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Biomedical subjects

W M Kozak

Publications and source records attributed to W M Kozak.

8 recordsLinked to original sources
PubMed1987

Electrically evoked skin vasodilatation: a quantitative test of nociceptor function in man.

Direct stimulation of intact forearm skin affects adjacent microvascular blood flux. Pulses of current, known to activate C-fibres effectively, were applied over a period of 1-16 seconds at 2 Hz using transcutaneous stimulation. An increase of up to 50% was observed in skin microvascular blood flux. Increased blood flux correlated well with increasingly painful sensations. Some subjects responded to one or two pulses at 2 Hz, 0.5 ms in duration and 150 volts. A response onset latency of 4-15 s, lasting up to 5 minutes, was recorded. At higher frequencies (4-8 Hz) and more pulses (16-32) vasoconstriction was frequently observed before the usual flux increase. After administration of local anaesthesia (2% ligocaine) the resting skin blood flux increased, but electrical stimulation still produced vasodilatation. The local cutaneous flare response to electrical stimulation was abolished or greatly reduced by capsaicin pretreatment. Excitation of small intracutanous forearm nerve C-fibres produces increased microvascular blood flux which is dependent on local release of vasodilator substances. Thus the neurogenic flare (axon reflex) may have a physiological role in regulating skin blood flow, and nociceptor function may be measured by applying the aforementioned transcutaneous electrical stimulation.

Axons↗
PubMed1986

Effects of aldose reductase inhibition on the retina and health indices of streptozotocin-diabetic rats.

Experiments were performed on Streptozotocin-diabetic rats to investigate the preventive effect of an aldose reductase inhibitor, Sorbinil, on the deterioration of electroretinograms and retinal tissue that normally occurs during diabetes, and to determine Sorbinil's effect on the general health indices: food and water intake, urine glucose and ketones, body weight, and blood glucose levels in diabetic rats. Two dosages of Sorbinil were tested, 60 mg/kg/24 hours and 10 mg/kg/24 hours. Electroretinograms and the above health indices were measured before injection of Streptozotocin and again after a three week period of diabetes. Sample eyes were then examined by electron microscope and the thickness of the retinal capillary basement membranes was measured. Statistical evaluation showed that Sorbinil-treated diabetic rats did not experience the same lengthening of latencies and reduction in amplitude of various electroretinogram components that occurred in non-treated diabetic rats. Sorbinil improved the general health of diabetic rats and reduced their mortality rates as well. Preliminary electron microscope studies showed a correlation between thickness of the retinal capillary basement membrane and various electroretinogram parameters.

Aldehyde Reductase↗
PubMed1979

Transient persistence of neural activity after periodic stimulation in the cat LGN.

Oscillatory neural activity recorded from gross concentric electrodes implanted in the lateral geniculate nucleus (LGN) of cat was investigated after trains of periodic electrical shock stimulation were applied to the contralateral optic nerve. Spectral analysis using repeated trials and spectral averaging revealed statistically significant spectral peaks (p less than 0.05) at the stimulus frequency when there was a 0.5 to 1.5 s delay between the last pulse of the stimulus train and the beginning of the data analysis window. This suggests that a loosely coupled neuronal net may allow for the continuation of activity far longer than the time accounted for by neuronal time constants and delays.

Animals↗
PubMed1979

Entrainment of oscillatory neural activity in the cat's lateral geniculate nucleus.

Oscillatory neural activity in the frequency range 7-12 Hz is observed in the lateral geniculate nucleus (LGN) of the lightly anesthetized cat. This paper describes a series of experiments in which the interactions between ongoing oscillatory potentials and periodic photic and electrical stimuli are analyzed using frequency domain techniques. The principal results of these experiments are consistent with a model of the neural system as an entrainable oscillator in which ongoing oscillations are suppressed by stimulation at nearby frequencies, but coexist with stimulus frequencies farther away. The physiological interpretation of these results may be closely tied to the role of the LGN as a "gating" mechanism between retina and cortex.

Alpha Rhythm↗
PubMed1974

Jerzy Konorski.

Explore the source record for details and available documents.

Animals↗
PubMed1973

Distribution coding in the visual pathway.

Although a variety of types of spike interval histograms have been reported, little attention has been given to the spike interval distribution as a neural code and to how different distributions are transmitted through neural networks. In this paper we present experimental results showing spike interval histograms recorded from retinal ganglion cells of the cat. These results exhibit a clear correlation between spike interval distribution and stimulus condition at the retinal ganglion cell level. The averaged mean rates of the cells studied were nearly the same in light as in darkness whereas the spike interval histograms were much more regular in light than in darkness. We present theoretical models which illustrate how such a distribution coding at the retinal level could be "interpreted" or recorded at some higher level of the nervous system such as the lateral geniculate nucleus. Interpretation is an essential requirement of a neural code which has often been overlooked in modeling studies. Analytical expressions are derived describing the role of distribution coding in determining the transfer characteristics of a simple interaction model and of a lateral inhibition network. Our work suggests that distribution coding might be interpreted by simply interconnected neural networks such as relay cell networks, in general, and the primary thalamic sensory nuclei in particular.

Animals↗