High-responsivity operation of quantum cascade detectors at 9 µm

Quantum cascade detectors (QCDs) are devices operating at zero external bias with a low dark-current. They show linear detection and high saturation intensities, making them suitable candidates for heterodyne detection in long-wave infrared (LWIR) free space optical communication systems. We present an approach to mitigate the performance limitation at long wavelengths, by a comparison of similar single and multi-period QCDs for optimizing their responsivity and noise behaviour. Our InGaAs/InAlAs/InP ridge QCDs are designed for operation at λ = 9.124 µm. Optical waveguide simulations support the accurate optical characterization. A detailed device analysis reveals room-temperature responsivities of 111 mA/W for the 15-period and 411 mA/W for the single-period device.

All-optical adaptive control of quantum cascade random lasers

Spectral fingerprints of molecules are mostly accessible in the terahertz (THz) and mid-infrared ranges, such that efficient molecular-detection technologies rely on broadband coherent light sources at such frequencies. If THz Quantum Cascade Lasers can achieve octave-spanning bandwidth, their tunability and wavelength selectivity are often constrained by the geometry of their cavity. Here we introduce an adaptive control scheme for the generation of THz light in Quantum Cascade Random Lasers, whose emission spectra are reshaped by applying an optical field that restructures the permittivity of the active medium. Using a spatial light modulator combined with an optimization procedure, a beam in the near infrared (NIR) is spatially patterned to transform an initially multi-mode THz random laser into a tunable single-mode source. Moreover, we show that local NIR illumination can be used to spatially sense complex near-field interactions amongst modes. Our approach provides access to new degrees of freedom that can be harnessed to create broadly-tunable sources with interesting potential for applications like self-referenced spectroscopy.

Tunable quantum cascade lasers can enable applications in multiple areas. Here, the authors demonstrate the adaptive control of the modes and emission spectra of quantum cascade random lasers through a spatially-tailored optical modulation of the active region.

4.3 μm quantum cascade detector in pixel configuration

We present the design simulation and characterization of a quantum cascade detector operating at 4.3μm wavelength. Array integration and packaging processes were investigated. The device operates in the 4.3μm CO₂ absorption region and consists of 64 pixels. The detector is designed fully compatible to standard processing and material growth methods for scalability to large pixel counts. The detector design is optimized for a high device resistance at elevated temperatures. A QCD simulation model was enhanced for resistance and responsivity optimization. The substrate illuminated pixels utilize a two dimensional Au diffraction grating to couple the light to the active region. A single pixel responsivity of 16mA/W at room temperature with a specific detectivity D^* of 5⋅10⁷ cmHz/W was measured.

Nucleation of Ga droplets on Si and SiOx surfaces

We report on gallium droplet nucleation on silicon (100) substrates with and without the presence of the native oxide. The gallium deposition is carried out under ultra-high vacuum conditions at temperatures between 580 and 630 °C. The total droplet volume, obtained from a fit to the diameter-density relation, is used for sample analysis on clean silicon surfaces. Through a variation of the 2D equivalent Ga thickness, the droplet diameter was found to be between 250-1000 nm. Longer annealing times resulted in a decrease of the total droplet volume. Substrate temperatures of 630 °C and above led to Ga etching into the Si substrates and caused Si precipitation around the droplets. In contrast, we obtained an almost constant diameter distribution around 75 nm over a density range of more than two orders of magnitude in the presence of a native oxide layer. Furthermore, the droplet nucleation was found to correlate with the density of surface features on the 'epi-ready' wafer.

Quantum cascade detector utilizing the diagonal-transition scheme for high quality cavities

A diagonal optically active transition in a quantum cascade detector is introduced as optimization parameter to obtain quality factor matching between a photodetector and a cavity. A more diagonal transition yields both higher extraction efficiency and lower noise, while the reduction of the absorption strength is compensated by the resonant cavity. The theoretical limits of such a scheme are obtained, and the impact of losses and cavity processing variations are evaluated. By optimizing the quantum design for a high quality cavity, a specific detectivity of 10(9) Jones can be calculated for λ = 8μm and T = 300K.

Resonant metamaterial detectors based on THz quantum-cascade structures

We present the design, fabrication and characterisation of an intersubband detector employing a resonant metamaterial coupling structure. The semiconductor heterostructure relies on a conventional THz quantum-cascade laser design and is operated at zero bias for the detector operation. The same active region can be used to generate or detect light depending on the bias conditions and the vertical confinement. The metamaterial is processed directly into the top metal contact and is used to couple normal incidence radiation resonantly to the intersubband transitions. The device is capable of detecting light below and above the reststrahlenband of gallium-arsenide corresponding to the mid-infrared and THz spectral region.

Detectivity enhancement in quantum well infrared photodetectors utilizing a photonic crystal slab resonator

We characterize the performance of a quantum well infrared photodetector (QWIP), which is fabricated as a photonic crystal slab (PCS) resonator. The strongest resonance of the PCS is designed to coincide with the absorption peak frequency at 7.6 µm of the QWIP. To accurately characterize the detector performance, it is illuminated by using single mode mid-infrared lasers. The strong resonant absorption enhancement yields a detectivity increase of up to 20 times. This enhancement is a combined effect of increased responsivity and noise current reduction. With increasing temperature, we observe a red shift of the PCS-QWIP resonance peak of -0.055 cm(-1)/K. We attribute this effect to a refractive index change and present a model based on the revised plane wave method.

