Biomedical subjects

R G MacKenzie

Publications and source records attributed to R G MacKenzie.

At least 37 records · Page 2Linked to original sources

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↗

PubMed1993

A D1/D2 chimeric dopamine receptor mediates a D1 response to a D2-selective agonist.

D1 and D2 dopamine receptors are G-protein coupled receptors and have seven transmembrane spanning regions (TM) typical of this receptor superfamily. Although dopamine binds equally to D1 and D2 receptors, many compounds are highly selective. To probe the receptors for regions that determine subtype specificity, plasmid constructs coding for the D1 or a D1/D2 chimeric receptor were made and transfected into cells to study the binding and agonist properties of non-selective or subtype-selective compounds. The results suggest that the D2-selective agonist, quinpirole, gains much of its selectivity by binding to within TM VI and VII of the D2 receptor.

Amino Acid Sequence↗

PubMed1993

Substance use among youth seen at a community-based health clinic.

Despite recent surveys reporting a decline in adolescents' use of alcohol and other drugs in the general population, substance abuse may actually be increasing among particular subgroups of high-risk youth. This study examined the prevalence of alcohol and other drug use reported by 1121 youth, ages 12-24 years, seen for an initial medical visit at a free community-based primary health clinic. The clinic, located in the Hollywood/Wilshire area of Los Angeles, serves both homeless (62%) and non-homeless (38%) youth. Bivariate and multivariate analyses revealed that the homeless youth were significantly more likely to report use of alcohol and illicit drugs (marijuana, stimulants, hallucinogens, and narcotics) and prior involvement in injecting drug use (IDU). Variables found to be significantly associated with substance use among the homeless youth included length of time homeless, an attempted suicide, physical and sexual abuse, and involvement in survival sex/prostitution. Among the non-homeless youth, age of first intercourse, a previous suicide attempt, and a history of physical and sexual abuse were significantly associated with substance use. These findings suggest that rates of alcohol and other drug use may be higher among youth seen at community-based primary health clinics, particularly homeless youth underscoring the need for screening for these risk variables.

Adolescent↗

PubMed1992

Serine mutations in transmembrane V of the dopamine D1 receptor affect ligand interactions and receptor activation.

Several serines present in transmembrane domain V are conserved among members of the G-protein-coupled receptor family that bind catecholamines. Two of these serines that are present in the beta-adrenergic receptor were previously shown by site-directed mutagenesis to affect agonist binding and receptor activation (Strader, C. D., Candelore, M. R., Hill, W. S., Sigal, I. S., and Dixon, R. A. F. (1989) J. Biol. Chem. 264, 13572-13578). We investigated the role of the serines present in transmembrane V of another catecholamine receptor, the dopamine D1 receptor, by site-directed mutagenesis, and the results show that mutations at serines 198, 199, and 202 affect dopamine binding. The substitution of serine 198 or serine 199 by an alanine also affects the binding of several other agonist and antagonist dopaminergic compounds while an alanine substitution at serine 202 has no effect on the binding of these compounds. Moreover, each single serine mutation decreased the maximal cAMP accumulation elicited by a dopamine D1 partial agonist. These results suggest that serines present in transmembrane V of the D1 receptor affect ligand interactions and receptor signal transduction, but not entirely in the manner that would be predicted from the model proposed for the beta-adrenergic receptor.

Amino Acid Sequence↗

PubMed1992

Runaway and homeless youth: the effects of attachment history on stabilization.

The effects of attachment antecedents on response to stabilization were examined in a group of runaway and homeless youth aged 12 to 17 years. The attachment histories of those who were not responsive to stabilization showed significant differences on several measurable criteria from the attachment histories of those who were responsive. The clinical and programmatic relevance of these findings is discussed.

Adolescent↗

PubMed1992

High-risk behaviors among male street youth in Hollywood, California.

High-risk sex and drug use behaviors are examined among 446 male street youth 14 to 23 years old in Hollywood, California (the area in Los Angeles County with the highest number of AIDS cases). Comparisons are made based on whether the sex behaviors occurred in situations of "survival sex" ("sex you gotta do") and "recreational sex" ("sex you wanna do"). Ninety-seven percent of the males were sexually active, with 27.1% involved in prostitution in the last 3 months. Involvement in prostitution is most common among older, gay identified males. The most prevalent risk factors seen among this group include inconsistent condom use (which also varies by social situation), high-risk sexual behaviors during both survival and recreational sex, large numbers of sexual partners, intravenous drug use, and the use of drugs and alcohol during all sex.

Adolescent↗

PubMed1991

Dopamine D1 receptor stimulation of cyclic AMP accumulation in COS-1 cells.

