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Biomedical subjects

D Shulz

Publications and source records attributed to D Shulz.

8 recordsLinked to original sources
PubMed1995

A multi-electrode array for combined microiontophoresis and multiple single-unit recordings.

A remotely controlled multi-electrode array, equipped with a combined electrode (CE) and 3 regular tungsten-in-glass electrodes (TEs) is described. The CE enables ejection of different neuroactive substances from 6 barrels and recording of single-unit activity from the etched tungsten rod placed in the central glass capillary. The CE is prepared with standard tungsten rod, glass-capillaries, and regular micropipette pullers. Such CEs possess a good stiffness-flexibility balance, length, easy cell isolation, high stability of recordings, effective ejection properties, and ability to survive penetration of dura. The efficiency of a 4-electrode array, including the CE, was tested by recording the effects of extracellularly ejected drugs (glutamate, acetylcholine and atropine) on single neurons in the auditory cortex of anesthetized guinea pigs. Induced modifications of single-neuron firing patterns and evoked responses were in agreement with the known effects of individual and combined applications of these drugs. Using this multi-electrode array and spike sorting techniques, the pharmacological environment of up to 12 simultaneously recorded cells can be modulated, and its effect on single neurons and on their interactions can be monitored at distances of up to 900 microns from the CE's tip.

Action Potentials↗
PubMed1992

Synaptic origin of rhythmic visually evoked activity in kitten area 17 neurones.

Rhythmic patterns in neuronal activity in response to moving stimuli were observed in 28% of cells recorded extracellularly or intracellularly in area 17 of 4-16 week old anaesthetized and paralysed kittens. In both recording modes, oscillation frequencies ranged between 7 and 71 Hz, and were confined for 88% of cells in the 7-20 Hz band of the spectrum. A comparative study of firing autocorrelograms) and subthreshold activity (autocorrelation functions) indicates that the regularity of discharge stemmed from visually evoked oscillations of membrane potential at the same frequency. These oscillations are shown to result from extrinsic excitatory activity, since their amplitude, but not their frequency, depends on the resting membrane potential. The dependency on stimulus configuration supports the hypothesis that oscillations in neuronal output are dictated by periodic activity in afferent circuits selectively recruited by different attributes of the visual input which are not exclusively processed at the cortical level.

Animals↗
PubMed1992

Cellular analogs of visual cortical epigenesis. I. Plasticity of orientation selectivity.

A differential pairing procedure was applied in vivo to individual neurons in the primary visual cortex of anesthetized paralyzed cats, in order to produce changes in their relative orientation preference. While we recorded from a single cell, its visual response to a light bar was driven iontophoretically to a "high" level when stimulating with an initially nonpreferred orientation (S+), and alternately reduced to a "low" level when stimulating with the preferred orientation (S). This associative procedure was devised to test the possible role of neuronal coactivity in controlling the plasticity of orientation selectivity. Among 87 cells tested, 35 (40%) showed significant long-lasting changes, either in the relative orientation preference for the two "paired" stimuli S+ and S-, in the global orientation tuning profile, or in both. Measurements of relative orientation preference demonstrated significant effects in 27 cells (31%), all in favor of the positively reinforced orientation (S+). Modifications of orientation selectivity (studied over the entire orientation spectrum in 45 of the conditioned cells) usually consisted (21 out of 25 modified cells) of a competitive reorganization of the orientation tuning curve: the preferred orientation shifted toward S+, and a loss of relative visual responsiveness was observed for orientations close to the negatively reinforced orientation (S-). The largest changes were found in deprived kittens at the peak of the critical period, although the probability of inducing a significant change studied during the first year of postnatal life was independent of age. These functional modifications demonstrated at the cellular level are analogous to those induced by a global manipulation of the visual environment, when only a restricted spectrum of orientations is experienced during the critical period. Our results support the hypothesis that covariance levels between pre- and postsynaptic activity determine the sign and the amplitude of the modification of efficacy of cortical synapses.

Animals↗
PubMed1992

Cellular analogs of visual cortical epigenesis. II. Plasticity of binocular integration.

