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At least 109 records · Page 6Linked to original sources
PubMed2003

Impact of intracoronary radiation on in-stent restenosis involving ostial lesions.

The aim of this study was to compare 6-month clinical outcomes of patients with in-stent restenosis (ISR) involving the ostium treated with intracoronary radiation therapy (IRT) compared to placebo therapy, and also to nonostial lesions treated with IRT. Coronary interventions in ostial lesions have a high rate of recurrence of restenosis. The impact of IRT on ostial ISR has been inadequately characterized. We assessed patients enrolled in gamma (192-iridium) and beta (90-yttrium, 32-phosphorus) radiation trials for ISR at the Washington Hospital Center. Of patients receiving IRT, 105 (8%) patients had ostial ISR and 1,289 (92%) patients had nonostial ISR. Twenty-seven patients had ostial ISR and received placebo therapy. Baseline demographic and angiographic and procedural details were similar, except ostial IRT patients had a trend toward shorter lesions (15.4 +/- 10.8 vs. 24.1 +/- 12.2 mm; P < 0.001) and had a higher rate of saphenous vein graft disease (46% vs. 19%; P < 0.001) compared to nonostial IRT patients. At 6 months, ostial lesions treated with IRT for ISR had a reduced rate of target lesion revascularization (TLR) compared to ostial lesions treated with placebo (15% vs. 43%; P = 0.004). Outcomes at 6 months were similar for the ostial and nonostial IRT groups including TLR (15% vs. 14%; P = 0.80) and composite major adverse cardiac events (18% vs. 15%; P = 0.46). Intracoronary radiation therapy is effective for ostial in-stent restenotic lesions and should be comfortably used for this challenging anatomic location.

Aged↗
PubMed2003

Correlates of failure following treatment with Sr-90 beta irradiation for in-stent restenosis.

We sought to determine the correlates of failure following intracoronary radiation therapy (IRT) with Sr-90 using the Novoste Beta-Cath system for the treatment of in-stent restenosis (ISR) in a broad range of patients. IRT has been shown to be more efficacious compared to placebo for the treatment of ISR in large randomized trials. However, even in patients treated with IRT, major adverse cardiac events occur in approximately 20% of cases on follow-up. This trial sought to elucidate the correlates of failure following successful IRT for ISR. To determine the correlates of IRT failure, we retrospectively compared the demographics, lesion characteristics, and clinical outcomes of 102 consecutive patients with ISR treated with Sr-90 from September 1998 to July 2001. IRT failure was defined as death, myocardial infarction (MI), or target vessel revascularization (TVR) due to repeat ISR on follow-up. A comparison of the clinical and angiographic profile of IRT failures (n = 16) vs. IRT successes (n = 86) revealed that a history of smoking (75% vs. 40%; P = 0.012), current use of calcium channel blockers (84% vs. 45%; P = 0.013), ostial location of target lesion (44% vs. 16%; P = 0.020), and mean posttreatment minimal luminal diameter (MLD; 1.64 +/- 0.19 vs. 2.21 +/- 0.29 mm; P < 0.001), respectively, were correlated with failure using univariate analysis. After multivariate regression analysis, the correlates of failure that remained significant were treatment of an ostial lesion (OR = 31.2; 95% CI = 2.6-382.7; P = 0.007) and final posttreatment MLD (P < 0.001). Ostial location of target lesion and smaller posttreatment MLD are correlated with subsequent death, MI, and TVR following therapy with Sr-90 for ISR.

Aged↗
PubMed1989

Immunoreactive trypsinogen screening for cystic fibrosis: characterization of infants with a false-positive screening test.

Blood immunoreactive trypsinogen (IRT) is elevated in newborns with cystic fibrosis (CF) and has been used as a neonatal screening test. However, not only is the benefit of early diagnosis unknown, but also the sensitivity, specificity, and time related decline of IRT values have yet to be comprehensively evaluated. This report describes the characteristics of infants with a false-positive IRT in our experience with CF screening of 87,000 infants. The IRT value was elevated in 92 newborns; 13 had a confirmed diagnosis of CF by quantitative pilocarpine iontophoresis sweat testing, and 79 infants did not have CF and were therefore classified as false positives by IRT screening. In order to test the hypothesis that perinatal stress factors are associated with high neonatal IRT values, we evaluated Apgar scores at 1 and 5 minutes. We found that the scores of false-positive infants were significantly lower (P = 0.0004 and P = 0.0102 at 1 and 5 minutes, respectively), compared with infants in the general population. While perinatal asphyxia as reflected by low Apgar scores is an associated factor accounting for an elevated IRT value, the majority of non-CF newborns with an elevated IRT have normal Apgar scores.

