Non-oriented Cells Research Articles

Changes in Gravitaxis and Gene-Expression in an Euglena gracilis Culture over Time.

Age-dependent changes in the transcription levels of 5-day-old Euglena gracilis cells, which showed positive gravitaxis, 6-day-old cells without gravitactic orientation, and older cells (9- and 11-day-old, which displayed a precise negative gravitaxis) were determined through microarray analysis. Hierarchical clustering of four independent cell cultures revealed pronounced similarities in transcription levels at the same culture age, which proves the reproducibility of the cultivation method. Employing the non-oriented cells from the 6-day-old culture as a reference, about 2779 transcripts were found to be differentially expressed. While positively gravitactic cells (5-day-old culture) showed only minor differences in gene expression compared to the 6-day reference, pronounced changes of mRNAs (mainly an increase) were found in older cells compared to the reference culture. Among others, genes coding for adenylyl cyclases, photosynthesis, and metabolic enzymes were identified to be differentially expressed. The investigated cells were grown in batch cultures, so variations in transcription levels most likely account for factors such as nutrient depletion in the medium and self-shading. Based on these findings, a particular transcript (e.g., transcript 19556) was downregulated using the RNA interference technique. Gravitaxis and phototaxis were impaired in the transformants, indicating the role of this transcript in signal transduction. Results of the experiment are discussed regarding the increasing importance of E. gracilis in biotechnology as a source of valuable products and the possible application of E. gracilis in life-support systems.

Pump-Controlled Plasmonic Random Lasers from Dye-Doped Nematic Liquid Crystals with TiN Nanoparticles in Non-Oriented Cells

Manipulation of the performance of the random lasers from dye-doped nematic liquid crystals with TiN nanoparticles in non-oriented cells is studied. The experimental results show that the introduction of TiN nanoparticles into dye-doped nematic liquid crystals significantly reduces the threshold of random lasing due to the localized surface plasmon resonance of TiN nanoparticles. The emission spectrum of random lasers can be controlled by the shape of the pump spot. The threshold of random lasers increases with the decrease of the length of pump stripe. In order to obtain the emission spectrum with fine discrete sharp peaks, the narrow pump stripe is more effective than the circular pump spot. When the pump area is more like a circle, the emission spectrum is more like an amplified spontaneous emission. The underlying mechanisms of these phenomena are discussed in detail. This study provides a promising platform for designing the high-quality and low-threshold random lasers which can be controlled by the shape of the pump spot.

Low threshold and coherent random lasing from dye-doped cholesteric liquid crystals using oriented cells

We demonstrate the realization of a coherent random laser in a strongly scattering medium, which contained a dispersive solution of Ag nanoparticles and laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in cholesteric liquid crystals that was injected into an oriented cell. Multiple scattering of Ag nanoparticles and helical domains greatly enhanced by the oriented cell confinement effect was experimentally verified to account for the coherent lasing observed in our oriented system. Based on non-oriented cells and oriented cells, this paper extends the active and scattering media-based random lasers from the incoherent regime to the coherent regime.

Random lasing from dye-doped chiral nematic liquid crystals in oriented and non-oriented cells

These are the experimental results describing random lasing in dye-doped chiral nematic liquid crystals. A novel random lasing emission is studied in this article based on the helical domains of dye-doped chiral nematic liquid crystals in oriented and non-oriented cells. Under frequency doubled 532 nm Nd:YAG (yttrium aluminum garnet) laser-pumped optical excitation, we carefully observed and analysed random lasing from dye-doped chiral nematic liquid crystals with wavelength ranges from 600 nm to 620 nm. In addition, the line-width of multi-mode peaks is less than 0.2 nm. The difference between the two random lasing behaviours in the oriented and non-oriented cells arises from the fact that random lasing appearing in the oriented cell results from stronger multiple scattering of light generated by the spiral domains of the liquid crystal molecules. Furthermore, chiral nematic liquid crystal micro-domains with different orientations can induce variation of the diffusion constant, thereby resulting in a decrease or increase in the lasing intensity of the random lasers, and an increase or decrease in their energy thresholds. In addition, a detailed comparison of the two experimental results is also presented in the article, showing the dependence of the lasing threshold and the number of lasing modes on the transport mean free path, the excited area, and the sample size. This process allows us to obtain a random laser by changing the structure of the sample, realising tunable random lasers at low cost.

