PubMed Health⌕ Search

Biomedical subjects

N S Kula

Publications and source records attributed to N S Kula.

At least 19 recordsLinked to original sources
PubMed1992

Interactions of fluoxetine with metabolism of dopamine and serotonin in rat brain regions.

Given evidence of inhibitory effects of serotonin on dopaminergic neurotransmission, a series of experiments sought neurochemical evidence of interactions between the selective serotonin transport inhibitor fluoxetine and the metabolism of dopamine (DA) or serotonin (5-HT) in regions of rat brain that might account for extrapyramidal side-effects associated with clinical use of fluoxetine. There were significant inhibitory effects of acute or repeated fluoxetine treatment on the turnover of 5-HT (accumulation of 5-hydroxytryptophan, or ratio of [5-hydroxyindoleacetic acid]/[5-HT]) in striatum, nucleus accumbens and frontal cerebral cortex, but only minor effects on metabolism of DA (accumulation of dihydroxyphenylalanine, or [homovanillic acid]/[DA] ratio), even at high doses or with repeated treatment, and no significant inhibition of the DA metabolism-increasing actions of haloperidol.

Animals↗
PubMed1992

Rate of recovery of D1 and D2 dopaminergic receptors in young vs. adult rat striatal tissue following alkylation with ethoxycarbonyl-ethoxy-dihydroquinoline (EEDQ).

The rate of recovery of D1 and D2 receptor binding sites in rat striatal tissue labeled with [3H]SCH-23390 or [3H]YM-09151-2 was followed daily after irreversible blockade of these receptors with the alkylating agent ethoxycarbonyl-ethoxy-dihydroquinoline (EEDQ). These rates were significantly higher in young post-weaning rats than in young adults (14% vs. 7% per day). The findings suggest that rates of synthesis of new D1 and D2 receptor proteins may be increased during a phase of neurodevelopment in the first postnatal month when the accumulation of both receptor types, especially of D1 receptors, is about maximal.

Alkylating Agents↗
PubMed1992

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.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1992

Prolonged D2 antidopaminergic activity of alkylating and nonalkylating derivatives of spiperone in rat brain.

Alkyl and arylalkyl derivatives of the dopamine (DA) D2 antagonist spiperone were prepared and characterized chemically and pharmacologically. They included the N-methyl, N-phenethyl (NPS), and N-p-aminophenethyl (NAPS) derivatives, as well as the alkylating isothiocyanato (NIPS), bromacetamido, and ethylfumaramido p-substituted N-phenethylspiperones. These compounds showed high lipophilicity (log P up to 6.0 with NIPS), as well as very high in vitro D2 affinity (Ki = 35-280 pM) and D2 versus D1 selectivity (540-9000-fold) in radioreceptor assays with corpus striatum of rat brain. Of the alkylating series, NIPS showed the highest D2 affinity (57 pM) and D2 versus D1 selectivity (2040-fold) and so was selected for further evaluation. NPS, NAPS, and NIPS showed little or no affinity for 34 non-DA binding sites defined by radioligand assays for monoamine, amino acid, and peptide neurotransmitters, ion channels, peptide growth factors, and transmission mediators but did show low alpha 2 and moderate alpha 1 and 5-hydroxytryptamine (5-HT2) affinity with rat forebrain tissue in vitro; NIPS showed a marked gain in D2 versus 5-HT2 selectivity, compared with spiperone (1520- versus 26-fold). Systemic injections of NIPS induced marked decreases in rat striatal D2 binding sites 24 hr later, with little effect on D1, 5-HT2, or alpha 1 sites; NIPS and NAPS lowered apparent Bmax values at D2 receptors with little change in ligand affinity, ex vivo as well as in vitro. NPS, NAPS, and NIPS all induced dose-dependent lowering of D2 binding ex vivo (ID50 = 1-9 mumol/kg, intraperitoneally) and blocked the behavioral effects of the DA agonist apomorphine (0.9 mumol/kg) potently (ID50 = 0.3-0.5 mumol/kg) at 24 hr. Recovery from these anti-DA actions required about 1 week after equimolar (15 mumol/kg) and similarly effective doses of NPS and NAPS, as well as NIPS. Thus, highly selective and avidly bound lipophilic D2 affinity ligands with similarly avid in vitro and prolonged in vivo anti-DA activities can be derived from N-phenethylspiperones with or without an alkylating moiety present. Such affinity ligands may represent useful additions to previously used, generally less selective, D2 affinity ligands.

Alkylating Agents↗
PubMed1991

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.

