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1.
V. A. Lukhtanov 《Entomological Review》2010,90(3):299-310
The maximum likelihood and Bayesian methods are based on parametric models of character evolution. They assume that if we
know these models as well as distribution of character states in studied organisms, we can infer the probability of different
phylogenetic trajectories leading from ancestors to modern forms. In fact, these methods are mathematized variants of the
traditional Haeckel’s approach to phylogeny reconstruction. In contrast to classical and parsimonious cladistics, they infer
phylogenies without such limitations as necessity of strictly dichotomous evolution, exclusion of plesiomorphic characters,
and acceptance of only holophyletic taxa. They assume that evolution may be reticulated, any homologous characters—both apomorphic
and plesiomorphic—can be used for inferring phylogenies, and interpretation of evolutionary lineages as taxa is optional.
Thus, the main difference between the new and more traditional approaches to phylogeny reconstruction lies not in the characters
used (molecular or morphological) but in the methodology of analysis. It must be admitted that a revolution began in phylogenetics
10–20 years ago. However, the fundamental changes in phylogenetics have been carried out so calmly and neatly by the people
who started this revolution, that many systematists still do not realize their importance. 相似文献
2.
Stian Ludvigsen Lars P. Folkow 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2009,195(11):1021-1030
Ducks are well-known to be more tolerant to asphyxia than non-diving birds, but it is not known if their defences include
enhanced neuronal hypoxia tolerance. To test this, we compared extracellular recordings of spontaneous activity in the Purkinje
cell layer of 400 μm thick isolated cerebellar slices from eider ducks, chickens and rats, before, during and after 60 min
hypoxia (95%N2–5%CO2) or chemical anoxia (hypoxia + 2 mM NaCN). Most slices rapidly lost activity in hypoxia, with or without recovery after rinse
and return to normoxia (95%O2–5%CO2), but some maintained spontaneous activity throughout the insult. Proportions of ‘surviving’ (i.e. recovering or active)
duck slices were significantly higher than for chickens in anoxia, and relative activity levels were higher for ducks than
for chickens during hypoxia, anoxia and recovery. Survival of rat slices was significantly poorer than for birds under all
conditions. Results suggest that (1) duck cerebellar neurons are intrinsically more hypoxia-tolerant than chicken neurons;
(2) avian neurons are more hypoxia-tolerant than rat neurons, and (3) the enhanced hypoxic tolerance of duck neurons largely
depended on efficient anaerobiosis since it mainly manifested itself in chemical anoxia. Mechanisms underlying the observed
differences in neuronal hypoxic responses remain to be elucidated. 相似文献
3.
Lang S Drouvelis P Tafaj E Bastian P Sakmann B 《Journal of computational neuroscience》2011,31(3):533-545
Neuron morphology is frequently used to classify cell-types in the mammalian cortex. Apart from the shape of the soma and
the axonal projections, morphological classification is largely defined by the dendrites of a neuron and their subcellular
compartments, referred to as dendritic spines. The dimensions of a neuron’s dendritic compartment, including its spines, is
also a major determinant of the passive and active electrical excitability of dendrites. Furthermore, the dimensions of dendritic
branches and spines change during postnatal development and, possibly, following some types of neuronal activity patterns,
changes depending on the activity of a neuron. Due to their small size, accurate quantitation of spine number and structure
is difficult to achieve (Larkman, J Comp Neurol 306:332, 1991). Here we follow an analysis approach using high-resolution EM techniques. Serial block-face scanning electron microscopy (SBFSEM) enables automated imaging of large specimen volumes at high resolution. The large data sets generated by this technique
make manual reconstruction of neuronal structure laborious. Here we present NeuroStruct, a reconstruction environment developed
for fast and automated analysis of large SBFSEM data sets containing individual stained neurons using optimized algorithms
for CPU and GPU hardware. NeuroStruct is based on 3D operators and integrates image information from image stacks of individual
neurons filled with biocytin and stained with osmium tetroxide. The focus of the presented work is the reconstruction of dendritic
branches with detailed representation of spines. NeuroStruct delivers both a 3D surface model of the reconstructed structures
and a 1D geometrical model corresponding to the skeleton of the reconstructed structures. Both representations are a prerequisite
for analysis of morphological characteristics and simulation signalling within a neuron that capture the influence of spines. 相似文献
4.
