Starting insulin therapy in elderly non-insulin-dependent diabetic patients at a health care centre. Methodological and economic aspects

We examined the association between gene polymorphisms related to central dopaminergic transmission and alcoholism in the Japanese population. Polymorphic gene loci examined included those encoding the dopamine D2 receptor (NcoI site and Ser-Cys site), the dopamine D3 receptor (BalI site), the dopamine D4 receptor (48 bp tandem repeat) and the dopamine transporter (40 bp tandem repeat). The genotype distribution at the NcoI site in the dopamine D2 receptor gene differed significantly (p < 0.5) between alcoholic patients and control subjects. The frequency of 7 repeats at the 40 bp/DAT tended to be higher (p < 0.1), and that of 9 repeats tended to be lower (p < 0.1) in alcoholic patients than in control subjects. The possible effects of dopamine-related gene polymorphisms, which might predispose individuals to alcoholism, are discussed.     

CYP2D6 allelic frequencies in young-onset Parkinson's disease

Parkinson's disease (PD) is thought to develop as a result of interactions between genetic susceptibility factors and environmental exposures. One candidate gene is CYP2D6, which codes for the debrisoquine 4-hydroxylase cytochrome P450. Impairment of debrisoquine 4-hydroxylase activity has been associated with an increased risk of PD in patients with younger age at disease onset. Genotyping studies in patients with an older age at onset have reported modest increases in risk associated with the CYP2D6 B and A alleles; however, the risk for young-onset PD has not been adequately evaluated. We designed a case-control study to investigate the role of nonfunctional CYP2D6 allelic risk factors for young-onset PD in a sizable patient population and compared the distributions of CYP2D6 genotypes between young-onset ( < or = 51 years) PD patients (n = 108) and controls (n = 236). In contrast with the results from genotyping studies conducted among patients with an older age at onset, there were no significant differences in CYP2D6 allelic frequencies between young-onset PD cases and controls. The frequency of the B allele was slightly lower in the young-onset PD cases than in the controls (0.14 versus 0.20) (X2 = 2.66, p = 0.10). The presence of one or more B alleles was not associated with an increased risk of young-onset PD (odds ratio 0.58; 95% CI 0.33 to 1.00), nor was the presence of one or more nonfunctional alleles (i.e., A, B, D, and D2) (odds ratio 0.68; 95% CI 0.41 to 1.13). This study suggests that the young-onset PD population may differ from the older-onset population with respect to risk factors.     

An association between the DAT1 polymorphism and smoking behavior in young adults from the national longitudinal study of adolescent health.

Associations between smoking behavior and polymorphisms in the dopaminergic genes (DAT1 and DRD2) were tested by using within- and between-family measures of allelic transmission in 2,448 young adults from the National Longitudinal Study of Adolescent Health. The 9-repeat allele of the dopamine transporter gene polymorphism (DAT1) was inversely associated with smoking in samples that included all subjects and only those who had initiated smoking, accounting for approximately 1% of the variance. Never smokers and current nonsmokers had an excess transmission of the 9-repeat allele compared with regular smokers, suggesting a protective effect of the 9-repeat allele, which is hypothesized to alter synaptic dopamine levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relations between multi-informant assessments of ADHD symptoms, DAT1, and DRD4.

Researchers conducting candidate gene studies of attention-deficit/hyperactivity disorder (ADHD) typically obtain symptom ratings from multiple informants (i.e., mothers, fathers, and teachers) and use a psychologist's best estimate or a simple algorithm, such as taking the highest symptom ratings across informants, to construct diagnostic phenotypes for estimating association. Nonetheless, these methods have never been empirically validated in the context of a molecular genetic study. In the current study, the authors systematically evaluated several methods of operationalizing phenotypes and the resulting evidence for association between ADHD and the candidate genes: dopamine transporter gene (DAT1) and dopamine D4 receptor gene (DRD4). Use of symptom scores as continuous scales in regression analysis suggested that the combination of mother and teacher ratings yielded the strongest evidence for association between hyperactive-impulsive ADHD symptoms and DAT1 and between inattentive ADHD symptoms and DRD4. Teacher ratings alone were sufficient for evaluating the association between inattentive symptoms and DAT1. Further, this regression-based method consistently yielded stronger evidence for association among ADHD symptoms, DAT1, and DRD4 than did three simple algorithms (i.e., the and, or, and averaging rules). The implications of these results for future molecular genetic studies of ADHD are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Polymorphisms in dopamine system genes are associated with individual differences in attention in infancy.

