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PubMedDate not supplied

Estimates of essential neural elements for stimulation through a cochlear prosthesis.

Electrical stimulation of afferent auditory pathways through electrodes placed within and outside of the cochlea were used to study stimulation and design parameters relevant to a cochlear prosthesis. In the acute guinea pig preparation, the tract response evoked in brachium of the inferior colliculus by electrical stimulation to an ear provided estimates of the effectiveness of various electrode placements. Stimulation between an electrode in the cochlea and a site along the eighth nerve was characterized by the lowest thresholds. Stimulation between intracochlear electrodes was somewhat less effective, and stimulation between external electrodes at the nerve, cochlear nucleus, or distant point was least effective. Thresholds, expressed as current, rose at approximately 6 dB per octave for stimulus frequencies from 1 kHz to 16 kHz. Thresholds below 10 microA rms were seen for optimal placements. These observations suggest that the neural elements being stimulated are the cell bodies of the spiral ganglion cells.

Afferent Pathways↗
PubMed1989

[Supplementation of essential trace elements during total parenteral nutrition--effects on trace element-deficient rats].

Thirty-one male SD rats, six weeks old, were fed a trace element-deficient diet for two weeks and then divided into three groups and maintained for 1 week as follows: group A with total parenteral nutrition (TPN) without supplementation of trace elements, group B with TPN supplemented with the following 5 trace elements ... iron, zinc, copper, manganese and iodine, and group C with a diet free of the above five trace elements. Another group of eight rats was fed a diet supplemented with the above five trace elements for three weeks as a control (group D). Feeding or TPN without supplementation of trace elements evoked microcytic hypochromic anemia and significant decreases in iron concentrations in plasma and tissues (groups A and C). Supplementation of trace elements in the TPN solution showed a tendency to cure anemia and a significant increase in the iron concentration in tibia (group B). Decreases in the zinc or copper concentrations in plasma and tissues during TPN without trace elements were prevented by supplementation of trace elements in the TPN solution (group B). The plasma zinc and copper concentrations correlated well with their levels in liver, kidney and tibia. Manganese deficiency was not recognized in this investigation (groups A and C), though supplementation of trace elements in the TPN solution increased tissue manganese concentration (group B). Feeding or TPN without supplementation of trace elements induced decreases in plasma triiodothyronine and thyroxine (groups A and C). Supplementation of trace elements in the TPN solution showed a tendency to increase plasma thyroxine (group B).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

The large cytoplasmic loop of the glucose transporter GLUT1 is an essential structural element for function.

Alanine scanning mutagenesis and the introduction of deletions and insertions were used to address the role of the large cytoplasmic loop in 2-deoxy-D-glucose (2-DOG) uptake by GLUT1 expressed in Xenopus oocytes. Alanine scanning mutagenesis of 29 amino acid residues that are identical or homologous in GLUT1 to GLUT4 demonstrated that the transport activities of only a few variants were affected. Progressive truncation of the loop by six deletions leaving intact 59 (delta236-241), 49 (delta231-246), 39 (delta226-251), 28 (delta221-257), 18 (delta216-262), or 10 (delta213-267) amino acid residues resulted in a progressive decrease in 2-DOG uptake. Compared with wild-type GLUT1 the uptake rates varied between 33% for the delta236-241 mutant and 4% for the delta213-267 mutant. Insertional mutagenesis using hexaalanine or hexaglycine to fill in the deletion 236D-241L restored 2-DOG uptake to 73% of wild-type GLUT1 in the case of hexaalanine, whereas hexaglycine insertion was without effect. Confocal laser microscopy demonstrated that a deletion of six amino acid residues did not influence the expression level in the plasma membrane (delta236-241 mutant), whereas the plasma membrane fluorescence of the delta213-267 mutant was comparable with that of water-injected Xenopus oocytes. Computer-aided secondary structure prediction of the loop suggested that it consists of a long alpha-helix bundle interrupted or kinked by the highly conserved glycine-233.

Alanine↗
PubMed1995

Evidence for chromium acting as an essential trace element in insulin-dependent glucose uptake in cultured mouse myotubes.

Previous work from this and other laboratories has suggested that the trace element chromium plays some role in glucose homeostasis. In this study, we sought to characterise an in vitro cell culture model in which the effects of chromium on insulin-dependent glucose uptake could be studied. Mouse C2C12 myoblasts were differentiated to form myotubes in culture in chromium-replete or chromium-poor media. Chromium levels in standard media were 0.56 +/- 0.01 micrograms/l (mean +/- S.E.M.) compared with 0.09 +/- 0.01 micrograms/l in chromium-poor media. In chromium-poor media, insulin-stimulated uptake of radiolabelled glucose was reduced by almost 50% compared with that found in chromium-replete media. This decreased response could be restored by the addition of physiologically relevant (0.3 micrograms/l) concentrations of inorganic chromium (P < 0.001). The sensitivity of these cells to insulin was reduced dramatically by a reduction in the chromium content of the medium and was again increased (P < 0.001) by chromium addition. The concentrations of chromium required to restore the sensitivity to insulin were of the same order as those found physiologically; much higher concentrations of chromium could also stimulate glucose uptake in the absence of insulin but such concentrations were supra-physiological.

Animals↗
PubMedDate not supplied

[Experimental study of the role of essential trace elements of mineral waters in prevention of atherosclerosis risk factors].

Hormonal and lipid spectra of the blood serum; antioxidant, biosynthetic, microcirculatory and elastic-inhibitory activity in the myocardium and liver; proliferative and genetic activity in the thymus; microcirculation and destruction in rats with atherosclerosis drinking Khadyzhenskaya mineral water and solution of natural macro- and trace elements in the spring water (temarox) in two dilutions. It was found that elimination of atherosclerosis risk factors in rats was most complete in a course temarox drinking in dilution 1/8000.

Aluminum Silicates↗
PubMed2001

Effect of hypoxia on the circulating levels of essential mineral elements in rats.

Changes occurring in concentrations of certain trace metals and electrolytes viz. chromium, copper, zinc, sodium, potassium, calcium, magenesium and chloride in plasma of rats exposed to intermittent hypobaric hypoxia were evaluated. Batches of Sprague-Dowley rats (12 in each group) were exposed for 1, 7,14 and 21 days to a simulated altitude 7,620 m for 6 h per day and one group of unexposed animals was kept as control. There was a significant rise of 153% in plasma chromium levels of 1 day exposed group in comparison to the unexposed group which tends to normalise on subsequent exposure. There was a gradual increase in plasma copper levels of 9.0, 28.2, 62.6 and 65.6% respectively in 1,7,14 and 21 days exposed rats in comparison to unexposed rats. On the other hand plasma zinc levels were seen to be decreasing during entire exposure. Plasma sodium levels decreased initially in 1 and 7 day exposed rats and increased in later groups whereas plasma potassium levels of exposed groups remained low in comparison to unexposed group. Chloride levels were found to be elevated in 14 and 21 day exposed groups. The plasma calcium and magnesium levels were higher in all exposed groups over unexposed groups. Changes in chromium, copper and zinc observed in the present study during exposure to hypoxic stress may be responsible for the hyperglycemia and anorexia encountered during intial phase of high altitude acclimatisation.

Animals↗