Pedro Herreros Luis M. Ballesteros-Esteban María Fe Laguna Inmaculada Leyva Irene Sendiña-Nadal Miguel Holgado 《Biotechnology journal》2021,16(7):2000355
Cultured neuronal networks (CNNs) are a robust model to closely investigate neuronal circuits’ formation and monitor their structural properties evolution. Typically, neurons are cultured in plastic plates or, more recently, in microfluidic platforms with potentially a wide variety of neuroscience applications. As a biological protocol, cell culture integration with a microfluidic system provides benefits such as accurate control of cell seeding area, culture medium renewal, or lower exposure to contamination. The objective of this report is to present a novel neuronal network on a chip device, including a chamber, fabricated from PDMS, vinyl and glass connected to a microfluidic platform to perfuse the continuous flow of culture medium. Network growth is compared in chips and traditional Petri dishes to validate the microfluidic chip performance. The network assessment is performed by computing relevant topological measures like the number of connected neurons, the clustering coefficient, and the shortest path between any pair of neurons throughout the culture's life. The results demonstrate that neuronal circuits on a chip have a more stable network structure and lifespan than developing in conventional settings, and therefore this setup is an advantageous alternative to current culture methods. This technology could lead to challenging applications such as batch drug testing of in vitro cell culture models. From the engineering perspective, a device's advantage is the chance to develop custom designs more efficiently than other microfluidic systems. 相似文献
5.
Ringler SL Aye J Byrne E Anderson M Turner CP 《Cellular and molecular neurobiology》2008,28(3):389-409
It has become increasingly clear that agents that disrupt calcium homeostasis may also be toxic to developing neurons. Using
isolated primary neurons, we sought to understand the neurotoxicity of agents such as MK801 (which blocks ligand-gated calcium
entry), BAPTA (which chelates intracellular calcium), and thapsigargin (TG; which inhibits the endoplasmic reticulum Ca2+-ATPase pump). Thus, E18 rat cortical neurons were grown for 1 day in vitro (DIV) and then exposed to vehicle (0.1% DMSO),
MK801 (0.01–20 μM), BAPTA (0.1–20 μM), or TG (0.001–1 μM) for 24 h. We found that all three agents could profoundly influence
early neuronal maturation (growth cone expansion, neurite length, neurite complexity), with the order of potency being MK801 < BAPTA < TG.
We next asked if cultures exposed to these agents were able to re-establish their developmental program once the agent was
removed. When we examined network maturity at 4 and 7 DIV, the order of recovery was MK801 > BAPTA > TG. Thus, mechanistically
distinct ways of disrupting calcium homeostasis differentially influenced both short-term and long-term neuronal maturation.
These observations suggest that agents that act by altering intracellular calcium and are used in obstetrics or neonatology
may be quite harmful to the still-developing human brain. 相似文献
6.
Jeanette Ridge Douglas A. Terle Evgenia Dragunsky Inessa Levenbook 《In vitro cellular & developmental biology. Animal》1996,32(4):238-248
Summary Neuroblastomas are neural crest-derived tumors that contain neuronal, melanocyte, and Schwann cell precursors. We examined
the effects of treatment with γ-interferon (γ-IFN) and nerve growth factor (NGF), alone, and in combination, on these progenitor
subpopulations in the human neuroblastoma cell line, SH-SY5Y. Using fluorescence-activated flow cytometry (FACS), changes
in expression of three differentiation-specific or-associated marker proteins, the 200 kD neurofilament protein, the myelin
basic protein, and the S-100 protein, were analyzed. Growth rates and morphological changes associated with each treatment
over the 2-wk incubation period were noted. The greatest effects were observed with combined IFN +NGF treatment. These were
significant increases in expression of all three proteins distinctive morphological signs of differentiation, and extensive
inhibition of proliferation compared to control cultures. Treatment with NGF alone resulted in increased neurofilament protein
expression and in the length and number of neurite extensions, but there was no effect on the growth rate. IFN induced striking
morphological changes, significant inhibition of growth, and changes in protein expression that correlated with neuronal to
non-neuronal subpopulation shifts due to the death of differentiated cells. When treatment was discontinued after 15 d, the
morphological changes induced by NGF were reversed within 2–3 d, while those induced by IFN±NGF were present up to 4 wk post-treatment.
