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1

Retinal origin of electrically evoked potentials in eye-eye and eye-neck montages

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Foik A., Kublik E., Popek A., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2013
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tom 73
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nr Suppl.1
Noninvasive current stimulation is a rapidly developing tool for rehabilitation of visual impairment. The therapeutic use of current stimulation requires solving many technical problems including optimal placement of stimulating electrodes (SE). In this study we asked the question about origin of electrically evoked potential (EEP) and it’s dependence on the placement of the SE. In acute experiments on rats under urethane anaesthesia, visually (VEP) and electrically evoked potentials were recorded using single- and multi-channel electrodes from 5 visual structures: retina (1 channel), lateral geniculate nucleus (8 channels), superior colliculus (7 channels) and visual cortex of both hemispheres (16 channels each). Recordings of EEPs were performed to electrical pulse current stimulation, delivered using two electrodes placed either on one eye-ball (eye-eye montage) or on the eye-ball and neck (eyeneck montage). To reveal the origin of EEPs in both electrode montages 5 µl of tetrotodoxine (TTX 0.5 mM), was injected into the eye to block retinal ganglion cells’ activity and EEPs were recorded for both SE configurations. Lack of VEPs confirmed the successful block of ganglion cells’ activity. We have observed full decay of EEPs after TTX injection independent on the SE configurations. These results indicate on the retinal origin of EEPs regardless of the reference electrode placement. Supported by ERA-NET Neuron project REVIS.
2

Role of inhibition in shaping reliability: trial-by-trial variability of visual responses in superior colliculus is influenced by GABA

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Wypych M., Mochol G., Foik A., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2011
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tom 71
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nr S
Previously we have shown that variability of visual responses of superior colliculus (SC) neurons depended on whether the main visual input to the cell was of Y- or W-channel origin (Mochol et al. 2010). To better understand the mechanisms underlying previous finding in this study we test whether GABAergic system influences the variability of SC visual responses. In acute experiments on anesthetized cats extracellular responses of single neurons to spot of light moving in broad range of velocities were recorded from retinorecipient, superficial layers of SC, allowing to determine the Y- or W-channel input. Simultaneously local iontophoretic injections of GABA (nonspecific GABA receptors agonist) or bicuculline (GABAA receptors antagonist) were performed. Trial-by-trial variability was assessed with Fano factor (FF; ratio of variance of spike counts to mean number of spikes in a given period of time). In the majority of cells application of GABA resulted in decrease of firing rate (FR) and changes of FF. These changes were consistent with previously found correlations between FR and FF. If major input to the tested neuron was of Y-channel origin and changes in FF correlated negatively with changes in FR, GABA-induced decrease of FR was accompanied by an increase of FF. In the case of major W-type input the result was opposite: FF followed changes in FR, consistent with positive correlation between the two in control trials. Injection of bicuculline however, which typically resulted in an increase of neural activity, did not lead to coherent changes of variability. The FF could change slightly or remain unchanged independently of the correlation of FF and FR in control trials. Our results show that GABAergic system may play different roles in shaping the reliability of visual responses in SC depending on the origin of visual input and types of GABA receptors involved. Supported by Polish MSHE grant N N303 070234.
3

Effect of temporary inactivation of rat visual cortex on visual responses in the superior colliculus

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Kordecka K., Foik A., Wierzbicka A., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2017
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tom 77
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nr Suppl.1
INTRODUCTION: It is generally accepted that neuronal plasticity can be induced at the cortical level. In our previous study we observed that relatively strong visual stimulation enhanced responses both at the cortical and subcortical level. The backward projection from the visual cortex to superior colliculus (SC) may facilitate the reinforcement of response in this midbrain structure. AIM(S): In the current study we examined how inactivation of the visual cortex affects responses in the SC after visual training. METHOD(S): Visual evoked potentials (VEPs) were recorded in anesthetized rats (n=5) from the primary visual cortex (VCx) and the SC, contralateral to stimulated eye, in response to flashing white‑light‑emitting diodes (LEDs) placed 10 cm in front of the rat. Monocular visual stimulation consisted of series of 300 repetitions of light flashes with 2 s intervals, presented every 15 minutes through 3 hours. In order to temporary block the activity of the cortex after 3-hour visual stimulation, a well above the contralateral VCx was fulfilled with xylocaine solution (2.5%). During cortical inactivation a single series of visual stimulation (300 stimulus repetitions) was presented and the SC VEP amplitudes were analysed. RESULTS: Chemical inactivation resulted in strong attenuation of cortical VEP amplitudes. In the case of the SC, cortical deactivation did not cause any significant difference in VEP amplitudes as compared to responses after 3 h of visual training. Collicular VEPs were still at the high level and significantly differed from control recording at the beginning of training, which indicates a minor impact of the VCx on response enhancement in the SC. CONCLUSIONS: Temporary deactivation of the visual cortex didn’t result in decline of VEP amplitudes in the SC, which indicates that increase of responses in SC after visual training is most likely due to enhancement of the retinal input to the SC. FINANCIAL SUPPORT: Supported by the Polish National Science Center grant Symfonia 1 (2013/08/W/NZ4/00691).
4

Oscillations in the activity of superior colliculus neurons: locked or non-locked to visual stimulus?

