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K Funke

Publications and source records attributed to K Funke.

At least 19 recordsLinked to original sources
PubMed2001

Changes of contrast gain in cat dorsal lateral geniculate nucleus by dopamine receptor agonists.

The modulatory effects of dopamine (DA) on the contrast gain of retino-geniculate transmission were tested with local micro-iontophoretical application of DA and the DA receptor agonists SKF38393 (SKF, D1/D5) and quinpirole (QUIN, D2/D3/D4) while recording visually induced spike activity of relay cells of the dorsal aspect of cat lateral geniculate nucleus (dLGN) in the anesthetised and paralyzed preparation. DA and QUIN could either facilitate or inhibit visual activity in a dose-dependent fashion: small amounts caused a facilitation while larger quantities resulted in a more (DA) or less (QUIN) strong inhibition. The effect of SKF was almost always suppressive and increased with the amount of drug applied. The absolute change in activity was depending on stimulus contrast and the strength of the elicited response: facilitation and inhibition of activity was proportional to stimulus contrast and response strength and thus resulted in a changed contrast gain. The results indicate that the visual deficits found in Parkinson's disease patients my be not solely related to retinal dysfunctions.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed2001

Changes in response modulation of cat perigeniculate neurons related to EEG state and application of neuromodulators.

Spike activity of single perigeniculate (PGN) neurons was recorded in the anaesthetized (N2O/halothane) and paralysed cat during presentation of moving gratings of optimal spatial frequency. Typically, the ongoing (tonic, spontaneous) activity of PGN cells increased during a rise in EEG delta power accompanied by a reduction and often a total loss of spike rate modulation by the moving grating. The opposite behaviour was found when the EEG delta power vanished. Micro-iontophoretically applied acetylcholine (ACh) had an effect similar to a decrease in EEG delta power, decreasing ongoing activity but increasing the response modulation depth. The opposite effect could be achieved with the excitatory action of serotonin (5-HT), mimicking a strengthened EEG delta power. These data support previous data indicating that PGN neurons contribute to spatio-temporal tuning of subcortical visual activity in a state-dependent way.

Acetylcholine↗
PubMed2000

Quantitative aspects of the state-dependent co-variation of cat lateral geniculate and perigeniculate visual activity.

The quantitative relationship between EEG-related changes in the visual activity of perigeniculate (PGN) and lateral geniculate (LGN) neurons with overlapping receptive fields was analyzed in the anesthetized and paralyzed cat. While transient response peaks were independent of the EEG state, we found opposite changes in spontaneous activity and tonic visual responses, with PGN cells increasing and LGN cells decreasing their spontaneous/tonic activity with increasing EEG delta activity in most cases. The tonic firing rates of PGN and LGN cell pairs were clearly correlated with a slope of about -0.5. Thus, LGN firing was low when PGN activity was high and vice versa. With a change from low to high EEG delta activity the difference between the tonic responses of PGN and LGN cells increased on average by 50 spikes/s, both for the whole population and at the single cell level, indicating that state-dependent changes in retino-geniculate transmission are regulated by a distinct ratio of PGN-LGN activity.

Action Potentials↗
PubMed2000

The size of the CAG repeat in exon 1 of the androgen receptor gene shows no significant relationship to impaired spermatogenesis in an infertile Caucasoid sample of German origin.

The androgen receptor (AR) gene, located on the X-chromosome at Xq11-12, contains in exon 1 a polymorphic CAG repeat which codes for a polyglutamine tract. Contractions of the CAG repeat are said to be related to prostate cancer. In contrast, sizeable expansion of the CAG repeat can cause spinal and bulbar muscular atrophy (SBMA). In infertile patients of Chinese origin and in a Melbourne multinational population impaired sperm production has been postulated to be related to moderate expansions of the polyglutamine tract. In a study of a Swedish population of infertile patients these findings could not be corroborated. The aim of our investigation was to examine the correlation between the length of the CAG repeat and impaired sperm production in an infertile Caucasoid patient sample of German ethnic origin. We found no statistically significant relationship between the size of the CAG repeat or polyglutamine tract and idiopathic impaired sperm production in the population studied. The variability of the results by various investigators may be attributed to different ethnic origins and hence different genetic modifiers of the populations studied and/or to the high probability that these infertile males may represent a heterogeneous group with respect to the causes of defective spermatogenesis.

Adult↗
PubMed1999

Correlated variations in EEG pattern and visual responsiveness of cat lateral geniculate relay cells.