Small, neuroblastic colonies were observed throughout the treatment period and within 4–6 wk after the cessation of treatment
this cell-type fully reconstituted the cultures suggesting the presence of a stem cell. Our results indicate that treatment
with γ-IFN±NGF can regulate growth and induce, either stem cells or progenitor neuronal, Schwann and melanocyte subpopulations
in the SH-SY5Y cell line to irreversibly differentiate. 相似文献
7.
A mathematical model is developed with a highly controlled birth and death process for precursor cells. This model is both
biologically- and statistically-based. The controlled growth and differentiation (CGD) model limits the number of replications
allowed in the development of a tissue or organ and thus, more closely reflects the presence of a true stem cell population.
Leroux et al. (1996) presented a biologically-based dose-response model for developmental toxicology that was derived from a partial differential
equation for the generating function. This formulation limits further expansion into more realistic models of mammalian development.
The same formulae for the probability of a defect (a system of ordinary differential equations) can be derived through the
Kolmogorov forward equations due to the nature of this Markov process. This modified approach is easily amenable to the expansion
of more complicated models of the developmental process such as the one presented here. Comparisons between the Leroux et al. (1996) model and the controlled growth and differentiation (CGD) model as developed in this paper are also discussed.
Received: 8 June 2001 / Revised version: 15 June 2002 / Published online: 26 September 2002
Keywords or phrases: Teratology – Multistate process – Cellular kinetics – Numerical simulation 相似文献
8.
Louis W. Chang 《Biological trace element research》1987,13(1):77-88
The extent of trimethyltin (TMT) induced lesions in the rat hippocampal formation was reviewed. Adult rats were treated with
a single dose of 6.0 mg TMT/kg body wt and were sacrificed between 3–60 d following exposure. In the hippocampal formation,
the granule cells of fascia dentata showed early changes, which subsided considerably at a later time of the intoxication.
On the other hand, destruction of the pyramidal neurons in the Ammon’s horn became more pronounced with time, resulting in
an extensive destruction of this structure. It is interesting to note that the CA3 neurons in the septal portion of the Ammon’s horn were more vulnerable than those located more temporally, whereas the reverse
pattern was observed for the dentate granule cells as well as for the CA1,2 neurons of the Ammon’s horn. Special stain for zinc (Timm’s method) also revealed a progressive depletion of zinc in the
mossy fibers. When neonatal rats were treated at various times with a single injection of TMT, rapid and progressive destruction
of the Ammon’s horn was observed in animals injected between postnatal day (PND) 5–15. The progression of neuronal involvement
was CA3b
→CA3a, b
→CA3(a,b,c)→CA3+CA2→entire Ammon’s horn (CA1,2,3). This pattern of pathological lesion was in good concert with morphological development and functional maturity of the hippocampal
formation. Destruction of the Ammon’s horn neurons was proposed to be the result of hyperexcitation of the dentate granule
neurons under the influence of TMT. Other possible mechanisms are also discussed.
Author to whom all correspondence and reprint requests should be addressed. 相似文献
9.
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
10.
We present a biologically-based mathematical model that accounts for several features of the human sleep/wake cycle. These
features include the timing of sleep and wakefulness under normal and sleep-deprived conditions, ultradian rhythms, more frequent
switching between sleep and wakefulness due to the loss of orexin and the circadian dependence of several sleep measures.
The model demonstrates how these features depend on interactions between a circadian pacemaker and a sleep homeostat and provides
a biological basis for the two-process model for sleep regulation. The model is based on previous “flip–flop” conceptual models
for sleep/wake and REM/NREM and we explore whether the neuronal components in these flip–flop models, with the inclusion of
a sleep-homeostatic process and the circadian pacemaker, are sufficient to account for the features of the sleep/wake cycle
listed above. The model is minimal in the sense that, besides the sleep homeostat and constant cortical drives, the model
includes only those nuclei described in the flip–flop models. Each of the cell groups is modeled by at most two differential
equations for the evolution of the total population activity, and the synaptic connections are consistent with those described
in the flip–flop models. A detailed analysis of the model leads to an understanding of the mathematical mechanisms, as well
as insights into the biological mechanisms, underlying sleep/wake dynamics. 相似文献
11.
