Behaviour of Humans in Concurrent Schedules Programmed on Spatially Separated Operanda

Six human subjects responded on either of two levers for monetary reinforcement in a continuous choice situation. Responses on one lever (lever A) were reinforced at different frequencies specified by five variable-interval schedules. Reinforcements for responding on the other lever (lever B) were delivered according to a variable-interval schedule of standard reinforcement frequency. Results indicated that absolute response rate on lever A increased, while absolute response rate on lever B decreased as a function of reinforcement frequency for lever A. In terms of preference, the data conformed closely to Baum's (1974) generalized matching equation. Performances departing from perfect matching were obtained in four cases, but these deviations were not systematic either in the direction of overmatching or undermatching.

Behaviour of Rats in Multiple Schedules of Response-Contingent and Response-Independent Food Presentation

During Phase I, three rats were exposed to two-component multiple schedules of response-independent food presentation. Low rates of lever-pressing were observed, and response rates in one component did not increase when food presentation was withheld in the other component. During Phase II, the same rats were exposed to two-component multiple schedules of response-contingent reinforcement. Much higher rates of lever-pressing were observed. Moreover, when reinforcement was withheld in one component, response rates in the other component increased (positive contrast), and when reinforcement was reinstated in the changed component, response rates in the other component declined (negative contrast). During Phase III, when food was again delivered independently of responding, the response rates declined again to low levels. These results indicate that the occurrence of non-instrumental lever-pressing is not a prerequisite for the occurrence of behavioural contrast in the rat, and thus cast doubt on the general applicability of the autoshaping theory of behavioural contrast

Matching in Multiple Schedules Using Long Component Durations

The performance of 3 rats in multiple variable-interval variable-interval schedules, employing 10-min. component durations, conformed to Herrnstein's Matching Law.

Accounting for the impact of conservation on human well-being

Conservationists are increasingly engaging with the concept of human well-being to improve the design and evaluation of their interventions. Since the convening of the influential Sarkozy Commission in 2009, development researchers have been refining conceptualizations and frameworks to understand and measure human well-being and are starting to converge on a common understanding of how best to do this. In conservation, the term human well-being is in widespread use, but there is a need for guidance on operationalizing it to measure the impacts of conservation interventions on people. We present a framework for understanding human well-being, which could be particularly useful in conservation. The framework includes 3 conditions; meeting needs, pursuing goals, and experiencing a satisfactory quality of life. We outline some of the complexities involved in evaluating the well-being effects of conservation interventions, with the understanding that well-being varies between people and over time and with the priorities of the evaluator. Key challenges for research into the well-being impacts of conservation interventions include the need to build up a collection of case studies so as to draw out generalizable lessons; harness the potential of modern technology to support well-being research; and contextualize evaluations of conservation impacts on well-being spatially and temporally within the wider landscape of social change. Pathways through the smog of confusion around the term well-being exist, and existing frameworks such as the Well-being in Developing Countries approach can help conservationists negotiate the challenges of operationalizing the concept. Conservationists have the opportunity to benefit from the recent flurry of research in the development field so as to carry out more nuanced and locally relevant evaluations of the effects of their interventions on human well-being.

Phase II randomised proof-of-concept study of the urokinase inhibitor upamostat (WX-671) in combination with gemcitabine compared with gemcitabine alone in patients with non-resectable, locally advanced pancreatic cancer

Background:

To evaluate the efficacy and tolerability of the urokinase plasminogen activator (uPA) inhibitor upamostat in combination with gemcitabine in locally advanced pancreatic adenocarcinoma (LAPC).

Methods:

Within a prospective multicenter study, LAPC patients were randomly assigned to receive 1000 mg m⁻² of gemcitabine IV weekly either alone (arm A) or in combination with 200 mg (arm B) or 400 mg (arm C) oral upamostat daily. Efficacy endpoints of this proof-of-concept study included response rate, time to first metastasis, progression-free and overall survival (OS).

Results:

Of the 95 enroled patients, 85 were evaluable for response and 93 for safety. Median OS was 12.5 months (95% CI 8.2–18.2) in arm C, 9.7 months (95% CI 8.4–17.1) in arm B and 9.9 months (95% CI 7.4–12.1) in arm A; corresponding 1-year survival rates were 50.6%, 40.7% and 33.9%, respectively. More patients achieved a partial remission (confirmed responses by RECIST) with upamostat combination therapy (arm C: 12.9% arm B: 7.1% arm A: 3.8%). Overall, only 12 patients progressed by developing detectable distant metastasis (arm A: 4, arm B: 6, arm C: 2). The most common adverse events considered to be related to upamostat were asthenia, fever and nausea.