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Foik A., Mochol G., Wypych M., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
|
2011
|
tom 71
|
nr S
It is suggested that oscillatory activity of visual neurons plays an important role in encoding of information about stimuli. There are a number of publications on oscillations in the retino-geniculo-cortical pathway, but less is known about oscillatory activity in the extrageniculate pathway. We try to understand the role of oscillations in the processing of visual information in the superior colliculus (SC), the first, retinorecipient structure of the extrageniculate pathway, playing an important role in visual perception, spatial localization of an object of interest, saccadic eye movements and visually guided behavior. Extracellular single unit activity was recorded from superficial layers of the SC in anesthetized and paralyzed cats. Recordings were performed during periods without visual stimulation and also during visual stimulation with spot of light moving in a broad range of velocities or flashing at different locations of the receptive field in pseudo-random order. Autocorrelation function and Fourier transform were calculated for background as well as for evoked neuronal activity. Two variants of autocorrelation method revealed two kinds of oscillatory patterns: non-locked and locked to stimulus onset. First type of oscillations was found in the majority of analyzed cells during visually evoked activity and the frequency patterns of these oscillations were in many cases similar to those observed in background activity. The stimulus-locked oscillations were observed in about half of recorded cells and strength of these oscillations varied depending on firing rate, stimulus velocity and direction. Such oscillations were clearly visible in the case of fast changes in the receptive field of tested neuron. Since two types of oscillations occurred independently and sometimes simultaneously in the recorded activity, thus they may play different role in the processing of visual information by collicular neurons. Supported by Polish MSHE grant N N303 070234.
5

How does the firing rate of superior colliculus neurons correlate with image of brain activity?

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Moloch G., Wypych M., Foik A., Wojcik D., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2011
|
tom 71
|
nr S
Firing rate of the majority of cells from superficial layers of cat’s superior colliculus (SC) is modulated in relatively long time scale. Such changes in spike generation do not depend on presented visual stimuli. To investigate whether these modulations of firing rate are related to changes in cortical states we analyzed visually evoked activity of SC neurons and electrocorticogram (ECoG) simultaneously recorded from the occipital lobe. The extracellular single unit activity was recorded from superficial, retinorecipient layers of the SC in anaesthetized and paralyzed cats. The level of anaesthesia was kept constant during recordings. As a visual stimulus we used light spot moving with different, randomly selected velocities. On average, each neuron was recorded continuously for 1 hour. Simultaneously we recorded ECoG from contralateral area 18 close to representation of the area centralis. The power spectra of ECoG data were calculated using fast Fourier transform in sliding windows. The firing rate of a given neuron was calculated in the same time windows and then correlated with the power in a given frequency band of ECoG. Most of the observed firing rate modulations were on the time scale from several to tens of minutes and were positively or negatively correlated with the changes in ECoG power in the band between 0.5 to 8 Hz, sometimes even to 13 Hz. For some neurons we also observed correlations between firing rate and power in the beta band (13 – 30 Hz) of ECoG and in most cases those correlations were opposite to correlations in lower bands. Rarely we observed also the relation between firing rate and the power of gamma band. Fast modulations of firing rate were not correlated with changes of ECoG power in any band. These results show that responsiveness of particular subpopulations of collicular neurons is differently related to the global state of brain activity. Supported by Polish MSHE grant N N303 070234.
6

