QTL and systems genetics analysis of mouse grooming and behavioral responses to novelty in an open field.

The open field is a classic test used to assess exploratory behavior, anxiety and locomotor activity in rodents. Here, we mapped quantitative trait loci (QTLs) underlying behaviors displayed in an open field, using a panel of 53 BXD recombinant inbred mouse strains with deep replication (10 per strain and sex). The use of these strains permits the integration and comparison of data obtained in different laboratories, and also offers the possibility to study trait covariance by exploiting powerful bioinformatics tools and resources. We quantified behavioral traits during 20-min test sessions including (1) percent time spent and distance traveled near the wall (thigmotaxis), (2) leaning against the wall, (3) rearing, (4) jumping, (5) grooming duration, (6) grooming frequency, (7) locomotion and (8) defecation. All traits exhibit moderate heritability making them amenable to genetic analysis. We identified a significant QTL on chromosome M.m. 4 at approximately 104 Mb that modulates grooming duration in both males and females (likelihood ratio statistic values of approximately 18, explaining 25% and 14% of the variance, respectively) and a suggestive QTL modulating locomotion that maps to the same locus. Bioinformatic analysis indicates Disabled 1 (Dab1, a key protein in the reelin signaling pathway) as a particularly strong candidate gene modulating these behaviors. We also found 2 highly suggestive QTLs for a sex by strain interaction for grooming duration on chromosomes 13 and 17. In addition, we identified a pairwise epistatic interaction between loci on chromosomes 12 at 36-37 Mb and 14 at 34-36 Mb that influences rearing frequency in males.

Systems genetic and pharmacological analysis identifies candidate genes underlying mechanosensation in the von Frey test.

Mechanical sensitivity is commonly affected in chronic pain and other neurological disorders. To discover mechanisms of individual differences in punctate mechanosensation, we performed quantitative trait locus (QTL) mapping of the response to von Frey monofilament stimulation in BXD recombinant inbred (BXD) mice. Significant loci were detected on mouse chromosome (Chr) 5 and 15, indicating the location of underlying polymorphisms that cause heritable variation in von Frey response. Convergent evidence from public gene expression data implicates candidate genes within the loci: von Frey thresholds were strongly correlated with baseline expression of Cacna2d1, Ift27 and Csnk1e in multiple brain regions of BXD strains. Systemic gabapentin and PF-670462, which target the protein products of Cacna2d1 and Csnk1e, respectively, significantly increased von Frey thresholds in a genotype-dependent manner in progenitors and BXD strains. Real-time polymerase chain reaction confirmed differential expression of Cacna2d1 and Csnk1e in multiple brain regions in progenitors and showed differential expression of Cacna2d1 and Csnk1e in the dorsal root ganglia of the progenitors and BXD strains grouped by QTL genotype. Thus, linkage mapping, transcript covariance and pharmacological testing suggest that genetic variation affecting Cacna2d1 and Csnk1e may contribute to individual differences in von Frey filament response. This study implicates Cacna2d1 and Ift27 in basal mechanosensation in line with their previously suspected role in mechanical hypersensitivity. Csnk1e is implicated for von Frey response for the first time. Further investigation is warranted to identify the specific polymorphisms involved and assess the relevance of these findings to clinical conditions of disturbed mechanosensation.

Identification of quantitative trait loci and candidate genes for an anxiolytic-like response to ethanol in BXD recombinant inbred strains.

Genetic differences in acute behavioral responses to ethanol contribute to the susceptibility to alcohol use disorder and the reduction of anxiety is a commonly reported motive underlying ethanol consumption among alcoholics. Therefore, we studied the genetic variance in anxiolytic-like responses to ethanol across the BXD recombinant inbred (RI) mouse panel using the light-dark transition model of anxiety. Strain-mean genetic mapping and a mixed-model quantitative trait loci (QTL) analysis replicated several previously published QTL for locomotor activity and identified several novel anxiety-related loci. Significant loci included a chromosome 11 saline anxiety-like QTL (Salanq1) and a chromosome 12 locus (Etanq1) influencing the anxiolytic-like response to ethanol. Etanq1 was successfully validated by studies with BXD advanced intercross strains and fine-mapped to a region comprising less than 3.5 Mb. Through integration of genome-wide mRNA expression profiles of the mesocorticolimbic reward circuit (prefrontal cortex, nucleus accumbens and ventral midbrain) across the BXD RI panel, we identified high priority candidate genes within Etanq1, the strongest of which was Ninein (Nin), a Gsk3ß-interacting protein that is highly expressed in the brain.