Animals↗
PubMed1991

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.

Animals↗
PubMed1991

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.

Animals↗
PubMed1990

Effects of isomers of hydroxyaporphines on dopamine metabolism in rat brain regions.

The effects of isomers of di- and monohydroxyaporphines on cerebral dopamine (DA) metabolism were evaluated in representative extrapyramidal (corpus striatum) and limbic (nucleus accumbens septi) tissues of rat brain by three methods: (1) changes in the ratio of homovanillic acid (HVA) to DA, (2) accumulation of L-dihydroxyphenylalanine (DOPA) after inhibiting its decarboxylation to DA under "open-loop" conditions, as well as (3) after gamma-butyrolactone (GBL) pretreatment to provide selective effects at presynaptic DA autoreceptors. The DA-agonist R(-) isomers of the aporphines apomorphine (APO), N-n-propylnorapomorphine (NPA), and 11-hydroxy-N-n-propylnoraporphine (11-OH-NPa) showed consistent dose-dependent inhibition of DA synthesis in both brain regions with all models; the neuroleptic haloperidol had the opposite effect in the first two models only, as expected. The S(+) isomers of NPA and 11-OH-NPa have shown behavioral evidence of antidopaminergic activity, especially in the limbic system. Unlike the neuroleptic, S(+)NPA did not show DA-synthesis enhancing actions in accumbens or striatal tissue but, instead, inhibited DA synthesis like its R(-) antipode in all three test paradigms. S(+)11-OH-NPa given alone produced minor changes in the HVA/DA ratio and did not antagonize R(-)11-OH-NPa, weakly increased accumulation of DOPA in the second model, and had no effect in the third--all without regional selectivity. In the test of autoreceptor functioning, the dihydroxyaporphine S(+)NPA, but not S(+)11-OH-NPa, inhibited DA synthesis and this effect, in turn, was largely reversed by haloperidol, as were the inhibitory effects of the three R(-)aporphines tested. In this model, however, neither S(+)NPA nor S(+)11-OH-NPa antagonized the DA-synthesis inhibiting effect of R(-)APO as haloperidol did. Overall, these results are consistent with evidence that R(-)NPA and 11-OH-NPa have high affinity at D-2 receptor sites in rat brain and show behavioral effects of typical DA agonists. The non-stereoselective inhibitory effects of NPA on DA synthesis may reflect its activity as a weak DA agonist with very low intrinsic activity, but may also include a direct "catechol-effect" on tyrosine hydroxylase. In contrast, R(-)11-OH-NPa appears to be a stereoselective D-2 agonist, active at autoreceptors as well as postsynaptic receptors, that lacks the nonstereospecific effects on DA metabolism of its catechol-aporphine congener. It may be a useful probe for the further characterization of dopamine receptors and autoreceptors.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1990

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.

Animals↗
PubMed1990

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.

Animals↗
PubMed1990

Presynaptic inhibition of dopamine synthesis in rat striatal tissue by enantiomeric mono- and dihydroxyaporphines.

Presynaptic autoreceptor-mediated modulation of dopamine (DA) synthesis was evaluated as the inhibition of tyrosine hydroxylase activity by enantiomeric mono- and dihydroxyaporphines with minced striatal tissue from rat brain. The isomers of N-n-propylnorapomorphine (NPA) both inhibited tyrosine hydroxylase activity [IC50 = 0.3 and 1.0 microM for (R)-(-)- and (S)-(+)-NPA, respectively; R/S potency = 3.6]. Their effects were fully blocked by the nonselective DA receptor antagonist fluphenazine, as well as by the D2-selective antagonist spiperone, but not by the D1 antagonist SCH-23390. These results suggest a D2-type autoreceptor-mediated inhibition of DA synthesis, with limited enantiomeric selectivity of this catechol-aporphine. The corresponding monohydroxy analogs, (R)-(-)- and (S)-(+)-11-hydroxy-N-n-propylnoraporphine (11-OH-NPa) were about 100 times less potent (IC50 = 42 and 87 microM, respectively) than the NPA isomers in fully inhibiting the enzyme activity in normal tissue but, after depletion of endogenous DA by acute in vivo pretreatment with reserpine (which did not alter the number of D1 or D2 specific binding sites), (R)-(-)-11-OH-NPa was a highly potent but partial agonist (IC25 = 7 nM). Fluphenazine and spiperone fully antagonized the inhibition of tyrosine hydroxylase by (R)-(-)-11-OH-NPa in reserpinized tissue, but SCH-23390 was ineffective. Actions mediated by endogenous DA probably contribute to the effect of high concentrations of (R)-(-)-11-Oh-NPa to evoke a full inhibition of DA synthesis, but its high potency partial agonist effects appear to be mediated by D2-autoreceptors. (S)-(+)-11-OH-NPa was a very weak partial agonist in reserpinized tissue, with an IC25 = 30 microM (essentially the same as normal tissue); thus, (R)-(-)-11-OH-NPa was greater than 4,000 times more potent than its S-(+)-enantiomer in the absence of endogenous DA. These results demonstrate that NPA, which contains a catechol moiety, acts as a full agonist to inhibit striatal DA synthesis via a presynaptic autoreceptor of the D2 type, with only slight stereoselectivity, and that its monohydroxy analog is a very potent but partial D2 autoreceptor agonist, with very high stereoselectivity.

