Temporary induction of hypoxic adaptations by preconditioning fails to enhance Schwann cell transplant survival after spinal cord injury.

Hypoxic preconditioning is protective in multiple models of injury and disease, but whether it is beneficial for cells transplanted into sites of spinal cord injury (SCI) is largely unexplored. In this study, we analyzed whether hypoxia-related preconditioning protected Schwann cells (SCs) transplanted into the contused thoracic rat spinal cord. Hypoxic preconditioning was induced in SCs prior to transplantation by exposure to either low oxygen (1% O2 ) or pharmacological agents (deferoxamine or adaptaquin). All preconditioning approaches induced hypoxic adaptations, including increased expression of HIF-1α and its target genes. These adaptations, however, were transient and resolved within 24 h of transplantation. Pharmacological preconditioning attenuated spinal cord oxidative stress and enhanced transplant vascularization, but it did not improve either transplanted cell survival or recovery of sensory or motor function. Together, these experiments show that hypoxia-related preconditioning is ineffective at augmenting either cell survival or the functional outcomes of SC-SCI transplants. They also reveal that the benefits of hypoxia-related adaptations induced by preconditioning for cell transplant therapies are not universal.

Generation of sub-100 fs ultraviolet pulses from a Kerr-lens mode-locked Ce:LiCAF laser.

We report the direct generation of mode-locked pulses as short as 91 fs from the broad-bandwidth gain medium of LiCaAlF6 (Ce:LiCAF) by combining Kerr-lens mode locking with synchronous pumping. The latter of these schemes, and the broad bandwidth of Ce:LiCAF, resulted in dispersion tuning of wavelength via cavity length in the spectral region of 290 nm; this mechanism facilitated a practical means of estimating intra-cavity dispersion, which was compensated for using a Brewster's-cut prism pair. The pulse duration was measured via split-beam asynchronous cross-correlation using a Ti:sapphire reference laser and a known time reference. From the Ce:LiCAF laser cavity, output powers of 110 mW and a 9% slope efficiency were achieved.

3D-M3: high-spatial-resolution spectroscopy with extreme AO and 3D-printed micro-lenslets.

By combining integral field spectroscopy with extreme adaptive optics, we are now able to resolve objects close to the diffraction limit of large telescopes, exploring new science cases. We introduce an integral field unit designed to couple light with a minimal plate scale from the SCExAO facility at NIR wavelengths to a single-mode spectrograph. The integral field unit has a 3D-printed micro-lens array on top of a custom single-mode multi-core fiber, to optimize the coupling of light into the fiber cores. We demonstrate the potential of the instrument via initial results from the first on-sky runs at the 8.2 m Subaru Telescope with a spectrograph using off-the-shelf optics, allowing for rapid development with low cost.

Treatment with hypoxia-mimetics protects cultured rat Schwann cells against oxidative stress-induced cell death.

Schwann cell (SC) grafts promote axon regeneration in the injured spinal cord, but transplant efficacy is diminished by a high death rate in the first 2-3 days postimplantation. Both hypoxic preconditioning and pharmacological induction of the cellular hypoxic response can drive cellular adaptations and improve transplant survival in a number of disease/injury models. Hypoxia-inducible factor 1 alpha (HIF-1α), a regulator of the cellular response to hypoxia, is implicated in preconditioning-associated protection. HIF-1α cellular levels are regulated by the HIF-prolyl hydroxylases (HIF-PHDs). Pharmacological inhibition of the HIF-PHDs mimics hypoxic preconditioning and provides a method to induce adaptive hypoxic responses without direct exposure to hypoxia. In this study, we show that hypoxia-mimetics, deferoxamine (DFO) and adaptaquin (AQ), enhance HIF-1α stability and HIF-1α target gene expression. Expression profiling of hypoxia-related genes demonstrates that HIF-dependent and HIF-independent expression changes occur. Analyses of transcription factor binding sites identify several candidate transcriptional co-regulators that vary in SCs along with HIF-1α. Using an in vitro model system, we show that hypoxia-mimetics are potent blockers of oxidative stress-induced death in SCs. In contrast, traditional hypoxic preconditioning was not protective. The robust protection induced by pharmacological preconditioning, particularly with DFO, indicates that pharmacological induction of hypoxic adaptations could be useful for promoting transplanted SC survival. These agents may also be more broadly useful for protecting SCs, as oxidative stress is a major pathway that drives cellular damage in the context of neurological injury and disease, including demyelinating diseases and peripheral neuropathies.

