Computation of object approach by a wide-field, motion-sensitive neuron

The lobula giant motion detector (LGMD) in the locust visual system is a wide-field, motion-sensitive neuron that responds vigorously to objects approaching the animal on a collision course. We investigated the computation performed by LGMD when it responds to approaching objects by recording the activity of its postsynaptic target, the descending contralateral motion detector (DCMD). In each animal, peak DCMD activity occurred a fixed delay delta (15 相似文献   

Electrophysiological evidence of developmental changes in the duration of auditory sensory memory

In behavioral studies, children's memory for tonal frequency has been found to persist for less time than adults' (T. A. Keller & N. Cowan, 1994). The present study was done to evaluate the argument that this effect is due to changes in auditory sensory memory and not to attentional mechanisms. This question was investigated using mismatch negativity (MMN), an auditory event-related potential considered to be insensitive to attention. Participants were 6-7-, 8-10-, and 11-12-year-old children and adults. They were presented with trains of stimuli, beginning with either a standard (1000 Hz) or a deviant (1200 Hz) tone with trains separated by either 1 s or 8 s. All 4 groups exhibited MMNs after delays of 1 s, but only the adults and oldest children exhibited MMNs after 8 s, indicating that there are maturational changes in the duration of auditory sensory memory.     

Characterization of human T-cell leukemia virus type I integrase expressed in Escherichia coli

The C-terminal part of the pol gene of the human T-cell leukemia virus type I (HTLV-I) is predicted to encode the integrase (IN) of the virus; however, this protein has not yet been detected in virions or infected cells. We expressed the putative IN from an infectious molecular clone of HTLV-I in Escherichia coli. Comparison with protein resulting from coexpression of HTLV-I protease (PR) and Pol in insect cells indicated that the bacterially expressed protein is identical with or very similar to IN released from a PR-Pol precursor by proteolytic cleavage. HTLV-I IN was purified from E. coli under native conditions. The protein behaved like a dimer in size-exclusion chromatography. It carried out activities characteristic of retroviral IN with high efficiency, displaying a strong preference for U5-derived vs. U3-derived sequences in the processing and strand-transfer reactions. In the disintegration reaction, HTLV-I IN not only accepted the double-stranded branched substrate corresponding to the product of a strand-transfer reaction, but was also able to carry out a phosphoryl transfer on a branched molecule with a single-stranded or a single adenosine overhang.     

Elastin degradation by matrix metalloproteinases. Cleavage site specificity and mechanisms of elastolysis

Insoluble elastin was used as a substrate to characterize the peptide bond specificities of human (HME) and mouse macrophage elastase (MME) and to compare these enzymes with other mammalian metalloproteinases and serine elastases. New amino termini detected by protein sequence analysis in insoluble elastin following proteolytic digestion reveal the P'1 residues in the carboxyl-terminal direction from the scissile bond. The relative proportion of each amino acid in this position reflects the proteolytic preference of the elastolytic enzyme. The predominant amino acids detected by protein sequence analysis following cleavage of insoluble elastin with HME, MME, and 92-kDa gelatinase were Leu, Ile, Ala, Gly, and Val. HME and MME were similar in their substrate specificity and showed a stronger preference for Leu/Ile than did the 92-kDa enzyme. Fibroblast collagenase showed no activity toward elastin. The amino acid residues detected in insoluble elastin following hydrolysis with porcine pancreatic elastase and human neutrophil elastase were predominantly Gly and Ala, with lesser amounts of Val, Phe, Ile, and Leu. There were interesting specificity differences between the two enzymes, however. For both the serine and matrix metalloproteinases, catalysis of peptide bond cleavage in insoluble elastin was characterized by temperature effects and water requirements typical of common enzyme-catalyzed reactions, even those involving soluble substrates. In contrast to what has been observed for collagen, the energy requirements for elastolysis were not extraordinary, consistent with cleavage sites in elastin being readily accessible to enzymatic attack.     

Breast-feeding exposure of infants to cadmium, lead, and mercury: a public health viewpoint

The purpose of this report is to provide an overview of the public health implications of exposure via breast milk to cadmium, lead, and mercury for nursing infants and to provide health-based guidance. Daily intakes were calculated and compared with guidance values used for public health assessments at hazardous waste sites. Cadmium, lead, and mercury under normal conditions are found in breast milk at concentration ranges of < 1 microgram/L, 2-5 micrograms/L, and 1.4-1.7 micrograms/L, respectively. Women exposed environmentally or occupationally can have higher levels in their breast milk. Concentrations of about 5 micrograms/L (cadmium), 20 micrograms/L (lead), and 3.5 micrograms/L (mercury) appear to be adequate screening levels. Many factors affect both the distribution of cadmium, lead, and mercury in breast milk and the health consequences to an infant. It is not clear what additional impact low-level exposure via breast milk may have on an infant born with a body burden to one of these metals. There is sufficient evidence to make the case that contaminated breast milk is a source of potential risk to infants in certain populations. Prevention strategies that include behavior modification and proper nutrition should be communicated to women at risk. Identification and elimination of exposure pathways and a critical analysis of the benefits of breast feeding versus heavy metal exposure are needed on a site-specific or individual basis. Research is required to better understand the impact of low-level exposure to heavy metals via breast milk. Breastfeeding should be encouraged under most circumstances.     

