Lack of referral for genetic counseling and testing in BRCA1/2 and Lynch syndromes: a nationwide study based on 240,134 consultations and 134,652 genetic tests.

Based on nationwide data from the French national cancer institute (INCa), we analyzed the evolution of cancer genetics consultations and testing over time, and the uptake of targeted tests in relatives of families with BRCA1/2 or MMR genes mutation. Genetic testing and consultations for familial high-risk individuals are exclusively funded and monitored by the INCa in France. All nationwide cancer genetics centers reported annually standardized parameters of activity from 2003 to 2011. The analysis included a total of 240,134 consultations and 134,652 genetic tests enabling to identify 32,494 mutation carriers. Referral for hereditary breast and ovarian cancer (HBOC) or colorectal cancer predisposition syndromes represented 59 % (141,639) and 23.2 % (55,698) consultations, respectively. From 2003 to 2011, we found a dramatic and steady increase of tests performed for BRCA1/2 (from 2,095 to 7,393 tests/year, P < 0.0001) but not for MMR genes (from 1,144 to 1,635/year, P = NS). The overall percentage of deleterious mutations identified in the probands tested was 13.8 and 20.9 % in HBOC and Lynch syndromes, respectively. Pooled analysis for BRCA1/2 and Lynch syndrome tests showed an inverse relationship between the percentage of mutation detected and the absolute number of tests performed over the time (overall Cochran-Armitage test for trend: P < 0.001). In families with BRCA1/2 or MMR identified mutations, there was an average number of 2.94 and 3.28 relatives performing targeted tests, respectively. This nationwide study shows a lack of referral and genetic testing in Lynch as compared to HBOC syndromes. Only a third of relatives of a proband with a predisposing mutation performed a targeted test. Enhanced information about benefit of genetic testing should be given to clinicians and patients for Lynch syndrome and relatives of a proband carrying an identified predisposing mutation.

Screening BRCA1 and BRCA2 unclassified variants for splicing mutations using reverse transcription PCR on patient RNA and an ex vivo assay based on a splicing reporter minigene.

BACKGROUND: Many unclassified variants (UV) of BRCA1 or BRCA2 may have an effect on pre-mRNA splicing. Patient blood samples suitable for RNA extraction are not always available for testing UVs at the RNA level. METHODS: Analyses of RNA from patient peripheral blood were performed, using a one-step reverse transcriptase-PCR (RT-PCR) protocol, and were compared with an ex vivo splicing assay based on PCR-amplified patient DNA inserted into a splicing reporter minigene. Using both methods 20 variants found in 17 patients were examined. RESULTS: Data from patient RNA and from the minigene assay were fully concordant, but the ex vivo splicing assay, which is monoallelic, clarified several ambiguities in the patient RNA data. Two intronic variants induced strong splicing defects: BRCA1 c.4987-5T-->A (IVS16-5T-->A) induced exon 17 skipping and BRCA2 c.316+5G-->C (IVS3+5G-->C) induced complete skipping of exon 3. Of the exonic variants, BRCA2 c.7805G-->C (p.Arg2602Thr), at the last base of exon 16, induced both exon skipping and activation of a cryptic exonic donor site, and BRCA2 c.8023A-->G (p.Ile2675Val) generated a strong donor site within exon 18. These four variants were thus classified as pathogenic, because of the total absence of a normal transcript from the corresponding allele. Variant BRCA2 c.9501+3A-->T (IVS25+3A-->T) induced incomplete skipping of exon 25, suggesting a mutation with incomplete penetrance, and BRCA2 c.8257_8259del (p.Leu2753del) modified the alternative splicing of exons 17 and 18. CONCLUSIONS: We show that functional analysis using a splicing reporter minigene is sensitive and specific, and should be used for initial screening of potential splicing defects, especially when patient RNA is not readily available.

Gastric involvement in juvenile polyposis associated with germline SMAD4 mutations: an entity characterized by a mixed hypertrophic and polypoid gastropathy.

Exclusively gastric form of juvenile polyposis associated with germline SMAD4 mutation is a rare clinical entity and is usually difficult to diagnose in the absence of colorectal lesions. We describe the phenotype of two unrelated cases of exclusive or predominant gastric expression of juvenile polyposis. Endoscopically, we found an unusual hypertrophic and polypoid gastropathy with abundant mucus adhering to the mucosal surface. Initially diagnosed as hyperplastic polyps, examination of gastric macrobiopsy specimens and identification of SMAD4 gene mutation in both cases confirmed the diagnosis. Close upper GI surveillance was proposed in case 1 and prophylactic total gastrectomy in the second one. Juvenile polyposis limited to the stomach is a rare condition that is linked to SMAD4 mutations. Such a diagnosis should be considered whenever a mixed, hypertrophic and polypoid gastropathy is encountered.

