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Biomedical subjects

M Mager

Publications and source records attributed to M Mager.

At least 19 recordsLinked to original sources
PubMed2000

Use of evoked potentials to objectively differentiate between selective vulnerability of cochlear and vestibular end organ function.

Auditory nerve brainstem evoked responses (ABR) have been used for several decades to investigate cochlear function. Recently techniques have been developed to elicit similar recordings from the vestibular end organs - short latency vestibular evoked potentials (VsEPs). Both ABR and VsEP reflect appropriate end organ function and may therefore be used to investigate the vulnerability of these end organs to various experimental insults, such as noise exposure and ototoxic drugs.

Animals↗
PubMed1997

Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses in rats.

In this study, short latency (t < 12.7 ms) vestibular evoked potentials (VsEPs) in response to linear acceleration impulses were recorded in 37 rats. A new technique (based on a solenoid) was used for generating linear force impulses that were delivered to the animal's head. The impulse had a maximal peak acceleration of 12 g. During the impulse, the displacement was 50 microns (at 4 g) and the rise time was 1.0 ms. A stimulation rate of 2/s was usually used. The VsEPs (averaged responses to 128 stimulations, digital filter: 300-1500 Hz) were recorded with electrodes on pinna and vertex, and were composed of 4-6 clear waves with mean amplitudes (for a 4 g stimulus) of 1-5 microV. The VsEPs were resistant to white noise masking, and were significantly suppressed (P < 0.05) following bilateral application of a saturated KCl solution to the inner ear, showing that contributions of the auditory and somatosensory systems are negligible. The latency of the response decreased as a power law function of stimulus magnitude, and the amplitude of the first wave increased as a sigmoid function of stimulus magnitude. VsEP responses were still present at the lowest intensities attainable (0.06-0.4 g) and reached saturation at 9 g. The amplitude of the later components was reduced when stimulus rate was elevated to 20/s. These results suggest that VsEPs in response to linear accelerations are similar in their nature to VsEPs in response to angular acceleration impulses that were previously recorded. These VsEPs to linear accelerations are most likely initiated in the otolith organs.

Acceleration↗
PubMed1992

[Status of the development of electron spin resonance measurement for the detection of irradiated food].

Electron spin resonance spectroscopy can be used for the detection of irradiation of various groups of foodstuffs. The results of ESR-measurements on irradiated meat and fish and fresh fruit, as well as dried fruit, spices and nuts as performed by the food irradiation laboratory of the German Federal Health Office are summarized in this report. For the detection of irradiated meat and fish, we examined the bones. Using the results from 10 different animal bones, we were able to develop an official method according to the German law section 35 LMBG. A similar routine method for fish will be established in 1992 (at the moment, an intercomparison with German food control laboratories is in progress). Irradiated dried fruit can be identified easily, because unirradiated samples give no ESR-spectra, while irradiated fruit show a partially resolved spectrum, which is caused by radiation induced sugar radicals. Interestingly, the structure of the resulting spectra is not identical for all irradiated species of fruit. We found three different types of ESR-spectra for irradiated dried fruit. Irradiated nutshells show an ESR-spectrum which reveals two additional lines (from cellulose-radicals) beside the main signal, while unirradiated samples show only the main signal. An official method for identifying irradiated nuts will be proposed in 1992. Irradiation specific ESR-signals of the cellulose radical were not only found for nutshells but also for fresh fruit and some spices, while most of the irradiated spices and herbs could not be identified by ESR-measurements.

Animals↗
PubMed1990

Effect of death anxiety on perception of death-related humor.

Scores on a humor scale containing both death-related and non-death-related items were compared among three groups of 10 college students who scored high, medium, or low on death anxiety. Ratings of humor differed significantly among the groups, but there was no significant interaction between death anxiety and ratings of death-related humor. Subjects high in death anxiety showed lower humor ratings over-all than the other two groups.

Adolescent↗
PubMed1984

Effects of pyridostigmine on ability of rats to work in the heat.

Adult, male rats (300-325 g) were treated with pyridostigmine bromide (n = 22) or saline (n = 22) to quantitate the effects of cholinesterase inhibition (64%) on the ability to work (9.14 m/min, level treadmill) in the heat (35 degrees C). Pyridostigmine-treated rats had a mean endurance of 23 min, whereas saline-treated animals ran for nearly 35 min (P less than 0.001). Rates of rectal and skin temperature increments were significantly higher (P less than 0.001) in pyridostigmine-treated rats as were water losses (P less than 0.001). Exercise in the heat to hyperthermic exhaustion effected anticipated increments in circulating urea nitrogen, creatinine, lactate dehydrogenase, and potassium levels, whereas pyridostigmine pretreatment had additive effects on lactate and creatine kinase concentrations. Additionally, pyridostigmine elicited a significant (P less than 0.01) hyperglycemia before exercise, an effect noted also with other organophosphate simulants. We concluded that pyridostigmine-induced cholinesterase inhibition had a variety of debilitating effects during work in the heat.

