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91.
The finer control of mating activity by testosterone in male sheep was investigated using the castrated ram (wether) as an experimental model. Adult wethers that had been castrated before puberty were injected with graded doses of testosterone propionate (TP) and mating behavior was assessed in standardized libido trials at various times during treatment. Doses of 1 to 2 mg TP/day elicited mounting behavior in wethers but did not result in intromission or ejaculation. On the other hand, TP doses of 4 mg/day or greater stimulated the complete mating response which included intromission and the ejaculatory reflex. The threshold dose of TP required for complete mating activity (4 mg/day) produced plasma testosterone levels which were lower than those normally observed in intact rams. The results of this study indicate that the behavioral aspects (arousal mechanisms) of mating in rams have a lower testosterone threshold than intromission and ejaculation (consummatory mechanisms). Also, since complete mating activity was stimulated in wethers having relatively low plasma testosterone levels, this may explain why there is no apparent relationship between plasma testosterone and mating drive in intact rams. 相似文献
92.
Rates of nutrient release byMysis relicta in Lake Michigan were measured on five nights at a 45-m station near Milwaukee, Wisconsin, U.S.A., in the summer of 1977. Nocturnal vertical migrations of the mysids were monitored with both echosounder tracings and vertical net tows. Estimates of the total areal dry mass of the mysids ranged from 600 to 1 820 mg m–2. Rates of release of dissolved reactive phosphorus, total phosphorus, ammonia, and urea were measured in dark incubations on shipboard. Excretion experiments were initiated immediately after mysids were collected from each of several vertical net hauls. The depths of maximum mysid densities corresponded approximately with a deep phytoplankton peak located in the vicinity of the thermocline. Semiquantitative demands for N and P by phytoplankton within this peak were obtained from14C estimates of primary production from a previous study, assuming a constant C:N:P ratio for the algae. These algal nutrient demands were compared to potential N and P release by the mysids to obtain a first approximation of the relative rates of nutrient supply and demand for the field phytoplankton populations. Our analysis indicates that mysids may directly supply about 1–10% of the daily N and P demands of the phytoplankton in the deep peak. However, indirect interactions betweenMysis relicta and other organisms, such as small zooplankton and fishes, could be major factors in nutrient recycling within the metalimnion and subthermocline region of Lake Michigan.Contribution No. 238, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Wisconsin.Contribution No. 238, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Wisconsin. 相似文献
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A passive hemagglutination assay was developed to measure Trypanosoma musculi-specific antibody in mice. Indicator-erythrocyte donor mice received 550 rad 60Co 24 hr before intraperitoneal injection of 3 × 104T. musculi. T. musculi antigen-coated erythrocytes were obtained from these mice on Day 9 postinfection. T. musculi antigen-coated erythrocytes obtained in this manner were used as indicator erythrocytes in a passive hemagglutination procedure. Serum from hyperimmunized mice (three consecutive infections at 21-day intervals) gave titers as high as 1:1024. Titers of 1:256 and 1:512 were obtained from singly infected mice on Days 18 and 28 postinfection, respectively. In marked contrast, nude mice infected with T. musculi did not produce a detectable agglutinating antibody response. Erythrocytes obtained from either irradiated (550 rad 60Co) uninfected mice, nonirradiated infected mice, or normal mice did not agglutinate when combined with any of the sera tested. These data suggest the usefulness of this passive hemagglutination assay for the measurement of antibody to T. musculi in the serum of infected mice. 相似文献
96.
The kidney exerts both prohypertensive and antihypertensive functions. Part of the anti-hypertensive function of the kidney is mediated by the renomedullary interstitial cells (RIC), as an endocrine-type function. Six experimental models of hypertension and their relation to the antihypertensive function of the RIC are discussed. It is proposed that the anti-hypertensive function of the RIC may be deficient by the three mechanisms: 1) absence of the cells (as in the renoprival state); 2) severe damage to the cells (as in partial nephrectomy-salt hypertension of the rat and late malignant hypertension of the rabbit); and 3) constraint of the function of these cells (as in angiotensin-salt hypertension due to a lower salt intake). The constraint may result from excessive angiotensin, either by a direct effect or via a hemodynamic mechanism. The converting enzyme inhibitors (CEI) fail to exert their antihypertensive function when the RIC are absent or damaged. Conversely, the CEI are effective in those models associated with intact RIC. CEI appear to exert their antihypertensive action partly through an effect on RIC. 相似文献
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This study describes and quantifies the social organization and agonistic behaviour of adult male collared lemmings (Dicrostonyx groenlandicus) in an indoor enclosure. Five groups of four lemmings were observed during separate 8-day tests. Experimental design permitted an increase in group size while density remained constant. When in groups of two, males established stable dominant-subordinate relationships and, when in groups of four, they formed stable non-linear dominance hierarchies. For either group size, frequency of agonistic behaviour declined over time. Habituation, formation of dominance relationships and spatio-temporal partitioning of space are suggested as possible explanations of this decline. Percentage of initial body weight lost during the experiments varied inversely with social rank. Possible causes of this weight loss are discussed. Social relationships in this study are discussed in light of field observations of male lemming home range distribution. 相似文献
99.
Cell electrophoresis experiments were performed at physiological, ionic strength on Hypaque-Ficoll separated normal human peripheral blood lymphocytes. The initial lymphocyte preparations averaged 72% T cells and 22% B cells as estimated by resetting techniques. A bimodal electrophoretic distribution of fast T cells and slow B cells such as has been repeatedly shown to exist for experimental animals could not be demonstrated. Neither B- nor T-enriched populations showed any correlation between mobility and degree of enrichment. A strong positive correlation was found between the non-rosetting cells and a very slow electrophoretic subpopulation produced during the B enrichment procedure. It was also found that considerable variability in lymphocyte mobilities existed from person to person and even in the same individual sampled over several months; these observations imply that the pooling of electrophoretic data can be misleading. The importance of these findings lies in the growing interest in relating lymphocyte electrophoresis to disease processes and immunological rejection phenomena. 相似文献
100.
A holidic diet for feeding the aster leafhopper, Macrosteles fascifrons, was formulated. The amino acids, B-vitamins, and sucrose are less concentrated than in aphid diets. Cholesterol, at 5 mg/ml, is required for the last ecdysis. Although leafhoppers reared on this diet have poorer survival and shorter life span than those reared on plants, they produce more progeny. Leafhoppers reared on this diet have completed the ninth generation and the culture is still thriving. 相似文献