and we propose that clinical investigation of novel dopamine uptake inhibitors will facilitate the discovery of cocaine-abuse medications.

Topics: Animals; Behavior, Animal; Benztropine; Cocaine-Related Disorders; Conditioning, Psychological; Disease Models, Animal; Dopamine Uptake Inhibitors; Dose-Response Relationship, Drug; Humans; Piperazines; Structure-Activity Relationship

The design, synthesis and pharmacological evaluation of novel dopamine transporter ligands, based on Benztropine [3a-(diphenylmethoxy) tropane], has been a focus of our research efforts toward the development of novel cocaine-abuse pharmacotherapeutics. Structure-activity relationships at the dopamine transporter, for this series of compounds, have been derived and compared to those of cocaine and GBR 12909. These studies suggest that structurally diverse dopamine uptake inhibitors may access different binding domains on the dopamine transporter. The distinctive behavioral profile displayed in this series of compounds, as compared to cocaine and other dopamine uptake inhibitors, is of particular interest and is proposed to be relevant to the pharmacodynamic and pharmacokinetic properties of this class of tropane-based molecules.

Topics: Benztropine; Carrier Proteins; Cocaine; Dopamine Plasma Membrane Transport Proteins; Dopamine Uptake Inhibitors; Drug Design; Humans; Membrane Glycoproteins; Membrane Transport Proteins; Nerve Tissue Proteins; Piperazines; Stereoisomerism; Structure-Activity Relationship; Substance-Related Disorders

The present studies compared the acute effects of benztropine analogs (4-Cl-BZT, JHW 007, AHN 1-055), which are atypical dopamine uptake inhibitors, with those of the standard dopamine uptake inhibitors GBR 12909 and cocaine, on the reinforcing efficacy of food and food intake in male Sprague-Dawley rats. Repeated drug effects of JHW 007 on food intake were also determined. The number of ratios completed under a progressive-ratio schedule of food delivery was used as an index of reinforcing efficacy. Food intake was determined by measuring powdered laboratory-chow consumption during daily 40 min food-availability time periods. Under the progressive-ratio schedule, cocaine and GBR 12909 dose-dependently increased the number of ratios completed. JHW 007 decreased ratios completed, whereas neither 4-Cl-BZT nor AHN 1-055 increased ratios completed with a magnitude that approximated any of the increases produced by cocaine or GBR 12909. Acute administration of each drug dose-dependently decreased food intake; however, the benztropine analogs were more potent than cocaine and GBR 12909. A reduction in food intake emerged after repeated administration of a low dose of JHW 007. Future studies that compare JHW 007 with standard anorectic drugs (e.g. phentermine) and continue investigation of the repeated drug effects under similar experimental procedures are clearly warranted.

Topics: Animals; Behavior, Animal; Benztropine; Cocaine; Dopamine Uptake Inhibitors; Dose-Response Relationship, Drug; Eating; Feeding Behavior; Male; Piperazines; Rats; Rats, Sprague-Dawley; Reinforcement Schedule

The benztropine analog N-(n-butyl)-3α-[bis(4'-fluorophenyl)methoxy]-tropane (JHW 007) displays high affinity for the dopamine transporter (DAT), but unlike typical DAT ligands, has relatively low abuse liability and blocks the effects of cocaine, including its self-administration. To determine sites responsible for the cocaine antagonist effects of JHW 007, its in vitro binding was compared with that of methyl (1R,2S,3S,5S)-3-(4-fluorophenyl)-8-methyl-8-azabicyclo[3.2.1]octane-2-carboxylate (WIN 35428) in rats, mice, and human DAT (hDAT)-transfected cells. A one-site model, with K(d) values of 4.21 (rat) and 8.99 nM (mouse) best fit the [(3)H]WIN 35428 data. [(3)H]JHW 007 binding best fit a two-site model (rat, 7.40/4400 nM; mouse, 8.18/2750 nM), although a one-site fit was observed with hDAT membranes (43.7 nM). Drugs selective for the norepinephrine and serotonin transporters had relatively low affinity in competition with [(3)H]JHW 007 binding, as did drugs selective for other sites identified previously as potential JHW 007 binding sites. The association of [(3)H]WIN 35428 best fit a one-phase model, whereas the association of [(3)H]JHW 007 best fit a two-phase model in all tissues. Because cocaine antagonist effects of JHW 007 have been observed previously soon after injection, its rapid association observed here may contribute to those effects. Multiple [(3)H]JHW 007 binding sites were obtained in tissue from mice lacking the DAT, suggesting these as yet unidentified sites as potential contributors to the cocaine antagonist effects of JHW 007. Unlike WIN 35428, the binding of JHW 007 was Na(+)-independent. This feature of JHW 007 has been linked to the conformational status of the DAT, which in turn may contribute to the antagonism of cocaine.