[Breast cancer prevention: from chemoprevention to prophylactic surgery]. / Prévention des cancers du sein : de la chimioprévention à la chirurgie prophylactique.

INTRODUCTION: The breast cancer prevention is based on mastectomy hormonal deprivation (surgical or chemical) and the use of drugs acting on cell signalization pathways, which provoke the cancerization (these drugs are not officially authorized in France). MATERIAL AND METHODS: Analysis of the literature selected from the Medline base on the keywords: breast cancer; chemoprevention; prophylactic surgery; tamoxifene; raloxifene; BRCA. RESULTS: Four trials on the chemoprevention by tamoxifene show a reduction in the breast cancer incidence from 22% up to 33% in the treated patients, limited to oestrogen-dependant cancers, especially in the populations at risk high (histological or genetic) even in the event of concomitant hormonal replacement therapy. The benefit seems continue in time. Raloxifene and tamoxifene effects are comparable with bone benefits and a less risk of endometrial cancer for raloxifene, but the risk of venous thrombosis is still persisting. The breast prophylactic surgery is effective mainly in case of genetic elevated risk when it is practiced in the young age, and requires a patient agreement (the decision needs to follow the patient advice after complete information). The prophylactic ovariectomy has a positive impact on the mammal risk even in the high genetic risk women. CONCLUSION: The breast cancer prevention requires a better selection of the patients, an adaptation of the type of prevention taking account of the balance risks and benefits (mammals and extramammals) before a clinical use in routine.

The contribution of germline rearrangements to the spectrum of BRCA2 mutations.

BACKGROUND: Few germline BRCA2 rearrangements have been described compared with the large number of germline rearrangements reported in the BRCA1 gene. However, some BRCA2 rearrangements have been reported in families that included at least one case of male breast cancer. OBJECTIVE: To estimate the contribution of large genomic rearrangements to the spectrum of BRCA2 defects. METHODS: Quantitative multiplex PCR of short fluorescent fragments (QMPSF) was used to screen the BRCA2 gene for germline rearrangements in highly selected families. QMPSF was previously used to detect heterozygous deletions/duplications in many genes including BRCA1 and BRCA2. RESULTS: We selected a subgroup of 194 high risk families with four or more breast cancers with an average age at diagnosis of < or = 50 years, who were recruited through 14 genetic counselling centres in France and one centre in Switzerland. BRCA2 mutations were detected in 18.6% (36 index cases) and BRCA1 mutations in 12.4% (24 index cases) of these families. Of the 134 BRCA1/2 negative index cases in this subgroup, 120 were screened for large rearrangements of BRCA2 using QMPSF. Novel and distinct BRCA2 deletions were detected in three families and their boundaries were determined. We found that genomic rearrangements represent 7.7% (95% confidence interval 0% to 16%) of the BRCA2 mutation spectrum. CONCLUSION: The molecular diagnosis of breast cancer predisposition should include screening for BRCA2 rearrangements, at least in families with a high probability of BRCA2 defects.

Familial hematological malignancies: ASXL1 gene investigation.

PURPOSE: Familial aggregation among patients with several hematological malignancies has been revealed. This emphasizes the importance of genetic factors. Only few genes predisposing to familial hematological malignancies have been reported until now due to the low occurrence. We have described in previous study PRF1 and CEBPA variants that might contribute to the background of genetic factors, which encourage us to extend our investigations to other cooperating genes. The aim of this study is to determine whether germline additional sex combs-like 1 (ASXL1) gene mutations may be involved? METHODS/PATIENTS: In this study, we investigated the candidate gene ASXL1 by direct sequencing in 88 unrelated Tunisian and French families with aggregated hematological malignancies. RESULTS: We report a new p.Arg402Gln germline missense substitution in two related Tunisian patients which has not been previously described. We identified here this variant for the first time in non-Hodgkin lymphoma. The p.Arg402Gln variant was not found in 200 control chromosomes. In silico analysis has predicted potential deleterious effect on ASXL1 protein. CONCLUSIONS: From an extended candidate genes analyzed in the field of familial hematological malignancies, ASXL1 might be involved. This variant should be considered since a potential damaging effect was predicted by in silico analysis, with a view to develop functional assay in order to investigate the biological assessment.