In the past decades, many studies have focussed on the relation between the input and output of neurons with the aim to understand
information processing by neurons. A particular aspect of neuronal information, which has not received much attention so far,
concerns the problem of information transfer when a neuron or a population of neurons receives input from two or more (populations
of) neurons, in particular when these (populations of) neurons carry different types of information. The aim of the present
study is to investigate the responses of neurons to multiple inputs modulated in the gamma frequency range. By a combination
of theoretical approaches and computer simulations, we test the hypothesis that enhanced modulation of synchronized excitatory
neuronal activity in the gamma frequency range provides an advantage over a less synchronized input for various types of neurons.
The results of this study show that the spike output of various types of neurons [i.e. the leaky integrate and fire neuron,
the quadratic integrate and fire neuron and the Hodgkin–Huxley (HH) neuron] and that of excitatory–inhibitory coupled pairs
of neurons, like the Pyramidal Interneuronal Network Gamma (PING) model, is highly phase-locked to the larger of two gamma-modulated
input signals. This implies that the neuron selectively responds to the input with the larger gamma modulation if the amplitude
of the gamma modulation exceeds that of the other signals by a certain amount. In that case, the output of the neuron is entrained
by one of multiple inputs and that other inputs are not represented in the output. This mechanism for selective information
transmission is enhanced for short membrane time constants of the neuron. 相似文献
12.
Although the neuronal circuits that generate leech movements have been studied for over 30 years, the list of interneurons
(INs) in these circuits remains incomplete. Previous studies showed that some motor neurons (MNs) are electrically coupled
to swim-related INs, e.g., rectifying junctions connect IN 28 to MN DI-1 (dorsal inhibitor), so we searched for additional
neurons in these behavioral circuits by co-injecting Neurobiotin and Alexa Fluor 488 into segmental MNs DI–1, VI–2, DE–3 and
VE–4. The high molecular weight Alexa dye is confined to the injected cell, whereas the smaller Neurobiotin molecules diffuse
through gap junctions to reveal electrical coupling. We found that MNs were each dye-coupled to approximately 25 neurons,
about half of which are likely to be INs. We also found that (1) dye-coupling was reliably correlated with physiologically
confirmed electrical connections, (2) dye-coupling is unidirectional between MNs that are linked by rectifying connections,
and (3) there are novel electrical connections between excitatory and inhibitory MNs, e.g. between excitatory MN VE-4 and
inhibitory MN DI-1. The INs found in this study provide a pool of novel candidate neurons for future studies of behavioral
circuits, including those underlying swimming, crawling, shortening, and bending movements. 相似文献
13.
The present study describes the localization and distribution of thyroid-stimulating hormone (TSH), thyroglobulin (TGB) and their receptors in Eisenia fetida (Annelida, Oligochaeta) as revealed by immunohistological methods. Immunopositive neuronal and non-neuronal cells are present in both the central nervous system and some peripheral organs (e.g. foregut and coelomocytes). TSH- and TGB-immunopositive neurons in the various ganglia of the central nervous system are differentailly distributed. Most of the immunoreactive cells are found in the suboesophageal ganglion. The stained cells also differ in their shapes (round, oval, pear-shaped) and sizes (small, 12–25 μm; medium, 20–35 μm; large, 30–50 μm). In all ganglia of the central nervous system, TSH-positive neurons additionally show gamma aminobutyric acid (GABA) immunopositivity. Non-neuronal cells also take part in hormone secretion and transport. Elongated TSH-positive cells have been detected in the capsule of the central ganglia and bear granules or vacuoles in areas lacking neurons. Many of capillaries show immunoreactivity for all four tested antibodies in the entire central nervous system and foregut. Among the coelomocytes, granulocytes and eleocytes stain for TSH and its receptor and for TGB but not for thyroid hormone receptor. Most of the granulocytes are large (25–50 μm) but a population of small cells (10–25 μm) are also immunoreactive. None of the coelomocytes stain for GABA. We therefore suggest that the members of this hormone system can modify both metabolism and immune functions in Eisenia. Coelomocytes might be able to secrete, transport and eliminate hormones in this system.This work was supported by the MTA-PTE Adaptation Biology Research Group and National Research and Developmental Fund (NKP 1/048/2001). M.W. is in receipt of a János Bolyai Scholarship. 相似文献
14.
