Long-term effects of S(+)N-n-propylnorapomorphine compared with typical and atypical antipsychotics: differential increases of cerebrocortical D2-like and striatolimbic D4-like dopamine receptors.

Changes in D2-like dopamine (DA) receptor binding in rat brain regions were compared by quantitative in vitro receptor autoradiography after 21-d treatment with a typical (fluphenazine), atypical (clozapine), or candidate atypical antipsychotic (S[+]-N-n-propylnorapomorphine, [+]-NPA). Fluphenazine treatment significantly increased binding of the D2,3,4 radioligands [3H]nemonapride and [3H]spiperone in caudate-putamen (CPu: 22%, 32%), nucleus accumbens (ACC: 67%, 52%), olfactory tubercle (OT: 53%, 43%), and medial prefrontal cerebral cortex (MPC: 46%, 47%) but not dorsolateral frontal cortex (DFC). D2-like binding in MPC was also increased by (+)-NPA (49%, 39%) and clozapine (60%, 40%), but not in DFC, CPu, ACC, or OT. Binding of D2,3-selective [3H]raclopride increased less after fluphenazine in ACC (27%) and CPu (16%) than with the nonselective radioligands, and not after clozapine or (+)-NPA. D3-selective binding of [3H]R (+)-7-OH-DPAT was not changed with any treatment or region including islands of Calleja. Binding of [3H]nemonapride or [3H]spiperone under D4-selective conditions (with 300 nM S[-]-raclopride and other masking agents, at sites occluded by D4 ligand L-745,870), was increased by fluphenazine, (+)-NPA, clozapine in ACC (120%, 76%, 70%, respectively), and CPu (54%, 37%, 35%), but not in OT, DFC or MPC. These results support the hypothesis that cerebrocortical D2-like and striatolimbic D4-like receptors contribute to antipsychotic actions of both typical and atypical drugs and encourage further consideration of S(+)aporphines as potential atypical antipsychotics.

Distribution of fluphenazine and its metabolites in brain regions and other tissues of the rat.

Rats were given 5, 10, or 20 mg/kg oral doses of fluphenazine (FLU) dihydrochloride daily for 15 days. FLU and its sulfoxide (FL-SO), 7-hydroxy (7-OH-FLU) and N4'-oxide (FLU-NO) metabolites were assayed in plasma, liver, kidney, fat, whole brain, and brain regions by specific and sensitive radioimmunoassays (RIA). All metabolites were detected in tissues at higher levels than in plasma, and the levels increased with dose. FLU was 10- to 27-fold higher in brain regions than in plasma. Brain vs plasma levels of FLU correlated more closely than levels of its metabolites. Liver contained the highest levels of all analytes at all doses. FLU-SO was the major metabolite in brain regions (24% to 96% of FLU) and accumulated in fat 43 to 75 times more than FLU. Levels of 7-OH-FLU and FLU-NO were very low in brain (1% to 20% of FLU). FLU-SO and FLU-NO had only 1% to 3% the affinity for D1 and D2 receptors, but 7-OH-FLU had 20% the D2 and 5% the D1 affinity of FLU. The low affinity for dopamine receptors and low brain-levels of metabolites of FLU indicate that they are not likely to contribute importantly to pharmacologic responses of FLU. Also, the estimated relative "activity factor" for these compounds in the brain indicated that the contribution to neuropharmacologic activity by metabolites is less than 1% of FLU. Consequently, clinical monitoring of plasma FLU alone may be sufficient.

Bromocriptine antagonizes behavioral effects of cocaine in the rat.

