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Biomedical subjects

A Mayevsky

Publications and source records attributed to A Mayevsky.

At least 73 records · Page 4Linked to original sources
PubMed1987

Effects of dibromochloropropane and ethylene dibromide on biochemical events and ultramorphology of ejaculated ram spermatozoa in vitro.

The effects of dibromochloropropane (DBCP) and ethylene dibromide (EDB) on the function and ultrastructure of freshly ejaculated washed ram spermatozoa were assessed. These two compounds inhibited the collective motility of the sperm in a dose-dependent fashion when the sperm cells generated their energy either by mitochondrial respiration (2-deoxyglucose-treated sperm cells) or by the intact energy production system. DBCP and EDB inhibited the oxygen uptake by the sperm in a dose-dependent manner. No change in lactic acid accumulation and glucose utilization by the sperm cells was noted following DBCP and EDB addition. No change in the collective motility of the sperm was noted when DBCP or EDB were added to spermatozoa treated with the electron transfer inhibitor, antimycin A. Electron microscopy studies of sperm cells treated with DBCP revealed lesions in the plasma membrane adjacent to the acrosome and in the acrosomal membrane forming vesiculations. The inner membrane and the matrix space of the mitochondria were condensed following DBCP treatment, leaving a large mitochondrial peripheral space, compared with the control. EDB, at the concentration studied, caused no change in the ultramorphological structure of the sperm. DBCP was more potent, at least 4-fold, compared with EDB. An in vitro direct effect of DBCP and EDB on ram spermatozoa was established. It is suggested that quantitative measurements of sperm collective motility derived by different metabolic pathways can be used as an in vitro toxicological model for evaluation of toxicological and environmental factors affecting biological systems.

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PubMed1986

Three-dimensional metabolic mapping of the freeze-trapped brain: effects of ischemia in the Mongolian gerbil.

The effects of unilateral carotid artery (left or right) occlusion on the three-dimensional metabolic mapping were studied in the Mongolian gerbil (Meriones unguiculatus). The brain was freeze-trapped by the liquid nitrogen funnel technique and was analyzed for the two-dimensional distribution of the reduced pyridine nucleotides and oxidized flavoprotein using a time-sharing micro-light guide surface fluorometer/reflectometer. The results could be summarized as follows. Bilateral carotid artery occlusion induced uniform effects in terms of redox state in the cerebral cortex and the olfactory bulbs. After unilateral carotid occlusion, the redox state of the ischemic ipsilateral hemisphere was higher and was not affected by blood volume changes as evaluated from the reflectance signal scanned in several brains. The narrow band of tissue near the midline of the ischemic hemisphere connected to the contralateral hemisphere blood supply appeared in a large number of gerbils. The anomaly in the redox state of the intracellular space also appeared in subcortical structures, as seen in all the two-dimensional mappings measured. It seems that blood circulation to the two olfactory bulbs is connected to the same blood vessel. It is suggested that unilateral carotid artery-occluded gerbils may show large variability inside the same hemisphere and therefore results must be evaluated very carefully.

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PubMed1985

Metabolic, ionic, and electrical responses of gerbil brain to ischemia.

The effects of short- or long-term complete cerebral ischemia were studied in the gerbil brain using a multi-parameter monitoring system. Metabolic (NADH redox state) and hemodynamic responses were monitored by surface fluorometry-reflectometry. Ionic activities (K+ and pH) were measured by surface macroelectrodes. Electrical activity was evaluated by monitoring the general electrocorticogram (ECoG) as well as local DC steady potential (two sites). Two groups of gerbils were studied to compare the effects of 4-5 min occlusions with those of 30 min complete ischemia. During bilateral carotid artery occlusion the cortex is exposed to complete ischemia resulting in the complete depletion of O2 with attendant maximal reduction of NADH. Extracellular K+ began to increase as soon as energy reserves were decreased with a time course suggesting two different kinetic areas. Surface pH decreased very shortly after the occlusion. During the recovery phase, NADH was reoxidized soon after recirculation, whereas the pH and K+ recovery showed a short delay. ECoG did not recover even when all other parameters reached base-line levels. The recovery of all the measured parameters was correlated to the duration of the ischemic insult; i.e., the recovery from 30 min of ischemia took significantly longer than after 5 min of ischemia. We conclude that pH recovery depends on recirculation and adequate O2 supply to the tissue, whereas K+ recovery required not only an adequate O2 supply but also the integrity of the adenosine triphosphatase system.

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PubMed1984

Brain NADH redox state monitored in vivo by fiber optic surface fluorometry.