High-precision genetic mapping of behavioral traits in the diversity outbred mouse population.

Historically our ability to identify genetic variants underlying complex behavioral traits in mice has been limited by low mapping resolution of conventional mouse crosses. The newly developed Diversity Outbred (DO) population promises to deliver improved resolution that will circumvent costly fine-mapping studies. The DO is derived from the same founder strains as the Collaborative Cross (CC), including three wild-derived strains. Thus the DO provides more allelic diversity and greater potential for discovery compared to crosses involving standard mouse strains. We have characterized 283 male and female DO mice using open-field, light-dark box, tail-suspension and visual-cliff avoidance tests to generate 38 behavioral measures. We identified several quantitative trait loci (QTL) for these traits with support intervals ranging from 1 to 3 Mb in size. These intervals contain relatively few genes (ranging from 5 to 96). For a majority of QTL, using the founder allelic effects together with whole genome sequence data, we could further narrow the positional candidates. Several QTL replicate previously published loci. Novel loci were also identified for anxiety- and activity-related traits. Half of the QTLs are associated with wild-derived alleles, confirming the value to behavioral genetics of added genetic diversity in the DO. In the presence of wild-alleles we sometimes observe behaviors that are qualitatively different from the expected response. Our results demonstrate that high-precision mapping of behavioral traits can be achieved with moderate numbers of DO animals, representing a significant advance in our ability to leverage the mouse as a tool for behavioral genetics.

High-throughput behavioral phenotyping in the expanded panel of BXD recombinant inbred strains.

Genetic reference populations, particularly the BXD recombinant inbred (BXD RI) strains derived from C57BL/6J and DBA/2J mice, are a valuable resource for the discovery of the bio-molecular substrates and genetic drivers responsible for trait variation and covariation. This approach can be profitably applied in the analysis of susceptibility and mechanisms of drug and alcohol use disorders for which many predisposing behaviors may predict the occurrence and manifestation of increased preference for these substances. Many of these traits are modeled by common mouse behavioral assays, facilitating the detection of patterns and sources of genetic coregulation of predisposing phenotypes and substance consumption. Members of the Tennessee Mouse Genome Consortium (TMGC) have obtained phenotype data from over 250 measures related to multiple behavioral assays across several batteries: response to, and withdrawal from cocaine, 3,4-methylenedioxymethamphetamine; "ecstasy" (MDMA), morphine and alcohol; novelty seeking; behavioral despair and related neurological phenomena; pain sensitivity; stress sensitivity; anxiety; hyperactivity and sleep/wake cycles. All traits have been measured in both sexes in approximately 70 strains of the recently expanded panel of BXD RI strains. Sex differences and heritability estimates were obtained for each trait, and a comparison of early (N = 32) and recent (N = 37) BXD RI lines was performed. Primary data are publicly available for heritability, sex difference and genetic analyses using the MouseTrack database, and are also available in GeneNetwork.org for quantitative trait locus (QTL) detection and genetic analysis of gene expression. Together with the results of related studies, these data form a public resource for integrative systems genetic analysis of neurobehavioral traits.

Heritability, correlations and in silico mapping of locomotor behavior and neurochemistry in inbred strains of mice.

The midbrain dopamine system mediates normal and pathologic behaviors related to motor activity, attention, motivation/reward and cognition. These are complex, quantitative traits whose variation among individuals is modulated by genetic, epigenetic and environmental factors. Conventional genetic methods have identified several genes important to this system, but the majority of factors contributing to the variation remain unknown. To understand these genetic and environmental factors, we initiated a study measuring 21 behavioral and neurochemical traits in 15 common inbred mouse strains. We report trait data, heritabilities and genetic and non-genetic correlations between pheno-types. In general, the behavioral traits were more heritable than neurochemical traits, and both genetic and non-genetic correlations within these trait sets were high. Surprisingly, there were few significant correlations between the behavioral and the individual neurochemical traits. However, striatal serotonin and one measure of dopamine turnover (DOPAC/DA) were highly correlated with most behavioral measures. The variable accounting for the most variation in behavior was mouse strain and not a specific neurochemical measure, suggesting that additional genetic factors remain to be determined to account for these behavioral differences. We also report the prospective use of the in silico method of quantitative trait loci (QTL) analysis and demonstrate difficulties in the use of this method, which failed to detect significant QTLs for the majority of these traits. These data serve as a framework for further studies of correlations between different midbrain dopamine traits and as a guide for experimental cross designs to identify QTLs and genes that contribute to these traits.

