Association of Upper GI Surgery of Great Britain and Ireland (AUGIS) Delphi consensus recommendations on the adoption of robotic upper GI surgery

BACKGROUND

The adoption of robotic platforms in upper gastrointestinal (GI) surgery is expanding rapidly. The absence of centralised guidance and governance in adoption of new surgical technologies may lead to an increased risk of patient harm.

METHODS

Surgeon stakeholders participated in a Delphi consensus process following a national open-invitation in-person meeting on the adoption of robotic upper GI surgery. Consensus agreement was deemed met if >80% agreement was achieved.

RESULTS

Following two rounds of Delphi voting, 25 statements were agreed on covering the training process, governance and good practice for surgeons' adoption in upper GI surgery. One statement failed to achieve consensus.

CONCLUSIONS

These recommendations are intended to support surgeons, patients and health systems in the adoption of robotics in upper GI surgery.

Outcomes of emergency laparoscopy in the elderly

INTRODUCTION

This paper assessed the association between operative approach and postoperative in-hospital mortality in elderly patients undergoing emergency abdominal surgery. Patients undergoing emergency laparotomy have high morbidity and mortality rates. One-third of patients requiring emergency surgery are over 75 years old, and their in-hospital mortality rate exceeds 17%. Fewer than 20% of emergency abdominal operations in the UK are attempted laparoscopically, and only 10% are completed laparoscopically. Little is known about how laparoscopic emergency surgery in the elderly might affect outcomes.

METHODS

An observational UK study was performed using the prospectively maintained National Emergency Laparotomy Audit (NELA) database. Operative approach, NELA risk-prediction score and in-hospital mortality were recorded. The effect of operative approach on in-hospital mortality was analysed, both on a national basis and in a high-volume laparoscopic centre.

RESULTS

A total of 47,667 patients were included in the study, of whom 15,068 were over 75 years of age. Nationally, surgery was completed by the laparoscopic approach in 7.8% of patients aged over 75; both crude mortality (9.2%) and risk-adjusted mortality (7.1%) were significantly reduced (p<0.0001). In our unit, surgery was completed laparoscopically in 48.4% of patients aged over 75; both crude mortality (6.6%) and risk-adjusted mortality (3.3%) were significantly reduced (p<0.0001).

CONCLUSION

Laparoscopy in emergency surgery has been shown in this study to significantly reduce in-hospital mortality in elderly patients and should be embraced in every centre dealing with emergency abdominal surgery.

Novel and Annotated Long Noncoding RNAs Associated with Ischemia in the Human Heart

BACKGROUND

Long noncoding RNAs (lncRNAs) have been implicated in the pathogenesis of cardiovascular diseases. We aimed to identify novel lncRNAs associated with the early response to ischemia in the heart.

METHODS AND RESULTS

RNA sequencing data gathered from 81 paired left ventricle samples from patients undergoing cardiopulmonary bypass was collected before and after a period of ischemia. Novel lncRNAs were validated with Oxford Nanopore Technologies long-read sequencing. Gene modules associated with an early ischemic response were identified and the subcellular location of selected lncRNAs was determined with RNAscope. A total of 2446 mRNAs, 270 annotated lncRNAs and one novel lncRNA differed in response to ischemia (adjusted p < 0.001, absolute fold change >1.2). The novel lncRNA belonged to a gene module of highly correlated genes that also included 39 annotated lncRNAs. This module associated with ischemia (Pearson correlation coefficient = -0.69, p = 1 × 10^-23) and activation of cell death pathways (p < 6 × 10^-9). A further nine novel cardiac lncRNAs were identified, of which, one overlapped five cis-eQTL eSNPs for the gene RWD Domain-Containing Sumoylation Enhancer (RWDD3) and was itself correlated with RWDD3 expression (Pearson correlation coefficient -0.2, p = 0.002).

CONCLUSION

We have identified 10 novel lncRNAs, one of which was associated with myocardial ischemia and may have potential as a novel therapeutic target or early marker for myocardial dysfunction.

O12 Artificial intelligence-based risk prediction for death after emergency laparotomy using multi slice contrast enhanced computerised tomography

Introduction

Emergency laparotomy has a considerable mortality risk, with more than one in ten patients not surviving to discharge. Preoperative risk prediction using clinical tools is well established, however implemented variably. Preoperative CT is undertaken almost universally and contains granular data beyond diagnostics, including body composition, disease severity and other abstract features with the potential to enhance risk prediction. In this study we established the value of features extracted in an automated fashion from pre-operative CT in predicting 90-day post-surgery mortality.

Method

Anonymised CTs were collated from patients undergoing emergency laparotomy at ten hospitals in Southern England (2016–2017). For each case, axial portal venous abdominal/pelvic series were analysed using a pre-trained neural network, with each image converted into a matrix of numerical features. An elastic-net regression model to predict 90-day mortality was trained using these features and evaluated by bootstrapping with 1000 resampled datasets.

Result

A total of 136,709 images from 274 cases were available for analysis with a mean of 503 per case. Mortality within 90 days occurred in 34 cases (12.4%) with an average NELA mortality prediction of 8.5%. On internal (bootstrap) validation, the elastic net model derived from CT yielded excellent performance (AUC 0.903 95%CI 0.897–0.909), significantly in excess of the NELA risk calculator (AUC 0.809 95%CI 0.736–0.875), with a broader prediction range (0.01%-89.71%).

Conclusion

Artificial intelligence techniques applied to routinely performed cross-sectional imaging predicts emergency laparotomy mortality with greater accuracy than clinical data alone. Integration of these automated tools may be possible in the future.

Take-home Message

Automated analysis of CT can accurately predict risk of mortality after emergency laparotomy.

Primary cilia defects causing mitral valve prolapse

Mitral valve prolapse (MVP) affects 1 in 40 people and is the most common indication for mitral valve surgery. MVP can cause arrhythmias, heart failure, and sudden cardiac death, and to date, the causes of this disease are poorly understood. We now demonstrate that defects in primary cilia genes and their regulated pathways can cause MVP in familial and sporadic nonsyndromic MVP cases. Our expression studies and genetic ablation experiments confirmed a role for primary cilia in regulating ECM deposition during cardiac development. Loss of primary cilia during development resulted in progressive myxomatous degeneration and profound mitral valve pathology in the adult setting. Analysis of a large family with inherited, autosomal dominant nonsyndromic MVP identified a deleterious missense mutation in a cilia gene, DZIP1 A mouse model harboring this variant confirmed the pathogenicity of this mutation and revealed impaired ciliogenesis during development, which progressed to adult myxomatous valve disease and functional MVP. Relevance of primary cilia in common forms of MVP was tested using pathway enrichment in a large population of patients with MVP and controls from previously generated genome-wide association studies (GWAS), which confirmed the involvement of primary cilia genes in MVP. Together, our studies establish a developmental basis for MVP through altered cilia-dependent regulation of ECM and suggest that defects in primary cilia genes can be causative to disease phenotype in some patients with MVP.

GATA6 Regulates Aortic Valve Remodeling, and Its Haploinsufficiency Leads to Right-Left Type Bicuspid Aortic Valve

BACKGROUND

Bicuspid aortic valve (BAV), the most common congenital heart defect affecting 1% to 2% of the population, is a major risk factor for premature aortic valve disease and accounts for the majority of valve replacement. The genetic basis and mechanisms of BAV etiology and pathogenesis remain largely undefined.

METHODS

Cardiac structure and function was assessed in mice lacking a Gata6 allele. Human GATA6 gene variants were analyzed in 452 BAV cases from the BAV consortium and 1849 controls from the Framingham GWAS (Genome Wide Association Study). GATA6 expression was determined in mice and human tissues using quantitative real-time polymerase chain reaction and immunohistochemistry. Mechanistic studies were carried out in cultured cells.

RESULTS

Gata6 heterozygous mice have highly penetrant right-left (RL)-type BAV, the most frequent type in humans. GATA6 transcript levels are lower in human BAV compared with normal tricuspid valves. Mechanistically, Gata6 haploinsufficiency disrupts valve remodeling and extracellular matrix composition through dysregulation of important signaling molecules, including matrix metalloproteinase 9. Cell-specific inactivation of Gata6 reveals an essential role for GATA6 in secondary heart field myocytes because loss of 1 Gata6 allele from Isl- 1-positive cells-but not from endothelial or neural crest cells-recapitulates the phenotype of Gata6 heterozygous mice.

CONCLUSIONS

The data identify a new cellular and molecular mechanism underlying BAV. The availability of an animal model for the most frequent human BAV opens the way for the elucidation of BAV pathogenesis and the development of much needed therapies.

