Myelin-Associated Glycoprotein: Electron Microscopic Immunocytochemical Localization in Compact Developing and Adult Central Nervous System Myelin

Light microscopic immunocytochemical studies have shown that myelin-associated glycoprotein (MAG) is localized in myelin of the developing CNS; but in the adult, MAG appears to be restricted to periaxonal regions of myelinated fibers. To extend these observations, we embedded optic nerves of 15-day-old rats, adult rats, and an adult human in epon after aldehyde and osmium tetroxide fixation. After 5% H2O2 pretreatment, thin sections were immunostained with 1:250-1:5,000 rabbit antiserum to rat CNS MAG according to the avidin-biotin-peroxidase complex (ABC) method. Dense deposits of reaction product covered compact myelin in both developing and adult optic nerves. When we used 1:500, 1:1,000, and 1:2,000 anti-MAG, less intense immunostaining of myelin was found. We also obtained the same localization in compact myelin with the peroxidase-antiperoxidase (PAP) method. With 1:250 anti-MAG, dense deposits of reaction product were not observed on axolemmal membranes or on oligodendroglial membranes located periaxonally and paranodally. In thin sections of adult human optic nerve, anti-MAG also stained compact myelin intensely. When thin sections of rat and human optic nerves were treated with preimmune or absorbed serum, no immunostaining was observed. Immunoblot tests showed that our MAG antisera did not react with any non-MAG myelin proteins. In contrast with earlier light microscopic data, this study shows that MAG localization does not change during CNS development; both developing and adult compact myelin sheaths contain MAG. As many biochemical studies also show that MAG is present in compact myelin, we suggest that this 100,000 dalton glycoprotein now be called myelin glycoprotein (MGP) instead of MAG.     

Hormonal effects, tolerability, and preliminary kinetics in men of MK-906, a 5 alpha-reductase inhibitor.

The hormonal effects following the acute (single dose) administration of a 4-azasteroid inhibitor of 5 alpha-reductase (MK-906) were evaluated in 10 healthy male volunteers. Marked suppression of serum dihydrotestosterone (DHT) was observed after the administration of single doses as low as 12.5 mg. The mean percent decrease in DHT at 24 hours in the group treated with a single 25-mg dose was 56% +/- 10% compared with the baseline. The suppression of plasma DHT levels continued for up to 72 hours. This study demonstrates that administration of single oral doses (12.5 to 400 mg) of MK-906 results in a significant decrease in the conversion of testosterone to DHT.     

Tributes to Truman G. Yuncker and Ethel Claflin Yuncker

Editor’s note: This tribute was prepared by Barbara Yuncker from a recorded interview she had with Dr. Callejas during his six-week visit to the Garden’s Herbarium in September 1988 to study the Piperaceae specimens received from DePauw University.     

Low temperature, gibberellin and acid lipase activity in removal of apple seed dormancy

The activity of acid lipase and the level of gibberellin A₄ (GA₄) were determined in apple embryos excised from seeds after different time periods of stratification and subsequently cultured in darkness at 4°C or at 25°C. Enzyme activity and GA₄ content were higher at 4°C. Exogenous gibberellin stimulated lipase activity, while AMO-1618, an inhibitor of gibberellin biosynthesis, inhibited, to the same degree, both the enzyme activity and the GA₄ accumulation. The involvement of GA₄ and lipolytic enzymes in cold-mediated removal of embryonal dormancy has been discussed and compared with the role of these two factors in light-stimulated germination of dormant apple embryos, described earlier (Smoleńska and Lewak 1974).     

Swelling and contraction of heart mitochondria suspended in ammonium phosphate

Bovine heart mitochondria which have been allowed to swell in isotonic NH ₄ ⁺ phosphate contract in response to initiation of oxidative phosphorylation. The contraction occurs optimally at pH 6.0 and appears from inhibition studies to result from P_i uptake being slower than removal of internal P_i via phosphorylation of external ADP. Similar results are obtained when K⁺ + nigericin is substituted for NH ₄ ⁺ . Mersalyl inhibition of P_i transport in respiring, nonphosphorylating mitochondria which have been allowed to swell in NH ₄ ⁺ phosphate reveals a contractile process having an alkaline pH optimum. This contraction resembles closely the contraction observed in salts of strong acids and presumably occurs by electrophoretic ejection of P_i anions driven by electrogenic H⁺ ejection.     