Topics: Adrenergic Uptake Inhibitors; Animals; Benztropine; Binding, Competitive; Cell Line, Tumor; Cell Membrane; Cocaine; Corpus Striatum; Dopamine Plasma Membrane Transport Proteins; Dopamine Uptake Inhibitors; Female; Histamine H1 Antagonists; Humans; Kinetics; Male; Mice; Mice, 129 Strain; Mice, Inbred Strains; Mice, Knockout; Neuroblastoma; Piperazines; Pirenzepine; Protein Binding; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M1; Selective Serotonin Reuptake Inhibitors; Sodium; Triprolidine

The widely abused psychostimulant cocaine is thought to elicit its reinforcing effects primarily via inhibition of the neuronal dopamine transporter (DAT). However, not all DAT inhibitors share cocaine's behavioral profile, despite similar or greater affinity for the DAT. This may be due to differential molecular interactions with the DAT. Our previous work using transporter mutants with altered conformational equilibrium (W84L and D313N) indicated that benztropine and GBR12909 interact with the DAT in a different manner than cocaine. Here, we expand upon these previous findings, studying a number of structurally different DAT inhibitors for their ability to inhibit [(3)H]CFT binding to wild-type, W84L and D313N transporters. We systematically tested structural intermediates between cocaine and benztropine, structural hybrids of benztropine and GBR12909 and a number of other structurally heterologous inhibitors. Derivatives of the stimulant desoxypipradrol (2-benzhydrylpiperidine) exhibited a cocaine-like binding profile with respect to mutation, whereas compounds possessing the diphenylmethoxy moiety of benztropine and GBR12909 were dissimilar to cocaine-like compounds. In tests with specific isomers of cocaine and tropane analogues, compounds with 3alpha stereochemistry tended to exhibit benztropine-like binding, whereas those with 3beta stereochemistry were more cocaine-like. Our results point to the importance of specific molecular features--most notably the presence of a diphenylmethoxy moiety--in determining a compound's binding profile. This study furthers the concept of using DAT mutants to differentiate cocaine-like inhibitors from atypical inhibitors in vitro. Further studies of the molecular features that define inhibitor-transporter interaction could lead to the development of DAT inhibitors with differential clinical utility.

Topics: Animals; Asparagine; Aspartic Acid; Benztropine; Binding, Competitive; Cell Line, Transformed; Cocaine; Dopamine Plasma Membrane Transport Proteins; Dopamine Uptake Inhibitors; Drug Interactions; Humans; Leucine; Models, Molecular; Mutation; Piperazines; Protein Binding; Protein Structure, Tertiary; Sodium; Structure-Activity Relationship; Transfection; Tritium; Tryptophan

Analogs of benztropine (BZT) bind to the dopamine (DA) transporter and inhibit DA uptake but often have behavioral effects that differ from those of cocaine and other DA-uptake inhibitors. To better understand these differences, we examined the relationship between locomotor-stimulant effects of cocaine, 1-{2-[bis-(4-fluorophenyl)methoxy]ethyl}-4-(3-phenylpropyl)-piperazine (GBR 12909), and BZT analogs [(3alpha-[bis(4'-fluorophenyl)methoxy]-tropane) (AHN 1-055) and (N-allyl-3alpha-[bis(4'-fluorophenyl)methoxy]-tropane) (AHN 2-005)] and their in vivo displacement of the DA transporter ligand [125I]3beta-(4-iodophenyl)-tropan-2beta-carboxylic acid isopropyl ester hydrochloride (RTI-121) in striatum. Cocaine, GBR 12909, and BZT analogs each displaced [125I]RTI-121 and stimulated locomotor activity in a dose- and time-dependent manner. The time course revealed a slower onset of both effects for AHN 1-055 and AHN 2-005 compared with cocaine and GBR 12909. The BZT analogs were less effective than cocaine and GBR 12909 in stimulating locomotor activity. Locomotor stimulant effects of cocaine were generally greater than predicted by the regression of displacement of [125I]RTI-121 and effect at short times after injection and less than predicted at longer times after injection. This result suggests that the apparent rate of occupancy of the DA transporter, in addition to percentage of sites occupied, contributes to the behavioral effects of cocaine. The present results suggest that among drugs that act at the DA transporter, the slower apparent rates of occupancy with the DA transporter by the BZT analogs may contribute in an important way to differences in their effectiveness.

