首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 593 毫秒
1.
1.  To determine reliability of stimulus intensity coding we measured the response variability of 30 hydroxy-L-proline sensitive chemoreceptor cells from antennules of Homarus americanus. First, cells were tested with 5 repeated presentations of 10-5 M and l0-4 M hydroxy-L-proline. Then a stimulus response function was determined in each cell from l0-6to 5 × l0-4 M in half log steps.
2.  Population mean responses to repetitive stimulation showed little variability and mean stimulus response functions increased monotonically. In contrast, most individual cells showed a high response variability and no single cell stimulus-response function increased monotonically. The greatest response variability occurred between different cells.
3.  Mean response magnitude of a 30 cell population allowed reliable discrimination between 10-5 M and l0-4 M hydroxy-L-proline for each of the 5 repetitions. It also allowed discrimination of all concentrations of hydroxy-L-proline tested. Across-fiber response patterns also differed significantly with concentration while they remained relatively stable with repetition of the same stimulus.
4.  We applied different analytical methods to test the reliability of response magnitude and across-fiber pattern as possible codes for intensity discrimination. We demonstrated that a random population of rather unreliable receptor cells could provide remarkably reliable intensity information to the CNS based on response magnitude or across-fiber pattern.
Dedicated to the memory of Vincent Dethier, who pioneered several of the questions addressed in this study.  相似文献   

2.
1.  The self-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using lobster (Homarus americanus) NH4 receptor cells.
2.  These receptors responded for several seconds to the onset of the backgrounds, and then returned to their initial level of spontaneous activity (usually zero). The strongest response always occurred only during the steepest concentration change; the response then decayed back to zero or to the earlier spontaneous firing level, while the background concentration was still rising, and remained silent during the entire time that the background was maintained constant (20–30 min) (Fig. 2).
3.  Exposure to constant self-adapting backgrounds eliminated the responses of NH4 receptor cells to stimuli of concentration lower than the background, and reduced the responses to all higher stimulus concentrations tested by a nearly equal amount. This resulted in a parallel shift of the stimulus-response function to the right along the abscissa (Figs. 3 and 4).
4.  Since the response threshold was completely re-set by adaptation to backgrounds, NH4 receptors seem to function mostly as detectors of relative rather than absolute stimulus intensity across their entire dynamic range: the response to a given stimulus-to-background ratio remained the same over 3 log step increases of background concentration (Fig. 6).
5.  As in other sensory modalities, a parallel shift of response functions appears to be an important property of chemoreceptor cells, allowing for this sensory system to function over a wider stimulus intensity range than the instantaneous dynamic range of individual receptor cells.
  相似文献   

3.
1.  The cross-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using NH4 receptor cells, of known spectral tuning, from the lobster (Homarus americanus).
2.  Spectrum experiments: The spectral tuning of NH4 receptor cells was investigated using NH4Cl and 7 other compounds selected as the most stimulatory non-best compounds for NH4 cells from a longer list of compounds tested in previous studies. Based on their responses to the compounds tested, 3 spectral subpopulations of NH4 cells were revealed: NH4-Glu cells which responded second-best to Glutamate (Glu); NH4- Bet cells which responded second-best to Betaine (Bet); and pure NH4 cells, which responded to NH4C1 only (Fig. 1).
3.  Cross-adaptation experiments: Overall, cross-adaptation with Glu and Bet backgrounds caused suppression of response of NH4 receptor cells to various concentrations of NH4Cl. However, the different subpopulations of NH4 cells were affected differently: (a) The stimulus-response functions of NH4-Glu cells were significantly suppressed by both a 3 M (G3) and 300 M (G300) Glu backgrounds, (b) The stimulus-response functions of NH4-Bet cells was not affected by a 3 M (B3), but significantly suppressed by a 300M (B300) Bet background. (c) The stimulus-response functions of pure NH4 cells were not affected by any of the Glu or Bet backgrounds (Figs. 3, 4).
4.  The stimulus-response functions of 5 cells from all different subpopulations were enhanced by cross-adaptation with the G300 and B300 backgrounds (Fig. 4, Table 1).
5.  Whereas self-adaptation caused parallel shifts in stimulus-response functions (Borroni and Atema 1988), cross-adaptation caused a decrease in slope of stimulus-response functions. Implications of the results from cross- and self-adaptation experiments on NH4 receptor cells, for a receptor cell model are discussed.
  相似文献   

