No description available.

No description available.

Photocopy of typescript. / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries / Department: Animal Sciences and Industry.

Thesis. 1975. M.Arch.--Massachusetts Institute of Technology. Dept. of Architecture. / Includes bibliographical references. / M.Arch.

Cyclic AMP-dependent protein kinase (cAMP-PK) is an important mediator of hormone action. Its activity ratio is an accurate indicator of cellular activity under various experimental conditions including: (1) age and sex, (2) hormone administration and (3) temperature and photoperiod. Pituitary activity in unstimulated birds is not altered by age, but thyroid activity is much higher in old birds than in young animals. Thyrotropin releasing hormone (TRH) increases pituitary, thyroid and liver activity of prepubescent chickens, but has no effect on aged males and increases only thyroid and liver activities in aged females, suggesting a reduction in pituitary-thyroid function with advancing age. In prepubertal females, TRH increases pituitary and thyroid cAMP-PK activity, plasma T₃ and T₄ levels and liver T₄ monodeiodination. Thyroid activity reaches maximum activity before the pituitary, while plasma T₄ and liver T₄ monodeodinating activity reach their highest levels 20 minutes before plasma T₃. These findings suggest that fluctuations in liver T₄ 5' monodeiodinating activity might be responsible for the cyclic response of plasma T₃ and T₄. Castrated cockerels have larger pituitaries than untreated birds, but contain the same amount of DNA. Methimazole-fed cockerels have pituitaries significantly smaller than controls, while castrated cockerels fed methimazole have pituitaries the same size as untreated birds. Pituitary DNA is less than controls in both groups of methimazole-fed birds. These results are considered to be due to a change in the thyrotroph population, without an increase in total cell numbers, and may indicate a transformation of basophils. Pituitary cAMP-PK activity during cold stress substantiates this conclusion. Thyroid glands of castrated and untreated cockerels are smaller in size, histological appearance and DNA content; however, cAMP-PK activity is much greater in the castrated birds. Methimazole-fed cockerels have enlarged thyroid glands, elevated cAMP-PK activity, increased DNA and cellular hypertrophy; however, these effects may be mitigated by castration. Seven days after removal of testosterone supplements, photostimulated castrates have a higher thyroid cAMP-PK activity ratio than short day castrates; however, both groups are elevated above control, suggesting that long photoperiods enhance the stimulatory effects of castration on thyroid activity. Pituitary activity is elevated in long and short day birds seven days after removal of testosterone, but remains high only in short day castrates. Therefore, a reduction in the sensitivity of the hypothalamic-pituitary axis to testosterone may occur only in long day cockerels.

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The aim of this study was to test the hypothesis that ryegrass and clover, when grown under optimal conditions in mixed stands, interact in response to available light energy. with other resources non-limiting, pasture yield is determined by the efficiency with which solar radiation is intercepted by canopies and converted into dry matter. The clover-ryegrass interaction under varying light regimes, as experienced in the canopies of these pastures, was studied by investigating the growth and production of ryegrass and clover in relation to light harvesting abilities and photosynthetic utilization of intercepted light. Pasture canopy structure and growth were studied under a four-weekly clipping treatment. The interception of photon flux density (PFD) in the pasture canopy was monitored diurnally and seasonally in mixed and mono cultures. Light use efficiency (C02 fixed/ unit absorbed PFD) as well as photochemical efficiency of photosystem II (Fv/Fm) were studied by monitoring CO2 assimilation rates and chlorophyll fluorescence respectively. The results obtained from this study indicated that interaction did occur between ryegrass and clover, cultivated in mixed pastures. The mixture was capable of more efficient light interception than the mono cultures, which resulted in higher productivity. Light interception abilities, as manifested in canopy architecture, and not physiological utilization of light energy, were found to govern the interaction between the two pasture components. / Thesis (M.Sc.)-University of Natal, Durban, 1993.

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Apparatus has been designed and developed for determining the response of the plankton Crustacean Simocephalus serrulatus (Koch) to horizontal gradients of light and temperature. These factors were varied independently or combined under standardized conditions. The temperature preferendum for this organism, cultured in a constant environment, was found to be 19.13°C, for animals previously held at 19°C. for 14 hours. The steepness of a temperature gradient was shown to influence the rate of aggregation at a preferendum temperature. At a constant temperature (temperature preferendum) reactions to light were then studied. Light intensity, gradients of light intensity, light quality, and gradients of light quality were considered. Animals were positively phototactic to the range of visible light intensities considered, but became indifferent to light on the addition of chemical substances to the water medium. An absolute optimum light intensity was demonstrated, at which the response to light is greatest in magnitude. The rate of rise of light intensity was shown to be directly related to the magnitude of the response and indirectly related to the time for the response to reach a peak up to the absolute optimum light intensity. The intensity of illumination was inversely related to the time for adaptation to occur. The magnitude of the light response was inversely related to the intensity of a pre-adaptation light stimulus. Wave lengths in the region of 3000 to 3500 Å, with a mean value of approximately 3300 Å, were shown to reverse the primary sign of the phototactic response. The spectral sensitivity curve for the positive phototactic response to visible light extended from 4000 to 6400 Å. Finally, light factors were applied to the animals in a temperature gradient and quantitative data on the response obtained. The interaction of the two factors produced a response which is the resultant of the factors acting in opposition. / Science, Faculty of / Zoology, Department of / Graduate