Explant culture of rat colon: A model system for studying metabolism of chemical carcinogens

Summary An explant culture system has been developed for the long-term maintenance of colonic tissue from the rat. Explants of 1 cm² in size were placed in tissue-culture dishes to which was added 2 ml of CMRL-1066 medium supplemented with glucose, hydrocortisone, β-retinyl acetate, and either 2.5% bovine albumin or 5% fetal bovine serum. The dishes were placed in a controlied-atmosphere chamber which was gassed with 95% O₂ and 5% CO₂. The chamber then was placed on a rocker platform which rocked at 10 cycles per min causing the medium to flow intermittently over the epithelial surface. The explants were incubated at 30°C. The viability of the tissue was measured both by incorporation of specific precursors into cellular macromolecules and by monitoring of tissue morphology with light and electron microscopy. Cultured rat colon was able to metabolize benzo[a]pyrene, 7,12-dimethylbenz[a]anthracene, aflatoxin B₁, dimethylnitrosamine, 1,2-dimethylhydrazine, and methylazoxymethanol acetate into chemical species that bind to cellular DNA and protein.     

Histochemical demonstration of collagen fibers in ascorbic-acid-fed cell cultures

Summary Nine cultures of fibroblast cell types and 13 epithelial-like cell types were maintained for 1 week in media supplemented with L-asborbic acid (50 μg per ml). All fibroblast-like cultures produced extracellular fibers that stained positively by a silver-impregnation reticulin stain. Nine of the 13 epithelial-like cultures produced fibers that stained positively for reticulin. Nearly all cultures not supplemented with ascorbic acid showed no fiber staining. Those few lines that stained positively for reticulin in the absence of ascorbic-acid supplementation demonstrated only slight reticulin formation. Reticulin from one fibroblast culture and one epithelial culture was examined by electron microscopy, and the silver-impregnated fibrils were morphologically identical to collagen. The reticulin was digestible with collagenase, providing further evidence that the silver-impregnation reticulin stain identifies collagen in culture. The demonstration of collagen can be performed easily in histology laboratories using Formalin-fixed cells, and provides a means of assaying a functional property of cells in culture which is characteristic of connective tissue fibroblasts in general as well as certain specialized epithelia.     

Sugar concentration of fruits and their detection via color in the Central American spider monkey (Ateles geoffroyi)

Although most arguments explaining the predominance of polymorphic color vision in platyrrhine monkeys are linked to the advantage of trichromacy over dichromacy for foraging for ripe fruits, little information exists on the relationship between nutritional reward and performance in fruit detection with different types of color vision. The principal reward of most fruits is sugar, and thus it seems logical to investigate whether fruit coloration provides a long-distance sensory cue to primates that correlates with sugar content. Here we test the hypothesis that fruit detection performance via trichromatic color vision phenotypes provides better information regarding sugar concentration than dichromatic phenotypes (i.e., is a color vision phenotype with sufficient red-green (RG) differentiation necessary to "reveal" the concentration of major sugars in fruits?). Accordingly, we studied the fruit foraging behavior of Ateles geoffroyi by measuring both the reflectance spectra and the concentrations of major sugars in the consumed fruits. We modeled detection performance with different color phenotypes. Our results provide some support for the hypothesis. The yellow-blue (YB) color signal, which is the only one available to dichromats, was not significantly related to sugar concentration. The RG color vision signal, which is present only in trichromats, was significantly correlated with sugar content, but only when the latter was defined by glucose. There was in fact a consistent negative relationship between fruit detection performance and sucrose concentration, although this was not significant for the 430 nm and 550 nm phenotypes. The regular trichromatic phenotypes (430 nm, 533 nm, and 565 nm) showed higher correlations between fruit performance and glucose concentration than the other two trichromatic phenotypes. Our study documents a trichromatic foraging advantage in terms of fruit quality, and suggests that trichromatic color vision is advantageous over dichromatic color vision for detecting sugar-rich fruits.