Generation of multinucleated giant cells by culture of monocyte-derived macrophages with IL-4.

Culturing human monocytes in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) has been reported to provoke the formation of multinucleated giant cells (GCs). In the present work, GCs were generated in a two-step procedure in which macrophages were first differentiated from monocytes before being fused into GCs. The two cytokines used acted sequentially. GM-CSF was required for monocyte differentiation and IL-4 for macrophage fusion. Macrophages were purified from cultures of blood mononuclear cells maintained for 7 days in plastic bags. When seeded in conventional plastic-ware in the presence of IL-4, these macrophages showed an increased motility, spread in thin cytoplasmic lamellas, regrouped in clusters, and within 1-3 weeks, differentiated into GCs. Multinucleated cells also appeared in IL-4-untreated macrophage cultures but the number of nuclei did not exceed 2 or 3, compared with more than 30 in the presence of IL-4. Scanning electron microscopy of GCs showed highly developed pseudopods. GCs reacted with anti-CD11b, -CD54, -CD68, -HLA-ABC, and -HLA-DR monoclonal antibodies and AMH-152 but were CD14- and CD64-negative. Both untreated and IL-4-treated macrophages conserved pinocytic and phagocytic activity. Thus, IL-4 induced a differentiation process in which macrophages lost markers like CD14 and CD64, acquired an enhanced membrane motility, and fused in multinucleated GCs.

Continuous in vivo monitoring of evoked dopamine release in the rat nucleus accumbens by amperometry.

The release of dopamine in the nucleus accumbens of anaesthetized rats was evoked either by electrical stimulation of the mesolimbic dopaminergic pathway or by local ejection of N-methyl-D-aspartate in the ventral tegmental area. Untreated carbon-fibre electrodes implanted in the nucleus accumbens were held at +400 mV versus a reference electrode, and the oxidation current was continuously monitored. Despite a poor selectivity to dopamine versus other oxidizable compounds such as ascorbic acid, the evoked responses were solely due to dopamine overflow in the extracellular fluid since they were closely correlated with the stimulations and exhibited all the expected characteristics related to a dopamine release. First, these effects were closely consistent with the anatomy of the mesolimbic dopaminergic system. Second, the responses to electrical stimulations were abolished by a tetrodotoxin ejection in the vicinity of the carbon-fibre electrode and they were strongly, but reversibly, diminished (60% decrease) when cadmium was substituted for calcium in an artificial cerebrospinal fluid ejected close to the electrode. Third, their maximal amplitudes were enhanced by amphetamine, pargyline, nomifensine and haloperidol. Fourth, inhibition of dopamine reuptake by nomifensine induced a five-fold decrease in the rate of decline of the evoked oxidation current. Fifth, contribution of noradrenaline and serotonin to the observed effects seems unlikely since specific reuptake blockers (desipramine and sertraline, respectively) did not alter them. Dopaminergic neurons discharge either in a single spike mode with a mean firing rate below 5 Hz or in a bursting pattern (intraburst frequency: 10 to 20 Hz).(ABSTRACT TRUNCATED AT 250 WORDS)

NF-Y binding is required for transactivation of neuronal aromatic L-amino acid decarboxylase gene promoter by the POU-domain protein Brn-2.

We have previously characterized binding sites for the NF-Y transcription factor (-71/-52) and Brn-2 POU-domain protein (-92/-71) in the neuronal promoter of the human aromatic L-amino acid decarboxylase gene [Mol. Brain Res. 56 (1998) 227]. We have now explored the functional role of these binding sites in transfected SK-N-BE neuroblastoma cells. Mutations of the NF-Y site that abolish binding depressed expression of a luciferase reporter gene up to 25-fold. The overexpression of a dominant negative mutant of NF-YA subunit depressed expression by 60%. Promoter activity was increased by the overexpression of Brn-2. Mutations or deletion of the binding site of Brn-2 did not suppress transcriptional activation by overexpressed Brn-2, while promoters defective in NF-Y binding were not transactivated by Brn-2. A GST-pulldown experiment showed that recombinant human Brn-2 protein weakly interacts with recombinant NF-Y outside of DNA. Cooperative binding of recombinant NF-Y and GST--Brn-2 proteins on the neuronal promoter was evidenced by an electrophoretic mobility shift assay. The POU-domain of Brn-2 was sufficient for such interaction. The results thus suggest that the activation of the neuronal promoter of the aromatic L-amino acid decarboxylase gene requires a direct interaction between the ubiquitous NF-Y factor and a cell-specific POU-domain protein. The NF-Y, but not the Brn-2 binding site, is essential for the recruitment of the NF-Y/Brn-2 complex on the promoter.

