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J Syka

Publications and source records attributed to J Syka.

At least 55 records · Page 3Linked to original sources
PubMed1984

Projections from auditory structures to the superior colliculus in the rat.

Auditory inputs to the middle and deep layers of the central area of the superior colliculus were studied in rats with horseradish peroxidase (HRP) injections into the superior colliculus. The most powerful projections were found from the dorsal nucleus of the lateral lemniscus bilaterally, with prevailing ipsilateral projections. A smaller number of labelled cells was observed in the ipsilateral external nucleus of the inferior colliculus and a few labelled cells were distributed in the dorsomedial part of the inferior colliculus ipsilaterally. Descending connections from the auditory cortex originated from the dorsal part of the ipsilateral auditory cortical area, in layer Vb.

Animals↗
PubMed1984

Binaural interaction in low-frequency neurons in inferior colliculus of the cat. IV. Comparison of monaural and binaural response properties.

We studied the monaural and binaural response properties of 82 low-frequency inferior colliculus (IC) neurons that display a clear sensitivity to changes in interaural phase. Most cells (60%) are excited by sound delivered to either ear, the remainder being excited only by stimulation of one ear; 70% of the neurons receive their stronger or sole excitatory input from the contralateral ear. A monotonic relation between spike discharge and sound pressure level (SPL) is seen in 65% of the monaural response areas, i.e., the range of stimulus frequencies and intensities effective in eliciting a response, while 30% show a nonmonotonic response pattern. In 33% of the cases there is a significant shift in the most effective frequency as a function of SPL. Most discharge patterns are classified as sustained (69%) and the remainder as onset. However, there is considerable variability within these patterns and often two types of discharges are present at different points in the same response area of a single cell. The sustained responses show a broad range of latencies, while onset patterns show a tighter distribution and shorter first spike latencies. Thus, IC neurons showing sensitivity to changes in interaural phase can differ in laterality preferences, response area characteristics, discharge patterns, and latency parameters. Given the diversity of inputs to the IC from lower brain stem structures, this heterogeneity is not surprising. For most neurons excited by stimulation to either ear, the characteristic frequencies, discharge patterns, and first spike latencies are similar, suggesting that the monaural inputs to a binaural cell are of the same type. A neuron's most effective frequencies at a particular SPL for monaural and binaural stimulation are, in general, the same. In some cases a neuron's monaural and binaural response areas can show remarkable similarities, suggesting that certain monaural features are intimately related to the binaural response. In 18% of the IC cells, phase locking to the monaural stimulating frequency is seen. When both inputs are phase locked, a simple coincidence model can predict the interaural phase or delay at which the maximal binaural discharge occurs.

Acoustic Stimulation↗
PubMed1984

Ascending and descending projections to the inferior colliculus in the rat.

The ascending and descending projections to the central nucleus of the inferior colliculus (IC) were studied with the aid of retrograde transport of horseradish peroxidase (HRP). HRP-labelled cells were found in contralateral cochlear nuclei, where the majority of different cell types was stained. Few labelled cells were observed in the ipsilateral cochlear nuclei. HRP-positive neurones were found in all nuclei of the superior olivary complex on the ipsilateral side with the exception of the medial nucleus of the trapezoid body, which was never labelled either ipsilaterally or contralaterally. The largest concentration of HRP-labelled cells was usually observed in the ipsilateral superior olivary nucleus. Smaller numbers of labelled cells were present in contralateral nuclei of the superior olivary complex. Massive projections to the inferior colliculus were found from the contralateral and ipsilateral dorsal nucleus of the lateral lemniscus and ipsilateral ventral nucleus of the lateral lemniscus. Many neurones of the central and external nuclei of the contralateral inferior colliculus were labelled with HRP. Topographic organisation of the pathways ascending to the colliculus was expressed in the cochlear nuclei, lateral superior olivary nucleus and in the dorsal nucleus of the lateral lemniscus. HRP--positive cells were found in layer V of the ipsilateral auditory cortex, however, the evidence for topographic organisation was lacking.

Afferent Pathways↗
PubMed1982

Noise impairment in the guinea pig. I. Changes in electrical evoked activity along the auditory pathway.