Rats given cocaine or bromocriptine under conditions of low basal arousal showed dose-dependent increases of locomotor activity for less than or equal to 1 hours, followed by depression of activity that diminished gradually over the next 2 hours. Arousal was related biphasically to dose (maximum at ca. 5 mg/kg) but depression increased monophasically with the dose of either agent. Both behavioral arousal and depression induced by cocaine were antagonized by bromocriptine, even at doses lacking behavioral effects alone (ID50 = 1.0 and 0.36 mg/kg [1.3 and 0.5 mumol/kg], respectively). Bromocriptine blocked depression of locomotion even when given after the initial stimulation by cocaine. Bromocriptine induced very weak stereotypy, and neither increased nor blocked stereotypy induced by cocaine or apomorphine. Cocaine, at maximally effective doses, did not deplete catecholamines or serotonin in brain regions at times of maximum behavioral arousal or depression, nor did bromocriptine after metabolic turnover of dopamine. Bromocriptine antagonized arousal induced by direct injection of dopamine into the nucleus accumbens. The ability of bromocriptine to block both the behavioral arousal and depression induced by cocaine may reflect activity of bromocriptine as a mixed agonist-antagonist with limited intrinsic agonistic activity at central dopaminergic D2 receptors, perhaps with particular reference to limbic mechanisms.

Fatty acid derivatives of clozapine: prolonged antidopaminergic activity of docosahexaenoylclozapine in the rat.

Stable amides of clozapine derived from fatty acids prominent in cerebral tissue might enhance the central activity of clozapine and reduce its exposure to peripheral tissues. Such derivatives might enhance the safety of this unique drug, which is the only agent with securely established superior antipsychotic effectiveness, but with a risk of potentially lethal systemic toxicity. Amide derivatives of clozapine were prepared from structurally varied fatty acid chlorides and evaluated for ability to inhibit behavioral arousal in rat induced by dopamine agonist apomorphine and to induce catalepsy. Their duration-of-action and potency were compared to free clozapine, and concentrations of clozapine were assayed in brain and blood. Selected agents were also evaluated for affinity at dopamine receptors and other potential drug-target sites. Clozapine-N-amides of linoleic, myristic, oleic, and palmitic acids had moderate initial central depressant activity but by 6 h, failed to inhibit arousal induced by apomorphine. However, the docosahexaenoic acid (DHA) derivative was orally bioavailable, 10-times more potent (ED(50) 5.0 micromol/kg) than clozapine itself, and very long-acting (>/= 24 h) against apomorphine, and did not induce catalepsy. DHA itself was inactive behaviorally. Clozapine showed expected dopamine receptor affinities, but DHA-clozapine was inactive at these and other potential target sites. After systemic administration of DHA-clozapine, serum levels of free clozapine were very low, and brain concentrations somewhat lower than after administering clozapine. DHA-clozapine is a long-acting central depressant with powerful and prolonged antidopaminergic activity after oral administration or injection without inducing catalepsy, and it markedly reduced peripheral exposure to free clozapine. It lacked the receptor-affinities shown by clozapine, suggesting that DHA-clozapine may be a precursor of free, pharmacologically active clozapine. Such agents may represent potential antipsychotic drugs with improved central/peripheral distribution, and possibly enhanced safety.

Lack of increase in dopamine transporter binding or function in rat brain tissue after treatment with blockers of neuronal uptake of dopamine.

Rats were pretreated daily for 10 days with a dopamine (DA) uptake blocker ([+]amphetamine, benztropine, cocaine, GBR-12909, mazindol, or nomifensine) or control vehicle and, after 1-4 days of no treatment, striatal tissue was fractionated to provide synaptosomes and membranes for assays of transport of 3H-DA or binding of 3H-GBR-12935. There were no significant increases of apparent maxima for uptake (Vmax) or binding (Bmax) or consistent changes in ligand affinity. Pharmacologic characterization of 3H-GBR-12935 binding extended the impression that this ligand has high affinity and selectivity for many agents which block neuronal uptake of DA uptake and much less for those which interact with DA receptors or other amine transporters. The results suggest that dopamine transporters are not regulated in the same way as receptors, nor influenced similarly toward upregulation and supersensitization by repeated treatment with antagonists.

Effects of cations on high-affinity binding of 3H-ADTN to dopaminergic sites in calf caudate tissue.

