Replicability of simulation studies for the investigation of statistical methods: the RepliSims project.

Results of simulation studies evaluating the performance of statistical methods can have a major impact on the way empirical research is implemented. However, so far there is limited evidence of the replicability of simulation studies. Eight highly cited statistical simulation studies were selected, and their replicability was assessed by teams of replicators with formal training in quantitative methodology. The teams used information in the original publications to write simulation code with the aim of replicating the results. The primary outcome was to determine the feasibility of replicability based on reported information in the original publications and supplementary materials. Replicasility varied greatly: some original studies provided detailed information leading to almost perfect replication of results, whereas other studies did not provide enough information to implement any of the reported simulations. Factors facilitating replication included availability of code, detailed reporting or visualization of data-generating procedures and methods, and replicator expertise. Replicability of statistical simulation studies was mainly impeded by lack of information and sustainability of information sources. We encourage researchers publishing simulation studies to transparently report all relevant implementation details either in the research paper itself or in easily accessible supplementary material and to make their simulation code publicly available using permanent links.

Evaluation of the clinical benefits of nanoparticle albumin-bound paclitaxel in women with metastatic breast cancer in British Columbia.

BACKGROUND: Altered formulations of taxanes may lack cross-resistance with standardly used solvent-based taxanes. The primary objective of the present study was to assess the clinical benefit of nanoparticle albumin-bound (nab)-paclitaxel in women with metastatic breast cancer previously treated with and without adjuvant taxane in British Columbia. METHODS: The BC Cancer Agency Pharmacy data repository and Breast Cancer Outcomes Unit database were linked to identify all patients who received nab-paclitaxel in British Columbia since its introduction in 2007. Hormone receptor status, demographic characteristics, number of cycles prescribed, and time to treatment failure were extracted and analyzed. RESULTS: From 2007 to 2011, 138 patients in British Columbia received nab-paclitaxel, with 122 patients available for analysis. Most (70.5%) received adjuvant chemotherapy; about a quarter (24.6%) received an adjuvant taxane. Patients who received adjuvant taxane were more likely to have node-positive (86.7% vs. 48.9%, p = 0.007), estrogen receptor-negative (46.7% vs. 13.0% p < 0.001) disease and to receive initial adjuvant radiotherapy (76.7% vs. 51.1%, p < 0.001). For the entire cohort, the median number of nab-paclitaxel cycles prescribed was 4.4 (range: 0.3-13). The median number of nab-paclitaxel cycles was greater when that agent was given as first- or second-line therapy than as third-line or greater therapy (5.0 cycles vs. 3.7 cycles respectively). The median time to treatment failure was 96 days in the prior adjuvant taxane group (range: 0-361) and 73.5 days in the no prior adjuvant taxane group (range: 0-1176). CONCLUSIONS: This retrospective study demonstrates potential clinical activity of nab-paclitaxel in metastatic breast cancer regardless of whether patients had prior exposure to adjuvant taxanes.

Thromboembolic events associated with immunoglobulin treatment.

OBJECTIVE: Due to an increasing number of reported thromboembolic events (TEE) after the administration of one intravenous immunoglobulin (IVIG) and one subcutaneous immunoglobulin (SCIG), pharmacovigilance and laboratory data were collected to analyse the root cause and assess the reporting frequency of TEEs for various IG products. METHODS: Paul-Ehrlich-Institut retrospectively analysed 228 reports of TEEs associated with six different IG products and estimated annual TEE-reporting rates based on worldwide sale figures over a period of 6 years (2006-2011). In addition, non-activated partial thromboplastin time (NAPTT) testing was performed to capture pro-coagulant potential of six IG products (four IVIG and two SCIG). RESULTS: For three IVIGs, the drug-related TEE-reporting rates remained stable from 2006 to 2011 (0-0·83 cases per 1000 kg IVIG distributed). In contrast, the TEE rate of one IVIG increased significantly from 0·33 cases in 2006 to nearly nine cases in 2010 (P < 0·001). The NAPTT testing of IG products with a low TEE rate revealed a NAPTT time >200 s and a NAPTT ratio >0·8, whereas TEE-associated batches of IG products with an increased TEE rate had a NAPTT ratio <0·8. After modifications of manufacturing processes, a normalization of NAPTT results and a decrease in TEE rates could be demonstrated.