Apgar Score↗
PubMed1989

Behaviour of serum immunoreactive trypsin after serum activation by enterokinase in normal and cystic fibrosis patients. Evidence of a trypsin-alpha 1-proteinase inhibitor complex in some cystic fibrosis patients.

Serum immunoreactive trypsin (IRT) concentrations are elevated in newborn children with cystic fibrosis (CF) and subsequently fall, in most cases, to values below normal. To evaluate the molecular form(s) of IRT present in serum, we have performed serum activation by enterokinase and have measured serum IRT before and after activation. This approach is based on the postulate that enterokinase converts trypsinogen into trypsin, and this trypsin would then be mainly trapped by alpha 2-macroglobulin, thus escaping the assay. This assumption was confirmed in the 28 controls studied, where the mean percentage (+/- S.D.) of IRT recovery after serum activation was 13.7 +/- 2.9. Previous inhibition of alpha 2-macroglobulin by methylamine raised the recovery over 85%, confirming that most of the serum IRT present in controls was in the form of trypsinogen. Identical results were obtained in the serum of 10 obligate heterozygotes and in 57 out of 80 CF patients. In 23 CF patients the mean percentage of IRT recovery after serum activation was 41.6 +/- 17.6. Gel-filtration studies were performed on the sera of the CF patients showing an abnormal increase in the IRT recovery after serum activation. We could demonstrate that IRT was distributed in two fractions: one eluted with the Mr 25,000 protein as usually found in controls and other CF sera, and the other eluted with the Mr 75,000 protein corresponding to a complex of trypsin with alpha 1-proteinase inhibitor. These results show that, in these sera, active trypsin has been directly released in blood. These findings suggest that in some patients with CF, subclinical attacks of acute pancreatitis may occur.

Chromatography, Gel↗
PubMed1998

Clinical inhibitor-resistant mutants of the beta-lactamase TEM-1 at amino-acid position 69. Kinetic analysis and molecular modelling.

The kinetic parameters of three IRT (Inhibitor-Resistant-TEM-derived-) beta-lactamases (IRT-5, IRT-6 and IRT-I69) were determined for substrates and the beta-lactamase inhibitors: clavulanic acid, sulbactam and tazobactam, and compared with those of TEM-1 beta-lactamase. The catalytic behaviour of the beta-lactamases towards substrates and inhibitors was correlated with the properties of the amino acid at position ABL69. The three IRT beta-lactamases contain at that position a residue Ile, Leu and Val, amino acids whose side-chain are branched. Molecular modelling shows that the methyl groups of Ile-69 (C gamma 2) and Val-69 (C gamma 1) produced steric constraints with the side chain of Asn-170 as well as the main chain nitrogen of Ser-70, a residue contributing to the oxyanion hole. We suggest that hydrophobicity could be the main factor responsible for the kinetic properties of Met69Leu (IRT-5), as no steric effects could be detected by molecular modelling. Hydrophobicity and steric constraints are combined in Met69Ile and Met69Val, IRT-I69 and IRT-6, respectively.

Anti-Bacterial Agents↗
PubMedDate not supplied

Three-year follow-up after intracoronary gamma radiation therapy for in-stent restenosis. Original WRIST. Washington Radiation for In-Stent Restenosis Trial.

BACKGROUND: The Washington Radiation for In-Stent Restenosis Trial (WRIST) is a double-blinded randomized study evaluating the effects of intracoronary radiation therapy (IRT) in patients with in-stent restenosis (ISR). METHODS: One hundred and thirty patients with ISR (100 native coronary and 30 vein grafts) underwent PTCA, laser ablation, rotational atherectomy, and/or additional stenting (36% of lesions). Patients were randomized to either Iridium-192 IRT or placebo, with a prescribed dose of 15 Gy to a 2-mm radial distance from the center of the source. RESULTS: Angiographic restenosis (27% vs. 56%, P=.002) and target vessel revascularization (TVR; 26% vs. 66%, P<.001) were dramatically reduced at 6 months in IRT patients. Between 6 and 36 months, IRT compared to placebo patients had more target lesion revascularization (TLR; IRT=17% vs. placebo=2%, P=.002) and TVR (IRT=17% vs. placebo=3%, P=.009). At 3 years, the major adverse cardiac event (MACE) rate was significantly reduced with IRT (39% vs. 65%, P=.003). CONCLUSIONS: In WRIST, patients with ISR treated with IRT using 192Ir had a marked reduction in the need for repeat target lesion and vessel revascularization at 6 months, with the clinical benefit maintained at 3 years.

