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Biomedical subjects

D C Hood

Publications and source records attributed to D C Hood.

At least 91 records · Page 5Linked to original sources
PubMed1981

Uptake of horseradish peroxidase by presynaptic terminals of bipolar cells and photoreceptors of the from retina.

The uptake of horseradish peroxidase (HRP) into synaptic vesicles of presynaptic terminals in the inner and outer plexiform layers of isolated frog retinas was studies by electron microscopy. Uptake into the terminals of bipolar cells was found to be enhanced by exposure of the preparations to elevated concentrations of potassium ions, and by exposure to aspartic acid or glutamic acid. Glycine had much less effect on the terminals. These results suggest that HRP uptake may prove useful in monitoring some aspects of the responses of inner plexiform layer cells to conditions of physiological interest. Uptake into photoreceptor terminals was also enhanced by elevated potassium concentrations; the effects of the amino acids were complex.

Amino Acids↗
PubMed1981

Gastrointestinal bleeding in patients with spinal cord trauma. Effects of steroids, cimetidine, and mini-dose heparin.

The frequency and degree of gastrointestinal (GI) bleeding were examined in 131 patients with spinal cord injuries. All patients were randomly assigned to either high- or low-dose steroid regimens and some form of GI prophylaxis. The latter consisted of antacids alone or antacids supplemented with cimetidine when this medication became available. Segments of the population were treated with mini-dose or full-dose heparin. The incidence and degree of GI bleeding did not appear to be affected by steroid dose level, regimen of prophylaxis, or mini-dose heparin. Only full heparinization was found to significantly increase bleeding. These results place in question the benefits of adding cimetidine to antacids as a prophylactic atreatment in patients with no history of ulcer.

Adrenal Cortex Hormones↗
PubMed1979

Comparison of changes in sensitivity and sensation: implications for the response-intensity function of the human photopic system.

Brightness magnitude estimations of foveally presented flashes deviate from a power function. Increment threshold functions for test lights presented upon these same flashes deviate drastically from a constant Weber fraction. These departures from the classic laws of sensation and sensitivity are shown to be in qualitative agreement and to be affected in similar ways by changes in steady adapting fields. Both sets of data can be fit over the lower range of flash intensities by models based on a saturating response function; both sets deviate from these models at high flash intensities in ways consistent with a nonsaturating response function.

Adaptation, Ocular↗
PubMed1976

Synaptic activity of frog retinal photoreceptors. A peroxidase uptake study.

The uptake of horseradish peroxidase (HRP) into membranous structures, detectable by light and electron microscopy, is used here to monitor the synaptic activity of photoreceptors of isolated frog retinas maintained in the dark or under various illumination conditions. The major findings are: (a) Neurotransmission from photoreceptor terminals seems to involve the same types of endocytic membrane-retrieval processes that occur at other nerve terminals. Presumably, the endocytic processes compensate for exocytic events associated with neurotransmission. The retrieved membrane is "recycled" to form vesicles. Some of these accumulate near the synaptic ribbons, perhaps indicating reutilization for exocytosis. On the other hand, some retrieved membrane evidently is degraded via multivesicular bodies that appear to undergo "retrograde" transport from the receptor synapses to the myoid regions. (b) Photoreceptor terminals take up much HRP in the dark. Steady illumination markedly decreases uptake by rods. Uptake by cones is notably reduced only at illumination intensities higher than those that have maximal effects on rods. (c) The decrease in rod HRP uptake with light is reversible when retinas are allowed to adapt to the dark, if the light exposures used were at intensities that bleach very little visual pigment. Such "recovery" is not observed after light exposures that bleach a considerable amount of visual pigment. The cones recover their dark levels of HRP uptake even after light exposures that bleach considerable amounts of visual pigment. The changes in HRP uptake that we observe parallel expectations for photoreceptor synaptic neurotransmission derived from indirect physiological evidence.

Animals↗
PubMed1974

Temporal summation of light by a vertebrate visual receptor.

Using aspartate to isolate mass receptor-activity, we have investigated the reciprocity of flash intensity and flash duration in determining the response of the frog's cone receptor. The duration over which reciprocity holds decrease with increases in either flash energy of ambient light intensity. These findings parallel those of human psychophysical experiments.

Animals↗