Comparison of Sex-Based Differences in Home or Nonhome Discharge Utilization of Rehabilitative Services and Outcomes Following Transcatheter Aortic Valve Implantation in the United States

Sex-based differences in outcomes have been shown to affect caregiving in medical disciplines. Increased spending due to postacute care transfer policies has led hospitals to further scrutinize patient outcomes and disposition patterns after inpatient admissions. We examined sex-based differences in rehabilitative service utilization after transcatheter aortic valve implantation (TAVI). We queried all TAVI discharges in the National Inpatient Sample database from 2012 to 2014 (n = 40,900). Thirteen thousand eight hundred fifteen patients were discharged to home and 12,175 patients were discharged to rehabilitation facility; those not discharged routinely or to a rehabilitation facility were excluded. Patients with nonhome discharges were older (83.3 vs 79.0 years) and female (58.3% vs 37.7%) with a greater number of chronic conditions (9.91 vs 9.03) and number of Elixhauser co-morbidities (6.5 vs 5.8, all p < 0.05). Nonhome discharge patients also had a significantly longer length of stay (LOS) (11.3 days vs 5.3 days) and higher hospitalization costs ($66,246 vs $48,710, all p < 0.001) compared to home-discharged patients. Overall in-hospital mortality for female patients who underwent TAVI was higher compared to males (4.6% vs 3.6%, p < 0.05). On multivariable logistic regression, female sex was an independent predictor for disposition to rehabilitation facilities after TAVI (odds ratio 2.17; 95% confidence interval: 1.88 to 2.50; p < 0.001). Other independent predictors for females discharged to rehabilitation included the presence of rheumatoid arthritis and collagen vascular disease, body mass index greater than 30 kg/m², depression, and sum of Elixhauser co-morbidities (all p < 0.001). In conclusion, nonhome discharge TAVI patients added LOS and hospital costs compared to home discharge TAVI patients, and female sex was one of the major predictors despite the lower co-morbidities.

Aortopathy and regurgitation in bicuspid valve patients increase the risk of aortopathy in relatives

BACKGROUND

Bicuspid aortic valve (BAV) is the most frequent cardiac congenital valvular disease. Although the BAV risk of first degree relatives (FDR) has been assessed (7-9%), there is little information as to the heritable risk for aortopathy.

OBJECTIVE

Identify the specific risk for regional aortopathy in FDR with tricuspid aortic valve (TAV) of BAV patients according to their aortic phenotype and aortic regurgitation (AR).

METHODS

Using an international consortium, BAV probands were assessed for aortopathy of the root, ascending aorta and for AR. Aortopathy was defined by the presence of segmental dilatation. The presence of segmental aortopathy and AR in BAV probands was evaluated as predictor for aortopathy in FDR with TAV.

RESULTS

We identified 74 FDR related to 49 probands with aortopathy and 66 FDR related to 31 probands without aortopathy. Demographic variables were similar between proband groups. Among FDR, 16 individuals had BAV (11.4%). TAV-FDR of probands with ascending aortopathy had higher incidence of root aortopathy (18.8% vs. 3.6% p < 0.05) while TAV-FDR of probands with root aortopathy had higher incidence of aortopathy at all aortic segments (55%vs25%, 55%vs21%, and 4%vs29% at annulus, root and ascending respectively, p < 0.05 for all). Independent predictors for root aortopathy in TAV-FDR were: ascending (OR = 6.23;95%CI:1.27-30.5) and root aortopathy (OR = 9.00;95%CI:1.58-51.1) in probands; and for ascending aortopathy: root aortopathy (OR = 4.04;95%CI:1.33-12.3) and AR in probands (OR = 4.84; 95%CI:1.75-13.4).

CONCLUSION

Root and ascending aortopathy in BAV probands are strong predictors of aortopathy in their TAV-FDR. AR in BAV patients has an independent effect on the risk for ascending aortopathy in TAV-FDR.

Cyclin D1 unbalances the redox status controlling cell adhesion, migration, and drug resistance in myeloma cells

The interactions of multiple myeloma (MM) cells with their microenvironment are crucial for pathogenesis. MM cells could interact differentially with their microenvironment depending on the type of cyclin D they express. We established several clones that constitutively express cyclin D1 from the parental RPMI8226 MM cell line and analyzed the impact of cyclin D1 expression on cell behavior. We performed a gene expression profiling study on cyclin D1-expressing vs. control cells and validated the results by semi-quantitative RT-PCR. The expression of cyclin D1 altered the transcription of genes that control adhesion and migration. We confirmed that cyclin D1 increases cell adhesion to stromal cells and fibronectin, stabilizes F-actin fibers, and enhances chemotaxis and inflammatory chemokine secretion. Both control and cyclin D1-expressing cells were more resistant to acute carfilzomib treatment when cultured on stromal cells than in suspension. However, this resistance was specifically reduced in cyclin D1-expressing cells after pomalidomide pre-treatment that modifies tumor cell/microenvironment interactions. Transcriptomic analysis revealed that cyclin D1 expression was also associated with changes in the expression of genes controlling metabolism. We also found that cyclin D1 expression disrupted the redox balance by producing reactive oxygen species. The resulting oxidative stress activated the p44/42 mitogen-activated protein kinase (or ERK1/2) signaling pathway, increased cell adhesion to fibronectin or stromal cells, and controlled drug sensitivity.

Our results have uncovered a new function for cyclin D1 in the control of redox metabolism and interactions of cyclin D1-expressing MM cells with their bone marrow microenvironment.

A lowered 26S proteasome activity correlates with mantle lymphoma cell lines resistance to genotoxic stress

Background

Mantle cell lymphoma (MCL) is a B-cell hemopathy characterized by the t(11;14) translocation and the aberrant overexpression of cyclin D1. This results in an unrestrained cell proliferation. Other genetic alterations are common in MCL cells such as SOX11 expression, mutations of ATM and/or TP53 genes, activation of the NF-κB signaling pathway and NOTCH receptors. These alterations lead to the deregulation of the apoptotic machinery and resistance to drugs. We observed that among a panel of MCL cell lines, REC1 cells were resistant towards genotoxic stress. We studied the molecular basis of this resistance.

Methods

We analyzed the cell response regarding apoptosis, senescence, cell cycle arrest, DNA damage response and finally the 26S proteasome activity following a genotoxic treatment that causes double strand DNA breaks.

Results

MCL cell lines displayed various sensitivity/resistance towards genotoxic stress and, in particular, REC1 cells did not enter apoptosis or senescence after an etoposide treatment. Moreover, the G2/M cell cycle checkpoint was deficient in REC1 cells. We observed that three main actors of apoptosis, senescence and cell cycle regulation (cyclin D1, MCL1 and CDC25A) failed to be degraded by the proteasome machinery in REC1 cells. We ruled out a default of the βTrCP E3-ubiquitine ligase but detected a lowered 26S proteasome activity in REC1 cells compared to other cell lines.

Conclusion

The resistance of MCL cells to genotoxic stress correlates with a low 26S proteasome activity. This could represent a relevant biomarker for a subtype of MCL patients with a poor response to therapies and a high risk of relapse.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3530-z) contains supplementary material, which is available to authorized users.

A role for primary cilia in aortic valve development and disease

BACKGROUND

Bicuspid aortic valve (BAV) disease is the most common congenital heart defect, affecting 0.5-1.2% of the population and causing significant morbidity and mortality. Only a few genes have been identified in pedigrees, and no single gene model explains BAV inheritance, thus supporting a complex genetic network of interacting genes. However, patients with rare syndromic diseases that stem from alterations in the structure and function of primary cilia ("ciliopathies") exhibit BAV as a frequent cardiovascular finding, suggesting primary cilia may factor broadly in disease etiology.

RESULTS

Our data are the first to demonstrate that primary cilia are expressed on aortic valve mesenchymal cells during embryonic development and are lost as these cells differentiate into collagen-secreting fibroblastic-like cells. The function of primary cilia was tested by genetically ablating the critical ciliogenic gene Ift88. Loss of Ift88 resulted in abrogation of primary cilia and increased fibrogenic extracellular matrix (ECM) production. Consequentially, stratification of ECM boundaries normally present in the aortic valve were lost and a highly penetrant BAV phenotype was evident at birth.

CONCLUSIONS

Our data support cilia as a novel cellular mechanism for restraining ECM production during aortic valve development and broadly implicate these structures in the etiology of BAV disease in humans. Developmental Dynamics 246:625-634, 2017. © 2017 Wiley Periodicals, Inc.

Histopathological assessment of calcification and inflammation of calcific aortic valves from patients with and without diabetes mellitus

BACKGROUND

Calcific aortic valve disease (CAVD) is the most common valvular heart disease and likely evolves from inflammatory pre-conditions in the valve. Type II diabetes mellitus (DMII) has been associated with pathogenesis of CAVD, however, the mechanism initiating CAVD in DMII is not well understood and the human valve pathology in DMII has not been described. We therefore performed quantitative histological analyses of aortic valves of CAVD patients with and without DMII.