The coding of uniform colour figures in monkey visual cortex

Psychophysical studies indicate that perception of the colour and brightness of a surface depends on neural signals evoked by the borders of the surface rather than its interior. The visual cortex emphasizes contrast borders, but it is unclear whether colour surface signals also exist, whether colour border signals are orientation selective or mainly non-oriented, and whether cortical processing tends to separate colour and form information. To address these questions we examined the representation of uniform colour figures by recording single neuron activity from areas V1 and V2 in alert macaque monkeys during behaviourally induced fixation. Three aspects of coding were quantified: colour, orientation and edge selectivity. The occurrence of colour selectivity was not correlated with orientation or edge selectivity. The fraction of colour-selective cells was the same (64 % in layers 2 and 3 of V1, 45 % in V2) for oriented and non-oriented cells, and for edge-selective and surface-responsive cells. Oriented cells were often highly selective in colour space, and about 40 % of them were selective for edge polarity or border ownership. Thus, contrary to the idea of feature maps, colour, orientation and edge polarity are multiplexed in cortical signals. The results from V2 were similar to those from upper-layer V1, indicating that cortical processing does not strive to separate form and colour information. Oriented cells were five times more frequent than non-oriented cells. Thus, the vast majority of colour-coded cells are orientation tuned. Based on response profiles across a 4 deg square figure, and the relative frequency of oriented and non-oriented cells, we estimate that the cortical colour signal is 5-6 times stronger for the edges than for the surface of the figure. The frequency of oriented colour cells and their ability to code edge polarity indicate that these cells play a major role in the representation of surface colour.

A novel express bioassay for detecting toxic substances in water by recording rhodopsin-mediated photoelectric responses in Chlamydomonas cell suspensions.

The influence of Cu2+, Zn2+, Cd2+, Pb2+ and formaldehyde on rhodopsin-mediated photoelectric responses in the green flagellate Chlamydomonas reinhardtii was investigated using three modifications of a recently developed population method for electrical recording (in nonoriented, phototactically preoriented (PO) and gravitactically preoriented cell suspensions). The addition of the heavy metal ions at concentrations several times lower than those known to affect swimming velocity and other physiological parameters in photosynthetic flagellates led to a rapid (one to several minutes) inhibition of the responses. Formaldehyde induced a significant temporary increase in the gravi-orientation of the cells simultaneously with an inhibition of their photoelectric cascade, photo-orientation and motility. The signals recorded in PO suspensions were more sensitive to all tested toxic substances than those recorded from nonoriented cells and indicated a switch from negative to positive phototaxis in the presence of the toxic substances. Of the two major components of the photoelectric cascade, the regenerative response was more sensitive to the tested heavy metal ions, but not to formaldehyde, than the photoreceptor current. The results obtained show that measurement of the photoinduced electrical responses in Chlamydomonas cell suspensions is a powerful novel bioassay for testing environmental pollutants in water samples.

Inputs from three brainstem sources to identified neurons of the mouse inferior colliculus slice

A total of 40 neurons from of the central nucleus of the mouse inferior colliculus (IC) were recorded intracellularly from brain slices to determine input properties by electrical stimulation of the ipsilateral lateral lemniscus (LL), commissure of Probst (CP), and commissure of the IC (CoIC) together with cellular morphology (in 25 neurons) by biocytin injection and staining. Nine neurons had oriented (bipolar), 16 neurons non-oriented (multipolar) dendritic trees of various sizes. Axon collaterals of a given neuron often ran in several directions to provide multiple input to adjacent isofrequency laminae, the lateral nucleus of the IC, the brachium of the IC, the LL, the CP, and the IC commissure. Neurons were classified by spike response patterns to depolarizing current injection into onset- and sustained-spiking cells. The former had significantly shorter membrane-time constants, significantly less frequently and smaller hyperpolarizations after spike occurrence, and more Ca 2+-humps. These properties and their preferred position in the dorsolateral ICC suggest a participation in binaural temporal processing. Almost all oriented cells showed only excitatory post-synaptic potentials (EPSPs) after LL stimulation, while in non-oriented cells inhibitory post-synaptic potentials (IPSPs) after the EPSPs were significantly more frequent. Neurons with largest dendritic trees and many dorsalward projecting axon collaterals were found in the ventral IC. There, neurons had average 4 ms (two synapses) shorter response latencies to LL stimulation than dorsally located neurons. Thus, neurons in the central and dorsal IC may receive mono- and disynaptic input from ventrally located neurons.

