Case report: paediatric intramuscular haemangiomata--don't overlook the phlebolith!

Three children presented with soft tissue masses which were clinically suspected to be soft tissue sarcomas. The identification of phleboliths on initial radiological studies should have suggested the correct diagnosis of benign intramuscular haemangiomata. Subsequent referral to a paediatric oncological unit, and the unnecessary parental anxiety so generated, could have been avoided.

Dopamine D2 receptors regulate in vitro melanotrope L-type Ca2+ channel activity via c-fos

Dopamine D2 receptor stimulation of cultured primary melanotropes was found to depress L-type calcium channel activity, whereas D2 receptor antagonist application increased it. When tested on culture days 10, 16, and 20, control cells displayed increasing rises of intracellular Ca2+ in response to K+ depolarization, indicating an increase in channel activity in the absence of dopaminergic regulation. When treated with 1 microM bromocriptine from culture day 1, cells showed minimal increase in channel activity. When bromocriptine was added on day 16, intracellular Ca2+ response to high K+ declined by day 20; removal of the agonist on day 16 resulted in the reappearance of increased responsiveness. Thus, in vitro inhibitions could be initiated or reversed with application or withdrawal of dopamine D2 receptor agonist. Cultured melanotropes were treated with antisense oligodeoxynucleotides directed against the start sequences of the D2 receptor and c-fos messenger RNA. D2 receptor antisense nucleotide prevented the depressive effect on channel activity induced by D2 agonist treatment. c-fos antisense oligodeoxynucleotide blocked the rise in channel activity. The dopamine D2 receptor antagonist haloperidol, which increased channel activity, could not reverse the c-fos antisense deoxynucleotide block. These results strongly support the idea that the chronic suppression of secretion-related activities by dopaminergic stimulation seen in the intermediate lobe in vivo is effected by chronic suppression of c-fos by D2 receptors.

Transient domains induced by influenza haemagglutinin during membrane fusion

During low pH-induced fusion of influenza virus with erythrocytes we have observed differential dispersion of viral lipid and haemagglutinin (HA) into the erythrocyte membrane, and viral RNA into the erythrocyte using fluorescence video microscopy. The movement of both viral lipid and HA from virus to cell was restricted during the initial stages of fusion relative to free diffusion. This indicates the existence of relatively long-lived barriers to diffusion subsequent to fusion pore formation. Fluorescence anisotropy of phospholipid analogues incorporated into the viral membrane decreased when the pH was lowered to levels required for optimum fusion. This indicates that the restricted motion of viral membrane components was not due to rigidification of membrane lipids. The movement of HA from the fusion site was also assessed by photosensitized labelling by means of a fluorescent substrate (NBD-taurine) passing through the band 3 sialoglycoprotein (the erythrocyte anion transporter). We also examined the flow of lipid and aqueous markers during fusion of HA-expressing cells with labelled erythrocytes. During this cell-cell fusion, movement of lipid between fusing membranes begins before the fusion pore is wide enough to allow diffusion of aqueous molecules (M(r) > 500). The data indicate that HA is capable of creating domains in the membrane and controlling continuity of aqueous compartments which are bounded by such domains.

Restricted movement of lipid and aqueous dyes through pores formed by influenza hemagglutinin during cell fusion

The fusion of cells by influenza hemagglutinin (HA) is the best characterized example of protein-mediated membrane fusion. In simultaneous measurements of pairs of assays for fusion, we determined the order of detectable events during fusion. Fusion pore formation in HA-triggered cell-cell fusion was first detected by changes in cell membrane capacitance, next by a flux of fluorescent lipid, and finally by flux of aqueous fluorescent dye. Fusion pore conductance increased by small steps. A retardation of lipid and aqueous dyes occurred during fusion pore fluctuations. The flux of aqueous dye depended on the size of the molecule. The lack of movement of aqueous dyes while total fusion pore conductance increased suggests that initial HA-triggered fusion events are characterized by the opening of multiple small pores: the formation of a "sieve".