METHODS

CAVD human aortic valves (n=45) obtained after surgical valve replacement were examined macroscopically with gross measurements of calcified areas. Inflammation and calcification were assessed by immunohistochemistry and immunofluorescence staining.

RESULTS

Calcification was increased in diabetic patients according to gross measurements (p<0.01) and alizarin red staining (p=0.05). Early calcification markers, including Runx2 (p=0.02) and alkaline phosphatase (ALP, p=0.03) were significantly elevated in diabetic patients. Furthermore, in diabetic patients we found significantly increased expression of annexin II (p=0.04) and annexin V (p=0.04), both of which are thought to play a role in microcalcification formation via apoptosis or extracellular vesicle release. Macrophage numbers were comparable in both groups (p=0.41), while the expression of the pro-inflammatory protein S100A9 (p<0.01) was significantly decreased in diabetic individuals. Evaluation of lymphocytes revealed similar CD8 (p=0.45) and CD4 (p=0.92) T cell counts in diabetic and non-diabetic aortic valves.

CONCLUSION

Aortic valves from diabetic patients show more calcification, while inflammation is similar in both patient populations. Considering the generally accepted theory of an inflammation-dependent mechanism of calcification, these data suggest that in patients with CAVD requiring valve replacement, diabetic patients could be molecularly in a more advanced disease stage with a higher grade of mineralization than non-diabetic patients.

Simulation of early calcific aortic valve disease in a 3D platform: A role for myofibroblast differentiation

PURPOSE

Calcific aortic valve disease (CAVD) is the most prevalent valve disease in the Western world. Recent difficulty in translating experimental results on statins to beneficial clinical effects warrants the need for understanding the role of valvular interstitial cells (VICs) in CAVD. In two-dimensional culture conditions, VICs undergo spontaneous activation similar to pathological differentiation, which intrinsically limits the use of in vitro models to study CAVD. Here, we hypothesized that a three-dimensional (3D) culture system based on naturally derived extracellular matrix polymers, mimicking the microenvironment of native valve tissue, could serve as a physiologically relevant platform to study the osteogenic differentiation of VICs.

PRINCIPAL RESULTS

Aortic VICs loaded into 3D hydrogel constructs maintained a quiescent phenotype, similar to healthy human valves. In contrast, osteogenic environment induced an initial myofibroblast differentiation (hallmarked by increased alpha smooth muscle actin [α-SMA] expression), followed by an osteoblastic differentiation, characterized by elevated Runx2 expression, and subsequent calcific nodule formation recapitulating CAVD conditions. Silencing of α-SMA under osteogenic conditions diminished VIC osteoblast-like differentiation and calcification, indicating that a VIC myofibroblast-like phenotype may precede osteogenic differentiation in CAVD.

MAJOR CONCLUSIONS

Using a 3D hydrogel model, we simulated events that occur during early CAVD in vivo and provided a platform to investigate mechanisms of CAVD. Differentiation of valvular interstitial cells to myofibroblasts was a key mechanistic step in the process of early mineralization. This novel approach can provide important insight into valve pathobiology and serve as a promising tool for drug screening.

Bicuspid Aortic Valve Associated Aortopathy: A Genetic Disease

As the most common congenital heart defect, understanding the etiology and progression of aortopathy in bicuspid aortic valve (BAV) is imperative to management of patients with BAV. A reasonable hypothesis, based on the strength of evidence for both genetic and hemodynamic causes of BAV-associated thoracic aortic disease (TAD), is that BAV is caused by genetic variant(s) that also predispose to TAD by a common mechanism; presumably by cell-signaling resulting in an embryologic defect that causes BAV and a postnatal risk of TAD that is accentuated by hemodynamic stress of abnormal flow through the BAV valve. Clinical heterogeneity seen in BAVassociated TAD is likely due to individual genetic variation and the severity of hemodynamic alteration.

Evidence for a role of 5-HT2C receptors in the motor aspects of performance, but not the efficacy of food reinforcers, in a progressive ratio schedule

RATIONALE

5-Hydroxytryptamine2C (5-HT2C) receptor agonists reduce the breakpoint in progressive ratio schedules of reinforcement, an effect that has been attributed to a decrease of the efficacy of positive reinforcers. However, a reduction of the breakpoint may also reflect motor impairment. Mathematical models can help to differentiate between these processes.

OBJECTIVE

The effects of the 5-HT2C receptor agonist Ro-600175 ((αS)-6-chloro-5-fluoro-α-methyl-1H-indole-1-ethanamine) and the non-selective 5-HT receptor agonist 1-(m-chlorophenyl)piperazine (mCPP) on rats' performance on a progressive ratio schedule maintained by food pellet reinforcers were assessed using a model derived from Killeen's Behav Brain Sci 17:105-172, 1994 general theory of schedule-controlled behaviour, 'mathematical principles of reinforcement'.

METHOD

Rats were trained under the progressive ratio schedule, and running and overall response rates in successive ratios were analysed using the model. The effects of the agonists on estimates of the model's parameters, and the sensitivity of these effects to selective antagonists, were examined.

RESULTS

Ro-600175 and mCPP reduced the breakpoint. Neither agonist significantly affected a (the parameter expressing incentive value), but both agonists increased δ (the parameter expressing minimum response time). The effects of both agonists could be attenuated by the selective 5-HT2C receptor antagonist SB-242084 (6-chloro-5-methyl-N-{6-[(2-methylpyridin-3-yl)oxy]pyridin-3-yl}indoline-1-carboxamide). The effect of mCPP was not altered by isamoltane, a selective 5-HT1B receptor antagonist, or MDL-100907 ((±)2,3-dimethoxyphenyl-1-(2-(4-piperidine)methanol)), a selective 5-HT2A receptor antagonist.

CONCLUSIONS

The results are consistent with the hypothesis that the effect of the 5-HT2C receptor agonists on progressive ratio schedule performance is mediated by an impairment of motor capacity rather than by a reduction of the incentive value of the food reinforcer.

New Findings on the Sensitivity of Free-Operant Timing Behaviour to 5-Hydroxytryptamine Receptor Stimulation

Timing performance maintained under the free-operant psychophysical procedure (FOPP) is sensitive to 5-hydroxytryptamine (5-HT)1A and 5-HT2A receptor stimulation. Agonists of these receptors displace the psychometric function towards shorter durations, reducing , the index of central tendency of timing. Here we report the effects of Ro-600175, a selective 5-HT2C receptor agonist, and mCPP, a 5-HT receptor agonist with high affinity for 5-HT2C receptors and lower affinity for 5-HT1A, 5-HT1B and 5-HT2A receptors, on timing behaviour. Rats were trained under the FOPP to press two levers (A and B) in 50-s trials in which reinforcers were provided intermittently for responding on A in the first half, and B in the second half of the trial. Percent responding on B (%B) was recorded in successive 5-s epochs of the trials; logistic psychometric curves were fitted to the data from each rat under each treatment condition for derivation of timing indices [ (time corresponding to %B = 50%), Weber fraction]. The rats received systemic treatment with Ro-600175, mCPP, and mCPP in combination with antagonists of 5-HT1A (WAY-100635), 5-HT1B (isamoltane), 5-HT2A (MDL-100907) or 5-HT2C (SB-242084) receptors. mCPP (2.5 mg kg−1 i.p.), but not Ro-600175 (1, 2, 4 mg kg−1 i.p.), reduced . SB-242084 (0.6 mg kg−1 i.p.) potentiated mCPP’s effect on . mCPP’s effect on was not altered by isamoltane (8.0 mg kg−1 i.p.), but was attenuated by MDL-100907 (1.0 mg kg−1 i.p.) and WAY-100635 (0.1 mg kg−1 s.c.). The results suggest that mCPP’s effect on timing is mediated by an agonistic action at 5-HT1A and 5-HT2A, but not 5-HT1B, receptors. The role of 5-HT2C receptors is unclear, in view of SB-242084’s ability to potentiate the effect of mCPP, while Ro-600175 had no effect on . The possibility is considered that 5-HT2C receptors may counteract 5-HT1A and/or 5-HT2A receptor-mediated effects on timing performance.

