Period Of Enrichment Research Articles

Environmental influences on brain and behavior of year-old rats.

AbstractThe brains of rats, almost a year old, were found to be similarly susceptible to the influences of differential housing as had been those of weanling rats. In 3 experiments, male S1 rats, about 285 days of age, remained for 30, 60, or 90 days in enriched (EC), impoverished (IC), or standard colony (SC) conditions before sacrifice for measures of weights and enzymatic activities of standardized brain sections. Occipital and total cortical brain weights increased significantly after EC, whereas subcortical regions seemed to be resistant to environmental influences. Year‐old rats responded with greater cortical weight increases and enhanced occipital cholinesterase activities from a period of enrichment extended beyond 60 days than SC agemates. The cortices of IC rats, in contrast, showed a decline in weights with longer duration in isolation. Environmental enrichment, furthermore, disposed year‐old rats to faster learning in the Lashley III maze.

Feasibility and economics of conditioning recirculated greenhouse air by means of evaporative cooling

If excess solar heat could be economically removed from greenhouse by keeping them closed and recirculating and conditioning the air, instead of by ventilation, CO 2 enrichment could be maintained throughout the period when it could be beneficial instead of for only about 50% of it. A value is calculated for the increase in financial return to be expected from an optimistic estimate of tomato yield increase due to this extension of the period of enrichment. Conditioning by refrigeration is shown to be uneconomic. Using data on the frequency of occurrence of combined levels of wet- and dry-bulb temperatures on the south coast of England in summer, the maximum temperatures and humidities likely to be obtained in a glasshouse with conditioning of recirculated air by two systems of indirect evaporative cooling were determined. Temperatures not too high for tomato growing could be achieved for about 95% of the time by single-stage cooling, or for about 98% of the time by two-stage cooling, but relative humidities would be very high. The annual cost of the single-stage system, although less than that for refrigeration, is also uneconomic, and that for the two-stage system exceeds that for refrigeration.

OSCILLAXANTHIN IN THE SEDIMENT OF LAKE WASHINGTON1

Oscillaxanthin was determined quantitatively in portions of five cores cut in slices 1 cm thick. The distribution varied with depth in a manner qualitatively consistent in all cores, although there were quantitative differences. The pigment was undetectable below 9 cm in two cores, below 8 in another, and below 13 in the remaining two. The amount of pigment per unit dry weight of sediment was highest at the surface and had two subsurface maxima, at 4 cm for the shallow maximum, with a deep maximum at 7 cm for three cores, 8 cm for the fourth, and 9 cm for the fifth. The total accumulated pigment under unit area of bottom mud varied from 27.10 to 6.66 µg/cm2. To some extent these differences also relate to accumulation of organic matter and to other pigments. The oscillaxanthin‐producing algae evidently are somewhat differently distributed during sedimentation, for the differences are not related to differences in distribution of the plankton.The vertical distribution of oscillaxanthin within the sediments is considered in relation to the recent history of sewage enrichment of the lake. Oscillaxanthin is known to be produced by Oscillatoria rubescens and O. agardhii, both of which have occurred in abundance in Lake Washington since 1955 when O. rubescens was observed for the first time, in a relatively dense population. Oscillatoria agardhii occurred in small quantities in 1950. Cultured Anabaena circinalis, Microcystis aeruginosa, and Aphanizomenon flos‐aquae had negligible amounts of oscillaxanthin.On the basis of available evidence about sedimentation rates, oscillaxanthin must have been produced in the lake before the appearance of O. rubescens in 1955 and also before 1950. The first appearance of oscillaxanthin probably came early in the period of sewage enrichment that led to the recent diversion of sewage from Lake Washington. The reasons for the two maxima in concentration are not known. The changes apparently cannot be attributed to destruction of pigment or dilution with other components of sediment in varying amounts over the years and therefore seem to reflect changes in the production of Oscillatoria.

The effect of whole-body x-irradiation of guinea pigs on liver ribosomes.

1. The size distribution of aggregates of liver ribosomes and their protein-synthesizing ability in vitro were studied shortly after X-irradiation of guinea pigs. 2. Sucrose-density-gradient analysis of the mitochondrial supernatant after treatment with deoxycholate revealed a gradual increase in the number of polysomes, reaching a maximum between 9 and 15 hr. after irradiation. At that period the amount of ribonucleoprotein particles reached a level 25-30% above the control. This finding was confirmed by analytical-ultracentrifugal analysis and electron microscopy. Experiments were conducted to exclude the possibility that the enrichment of polysomes in the irradiated animals had occurred during the isolation procedure. 3. The protein-synthesizing ability of total ribosomal particles was measured in vitro. This showed an increase in amino acid incorporation parallel to the progressive enrichment of polysomes. At radiation doses of up to 1000r. the protein-synthesizing capacity was dependent on the radiation dose: the higher the dose the higher the amino acid incorporation, reaching 40-60% above the control at the period of maximal polysome enrichment. Amino acid incorporation remained at this level after radiation doses of between 1000 and 3000r. The enhanced protein-synthesizing activity was due solely to the increase in the proportion of polysomes, since irradiation was without effect on the activity of single ribosomes. 4. The results of the experiments are discussed in the light of our knowledge of the effect of radiation on protein synthesis.