Patterning small-molecule biocapture surfaces: microcontact insertion printing vs. photolithography

Chemical patterns prepared by self-assembly, combined with soft lithography or photolithography, are directly compared. Pattern fidelity can be controlled in both cases but patterning at the low densities necessary for small-molecule probe capture of large biomolecule targets is better accomplished using microcontact insertion printing (μCIP). Surfaces patterned by μCIP are used to capture biomolecule binding partners for the small molecules dopamine and biotin.

Ultrastrong light-matter coupling regime with polariton dots

The regime of ultrastrong light-matter interaction has been investigated theoretically and experimentally, using zero-dimensional electromagnetic resonators coupled with an electronic transition between two confined states of a semiconductor quantum well. We have measured a splitting between the coupled modes that amounts to 48% of the energy transition, the highest ratio ever observed in a light-matter coupled system. Our analysis, based on a microscopic quantum theory, shows that the nonlinear polariton splitting, a signature of this regime, is a dynamical effect arising from the self-interaction of the collective electronic polarization with its own emitted field.

Optical properties of metal-dielectric-metal microcavities in the THz frequency range

We present an experimental and theoretical study of the optical properties of metal-dielectric-metal structures with patterned top metallic surfaces, in the THz frequency range. When the thickness of the dielectric slab is very small with respect to the wavelength, these structures are able to support strongly localized electromagnetic modes, concentrated in the subwavelength metal-metal regions. We provide a detailed analysis of the physical mechanisms which give rise to these photonic modes. Furthermore, our model quantitatively predicts the resonance positions and their coupling to free space photons. We demonstrate that these structures provide an efficient and controllable way to convert the energy of far field propagating waves into near field energy.

Electrically controllable photonic molecule laser

We have studied the coherent intercavity coupling of the evanescent fields of two microdisk terahertz quantum-cascade lasers. The electrically controllable optical coupling of the single-mode operating lasers has been observed for cavity spacings up to 30 mum. The strongest coupled photonic molecule with 2 mum intercavity spacing allows to conditionally switch the optical emission by the electrical modulation of only one microdisk. The lasing threshold characteristics demonstrate the linear dependence of the gain of a quantum-cascade laser on the applied electric field.

Strong light-matter coupling in subwavelength metal-dielectric microcavities at terahertz frequencies

We have demonstrated that a metal-dielectric-metal microcavity combined with quantum well intersubband transitions is an ideal system for the generation of cavity polariton states in the terahertz region. The metallic cavity has highly confined radiation modes that can be tuned in resonance with the intersubband transition. In this system we were able to measure a very strong light-matter splitting (the Rabi splitting 2 variant Planck's over 2pi Omega R), corresponding to 22% of the transition energy. We believe this result to be the first demonstration of intersubband polaritons in the terahertz frequency range.

Fano signatures in the intersubband terahertz response of optically excited semiconductor quantum wells

Absorption and transmission spectra of broadband terahertz pulses are measured to probe the intersubband response of an optically excited quantum-well heterostructure. While the terahertz absorption shows the single peak of the resonant intersubband transition, the transmission spectra display strong Fano signatures due to the phase sensitive superposition of ponderomotive and terahertz currents as predicted by our microscopic theory.

Active photonic crystal terahertz laser

We present the design and the realization of active photonic crystal (PhC) semiconductor lasers. The PhC consists of semiconductor nanostructure pillars which provide gain at a quantized transition energy. The vertical layer sequence is that of a terahertz quantum cascade laser. Thereby, the artificial crystal itself provides the optical gain and the lateral confinement. The cavities do not rely on a central defect, the lasing is observed in flat-band regions at high symmetry points. The experimental results are in excellent agreement with the finite-difference time-domain simulations. For the vertical confinement a double-metal waveguide is used. The lasers are showing a stable single-mode emission under all driving conditions. Varying the period of the PhC allows to tune the frequency by 400 GHz.

Terahertz photonic crystal resonators in double-metal waveguides

We present the design and the fabrication of photonic crystals with a complete bandgap for TM-modes used as a resonator for terahertz quantum-cascade lasers (QCL), which are lasing around 2.7 THz. The emission of the devices with and without a photonic crystal shows a shift in the emission from the gain maximum to the bandgap of the crystal. The devices are built up by a core, which provides the optical gain, and by a surrounding photonic crystal, which acts as a frequency selective mirror. The whole device is processed into a double-metal waveguide.

Reduced brain-derived neurotrophic factor is associated with a loss of serotonergic innervation in the hippocampus of aging mice

Brain-derived neurotrophic factor (BDNF) regulates monoamine neuronal growth, survival and function in development and throughout adulthood. At 18 months of age, mice with constitutive reductions in BDNF expression show decreased serotonin innervation in the hippocampus compared with age-matched wildtype mice. It is not known, however, whether age-accelerated loss of serotonergic innervation in BDNF(+/-) mice occurs in other brain regions, advances beyond 18 months or is associated with alterations in other neurotransmitter systems. In this study, immunocytochemistry was used to assess serotonergic and catecholaminergic innervation in 26-month-old BDNF(+/-) mice. Age-related loss of serotonin axons in the hippocampus was potentiated in BDNF(+/-) mice compared with wildtype mice at this late age, particularly in the CA1 subregion. By contrast, aging BDNF(+/-) mice showed increased serotonin innervation of the basomedial nucleus of the amygdala. In the noradrenergic system, BDNF(+/-) mice showed reduced numbers of cell bodies and fibers in the locus coeruleus compared with age-matched wildtype mice, whereas no changes were observed in dopaminergic innervation with respect to genotype. In vivo zero net flux microdialysis in awake mice showed a significant decrease in extracellular serotonin levels in the hippocampus in BDNF(+/-) mice at 20 months of age. Thus, reduced BDNF is associated with altered serotonergic and noradrenergic innervation in aging mice and, in particular, with accelerated loss of serotonergic innervation to the hippocampus that is manifest as a decrease in basal neurotransmission.