Effects of amisulpride and aripiprazole on progressive-ratio schedule performance: comparison with clozapine and haloperidol

Clozapine and some other atypical antipsychotics (e.g. quetiapine, olanzapine) have been found to exert a characteristic profile of action on operant behaviour maintained by progressive-ratio schedules, as revealed by Killeen's Mathematical Principles of Reinforcement model of schedule-controlled behaviour. These drugs increase the value of a parameter that expresses the 'incentive value' of the reinforcer (a) and a parameter that is inversely related to the organism's 'motor capacity' (δ). This experiment examined the effects of two further atypical antipsychotics, aripiprazole and amisulpride, on progressive-ratio schedule performance in rats; the effects of clozapine and a conventional antipsychotic, haloperidol, were also examined. In agreement with previous findings, clozapine (4, 8 mg kg⁻¹) increased a and δ, whereas haloperidol (0.05, 0.1 mg kg⁻¹) reduced a and increased δ. Aripiprazole (3,30 mg kg⁻¹) increased δ but did not affect a. Amisulpride (5, 50 mg kg⁻¹) had a delayed and protracted effect: δ was increased 3-6 hours after treatment; a was increased 1.5 hours, and reduced 12-24 hours after treatment. Interpretation based on Killeen's model suggests that aripiprazole does not share clozapine's ability to enhance reinforcer value. Amisulpride produced a short-lived enhancement, followed by a long-lasting reduction, of reinforcer value. Both drugs impaired motor performance.

Fos expression in the prefrontal cortex and ventral striatum after exposure to a free-operant timing schedule

It has been proposed that cortico-striato-thalamo-cortical circuits that incorporate the prefrontal cortex and corpus striatum regulate interval timing behaviour. In the present experiment regional Fos expression was compared between rats trained under an immediate timing schedule, the free-operant psychophysical procedure (FOPP), which entails temporally regulated switching between two operanda, and a yoked variable-interval (VI) schedule matched to the timing task for food deprivation level, reinforcement rate and overall response rate. The density of Fos-positive neurones (counts mm⁻²) in the orbital prefrontal cortex (OPFC) and the shell of the nucleus accumbens (AcbS) was greater in rats exposed to the FOPP than in rats exposed to the VI schedule, suggesting a greater activation of these areas during the performance of the former task. The enhancement of Fos expression in the OPFC is consistent with previous findings with both immediate and retrospective timing schedules. Enhanced Fos expression in the AcbS was previously found in retrospective timing schedules based on conditional discrimination tasks, but not in a single-operandum immediate timing schedule, the fixed-interval peak procedure. It is suggested that the ventral striatum may be engaged during performance on timing schedules that entail operant choice, irrespective of whether they belong to the immediate or retrospective categories.

A clozapine-like effect of cyproheptadine on progressive ratio schedule performance

The atypical antipsychotic drug clozapine has multiple pharmacological actions, some of which, including 5-hydroxytryptamine (5-HT₂) and histamine (H₁) receptor antagonist effects, are shared by the non-selective 5-HT receptor antagonist cyproheptadine. Atypical antipsychotics have a characteristic profile of action on operant behaviour maintained by progressive ratio schedules, as revealed by Killeen's (1994) mathematical model of schedule controlled behaviour. These drugs increase the values of a parameter that expresses the 'incentive value' of the reinforcer (a) and a parameter that is inversely related to the 'motor capacity' of the organism (δ). This experiment examined the effects of acute treatment with cyproheptadine and clozapine on performance on a progressive ratio schedule of food reinforcement in rats; the effects of a conventional antipsychotic, haloperidol, and two drugs with food intake-enhancing effects, chlordiazepoxide and Δ⁹-tetrahydrocannabinol (THC), were also examined. Cyproheptadine (1, 5 mg kg⁻¹) and clozapine (3.75, 7.5 mg kg⁻¹) increased a and δ. Haloperidol (0.05, 0.1 mg kg⁻¹) reduced a and increased δ. Chlordiazepoxide (3, 10 mg kg⁻¹) increased a but reduced δ. THC (1, 3 mg kg⁻¹) had no effect. Interpretation based on Killeen's (1994) model suggests that cyproheptadine and clozapine enhanced the incentive value of the reinforcer and impaired motor performance. Motor impairment may be due to sedation (possibly reflecting H₁ receptor blockade). Enhancement of incentive value may reflect simultaneous blockade of H₁ and 5-HT₂ receptors, which has been proposed as the mechanism underlying the food intake-enhancing effect of cyproheptadine. In agreement with previous findings, haloperidol impaired motor performance and reduced the incentive value of the reinforcer. Chlordiazepoxide's effect on a is consistent with its food intake-enhancing effect.

Effect of orexin-B-saporin-induced lesions of the lateral hypothalamus on performance on a progressive ratio schedule

It has been suggested that a sub-population of orexinergic neurones whose somata lie in the lateral hypothalamic area (LHA) play an important role in regulating the reinforcing value of both food and drugs. This experiment examined the effect of disruption of orexinergic mechanisms in the LHA on performance on the progressive ratio schedule of reinforcement, in which the response requirement increases progressively for successive reinforcers. The data were analysed using a mathematical model which yields a quantitative index of reinforcer value and dissociates effects of interventions on motor and motivational processes. Rats were trained under a progressive ratio schedule using food-pellet reinforcement. They received bilateral injections of conjugated orexin-B-saporin (OxSap) into the LHA or sham lesions. Training continued for a further 40 sessions after surgery. Equations were fitted to the response rate data from each rat, and the parameters of the model were derived for successive blocks of 10 sessions. The OxSap lesion reduced the number of orexin-containing neurones in the LHA by approximately 50% compared with the sham-lesioned group. The parameter expressing the incentive value of the reinforcer was not significantly altered by the lesion. However, the parameter related to the maximum response rate was significantly affected, suggesting that motor capacity was diminished in the OxSap-lesioned group. The results indicate that OxSap lesions of the LHA disrupted food-reinforced responding on the progressive ratio schedule. It is suggested that this disruption was brought about by a change in non-motivational (motor) processes.

Fos expression in the orbital prefrontal cortex after exposure to the fixed-interval peak procedure

It has been proposed that cortico-striato-thalamo-cortical circuits that incorporate the prefrontal cortex and dorsal striatum regulate interval timing behaviour. The present experiment examined whether performance on the fixed-interval peak procedure (FIPP), an immediate timing schedule, would induce neuronal activity in cortical and striatal areas, as revealed by enhanced expression of the Fos protein, a marker for neuronal activation. Regional Fos expression was compared between rats trained on the FIPP and rats trained on a variable-interval (VI) schedule matched to the FIPP for overall response rate and reinforcer delivery. Response rate in the peak trials of the FIPP conformed to a temporally differentiated pattern, which was well described by a modified Gaussian function; in agreement with previous findings, the peak time occurred close to the time at which the reinforcer was delivered in the fixed-interval trials, and the Weber fraction was within the range of values reported previously. The density of Fos-positive neurones (counts mm⁻²) in the orbital prefrontal cortex (OPFC) was greater in rats exposed to the FIPP than in rats exposed to the VI schedule, suggesting a greater activation of this area during the performance of the former task. This is consistent with the results of previous studies that have implicated the OPFC in interval timing behaviour. However, there was no significant difference between the levels of Fos expression in the dorsal or ventral striatum of the rats trained under the two schedules.

Fos expression in the prefrontal cortex and nucleus accumbens following exposure to retrospective timing tasks

The dorsal striatum and prefrontal cortex have been implicated in interval timing. We examined whether performance of temporal discrimination tasks is associated with increased neuronal activation in these areas, as revealed by Fos expression, a marker for neuronal activation. In Experiment 1, rats were trained on a discrete-trials temporal discrimination task in which a light (22 cd/m²) was presented for a variable time, t (2.5-47.5 s), after which levers A and B were presented. A response on lever A was reinforced if t < 25 s, and a response on lever B was reinforced if t > 25 s. A second group was trained on a light-intensity discrimination procedure, in which a light of variable intensity, i (3.6-128.5 cd/m²) was presented for 25 s. A response on lever A was reinforced if i < 22 cd/m², and a response on lever B was reinforced if i > 22 cd/m². In Experiment 2, bisection procedures were used to assess temporal (200-800 ms, 22 cd/m²) and light-intensity (3.6-128.5 cd/m², 400 ms) discrimination. The increase in proportional choice of lever B as a function of stimulus duration or intensity conformed to a two-parameter logistic equation. Fos expression in the prefrontal cortex and nucleus accumbens was higher in rats performing temporal discrimination tasks than in those performing light-intensity discrimination tasks, indicating greater neuronal activation in these areas during temporal discrimination tasks. Fos expression in the dorsal striatum did not differ between rats performing temporal and light-intensity discrimination tasks. These results suggest that the prefrontal cortex and nucleus accumbens are involved in temporal discrimination.

Nucleus accumbens and delay discounting in rats: evidence from a new quantitative protocol for analysing inter-temporal choice

RATIONALE

There is evidence that the core of the nucleus accumbens (AcbC) is involved in inter-temporal choice behaviour.

OBJECTIVE

A new behavioural protocol was used to examine the effect of destruction of the AcbC on delay discounting in inter-temporal choice schedules in rats.

