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Biomedical subjects

T G Wheeler

Publications and source records attributed to T G Wheeler.

16 recordsLinked to original sources
PubMed1989

Soman toxicity during and after exposure to different environmental temperatures.

A systematic study has been conducted to determine physiological susceptibility to the potent anticholinesterase soman during and after exposure to different environmental temperatures. Rats were placed in an environmental chamber set at -1, 7, 15, 23, or 31 degrees C (80% relative humidity, RH) from 0000 to 0800 h. Soman injections were given subcutaneously (sc) at 0600 h (during thermal stress), or at 0810 h after removal from the chamber (injected and tested at 23 degrees C, 60% RH). The measures (taken 30 min after soman injection) included core temperature, grip strength, general state of health, and LD10 estimates (taken 2 h post injection). Soman exposure produced a dose-related effect on each measure under all thermal stress conditions. During thermal stress, soman exposure produced major changes in core temperature ranging from 26 to 41 degrees C, which were linearly related to the environmental temperature condition. After removal from the chamber, soman exposure reduced core temperature by only 1 degree C without regard to prior thermal stress temperature. Grip strength and subjective health rating were soman dose-related with only a minor chamber temperature influence. The toxicity of soman was increased during exposure to either cold or hot environments and after removal from the cold environments. The adrenal-cortical stress response to cold involves increased metabolism and oxygen requirement. The exception was the decreased toxicity observed when soman exposure occurred after removal from a hot environment, exacerbated by a failure in the respiratory system due to anticholinesterase exposure. The increased toxicity of soman while in or after removal from a cold environment is believed to be due to a generalized adrenal-cortical stress response. The increased soman toxicity while in a hot environment, but decreased toxicity after removal from the hot environment, provides an interesting subject for further research.

Animals↗
PubMed1987

Goldfish spectral sensitivity increase and shift with decreasing temperature.

Goldfish spectral sensitivity is shown to be a function of temperature. Optic nerve responses (compound action potentials) to the onset (ON) and cessation (OFF) of a step stimulus were obtained at 10 degrees C and 22 degrees C. At 22 degrees C the ON sensitivity peak at 460 nm with a secondary peak at 620 nm. The OFF sensitivity had a single peak at 620 nm. The peak sensitivities at 10 degrees C were all shifted to longer wavelengths. At 10 degrees C the ON sensitivity peaked at 500 nm and the secondary peak shifted to 660 nm and was 300% higher than the 660 nm sensitivity at 22 degrees C. The red OFF sensitivity shifted to 660 nm at 10 degrees C was also 300% greater than the 22 degrees C OFF sensitivity at 660 nm. The peak sensitivity shifts observed between the 22 degrees C and 10 degrees C data may be due to a change in concentration of the A1-vs. A2-based visual pigments: at 22 degrees C the A1-based pigments predominate and at 10 degrees C the A2-based pigments prevail. The increase in red sensitivity at 10 degrees C for both the ON and OFF data could reflect the increased concentration of O2 at the lower temperature. Only red sensitivity was affected by temperature. Both the shift in peak sensitivity across the spectrum at lower temperatures and the increase in red sensitivity are consistent with survival capabilities.

Action Potentials↗
PubMed1987

The behavioral effects of anticholinesterase insult following exposure to different environmental temperatures.

This study evaluates soman toxicity via a number of behavioral tasks after an 8-h exposure to one of five thermal stress conditions (-1,7,15,23, or 31 degrees C at 80 +/- 5% RH). Animals were removed from the environmental chamber, injected with soman (0-160 micrograms X kg-1), and tested 30 min post-injection. The test battery included: motor activity, grip strength, core temperature, sensitivity to heat, effects on memory and learning, and a subjective rating of the animal's state of health. A significant thermal stress/soman interaction was observed for all measures. This interaction was seen as a shift of the soman dose-response functions to the right for the higher temperature groups, i.e., the lower the stress temperature, the greater the susceptibility to soman. For example, the ED50 for the activity measure was 38 micrograms X kg-1 for the -1 degree C exposure group and 94 micrograms X kg-1 for the 31 degrees C group. The thermal stress influence on soman toxicity may be a function of previous motor activity.

