共查询到20条相似文献,搜索用时 78 毫秒
1.
Anatol Rapoport 《Bulletin of mathematical biology》1950,12(4):317-325
The input-output formula is derived for a neuron upon which converge the axones of two other neurons (one excitatory, the
other inhibitory) which are themselves subjected to a “Poisson shower” of excitatory stimuli. If the period of latent inhibition,
σ, does not exceed one half the refractory period, δ, the input-output curve has no maximum. If, however, σ>δ/2, a maximum
exists in the input-output curve. As the outside frequencyx increases without bound, the output frequencyx
3 approaches an asymptotic value which ranges from 1/δ to 0, depending on the ratio σ/δ. The maximum output (if it exists)
is also derived as a function of σ and δ. 相似文献
2.
Yan Xu Haihui Ye Jun Ma Huiyang Huang Guizhong Wang 《In vitro cellular & developmental biology. Animal》2010,46(8):708-717
Crustacean neurons, obtained from the cerebral ganglion of the mud crab Scylla paramamosain, were successfully cultured in vitro. They maintained typical morphological characteristics and showed better outgrowth in
modified Medium 199 (M199) medium than that in Liebowitz’s L-15 medium. Fetal bovine serum (FBS), muscle extracts, and hemolymph
of the mud crab S. paramamosain were added as supplements. Only 20% FBS could promote neuron outgrowth, while muscle extracts and hemolymph of S. paramamosain did not improve neuron outgrowth. For cell dissociation, both collagenase type I and trypsin worked well as determined by
initial cell viability and following cell outgrowth potential. More than six kinds of cells with different morphological characteristics
were identified in the neuron outgrowth. They were “small cells”, “veilers”, “branchers”, “multipolar cells”, “super-large
cell”, and “bipolar cells”. Among all of the cells, bipolar cells were identified for the first time in crustacean neurons
culture and they could live longer than other cells. The neurons could grow for more than a week before retraction and eventual
degradation. 相似文献
3.
S. R. Soffe 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):711-715
Young Xenopus tadpoles were used to test whether the pattern of discharge in specific sensory neurons can determine the motor response
of a whole animal. Young Xenopus tadpoles show two main rhythmic behaviours: swimming and struggling. Touch-sensitive skin sensory neurons in the spinal cord
of immobilised tadpoles were penetrated singly or in pairs using microelectrodes to allow precise control of their firing
patterns. A single impulse in one Rohon-Beard neuron (= light touch) could sometimes trigger “fictive” swimming. Two to six
impulses at 30–50 Hz (= a light stroke) reliably triggered fictive swimming. Neither stimulus evoked fictive struggling. Twenty-five
or more impulses at 30–50 Hz (= pressure) could evoke a pattern of rhythmic bursts, distinct from swimming and suitable to
drive slower, stronger movements. This pattern showed some or all the characteristics of “fictive” struggling. These results
demonstrate clearly that sensory neurons can determine the pattern of motor output simply by their pattern of discharge. This
provides a simple form of behavioural selection according to stimulus.
Accepted: 28 November 1996 相似文献
4.
Weizhe Li Yufeng Pan Zhipeng Wang Haiyun Gong Zhefeng Gong Li Liu 《Cell and tissue research》2009,336(3):509-519
The fan-shaped body is the largest substructure of the central complex in Drosophila melanogaster. Two groups of large-field neurons that innervate the fan-shaped body, viz., F1 and F5 neurons, have recently been found
to be involved in visual pattern memory for “contour orientation” and “elevation” in a rut-dependent manner. The F5 neurons have been found to be responsible for the parameter “elevation” in a for-dependent manner. We have shown here that the F1 neuron also affects visual memory for “contour orientation” in a for-dependent way. With the help of Gal4/UAS and FLP-out techniques, we have characterized the morphological features of these
two groups of neurons at single neuron resolution. We have observed that F1 or F5 neurons are groups of isomorphic individual
neurons. Single F1 neurons have three main arborization regions: one in the first layer of the fan-shaped body, one in the
ventral body, and another in the inferior medial protocerebrum. Single F5 neurons have two arborization regions: one in the
fifth layer of the fan-shaped body and the other in the superior medial protocerebrum. The polarity of the F1 and F5 neurons
has been studied with the Syt-GFP marker. Our results indicate the existence of presynaptic sites of both F1 and F5 neurons
located in the fan-shaped body and postsynaptic sites outside of the fan-shaped body.