One-year follow-up evaluation of the sexually transmitted diseases/human immunodeficiency virus intervention program in a marine corps sample

Although a substantial number of studies have been conducted to evaluate the impact of various human immunodeficiency virus (HIV) prevention programs, most of them have focused on civilian populations. There is a clear need to develop and evaluate sexually transmitted diseases (STD)/HIV prevention programs designed specifically for U.S. military populations. The objective of the present study was to determine whether a behavioral intervention known as the STD/HIV Intervention Program (SHIP) would have a sustained positive impact on the behavior of a sample of Marines. A 1-year follow-up telephone interview was administered to (1) Marines who participated in the SHIP course (intervention group), and (2) a quasi-control group of Marines who were not exposed to the SHIP course. The intervention and control groups differed significantly in the percentage of the time they had used condoms during the past year. The intervention participants reported using condoms a greater percentage of the time than the nonparticipants.

Molecular mechanisms of cocaine reward: combined dopamine and serotonin transporter knockouts eliminate cocaine place preference

Cocaine blocks uptake by neuronal plasma membrane transporters for dopamine (DAT), serotonin (SERT), and norepinephrine (NET). Cocaine reward/reinforcement has been linked to actions at DAT or to blockade of SERT. However, knockouts of neither DAT, SERT, or NET reduce cocaine reward/reinforcement, leaving substantial uncertainty about cocaine's molecular mechanisms for reward. Conceivably, the molecular bases of cocaine reward might display sufficient redundancy that either DAT or SERT might be able to mediate cocaine reward in the other's absence. To test this hypothesis, we examined double knockout mice with deletions of one or both copies of both the DAT and SERT genes. These mice display viability, weight gain, histologic features, neurochemical parameters, and baseline behavioral features that allow tests of cocaine influences. Mice with even a single wild-type DAT gene copy and no SERT copies retain cocaine reward/reinforcement, as measured by conditioned place-preference testing. However, mice with no DAT and either no or one SERT gene copy display no preference for places where they have previously received cocaine. The serotonin dependence of cocaine reward in DAT knockout mice is thus confirmed by the elimination of cocaine place preference in DAT/SERT double knockout mice. These results provide insights into the brain molecular targets necessary for cocaine reward in knockout mice that develop in their absence and suggest novel strategies for anticocaine medication development.

Systemic administration of domoic acid-induced spinal cord lesions in neonatal rats

Domoic acid (Dom) is a glutamate analog and a seafood toxin that has caused neurological disturbance and death in humans. Brain lesions caused by Dom have been documented in the literature, but the effect of Dom on the spinal cord has not been investigated as extensively. Systemic administration of glutamate agonists (i.e., homocysteate, kainate, and a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) caused spinal cord lesions in infant rats. In the present study, the toxic effects of Dom on the developing spinal cord are examined. Neonatal rats on Postnatal Day 7 were administered Dom subcutaneously at doses of 0.10, 0.17, 0.25, 0.33, 0.42, and 0.50 mg/kg, respectively. Motor seizures characterized by scratching, tail flicking, and swimming-like movement were induced by Dom at all doses. High doses of Dom (> or = 0.33 mg/kg) further induced a hindlimb paralysis, a forelimb tremor, and death that occurred in less than 2 hours. The percentages of death and paralysis induced by 0.33 mg/kg Dom were 47% and 65%, respectively (n = 17). At this dose, electrocorticogram was recorded and synchronized interrupted electrical activities in brains of these animals were detected. However, no brain damage was detected in these rats. Spinal cord lesions characterized by focal hemorrhage, neuronal swelling, and neuronal vacuolization were found in 73% of the animals that had shown the paralysis/tremor in their extremities, as examined 1 to 2 hours after Dom injection. These lesions were seen at all spinal cord levels. Neuronal degeneration was mainly found in the ventral and intermediate gray matter, whereas cells in the dorsal portion of the spinal cord were relatively spared. Data suggest that observed behavioral changes were due to spinal cord damage rather than seizures or brain lesions.

The anti-microbial activity of maggot secretions: results of a preliminary study

The ability of larval secretions to kill or prevent the growth of a range of potentially pathogenic bacteria was investigated in a preliminary laboratory study. Marked anti-microbial activity was detected against Streptococcus A and B and Staphylococcus aureus. Some activity was also detected against Pseudomonas sp. and a clinical isolate of a resistant strain of S. aureus (MRSA). No evidence of inhibition was recorded against Enterococcus or the Gram-negative bacteria Escherichia coli and Proteus. These findings are consistent with clinical observations made by us and others that larvae of the common greenbottle are able to combat clinical infections in a variety of wound types including those caused by antibiotic-resistant strains of bacteria.