Animals↗
PubMed1984

Albumin-induced plasma volume expansion: diurnal and temperature effects.

To develop a reliable procedure for the acute expansion of plasma volume (PV), 26 male volunteers were randomly assigned to either a thermoneutral (25 degrees C and 40% relative humidity) or hot-dry (37 degrees C and 25% relative humidity) environment; subsequently each subject was seated for at least 1 h and then infused intravenously with either 100 or 200 ml of a 25% albumin solution or 0.9% saline. On the day before each infusion, PV was estimated by dye dilution using indocyanine green. Net percent change in PV (using hematocrit and hemoglobin values) was calculated at 1, 3, 6, 9, 12, and 24 h postinfusion. The PV of subjects residing in the heat after a 100-ml saline infusion increased significantly over 1-h values at 6, 9, and 12 h postinfusion but not at 24 h. The same trend, although not significant, was apparent at room temperature. The data suggest a slow isooncotic circadian pattern of PV expansion and contraction. The infusion of hyperoncotic albumin produced rapid expansion of plasma volume. With the low dose (25 g) at 1 h postinfusion, the expansion was 379 +/- 102 ml in the heat and 301 +/- 160 ml at room temperature. With the high dose (50 g) at 1 h postinfusion, the expansion was 479 +/- 84 ml in the heat and 427 +/- 147 ml at room temperature. The high dose produced an expansion that persisted for at least 9 h in subjects in either environment. The data suggest a mechanism for the retention of fluid during heat acclimatization and a useful procedure for plasma volume expansion in humans.

Acclimatization↗
PubMed1983

Acute heat/exercise stress in rats: effects on fluid and electrolyte regulatory hormones.

Adult, male rats were exercised in the heat until hyperthermic exhaustion ensued. Plasma aldosterone levels were significantly (p less than 0.001) elevated after 8 min of exercise and remained increased throughout the exercise and recovery periods. Alternatively, plasma angiotensin I levels were unaffected during exercise, but increased significantly (p less than 0.001) during the recovery period. These rapid elevations in hormonal levels may be part of a sympathicoadrenal response to heat/exercise stress as well as an adaptational response to maintain plasma volume during and following exercise in the heat.

Aldosterone↗
PubMed1983

Acute albumin-induced plasma volume expansion and exercise in the heat: effects on hormonal responses in men.

To assess the responses of fluid regulatory and stress hormones to acute expansion of plasma volume and exercise in the heat, 50 g of albumin dissolved in 200 ml normal saline or 200 ml saline alone was administered intravenously to 7 adult, male test subjects followed by exercise (40% VO2 max) in the heat (Tdb = 45 degrees C, Twb = 25 degrees C). Blood samples were obtained after sitting in the heat for 1 h, 1 h after completion of infusion which itself required approximately 1.5 h, after standing for 30 min, and 15, 30, 45, and 60 min after commencing exercise. Plasma cortisol levels were generally unaffected by these treatments. Responses of plasma aldosterone levels to postural change and exercise in the heat were attenuated in the albumin trial, and growth hormone levels were unaffected by albumin administration. Angiotensin I levels' were significantly decreased at several sampling intervals during the albumin trial, but unaffected by exercise. We concluded from these studies that plasma volume expansion by intravascular albumin administration had no effect on stress hormone responses during exercise in the heat, while regulatory hormone levels were lower in several instances during the albumin trial.

Adult↗
PubMed1983

Malathion administration: effects on physiological and physical performance in the heat.

To determine the effects of low-dosage organophosphate administration on exercise in a hot environment, malathion (7.5 mg/day, 4 days) was administered IP to rats, and effected a 35% (p less than 0.01) reduction in plasma cholinesterase levels. Treadmill endurance (9.14 m/min, no incline, 35 degrees C ambient) was unaffected when the animals were exercised to hyperthermic exhaustion (Tre approximately 43 degrees C). While rates of heat gain were similar between groups, malathion-treated rats displayed higher Tsk (p less than 0.05) at a number of sampling times during the treadmill run. While creatine phosphokinase levels were unaffected by either cholinesterase inhibition or exercise in the heat, lactate dehydrogenase activities were increased (p less than 0.01) in both groups following hyperthermic exhaustion. Although plasma levels of lactate, potassium, urea nitrogen, and creatinine were all significantly (p less than 0.01) increased as a result of exercise in the heat, these increments were not exacerbated by cholinesterase inhibition. Results generally indicated that at this moderate level cholinesterase inhibition, malathion administration did not adversely affect physiological, physical, or thermoregulatory efficacy.