A new approach for the evaluation of brain energy metabolism in awake animals became possible as UV transmitting optical fibers became available. A variety of surface fiber optic fluorometers / reflectometers which were developed during the past decade enabled the monitoring of intramitochondrial NADH redox state in unanesthetized animals. The bundle of flexible fibers was connected to the brain via a cemented light guide holder implanted epidurally. The two signals obtained, 366 nm reflectance and 450 nm fluorescence, are subjected to various artifacts not connected to the intramitochondrial NADH redox state. In our system, the effects of movement artifacts and changes in blood oxygenation are negligible while the effects of tissue absorption or blood volume changes are considerable and could be minimized by subtraction of the two signals (1:1 ratio) providing the corrected fluorescence signal. The brain was exposed to various physiological and pathological conditions which resulted in the increase or decrease in the level of NADH. Under anoxia, hypoxia and ischemia, oxygen availability decreased and the metabolic state of the brain became more reduced (state 4-5 transition). When the brain was activated by seizures, spreading depression of hyperbaric oxygenation NADH became more oxidized (state 4-3 transition).

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PubMed1984

The effect of testosterone on ram spermatozoa collective motility treated by antimycin A.

The effect of testosterone on collective motility of antimycin A-treated, Ficoll-400-washed ejaculated ram spermatozoa was studied. The lowest concentration of antimycin A which blocked collective motility in hexose deprived cells (0.4 X 10(9) cells/ml) was 2 X 10(-7) M. Fructose, glucose and mannose, but not galactose, sorbitol or inositol, served as energy sources for collective motility. Cortisol, 5-beta-DHT, androsterone and 5-alpha-pregnan 3-beta-ol-20-one did not affect collective motility. Testosterone inhibited collective motility in a dose-dependent fashion. However, it did not affect lactic acid accumulation. The effect of testosterone was noted both on cells suspended in buffer containing fructose and on exogenously starved cells treated with fructose after collective motility arrest. It was concluded that testosterone might exert its inhibitory effect on motility by uncoupling fructolytic energy production to the tail motility system.

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PubMed1983

Brain metabolic responses to ischemia in the mongolian gerbil: in vivo and freeze trapped redox scanning.

The interrelation between the metabolic responses to ischemia and seizure propensity was studied in two groups of seizure prone (SP) and non-seizure prone (NSP) gerbils. The metabolic state was evaluated in vivo using the light guide surface fluorometry as well as in the frozen brain scanned at liquid N2 temperature for Fp/PN ratio after monitoring the brain in vivo. The results could be summarized as follows. (1) Unilateral carotid artery occlusion led to partial ischemia in the ipsilateral hemisphere while the contralateral hemisphere remained normoxic. (2) Animal variability in the degree of the ischemia insult due to unilateral occlusion was not side dependent or in correlation with seizure propensity. (3) Significant correlation was found between the NADH increase during ischemia and the redox state measurements done in the same brain after funnel freezing with liquid nitrogen. (4) In a large number of the gerbils (not depending on the origin or strain) a peculiar inter-hemispheric blood supply connection was found. A narrow band (1 mm in width) of tissue near the midline obtained its blood via the same vessels supplying the contralateral hemisphere. (5) We did not find any correlation between blood vessel anatomy to the brain and seizure propensity.

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PubMed1983

Sperm cell motility as a new experimental model for toxicological studies.

The effects of environmental and toxicological factors were tested in a new and "simple" biological system; the collective motility exhibited by ram spermatozoa. Motility of highly concentrated semen (greater than 1 X 10(9) cells/ml) was evaluated objectively with a multichannel reflectospermiograph (RSG) connected to a minicomputer for an on-line analysis. The effect was tested on one of the energy-producing systems in the sperm cells, while the other was inhibited by 2-deoxy-D-glucose or antimycin-A so that the energy source for motility was known. The effects of the addition of ethanol to the semen in various concentrations, as well as various levels of oxygen in the environment were tested. When motility of the sperm cells was driven by mitochondrial respiration, the intensity and duration of motility was inhibited significantly above a threshold level. At the same level of ethanol, the motility was not significantly affected when the energy source was the fructolysis pathway. The effects of oxygen level were tested below and above the normal oxygen level (21% O2). When fructolysis was inhibited, the motility was fully dependent on oxygen supply, namely, that lower levels of oxygen inhibited motility. It was also found that under higher levels of O2 (hyperbaric hyperoxia conditions) the motility was inhibited due to the known oxygen toxicity effects.

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PubMed1982

Intracellular oxidation-reduction state measured in situ by a multichannel fiber-optic surface fluorometer.