Tau hyperphosphorylation, amyloid plaques, and neuronal death are major neuropathological features of Alzheimer’s disease
(AD) and Prion-related encephalopathies (PRE). Cyclin-dependent kinase 5 (Cdk5) is a serine/threonine kinase, active in post-mitotic
neurons, where it regulates survival and death pathways. Overactivation of Cdk5 is conferred by p25, a truncated fragment
of the p35 activator formed upon calpain activation. Cdk5 deregulation causes abnormal phosphorylation of microtubule-associated
protein tau, leading to neurodegeneration. In this work we investigated the involvement of Cdk5 in the neurodegeneration triggered
by amyloid-beta (Aβ) and prion (PrP) peptides, the culprit agents of AD and PRE. As a work model, we used cultured rat cortical
neurons treated with Aβ1–40 and PrP106–126 synthetic peptides. The obtained data show that apoptotic neuronal death caused by both the peptides was in part due to Cdk5
deregulation. After peptide treatment, p25 levels were significantly enhanced in a pattern consistent with the augment in
calpain activity. Moreover, Aβ1–40 and PrP106–126 increased the levels of tau protein phosphorylated at Ser202/Thr205. Cdk5 (roscovitine) and calpain (MDL28170) inhibitors
reverted tau hyperphosphorylation and prevented neuronal death caused by Aβ1–40 and PrP106–126. This study demonstrates, for the first time, that Cdk5 is involved in PrP-neurotoxicity. Altogether, our data suggests that
Cdk5 plays an active role in the pathogenesis of AD and PRE. 相似文献
15.
A new approach is presented here to better take into account inter-individual growth variability in age-structured models used for stock assessment. Cohort analysis requires knowledge of the age structure of the catch, generally derived from an age–length key and length-structure information. Age distribution at length is estimated by applying conditional quantile regression to a data set of lengths and ages estimated from calcareous parts. A “stochastic” age–length key that describes the probability of age-at-length is applied to the English Channel squid Loligo forbesi. Age distribution at length from quantile regression proved to be considerably less biased than that resulting from both polymodal decomposition (PD) and two separate slicing methods. Both catch-at-age and stock size were underestimated using classical methods. Estimations of fishing mortalities from classical methods were higher causing underestimation in yield simulations. Quantile regression offers a more complete statistical analysis of the stochastic relationships among random variables than mean regression and PD. 相似文献
16.
Ammonia is a neurotoxin that is implicated in the CNS dysfunction associated with hepatic encephalopathy, urea cycle disorders,
Reye’s syndrome and other neurological conditions. While in vivo studies suggest that astrocytes are the principal target of ammonia toxicity, recent in vitro investigations suggest that neurons may also be directly affected by ammonia. To further examine the issue of neural cell
sensitivity to ammonia, pure rat cortical neuronal cultures, as well as co-cultures of neurons and astrocytes, were exposed
to 5 mM NH4Cl for 48 h. Cultures were examined for morphological changes by light microscopy, measures of cell death, free radical production
and changes in the mitochondrial inner membrane potential. Ammonia caused extensive degenerative changes in pure cultured
neurons, while such neuronal changes were minor in the co-cultures. Similarly, processes of pure cultured neurons displayed
a significant loss of the mitochondrial inner membrane potential, as compared to neurons in co-cultures. Cell death (LDH release)
in ammonia-treated neuronal cultures was twice as great as untreated controls, while in co-cultures ammonia did not significantly
increase cell death. Free radical production at 3 min was increased (69%, P<0.05) in pure neuronal cultures but not in co-cultures. The neuroprotective effects observed in co-cultures may have been
mediated by the astrocyte’s ability to scavenge free radicals, by their detoxification of ammonia and/or by their neurotrophic
actions. The neuroprotective action of astrocytes may explain the failure to detect significant pathological changes in neurons
in ammonia toxicity in vivo.
Special issue dedicated to Dr. Bernd Hamprecht. 相似文献
17.
