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 250 毫秒
1.
1.  Phage-like particles were found in the supernatants of cultures of strains of Myxococcus xanthus, M. virescens and M. fulvus. The largest number of such particles was associated with M. virescens V2. Most of the particles were similar in morphology to the virulent Myxococcus phage, MX-1.
2.  Several new phages were isolated from soil and animal droppings. A new phage was isolated from cultures of M. virescens V2. All resembled phage MX-1 in morphology and were related to phage MX-1 serologically. One of these phage, øm, was characterized by fractionation of its proteins by SDS-polyacrylamide gel electrophoresis and by analysis of the restriction fragments of its DNA. The very close relatedness with MX-1 was confirmed by these techniques. Phage øm, was found to exist in a state of pseudolysogeny with strains of M. virescens and M. fulvus.
3.  Two types of bacteriocin-like activity were found associated with Myxococcus strains. In one case, the activity was extracted from chloroform-killed or from sonicated cells. In the second case it was associated with extracellular material. Strains of Salmonella and Cytophaga were found to be good indicators for this latter activity. These strains were found to be killed by phage MX-1.
4.  The significance of these data for origin of the phages of myxococci are discussed and it is proposed that MX-1 and the newly isolated phages may be virulent mutants of a family of lysogenic phages.
  相似文献   

2.
The angular distribution of the optical axes of the ommatidia in the eyes of waterstriders (Gerris lacustris) has been investigated using antidromic illumination.
1.  Each eye contains about 920 ommatidia arranged in approximately 40 nearly horizontal rows (Figs. 5, 6).
2.  There is an acute zone (visual streak) of ±5° around the eye equator with high vertical resolution (Fig. 9).
3.  The horizontal interommatidial angle oh varies little with altitude and is in the frontal parts of the eye equal to the (horizontal) interrhabdomere angle rh (Fig. 10).
4.  Above and below the visual streak the eye is adapted to the perception of relative height or depth constancy (Fig. 13).
5.  Reconstruction of the viewing directions of the rhabdomeres in the visual streak reveals that characteristic groups of rhabdomeres in different ommatidia coincide in their receptive fields. Optical prerequisites for two types of neural superposition can be found: one of medium neural summation but highest sampling frequency, the other of highest neural summation at the cost of resolution (Fig. 11).
6.  The correspondence of the limits of resolution due to diffraction and finite sampling frequency is discussed.
  相似文献   