Changes in the cochlear microphonics (CM), auditory nerve action potential (AP), and evoked responses from the inferior colliculus (IC-ER) and auditory cortex (AC-ER) of the guinea pig were assessed after exposure to white noise of 115 dB for 30 min. Both continuous and intermittent (200 ms noise and 200 ms pause) exposures were used. In comparison with the pre-exposure level, CM isopotential curves were shifted by 1.1 +/- 0.5 dB (means +/- S.E.) on the average in the range of 0.5-8 kHz (recorded at the round window). The amplitude-intensity function of the click-evoked auditory nerve action potential decreased by 8.4 +/- 1.2 dB, that of the inferior colliculus evoked response by 20.9 +/- 3.7 dB, and the amplitude-intensity function of the auditory cortex evoked potential decreased by 6.2 +/- 4.7 dB. A similar reduction in the amplitude was found after both continuous and intermittent noise exposure. In contrast to the decrease in amplitudes of evoked potentials, the latency-intensity functions of the individual waves of potentials evoked along the auditory pathway did not change when compared at the same click intensity before and after the exposure. The results suggest that individual auditory nuclei are impaired by the noise to different extents and that the impairment does not increase linearly up to the auditory cortex.

Action Potentials↗
PubMed1982

Noise impairment in the guinea pig. II. Changes of single unit responses in the inferior colliculus.

Spontaneous and evoked activity of neurons in the inferior colliculus of guinea pigs was recorded before and after exposure to noise (continuous or intermittent white noise, 115 dB SPL for 30 min). A single unit was investigated in each animal, and its activity was monitored for several hours. Exposure to noise elevated the threshold of the tip of the tuning curve, resulting in a broadening of the tuning curve. Threshold elevation at the characteristic frequency was greater after exposure to intermittent noise (200 ms noise and 200 ms pause), reaching values of 22.8 +/- 3.7 dB (means +/- S.E.) than it was after exposure to continuous noise (threshold elevation of 13.1 +/- 1.7 dB). The average threshold shift was 17.1 +/- 2 dB. Neither the shape of the poststimulus histograms nor the slope of the spike-intensity curves changed with the noise exposure. The total number of spikes during the response was, however, reduced, and the reduction was in proportion to the threshold elevation. Monaural noise exposure had no effect on the neuronal activity evoked by stimulation of the opposite, nonexposed ear. The latencies of responses recorded after exposure to noise were also longer than the latencies at the same absolute intensity recorded before the exposure. Thus the latencies during the original pre-exposure and acquired postexposure thresholds were practically identical.

Action Potentials↗
PubMed1982

Response properties of neurons in the inferior colliculus of the guinea-pig.

Single unit responses to tone pips (200 ms duration) or clicks were studied in the inferior colliculus of anaesthetized guinea-pigs. In all, 360 neurons were investigated. The tonotopic organization of neurons in the inferior colliculus and shapes of the threshold tuning curves were comparable with the data known in other laboratory animals. The majority of neurons (83.5 percent) displayed a tonic response to tonal stimuli, the remaining 16.5 percent of units responded with a typical "on" reaction at the beginning of the stimulus. The spike-intensity functions of 50 percent of neurons were of the non-monotonic type, the saturation of response was observed usually at 20-30 dB above the threshold. Monaural stimulation of the contralateral ear evoked an excitatory response in all cases; ipsilateral ear stimulation exerted an excitatory response in 61.8 percent of neurons, an inhibitory response in 17.6 percent of neurons and for 20.6 percent of units ipsilateral ear stimulation was uneffective. The occurrence of neuronal responses to stimuli with an interaural time delay or intensity differences was also investigated.

Acoustic Stimulation↗
PubMed1981

Discharge characteristics of neuronal pairs in the rabbit inferior colliculus.

Activity of neuronal pairs in the inferior colliculus of the rabbit was recorded with a single stainless-steel microelectrode. Seventy pairs were investigated with monaural and binaural tonal stimuli. The most common parameter of the response in neuronal pairs was the best frequency, which was similar in 100% of the pairs (n = 45). Q10 values were identical in 44% of pairs and threshold tuning curves in 27% of pairs. Units with a smaller spike amplitude usually had a shorter latency to both binaural and monaural stimuli, when measured 10-20 dB above the best frequency threshold. Most units discharged during the entire period of the 100 ms tone stimulation at their best frequency; large differences, however, were found in their firing pattern, when peristimulus histograms were compared. High correlation was found in pairs where both neurones exhibited the same type of binaural interaction. The following types of binaural interaction were found: binaural excitatory drive with occlusion, binaural excitatory drive with facilitation; monaural excitatory drive with inhibition from the other ear and pure monaural excitatory drive. In a significant number of neuronal pairs the influence of binaural stimulation was similar for both neurones. The results suggest that: (a) many adjacent neurones in the inferior colliculus convey parallel information concerning features of the auditory stimulus; (b) units with a similar type of binaural interaction may be organized in clusters within isofrequency layers.

Acoustic Stimulation↗
PubMed1981

Longitudinal distribution of cochlear potentials and the K+ concentration in the endolymph after acoustic trauma.