This work was supported by the “973 Program” (2005CB522804 and 2009CB918702), the National Natural Sciences Foundation of
China (30621004, 30625022, and 30770682), and the Knowledge Innovation Program of the Chinese Academy of Sciences (KSCX2-YW-R-28). 相似文献
5.
The exponential decay model of a neuron has been analyzed using the “random walk” approach of stochastic processes and an
“absorbing barrier” solution is obtained forg
T
(s)—the Laplace transform of the output pulse interval density function. An expression for the mean output frequency is derived
from this and a variety of input-output curves plotted which show frequency threshold effects in single neurons. Our results
are compared with those of other authors obtained by computer simulation techniques, and the significance of these results
discussed with reference to the possible behavior of networks constructed of such neuron units. 相似文献
6.
Morris H. Baslow 《Amino acids》2010,38(1):51-55
There are two kinds of neurotransmissions that occur in brain. One is neuron to neuron at synapses, and the other is neuron
to glia via extracellular fluid (ECF), both of which are important for maintenance of proper neuronal functioning. For neuron
to neuron communications, several potent amino acid neurotransmitters are used within the confines of synaptic space. However,
their presence at elevated concentrations in extra-synaptic space could be detrimental to well organized neuronal functioning.
The significance of the synthesis and release of N-acetylaspartylglutamate (NAAG) by neurons has long been a puzzle since glutamate (Glu) itself is the “key” that can interact
with all Glu receptors on membranes of all cells. Nonetheless, neurons synthesize this acetylated dipeptide, which cannot
be catabolized by neurons, and release it to ECF where its specific physiological target is the Glu metabotropic receptor
3 on the surface of astrocytes. Since Glu is excitotoxic at elevated concentrations, it is proposed that formation and release
of NAAG by neurons allows large quantities of Glu to be transported in ECF without the risk of injurious excitotoxic effects.
The metabolic mechanism used by neurons is a key–lock system to detoxify Glu during its intercellular transit. This is accomplished
by first synthesizing N-acetylaspartate (NAA), and then joining this molecule via a peptide bond to Glu. In this paper, a hypothesis is presented
that neurons synthesize a variety of relatively nontoxic peptides and peptide derivatives, including NAA, NAAG, homocarnosine
(γ-aminobutyrylhistidine) and carnosine (β-alanylhistidine) from potent excitatory and inhibitory amino acids for the purpose
of releasing them to ECF to function as cell-specific neuron-to-glia neurotransmitters. 相似文献
7.
S. O. Zhuravleva A. V. Sotkis D. S. Isaev A. V. Eremin A. N. Tarasenko P. G. Kostyuk Ya. M. Shuba 《Neurophysiology》1998,30(4-5):194-198
Low voltage-activated (LVA) Ca2+ conductances were characterized in the neurons of the associative laterodorsal (LD) thalamic nucleus in rat brain slices
and in enzymatically isolated thalamic units using electrophysiological techniques. Voltage dependence, kinetics of inactivation,
pharmacology, and selectivity of the LVA current in the thalamic neurons from animals older than 14 postnatal days were consistent
with the existence of two, “fast” and “slow,” subtypes of LVA Ca2+ channels. “Slow” LVA current in enzymatically isolated thalamic neurons was much less prominent, compared with that in slice
neurons, suggesting that respective channels are predominatly located on the distal dendrites. “Fast” Ca2+ channels were sensitive to nifedipine (K
d−2.6 μM) and La3+ (K
d−1.0 mM), whereas “slow” Ca2+ channels were sensitive to Ni2+ (25 μM). Selectivity of the “fast” Ca2+ channels was similar to that found for the LVA Ca2+ channels in other preparations (I
Ca:I
Sr:I
Ba−1.0: 1.23: 0.94), while selectivity of the “slow” Ca2+ channels more resembled selectivity of the HVA Ca2+ channels (I
Ca:I
Sr:I
Ba−1.0: 2.5: 3.4). 相似文献
8.