Age-related decrease of GABAA receptor subunits and glutamic acid decarboxylase in the rat inferior colliculus

A selective age-related decrease in both the protein and mRNA levels of the most abundant GABAA receptor subunits has been revealed in the rat inferior colliculus. The number (not affinity) of the native and fully assembled GABAA receptors assayed by 3H-muscimol binding was also decreased (35-49%). The decrease in GABA receptors was accompanied by a decrease in the protein and mRNA of the GABA-synthesizing enzyme glutamic acid decarboxylase. No other region of the rat brain showed such large age-related changes in these GABAergic synaptic molecules. Specific antibodies and riboprobes in conjunction with a computerized image analysis system were used to quantify immunocytochemistry and in situ hybridization. In old Sprague-Dawley rats, the combination of beta 2 and beta 3 peptide subunits was reduced 55%, while the beta 2 and beta 3 mRNAs were decreased 31% and 22%, respectively. The gamma 2S and gamma 2L subunit proteins decreased 43% and 21%, respectively, while the gamma 2 mRNA, including both short and long forms, was reduced 61%. The alpha 1 subunit protein was decreased 28%, whereas the alpha 1 mRNA decreased 40%. The glutamic acid decarboxylase protein was reduced 62% while GAD65 mRNA decreased 42%. Similar age-related changes were also observed in the inferior colliculus of Fischer-344 rats. In contrast, no changes were observed in the level of expression of some glial and/or neuronal proteins such as S-100, glial fibrillary acidic protein, and 160 KDa neurofilament protein in the inferior colliculus.(ABSTRACT TRUNCATED AT 250 WORDS)

Antisense knockouts: molecular scalpels for the dissection of signal transduction

The complexity of signal transduction is becoming increasingly apparent following the cloning of multiple families of receptors, G proteins, and effectors. Therefore, new tools are needed to assess the importance of particular subtypes in receptor-mediated signal transduction. One such tool is the use of antisense approaches to specifically 'knockout' particular G protein subtypes and then assess the functional consequences for receptor-signalling pathways. In this article by Paul Albert and Stephen Morris, various antisense approaches (including transfection of full-length cDNA) are discussed and compared for their specificity and efficiency. The antisense approach is argued to be applicable to a wide variety of signal-transduction systems, including G-protein-coupled receptor signalling, for analysis of the downstream events that dictate biological responsiveness.

Community-directed cancer screening program

The Atlanta Project, one of six American Cancer Society demonstration projects, is a community-designed and -directed breast and cervical cancer screening program focused on empowering African-American women to accept responsibility for their health maintenance. This article reports the project's goals, objectives, intervention strategies, roles of key project personnel, and outcomes. A total of 3852 women older than 40 years received breast clinical examinations, were taught breast self-examination, and had a screening mammogram; 2689 women obtained a pelvic examination and were screened for cervical cancer with a Papanicolaou smear. Of those women screened, 12 breast and 1 cervical cancers were identified and treated. Important lessons learned and successes achieved from this project were: (1) there is a need for joint planning with community representatives and their involvement in all aspects of the program's implementation and evaluation; (2) in addition to the commitment of the major participants, the community must "buy in" to the proposed health intervention; (3) the focus of the intervention should be on positive health messages; (4) cancer education materials should be culturally and literacy-appropriate; (5) the project's activities were planned to be sustained after the project period; (6) women can be empowered to accept responsibility for and control over their health.

POMC mRNA levels in individual melanotropes and GFAP in glial-like cells in rat pituitary

In this study we demonstrated that individual melanotropes expressed differing levels of POMC mRNA. Interspersed among the melanotropes was a small population of process-bearing cells expressing GFAP. We compared cellular resolution and feasibility for quantitation of hybrids formed by oligonucleotide probes labeled with two different markers using in situ hybridization histochemistry. In hybridizations using [35S]-labeled probes the signal could not easily be assigned to individual melanotropes, although digoxigenin-labeled probes provided good cellular resolution. Heterogeneous staining intensities of individual melanotropes for POMC mRNA were measured, and relative quantitation of changes in POMC mRNA levels following interactions with the D2 dopamine receptor was performed. We combined in situ hybridization histochemistry with immunohistochemistry to demonstrate that cells within the lobe parenchyma not expressing POMC mRNA were immunoreactive for GFAP.

