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61.
George Dunea 《BMJ (Clinical research ed.)》1987,294(6581):1211-1212
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George W. Uetz 《Oecologia》1989,81(2):154-159
Summary Increased prey capture efficiency in colonial spiders is a consequence of the ricochet effect, as prey are captured after they bounce off several webs in succession. In this study, the prey capture of three species of colonial spiders in the genus Metepeira from Mexico are compared. These species, from different habitats, show varying levels of social organization (group size and withingroup spacing) that affect prey capture from ricochets. Metepeira sp. a (a presumed new species tentatively named atascadero) from desert grassland habitats, occur solitarily or in small groups, and gain little from prey ricochets: prey capture rates are low and variance in prey captured/spider is high. M. spinipes, from mesic agricultural sites, occur in groups of 10–150, and show a ricochet effect resulting in more and larger prey, and reduced variance in capture rate. M. incrassata, from tropical rainforest/agricultural sites, occur in large colonies of hundreds to thousands of individuals, and show a similar ricochet effect. The ricochet effect does not influence taxonomic composition of prey in either M. atascadero or M. spinipes, but does in tropical M. incrassata. This result, however, is primarily due to the capacity of certain taxa (eg., Lepidoptera), more common in the tropics, to escape more easily from spider webs. A comparison of prey capture efficiency of colonial M. incrassata with that of solitary M. atascadero shows that the ricochet effect provides an increase in efficiency across all size classes of prey. 相似文献
64.
Prescription drug laws: justified hard paternalism 总被引:2,自引:0,他引:2
Rainbolt GW 《Bioethics》1989,3(1):45-58
65.
1. The working hypothesis that neuropeptide gene expression in a neuron is an indicator of that neuron's physiological activity is discussed. 2. Representative examples from the literature are presented to support the hypothesis. 3. Further, we discuss the regulation of expression of two opioid peptides, preproenkephalin and preprodynorphin, in laminae I and II of the spinal cord and in nucleus caudalis of the trigeminal nuclear complex, where they may play a role in pain modulation. 4. The expression of the opioid peptide genes can be induced by both painful and nonnoxious stimuli in neurons in time-dependent and sensory-specific fashions. 相似文献
66.
Robert A. Mueller Thomas J. McCown Ricky D. Hunt Cecilia Lundberg George R. Breese 《Cellular and molecular neurobiology》1990,10(3):327-336
1. | Rats which survived hypoglycemia by insulin, hypoxia by 10% O2, or ischemia by carotid ligation and hypotension to 40 mm Hg, evidenced no changes in cerebrospinal fluid (CSF) uridine. Animals which died soon after the above interventions or as a result of KCl-induced cardiac arrest had elevated CSF uridine concentrations. |
2. | Injection of whole blood or the soluble contents of lysed blood cells into the lateral ventricle of rats reduced CSF uridine to less than one-half normal at 24 hrs but values returned to normal 3 days later. Changes in hypoxanthine resembled those of uridine, but were less dramatic, whereas xanthine concentrations were largely unaltered. Intraventricular injection of plasma or saline did not alter CSF uridine. |
3. | It seems most likely that low CSF uridine concentrations previously reported in head injury patients may be secondary to the effects of blood cell contents in the cerebrospinal fluid, rather than responses to altered metabolism in neurons or glia cells. |
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A method is proposed for predicting the adjacency order in which strands pack in a -sheet in a protein, on the basis of its amino acid sequence alone. The method is based on the construction of a predicted contact map for the protein, in which the probability that various residue pairs are close to each other is computed from statistically determined average distances of residue pairs in globular proteins of known structure. Compact regions, i.e., portions of the sequence with many interresidue contacts, are determined on the map by using an objective search procedure. The proximity of strands in a -sheet is predicted from the density of contacts in compact regions associated with each pair of strands. The most probable -sheet structures are those with the highest density of contacts. The method has been tested by computing the probable strand arrangements in a five-strand -sheet in five proteins or protein domains, containing 62–138 residues. Of the theoretically possible 60 strand arrangements, the method selects two to eight arrangements as most probable; i.e., it leads to a large reduction in the number of possibilities. The native strand arrangement is among those predicted for three of the five proteins. For the other two, it would be included in the prediction by a slight relaxation of the cutoff criteria used to analyze the density of contacts. 相似文献
70.
A strain of Cryptococcus neoformans that was isolated from the cerebrospinal fluid of a human diagnosed as having acquired immunodeficiency syndrome (AIDS), and that produced cutaneous lesions in experimentally infected, normal mice is described. Although no unusual cutaneous manifestations were noted in the patient's records, this isolate of C. neoformans proved to be dermotropic when injected intravenously into CD-1 mice. The LD50 at 28 days post infection ranged from 3.6–7.5×105 cells per mouse, and in vitro growth rate studies demonstrated that this isolate grew well at 35 °C and at 37 °C, but did not grow at 40 °C and higher. This isolate was rhinotropic producing large granulomatous lesions in the nasal tissues. Other cutaneous tissues affected were the periocular tissues, ears, feet and tail, although the granulomas were nodular in structure and less necrotic than the nasal lesions. The brain, lungs, liver, kidneys and spleen also were culture positive for C. neoformans. Histopathologically, each affected tissue examined had large densities of yeast cells and a chronic, granulomatous host response. Animals surviving the infection appeared to develop a commensal-type relationship with the infective yeast. This is the first report of an isolate of C. neoformans from an AIDS patient that has caused cutaneous manifestations in an animal model. The model described in this report may be useful for elucidating pathogenic mechanisms of cryptococcosis, particularly cutaneous manifestations of the disease. 相似文献