Beam shaping of a broad-area laser diode using 3D integrated optics.

Typical high power broad-area semiconductor lasers exhibit a highly astigmatic beam profile. However, many applications require a homogenous and circular symmetric beam. Thus coupling into circular multimode optical fibers is often employed. The strip-like astigmatic output of the diode laser underfills the circular multimode fiber, thus a decrease in beam quality occurs after fiber coupling due to mode mixing inside the optical fiber. This Letter presents a 3D integrated optics approach to shape the output of a broad-area laser diode. Ultrafast laser inscription is utilized to create a pair of photonic lanterns connected back to back inside a glass chip that captures and shapes the output of a commercial 976 nm wavelength broad-area laser diode with 95 µm emitter width. Compared to coupling to a 105 µm diameter, 0.15 numerical aperture step-index multimode fiber, the photonic chip-based approach results in a 13× higher beam quality and 7× greater brightness.

Efficient Remyelination Requires DNA Methylation.

Oligodendrocyte progenitor cells (OPCs) are the principal source of new myelin in the central nervous system. A better understanding of how they mature into myelin-forming cells is of high relevance for remyelination. It has recently been demonstrated that during developmental myelination, the DNA methyltransferase 1 (DNMT1), but not DNMT3A, is critical for regulating proliferation and differentiation of OPCs into myelinating oligodendrocytes (OLs). However, it remains to be determined whether DNA methylation is also critical for the differentiation of adult OPCs during remyelination. After lysolecithin-induced demyelination in the ventrolateral spinal cord white matter of adult mice of either sex, we detected increased levels of DNA methylation and higher expression levels of the DNA methyltransferase DNMT3A and lower levels of DNMT1 in differentiating adult OLs. To functionally assess the role of DNMT1 and DNMT3 in adult OPCs, we used mice with inducible and lineage-specific ablation of Dnmt3a and/or Dnmt1 (i.e., Plp-creER(t);Dnmt3a-flox, Plp-creER(t);Dnmt1-flox, Plp-creER(t);Dnmt1-flox;Dnmt3a-flox). Upon lysolecithin injection in the spinal cord of these transgenic mice, we detected defective OPC differentiation and inefficient remyelination in the Dnmt3a null and Dnmt1/Dnmt3a null mice, but not in the Dnmt1 null mice. Taken together with previous results in the developing spinal cord, these data suggest an age-dependent role of distinct DNA methyltransferases in the oligodendrocyte lineage, with a dominant role for DNMT1 in neonatal OPCs and for DNMT3A in adult OPCs.

Linewidth narrowing of a tunable mode-locked pumped continuous-wave Ce:LiCAF laser.

We report birefringent tuning using single and multiple magnesium fluoride (MgF(2)) Brewster tuning plates in a mode-locked pumped continuous-wave Ce:LiCAF laser. Depending on the thickness of the MgF(2) plates used, continuous tuning over a range of up to 13 nm from 284.5 to 297.5 nm with a full width at half-maximum linewidth of 14 pm (50 GHz) was achieved. By combining MgF(2) plates with etalons, the linewidth of the laser was narrowed down to 0.75 pm (2.7 GHz). This generated narrowband output is suitable for many applications in spectroscopy, cold-atom manipulation, and sensing.

SRS in the strong-focusing regime for Raman amplifiers.

The theoretical analysis of stimulated Raman scattering (SRS) in crystalline amplifiers with a tightly-focused pump geometry is presented. We predict the minimum Stokes seed power required for an efficient Raman power amplifier and verify this result experimentally. Conversion of a pump to a Stokes beam in a single-pass diamond amplifier is demonstrated using nanosecond pulses with gains of 5.8 from a 1.2-kW peak-power Stokes seed beam. The results demonstrate the possibility of amplifying and combining high-power continuous-wave lasers using current diamond Raman laser technology.