Conclusion:

In this proof-of-concept study targeting the uPA system in LAPC, the addition of upamostat to gemcitabine was tolerated well; similar survival results were observed for the three treatment arms.

Abstract P5-20-01: A randomized double-blind phase II study of the combination of oral WX-671 plus capecitabine vs. capecitabine monotherapy in first-line HER2− negative metastatic breast cancer (MBC)

Background: uPA and its inhibitor PAI-1 play a key role in tumor invasion, metastasis and tumor growth. High levels of uPA and PAI-1 in breast tumors are statistically significant prognostic factors of disease-free (DFS) and overall survival (OS), which were validated at the highest level of evidence, as well as predictors for benefit of adjuvant chemotherapy. WX-UK1 is an active site competitive inhibitor of uPA with an inhibition constant in the submicromolar range. WX-671 (upamostat) is an oral prodrug of WX-UK1. In preclinical animal tumor models, both WX-UK1 and WX-671 have been shown to reduce the growth rate of implanted tumors, to inhibit invasion, and reduce metastases. This current proof of concept study is designed to substantiate the anti-metastatic properties of upamostat for patients appropriate for first line therapy for MBC.

Methods: Female patients aged >18, with HER2 negative MBC appropriate for first line monotherapy with capecitabine, with adequate performance status, organ function, bone marrow reserve without brain metastases were eligible. Patients were randomized in a double-blind fashion to receive upamostat (200mg orally daily for 21 days) plus capecitabine (1000 mg/m2 orally twice daily for 14 days) vs. capecitabine (1000 mg/m2 orally twice daily for 14 days) in 3 week treatment cycles until progressive disease or unacceptable toxicity. The primary endpoint is to evaluate the efficacy of the combination of upamostat plus capecitabine compared to monotherapy as assessed by comparison of progression free survival. The secondary objectives are OS, objective response rates, safety and tolerability, and to assess the pharmacokinetics (PK) of upamostat and capecitabine when combined.

Results: Between August 2008 and April 2011,132 patients were enrolled. 17 patients are still receiving treatment. 26% of the patients are characterized as triple negative, 13% as only Estrogen Receptor (ER) positive and 4% as only Progesteron Receptor (PR) positive. 57 % of the patients are ER and PR positive.

Conclusions: Progression free survival, response rates and safety will be reported. This abstract is being submitted as a placeholder. A completed abstract will be submitted when the analyses are completed.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-20-01.

Effect of variable-interval punishment on the behavior of humans in variable-interval schedules of monetary reinforcement

One male and three female human subjects pressed a button for monetary reinforcement under a range of variable-interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtraction of money) according to a variable-interval 170-second schedule. In the absence of punishment, the rate of responding was an increasing negatively accelerated function of reinforcement frequency, as predicted by Herrnstein's equation. The effect of the punishment schedule was to suppress responding under lower frequencies of reinforcement; responding under higher reinforcement frequencies was much less affected. This was reflected in an increase in the value of K(H) (the constant expressing the reinforcement frequency corresponding to the half-maximal response rate), whereas there was no significant change in the value of R(max) (the constant expressing the maximum response rate). Previous results had shown that variable-ratio punishment resulted in a change in the values of both constants (Bradshaw, Szabadi, and Bevan, 1977). The results of the present study were consistent with the concept that the suppressive effects of punishment on responding depend on the nature of the punishment schedule.

Relationship between response rate and reinforcement frequency in variable-interval schedules: the effect of the concentration of sucrose reinforcement

Four rats were exposed to variable-interval schedules specifying a range of different reinforcement frequencies, using sucrose of two different concentrations and distilled water as the reinforcer. With sucrose, the rates of responding of all four rats were increasing negatively accelerated functions of reinforcement frequency, the data conforming closely to Herrnstein's equation; this was also true of the data from three of the four rats when distilled water was used as the reinforcer. The values of both constants in Herrnstein's equation were related to the sucrose concentration: the asymptotic response rate decreased, and the reinforcement frequency corresponding to the half-maximal response rate increased, with decreasing sucrose concentration.