Winged helix hepatocyte nuclear factor 3 and POU-domain protein brn-2/N-oct-3 bind overlapping sites on the neuronal promoter of human aromatic L-amino acid decarboxylase gene.

The neuronal promoter of human aromatic l-amino acid decarboxylase gene has been analysed to elucidate the mechanisms of neuron type-specific expression. The (-560/+92) promoter segment was sufficient to direct luciferase expression at a higher level in SK-N-BE neuroblastoma cells, than in CHP126 neuroepithelia, HepG2 hepatoma or SK-Hep1 epithelioma cells. Deletions experiments showed that this segment contained a neuronal-specific (element T1) and a SK-N-BE-specific (element N1) cis-activating sequences. Element T1 (-72/-36) bound Sp1 and NF-Y proteins, and unidentified neuronal-specific factors. Element N1 (-102/-72) bound cell-specific factors, identified as HNF-3, N-Oct-3/Brn-2 and N-Oct-2. HNF-3 proteins recognized the sequence TCAGTAAATA that matches the consensus motif. Oct-1, N-Oct-2 and N-Oct-3 bound the AAATAATGC sequence that overlaps the HNF-3 binding site. In addition, we show that the HNF-3 binding sites from aldolase C and HNF-3beta gene promoters also bind N-Oct-2 and N-Oct-3 proteins. These data suggest a functional interplay of winged helix/forkhead and POU-domain transcription factors on a variety of neuronal gene promoters.

Is the potent 5-HT1A receptor agonist, alnespirone (S-20499), affecting dopaminergic systems in the rat brain?

The effects of the new methoxy-chroman 5-HT1A receptor agonist, alnespirone (S-20499), on the dopamine systems in the rat brain were assessed in vivo by means of electrophysiological and neurochemical techniques. Cumulative doses of alnespirone (0.032-4.1 mg kg(-1), i.v.) did not modify the spontaneous firing rate of dopamine neurons in the substantia nigra as well as in the ventral tegmental area. The local application of alnespirone (0.1-10 microM) by reverse microdialysis into the dorsal striatum did not affect the dopamine output but induced a moderate, although dose-independent, increase of 5-HT (5-hydroxytryptamine, serotonin) concentrations in the dialysate. As expected of a 5-HT1A receptor agonist, intraperitoneal (i.p.) administration of alnespirone at 2-32 mg kg(-1) markedly decreased 5-HT turnover in the striatum. Parallel measurements of dopamine turnover showed that alnespirone exerted no effect except at the highest dose (32 mg kg(-1), i.p.) for which a significant increase was observed. Interestingly, both alnespirone-induced reduction in 5-HT turnover and increase in dopamine turnover could be prevented by pretreatment with the selective 5-HT1A receptor antagonist WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexa ne carboxamide). Altogether, these data indicate that alnespirone does not exert any direct influence on central dopamine systems. The enhanced dopamine turnover due to alnespirone at high dose appeared to result from 5-HT1A receptor stimulation, further supporting the idea that this receptor type may play a key role in 5-HT-dopamine interactions in brain.

Regulation of substantia nigra pars reticulata neuronal activity by excitatory amino acids.

Midbrain non-dopaminergic neurons of the substantia nigra pars reticulata play an important role in the basal ganglia circuitry. The regulation of their electrical activity by excitatory amino acid (EAA) inputs was investigated using in vivo electrophysiological methods in chloral hydrate-anaesthetized rats. We first determined the subtypes of EAA receptors present on reticulata neurons, using microiontophoretic application of selective agonists: kainic acid (KA), (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), N-methyl-D-aspartic acid (NMDA), and trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (trans-ACPD). Each agonist activated reticulata neurons and the apparent rank order of efficacy was: KA> or =AMPA=NMDA>trans-ACPD. Using pressure or iontophoretic microejections of ionotropic and metabotropic receptor antagonists, we then investigated EAA receptor subtypes involved in the spontaneous firing rate of reticulata neurons. Kynurenic acid and (+/-)-2-amino-5-phosphonopentanoic acid (AP-5) markedly decreased the spontaneous firing rate of reticulata neurons, while 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) was much less effective. The metabotropic receptor antagonist (R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG) failed to affect the spontaneous electrical activity. In contrast to CNQX, microapplications of AP-5 sometimes produced total inhibition. This powerful effect may reflect the potential importance of NMDA receptors in regulating the activity of some reticulata neurons. These results indicate that both functional ionotropic (NMDA and non-NMDA) and metabotropic EAA receptors are present on non-dopaminergic substantia nigra pars reticulata neurons. Moreover, in the anaesthetized animal, the spontaneous firing rate of these neurons, mediated by EAA inputs, seems mainly due to the tonic activation of ionotropic, but not metabotropic, receptors.

