Mu opioid receptor modulation of somatodendritic dopamine overflow: GABAergic and glutamatergic mechanisms

Mu opioid receptor (MOR) regulation of somatodendritic dopamine neurotransmission in the ventral tegmental area (VTA) was investigated using conventional microdialysis in freely moving rats and mice. Reverse dialysis of the MOR agonist DAMGO (50 and 100 microm) into the VTA of rats produced a concentration-dependent increase in dialysate dopamine concentrations. Basal dopamine overflow in the VTA was unaltered in mice lacking the MOR gene. However, basal gamma-aminobutyric acid (GABA) overflow in these animals was significantly increased, whereas glutamate overflow was decreased. Intra-VTA perfusion of DAMGO into wild-type (WT) mice increased dopamine overflow. GABA concentrations were decreased, whereas glutamate concentrations in the VTA were unaltered. Consistent with the loss of MOR, no effect of DAMGO was observed in MOR knockout (KO) mice. These data provide the first direct demonstration of tonically active MOR systems in the VTA that regulate basal glutamatergic and GABAergic neurotransmission in this region. We hypothesize that increased GABAergic neurotransmission following constitutive deletion of MOR is due to the elimination of a tonic inhibitory influence of MOR on GABAergic neurons in the VTA, whereas decreased glutamatergic neurotransmission in MOR KO mice is a consequence of intensified GABA tone on glutamatergic neurons and/or terminals. As a consequence, somatodendritic dopamine release is unaltered. Furthermore, MOR KO mice do not exhibit the positive correlation between basal dopamine levels and the glutamate/GABA ratio observed in WT mice. Together, our findings indicate a critical role of VTA MOR in maintaining an intricate balance between excitatory and inhibitory inputs to dopaminergic neurons.

Solar photo-Fenton as finishing step for biological treatment of a pharmaceutical wastewater

Remediation of pharmaceutical wastewater, containing nalidixic acid (NXA; 38 mg/L), a quinolone antibacterial agent commonly used in human and veterinary medicine, and characterized as having mainly 725 mg/L dissolved organic carbon (DOC), 3400 mg/L chemical oxygen demand, and around 4 g/L NaCl, was studied. A prior biodegradability study (Zahn-Wellens test) had demonstrated that the matrix was biodegradable after a rather long biomass adaptation period. After 4 days of treatment in an immobilized biomass reactor (IBR), 96% of the original DOC was removed by the biological treatment however, more than 50% of NXA was adsorbed on the biomass. As development of chronic toxicity in the IBR is possible after long exposure to NXA, adsorption and biomass stability during continuous exposure to NXA were studied in different cycles for one month. Afterthe biotreatment, the effluent was treated by solar photo-Fenton. Total degradation of NXA and reduction in toxicity were observed. The intermediates formed during degradation by biotreatment and subsequent photo-Fenton were studied by liquid chromatography-time-of-flight mass spectrometry.

Decontamination industrial pharmaceutical wastewater by combining solar photo-Fenton and biological treatment

Characterization and treatment of a real pharmaceutical wastewater containing 775 mg dissolved organic carbon per liter by a solar photo-Fenton/biotreatment were studied. There were also many inorganic compounds present in the matrix. The most important chemical in this wastewater was nalidixic acid (45 mg/L), an antibiotic pertaining to the quinolone group. A Zahn-Wellens test demonstrated that the real bulk organic content of the wastewater was biodegradable, but only after long biomass adaptation; however, the nalidixic acid concentration remained constant, showing that it cannot be biodegraded. An alternative is chemical oxidation (photo-Fenton process) first to enhance biodegradability, followed by a biological treatment (Immobilized Biomass Reactor--IBR). In this case, two studies of photo-Fenton treatment of the real wastewater were performed, one with an excess of H2O2 (kinetic study) and another with controlled H2O2 dosing (biodegradability and toxicity studies). In the kinetic study, nalidixic acid completely disappeared after 190 min. In the other experiment with controlled H2O2, nalidixic acid degradation was complete at 66 mM of H2O2 consumed. Biodegradability and toxicity bioassays showed that photo-Fenton should be performed until total degradation of nalidixic acid before coupling a biological treatment. Analysis of the average oxidation state (AOS) demonstrated the formation of more oxidized intermediates. With this information, the photo-Fenton treatment time (190 min) and H2O2 dose (66 mM) necessary for adequate biodegradability of the wastewater could be determined. An IBR operated in batch mode was able to reduce the remaining DOC to less than 35 mg/L. Ammonium consumption and NO3- generation demonstrated that nitrification was also attained in the IBR. Overall DOC degradation efficiency of the combined photo-Fenton and biological treatment was over 95%, of which 33% correspond to the solar photochemical process and 62% to the biological treatment.