Benefit of transfusion-related acute lung injury risk-minimization measures--German haemovigilance data (2006-2010).

OBJECTIVE: Based on the frequency of immune-mediated and non-immune-mediated transfusion-related acute lung injury (TRALI), the effect of risk-minimization measures was evaluated during a period of 5 years (2006-2010). Risk-minimization measures were implemented in 2008/2009, consisting of exclusion of female donors with a history of pregnancy or exclusion of female donors with human leucocyte antigen (HLA)/human neutrophil alloantigen (HNA) antibodies. METHODS: TRALI was confirmed according to the criteria of the International Haemovigilance Network. Based upon the results of donor testing of white-blood-cell antibodies (WBC-Ab) against HLA or HNAs, confirmed cases were classified as immune- or non-immune-mediated TRALI. Reporting rates were calculated on the basis of the annually transfused blood components, and pre- and post-implementation periods were compared. RESULTS: In total, 60 immune-mediated (75%) and 20 non-immune-mediated (25%) TRALI reactions were confirmed. A total of 68 (64 women and four men) donors were involved: seven red-blood-cell concentrates donors (13%), six platelet concentrate donors (10%), and 48 fresh frozen plasma (FFP) donors (77%). The reporting rate of immune-mediated TRALI caused by FFP decreased continuously; from 12·71 per million units in 2006/2007 to 6·81 per million units in 2008/2009 and no case in 2010. CONCLUSION: The comparison of the pre- and the post-implementation period demonstrated a significantly reduced risk of TRALI events comparing 2006/2007 with 2010 (P-value: <0·01). Furthermore, no case of TRALI-induced fatality occurred after the implementation of risk-minimization measures.

[Evaluation of measures aimed to reduce serious adverse transfusion reactions (hemovigilance data from 1997 to 2008)]. / Bewertung der Massnahmen zur Reduktion schwerwiegender Transfusionsreaktionen (Hämovigilanzdaten von 1997 bis 2008).

On the basis of reports of serious transfusion reactions, measures aimed to improve the safety standard of the manufacturing process of blood components were evaluated from 1997-2008. Measures of the Paul-Ehrlich-Institut (PEI) as well as recommendations of the Advisory Committee "Blood" were considered. Reporting frequencies before and after the implementation of measures were compared. After the implementation of NAT pool testing, a reduction of virus transmission was seen for red blood cell concentrates (RBC) from 1.0/10(6) to 0.5/10(6) units and for platelet concentrates (PC) from 3.0/10(6) to 0.0/10(6) units. After the implementation of a pre-donation sampling, however, no reduction of bacterial infections associated with PC administration (>9.0/10(6)) was identified. To reduce the frequency of TRALI associated with FFP administration (11.2/10(6) units), the use of plasma from male donors or female donors without a history of pregnancy was established in September 2009. Without specific measures of risk reduction, the reporting frequency of severe allergic transfusion reaction increased for all blood components during the investigation period (from 0.8/10(6) to 6.2/10(6) RBC units). The benefit of measures to improve safety standards should be evaluated repeatedly by collecting precise hemovigilance data.

Digestibilidade da silagem de grãos úmidos de milho com diferentes granulometrias para suínos / Digestibility of high moisture corn grain silage with different particle size for swines

Avaliou-se a composição química e determinaram-se os valores de energia digestível (ED) e metabolizável (EM), os coeficientes de digestibilidade da matéria seca (CDMS), da proteína bruta (CDPB), da matéria mineral (CDMM); do extrato etéreo (CDEE); da fibra bruta (CDFB), da energia bruta (CDEB) e do extrativo não nitrogenado (CDENN) e os coeficientes de digestibilidade (CDEB) e metabolizabilidade da energia bruta (CMEB) da silagem de grãos úmidos de milho (SGUM). Foram utilizados 20 suínos, com peso vivo inicial de 28,89±4,9kg, distribuídos em gaiolas de metabolismo. Foi utilizada uma única SGUM, com quatro diferentes granulometrias 513, 587, 717 e 1363µm, que substituiu em 30 por cento a dieta-referência. Os CDMS, CDPB, CDEE, CDMM e CDENN diminuíram com o aumento da granulometria da SGUM. Os CDEB e CMEB também diminuíram de 89,0 para 94,3 por cento, e de 82,9 para 88,5 por cento, respectivamente. Os valores energéticos variaram de 4439 a 4493kcal EB/kg, de 3999 a 4194kcal ED/kg e de 3729 a 3939kcal EM/kg, na matéria seca. Os CDEB e CMEB se reduziram até os diâmetros geométricos médios de 754 e 831µm, respectivamente. A digestibilidade dos nutrientes da SGUM foi influenciada negativamente ao se aumentar o diâmetro geométrico médio das partículas.

