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21.
Raphael Chalmeau 《Primates; journal of primatology》1994,35(3):385-392
The aim of this study was to assess the ability of chimpanzees (Pan troglodytes) to cooperate in an instrumental task. A specially constructed fruit distributor was presented to a group of six captive
chimpanzees. A cooperative response required two chimpanzees: both had to pull a handle simultaneously to make a fruit fall
into the cage. The dominant male of the group and an infant produced most of the operant responses, and the male got nearly
all the fruits. Other conspecifics avoided the dominant male at the apparatus. Social influences appear to limit the possibility
of co-operation between individuals because a certain level of interindividual tolerance is required. The results revealed
a significant increase in the number of pulls each time both chimpanzees were together at the apparatus. Operant chimpanzees
learn to coordinate their actions in time and space. 相似文献
22.
Hebbian learning allows a network of spiking neurons to store and retrieve spatio-temporal patterns with a time resolution of 1 ms, despite the long postsynaptic and dendritic integration times. To show this, we introduce and analyze a model of spiking neurons, the spike response model, with a realistic distribution of axonal delays and with realistic postsynaptic potentials. Learning is performed by a local Hebbian rule which is based on the synchronism of presynaptic neurotransmitter release and some short-acting postsynaptic process. The time window of this synchronism determines the temporal resolution of pattern retrieval, which can be initiated by applying a short external stimulus pattern. Furthermore, a rate quantization is found in dependence upon the threshold value of the neurons, i.e., in a given time a pattern runsn times as often as learned, wheren is a positive integer (n 0). We show that all information about the spike pattern is lost if only mean firing rates (temporal average) or ensemble activities (spatial average) are considered. An average over several retrieval runs in order to generate a post-stimulus time histogram may also deteriorate the signal. The full information on a pattern is contained in the spike raster of a single run. Our results stress the importance, and advantage, of coding by spatio-temporal spike patterns instead of firing rates and average ensemble activity. The implications regarding modelling and experimental data analysis are discussed. 相似文献
23.
Fritz Thümmler Margarete Kirchner Raphael Teuber Peter Dittrich 《Plant molecular biology》1995,29(3):551-565
22 novel members of the Arabidopsis thaliana protein kinase family (AKs) were identified by using degenerate oligonucleotide primers directed to highly conserved amino acid sequences of the protein kinase (PK) catalytic domain. Of these 22 genes, 16 turned out to carry intron sequences. Homologies of AK sequences were detected to S-locus receptor protein kinases (SRKs) from Brassica spp., to SRK-like PKs from maize and A. thaliana and to several other receptor PKs from A. thaliana. Sequence similarity was also detected to Ca2+-dependent PKs (CDPKs) from rape and soybean, to SNF1 and to CDC2 homologues. The genomic organization and the accumulation of the mRNAs from these 22 AK genes were investigated. 相似文献
24.
Nikolay K. Popnikolov Jason Yang Raphael C. Guzman Steven M. Swanson Gudmundur Thordarson Gail Collins Frank Talamantes Satyabrata Nandi 《Journal of cellular physiology》1995,163(1):51-60
A new system for studying growth of normal human mammary epithelial cells in an in vivo environment using athymic nude mice is described. Human mammary epithelial cells dissociated from reduction mammoplasty specimens were embedded within collagen gels and subsequently transplanted subcutaneously into nude mice. Histological sections of recovered collagen gels showed epithelial cells arranged as short tubules with some branching. Proliferation of mammary epithelial cells was quantitated in vivo by 3 days' continuous infusion with 5 bromo-2′-deoxy-uridine followed by immunostaining of sections from recovered gels. Ovarian steroids administered to the host animals, resulting in blood serum levels normally found in the human female, had little or no effect on the proliferation of human mammary epithelial cells. Collagen gel embedded mouse mammary epithelial cells, mouse mammary explants, and host mammary glands all responded similarly to ovarian steroids, suggesting that the unresponsiveness of the human mammary epithelial cells under these conditions was not due to dissociation per se. However, an increased dose of 17β-estradiol or a growth factor combination containing epidermal growth factor, cholera toxin, and cortisol significantly stimulated the proliferation of human outgrowths. The growth factor response was dependent on the location of the cells, with the greatest response seen in the part of the gel proximal to the osmotic pump delivering the growth factors and the effect gradually waning in area more distal to the pump. The effect was especially striking since the mitotic figures could be easily identified and the labeling index was as high as 75%. The host mouse mammary gland also responded to growth factors, resulting in ductal hyperplasia. The proliferative and morphogenetic effects of various agents on normal human mammary epithelial cells embedded in collagen gel can be studied in vivo in nude mice. © 1995 Wiley-Liss, Inc. 相似文献
25.
William G. Dail Vera Barba Leonard Leyba Raphael Galindo 《Cell and tissue research》1995,282(1):109-116
NADPH-diaphorase (NADPH-D) activity and immunoreactivity for neural and endothelial nitric oxide synthase (nNOS and eNOS, respectively) were used to investigate nitric oxide (NO) regulation of penile vasculature. Both the histochemical and immunohistochemical techniques for NOS showed that all smooth muscles regions of the penis (dorsal penile artery and vein, deep penile vessels, and cavernosal muscles) were richly innervated. The endothelium of penile arteries, deep dorsal penile vein, and select veins in the crura and shaft were also stained for NADPH-D and eNOS. However, the endothelium of cavernous sinuses was unstained by both techniques. Fewer fibers were seen in the glans penis, those present being associated with small blood vessels and large nerve bundles near the trabecular walls. All penile neurons in the pelvic plexus, located by retrograde transport of a dye placed in the corpora cavernosa penis, were stained by the NADPH-D method. Essentially similar results were obtained with an antibody to nNOS. These data suggest that penile parasympathetic neurons comprise a uniform population, as all seem capable of forming nitric oxide. However, in contrast to the endothelium of penile vessels, the endothelium lining the cavernosal spaces may not be capable of nitric oxide synthesis. 相似文献
26.