The dopamine D3/D2 agonist (+)-PD-128,907 [(R-(+)-trans-3,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-ol)] protects against acute and cocaine-kindled seizures in mice: further evidence for the involvement of D3 receptors

Previous findings have demonstrated a protective role for dopamine D(3)/D(2) receptor agonists in the convulsant and lethal effects of acutely administered cocaine. Data are provided here to establish that the protection occurs through a D(3)-linked mechanism and that protection is extended to seizure kindling. The D(3) antagonist SB-277011-A [4-quinolinecarboxamide,N-[trans-4-[2-(6-cyano-3,4-dihydro-2(1H)-isoquinolinyl)ethyl]-cyclohexyl]-(9CI)] prevented the anticonvulsant effect of the D(3)/D(2) receptor agonist (+)-PD-128,907 [(R-(+)-trans-3,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-ol)] on cocaine-induced seizures. The protection afforded by the D(3)/D(2) agonist, (+)-PD-128,907, was eliminated in D(3) receptor-deficient mice. In D(2) receptor knockout mice, the anticonvulsant effects of (+)-PD-128,907 were preserved. (+)-PD-128,907 also prevented the acquisition and expression of cocaine-kindled seizures engendered by repeated daily dosing with 60 mg/kg cocaine. (+)-PD-128,907 also blocked the seizures induced in mice fully seizure kindled to cocaine. Although repeated dosing with cocaine increased the potency of cocaine to produce seizures and lethality (decreased ED(50) values), daily coadministration of (+)-PD-128,907 significantly prevented this potency shift. In mice treated daily with cocaine and (+)-PD-128,907, the density, but not the affinity, of D(3) receptors was increased. The specificity with which (+)-PD-128,907 acts upon this cocaine-driven process was demonstrated by the lack of a significant effect of (+)-PD-128,907 on seizure kindling to a GABA(A) receptor antagonist, pentylenetetrazol. Taken together and with literature findings, the data indicate that dopamine D(3) receptors function in the initiation of a dampening mechanism against the toxic effects of cocaine, a finding that might have relevance to psychiatric disorders of drug dependence, schizophrenia, and bipolar depression.

[Registry of home-based enteral nutrition in Spain for the year 2006 (NADYA-SENPE Group)]

OBJECTIVE

To communicate the results obtained from the registry of Home-Based Enteral Nutrition (HBEN) of the NADYA-SENPE group for the year 2006.

MATERIAL AND METHODS

Recompilation of the data from the HBEN registry of the NADYA-SENPE group from January 1st to December 31st of 2006.

RESULTS

During the year 2006, 3,921 patients (51% men) from 27 hospital centers were registered. Ninety-seven percent were older than 14 years. The mean age for those < 14 years was 4.9 +/- 3.9 (m +/- SD) and in those > or = 14 years, it was 68.5 +/- 18.2 years. The most common underlying disease was neurological pathology (42%), followed by cancer (28%). Enteral nutrition was administered p.o. in 44% of the patients, through nasogastric tube in 40%, gastrostomy in 14%, and jejunostomy in 1%. The average time of nutritional support was 8.8 months. The most common reasons for ending the therapy were patient's death (54%) and switching to oral feeding (32%). Thirty-one percent of the patients presented a limited activity and 40% were confined to bed/coach. Most of the patients required partial (25%) or total (43%) care assistance. The nutritional formula was provided by the hospital in 62% of the cases and from the reference pharmacy in 27%. The fungible material was provided by the hospital in 80% of the cases and by primary care in the remaining patients.

CONCLUSIONS

Although the number of registered patients is slightly higher than that from the last years, there are no important changes in the patients characteristics, or way of administration and duration of enteral nutrition.