The Wilson–Cowan model of interacting neurons (1973) is one of the most influential papers published in Biological Cybernetics (Kybernetik). This paper and a companion paper published in 1972 have been cited over 1000 times. Rather than focus on the microscopic
properties of neurons, Wilson and Cowan analyzed the collective properties of large numbers of neurons using methods from
statistical mechanics, based on the mean-field approach. New experimental techniques to measure neuronal activity at the level of large populations are now available to
test these models, including optical recording of brain activity with intrinsic signals and voltage sensitive dyes, and new
methods for analyzing EEG and MEG. These measurement techniques have revealed patterns of coherent activity that span centimetres
of tissue in the cerebral cortex. Here the underlying ideas are reviewed in a historic context.
This note was written by Alain Destexhe and Terry Sejnowski, the Editors-in-Chief of the Journal of Computational Neuroscience and Neural Computation, on the occasion of the appearance of Volume 100 of Biological Cybernetics. 相似文献
18.
A cohesive sediment balance for the Scheldt estuary 总被引:3,自引:0,他引:3
This article present a method to generate a cohesive sediment balance for the Scheldt estuary (The Netherlands and Belgium).
In this balance the net transports have been determined on a regional scale. The complicated circulation patterns on a smaller
scale are considered as a black box.
The cohesive sediments in the balance are defined as the inorganic sediment with a particle size smaller than 63 μm. In the
balance a distinction is made between the relatively ‘clean’ marine mud fraction and the more polluted fluvial fraction. The
calculations are made on a basis of field data. The field data of the morphological changes in the estuary are based on the
period of 1975–1985.
The net natural transport of fluvial mud is estimated to reach beyond the mouth of the estuary. The net marine import of mud
is estimated to reach beyond the brackish part of the estuary, located in Belgium.
The sediment balance also provides the time scale for the response of an estuary. The time scale related to the reduction
in pollution proves to be quite large. Calculations with a simple analytic model with typical values for the Scheldt estuary
indicate that several decades will pass until a significant improvement in bottom sediment quality is reached even after a
100% reduction of the loading of pollutants.
The presented balance is not the final answer. Improvements can be achieved by more accurate field data, smaller morphological
units and verification by other methods (cf. tracer methods, mathematical models). 相似文献
19.
Lynne A. Oland Herbert Oberlander 《In vitro cellular & developmental biology. Animal》1994,30(10):709-716
Summary During metamorphic adult development, neurons and glial cells in the developing olfactory (antennal) lobes of the moth undergo
characteristic and extensive changes in shape. These changes depend on an interplay among these two cell types and ingrowing
sensory axons. All of the direct cellular interactions occur against a background of changing steroid hormone titers. Antennal-lobe
(AL) neurons dissociated from stage-5 (of 18 stages) metamorphosing animals survive at least 3 wk in primary cell culture.
We describe here the morphological influences on AL neurons of (1) exposure to the steroid hormone 20-hydroxyecdysone, (2)
exposure to sensory axons, and (3) interactions among the AL neurons. Cultured AL neurons respond only weakly, if at all,
to 20-hydroxyecdysone. They do, however, show greater total outgrowth and branching when they had been exposed in vivo to
sensory axons. Because there is no direct contact between some of the neuronal types and the sensory axons at the time of
dissociation, the increase in outgrowth must have been mediated via a diffusible factor(s). When AL cells (neurons and glia)
are plated at high density in low volumes of medium, or when the cells are plated at low density but in the presence of medium
conditioned by high-density cultures, neurite outgrowth and cell survival are increased. Nerve growth factor (NGF), epidermal
growth factor (EGF), fibroblast growth factor-basic (bFGF), transforming growth factor-β (TGF
β
) and insulin-like growth factor (ILGF) had no obvious effect on neuronal morphology and thus are unlikely to underlie these
effects. Our results suggest that the mature shape of AL neurons depends on developmental interactions among a number of diffusible
factors. 相似文献
20.
Electrotonic properties are important aspects of neuronal function but have been difficult to estimate without accurate morphological reconstruction. The complexity of the branching dendritic cables often gives charging curves composed of a very large number of exponential functions, making it difficult to distinguish the time constants that are needed for electrotonic estimates. We describe an estimator P for the electrotonic size of neurons based on simple measures from voltage and current clamp recordings that does not rely on the higher rank exponential components of the response. Our estimator gives a bounded scale for the electrotonic size of the cell and can be used for categorization and comparison when morphology is not available. 相似文献