METHOD

Rats with excitotoxic lesions of the AcbC or sham lesions made repeated choices on an adjusting-delay schedule between a smaller reinforcer (A) that was delivered immediately and a larger reinforcer (B) that was delivered after a delay which increased or decreased depending on the subject's choices. In two phases of the experiment, reinforcer sizes were selected which enabled theoretical parameters expressing delay discounting and sensitivity to reinforcer size to be estimated from the ratio of the indifference delays (i.e. the quasi-stable values of the adjusting delay seen after extended training) obtained in the two phases.

RESULTS

In both groups, indifference delays were shorter when the sizes of A and B were 14 and 25 μl than when they were 25 and 100 μl of a 0.6 M sucrose solution. Indifference delays were shorter in AcbC-lesioned than in sham-lesioned rats. Estimates of delay discounting rate based on the ratio of the indifference delays were lower in the AcbC-lesioned than in the sham-lesioned rats. The size sensitivity parameter did not differ between the groups. Adjusting delays in successive blocks of trials were analysed using Fourier transform. The period corresponding to the dominant frequency of the power spectrum and power within the dominant frequency band did not differ between the groups.

CONCLUSIONS

Destruction of the AcbC increased the rate of delay discounting.

Transitional and steady-state choice behavior under an adjusting-delay schedule

Twelve rats made repeated choices on an adjusting-delay schedule between a smaller reinforcer (A) that was delivered immediately after a response and a larger reinforcer (B) that was delivered after a delay which increased or decreased by 20% depending on the subject's choices in successive blocks of trials. In two phases of the experiment (100 sessions and 40 sessions), reinforcer sizes were selected which enabled theoretical parameters expressing the rate of delay discounting and sensitivity to reinforcer size to be estimated from the ratio of the indifference delays obtained in the two phases. Indifference delays, calculated from adjusting delays in the last 10 sessions of each phase, were shorter when the sizes of A and B were 14 and 25 µl of a 0.6 M sucrose solution than when they were 25 and 100 µl of the same solution. The ratio of the indifference delays was significantly smaller than that predicted on the basis of an assumed linear relation between reinforcer size and instantaneous reinforcer value, consistent with a previous proposal that this relation may be hyperbolic in form. Estimates of the rate of delay discounting based on the ratio of the two indifference delays (mean, 0.08 s(-1)) were similar to values obtained previously using different intertemporal choice protocols. Estimates of the size-sensitivity parameter (mean 113 µl) were similar to estimates recently derived from performance on progressive-ratio schedules. In both phases of the experiment, adjusting delays in successive blocks of trials were analyzed using the Fourier transform. The power spectrum obtained from individual rats had a dominant frequency that corresponded to a period of oscillation of the adjusting delay between 30 and 100 trial blocks (mean, 78). Power in the dominant frequency band was highest in the early sessions of the first phase and declined with extended training. It is suggested that this experimental protocol may have utility in neurobehavioral studies of intertemporal choice.

Inferring genetic causal effects on survival data with associated endo-phenotypes

Age-at-onset phenotypes are important traits in genetic association analyses. Often, intermediate phenotypes that are related to the age-at-onset phenotype are also associated with the marker loci that are associated with the age-at-onset phenotype. In order to understand the genetic etiology of the observed associations, statistical methodology is needed to distinguish between a direct genetic effect on the age-at-onset phenotype and an indirect effect induced by the genetic association with the endo-phenotype that is correlated with the age-at-onset phenotype. In this communication, we introduce a new statistical approach to detect causal genetic effects on survival data in the presence of genetic associations with secondary phenotypes that might influence survival as well and thereby induce seemingly causal relationships. Derived using causal inference methodology, the proposed method is based on standard statistical methodology and can be implemented straight-forwardly, using standard software. Using simulation studies, the theoretical properties of the approach are verified and the power is assessed under realistic scenarios. The practical relevance of the approach is illustrated by an application to survival after cardiac surgery, where genetic components of myocardial infarctions are determined to not influence post-surgery hospital duration except through the MI-pathway.

Choice between reinforcer delays versus choice between reinforcer magnitudes: differential Fos expression in the orbital prefrontal cortex and nucleus accumbens core

Lesions of the orbital prefrontal cortex (OPFC) and the nucleus accumbens core (AcbC) can disrupt performance in inter-temporal choice tasks, possibly by increasing the organism's sensitivity to delay and/or magnitude of reinforcement. This experiment examined whether exposure to an inter-temporal choice would induce neuronal activation in these areas, as indicated by enhanced expression of the Fos protein. Twelve rats were trained to press levers A and B under an adjusting-delay schedule in which a response on A delivered 50 microl of a sucrose reinforcer after 2 or 18s, whereas a response on B delivered the same reinforcer after a delay that was adjusted in accordance with the rat's choices. Another 12 rats were trained under a similar schedule in which a response on A delivered an immediate reinforcer of size 20 or 180 microl, whereas a response on B delivered an immediate reinforcer whose size was adjusted in accordance with the rat's choices. A third group received training under a schedule that did not entail variation of reinforcer size or delay, or choice between reinforcers, and a control group underwent food restriction without behavioural training. Exposure to the adjusting-delay schedule was associated with enhanced Fos expression in both the OPFC and AcbC, whereas exposure to the adjusting-magnitude schedule was associated with enhanced Fos expression in the OPFC but not the AcbC, compared to the control group. The results are consistent with previous findings that implicated the AcbC and OPFC in delay discounting, and the OPFC in sensitivity to reinforcer size.

Quantitative analysis of the effect of lesions of the subthalamic nucleus on intertemporal choice: further evidence for enhancement of the incentive value of food reinforcers

Recent evidence suggests that the subthalamic nucleus (STN) is involved in regulating the incentive value of food reinforcers. The objective of this study was to examine the effect of lesions of the STN on intertemporal choice (choice between reinforcers differing in size and delay). Rats with bilateral quinolinic acid-induced lesions of the STN (n = 15) or sham lesions (n = 14) were trained in a discrete-trials progressive delay schedule to press levers A and B for a sucrose solution. Responses on A delivered 50 microl of the solution after a delay d(A); responses on B delivered 100 microl after a delay d(B). d(B) increased across blocks of trials; d(A) was manipulated across phases of the experiment. Indifference delay, d(B(50)) (value of d(B) corresponding to 50% choice of B), was estimated for each rat in each phase, and linear indifference functions (d(B(50)) vs. d(A)) were derived. The STN-lesioned group showed a flatter slope of the indifference function (implying higher instantaneous reinforcer values) than the sham-lesioned group; the intercepts did not differ between the groups. The results agree with recent evidence for a role of the STN in incentive value. Unlike some earlier studies, these results do not indicate a role of the STN in delay discounting.

Effect of reinforcer magnitude on performance maintained by progressive-ratio schedules

This experiment examined the relationship between reinforcer magnitude and quantitative measures of performance on progressive-ratio schedules. Fifteen rats were trained under a progressive-ratio schedule in seven phases of the experiment in which the volume of a 0.6-M sucrose solution reinforcer was varied within the range 6-300 microl. Overall response rates in successive ratios conformed to a bitonic equation derived from Killeen's (1994) Mathematical Principles of Reinforcement. The "specific activation" parameter, a, which is presumed to reflect the incentive value of the reinforcer, was a monotonically increasing function of reinforcer volume; the "response time" parameter, delta, which defines the minimum response time, increased as a function of reinforcer volume; the "currency" parameter, beta, which is presumed to reflect the coupling of responses to the reinforcer, declined as a function of volume. Running response rate (response rate calculated after exclusion of the postreinforcement pause) decayed monotonically as a function of ratio size; the index of curvature of this function increased as a function of reinforcer volume. Postreinforcement pause increased as a function of ratio size. Estimates of a derived from overall response rates and postreinforcement pauses showed a modest positive correlation across conditions and between animals. Implications of the results for the quantification of reinforcer value and for the use of progressive-ratio schedules in behavioral neuroscience are discussed.

Effect of quinolinic acid-induced lesions of the subthalamic nucleus on performance on a progressive-ratio schedule of reinforcement: a quantitative analysis

The subthalamic nucleus (STN), a major relay in the indirect striatofugal pathway, plays an important role in extrapyramidal motor control. Recent evidence indicates that it may also be involved in regulating the incentive value of food reinforcers.

OBJECTIVE

To examine the effect of lesions of the STN on performance on a progressive-ratio schedule using a quantitative model that dissociates effects of interventions on motor and motivational processes [Killeen PR. Mathematical principles of reinforcement. Behav Brain Sci 1994;17:105-72]. Rats with bilateral quinolinic acid-induced lesions of the STN (n=14) or sham lesions (n=14) were trained to press a lever for food-pellet reinforcers under a progressive-ratio schedule. In Phase 1 (90 sessions) the reinforcer was one pellet; in Phase 2 (30 sessions) it was two pellets; in Phase 3 (30 sessions) it was again one pellet.