The effect of punishment on free-operant choice behavior in humans

During Phase I, three female human subjects pressed a button for monetary reinforcement in five variable-interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtracting money) according to a variable-ratio 34 schedule. In the absence of punishment, response rates conformed to Herrnstein's equation for single variable-interval schedules. Punishment suppressed responding at all frequencies of reinforcement. This was reflected in a change in the values of both constants in Herrnstein's equation: the value of the theoretical maximum response-rate parameter was reduced, and the parameter describing the reinforcement frequency corresponding to the half-maximal response rate was elevated. During Phase II, the same five schedules (A) were in operation (without punishment), but in addition, a concurrent variable-interval schedule (B) of standard reinforcement frequency was introduced. On alternate days, responding in Component B was punished according to a variable-ratio 34 schedule. In the absence of punishment, absolute response rates conformed to equations proposed by Herrnstein to describe performance in concurrent schedules; the ratios of the response rates in the two components and the ratios of the times spent in the two components conformed to the Matching Law. When responding in Component B was punished, response rates in Component B were reduced and those in Component A were elevated, these changes being reflected in distortions of the matching relationship.

Behavior of humans in variable-interval schedules of reinforcement

During Phase I, human subjects pressed a button for monetary reinforcement in five variable-interval schedules, each of which specified a different frequency of reinforcement. The rate of responding was an increasing, negatively accelerated function of reinforcement frequency; the data conformed closely to Herrnstein's equation. During Phase II, the same five schedules were in operation, but in addition a concurrent variable-interval schedule (B) was introduced, responses on which were always reinforced at the same frequency. Response rate in component A increased while the response rate in B decreased, as a function of the reinforcement frequency in component A. Relative response rates in the two component schedules matched the relative frequencies of reinforcement. Comparing the absolute response rates in component A during Phase I and Phase II it was found that introduction of the concurrent schedule did not affect the value of the theoretical maximum response rate, but did increase the value of the reinforcement frequency needed to obtain any particular submaximal response rate.

The effect of signaled reinforcement availability on concurrent performances in humans

During Phase I, three female human subjects pressed a button for monetary reinforcement in two-component concurrent variable-interval schedules. Five different reinforcement frequencies were used in component A, whereas the reinforcement frequency in component B was held constant. Absolute rates of responding conformed to equations proposed by Herrnstein to describe concurent performances, and the ratios of the response rates and the times spent in the two components conformed to the matching law. During Phase II, the availability of reinforcement in component A was signaled by the illumination of a lamp. This resulted in suppression of response rates in component A and elevation of response rates in component B, these changes being reflected in a distortion of the matching relationship which took the form of a bias in favor of component B.

Effect of punishment on human variable-interval performance

Three female human subjects pressed a button for monetary reinforcement in a range of variable-interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtracting money) according to a variable-ratio 34 schedule. In the absence of punishment, rate of responding was an increasing negatively accelerated function of reinforcement frequency; the relationship between response rate and reinforcement frequency conformed to Herrnstein's equation. The effect of the punishment schedule was to suppress responding at all frequencies of reinforcement. This was reflected in a change in the values of both constants in Herrnstein's equation: the value of the theoretical maximum response-rate parameter was reduced, while the parameter describing the reinforcement frequency corresponding to the half-maximal response rate was increased.

A Phase I pharmacokinetic (PK) study of single dose oral therapy with a uPA inhibitor (WX-671)

13091

Background: WX-671 is an orally available prodrug of WX-UK1, a serine protease inhibitor that inhibits uPA as well as other serine proteases. WX-UK1 (Setyono-Han et al., Thromb Haemost 2005) and WX-671 have shown to efficiently reduce primary tumor growth and metastasis formation in a variety of animal models. First PK and safety data of the prodrug WX-671 were obtained in healthy volunteers. Methods: Male healthy volunteers received WX-671 as hydrogen sulfate given as single oral doses corresponding to 50, 100, 200 and 400 mg WX-671 free base. Each subject received two single doses, the first dose pre-prandially and the second dose one week later post-prandially. PK profiles were obtained over 48h for both the prodrug WX-671 and the active metabolite WX-UK1. Safety was assessed by measuring vital signs, laboratory parameters (hematology, blood chemistry, coagulation) and ECGs. Results: 16 healthy male volunteers were included, four per dose level. Both the Cmax levels as well as the plasma AUCs of both WX-671 and WX-UK1 were overproportionally related with dose levels. Administration with food slightly increased AUCs at the two higher doses. Terminal phase half life was fairly constant for WX-671 at all doses (approximately 5.8 h) and for WX-UK1 at least in the two highest dose groups with 17–21 h. Four subjects out of 16 (25%) experienced a total number of 11 adverse events. These events were nervous system disorders (headache, 7 events) and gastrointestinal disorders (diarrhea, 2 events; flatulence, 2 events). All adverse events occurred at the lower dose levels of 50 mg and 100 mg WX-671. No adverse events were observed at the dose levels of 200 and 400 mg WX-671. All adverse events were rated as mild and all subjects completely recovered within a maximum time period of 18h. Conclusions: The administration of oral doses of WX-671 (as hydrogen sulfate) resulted in the formation of WX-UK1 in the plasma uniformly across all individuals. At all dose levels tested, WX-671 was well tolerated systemically as judged by assessment of vital signs, ECG, general safety laboratory and coagulation data as well as by adverse event profiles. Two phase I PK and safety studies with daily dosing over 15 days at the above tested dose levels are currently ongoing, one in healthy volunteers and the other in patients.

