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Notes: Abstract Choline acetyltransferease (ChAT) is the enzyme catalyzing the biosynthesis of acetylcholine and is considered to be a phenotypically specific marker for cholinergic neurons. We have examined the distribution of ChAT-expressing neurons in the larval nervous system of Drosophila melanogaster by three different but complementary techniques: in situ hybridization with a cRNA probe to ChAT messenger RNA, immunocytochemistry using a monoclonal anti-ChAT antibody, and X-gal staining of transformed animals carrying a reporter gene composed of 7.4 kb of 5′ flanking DNA from the ChAT gene fused to a lacZ reporter gene. All three techniques demonstrated ChAT-expressing neurons in the larval visual system. In embryos, the photoreceptor organ (Bolwig's organ) exhibited strong cRNA hybridization signals. The optic lobe of late third-instar larvae displayed ChAT immunoreactivity in Bolwig's nerve and a neuron close to the insertion site of the optic stalk. This neuron's axon ran in parallel with Bolwig's nerve to the larval optic neuropil. This neuron is likely to be a first-order interneuron of the larval visual system. Expression of the lacZ reporter gene was also detected in Bolwig's organ and the neuron stained by anti-ChAT antibody. Our observations indicate that acetylcholine may be a neurotransmitter in the larval photoreceptor cells as well as in a first-order interneuron in the larval visual system of Drosophila melanogaster.

Notes: Abstract Recently the use of stereotactic radiosurgery to treat functional disorders such as Parkinson's disease, epilepsy, and intractable pain has been reported in the literature. In such applications, a large single dose is typically delivered to an extremely small (〈0.05 cm3) target volume. The purpose of this work is to investigate whether the dosimetric and imaging characteristics of radiosurgery treatment planning provide sufficient accuracy to allow efficacious therapy of functional disorders. We have begun treating trigeminal neuralgia using our linear accelerator-based radiosurgery system: 70 Gy is prescribed to the maximum dose in the volume (in our case the 100% isodose level) and delivered to the base of the fifth nerve in a single fraction using a 5 mm collimator, with the standard Brown–Roberts–Wells (BRW) radiosurgery accessories employed for fixation and localization. Because the fifth nerve cannot be visualized on x-ray computed tomography (CT), our radiosurgery treatment planning system was modified to use magnetic resonance images for localization, though dose calculations are still performed using CT. Isocentric accuracy of our original radiosurgery system, consisting of a floor stand and isocentric subunit, and our new couch mount system, was evaluated using the Winston–Lutz film test method. In order to evaluate the spatial accuracy of magnetic resonance (MR) treatment planning, eight 4 mm sections of a 7 French catheter were filled with CuSO4 contrast material and attached rigidly to the stereotactic fixation posts of our BRW frame, four each in orientations parallel and perpendicular to the axial plane. The position of the externally placed fiducial markers, as well as internal anatomical structures, were then compared with CT. Monte Carlo calculations were compared with those from a commercial radiosurgery treatment planning system in order to investigate the effects of tissue heterogeneities on the resulting dose distributions. While commercial radiosurgery systems assume tissue homogeneity, the Monte Carlo calculations were performed in a patient-specific CT geometry accounting for all tissue inhomogeneities. The resulting 128 × 128 Monte Carlo dose grid was superimposed on the original CT data for analysis and comparison with identical treatment plans from the commercial system. The ability of our LINAC-based systems to accurately target a desired point in space has been effectively demonstrated: 0.32 ± 0.32 mm (N = 556) for our floor stand system and 0.34 ± 0.23 mm (N = 50) for our newer couch-mounted system. Inaccuracies introduced by tomographic imaging devices are significantly greater. The use of gel-filled fiducial markers in magnetic resonance imaging (MRI) guided radiosurgery produces significant spatial distortion, resulting in Euclidean root-mean-square deviations of 2.32 ± 0.96 mm (N = 31) and 3.64 ± 1.28 mm (N = 27) at the center and periphery (extracranial) of the field of view respectively, as compared with CT. Use of water of CuSO4 filled rods had a minimal effect on these deviations: 2.51 ± 1.25 mm (N = 31) and 3.37 ± 1.28 mm (N =27) for central and peripheral targets respectively. Magnetic susceptibility artifacts in the frequency encoding (AP) direction produce a systematic posterior shift. This together with axial slice spacing accounts for the majority of the deviation. Tissue heterogeneities such as bone and air cavities produce a lateral spreading of the dose from small photon beams, resulting in a prescription dose volume smaller than predicted by conventional treatment planning systems. For a typical are configuration designed to produce a spherical dose volume, Monte Carlo calculations show the 90% dose volume to be significantly smaller than that predicted by the commercial system when either 5 mm or 10 mm collimators are used. Use of a LINAC-based system does not preclude accurate treatment of small functional targets. Isocentric uncertainty for either of two LINAC systems that we evaluated is small compared to imaging and dosimetric factors. However, chemical shifts and object-induced magnetic susceptibility artifacts can produce systematic spatial distortions in magnetic resonance images; thus, MR imaging may not possess the inherent accuracy necessary for stereotactic localization and targeting of small cranial structures. In addition, both CT and MR possess an inherent inaccuracy of at least one-half of the axial slice thickness; thus, for localization purposes, a slice spacing as small as possible should be used when treating small targets. Tissue heterogeneities decrease the volume covered by the higher isodose lines. As a result, the target may be only partially covered by the intended dose level, with the remainder lying in the high gradient region. This same lateral spreading may also increase the risk to adjacent normal structures. Imaging and dosimetric considerations are not unique to linear accelerator systems but apply equally to all stereotactic photon irradiation. Until spatial and dosimetric errors can be accounted for, use of a larger collimator will ensure better coverage of small targets.