Spatial-frequency tuning of sustained nonoriented units of the red-green channel.

The existence of nonoriented cells but not of sustained orthogonal masking for achromatic stimuli led to an investigation of the spatial-frequency (SF) tuning of sustained nonoriented color units. For this purpose the Red-Green channel was isolated by the minimum flicker and hue cancellation techniques. Chromatic contrast sensitivity functions (CSF's), threshold elevation (TE) curves, and contrast nonlinearities (TE-versus-mask-contrast curves) were measured with spatially localized vertical color tests and sinusoidal orthogonal color masks by the method of constant stimuli under Gaussian temporal presentation. Results show that (1) color CSF's are a low-pass function of SF, whereas TE curves are a bandpass function of mask SF, and (2) a minimum of six SF-tuned color mechanisms (one low pass and five bandpass functions of SF, with peak SF's of 0.13, 0.5, 2, 4, and 8 cycles per degree and bandwidths of 3.9, 4.4, 2.9, 2.1, 1.1, and 1.2 octaves), similar to oblique-masking color mechanisms, are extracted by the multiple-mechanisms model. These data imply that (1) most of the SF tuning of the broadly oriented color units is already present in the circularly symmetric units, and (2) the latter may be an input to the former.

Context-dependent interactions and visual processing in V1

We examined the influence of stimulus context on the response of cells in primate V1 utilising both concentric and spatially discrete stimuli. The majority of cells ( 63 71 ) showed marked patch suppression, including non-oriented cells. This suppression was reduced or lost if there was an orientation discontinuity in the stimulus overlying the receptive field. Cross-oriented stimuli could exert strong facilitatory effects so that a cell's response to an optimally oriented stimulus over its receptive field was increased by the presence of an adjacent cross-oriented stimulus. This increase appeared to involve both disinhibition as well as a direct facilitation. The strength of the cross-orientation effects was such that for some cells it seemed appropriate to define a cross-oriented stimulus configuration as the ‘optimal’ stimulus. Effects following from orientation context could be strongly influenced by stimulus direction. Subcortical as well as cortical interactions may contribute to these observations. It is suggested that the properties of the network as a whole define the responses of individual cells and that the representation of discontinuities is an important component of network function in V1.

Visual projections routed to the auditory pathway in ferrets: receptive fields of visual neurons in primary auditory cortex

How does cortex that normally processes inputs from one sensory modality respond when provided with input from a different modality? We have addressed such a question with an experimental preparation in which retinal input is routed to the auditory pathway in ferrets. Following neonatal surgical manipulations, a specific population of retinal ganglion cells is induced to innervate the auditory thalamus and provides visual input to cells in auditory cortex (Sur et al., 1988). We have now examined in detail the visual response properties of single cells in primary auditory cortex (A1) of these rewired animals and compared the responses to those in primary visual cortex (V1) of normal animals. Cells in A1 of rewired animals differed from cells in normal V1: they exhibited larger receptive field sizes and poorer visual responsivity, and responded with longer latencies to electrical stimulation of their inputs. However, striking similarities were also found. Like cells in normal V1, A1 cells in rewired animals exhibited orientation and direction selectivity and had simple and complex receptive field organizations. Furthermore, the degree of orientation and directional selectivity as well as the proportions of simple, complex, and nonoriented cells found in A1 and V1 were very similar. These results have significant implications for possible commonalities in intracortical processing circuits between sensory cortices, and for the role of inputs in specifying intracortical circuitry.