Knowledge about the functional status of the frontal cortex in infancy is limited. This study investigated the effects of polymorphisms in four dopamine system genes on performance in a task developed to assess such functioning, the Freeze-Frame task, at 9 months of age. Polymorphisms in the catechol-O-methyltransferase (COMT) and the dopamine D4 receptor (DRD4) genes are likely to impact directly on the functioning of the frontal cortex, whereas polymorphisms in the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) genes might influence frontal cortex functioning indirectly via strong frontostriatal connections. A significant effect of the COMT valine1??methionine (Val158Met) polymorphism was found. Infants with the Met/Met genotype were significantly less distractible than infants with the Val/Val genotype in Freeze-Frame trials presenting an engaging central stimulus. In addition, there was an interaction with the DAT1 3` variable number of tandem repeats polymorphism; the COMT effect was present only in infants who did not have two copies of the DAT1 10-repeat allele. These findings indicate that dopaminergic polymorphisms affect selective aspects of attention as early as infancy and further validate the Freeze-Frame task as a frontal cortex task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of in utero cocaine exposure on the expression of mRNAS encoding the dopamine transporter and the D1, D2 and D5 dopamine receptor subtypes in fetal rhesus monkey

The effects of in utero cocaine exposure on the development of the mRNAs encoding the dopamine transporter (DAT) and the D1, D2 and D5 dopamine receptor subtypes were determined in fetal monkey brains at day 45 and day 60 of gestation. Pregnant monkeys were treated with cocaine 3 mg/kg or saline i.m., four times a day from day 18 of gestation until the pregnancy was terminated at day 45 or day 60. The fetal brains were dissected, and tissue RNA extracted and quantified using ribonuclease protection assay analysis. In day 45 fetal monkeys, dopamine D1 and D2 receptor subtype mRNAs and DAT mRNA were found in low quantities both in control and cocaine-treated subjects. In day 60 fetal monkeys, D1 receptor mRNA levels were highest in the frontal cortex/striatal area, and low to moderate quantities were found in diencephalic and mesencephalic fetal brain regions. Dopamine D2 receptor mRNA levels were highest in the frontal cortex/striatal area, diencephalon and the midbrain, moderate in the brainstem and low in the caudal temporal lobe and surrounding cortical areas. Dopamine D5 receptor mRNA was expressed in low quantities throughout the day 60 fetal monkey brain, whereas DAT mRNA was found in the midbrain only. In utero cocaine exposure caused a significant increase in dopamine D1, D2 and D5 receptor subtype mRNAs in the frontal cortex/striatal area of day 60 fetal monkeys. These results support the hypothesis that dopamine synthesis and release may be reduced in cocaine-treated fetuses, which results in dopamine receptor up-regulation.     

Cyclic HIV-1 protease inhibitors derived from mannitol: synthesis, inhibitory potencies, and computational predictions of binding affinities