Notes: Abstract Fractionated stereotactic radiation therapy is a useful new approach for treating a number of intracranial neoplasms including meningiomas, pituitary adenomas, craniopharyngiomas, and recurrent gliomas. For the majority of these we employ a conventional fractionation scheme of 180 cGy per fraction for 25 to 30 fractions, using a modified Gill–Thomas–Cosman (GTC) relocatable frame to accommodate fractionated delivery. The GTC system uses a custom acrylic dental appliance to set the frame position and an occipital plate and Velcro straps fix the head in place. Daily reproducibility is evaluated through use of a “depth helmet,” a plastic hemispherical shell containing 25 holes at regularly spaced intervals. The depth helmet attaches to the GTC frame and the distance from the shell to the patient's head is recorded at each of the 25 positions. This paper describes a new simplified approach to the quantitative assessment of day-to-day variability in head fixation using the depth helmet measurements. This approach avoids the need to try and decide on the relative merit of 25 numerical differences at each fitting and provides a straightforward mathematical and conceptual framework for the description of fit and clinical decision making. The mathematical analysis and computer program we have developed uses all 25 measurements to provide a single three-dimensional displacement vector as well as displacement values in the three principal patient dimensions. Measurements at each of the 25 depth helmet positions are automatically separated into three principal axes corresponding to the patients left/right (x), anterior/posterior (y), and superior/inferior (z) using the spherical relations: x = r sin(Φ) cos(θ), y = r sin(Φ) sin(θ), z = r cos(Φ), where θ and Φ are the polar and azimuthal angles respectively and ris the distance from the center of the depth helmet to the surface of the patient's head. For each patient, a set of initial measurements is taken at the CT scanner with the patient in the treatment (supine) position. Because treatment planning is based on the CT scan, this serves as the baseline from which subsequent deviations are recorded. In an analysis of our first 30 patients representing over 750 fractions, the mean RMS deviation, that is, the mean three-dimensional displacement from baseline, was 0.468 ± 0.296 mm. Among individual patients the range was 0.169 mm to 1.438 mm. A closer analysis suggests that in-plane (AP/PA-lateral) deviations occur randomly. Deviations along the superior/inferior direction are greater than those in-plane, and in several patients a small shift along this axis, possibly due to a loosening or stretching of the Velcro straps, has been noted over time. We have found our method to be a useful indicator of day-to-day reproducibility, allowing ready identification and correction of three-dimensional shifts relative to the patient axes. Based on our initial analysis, we can now define quantitative limits of acceptability in repositioning for subsequent fractionated delivery.

Notes: Abstract We used the reverse transcription-polymerase chain reaction (RT-PCR) to amplify choline acetyltransferase (ChAT) mRNA fragments from two temperature-sensitive alleles of Drosophila melanogaster, Cha ts1 and Cha ts2. Single base substitutions in the mutants (T1614A in Cha ts1 and G1596A in Cha ts2) would result in amino acid changes for ChAT protein (Met403Lys in Cha ts1 and Arg397His in Cha ts2). These base substitutions were confirmed in mRNA extracted from homozygous mutants using a Single Nucleotide Primer Extension assay (SNuPE) and are sufficient to produce thermolabile enzyme. Our results indicate that these temperature-sensitive mutants are point mutations in the structural gene for ChAT. Using a quantitative SNuPE assay we also show that similar levels of Cha ts and wild type transcripts are present in heterozygous flies (Cha ts1/+ and Cha ts2 /+) at both restrictive and permissive temperatures. This contrasts with RNase protection assays of ChAT mRNA in homozygous mutant animals where the levels of mutant mRNA decrease at restrictive temperature.