Photoelectric responses in phototactic flagellated algae measured in cell suspension

A new method for the investigation of electric responses involved in the light reception in microorganisms has been developed. It is based on the detection of photoelectric signals in suspensions of cells (instead of a single cell) by two different techniques: (a) by unilateral excitation of non-oriented cells and (b) after preorientation of the cells ( e.g. by gravitaxis or weak, phototactically active light). The method was applied to the flagellated green algae Haematococcus and Chlamydomonas (and several of its mutants). Three main components of the electric signal, which differs in their origin and the mechanisms underlying that registration, were identified. Fast (microsecond) responses reflect charge separation in reaction centres of photosynthesis and are due to the classical light gradient effect on unilateral flash excitation. The later components of the electric signal are involved in photoreception and represent the photoreceptor potential of phototaxis and the calcium-dependent regenerative response. They are measured because of the directional sensitivity of the photoreceptor antenna and the asymmetry of localization of the electric currents involved in the sensory transduction chain. A general similarity between the electric responses in both organisms shows that the sensory transduction chain of photomovements in Chlamydomonas is similar to that described previously for Haematococcus. The advantages of the proposed method are discussed.

Functional analysis of the eyespot in Chlamydomonas reinhardtii mutant ey 627, mt ?

The function of the eyespot in phototaxis of the flagellate green alga Chlamydomonas reinhardtii Dangeard was studied using quantitative reflection confocal laser scanning microscopy and photoelectric measurements. The reflective properties of the eyespot and the photoreceptor current of the C. reinhardtii eyespot mutant ey 627, mt (-) were compared with those of Chlamydomonas strains possessing a well-developed eyespot. Under growth conditions in which strongly disorganized eyespots were observed in the mutant by electron microscopy, there was a significant reduction in the reflection intensity of the eyespot and in the amplitude ratio (500∶440 nm) of photoreceptor currents induced by flashes of 500- and 440-nm light in non-oriented cells. Photoelectrical responses of pre-oriented cells revealed that the latter effect is caused by an altered directional sensitivity of the antenna complex, whereas the functional state of the photoreceptor pigment is not strongly affected in mutant cells. Both the reflection intensity and the amplitude ratio of photoreceptor currents increased to the level of reference strains under conditions supporting the development of a well-organized eyespot in the mutant. Furthermore, incubation of the mutant with high concentrations of all-trans-retinal (10 μM), independent of whether carotenoid biosynthesis was inhibited or not, was found to increase the reflection intensity of the eyespot. An increase in the rate of photoorientation of the mutant occurred concomitant with the increase in the reflective properties of the mutant eyespot. These observations demonstrate the importance of an intact eyespot for interference reflection and absorption of phototactically active light, and thus for the directional sensitivity of the eyespot apparatus.

Representation of color in the central visual system of the monkey.

When the color of a visual stimulus is changed, neurons in the lateral geniculate nucleus and non-oriented cells in the primary visual cortex (V1) of the monkey behave linearly in the color space. This indicates that these neurons combine signals from different types of cones linearly. A major difference between cells in these two structures is the increase of variability of the weights on the inputs from different types of cones seen in V1. In contrast, in the inferior temporal cortex, the behavior of many color selective neurons in the color space is highly non-linear. Such deviation from linear to non-linear behavior seems important to generate a sharp sensitivity to particular hues.

'Real-motion' cells in visual area V2 of behaving macaque monkeys.