Topics: Animals; Benztropine; Cocaine; Dopamine Uptake Inhibitors; Dose-Response Relationship, Drug; Male; Mice; Motor Activity; Piperazines

The different psychomotor-stimulant effects of cocaine, GBR12909, and benztropine may partially stem from their different molecular actions on the dopamine transporter (DAT). To explore this possibility, we examined binding of these inhibitors to mutated DATs with altered Na(+) dependence of DAT activities and with enhanced binding of a cocaine analog, [(3)H]2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane (CFT). In [(3)H]CFT competition assays with intact cells, the mutation-induced change in the ability of Na(+) to enhance the apparent affinity of CFT, cocaine, GBR12909, and benztropine was inhibitor-independent. Thus, for the four inhibitors, the curve of [Na(+)] versus apparent ligand affinity was steeper at W84L compared with wild type, shallower at D313N, and flat at W84LD313N. At each mutant, the apparent affinity of CFT and cocaine was enhanced regardless of whether Na(+) was present. However, the apparent affinity of GBR12909 and benztropine for W84L was reduced in the absence of Na(+) but near normal in the presence of 130 mm Na(+), and that for D313N and W84LD313N was barely changed. At the single mutants, the alterations in Na(+) dependence and apparent affinity of the four inhibitors were comparable between [(3)H]CFT competition assays and [(3)H]dopamine uptake inhibition assays. These results demonstrate that DAT inhibitors producing different behavioral profiles can respond in an opposite way when residues of the DAT protein are mutated. For GBR12909 and benztropine, their cocaine-like changes in Na(+) dependence suggest that they prefer a DAT state similar to that for cocaine. However, their cocaine-unlike changes in apparent affinity argue that they, likely via their diphenylmethoxy moiety, share DAT binding epitopes that are different from those for cocaine.

Topics: Amino Acid Substitution; Benztropine; Binding, Competitive; Cell Line; Cocaine; Dopamine; Dopamine Plasma Membrane Transport Proteins; Dopamine Uptake Inhibitors; Humans; Kidney; Ligands; Membrane Glycoproteins; Membrane Transport Proteins; Muscarinic Antagonists; Mutagenesis, Site-Directed; Nerve Tissue Proteins; Piperazines; Protein Binding; Sodium; Structure-Activity Relationship; Zinc

We have prepared azabicyclo[3.2.1] derivatives (C-3-substituted tropanes) that bind with high affinity to the dopamine transporter and inhibit dopamine reuptake. Within the series, 3-[2-[bis-(4-fluorophenyl)methoxy]ethylidene]-8-methyl-8-azabicyclo[3.2.1]octane (8) was found to have the highest affinity and selectivity for the dopamine transporter. These azabicyclo[3.2.1] (bridged piperidine) series of compounds differ from the well-known benztropines by a 2-carbon spacer between C-3 and a diarylmethoxy moiety. Interestingly, these new compounds demonstrated a much lower affinity for the muscarinic-1 site, at least a 100-fold decrease compared to benztropine. Replacing N-methyl with N-phenylpropyl in two of the compounds resulted in a 3-10-fold increase in binding affinity for the dopamine transporter. However, those compounds lost selectivity for the dopamine transporter over the serotonin transporter. Replacement of the ether oxygen in the diarylmethoxy moiety with a nitrogen atom gave relatively inactive amines, indicating the important role which is played by the ether oxygen in transporter binding. Reduction of the C-3 double bond in 8 gave 3 alpha-substituted tropanes, as shown by X-ray crystallographic analyses of 11, 12, and 19. The 3 alpha-substituted tropanes had lower affinity and less selectivity than the comparable unsaturated ligands.

