Optical Resonance Shifts in the Fluorescence of Thermal and Cold Atomic Gases.

We show that the resonance shifts in the fluorescence of a cold gas of rubidium atoms substantially differ from those of thermal atomic ensembles that obey the standard continuous medium electrodynamics. The analysis is based on large-scale microscopic numerical simulations and experimental measurements of the resonance shifts in a steady-state response in light propagation.

Observation of suppression of light scattering induced by dipole-dipole interactions in a cold-atom ensemble.

We study the emergence of collective scattering in the presence of dipole-dipole interactions when we illuminate a cold cloud of rubidium atoms with a near-resonant and weak intensity laser. The size of the atomic sample is comparable to the wavelength of light. When we gradually increase the number of atoms from 1 to ~450, we observe a broadening of the line, a small redshift and, consistently with these, a strong suppression of the scattered light with respect to the noninteracting atom case. We compare our data to numerical simulations of the optical response, which include the internal level structure of the atoms.

Direct measurement of the Wigner time delay for the scattering of light by a single atom.

We have implemented the Gedanken experiment of an individual atom scattering a wave packet of near-resonant light, and measured the associated Wigner time delay as a function of the frequency of the light. In our apparatus, the atom behaves as a two-level system and we have found delays as large as 42 ns at resonance, limited by the lifetime of the excited state. This delay is an important parameter in the problem of collective near-resonant scattering by an ensemble of interacting particles, which is encountered in many areas of physics.

Free-space lossless state detection of a single trapped atom.

We demonstrate the lossless state-selective detection of a single rubidium 87 atom trapped in an optical tweezer. This detection is analogous to the one used on trapped ions. After preparation in either a dark or a bright state, we probe the atom internal state by sending laser light that couples an excited state to the bright state only. The laser-induced fluorescence is collected by a high numerical aperture lens. The single-shot fidelity of the detection is 98.6±0.2% and is presently limited by the dark count noise of the detector. The simplicity of this method opens new perspectives in view of applications to quantum manipulations of neutral atoms.

An optoelectronic registration method as applied to PAF-mediated hydrogen peroxide induced arterial thrombosis.

In the present paper, a standardized method for the induction and registration of platelet thrombi in arterioles (500 microns diameter) of small laboratory animals is described in full detail. Using an optoelectronic analogue computer device, different discriminating parameters characteristic for the thrombotic phenomenon are presented. As the topical application of exogenous PAF-acether induces the generation of endogenous PAF-acether according to previous investigations (Bourgain et al. (1985) Prostaglandins 30, 185) it was deemed interesting to investigate the effect of hydrogen peroxide using the described methodology. It was found that the latter substance not only primes the effect of PAF-acether-induced thrombosis, but also can trigger by itself PAF-acether modulated arterial thrombus formation. Experimental evidence is adduced that these thrombotic phenomena can be most efficiently down regulated by specific PAF-acether antagonists.

Effect of the nifedipine-atenolol association on arterial myocyte migration and proliferation.

The in vitro effect of nifedipine and atenolol, either alone or in combination, on the proliferation and migration of rat aortic smooth muscle cells was investigated. Nifedipine inhibited the replication of arterial myocytes in concentrations ranging between 10 and 100 microM. The inhibition, evaluated as cell number, was dose- and time-dependent with an IC50 of 39 and 34 microM after 48 and 72 h, respectively; the cell doubling time increased with drug concentrations up to 118 h versus 28 h for controls. Atenolol alone failed to reduce arterial myocyte proliferation, and did not influence the effect of nifedipine on cell proliferation. Nifedipine and atenolol alone inhibited in a dose-dependent manner rat aortic myocytes migration induced by fibrinogen as chemotactic agent. When the combination nifedipine-atenolol was investigated, an additive inhibitory effect on cell migration was observed. These results provide in vitro support for a potential effect of this drug association on early steps of atherogenesis.

Peptide mapping of mammalian brain protein h3 in subsets of tissues and ligand binding studies.

In this report the structure of the novel polypeptide h3, isolated from subsets of tissues of a single species, and the structural similarity between interspecies h3 were investigated by peptide mapping of enzymatic and chemical cleavage fragments of h3 in one-dimensional SDS-PAGE; the peptide maps were commented on in comparison with the known sequence of 21 kDa protein, a h3-like ox brain protein. The following results were obtained: peptides generated by chymotrypsin, protease XX, BNPS-skatole and CNBr cleavage of different tissues in a single species were strikingly identical, whereas peptide maps obtained from analogue tissues in different species revealed slight structural differences. Possible ligand-h3 binding was studied by comparing the c.d. spectra of native h3, and h3 incubated with several phospholipids. Given the presence of h3 or h3-like protein in rat and human platelets, h3 was also assessed in platelet aggregation in the presence of h3 and specific anti-h3 antiserum. So far, the results emphasize the unique intra- and interspecies molecular form of h3, allow us to assign to known amino acid sequence of 21 kDa to a large extent to human h3, but do not identify h3 as a phospholipid binding protein.

Photothrombosis in rabbit brain cortex: follow up by continuous pO2 measurement.

