The RBE of the leakage radiation from the Hiletron neutron therapy unit

The RBE of the leakage radiation from the Hiletron 14.7 MeV neutron therapy unit has been measured using three sensitive biological systems in mice, which differ markedly in their radiobiological characteristics. These systems comprise type A spermatogonia and bone marrow stem cells, which are affected insignificantly by dose rate, and pigment abnormalities in hair follicles which are affected markedly by dose rate. For mice irradiated at 10 cm depth in a water phantom, the leakage radiation up to 40 cm from the beam axis was virtually as effective as the primary beam for the latter two biological systems, and for spermatogonia in mice when irradiated in air. At this distance, the total dose rate was about 0.2 cGy (rad) per minute (3% of that in the primary beam), and the gamma-ray component was about 70%. This equal effectiveness of the total dose for all three systems was considered fortuitous, and it implied high RBE values for equal effect with the small neutron component at far distances. Considering published data on RBE versus neutron energy, the evidence suggested either a positive interaction of neutron and gamma-ray components in killing bone marrow stem cells when the neutron component was less than 40% of the total dose, or an increased efficiency of neutrons when delivered at very low dose rates. However the components were additive in killing spermatogonia.

Measurement of velocity of propagation from ultrasonic pulse-echo data

A method is proposed for determining velocity of propagation of ultrasound in tissue by processing the pulse-echo data obtained from a compound scan. Individual sectors from different transducer positions are reconstructed and a suitable area common to the two sectors is selected. Cross-correlation of the region of interest is used to detect an apparent shift in the image due to refractive effects. The refractive effects are analysed by a ray-tracing procedure to determine an effective velocity within the tissue. The system has been tested using the U.I. Octoson as input device and both model targets with known velocity of propagation and in vivo liver tissue. The accuracy in the model experiment was +/- 5 ms-1 while the repeatability of measurements in tissue was +/- 15 ms-1. techniques for extending the method to multiple region systems are suggested.

Traumatically acquired color vision defect

A 24-year-old man acquired a color vision defect shortly after an accident in which he struck the back of his head. Results of the Farnsworth-Munsell 100-hue test showed that the patient had poor color discrimination in both eyes. His color matches on the Nagel anomaloscope suggested a red/green disturbance. Results from increment threshold testing demonstrated on absence of the blue mechanism. Results of field sensitivity measurements confirmed that foveal vision was mediated by the red or green mechanism. This case showed both similarities and differences to previously reported cases of acquired color vision defects secondary to cortical trauma.

Previous strabismus surgery and eye position under anesthesia

We studied eye position under general anesthesia in 51 patients with concomitant esotropia or exotropia, divided into two groups. One group consisted of strabismus patients who had had no previous surgery. The second group consisted of strabismus patients who had undergone previous surgery on one (asymmetric) or both (symmetric) eyes. We found that both groups showed either no change or more divergence under general anesthesia in comparison to their preoperative state. Those patients who had had no previous surgery revealed an equal divergence in both eyes. This relationship also held true for those patients who had undergone symmetrical surgery in both eyes. However, those patients who had had surgery in one eye only showed more divergence in the operated eye than in the unoperated one. These findings reflect the mechanical--anatomical factors created by the surgery itself.

The formation of photoreceptor synapses in the retina of larval Xenopus

The first appearance and early development of synapses between photoreceptors, bipolar cells and horizontal cells were studied in the retina of larval Xenopus, between stages 37/8 and 46. Synapse morphology was reconstructed from examination of serial sections. Additional data were obtained from E-PTA stained tissue, Photoreceptors initially contacted horizontal cell dendrites via ribbon synapses at the photoreceptor basal surface (stages 37/8--39). Later, horizontal cell dendrites penetrated the receptor as digitiform processes (stages 39--40) which subsequently expanded extensively within the invagination (stages 40--44). At stages 41--46, a photoreceptor ribbon generally was associated with two horizontal processes in a synaptic dyad complex; each ribbon participated in 1 or 2 such complexes. Bipolar cell dendrites made contact with receptors via superficial or invaginating basal-type junctions. Such junctions were observed first at stage 39, but increased greatly in number beginning at stage 42. Basal junctions were characterized by marked staining of the paramembranous receptor cell cytoplasm and a 9--13 nm wide cleft containing an electron-dense material. No association of bipolar cell dendrites with photoreceptor ribbons was noted. Junctional complexes presumed to be gap junctions first were observed at stage 39 between photoreceptor bases and basal processes emitted by neighbouring photoreceptors.

Cholesterol oxidase: thermochemical studies and the influence of hydroorganic solvents on enzyme activity

Thermal and binary cosolvent studies of the cholesterol oxidase (cholesterol: oxygen oxidoreductase, EC 1.1.3.6) reaction have been carried out using batch microcalorimetry and ultraviolet spectrophotometry respectively. Heat conduction measurements are shown to provide the basis for a serum cholesterol assay yielding results comparable to conventional automated clinical assay. The enthalpy of the reaction for cholesterol oxidation, measured with different sources of the enzyme in the presence and absence of catalase is -113 +/- 7.2 mJ/mumol. The value is agreement with calculated estimates based on bond energies, enthalpies of formation and trigonal additivity contribution calculations. From this heat of reaction the deltaHf0 of cholestenone (c) is calculated to be -490 kJ . mol-1. No evidence for the reverse reaction could be adduced. Enzyme activation with detergent (Surfal) is attributed to the formation of mixed micelles of cholesterol with detergent molecules. The detergent concentration at which the enzyme is half activated corresponds to the critical micelle concentration of Surfal. The enhanced enzyme activity found when ethanol, acetonitrile and dioxane were examined as binary cosolvents with water is ascribed to a conformational change in the enzyme mediated through the altered structuredness of water. This cosolvent effect is abolished in the presence of 0.18% Surfal due to the formation of inverted mixed micelles of detergent with cholesterol.

Effects of pressure on visible spectra of complexes of myoglobin, hemoglobin, cytochrome c, and horse radish peroxidase

The spectra of the ferric form of most heme proteins [metmyoglobin, methemoglobin, horse radish peroxidase (EC 1.11.1.7), and ferricytochrome c at pH 1.5] are converted from high-spin (open crevice) structure to low-spin (closed crevice) form under pressure. Pressures up to 8000 kg/cm2 (780 MPa) have no effect on the spectra of high-spin ferro- and ferricytochrome c, which have a closed crevice structure at pH 7.0. Spectra of deoxy-ferromyoglobin and deoxy-ferrohemoglobin are reduced in intensity, but pressure does not change the positions of the absorption maxima. Cyanide ion prevents pressure-induced spectral changes in metmyoglobin and methemoglobin up to 8000 kg/cm2. Carbon monoxide (with a high affinity for the ferro heme iron) has a similar effect on ferromyoglobin and ferrohemoglobin. The pressure required to cause spectral changes in the heme proteins falls in the order, cytochrome c (pH 7.0) greater than horse radish peroxidase greater than myoglobin greater than hemoglobin. We have calculated a volume change of --50 cm3/mol associated with the configurational change accompanying the reformation of the iron-methionine bond in cytochrome c at low pH.