Effects of cations on binding of 0.1-10 nM 3H-ADTN to calf caudate membranes included decreased apparent Bmax by [Na+] greater than or equal to 100 mM, little effect on Kd or on affinity of other dopamine (DA) agonists (DA and apomorphine), decreased slopes of inhibition curves produced by agonists, but increased affinity of the antagonists (+)butaclamol; in contrast, low (10-20 mM) [Na+] did not decrease Bmax, increased ligand and agonist affinity and specific binding, and gave steep monophasic inhibition curves for DA agonists. K+, Li+, and Rb+ had little effect at a wide range of concentrations. Mg++ and Ca++, in physiologic concentrations, moderately increased binding of 3H-ADTN, as did microM Mn++ or Co++; the latter ions inhibited binding at greater than or equal to 10 mM, as did Cu++ (IC50 = 10 microM). The results extend impressions that physiologic [Na+] favors binding of DA antagonists and diminishes binding of agonists, but optimal agonist binding occurred at low [Na+] (10-20 mM), while divalent cations had complex actions.

Alkylation of rat dopamine transporters and blockade of dopamine uptake by EEDQ.

Effects of the alkylating agent EEDQ (N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline) on levels of dopamine transporter (DA(T)) and function were examined in caudate-putamen (CPu) tissue from rat brain. EEDQ produced profound, dose-dependent decreases in DA(T) binding in homogenates (IC(50)=78 microM) and frozen sections (IC(75)=200 microM) that were not reversed by washing. EEDQ also blocked uptake of [(3)H]DA in CPu synaptosomes (IC(50)=17 microM). However, single (10 mg/kg) or repeated administration of EEDQ in vivo (15 mg/kg/day x 3) did not alter DA(T) levels or DA uptake in CPu. Pretreatment of rats with alpha-methyl-p-tyrosine and reserpine to deplete endogenous dopamine also failed to lower DA(T) levels in CPu after injections of EEDQ. EEDQ is an effective alkylating agent for DA(T) in vitro, but not to evaluate metabolic turnover or function of DA(T) in vivo. The results encourage development of selective and in vivo-active DA(T)-alkylating agents.

Differential effects of ascorbate and EDTA on high-affinity binding of 3H-apomorphine and 3H-ADTN to calf caudate membranes.

Recent reports describe effects of ascorbate on binding of dopaminergic agonists to membrane preparations of brain tissue. We now report that with calf caudate membranes, in the absence of EDTA, ascorbate (up to 10 mM) lowered the binding of [3H] (-)apomorphine (3H-APO) by up to 34%, and the proportion "specific," from 69% to 36%, and lowered binding of [3H] (+/-)2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (3H-ADTN) by up to 38%, with little effect on the proportion of its specific binding. EDTA (5 mM), alone, also reduced binding of both ligands by 40-50% but had no effect on the proportion specific. With ascorbate plus EDTA, although total binding was lowered, the proportion of specific binding of 3H-APO rose to a maximum of 82% at 2.5 mM ascorbate, whereas that of 3H-ADTN was only slightly increased. Moreover, TLC revealed that the antioxidants were required during incubation to prevent temperature- and time-dependent degradation of APO much more than ADTN. Thus, while each additive, alone, lowered binding of 3H-APO and of 3H-ADTN, ascorbate plus EDTA increased the proportion of specific binding, especially of 3H-APO, and protected both from degradation.

R(-)2-fluoro-N-n-propylnorapomorphine: a very potent and D2-selective dopamine agonist.

A series of 2-substituted N-n-propylnorapomorphine (NPA) derivatives were synthesized and compared with other DA agonists for affinity to D1 and D2 dopamine (DA) receptors in rat brain corpus striatum tissue. The 2-substituents tested reduced D1 affinity similarly, but enhanced D2 affinity in the rank order: F greater than OH greater than Br greater than OCH3 greater than H greater than or equal to NH2. The extraordinarily high D2 affinity (Ki = 12 pM) and D2 vs. D1 selectivity (57,500) of 2-F-NPA far-exceeded that of all other DA agonists tested, and it was about 10-times more potent than NPA in vivo.