Continuous recording of changes in local pO2 during and after brain infarction in surviving animals which can be followed for months or years, may provide interesting information concerning pathophysiology and treatment of stroke and thrombosis. We performed such measurements before, during and till 4 weeks after photochemical induction of a cerebrocortical infarction in three rabbits. Rose bengal--a photosensitive dye which sticks to endothelial cells and gives rise to endothelial damage and thrombosis when illuminated--was injected intravenously. After injection, a circular area (diameter 3 mm) of the brain cortex was illuminated using an optic fiber conducting light from a halogen lamp, whether or not filtered by heat and colour filters. In order to enable pO2 measurement in and near the infarct zone, we constructed a transparent plastic frame in which pO2 electrodes were fixed beneath and 1 mm besides a shaft permitting mounting of the optic fiber. A black adhesive ring (inner diameter 3 mm) was attached to the bottom of the frame providing a perfectly demarcated illumination area. After fixation the electrodes were calibrated and the frame was implanted in the rabbit's skull. Ten days later an infarction was induced; pO2 was monitored continuously before, during and till 4 hours after this induction. Furthermore, pO2 was recorded 24 hours, 48 hours, 5 days, 14 days and 4 weeks after infarction. Parameters describing the time course of pO2 were determined. In the illuminated area pO2 decreased after a certain latency time to reach a very low level, probably zero level, where it remained for at least 24 hours. Gradually, recovery was observed during the following days, and four weeks after infarction both level and pattern of electrode current appeared to be normal again. In the border zone pO2 decreased but did not reach zero level. Recovery was observed earlier than in the illuminated area.

PAF-acether induced arterial thrombosis and the effect of specific antagonists.

Platelet-vessel wall interactions and local thrombosis are investigated in vivo in a branch of the mesenteric artery of the guinea pig, using optoelectronic registration and ultrastructural control. Following an electrical challenge resulting in changes of cell membrane polarization, subsequent superfusion by PAF-acether or a stable analogue, (1-O-alkyl-2-N-methylcarbamyl-sn-glycero-3-phosphocholine, 10(-8) M focal concentration (f.c.)) for a restricted period results in endothelial cell retraction and bleb formation followed by platelet adhesion and the development of a thrombus which over time becomes invaded by leukocytes and eventually occludes the vascular lumen. It was demonstrated in a previous investigation that these phenomena are triggered by the generation of endogenous PAF-acether by the endothelial cells. Specific PAF-acether-antagonists, such as BN 52021 a ginkgolide, but also synthetic molecules, derivatives of the triazolo-pyridino-diazepine group (BN 50727, BN 50755 and BN 50789), significantly inhibit platelet-vessel wall interactions and thrombosis, but not the formation of blebs in the endothelial cells. Hydrogen peroxide (10(-5)M f.c.) not only primes the effect of PAF-acether, but is by itself capable of inducing thrombosis through a PAF-acether-mediated mechanism. Inhibition of acetyl hydrolase by PMSF (phenyl-methyl-sulfonyl-fluoride, 10(-5)M f.c.) invariably results in a significant enhancement of thrombosis, while conversely, inhibition of acetyl transferase by 27584 RP (4-(naphtylvinyl)pyridine hydrochloride, 10(-6)M f.c.) inhibits thromboformation indicating that the remodeling pathway is involved.

Construction, calibration and evaluation of pO2 electrodes for chronical implantation in the rabbit brain cortex.

Aiming at continuous polarographic measurement of the mean pO2 in the rabbit brain cortex before, during and after photochemically induced infarction, we designed and constructed monopolar platinum oxygen electrodes of the open type for chronical implantation. The measuring tip (length 1 mm, diameter 0.1 mm) is covered with a homogenous membrane of cellulose acetate. The electrode currents are measured by a four-channel amplifier of proper design; the device permits accurate and stable polarisation, identical for each channel. Moreover, a calibration device has been constructed. It consists of a Buchner funnel filled with Ringer solution and mounted in a temperature-controlled bath. In order to create a specific partial pressure of oxygen in the calibration chamber, predetermined gasmixtures are bubbled through the solution using computer controlled mass flow regulators. The calibration device thus permits the determination of primary and secondary electrode parameters, i.e. linearity, oxygen sensitivity and residual current, and polarisation dependency, temperature dependency, sensitivity to CO2, electrode stability, dynamic behaviour and oxygen consumption. Three groups, each of them containing ten electrodes, have been tested with regard to electrode parameters: the first group contains bare electrodes, the second and the third group contain membrane covered electrodes, with a membrane thickness of 10 and 20 microns respectively. In order to evaluate acute and long-term effects of implantation on the brain cortical tissue and on the sensors' measuring qualities, electrodes have been implanted for different time periods (51 days, 30 days, 9 days, 5 min). pO2 was recorded regularly and polarograms have been registered. The effects on cortical tissue have been studied with the aid of light microscopy.

Dual inhibition of thromboxane A2 synthesis and thromboxane A2/prostaglandin endoperoxide receptors by ridogrel: anti-thrombotic effect in vivo in rat mesenteric arteries.