Omega-agatoxin IVA, a P-type calcium channel antagonist, reduces nociceptive processing in spinal cord neurons with input from the inflamed but not from the normal knee joint--an electrophysiological study in the rat in vivo

High threshold voltage-dependent P- and Q-type calcium channels are involved in neurotransmitter release. In order to investigate the role of P- and Q-type calcium channels in the mechanosensory (nociceptive) processing in the spinal cord, their participation in the responses of spinal wide-dynamic-range neurons to innocuous and noxious mechanical stimulation of the knee and ankle joints was studied in 30 anaesthetized rats. The knee was either normal or acutely inflamed by kaolin/carrageenan. During the topical application of omega-agatoxin IVA (P-type channel antagonist, 0.1 microM) onto the dorsal surface of the spinal cord, the responses to innocuous and noxious pressure applied to the normal knee were increased to respectively 124 +/- 42% and 114 +/- 23% of predrug values (mean +/- SD, P < 0.05, 14 neurons). By contrast, in rats with an inflamed knee, the responses to innocuous and noxious pressure applied to the knee were reduced to respectively 72 +/- 19 and 73 +/- 22% of baseline (mean +/- SD, P < 0.01, 13 neurons). In the same neurons, omega-agatoxin IVA slightly increased the responses to pressure on the non-inflamed ankle whether the knee was normal or inflamed. Thus P-type calcium channels seem to acquire a predominant importance in the excitation of spinal cord neurons by mechanosensory input from inflamed tissue and hence in the generation of inflammatory pain. By contrast, the Q-type channel antagonist, omega-conotoxin MVIIC (1 or 100 microM), had no significant effect upon responses to innocuous or noxious pressure applied to either normal or inflamed knees (25 neurons).     

Phospholipase A2--from basic research to clinical reality]

Phospholipase A2 (PLA2) is a group of secretory as well as intracellular enzymes that release phospholipids as an early step in inflammation and play a physiologic role in digestion. In humans, the group of secretory, low-molecular-weight PLA2 (sPLA2) is differentiated from the cytosolic, high-molecular-weight PLA2 (cPLA2). The two known cPLA2 mediate the intracellular response to inflammation by releasing arachidonic acid from membrane phospholipids. Secretory pancreatic PLA2 (sPLA2-I) is a digestive zymogen secreted from pancreatic acinar cells in its inactive form. Activated by trypsin in the duodenum, it is an important digestive enzyme. In acute pancreatitis, circulating sPLA2-I indicates pancreatic injury but is mostly inactive. Synovial-type secretory PLA2 (sPLA2-II), first isolated from synovial fluid of arthritis patients, is increased in inflammation, after surgery or trauma, and in various inflammatory diseases. Unlike sPLA2-I, its catalytic activity is held responsible for mediating the systemic inflammatory reaction and its complications by regulating the synthesis of prostaglandins, leukotrienes and platelet activating factor. Clinically, sPLA2-II offers new possibilities as an early marker for severe inflammation and predicting systemic complications in severely ill patients.     

Magnetic resonance imaging of articular cartilage in the knee. An evaluation with use of fast-spin-echo imaging

The purpose of this study was to demonstrate that specialized magnetic resonance imaging provides an accurate assessment of lesions of the articular cartilage of the knee. Arthroscopy was used as the comparative standard. Eighty-eight patients who had an average age of thirty-eight years were evaluated with magnetic resonance imaging and subsequent arthroscopy because of a suspected meniscal or ligamentous injury. The magnetic resonance imaging was performed with a specialized sequence in the sagittal, coronal, and axial planes. Seven articular surfaces (the patellar facets, the trochlea, the femoral condyles, and the tibial plateaus) were graded prospectively on the magnetic resonance images by two independent readers with use of the 5-point classification system of Outerbridge, which was also used at arthroscopy. Six hundred and sixteen articular surfaces were assessed, and 248 lesions were identified at arthroscopy. Eighty-two surfaces had chondral softening; seventy-five, mild ulceration; fifty-three, deep ulceration, fibrillation, or a flap without exposure of subchondral bone; and thirty-eight, full-thickness wear. To simplify the statistical analysis, grades 0 and 1 were regarded as disease-negative status and grades 2, 3, and 4 were regarded as disease-positive status. When the grades that had been assigned by reader 1 were used for the analysis, magnetic resonance imaging had a sensitivity of 87 per cent (144 of 166), a specificity of 94 per cent (424 of 450), an accuracy of 92 per cent (568 of 616), a positive predictive value of 85 per cent (144 of 170), and a negative predictive value of 95 per cent (424 of 446) for the detection of a chondral lesion. Interobserver variability was minimum, as indicated by a weighted kappa statistic of 0.93 (almost perfect agreement). With use of this readily available modified magnetic resonance imaging sequence, it is possible to assess all articular surfaces of the knee accurately and thereby identify lesions that are amenable to arthroscopic treatment.     

Religious activity and depression among community-dwelling elderly persons with cancer: the moderating effect of race

OBJECTIVES: Research has been oriented toward elucidating the links between religion and mental health. The purpose of this article is to further our knowledge in this area by examining the effect of religious activity on depressive symptomatology among community-dwelling elderly persons with cancer. We also test whether these effects differ between Blacks and Whites. METHODS: We use two waves of data collected from a community-dwelling sample of elderly persons living in North Carolina. Depressive symptomatology is measured using four subscales from the CES-D 20 scale: somatic-retarded activity, depressed affect, positive affect, and interpersonal relations. Measures of religious activity include service attendance, religious devotion, and watching or listening to religious programs. RESULTS: The findings indicate that among Blacks with cancer, religious activity is related to lower levels of depressive symptomatology; no such relationship is found for respondent with other illnesses or no illness. Further, the effects of religious activity are stronger among Blacks than Whites. DISCUSSION: The analyses lend support to the hypothesis that religious activity is a strong predictor of depression in elderly adults with cancer. This finding, however, is not as strong as we had anticipated.