Dynamics of solid-state lasers pumped by mode-locked lasers.

We analyze the dynamics of mode-locked pumped solid-state lasers focusing on the transition between mode-locked and CW behavior. Where the ratio of the pump and laser cavity lengths is a rational number, 'rational-harmonic mode-locking' is obtained. When the cavity length is detuned away from such resonances, modulated continuous output is generated. The transition from mode-locked to modulated CW operation is explored experimentally for a Ce:LiCAF laser operating at 290 nm and pumped by a 78.75 MHz mode-locked frequency quadrupled Nd:YVO(4) laser. Both CW output and mode-locked output with pulse repetition rates up to 1.1 GHz were achieved. A rate equation model is developed to predict optimum cavity lengths for achieving CW output with minimized modulation.

Acetaldehyde, not ethanol, impairs myelin formation and viability in primary mouse oligodendrocytes.

BACKGROUND: Excessive ethanol (EtOH) drinking is associated with white matter loss in the brain at all stages of life. Myelin-forming oligodendrocytes (OLs) are a major component of white matter, but their involvement in EtOH-mediated white matter loss is unclear. Myelination continues throughout the life with highest rates during fetal development and adolescence. However, little is known about the effects of EtOH and its principal metabolite acetaldehyde (ACD) on OLs at the cellular level. METHODS: We compared the responses to different concentrations of EtOH or ACD by primary OLs in culture. RESULTS: EtOH did not cause significant cell death at concentrations lower than 120 mM, even after 24 hours. In comparison, ACD was highly lethal at doses above 50 µM. High concentrations of EtOH (120 mM) and ACD (500 µM) for 24 hours did not reduce myelin in mature OLs. Myelin production and OL differentiation were significantly impaired by 7 days exposure to 500 or 50 µM ACD but not 120 mM EtOH. CONCLUSIONS: This study shows that OLs are relatively resistant to EtOH, even at a concentration more than 4 times the typical blood EtOH concentrations associated with social drinking (10 to 30 mM). In contrast, OLs are much more sensitive to ACD than EtOH, particularly with long-term exposure. This suggests that part of white matter loss in response to EtOH, especially during high rates of myelin formation, may be due in part to the effects of its principal metabolite ACD.

Tunable continuous-wave deep-ultraviolet laser based on Ce:LiCAF.

We demonstrate chopped-cw lasing in a Ce:LiCAF oscillator directly generating deep-UV light around 290 nm. The cw output was achieved by asynchronous pumping of a Ce:LiCAF oscillator by a mode-locked frequency quadrupled Nd:YVO4 laser that generates 23 ps pulses of 266 nm light at a repetition rate of 80 MHz. The pump laser was chopped with 8.3% duty cycle to minimize thermal effects in the frequency quadrupling stage. The maximum output power achieved was 384 mW when pumped with 3.3 W of pulsed 266 nm light, with a slope efficiency of 33%. The laser output was tunable from 286 to 295 nm with the potential to be broadened over the full gain bandwidth of Ce:LiCAF from 280 to 315 nm.

Highly efficient picosecond diamond Raman laser at 1240 and 1485 nm.

We present a highly efficient picosecond diamond Raman laser synchronously-pumped by a 4.8 W mode-locked laser at 1064 nm. A ring cavity was adopted for efficient operation. With a low-Q cavity for first-Stokes 1240 nm, we have achieved 2.75 W output power at 1240 nm with 59% overall conversion efficiency. The slope efficiency tended towards 76% far above the SRS threshold, approaching the SRS quantum limit for diamond. A high-Q first-Stokes cavity was employed for second-Stokes 1485 nm generation through the combined processes of four-wave mixing and single-pass stimulated Raman scattering. Up to 1.0 W of second-stokes at 1485 nm was obtained, corresponding to 21% overall conversion efficiency. The minimum output pulse duration was compressed relative to the 15 ps pump, producing pulses as short as 9 ps for 1240 nm and 6 ps for 1485 nm respectively.