On the involvement of a tonic dopamine D2-autoinhibition in the regulation of pulse-to-pulse-evoked dopamine release in the rat striatum in vivo.

The dopamine overflow evoked by trains of electrical stimulation pulses applied to the ascending dopaminergic pathway was measured with continuous amperometry in the striatum of anesthetised rats. As previously observed in in vitro studies, a pulse by pulse analysis showed a fall in dopamine overflow evoked by pulses 2 to 6, compared to the response evoked by pulse 1. However, in contrast with in vitro findings, the present in vivo data showed that the dopamine receptor antagonist haloperidol i) completely reverses the fall in dopamine overflow between pulse 1 and subsequent pulses, ii) enhances the dopamine overflow elicited by pulse 1. These results suggest that in vivo, both basal and pulse-evoked dopamine overflow results in stimulation of dopamine D2-type autoreceptors and therefore in regulation of dopamine release.

[Problems raised by the gynaecologic management of women with BRCA 1 & 2 mutations]. / Problèmes posés par la prise en charge gynécologique des femmes porteuses d'une mutation germinale des gènes BRCA 1 & 2.

Breast and ovarian cancer occur more frequently in young women with BRCA 1 &2 mutations (respective cumulative risks from 37 to 85% and 10 to 20%), and raise specific gynaecologic problems as prophylactic surgery and hormonal treatments. Two medical files from 2 sisters with BRCA 1 mutation (exon 11) are presented and the authors discuss the therapeutic options chosen. BRCA 1 & 2 tumour suppressor genes seem to play a major role in the repair of cellular damages inducing by the estrogenic proliferative signal. The prophylactic mastectomy is effective for the breast cancer prevention but its acceptance is low. The oophorectomydecreases the ovarian risk (knowing the occurrence of peritoneal carcinomatosis in 1.8% of cases) and currently the breast cancer risk (RR = 0.47) by the hormonal privation: the hormone replacement therapy does not seem to increase the breast cancer risk in the small series published. The HRT is possible in women with BRCA mutation under medical supervision and if the doses of hormones are light. The first results concerning the chemoprevention by Tamoxifen are encouraging (RR = 0.38) in these patients, but more studies are needed. The oral contraception exerts an uncertain effect against ovarian cancer, but possibly enhances the breast cancer risk in this group of women (RR = 3.3). The management of women with BRCA mutation is varying according to their own priorities, which can change during their life.

Molecular study of CEBPA in familial hematological malignancies.

Familial aggregation in patients with several haematological malignancies has been described, but the genetic basis for this familial clustering is not known. Few genes predisposing to familial haematological malignancies have been identified, among which RUNX1 and CEBPA have been described as predisposing genes to acute myeloid leukemia (AML). Recent studies on RUNX1 suggest that germline mutations in this gene predispose to a larger panel of familial haematological malignancies than AML. In order to strengthen this hypothesis, we have screened CEBPA for germline mutations in several families presenting aggregation of hematological malignancies (including chronic or acute, lymphoid or myeloid leukemias, Hodgkin's or non Hodgkin's lymphomas, and myeloproliferative or myelodysplastic syndromes) with or without solid tumours. Although no deleterious mutations were found, we report two novel and rare variants of uncertain significance. In addition, we confirm that the in frame insertion c.1175_1180dup (p.P194_H195dup) is a germline polymorphism.

[Sebaceous tumors of the eyelids in a patient with Muir-Torre syndrome]. / Tumeurs palpébrales à différenciation sébacée dans le cadre d'un syndrome de Muir-Torre.