Stereoisomeric probes for the D1 dopamine receptor: synthesis and characterization of R-(+) and S-(-) enantiomers of 3-allyl-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine and its 6-bromo analogue.

Substituted 1-phenyl-3-benzazepines (e.g., SKF 38393 and fenoldopam) exhibit stereoselectivity in moderately high-affinity binding to and partial agonist activation of D1 dopamine receptors. The 3-allyl (APB) and the 3-allyl-6-chloro (6-Cl-APB) analogues of SKF 38393 are reported to have higher affinity and selectivity for the D1 DA receptor and higher in vivo central neuropharmacologic activity than SKF 38393. We recently reported the corresponding 3-allyl-6-bromo analogue (6-Br-APB) also to be a high-affinity D1 agonist. We now describe the synthesis and characterization of the R-(+) and S-(-) enantiomers of both APB and 6-Br-APB and their comparison with corresponding enantiomers of SKF 38393 with respect to D1 receptor binding affinity and D1 and D2 selectivity. The R-(+) enantiomers of both novel substituted 1-phenyl-3-benzazepines bound to the D1 receptor sites in rat forebrain tissue with much higher affinity and selectivity than their S-(-) antipodes. R-(+)-3-Allyl-6-bromo-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3- benzazepine [(R)-(+)-6-Br-APB, 18] exhibits the highest affinity of the reported 1-phenyl-3-benzazepine D1 agonists.

Synthesis and dopamine agonist and antagonist effects of (R)-(-)- and (S)-(+)-11-hydroxy-N-n-propylnoraporphine.

The R-(-) and S-(+) enantiomers of 11-hydroxy-N-n-propylnoraporphine, (R)-3 and (S)-3, were synthesized in six steps from 1-(3-methoxy-2-nitrobenzyl)isoquinoline. Neuropharmacological evaluation of the R and S isomers (by affinity to dopamine receptor sites in rat brain tissues, induction of stereotyped behavior, and interaction with motor arousal induced by (R)-apomorphine in the rat) indicated that, similar to the 10,11-dihydroxy congener 2, both enantiomers can bind to dopamine receptors but that only (R)-3 activates them, whereas (S)-3 shows activity as a dopaminergic antagonist.

Synthesis and dopamine receptor affinities of enantiomers of 2-substituted apomorphines and their N-n-propyl analogues.

Syntheses of (R)-(-)-2-methoxyapomorphine (R-8), its antipode S-8, and its (R)-(-)-N-n-propyl R-9 derivatives are described. The dopaminergic receptor affinities of these compounds and their 2-unsubstituted counterparts (R)-(-)-apomorphine (R(-)-APO, R-1), (S)-(+)-apomorphine (S(+)-APO, S-1), and (R)-(-)-N-n-propylnorapomorphine (R(-)-NPA, R-2), as well as those of (R)-(-)-2-chloroapomorphine (R(-)-2-Cl-APO, R-6), (R)-(-)-2-bromoapomorphine (R(-)-2-Br-APO, R-6), were determined with tissue membrane preparations of corpus striatum from rat brain. Contribution of both an N-n-propyl and a 2-hydroxy in (R)-(-)-2-hydroxy-N-n-propylnorapomorphine (R(-)-2-OH-NPA, R-7) or a methoxy group in (R)-(-)-2-methoxy-N-n-propylnorapomorphine (R(-)-2-OCH3-NPA, R-9) produced the highest D2 affinity (0.053 and 0.17 nM) and D2 over D1 selectivity (17,300 and 10,500 times) of the compounds evaluated. The structure-affinity relationships of these 2-substituted aporphines suggest that secondary binding sites of D2 receptors interact with 2-substituents on the A ring of aporphines through H-bonding.