The molecular characteristics of midbrain dopamine (DA) neurons have been extensively studied in Parkinson's disease (PD). No such studies of the characteristics of midbrain DA neurons in Alzheimer's disease (AD) or Alzheimer's disease with parkinsonism (AD/Park) have been published. We examined the levels of tyrosine hydroxylase (TH) protein, and the expression of TH and dopamine transporter (DAT) mRNAs, in midbrain neurons of PD, AD, and AD/Park cases. In PD, the loss of TH protein in the ventral tier of the substantia nigra pars compacta (SNpc) of the PD group in accompanied by severe losses in the number of neurons that express TH mRNA and DAT mRNA (74% loss). Remaining neurons show a shift to higher concentrations of TH mRNA but a shift to lower concentrations of DAT mRNA per cell. Hence, there is evidence that compensation in the remaining neurons can elevate concentrations of TH mRNA and lower DAT mRNA. Alternatively, there may be a predilection for a loss of neurons with high levels of DAT mRNA and low TH mRNA levels within the SNpc of PD cases. There was no change in TH protein but an elevation of TH mRNA concentrations per neuron without any change in concentrations of DAT mRNA in the AD group. The AD/Park group did not exhibit changes in the level of TH protein, but showed a small loss (26%) of neurons in the SNpc and a greater loss in other regions of the midbrain (43-53%). Remaining DA neurons showed a marked shift to lower concentrations of DAT mRNA per neuron and a nonsignificant shift in cellular concentration of TH mRNA to higher levels. This is consistent with our previous work showing that with AD/Park there is a significant reduction in the number of DAT sites located on DA terminals in the striatum, but the midbrain neurons have not died. Our results indicate that the differential regulation of mRNAs encoding TH and DAT is similar in the parkinsonian disorders (PD and AD/Park) even though the degree of cell death is very different. This might suggest that compensatory events occur in these DA neurons in AD/Park that are similar to those in PD and that result in differential effects on mRNAs encoding TH and DAT proteins.     

Dopamine agonist-induced hypothermia and disruption of prepulse inhibition: evidence for a role of D3 receptors?

The dopamine D3/D2 receptor agonists 7-OH-DPAT, quinpirole, quinelorane, and PD128907, the mixed dopamine agonist apomorphine, the D2 agonist bromocriptine, and the D1/D5 agonist SKF38393 were examined in models of hypothermia and prepulse inhibition (PPI) in Wistar rats. As dopamine agonist-induced hypothermia has been proposed as a model of D3 receptor function, and dopamine agonists are known to disrupt PPI, drug potencies to induce hypothermia were established and compared with doses necessary to disrupt PPI. 7-OH-DPAT, quinpirole, quinelorane, PD128907, and apomorphine, reduced body temperature and disrupted PPI with a similar rank order of potency (quinelorane > quinpirole = 7-OH-DPAT > PD128907 = apomorphine). Bromocriptine and SKF38393 were ineffective in both models. In a separate study, the dopamine reuptake inhibitors cocaine and GBR 12909 had no effect on PPI. In a final set of studies, the D2/D3 antagonist raclopride blocked both 7-OH-DPAT-induced hypothermia and 7-OH-DPAT-induced PPI disruption. The 5-HT1A antagonist WAY 100,135, and the peripheral D2-like antagonist domperidone had no effect. These findings suggest that the hypothermia and PPI disruptions seen with some of these dopamine agonists may be mediated by central D3 receptors; however, only studies using more selective dopamine receptor ligands can definitively rule out effects at the D2 or D4 receptors.     

Motor response to a dopamine D3 receptor preferring agonist compared to apomorphine in levodopa-primed 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine monkeys