Dopamine is shown to stimulate cAMP accumulation in COS-1 cells via endogenously expressed dopamine D1 receptors. A dissociation of dopamine and beta-adrenoceptor responses is demonstrated by the use of selective antagonists and different desensitization patterns following exposure of the cells to dopamine or the beta-adrenoceptor agonist, isoproterenol. The dopamine response in COS-1 cells exhibits a pharmacological profile similar to that found in dopamine D1 tissues such as rat striatum and fish retina. The presence of DARPP-32 (dopamine- and cAMP-regulated phosphoprotein, Mr 32,000) immunoreactivity in COS-1 cells is shown by Western blotting and is consistent with the endogenous expression of a dopamine D1 receptor in these cells. It is concluded that a dopamine D1 receptor is expressed in COS-1 cells and the implications of this are discussed.

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

PubMed1990

Two forms of the rat D2 dopamine receptor as revealed by the polymerase chain reaction.

We have used the polymerase chain reaction technique (PCR) to clone the cDNA of the D2 dopamine receptor from rat striatal mRNA. Two major PCR products were produced; one product was identical to a previously published rat cDNA, while the other, more abundant product differed only by an 87-nucleotide insert located in the region of the putative third cytoplasmic loop of the D2 receptor. A PCR approach for determining message abundance was used to determine the relative message abundance of the two forms of the D2 receptor in a variety of tissues. Possible implications of the two forms of the D2 receptor for dopamine-mediated signal transduction are discussed.

Amino Acid Sequence↗

PubMed1990

Runaway and homeless youth in Los Angeles County, California.

Data collected over one year from agencies in Los Angeles County serving homeless youth suggest that shelter and outreach/drop-in agencies serve different populations. Shelters serve about equal numbers of males and females, almost half of whom are 15 years old or younger. Slightly more than half of these young people are minority youth who live in Los Angeles County. Seven of 10 go on to live in a stable environment. Outreach/drop-in agencies serve predominantly males, almost all of whom are 16 years old or older. These clients are primarily white and from outside Los Angeles. Four of 10 get off the streets. Both shelters and outreach/drop-in agencies serve primarily multiproblem chronic runaway or homeless youth who have neither families nor independent living skills and have survived as best they could. To help these young people, more emergency shelter beds and transitional living programs are needed. The geographic location and program structure of services however must be carefully considered.

Adolescent↗

PubMed1990

Approach to the adolescent in the clinical setting.

Life is a series of adolescent experiences, whether these be personal, professional, familial, or community oriented. The biogenesis of puberty, although striking, reveals only a small part of the change that occurs. The accompanying psychosocial changes (adolescence) dynamically interact to create an indelible mark on maturation. A healthy adolescence is one that reflects flexibility within established boundaries, adaptation to change, and growth, all manifested through an increased sense of well-being. Youth becomes not a time of life, but a frame of mind. Physicians who enjoy working with adolescents are those who can tolerate and enjoy growth and change. The venture requires awareness, courage, and sensitivity, but the rewards are commensurate with the commitment.

Adolescent↗

PubMed1990

A68930: a potent and specific agonist for the D-1 dopamine receptor.

A68930 (5,6-dihydroxy-3-phenyl-1-aminomethyl-isochroman) is a potent (EC50 = 2.5 nmol/L) partial agonist at the D-1 dopamine receptor. In contrast, A68930 is a much weaker agonist (EC50 = 3,920 nmol/L) at the D-2 dopamine receptor. The orientation of the 3-phenyl substituent in the molecule is critical for the affinity and selectivity of the molecule towards the D-1 receptor in vitro and in vivo. The role of the D-1 receptor in the functioning of the basal ganglia is discussed.

Animals↗

PubMed1989

Dopaminergic inhibition of striatal acetylcholine release after 6-hydroxydopamine.

Field stimulation increased tritium efflux from rat striatal slices preincubated with [3H]choline, an index of acetylcholine release. When stimulated at low frequency (1 Hz for 2 min), nomifensine (10 microM) reduced acetylcholine release, while at high frequency (8 Hz for 1 min), sulpiride (1 microM) increased release. After 6-hydroxydopamine-induced damage to dopamine neurons, these effects were reduced but the extent of the depletion necessary to block the drug effects increased with the passage of time. Up-regulation of dopamine D-2 receptors seen at 2 months was not detected unless dopamine depletion was very large (90%). These findings indicate that dopamine, acting at the dopamine D-2 receptor, normally exerts an inhibitory influence over acetylcholine release in striatum, that after partial injury the dopaminergic influence over acetylcholine release can recover with time, and that the recovery involves processes other than changes in the number of D-2 receptors.

Acetylcholine↗