Aporphines. 39. Synthesis, dopamine receptor binding, and pharmacological activity of (R)-(-)- and (S)-(+)-2-hydroxyapomorphine.

The enantiomers (6aR and 6aS) of 2,10,11-trihydroxyaporphine (THA) were synthesized from thebaine and bulbocapnine and evaluated pharmacologically in vitro in comparison with (-)-apomorphine [(-)-APO] and dopamine by competition with tritiated apomorphine, ADTN, and spiroperidol for binding to a membrane fraction of calf caudate nucleus, as well as for ability to stimulate adenylate cyclase. In all four tests, the rank order of potency was (-)-APO greater than (-)-THA much greater than (+)-THA. Thus, these results extend the impression that the 6aR configuration for hydroxyaporphines is preferred for interactions with putative dopamine receptors and that 2-hydroxylation reduces potency in comparison with 10,11-dihydroxyaporphines.

R and S enantiomers of 11-hydroxy- and 10,11-dihydroxy-N-allylnoraporphine: synthesis and affinity for dopamine receptors in rat brain tissue.

The R-(-)- and S-(+)-enantiomers of 11-hydroxy-N-allyl (4), and 10,11-dihydroxy-N-allyl (3) congeners of 11-hydroxy-N-n-propylnorapomorphine (11-OH-NPa, 2) or N-n-propylnorapomorphine (NPA, 1) were synthesized. Binding affinity of these compounds at dopamine (DA) receptor sites was evaluated with a membrane preparation of corpus striatum from rat brain. The R/S enantiomeric receptor affinity ratio was enhanced by allylic substitution of 3 and 4 and their R isomers had high DA receptor affinity similar to that of the N-n-propyl congeners. These N-allylnoraporphines are proposed as useful precursors to the preparation of their tritiated N-n-propyl enantiomers.

Synthesis and structural requirements of N-substituted norapomorphines for affinity and activity at dopamine D-1, D-2, and agonist receptor sites in rat brain.

A series of N-substituted analogues of (R)-(-)-norapomorphine were synthesized to study the optimal structural requirements of the N-alkyl side chain to interact with D-1 and D-2 dopaminergic receptors as well as dopamine (DA) agonist binding sites. Evaluations included testing the affinity of these compounds for DA receptor sites in rat striatal tissue and assessing stereotypy as a behavioral index of dopaminergic activity. The electronic, steric, and lipophilic properties of the N-alkyl side chain were found to be related to affinity, D-2 selectivity, and dopaminergic activity. All 11 compounds evaluated had relatively low affinity at D-1 sites. Optimum D-2 and agonist-site affinity as well as agonist activity were exhibited by N-cyclopropylmethyl (7) greater than or equal to N-allyl (8) greater than or equal to N-propyl (4) or N-ethyl (3) substituted compounds. Branching of the N-alkyl side chain as in N-isopropyl (5) and N-isobutyl (6) markedly reduced the D-2 affinity and activity, presumably due to steric effects. The N-trifluoroethyl (10) and N-pentafluoropropyl (11) derivatives had low affinity for all their dopamine receptor sites and no agonistic activity; evidently, the highly electronegative F atoms decrease basicity of the N atom and therefore decrease the ability of the N atom to be cationic at physiological pH, a proposed requirement for high-affinity binding to DA receptors.

Aporphines, 36. Dopamine receptor interactions of trihydroxyaporphines. Synthesis, radioreceptor binding, and striatal adenylate cyclase stimulation of 2,10,11-trihydroxyaporphines in comparison with other hydroxylated aporphines.