1. Simultaneous recordings of the EEG and the visual activity of cat dorsal lateral geniculate nucleus (dLGN) relay cells were analysed for covariance. Sliding time-window analyses were performed in parallel for the EEG power spectrum and single unit visual activity. The EEG power ratio (EEG-PR) of low (1-8 Hz) to high (20-40 Hz) frequencies was chosen to achieve a quantitative measure of the EEG which could be compared with the spike rate of a dLGN unit at any time. A high EEG-PR value indicates a synchronized EEG dominated by low frequencies (delta waves and sleep spindles), a low value indicates a less synchronized EEG. 2. In the anaesthetized animal, two different underlying patterns of activity in the EEG-PR were found: slow gradual changes (slow gradations) and oscillatory changes. In many cases both were accompanied by correlated variations in dLGN spike rate, either for overall activity or for burst firing. 3. The slow gradations appear for long time periods of up to 200 s and, in most cases (76.3 %), show a negative correlation between EEG-PR and overall spike rate, but predominantly a positive correlation for burst firing (85.1 %). 4. The oscillatory changes, which have not previously been reported, appear as temporally well-coupled variations in EEG-PR and spike rate with a stable cycle length within the range 4-10 s. In about 77 % of correlated changes the temporal delay between the change in EEG-PR and that of the spike rate was less than +/- 1.0 s. 5. During simultaneous recordings from two dLGN cells the variations in spike rate tend to show the same sign of correlation with respect to the EEG pattern. This relationship is more pronounced with the slow gradations than with the oscillatory changes. 6. Slow gradations in the spectral composition of the EEG may indicate global transitions between different stages within the sleep-wake cycle, reflecting the well-known influences of the brainstem arousal system. The oscillations in the spectral composition of the EEG are accompanied by gradual variations in thalamic transmission mode and are more likely to be due to involvement of a local feedback system via the thalamo-cortico-thalamic loop. The difference between the effects on overall and burst firing activity supports the notion that phasic (burst firing) and tonic visual responses may play distinctive roles in information processing, which are functionally related to the animal's behavioural state.

Animals↗
PubMed1998

State-dependent receptive-field restructuring in the visual cortex.

To extract important information from the environment on a useful timescale, the visual system must be able to adapt rapidly to constantly changing scenes. This requires dynamic control of visual resolution, possibly at the level of the responses of single neurons. Individual cells in the visual cortex respond to light stimuli on particular locations (receptive fields) on the retina, and the structure of these receptive fields can change in different contexts. Here we show experimentally that the shape of receptive fields in the primary visual cortex of anaesthetized cats undergoes significant modifications, which are correlated with the general state of the brain as assessed by electroencephalography: receptive fields are wider during synchronized states and smaller during non-synchronized states. We also show that cortical receptive fields shrink over time when stimulated with flashing light spots. Finally, by using a network model we account for the changing size of the cortical receptive fields by dynamically rescaling the levels of excitation and inhibition in the visual thalamus and cortex. The observed dynamic changes in the sizes of the cortical receptive field could be a reflection of a process that adapts the spatial resolution within the primary visual pathway to different states of excitability.

Animals↗
PubMed1998

The influence of corticofugal feedback on the temporal structure of visual responses of cat thalamic relay cells.

1. Visually driven single-unit activity was recorded in the dorsal lateral geniculate nucleus (dLGN) of the anaesthetized cat while inactivating or stimulating the corticofugal feedback from area 17/18 by means of cortical cooling or application of GABA (inactivation), or application of glutamate or quisqualate (Glu, Quis; stimulation) to layer VI. 2. Manipulations of the corticofugal feedback primarily affected the multimodal interspike interval pattern previously reported to be present in the tonic component of visual responses elicited by spot-like stimuli. 3. Sixty-three per cent of all neurons could be influenced, and temporally localized interspike interval distributions were measured which commonly consisted of one fundamental interval peak (leftmost peak) and integer multiples thereof (higher order peaks). During blockade of the corticofugal feedback, interspike intervals were redistributed into the higher order peaks in about 70 % of the cases, accompanied by a reduced mean firing rate. During stimulation the reverse effect occurred in 69 % of cases. 4. Increased synchronization of the EEG (increased power in the delta-wave range, 1-4 Hz) had an effect similar to cortex inactivation. The specificity of corticofugal effects was verified by consideration of these EEG effects and by dLGN double recordings with one dLGN cell topographically matched with the cortical inactivation/activation site and the second cell outside this area. Clear effects due to manipulation of the corticofugal feedback were found only for the matched dLGN site. 5. In addition we observed that the peaks of the interval distributions were narrower during active corticofugal feedback, such that the temporal dispersion of the signal transmission to the cortex was reduced. 6. The mechanisms underlying this effect were further analysed in a biophysically realistic model demonstrating that the timing of the spikes in the dLGN is improved as soon as the cortical feedback is active. The high degree of convergence/divergence between neurons along the closed feedback loop thereby leads to a temporal averaging effect which reduces the interval dispersion and also introduces synchronization between dLGN cells. 7. Such a mechanism may thus counteract the deterioration of spike timing accuracy which would otherwise occur as a consequence of synaptic noise and other uncorrelated sources of activity at a given neuron.