Dynorphin and the pathophysiology of drug addiction

Drug addiction is a chronic relapsing disease in which drug administration becomes the primary stimulus that drives behavior regardless of the adverse consequence that may ensue. As drug use becomes more compulsive, motivation for natural rewards that normally drive behavior decreases. The discontinuation of drug use is associated with somatic signs of withdrawal, dysphoria, anxiety, and anhedonia. These consequences of drug use are thought to contribute to the maintenance of drug use and to the reinstatement of compulsive drug use that occurs during the early phase of abstinence. Even, however, after prolonged periods of abstinence, 80-90% of human addicts relapse to addiction, suggesting that repeated drug use produces enduring changes in brain circuits that subserve incentive motivation and stimulus-response (habit) learning. A major goal of addiction research is the identification of the neural mechanisms by which drugs of abuse produce these effects. This article will review data showing that the dynorphin/kappa-opioid receptor (KOPr) system serves an essential function in opposing alterations in behavior and brain neurochemistry that occur as a consequence of repeated drug use and that aberrant activity of this system may not only contribute to the dysregulation of behavior that characterizes addiction but to individual differences in vulnerability to the pharmacological actions of cocaine and alcohol. We will provide evidence that the repeated administration of cocaine and alcohol up-regulates the dynorphin/KOPr system and that pharmacological treatments that target this system may prove effective in the treatment of drug addiction.

[Spanish registry of Home-Based Parenteral Nutrition for the years 2004 and 2005 (NADYA-SENPE Group)]

OBJECTIVE

To report the results of the Home Parenteral Nutrition (HPN) registry of the NADYA-SENPE working group of the years 2004 and 2005.

MATERIAL AND METHODS

We summarized the data of the new on-line HPN registry of the NADYA-SENPE group for the period 2004-2005.

RESULTS

During the year 2004, 70 HPN-patients (23 males and 47 females) were registered from 14 hospitals. Mean age of adults was 53,7 +/- 14,87 years (m +/- SD) and 6 +/- 2,83 years for those younger than 14 years. The most frequent etiologies of the intestinal failure were neoplasia (24%) and mesenteric ischaemia (19%). Tunnelled catheters were used in 75% of the patients. The catheter-related infections were the most frequent complications, with a rate of 0,98 episodes/10(3) days. In 69% of the cases the nutritional support was maintained for more than 2 years. HPN solutions and disposables were supplied by the hospital pharmacy in 81% and 83%, respectively. Up to 54% of the patients had a normal activity level. The most frequent reasons to end HPN treatment were the transition to oral intake (41%), or exitus (28%). During the year 2005, 79 patients (33 males and 46 females) were registered from 14 hospitals. Mean age of adults was 52,39 +/- 14,21 years and 6,5 +/- 5,21 years for those younger than 14 yrs. The most frequent etiologies of the intestinal failure were neoplasia (22%), and mesenteric ischaemia (15%). Tunnelled catheters were used in 63% of the patients. The catheter-related infections were the most frequent complications, with a rate of 1,14 episodes/10(3) days. In 51% of the cases the nutritional support was maintained for more than 2 years. HPN solutions and disposables were supplied by the hospital pharmacy in 76% and 81%, respectively. Up to 50% of the patients had a normal activity level. The most frequent reasons to end HPN treatment were the transition to oral/enteral feeding (41%) and exitus (31%).

CONCLUSIONS

We have observed a mild decrease in the number of HPN patients registered in the period 2004-2005, probably related to the change of the registry. The characteristics of the patients are similar to previous years. We have observed an increase in the septic catheter-related complications in the year 2005.

[Cat-scratch disease. Review of eight adult patients hospitalized for fever or adenopathy]

BACKGROUND

Cat-scratch disease is common among children. Among adults the disease is less often considered in the differential diagnosis of enlarged lymph nodes and fever.

AIM

To report the clinical and laboratory features of eight patients with cat-scratch disease.

MATERIAL AND METHODS

Review of the medical records of eight patients (aged 22 to 57 years, six males) with a serological diagnosis of cat-scratch disease (an IgG titer over 1:256, by immunofluorescence).

RESULTS

Only five patients recalled having had contact with cats. Seven had fever and weight loss. Six had excessive sweating and five had chills. Seven had painfully enlarged lymph nodes mainly in submandibular and axillary regions. All had an increased C reactive protein and six had elevated erythrocyte sedimentation rate. Five had leukocytosis and four an elevated serum lactate dehydrogenase. The disease subsided in all, even in one patient that did not receive antimicrobials.