Simultaneous imaging of intracellular [Ca2+] and pH in single MDCK and glomerular epithelial cells

The interrelationships between changes in intracellular calcium concentration ([Ca2+]i) and intracellular pH in Madin-Darby canine kidney cells and kidney glomerular epithelial cells exposed to various stimuli were analyzed simultaneously using a new design of a fluorescence video microscope. Cells were double labeled with indo 1 and SNARF 1 dyes and were excited simultaneously at 350 and 540 nm. Images at four emission wavelengths were captured simultaneously at 405, 475, 575, and 640 nm at 30 frames/s for the two ratio dyes. SNARF sensitivity to pH between 6.5 and 8.0 was unchanged by [Ca2+]i. The SNARF ratio maps were used to correct the pH-dependent changes in the calculation of local cell calcium. NH4Cl loading produced the expected alkalinization and a concurrent rise in [Ca2+]i. When the NH4Cl was removed and the cells became acidic, a second rise in [Ca2+]i was recorded. Both changes in [Ca2+]i were from intracellular stores since they persisted in the absence of extracellular calcium. The findings demonstrate the need for pH correction of indo 1 recordings.

Calcium regulation of intracellular pH in pituitary intermediate lobe melanotropes

The regulatory activities of both intracellular calcium ([Ca2+]i) and intracellular pH (pHi) have greatly increased interest in the study of their interdependence. We have designed an epifluorescence video microscope that will image the fluorescence from two ratio dyes, indo-1 (for [Ca2+]i) and SNARF-1 (for pHi) at video rates. We examined primary cultures of pituitary intermediate lobe melanotropes loaded with both dyes. After experimentation, cells were positively identified by fluorescence immunohistochemistry. K(+)-induced depolarization of melanotropes produced increases in [Ca2+]i due to activation of L-type Ca channels. A secondary Ca2+ peak or oscillations were often seen. After treatment with carbonyl cyanide m-chlorophenylhydrozone, depolarization produced a rise in intracellular [Ca2+]i as well as oscillations. After thapsigargin or cyclopiazonic acid treatment, depolarization produced a primary Ca2+ elevation, but the secondary Ca2+ changes disappeared. This suggests that the oscillations were due to Ca2+ release from an endoplasmic reticulum type of intracellular store. All of these increases in [Ca2+]i were also directly coupled to a rise in intracellular H+. The close association between intracellular Ca2+ and H+ suggests that the observed pHi changes were due to the release of H+ upon binding of Ca2+ to intracellular buffers. This direct obligate coupling of intracellular Ca2+ and H+ suggests the possibility that pH-dependent cellular processes are directly activated by sudden increases in intracellular Ca2+ levels. This second messenger type of signaling system would be activated whether the Ca2+ was released from intracellular stores or entered the cell via plasma membrane Ca2+ channels.

Calcium influx mediated by the Escherichia coli heat-stable enterotoxin B (STB)

The heat-stable enterotoxin B (STB) of Escherichia coli is a 48-amino acid extracellular peptide that induces rapid fluid accumulation in animal intestinal models. Unlike other E. coli enterotoxins that elicit cAMP or cGMP responses in the gut [heat-labile toxin (LT) and heat-stable toxin A (STA), respectively], STB induces fluid loss by an undefined mechanism that is independent of cyclic nucleotide elevation. Here we studied the effects of STB on intracellular calcium concentration ([Ca2+]i), another known mediator of intestinal ion and fluid movement. Ca2+ and pH measurements were performed on different cell types including Madin-Darby canine kidney (MDCK), HT-29/C1 intestinal epithelial cells, and primary rat pituitary cells. Ca2+ and pH determinations were performed by simultaneous real-time fluorescence imaging at four emission wavelengths. This allowed dual imaging of the Ca(2+)- and pH-specific ratio dyes (indo-1 and SNARF-1, respectively). STB treatment induced a dose-dependent increase in [Ca2+]i with virtually no effect on internal pH in all of the cell types tested. STB-mediated [Ca2+]i elevation was not inhibited by drugs that block voltage-gated Ca2+ channels including nitrendipine, verapamil (L-type), omega-conotoxin (N-type), and Ni2+ (T-type). The increase in [Ca2+]i was dependent on a source of extracellular Ca2+ and was not affected by prior treatment of MDCK cells with thapsigargin or cyclopiazonic acid, agents that deplete and block internal Ca2+ stores. In contrast to these results, somatostatin and pertussis toxin pretreatment of MDCK cells completely blocked the STB-induced increase in [Ca2+]i. Taken together, these data suggest that STB opens a GTP-binding regulatory protein-linked receptor-operated Ca2+ channel in the plasma membrane. The nature of the STB-sensitive Ca2+ channel is presently under investigation.