Brachytherapy↗
PubMedDate not supplied

Clinical outcomes of patients treated with the cutting balloon and Sr-90 beta-irradiation for instent restenosis.

BACKGROUND: The cutting balloon (CB) is an emerging therapy for the treatment of instent restenosis (ISR), but its impact on the clinical outcomes of patients treated with intracoronary radiation therapy (IRT) with Sr-90 compared with conventional PTCA and IRT is not clearly defined. METHODS: We compared the baseline demographics, angiographic characteristics and clinical outcomes of 102 consecutive patients with ISR treated either with CB+IRT (n=45) or with conventional PTCA+IRT (n=57). The combined endpoint was the occurrence of major adverse cardiac events (MACE), which was defined as a composite of death, myocardial infarction (MI) or target vessel revascularization (TVR) at 6 months. RESULTS: The CB+IRT group had a shorter mean lesion length (14.3+/-6.5 vs. 21.1+/-15.7, P=.009), and greater utilization of glycoprotein IIb/IIIa inhibitors during the procedure (48.9% vs. 26.3%, P=.02) compared to the PTCA+IRT group. There were no significant differences in the baseline demographics, angiographic and procedural results, or subsequent MACE at 6 months between the two groups. CONCLUSION: The strategy of CB+IRT using Sr-90 for ISR is associated with similar procedural and clinical outcomes compared to conventional PTCA+IRT. Further study is warranted to determine which patient subgroups would derive the most benefit from this approach.

Aged↗
PubMed2003

Using item response theory to calibrate the Headache Impact Test (HIT) to the metric of traditional headache scales.

BACKGROUND: Item response theory (IRT) scoring of health status questionnaires offers many advantages. However, to ensure 'backwards comparability' and to facilitate interpretations of results, we need the ability to express the IRT score in the metrics of the traditional scales. OBJECTIVES: To develop procedures to calibrate IRT-based scores on the Headache Impact Test (HIT) into the metrics of the traditional headache scales. To assess the degree to which the calibrated HIT scores agree with the observed traditional scores and lead to the same conclusions in group comparisons. METHODS: We used telephone interview data (n = 1016) and Internet data (n = 1103) from general population surveys of recent headache sufferers. Analyses were conducted in four steps: (1) develop IRT models for all items, (2) for each IRT score level, calculate the expected score on each of the traditional scales (calibration), (3) adjust this calibrated score for measurement error in the IRT score, (4) for each of the traditional scales, assess agreement between calibrated HIT scores and observed scores using intraclass correlation (ICC) and evaluate the agreement of mean scores and the relative validity (RV) in discriminating among groups differing in migraine diagnosis, headache severity, and change in impact over time. RESULTS: For the traditional categorical questionnaire items (the Migraine Specific Questionnaire (MSQ) and the Headache Disability Inventory (HDI)) the calibrated HIT agreed with the observed traditional scores: ICC's were between 0.80 and 0.94. In RV analyses the maximum mean difference between the observed and expected scores was 1.7 points on a 0-100 scale for comparisons at one point in time. Analyses of change over time and analyses calibrating scores from the fixed-form HIT-6 to the metric of other questionnaires were also satisfactory although less precise. Analysis of non-standard questionnaire items (e.g. On how many days in the past 3 months did you have a headache, from the HIMQ and the MIDAS) required special IRT models. Agreement was less good: ICC's were between 0.56 and 0.61 and the maximum mean differences were 2.9 (on a 0-270 scale) and 3.8 (on a 0-450 scale) in RV analyses at one point in time. The ability of the calibrated scale scores to discriminate between groups was at least as good as the ability of the observed sum scales and often remarkably better. CONCLUSION: The theoretical advantage of IRT models in scale calibration is supported by our results. This approach to achieving comparability of new and widely-used scales and accelerating the accumulation of interpretation guidelines based on previous work warrant testing for measures of other generic and disease-specific concepts.