3.
With the aim of clarifying the role of screening pigments in photoreceptor optics of the compound eye, a comparative study of the optical properties of the honeybee eye in the visible region of the spectrum was carried out using wild-type bees and eye colour mutantssnow, snow laranja, ivoryumberandchartreuse with total or partial blockage of the tryptophane-ommochrome pathway.
1.  The electroretinogram (ERG) of mutant eyes displayed a sharp on-peak, this component being absent from normal heterozygote eyes (Fig. 6).
2.  The ERG of newly emerged bees (a) lacked the above on-peak and showed oscillations in mutants, and (b) lacked the off-peak which always occurs in the ERG of adults in all the genotypes studied when stimulated by visible light.
3.  The resting potentials of the receptor and cone cells were not found to be affected by mutations la, and the receptor potential ins/s ands la/slaphotoreceptors appeared to be similar to that in +/+
4.  Analysis of the amplitude characteristics of the whole eye of eight genotypes showed that the relative numbers of photons absorbed from an extended light source (4.5°×16.5°) and needed to elicit a standard ERG amplitude of 1 mV were as follows:s/si u/iusla/slach1/ch1(+/+; s/+ iu/+; sla/+)=14.38.612.2(100–250). These ratios are believed to reflect the progress in ommochrome formation in these strains.
5.  Spectral sensitivity curves (SSC) were obtained using an automatic spectrosensitometer and a spectral scan method which gave accurate results. The SSC of the whole eye in+/+ peaked at a max of 543±7 nm (SD,n=6), whereas max ins/s ands la/slashifted to 528±6 nm (n=9) and 548 ±3nm (n=6) respectively. The SSC ins/+ was the same as that in+/+. The bandwidth (width at 50% of peak sensitivity) of the SSC proved to be similar in+/+ ands/+ (126±10 nm and 128±8 nm), although ins/s the SSC appeared to be significantly narrower (106±7 nm;P<0.01; fig.=" 8,=" table=" 2).=">
6.  The peak spectral sensitivity of long-wave (LW) receptors lay at 541±5 nm (SD,n=14) in+/+ and at 526±5 nm (n=13) ins/s; the spectral distributions of the peaks in these genotypes were different. The bandwidth of the SSCs of the photoreceptors were 109±11 nm in+/+ and 103±4 nm ins/s, the difference being insignificant (Fig. 8, Table 2). The SSCs ins/s fit the absorption spectrum of pigment 526 (P 526) rather well whereas those in+/+ are noticeably distorted. The same is true for the whole-eye data.
7.  A theory is advanced to account for the acceptance functions of the photoreceptors of eyes with imperfect pigmentation. Light scattering in imperfectly screened eyes was estimated using a factor which the termed we parasitic absorption coefficientp (see Theory).
8.  The acceptance functions of LW photoreceptors were measured by three methods, and the results were similar to those predicted from the theory. On this basis the coefficientp was estimated; fors/s photoreceptors it lay between 0.65 and 0.76 according to experiments with a point light source (method 1), and was as great as 2.5 according to measurements with an extended light source (method 2). The latter technique, an integral method, made it possible to detect light scattering in normal bee eye, the coefficientp reaching 0.02 (Fig. 1, Table 3).
9.  In genotypes+/+ ands la/slathe absorption spectra of screening pigments were recorded by microspectrophotometry (MSP), and greater transmission of red light than blue-green was found (Fig. 11).
10.  Taking into account the screening effect of ommochromes, it is suggested that the visual pigment of LW photoreceptors in the honeybee eye is P 526; the absorption spectrum of this is highly similar to the SSC of LW photoreceptors in thes/s eye.
11.  On the basis of our theory and experimental results, the contrast transfer function (CTF) for the white honeybee eye was estimated to be only 0.1 (for white and black patterns with the spatial wavelength sp, the acceptance angle). Thus, the absence of screening pigments from the compound eye ofsnow mutants causes the great decrease in image contrast, and this serious sensory defect may be responsible for the fact that these mutants fail to find their way home.
Dedicated to Professor H. Autrum on the occasion of his 80th birthday  相似文献   

4.
1.  Responses of single olfactory receptor neurons to pheromones were recorded with tungsten microelectrodes on the antennae of male Helicoverpa (Heliothis) zea. Recordings were obtained from the male specific sensilla trichodea type 1.
2.  More than half (49/91 units) could be classified as olfactory receptor neurons, 35 of which were selective for pheromone components of the heliothine moths H. zea and Heliothis virescens. The majority (31/35) were most responsive to the principal component (Z)-11-hexadecenal (Z11-16AL). The other 4 were tuned to (Z)-9-tetradecenal (Z9-14AL), which is a pheromone component in the sympatric species H. virescens, and also interrupts attraction of H. zea males.
3.  The specificity and sensitivity of these neurons were similar to the corresponding neurons in H. virescens, suggesting homologous populations of neurons in the two species. No other neurons selective for other pheromone compounds were identified.
4.  Receptor neurons of both types (tuned to Z11-16AL and Z9-14AL respectively) showed variations in temporal response characteristics. Some responses showed a pronounced phasic spiking component, a rapid decay, and return to background activity after stimulation. Other responses were more prolonged, far outlasting the stimulation period. Phasic neurons also followed short, rapid stimulus pulses better than tonic neurons, suggesting that they may encode different features of an intermittent pheromone plume.
  相似文献   

5.
  相似文献   

6.
  1. Bacteriophage MX-1 is a virulent DNA phage whose hosts include strains of Myxococcus xanthus, M. fulvus and M. virescens. DNA was extracted from purified phage preparations. The molecular weight of phage DNA was measured by sedimentation-velocity and by rate-zonal ultracentrifugation. The apparent molecular weight was found to vary for reasons discussed in the text. From ratezonal ultracentrifugation, using calibrated sucrose gradients, the molecular weight was calculated to be 149 (± 22)×106 daltons. The base composition of the DNA was estimated by different methods and was found to be 50–52% (G+C). The DNA demonstrated an anomalous thermal denaturation profile in dilute buffer. Denatured DNA was fractionated by ion-exchange chromatography and by buoyant-density centrifugation. No significant strand separation was obtained and it was concluded that overall base compositions of the two strands are very similar.
  2. DNA from bacteriophage MX-1 was hydrolysed with restriction endonucleases R. EcoRI, R. EcoRII and R. HindIII. The restriction fragments were catalogued and their apparent molecular weights calculated from electrophoresis gels calibrated with fragments from the DNA of coliphage λ. From the total fragments obtained with nuclease R. EcoRI, the minimum apparent molecular weight of MX-1 DNA was found to be 130×106 daltons.
  相似文献   

