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R G MacKenzie

Publications and source records attributed to R G MacKenzie.

At least 19 recordsLinked to original sources
PubMed1998

Regulation of RGS mRNAs by cAMP in PC12 cells.

The RGS (regulators of G protein signaling) proteins represent a novel family of proteins which attenuate G protein mediated signaling. Using antisense riboprobes selective for rat RGS4, RGS7, and RGS2, we examined the regulation of these RGS mRNAs in PC12 cells in response to agents which elevate intracellular cAMP. Treatment of the PC12 cells with forskolin, dibutryl cAMP, or 8-CPT-cAMP for three hours decreased RGS4 message by nearly 50%. Actinomycin D, a potent inhibitor of transcription, did not affect the forskolin-induced decrease in RGS4 message, suggesting that forskolin does not alter RGS4 message half-life. RGS7 message is also present in these cells, but was not affected by forskolin. In contrast, RGS2 message is not evident in unstimulated cells but is strongly induced by one hour of treatment with forskolin. Taken together, these data suggest that mRNA levels of different RGS2 family members respond in an idiosynchratic fashion to cAMP challenge.

Adenosine-5'-(N-ethylcarboxamide)↗
PubMed1997

(Aryloxy)alkylamines as selective human dopamine D4 receptor antagonists: potential antipsychotic agents.

The discovery of a series of novel (aryloxy)alkylamines with selective affinity for the dopamine D4 receptor is described. Target compounds were tested for binding to cloned human dopamine D2, D3, and D4 receptor subtypes expressed in Chinese hamster ovary (CHO) K-1 cells. A number of compounds demonstrated subnanomolar Ki values for binding to the D4 receptor, with several 100-fold selectivities toward the D2 and D3 receptors. Several compounds with combined D3/D4 receptor binding selectivity were also identified. A limited structure-activity relationship study of this chemical series is discussed. In a mitogenesis functional assay, the effect of the test compounds on cellular uptake of [3H]thymidine in D4-transfected CHO 10,001 cells was measured and compared to the response of the full dopamine agonist quinpirole. The activity of the compounds varied from full antagonist to weak partial agonist activity (intrinsic activity of 0-19% in comparison to quinpirole).

Animals↗
PubMed1997

Chromeno[3,4-c]pyridin-5-ones: selective human dopamine D4 receptor antagonists as potential antipsychotic agents.

The discovery of a series of chromeno[3,4-c]pyridin-5-ones with selective affinity for the dopamine D4 receptor is described. Target compounds were tested for binding to cloned human dopamine D2, D3, and D4 receptor subtypes expressed in Chinese hamster ovary (CHO) K-1 cells. Several compounds demonstrated single digit nanomolar Ki values for binding to the D4 receptor with several hundred-fold selectivities toward the D2 and D3 receptors. A limited SAR study of this series is discussed. In a mitogenesis assay measuring [3H]thymidine uptake, the target compounds showed antagonist to weak partial agonist activity at the D4 receptor, with intrinsic activities ranging from 0 to 35%. Compound 6, 3-benzyl-8-methyl-1,2,3,4-tetrahydrochromeno[3,4-c]pyridin-5-one, increased DOPA (L-3,4-dihydroxyphenylalanine) synthesis 84% in the hippocampus and 10% in the striatum of rat brain when dosed orally at 10 mg/kg.

Animals↗
PubMed1997

Characterization of Y3 receptor-mediated synaptic inhibition by chimeric neuropeptide Y-peptide YY peptides in the rat brainstem.