[Table: see text]

Ensembl 2004

The Ensembl (http://www.ensembl.org/) database project provides a bioinformatics framework to organize biology around the sequences of large genomes. It is a comprehensive and integrated source of annotation of large genome sequences, available via interactive website, web services or flat files. As well as being one of the leading sources of genome annotation, Ensembl is an open source software engineering project to develop a portable system able to handle very large genomes and associated requirements. The facilities of the system range from sequence analysis to data storage and visualization and installations exist around the world both in companies and at academic sites. With a total of nine genome sequences available from Ensembl and more genomes to follow, recent developments have focused mainly on closer integration between genomes and external data.

Ensembl 2002: accommodating comparative genomics

The Ensembl (http://www.ensembl.org/) database project provides a bioinformatics framework to organise biology around the sequences of large genomes. It is a comprehensive source of stable automatic annotation of human, mouse and other genome sequences, available as either an interactive web site or as flat files. Ensembl also integrates manually annotated gene structures from external sources where available. As well as being one of the leading sources of genome annotation, Ensembl is an open source software engineering project to develop a portable system able to handle very large genomes and associated requirements. These range from sequence analysis to data storage and visualisation and installations exist around the world in both companies and at academic sites. With both human and mouse genome sequences available and more vertebrate sequences to follow, many of the recent developments in Ensembl have focusing on developing automatic comparative genome analysis and visualisation.

Phase I trial of XR9576 in healthy volunteers demonstrates modulation of P-glycoprotein in CD56+ lymphocytes after oral and intravenous administration

XR9576 is a novel inhibitor of P-glycoprotein (P-gp) that has been shown to reverse P-gp-dependent multidrug-resistance in tumor cell lines and tumor-bearing animals. Here we report the first i.v. and p.o. administration to healthy volunteers of XR9576 in dose-escalating studies with the aim of investigating its effects on safety, its pharmacokinetics, and a surrogate marker of efficacy. XR9576 was administered as a single dose-upward titration of 0.1, 0.2, 0.5, 1.0, and 2 mg/kg XR9576 i.v. or 50, 100, 200, 500, and 750 mg/volunteer p.o. The surrogate marker for in vivo efficacy examined the accumulation of the P-gp substrate Rhodamine-123 (Rh-123) in P-gp-expressing CD56+ lymphocytes by flow cytometry. Addition of Rh-123 to blood samples from subjects given XR9576 or a placebo demonstrated drug-dependent modulation of P-gp activity. Even at the lowest doses, significant effects were observed on Rh-123 accumulation in CD56+ cells. Maximal effects were seen during the i.v. infusion or 4-6 h after oral administration. As the dose was increased, a concomitant rise in the level and duration of P-gp blockade was observed. A dose of 2.0 mg/kg i.v. and > or = 200 mg/volunteer p.o. gave approximately 100% inhibition of P-gp for in excess of 24 h. All doses of XR9576 were well tolerated. Inhibition increased with XR9576 plasma concentration, and maximal activity was achieved at 150-200 ng/ml XR9576. In conclusion, XR9576 has demonstrated sustained inhibition of P-gp after i.v. and oral administration and, supported by the elimination half-life of about 24 h, XR9576 is being taken into Phase II as a once-daily agent.

Reversal of P-glycoprotein-mediated multidrug resistance by XR9051, a novel diketopiperazine derivative