A non-constant-sum continuous game analyzed in a previous paper by one of the authors (A. Rapoport,Bull. Math. Biophysics,18, 15–30, 1956) is extended from two toN players with special emphasis onN=3. It is shown that the concept of stability becomes in this case one of “pairwise stability,” and depends on the so-called
distribution matrix of rewards. The distribution matrix and the collusion structure jointly determine the end states of the
game. Conditions which lead to the emergence of one, two, or no “parasites” are derived. An apparatus is described which provides
a physical analogue of the game, making possible the isolation of behavioral variables under the prescribed conditions of
the game. 相似文献
9.
Francesco Moccia Carlo Di Cristo William Winlow Anna Di Cosmo 《Invertebrate neuroscience : IN》2009,9(1):29-41
To examine the neurochemistry underlying the firing of the RPeD1 neuron in the respiratory central pattern generator of the
pond snail, Lymnaea stagnalis, we examined electrophysiologically and pharmacologically either “active” or “silent” preparations by intracellular recording
and pharmacology. GABA inhibited electrical firing by hyperpolarizing RPeD1, while picrotoxin, an antagonist of GABAA receptors, excited silent cells and reversed GABA-induced inhibition. Action potential activity was terminated by 1 mM glutamate
(Glu) while silent cells were depolarized by the GluR agonists, AMPA, and NMDA. Kainate exerted a complex triphasic effect
on membrane potential. However, only bath application of AMPA desensitized the firing. These data indicate that GABA inhibits
RPeD1 via activation of GABAA receptors, while Glu stimulates the neuron by activating AMPA-sensitive GluRs. 相似文献
10.
Ernesto Trucco 《Bulletin of mathematical biology》1952,14(4):365-374
As shown by A. Rapoport (1952), when a very brief stimulation or “instantaneous input” is applied to a random net, the subsequent
events are determined by the parameters of the net as follows: If the axon densitya is sufficiently large and the fraction γ of the neurons initially stimulated exceeds a certain value γ1 (theover-all threshold of the net for instantaneous stimulation), excitation will spread through the net until a steady state is reached
in which a fraction γ2 ⩾ γ1 of the neurons is firing (“ignition phenomenon”). If γ < γ1 the activity in the net dies out. However, if the axon density is too small, the activity will ultimately die out, no matter
how large the fraction of initially stimulated neurons. Thus there exists a limiting valueA of the axon density below which the net cannot “ignite”. ThisA is a function ofh, theindividual threshold of the neurons constituting the net (we assume hereh≥2, since forh=1 the situation is essentially different). Geometrically γ1 and γ2 are determined as the two intersection points of a straight line with a sigmoid curve. Whena<A the two curves do not intersect and fora=A they are tangent.
In this paper the “tangency case” is investigated and the general features of the functionA(h) are determined. It is shown thatA increases monotonically withh (as one would expect). For all values ofh>1 we haveA(h)>h, but the fractionA(h)/h and the derivativedA(h)/dh approach unity ash increases. An analytical expression of the functionA(h) valid for very large values ofh is derived. 相似文献
11.
L. Rossini M. E. Pè C. Frova K. Hein M. Sari-Gorla 《Molecular & general genetics : MGG》1995,248(5):535-539
Maize glutathione S-transferase (GST) isozymes are encoded by a gene family comprising at least five genes, three of which
(Gst I, II andIII) have recently been isolated and sequenced. The enzymes are active as homo or heterodimers and exhibit intraspecific polymorphism
including a “null” variant for the two major isoforms expressed in roots. Northern blot analyses performed on total root RNA
from “null” and “plus” genotypes, usingGst I- andGst II-specific probes, indicated that theGst I gene controls the expression of the two major GST isoforms expressed in roots.Gst I andGst II were mapped by RFLP analysis using an F2 population of 149 individuals previously characterized.Gst I was localized on the long arm of chromosome 8, while two putativeGst II loci were mapped to chromosomes 8 (70 cM fromGst I) and 10, respectively. 相似文献
12.