RESULTS

The performance of both groups conformed to the model of progressive-ratio schedule performance. The motor parameter, delta, was significantly higher in the STN-lesioned than the sham-lesioned group, reflecting lower overall response rates in the lesioned group. The motivational parameter, a, was significantly higher in the STN-lesioned group than in the sham-lesioned group, consistent with enhanced reinforcer value in the STN-lesioned group compared to the sham-lesioned group. In both groups, a was sensitive to changes in reinforcer size, being significantly greater under the two-pellet condition (Phase 2) than under the one-pellet condition (Phases 1 and 3). The results suggest that destruction of the STN impairs response capacity and enhances the incentive value of food reinforcers.

Effect of disconnecting the orbital prefrontal cortex from the nucleus accumbens core on inter-temporal choice behaviour: a quantitative analysis

Previous experiments showed that destruction of the orbital prefrontal cortex (OPFC) or the nucleus accumbens core (AcbC) in rats altered choice between two delayed food reinforcers. Application of a quantitative model of inter-temporal choice suggested that lesions of either structure increased the delay-dependent degradation of reinforcer value (delay discounting); destruction of the OPFC (but not the AcbC) also increased the relative value of the larger reinforcer. This experiment examined the effect of disconnecting the OPFC from the AcbC on inter-temporal choice. Rats received excitotoxin-induced contralateral lesions of the OPFC and AcbC (disconnection), severing of the anterior corpus callosum (callosotomy), a combined lesion (disconnection+callosotomy) or sham lesions. They were trained in a discrete-trials progressive delay schedule to press levers A and B for a sucrose solution. Responses on A delivered 50 microl of the solution after a delay d(A); responses on B delivered 100 microl after a delay d(B). d(B) increased across blocks of trials; d(A) was manipulated across phases of the experiment. Indifference delay, d(B50) (value of d(B) corresponding to 50% choice of B), was estimated for each rat in each phase, and linear indifference functions (d(B50)vs. d(A)) were derived. The disconnection+callosotomy group showed a lower intercept of the indifference function (implying a higher rate of delay discounting) than the sham-lesioned group; the disconnection group showed a similar but less robust effect, whereas the callosotomy group did not differ significantly from the sham-lesioned group. The results suggest that OPFC-AcbC connections are involved in delay discounting of food reinforcers, but provide no evidence for an involvement of OPFC-AcbC connections in regulating sensitivity to reinforcer size.

Evidence for the sensitivity of operant timing behaviour to stimulation of D1 dopamine receptors

RATIONALE

Temporal differentiation of operant behaviour is sensitive to dopaminergic manipulations. Previous studies using the fixed-interval peak procedure implicated D(2)-like dopamine receptors in these effects. However, recent findings suggest that d-amphetamine alters timing performance on the free-operant psychophysical procedure via D(1)-like receptors. It is not known whether this effect of d-amphetamine is mimicked by direct D(1)-like receptor stimulation.

OBJECTIVE

The effects of a D(1)-like receptor agonist 6-chloro-2,3,4,5-tetrahydro-1-phenyl-1H-3-benzazepine (SKF-81297) on performance on the free-operant psychophysical procedure and the interaction between SKF-81297 and a D(1)-like receptor antagonist 8-bromo-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol (SKF-83566) and a D(2)-like receptor antagonist haloperidol, were examined.

MATERIALS AND METHODS

Rats were trained to respond on two levers (A and B) under a free-operant psychophysical schedule, in which sucrose reinforcement was provided intermittently for responding on A during the first half and on B during the second half of 50-s trials. Logistic psychometric functions were fitted to the relative response rate data (percent responding on B [%B] vs time from trial onset [t]) under each treatment condition, and quantitative indices of timing (T(50) [value of t corresponding to %B = 50] and the Weber fraction [(T(75)-T(25))/2T(50); T(25) and T(75) are values of t corresponding to %B = 25 and %B = 75] were compared among treatments.

RESULTS

SKF-81297 (0.8 mg kg(-1)) reduced T(50); this effect was antagonized by SKF-83566 (0.03 mg kg(-1)) but not by haloperidol (0.05, 0.1 mg kg(-1)).

CONCLUSIONS

Stimulation of D(1)-like dopamine receptors affects performance in the free-operant psychophysical procedure.

Effects of quinolinic acid-induced lesions of the nucleus accumbens core on inter-temporal choice: a quantitative analysis

RATIONALE

There is evidence that lesions of the nucleus accumbens core (AcbC) promote preference for smaller earlier reinforcers over larger delayed reinforcers in inter-temporal choice paradigms. It is not known whether this reflects an effect of the lesion on the rate of delay discounting, on sensitivity to reinforcer magnitude, or both.

AIM

We examined the effect of AcbC lesions on inter-temporal choice using a quantitative method that allows effects on delay discounting to be distinguished from effects on sensitivity to reinforcer size.

MATERIALS AND METHODS

Sixteen rats received bilateral quinolinic acid-induced lesions of the AcbC; 14 received sham lesions. They were trained under a discrete-trials progressive delay schedule to press two levers (A and B) for a sucrose solution. Responses on A delivered 50 microl of the solution after a delay d(A); responses on B delivered 100 microl after d(B). d(B) increased across blocks of trials, while d(A) was manipulated across phases of the experiment. Indifference delay d(B(50)) (value of d(B) corresponding to 50% choice of B) was estimated in each phase, and linear indifference functions (d(B(50)) vs d(A)) derived.

RESULTS

d(B(50)) increased linearly with d(A) (r(2) > 0.95 in each group). The intercept of the indifference function was lower in the lesioned than the sham-lesioned group; slope did not differ between groups. The lesioned rats had extensive neuronal loss in the AcbC.

CONCLUSIONS

The results confirm that lesions of the AcbC promote preference for smaller, earlier reinforcers and suggest that this reflects an effect of the lesion on the rate of delay discounting.

Effect of quinpirole on timing behaviour in the free-operant psychophysical procedure: evidence for the involvement of D2 dopamine receptors

RATIONALE

Operant timing behaviour is sensitive to dopaminergic manipulations. It has been proposed that this effect is mediated principally by D(2)-like dopamine receptors. However, we recently found that the effect of d-amphetamine on timing in the free-operant psychophysical procedure was mediated by D(1)-like dopamine receptors. It has not been established whether stimulation of D(2)-like receptors affects timing in this schedule.

OBJECTIVE

To examine the effects of a D(2)-like receptor agonist quinpirole on second-range timing and the ability of dopamine receptor antagonists to reverse quinpirole's effects.

MATERIALS AND METHODS

Rats responded on two levers (A and B) under a free-operant psychophysical schedule in which reinforcement was provided intermittently for responding on A during the first half, and B during the second half, of 50-s trials. Logistic functions were fitted to the relative response rates [percent responding on B (%B) vs time (t)] under each treatment; quantitative timing indices [T (50) (value of t when %B = 50) and Weber fraction] were compared among treatments.

RESULTS

Quinpirole (0.04, 0.08 mg kg(-1)) reduced T (50). This effect was attenuated by D(2)-like receptor antagonists haloperidol (0.05, 0.1 mg kg(-1)), eticlopride (0.04, 0.08 mg kg(-1)) and sulpiride (30, 60 mg kg(-1)), but not by the D(3) receptor-preferring antagonist nafadotride (0.5, 1 mg kg(-1)), the D(4) receptor antagonist L-745870 (1, 3 mg kg(-1)) or the D(1)-like receptor antagonist SKF-83566 (0.015 mg kg(-1)).

CONCLUSIONS

Results suggest that quinpirole reduced T (50) via an action at D(2) receptors. D(1)-like and D(2)-like receptors may mediate behaviourally similar but pharmacologically distinct effects on timing behaviour.

Tolerance to the effect of 2,5-dimethoxy-4-iodoamphetamine (DOI) on free-operant timing behaviour: interaction between behavioural and pharmacological mechanisms

RATIONALE

The psychostimulant d-amphetamine, the D(2/3) dopamine receptor agonist quinpirole and the 5-HT(2) receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) have similar effects on free-operant timing behaviour. There is evidence that tolerance develops to the effects of psychostimulants on timing performance during chronic treatment; this tolerance is generally attributed to behavioural adaptation rather than to pharmacological desensitisation. There have been no previous investigations of tolerance to the effect of DOI on free-operant timing behaviour.

OBJECTIVE

To demonstrate tolerance to DOI's effect on timing performance and to examine the nature of this tolerance.

MATERIALS AND METHODS

Rats were trained under the free-operant psychophysical procedure to press two levers (A and B) in 80-s trials in which reinforcement was provided intermittently for responding on A in the first half and B in the second half of the trial. Percent responding on B (%B) was recorded in successive 8-s epochs of the trials; logistic functions were fitted to the data from each rat for the derivation of timing indices (T (50) [time corresponding to %B = 50]; Weber fraction).