Animals↗
PubMed1989

Pharmacology of binding of 3H-SCH-23390 to D-1 dopaminergic receptor sites in rat striatal tissue.

3H-SCH-23390, a selective antagonist of D-1 dopamine (DA) receptors, was used in a radioreceptor assay with rat brain striatal tissue, optimized biochemically, and extensively characterized pharmacologically with striatal membranes. Nonspecific binding, defined with excess cis(Z)-flupenthixol (300 nM), averaged 20-25% of total counts bound. Specific binding was linearly dependent on the amount of original striatal tissue (0-4 mg) or protein (0-250 micrograms), temperature dependent, saturable and reversible, and appeared to involve a single site at ligand concentrations limited to less than 10 nM. Binding in rat brain regions ranked as: striatum greater than accumbens greater than prefrontal cortex greater than posterior cerebral cortex greater than cerebellum. Association was virtually complete within 30 min at 30 degrees, and the rate of dissociation at 30 degrees was 0.0377 min-1 (half-time = 18.4 min). Affinity (Ka or Kd) determined from association and dissociation rate constants and from concentration isotherms averaged 0.349 and 0.340 nM respectively. Including Na+ at 150 mM increased apparent maximum specific binding (Bmax) by 19%, with a 29% increase in affinity; other monovalent cations alone had small effects on specific binding; Ca2+ and Mg2+ reduced binding by 42%. Agents (N = 85) were tested for potency (Ki or IC50) in competition with the ligand (at 0.30 nM). Those known to have selective effects at D-1 receptors, generally, were most potent and stereoselective. Na+ (150 mM) had little effect on the affinity of cis-thioxanthenes but decreased that of most other agents tested with high D-1 affinity. For antipsychotic agents, the correlation of typical clinical daily doses versus Ki at D-1 sites (r = 0.06) was much lower than at D-2 sites (r = 0.94). (-)Thioridazine was discovered to be D-1 selective, whereas the (+) enantiomer was selective for D-2 sites labeled with 3H-spiperone. Relatively sedating antidepressants had greater D-1 affinity than their less-sedating, secondary amine congeners.

Animals↗
PubMed1989

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.

Animals↗
PubMed1988

Determination of N-n-propylnorapomorphine in serum and brain tissue by gas chromatography-negative ion chemical ionization mass spectrometry.

A method for the determination of the neuroactive compound N-n-propylnorapomorphine (NPA) in biological tissues is described. Isolation of NPA from serum or brain tissue was achieved via liquid-liquid extraction from phosphate-buffered tissue extract (0.25 M, pH 7.2) into ethyl acetate. The NPA, along with a [2H7]NPA analogue serving as internal standard, was converted to the corresponding bis(trifluoroacetyl) ester by treatment with excess trifluoroacetic anhydride at 75 degrees C. The electrophoric derivatives were analyzed by fused-silica capillary gas chromatography-mass spectrometry in the negative ion chemical ionization mode. Selected ion monitoring of the [M-CF3CO]- ions of derivatized NPA (m/z 390) and internal standard [2H7]NPA (m/z 397) permitted the quantitation of NPA in serum and brain samples obtained from rats treated with either free NPA or the prodrug methylenedioxy-NPA (MDO-NPA). Calibration was conducted down to a practical limit of assay sensitivity, at 0.50 ng NPA per ml of serum and 0.50 ng NPA per g of brain. The relative standard deviation for replicate serum samples spiked at 20 ng/ml was 4.2% (n = 5) and for brain samples at 10 ng/g, it was 3.6%. This method revealed differences in the free NPA brain/serum ratios in rats treated separately with the stereoisomers R-(-)-MDO-NPA and S-(+)-MDO-NPA.

Animals↗
PubMed1988

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.

Animals↗