Thermal inhibition of repair of methylmethane sulfonate-damaged DNA in chick embryo fibroblasts

Chick embryo fibroblasts were treated with the monofunctional alkylating agent methylmethane sulfonate at various concentrations for 1 h at 42°C, rinsed and then incubated post-treatment at various temperatures at which the kinetics of alkali-labile bond disappearance was followed. Growth experiments showed that these cells grew similarly at temperatures of either 37°C or 42°C. Repair as assessed by removal of alkali-labile bond was also similar for postincubation in the temperature range 37–42°C for damage due to methylmethane sulfonate treatment at concentrations less than 1.5 mM. When the postincubation temperature was raised higher than 42.5–43°C, this type of repair was stopped. The normal internal body temperature of adult chickens is about 41.6°C. Hence the present finding indicates that chick cells are much more severely restricted in DNA repair at temperatures above normal than are mammalian cells, which can function in this respect for several deg. C above 37°C.     

Parelaphostrongylus tenuis in New Brunswick: the parasite in white-tailed deer (Odocoileus virginianus) and moose (Alces alces)

Research was initiated in 1983 to investigate the ecology of Parelaphostrongylus tenuis in New Brunswick. The objectives were to determine the prevalence and intensity of infection in white-tailed deer, and to determine whether or not moose feces contained first stage larvae, signifying the completion of the life cycle of P. tenuis in this host. Forty-nine percent of deer pellet samples were positive and 60% of deer heads contained adults of P. tenuis. None of the moose pellet samples contained first stage larvae.     

Three theories of stroboscopic motion detection

The three theories derive from three different paradigms. Suprathreshold judgements of perceived quality of motion in multi-flash displays are modelled by space-time Fourier analysis of the motion stimulus. Stroboscopic motion is perceived as being different from real motion to the extent that the additional Fourier components in stroboscopic motion are detectable. Stroboscopic motion of dots along conflicting paths leads to perceptual competition. The theory to describe perceptual I solution derives and proves the uniqueness of strength functions computed only from the time and from the distance between successive points on each path. Time-strength and motion-strength add to determine path-strength; only the strongest path is perceived. Motion-direction detection in continuously drifting two-flash combinations of sinusoidal gratings is described by elaborated Reichardt detectors (ERDs) that compute the covariance of temporal events in two adjacent locations. Other apparently different, detectors that account for direction-detection data are shown to be equivalent to ERDs.     

Effect of indomethacin on proteinuria in rats with autologous immune complex nephropathy

Although non-steroidal anti-inflammatory agents have been used to reduce levels of urinary protein excretion in patients with the nephrotic syndrome, the general usefulness of these drugs in proteinuric states remains unclear. The present study was designed to confirm the efficacy and to investigate some of the mechanism/s of action of non-steroidal anti-inflammatory agents in animals with proteinuria as the result of a single form experimental renal disease. Autologous immune complex nephropathy was produced in groups of Lewis rats by the administration of autologous tubular F×1A antigen. After marked proteinuria developed, indomethacin (8 mg/kg/day) was administered orally to one group of animals for five days while a control group received only vehicle. The level of urinary protein excretion in the indomethacin treated animals was 420 ± 198 mg/day compared to a level of 1180 ± 306 seen in the untreated animals (p < 0.05). When the indomethacin-treated and control animals were compared, the reduction in proteinuria could not be found to be associated with a change in the glomerular filtration rate, urine electrolyte or osmolar excretion rates, electron microscopic appearance of the glomerular basement membrane, or a change in the glomerular permeability to neutral dextran. Treatment of animals with either sodium salicylate or lower doses of indomethacin (both of which resulted also in significant falls in urinary prostaglandin E excretion rates) failed to reduce the levels of proteinuria. Thus, indomethacin was capable of reducing the levels of protein excretion in rats with autologous immune complex nephropathy although the mechanism of action of this agent remains unclear.     