Overexpression of human copper/zinc superoxide dismutase in transgenic mice attenuates oxidative stress caused by methylenedioxymethamphetamine (Ecstasy)

Administration of 3,4-methylenedioxymethamphetamine (4 x 20 mg/kg) to non-transgenic CD-1 mice caused marked depletion in dopamine, 3,4-dihydroxyphenylacetic acid and 5-hydroxytryptamine in the caudate-putamen. There were no significant changes in serotonergic markers in the hippocampus and frontal cortex. Homozygous and heterozygous copper/zinc superoxide dismutase transgenic mice show partial protection against the toxic effects of 3,4-methylenedioxymethamphetamine on striatal dopaminergic markers. In addition, 3,4-methylenedioxymethamphetamine injections caused marked decreases in copper/zinc superoxide dismutase activity in the frontal cortex, caudate-putamen and hippocampus of wild-type mice. Moreover, there were concomitant 3,4-methylenedioxymethamphetamine-induced decreases in catalase activity in the caudate-putamen and hippocampus, decreases in glutathione peroxidase activity in the frontal cortex as well as increases in lipid peroxidation in the frontal cortex, caudate-putamen, and hippocampus of wild-type mice. In contrast, administration of 3,4-methylenedioxymethamphetamine to homozygous superoxide dismutase transgenic mice caused no significant changes in antioxidant enzyme activities nor in lipid peroxidation. These results provide further substantiation of a role for oxygen-based radicals in 3,4-methylenedioxymethamphetamine-induced neurotoxicity. The present data also suggest that free radicals generated during 3,4-methylenedioxymethamphetamine administration may perturb antioxidant enzymes. Consequently, there might be further overproduction of free radicals with associated peroxidative damage to cell membranes and associated terminal degeneration.

Brain serotonin neurotransmission: an overview and update with an emphasis on serotonin subsystem heterogeneity, multiple receptors, interactions with other neurotransmitter systems, and consequent implications for understanding the actions of serotonergic drugs

Knowledge about serotonergic neurotransmission has been expanding rapidly. Recent research has delineated 15 molecularly different serotonin receptors and multiple, discrete neuronal and nonneuronal (including endocrine) pathways and mechanisms that mediate the many functions of serotonin. Nonetheless, gaps remain regarding aspects of the anatomy and physiology of serotonin in its roles as a neurotransmitter, a neuromodulator, and a hormone. Few serotonin receptor-selective drugs are available for clinical use. A group of selective serotonin reuptake inhibitors (SSRIs) remain the agents with greatest therapeutic utility, although the mechanisms underlying their delayed efficacy, which clearly result from adaptive consequences following repeated administration rather than early uptake inhibition of serotonin by itself, are incompletely understood and appear to involve changes in signal transduction and gene expression in serotonergic and other neurotransmitter systems.

Delta opioid peptide [D-Ala2,D-leu5]enkephalin blocks the long-term loss of dopamine transporters induced by multiple administrations of methamphetamine: involvement of opioid receptors and reactive oxygen species

Delta opioid peptide [D-Ala2,D-leu5]enkephalin (DADLE) can prolong organ preservation and increases myocardial tolerance to ischemia. Our study examined the protective property of DADLE against methamphetamine- (METH) induced dopaminergic terminal damage in the central nervous system. Because the neurotoxicity of METH involves reactive oxygen species, we also examined if DADLE might be an antioxidative agent in vitro. DADLE at 2 and 4 mg/kg (i.p.), given 30 min before each METH administration (5 or 10 mg/kg, i.p., four injections in a day at 2-hr intervals), dose-dependently blocked the METH-induced long-term dopamine transporter loss. The opioid antagonist naltrexone blocked this action of DADLE in both aspects of striata but tends not to affect the effects of DADLE in the nucleus accumbens. DADLE did not alter changes in body temperature induced by METH. The reduction of striatal dopaminergic content and tyrosine hydroxylase activity caused by METH, however, were not blocked by DADLE. In vitro, DADLE was approximately equipotent to glutathione in inhibiting both superoxide anion formation induced by xanthine oxidase and hydroxyl radical formation evoked by ferrous/citrate complex. DADLE was only slightly less potent than glutathione in inhibiting the iron/ascorbate-induced brain lipid peroxidation. These results suggest that DADLE can protect the terminal membranes of dopaminergic neurons against METH-induced insult but not the loss of dopaminergic content and tyrosine hydroxylase activity and that this action of DADLE might involve opioid receptors as well as the sequestration of free radical.

Altered brain serotonin homeostasis and locomotor insensitivity to 3, 4-methylenedioxymethamphetamine ("Ecstasy") in serotonin transporter-deficient mice

The sodium-dependent, high affinity serotonin [5-hydroxytryptamine (5-HT)] transporter (5-HTT) provides the primary mechanism for inactivation of 5-HT after its release into the synaptic cleft. To further evaluate the function of the 5-HTT, the murine gene was disrupted by homologous recombination. Despite evidence that excess extracellular 5-HT during embryonic development, including that produced by drugs that inhibit the 5-HTT, may lead to severe craniofacial and cardiac malformations, no obvious developmental phenotype was observed in the 5-HTT-/- mice. High affinity [3H]5-HT uptake was completely absent in 5-HTT-/- mice, confirming a physiologically effective knockout of the 5-HTT gene. 5-HTT binding sites labeled with [125I] 3 beta-(4'-iodophenyl)tropan-2 beta-carboxylic acid methyl ester were reduced in a gene dose-dependent manner, with no demonstrable binding in 5-HTT-/- mutants. In adult 5-HTT-/- mice, marked reductions (60-80%) in 5-HT concentrations were measured in several brain regions. While (+)-amphetamine-induced hyperactivity did not differ across genotypes, the locomotor enhancing effects of (+)-3, 4-methylenedioxymethamphetamine, a substituted amphetamine that releases 5-HT via a transporter-dependent mechanism, was completely absent in 5-HTT-/- mutants. Together, these data suggest that the presence of a functional 5-HTT is essential for brain 5-HT homeostasis and for 3,4-methylenedioxymethamphetamine-induced hyperactivity.