The chemical composition; the values of digestible (DE) and metabolizable (ME) energy; the coefficients of digestibility of dry matter (CDDM), crude protein (CDCP), mineral matter (CDMM), ether extract (CDEE), crude fiber (CDFB), crude energy (CDCE), and non nitrogen extractive (CDENN); as well as the coefficient of metabolizability of gross energy (CMGE) of high moisture corn grain silage (HMCGS) were evaluated. Twenty swines, averaging 28.89±4.9kg of live weight, randomly allotted in metabolism cages were used. HMCGS with different particle sizes 513, 587, 717, and 1363µm, replacing 30 percent of basal diet was used. CDDM, CDCP, CDEE, CDMM, and CDENN decreased as the particle size of the HMCGS increased. CDGE and CMGE also decreased from 89.0 to 94.3 percent and from 82.9 to 88.5 percent, respectively. The energy values varied from 4,439 to 4,493kcal of GE/kg, 3,999 to 4,194kcal DE/kg, and 3,729 to 3,939kcal ME/kg, in dry matter basis. CDGE and CMGE decreased until the medium geometric diameters of 754 and 831µm, respectively, and the digestibility of the nutrients of the HMCGS was negatively influenced as the medium geometric diameter of the particles increased.

The German Haemovigilance System--reports of serious adverse transfusion reactions between 1997 and 2007.

Data of the German Haemovigilance System were collected from 1997 to 2007 and assessed on the basis of pre-defined safety standards. Suspected cases of serious adverse reactions following transfusions reported to the Paul-Ehrlich-Institut were evaluated on the basis of national criteria, and the definitions of International Society of Blood Transfusion (ISBT) in compliance with defined causality criteria. The suspected cases were rated as confirmed and unconfirmed transfusion reactions. Assessment of causality took into consideration the clinical course of the adverse reaction and, if necessary, information about donation and manufacturing. Of the 5128 suspected serious adverse reactions, 1603 could be confirmed. Referring to the absolute figures, acute transfusion reactions (e.g. allergic reactions, hypotension and dyspnoea) were recorded most frequently, followed by transfusion-related acute lung injury (TRALI), haemolytic reactions, transfusion-related bacterial infections and virus infections. The majority of the 52 transfusion-related fatalities (14 each) were due to TRALI and acute transfusion reactions (mostly severe allergic reactions). Referred to the blood products administered, immune TRALI cases and TRALI-related fatal courses were most frequently reported after administration of fresh frozen plasma (FFP) (15/10(6) and 3.5/10(6) units, respectively), transfusion-related bacterial infections after administration of platelet concentrates (7/10(6) units), acute haemolytic transfusion reactions after administration of red blood cell concentrates (2.3/10(6)units) and acute transfusion reactions after administration of red blood cell or platelet concentrates (7.8/10(6) and 13/10(6) units, respectively). Despite the high safety standard required for blood products in Germany, there is still room for reducing the frequency of isolated cases of transfusion reactions by targeted action.

Flatland optics. III. Achromatic diffraction.

In the previous two sections of "Flatland optics" [J. Opt. Soc. Am. A 17, 1755 (2000); 18, 1056 (2001)] we described the basic principles of two-dimensional (2D) optics and showed that a wavelength lambda in three-dimensional (3D) space (x, y, z) may appear in Flatland (x, z) as a wave with another wavelength Lambda=lambda/cos alpha. The tilt angle alpha can be modified by a 3D-Spaceland individual, who then is able to influence the 2D optics in a way that must appear to be magical to 2D-Flatland individuals-in the spirit of E. A. Abbott's science fiction story of 1884 [Flatland, a Romance of Many Dimensions, 6th ed. (Dover, New York, 1952)]. Here we show how the light from a white source can be perceived in Flatland as perfectly monochromatic, so diffraction with white light will be free of color blurring and the contrast of interference fringes can be 100%. The basic considerations for perfectly achromatic diffraction are presented, along with experimental illustration of Talbot self-imaging performed with broadband illumination.