7.
1.  Honey bees (Apis mellifera, worker) were trained to discriminate between two random gratings oriented perpendicularly to each other. This task was quickly learned with vertical, horizontal, and oblique gratings. After being trained on perpendicularly-oriented random gratings, bees could discriminate between other perpendicularly-oriented patterns (black bars, white bars, thin lines, edges, spatial sinusoids, broken bars) as well.
2.  Several tests indicate that the stimuli were not discriminated on the basis of a literal image (eidetic template), but, rather, on the basis of orientation as a single parameter. An attempt to train bees to discriminate between two different random gratings oriented in the same direction was not successful, also indicating that the bees were not able to form a template of random gratings.
3.  Preliminary experiments with oriented Kanizsa rectangles (analogue of Kanizsa triangle) suggest that edge detection in the bee may involve mechanisms similar to those that lead to the percept of illusory contours in humans.
  相似文献   

8.
Somatic embryos and adult plants were regenerated from mesophyll protoplasts of a clone of chicory 474 (Cichorium intybus L. x Cichorium endivia L.). Embryos were obtained in three different ways:
–  - plating of 7-day-old protoplast cultures on PM-3 solid induction medium with 2.5 M 2-isopentenyladenine (2-iP) and 0.5 M naphthaleneacetic acid (NAA);
–  - transfer of 1–2 mm microcolonies into liquid M-17 induction medium with 2.5 M (2-iP) and 0.1 M (NAA);
–  - transfer of well-established protoplast-derived calluses onto M-17.
Development of embryos was accomplished in agitated liquid Heller medium with 0.15 M gibberellic acid and germination on solid Heller medium without growth regulators. The total time for plantlet (4-leaves stage) recovery, following protoplast isolation, was 13 to 15 weeks. After acclimatization all protoplast-derived plants of Cichorium 474 were phenotypically normal and fertile.  相似文献   

9.
1.  The neuroantibody approach, based on the expression of selected monoclonal antibodies by cells of the nervous system, has recently been described (Cattaneo and Neuberger, 1987; Piccioliet al., 1991). In order to apply this experimental strategy to study the role of nerve growth factor (NGF) in the central nervous system (CNS), we exploited the monoclonal antibody (mAb),D11, which neutralizes very efficiently the biological activity of NGF, bothin vitro andin vivo (Cattaneoet al., 1988).
2.  TheD11 antibody chains were cloned and expressed in COS cells as rat/human chimaeric proteins. The cloned antibody was shown to display all the properties of the parentalD11 antibody, including its ability to neutralize NGF biological activity.
3.  This will allow us to engineer the expression of recombinantD11 antibodies in the CNS, to study the role of NGF in the developing and adult nervous system. This approach can be extended to other neurotrophic factors for which neutralizing monoclonal antibodies are available.
  相似文献   

10.
1.  Chronic ingestion of caffeine by male NIH strain mice alters the density of a variety of central receptors.
2.  The density of cortical A1 adenosine receptors is increased by 20%, while the density of striatal A2A adenosine receptors is unaltered.
3.  The densities of cortical 1 and cerebellar 2 adrenergic receptors are reduced byca. 25%, while the densities of cortical 1 and 2 adrenergic receptors are not significantly altered. Densities of striatal D1 and D2 dopaminergic receptors are unaltered. The densities of cortical 5 HT1 and 5 HT2 serotonergic receptors are increased by 26–30%. Densities of cortical muscarinic and nicotinic receptors are increased by 40–50%. The density of cortical benzodiazepine-binding sites associated with GABAA receptors is increased by 65%, and the affinity appears slightly decreased. The density of cortical MK-801 sites associated with NMDA-glutaminergic receptors appear unaltered.
4.  The density of cortical nitrendipine-binding sites associated with calcium channels is increased by 18%.
5.  The results indicate that chronic ingestion of caffeine equivalent to about 100 mg/kg/day in mice causes a wide range of biochemical alterations in the central nervous system.
  相似文献   