The profile of dopamine receptor subtype activation contributing to the therapeutic efficacy and motor response complications of levodopa (nonselective pro-agonist) in Parkinson's disease remains unclear. Potent, selective, short-acting dopamine D2 receptor subfamily agonists show good antiparkinsonian efficacy but produce dyskinesias comparable to levodopa. Nonetheless, agonists displaying higher affinity for dopamine receptors other than the D2 subtype may have a better therapeutic index. To clarify this issue, we compared the nonselective dopamine D1/D2 receptor subfamilies agonist apomorphine to the dopamine D3 receptor preferring agonist [R-(+)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4 , 3-b]-1,4-oxazin-9-ol] (PD 128,907) in 6 levodopa-primed , 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned parkinsonian monkeys with reproducible dyskinesias. Single s.c. dosing with the lowest fully effective dose of apomorphine (averaging 27.9 +/- 4.5 microg/kg) and PD 128,907 (averaging 41.7 +/- 4.4 microg/kg) yielded equivalent antiparkinsonian efficacy on the behavioral scale and portable activity monitoring used. A comparable significant dose-dependent increase in the response magnitude and duration was seen with two higher doses. The severity of dyskinesia was also similar between the two drugs. When the lower dose for each drug was administered six times at a fixed 90-min interval, both drugs remained efficacious with no significant tolerance observed. The D3 receptor preferring antagonist U-99194A significantly reduced the motor effects of both apomorphine and PD 128,907. Thus, increased D3 receptor tone does not acutely ameliorate dyskinesias in levodopa-primed parkinsonian monkeys. Given the reported lack of affinity of PD 128,907 for central D1 receptors, our data support the concept that the pharmacological activation of D1 receptors is not mandatory for relief of parkinsonism and production of dyskinesia.     

Immunochemical analysis of dopamine transporter protein in Parkinson's disease

The plasma membrane dopamine transporter (DAT) is considered to be a reliable marker of presynaptic dopaminergic terminal loss. Previous in vivo imaging and postmortem binding studies have detected a loss in striatal DAT binding in Parkinson's diseased (PD) brain; however, these techniques have poor spatial resolution and may suffer from nonspecific binding of some ligands. In this study, we use novel highly specific monoclonal antibodies to distinct epitopes of human DAT to quantify and localize the protein. Western blot analysis revealed marked reductions in DAT immunoreactivity in putamen, caudate, and nucleus accumbens of PD brain compared with control cases, and the reductions were significantly correlated to disease duration. Immunohistochemistry revealed DAT-immunoreactive fibers and puncta that were dense throughout the striatum of control brains but that were drastically reduced in putamen of PD brains. Caudate from PD brains showed a significant degree of sparing along the border of the ventricle, and the nucleus accumbens was relatively preserved. An unexpected finding was that discrete islands of DAT immunoreactivity were preserved within the matrix of PD putamen. Thus, immunological analysis of DAT protein provides novel and sensitive means for localizing and quantifying DAT protein in PD and other neurological disorders involving dopaminergic systems.     

Effects of the dopamine D3 antagonist PD 58491 and its interaction with the dopamine D3 agonist PD 128907 on brain dopamine synthesis in rat

The dopamine (DA) D3 receptor antagonist PD 58491 [3-[4-[1-[4-[2-[4-(3-diethylaminopropoxy)phenyl]benzoimidazol++ +-1-yl-butyl]-1H-benzoimidazol-2-yl]phenoxy]propyl]diethylamine] bound with high affinity and selectivity to recombinant human DA D3 versus D2L and D4.2 receptors transfected into Chinese hamster ovary cells: Ki values of 19.5 nM versus 2,362 and >3,000 nM, respectively. In contrast, the putative DA D3 receptor antagonist (+)-AJ76 displayed low affinity and selectivity for D3 versus D2L and D4.2 receptors (91 nM vs. 253 and 193 nM, respectively). In vitro, PD 58491 (1 nM-1 microM) exhibited D3 receptor antagonist activity, reversing the quinpirole (10 nM)-induced stimulation of [3H]thymidine uptake in D3 CHOpro-5 cells, but did not have any significant intrinsic activity by itself in this assay. PD 58491 did not decrease the gamma-butyrolactone-induced increase in DA synthesis (L-3,4-dihydroxyphenylalanine accumulation) in rat striatum, indicating that the compound possessed no in vivo DA D2/D3 receptor agonist action at DA autoreceptors. PD 58491 (3-30 mg/kg, i.p.) generally did not alter DA or serotonin synthesis in either the striatum or mesolimbic region of rat brain. The D3-preferring agonist PD 128907 decreased DA synthesis in striatum and mesolimbic regions, and this effect was attenuated by pretreatment with PD 58491. These findings support the hypothesis that DA D3 autoreceptors may in part modulate the synthesis and release of DA in striatum and mesolimbic regions.     

