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Physiological and psychological response to a three-month mental strain period in students

Biochemical and immunological parameters, physical and mental performance, subjective complaints and behavioural characteristics were compared before and after 14 final examinations undertaken by 64 students during a three-month examination period. A decrease in cholesterol, triglycerides, HDL-cholesterol, physical performance and an increase in LDL/HDL cholesterol quotient, lactate level, mental performance were accompanied by a lower frequency of mental complaints and higher frequency of physical complaints. From the multidimensional variance and discriminant analysis 17 of the 44 variables discriminated between the state prior to and after the examination period. The results are interpreted in terms of the psychophysiological adaptation to adequate mental stress.     

Heat treatment results in a loss of transgene-encoded activities in several tobacco lines.

Heat treatment (37 degrees C) of transgenic tobacco (Nicotiana tabacum) plants led to a reversible reduction or complete loss of transgene-encoded activities in about 40% of 10 independent transformants carrying the luciferase-coding region fused to the 355 cauliflower mosaic virus or the soybean small subunit promoter and the nopaline synthase promoter driving the neomycin phosphotransferase gene, whereas the other lines had temperature-tolerant activities. Temperature sensitivity or tolerance of transgene-encoded activities was heritable. In some of the lines, temperature sensitivity of the transgene-encoded activities depended on the stage of development, occurring in either seedlings (40% luciferase and 50% neomycin phosphotransferase) or adult plants (both 40%). The phenomenon did not correlate with copy numbers or the homo- or hemizygous state of the transgenes. In lines harboring a temperature-sensitive luciferase activity, reduction of bioluminescence was observed after 2 to 3 h at 37 degrees C. Activity was regained after 2 h of subsequent cultivation at 25 degrees C. Irrespective of the reaction to the heat treatment, the level of luciferase RNA was slightly increased at 37 degrees C. Only in lines showing temperature sensitivity of transgene-encoded activities was the amount of luciferase and neomycin phosphotransferase strongly reduced. In sterile culture, heat treatment for 15 d did not cause visible damage or changes in plant morphology. In all plants tested a slight induction of the heat-shock response was observed at 37 degrees C.     

Sexually dimorphic expression of myosin heavy chains in the adult mouse masseter.

Little is known regarding the role of androgenic hormones in the maintenance of myosin heavy chain (MHC) composition of rodent masticatory muscles. Because the masseter is the principal jaw closer in rodents, we felt it was important to characterize the influence of androgenic hormones on the MHC composition of the masseter. To determine the extent of sexual dimorphism in the phenotype of masseter muscle fibers of adult (10-mo-old) C57 mice, we stained tissue sections with antibodies specific to type IIa and IIb MHC isoforms. Females contain twice as many fibers containing the IIa MHC as males, and males contain twice as many fibers containing the IIb MHC as females. There is a modest amount of regionalization of MHC phenotypes in the mouse masseter. The rostral portions of the masseter are composed mostly of type IIa fibers, whereas the midsuperficial and caudal regions contain mostly type IIb fibers. Using immunoblots, we showed that castration results in an increase in the expression of type IIa MHC fibers in males. Ovariectomy has no effect on the fiber type composition in females. We conclude that testosterone plays a role in the maintenance of MHC expression in the adult male mouse masseter.     

Red-breasted goose colonies on the Taimyr Peninsula: Factors responsible for the proximity of goose nests to nests of peregrine falcons,rough-legged buzzards,and snowy owls

Red-breasted goose colonies have been studied near Medusa Bay (73°21′N, 80°32′E), on the northwestern Taimyr Peninsula, and along the Agapa River (70°11′N, 86°15′E) down to its mouth (71°26′N, 89° 13′E), in the central Taimyr Peninsula. Red-breasted geese nesting near peregrine falcons are protected by the falcons from arctic foxes; however, they are sometimes attacked by the falcons themselves. In the colonies near peregrine falcon nests, the vast majority of goose nests were situated no farther than 100 m from the falcon nest. When food is abundant, falcons protect a larger area around their nest. The distance between the falcon nest and the surrounding goose nests is inversely related to the falcon’s activity. In years of higher falcon activity, falcons prevent red-breasted geese from nesting as close to their nest as in years of lower falcon activity. Additional stimuli are required for red-breasted geese to form colonies near rough-legged buzzard nests. The distance between snowy owl nests and red-breasted goose nests was smaller when arctic foxes were abundant than when they were scarce.     

Diel emigration and colonization responses of blackfly larvae (Diptera: Simuliidae) to ultraviolet radiation

1. Total counts of blackfly larvae densities over 30- and 57-h periods in experimental channels during May of 1996 & 1997 indicate that ultraviolet radiation (UV; 290–400 nm) may be important in stimulating emigration.
2. Under experimentally controlled solar UV exposure, larval densities at dawn in UV-shielded channels were 161% and 168% higher than in the UV-exposed channels. Larval densities in UV-exposed channels then decreased by 68.2% and 81.1% between dawn and early afternoon of the two days; density decreases in UV-shielded channels were slight, and not statistically significant, during the same periods.
3. Larvae within UV-exposed channels occupied shaded microhabitats during hours of intense solar radiation, suggesting that simuliid larvae can detect and respond to UV radiation over very short periods of time.
4. A cyclical pattern of UV-induced emigration during hours of increasing solar flux (06.30–13.30) and net immigration in the hours of decreasing solar flux and at night emerged. Thus stream invertebrates may be very sensitive to environmental changes, resulting in either increased UV flux or decreased shading of streams. Diel cycles in invertebrate densities should be taken into account in research designs and sampling protocols in order to identify and interpret correctly results of both periodic surveys and experiments.     

Life Cycles of Ground Beetles (Coleoptera,Carabidae) from the Mountain Taiga and Mountain Forest-Steppe in the Eastern Sayan

Seasonal dynamics and demographic structure was studied in 15 dominant ground beetle species in the mountain taiga and mountain forest-steppe belts of the Eastern Sayan (Okinskoe Plateau). Life cycles of the dominant ground beetle species were classified by developmental time, seasonal dynamics, and intrapopulation groups with different reproduction timing. The strategies of carabid life cycles adapted to severe mountain conditions of the Eastern Sayan were revealed.