1. Neuropeptide Y (NPY) and peptide YY (PYY) act at receptors referred to as Y1 and Y2, while the Y3 receptor is specific to NPY and does not recognize PYY. The effects of NPY, its related peptides and a series of newly constructed chimeric NPY-PYY peptides were examined on excitatory and inhibitory postsynaptic currents (e.p.s.cs and i.p.s.cs, respectively) in rat dorsomedial nucleus tractus solitarius (NTS) neurones recorded in coronal brainstem slices. Monosynaptic activity was evoked by electrical stimulation in the region of the tractus solitarius. 2. NPY (5-500 nM) inhibited e.p.s.cs and i.p.s.cs in a concentration-dependent manner. In contrast, PYY (500 nM) failed to affect either e.p.s.cs or i.p.s.cs. The N- and C-terminal parts of a series of chimeric NPY-PYY peptides were joined at positions where NPY and PYY sequences differ. In binding experiments the chimeric peptides were all about equipotent with NPY and PYY in displacing [125I]-PYY from Y1 and Y2 binding sites on SK-N-MC cells and rat hippocampus respectively. 3. In the whole cell voltage clamp recordings of NTS neurones, NPY(1-23)-PYY(24-36) and NPY(1-14)-PYY(15-36) evoked a concentration-dependent inhibition of e.p.s.cs and i.p.s.cs, while NPY(1-7)-PYY(8-36) and NPY(1-3)-PYY(4-36) were inactive. The only differences in amino acid residues between NPY(1-14)-PYY(15-36) and NPY(1-7)-PYY(8-36) reside in positions 13 and 14. 4. Furthermore, [Pro34]NPY (500 nM) was equivalent in potency to NPY itself at inhibiting monosynaptic transmission in NTS, while [Leu31,Pro34]NPY and pancreatic polypeptide (both at 500 nM) failed to affect synaptic transmission. 5. The present study has shown that NPY acts at Y3 receptors to suppress both excitatory and inhibitory currents in the NTS. The different efficacy of the chimeric NPY-PYY peptides suggests that positions 13 and 14 are of great importance for Y3 receptor recognition. Finally, this receptor type readily recognizes [Pro34]NPY, but not [Leu31,Pro34]NPY.

Amino Acid Sequence↗
PubMed1997

Methamphetamine.

Explore the source record for details and available documents.

Adolescent↗
PubMed1996

Aryl 1-but-3-ynyl-4-phenyl-1,2,3,6-tetrahydropyridines as potential antipsychotic agents: synthesis and structure-activity relationships.

A novel series of aryl 1-but-3-ynyl-4-phenyl-1,2,3,6-tetrahydropyridines with dopaminergic activity is described. The structure-activity relationships of this series were studied by synthesis of analogs and evaluation of their affinities for the dopamine (DA) D2 receptor and inhibition of locomotor activity (LMA) in rodents. The basic amine, alkyne chain length, and aryl groups were varied. Compounds having a 4-phenyl-1,2,3,6-tetrahydropyridine and an aryl group with hydrogen-bonding substituents separated by a butynyl chain were found to have the most potent dopaminergic activity. Several compounds that were found to have exceptional in vivo activity in LMA inhibition in rodents were evaluated for additional pharmacological activity including binding affinities for other DA receptor subtypes as well as effects on brain DA synthesis, DA neuronal firing, and conditioned avoidance responding in squirrel monkeys.

Alkynes↗
PubMed1995

Identification, characterization and pharmacological profile of three metabolites of (R)-(+)-1,2,3,6-tetrahydro-4-phenyl-1-[(3-phenylcyclohexen-1- yl)methyl]pyridine (CI-1007), a dopamine autoreceptor agonist and potential antipsychotic agent.

Liquid chromatographic-mass spectrometric (LC-MS) analysis of plasma taken from cynomolgus monkeys dosed orally with (R)-(+)-1,2,3,6-tetrahydro-4-phenyl-1-[(3-phenylcyclohexen-1- yl)methyl]pyridine (1), a dopamine (DA) autoreceptor agonist and potential antipsychotic agent, revealed several metabolites. The molecular masses of three major metabolites suggested that they were mono- and dihydroxylated derivatives of 1. We synthesized compounds 2 and 3, the two possible mono-p-hydroxyphenyl derivatives of 1, along with the bis-p-hydroxyphenyl derivative 4. These compounds coeluted by HPLC with the three hydroxylated metabolites of 1. Compounds 2-4 all had high affinities for DA D2 and D3 receptors and moderate affinities for D4 receptors. Like 1, compound 2 decreased DA synthesis and neuronal firing in rat brain, indicative of DA autoreceptor activation. Compound 2 inhibited exploratory locomotor activity in rodents and was active in the Sidman avoidance test in squirrel monkeys, predictive of antipsychotic activity in humans. Compounds 3 and 4 showed weak activity in all these tests. After squirrel monkeys were dosed with 1 orally at the ED100 dose of the Sidman avoidance test, the plasma concentration of 2 was below the limit of quantitation. Therefore, these metabolites are unlikely to contribute greatly to the potent activity seen with 1 in the Sidman avoidance test.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1995

Street youth in Los Angeles. Profile of a group at high risk for human immunodeficiency virus infection.