RESULTS

In experiment 1, DOI (0.25 mg kg(-1)) reduced T (50) compared to vehicle; tolerance to this effect was seen after repeated daily treatments with DOI if the rats were exposed to behavioural training during the period of treatment but not if the repeated treatments took place during a 'holiday' from behavioural training. In experiment 2, repeated treatment with DOI resulted in tolerance to the effect of DOI on T (50) and cross-tolerance to the effect of d-amphetamine (0.4 mg kg(-1)), but no cross-tolerance was seen to the effect of quinpirole (0.08 mg kg(-1)).

CONCLUSIONS

The results indicate that behavioural adaptation is involved in the development of tolerance to DOI's effect on timing. The finding of cross-tolerance to d-amphetamine but not to quinpirole suggests that the reduction of T (50) in the free-operant psychophysical procedure may be brought about by two distinct pharmacological mechanisms, one activated by DOI and d-amphetamine, and the other by quinpirole.

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline

BACKGROUND

A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes.

METHODS

We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme.

RESULTS

Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions.

CONCLUSIONS

Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

Effects of d-amphetamine and DOI (2,5-dimethoxy-4-iodoamphetamine) on timing behavior: interaction between D1 and 5-HT2A receptors

RATIONALE

The dopamine-releasing agent d-amphetamine and the 5-HT(2) receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) have similar effects on free-operant timing behavior. The selective D(1) dopamine receptor antagonist 8-bromo-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol (SKF-83566), but not the D(2) dopamine receptor antagonist haloperidol, can antagonize the effect of d-amphetamine, and the selective 5-HT(2A) receptor antagonist (+/-)2,3-dimethoxyphenyl-1-(2-(4-piperidine)-methanol (MDL-100907) can antagonize the effect of DOI. However, it is not known whether the effect of d-amphetamine can be reversed by MDL-100907 and the effect of DOI by dopamine receptor antagonists.

OBJECTIVE

The objective of this work is to examine the interactions of d-amphetamine and DOI with MDL-100907, SKF-83566, and haloperidol on timing performance.

MATERIALS AND METHODS

Rats (n = 12-15 per experiment) were trained under the free-operant psychophysical procedure to press two levers (A and B) in 50-s trials in which reinforcement was provided intermittently for responding on A in the first half, and B in the second half of the trial. Percent responding on B (%B) was recorded in successive 5-s epochs of the trials; logistic functions were fitted to the data from each rat for the derivation of timing indices [T (50) (time corresponding to %B = 50); Weber fraction]. Rats were treated systemically with d-amphetamine or DOI, alone and in combination with haloperidol, SKF-83566, or MDL-100907.

RESULTS

d-Amphetamine (0.4 mg kg(-1)) reduced T (50) compared to vehicle; this effect was antagonized by SKF-83566 (0.03 mg kg(-1)) and MDL-100907 (0.5 mg kg(-1)), but not by haloperidol (0.05, 0.1 mg kg(-1)). DOI (0.25 mg kg(-1)) also reduced T (50); this effect was reversed by MDL-100907 (0.5 mg kg(-1)), but not by SKF-83566 (0.03 mg kg(-1)) or haloperidol (0.05 mg kg(-1)).

CONCLUSIONS

The results suggest that both 5-HT(2A) and D(1) receptors, but not D(2) receptors, are involved in d-amphetamine's effect on timing behavior in the free-operant psychophysical procedure. DOI's effect on timing is mediated by 5-HT(2A) receptors, but neither D(1) nor D(2) receptors are involved in this effect.

Evidence for a role of D1 dopamine receptors in d-amphetamine's effect on timing behaviour in the free-operant psychophysical procedure

RATIONALE

Temporal differentiation of operant behaviour is sensitive to dopaminergic manipulations. Studies using the fixed-interval peak procedure implicated D2 dopamine receptors in these effects. Less is known about the effects of dopaminergic manipulations on temporal differentiation in other timing schedules.

OBJECTIVE

To examine the effects of a D1 antagonist,8-bromo-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol (SKF-83566), and a D2 antagonist, haloperidol, on performance on the free-operant psychophysical procedure, and the ability of these antagonists to reverse the effects of the catecholamine-releasing agent, d-amphetamine on performance. The antagonists' ability to reverse d-amphetamine-induced hyperlocomotion was also examined.

MATERIALS AND METHODS

Rats responded on two levers (A and B) under a free-operant psychophysical schedule, in which reinforcement was provided intermittently for responding on A during the first half, and B during the second half, of 50-s trials. Logistic functions were fitted to the relative response rate data (percent responding on B [%B] vs time [t]) in each treatment condition, and quantitative timing indices [T50 (value of t corresponding to %B=50) and Weber fraction] were compared among treatments. Effects of the treatments on locomotion were measured in a separate experiment.

RESULTS

SKF-83566 (0.015, 0.03, 0.06 mg kg(-1)) did not affect timing performance. Haloperidol (0.025, 0.05 mg kg(-1)) had no effect; a higher dose (0.1 mg kg(-1)) reduced T (50). d-Amphetamine (0.4 mg kg(-1)) reduced T50; this effect was antagonised by SKF-83566 but not by haloperidol. Both antagonists reduced d-amphetamine-induced hyperlocomotion.

CONCLUSIONS

The results suggest that d-amphetamine's effect on performance in the free-operant psychophysical procedure is mediated by D1 rather than D2 receptors.

Effects of 5-HT1A and 5-HT2A receptor stimulation on temporal differentiation performance in the fixed-interval peak procedure

We examined the effects of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-HT(2A/2C) receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) on performance on the fixed-interval peak procedure, and the sensitivity of these effects to 5-HT1A and 5-HT2A receptor antagonists (N-[2-(4-[2-methoxyphenyl]-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide [WAY-100635] and ketanserin). Rats were trained to press a lever for food reinforcement in 50 min sessions consisting of 32 trials in which the lever was continuously available, separated by 10 s inter-trial intervals. In 16 trials, reinforcement was delivered following the first response after 30 s had elapsed since trial onset (fixed-interval 30 s). In 16 randomly interposed (peak/probe) trials, reinforcement was omitted, and the lever remained in the operant chamber for 120 s. Response rate in probe trials was plotted against time from trial onset. Time to peak response rate (t(peak)) and the Weber fraction were derived from modified Gaussian curves fitted to each rat's data. 8-OH-DPAT (0.05 mg kg(-1)) reduced t(peak) and increased the Weber fraction; the effect on t(peak) was antagonized by WAY-100635 (0.1 mg kg(-1)). DOI (0.25 mg kg(-1)) also reduced t(peak) and increased the Weber fraction; the reduction of t(peak) was antagonized by ketanserin (2 mg kg(-1)). Stimulation of 5-HT1A and 5-HT2A receptors alters temporal differentiation in qualitatively similar ways.

Evidence that the effect of 5-HT2 receptor stimulation on temporal differentiation is not mediated by receptors in the dorsal striatum

5-HT2 receptor stimulation alters temporal differentiation in free-operant timing schedules. The anatomical location of the receptor population responsible for this effect is unknown. We examined the effect of a 5-HT2 receptor agonist and antagonists, injected systemically and into the dorsal striatum, a region that is believed to play a major role in interval timing. Rats were trained under the free-operant psychophysical procedure to press levers A and B in 50s trials in which reinforcement was provided intermittently for responding on A in the first half, and B in the second half of the trial. Percent responding on B (%B) was recorded in successive 5s epochs of the trials; logistic functions were fitted to the data from each rat to derive timing indices (T50: time corresponding to %B = 50; Weber fraction: [T75-T25]/2T50, where T75 and T25 are the times corresponding to %B = 75 and %B = 25). Systemic treatment with the 5-HT(2A/2C) receptor agonist 2,5,-dimethoxy-4-iodo-amphetamine (DOI) (0.25 mg/kg, s.c.) reduced T50; the 5-HT2A receptor antagonist MDL-100907 (0.5 mg/kg, i.p.) did not affect performance, but completely blocked the effect of DOI. DOI (1 and 3 microg) injected bilaterally into the dorsal striatum did not alter T50. The effect of systemic treatment with DOI (0.25 mg/kg, s.c.) was not altered by intra-striatal injection of MDL-100907 (0.3 microg) or the 5-HT2C receptor antagonist RS-102221 (0.15 microg). The ability of systemically administered MDL-100907 to reverse DOI's effect on T50 confirms the sensitivity of temporal differentiation to 5-HT2A receptor stimulation. The failure of intra-striatal MDL-100907 to antagonize the effects of DOI suggests that 5-HT2A receptors in the dorsal striatum are unlikely to be primarily responsible for DOI's effects on timing. Furthermore, the results provide no evidence for a role of striatal 5-HT2C receptors in DOI's effect on timing.