CONCLUSIONS

Cat-scratch disease should be considered in the differential diagnosis of adult patients with lymph adenitis and fever.

Clinical pharmacokinetics of parenteral dexketoprofen trometamol in healthy subjects

Dexketoprofen trometamol, a highly water-soluble salt of the active enantiomer of rac-ketoprofen, is a nonsteroidal antiinflammatory drug used for pain relief. Two studies were conducted to determine the pharmacokinetics of the drug in healthy subjects following single intravenous (i.v.) and intramuscular (i.m.) doses of dexketoprofen. In the first study, 6 male and 6 female volunteers received 50 mg dexketoprofen (74 mg dexketoprofen trometamol) by i.v. bolus. In the second one, another 6 male and 6 female subjects received 25 mg and 50 mg of dexketoprofen by the i.m. route. Dexketoprofen plasma concentrations were determined by reverse-phase high-performance liquid chromatography (HPLC). No serious adverse events were observed and all volunteers completed the study. The main pharmacokinetic parameters were determined by a noncompartmental approach. Following the i.v. bolus, mean (+/- SEM) area under the curve AUC0-x and clearance (CL) were 9005 +/- 422 ng.h/ml and 0.089 +/- 0.004 l/h/kg. Volumes of distribution Vi and Vss averaged 0.060 +/- 0.006 l/kg and 0.104 +/- 0.003 l/kg. Mean elimination half-life (t1/2e) and MRT were 1.05 +/- 0.04 h and 1.18 +/- 0.05 h. Following single i.m. 25 mg and 50 mg dexketoprofen, a rapid absorption was observed, with tmax values ranging from 0.17 h to 0.75 h. The corresponding Cmax averaged 1851 +/- 182 ng/ml and 3813 +/- 169 ng/ml, and mean AUC0-x were 3033 +/- 193 ng.h/ml and 5878 +/- 228 ng.h/ml, respectively. No significant differences by gender were obtained following both parenteral routes. A dose proportionality in Cmax and AUC0-x was observed. Dexketoprofen pharmacokinetics following i.v. and i.m. routes, together with the availability of a single 2 ml formulation, allows for a potential advantageous rapid switch to the oral formulation when clinically possible.

Ontogeny of the immune system of fish

Information on the ontogeny of the fish immune system is largely restricted to a few species of teleosts (e.g., rainbow trout, catfish, zebrafish, sea bass) and has previously focused on morphological features. However, basic questions including the identification of the first lympho-hematopoietic sites, the origin of T- and B-lymphocytes and the acquisition of full immunological capacities remain to be resolved. We review these three main topics with special emphasis on recent results obtained from the zebrafish, a new experimental model particularly suitable for study of the ontogeny of the immune system because of its rapid development and easy manipulation. This species also provides an easy way of creating mutations that can be detected by various types of screens. In some teleosts (i.e., angelfish) the first blood cells are formed in the yolk sac. In others, such as zebrafish, the first hematopoietic site is an intraembryonic locus, the intermediate cell mass (ICM), whereas in both killifish and rainbow trout the first blood cells appear for a short time in the yolk sac but later the ICM becomes the main hematopoietic area. Erythrocytes and macrophages are the first blood cells to be identified in zebrafish embryos. They occur in the ICM, the duct of Cuvier and the peripheral circulation. Between 24 and 30 hour post-fertilization (hpf) at a temperature of 28 degrees C a few myeloblasts and myelocytes appear between the yolk sac and the body walls, and the ventral region of the tail of 1-2 day-old zebrafish also contains developing blood cells. The thymus, kidney and spleen are the major lymphoid organs of teleosts. The thymus is the first organ to become lymphoid, although earlier the kidney can contain hematopoietic precursors but not lymphocytes. In freshwater, but not in marine, teleosts the spleen is the last organ to acquire that condition. We and other authors have demonstrated an early expression of Rag-1 in the zebrafish thymus that correlates well with the morphological identification of lymphoid cells. On the other hand, the origins and time of appearance of B lymphocytes in teleosts are a matter of discussion and recent results are summarized here. The functioning rather than the mere morphological evidence of lymphocytes determines when the full immunocompetence in fish is attained. Information on the histogenesis of fish lymphoid organs can also be obtained by analysing zebrafish mutants with defects in the development of immune progenitors and/or in the maturation of non-lymphoid stromal elements of the lymphoid organs. The main characteristics of some of these mutants will also be described.