OBJECTIVE: To characterize an urban street youth population, their self-reported rates of drug use, and their involvement in behaviors that put them at risk for infection with the human immunodeficiency virus. DESIGN: A brief structured interview was administered to 409 youths who had been living on the streets for 2 or more consecutive months, or who were fully integrated into the "street economy." SETTING: Thirty percent of the sample were recruited from community-based service sites and 70% were recruited from street locations and at natural hangouts. PARTICIPANTS: Youths were aged 12 to 23 years; 74% were male, 48% were ethnic minorities, 72% were homeless, 14% were gang affiliated, 20% were involved in drug dealing, 43% were engaged in survival sex (ie, the exchange of a sexual favor for money, food, a place to stay, clothes, and/or drugs), and 40% were homosexual or bisexual. RESULTS: Seventy percent of the youths were sexually active, with an average of 11.7 sexual partners (past 30 days). Youths with multiple sexual partners were more likely to have had a previous sexually transmitted disease (P < .01), to use drugs during sex (P < .001), and to be involved in survival sex (P < .001). Marijuana (55%), methamphetamine (62%), and crack (38%) were the drugs of choice, with 30% of the sample reporting injecting drug use (58% of this subset reported injecting drug use within the past 30 days). Substance-abusing youth were 3.6 times more likely to use drugs during sex, 2.2 times more likely to engage in survival sex, and 2.5 times more likely to have been diagnosed as having a sexually transmitted disease. CONCLUSIONS: High-risk sexual and drug use behaviors were prevalent and interrelated in this urban street youth sample. This suggests the need for new and innovative educational promotions and prevention interventions targeted to this population.

Adolescent↗
PubMed1995

CI-1007, a dopamine partial agonist and potential antipsychotic agent. I. Neurochemical effects.

The receptor binding and biochemical effects of the putative dopamine (DA) partial agonist CI-1007 ([R(+)-1,2,3,6-tetrahydro-4-phenyl- 1-[(3-phenyl-3-cyclohexen-1-yl)methyl]pyridine] maleate) and potential antipsychotic were evaluated with a variety of biochemical methods. In receptor binding studies, CI-1007 bound to rat striatal DA receptors exhibiting a Ki of 3 nM as assessed by inhibition of [3H]N-propylnorapomorphine binding. CI-1007 also exhibited high affinity for cloned human D2L (Ki = 25.5 nM) and D3 (Ki = 16.6 nM) receptors with less affinity for D4.2 receptors (Ki = 90.9 nM). The affinity for serotonin-1A (5-HT-1A), alpha-2 adrenergic and 5-HT-2 receptors was moderate (submicromolar range) and slight or negligible for alpha-1, DA D1 and various other receptors. Unlike dopamine, the inhibition of [3H]spiperone binding was monophasic for CI-1007 and only slightly affected by the addition of Gpp-(NH)p. In vitro CI-1007 antagonized the forskolin-induced increases in cyclic AMP levels in GH4C1 cells expressing the human D2L receptor, having an intrinsic activity of 53% of that seen with the full agonist quinpirole. In vivo CI-1007 antagonized the gamma-butyrolactone (GBL)-induced accumulation of L-3,4-dihydroxyphenylalanine in striatum and mesolimbic regions of rat brain, causing a maximal 64% reversal in striatum, consistent with a partial agonist profile. In microdialysis studies it decreased DA overflow in both striatum and nucleus accumbens, indicating decreased release of DA. CI-1007 also reduced brain DA synthesis (DOPA accumulation), metabolism (DOPAC and HVA) and utilization (after tyrosine hydroxylase inhibition with alpha-methyl-p-tyrosine). CI-1007 did not affect striatal acetylcholine levels indicating lack of potent postsynaptic DA actions. CI-1007 seemed to be selective for DA neurons as it did not alter rat brain norepinephrine (NE) synthesis in the NE-enriched brainstem or NE utilization in the mesolimbic region. In addition, it did not affect in general 5-HT synthesis and metabolism in striatum and mesolimbic regions. These neurochemical results demonstrate that CI-1007 is a selective potent brain dopamine partial agonist with limited agonist activity at postsynaptic DA receptors.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1995

Characterization of a chimeric human dopamine D3/D2 receptor functionally coupled to adenylyl cyclase in Chinese hamster ovary cells.