Animals↗
PubMed1983

Chronic low-sodium diet in rats: hormonal and physiological effects during exercise in the heat.

To elucidate the effects of sodium (Na+) deficiency on the ability to work in the heat, immature rats were fed a diet deficient in Na+ for approximately 2 mo. Rates of weight gain were severely affected (P less than 0.01) in the Na+-deficient rats (1.7 vs. 7.2 g/day in controls), although fluid consumption was unaffected. The low-Na+ diet effected no alterations in endurance or weight loss during exercise in the heat to hyperthermic exhaustion, but final core and skin temperatures were significantly reduced in the low-Na+ group (P less than 0.02) and hematocrit ratios were significantly (P less than 0.001) increased. Circulating Na+ and potassium (K+) concentrations were significantly (P less than 0.05) increased in both groups after hyperthermic exhaustion. In the Na+-deficient groups, plasma levels of both aldosterone and cortisol/corticosterone were significantly (P less than 0.05) increased, and these increments were exacerbated following exercise to hyperthermic exhaustion. Consumption of the low-Na+ diet elicited significant increments in circulating levels of lactate (P less than 0.01) and creatinine (P less than 0.01), both of which were increased further after exercise. We concluded that hormonal adaptations prevented circulatory hyponatremia and decrements in physical performance, but other clinical and metabolic effects of the low-Na+ diet were noted.

Adrenal Cortex Hormones↗
PubMed1983

Hypo- and hyperglycemia in rats: effects on endurance and heat/exercise injury.

To investigate the hypothesis that circulating glucose levels may affect exercise performance and the severity of hyperthermic injury, rats were made hypoglycemic (n = 12, IV insulin, 4 U) or hyperglycemic (n = 12, IP glucose, 750mg) before exercise in the heat to hyperthermic exhaustion (Tco = 42.5-43 degrees C). The endurance of rats administered glucose was significantly greater than insulin-treated controls (n = 12). Hematocrit levels were unaffected by exercise in control and insulin-treated rats, but were significantly (p less than 0.01) increased in those glucose-treated. Lactate levels were increased (p less than 0.001) post-run in all groups, and these increments were exacerebated in glucose-treated rats. Glucose levels pre-run were decreased by insulin and increased by glucose, and remained depressed (p less than 0.01) post-run in the insulin-treated group. Potassium concentrations were reduced (p less than 0.05) by insulin administration. Urea nitrogen and creatinine were increased (p less than 0.001) post-run in all groups. We concluded that, while hyperglycemic rats had increased endurance compared to hypoglycemic animals, mortality of at least 50% in all groups was unaffected by circulating glucose levels.

Animals↗
PubMed1982

Thermoregulatory responses in the rat to exercise in the heat following prolonged heat exposure.

To determine the effects of prolonged exposure to severe thermal stress on the subsequent ability to exercise in the heat, rats were exposed to a hot (35 degrees C) environment for 1, 2, 3, or 4 wk. At each of these weekly intervals the rats ran on a treadmill to hyperthermic exhaustion (41.5--43.0 degrees C), and tail-skin (Tt-sk) and rectal (Tre) temperatures were monitored. The results indicated that prolonged heat exposure did not enhance the rats' endurance capacity. Further, as the period of heat stress increased, there was a concomitant significant decrement in tail-skin vasodilation; indeed, after 3 and 4 wk at 35 degrees C Tt-sk reflects a complete shutdown of blood flow to the tail during exercise. Additionally, slight evaporative cooling from exogenous fluid (saliva or urine from the treadmill surface) might account for the low Tt-sk in relation to Tre and Ta. Hematocrit ratios ordinarily decreased from week to week during heat exposure, whereas body weights remained very consistent throughout the 4-wk interval. The mechanism of this decrement in vasodilation is undergoing further study.

Adaptation, Physiological↗
PubMed1981

Thermoregulatory effects of centrally administered bombesin, bradykinin, and methionine-enkephalin.