Methodological aspects of the genetic dissection of gene expression.

MOTIVATION: Dissection of the genetics underlying gene expression utilizes techniques from microarray analyses as well as quantitative trait loci (QTL) mapping. Available QLT mapping methods are not tailored for the highly automated analyses required to deal with the thousand of gene transcripts encountered in the mapping of QTL affecting gene expression (sometimes referred to as eQTL). This report focuses on the adaptation of QTL mapping methodology to perform automated mapping of QTL affecting gene expression. RESULTS: The analyses of expression data on > 12,000 gene transcripts in BXD recombinant inbred mice found, on average, 629 QTL exceeding the genome-wide 5% threshold. Using additional information on trait repeatabilities and QTL location, 168 of these were classified as 'high confidence' QTL. Current sample sizes of genetical genomics studies make it possible to detect a reasonable number of QTL using simple genetic models, but considerably larger studies are needed to evaluate more complex genetic models. After extensive analyses of real data and additional simulated data (altogether > 300,000 genome scans) we make the following recommendations for detection of QTL for gene expression: (1) For populations with an unbalanced number of replicates on each genotype, weighted least squares should be preferred above ordinary least squares. Weights can be based on repeatability of the trait and the number of replicates. (2) A genome scan based on multiple marker information but analysing only at marker locations is a good approximation to a full interval mapping procedure. (3) Significance testing should be based on empirical genome-wide significance thresholds that are derived for each trait separately. (4) The significant QTL can be separated into high and low confidence QTL using a false discovery rate that incorporates prior information such as transcript repeatabilities and co-localization of gene-transcripts and QTL. (5) Including observations on the founder lines in the QTL analysis should be avoided as it inflates the test statistic and increases the Type I error. (6) To increase the computational efficiency of the study, use of parallel computing is advised. These recommendations are summarized in a possible strategy for mapping of QTL in a least squares framework. AVAILABILITY: The software used for this study is available on request from the authors.

Genetic architecture of the mouse hippocampus: identification of gene loci with selective regional effects.

We recently mapped two quantitative trait loci that have widespread effects on hippocampal architecture in mouse: Hipp1a and Hipp5a. We also noted remarkable strain differences in the relative sizes of different hippocampal regions. Estimated heritable variation for these differences was 42% in hippocampus proper, 40% in dentate gyrus, 31% in granule cell layer and 18% in pyramidal cell layer. Region size varied at least 50% from largest to smallest measurement. Here we have utilized these differences to identify loci with effects on the dentate gyrus, granule cell layer, hippocampus proper and pyramidal cell layer. Our sample consists of C57BL/6J and DBA/2J and 32 BXD recombinant inbred strains. Volumetric data were corrected for shrinkage and for differences in brain weight. We identified significant loci on chromosomes (Chr) 6, 13 and 15, and a significant interaction locus on proximal Chr 11. A suggestive distal Chr 1 locus overlaps with Hipp1a. HipV13a (Chr 13, 42-78Mb) has an additive effect of 0.56 mm3 (12.1%) on dentate gyrus volume, while GrV6a (Chr 6, 29-65 Mb) has additive effects of 0.14 mm3 (16.0%) on the volume of the granule cell layer. HipV13a also interacts with DGVi11a, a locus on proximal Chr 11 that operates exclusively through its epistatic effect on HipV13a and has no independent main effect HipV15a (Chr 15, 0-51 Mb) has an additive effect of 1.76 mm3 (9.0%) on the volume of the hippocampus proper. We used WebOTL, a recently described web-based tool, to examine genetic correlation of gene expression with hippocampal volume. We identified a number of genes that map within the OTL intervals and have highly correlated expression patterns. Using WebQTL's extensive database of published BXD phenotypes, we also detected a strong and potentially biologically meaningful correlation between hippocampal volume and the acoustic startle response.

Transgenic studies of pain and analgesia: mutation or background genotype?

The application of transgenic (knockout) technology to the study of pain is rapidly expanding. Despite its power, this technique has several shortcomings that complicate the interpretation of the data obtained. Although compensation by other genes is a well recognized problem, issues related to the background genotype of the mutant mice are less well appreciated. This review describes these confounds as they apply to studies of pain and pain inhibition. We show that the 129 and C57BL/6 mouse strains, which provide the default genetic background on which null mutants are constructed, display significant and sometimes extreme phenotypic differences in many assays of nociception, hypersensitivity, and analgesia. Although problems related to the differential responsiveness of the two strains are minimized by placing knockouts onto "pure" 129 and/or C57BL/6 backgrounds, we also illustrate that neither of these strains are particularly representative of inbred mice in general. Procedures to reduce confounds and converging evidence must be used to accurately determine the functions of the targeted genes in pain-related phenomena.