Polyunsaturated fatty acid incorporation into plasmalogens in plasma membrane of glioma cells is preceded temporally by acylation in microsomes

Plasmalogens (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) are major phospholipids in many tissues and cells, particularly of neural origin. Using cultured C6 glioma cells and subcellular fractions isolated on Percoll gradients we investigated selectivity for esterification of several polyunsaturated fatty acids (PUFA) in the sn-2 position of plasmalogens compared to [1-14C]hexadecanol, representative of de novo synthesis of the ether-linked sn-1 position. In whole cells at a final concentration of 105 microM PUFA, 2-4 nmol plasmalogen/mg protein was labeled in 4 h and 10-14 nmol in 24 h, representing 8-15% and 35-50%, respectively, of initial plasmalogen mass. Incorporation of label from hexadecanol was lower than PUFA incorporation (20:5(n-3) greater than 20:4(n-6) greater than 18:3(n-3) much greater than 18:2(n-6)) suggesting deacylation-reacylation at the sn-2 position. Plasmalogens accounted for 50% of total cell ethanolamine phospholipids and 75% in plasma membrane. Using a novel, improved method for extraction of subcellular fractions containing Percoll, plasma membrane also was enriched in plasmalogen relative to microsomes (107.4 +/- 5.2 vs. 40.0 +/- 2.9 nmol/mg protein). Selectivity for esterification at the sn-2 position of plasmalogens with respect to chain length and unsaturation of the fatty acyl chain was similar in both subcellular fractions and reflected that of whole cells. Labeling of plasma membrane with PUFA and fatty alcohol lagged behind that of microsomes. Chase experiments in cells prelabeled with [1-14C]18:3(n-3) for 2 h showed no significant reduction of label in plasmalogen of any subcellular fraction although accumulation of label in the microsomal fraction was slowed initially. Reduction of plasmalogen label (40-50%) did occur in microsomes and plasma membrane when cells prelabeled for 24 h were switched to chase medium with or without chase fatty acid. Our data suggest that esterification of PUFA to plasmalogen may occur at the endoplasmic reticulum with subsequent translocation to plasma membrane resulting in accumulation of relatively stable pools of plasmalogen that are not readily accessible for deacylation-reacylation exchange with newly appearing PUFA. Alternatively, deacylation-reacylation may occur in a more stable phospholipid pool within the plasma membrane but would involve a slower process than at the endoplasmic reticulum.

Shock wave lithotripsy of gallstones: results and 12-month follow-up in 174 patients

At the authors' institution, as part of the on-going Dornier National Biliary Lithotripsy Study, 174 patients with gallstones were randomly assigned to receive either ursodeoxycholic acid (UDCA) or placebo for 6 months after undergoing extracorporeal shock wave lithotripsy (ESWL). Six weeks after ESWL, 40 (23%) patients were re-treated for gallstone fragments larger than 5 mm in diameter. No significant difference in the UDCA- and placebo-treated patients was noted. The overall 6- and 12-month stone-free rates for all patients with initially noncalcified stones were as follows: UDCA patients, 31% and 36%, respectively, and placebo patients, 21% and 23%, respectively (P less than .05). In patients with a single, noncalcified gallstone that was at most 20 mm in diameter, the 12-month stone-free rates were as follows: UDCA patients, 60%, and placebo patients, 33% (P less than .01). Patients with noncalcified stones that were 11-20 mm in diameter who were treated with UDCA had a higher rate of stone clearance than placebo patients. At 6 months, the authors' previous study demonstrated no significant difference in the two groups of patients. However, the stone-free rate at 12 months was noted to be significantly higher for patients with a single, noncalcified stone that was at most 20 mm in diameter begun on UDCA than for all other groups of patients.