Adolescent↗
PubMed1995

Molecular characterization of nine different types of mutants among 107 inhibitor-resistant TEM beta-lactamases from clinical isolates of Escherichia coli.

DNA-DNA hybridization and sequencing were performed to determine the molecular basis of resistance to clavulanic acid in 107 inhibitor-resistant TEM (IRT) enzymes produced by Escherichia coli clinical isolates. These beta-lactamases derived from TEM-1 enzyme focused at pI 5.2 (n = 68) or 5.4 (n = 39) and were very poorly inhibited by clavulanic acid compared with TEM-1 enzyme. Results showed that the amino acid sequences of 84 of the 107 enzymes differ from TEM-1 by one or two substitutions previously described: Arg-244-->Ser (IRT-2) in 22 strains, Met-69-->Leu (TEM-33) in 17 strains, Met-69-->Val (TEM-34) in 14 strains, Met-69-->Ile (IRT-3) in 6 strains, Met-69-->Leu associated with Asn-276-->Asp (IRT-4) in 13 strains, and Met-69-->Val associated with Asn-276-->Asp (TEM-36) in 12 strains. A new combination, Met-69-->Ile with Asn-276-->Asp, was found in 20 strains and was called IRT-8. Two IRT enzymes not previously described were characterized. The substitution Met-69-->Val associated with a novel substitution Arg-275-->Leu occurred in one strain. The combination Met-69-->Leu and Asn-276-->Asp was associated with the novel substitution Trp-165-->Arg in two strains. These two novel enzymes were called IRT-9 and IRT-10, respectively. The implication of these novel mutated positions, 165 and 275, in resistance to inactivation by clavulanate was supported by crystallographic data on the TEM-1 enzyme and results of site-directed mutagenesis. Molecular characterization of these mutants showed great diversity among the genes coding for inhibitor-resistant TEM enzymes produced by clinical E. coli isolates.

Base Sequence↗
PubMed1981

Serum immunoreactive trypsin in cystic fibrosis.

Serum immunoreactive trypsin (IRT) concentrations were measured blind in sera from 33 patients with cystic fibrosis and in 32 age-matched controls. Thirty-two patients had abnormal trypsin concentrations. In 30 of these patients the level of IRT was very low whereas in the other two (the youngest of the group) it was extremely high. All 30 patients with low IRT concentrations had clinical or biochemical evidence of malabsorption. Serum IRT concentration may thus be a useful diagnostic test for cystic fibrosis. In view of the recent observation that neonates with cystic fibrosis consistently have raised IRT concentrations, and the fact that the youngest two patients in our series also had markedly increased IRT, it would appear that the initial elevation of IRT reflects early damage to the pancreas with release of enzyme/zymogen; this is thereafter superseded by a progressive destruction of the pancreas resulting in low IRT concentrations in adults with cystic fibrosis.

Adolescent↗
PubMed2004

Five-year follow-up after intracoronary gamma radiation therapy for in-stent restenosis.

BACKGROUND: The Washington Radiation for In-Stent Restenosis Trial is a double-blinded randomized study evaluating the effects of intracoronary radiation therapy (IRT) in patients with in-stent restenosis (ISR). METHODS AND RESULTS: One hundred thirty patients with ISR (100 native coronary and 30 vein grafts) underwent percutaneous transluminal coronary angioplasty, laser ablation, rotational atherectomy, or additional stenting (36% of lesions). Patients were randomized to either 192-Iridium IRT or placebo, with a prescribed dose of 15 Gy to a 2-mm radial distance from the center of the source. Angiographic restenosis (27% versus 56%, P=0.002) and target vessel revascularization (26% versus 68%, P<0.001) were reduced at 6 months in patients treated with IRT. Between 6 and 60 months, patients treated with IRT compared with placebo had more target lesion revascularization (IRT, 21.6% versus placebo, 4.7%; P=0.04) and target vessel revascularization (IRT, 21.5% versus placebo, 6.1%; P=0.03). At 5 years, the major adverse cardiac event rate was significantly reduced with IRT (46.2% versus 69.2%, P=0.008). CONCLUSIONS: In the Washington Radiation for In-Stent Restenosis Trial, patients with ISR treated with IRT using 192-Iridium had a reduction in the need for repeat target lesion and vessel revascularization at 6 months and 5 years.

Cardiac Catheterization↗
PubMed1966

Discrimination and emission of temporal intervals by pigeons.