11.
1.  When Xenopus laevis embryos swim into an obstruction they usually stop. This stopping response to stimulation on the head is present from stage 28 to 45. At stage 37/38 it is more reliable in restrained than in free-swimming animals, and to stimuli to the cement gland than to the head skin. Fictive swimming also stops reliably after the same stimuli but struggling and fictive struggling do not.
2.  Discharge of deformation-sensitive trigeminal sensory neurons in response to pressure on the cement gland or head skin precedes the fictive stopping response. When the embryo hangs from cement gland mucus, trigeminal neurons are active and the embryo is less responsive to stimulation.
3.  Lesions of the central nervous system have allowed us to draw the following conclusions about this inhibitory pathway: (a) either the cement gland or the head skin must be intact; (b) one trigeminal ganglion is both sufficient and necessary; (c) the pathway is independent of the forebrain and midbrain; (d) it can take an ipsilateral or contralateral route through the hindbrain; (e) at least two hindbrain interneuron components are involved.
4.  A similar stopping response is present in embryos and larvae of the urodele Ambystoma mexicanum.
  相似文献   

12.
1.  Oxygen uptake, carbon dioxide release, water release and heart frequency were studied in the tarantula,Eurypelma californicum. Oxygen uptake also was studied in the scorpion,Pandinus imperator.
2.  Basal metabolic rate, oxygen uptake of animals at rest as measured bymanometric respirometry, was very low in both species [mostly well below 1 ml O2 (STPD)·h–1]. Its relation to body mass and temperature was examined. A respiratory quotient of 0.71 inEurypelma at rest indicates oxidation of fat.
3.  To assess short-term changes and maximum rates, gas exchange at the four book lungs and heart frequency were simultaneously measured inEurypelma by using respiratory masks andflowthrough respirometry.
4.  During maximum activity, and were often reduced. During rest and in a later phase of recovery, slow fluctuations in oxygen uptake, carbon dioxide and water release occurred. These are probably caused by fluctuations in heart frequency.
5.  After 1 min of maximum activity, on average, increased to a maximum of 81 l (STPD)·min–1, to 50 l (STPD)·min–1, and heart frequency to 75 beats·min–1. Typical values for pulmonary water release were 50 (at rest) and 100–120 (maximum) g H2O·min–1.
6.  During recovery, and heart frequency changed faster than , causing changes in the respiratory quotient. It initially dropped, then increased and finally returned to the original value.
7.  A plot of heart frequency vs during recovery revealed a linear relationship between both variables.
This and the following two papers are dedicated to the memory of Prof. Bernt Linzen, who promoted our work by his continuous support and the creation of an extraordinarily encouraging work atmosphere. R.P., T.F.  相似文献   

13.
1.  Underwater downwelling quantal irradiance spectra were measured in estuarine and coastal areas under various tidal and rainfall conditions. At midday the available spectrum near the bottom has maximal irradiance in the region of about 570 to 700 nm in the estuary, whereas in offshore coastal areas greatest irradiance occurs between 500 and 570 nm. At twilight in an estuary, maximal underwater downwelling irradiance shifts to the 490–520 nm region.
2.  The visual pigment absorption maxima of 27 species of benthic crustaceans from semi-terrestrial, estuarine and coastal areas have values ranging from 483 to 516 nm. There is no obvious shift in the max from long wavelengths in estuarine species to shorter wavelengths in coastal species. The only match between max and midday spectrum was for a continental shelf species,Geryon quinquedens.
3.  The Sensitivity Hypothesis is predicted to account for the visual sensitivity of benthic crabs from estuarine and coastal areas. To assess the match between visual spectral sensitivity and environmental spectra, photon capture effectiveness was calculated for a range of idealized visual pigment absorption functions operating in the measured environmental spectra.
4.  All crab species are poorly adapted for maximal photon capture at midday, since pigments having max longer than 540 nm function best under all daytime spectral conditions. Photon capture of visual pigments with max near 500 nm improves dramatically at twilight, particularly at lower visual pigment densities and shallow depths. However, pigments having max at wavelengths longer than those for the crabs are equally or more efficient at photon capture. Therefore the Sensitivity Hypothesis is not supported for crustaceans.
  相似文献   

