Search PubMed⌕ Search

Biomedical subjects

R R Levine

Publications and source records attributed to R R Levine.

At least 19 recordsLinked to original sources
PubMed1996

U.S. Army sunglasses: issues and solutions.

BACKGROUND: Some military aviators have reported difficulty discriminating the color of cockpit warning lights when wearing plastic sunglasses. This difficulty could be due to lenses that are too dark or are nonneutral and thus alter color vision. A study was performed to identify the origin of this problem, recommend solutions, and determine a sunglass transmittance that optimizes visual performance. METHODS: Five pairs of plastic sunglasses (-4 to +4 D) were ordered from each of seven military optical laboratories (70 lenses total). Each laboratory was instructed to dye the lenses neutral gray with 21 percent transmittance. Light transmittance and color distortion were evaluated across laboratory and lens power. Spatial and color vision were assessed through a range of sunglass transmittances. RESULTS: There was no systematic effect of lens power, but light transmittance and color distortion varied widely across laboratories (transmittance = 1 to 30 percent; p < 0.001). CONCLUSIONS: Because light transmittance and color distortion were related inversely, it was believed that both factors could be corrected by accurate verification of transmittance, but commercial transmittance meters proved to be inaccurate. The high transmittance of deep red and infrared light through plastic lens dyes is read as visible light by transmittance meters, making readings too high. A filter was identified that provides accurate readings when used with transmittance meters. A sunglass transmittance of 23 percent resulted in minimal decrease in visual performance relative to normal clinical test conditions.

Analysis of Variance↗
PubMed1995

Evaluation of a potential enantioselective interaction between ticlopidine and warfarin in chronically anticoagulated patients.

Ticlopidine is a novel antiplatelet drug reported to cause significant inhibition of several drugs metabolized by the hepatic cytochrome P-450 enzyme system, including antipyrine and theophylline. Warfarin, a racemic mixture of two enantiomers (R and S), is extensively metabolized by the CYP-450 system. S-Warfarin is five to eight times as active as R-warfarin. The effects of ticlopidine on the pharmacokinetics and pharmacodynamics of warfarin were examined in nine elderly men (69 +/- 4 years) receiving long-term warfarin therapy. Steady-state warfarin enantiomer concentrations and International Normalized Ratios (INRs) were determined at baseline and after 14 days of treatment with oral ticlopidine, 250 mg twice daily. Warfarin enantiomer serum concentrations were determined by high-performance liquid chromatography after chiral derivitization. Ticlopidine co-medication resulted in a significant increase in mean R-warfarin concentrations (+25.7%, p < 0.05), while no significant difference in S-warfarin concentrations was noted (+0.8%). Mean INR values were not significantly different from the baseline (+8.3%), although substantial interindividual variability was noted. We conclude that ticlopidine co-medication does result in an enantioselective kinetic interaction with warfarin; however, this interaction is likely to be of minimal clinical significance in most patients.

Aged↗
PubMed1981

Extratelencephalic pathways and feeding behavior in the pigeon (Columba livia).

Electrolytic lesions were placed in the tractus septomesencephalicus (TSM) and tractus occipitomesencephalicus (TOM), efferent pathways originating in visual and somatosensorimotor areas of the avian telencephalon and distributing widely to brain stem and spinal nuclear regions. Lesion effects upon several aspects of ingestive behavior were examined using high speed cinematography, operant conditioning procedures and monitoring of intake and feeding responses. While there was no evidence for direct effects upon drinking, both TSM adn TOM lesions were followed by periods of reduced food intake. Disruptions of feeding in TSM birds were mild and relatively transient but birds were hypophagic for prolonged periods. While there were no deficits in the efficiency or accuracy of their feeding responses or their performance in an operant situation, TSM birds displayed an inappropriate seed "sorting" behavior suggestive of lesion effects upon visually controlled food preferences. TOM lesions produced a significant reduction in responsiveness to food (aphagia, hypophagia), impairments in the control of grasping and peck accuracy and a disruption in operant key pecking reinforced by food. These "sensorimotor" and "motivational" deficits were similar to those seen after damage to central trigeminal structures in the pigeon and suggest that TOM is also a component of a putative "feeding system" in the pigeon.

Animals↗
PubMed1979

The role of plasma concentrations in the use of tricyclic antidepressant drugs.