Gene expression in gastric biopsies from patients infected with Helicobacter pylori

BACKGROUND

Helicobacter pylori infection has protean effects on gene expression in the host gastric mucosa, which have been investigated by gene chip analysis in vitro. In this study the effects of H. pylori infection on host gene expression in the gastric antral mucosa in patients were examined.

METHODS

One gastric antral biopsy was obtained from a total of 18 untreated patients undergoing routine endoscopic evaluation of chronic abdominal complaints. Nine patients had histologic evidence of H. pylori infection and 9 age- and sex-matched patients had no histologic evidence of H. pylori infection. A microarray analysis was performed using a gene chip containing 35,000 human expressed sequence tags on RNA extracted from endoscopic, gastric antral biopsies, and average gene expression among infected and uninfected patients was compared.

RESULTS

Underexpressed genes in infected patients' mucosa included gastric intrinsic factor and several metallothionein isoforms. Overexpressed genes in infected patients' mucosa comprised MHC Class II molecules, immunoglobulin and B-cell activation genes, as well as genes known to induce apoptosis. Changes in expression were confirmed for a subset of genes by SYBR green real-time PCR.

CONCLUSIONS

Microarray analysis of antral biopsies from patients with and without H. pylori infection revealed differential expression of metal regulatory, immunity and inflammation-related genes.

Protection against Cocaine Toxicity in Mice by the Dopamine D3/D2 Agonist R-(+)-trans-3,4a,10b-Tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-ol [(+)-PD 128,907]

Cocaine abuse is a public health concern with seizures and death being one consequence of overdose. In the present study, dopamine D(3/)D(2) receptor agonists dose dependently and completely prevented the convulsant and lethal effects of cocaine. The D(3)-preferring agonists R-(+)-trans-3,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-ol) [(+)-PD 128,907], (+)-7-hydroxy-dipropylaminotetralin, and the mixed D(3/)D(2) agonists quinpirole and quinelorane were all effective against cocaine toxicity in mice. The anticonvulsant effects of these compounds occurred at doses below those that produced motor impairment as assessed in the inverted screen test. Protection against the convulsant effects of the selective dopamine uptake inhibitor 1-[2-[bis(4-fluorophenyl)methoxy] ethyl]-4-[3-phenyl-propyl]piperazine (GBR 12909) was also conferred by (+)-PD 128,907. The possible selectivity of the effects of (+)-PD 128,907 (3 mg/kg) for these dopaminergic compounds was demonstrated by its general lack of protective efficacy against a host of convulsants acting through other neural mechanisms [pentylenetetrazol, (+)-bicuculline, and picrotoxin, 4-aminopyridine, and t-butylbiclyclophosphoorothionate, N-methyl-d-aspartate, kainate, pilocarpine, nicotine, strychnine, aminophylline, threshold electric shock, and 6-Hz electrical stimulation]. Direct and correlational evidence suggests that these effects were mediated by D(3) receptors. Protection was stereospecific and reversible by an antagonist of D(3) receptors [3-[4[1-(4-[2[4-(3-diethyamino-propoxy)-phenyl]-benzoimidazol-l-yl]-butyl)-1H-benzoimidazol-2-yl]-phenoxy]-propyl)-diethyl-amine; PD 58491] but not D(2) receptors [3[[4-(4-chlorophenyl)-4 hydroxypipeidin-1-yl]methyl-1H-indole; L-741,626]. Anticonvulsant potencies were positively associated with potencies in a functional assay of D(3) but not D(2) receptor function. Together, these findings suggest that the prevention of cocaine convulsions and lethality by (+)-PD 128,907 may be due to D(3) receptor-mediated events.