XR9051 (N-(4-(2-(6,7-Dimethoxy-1,2,3,4-tetrahydro-2-isoquinolyl)ethyl)phe nyl)-3-((3Z,6Z)-6-benzylidene-1-methyl-2,5-dioxo-3-pipera zinylidene) methylbenzamide) was identified as a potent modulator of P-glycoprotein-mediated multidrug resistance (MDR) following a synthetic chemistry programme based on a natural product lead compound. The activity of XR9051 was determined using a panel of human and murine drug-resistant cell lines (H69/LX4, 2780AD, EMT6/AR 1.0, MC26 and P388/DX Johnson). XR9051 was able to reverse resistance to a variety of cytotoxic drugs, including doxorubicin, etoposide and vincristine, which are associated with classical MDR. At a concentration of 0.3-0.5 microM, XR9051 was able to fully sensitize resistant cells to cytotoxics, whereas little or no effect was observed on the corresponding parental cell lines. No effect of XR9051 was observed on the response of cells to non-MDR cytotoxics such as methotrexate and 5-fluorouracil. XR9051 was consistently more potent than cyclosporin A (CsA) and verapamil (Vpm) in all assays used. XR9051 inhibited the efflux of [3H]daunorubicin from preloaded cells and, unlike CsA and Vpm, remained active for several hours after removal of resistance-modifying agent. In photoaffinity labelling experiments employing [3H]azidopine, XR9051 was able to displace binding to P-glycoprotein. In binding studies using [3H]vinblastine, XR9051 was shown to be a potent inhibitor of the binding of the cytotoxic to P-glycoprotein (EC50 = 1.4 +/- 0.5 nM). Taken together, the results indicate that XR9051 reverses the MDR phenotype through direct interaction with P-glycoprotein.

Novel low-molecular-weight inhibitor of PAI-1 (XR5118) promotes endogenous fibrinolysis and reduces postthrombolysis thrombus growth in rabbits

BACKGROUND

Elevated levels of plasminogen activator inhibitor 1 (PAI-1) have been associated with the occurrence of thrombotic disease, and inhibition of PAI-1 activity in vivo resulted in enhanced thrombolysis and a reduction in reocclusion. Besides monoclonal antibodies and peptides, no suitable agents that are able to block PAI-1 activity are available to date. The present study was designed to test the interaction between a nonantibody, nonpeptide, diketopiperazine-based inhibitor of PAI-1, XR5118, and PAI-1 and to assess the effect of XR5118 on PAI-1 activity in vitro and on in vivo thrombolysis and thrombus growth in an experimental thrombosis model in rabbits.

METHODS AND RESULTS

The binding site of XR5118 on the PAI-1 molecule was studied by competitive binding experiments with mapped anti-PAI-1 monoclonal antibodies by use of surface plasmon resonance experiments. XR5118 selectively and competitively inhibited binding of the PAl-1-inhibiting monoclonal antibody CLB-2C8, indicating that binding of XR5118 to PAI-1 takes place at the area between amino acids 110 and 145 of the PAI-1 molecule, which is known to be involved with the binding of PAI-1 to tissue plasminogen activator (TPA). Incubation of plasma or platelet releasate with XR5118 resulted in a dose-dependent inhibition of PAI-1 activity. Systemic infusion of XR5118 induced a significant reduction in plasma PAI-1 activity levels from 23.7+/-4.9 to 10.9+/-3.4 IU/mL. Administration of XR5118 resulted in a significant, twofold increase in endogenous thrombolysis compared with the control. Thrombus growth in rabbits receiving both XR5118 and rTPA was significantly attenuated compared with rabbits receiving rTPA alone (13.5+/-2.7% versus 19.9+/-3.8%, respectively).

CONCLUSIONS

XR5118 binds to PAI-1 and reduces plasma PAI-1 activity levels. Furthermore, XR5118 promotes endogenous thrombolysis and inhibits thrombus accretion and is the first nonpeptide compound with significant anti-PAI-1 activity in vivo in these models.

Regulation of neuronal and recombinant GABA(A) receptor ion channels by xenovulene A, a natural product isolated from Acremonium strictum

Xenovulene A (XR368) is a natural product exhibiting little structural resemblance with classical benzodiazepines yet is able to displace high-affinity ligand binding to the benzodiazepine site of the gamma-aminobutyric acid (GABA)A receptor. We have characterized this compound and an associated congener (XR7009) by use of radioligand binding and electrophysiological methodologies with native neurons and the Xenopus oocyte expression system. Xenovulene A, and the more potent XR7009, inhibited [3H]flunitrazepam binding to rat forebrain with Ki values of 7 and 192 nM, and 1.7 and 42 nM, respectively, each site accounting for approximately 50% of the total specific binding. In cerebellar and spinal cord membranes, these ligands identified only single binding sites. These ligands demonstrated no intrinsic agonist activity at recombinant GABA(A) receptors comprising alpha1beta1gamma2S subunits expressed in Xenopus oocytes, yet at 1 microM both significantly potentiated the GABA-induced response and reduced the GABA EC50 from 10.9 (control) to 5.1 (Xenovulene A) or 2.7 microM (XR7009). The rank potency order for enhancement of the 10 microM GABA response is: XR7009 (EC50, 0.02 microM) > diazepam (0.03) > Xenovulene A (0.05) > flurazepam (0.17). The activity of XR368 and XR7009 was reduced by the benzodiazepine antagonist, flumazenil, and absent in receptors devoid of the gamma2 subunit. These agents exhibited receptor subtype selectivity because alpha3beta1gamma2S receptors were less sensitive to these compounds relative to alpha1 subunit-containing receptors, whereas alpha6beta1gamma2S receptors were completely insensitive. Potentiation of the response to GABA on native GABA(A) receptors in cortical neurons substantiates the profile of the novel structures of Xenovulene A and XR7009 as specific benzodiazepine agonists.