Evaluation of the electrophilicity of DNA-binding pyrrolo[2,1-c][1,4]benzodiazepines by HPLC

An HPLC assay is described that can be used to study the covalent bonding interaction of carbinolamine-containing pyrrolo[2,1-c][1,4]benzodiazepines with the model nucleophile thiophenol, in order to evaluate electrophilicity at the C-11-position. Preliminary experiments with anthramycin, tomaymycin and neothramycin show that their reaction with thiophenol follows second-order kinetics, but the ranking order of reactivity (neothramycin greater than tomaymycin greater than anthramycin), does not correlate with either in vitro cytotoxicity or in vivo antitumour activity. This suggests that other factors such as non-covalent DNA-interaction or drug transport play a more crucial role in biological activity than simple alkylating ability. This assay should, however, prove a useful tool in the study of structure-activity relationships for this series of compounds and provide "C-11-electrophilicity" parameters for use in Hansch analysis and related studies.

Effect of erythrocyte transbilayer phospholipid distribution on fusion with vesicular stomatitis virus

To identify the specific component(s) in the target membrane involved in fusion of vesicular stomatitis virus (VSV), we examined the interaction of the virus with human erythrocyte membranes with asymmetric and symmetric bilayer distributions of phospholipids. Fusion was monitored spectrofluorometrically by the octadecylrhodamine dequenching assay. Fusion of VSV with lipid-symmetric erythrocyte ghosts was rapid at 37 degrees C and low pH, whereas little or no fusion was observed with lipid-asymmetric ghosts. Conversion of phosphatidylserine in the lipid-symmetric ghost membrane to phosphatidylethanolamine by means of the enzyme phosphatidylserine decarboxylase did not alter the target membrane's susceptibility to VSV fusion. Spin-labeled phospholipid analogues with phosphatidylserine, phosphatidylethanolamine, and phosphatidylcholine headgroups incorporated into the outer leaflet of lipid-asymmetric erythrocytes did not render those membranes fusogenic. Electron spin resonance spectra showed an increased mobility of a phosphatidylcholine spin-label incorporated into the outer leaflet of lipid-symmetric erythrocyte ghosts as compared to that of lipid-asymmetric ghosts. These results indicate that the susceptibility to VSV fusion is not dependent on any particular phospholipid but rather is related to packing characteristics of the target membrane.

Real-time multi-wavelength fluorescence imaging of living cells

We describe a new real-time fluorescence video microscope design for capturing intensified images of cells containing dual wavelength "ratio" dyes or multiple dyes. The microscope will perform real-time capture of two separate fluorescence emission images simultaneously, improving the time resolution of spatial distribution of fluorescence to video frame rates (30 frames/s or faster). Each emission wavelength is imaged simultaneously by one of two cameras, then digitized, background corrected and appropriately combined at standard video frame rates to be stored at high resolution on tape or digital video disk for further off-line analysis. Use of low noise, high sensitivity image intensifiers, coupled to CCD cameras produce stable, high contrast images using ultra low light levels with little persistence or bloom. The design has no moving parts in its optical train, which overcomes a number of technical difficulties encountered in the present filter wheel designs for multiple imaging. Coupled to compatible image processing software utilizing PC-AT computers, the new design can be built for a significantly lower cost than many presently available commercial machines. The system is ideal for ratio imaging applications; the software can calculate the ratio of fluorescence intensities pixel by pixel and provide the information to generate false-color images of the intensity data as well as other calculations based on the two images. Thus, it provides a powerful, inexpensive tool for studying the real-time kinetics of changes in living cells. Examples are presented for the kinetics of rapidly changing intracellular calcium detected by the calcium indicator probe indo-1 and the redistribution kinetics of multiple vital dyes placed in cells undergoing cell fusion.

Phosphoinositide metabolism in cultured glioma and neuroblastoma cells: subcellular distribution of enzymes indicate incomplete turnover at the plasma membrane