Action Potentials↗
PubMed1997

On the significance of temporally structured activity in the dorsal lateral geniculate nucleus (LGN).

Higher organisms perceive information about external or internal physical or chemical stimuli with specialized sensors that encode characteristics of that stimulus by a train of action potentials. Usually, the location and modality of the stimulus is represented by the location and specificity of the receptor and the intensity of the stimulus and its temporal modulation is thought to be encoded by the instantaneous firing rate. Recent studies have shown that, primarily in cortical structures, special features of a stimulus also are represented in the temporal pattern of spike activity. Typical attributes of this time structure are oscillatory patterns of activity and synchronous discharges in spatially distributed neurons that respond to inputs evoked by a coherent object. The origin and functional significance of this kind of activity is less clear. Cortical, subcortical and even very peripheral sources seem to be involved. Most of the relevant studies were devoted to the mammalian visual system and cortical findings on temporally structured activity were reviewed recently (Eckhorn, 1994, Progr. Brain Res., Vol. 102, pp. 405-426; Singer and Gray, 1995, Annu. Rev. Neurosci., Vol. 18, pp. 555-586). Therefore, this article is designed to give an overview, especially of those studies concerned with the temporal structure of visual activity in subcortical centers of the primary visual pathway, which are the retina and the dorsal lateral geniculate nucleus (LGN). We discuss the mechanisms that possibly contribute to the generation and modulation of the subcortical activity time structure and we try to relate to each other the subcortical and cortical patterns of sensory activity.

Action Potentials↗
PubMed1996

Linear and non-linear components in the centre-surround response of X- and Y-cells in the cat lateral geniculate nucleus.

Thalamocortical projection cells of cat dorsal lateral geniculate nucleus (dLGN) have been described to exhibit different types of non-linear integration of spatial contrast in addition to the linear integration inside their classical receptive field (CRF). We analysed whether a single mechanism might generate the two harmonic distortions of a linear response elicited inside the CRF and the shift effect elicited from regions outside the CRF. Therefore, both non-linear response types were investigated with identical stimulus conditions in the same cell. A quantitative analysis revealed that both response types can be elicited in nearly all Y-cells and in at least 50% of the X-cells. With blockade of GABA(A) inhibition by bicuculline methiodide (BICU) the number of X-cells with shift effect (SE) and second harmonics (2H) increased to more than 80%. Both, SE and 2H exhibited significantly correlated variations in their response-amplitude and -latency and in the frequency of their occurrence with changes in stimulus parameters (contrast, spatial frequency, area) and during BICU application. We assume that both non-linear contrast responses, the SE and the 2H might depend on the same (most probably retinal) mechanisms. We further suggest that the principal organisation of X- and Y-cell receptive fields might be very similar and that the differing spatial contrast responses may result from the different spatial resolution of their CRF subunits.

Animals↗
PubMed1996

Corticofugal feedback improves the timing of retino-geniculate signal transmission.

The temporal accuracy of visually induced spike patterns can be expected to deteriorate with increasing distance from the retina due to synaptic noise and other sources of activity unrelated to the retinal signal. Here we report the opposite effect: the interspike interval distributions of relay cells of cat lateral geniculate nucleus (LGN) are sharper than those of their retinal afferents. A biophysically realistical simulation of the retino-cortical pathway, including excitatory cortico-geniculate feedback, produced a similar effect. Without the feedback the mean firing rate in the LGN dropped and interval peaks broadened by an average of 25%. The same effect was found during reversible experimental inactivation of the visual cortex in cat. This indicates that cortico-geniculate feedback could be employed to improve the temporal accuracy of signal transmission.