Dopamine D3 receptor pharmacology differs from that of the dopamine D2 receptor despite a high degree of receptor sequence similarity. The greatest divergence of the primary sequences of D3 and D2 receptors occurs in the predicted third intracellular loops of the receptors, a region implicated in G protein binding and function. To determine whether this domain specifies the distinct ligand binding and signal transduction characteristics of the D3 receptor, we developed a chimeric receptor, replacing the third intracellular loop of the human D3 receptor with the third intracellular loop of the human D2 receptor. The pharmacology of the chimeric receptor expressed in Chinese hamster ovary cells was examined and compared with that of human dopamine D2 and D3 receptors expressed in the same cell line. The chimeric receptor retained characteristic human D3 receptor binding; the D2 third intracellular loop present in the chimeric receptor did not reduce high affinity agonist binding, characteristic of the D3 receptor, or make high affinity sites sensitive to GTP analogs. Unlike the native human D3 receptor, the chimeric receptor was negatively coupled to adenylyl cyclase through a pertussis toxin-sensitive pathway, apparently mediated by the D2 third intracellular loop. The ability of D3 ligand binding domains to produce a D2 functional response implies that the third intracellular loop of the D3 receptor is unable to mediate this D2 response in Chinese hamster ovary cells. The inhibition of adenylyl cyclase seen with the chimeric receptor is less than the inhibition produced by D2 receptor coupling, suggesting that additional sequences in the D2 receptor contribute to normal G protein coupling.

Adenylyl Cyclases↗
PubMed1995

Neurochemical and functional characterization of the preferentially selective dopamine D3 agonist PD 128907.

The present study determined the biochemical and pharmacological effects of PD 128907 [R-(+)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H- [1]benzopyrano[4,3-b]-1,4-oxazin-9-ol], a dopamine (DA) receptor agonist that shows a preference for the human D3 receptor. In transfected Chinese hamster ovary cells (CHO K1), PD 128907 displaced [3H]spiperone in a biphasic fashion which fit best to a two-site model, generating Ki values of 20 and 6964 nM for the high- and low-affinity sites for the D2L receptors and 1.43 and 413 nM for the corresponding sites for the D3 receptors. Addition of sodium and the GTP analog Gpp(NH)p to both the D2L and D3 caused a modest reduction in the affinity of the compound suggestive of an agonist type action. In agonist binding ([3H]N-0437), PD 128907 exhibited an 18-fold selectivity for D3 versus D2L, a selectivity similar to that found with antagonist binding to the high-affinity sites. PD 128907 exhibited only weak affinity for D4.2 receptors (Ki = 169 nM). No significant affinity for a variety of other receptors was observed. PD 128907 stimulated cell division (measured by [3H]thymidine uptake) in CHO p-5 cells transfected with either D2L or D3 receptors exhibiting about a 6.3-fold greater potency in activating D3 as compared to D2L receptors. In vivo the compound was active in reducing DA synthesis both in normal and gamma-butyrolactone (GBL) treated rats; in the GBL model, the decrease was greater in the higher D3-expressing mesolimbic region as compared with striatum which has a lower expression of D3 receptors. PD 128907 decreased DA release (as measured by brain microdialysis) both in rat striatum, nucleus accumbens and medial frontal cortex, as well as in monkey putamen. Behaviorally PD 128907 decreased spontaneous locomotor activity (LMA) in rats at low doses, whereas at higher doses stimulatory effects were observed. PD 128907 at high doses reversed the reserpine-induced decrease in LMA and induced stereotypy in combination with the D1 agonist SKF 38393 indicating postsynaptic DA agonist actions. It is unclear which of the subtypes of DA receptors might be mediating the pharmacological effects of PD 128907. However, the present findings indicating that PD 128907 shows a preference for DA D3 over D2L and D4.2 receptors indicates that its action at low doses may be due to interaction with D3 receptors and at higher doses, with both D2 and D3 receptors.