The hypothesis that the small portion of cellular phosphoinositide participating in signal transduction might be preferentially recycled within the plasma membrane was tested in rat glioma (C6) and murine neuroblastoma (N1E-115) cells. Percoll density gradient centrifugation was used to isolate a purified plasma membrane fraction and the subcellular distribution of all enzymes mediating phosphoinositide turnover was assessed. A small but significant proportion of PtdInsP2-specific phosphodiesterase was located in the plasma membrane but only two of the five enzymes required to replace PtdInsP2 (diacylglycerol kinase and PtdInsP kinase) also were present. CTP:phosphatidate cytidylyltransferase and CMP-phosphatidate:inositol phosphatidyltransferase were located exclusively in a microsomal fraction containing enriched levels of endoplasmic reticulum markers. Thus, diacylglycerol from agonist-stimulated cleavage of PtdInsP2, or phosphatidic acid formed from it, must be transferred to the endoplasmic reticulum for conversion to PtdIns. Plasma membrane also lacked PtdIns kinase. If the soluble PtdIns kinase has access to membrane-bound substrate, PtdIns may be phosphorylated to PtdInsP before or during transport to the plasma membrane. Phosphorylation by the predominantly plasma membrane PtdInsP kinase to form PtdInsP2 completes the cycle. PtdInsP phosphatase was present in all membrane fractions suggesting that PtdInsP can be returned to the PtdIns pool in plasma membrane and elsewhere. PtdInsP2 phosphatase was almost exclusively in the cytosol suggesting that reversible interchange between PtdInsP and PtdInsP2 in the plasma membrane may be modulated by the ability of this phosphatase to act on PtdInsP2 in the membrane. Thus, PtdIns resynthesis in the plasma membrane of these cells does not occur and is not required for phosphoinositide-mediated signal transduction.

Initial stages of influenza hemagglutinin-induced cell fusion monitored simultaneously by two fluorescent events: cytoplasmic continuity and lipid mixing

We have monitored the mixing of both aqueous intracellular and membrane-bound fluorescent dyes during the fusion of human red blood cells to influenza hemagglutinin-expressing fibroblasts using fluorescence spectroscopy and low light, image-enhanced video microscopy. The water-soluble fluorescent dye, N-(7-nitrobenzofurazan-4-yl)taurine, was incorporated into intact human red blood cells. The fluorescence of the dye in the intact red blood cell was partially quenched by hemoglobin. The lipid fluorophore, octadecylrhodamine, was incorporated into the membrane of the same red blood cell at self-quenching concentrations (Morris, S. J., D. P. Sarkar, J. M. White, and R. Blumenthal. 1989. J. Biol. Chem. 264: 3972-3978). Fusion, which allowed movement of the water-soluble dye from the cytoplasm of the red blood cell into the hemagglutinin-expressing fibroblasts, and movement of octadecylrhodamine from membranes of red blood cell to the plasma membrane of the fibroblasts, was observed by fluorescence microscopy as a spatial relocation of dyes, and monitored by spectrofluorometry as an increase in fluorescence. Upon lowering the pH below 5.4, fluorescence increased after a delay of about 30 s at 37 degrees C, reaching a maximum within 3 min. The kinetics, pH profile, and temperature dependence were similar for both fluorescent events measured simultaneously, indicating that influenza hemagglutinin-induced fusion rapidly establishes bilayer continuity and exchange of cytoplasmic contents.

Kinetics of pH-dependent fusion between 3T3 fibroblasts expressing influenza hemagglutinin and red blood cells. Measurement by dequenching of fluorescence

Fusion between membranes of 3T3 fibroblasts expressing hemagglutinin (HA) from the Japan strain of influenza virus and human red blood cells (RBC) was measured using an assay for lipid mixing based on the relief of self-quenching (dequenching) of fluorescence of the lipid probe octadecylrhodamine (R18). The probe was incorporated into the membrane of intact RBC at self-quenching concentrations, and the RBCs were bound to the 3T3 cells. Fusion, which allowed movement of R18 into 3T3 cell membranes, was monitored by spectrofluorometry as an increase in fluorescence. Upon lowering the pH below 5.4, the fluorescence increased after a delay of about 30 s at 37 degrees C, and leveled off within 2 min. In control experiments where R18 RBCs bound to 3T3 cells expressing the uncleaved precursor hemagglutinin (HA0) were incubated at 37 degrees C and low pH, no fluorescence increase was observed. This indicated that the R18 dequenching occurred as a result of HA-induced fusion of plasma membranes. Fusion showed a very steep pH dependence with a threshold at pH 5.4 and a maximum at pH 5.0, similar to HA-induced fusion seen previously using cell biological techniques. The fusion rate increased and the delay for the onset of fusion decreased as the temperature was raised above 20 degrees C. Low pH activation of the fusion process at 37 degrees C could be partially arrested by raising the pH after 2-10 s, but not after 15 s, indicating that the irreversible pH-activated conformational change of HA necessary for fusion was complete within about 15 s. Analysis of the data indicates that the pH-induced membrane fusion activity of HA is a highly cooperative event.