Guinea pigs were exposed to 142 dB third-octave band of noise control at 1 kHz for 1 h. At different times after exposure the endocochlear potential (EP), the anoxic negative endocochlear potential (-EP), the concentration of K+ (K+e) and microphonic potentials were recorded in scala media in four cochlear turns. The remaining hair cells were counted in each animal. Immediately after the exposure, the EP and K+e decreased evenly in all four cochlear turns and gradually returned to normal physiological values in 5-20 days. When measured 20 days after the exposure, essentially normal EP and K+e values were observed, with an apicalwards decline, which was similar to that found along the cochlea in nonexposed animals. Abnormal increased EP was observed in some animals 20 days after the exposure in the first and second turns. In contrast to positive EP and K+e values, the anoxic negative EP attained less negative values in the second turn of exposed animals, i.e., in the turn where the narrow band noise exerted the major destructive effect. An almost normal distribution of hair cells and most negative EP values were found in the fourth turn. The distribution of persistent hair cells correlated positively with the values of the anoxic negative EP and amplitudes of the microphonic potentials. It is assumed that, in addition to the difference in K+ concentration between endolymph and perilymph, the anoxic negative EP is dependent upon the functional state of the organ of Corti.

Animals↗
PubMed1980

Recovery of the endocochlear potential and the K+ concentrations in the cochlear fluids after acoustic trauma.

Intense noise stimulation (142 dB, 1/3-octave-band noise centred at 1 kHz for 1 h) causes damage mainly in the second turn of the cochlea. Several hours (3-5) after the noise exposure, the endocochlear potential (EP) was found to be very low (5.7 +/- 6.0 mV). Similarly, the K+ concentration in the endolymph (Ke+) had decreased to low values (18.9 +/- 9.5 mM). The return of EP and Ke+ to normal values took 5-20 days. In contrast to the Ke+ changes, the perilymph K+ concentration (Kp+) increased slightly after the noise exposure to 4.5 +/- 1.7 mM and returned to normal values one day after the exposure. Differences were found in the time course of the EP, Ke+ and Kp+ changes after the arrest of ventilat ion when animals with acoustic trauma were com,ared with normal healthy individuals. The anoxic EP in noise-exposed animals never decreased to values more negative than -20 mV. The results imply that the inner ear mechanisms maintaining positive EP, Ke+ and Kp+ are severely damaged after acoustic trauma and that their function is restored in 5-20 days. With respect to some parameters (decrease of the EP during anoxia, the value of anoxic negative EP, EP overshoot after reventilation) the inner ear mechanisms are, however, still abnormal.

Acoustic Stimulation↗
PubMed1980

Hearing threshold shifts from prolonged exposure to noise in guinea pigs.

Auditory thresholds were assessed in three guinea pigs with a conditioning procedure based on the positive reinforcement paradigm. Thereafter, the guinea pigs were exposed for 5 days to third octave band noise centred at 2 kHz at 100 dB SPL. Thresholds at 0.5, 2 and 4 kHz were controlled during the exposure and up to 120 days after exposure. After 6 h of exposure, the threshold shift at 4 kHz reached 40 dB and increased slowly to 45 dB by the fifth day. The quasi-asymptotic shift was less expressed at 2 kHz, where the initial threshold shift amounted to 20 dB and rose to 40 dB by the fifth day. Thresholds recovered in the time course of 5 days after exposure and a significant permanent threshold shift was present 120 days after exposure. It amounted to 35 dB at 4 kHz and to 20 dB at 2 kHz. Auditory thresholds were dependent upon the duration of the stimulus: the decrease in duration of a tone from 200 ms to 2 ms caused a rise in threshold of about 10 dB before as well as after the exposure. The effects of prolonged noise exposure upon guinea pigs are similar to those found in chinchillas with the exception of the permanent threshold shift, which is more marked in guinea pigs.

Acoustic Stimulation↗
PubMed1978

Effect of high-intensity sound on cochlear microphonics and activity of inferior colliculus neurons in the guinea pig.

The input-output functions of cochlear microphonics (recorded from the round window) in guinea pigs exposed briefly to high-intensity sound (2 kHz, 130 dB, 30 min) were shifted toward higher intensities by about 15 dB in comparison with normal animals. 2-4 h after the exposure this shift decreases to 10 dB. The response characteristics of the inferior colliculus neurons were compared under similar conditions. Thresholds at the characteristc frequencies (CF) measured 2-4 h after exposure, were raised by 30-50 dB, a higher threshold increase was observed at frequencies from 5-7 kHz. 48 h after exposure the thresholds approached those obtained in normal animals. There was no pronounced hair cell loss after exposure. It is assumed that in addition to the impairment of sound transduction in hair cells there may be a specific effect of high-intensity sound exposure on neuronal transmission in the auditory pathway.

Animals↗