Biocompatibility of potential wound management products: hydrogen peroxide generation by fungal chitin/chitosans and their effects on the proliferation of murine L929 fibroblasts in culture

Agaricus bisporus, Fusarium graminearum, Phycomyces blakesleeanus, unbleached and bleached, Rhizomucor miehei, and Rhizopus oryzae were examined as sources of fungal chitin/chitosan. The nitrogen content of the alkalitreated mycelia/sporangiophores obtained after optimization of culture conditions, and of similarly treated A. bisporus stipes, was 2.87, 1.29, 6.27, 6.50, 4.80, and 4.95% w/w, respectively, which relates to an estimated chitin content of 42, 19, 91, 94, 70, and 72%, respectively. The hydrogen peroxide (H2O2)-generating ability of the treated fungal materials after 8 h at pH 7.4 and 37 degrees C decreased in the order R. oryzae > P. blakesleeanus unbleached approximately R. miehi > F. graminearum > A. bisporus > P. blakesleeanus bleached. This did not correlate with estimated chitin content. The effect of these fungal materials on the rate of proliferation of murine L929 fibroblasts in culture also was examined. Both pro- and antiproliferant effects were observed. Significant (P < .05) proproliferant effects were observed on day 6 with R. miehei, R. oryzae, and P. blakesleeanus (unbleached and bleached) at 0.01% w/v. The greatest antiproliferant effect was observed with R. oryzae at 0.05% w/v on day 6 (-63% relative to the control, P < .05; cell viability, 95%). In contrast, A. bisporus failed to affect cell yield significantly at either 0.01 or 0.05% w/v. Addition of catalase to cultures containing R. oryzae or R. miehei at 0.05% w/v failed to abolish the antiproliferant effect on day 3, instead producing a small but significant (P < .05) increase in the effect. Catalase also failed to affect significantly the antiproliferant effect of F. graminearum at 0.05% w/v, but did abolish the proproliferant effect of P. blakesleeanus (unbleached and bleached) on day 3. Overall, our results suggest that the H2O2 being generated by the fungal materials modulates cell proliferation but that this effect is superimposed upon a H2O2-independent antiproliferant effect manifesting itself at the higher concentrations of fungal material. The antiproliferant effect was not attributable to Ca2+, Mg2+, or Fe2+ depletion although chelation of Fe2+ did correlate with H2O2-generating ability. Only P. blakesleeanus appears to lack this antiproliferant activity while retaining H2O2-generating activity. These results may aid the selection of fungal chitin/chitosan for further evaluation as a potential wound management material.

Critical pathways: occupational therapists' role in development and utilization

Managed care is mandating that healthcare facilities implement cost containment measures. Critical pathways are one popular tool used to meet this demand. The purpose of this study was to explore current involvement of occupational therapists (OTRs) in the use and creation of critical pathways. Results of a national survey showed 70.5% of the respondents reported they are not currently using critical pathways. A majority of OTRs are not and have not taken an active role in critical pathway development. Furthermore, the majority indicated having no knowledge of future critical pathway implementation in their facilities. Information gathered from those OTRs reporting critical path use included most common diagnoses using the paths and percentages of OTRs utilizing critical paths in specific occupational therapy areas. The conclusions drawn by the researchers indicated the need for OTRs to become more involved in the development and utilization of this multi-disciplinary approach to treatment. For OTRs to maintain and enhance their positions within the allied health profession, proactive involvement with these managed care driven quality assurance methods is essential.

Cellular localization and expression of the serotonin transporter in mouse brain

The high-affinity serotonin (5-HT) transporter (5-HTT) plays an important role in the removal of extracellular serotonin, thereby modulating and terminating the action of this neurotransmitter at various pre- and post-synaptic serotonergic receptors and heteroreceptors. In order to characterize the anatomical distribution of the 5-HTT in mouse brain, in situ hybridization histochemistry using 35S-labeled riboprobes was performed. These results were compared with 5-HTT binding site distribution as evaluated by [125I]RTI-55 autoradiography. High levels of 5-HTT mRNA were detected in all brain stem raphe nuclei, with variations in labeling among the various subnuclei. Those brain areas known to possess serotonergic cell bodies stained intensely for both 5-HTT mRNA and 5-HTT binding sites. In contrast to previous findings in rat brain, the highest densities of 5-HTT sites were found in areas outside the raphe complex, particularly in the substantia nigra, globus pallidus, and superior colliculi.

Infrared Diode-Laser Molecular-Beam Spectrum of the nu2 Band of Chlorine Nitrate at 1293 cm-1

The nu2 band of chlorine nitrate (ClONO2 ) near 1293 cm-1 has been measured in a molecular beam with a diode-laser spectrometer. The low rotational temperature of the molecular beam, approximately 23 K, simplifies the spectrum allowing essentially complete assignment of the 35 Cl and 37 Cl lines. An a /b hybrid band is observed with the a -type transition moment being approximately a factor of 2 larger than the b -type transition moment. An inverted shift of the band origins is found with the 37 Cl band origin blue shifted from the 35 Cl by +0.37 cm-1 . This isotopic shift is attributed to an unidentified anharmonic resonance. Precise spectroscopic constants for the bands of each isotopic species are determined to allow future simulations for modeling atmospheric transmission and for remote sensing applications.

