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Biomedical subjects

J Syka

Publications and source records attributed to J Syka.

At least 73 records · Page 4Linked to original sources
PubMed1978

The effects of ethacrynic acid upon the potassium concentration in guinea pig cochlear fluids.

After i.v. injection of 50 mg/kg ethacrynic acid (EA), potassium concentration in the endolymph (Ke+) measured with K+-specific microelectrodes decreases by 10 mM at the most and endocochlear potential falls to negative values. Potassium concentration in the perilymph (Kp+) generally does not change, but sometimes a transient decrease in Kp+ level of about 0.5 mM was observed, presumably due to the electrogenic effect of the time-related decrease of the endocochlear potential. When anoxia is induced approximately 120 min after EA administration Ke+ slowly decreases. The decrease in Ke+ 50 min after the arrest of ventilation is smaller when compared with the Ke+ anoxic decrease without preceding EA administration. The endocochlear potential, which falls to negative values during anoxia after EA administration, does not return to the zero level as in the case when only anoxia is applied. Similarly, during anoxia, which follows EA administration, the perilymphatic Ke+ concentration increases more slowly than in the case when only anoxia is introduced. It is assumed from the results that EA abolishes activity of the positive electrogenic K+ pump and reduces the passive permeability of the walls of the cochlear duct to the potassium ions.

Animals↗
PubMed1977

Time course of anoxia-induced K+ concentration changes in the cochlea measured with K+ specific microelectrodes.

The endocochlear potential (EP), potassium concentration in the endolymph (Ke+) and in the perilymph (Kp+) were measured in guinea-pigs during anoxia of different duration. Specific K+ double-barrel microelectrodes with liquid ion exchanger were used. The resting K+ concentration in the endolymph was 146.8 +/- 9.2 mM and in the perilymph 3.2 +/- 0.5 mM. The following time course of events was observed in the cochlea during anoxia: 40-50 s after the arrest of ventilation the K+ concentration decreased by 0.1-0.2 mM in the scala vestibuli, which was time related to a rapid fall of EP to negative values. Perilymphatic K+ started to increase in both scalae with a latency of 2-2.5 min, reaching a concentration of about 14 mM 60 min after the arrest of ventilation. The endolymphatic K+ began to decrease after a latency of 2.5-3 min, and 60 min after the arrest of ventilation an 80% concentration (average 112 mM K+) was reached as compared to the initial value. From the comparison of K+ concentration changes with the experimental values of the negative EP, it may be assumed that the negative EP is mainly generated by the K+ gradient between the perilymph and endolymph.

Animals↗
PubMed1977

Comparison of spontaneous activity of mesencephalic reticular neurones in the waking state and during pentobarbital anaesthesia.

In rats immobilized by d-Tubocurarine the spontaneous activity of 100 mesencephalic reticular neurones was recorded extracellularly and statistically evaluated before and after repeated intravenous administration of 15 mg/kg doses of Pentobarbital. Number of spontaneously active neurones decreases quasi-linearly with repeated 15 mg/kg Pentobarbital doses. After a 75 mg/kg cumulative dose practically all neurones ceased firing spontaneously, whereas cortical EEG activity fully disappeared after the 90 mg/kg Pentobarbital dose. The firing rate was characterized by the mean interval with its standard deviation. Mean value for the total sample of spontaneously active neurones was 146.7 +/- 192.3 msec without Pentobarbital and increased to 302.7 +/- 367.5 msec after 15 mg/kg and to 400.6 +/- 452.5 msec after 30 mg/kg cumulative dose of Pentobarbital. The 15 mg/kg dose increased the frequency of firing in 5% of neurones only. The most often encountered type of interval histogram in the mesencephalic reticular formation was the exponential type (59% in unanaesthetized state), which was also most sensitive to Pentobarbital. Synchronized activity in bursts, characterized by periodical peaks and dips frequently occurred in neurones with the exponential-like interspike interval density after Pentobarbital administration. On the contrary, neurones with gamma-like and especially with symmetrical-like types of density were less influenced by Pentobarbital. In many neurones a periodical increase in the firing rate (with intervals of tens of seconds) related to the occurrence of spindles was present in the cortical EEG activity.

Action Potentials↗
PubMed1976

Electrical responses of the auditory area of the cerebellar cortex to acoustic stimulation.

Single unit activity from the VI and VII lobuli of the cerebellar vermis cortex was studied following acoustical stimulation with sound signals of different parameters. Cerebellar neurons, as compared to those from the auditory system, showed low selectivity to sound frequency, intensity and duration. However, about 2/3 of the neurons were selectively sensitive to interaural time and intensity differences; about 1/3 of neurons showed a specific response to signals simulating sound motion in a definite direction. Thus, cerebellar neurons seem to be mainly responsive to those sound parameters which are essential for sound localization.

Acoustic Stimulation↗
PubMed1975

Influence of increasing doses of pentobarbital on the mesencephalic reticular formation in rats. Spontaneous firing of neuronal pairs and activity evoked by polarization.

In rats immobilized by D-tubocurarine the spontaneous activity in pairs of mesencephalic reticular neurons was recorded by means of one microelectrode and differentiated by amplitude discriminators. Spontaneous activity of neuronal pairs and activity evoked by electrical polarization of cells (5-235 nA) through the recording microelectrode was evaluated in the curarized state and after cumulative doses of 15 mg/kg pentobarbital. No correlation between mean interspike interval duration in pairs of adjacent neurons was found in the unanesthetized state. After pentobarbital a slight dependence was observed between the values. Furthermore, it is probable that adjacent neurons will both cease firing at the same dose of pentobarbital. Cross-correlation of the spike trains of two adjacent neurons was found in the range of minus 10 msec to plus 10 msec (which is probably an expression of direct interaction or of a common input) in 6 of 50 pairs analyzed in the unanesthetized state. This dependence fully disappeared after 15-30 mg/kg of pentobarbital. After 15 mg/kg of pentobarbital in 17 recorded pairs (out of 50 analyzed) peaks in the cross-correlograms appeared in a range of about 100 msec and at a distance of 150-300 msec. Such a relationship was already present in 4 pairs of neurons in the unanesthetized state. The similarity of autocorrelation and cross-correlation histograms in this case favors the hypothesis that spontaneous activity of many mesencephalic reticular neurons is synchronized after pentobarbital administration. In many reticular neurons the firing may be evoked by direct cell polarization through the recording microelectrode even at cumulative doses of pentobarbital much higher than those sufficient to block spontaneous activity.

Action Potentials↗