Two differential pairing procedures were applied in the primary visual cortex of anesthetized and paralyzed kittens and cats, to produce changes in ocular dominance and interocular orientation disparity (IOD) during the time of recording of a single neuron. A first experiment was devised to demonstrate plasticity in the balance of monocular responses. The visual activity of the cell was driven iontophoretically to either a "high" or a "low" level, depending on the ocularity of the visual stimulation. Ocular dominance measurements before and after pairing revealed significant long-lasting changes in 33% of cases. Relative ocular preference shifted in most cases (87.5%) in favor of the reinforced eye. Similar proportions of significant changes were observed in kitten and adult cortex. The amplitude of the functional modifications was not significantly related with age, although the largest changes in ocular dominance were recorded at the peak of the critical period. The second experiment more specifically addressed the plasticity of binocular interaction. The activity of a binocular cell was driven iontophoretically to either a "high" or a "low" level, depending on the orientation disparity between two oriented stimuli, presented simultaneously and separately in the receptive field of each eye. Significant long-lasting changes in binocular responses were induced in 40% of cases. The relative IOD preference generally shifted (67%) in favor of the reinforced disparity. In half of the modified cells, functional changes were expressed only in the dichoptic viewing condition used during the pairing procedure. These functional modifications of binocular integration, demonstrated at the cellular level, are analogous to those induced by global manipulations of the visual environment (Hubel and Wiesel, 1970; Shinkman and Bruce, 1977). They are interpreted as evidence for synaptic plasticity. Our results support the hypothesis that covariance levels between pre- and postsynaptic activities determine the sign and the amplitude of changes in synaptic efficacy.

Animals↗
PubMed1988

A cellular analogue of visual cortical plasticity.

Neuronal activity plays an important role in the development of the visual pathway. The modulation of synaptic transmission by temporal correlation between pre- and postsynaptic activity is one mechanism which could underly visual cortical plasticity. We report here that functional changes in single neurons of area 17, analogous to those known to take place during epigenesis of visual cortex, can be induced experimentally during the time of recording. This was done by a differential pairing procedure, during which iontophoresis was used to artificially increase the visual response for a given stimulus, and to decrease (or block) the response for a second stimulus which differed in ocularity or orientation. Long-term modifications in ocular dominance and orientation selectivity were produced in 33% and 43% of recorded cells respectively. Neuronal selectivity was nearly always displaced towards the stimulus paired with the reinforced visual response. The largest changes were obtained at the peak of the critical period in normally reared and visually deprived kittens, but changes were also observed in adults. Our findings support the role of temporal correlation between pre- and postsynaptic activity in the induction of long-lasting modifications of synaptic transmission during development, and in associative learning.

Afferent Pathways↗
PubMed1988

Exponential data-analysis of passive-avoidance behavior in rats and mice.

Data obtained with the passive-avoidance task are usually presented as the median values of the latencies to respond. In an earlier publication we described a better way of presenting such data based on the observation that the complement of the cumulative distribution of step-through latencies can be closely fitted by a simple exponential function. Thus the "step-through rate constant" (STRC) is concise and accurate quantitative description of population behavior in this test. In this paper we present two examples of the application of this procedure. In the first, variation in the interval between training and testing in rats changes the STRCs of the different groups. In the second (based on data published by Flood et al.) administration of cycloheximide is seen to partition the experimental population of mice into two subgroups with different STRCs.

Animals↗
PubMed1986

A novel method for quantifying passive-avoidance behavior based on the exponential distribution of step-through latencies.

In the extensive literature dealing with the one-trial passive-avoidance task the data are usually represented by the median latency to respond. We propose here a novel representation and analysis of passive-avoidance data which is based on the observation that the complement of the cumulative distribution of step-through latencies (i.e., the fraction of animals remaining in the safe compartment) decays exponentially with time from the onset of the trial. A remarkably close fit of this complementary distribution is seen when the best-fitting straight line is drawn through the data points plotted on semilog coordinates. The slope of this line k, which we call "the step-through rate constant," (or alternatively, the T1/2 which is equal to 0.69/k) provides an accurate description of the population behavior as a whole in most cases. In view of the exponential distribution of passive-avoidance data this treatment appears to be more appropriate than the widely-used measures of central tendency, the median and mean. It is applicable to research on the effects of drugs on passive-avoidance memory, and probably appropriate to other behavioral paradigms and species.

Animals↗