4.
1.  A prominent population of olfactory receptor cells from the lobsterHomarus americanus is narrowly tuned to trans-4-hydroxyl-L-proline (Hyp, Fig. 1) suggesting that Hyp may be an important chemical signal for this animal (Johnson and Atema 1983). However, Hyp is usually bound in connective tissue proteins of lobster prey and thus may be unavailable in sufficient quantities as a free amino acid to stimulate chemoreceptors. To determine other possible adequate stimuli for Hyp sensitive cells we further examined their tuning using a variety of substances including other amino acids also found in collagens, Hyp isomers (Fig. 1), synaptic receptor agonists, ecdysones, purified natural collagens and their gelatins (Fig. 2), and different molecular weight fractions of a commercial gelatin solution (Table 1).
2.  Of a first group of Hyp sensitive cells (N=29) tested with the compounds in Table 1 A, 21 responded best to Hyp. Only a commercial gelatin solution (SG1) and its one-tenth dilution consistently elicited responses from these cells (Fig. 3). The remaining 8 cells responded best to the SG1 solutions (5 cells) or to one of the other test substances (Table 2).
3.  Of a second group of Hyp sensitive cells (N=27) tested with the collagen and gelatin solutions (Table 1b), 19 responded best to Hyp. Again, the Hyp best cells rarely responded to any test substance other than Hyp and a commercial gelatin solution, SG2, and its greater than 12 kD fraction, SG2-12 (Fig. 4). SG2 and SG2-12 were equally effective for the Hyp best cells. The remaining 8 cells responded best to either SG2 (2 cells), SG2-12 (2 cells) or one of the purified gelatin or collagen solutions (Table 3).
4.  A third group of Hyp sensitive cells (N=21) was tested with SG2, SG2-12, and a greater than 1 kD fraction of SG2 (SG2-1; Table 1c). Based on the mean response, the most effective stimulus for these cells was SG2-12, followed by SG2-1, SG2 and Hyp. The high mean response for the SG2 solutions was mainly due to a few cells giving large responses to these stimuli (Fig. 6). Ten of these 21 cells responded best to Hyp; all but 2 responded to one or more of the SG2 solutions; the other 11 cells responded best to either SG2, SG2-12 or SG2-1, which were all best stimuli for different cells (Fig. 5).
5.  Overall, the 77 Hyp sensitive cells tested here can be divided into two main types; 65% Hyp best cells and 31% gelatin best cells. The Hyp best cells seem to be a distinct population of receptors: they have no spontaneous activity and give low responses (15 spikes in 5 s) even to their best stimulus, Hyp. In contrast, the gelatin best cells are not infrequently spontaneously active and can give high responses to their best stimulus (up to 150 spikes in 5 s). In addition, when tested specifically in the third group, the Hyp cells appear to have a tuning spectrum distinct from the gelatin best cells (Fig. 7).
6.  Stimulation of Hyp cells by gelatin solutions may be due to Hyp-containing peptides derived from the gelatin. Enzymatic tissue breakdown from the lobster's prey could produce chemical mixtures that stimulate prominent receptor populations which respond to both high (gelatin best cells) and low (Hyp best cells) molecular weight substances. This could create a central representation of food based on parallel receptor lines of somewhat overlapping sensitivity. Together, Hyp best and gelatin best receptor cell populations may give important information on the presence and state of decay of the lobster's food.
Abbreviations: see Table 1  相似文献   