14.
1.  Spectral-sensitivity functions of large-field movement-detecting units in the lobula plate of the dronefly Eristalis tenax L., which is a Batesian mimic of the honeybee, were measured using visual stimuli consisting of light flashes, or moving gratings. Two classes of units were studied, one class responding to inward horizontal motion in the contralateral eye (presumably the homologue of the well-known HI in other fly species), and the other class responding to vertically-down-ward motion in the contralateral eye.
2.  In both classes of units, the spectral-sensitivity function of the response to flashes is characterized by two peaks, one in the UV at ca. 350 nm and the other in the blue at ca. 475 nm (Figs. 3, 8). It resembles the spectral-sensitivity function of the R1-R6 class of receptors in other flies.
3.  In both classes of units, the spectral-sensitivity function of the response to movement is characterized by a single peak, occurring in the blue at ca. 450 nm (Figs. 7, 9).
4.  Control experiments on homologous units in the Australian Sheep Blowfly Lucilia cuprina, using identical stimulating conditions reveal that the response to flashes as well as movement possesses a dual-peaked spectral sensitivity, with one peak in the UV and the other in the blue-green region of the spectrum (Figs. 10–12).
5.  The results indicate that the pathways subserving the inputs to movement-detecting neurons in Eristalis are driven by more than one spectral class of photoreceptors. They also reveal that the spectral sensitivity of movement detection in Eristalis bears a closer resemblance to that of the honeybee, than to that of other flies. This similarity to the honeybee may arise from the fact that the dronefly and the honeybee occupy similar ecological niches, both foraging for nectar in flowers.
  相似文献   

15.
Beobachtungen über Nest und Nestbautechnik von Winter- und Sommergoldhähnchen(Regulus regulus, R. ignicapillus) im Freiland und in Volieren zeigen:
1.  Die Neststandorte von WG und SG gleichen einander, ihre Brutreviere können sich überlappen.
2.  Das Nest zeigt 3 deutlich getrennte Schichten. Die Außenschicht besteht aus Spinnstoff, Moos, Flechten — Moose (bei WG auch Flechten) bilden die Mittelschicht, Federn und Haare die Polsterung. Hochgebirgsnester weisen gegenüber Mittelgebirgsnestern einen Materialzuwachs besonders in der Mittel- und Polsterschicht auf.
3.  Der Nestbau dauert ca. 20 Tage, Zweitnester können rascher entstehen.
4.  Die Bautechnik wechselte mit fortschreitendem Bau. Baubewegungen für Grundgerüst, Rohbau und Polsterung waren verschieden. 14 (WG) bis 15 (SG) Baubewegungen konnten unterschieden und den 3 Bauphasen zugeordnet werden: a) Bei der Anlage des Grundgerüsts wurden die Tragästchen mit Spinnstoff bedeckt/umwickelt. Die Gespinste wurden dabei abgerieben, verspannt, und beim Außen säubern mit dem Ast fest verbunden. b) Der Rohbau entstand durch weiteres Einbringen von Spinnstoff und zunehmend häufiger Moosen/Flechten. Die Wände wurden durch Wegschieben (bzw. Einvibrieren) der Baustoffe geformt und gefestigt, beim WG auch maskiert, der Boden durch Unten säubern geschlossen. Zuletzt eingestopfte Moose der Mittelschicht wurden verstrampelt, der Rand durch Verstreichen verstärkt und geglättet. c) Die Mulde wurde mit Federn/Haaren ausgekleidet, das Polstermaterial durch Strampeln geordnet, sperrige oder auffallende Polsterstoffe wieder entfernt. Gleichzeitig wurde der Nestrand eng zusammengezogen, die Tragästchen von Spinnstoffresten gesäubert; SG verdeckten durch aufgesteckte Federn die Nestmulde.
5.  Die beiden Arten stimmten auch in ihrer Nestbautechnik weitgehend überein. Auffälligster Unterschied war, daß sich SG am Nestbau nicht beteiligen und nur begleiten. Doch führten juvenile beider Arten fast alle Baubewegungen spielerisch aus. Unterschiede gab es auch in den Baubewegungen der : SG vibrierten beim Wegschieben (2 e) und Randverstreichen (2 g) und verdeckten die Mulde durch aufgesteckte Federn.
  相似文献   