The principles of the measurement in vivo of the oxidation-reduction state of intramitochrondrial pyridine nucleotides were used in establishing a multichannel fluorometer-reflectometer. This approach made possible the study of changes of mitochrondrial redox states in four different organs (brain, liver, kidney, and testis) of the same animal, as well as the monitoring of four different cortical areas of the same brain hemisphere. In the measurement of reduced nicotinamide adenine dinucleotide fluorescence, oximetric and movement artifacts are negligible, but blood volume changes and tissue absorption properties are a source of error. The corrected fluorescence is obtained by subtracting the reflectance from the fluorescence signed in 1:1 ratio., During graded hypoxia, the corrected fluorescence showed a gradual increase and was maximal during anoxia in all four organs tested.

Animals↗
PubMed1982

Factors affecting the oxygen balance in the awake cerebral cortex exposed to spreading depression.

Oxygen balance was evaluated in the cerebral cortex, using the surface fluorometry technique of the intramitochondrial NADH redox state, exposed to various physiological and pathological situations. Using flexible fiber optic light guide, connected to the brain surface via a cemented holder, the measurements were done continuously from the awake rat and gerbil. In few experiments the NADH redox state was correlated with the electrical and ionic activity (measured by surface K+ and DC electrodes). Three different animal models were used in the study: the adult rat, the very young rat (20 g) and the adult gerbil. Those 3 models were used in studying the effect of hypoxia, partial ischemia, and anesthesia on the metabolic and ionic activities measured from the awake brain. Spreading cortical depression (elicited by topical KCl solution) was used as a standard stimulation of the ionic and metabolic activities of the cerebral cortex. Two typical metabolic responses to spreading depression (SD) were recorded, namely 'oxidation cycle' and 'reduction cycle' depending upon the ability of the tissue to compensate for the extra amount of oxygen needed for the higher mitochondrial activity. It was found that the adult rat brain showed oxidation cycles in most conditions (besides partial ischemia), while the young rat and the gerbil brains were much more sensitive to the various perturbations of the brain and exhibited reduction cycle ( as a response to SD) under all pathological situations tested. We conclude from our detailed studies that the type of response to SD, as measured by NADH surface fluorometry, represents the oxygen balance which exists in the tissue under various conditions.

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PubMed1982

Effect of local ischaemia on the myocardial oxygen balance and its response to heart rate elevation.

The capacity of ischaemic myocardium to respond to the inotropic stimulus of tachycardia was investigated in open-chest anaesthetized dogs following ligation of a branch of the anterior descending coronary artery. In two areas of the left ventricular surface (ischaemic and non-ischaemic), local coronary blood flow was measured by thermistors and isometric contractile force was recorded with strain gauge arches. NADH redox state was measured simultaneously in both regions using a two-channel surface fluorometer. It was found that ligation was followed by an immediate fall in local coronary blood flow to the ischaemic region, accompanied by a sharp elevation in NADH redox level. Local contractile force in the ischaemic region was also reduced. The non-ischaemic region showed little or no change following occlusion. Response to heart rate elevation before ligation was increased work, elevation of NADH redox levels, and increased coronary flow. Following ligation, this response was attenuated in the ischaemic region, but not abolished. It is concluded that ischaemic myocardium retains the capacity for inotropic response even when intracellular O2 levels are low.

Animals↗
PubMed1982

Multiprobe monitoring of ionic, metabolic, and electrical activities in the awake brain.

A new approach for studying brain metabolic, ionic, and electrical activities in the awake animal is described. We developed a multiprobe assembly holding electrodes for extracellular K+, pH, DC potential, electrocorticogram, and temperature as well as a light guide for monitoring intramitochondrial NADH oxidation-reduction state. The assembly was designed so that because of the type of electrodes used and the protection system around them, the same system could be used in many experiments. The results presented here are typical and show the potential use of the multiprobe approach for studying the effects of hypoxia, anoxia, spreading depression, and ischemia on the awake brain. From the results obtained the following conclusions can be drawn. 1) The DC correction for the K+ and H+ measurements is necessary, although it was not as good for the H+ as for the K+ signals. 2) During ischemia (complete or partial) a clear acidification of the brain was found in correlation with the decrease in oxygen availability as evaluated by the NADH fluorescence signal. 3) During brain activation (induced by spreading depression) extracellular K+ was elevated and then actively pumped back into the cells. The NADH showed an oxidation response, and the pH response started with an alkalinization followed by a short acidification.

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PubMed1981

The effects of unilateral carotid occlusion on the responses to decapitation in the gerbil brain.

The effects of partial ischemia (unilateral carotid artery occlusion) on the metabolic and electrical responses to decapitation were studied in the awake and anesthetized gerbils' brains. The gerbil was connected to the 2 channel fluorometer/reflectometer by flexible light guides implanted above the two hemispheres of the brain. The results show that: (1) the metabolic rate as measured by this present technique is lower in the gerbil than in the rat; (2) the metabolic rate of the ischemic hemisphere is lower as compared to that of the normoxic contralateral hemisphere.

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