Transgenic mice with high levels of superoxide dismutase activity are protected from the neurotoxic effects of 2'-NH2-MPTP on serotonergic and noradrenergic nerve terminals

Administration of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) analog 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP; 4 x 15 mg/kg) to CD-1 mice was found to cause substantial decreases in cortical and hippocampal 5-hydroxytryptamine (5-HT) and norepinephrine (NE) to 20-30% of control 3 weeks after treatment. The magnitude of these depletions was similar to those reported previously in Swiss Webster and C57BL/6 mice given 4 x 20 mg/kg 2'-NH2-MPTP, and in keeping with these prior studies, striatal dopamine levels were unchanged by 2'-NH2-MPTP treatment in CD-1 mice. Subsequently, transgenic CD-1 mice producing high levels of human cytosolic Cu-Zn superoxide dismutase (SOD) were studied to assess the role of oxygen radicals in the mechanism of action of 2'-NH2-MPTP. In contrast to the results described above, 5-HT and NE levels were almost completely unaffected by 2'-NH2-MPTP treatment in homozygous SOD mice bearing 5-fold increases in brain SOD activity. In 2'-NH2-MPTP-treated heterozygous SOD mice, which showed an average 3-fold increase in brain SOD activity, only moderate depletions in cortical and hippocampal 5-HT (50-60% of control) and NE (30-40% of control) were observed. Additionally, the density of [125I]RTI-55-labeled 5-HT uptake sites was studied to further assess possible 5-HT terminal loss. In various cortical and hippocampal subregions of nontransgenic mice, 5-HT uptake sites were reduced to 20-35% of control after 2'-NH2-MPTP treatment, in comparison with homozygous SOD mice, which were affected only minimally by 2'-NH2-MPTP administration, and heterozygous SOD mice, which showed intermediate reductions in 5-HT uptake site density on the order of 55-80% of control. Together, these data indicate that mice genetically endowed with increased SOD activity are protected from 2'-NH2-MPTP-induced toxicity, thereby implicating superoxide radicals in the mechanism of action of a neurotoxin that selectively depletes 5-HT and NE without affecting dopamine.

Differential reinforcing effects of cocaine and GBR-12909: biochemical evidence for divergent neuroadaptive changes in the mesolimbic dopaminergic system

The dopamine (DA) transporter is thought to be the primary mediator of reinforcing effects of cocaine. In the present study, an intravenous drug self-administration procedure, in vitro autoradiography, and HPLC methods were used to investigate possible differences in reinforcing and neuroadaptive responses to cocaine versus GBR-12909, a selective inhibitor of the DA transporter with a postulated therapeutic use in cocaine abuse. Drug-naive rats readily acquired and subsequently maintained cocaine self-administration behavior during 2 hr daily sessions over a prolonged period. In contrast, although GBR-12909 was initially self-administered, both cocaine-naive and cocaine-trained rats failed to maintain self-administration behavior for GBR-12909 over prolonged periods of time. After self-administration responding decreased with GBR-12909, rats showed a delay of 6.6 +/- 1.3 sessions in reacquiring consistent cocaine self-administration. Moreover, when GBR-12909 was again substituted for cocaine, they failed to self-administer GBR-12909, even during the initial days of testing. In contrast, after extinction of self-administration responding by water substitution, rats readily self-administered both cocaine and GBR-12909. Cocaine self-administration upregulated DA transporters, whereas water-substituted cocaine withdrawal upregulated both DA transporters and D1 receptors. Unlike cocaine, GBR-12909 self-administration by itself altered neither DA transporters nor D1 or D2 receptors. Nevertheless, substitution of GBR-12909 for cocaine reversed the cocaine-induced upregulation of DA transporters and reduced DA and dihydroxyphenylacetic acid levels in the mesolimbic system. These data suggest that cocaine and GBR-12909 differentially affect dopaminergic systems and also cause different reinforcing and neuroadaptive effects. GBR-12909-like compounds may be useful pharmacotherapeutic agents for cocaine addiction. Upregulation of DA transporters and D1 receptors might play important roles in the neuroadaptive cascade that leads to cocaine addiction and withdrawal.

A role for apoptosis in the toxicity and mutagenicity of bleomycin in AHH-1 tk+/- human lymphoblastoid cells

The chromosomal mutagen, bleomycin, is also noted for its toxic properties, although the mechanism of cell death is not fully understood. In order to determine if cell death occurred by apoptosis or necrosis, AHH-1 tk+/- cells were exposed to bleomycin and the percentage of viable, apoptotic and necrotic cells quantified by flow cytometry. Logistic regression analysis indicated that the primary manner of cell death was through the apoptosis pathways, that apoptosis was delayed, and that apoptosis was accompanied by an arrest in the G2 phase of the cell cycle. Once apoptosis was established as a mechanism for cell death, the efficiency with which these pathways removed damaged cells from the population was evaluated with the use of specific-locus mutation assays (tk and hprt) as indicators of cells with DNA damage that maintained viability and clonogenicity. Linear regression analysis detected a significant, concentration-dependent increase in the numbers of TFTr clones with the slow-growth phenotype. This suggests that a proportion of cells with bleomycin-induced DNA damage did not undergo cell death by apoptosis and that apoptosis, a mechanism for the destruction of damaged cells, is not fully efficient in the AHH-1 tk +/- cell line.