16.
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   

17.
The rich deciduous woodland at Loi, Luster, Inner Sogn, 61° 20 N., was traditionally used for fodder production from both tree and field layer. After more than nearly 40 years of disuse and secondary forest succession, experimental efforts were made to restore the traditional agricultural meadow woodland. Following a detailed preliminary registration of the vegetation the following measures were taken:
1.  The understory tree layer, mainly Alnus incana was removed.
2.  The old Ulmus glabra pollards were pruned back to traditional shape, as were some tall shurbs of Corylus avellana.
3.  The field layer was mown once or twice yearly.
The main results are:
1.  The pollarded elms have developed bundles of new twigs at the pruning points and are in good condition.
2.  After an expansion of tall, nitrophilic herbs, e.g. Urtica dioica, Impatiens noli-tangere and Rubus idaeus, low and medium sized herbs and grasses have increased both in numbers, frequency and abundance. Helio- and thermophilic forest margin species are also more prominent. The moss layer has also become more dense and varied.
3.  The average number of species in permanent plots has nearly doubled.
  相似文献   

18.
1.  After the intact compound eyes of the butterflyPapilio xuthus were adapted to darkness, white, blue ( max 460 nm) or orange light ( max 580 nm), the eyes were separated into the distal (primary pigment cells, the dioptric apparatus and ca. 30% of retinal tissue) and the proximal layers (the rest of the retinal tissues). Each layer was separated into a supernatant and a precipitate. Both in white and blue light-adapted eyes, the amount of 11-cis 3-hydroxyretinal increased in the supernatant of the distal layer (Sup-DL) much more than it did in dark-adapted eyes. No increase was observed in the Sup-DL of orange light-adapted eyes.
2.  When all-trans retinol (non-native chemical) was added to the Sup-DL, it was converted to all-trans retinal under the darkness, and to all-trans and 11-cis retinal by blue light irradiation. When all-trans retinal was added to the Sup-DL, the isomerization of all-trans retinal to 11-cis retinal was accelerated by the blue light.
3.  The Sup-DL was separated into ammonium sulfate soluble (AS-sup) and insoluble (AS-ppt) fractions. The AS-ppt fraction contained 3-hydroxyretinal but no 3-hydroxyretinol. Blue light irradiation to the AS-ppt fraction induced an increase in 11-cis 3-hydroxyretinal, with a concomitant decrease in all-trans 3-hydroxyretinal.
These results indicate that both the oxidation of all-trans 3-hydroxyretinol to all-trans 3-hydroxyretinal and the light-dependent isomerization of all-trans 3-hydroxyretinal to 11-cis isomer take place in the tissues of the distal layer of the eyes.  相似文献   

19.
Ipsilateral retino-tecto-tectal (IRTT) units were recorded extracellularly in the rostral optic tectum of the frog (Rana esculenta). The activity of 79 superficial units (II type) was quantified in response to black disks of various sizes, moved vertically at various angular velocities and against a white background. The contrast ¦C¦ was constant during the experiments. Neuronal activity was analysed by two methods, yielding identical results:
(1)  I1 units responded transiently to moving and movement gated stationary stimuli; these units did not seem to be directionally sensitive nor responsive to changes in background illumination. Fifty-three % of units had a low spontaneous activity.
(2)  A power function relating mean firing frequency (¯R) and angular velocity (v) was established in the majority (78%) of units. The exponent and the constantk were 0.44–0.8 and 8.9–20, respectively.
(3)  The relationship between¯R and stimulus diameter (D) was best expressed by a logarithmic function. The maximum response occurred forD= 2–4. The optimal stimulus diameter was found to be independent of stimulus velocity.
(4)  When stimulated repetitively under steady conditions, I1 units showed about 10% fluctuations in mean response, which seemed to increase with stimulus diameter.
The results show that qualitatively and quantitatively, the properties of I1 units are very similar to R1–R2 (sustained) ganglion cells.  相似文献   

20.
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   

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