In rats treated with acetylsalicylic acid (100 mg/kg i.v., -3 h) to block platelet cyclo-oxygenase, a superfusion with tranylcypromine (TCP, 3 x 10(-3) M) plus arachidonic acid (AA; 1 x 10(-4) M) significantly enhances (+70%) the opto-electronically monitored formation of a thrombus, elicited by a superfusion with ADP (4 x 10(-4) M for 45 s) over a de-endothelialized site of a mesenteric artery (200-300 microns diameter). Treatment with ridogrel at doses blocking either singly thromboxane A2 (TxA2) synthetase (0.63 mg/kg i.v., -15 min, n = 6) or additionally TxA2/prostaglandin endoperoxide receptors (5 mg/kg i.v., -15 min, n = 6) reduces (-74%) or abolishes (-100%) respectively the enhancement by TCP + AA of the ADP-induced thrombus formation. These observations demonstrate (1) a transfer of prostaglandin endoperoxides from the vessel wall to the platelets to reinforce thrombus formation in vivo; (2) the antithrombotic potential of combined TxA2 synthetase inhibition plus TxA2/prostaglandin endoperoxide receptor blockade with ridogrel.

Endotoxin, PAF and arterial thrombosis.

Using an optoelectronic device, we demonstrated that endotoxin modulates platelet-activating factor (PAF)-induced arterial thrombosis in a mesenteric artery of the guinea-pig. Indeed, topical superfusion by PAF induces the generation of platelet-vessel wall interactions, invariably followed by thrombus formation. A low dose of endotoxin markedly increased, while a high dose significantly reduced thrombus formation. The reducing effect of the high dose can be completely offset by indometacin, indicating the involvement of prostaglandin I2.

[Effect of cicletanine on prostacyclin generation in vivo]. / Effet du ciclétanine sur la génération de prostacycline in vivo.

The administration of arachidonic acid to live rabbits if followed by the generation of prostacyclin and/or thromboxane. Cicletanine increased the production of prostacyclin in a first group of rabbits and amplified the prostacyclin/thromboxane ratio in a second group of the thromboxane type. The most probable mechanism for this action is activation of prostacyclin synthase by cicletanine. This was confirmed in the in vivo model by a study of the platelet-vascular wall interaction: tranylcyprominE, a prostacyclin synthase inhibitor, increased the interaction. Under these experimental conditions, cicletanine inhibited the effect of tranylcypromine and completely restored the enzymatic activity of prostacyclin synthase.

PAF/cytokine auto-generated feedback networks in microvascular immune injury: consequences in shock, ischemia and graft rejection.

The catastrophe theory evolved by Thom and Zeeman proposes a mathematical definition for the abrupt or 'catastrophic' changes that can suddenly occur in normally well-ordered and smooth-running systems. We have integrated this theory with our own PAF/cytokine feedback network hypothesis to explain the control and dysfunction of the inflammatory response. This process involves the activation of cells and factors such as proteases, and is coordinated by mediators such as PAF, cytokines and growth factors, minute amounts of which can prime cells to respond in an enhanced manner to subsequent agonistic stimuli. PAF and certain cytokines also possess the unique property of being able to induce the release of each other and their own generation in vivo. This 'singularity' may enable a self-generating feedback network to become established. The priming ability of these mediators indicates the extreme sensitivity of the inflammatory process and importance of a homeostatic equilibrium between the vectors involved in the priming and feedback processes and internal suppressive mechanisms. In pathological conditions, one can consider the phenomenon of PAF and cytokine autogeneration as a 'fold' in the feedback network and an expression of the singularity characteristic of the catastrophe hypothesis. This may lead to systemic toxicity and microcirculatory collapse, a characteristic feature of shock, sepsis, asthma, ischemia and graft rejection. A combination of drugs antagonizing the various feedback components may inhibit this catastrophic process and thus provide more successful therapy of these conditions.

Is there a case for PAF antagonists in the treatment of ischemic states?

It is becoming clear that PAF plays an important role in a variety of life-threatening pathologies including shock, asthma, graft rejection and ischemia-induced damage. Pierre Braquet and colleagues analyse recent reports on PAF and ischemia and propose a hypothesis based on the catastrophe theory to explain why PAF antagonists are effective in countering ischemic injury and many other disorders. PAF antagonists, perhaps in combination with other agents, may consequently prove to have extensive therapeutic potential.

Role of cytokines and platelet-activating factor in microvascular immune injury.

Inflammation is usually a tightly controlled process which confines tissue damage, prevents infection, and assists in cellular regeneration. However, if the inflammatory response becomes unregulated, this normally beneficial local event may escalate into a wider malignant activity, characterized by endothelial injury, excessive cell infiltration, and vascular leakage. Due to the ability of platelet-activating factor and tumor necrosis factor to elicit the release of each other, 'prime' cell responses, and influence the activity of other cytokines, we propose that these two mediators play a pivotal role in the formation of deleterious feedback cycles leading to the above endothelial damage which may underlie pathologies such as shock, sepsis, ischemia, and asthma. Platelet-activating factor antagonists such as BN 52021 inhibit the priming and other effects induced by platelet-activating factor and thus may be of therapeutic value in such conditions.