5.
1.  The electrogenic Na-K pump activity was studied in thePlotosus electroreceptor. Single ampullae (sensory epithelium) were dissected free, and mounted over an air gap at the ampullary duct, to electrically isolate the receptor activity for current- and voltage-clamp experiments.
2.  After equilibration in K-free saline, the bathing medium around the ampulla was exchanged to test saline. Under current-clamp, 4 mM K saline induced reversible hyperpolarization of about 13 mV. Under voltage-clamp, the 4 mM saline induced an outward current of about 10 nA.
3.  Both responses were suppressed by ouabain, with a half suppression at 1.5×10–7 M for current, which suggested involvement of ionic pumps. In the K-free saline, ouabain alone induced no response.
4.  The current response to high K saline was always outward, and was dependent on K concentration. In the presence of ouabain, high K saline as high as 40 mM, ten times the standard K, induced no inward current, which suggested little contribution of K conductance to the responses.
5.  The outward current responses were induced, also dose-dependently, by various alkali metal cations. The apparent dissociation constants were 6.8, 1.2, 21.7, and 85.1 mM for K, Rb, Cs, and Li, suggesting their potency in the order of Rb>K> Cs>Li.
6.  Thus, the hyperpolarization and outward current responses were due to an electrogenic NaK pump in the basal face of the sensory epithelium. The Na-K pump seems to be responsible, to a certain extent, for maintenance of the negative DC potential in the standard 4 mM K saline, which supplies an outward current to bias the sensory epithelium in situ.
  相似文献   

6.
1.  Three cyclic diterpenoids isolated from gorgonians of theEunicea genus and characterized as eupalmerin acetate (EUAC), 12,13-bisepieupalmerin (BEEP), and eunicin (EUNI) were found to be pharmacologically active on the nicotinic acetylcholine receptor (AChR).
2.  The receptor from the BC3H-1 muscle cell line was expressed inXenopus laevis oocytes and studied with a two-electrode voltage clamp apparatus.
3.  All three compounds reversibly inhibited ACh-induced currents, with IC50's from 6 to 35µM. ACh dose-response curves suggested that his inhibition was noncompetitive. The cembranoids also increased the rate of receptor desensitization.
4.  Radioligand-binding studies using AChR-rich membranes fromTorpedo electric organ indicated that all three cembranoids inhibited high-affinity [3H]phencyclidine binding, with IC50's of 0.8, 11.6, and 63.8µM for EUNI, EUAC, and BEEP, respectively. The cembranoids at a 100µM concentration did not inhibit [-125I]bungarotoxin binding to either membrane-bound or solubilized AChR.
5.  It is concluded that these compounds act as noncompetitive inhibitors of peripheral AChR.
  相似文献   

7.
1.  Muscles of the posterior cardiac plate (pcp) and pyloric regions in the stomach of Squilla are innervated by motoneurons located in the stomatogastric ganglion (STG). The pattern of innervation of various muscles in these regions was determined using electrophysiological methods.
2.  The dilator muscles are singly or doubly innervated by the pyloric dilator neurons (PDs). The constrictor muscles are singly or doubly innervated by the pcp neuron (PCP) or the pyloric neurons (PYs). These muscles are sequentially activated by pcp-pyloric motor outputs produced by the PCP, PY, and PD. All muscles can generate an all-or-nothing spike.
3.  The constrictor muscles generate spikes followed by depolarizing afterpotentials which lead to a sustained depolarization with repetitive spikes. The PYs can entrain rhythmic spike discharges of these muscles.
4.  The spike of muscles remains unchanged by bath application of tetrodotoxin (10-7 M) to suppress neuronal impulse activities, but it is blocked by Mn2+ (10 mM).
5.  The constrictor muscle isolated from the STG displays an endogenous property of spontaneous membrane oscillation that produces a train of spikes. Brief depolarizing or hyperpolarizing stimuli can trigger or terminate an oscillatory potential, respectively, and reset the subsequent rhythm.
6.  The possible functions of myogenicity under the control of discharges of motoneurons in the pyloric constrictor neuromuscular system are discussed.
  相似文献   