Afferent Pathways↗
PubMed1996

Utilizing latency for object recognition in real and artificial neural networks.

A consistent analysis of a visual scene requires the recognition of different objects. In vertebrate brains this could be achieved by synchronization of the activity of disjunct nerve cell assemblies. During such a process cross-talk between spatially adjacent image parts occurs, preventing efficient synchronization. Temporal differences, naturally introduced by stimulus latencies in every sensory system, were utilized in this study to counteract this effect and strongly improve network performance. To this end in our model the image is 'spread out' in time as a function of contrast-dependent visual latencies, and synchronization of cell assemblies occurs without mutual disturbance. The network model requires a direct link between visual latencies and the onset of synchronous oscillations in cortical cells. This was confirmed experimentally.

Cognition↗
PubMed1995

Temporal structure in the light response of relay cells in the dorsal lateral geniculate nucleus of the cat.

1. The spike interval pattern during the light responses of 155 on- and 81 off-centre cells of the dorsal lateral geniculate nucleus (LGN) was studied in anaesthetized and paralysed cats by the use of a novel analysis. Temporally localized interval distributions were computed from a 100 ms time window, which was shifted along the time axis in 10 ms steps, resulting in a 90% overlap between two adjacent windows. For each step the interval distribution was computed inside the time window with 1 ms resolution, and plotted as a greyscale-coded pixel line orthogonal to the time axis. For visual stimulation, light or dark spots of different size and contrast were presented with different background illumination levels. 2. Two characteristic interval patterns were observed during the sustained response component of the cells. Mainly on-cells (77%) responded with multimodal interval distributions, resulting in elongated 'bands' in the 2-dimensional time window plots. In similar situations, the interval distributions for most (71%) off-cells were rather wide and featureless. In those cases where interval bands (i.e. multimodal interval distributions) were observed for off-cells (14%), they were always much wider than for the on-cells. This difference between the on- and off-cell population was independent of the background illumination and the contrast of the stimulus. Y on-cells also tended to produce wider interval bands than X on-cells. 3. For most stimulation situations the first interval band was centred around 6-9 ms, which has been called the fundamental interval; higher order bands are multiples thereof. The fundamental interval shifted towards larger sizes with decreasing stimulus contrast. Increasing stimulus size, on the other hand, resulted in a redistribution of the intervals into higher order bands, while at the same time the location of the fundamental interval remained largely unaffected. This was interpreted as an effect of the increasing surround inhibition at the geniculate level, by which individual retinal EPSPs were cancelled. A changing level of adaptation can result in a mixed shift/redistribution effect because of the changing stimulus contrast and changing level of tonic inhibition. 4. The occurrence of interval bands is not directly related to the shape of the autocorrelation function, which can be flat, weakly oscillatory or strongly oscillatory, regardless of the interval band pattern. 5. A simple computer model was devised to account for the observed cell behaviour. The model is highly robust against parameter variations.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1995

Possible enhancement of GABAergic inputs to cat dorsal lateral geniculate relay cells by serotonin.

The possible enhancement of inhibitory inputs to relay cells of the dorsal lateral geniculate nucleus (dLGN) by serotonin (5-HT) was studied during blockade of GABAA-receptor mediated inhibition with bicuculline (BICU). Visually induced spike activity of single units was recorded during simultaneous micro-iontophoretic application of BICU or 5-HT. All 28 relay cells studied were disinhibited by BICU and strongly inhibited by 5-HT. The responses during BICU or 5-HT were on average statistically different from the controls (p < 0.01, Student's t-test). The inhibition by 5-HT could be almost totally abolished by the simultaneous application of BICU and responses during the combined application of both substances were only slightly different from those obtained during BICU alone (p < 0.3).

Animals↗
PubMed1995

Differences in the temporal dynamics of the visual ON and OFF pathways.

The temporal structure of spike trains recorded from optic fibers and single units of the lateral geniculate nucleus (LGN) and primary visual cortex of the cat was studied with a novel method of inter-spike interval analysis. ON type relay cells of the LGN exhibited a multimodal interval distribution preferring a distinct interval (fundamental interval) and its multiples during the sustained light response, whereas most OFF cells showed a broad, unimodal distribution. The general pattern of the interval distribution was relatively independent of stimulus size and contrast and the degree of light adaptation. Simultaneously recorded S-potentials originating from the retinal input generally produced only a single peak at the fundamental interval length. Therefore, the multimodal interval distribution of LGN cells seems to be a result of intra-geniculate inhibition. Cortical cells also showed a weak tendency to fire with spike intervals similar to LGN cells. Therefore, the regular firing pattern observed at peripheral stages of the visual pathway can persist at higher levels and might promote the occurrence of oscillatory activity.