Raphael Falk 《Human genetics》1984,68(3):195-204
Summary The concept of the difference between the potential for a trait and the trait proper, i.e., between the genotype and the phenotype, became clear only during the first decade of the century, mainly through the work of Johannsen. Although Johannsen insisted on that the terms he coined were only helpful devices to organize data about heredity, it is obvious that they were bound from the beginning to the hypothesis that there was something in the gametes that could be rendered to analysis as discrete units. These units were the genes.This reductionist yet materially non-committed attitude has been developed into what I called instrumental-reductionism: the genes were hypothetical constructs that were accepted as if they were real entities. The research program developed on such a concept was very successful, not least because this instrumental approach allowed maximum flexibility in the attachment of meaning of the genes. While most geneticists accepted one or another position of this flexible concept, others took more extreme positions. At the one extreme end of the conceptual continuum was the realist approach that argued that genes were discrete, measurable, material particles, and on the other end, the claim that the attempts to identify discrete units only led to hyperatomism of a holistic view appropriate to heredity.The acceptance of the gene as a material and discrete unit, in the beginning of 1950s, opened the way to a deeper level of conceptualizing both its structure (cistron-recon-muton) and function (one gene—one enzyme). The discovery of the structure of DNA finally offered a chemical-physical explanation to the geneticist's requirements of a material gene. Thus, within less than 20 years the gene has been established as a sharply limited segment of the linear structure that is involved in the structrue of a product or its regulation.However, with turning of much of the attention to the eucaryotic DNA, it was necessary to accommodate the gene to an increasing flood of findings that did not tally with its concept as a discrete material unit. Without much heart-seeking among geneticists, the gene regained its role as an instrumental unit, or even as just an intervening variable, a quantity obtained by specified manipulation of the values of empirical variables. Though this flexibility demonstrated again that the most fruitful concepts are those to which it is impossible to attach a well defined meaning, it brought us also into a situation in which the same term has a different meaning for each group of scientists. In order to avoid the danger to be scattered over the face of all the earth because of lack of communicable language, it might be advisable to halt a little and reflect on the meaning of our concepts and their function. 相似文献
27.
Howard J. Bryant Raphael Gruener Rein Kilkson William S. Bickel 《生物化学与生物物理学报:生物膜》1977,464(1):188-201
Changes in the light scattering signal from single giant axons of lobster were observed during the propagation of the action potential in order to correlate membrane excitability with possible structural changes reflected in the optical properties of the axolemma. Substitution of guanidine and aminoguanidine for sodium resulted in a decreased action potential amplitude to 69 and 50% of control values, respectively. The amplitude of the light signal was, however, not significantly changed by these substitutions and is, therefore, reported to be independent of the transmembrane potential and current. The venom of the scorpion Leiurus quinquestriatus caused a marked prolongation of the action potential and the light scattering signal without significantly altering their amplitudes. A two-state model of the early (sodium) activation channel is suggested, in which the light scattering signal is correlated with a possible difference in the scattering efficiency between the states of the channel. 相似文献
28.
29.
Acetylcholine receptors in the muscle cell membrane accumulate at the nerve contact area in Xenopus cell cultures. The correlation between spontaneous synaptic potential properties and extent of acetylcholine receptor accumulation was studied. Small and infrequent miniature endplate potentials were measured before acetylcholine receptor accumulation which was observed with fluorescence microscopy using tetramethylrhodamine-conjugated α-bungarotoxin. As acetylcholine receptors accumulate at the nerve contact area, these synaptic potentials become larger and their frequency increases dramatically. In nerve-contacted muscle cells where spontaneous synaptic activity could not be detected, extensive acetylcholine receptor accumulation was not found at sites of nerve contact. Furthermore, muscle cells which exhibited extensive acetylcholine receptor accumulation along the nerve always produced miniature endplate potentials. Thus acetylcholine receptor accumulation and the presence of miniature endplate potentials were strongly correlated. Noncholinergic neurons from dorsal root ganglia did not form functional synaptic contacts with muscle cells nor acetylcholine receptor accumulation along the path of contact. Furthermore, explants from tadpole spinal cord formed functional synaptic contacts with muscle cells but rarely caused AChR localization. These data are discussed in terms of developmental processes during neuromuscular junction formation. 相似文献
30.
In this paper, we report on two experiments concerning the effect of the visual field of fovea on the subjective estimation of angular velocity. Experiment 1 investigates the effect of a slow moving target on the perception of self motion. The result of this experiment can be summarized as follows: a slow moving target seen in the visual field of fovea by a stationary person generates in this person a sensation of self rotation in the same direction as the motion of the target. This phenomenon will be called foveal induced ego motion. Experiment 2 investigates the latency for the detection of a self angular acceleration when the person focusses his fovea on a slowly moving target. From the results of this experiment we conclude that the latency for detection of a small self angular acceleration is shorter if the person sees a small foveal target moving with respect to the person in the direction of self rotation than if that small foveal target is moving (with respect to the person) in the opposite direction. The results of these experiments help us in refining existing models of visual-vestibular interaction, by providing a model which accounts for the phenomenon of oculogyral illusion.This research was conducted while serving as a Visiting Professor at the Man Vehicle Laboratory, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 相似文献