Extracellular recordings were made in area V2 of behaving macaque monkeys. Neurons were classified into three groups: non-oriented cells, oriented cells with antagonistic areas and oriented cells without antagonistic areas in their receptive field. All neurons were tested with standard visual stimulations in order to assess whether they gave different responses to the movement of a stimulus and to the movement of its retinal image alone, when the stimulus was motionless and the animal voluntarily moved its eyes. To do this, neuronal responses obtained when a moving stimulus swept a stationary receptive field (during steady fixation) and when a moving receptive field swept a stationary stimulus (during tracking eye movements), were compared. The receptive field stimulation at retinal level was physically the same in both cases, but only in the first was there actual movement of the visual stimulus. Control trials, where the monkeys performed tracking eye movements without any intentional receptive field stimulation, were also carried out. Out of a total of 263 neurons isolated in the central 10 deg representation of area V2, 101 were fully studied with the visual stimulation described above. Most of these (83/101; 82%) gave about the same response to the two situations. About 14% (14/101) gave a good response to stimulus movements during steady fixation and a very weak one to retinal image displacements of stationary stimuli during visual tracking. We have called neurons of this type "real-motion cells" (cf. Galletti et al. 1984). None of the non-oriented cells was a real-motion one, while about an equal percentage of real-motion cells was found among the oriented cells with and without antagonistic areas. Finally, we found only 4 neurons which showed behaviour opposite to that of real-motion cells, i.e. they showed a better response to displacement of the retinal image of stationary stimuli than to actual movement of stimuli. We suggest that real-motion cells might contribute to correctly evaluating movement in the visual field in spite of eye movements and that they might allow recognition of the movement of an object even if it moves across a non-patterned visual background. Present data on area V2, together with similar results observed in area V1 (Galletti et al. 1984; Battaglini et al. 1986), support the view that these two cortical areas analyse the movement in a parallel fashion along with many other characteristics of the visual stimulus.

GABAergic inhibition and orientation selectivity of neurons in the kitten visual cortex at the time of eye opening

Effects of iontophoretic application of γ-aminobutyric acid (GABA) and its antagonist, N-methyl-bicuculline (BIC), on visual responses of striate cortical neurons were studied in kittens 6–13 days old. Visually responsive cells were classified into three groups, i.e. orientation-selective, orientation-bias and nonoriented cells. In almost all of the orientation-selective cells, their responses were completely suppressed by GABA while the majority of the others were not significantly or only weakly suppressed. An application of BIC abolished or reduced the selectivity of all the orientation-selective cells but did not affect any of the nonoriented cells tested. These results suggest that GABAergic inhibition already operates on a group of cortical neurons to make them orientation-selective at the time of eye opening, but such an action of GABA on other groups of neurons develops later.

‘Real-motion’ cells in the primary visual cortex of macaque monkeys

Extracellular recordings were carried out in the primary visual cortex of behaving macaque monkeys. Neurons were activated by moving a visual stimulus across their receptive fields during periods of steady fixation and by moving their receptive fields (by visual tracking) across a motionless visual stimulus, taking care that the velocities of stimulus and eye movements were the same. The total cell population (108 neurons) was divided into 3 groups according to the cell sensitivity to visual stimulus orientation (non-oriented cells and oriented cells) and to the presence or absence of antagonistic areas in the receptive fields (oriented cells with antagonistic areas). All the non-oriented cells(n= 4) showed almost the same response to visual stimulation both during steady fixation and during visual tracking. Out of a total number of 86 oriented cells, 77 turned out to be activated by the visual stimulation both during fixation and tracking. Eight oriented cells gave a very weak response or no response at all to visual stimulation during smooth pursuit eye movements and one neuron of the same group showed a greater response during visual tracking than during fixation. Six out of 8 oriented cells with antagonistic areas showed almost the same response to the two types of visual stimulation, while the remaining two neurons showed very weak responses during smooth pursuit eye movements. Our results show that a small percentage (about 10%) of striate neurons in macaque monkeys gave very different responses to the same physical stimulation at retinal level, according to the presence or absence of slow eye movements (smooth pursuit eye movements). The activity of these neurons seems to be related to the real movement of something in the visual world, in spite of the retinal image movement per se.

GABAergic inhibition already operates on a group of neurons in the kitten visual cortex at the time of eye opening

Effects of iontophoretic application of γ-aminobutyric acid (GABA) and its antagonist, N-methyl-bicuculline (BIC), on visual responses of striate cortical neurons were studied in kittens 6–13 days old. Visually responsive cells were classified into 3 groups, i.e., orientation-selective, orientational bias and non-oriented cells. In almost all of the orientation-selective cells their responses were completely suppressed by GABA while the majority of the others were not significantly or only weakly suppressed. BIC abolished or reduced the selectivity of all the orientation-selective cells while it did not affect any of the non-oriented cells tested. These results suggest that GABAergic inhibition already operates on a group of cortical neurons to make them orientation-selective at the time of eye opening.