Bombesin (BO, 100 ng), bradykinin (BR, 10 microgram), or methionine-enkephalin (EN, 10 microgram) was administered intracerebroventricularly to adult male rats at an environmental temperature of 4 degrees C, 22 degrees C, or 35 degrees C, and rectal (Tre) and tail-skin (Tsk) temperatures were monitored for 5 hours. At 4 degrees C and 22 degrees C BO-treated animals developed acute hypothermia (max delta Tre=-3.25 degrees C and -2.71 degrees C, respectively) which persisted for 2 hours (p less than 0.05). At 22 degrees C and at 300 min post-injection, BO-treated animals became significantly (p less than 0.05) hyperthermic (deltaTre = +1.28 degrees C) when compared to controls. While BR had no effects at 22 degrees C, en-injected rats demonstrated significant (p less than 0.05) hyperthermia from 180 min through 300 min (delta Tre=+1.40 degrees C). At 22 degrees C both BO and, surprisingly, EN increased Tsk (e.g. delta Tsk =+ 3.49 degrees C and + 2.01 degrees C at 60 min). At 35 degrees C EN elicited hyperthermia which was significantly (p less than 0.05) increased from time 0 at all sampling time (mean delta Tre =+ 1.85 degrees C) and from control levels at 300 min (delta Tre =+1.07 degrees C, p less than 0.05). BO again caused a significant (p less than 0.05, BO vs control, 30 min) decrement (delta Tre =-1.22 degrees C) followed by increments (p less than 0.05) from 12-0-300 min. We conclude that the hypothermic effect of BO is dependent upon environmental temperature, partially caused by vasodilation, and possible biphasic in nature; EN treatment generally elicits hyperthermia under these conditions while BR produced no effects on thermoregulation.

Animals↗
PubMed1981

Chronic chlorpromazine administration in rats: effects on ability to work in the heat.

To identify and quantitate the effects of chronic chlorpromazine (CPZ) administration on the ability to work in the heat, 2 mg CPZ were administered by intraperitoneal injection daily for 14 days to rats weighing between 250 and 350 g at the time of experimentation. When these animals exercised in the heat (35 degrees C) to hyperthermic exhaustion (Tre = 42.5-43 degrees C), it was demonstrated that their endurance capacity was significantly reduced (P less than 0.001) when compared with saline-treated controls. Increments in rectal temperature while on the treadmill were significantly (P less than 0.02) elevated among th CPZ-treated rats. Exercise on the treadmill to hyperthermic exhaustion resulted in significantly (P less than 0.001) increased circulating levels of lactate and potassium when these were compared in blood samples taken immediately before and after exercise in the heat for both groups, but creatine phosphokinase levels were unaffected. Additionally, lactate levels were significantly (P less than 0.05) increased in the postrun blood samples of CPZ-treated rats when compared with the appropriate saline-treated controls. We concluded from these studies that chronic administration of CPZ in rats reduces their ability to work in the heat. Further, their rate of heat gain while exercising in the heat is increased, and the combined effects of exercise in the heat and CPZ administration exacerbated the effects on the clinical chemical indices of heat-exercise injury.

Animals↗
PubMed1981

Alcohol consumption in rats: effects on work capacity in the heat.

To quantitate the effects of ingestion of ethanol (EtOH)-water mixtures on the ability to work in the heat (35 degrees C), adult male rats (250-350 g) were given 0, 4, 8, 12, or 16% EtOH as the sole source of drinking water for 14 days. The endurance capacity (treadmill time) of rats drinking 4% EtOH was similar to that of rats consuming water (32 vs. 32.9 min, respectively). However, the treadmill time of rats drinking of 16% EtOH was significantly (P less than 0.05) reduced when compared with that of animals drinking 4 or 8% EtOH. Maximal rectal and skin temperatures were likewise lower in the group consuming 16% EtOH, whereas increments in rectal and skin temperatures during treadmill exercise were unaffected. Although hematocrit and plasma protein levels were unaltered, plasma levels of the commonly reported indices of heat-exercise injury were exacerbated by consumption of increasing concentrations of EtOH. We concluded that ingestion of EtOH for 2 wk had minimal effects on thermoregulation and that the decrements in work capacity noted were probably the result of alterations in hepatic and muscle metabolism.

Alcohol Drinking↗
PubMed1981

Prostaglandin E1 hyperthermia: effects on ability to work in the heat.

To assess the effects of preinduced hyperthermia on the ability to exercise in the heat, prostaglandin E1 (PGE1) was administered intracerebroventricularly to male rats weighing 275-350 g. Following injection of PGE1, a fever of 2 degrees developed within 20-30 min, at which time a 1-ml blood sample was taken. When these animals exercised in the heat (37 degrees C) to hyperthermic exhaustion (42.5-43 degrees C), their endurance capacity was significantly reduced (P less than 0.001) when compared with controls. Exercise to hyperthermic exhaustion resulted in significantly (P less than 0.05, minimal) increased plasma levels of lactate, potassium, and urea nitrogen in both control animals and those receiving PGE1. However, PGE1 pretreatment did not exacerbate these increments. Plasma glucose and sodium levels were significantly (P less than 0.05) increased in PGE1-treated animals, whereas glucose levels were reduced significantly (P less than 0.05) in both groups postrun. We concluded that preinduced hyperthermia severely reduces the ability to work in the heat. Although the clinical chemical indices of heat injury are unaffected by PGE1 pretreatment, the effects of PGE1 administration on circulating levels of glucose and sodium require further study.

Animals↗