Animals↗
PubMed1994

Studies of the active conformation of a novel series of benzamide dopamine D2 agonists.

Analogs of dopamine D2 agonist 11 were prepared in which a rigid trans decalin ring system was used to mimic various conformations of 11. The four rigid analogs where compared for their ability to bind to the DA D2 receptor and to inhibit forskolin-stimulated cAMP formation, a measure of DA agonist activity. Of the four rigid analogs of compound 11, only compound 12b had significant activity in both assays. Molecular modeling studies of 12a-d showed each had a single conformation with regard to the distance between the benzamide aryl-centroid and the 4-nitrogen atom of the pyridylpiperazine. Compound 12b was shown to have a greater distance between these functionalities (11.8 A) as compared to the other isomers (9.8-10.4 A). The distance between these two functionalities in 12b was similar to that of a conformer of 11 which has an extended conformation. This suggest that 11 is likely in an extended conformation when bound to the DA D2 receptor.

Animals↗
PubMed1994

The discovery and structure-activity relationships of 1,2,3,6-tetrahydro-4-phenyl-1-[(arylcyclohexenyl)alkyl]pyridines. Dopamine autoreceptor agonists and potential antipsychotic agents.

A novel dopamine (DA) autoreceptor agonist, 1,2,3,6-tetrahydro-4-phenyl-1- [(3-phenyl-3-cyclohexen-1-yl)methyl]pyridine (14), was identified. The structure-activity relationships surrounding this compound were studied by synthesis of analogues and evaluation of their dopaminergic activity. The cyclohexene substitution pattern was varied along with the length of the chain connecting the 1,2,3,6-tetrahydro-4-phenylpyridine to the cyclohexene. Compound 14, having the 1,3-substitution pattern and a single methylene chain, was the most potent. The 1,2,3,6-tetrahydro-4-phenylpyridine could be replaced by other aryl-cyclic amines with a slight loss in activity. The phenyl group on the cyclohexene ring could be para substituted; electron-donating groups were better tolerated than electron-withdrawing groups. Finally, the enantiomers of 14 were resolved via the 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate salts. Although both isomers were partial DA agonists, the (+)-enantiomer had higher intrinsic activity than the (-)-enantiomer. Syntheses were developed that allowed rapid preparation of analogues. An X-ray crystal structure determination of an intermediate identified the (+)-isomer of 14 as having R configuration. This compound, designated CI-1007 (PD 143188), was found to have antipsychotic-like activity in behavioral tests; in particular, it was orally active in the conditioned avoidance test in squirrel monkeys with an ED50 of 0.6 mg/kg. The overall profile suggests that (R)-(+)-14 may be a clinically useful antipsychotic agent.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1994

Characterization of the human dopamine D3 receptor expressed in transfected cell lines.

A full-length cDNA clone of the human dopamine D3 receptor was obtained by the polymerase chain reaction (PCR) using reverse-transcribed RNA from human brain as the template. The cDNA was inserted into an expression vector which was then stably transfected into either Chinese hamster ovary (CHO), SK-N-MC human epithelioma or mouse CCL1.3 fibroblast cell lines. Post-transfection, the Bmax for D3 receptor expression was 1.9, 1.1 and 0.4 pmol/mg protein in the CHO-K1, SK-N-MC and CCL1.3 cell lines, respectively. The D3 receptor expressed in CHO-K1 and CCL1.3 cells exhibited similar radioligand binding profiles, especially for the D3-selective compound, 7-hydroxy-2-(di-n-propylamino)tetralin (7-OH-DPAT). Radioligand-binding competition curves of presumed D3 agonists were shifted to the right by the addition of guanine nucleotides and Na+ to the assay buffer. Presumed D3-receptor agonists had no effect on cAMP accumulation in any of the D3-transfected cell lines although cAMP accumulation was inhibited by dopamine D2 receptor activation in D2-transfected CHO and CCL1.3 cells and by activation of the exogenously expressed neuropeptide Y receptor in SK-N-MC cells. Also, D3 receptor activation neither potentiated ATP-stimulated arachidonic acid release from CHO cells nor stimulated inositol phosphate production in CCL1.3-cells although both of these responses were elicited by D2 agonists in D2-transfected cells. We conclude that the signalling properties of the D3 receptor differ from those of its closest homolog, the D2 receptor.