Acute administration of estrogen and progesterone impairs the acquisition of the spatial morris water maze in ovariectomized rats.

Although several markers of synaptic efficacy are enhanced during proestrus, spatial water maze performance is impaired. Because levels of both estrogen and progesterone are elevated in proestrus, the nature of their individual and combined effects on spatial learning was examined. Long-Evans hooded rats were ovariectomized postpubertally and pretrained on a water maze with a visible platform (nonspatial). Following pretraining, rats were administered estrogen (5 microg sc) or oil 48 and 24 h prior to testing and progesterone (500 microg sc) or oil 4 h prior to testing. Rats were tested on a water maze in a different room with a submerged platform (spatial) for 16 trials with random start location in a single testing day. Latency and path length to the target platform were significantly greater in estrogen plus progesterone-treated animals than in controls. Neither estrogen nor progesterone alone significantly impaired performance relative to controls on either measure. Swim speed was not significantly affected by any of the hormone treatments. Performance on a nonspatial cue task was not significantly altered by ovarian steroids. Thus, the combination of estrogen and progesterone produces deficits in the acquisition of the Morris water maze that may be specific to spatial reference memory. These deficits could be due to hormonal influences on extrahippocampal structures or to detrimental effects on behavior resulting from the increased synaptic activity intrinsic to the hippocampus proper.

Utility of positron emission tomography in predicting improved left ventricular ejection fraction after coronary artery bypass grafting among patients with ischemic cardiomyopathy.

The objective of this study was to determine whether preoperative estimates of regional myocardial uptake of (18)-F-fluorodeoxyglucose (FDG) could predict postoperative improvement in ejection fraction in patients undergoing coronary artery bypass grafting (CABG) for ischemic cardiomyopathy. 20 consecutive patients [left ventricular ejection fraction (LVEF) /=5% change noted in 7 patients (group 1) and <5% noted in 10 patients (group 2). No preoperative or perioperative clinical variable could predict those with improved ventricular function. The relative amount of FDG uptake in the anterior wall was higher in group 1 compared with group 2 (93 +/- 9 vs. 81 +/- 13%; p < 0.05) and correlated with the change in LVEF post-CABG (r = 0.50; p < 0.05). >88% of FDG uptake in the LAD region had a positive predictive accuracy of 67% and negative predictive accuracy of 88% for improved LVEF postbypass. Late follow-up estimates of LVEF (median of 10 months) showed that early changes in function were sustained. In summary, among patients with severe coronary artery disease and depressed LVEF, ventricular function may improve early postrevascularization. PET estimates of relative FDG uptake in the anterior wall help predict those individuals who are likely to have the greatest increment in LVEF.

Sex differences in thermal nociception and morphine antinociception in rodents depend on genotype.

It has been appreciated for some time that the sexes can differ in their sensitivity to pain and its inhibition. Both the human and rodent literatures remain quite contentious, with many investigators failing to observe sex differences that others document clearly. Recent data from our laboratory have pointed to an interaction between sex and genotype in rodents, such that sex differences are observed in some strains but not others. However, these studies employed inbred mouse strains and are thus not directly relevant to existing data. We presently examined whether the observation of statistically significant sex differences in nociception and morphine antinociception might depend on the particular outbred rodent population chosen for study. Rats of both sexes and three common outbred strains were obtained from three suppliers (Long Evans, Simonsen; Sprague Dawley, Harlan; Wistar Kyoto, Taconic) and tested for nociceptive sensitivity on the 49 degrees C tail-withdrawal assay, and antinociception following morphine (1-10mg/kg, i.p.). In further studies, three outbred populations of mice (CD-1, Harlan; Swiss Webster, Harlan; Swiss Webster, Simonsen) were bred in our vivarium for several generations and tested for tail-withdrawal sensitivity and morphine antinociception (1-20male, and no significant difference. In a separate study in which the estrous cycle was tracked in female mice, we found evidence for an interaction between genotype and estrous phase relevant to morphine antinociception. However, estrous cyclicity did not explain the observed sex differences. These data are discussed with respect to the existing sex difference and pain literature, and also as they pertain to future investigations of these phenomena.