Anatol Rapoport 《Bulletin of mathematical biology》1950,12(2):109-121
Aggregates of neurons are considered in which the frequency of occurrence of neurons with a specified value of the refractory
period follows certain probability distributions. Input-output functions are derived for such aggregates. In particular, if
input and output intensities are defined in terms of stimulus frequencies and firing frequencies per neuron respectively,
it is shown that a rectangular distribution of refractory periods leads to a logarithmic input-output curve. If input and
output are defined in terms of the total number of stimuli and firings in the aggregate, it is shown how the “mobilization”
picture leads to the logarithmic input-output curve.
By randomizing the intervals between stimuli received by a single neuron and by introducing an inhibitory neuron a very simple
“filter net” can be constructed whose output will be sensitive to a particular range of the input, and this range can be made
arbitrarily small. 相似文献
13.
Rocket line immunoelectrophoresis was used to study the taxonomy ofAzotobacter andAzomonas assessed by reaction with antiserum to the AVO2 strain ofAzotobacter. Forty-five cultures, comprising seventeen species in five genera, showed that antigen “β”, like high-titer somatic agglutination,
was restricted to all 11 strains ofAzotobacter vinelandii and to one strain which has been namedAzotobacter macrocytogenes (10EM). A thermoresistant antigen (“γ”) was found to be shared by all strains and species ofAzotobacter andAzomonas investigated. 相似文献
14.
Here, we have characterized four pH-dependent states: alkaline state, “B” (pH 9.0), native state, “N” (pH 7.4), acid-induced
state, “A” (pH 2.2) and molten globule state, “MG” (pH 1.8) of Rhizopus niveus lipase (RNL) by CD, tryptophanyl fluorescence, ANS binding, DLS, and enzyme activity assay. This “MG” state lacks catalytic
activity and tertiary structure but it has native-like significant secondary structure. The “R
h” of all the four states of RNL obtained from DLS study suggests that the molecular compactness of the protein increases as
the pH of solution decreases. Kinetic analysis of RNL shows that it has maximum catalytic efficiency at state “B” which is
15-fold higher than state “N.” The CD and tryptophanyl fluorescence studies of RNL on GuHCl and temperature-induced unfolding reveal that the “MG” state
is more stable than the other states. The DSC endotherms of RNL obtained at pH 9.0, 7.4, and 2.2 were with two transitions,
while at pH 1.8 it showed only a single transition. 相似文献
15.
I. W. Richardson 《Bulletin of mathematical biology》1970,32(2):237-247
The Kedem-Katchalsky equation for the flow of a non-electrolyte through a homogeneous membrane is shown to be a first order
expansion of an exact integral of the Spiegler-Bearman-Kirkwood frictional equations under the assumption that the partial
frictional coefficients, ζ
ij
, are concentration independent. The equations are solved in terms of volume flow; there are no water-to-volume flow correction
terms for the permeability, ω, or the reflection coefficient, σ. The precision of the expansion depends upon the magnitude
of the water flow. The frictional coefficientsf
sm
andf
sw
are given as functions of the experimentally determined parameters ω and σ; the frictions, are shown to be independent ofL
p
. 相似文献
16.
Mammalian prenatal neocortical development is dominated by the synchronized formation of the laminae and migration of neurons.
Postnatal development likewise contains “sensitive periods” during which functions such as ocular dominance emerge. Here we
introduce a novel neuroinformatics approach to identify and study these periods of active development. Although many aspects
of the approach can be used in other studies, some specific techniques were chosen because of a legacy dataset of human histological
data (Conel in The postnatal development of the human cerebral cortex, vol 1–8. Harvard University Press, Cambridge, 1939–1967). Our method calculates normalized change vectors from the raw histological data, and then employs k-means cluster analysis of the change vectors to explore the population dynamics of neurons from 37 neocortical areas across
eight postnatal developmental stages from birth to 72 months in 54 subjects. We show that the cortical “address” (Brodmann
area/sub-area and layer) provides the necessary resolution to segregate neuron population changes into seven correlated “k-clusters” in k-means cluster analysis. The members in each k-cluster share a single change interval where the relative share of the cortex by the members undergoes its maximum change.