Profound neuronal plasticity in response to inactivation of the dopamine transporter

The dopamine transporter (DAT) plays an important role in calibrating the duration and intensity of dopamine neurotransmission in the central nervous system. We have used a strain of mice in which the gene for the DAT has been genetically deleted to identify the DAT's homeostatic role. We find that removal of the DAT dramatically prolongs the lifetime (300 times) of extracellular dopamine. Within the time frame of neurotransmission, no other processes besides diffusion can compensate for the lack of the DAT, and the absence of the DAT produces extensive adaptive changes to control dopamine neurotransmission. Despite the absence of a clearance mechanism, dopamine extracellular levels were only 5 times greater than control animals due to a 95% reduction in content and a 75% reduction in release. Paradoxically, dopamine synthesis rates are doubled despite a decrease of 90% in the levels of tyrosine hydroxylase and degradation is markedly enhanced. Thus, the DAT not only controls the duration of extracellular dopamine signals but also plays a critical role in regulating presynaptic dopamine homeostasis. It is interesting to consider that the switch to a dopamine-deficient, but functionally hyperactive, mode of neurotransmission observed in mice lacking the DAT may represent an extreme example of neuronal plasticity resulting from long-term psychostimulant abuse.     

Depletion of striatal dopamine transporter does not affect psychostimulant-induced locomotor activity

The effect of neurotoxin-induced depletion of striatal dopamine transporter (DAT) binding sites on animals' responses to psychostimulants was investigated. Multiple 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (METH) injections but not a single METH injection to Swiss Webster mice resulted in > 60% depletion of striatal DAT. MPTP-induced depletion of DAT did not affect METH- and cocaine-stimulated locomotor activity compared with the response of control mice. Pre-exposure to either the neurotoxic or the single non-neurotoxic dose of METH resulted in a marked locomotor sensitization in response to METH or cocaine challenge injections. The present results indicate that > 60% loss in striatal DAT binding sites has no effect on animals' responses to psychostimulants, and suggest that neural systems other than striatal DAT may contribute to the induction of locomotor sensitization to METH and cocaine.     

Reduced striatal dopamine transporter density in abstinent methamphetamine and methcathinone users: evidence from positron emission tomography studies with [11C]WIN-35,428

Methamphetamine and methcathinone are psychostimulant drugs with high potential for abuse. In animals, methamphetamine and related drugs are known to damage brain dopamine (DA) neurons, and this damage has recently been shown to be detectable in living nonhuman primates by means of positron emission tomography (PET) with [11C]WIN-35,428, a DA transporter (DAT) ligand. The present studies determined whether living humans with a history of methamphetamine or methcathinone abuse showed evidence of lasting decrements in brain DAT density. PET studies were performed in 10 control subjects, six abstinent methamphetamine users, four abstinent methcathinone users, and three patients with Parkinson's disease (PD). On average, subjects had abstained from amphetamine use for approximately 3 years. Before PET studies, all subjects underwent urine and blood toxicology screens to rule out recent drug use. Compared with controls, abstinent methamphetamine and methcathinone users had significant decreases in DAT density in the caudate nucleus (-23 and -24%, respectively) and putamen (-25 and -16%, respectively). Larger decreases in DAT density were evident in patients with PD (47 and 68% in caudate and putamen, respectively). Neither methamphetamine nor methcathinone users showed clinical signs of parkinsonism. Persistent reductions of DAT density in methamphetamine and methcathinone users are suggestive of loss of DAT or loss of DA terminals and raise the possibility that as these individuals age, they may be at increased risk for the development of parkinsonism or neuropsychiatric conditions in which brain DA neurons have been implicated.     