Flatland optics. II. Basic experiments.

In "Flatland optics: fundamentals" [J. Opt. Soc. Am. A 17, 1755 (2000)] we described the basic principles of two-dimensional (2D) optics and showed that a wavelength lambda in three-dimensional (3D) space (x,y,z) may appear in Flatland (x,z) as a wave with another wavelength, lambda = lambda/cosalpha. The tilt angle alpha can be modified by a 3D (Spaceland) individual who then is able to influence the 2D optics in a way that must appear to be magical to 2D Flatland individuals-in the spirit of E. A. Abbott's science fiction story [Flatland, a Romance of Many Dimensions, 6th ed. (Dover, New York, 1952)] of 1884. We now want to establish the reality or objectivity of the 2D wavelength lambda by some basic experiments similar to those that demonstrated roughly 200 years ago the wave nature of light. Specifically, we describe how to measure the 2D wavelength lambda by mean of five different arrangements that involve Young's biprism configuration, Talbot's self-imaging effect, measuring the focal length of a Fresnel zone plate, and letting light be diffracted by a double slit and by a grating. We also performed experiments with most of these arrangements. The results reveal that the theoretical wavelength, as predicted by our Flatland optics theory, does indeed coincide with the wavelength lambda as measured by Flatland experiments. Finally, we present an alternative way to understand Flatland optics in the spatial frequency domains of Flatland and Spaceland.

Buprenorphine substitution ameliorates spontaneous withdrawal in fentanyl-dependent rat pups.

Iatrogenic physical dependence has been documented in human infants infused i.v. with fentanyl or morphine to maintain continuous analgesia and sedation during extracorporeal membrane oxygenation and mechanical ventilation. Many infants are slowly weaned from the opioid. However, this approach requires extended hospital stays. Little is known about the potential benefits of substitution therapy to prevent abstinence. Therefore, the hypothesis was tested that s.c. and p.o. buprenorphine substitution would ameliorate spontaneous withdrawal in fentanyl-dependent rat pups. Analgesia in the tail-flick test was used to indicate behaviorally active doses of buprenorphine in opioid-naïve postnatal day 17 rats. Other postnatal day 14 rat pups were surgically implanted with osmotic minipumps that infused saline (1 microL/h) or fentanyl (60 microg/kg/h) for 72 h. Vehicle or buprenorphine was administered s.c. or p.o. before the initiation of spontaneous withdrawal brought about the removal of the osmotic minipumps. The major withdrawal signs of wet-dog shakes, jumping, wall climbing, forepaw tremor, and mastication were counted during a 3-h period of withdrawal. The major scored sign, scream on touch, was assessed every 15 min for 3 h. Injection of naloxone after the 3-h observation did not reveal any residual dependence. Subcutaneous buprenorphine administration significantly ameliorated all signs of withdrawal. Surprisingly, p.o. buprenorphine was nearly as efficacious as the s.c. route of administration. These results indicate that buprenorphine substitution therapy may be effective in fentanyl-dependent human infants.

Wigner formulation of optical processing with light of arbitrary coherence.

A unified mathematical formulation for designing and analyzing even the most general optical processor is presented. It exploits the Wigner distribution function to characterize the illumination, the input, the inherent filter, and the output results. To characterize the propagation of the light through the optical processor setup, we exploit the Wigner matrix formalism, which is appealing because it allows simple geometric analysis. The Wigner distribution function was extended to include illumination of arbitrary coherence so that processors using either coherent light or partially coherent light can be designed and analyzed with the same Wigner formalism. The basic principles, design, and analysis of the imaging and Fourier-transform operations and use of the Wigner formalism to evaluate the performance and tolerances of optical processors are presented.

Flatland optics: fundamentals.