Topics: Animals; Brain; Carrier Proteins; Crystallography, X-Ray; Dopamine; Dopamine Plasma Membrane Transport Proteins; Dopamine Uptake Inhibitors; In Vitro Techniques; Male; Membrane Glycoproteins; Membrane Transport Proteins; Nerve Tissue Proteins; Piperazines; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M1; Receptors, Muscarinic; Serotonin; Serotonin Plasma Membrane Transport Proteins; Structure-Activity Relationship; Tropanes

Several halogenated analogs of benztropine (BZT) have previously been characterized as potent DA uptake inhibitors with behavioral profiles that indicate diminished psychomotor stimulant effects relative to cocaine. In a previous study using a fixed-ratio 10 schedule, two chloro-analogs (3'-Cl-BZT and 4'-Cl-BZT) maintained i.v. self-administration in monkeys but appeared to be weak positive reinforcers.. The present experiments were designed to test the hypothesis that 3'-Cl-BZT and 4'-Cl-BZT are relatively weak reinforcers by evaluating reinforcing effects under increased response requirements. To examine further the effect of this halogen substitution on self-administration, 3',4"-diCl-BZT was also evaluated for reinforcing effects.. Four rhesus monkeys self-administered cocaine (0.03 mg/kg per injection, i.v.) under a fixed-ratio 25 (FR25) schedule until stable responding was established. Saline, various doses of cocaine (0.003-0.2 mg/kg per injection), the BZT analogs (0.012-0.2 mg/kg per injection), GBR 12909 (0.012-0.2 mg/kg per injection), and compounds with known reinforcing effects (d-amphetamine, morphine, pentobarbital, ketamine) were then made available for self-administration. Various doses (0.01-0.3 mg/kg per injection) of the compounds that maintained self-administration under the FR schedule were then substituted for cocaine (0.1 mg/kg per injection) under progressive-ratio (PR) schedules.. Reinforcing effects were evident under the FR schedule for 3'-Cl-BZT, 4'-Cl-BZT, GBR 12909, and the control compounds, but not by 3',4"-diCl-BZT. Results with the PR suggested that the rank order of these compounds for their effectiveness as reinforcers was cocaine > GBR 12909 > 3'-Cl-BZT = 4'-Cl-BZT >> 3',4"-diCl-BZT.. This study confirms and extends previous results suggesting that compounds with high DAT affinity can have strong, moderate, weak, or no effectiveness as reinforcers. The mechanisms that may underlie this variation in reinforcing effectiveness of these DAT ligands remain to be established.

Topics: Animals; Benztropine; Cocaine; Dopamine Uptake Inhibitors; Female; Macaca mulatta; Male; Piperazines; Reaction Time; Reinforcement Schedule; Self Administration

The inhibition by cocaine of the apparent initial rate of the transport of striatal dopamine was compared with inhibitions produced by cocaethylene, benztropine, GBR-12909, mazindol, and nomifensine. Rotating disk electrode voltammetry was used to measure the kinetically resolved, inwardly directed transport of dopamine in striatal suspensions. Evidence is presented that the primary site of action of cocaine may be at the external face of the transporter. Experiments to determine whether or not the other inhibitors bind to the same site as cocaine were conducted by comparing the inhibitions observed for each of the inhibitors alone with that observed when paired with cocaine. The resulting changes in the velocity of the transport of dopamine induced by the inhibitors were then fit to one of the previously developed models of inhibition by pairs of inhibitors affecting the kinetics of actively transporting systems: a single-site model, a two-site model in which the two binding sites for the inhibitors interact, and a two-site model in which the two binding sites for the two inhibitors act independently. Cocaine inhibited the transport of dopamine competitively with its structural analogues, cocaethylene and benztropine. The structurally dissimilar inhibitor, GBR-12909, was found also to be competitive with cocaine. In contrast, mazindol and nomifensine were found to bind to separate interactive sites when individually paired with cocaine. These results suggest that mazindol and nomifensine may interact with the kinetically active transporter for dopamine in a manner different from that of cocaine. Mazindol was tested and found to inhibit competitively the inward transport of dopamine into striatal suspensions. In contrast, our previous published findings show cocaine to be an uncompetitive inhibitor of the transport of striatal dopamine. These results suggest that cocaine inhibits inward transport of dopamine by reducing the intramembrane turnover of the transporter, whereas mazindol alters the kinetics of the recognition of dopamine by the transporter. Finally, the potential effects of these binding modes of inhibitors on synaptic chemical communication in dopaminergic systems were analyzed. The results of these analyses suggest that different effects on the extracellular concentrations of dopamine can result from the different patterns of inhibition, suggesting that different modulatory influences on pre- and postsynaptic receptor occupation can result f

Topics: Animals; Benztropine; Biological Transport; Cocaine; Corpus Striatum; Dopamine; Male; Mazindol; Models, Biological; Neurotransmitter Uptake Inhibitors; Nomifensine; Piperazines; Rats; Rats, Sprague-Dawley