Association between dopamine receptor genes and migraine without aura in a Sardinian sample

BACKGROUND: Migraine seems to be caused by a combination of environmental and genetic factors. Clinical and pharmacologic evidence supports the hypothesis that dopaminergic transmission is involved in the pathogenesis of migraine. OBJECTIVE: The current report concerns a genetic study to test the involvement of genes for dopamine (DA) receptors D2 (DRD2), D3 (DRD3), and D4 (DRD4) in migraine without aura, particularly in a subgroup with enhanced DA sensitivity. METHODS: For the first time, a family-based association method--the Transmission Disequilibrium Test (TDT)--was used to examine an isolated population, such as Sardinians. We studied 50 nuclear families of patients affected by migraine without aura. The subgroup of dopaminergic migraineurs was selected based on the presence of both nausea and yawning immediately before or during the pain phase of migraine. RESULTS: No association was detected using the TDT between DRD3, DRD4, and migraine without aura either in the overall sample or in the subgroup. No difference was observed in DRD2 allelic distribution in the overall sample, although the allelic distribution at the DRD2 locus differed significantly in the subgroup of dopaminergic migraineurs (p = 0.004). Allele 1 of the TG dinucleotide intronic noncoding polymorphism of the DRD2 locus was the individual allele that appeared to be in disequilibrium with migraine without aura (p = 0.02). CONCLUSIONS: Our data suggest that a genetic approach could be useful in providing molecular support to the hypothesis that hypersensitivity of the dopaminergic system may represent the pathophysiologic basis of migraine, at least in a subgroup of patients.     

Pharmacological characterization of PD 152255, a novel dimeric benzimidazole dopamine D3 antagonist

152255 (E-1,1'-(2-butene-1,4-diyl)bis[2-[4-[3-(1-piperidinyl)propoxy]-phe nyl]-1H-benzimidazole]) exhibited high affinity (Ki = 12.7 nM) for human dopamine (DA) D3 receptors expressed in CHO K1 cells but not for DA D2L receptors (Ki = 565 nM), DA D42 or DA D1 receptors (Ki > 3 microM) and a number of other neurotransmitter receptors. Affinity for human muscarinic receptors was seen in vitro but no functional muscarinic agonist and/or antagonist action was observed in vivo. Antagonist activity at DA D3 receptors was demonstrated by blockade of quinpirole-stimulated [3H]-thymidine uptake in D3 transfected cells, an effect that was 28-fold more potent than in D2-transfected cells. Unlike classical DA D2 antagonists, PD 152255 did not increase rat brain DA synthesis and it increased locomotion in habituated rats. However, like antipsychotics, PD 152255 reduced locomotor activity in mice and reduced spontaneous and amphetamine-stimulated locomotion in nonhabituated rats. These results demonstrate that PD 152255 is a DA D3 antagonist that may have antipsychotic activity.     

A highly polymorphic microsatellite marker located within the choroideremia gene

Although serotonergic dysregulation is a leading pathogenetic hypothesis for obsessive-compulsive disorder (OCD), some evidence also suggests a possible dysregulation of the dopaminergic system in this disorder. Therefore, individual differences in deoxyribonucleic acid (DNA) coding for dopamine receptor proteins might contribute to the genetic background of this disorder. Previously we reported a null mutation in exon 1 of the dopamine D4 receptor gene. The variant type is characterized by a 13 bp deletion and is predicted to code for a truncated, non-functional receptor. We assessed the frequency of this polymorphism in 157 OCD patients, 196 schizophrenics, 111 bipolars and 162 healthy controls of Italian descent. Our findings do not implicate a role for this mutation in conferring a susceptibility to OCD and confirm previous negative results regarding its involvement in schizophrenia and bipolar disorder.     