"Flatland" is the title of a 120-year-old science fiction story. It describes the life of creatures living in a two-dimensional (2D) Flatland. A superior creature living in the three-dimensional (3D) spaceland, as we do, can easily inspect, for example, the inside of a Flatland house, as well as the content of a flat man's stomach without leaving any trace. Furthermore, the 3D person has supernatural powers that enable him to change the laws of physics in Flatland. We present here the concept of a 2D Flatland optics with one transversal coordinate x and one longitudinal coordinate z. The other transversal coordinate y allows total inspection of Flatland optics, and the freedom to change the wavelength, without using something like nonlinear optics or a Doppler shift. Monochromatic 3D light can be converted reversibly into polychromatic 2D light. A large variety of 2D systems and 2D effects will be presented here and in follow-up contributions. An epilogue faces the question, how "real" is Flatland optics?

General linear optical coordinate tranformations.

New optical configurations for performing general coordinate transformation operations of shear, rotation, and their combination are presented. These configurations consist of refractive spherical and cylindrical lenses that are readily available. Typically, high-resolution imagery can be obtained, depending on the size of the input object, the illumination wavelength, and the f-number of the lenses. Basic and more general configurations are presented, along with experimental results clearly showing image shearing, rotation, and a combination of these with high-quality output imagery.

Downregulation of a mitogen-activated protein kinase signaling pathway in the placentas of women with preeclampsia.

OBJECTIVE: To investigate whether the activity of the three mitogen-activated protein kinases (Jun aminoterminal kinase, extracellular regulated kinase, and p38) is altered in placental tissue of women with preeclampsia and hemolysis, elevated liver enzymes, low platelets (HELLP) syndrome. METHODS: Placental activity (measured by immunoprecipitation-kinase assay) and protein expression (measured by western blot) of Jun aminoterminal kinase, extracellular regulated kinase, and p38 mitogen-activated protein kinase were measured in four groups of eight women each with preeclampsia, HELLP syndrome, and normal vaginal or cesarean deliveries. To further characterize the Jun aminoterminal kinase signal transduction pathway, phosphorylation of c-Jun, a downstream effector of Jun aminoterminal kinase- mitogen-activated protein kinase, was analyzed by western blotting, and the activity of Rac1, an upstream activator of the Jun aminoterminal kinase signaling pathway, was determined by pull-down assay. RESULTS: The activity of Jun aminoterminal kinase was significantly lower in placentas of women with preeclampsia or HELLP syndrome compared with those who had normal vaginal or cesarean delivery, whereas levels of Jun aminoterminal kinase protein expression were similar. Phosphorylation of the transcription factor c-Jun and Rac1 activity also were significantly lower in women with preeclampsia and HELLP than in controls. p38 mitogen-activated protein kinase activity was significantly higher in women with preeclampsia than with HELLP syndrome. There was no change in extracellular regulated kinase activity or protein expression between subgroups. CONCLUSION: In placentas of women with preeclampsia or HELLP syndrome, a Rac1-Jun aminoterminal kinase-c-Jun-dependent signal transduction pathway was downregulated.

Fentanyl self-administration in juvenile rats that were tolerant and dependent to fentanyl as infants.

Human neonates and infants can become tolerant and dependent during continuous fentanyl or morphine administration. The long-term consequences in these individuals as juveniles and adults are unknown. This study compared fentanyl self-administration behavior in juvenile rats that were opioid naive or were exposed chronically to fentanyl as infants. Postnatal day 14 infant rats remained naive or were implanted with saline- or fentanyl-filled Alzet minipumps. After 72 h, fentanyl's antinociceptive potency was 3.0-fold lower in the fentanyl-infused rats. Naloxone precipitated withdrawal occurred only in the fentanyl-infused animals. Other similarly treated infant rats were allowed to mature into P42 juvenile rats before enrolling them in an oral fentanyl self-administration study. Rats from each group consumed significantly more fentanyl than quinine. However, those rats, tolerant and dependent to fentanyl as infants, did not self-administer more fentanyl than their opiate-naive littermates. The issue of whether fentanyl was consumed for its reinforcing properties was demonstrated when noncontingent administration of opiate antagonists significantly reduced fentanyl intake in another group of juvenile rats. These data indicate that fentanyl is consumed for its reinforcing properties, but that infant fentanyl tolerance and dependence did not predispose them to self-administer more fentanyl than opiate-naive animals.

Understanding superresolution in Wigner space.

Superresolution permits fine details to be observed that cannot be resolved by standard optical instruments. We demonstrate that superresolution is nothing more than an adaptation of degrees of freedom converted from the spatial domain to some other domains and vice versa. The tool used for the required conversion and adaptation is the Wigner chart. In addition, we show that the Wigner chart may be naturally applied for analyzing and understanding complex optical setups used for obtaining superresolution.