The influence of perioperative myocardial infarction on long-term prognosis following elective vascular surgery.

STUDY OBJECTIVE: The present study was performed to determine the influence of a perioperative myocardial infarction on long-term mortality in patients who have undergone elective vascular surgery. STUDY DESIGN: This was a 4-year follow-up of patients who had undergone elective vascular procedures at a Veterans Affairs Medical Center. Between January 1989 and December 1990, 115 consecutive patients underwent surgery for either an expanding abdominal aortic aneurysm (AAA) (38%) or for pain in the lower extremities (62%). RESULTS: Vital status at 4 years postsurgery was determined for all patients. Thirty-day postoperative mortality was 3%, while estimates at 1, 2, 3, and 4 years were 19%, 26%, 35%, and 39%, respectively. Of the 45 patients who died within 4 years following surgery, the major causes of death were cardiac (40%), cancer (18%), cerebrovascular (13%), and peripheral vascular disease (11%). Univariate predictors of 1-year mortality on preoperative evaluation were an abnormal ECG, moderate or greater sized exercise thallium defect and left ventricular ejection fraction < or =40%, and a perioperative myocardial infarction. Univariate predictors of 4-year mortality were non-AAA surgery and diabetes mellitus. Perioperative myocardial infarction was a marginally significant independent predictor of 1-year mortality (p=0.06), while the need for non-AAA surgery was a strong independent predictor at 4 years. CONCLUSIONS: Cardiac mortality is the major cause of late death among patients undergoing elective vascular surgery. Although preoperative indicators of symptomatic coronary artery disease and nonfatal perioperative myocardial infarction identified those individuals at increased mortality in the first postoperative year, the extent of vascular disease at presentation may be a more important determinant of long-term survival. A randomized trial in such patients is needed to assess the best strategy for treating patients with coexistent coronary artery and vascular diseases.

Effects of acute and repeated clozapine injections on cholinomimetic-induced vacuous jaw movements.

Three studies were undertaken to investigate the effects of the atypical neuroleptic clozapine on the vacuous jaw movements induced by cholinergic stimulation in rats. In the first experiment, acute clozapine injections (4.0-16.0 mg/kg) produced a dose-related suppression of the vacuous jaw movements induced by 0.4 mg/kg physostigmine. In the second experiment, acute injections of clozapine (2.0-16.0 mg/kg) also suppressed vacuous jaw movements induced by 4.0 mg/kg pilocarpine in a dose-related manner. The third experiment was designed to compare the effects of acute and repeated administration of 16.0 mg/kg clozapine. In this experiment, there were three groups: one that received 4.0 mg/kg pilocarpine, a second group that received pilocarpine plus an acute injection of 16.0 mg/kg clozapine, and a third group that received injections of 16.0 mg/kg clozapine for 14 consecutive days, including the final day in which they also were injected with pilocarpine. For the third experiment, animals were assessed for the sedative effects of clozapine as well as vacuous jaw movements. The results indicated that either acute or repeated injections of 16.0 mg/kg clozapine reduced vacuous jaw movements relative to rats that received pilocarpine alone, and the two clozapine-treated groups did not differ from each other. The sedation ratings indicated that acute injections of 16.0 mg/kg clozapine produced substantial drowsiness and sedation, whereas rats that had received clozapine for 14 days did not show substantial sedation. These results indicate that clozapine can suppress cholinomimetic-induced vacuous jaw movements. The suppressive effects of clozapine on pilocarpine-induced vacuous jaw movements do not show tolerance within the 14-day period of repeated injections, whereas the sedative effects of clozapine do show tolerance. Thus, these results demonstrate that the suppression of pilocarpine-induced vacuous jaw movements by clozapine is not merely an artifact of clozapine-induced sedation. Because pilocarpine-induced vacuous jaw movements share some characteristics with human parkinsonian symptoms, the present results are consistent with previous reports indicating that repeated injections of clozapine produce anti-parkinsonian effects.

Usefulness of mean aortic valve gradient and left ventricular diastolic filling pattern for distinguishing symptomatic from asymptomatic patients.