8.
1.  Coupling mechanisms between ciliary beating and the membrane potential in Paramecium were investigated under voltage clamp applying intracellular pressure injection of cAMP, cGMP and Ca-EGTA buffer. Ciliary responses following step changes in membrane potential were recorded by high-speed video on magnetic tape.
2.  Injections of cAMP and cGMP up to millimolar concentrations caused no detectable changes in the frequency voltage relationship. A minor effect was that the ciliary reorientation towards the anterior cell end (reversal) tended to be inhibited with depolarization up to 10 mV.
3.  Injection of Ca2+ into the cell clamped at the resting potential caused a transient anteriad ciliary reorientation and a simultaneous increase in the beating frequency.
4.  Injection of EGTA (to buffer Ca2+ below 10–8 M) was ineffective in relation to frequency for several minutes. After this time, hyperpolarization- and depolarization activated frequency responses of EGTA-injected cells were increasingly inhibited. The ciliary reorientation following depolarization was not affected by EGTA.
5.  A posterior contraction of the cell diameter was noticed upon membrane hyperpolarization. The contraction coincided in time with the increase in beating frequency.
6.  The results support the view that the voltage-dependent augmentation of the ciliary beating rate is not directly mediated by an intracellular increase in either cAMP or cGMP.
7.  The role of Ca2+ as intracellular messenger in the ciliary and somatic compartments is discussed.
  相似文献   

9.
1.  The specificity and sensitivity of the olfactory organ of adult zebrafish, Danio rerio, to selected amino acid, bile acid, and steroid odorants were characterized using the electro-olfactogram recording technique. The olfactory organ was responsive to 28 of the 29 odorants tested.
2.  All of the 100 M amino acid and bile acid stimulants elicited a negative-going response that was significantly greater than the response to the artificial freshwater control. The general pattern of relative stimulatory effectiveness established for the amino acid stimuli was neutral amino acids > basic amino acids > acidic amino acids > imino acids. The general pattern of relative stimulatory effectiveness of 100 M bile acid stimuli was taurine-conjugated bile acids > glycineconjugated bile acids non-conjugated bile acids. The responses to the most stimulatory bile acid odorants were up to 40% larger than the responses to the most stimulatory amino acid odorants.
3.  The response threshold for cysteine and taurocholic acid, the most stimulatory of the amino acid and bile acid stimuli tested, was approximately 10-8 M. Females are significantly more sensitive to these odorants than males.
  相似文献   

10.
1.  Rates of oxygen consumption were measured during locomotion in five species of marsupials of the family Dasyuridae. The body weights of the animals ranged between 0.15 and 1.12 kilograms.
2.  The rate of change of power input with speed was generally lower than equivalent eutherian values. The extrapolation to zero speed was consistently a higher multiple of resting metabolic levels than found in eutherians.
3.  The minimum cost of locomotion (M run) as a function of body mass (wt) is described by the equationM run=4.75 wt–0.34. The exponent is similar to that described for eutherians and reptiles, but the constant term is significantly lower.
4.  Metabolic scope in these animals is similar over the size range used and may be greater than in eutherians.
5.  Heat dissipation during locomotion has been partitioned into evaporative and non-evaporative routes. Storage of heat during locomotion was never more than fifty per cent of total production.
  相似文献   

11.
1.  Interactions of cockroaches with 4 different predator species were recorded by videography. Some predators, especially spiders, struck from relatively short distances and usually contacted a cockroach prior to initiation of escape (Table 1, Fig. 3). This touch frequently occurred on an antenna. Cockroaches turned away from the side on which an antenna was touched.
2.  We then measured the success of escape from predators for cockroaches with either cerci or antennae ablated. Only antennal removal caused a significant decrease in the success of escape from spiders (Fig. 5).
3.  With controlled stimuli, cockroaches responded reliably to abrupt touch of antennae, legs or body (Fig. 6). Responses resembled wind-elicited escape: they consisted of a short latency turn (away from the stimulus) followed by running (Figs. 7, 8). However, lesions show that touchevoked escape does not depend on the giant interneuron system (Table 2).
4.  Following section of one cervical connective, cockroaches continued to respond to touching either antenna, but often turned inappropriately toward, rather than away from, stimuli applied to the antenna contralateral to the severed connective (Table 3, Fig. 10).
5.  For certain types of predators touch may be a primary cue by which cockroaches detect predatory attack. Descending somatosensory pathways for escape are distinct from the GI system.
  相似文献   