Embryonic-derived olfactory ensheathing cells remyelinate focal areas of spinal cord demyelination more efficiently than neonatal or adult-derived cells.

Transplanted olfactory ensheathing cells (OECs) contribute to functional recovery in a range of CNS injuries by several mechanisms, one of which is potentially their ability to form myelin sheaths. OECs sourced from donors of different ages have been shown to remyelinate in several in vitro and in vivo models. However, the optimal donor age for OEC associated remyelination is unclear. This project directly compared the remyelinating potential of p75 purified OEC transplants from three donor ages. OECs were sourced from the olfactory bulbs of embryonic, neonatal, and adult rats and purified by immunopanning, and their remyelinating potential was directly compared by transplantation into the same adult rat toxin-induced model of spinal cord demyelination. Remyelination efficiency 3 weeks after transplantation was assessed morphologically and by immunostaining. Our results indicate that all donor ages remyelinate; however, this process is most efficiently achieved by embryonic-derived OECs.

Hypoxia-inducible factor 1alpha induces corticosteroid-insensitive inflammation via reduction of histone deacetylase-2 transcription.

Corticosteroids are potent anti-inflammatory agents, but corticosteroid insensitivity is a major barrier for the treatment of some chronic inflammatory diseases. Here, we show that hypoxia induces corticosteroid-insensitive inflammation via reduced transcription of histone deacetylase-2 (HDAC2) in lung epithelial and macrophage cells. HDAC2 mRNA and protein expression was reduced under hypoxic conditions (1% O(2)). Hypoxia enhanced interleukin-1beta-induced interleukin-8 (CXCL8) production in A549 cells and decreased the ability of dexamethasone to suppress the CXCL8 production. Deletion or point mutation studies revealed that binding of the transcription factor hypoxia-inducible factor (HIF) 1alpha to a HIF response element at position -320, but not HIF-1beta or HIF-2alpha, results in reduced polymerase II binding at the site, leading to reduced promoter activity of HDAC2. Our results suggest that activation of HIF-1alpha by hypoxia decreases HDAC2 levels, resulting in amplified inflammation and corticosteroid resistance.

Mode-locked deep ultraviolet Ce:LiCAF laser.

We report mode-locked operation of a synchronously pumped Ce:LiCAF oscillator. The laser operated in the deep UV with output radiation centered at 291 nm and a pulse duration of 6 ps. The maximum output power measured was 52 mW, with 13% slope efficiency. The Ce:LiCAF crystal has a gain bandwidth capable of supporting few-femtosecond pulses, and so our results demonstrate the potential to form a new class of ultrafast lasers operating directly at deep UV wavelengths.

Method for determination of the volume of material ejected as molten droplets during visible nanosecond ablation.

A novel method is presented for determining the volume of molten material ejected from a substrate as a result of visible pulsed-laser ablation. A 100-microm-wide pulsed-laser light sheet (tau approximately 5 ns, lambda = 532 nm) was used in conjunction with a CCD camera to provide high-speed cross-sectional images of single-pulse ablation of aluminum with a visible nanosecond laser source. Computational analysis of the two-dimensional gray-scale images was used to determine the total volume of material ejected from the substrate in the form of molten droplets. Ablation with dual-wavelength (511- and 578-nm) pulses of 30-ns duration was characterized under various fluence conditions (0-25 J cm(-2)), allowing a quantitative threshold for explosive melt ejection in aluminum to be established at approximately 10 J cm(-2). The temporal evolution of the ejected material showed that, for an incident fluence of approximately 40 J cm(-2), molten-droplet ejection commenced at approximately 400 ns and ceased after approximately 2 micros.

Compact 2.5-W 10-kHz Nd:YLF-pumped dye laser.

A 10-kHz pulse repetition frequency dye laser, end pumped by a Nd:YLF laser, is reported. This laser was tunable from 590 to 655 nm, and up to 2.55 W of output power was obtained at the 609-nm peak tuning wavelength. By inserting an etalon into the dye laser cavity and frequency doubling using a beta-barium borate crystal, we obtained up to 125 mW of 308-nm single-etalon-mode output, which shows potential for the performance of airborne measurements of tropospheric hydroxyl radical concentrations.