Evaluation of a low molecular weight modulator of human plasminogen activator inhibitor-1 activity

A critical component in the regulation of thrombus formation and clearance is the balance between tissue plasminogen activator (tPA) and plasminogen activator inhibitor type-1 (PAI-1). An increase in the plasma concentration of PAI-1 has been proposed as a risk factor in thrombotic disease. Inhibition of PAI-1 activity may have utility in the treatment of thromboembolic disease. We report here the evaluation of three diketopiperazine-based low molecular weight inhibitors of PAI-1 activity (XR334, XR1853 and XR5082). In vitro these compounds reversed the inhibitory effects of PAI-1 against both tPA and urokinase (UK) (IC50: 5 to 80 muM). In contrast, other serpin-serine protease interactions, including alpha 1-antitrypsin-trypsin, alpha 2-antiplasmin- plasmin and antithrombin-thrombin, were not affected, neither did these inhibitors affect global tests of haemostasis. In the light of this promising in vitro profile these compounds were evaluated in a standard radioisotopic assay of clot lysis in whole rat blood following intravenous administration. In this assay these compounds dose-dependently enhanced fibrinolysis ex vivo. After intravenous bolus administration XR334, XR1853 and XR5082 at 5 mg/kg increased clot lysis by 32.0 +/- 5.1% SEM (n = 25, p < 0.01), 36.7 +/- 3.5% SEM (n = 36, p < 0.01) and 60.0 +/- 2.8% SEM (n = 17, p < 0.01) respectively compared to vehicle. Intravenous infusion of these compounds (1 mg/kg/min for 20 min) significantly prolonged (approximately twofold) the time to blood vessel occlusion in the rat electrically-stimulated carotid artery thrombosis model. Thus, these low molecular weight inhibitors of PAI-1 activity enhanced fibrinolysis ex vivo and protected against thrombus formation in the rat.

Identifying small-molecule lead compounds: the screening approach to drug discovery

A number of new technologies that enable high-throughput, cost-effective screening of potential drug candidates have been developed in recent years. Such compounds may be derived from the large proprietary collections held by pharmaceutical companies, from new synthetic approaches such as combinatorial chemistry, or from natural sources. The latter remain a major source of new chemicals: many are already used in human treatment and many others are currently undergoing evaluation as the potential medicines of the future.

Evidence that the novel antihypertensive agent, flesinoxan, causes differential sympathoinhibition and also increases vagal tone by a central action

The effects of flesinoxan were studied on thoracic preganglionic, splanchnic and renal sympathetic nerve activity, carotid sinus nerve activity, blood pressure and heart rate in anaesthetised cats. In some experiments femoral or renal arterial conductance was also recorded. Flesinoxan (3-300 micrograms kg-1) caused a dose-related fall in blood pressure and heart rate and also caused sympathoinhibition. This fall in blood pressure was not associated with changes in femoral arterial conductance but was with a large increase in renal arterial conductance. In this respect flesinoxan had a greater sympathoinhibitory action on the renal nerve compared with the other sympathetic outflows. The bradycardia was unaffected by the 5-HT3 antagonist, MDL 72222, but was reversed by atropine and was abolished in bi-vagotomised cats. Flesinoxan also caused sympathoinhibition in bi-vagotomised cats and decreased carotid sinus nerve activity and blood pressure. It is concluded that flesinoxan acts centrally to cause sympathoinhibition and an increase in vagal tone.

Flesinoxan lowers blood pressure and heart rate in cats via 5-HT1A receptors

Flesinoxan, a new phenylpiperazine derivative has been shown to lower blood pressure in different species after both oral and i.v. administration. The present study shows that the hypotensive potency of flesinoxan in anaesthetised cats increased 35 times after administration via the vertebral arteries compared to i.v. administration. These results, which were confirmed by intracisternal administration, point strongly to a central site of action. Haemodynamic studies indicated that the blood pressure reduction in anaesthetised cats was mainly due to a reduction in the total peripheral resistance and only to some extent to a reduced cardiac output. Flesinoxan seems not to affect sympathetic function by a peripheral mechanism. Its cardiovascular profile can be explained by a centrally mediated reduction of sympathetic tone and increase in vagal tone. Receptor binding studies indicated that flesinoxan is a very potent and selective 5-HT1A ligand. The decreases in blood pressure and heart rate induced by centrally administered flesinoxan and 8-OH-DPAT, could be antagonized effectively by the putative 5-HT1A antagonist pindolol. This suggests a relationship between blood pressure reduction and central 5-HT1A receptors.