Non-oriented cells of the striate cortex activated during smooth pursuit eye movements and steady fixations in behaving monkeys

Extracellular recording were carried out in the primary visual cortex of behaving monkeys. Neurons were activated by moving a visual stimulus on their receptive fields during periods of steady fixation and by moving their receptive fields (smooth pursuit eye movements) on a motionless visual stimulus. Regarding non-oriented cells, they turned out to be activated by the visual stimulation both during steady fixations and smooth pursuit eye movements. Therefore, the non-oriented cells we studied seem not to receive an extraretinal signal related to the slow eye movements.

Recovery from monocular deprivation in the monkey. I. Reversal of physiological effects in the visual cortex.

This is a study of the effects of monocular deprivation, reverse suturing (opening the deprived eye with closure of the other) and reopening of the deprived eye alone (without closing the other) on the physiological organization of the primary visual cortex in monkeys (Erythrocebus patas). All animals were initially monocularly deprived by suture of the lids of the right eye from soon after birth until about 4 weeks of age (24-29 days). In a monocularly deprived animal, recordings were taken from area 17 at 24 days. Already most neurons recorded outside layer IVc, were strongly or completely dominated by functional input from the left eye. The Non-oriented cells of layer IVc, where the bulk of the afferent input terminates, were also mainly dominated by the left eye. Although segregation of input from the two eyes was not complete, large areas of layer IVc were already monocularly dominated by the left eye. Four animals were reverse-sutured at about 4 weeks and recorded 3, 6, 15 and 126 days later. In each animal the pattern of ocular dominance was fairly similar within and outside layer IVc. Even with only 3 days of forced usage of the initially deprived right eye, about half of all cells recorded had become dominated by it, and the process of "recapture' of cortical cells by the initially deprived eye was apparently complete within 15 days. In layer IVc, the recovery took the form of an expansion of zones dominated by the deprived eye, as if the originally shrunken stripes of afferent termination had become enlarged. Binocularly driven neurons were rare at all stages, in all layers, but when present and orientation-selective, they had similar preferred orientations in the two eyes. Likewise the "columnar' sequences of preferred orientation continued without obvious disruption on shifting from regions dominated by one eye to those dominated by the other. Simply reopening the deprived eye at about 4 weeks, for 15 to 96 days caused no detectable change in the overall ocular dominance of cortical cells and, on average, no expansion of right-eye dominance columns in layer IVc. Therefore the recovery seen after reverse suturing depends not just on the restoration of normal activity to axons carrying information from the right eye, but on the establishment of a competitive advantage, through the right eye being made more active than the left.

Effects of monocular lid closure on development of receptive-field characteristics of neurons in rabbit superior colliculus.

1. The receptive-field characteristics of superior colliculus neurons were studied in rabbit pups that had one eyelid sutured prior to eye opening. Units recorded from the superior colliculus (SC) receiving input from the unsutured eye provided normal developmental data, and those from the colliculus receiving input from the sutured eye were used to study the effect of visual deprivation. 2. A total of 1,054 cells recorded from 89 animals ranging in age from 7 to 35 days were obtained, 514 cells in the normal colliculus and 540 cells in the deprived colliculus. During normal development, three nonoriented cell types (concentric, uniform, motion) showed a progressive increase in relative frequency of occurrence, starting at about 7 days and reaching the adult level at about 15 days. Directionally selective cells developed slightly later, reaching an adult level at 3 wk. Oriented directional cells were the slowest to mature, requiring about 4 wk to reach the final level. 3. Eyelid suturing significantly affected the oriented directional cell development; these cells developed at a normal rate for about 3 wk, then rather abruptly began to decrease in number; a stable relative frequency of about one-fourth the normal value was reached at about 4 wk. A corresponding increase in the relative number of indefinite cells to above the normal level also occurred. In contrast, the development of nonoriented cells and directionally selective cells was not affected by the deprivation. 4. The development of rabbit superior colliculus receptive fields was found to be, in general, similar to development of kitten SC receptive fields. It also correlates well with developmental changes seen in rabbit ganglion cell receptive fields and with anatomical changes in developing rabbit SC. Indirect support is given for the hypothesis that changes seen in SC with deprivation are secondary to changes in the visual cortex.