Electrophysiology on Isolated Brainstem-spinal Cord Preparations from Newborn Rodents Allows Neural Respiratory Network Output Recording

While it is well known that the central respiratory drive is located in the brainstem, several aspects of its basic function, development, and response to ...

Laval University

We demonstrate that a beam of x-ray radiation can be generated by simply focusing a single high-intensity laser pulse into a gas jet. A millimeter-scale laser-produced plasma creates, accelerates, and wiggles an ultrashort and relativistic electron bunch. As they propagate in the ion channel produced in the wake of the laser pulse, the accelerated electrons undergo betatron oscillations, generating a femtosecond pulse of synchrotron radiation, which has keV energy and lies within a narrow (50 mrad) cone angle.

Production of a keV x-ray beam from synchrotron radiation in relativistic laser-plasma interaction.

We take advantage of nonlinear properties associated with chi(3) tensor elements in BaF2 cubic crystal to improve the temporal contrast of femtosecond laser pulses. The technique presented is based on cross-polarized wave (XPW) generation. We have obtained a transmission efficiency of 10% and 10(-10) contrast with an input pulse in the millijoule range. This filter does not affect the spectral shape or the phase of the cleaned pulse. It also acts as an efficient spatial filter. In this method the contrast enhancement is limited only by the extinction ratio of the polarization discrimination device.

10(-10) temporal contrast for femtosecond ultraintense lasers by cross-polarized wave generation.

We demonstrate that betatron x-ray radiation accurately provides direct imaging of electrons trajectories accelerated in laser wakefields. Experimental far field x-ray beam profiles reveal that electrons can follow similar transverse trajectories with typical excursions of 1.5 microm+/-0.5 microm in the plane of laser polarization and 0.7 microm+/-0.2 microm in the plane perpendicular.

Imaging electron trajectories in a laser-wakefield cavity using betatron X-ray radiation.

Relativistic electrons accelerated by laser wakefields can produce x-ray beams from their motion in plasma termed betatron oscillations. Detailed spectral characterization is presented in which the amplitude of the betatron oscillations r is studied by numerical analysis of electron and x-ray spectra measured simultaneously. We find that r reaches as low as 1 mum in agreement with previous studies of radiation based on coherence and far-field spatial profile.

Betatron oscillations of electrons accelerated in laser wakefields characterized by spectral x-ray analysis.

We propose a highly efficient scheme for temporal filters devoted to femtosecond pulse contrast enhancement. The filter is based on cross-polarized wave generation with a spatially suger-Gaussian-shaped beam. In a single nonlinear crystal scheme the energy conversion to the cross-polarized pulse can reach 28%. We demonstrate that the process enables a significant spectral broadening. For an efficiency of 23% the pulse shortening is estimated to 2.2, leading to an intensity transmission of the nonlinear filter of 50%.

Highly efficient nonlinear filter for femtosecond pulse contrast enhancement and pulse shortening.

We report on a compact energy-scalable device for generating high-fidelity femtosecond laser pulses based on spatial filtering through a hollow-core fiber followed by a nonlinear crystal for cross-polarized wave (XPW) generation. This versatile device is suited for temporal pulse cleaning over a wide range of input energies (from 0.1 to >10 mJ) and is successfully qualified on different ultrafast laser systems. Full characterization of the XPW output is presented. In particular, we demonstrate the generation of 1.6 mJ energy pulses starting from 11 mJ input pulse energy. The temporal contrast of the pulses is enhanced by more than 4 orders of magnitude. In addition, pulse shortening from 40 fs down to 15 fs Fourier-transform limit yields an overall peak-power transmission of up to 50%. This device not only serves as an integrated pulse contrast filter inside an ultrafast laser amplifier but also as a simple back-end solution for temporal post-compression of amplified pulses.

Energy-scalable temporal cleaning device for femtosecond laser pulses based on cross-polarized wave generation.