Animals↗
PubMed1995

A characteristic ventricular shape in myelomeningocele-associated hydrocephalus? A CT stereology study.

We measured the volume of the supratentorial ventricles in 39 consecutive children with myelomeningocele (MMC) and associated hydrocephalus, using a stereological method based on the Cavalieri theorem of systematic sampling. We distinguished the following groups: newborns before and after cerebrospinal fluid shunting (14), a somewhat larger group of newborns with an untreated MMC-associated hydrocephalus (25) and a group of shunted children at a mean age of 1.5 years (28). We paid special attention to the shape of the lateral ventricles, looking separately at the anterior and posterior halves. The measurements were compared with a healthy control group (10) and with children with hydrocephalus unrelated to MMC (15). The average volume ratio of the posterior to the anterior half of the lateral ventricles was 1.05 +/- 0.39 in non-hydrocephalic children, 1.11 +/- 0.55 in untreated hydrocephalic children without MMC, and 2.15 +/- 0.65 in MMC-associated hydrocephalus prior to shunting. These ratios did not change significantly after shunting. This confirms our impression that MMC-associated hydrocephalus shows a characteristic shape, with a disproportionate enlargement of the posterior part of the lateral ventricles, in clear contrast to the normal-width frontal horns. This shape is reminiscent of the fetal ventricular shape. It reveals disturbance of brain development in children with MMC, which goes beyond the classic description of the Chiari malformation.

Arnold-Chiari Malformation↗
PubMed1993

Modulatory effects of acetylcholine, serotonin and noradrenaline on the activity of cat perigeniculate neurons.

We studied the modulatory actions of microiontophoretically applied acetylcholine (ACH), serotonin (5-HT, 5-hydroxytryptamine) and noradrenaline (NA), and those of the adrenoceptor agonists phenylephrine (PHE, alpha 1), clonidine (CLO, alpha 2) and isoprenaline (ISO, beta) on spontaneous and visually induced activities in cat perigeniculate (PGN) and thalamic reticular (NRT) neurons (only spontaneous) during extracellular recordings performed in vivo. ACH and 5-HT were found to affect the ongoing (spontaneous) and visually evoked activity of PGN cells and also the spontaneous activity of NRT cells in an opposite fashion. ACH inhibited tonic firing and often induced burst activity. By contrast, 5-HT exerted an excitatory influence, which caused a long-lasting, very regular, high-frequency activity between about 35 and 120 Hz. Spontaneous as well as 5-HT-induced firing was found to prefer three distinct frequency ranges: 35-42 Hz, 60-67 Hz and 80-120 Hz. Opposite actions of ACH and 5-HT were also evident when applied simultaneously. ACH dampened the high-frequency activity elicited with 5-HT, and 5-HT could replace the burst activity induced with ACH application by a regular tonic activity. The absolute strength of visual responses (in spikes per second) was only slightly enhanced or reduced by ACH and 5-HT, respectively, but due to the strong effects on background activity, ACH clearly elevated the signal-to-noise ratio and 5-HT reduced it. Despite its excitatory action, 5-HT did not facilitate visual responses. Spontaneous changes in ongoing activity were found to affect the visual response amplitude in the same way. Noradrenaline, the alpha 1-agonist PHE and the beta-agonist ISO exerted a weak depressant action on high-frequency maintained activity, but during low-frequency single spike activity and/or burst activity a facilitatory effect was evident, which prevented the generation of burst discharges and slightly increased single spike firing. Visually evoked activity was little affected, but signal-to-noise ratio changed with changes in ongoing activity. The alpha 2-agonist CLO clearly attenuated both spontaneous activity and visual responses. We suggest that, in addition to direct effects of ACH and 5-HT on geniculate relay cells, the balance between the opposite actions of ACH and 5-HT on PGN cells determines the mode of operation in the recurrent inhibitory circuit: either a global, tonic inhibition of relay cells during a dominating 5-HT influence or a less tonic but phasic inhibition during increased activity in the cholinergic system.

Acetylcholine↗