An in vitro mature spinal cord preparation from the rat

The preparation of an isolated hemisected spinal cord preparation, maintained in vitro, from mature (180-300 g body weight) rats is described. Sacral and coccygeal segments (S2-Co1) gave consistent ventral root reflexes (DR-VRP) from electrical stimulation of dorsal roots. The mean latency and amplitude of the fastest component in the ventral root reflex, at 25 degrees C, were 1.6 msec +/- 0.4 SE mean and 8.2 mV +/- 0.9 SE mean, respectively (28 preparations). This component was resistant to the NMDA antagonist, 2-amino-5-phosphonopentanoate (AP5) but was depressed markedly by kynurenate. A slow component of the ventral root reflex, which was sensitive to AP5 was enhanced and spontaneous AP5-sensitive synaptic potentials sensitive to AP5 appeared in the absence of magnesium ions. The excitant amino acids L-aspartate, L-glutamate, N-methyl-D-aspartate (NMDA), kainate and quisqualate produced dose-dependent depolarizing responses in the ventral roots. The relative depolarizing potencies +/- SE mean (N) of NMDA, kainate and quisqualate, relative to L-glutamate = 1, were 96 +/- 30 (6), 234 +/- 57 (6) and 145 +/- 40 (5), respectively. These properties, apart from reduced latency of synaptic responses, are similar to those described previously for preparations from immature animals. However, it will be easier with the mature preparation to selective activate high and low threshold primary afferents.

Effect of muscarinic ligands on the electrical activity recorded from the hippocampus: a quantitative approach

The electrical activity of the hippocampus was recorded from the CA 1 region in rats anaesthetized with halothane and the effects of compounds assessed following their intravenous injection. Quantification of the effects was achieved following on-line fast Fourier transformation of the signal. The electrical activity recorded from the hippocampus of the halothane-anaesthetized rat demonstrated identical characteristics to that recorded from the freely-moving animal. Three types of activity could be distinguished: rhythmical slow wave activity (RSA or theta); large amplitude slow wave activity (LIA); and small amplitude fast wave activity. Muscarinic agonists induced RSA with a consequent reduction in power. The effects were dose-dependent and were reversibly antagonized by scopolamine, but not methyl-scopolamine, indicating that the effects are mediated centrally by muscarinic receptors. The results show that, in halothane anaesthetized rats, a muscarinic RSA occurs which is unrelated to movement or behavioural arousal.

[3H]Oxotremorine-M binding to membranes prepared from rat brain and heart: Evidence for subtypes of muscarinic receptors

[3H]Oxotremorine-M has been used as a ligand to label muscarinic binding sites on membranes prepared from rat fore-brain and heart. In rat brain membranes, two binding sites could be identified: a high affinity low capacity site and a low affinity high capacity site. In contrast, only a high affinity site could be labelled in heart membranes. The potency order of agonists for the high affinity site in brain membranes and heart membranes was the same, suggesting that these binding sites represent the same subtype of muscarinic receptors. However, the affinity of pirenzepine for the brain high affinity site was higher than that for the heart high affinity site suggesting that these sites may represent different receptor populations. The potency order of agonists for the high affinity and low affinity sites in brain membranes were significantly different suggesting that these binding sites represent pharmacologically distinct binding sites. GTP abolished the high affinity sites in heart and brain membranes, but the low affinity site in brain membranes appeared unaffected. These results are consistent with the hypothesis proposing subtypes of muscarinic receptors.

beta-RTX. A receptor-active protein from Russell's viper (Vipera russelli russelli) venom

A single chain polypeptide, termed beta-RTX, with an apparent Mr = 9600 has been isolated from the venom of Vipera russelli russelli. It was purified by cation exchange chromatography, followed by preparative isoelectric focusing and chromatofocusing. Purity was confirmed by gel filtration, high performance liquid chromatography, gel electrophoresis, and analytical ultracentrifugation. Amino acid analysis revealed the presence of eight half-cystines, one being located at the NH2 terminus, which are linked to form four intramolecular disulfide bridges. Chromatofocusing revealed some microheterogeneity yielding three isoforms with pI values of 9.3, 9.37, and 9.48, respectively. In its native configuration, beta-RTX was not susceptible to tryptic degradation but was readily digested after reduction and alkylation. beta-RTX possesses weak phospholipase A2 activity and competes with the binding of monoamines and opiate ligands to their respective receptors. No binding to histamine, gamma-aminobutyric acid, benzodiazepine, or muscarinic receptors was observed. In vivo, whereas 100 micrograms/kg intravenous beta-RTX seemed to be without apparent effects in the rat, 10 ng/kg beta-RTX injected intracerebroventricularly caused marked sedation, with full recovery within 3 h.