Because the frequency distribution of IRTs showed little or no control by a DRL schedule, the schedule was modified so that the pigeon's behavior after each IRT would indicate whether or not it had discriminated the duration of the IRT. After every two pecks on a red key, the key changed to blue for 30 sec. Then it automatically became red again. Pecks on the blue key were reinforced with food on a VI schedule only when the preceding IRT on the red key had been longer than 18 sec. The birds did not selectively emit longer IRTs on the red key: the value of IRTs/op did not increase with IRT duration. However, they did discriminate the duration of the IRT emitted on the red key: the rate of pecking on the blue key was an increasing function of the duration of the preceding IRT on the red key.

Animals↗
PubMed1982

Fixed-ratio performance with and without a postreinforcement timeout.

Pigeons pecked a key, producing food reinforcement on fixed-ratio (FR) schedules requiring 50, 100, or 150 responses. In each session, 30-second timeouts were inserted before a random half of the FR trials, whereas the other trials began immediately after reinforcement. In general, preratio pauses were shorter on trials preceded by timeouts. On these trials, the probability of a first response tended to be highest in the first 20 seconds of the trials, suggesting that the shorter pauses were the result of transient behavioral contrast. Direct observations and analyses of interresponse times (IRTs) after the preratio pause indicated that IRTs could be grouped into three categories: (1) IRTs of about .1 second, which were produced by small head movements in the vicinity of the key; (2) IRTs of about .3 second, which were produced by distinct pecking motions; and (3) IRTs greater than .5 second, which were accompanied by pausing or movements away from the key. At all ratio sizes, as a subject progressed through a trial, the probability of a long IRT decreased, whereas the probability of an intermediate IRT usually increased at first and then decreased. The probability of a short IRT increased monotonically across a trial. The results show that responding changes systematically as a subject progresses through a ratio on an FR schedule. Some characteristics of performance varied as functions of the absolute size of the response requirement, whereas others appeared to depend on the relative location within a ratio (i.e., the proportion of the ratio completed at a given moment).

Journal Article↗
PubMed2005

Using SAS PROC NLMIXED to fit item response theory models.

Researchers routinely construct tests or questionnaires containing a set of items that measure personality traits, cognitive abilities, political attitudes, and so forth. Typically, responses to these items are scored in discrete categories, such as points on a Likert scale or a choice out of several mutually exclusive alternatives. Item response theory (IRT) explains observed responses to items on a test (questionnaire) by a person's unobserved trait, ability, or attitude. Although applications of IRT modeling have increased considerably because of its utility in developing and assessing measuring instruments, IRT modeling has not been fully integrated into the curriculum of colleges and universities, mainly because existing general purpose statistical packages do not provide built-in routines with which to perform IRT modeling. Recent advances in statistical theory and the incorporation of those advances into general purpose statistical software such as the Statistical Analysis System (SAS) allow researchers to analyze measurement data by using a class of models known as generalized linear mixed effects models (McCulloch & Searle, 2001), which include IRT models as special cases. The purpose of this article is to demonstrate the generality and flexibility of using SAS to estimate IRT model parameters. With real data examples, we illustrate the implementations of a variety of IRT models for dichotomous, polytomous, and nominal responses. Since SAS is widely available in educational institutions, it is hoped that this article will contribute to the spread of IRT modeling in quantitative courses.

Attitude↗
PubMed1992

[Mucoviscidosis screening with immunoreactive trypsin].

Up to now 49,116 immunoreactive trypsin (IRT) measurements have been carried out in Austrian newborns in the first week of life. Related to provisionally chosen cut-off points, 301 newborns (0.61%) showed an elevated IRT value; 253 of them were successfully recalled. According to a direct strategy, sweat tests were done without a second IRT measurement in 101 infants; eleven of them were identified as cystic fibrosis (CF) patients. In accordance with a 2-step strategy, 152 infants were reinvestigated by a second IRT determination. Twenty-eight of them again showed an elevated IRT value, as based on provisional, age-dependent reference values; seven were subsequently identified as CF patients by sweat testing. So far two false-negative findings were obtained on IRT screening: one child was later identified as having CF on the basis of typical clinical symptoms and a positive sweat test, the other patient presenting with meconium ileus showed a normal IRT value after surgery, but was subjected to a sweat test in view of the underlying condition. These preliminary results suggest a CF incidence of 1 to 2460 newborns in Austria. Hence, IRT screening appears to be a reliable method for identifying CF patients in the newborn period, thereby facilitating early treatment and genetic counselling.