Consecutive, symptomatic (n = 15) and asymptomatic (n = 25) men with aortic stenosis (valve area < 1.2 cm2) and no clinical evidence of myocardial ischemia underwent radionuclide angiography at rest and during supine bicycle ergometry. Ejection fraction, diastolic filling pattern and aortic valve area/gradient were measured on enrollment and when patients became symptomatic (n = 10) or underwent valve replacement (n = 22) during a 2-year follow-up period. Both groups had similar heart rate, blood pressure and ejection fractions, but mean aortic gradients were higher in symptomatic (53 +/- 4 mm Hg) than asymptomatic (37 +/- 2 mm Hg) subjects p < 0.01. Functional limitation evoked by exercise was prevalent even in the asymptomatic group but symptomatic patients exercised to lower work levels than asymptomatic subjects (184 +/- 27 and 307 +/- 32 kg.m/min, respectively, p = 0.02). Ejection fraction failed to increase with exercise in either group. Symptomatic subjects had supranormalization of early diastolic filling with shorter time to the peak filling rate than asymptomatic subjects (137 +/- 16 and 172 +/- 9 ms, respectively, p < 0.05) and a greater first 1/3 filling fraction. The 10 patients who became symptomatic during follow-up had higher first 1/3 filling fractions (53 +/- 7 and 42 +/- 5%, respectively) and mean gradients (41 +/- 4 and 33 +/- 2 mm Hg, respectively) than subjects who remained asymptomatic, p < 0.05. High mean aortic gradients, impaired exercise tolerance and enhanced early diastolic filling distinguish symptomatic from asymptomatic patients.

Angina and persistent exercise thallium defects: independent risk factors in elective vascular surgery.

OBJECTIVES: In this study, we assessed the utility of exercise thallium-201 scintigraphy and other clinical factors in predicting perioperative cardiac complications in patients undergoing elective vascular surgery. BACKGROUND: The risk of cardiac complications among such patients is very high. METHODS: The study group comprised 116 men (mean age 67 years). Fifty patients (43%) had a history of coronary artery disease, including angina pectoris in 26 (22%), myocardial infarction in 32 (28%) and coronary artery bypass surgery in 19 (16%). RESULTS: There were a total of 22 perioperative myocardial infarctions (18.9%), including 2 cardiac deaths (1.7%). A significantly greater proportion (p < 0.05) of patients with than without perioperative complications had a history of coronary artery disease (77% vs. 35%), angina (59% vs. 14%), prior myocardial infarction (50% vs. 22%), abnormal electrocardiogram (68% vs. 40%) and abnormal exercise thallium test (75% vs. 47%). The patient group with complications also had a significantly lower mean rest ejection fraction (45 +/- 3% vs. 55 +/- 2%, p < 0.005). Independent predictors of complication, as determined by straight logistic regression, were angina and fixed thallium defects after exercise. CONCLUSIONS: Our data indicate that angina and the presence of fixed thallium defects after exercise are independent predictors of cardiac risk in patients undergoing elective vascular surgery. These findings are compatible with other studies showing that nonredistribution on standard 3- to 4-h delayed studies cannot exclude viable myocardium at risk.

Saphenous vein graft patency 1 year after coronary artery bypass surgery and effects of antiplatelet therapy. Results of a Veterans Administration Cooperative Study.

To determine whether antiplatelet therapies improve saphenous vein graft patency after coronary artery bypass grafting, we compared 1) aspirin (325 mg once daily), 2) aspirin (325 mg three times daily), 3) aspirin and dipyridamole (325 mg and 75 mg, respectively, three times daily), 4) sulfinpyrazone (267 mg three times daily), and 5) placebo (three times daily). Therapy with dipyridamole and sulfinpyrazone was started 48 hours before bypass graft surgery, and aspirin treatment was begun 12 hours before surgery as a single 325-mg dose. Postoperative treatment was started 6 hours after surgery and continued for 1 year. Graft patency data were obtained early (median, 9 days) and late (median, 367 days) after surgery. The early graft occlusion rate was decreased with all aspirin treatment regimens compared with that of the placebo regimen. At 1 year, in 406 patients with 1,315 grafts, the graft occlusion rate in all of the aspirin groups combined was 15.8% compared with 22.6% for the placebo group (p = 0.029). The patients taking aspirin once daily had a lower occlusion rate (13.2%) compared with the patients receiving placebo (p = 0.050). At 1 year, in the vein grafts placed to vessels less than or equal to 2.0 mm in diameter (804 distal sites), the graft occlusion rate in all of the aspirin groups was 20.1% compared with 32.3% for the placebo group (p = 0.008). In the vein grafts placed to vessels greater than 2.0 mm in diameter (511 distal sites), there was no difference in the occlusion rates between aspirin and the placebo group at 1 year (8.7% vs. 9.0%, p = 0.918).(ABSTRACT TRUNCATED AT 250 WORDS)