Repeated apomorphine treatment causes behavioural supersensitivity and dopamine D2 receptor hyposensitivity

This study reports the changes in the behavioural responsiveness of rats in the "Ungerstedt Model' following repeated injections of apomorphine. The changes in striatal [3H]haloperidol binding coincident with the behavioural responses are also estimated. Following unilateral lesions of the substantia nigra, the number of [3H]haloperidol binding sites in the ipsilateral striatum increase, and this effect correlates with the behavioural effect following a single apomorphine injection. Repeated apomorphine treatment, however, results in a decrease of neuroleptic binding sites in the ipsilateral and contralateral striatum accompanied by increased behavioural responses. Thus repeated apomorphine treatment discriminates the receptor mechanisms involved in the behavioural response from those receptors labelled by neuroleptics.

Visual sensitivity to two-dimensional spatial phase

We investigate some limits to phase processing in the human visual system with two-dimensional textured images. Results indicate that, although phase sensitivity increases with contrast and energy components of the image, observers cannot discriminate between images and their 45 degrees phase-quantized versions under brief exposure and lower- (less than or equal to 30%) contrast conditions. These results seem to be frequency independent although modulated by different energy levels at each two-dimensional frequency band. Finally, we have analyzed some past texture-discrimination results that occur under identical amplitude-spectra conditions. Here also phase-quantization differences seem to constitute an adequate explanation of discrimination performance.

The action of microelectrophoretically applied (3,4-dihydroxy-phenylamino)-2-imidazoline (DPI) on single cortical neurones

1. The technique of microelectrophoresis was used in order to compare the actions of the imidazoline derivative, (3,4-dihydroxy-phenylamino)-2-imidazoline (DPI), with those of dopamine and phenylephrine on single neurones in the cerebral cortex of the rat anaesthetized with halothane. 2. DPI and phenylephrine were almost exclusively excitatory, whereas dopamine could evoke both excitatory and depressant responses. 3. In the case of excitatory responses, DPI appeared to be more potent than dopamine, and was approximately equipotent with phenylephrine. 4. The dopamine antagonist, haloperidol, could discriminate between excitatory responses to DPI and dopamine: responses to dopamine were abolished, whereas responses to DPI, and to a control agonist, acetylcholine, were unaffected. 5. The alpha-adrenoceptor antagonist, phenoxybenzamine, antagonized equally excitatory responses to DPI and phenylephrine. Responses to acetylcholine were not affected. 6. It is concluded that DPI does not stimulate dopamine receptors on cortical neurones; the excitatory responses of these cells to DPI may be mediated by alpha-adrenoceptors.

Comparison of the responses of single cortical neurones to tyramine and noradrenaline: effects of desipramine

1 The technique of microelectrophoresis was used in order to compare the actions of tyramine and noradrenaline on single neurones in the cerebral cortex of the rat.2 Tyramine could both excite and depress cortical neurones. Each tyramine-sensitive cell was also sensitive to noradrenaline. There was a high correlation between the directions of responses to tyramine and noradrenaline, most cells excited by tyramine being excited by noradrenaline, and most cells depressed by tyramine being depressed by noradrenaline.3 In the case of both excitatory and depressant responses, tyramine appeared to be less potent than noradrenaline.4 Tyramine evoked ;slower' responses than noradrenaline, both the latencies to onset and the recovery times being longer for responses to tyramine than for responses to noradrenaline.5 When the rates of release of tyramine and noradrenaline from micropipettes were measured in vitro, no significant difference could be observed between the transport numbers of the two drugs. Thus the difference in potency between the two drugs, and the difference in the time courses of responses to the two drugs, are presumably of biological origin.6 Desipramine could discriminate between neuronal responses to tyramine and noradrenaline: responses to tyramine were antagonized, while responses to noradrenaline were either potentiated or unaffected. Responses to DL-homocysteic acid were not affected by desipramine.7 The results are consistent with the hypothesis that tyramine is an indirectly acting sympathomimetic amine in the brain, and desipramine acts by blocking the uptake of both tyramine and noradrenaline into presynaptic noradrenergic nerve terminals.