Comparison of the effects of clozapine and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on progressive ratio schedule performance: evidence against the involvement of 5-HT1A receptors in the behavioural effects of clozapine

RATIONALE

Performance on progressive ratio schedules has been proposed as a means of assessing the effects of drugs on the efficacy of reinforcers. A mathematical model (Killeen PR (1994) Mathematical principles of reinforcement. Behav Brain Sci 17:105-172) affords a basis for quantifying the effects of drugs on progressive ratio schedule performance. The model postulates a bitonic function relating response rate and ratio size. One parameter of the function, a, expresses the motivational effect of the reinforcer, whereas another parameter, delta, expresses the minimum time needed to execute a response, and is regarded as an index of 'motor capacity'. Previously we found that the atypical antipsychotic clozapine increased a, indicating an increase in reinforcer efficacy; a similar effect was observed with the 5-hydroxytryptamine (5-HT)(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). It has been suggested that some of clozapine's behavioural effects are mediated by agonistic action at 5-HT(1A) receptors.

OBJECTIVE

This study was conducted to compare the effects of clozapine and 8-OH-DPAT on progressive ratio schedule performance.

METHODS

Rats were trained under a time-constrained progressive ratio schedule (50-min sessions). In experiment 1, they received acute doses of clozapine (4 mg kg(-1)) and 8-OH-DPAT (100 microg kg(-1)), alone and in combination with the 5-HT(1A) receptor antagonist N-[2-(4-[2-methoxyphenyl]-1-piperazinyl)ethyl]-N-2-yridinylcyclohexanecarboxamide (WAY-100635; 30 microg kg(-1)). In experiment 2, the effects of clozapine (2, 4 and 8 mg kg(-1)) and 8-OH-DPAT (25, 50 and 100 microg kg(-1)) were compared between intact rats and rats whose 5-HTergic pathways had been ablated by 5,7-dihydroxytryptamine (5,7-DHT).

RESULTS

In both experiments, clozapine and 8-OH-DPAT increased a and delta. In experiment 1, WAY-100635 abolished the effect of 8-OH-DPAT on a and delta, but did not alter clozapine's effects on these parameters. In experiment 2, the effects of clozapine and 8-OH-DPAT did not differ between sham-lesioned and 5,7-DHT-lesioned rats.

CONCLUSIONS

The results confirm previous findings on the effects of clozapine and 8-OH-DPAT on progressive ratio schedule performance. 8-OH-DPAT's effects are probably mediated by post-synaptic 5-HT(1A) receptors; clozapine's effects are mediated by a different mechanism, which does not appear to involve 5-HT(1A) receptors and which does not depend upon an intact 5-HTergic pathway.

Effects of quipazine and m-chlorophenylbiguanide (m-CPBG) on temporal differentiation: evidence for the involvement of 5-HT2A but not 5-HT3 receptors in interval timing behaviour

RATIONALE

Temporal differentiation refers to animals' ability to regulate their behaviour during an ongoing interval. Striatal dopaminergic mechanisms are purported to be involved in temporal differentiation, and recent evidence also implicates 5-hydroxytryptaminergic (5-HTergic) mechanisms, possibly mediated by 5-HT(2A) receptors. There is evidence that 5-HT(3) receptors contribute to the regulation of dopamine release in the basal ganglia; however, it is not known whether 5-HT(3) receptor stimulation can influence temporal differentiation.

OBJECTIVE

We examined the effects of a selective 5-HT(3) receptor agonist m-CPBG, a mixed 5-HT(2A/3) receptor agonist quipazine, and selective 5-HT(3) and 5-HT(2A) receptor antagonists (MDL-72222 and ketanserin, respectively) on temporal differentiation in a free-operant psychophysical procedure.

METHODS

Twenty-four rats were trained to respond on two levers (A and B) under a free-operant psychophysical schedule, in which sucrose reinforcement (0.6 M: , 50 microl) was provided intermittently for responding on A during the first half and on B during the second half of 50-s trials. Logistic psychometric functions were fitted to the relative response rate data [percent responding on B (%B) vs time from trial onset (t)], and quantitative indices of timing performance [T (50) (value of t corresponding to %B=50), Weber fraction, and mean time of switching from A to B, S (50)] were derived.

RESULTS

Quipazine (0.5, 1, and 2 mg kg(-1)) altered timing performance, dose-dependently reducing T (50) and S (50); m-CPBG (2.5, 5, and 10 mg kg(-1)) had no significant effect. The effect of quipazine was antagonized by ketanserin (2 mg kg(-1)), but not by MDL-72222 (1 mg kg(-1)).

CONCLUSIONS

The present results provide no evidence for the involvement of 5-HT(3) receptors in temporal differentiation and indicate that the effect of quipazine on performance was mediated by 5-HT(2A) receptor stimulation. The results are consistent with previous evidence for the involvement of 5-HT(2A) receptors in interval timing behaviour.

Quantitative analysis of the effects of some "atypical" and "conventional" antipsychotics on progressive ratio schedule performance

RATIONALE

Performance on progressive ratio schedules has been proposed as a means of assessing the effects of drugs on the value or "efficacy" of reinforcers. A mathematical model affords a basis for quantifying the effects of drugs on progressive ratio schedule performance. According to this model, the relation between response rate and ratio size is described by a bitonic (inverted-U) function. One parameter of the function, alpha, expresses the motivational or "activating" effect of the reinforcer (duration of activation of responding produced by the reinforcer), whereas another parameter, delta, expresses the minimum time needed to execute a response, and is regarded as an index of "motor capacity". In a previous experiment we found that the "atypical" antipsychotic clozapine increased alpha, indicating an increase in the efficacy of a food reinforcer.

OBJECTIVE

We examined the effects of four "atypical" and four "conventional" antipsychotics on progressive ratio schedule performance.

METHODS

Rats responded for a sucrose reinforcer (0.6 M, 50 microl) on a time-constrained progressive ratio schedule (50-min sessions). After 90 preliminary training sessions, they received acute doses of antipsychotics (doses in mg kg(-1)): atypical: clozapine (2, 4, 8, IP; n=15), quetiapine (1.25, 2.5, 5, 10, SC; n=23), olanzapine (0.25, 0.5, 1, IP; n=15), ziprasidone (0.625, 1.25, 2.5, IP, n=15); conventional: haloperidol (0.025, 0.05, 0.1, IP, n=15), pimozide (0.125, 0.25, 0.5, IP; n=15), raclopride (0.25, 0.5, 1, SC; n=12), cis-flupenthixol (0.2, 0.4, 0.8, SC; n=15). Values of a and delta were estimated from the response rate functions obtained under each treatment condition, and were compared between drug and vehicle-alone treatments.

RESULTS

The atypical antipsychotics significantly increased alpha (indicating enhancement of reinforcer efficacy), and also increased delta (indicating reduction of motor capacity). Haloperidol, pimozide and raclopride significantly increased delta; none of the conventional antipsychotics significantly altered alpha.

CONCLUSIONS

The results extend previous findings with clozapine to other atypical antipsychotics and suggest that enhancement of the efficacy of reinforcers may be a common feature of atypical antipsychotics not shared by conventional antipsychotics.

Effects of quipazine and m-chlorophenylbiguanide (m-CPBG) on the discrimination of durations: evidence for the involvement of 5-HT2A but not 5-HT3 receptors

The ability of rats to discriminate durations of exteroceptive stimuli is disrupted by 5-HT(1A) receptor agonists; it is not known whether temporal discrimination is sensitive to stimulation of other 5-HT receptor subtypes. We examined the effect of quipazine, a 5-HT receptor agonist with nanomolar affinity for 5-HT(3) receptors and micromolar affinity for 5-HT(2A) receptors, and m-chlorophenylbiguanide (m-CPBG), a selective 5-HT(3) receptor agonist, on temporal discrimination. Twenty-four rats pressed levers for sucrose reinforcement under a discrete-trials psychophysical procedure. In each 50-s trial, a light was presented for t s, following which two levers (A and B) were presented. A response on A was reinforced if t < 25 s, and a response on B if t > 25 s. Logistic psychometric functions were fitted to the data, and timing parameters estimated (T(50): value of t corresponding to %B = 50; Weber fraction: [T(75)-T(25)]/2T(50), where T(75) and T(25) are values of t corresponding to %B = 75 and %B = 25). Quipazine (0.5-2 mg/kg) displaced the psychometric curve to the right and reduced its slope, reflected in increases in T50 and the Weber fraction; m-CPBG (2.5-10 mg/kg) had no effect. The effects of quipazine were reversed by the 5-HT(2A) receptor antagonist ketanserin (2 mg/kg) but not by the 5-HT3 receptor antagonist topanyl 3,5-dichlorobenzoate (MDL-72222) (1 mg/kg). The results indicate that 5-HT(2A) but not 5-HT(3) receptor stimulation disrupts temporal discrimination.