In vitro brain stem preparations from goldfish (Carassius auratus) were used to first determine whether this species possesses central chemoreceptors able to modulate respiratory activity. Preparations were superfused with an artificial cerebrospinal fluid (aCSF); fictive breathing was recorded extracellularly by placing a suction electrode on cranial nerve VII. Reducing the level of O2 in the gas mixture used to bubble the aCSF from a hyperoxic level (80% or 98.7% O2) to a relative hypoxic level (20% or 40% O2) increased the frequency of the fictive respiratory burst (P = 0.0002). Reducing the pH of the aCSF from 7.9 to 7.4 by increasing CO2 in the superfusate did not affect fictive breathing. Chloride-mediated neurotransmission (GABA/glycine) is a major modulator of respiratory activity; however, its effect on the neural circuits that regulate breathing in teleosts remains unknown. Bath application of GABA (0.5, 5.0 mM) decreased burst frequency but not amplitude; this effect was dose dependent (drug × concentration: P = 0.01). Superfusion of the preparations with aCSF containing 1.25 μM of bicuculline methochloride and 1.50 μM of strychnine hydrochloride (GABAA and glycine receptor antagonists, respectively) increased burst frequency (P = 0.002) and amplitude (P < 0.001). We conclude that respiratory activity produced by the goldfish brain stem is not responsive to the moderate CO2 levels used in this study; it may contain O2 chemoreceptors, but the relatively small response could also reflect nonspecific effects of hypoxia on the central nervous system. Cl(-)-mediated neurotransmission inhibits fictive breathing; this aspect of respiratory regulation is similar to other groups of vertebrates.

Control of breathing in in vitro brain stem preparation from goldfish (Carassius auratus; Linnaeus).

We present the first carrier-envelope-phase stable chirped-pulse amplifier (CPA) featuring high temporal contrast for relativistic intensity laser-plasma interactions at 1 kHz repetition rate. The laser is based on a double-CPA architecture including cross-polarized wave (XPW) filtering technique and a high-energy grism-based compressor. The 8 mJ, 22 fs pulses feature 10⁻¹¹ temporal contrast at -20  ps and a carrier-envelope-phase drift of 240 mrad root mean square.

Carrier-envelope-phase stable, high-contrast, double chirped-pulse-amplification laser system.

The emergence of air breathing during Lithobates catesbeianus development requires significant changes to the brainstem circuits that generate and regulate breathing; however, the mechanisms responsible for initiating this transformation remain largely unknown. Because amphibian metamorphosis is regulated by hormones such as aldosterone, corticosterone, and thyroid hormone (T3), we tested the hypothesis that exposing the brainstem to these hormones augments the fictive air breathing frequency in pre-metamorphic tadpoles. Brainstems were isolated and were placed either in the recording chamber (acute; 1h+1h recovery) or in a bottle (chronic exposure; 24h) for treatment. Brainstems were exposed to artificial cerebrospinal fluid (aCSF; sham treatment) or one of the following hormones: aldosterone (100nM), corticosterone (100nM), or T3 (100nM). While acute exposure had limited effects on respiratory motor output, chronic incubation with any hormone significantly increased fictive air breathing; the burst frequencies observed following treatment were similar to those observed in adult bullfrogs. We conclude that through their long term effects, hormones regulating metamorphosis can initiate the maturation of the neural circuits that generate and regulate breathing in this species.

Aldosterone, corticosterone, and thyroid hormone and their influence on respiratory control development in Lithobates catesbeianus: An in vitro study.

We present a setup for complete characterization of femtosecond pulses generated by seeded free-electron lasers (FELs) in the extreme-ultraviolet spectral region. Two delayed and spectrally shifted replicas are produced and used for spectral phase interferometry for direct electric field reconstruction (SPIDER). We show that it can be achieved by a simple arrangement of the seed laser. Temporal shape and phase obtained in FEL simulations are well retrieved by SPIDER reconstructions, allowing to foresee the implementation of this diagnostics tool on existing and future sources. This will be a significant step towards an experimental investigation and control of FEL spectral phase.

Spectral-phase interferometry for direct electric-field reconstruction applied to seeded extreme-ultraviolet free-electron lasers.

Respiratory reflexes and tolerance to hypoxia show significant sexual dimorphism. However, the data supporting this notion originates exclusively from mammals. To determine whether this concept is limited to this group of vertebrates, we examined the sex-specific response to acute hypoxia in an adult reduced brainstem preparation from adult Xenopus laevis. Within the first 5min of exposure to hypoxic aCSF (98% N2/2% CO2), recordings of respiratory-related activity show a stronger increase in fictive breathing frequency in males than females. This initial response was followed by a decrease in respiratory-related activity; this depression occurred 6min sooner in males than females. These results represent new evidences of sexual dimorphism in respiratory control in amphibians and provide potential insight in understanding the homology with other groups of vertebrates, including mammals.

Jean-Philippe Rousseau

Department of Pediatrics

Laval University

Electrophysiology on Isolated Brainstem-spinal Cord Preparations from Newborn Rodents Allows Neural Respiratory Network Output Recording

Jean-Philippe Rousseau

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Pediatrics

Laval University

Electrophysiology on Isolated Brainstem-spinal Cord Preparations from Newborn Rodents Allows Neural Respiratory Network Output Recording

Department of Pediatrics