Apochromatic optical correlation.

Optical correlation, or matched filtering, can now be applied more widely than before, because the light is now allowed to be totally incoherent, spatially and spectrally. Two such correlators were demonstrated recently. Their state of chromatic correction can be called achromatic, since the scaling error has two zero crossings within the visible range of wavelengths. We present a new apochromatic correlator, in which the scaling error has three zero crossings. The maximum error and the rms error are reduced by a factor of 5. Our apochromatic correlator is composed of two highly dispersive heavy flint lenses that are in contact with two diffractive lenses and two chromatic corrected refractive lenses. The uncommon combination of flint dispersion and diffractive dispersion enabled us to achieve apochromatic correction of the scaling factor of the correlator.

Antisenses to opioid receptors attenuate ATP-gated K(+) channel opener-induced antinociception.

The ATP-gated K(+) channel openers diazoxide, levcromakalim and morphine induce cell hyperpolarization by opening the K(+) channels and enhancing K(+) efflux. This hyperpolarization decreases intracellular Ca(2+) levels, lessening neurotransmitter release thus leading to antinociception. Previous findings implicate the release of endogenous opioids as the mediator of the antinociceptive effects of ATP-gated K(+) channel openers. Antisense oligodeoxynucleotides to the opioid receptor clones, which decrease the number of available receptors, were used to demonstrate the involvement of endogenous opioids in diazoxide- and levcromakalim-induced antinociception. Antisense to all three opioid receptors attenuated the effect of diazoxide, suggesting that diazoxide is inducing the release of endogenous opioids activating the mu(MOR-1)-, delta(DOR-1)-, and kappa(KOR-1)-opioid receptors. Antisense to the mu-opioid receptor clone and delta-opioid receptor clone attenuated levcromakalim-induced antinociception, indicating that endogenous opioids acting at the mu- and delta-opioid receptors are potential candidates for the mediation of the antinociceptive effects of levcromakalim.

ATP-gated K(+) channel openers enhance opioid antinociception: indirect evidence for the release of endogenous opioid peptides.

The ATP-gated K(+) channel openers - diazoxide, levcromakalim and morphine - enhance K(+) efflux by opening ATP-gated K(+) channels, thereby inducing cell hyperpolarization. Hyperpolarization decreases intracellular Ca(2+) levels, which leads to a decrease in neurotransmitter release contributing to the antinociceptive effects of the drugs. Previous findings implicate the release of endogenous opioids as the mediator of the antinociceptive effects of ATP-gated K(+) channel openers. Diazoxide and levcromakalim, administered intracerebroventricularly (i.c.v.), produced dose-dependent antinociception as determined by the tail-flick method ¿ED(50) 44 microg/mouse [95% confidence limits (CLs) from 28 to 68 microg/mouse] for diazoxide¿. Glyburide (10 microg/mouse), an ATP-gated K(+) channel antagonist, attenuated the effects of diazoxide, levcromakalim and morphine. Diazoxide- and levcromakalim-induced antinociception were both antagonized by CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr amide), a mu-opioid receptor selective antagonist, and ICI 174,864 (N, N-diallyl-Tyr-Aib-Aib-Phe-Leu), a delta-opioid receptor antagonist, but were differentially attenuated by the kappa-opioid receptor antagonist, nor-Binaltorphimine. Combinations of inactive doses of the K(+) channel openers and opioid receptor agonists produced significant antinociceptive enhancement. Diazoxide (2 microg/mouse) shifted morphine's dose-response curve 47-fold, while levcromakalim (0.1 microg/mouse) shifted the curve 27-fold. The dose-response curve of kappa-opioid receptor agonist U50,488H (trans-(+/-)-3, 4 Dichloro-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methane sulfonate) was shifted 106-fold by diazoxide in a parallel manner, while levcromakalim administration increased the potency of U50,488H by 15-fold. Diazoxide shifted the dose-response curve of the delta-opioid receptor agonist, DPDPE [(D-Pen(2,5))-enkephalin], leftward in a non-parallel manner, while DPDPE was 6-fold more potent when combined with levcromakalim. We hypothesize that endogenous opioids mediate ATP-gated K(+) channel opener-induced antinociception and enhancement of opioids.