Effect of acute pH depression on the survival of the freshwater amphipod Hyalella azteca at variable temperatures: field and laboratory studies

Field observations on temperature and pH of a small pond showed that a amphipod population of Hyalella azteca was exposed to variable seasonal pH between 5.10–5.85, and water temperatures between 2–21 °C. Laboratory experiments were designed to simulate seasonal temperatures and field pHs of a small pond habitat. Laboratory bioassay experiments were conducted to determine the survival of Hyalella azteca at pHs 4, 5, 6 and 7, and varying temperatures of 5°, 10°, 15°, 20° and 25 °C.The LT₁₀₀ at pH 4 and 25 °C was 5.7 ± 0.47 days, compared to 47.3 ± 2.49 days at 5 °C. An Analysis of Variance (ANOVA) showed temperature was a significant (p > 0.0001) source of variation in the acute lethality of pH to H. azteca. A Duncans Multiple Range Test (DMRT) further showed that in laboratory experiments at pH 4, there was a significant difference ( = 0.01) between the LT_100s at 5°, 10°, 15° and 20 °C, but not between temperatures 20° and 25 °C.     

The fluorinated anesthetic halothane as a potential NMR biologic probe

Fluorinated anesthetics such as halothane preferentially partition into hydrophobic environments such as cell membranes. The 19F-NMR spectrum of halothane in a rat adenocarcinoma (with known altered lipid metabolism and membrane composition) shows an altered chemical shift pattern compared to the anesthetic in normal tissue. In eight tumor samples examined, the 19F-NMR spectra exhibit two distinct resonances, compared to a single resonance observed in normal tissues. This is explained by an enhanced or altered hydrophobic component in the tumor tissue giving rise to two discrete halothane environments. Another fluorinated anesthetic, isoflurane, shows similar behavior in distinguishing normal from diseased tissue. Given the large chemical shift range of fluorine and the inherent sensitivity of this nucleus, 19F-NMR spectra of fluorinated anesthetics can also be used to follow anesthetic degradation by the liver. The ability of fluorinated anesthetics to discriminate tissues and to monitor metabolic processes is potentially useful for in vivo 19F-NMR surface coil and imaging studies.     

A retroviral provirus closely associated with the Ren-2 gene of DBA/2 mice.

We have determined the entire nucleotide sequence of an intra-cisternal A particle (IAP) genome, associated with the Ren-2 gene of DBA/2 mice. This genome (MIARN) displays features common to other IAP retroviral-like genomes. Long terminal repeats (LTRs) are approximately 430 base pairs (bp) in length and show typical retroviral U3-R-U5 organisation, though the R-region, at 120 bp, is much larger than the average IAP. This difference probably arose by the amplification of a pyrimidine-rich sequence, by a slippage-mispairing mechanism. Flanking the 5' LTR is a sequence complementary to a phenylalanine tRNA, strongly conserved in all rodent IAP genomes and probably required to prime the initiation of (-) strand synthesis. Flanking the 3' LTR, is a purine-rich sequence probably required for (+) strand synthesis. The tRNA binding site (TBS) is flanked by six tandem copies of a sequence homologous to the TBS. The relationship of the MIARN element to other IAP genomes and the significance of its association with the highly expressed Ren-2 is discussed.     

Parasympathetic denervation decreases muscarinic receptor binding in rat parotid.

After unilateral postganglionic parasympathetic denervation of rat parotid glands for 3, 6 or 16 days, the binding of [³H] quinuclidinylbenzilate, a potent and specific muscarinic antagonist, was decreased by 28–45%. The largest part of the decrease was already present at 3 days, and thus appeared to coincide with the loss of parasympathetic terminals (as shown by a 94% reduction in choline acetyltransferase activity). The decrease in binding was expressed as a reduced number of membrane sites, with no significant change in affinity, and could be accounted for only in part by a reduction in the size of denervated glands. The rapid loss of binding suggests the existence of muscarinic receptors on parasympathetic terminals. The clear absence of any receptor increases at longer periods of denervation, when parotid glands are reported to give supersensitive secretory responses, suggests that mechanisms other than receptor increases are important in denervation supersensitivity in exocrine glands.