1. The range of tricyclic antidepressant plasma levels (or doses) needed for therapeutic response remains largely unresolved, since quantal plasma concentration (or dose)--response relationships have not been clearly defined for either therapeutic or nontherapeutic effects. 2. The fact that certain patients apparently became more depressed at higher plasma levels must be balanced against the facts that "depression" is a mixture of disorders as yet poorly distinguishable and that tricyclic antidepressants have multiple pharmacologic effects. 3. There is presently no justification for routinely monitoring tricyclic antidepressant plasma levels, even though, as for any drug, such determinations are justifiable in patients who are unresponsive or show signs of toxicity. 4. Plasma level determinations can never replace sound clinical judgment and dosage adjustment for individual patients.

Amitriptyline↗
PubMed1979

Methods for the analysis of intestinal function.

The intestinal tract, an organ of considerable complexity, requires application of numerous techniques for analysis of its physiology and perturbations by toxicologic agents. This review describes the methodology of importance in analysis of the absorptive function of the intestine and the transit of intestinal contents. Methods for studying absorption are categorized according to the technique for administering the test substance such as inclusion in the diet or by gastric and intestinal placement and the method of quantitating the degree of absorption such as determining the appearance of a test substance in systemic fluids or its disappearance from its site of administration in the intestine. In vitro techniques which have no in vivo analogs, such as the use of the everted sac, are briefly described and their limitations emphasized. Procedures of importance in the clinical diagnosis of malabsorption or in the experimental analysis of absorptive function in man are included and distinguished from techniques used in animal models. In addition, methods for studying aspects of gastrointestinal motility, including the use of luminal markers and analysis of the contractile and electrical activity of intestinal smooth muscle, are reviewed.

Animals↗
PubMed1978

Regeneration of olfactory axons and synapse formation in the forebrain after bulbectomy in neonatal mice.

We removed the right olfactory bulb in neonatal mice, leaving the bulb on the left side intact as an internal control. At 5 days of survival time, we observed that the right cerebral hemisphere was displaced forward to occupy the region made vacant by removal of the bulb. The frontal cortex was, consequently, in close proximity to the lamina cribrosa. As a result of bulb ablation and severance of the fila olfactoria, the sensory perikarya underwent total retrograde degeneration, which peaked at 8 days. New neurons differentiated in the neuroepithelium from basal stem cells and, at 30 days of survival, mature sensory neurons were reconstituted. These new elements sent their axons through the lamina cribrosa to reach the protruding cerebral hemisphere, penetrating it and forming glomeruli-like structures directly in the host tissue. The "glomerulization" of the sensory fibers persisted and actually expanded between 60 and 120 days. The new glomeruli were organized intimately within the brain tissue, and large neurons of the cortex were observed to be in close proximity. Ultrastructural observations of the newly formed glomeruli demonstrated that typical sensory axon terminals profusely branched and synapsed with unidentified postsynaptic processes that penetrated the glomeruli from the surrounding cerebral tissue.

Animals↗
PubMed1975

Studies of the enterohepatic circulation of morphine in the rat.

The disposition of 14C-morphine was studied after gastrointestinal and subcutaneous administration to female Sprague-Dawley rats. Morphine was found to be rapidly and nearly completely absorbed from the small intestine. After s.c. administration, approximately half the 5 mg/kg dose of morphine was excreted via the bile into the intestinal tract, largely as morphine glucuronide. Unlike morphine, the glucuronide conjugate in bile was poorly absorbed from the small intestine where its hydrolysis occurred slowly. After administration into the cecum, however, hydrolysis of the conjugate was rapid, and the rate of absorption of radioactive material was similar to that of free morphine. Treatment of rats with lincomycin (500 mg/1 in drinking water and 25 mg twice a day by gastric intubation for 4 days) significantly decreased cecal hydrolysis of the conjugate and the cecal absorption of radioactive material. Lincomycin treatment also increased fecal excretion of the conjugate in rats given morphine s.c. (5 mg/kg). These findings indicated that hydrolysis of morphine glucuronide is dependent upon the status of enteric bacteria and is a prerequisite to the enterohepatic circulation of morphine. In addition, after lincomycin treatment, a greater percentage of radioactivity excreted in the urine was associated with free morphine. This finding could be expained by the demonstration of pH dependence of renal excretion of morphine and a first-pass effect for this drug.

Ammonium Chloride↗