Sensory experience influences magnitude of responses in the rat visual system

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Zeber K., Foik A., Urban P., Porowska A., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2015
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tom 75
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nr Supl.
BACKGROUND AND AIMS: The aim of this study was to evoke plasticity in chosen structures of the rat visual system by visual training (sensory experience). METHODS: Local field potentials (LFPs) were recorded from the rat superior colliculus (SC) and primary visual cortex (VCx) of contralateral hemisphere to stimulated eye. LFPs were collected before, during and after visual training. The training consisted of series of 300 repetitions of light flashes separated by 2–3 s intervals. The series of stimuli were presented to the one eye every 15 minutes through three hours. RESULTS: Our data show that visual stimulation significantly enhanced magnitude of visual responses in both recorded structures. A significant increase of visual responses occurred after first hour of training (four stimulating series) both in SC and VCx. The largest increase of VEP amplitudes in the SC was observed after the third hour of stimulation and that was significantly different compared to the first and the second hour of training. Regarding the VCx, advanced alterations of VEPs were observed already after the first hour and then the amplitudes of cortical VEPs remained at a similar level to the end of training. To examine whether the above changes did not result from the changes in the level of anesthesia and global brain state, we considered the VCx LFP power ratio in delta (1–4 Hz) and beta (13–30 Hz) frequency range of the signal recorded for 30 s before each series of stimulation. Changes in the course of delta/beta ratio were similar for all channels in VCx during three hours of visual training and didn’t correlate with increase of VEPs. CONCLUSIONS: Repetitive visual stimulation enhance responses in the visual system, both at cortical and subcortical level, independently of the global brain state, thus may constitute a fundamental approach to improve visual functions. Supported by ERA-NET Neuron project REVIS.
7

Stimulus dependent oscillations in visually evoked activity of cat's superior colliculus

88%
Foik A., Silva A., Wypych M., Mochol G., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2012
|
tom 72
|
nr 2
Visual information is transferred from retina to higher order cortical areas by few parallel pathways and encoded in different ways. In this study, we focused on encoding of visual information in the superior colliculus, which is the first stage of extrageniculate pathway. One of ways in which neurons encode information is rate coding based on the change in a number of action potentials in response to stimulus presentation. The other coding scheme is temporal coding, which include information about temporal patterns of neuronal spiking, present, for example, in the form of oscillations. The aim of this study was to reveal the presence of stimulus dependent oscillations in visually evoked activity of neurons in the superficial layers of the cat’s superior colliculus. Neuronal activity was recorded from anesthetized (isoflurane in N2O/O2) animals during visual stimulation by spot of light moving in broad range of velocities as well as during presentation of light spot flashing in random locations within the receptive field of recorded neuron. Oscillations were identified by means of auto-correlation and spectral analyses. We found stimulus dependent oscillations in half of tested neurons. Moreover, oscillatory activity appeared to depend on the stimulus velocity. Different measures of oscillations strength (SO), such as z-score, oscillation score or F-statistics revealed positive correlation between SO and velocity. Stimulus dependent oscillations appeared also in responses to onset of the light spot. These results suggest importance of oscillations for processing of information about fast changes within receptive fields of neurons in the extrageniculate pathway. Supposedly presence of oscillations in responses of collicular cells can increase probability of information transfer to higher level of visual processing. Supported by NCN grant N N303 820640.
8

Focal cortical stroke in the cat visual cortex

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Szczerba M., Urban P., Foik A., Kublik E., Ghazaryar A., Borowska J., Sadowska M., Jablonka J., Waleszczyk W.
Acta Neurobiologiae Experimentalis
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2015
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tom 75
|
nr Supl.
BACKGROUNS AND AIMS: The study develops methodology of photothrombotic stroke (PtS) induction in cats visual cortex for future studies of post-stroke visual recovery. Considering its well known organisation and similarity to the human, cat visual system is a good model for spontaneous and supported brain reorganisation after ischemia. METHODS: Photothrombosis was used as a model of focal ischemic cortical stroke. Standardisation of the methodology of cortical PtS was performed on four experimental cats with parallel local field potential (LFP) recordings in and around the stroke core – before, during and after the infarct. Intravenously injected Bengal Rose was locally irradiated by cold light via an optic bundle placed on the skull, thinned skull or directly on dura surface. Different light source parameters and irradiation time were tested. Postoperatively isolated brains were preserved and frozen, cut and stained. Final position of the electrodes was monitored on dried 50 μm slices. The cytochrome oxidase (CO) activity and Nissl staining were used to monitor the state of the tissue injury. RESULTS: The aimed unilateral stroke was performed in the dorsal zone of the left marginal gyrus over the visual cortex on a border of the cortical areas 17 and 18. CO visualizes the areas of lower mitochondrial activity in the illuminated tissue of the irradiated cortex in comparison to the contralateral intact homotopic areas. The spontaneous LFP dynamic decreased for at least three hours within the irradiated cortex but not in opposite hemisphere or surrounding tissue. CONCLUSIONS: The 25 minutes of the unilateral irradiation directly to the dura surface with the light temperature 2750K resulted in the most accurate lesion covering all the width of the marginal gyrus and partially the sulcus area not spreading on adjacent gyri or further blood vessels. The infarct reaches the white matter without its pronounced injury. Supported by:ERA-NET:REVIS&MNiSW0292/IP1/2013/72.
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