The presence of the A ring of aporphines and the addition of substituents to it and to other portions of the aporphine ring systems can extend explorations of the dimensions and other characteristics of the dopamine receptors. Accordingly, the synthesis and some physical and pharmacological properties of a series of (-)-2,10,11-trihydroxyaporphines (3a-g) are described. Structure-activity relationships among mono-, di-, and trihydroxyaporphines were evaluated against the high-affinity (nanomolar) binding of [3H]apomorphine (APO) and [3H]spiroperidol (SPR) with a subcellular fraction (P4) of caudate nucleus from bovine brain. In addition, DA-sensitive adenylate cyclase activity was evaluated in homogenates of rat brain striatal tissue. The rank order of displacement of [3H]APO by potent aporphines (IC50 less than or equal to 30 nM) correlated approximately with their ability to stimulate cyclic AMP synthesis. Potency orders against two ligands were dissimilar; for example, increasing the size of N6-alkyl substituents increased potency vs. [3H]SPR but not vs. [3H]APO binding. Moreover, [3H]SPR binding correlated poorly with cyclase activity or [3H]APO binding, suggesting a closer relationship of [3H]APO binding to dopamine-sensitive adenylate cyclase activity.

Rigid analogues of dopamine: synthesis and interaction of 6-exo- and 6-endo-(3',4'-dihydroxyphenyl)-2-azabicyclo[2.2.2]octanes with dopamine uptake sites and receptors.

Two isomeric 6-endo- and 6-exo-(3',4'-dihydroxyphenyl) derivatives (1 and 2) of 2-azabicyclo[2.2.2]octane were synthesized as semirigid analogues of dopamine (DA) to help evaluate the preferred conformation of dopamine at the uptake site of the presynaptic nerve terminal and at the DA receptor. Against the uptake of 0.1 microM [3H]DA by a synaptosomal preparation of corpus striatum from the reserpine-pretreated rat, 2 was found to have a weak inhibitory effect that was three times greater than that of 1 (IC50 = 32 vs. 110 microM). Interactions with DA receptors were assessed with competition for binding of [3H]apomorphine (APO) and on the effect on DA-sensitive adenylate cyclase. Compounds 1 and 2 were both virtually inactive against the binding of 0.5 nM [3H]APO at a screening concentration of 100 microM. The experimental compounds also exhibited only slight adenylate cyclase stimulation in rat striatal homogenates, with 1 appearing to be somewhat more active (at 50 or 400 microM). The weak activities of 1 and 2 and their relatively small differences in activity in these test systems suggest that the DA analogues interact only weakly with the DA transport and receptor sites, possibly as a result of the steric interference caused by the bulky bicyclic ring.

Conformational analysis, pharmacophore identification, and comparative molecular field analysis of ligands for the neuromodulatory sigma 3 receptor.

Molecular modeling studies were carried out on a series of 1-phenyl-3-amino-1,2,3,4-tetrahydronaphthalenes (phenylaminotetralins, PATs), several PAT structural analogs, and various non-PAT ligands that demonstrate a range of affinities for a novel sigma 3 receptor linked to stimulation of tyrosine hydroxylase and dopamine synthesis in rodent brain. In an effort to develop a ligand-binding model for the sigma 3 receptor, a pharmacophore mapping program (DISCO) was used to identify structural features that are common to ligands that exhibit moderate to high binding affinity for sigma 3 sites. DISCO then was utilized to propose a common pharmacophoric region that included one low-energy conformation of each compound in the training set. The resulting alignment was utilized in a comparative molecular field analysis (CoMFA) study in an attempt to correlate the steric and electrostatic fields of the molecules with the respective binding affinities at the sigma 3 receptor. A suitably predictive model was obtained from the CoMFA analysis which will be employed in the development of additional PAT analogs that could potentially display high affinity and selectivity for the sigma 3 receptor. The excluded volumes which resulted from comparing molecular volumes of active and inactive compounds were visualized to examine the limits of steric tolerance imposed by the sigma 3 receptor.

Synthesis and pharmacological evaluation of 1-phenyl-3-amino-1,2,3,4-tetrahydronaphthalenes as ligands for a novel receptor with sigma-like neuromodulatory activity.