Animals↗
PubMed1985

Retrograde amnesia produced by electron beam exposure: causal parameters and duration of memory loss.

The production of retrograde amnesia (RA) upon electron beam exposure has been investigated. RA production was evaluated using a single-trial avoidance task across a 10(4) dose range for 10-, 1-, and 0.1-microsecond pulsed exposures. The dose-response curve obtained at each pulse duration showed significant RA production. The most effective dose range was 0.1-10 rad at a dose rate of 10(6) rad/sec. By employing a 10 rad (10(6) rad/sec) pulse, a memory loss of the events occurring in the previous 4 sec was demonstrated. The conclusion was that the RA effect might be due to sensory system activation which provided a novel stimulus that masked previous stimuli.

Amnesia↗
PubMed1983

Scotopic sensitivity to ON and OFF stimulus transients.

The luminance of a large diffuse field, viewed peripherally, was temporally modulated near absolute detection threshold. The field luminance either increased abruptly and decreased gradually (ON stimulus) or increased gradually and decreased abruptly (OFF stimulus). For all wavelengths shorter than 620 nm, sensitivity to the ON stimulus was greater than to the OFF. The spectral sensitivity curves obtained indicate that rods and/or their associated neural pathways are more sensitive to ON stimulus transients than to OFF.

Adult↗
PubMed1975

Goldfish retina: functional polarization of cone horizontal cell dendrites and synapses.

In serial electron micrographs we observed that dendrites of goldfish cone horizontal cells are either central or lateral in ribbon synaptic triads, depending on cone and horizontal cell type. The chromatic properties of cone horizontal cell responses may be explained if the cone horizontal cells act as interneurons, receiving from cones through their central processes but acting on cones through their lateral processes.

Animals↗
PubMed1975

Visual membranes: specificity of fatty acid precursors for the electrical response to illumination.

Rat electroretinograms were measured as a function of dietary supplements of purified ethyl esters of linolenic acid, linoleic acid, and oleic acid. Polyunsaturated fatty acids derived from precursors of linolenic and linoleic acids appear to be important functional components of photoreceptor cell membranes, although in equal dietary concentrations, linolenic acid precursors affect electroretinogram amplitudes to a greater extent than linoleic acid precursors. The electrical response of photoreceptor cell membranes appears to be a function of the position of the double bonds as well as a function of the total number of double bonds in fatty acid supplements.

Animals↗
PubMed1975

Determination of bacterial cell concentrations by electrical measurements.

An instrument was developed to measure the concentration of bacterial suspensions by their electrical characteristics. It employed a square-wave signal generator, a tetra-polar electrode probe, and a voltage detector in the form of an oscilloscope. When electrical measurements were made on washed bacteria obtained from cultures or urine specimens, there was a direct relationship between the concentration of the cells and the electrical characteristics of the system as reflected by voltage changes. As little as 10(3) organisms per ml could be detected. The resolution between readings taken on samples containing 10(3) to 10(9) cells per ml was found to be a function of the input frequency. The maximal resolution between concentration readings was obtained at a input frequency of 10 Hz. Thus, with relatively simple instrumentation, bacterial concentrations could be determined within a few minutes. This technique, therefore, eliminates the more lengthy laboratory procedures as plate counts or the accumulation of measurable metabolic changes (such as the utilization of radioactive or other substrates). This method can efficiently monitor clinical urine specimens when a bacteriuria is suspected.

Bacillus cereus↗
PubMed1973

Membrane fatty acids associated with the electrical response in visual excitation.

The fatty acid composition of rat photoreceptor membranes was altered by dietary manipulation. A functional alteration was also observed in the component of the electroretinogram which is generated by the photoreceptors. A membrane fatty acid, docosahexaenoic acid, appears to be involved in the transduction process of visual excitation.

Animals↗