Biocompatibility of potential wound management products: fungal mycelia as a source of chitin/chitosan and their effect on the proliferation of human F1000 fibroblasts in culture

Aspergillus oryzae, Mucor mucedo, and Phycomyces blakesleeanus cultures were examined as sources of chitin/chitosan. The nitrogen content of the alkali-treated mycelia/sporangiophores of A. oryzae, M. mucedo, and P. blakesleeanus was 2.52, 3.61, and 6.27% w/w, which relates to an estimated chitin content of 37, 52, and 91%, respectively. The effect of these fungal materials on the rate of proliferation of human F1000 fibroblasts in culture was examined. At 0.01% w/v, all three materials exhibited significant (P < .05) proproliferant activity over a period of 13 days. However, at 0.05% w/v, P. blakesleeanus further enhanced cell proliferation, whereas A. oryzae and M. mucedo produced a significant (P < .05) antiproliferant effect. Higher concentrations of P. blakesleeanus (0.1 and 0.5%) caused marked inhibition of F1000 cell proliferation when measured on days 3 and 6. Only the proproliferant effect of these fungal materials appears to correlate to their chitin content. Furthermore, the cytomorphology of the fibroblasts indicated that P. blakesleeanus, and to a lesser extent M. mucedo, possessed cell attractant properties, again correlating with chitin content. If developed for use as wound management materials, the sporangiophores of P. blakesleeanus and the mycelium of M. mucedo could possibly promote the growth of fibroblasts and provide a matrix for their anchorage, thus contributing to the granulation phase of the healing cascade.

Fluoxetine and desipramine selectively attenuate 2'-NH2-MPTP-induced depletions in serotonin and norepinephrine

We recently reported that the novel MPTP analog 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP) administered to C57BL/6 mice produced substantial decreases in forebrain serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and norepinephrine, with negligible effects on brain dopamine or dopamine metabolites. In the present report, we confirm and extend our original results to include dose-response data and the effect of selective uptake inhibition on the levels of monoamine neurotransmitters in various regions of the mouse brain following treatment with 2'-NH2-MPTP. In a dose-ranging study, 2'-NH2-MPTP (10 mg/kg x 4) produced a 25-30% reduction in frontal cortex 5-HT, 5-HIAA, and norepinephrine. When 4 x 20 mg/kg 2'-NH2-MPTP was administered, 70-75% reductions in 5-HT, 5-HIAA, and norepinephrine in both frontal cortex and hippocampus were seen 1 week after treatment. No changes in dopamine were found in striatum or in any of the other brain regions examined at either dose. Doses of 40 and 60 mg/kg were lethal shortly after a single injection. In mice receiving either fluoxetine or desipramine (10 mg/kg) prior to 2'-NH2-MPTP (20 mg/kg x 4), decreases in 5-HT and norepinephrine, respectively, were significantly attenuated by approximately 30-40%. These data suggest that 2'-NH2-MPTP acts in a dose-dependent manner and that the serotonergic and noradrenergic uptake systems are involved in the mechanism by which 2'-NH2-MPTP causes selective deficits in cortical and hippocampal 5-HT and norepinephrine.

2'-NH2-MPTP in Swiss Webster mice: evidence for long-term (6-month) depletions in cortical and hippocampal serotonin and norepinephrine, differential protection by selective uptake inhibitors or clorgyline and functional changes in central serotonin neurotransmission

The i.p. administration of 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP; 4 x 20 mg/kg) to Swiss Webster mice caused substantial decreases in cortical and hippocampal 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid and norepinephrine (NE) measured 1 week post-treatment. Compared with the authors' previously reported results in C57BL/6 mice, these effects were significantly greater in hippocampus (80-90% vs. 60%) and of a similar magnitude in frontal cortex (60-75%). A long-term study showed that cortical and hippocampal 5-HT, 5-hydroxyindoleacetic acid and NE were still decreased 40% to 50% 6 months after treatment. Regional brain dopamine was essentially unchanged during the 6-month period. Pretreatment with the 5-HT-selective uptake inhibitors, fluoxetine or paroxetine, or with the NE-selective uptake inhibitor, desipramine, prevented decreases in cortical and hippocampal 5-HT and NE, respectively, 3 weeks after 2'-NH2-MPTP (4 x 20 mg/kg). In addition, pretreatment with the monoamine oxidase type-A inhibitor, clorgyline, also prevented the more modest decreases in 5-HT and NE caused by 4 x 15 mg/kg 2'-NH2-MPTP. Selegiline, a monoamine oxidase-B inhibitor, did not provide similar protection. Lastly, 2'-NH2-MPTP administered 3 weeks earlier, abolished hypothermia caused by the serotonin agonist, m-chlorophenylpiperazine, which provided preliminary evidence for an associated functional change in the central serotonergic system. Together, these data suggest that 2'-NH2-MPTP is a novel agent capable of producing long-lasting depletions in forebrain 5-HT and NE but not dopamine in two different strains of mice by some mechanisms that resemble those of the parent dopamine-depleting neurotoxin, MPTP.

A study of hydrogen peroxide generation by, and antioxidant activity of, Granuflex (DuoDERM) Hydrocolloid Granules and some other hydrogel/hydrocolloid wound management materials

The effect of Granuflex Hydrocolloid Granules (0.01-0.50% w/v) on the rate of proliferation of murine (L929) fibroblasts was examined. The dose-response curve showed a significant (P < 0.02) pro-proliferant effect at 0.05%, and a significant (P < 0.02) antiproliferant effect at 0.50%, mirroring the dose-response curve produced by hydrogen peroxide in the concentration range 10(-9) - 10(-4) mol/l. The antiproliferant effect at 0.20% w/v was abolished by catalase, suggesting that the biological activity of Granuflex was mediated by the in situ generation of hydrogen peroxide. Formation of hydrogen peroxide by Granuflex was confirmed by performing the scopoletin-horseradish peroxidase assay in the presence and absence of catalase. The total concentration of hydrogen peroxide detected was about 8 x 10(-6) mol/l (using 0.5% w/v Granuflex) after 48 h at 37 degrees C. In contrast, when hydrogen peroxide itself was added to L929 cultures, a similar antiproliferant activity was observed at concentrations between 10(-4) and 10(-5) mol/l. These results suggested that Granuflex was undergoing autoxidation in the culture medium, and hence that it might possess antioxidant activity. In assays for antioxidant activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH), Granuflex, and two other hydrocolloid dressings (Comfeel Powder and Bard Absorption Dressing) showed significant ability to reduce DPPH to DPPH2. These three dressings also displayed superoxide scavenging activity in a nitroblue tetrazolium reduction assay. We conclude that, in addition to providing a moist wound-healing environment, Granuflex and certain other hydrocolloids might contribute to the establishment and maintenance of the reducing environment necessary for energy production and hence cell division.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatibility of wound management products: a study of the effects of various polysaccharides on murine L929 fibroblast proliferation and macrophage respiratory burst