Muir-Torre syndrome is an autosomal dominant hereditary condition predisposing to cancer. It is characterized by cutaneous tumors (such as sebaceous adenomas, epitheliomas, or carcinoma, and/or keratoacanthomas) and internal malignancies. A 47-year-old male patient with cancer antecedents consulted for two tumors of the eyelid. Histological study of the exeresis biopsies of the eyelid lesions showed a sebaceous adenoma and an epidermoid carcinoma with sebaceous differentiation. With the suspicion of Muir-Torre syndrome, a genetic consultation was requested. The geneticist found a mutation of the MSH2 gene, which was not classified as pathological. Cancer screening was begun for the patient and his descendants. The clinical outcome was death from urothelial carcinoma. Eyelid sebaceous tumors require complete medical check-up in search of carcinoma. Demonstrating Muir-Torre syndrome allows the medical team to propose early cutaneous and visceral carcinoma screening for patients, their collaterals, and their descendants.

A survey of factors determining the utilization of autologous blood donation in hip replacement surgery.

A prospective survey was conducted among anaesthesiologists to determine their criteria for excluding a patient from autologous blood donation prior to total hip prosthesis. Information on patients operated on during a 5-week period was obtained using a questionnaire, consisting of a set of possible responses to simple questions, matched with some parametric values. Sixty-eight of the 99 patients included in the survey underwent surgery without donation. Age was the main cause for exclusion (34%). The age of patients excluded because of their age alone was 75 +/- 11 years (standard deviation). The age of patients excluded from donation and who did not subsequently receive homologous blood was comparable with that of patients not autotransfused but who received homologous blood (68 +/- 4 vs. 69 +/- 6 years, respectively). Post-operative haemoglobin concentrations were similar whether transfusion was performed or not, and regardless of the origin of blood given. Since age is no longer taken into consideration at the time of transfusion, it is likely that exclusion of a patient from autologous blood donation because of age is an arbitrary choice.

In vivo monitoring of evoked noradrenaline release in the rat anteroventral thalamic nucleus by continuous amperometry.

Continuous amperometry coupled with untreated carbon-fibre electrodes was used in anaesthetized rats to measure the noradrenaline release evoked in the anteroventral thalamic nucleus by electrical stimulation of the dorsal noradrenergic bundle. As expected, the variations in the oxidation current detected in the anteroventral thalamic nucleus exhibited the characteristics of the in vivo noradrenaline release. They were closely correlated with stimulation and consistent with the anatomy of the noradrenergic system involved. They were abolished by the ejection of tetrodotoxin in the vicinity of the carbon-fibre electrode, diminished by clonidine, an alpha-2 agonist, and restored by yohimbine, an alpha-2 antagonist. Furthermore, the time course of these variations was dramatically increased by desipramine, a specific noradrenaline reuptake blocker. In contrast, neither dopamine nor serotonin reuptake blockers, nor the monoamine oxidase inhibitor pargyline were able to alter them. The main advantage of the present approach is its excellent time resolution. We show here for the first time that after single pulse stimulation, noradrenaline is released and eliminated in 118 milliseconds, this time lapse corresponding to the maximal period beyond which subsequent noradrenaline releases could not add up. These observations are in good agreement with the physiological relationship previously observed between impulse flow and noradrenaline overflow.

Uptake of dopamine released by impulse flow in the rat mesolimbic and striatal systems in vivo.

The release of dopamine in the striatum, nucleus accumbens, and olfactory tubercle of anesthetized rats was evoked by electrical stimulation of the mesolimbic dopaminergic pathway (four pulses at 15 Hz or four pulses at 200 Hz). Carbon fiber electrodes were implanted in these regions to monitor evoked dopamine overflow by continuous amperometry. The kinetics of dopamine elimination were estimated by measuring the time to 50% decay of the dopamine oxidation current after stimulation ceased. This time ranged from 64 ms in the striatum to 113 ms in the nucleus accumbens. Inhibition of dopamine uptake by nomifensine (2-20 mg/kg), GBR 12909 (20 mg/kg), cocaine (20 mg/kg), mazindol (10 mg/kg), or bupropion (25 mg/kg) enhanced this decay time by up to +602%. Uptake inhibition also produced an increase in the maximal amplitude of dopamine overflow evoked by four pulses at 15 Hz. This latter effect was larger in the striatum (+420%) than in mesolimbic areas (+140%). These results show in vivo that these uptake inhibitors actually slow the clearance of dopamine released by action potentials and suggest that dopaminergic transmission is both prolonged and potentiated strongly by these drugs, in particular in the striatum.