Association and linkage of the dopamine transporter gene and attention-deficit hyperactivity disorder in children: heterogeneity owing to diagnostic subtype and severity

Attention-deficit hyperactivity disorder (ADHD) affects approximately 3%-5% of children in the United States. In the current psychiatric nomenclature, ADHD comprises three subtypes: inattentive, hyperactive-impulsive, and combined. In this study, we used four analytic strategies to examine the association and linkage of the dopamine transporter gene (DAT1) and ADHD. Our sample included 122 children referred to psychiatric clinics for behavioral and learning problems that included but were not limited to ADHD, as well as their parents and siblings. Within-family analyses of linkage disequilibrium, using the transmission disequilibrium test (TDT), confirmed the 480-bp allele as the high-risk allele. In between-family association analyses, levels of hyperactive-impulsive symptoms but not inattentive symptoms were related to the number of DAT1 high-risk alleles. Siblings discordant for the number of DAT1 high-risk alleles differed markedly in their levels of both hyperactive-impulsive and inattentive symptoms, such that the sibling with the higher number of high-risk alleles had much higher symptom levels. Within-family analyses of linkage disequilibrium, using the TDT, suggested association and linkage of ADHD with DAT1 and that this relation was especially strong with the combined but not the inattentive subtype. The relation of DAT1 to ADHD increased monotonically, from low to medium to high levels of symptom severity. Our results replicate and extend previous findings of the association between the DAT1 gene and childhood ADHD. This represents one of the first replicated relations of a candidate gene and a psychiatric disorder in children.     

Alterations in dopamine release but not dopamine autoreceptor function in dopamine D3 receptor mutant mice

Dopamine (DA) autoreceptors expressed along the somatodendritic extent of midbrain DA neurons modulate impulse activity, whereas those expressed at DA nerve terminals regulate both DA synthesis and release. Considerable evidence has indicated that these DA autoreceptors are of the D2 subtype of DA receptors. However, many pharmacological studies have suggested an autoreceptor role for the DA D3 receptor. This possibility was tested with mice lacking the D3 receptor as a result of gene targeting. The basal firing rates of DA neurons within both the substantia nigra and ventral tegmental area were not different in D3 receptor mutant and wild-type mice. The putative D3 receptor-selective agonist R(+)-trans-3,4,4a, 10b-tetrahydro-4-propyl-2H,5H-(1)benzopyrano(4,3-b)-1,4-oxazin+ ++-9-ol (PD 128907) was equipotent at inhibiting the activity of both populations of midbrain DA neurons in the two groups of mice. In the gamma-butyrolactone (GBL) model of DA autoreceptor function, mutant and wild-type mice were identical with respect to striatal DA synthesis and its suppression by PD 128907. In vivo microdialysis studies of DA release in ventral striatum revealed higher basal levels of extracellular DA in mutant mice but similar inhibitory effects of PD 128907 in mutant and wild-type mice. These results suggest that the effects of PD 128907 on dopamine cell function reflect stimulation of D2 as opposed to D3 receptors. Although D3 receptors do not seem to be significantly involved in DA autoreceptor function, they may participate in postsynaptically activated short-loop feedback modulation of DA release.     

Association of a monoamine oxidase B allele with Parkinson's disease

Monoamine oxidase B (MAO-B) is implicated in the cause of Parkinson's disease (PD) because of its role in metabolizing the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and forming H2O2 during dopamine metabolism. Altered MAO-B activity has been observed in PD platelets. Polymerase chain reaction was used to amplify a portion of the MAO-B gene. Polymerase chain reaction products were screened with restriction enzymes to identify fragments useful for single-stranded conformational polymorphism analysis. A single-stranded conformational polymorphism was identified in an MAO-B polymerase chain reaction product after Hae III digestion. One hundred twenty-one control individuals were allelotyped with frequencies of 0.45 and 0.55 for alleles 1 and 2, respectively. Frequencies of 0.62 and 0.38 (1 and 2, respectively) were observed in a population of 46 patients with PD. The presence of MAO-B allele 1 is associated with a relative risk for PD of 2.03-fold (confidence interval, 1.44-2.61; p < 0.02). For comparison, a monoamine oxidase A polymorphism was used to determine allelic frequencies in these same populations and no statistically significant differences were found. These results suggest that an inherited variant of MAO-B may be involved in a genetic predisposition for PD.