An in-vitro screening method to examine the biocompatibility of materials used in wound management has been evaluated. This involved the use of a macrophage respiratory-burst assay and a fibroblast proliferation assay to represent respectively the inflammatory and the granulation phases in wound healing. Standard polysaccharides (calcium and sodium alginates, l-carrageenan, chitin, chitosan lactate, chondroitin sulphate and pectic acid) were used as test compounds. None of the polysaccharide samples caused a significant increase in L929 fibroblast cell numbers relative to control after 6 days incubation. The overall effect of exposure of the fibroblast cultures to the alginates, carrageenan and chondroitin sulphate was an extension of lag phase followed by an enhanced rate of cell proliferation in the logarithmic phase. Only calcium and sodium alginates and chondroitin sulphate enhanced the respiratory burst activity of murine macrophages; l-carrageenan and chitosan lactate were markedly inhibitory. The results suggest that a macrophage activity assay should be included as part of an in-vitro screening program to evaluate the biocompatibility of wound management materials and to detect intrinsic biological activity.

Toxicity of L-ascorbic acid to L929 fibroblast cultures: relevance to biocompatibility testing of materials for use in wound management

Fibroblast cultures are often used to evaluate materials intended for medical use, cytotoxicity being taken as an indicator of bioincompatibility. Such an approach has previously been taken with ascorbic acid in determining its value in wound healing. We have now reexamined the toxicity of L-ascorbic acid to L929 fibroblast cells in culture. Concentrations of ascorbic acid between 0.5 mM and 11 mM were tested. At concentrations above 2 mM, ascorbic acid was found to inhibit cell proliferation, with cell viability decreasing as the concentration was increased. This effect could be prevented by the addition of either superoxide dismutase or catalase to the culture medium. Assays of glutathione and glutathione disulfide were carried out on 8 day old cultures exposed for 24 h to the same concentrations of ascorbic acid. A dose-related depletion of glutathione occurred whilst glutathione disulfide levels remained essentially constant. Lactate dehydrogenase and glucose-6-phosphate dehydrogenase activities were induced by ascorbic acid at all concentrations tested but the ratio of NADP to NADPH nevertheless increased as the concentration of ascorbic acid increased. Finally, ATP in cells from 8-day-old cultures became depleted in the presence of ascorbic acid at concentrations in excess of about 5 mM when assayed after 24 h incubation. These biochemical changes and the concomitant cytostatic/cytotoxic effects may be ascribed to the reactive oxygen species produced by the autoxidation of ascorbic acid in the culture medium. Ascorbic acid breakdown products appeared not to be directly involved. In addition, our results suggested that superoxide acted cooperatively with hydroxyl to elicit these effects on the fibroblasts. It is evident from this study that the microenvironment surrounding fibroblasts in culture may differ fundamentally from that surrounding fibroblasts in a healing wound, making it impossible to extrapolate directly to an in vivo situation and hence to make any recommendations from these results concerning the use of ascorbic acid in wound healing.

Sustained depletion of cortical and hippocampal serotonin and norepinephrine but not striatal dopamine by 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP): a comparative study with 2'-CH3-MPTP and MPTP

Unlike 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces consistent decreases in levels of striatal dopamine (DA) with considerably smaller and more variable effects on mouse brain levels of serotonin (5-HT) and norepinephrine (NE), a novel amine-substituted MPTP analogue, 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP), administered in a standard mouse dosing paradigm for MPTP (20 mg/kg x 4) did not affect striatal DA but led to marked reductions (60-70%) in levels of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), and NE measured in frontal cortex and hippocampus 1 week after treatment. Another 2'-substituted MPTP analogue, 1-methyl-4-(2'-methylphenyl)-1,2,3,6- tetrahydropyridine, affected cortical and hippocampal 5-HT, 5-HIAA, and NE only minimally, while markedly reducing the DA content in striatum (90%), thus indicating that the substituent (-NH2 versus -CH3) at the 2' position is important for the differential effects of these MPTP analogues. In a replication study with a 3-week end point, hippocampal and cortical 5-HT, 5-HIAA,, and NE levels remained depressed with no indication of recovery. These results suggest that 2'-NH2-MPTP may be a novel, regionally selective neurotoxin for serotonergic and noradrenergic nerve terminals.

Myotonic dystrophy and hyperparathyroidism: association with neurofibromatosis and multiple endocrine adenomatosis type 2A

Four patients with hyperparathyroidism associated with myotonic dystrophy have been identified. All were females aged between 2 and 45 years. They were from three separate families, with two related patients being mother and daughter. In addition, one patient had medullary carcinoma of the thyroid and was diagnosed as having multiple endocrine adenomatosis, type 2A; another had an unspecified thyroid carcinoma; a third patient had neurofibromatosis. Our data suggest that myotonic dystrophy may somehow be associated with one or more of these disorders of neural crest origin.