12.
1.  Properties of the membrane currents ofDidinium nasutum have been investigated under voltage clamp in different solutions and after deciliation.
2.  Theearly transient Ca2+ inward current activates in a voltage-dependent manner. Inactivation is both Ca2+ -dependent and voltage-dependent.
3.  Alate Ca2+ current rises with time to peak > 50 ms and decays in the order of seconds.
4.  Activation and inactivation of the late Ca2+ current is voltage-dependent.
5.  The delayed outward current is activated by voltage. The kinetics of this K+ current, but not its amplitude, are enhanced in the presence of intracellular EGTA.
6.  The two voltage-dependent Ca2+ channels are located in the cilia, whereas all K+ channels are restricted to the somatic membrane.
  相似文献   

13.
Conclusions  
(1)  The aminoesters inhibit glucose-stimulated proton extrusion by yeast cells.
(2)  The inhibitory activity depends on aliphatic carbon chain length.
(3)  The inhibition of proton extrusion is concentration-dependent.
(4)  The aminoesters stimulate quinacrine accumulation in vacuoles of yeast cells so they should possess affinities for lysosomes.
This work was supported byKBN grant no. 7 A203 013 07.  相似文献   

14.
1.  In a concentration-dependent manner neuropeptide Y was found to be a potent inhibitor of the spontaneous activation of human granulocytes and macrophages as well asMytilus edulis immunocytes.
2.  Neuropeptide Y also inhibited the chemotaxic response of these immunocytes to the chemoattractant f-MLP.
3.  Incubation of both the human and the invertebrate immunocytes in f-MLP (10–9 M) causes activation as noted by random locomotion (chemokinesis). Neuropeptide Y also blocked f-MLP-induced chemokinesis.
4.  The results suggest that neuropeptide Y may, in addition to other functions, serve as an endogenous regulator of immunocyte function.
  相似文献   

15.
1.  Direct contact between intra-epithelial nerve endings and ciliated cells was observed in frog (Rana pipiens) palate epithelium.
2.  Electrical stimulation of the palatine nerve to the explant or the explant culture induced an increase in ciliary beat frequency in explant and outgrowth cells.
3.  Atropine inhibited electrically stimulated ciliary beat frequency increase in the explant and outgrowth cells.
4.  Gap junctional intercellular communication appears to be involved in the propagation of stimulated ciliary beat frequency increase from innervated to non-innervated ciliated cells.
  相似文献   

16.
3DFS is a 3D flexible searching system for lead discovery. Version 1.0 of 3DFS was published recently (Wang, T.; Zhou, J. J. Chem. Inf. Comput. Sci., 1998, 38, 71–77). Here version 1.2 represents a substantial improvement over version 1.0. There are six major changes in version 1.2 compared to version 1.0.
1.  A new rule of aromatic ring recognition.
2.  The inclusion of multiple-type atoms and chains in queries.
3.  The inclusion of more spatial constraints, especially the directions of lone pairs.
4.  The improvement of the query file format.
5.  The addition of genetic search for flexible search.
6.  An output option for generating MOLfiles of hits.
Besides the above, this paper supplies:
1.  More query examples.
2.  A comparison between genetic search and Powell optimization.
3.  More detailed comparison between 3DFS and Chem-X.
4.  A preliminary application of 3DFS to K+ channel opener studies.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s0089490050231  相似文献   