Animals↗
PubMed1994

Differential interaction of beta 1- and beta 3-adrenergic receptors with Gi in rat adipocytes.

The interaction of beta 1- and beta 3-adrenergic receptors and G(i) proteins was examined in rat adipocytes. In intact adipocytes, cyclic AMP accumulation stimulated by the beta 3-selective agonist, BRL 37344 (BRL), was potentiated by pertussis toxin (PTX), as was the beta 1-sensitive component of isoproterenol (ISO)-stimulated cyclic AMP accumulation. These data suggest that beta 1 and beta 3-receptors interact with both Gs and G(i) in intact adipocytes. Further analysis of the activation of adenylyl cyclase by the beta-receptor subtypes was performed in adipocyte membranes in which the activity of G(i) was manipulated by both GTP and PTX. Unlike cyclic AMP accumulation in cells, the activation of membrane adenylyl cyclase by ISO could be clearly resolved into components mediated by beta 1-(high affinity) or beta 3-(low affinity) receptors. The beta 3-receptor-mediated activity was dramatically reduced at 0.1 mM GTP compared to 0.1 microM GTP, but the activity mediated by beta 3-receptors was significantly reduced at concentrations of GTP in which G(i) proteins are active. Adenylyl cyclase activity stimulated by BRL was also inhibited at high concentrations of GTP. PTX abolished the inhibition of beta 3-receptor-stimulated activity by high GTP concentrations. This is the first study to indicate that G(i) proteins can limit beta 3- but not beta 1-stimulated adenylyl cyclase activity and are consistent with the hypothesis that beta 3-receptors interact with both Gs and G(i), whereas beta 1-receptors couple predominantly to Gs.

Adenylate Cyclase Toxin↗
PubMed1993

Pharmacological aspects of R-(+)-7-OH-DPAT, a putative dopamine D3 receptor ligand.

The R-(+)-isomer of 7-hydroxy-2-(N,N-di-n-propylamino)tetralin (7-OH-DPAT) bound with a more than 200-fold higher affinity to cloned human dopamine D3 receptors (Ki = 0.57 nM) than to dopamine D2 receptors; the corresponding S-(-)-enantiomer had considerably less affinity for both dopamine receptor subtypes, indicating that the known enantiomer selectivity of 7-OH-DPAT for the 'classical' dopamine D2 receptor subtype extends to the recently discovered dopamine D3 receptor subtype. In rats R-(+)-7-OH-DPAT dose dependently (10-1000 nmol/kg) decreased dopamine release and induced yawning, while sniffing behaviour occurred at the highest dose tested (1000 nmol/kg). The possibility that the inhibition of dopamine release and the elicitation of yawning are mediated by dopamine D3 receptors is considered.

Animals↗
PubMed1993

Further characterization of the D2 dopamine receptor expressed in MMQ cells.

The D2 dopamine receptor expressed in the MMQ cell line was characterized by saturation binding using the D2 dopamine radioligand [3H]spiperone. The KD for spiperone was 41 pM and the Bmax for these sites was 34 fmol/mg protein. Inhibition of forskolin-stimulated cAMP accumulation occurred in response to a variety of D2 agonists, and the agonist effects were reversed by D2 antagonists. Pertussis toxin pretreatment abolished agonist inhibition of cAMP accumulation. In addition, the alpha 2-adrenergic agonist UK 14304 inhibited cAMP accumulation; this effect was reversed by an alpha 2-adrenergic antagonist but not by a D2 antagonist, indicating the presence of alpha 2-adrenergic receptors on these cells. Specific oligonucleotide primers were used in the polymerase chain reaction to determine, by restriction enzyme analysis and Southern blotting, that the long form of the two alternatively spliced variants of the D2 dopamine receptor was the predominant variant expressed in these cells.

Animals↗