The maximum change occurs in a different change interval for each k-cluster. Each k-cluster has at least one totally connected maximal “clique” which appears to correspond to cortical function. 相似文献
17.
Cellular mechanisms of pilocarpine-induced epileptiform activity in isolatedCA1 andCA3 hippocampal neurons were studied using a current-clamp technique. Isolated unipolar neurons dominate after enzymatic treatment
of theCA1 tissue, whereas large multipolar neurons are mainly located in theCA3 area. Measurements of the membrane potential in these two groups of neurons showed that most of them are “silent” cells.
Only a small group of neurons from theCA3 area displayed spontaneous electrical activity. Pilocarpine, a well known epileptogenic compound, induced rhythmic waveform
changes in the membrane potential in some “silent” unipolar neurons from theCA1 area, whereas in another more numerous group of neurons it induced only steady depolarization of the membrane. Application
of tetrodotoxin, the selective blocker of Na+ channels, blocked generation of action potentials induced inCA1 neurons by pilocarpine, but exerted no effect on waveform shifts of the membrane potential. It is suggested that the mechanism
underlying epileptogenic action of pilocarpine on the brain activity in rats is based on the induction of waveform changes
in the membrane potential in unipolar neurons of theCA1 hippocampal area. 相似文献
18.
Patrick J. Brennan 《Journal of biosciences》1984,6(5):685-689
There is now a considerable body of evidence to suggest that the phthiocerol-containing lipids, including the phenolic glycolipids,
comprise the so-called “peribacillary substance”, “spherical droplets”, “foamy structures” and “capsular materials” ofMycobacterium leprae. Thus, the phthiocerol-containing lipid capsule may be directly responsible for the intracellular survival ofMycobacterium leprae. 相似文献
19.
N. Rashevsky 《Bulletin of mathematical biology》1968,30(1):163-174
The theory of organismic sets, developed in previous papers (Bull. Math. Biophysics,29, 139–152; 389–393; 643–647) is further generalized. To conform better with some biological and sociological facts the basic
definitions are made more general. The conclusion is reached that every organismic setS
o
is in general the union of three disjoined subsetsS
o1
,S
o2
andS
o3
. Of these the subsetS
o1
, called the “core” is equivalent to an organismic set defined in previous publications. Its functioning is essential for
the functioning ofS
o
. The subsetsS
o2
andS
o3
, taken alone, are not organismic sets. The first of them is responsible for such biological or sociological functions which
are not necessary for the “immediate” survival ofS
o
but which are important for adaptation to changing environment and are therefore essential for a “long range survival.” The
second one,S
o3
, is responsible for biological or social functions which are irrelevant for the survival ofS
o
. Biological and sociological examples ofS
o2
andS
o3
are given. In addition to the fundamental theorem established in the first of the above mentioned papers, three new conclusions
are derived. One is that in organismic sets of order higher than zero not all elements are specialized. The second is that
every organismic set of order higher than zero is mortal. The third is that with increasing specialization the intensities
of some activities in some elements ofS
o
are reduced. Again the biological and sociological examples are given.
At the end some very general speculations are made on the possible relation between biology and physics and on the possibility
of “relationalizing” physics. 相似文献
20.
Coombes S Timofeeva Y Svensson CM Lord GJ Josić K Cox SJ Colbert CM 《Biological cybernetics》2007,97(2):137-149
Dendrites form the major components of neurons. They are complex branching structures that receive and process thousands of
synaptic inputs from other neurons. It is well known that dendritic morphology plays an important role in the function of
dendrites. Another important contribution to the response characteristics of a single neuron comes from the intrinsic resonant
properties of dendritic membrane. In this paper we combine the effects of dendritic branching and resonant membrane dynamics
by generalising the “sum-over-trips” approach (Abbott et al. in Biol Cybernetics 66, 49–60 1991). To illustrate how this formalism
can shed light on the role of architecture and resonances in determining neuronal output we consider dual recording and reconstruction
data from a rat CA1 hippocampal pyramidal cell. Specifically we explore the way in which an I
h
current contributes to a voltage overshoot at the soma. 相似文献