17.
1.  Authentic human acetylcholinesterase (AChE) was expressed inEscherichia coli under regulation of the constitutivedeo promoter or the thermoinduciblePL promoter.
2.  To facilitate expression in the prokaryotic system, recombinant human AChE (rhAChE) cDNA was modified at the N terminus by oligonucleotide substitutions in order to replace some of the GC-rich regions by AT. These modifications did not alter the amino acid sequence but resulted in ample production of the protein.
3.  rhAChE accumulated in the cells and reached a level of 10% of total bacterial proteins. A partially purified inactive recombinant protein was recovered from inclusion bodies.
4.  Active rhAChE was obtained after solubilization, folding, and oxidation, although the recovery of the active enzyme was low. A 20- to 40-fold increase in enzymatically active rhAChE was achieved by replacing Cys580 by serine.
5.  The recombinant enzyme analogue was indistinguishable from native AChE isolated from erythrocytes in terms of substrate specificity and inhibitor selectivity.
  相似文献   

18.
Twelve of the main European LCA software packages currently available are examined wirh the aim of establishing which are the most appropriate for LCAs on industrial processes. The packages performances are assessed in terms of
–  • Volume of Data
–  • WindowsTM environment
–  • Network Capabilities
–  • Impact Assessment
–  • Graphical representation of the inventory results
–  • Sensitivity analysis
–  • Units
–  • Cost
–  • User Support
–  • Flow Diagrams
–  • Burdens allocation
–  • Transparency of data
–  • Input & output parameters
–  • Demo version
–  • Quality of data
The review concludes with a Specification Table which summarises the facilities available on each software package. The general conclusion from this study is that for industrially based LCAs, there are four packages which may offer advantages over the rest. These are The Boustead Model, The Ecobilan Group’s TEAM™, PEMS 3.0 and SimaPro 3.1.  相似文献   

19.
We have identified a nerve carrying auditory afferents and characterized their physiological responses in the tiger beetle,Cicindela marutha.
1.  The tympana are located at the lateral margins of the first abdominal tergum. The nerve carrying the tympanal afferents is a branch of the dorsal root from the first abdominal ganglion.
2.  Both male and female auditory afferent responses are sharply tuned to 30 kHz with sensitivities of 50–55 dB SPL.
3.  The auditory afferents show little adaptation and accurately code the temporal characteristics of the stimulus with the limit of a resolution of 6–10 ms.
4.  The difference in threshold between contralateral and ipsilateral afferents for lateral stimuli is greatest at 30 kHz and is at least 10–15 dB.
5.  Ablation studies indicate that the floppy membrane in the anterolateral corner of the tympanum is crucial for transduction while the medial portion of the tympanum is less important.
6.  The tiger beetle and acridid (locust and grasshopper) ears have evolved independently from homologous peripheral structures. The neural precursor of the tympanal organs in both animals is likely the pleural chordotonal organ of the first abdominal segment.
  相似文献   

20.
Müller  D. G.  Frenzer  K. 《Hydrobiologia》1993,(1):37-44
Culture studies with healthy and virus-infected isolates of Ectocarpus siliculosus, Feldmannia simplex and F. irregularis gave the following results:
–  Virus particles are produced in deformed reproductive organs (sporangia or gametangia) of the hosts and are released into the surrounding seawater.
–  Their infective potential is lost after several days of storage under laboratory conditions.
–  New infections occur when gametes or spores of the host get in contact with virus particles. The virus genome enters all cells of the developing new plant via mitosis.
–  Virus expression is variable, and in many cases the viability of the host is not impaired. Infected host plants may be partly fertile and pass the infection to their daughter plants.
–  Meiosis of the host can eliminate the virus genome and generate healthy progeny.
–  The genome of the Ectocarpus virus consists of dsDNA. Meiotic segregation patterns suggest an intimate association between virus genome and host chromosomes.
–  An extra-generic host range has been demonstrated for the Ectocarpus virus.
–  Field observations suggest that virus infections in ectocarpalean algae occur on all coasts of the world, and many or all Ectocarpus and Feldmannia populations are subject to contact with virus genomes.
  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号