Histidyl-proline-diketopiperazine [Cyclo (His-Pro) (CHP)] was discovered to be one of the metabolites of TRH. To understand the specific role of CHP in rat hypothalamic dopamine neurons, we examined the in vivo effects of intraventricular (icv) infusion of CHP on the release and synthesis of PRL in the rat pituitary and the 3,4-dihydroxyphenylacetic acid (DOPAC)/dopamine ratio in the rat hypothalamus. We also examined the in vitro effects of CHP on the release of [3H]dopamine from dispersed tuberoinfundibular dopamine neurons, [3H]dopamine reuptake in hypothalamic membrane fractions, and PRL release from rat pituitary cultured cells. Female rats were treated by icv infusion of 1 microM CHP daily for 1, 3, and 7 days, using Alzet osmotic pumps. After 1 day of treatment, the serum PRL concentration was significantly decreased. Northern blot analysis of the total RNA isolated from the pituitary glands of control animals using 32P-labeled PRL cDNA as a probe indicated the presence of PRL gene transcript, 1.0 kilobase in size, and its amount was decreased by CHP treatment. CHP did not affect [3H]dopamine release from dispersed tuberoinfundibular dopaminergic neurons at any concentration up to 1 microM. CHP did not inhibit PRL release from cultured pituitary cells at low concentrations (1-100 nM), but it stimulated PRL release at high concentrations (1 and 10 microM). We also examined the concentrations of dopamine and DOPAC in the rat hypothalamus when CHP was administered icv for 1 or 7 days. There was a significant decrease in the DOPAC/dopamine ratio after CHP treatment for 1 day. Furthermore, CHP caused dose-dependent inhibition of [3H]dopamine uptake by the rat hypothalamus similar to other dopamine uptake blockers, such as benztropine and GBR12909. These data suggest that icv administration of CHP might decrease both PRL secretion and accumulation of PRL gene transcripts in the pituitary by decreasing the DOPAC/dopamine ratio and inhibiting dopamine reuptake in the rat hypothalamus.

Topics: 3,4-Dihydroxyphenylacetic Acid; Animals; Benztropine; Blotting, Northern; Cells, Cultured; Cerebral Ventricles; Dopamine; Dopamine Antagonists; Female; Hypothalamus; Infusions, Parenteral; Kinetics; Neurotransmitter Uptake Inhibitors; Peptides, Cyclic; Piperazines; Pituitary Gland, Anterior; Prolactin; Rats; Rats, Wistar; RNA; Transcription, Genetic

Recent evidence indicates that the cerebellum has a dopaminergic system. In order to elucidate further the dopaminergic system in the cerebellum, we investigated the transport of dopamine (DA) in synaptosomal preparations of normal and reeler mice. For comparative purposes we also studied DA transport in synaptosomal preparations from striatum and frontal cortex and compared DA transport to noradrenaline (NA) transport. [3H]-DA transport into cerebellar synaptosomes was found to be a Na(+)-dependent, two component system--a high affinity, low capacity and a low affinity, high capacity. In striatum [3H]-DA is transported by a similar high but different low affinity component. Maximal velocities of both transport components in the striatum were higher than the corresponding ones in the cerebellum. In the frontal cortex we also observed two [3H]-DA transport components with affinities significantly lower than those in cerebellum and striatum. [3H]-NA transport into synaptosomes, prepared from the three brain regions studied, showed two transport components with similar Kt and Vmax values, except for the high affinity component in striatum whose affinity is lower. In reeler mice [3H]-DA transport was different from normal only in the cerebellum where the maximal velocity for both transport components was significantly higher (2x). In contrast, no significant difference was observed in the transport of [3H]-NA. The accumulated [3H]-DA from cerebellar slices was found to be releasable by K+ stimulation, in a Ca(++)-dependent manner, and most of the released radioactivity was in the form of [3H]-DA. These results indicate that in the cerebellum there is a low-density dopaminergic system which is distinct from the corresponding noradrenergic system.