D(3) receptor ligands modulate extracellular dopamine clearance in the nucleus accumbens

An involvement of the D(3) dopamine receptor in the regulation of extracellular dopamine has been suggested. However, the mechanisms mediating this effect are unclear. We have used the technique of no net flux microdialysis under transient conditions to examine the influence of the D(3) -preferring agonist (+)-PD128907 upon extracellular dopamine levels in the nucleus accumbens of the mouse. (+)-PD 128907 (0.1 mg/kg intraperitoneally) significantly decreased extracellular dopamine. This decrease was associated with a marked increase in the extraction fraction, which suggests an increase in dopamine clearance. The ability of D(3) -preferring compounds to modulate dopamine uptake was investigated in vitro using rotating disk electrode voltammetry. (+)-PD 128907 (10 nm) significantly increased the initial clearance rate of 3 microm dopamine in rat nucleus accumbens tissue suspensions. Kinetic analysis revealed no change in the apparent K (m) of uptake but it showed a 33% increase in V (max). In contrast, the D(3) antagonist GR 103691 (10 nm) significantly decreased dopamine uptake. Consistent with the low levels of D(3) receptors in the dorsal striatum, neither compound affected uptake in tissue suspensions from this brain region. These data indicate that D(3) receptor activation increases dopamine uptake in the nucleus accumbens and suggest that this receptor subtype can regulate extracellular dopamine by modulating the DA transporter activity.

Diabetes in Bolivia

OBJECTIVE

To measure the prevalence of diabetes mellitus (DM), hypertension, obesity, and related risk factors in major cities in Bolivia.

METHODS

A population-based survey was conducted in four Bolivian cities: La Paz, El Alto, Santa Cruz, and Cochabamba. The total sample size was chosen to be 2,948 persons. The overall response rate was 86%, with the rate varying somewhat among the four cities. DM was diagnosed through an oral glucose tolerance test (OGTT) 2 hours after an overload of 75 grams of glucose, using World Health Organization criteria.

RESULTS

The overall prevalence of DM in the four urban areas combined was 7.2% (95% confidence interval (CI): 6.2%-8.3%) and of impaired glucose tolerance (IGT) was 7.8%. A total of 73.1% (95% CI: 65.0%-81.0%) of those previously diagnosed with DM and 73.7% (95% CI: 61.0%-86.4%) of newly diagnosed cases were overweight, according to measurements of body mass index. Hypertension was found in 36.5% (95% CI: 27.6%-45.5%) of known diabetics and in 36.6% (95% CI: 23.0%-50.1%) of newly diagnosed cases, compared to only 15.9% (95% CI: 14.3%-17.5%) among people without DM. The disease was most common among older persons and those with little education.

CONCLUSIONS

Diabetes is a genuine public health problem in Bolivia. Further, the high prevalence of IGT that was found suggests that diabetes prevalence will increase in the near future in the country unless prevention strategies are implemented.

Selective D3 receptor agonist effects of (+)-PD 128907 on dialysate dopamine at low doses

An involvement of the D3 dopamine receptor in the modulation of extracellular dopamine concentrations is suggested by pharmacological studies. However, recent studies using D3 receptor knock out mice indicated that several functions previously attributed to the D3 receptor are mediated by other receptor types. In the present study, we used the no-net flux microdialysis technique to characterize: (i) basal dopamine dynamics in the ventral striatum of D3 knock out and wild type mice and (ii) the effects of the putative D3-receptor selective agonist (+)-PD 128907. Neither the extracellular dopamine concentration nor the in vivo extraction fraction, an indirect measure of basal dopamine uptake, differed between D3 knock out and wild type mice. Moreover, no differences in potassium (60 mM) or cocaine (5 or 20 mg/kg i.p.) evoked dopamine concentrations were detected between the two genotypes. However, intra-striatal or systemic administration of doses of (+)-PD 128907 that failed to modify dopamine concentrations in knock out mice significantly decreased dialysate dopamine concentrations in the wild type. Comparison of the concentration-response curve for (+)-PD 128907 revealed IC(25) values of 61 and 1327 nM in wild type and knock out mice, respectively, after intra-striatal infusions. Similar differences were obtained after systemic administration of the D3 preferring agonist (IC(25) 0.05 and 0.44 mg/kg i.p. in wild type and knock out mice, respectively). We conclude that the activation of the D3 receptor decreases extracellular dopamine levels and that, at sufficiently low doses, the effects of (+)-PD 128907 on extracellular dopamine are selectively mediated by the D3 receptor.