Notes: A photochemical precursor to a pendant conjugated polyradical has been synthesized, poly[3,5-di-tert-butyl-4-[(2,4,6-tri-tert-butylphenyl)oxalato]phenylacetylene], 3. Irradiation of 3 at 77 K in the solid state at 〈 300 nm yielded poly(3-5-di-tert-butyl-2-oxyphenyl acetylene), 2, with 30-40% of the expected number of radical spins. Spin yields on the surface of solid samples appears to be considerably higher. Electron spin resonance experiments showed no evidence of cooperative exchange interaction between the pendant spins. Computational modeling indicated that a major reason for the failure of this and other polyphenylacetylenes to show ferromagnetic exchange between spins is the substantial twisting of the polyacetylene backbone required by steric interactions, leading to deconjugation and a loss of exchange interaction between pendant radicals along the chain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2167-2176, 1997

Notes: An Chip-on-Board (COB)-Aufbauten wurde die Degradation (Funktionsminderung) von mikroelektronischen Drahtbondverbindungen unter thermischer und korrosiver Belastung untersucht. Als Maß der Degradation wurde die Veränderung des elektrischen Widerstandes verfolgt. Die Bondverbindung zwischen dem Si-Halbleiterchip und dem Substrat (Leiterplatte) wurde mil dem bekannten Ultraschalldrahtbondverfahren realisiert. Die Metallisierung der Leiterbahnen erfolgte durch galvanische oder außenstromlose Abscheidung der funktionellen Schichten Nickel und Gold. Das Degradationsverhalten unter korrosiver und/odor thermischer Belastung hängt wesentlich von der Art der Schichtabscheidung (Ahscheideverfahren, Schichtdicken) der Ni- und Au-Schichten ab. Bondkontakte auf galvanisch aufgebrachten dicken Goldschichten (≥ 1,5 μm) führen nach den vorliegenden Ergebnissen bedeutend schneller zur Degradation als auf außenstromlos abgeschiedenen, dünnen (etwa 0,1 μm) Flashgold-Schichten.

Notes: Im Rahmen der vorliegenden Arbeit wurden die Möglichkeiten zur Herstellung von Tantalbeschichtungen durch Vakuumplasmaspritzen untersucht. Neben den Arbeiten zur Ermittlung geeigneter Beschichtungsbedingungen erfolgte eine Qualitätsbewertung der Tantalspritzschichten u. a. hinsichtlich chemischer Zusammensetzung, Haftfestigkeit, Dichte und Korrosionsbeständigkeit. Zur Erzielung qualitativ hochwertiger Schichten ist neben einer ausreichenden Plasmaleistung eine optimale Injektion des Spritzpulvers erforderlich. Ein vollständiges Aufschmelzen der Tantalpartikel war nicht erreichbar. Die erzielten Spritzschichten wiesen bei geringer Verformbarkeit eine gute Haftfestigkeit auf. Die Korrosionsbeständigkeit in einer Säuremischung aus HCl und HNO3 wurde durch Aufnahme von Stromdichte-Potentialkurven bewertet. Anhand der Passivstromdichte wurde festgestellt, daß die Korrosionsbeständigkeit von kompaktem Tantal nicht erreicht werden konnte. Die erhöhte Oberflächenrauhigkeit spielt dabei eine untergeordnete Rolle. Als mögliche Ursache der verringerten Korrosionsbeständigkeit wird ein erhöhter Sauerstoffgehalt im Spritzpulver angesehen.Ergänzend durchgeführte Untersuchungen an Titan ergaben, daß eine Titanspritzschicht sich hinsichtlich des Korrosionsverhaltens unter den gewählten Prüfbedingungen vom kompakten Titan nicht unterscheidet.

Notes: The polymerisation of methyl methacrylate (MMA) using triisobutylaluminium/tert-butyllithium in hydrocarbon at 0°C and -78°C has been investigated by matrixassisted laser desorption ionisation time-of-flight mass spectrometry (MALDI TOF MS). Although the system gives extremely good control over molecular weight and narrow molecular weight distribution, initiation of polymerization can be complicated by formation of small amounts of tert-butyl isoprenyl ketone (1), and termination of polymerization can occur by end cyclisation of the end unit of 3. Both complications in initiation and termination can be avoided by suitable reaction conditions. Incorporation of 1 is suppressed by increasing the alkylaluminium content and by higher temperature. Termination by cyclisation has been found to occur over much longer time scales than propagation and can therefore be avoided by controlled termination after the appropriate reaction time.