Topics: Animals; Benztropine; Biological Transport; Cerebellum; Cerebral Cortex; Corpus Striatum; Dopamine; Female; In Vitro Techniques; Kinetics; Male; Mice; Mice, Neurologic Mutants; Neurotransmitter Uptake Inhibitors; Nomifensine; Norepinephrine; Piperazines; Reference Values; Synaptosomes

Because of the importance of the catecholamine system in Parkinson's disease and its relevance to a variety of clinical movement disorders, catecholamine uptake sites were mapped in the human brain using [3H] mazindol autoradiography. Displacement studies with known dopamine (DA) and noradrenaline (NA) uptake blockers showed that binding in the striatum was to dopamine uptake sites; binding in the locus coeruleus was to noradrenergic uptake sites. By using the selective noradrenergic uptake blocker desmethylimipramine (DMI), a comprehensive map of both DA and NA uptake sites was generated. In general, catecholamine uptake sites were better seen in terminals than in cells of origin or axonal projections. In some areas, such as the locus coeruleus, punctate binding could be seen over individual pigmented cells. A variegated pattern of binding was seen in caudate nucleus and putamen and some correspondence of patches of low binding with striosomes was observed in the caudate. The highest levels of binding to DA uptake sites was observed in the striatum, where regional differences in binding occurred. The most dense binding was seen in the ventral striatum, and a rostral-to-caudal decrement in binding levels in caudate nucleus and putamen was evident. Binding was more intense in the putamen compared to the caudate and within the caudate lower values were seen laterally. The highest levels of binding to noradrenergic uptake sites were in the locus coeruleus and dorsal raphé, although these sites may be on terminals from other projections. Whereas uptake sites were more often evident in known catecholamine pathways, [3H] mazindol binding was seen in some areas where catecholamine neurons or terminals had not been identified previously. These maps of the catecholamine uptake system add further information concerning the nature of the distribution of catecholamines in human brain and provide an important baseline for the study of disease and ageing processes.

Topics: Aged; Benztropine; Binding, Competitive; Biological Transport; Brain Chemistry; Brain Mapping; Caudate Nucleus; Citalopram; Clomipramine; Corpus Striatum; Desipramine; Dopamine; Humans; Locus Coeruleus; Mazindol; Medulla Oblongata; Mianserin; Middle Aged; Norepinephrine; Piperazines; Pons; Substantia Nigra

Fast cyclic voltammetry, at carbon fibre microelectrodes, was used to monitor stimulated overflow and uptake of DA in the nucleus accumbens of the rat. Several recognised blockers of neuronal uptake of DA were examined for their actions on each process. Benztropine, cocaine, GBR 12909 and nomifensine elevated the overflow of DA, while only nomifensine and bupropion blocked uptake. The actions of the drugs upon uptake did not correlate with their effects on overflow of DA. It is therefore concluded that the mechanisms by which the drugs influence overflow and uptake are different. It cannot be assumed that the elevation of extracellular DA is solely the result of blockade of uptake by these drugs.

Topics: Animals; Benztropine; Bupropion; Cocaine; Dopamine; Electric Stimulation; Electrochemistry; Levodopa; Male; Microelectrodes; Neurotransmitter Uptake Inhibitors; Nomifensine; Nucleus Accumbens; Piperazines; Propiophenones; Rats; Rats, Inbred Strains; Septal Nuclei

Stimulated overflow of dopamine (DA) into the extracellular fluid of the rat caudate nucleus was measured with fast-scan cyclic voltammetry. DA concentrations were sampled in less than 10 ms at 100-ms intervals with a Nafion-coated, carbon-fiber microelectrode. Overflow of DA was induced by electrical stimulation of the medial forebrain bundle with 300-microA pulses of various duration and frequency. Stimulated overflow was measured as a function of stimulus duration before and after administration of benztropine, bupropion, and amphetamine. These results were correlated with simulated curves based on a simple uptake/overflow model. The observed overflow was assumed to be a function of [DA]p, the concentration of DA which overflows per stimulus pulse, and the kinetics of cellular uptake of DA. Correlation of experimental with stimulated results was obtained at the 95% confidence limit for the duration studies; however, it was not possible to distinguish between the effects of pharmacological agents on uptake and overflow. In contrast, modulation of stimulus frequency did permit such distinction. Simulations of an increase in [DA]p fit results following dihydroxyphenylalanine methyl ester at 95% confidence limits, whereas an equivalent change in the apparent Km did not fit. An increase in the apparent value of Km correlated with results obtained at different frequencies following nomifensine and bupropion administration at the 95% confidence limit, whereas an equivalent increase in [DA]p did not fit. The effects of GBR 12909 best correlated with an increase in the DA available for overflow.

Topics: 3,4-Dihydroxyphenylacetic Acid; Amphetamine; Animals; Benztropine; Bupropion; Caudate Nucleus; Dopamine; Electric Stimulation; Electrochemistry; Extracellular Space; Kinetics; Levodopa; Male; Microelectrodes; Neurotransmitter Uptake Inhibitors; Nomifensine; Piperazines; Propiophenones; Rats; Rats, Inbred Strains