Certain novel 1-phenyl-3-amino-1,2,3,4-tetrahydronaphthalenes (1-phenyl-3-aminotetralins, PATs) produced stimulation (ca. 30% above basal levels) of tyrosine hydroxylase (TH) activity at 0.1 microM concentrations in rodent brain tissue. This effect on TH was blocked by the putative sigma-receptor antagonist BMY-14802, suggesting involvement of a novel neuromodulatory sigma-like receptor. Within the new phenylaminotetralin series, a correlation was found between the ability to stimulate TH and the potency to compete for binding sites labeled by (+/-)-[3H]1-phenyl-3-(N,N-dimethylamino)-6-chloro-7-hydroxy-1,2,3,4- tetrahydronaphthalene ([3H](+/-)-4). trans-Catechol analogs had low affinity for [3H]4 sites, and although they inhibited TH activity, this effect was not blocked by known sigma or dopamine antagonists. Analogs with dihydroxy substituents (catechols), as well as nitrogen substituents larger than methyl, had little affinity for [3H]4 binding sites and did not significantly affect TH activity. The pharmacology of the [3H]4 binding site is unique from that of any known sigma or dopamine receptor, thus the effects appear to be mediated by a previously uncharacterized binding site/receptor. The site has stereoselectivity for the (1R,3S)-(-)-isomer of 1-phenyl-3-(N,N-dimethylamino)-1,2,3,4-tetrahydronaphthalene; this isomer is also more active at stimulating TH. Thus, certain 1-phenyl-3-amino-1,2,3,4-tetrahydronaphthalenes appear to be selective probes of a novel receptor type that mediates sigma-like neuromodulatory activity and may have pharmacotherapeutic utility in conditions in which modulation of dopamine function is important.

N-substituted analogs of 2 beta-carbomethoxy-3 beta- (4'-iodophenyl)tropane (beta-CIT) with selective affinity to dopamine or serotonin transporters in rat forebrain.

This report concerns the synthesis and chemical characterization of novel series of N-substituted 2 beta-carbomethoxy-3 beta-(4'-iodophenyl)tropane (beta-CIT, 2) analogs and their neuropharmacological evaluation for affinity at dopamine (DAT), serotonin (5-HTT), and norepinephrine membrane transporters in rat brain tissue. N-Substituted analogs of beta-CIT with a 2 beta-carbomethoxy ester moiety showed lower DAT affinity than beta-CIT for the DAT, and some were more selective for the 5-HTT over the DAT. 2 beta-Carbomethoxy(iodophenyl)nortropane analogs of beta-CIT with the N-substituents difluoroethyl, mesoxypropyl, iodopropyl, and methylpropionyl all yielded > 10-fold lower DAT affinity than beta-CIT itself, whereas the N-(fluoropropyl)-2 beta- isopropyl ester analog (1) of beta-CIT exceeded beta-CIT (2, an N-methyl-2 beta-carbomethoxy ester) in DAT affinity. Several N-haloalkyl-substituted beta-CIT analogs yielded high 5-HTT affinity (Ki < 0.6 nM), ranking: N-fluoropropyl (5) > N-chloropropyl (4) > or = N-bromopropyl (3) > beta-CIT (2) > N-3'-phtalimidopropyl (11), with particularly high (ca. 30-fold) 5-HTT-over-DAT selectivity found in the N-fluoropropyl (5) and N-fluoroethyl (6) compounds, compared to only 3.o-fold 5-HTT selectivity in beta-CIT itself. Highly 5-HTT selective agents such as 5 and 6 may be useful as brain-imaging ligands for serotonin neurons or as mood-elevating drugs, while the high affinity and selectivity for the DA transporter found in N-(fluoropropyl)-2 beta-(carboxyisopropyl)-3 beta-(4'-iodophenyl)-nortropane (1) and N-(fluoropropyl)-2 beta-carboxymethoxy-3 bet-(4'-iodophenyl)nortropane (FP-beta-CIT, 5) support their use as improved markers for DA neurons.