Austria↗
PubMed1990

Renal handling of amylase and immunoreactive trypsin in pancreatic cancer and chronic pancreatitis.

In order to evaluate the renal metabolism of amylase and immunoreactive trypsin (IRT) in chronic pancreatic disease, we assayed amylase, IRT and creatinine in serum and urine and gamma-glutamyl transferase (GGT) in dialyzed urine as well as alpha-glucosidase (AGL) and ribonuclease (RNase) in 24 control subjects, 34 patients with pancreatic cancer, 52 with chronic pancreatitis and 32 with extra-pancreatic diseases. Urinary amylase and IRT outputs were found to be more elevated in chronic pancreatitis than in control subjects. The levels of serum amylase, its renal inputs and outputs were correlated with the corresponding IRT values. Multiple regression analyses (dependent on amylase or IRT urinary outputs, circulating levels of the two enzymes, creatinine clearance and the excretion of GGT, AGL and RNase predictor variables) showed significant correlations. The standardized partial regression coefficients found to be significant were: GGT, RNase and serum amylase for amylase, and GGT and RNase for IRT. No difference was found between amylase and IRT outputs in patients with chronic pancreatitis, taking the presence or the absence of alcohol abuse, exocrine insufficiency and pancreatic pseudocysts into consideration. Urinary GGT excretion correlated with serum amylase and IRT levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1980

Basal and stimulated serum immunoreactive trypsin in normal subjects.

Fasting serum immunoreactive trypsin (IRT) concentrations were measured in 35 healthy subjects. In 10 of them serum IRT levels were also evaluated after administration of secretin (GIH, 75 CU i.v. over 2 minutes); in 7 after a Lundh meal; in 12 after a standard protein meal (Liebig meat extract, 15 g in 150 ml of water) and in 13 after a glucose (1 g/Kg) oral load. Serum IRT was measured by radioimmunoassay (Trypsik kit, CIS, Sorin-Biomedica, Saluggia, Vercelli, Italy). Fasting serum IRT was 25.8 +/- 9 ng/ml (mean +/- SD). No correlation was found between age and serum IRT levels, nor were any statistical differrences observed in IRT concentration between the two sexes. A standard protein meal, Lundh meal or oral load of glucose did not provoke a significant increase in serum IRT levels. Only rapid i.v. injection of secretin was able to induce a significant rise of IRT over basal levels in healthy subjects. This behaviour is probably due more to an engorgement of the pancreatic ductal system with regurgitation of trypsinogen into the blood steam rather than to a direct effect of secretin on the synthesis and secretion of trypsin or to intestinal reabsorption of this enzyme.

Adolescent↗
PubMed1997

Effects of drugs on response duration differentiation. VI: differential effects under differential reinforcement of low rates of responding schedules.

The effects of methamphetamine, phencyclidine and delta9-tetrahydrocannabinol on responding under differential reinforcement of low rate schedules (DRL schedules) were studied under three different DRL time requirements. Under the DRL schedules studied, rats were required to space responses at least a minimum, but not more than a maximum, time interval apart. The time intervals between responses (interresponse times, or IRTs), when plotted as a frequency distribution, were usually a normal distribution with the peak at or near the minimum IRT required for delivery of the reinforcer. Methamphetamine flattened the IRT distribution and increased the frequency of long pauses under the DRL 1-1.3 sec schedule, but shifted the IRT distribution toward shorter IRTs under the DRL 4-5.2 and 10-13 sec schedules. Under the DRL 1-1.3 sec schedule, phencyclidine also increased long pauses. Under the DRL 4-5.2 sec and 10-13 sec schedules, phencyclidine produced dual effects on the IRT relative frequency distributions producing increases in the proportion of short IRTs similar to methamphetamine at low doses, but higher doses increased long pauses as well. delta9-Tetrahydrocannabinol had little effect on responding under the DRL 1-1.3 sec and DRL 4-5.2 sec schedules, but it greatly increased the relative frequency of short IRTs under the DRL 10-13 sec schedule. Thus the effects of drugs on responding under these DRL schedules depended on the drug, the dose and the time requirements of the schedule, which suggests that a simple description of the effects of drugs on timing behavior or time perception is inadequate.

Animals↗