Biomedical subjects

R Vargas

Publications and source records attributed to R Vargas.

At least 19 recordsLinked to original sources

PubMed1995

Topological properties of two cubic phases of a phospholipid:cholesterol:diacylglycerol aqueous system and their possible implications in the phospholipase C-induced liposome fusion.

Water dispersions of phospholipid:cholesterol:diacylglycerol may, under certain conditions, originate either the lipid- and water-permeable Q224 cubic phase, or the lipid-permeable but water-impermeable Q227 cubic phase. These results are discussed within the framework of the phospholipase C-induced fusion of liposomes [Nieva et al. (1993) Biochemistry 32, 1054]. It is suggested that the cubic phases Q224 and Q227 represent two classes of lipid organization, one promoting, the other hindering the mixing of aqueous contents that is characteristic of membrane fusion. In this context, inverted micelles appear to be the end point of the fusion process, rather than fusion intermediates.

Bacillus cereus↗

PubMed1995

Order-disorder phenomena in myelinated nerve sheaths: V. Effects of temperature on rat sciatic and optic nerves, and structural differences between the two types of nerve.

We describe in this work X-ray scattering and electron microscope studies of rat sciatic and optic nerves as a function of temperature. The scattering experiments were analyzed as described in the previous papers of this series: a variety of parameters were determined, some of which characterize the lattice disorder, others the structure of the motif. The main results are the following. All the parameters determined by the X-ray scattering study vary with temperature and the temperature-dependence is specific for the type of nerve (sciatic or optic). Most of the disorder-related parameters display a minimum or a maximum in the vicinity of physiological temperature (38 degrees C in rat); this observation, strongly supported by the electron microscope study, shows that the degree of organization of myelin is highest near physiological temperature. The structure of the motif, as revealed by the electron density profile, is fairly different in the two types of nerves (in contrast with the assumption made by previous workers); the structure also varies with temperature and the temperature-induced alterations are nerve-type specific. In the two types of nerve the thickness of the lipid bilayer varies with temperature as expected for a lipid-containing system with hydrocarbon chains in the disordered conformation. In sciatic nerve the thickness of the (thinner) cytoplasmic polar layer, which is also the layer most affected by lattice disorder in this type of nerve, decreases dramatically with increasing temperature. In optic nerve, in which lattice disorder predominantly affects the extracellular layer, the thickness of both the cytoplasmic and the extracellular layer is barely affected by temperature.

Algorithms↗

PubMed1995

The interaction between endothelium-derived relaxing factor (EDRF) and eicosanoids in the regulation of the mesenteric microcirculation.

Locally produced eicosanoids and endothelium-derived factors are believed to be the mediators of vascular tone of various vascular beds including the mesentery. Using a small vessel isometric myograph which allows direct measurement of microvascular reactivity, the interaction of eicosanoids and endothelium-derived relaxing factor (EDRF) in regulating vascular tone of mesenteric microcirculation of the rat was characterized. The microvascular response to various vasoactive agents before and after inhibition of prostacyclin production with indomethacin (INDO, 5 microM) and inhibition of EDRF synthesis with N omega-nitro-L-arginine methyl ester (L-NAME, 50 microM) was compared. Analysis of dose-response curves for prostaglandin F2 alpha (PGF2 alpha), U46619, a stable thromboxane analog, and norepinephrine (NE) after pretreatment with INDO demonstrated that inhibition of endogenous eicosanoids significantly attenuated the vasoconstrictor response to PGF2 alpha and U46619 but not to NE. Inhibition of EDRF synthesis with L-NAME potentiated the vasoconstrictor response to PGF2 alpha, U46619, and NE. These results suggest that EDRF acts as the primary mediator of vasodilator tone in the mesenteric microcirculation rather than vasodilator cyclooxygenase products such as prostacyclin. It also appears that the vasoconstrictor action of PGF2 alpha and U46619 may be mediated by a release of an endogenous indomethacin-sensitive factor.

Animals↗

PubMed1995

Deleterious effects of inhibition of the renin-angiotensin system in neonatal rats.

The angiotensin I converting enzyme inhibitor (ACEI) perindopril (2 mg/kg body weight), the peripheral vasodilator dihydralazine (DHL) (25 mg/kg body weight) or distilled water was given daily from birth to day 14 to neonatal rats. Blood pressure, plasma creatinine, plasma renin activity (PRA), substrate (PRS) and concentration (PRC) and renin content of kidney tissue sections were evaluated on days 14 and 28. By day 14, a high mortality in the ACEI group was observed. ACEI, but not DHL, led to a significant fall (P < 0.01) in blood pressure, 57 +/- 11 versus 89 +/- 25 in the DHL group and 103 +/- 24 mmHg in controls, and to a dramatic increase in plasma creatinine. PRA and PRS were undetectable in ACEI-treated rats; in contrast, PRC and renal staining with anti-renin antibody were significantly increased in ACEI rats. On day 28, the blood pressure was normal in all groups and plasma creatinine returned to the normal range in ACEI rats. PRA, PRS and PRC were not significantly different in the ACEI group and controls. These results suggest that the renin-angiotensin system (RAS) plays a major postnatal role in the neonatal rat. Inhibition of the RAS during the first 2 weeks of life leads to high mortality, severe hypotension, reversible renal failure and a defect in circulating angiotensinogen.

Aging↗

PubMed1995

Pretreatment of normal humans with monophosphoryl lipid A induces tolerance to endotoxin: a prospective, double-blind, randomized, controlled trial.

OBJECTIVES: Endotoxin is one of the principal mediators of Gram-negative septic shock. Pretreatment with monophosphoryl lipid A, a hydrolyzed derivative of endotoxin from Salmonella minnesota R595, induces endotoxin tolerance and nonspecific resistance to infection in experimental animals. The present clinical trial was undertaken to test the response to monophosphoryl lipid A in humans and the ability of monophosphoryl lipid A to attenuate the response of normal human volunteers to U.S. Reference Ec-5 endotoxin. DESIGN: Prospective, double-blind, randomized, controlled trial. SETTING: Clinical research center. PATIENTS: Forty-four healthy volunteers. INTERVENTIONS: In part 1 of the study, 29 volunteers were randomized in varying ratios to receive vehicle control or monophosphoryl lipid A intravenously in a double-blind dose escalation trial. In part 2 of the study, 12 volunteers were randomized to receive either monophosphoryl lipid A (20 micrograms/kg) or vehicle control and, 24 hrs later, all 12 volunteers were challenged with U.S. Reference Ec-5 endotoxin (20 units/kg intravenous, bolus injection). Systemic response to endotoxin challenge was evaluated and compared between the monophosphoryl lipid A and vehicle control-pretreated subjects. MEASUREMENTS AND MAIN RESULTS: In part 1 of the study, subjective effects and increases in cytokine levels were not observed until a dose of 10 micrograms/kg of monophosphoryl lipid A was administered. Six volunteers receiving a maximum dose of 20 micrograms/kg experienced mild-to-moderate symptoms that did not require therapy. Moderate increases in temperature, heart rate, and tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-8 release were observed. IL-1 alpha and IL-1 beta were not detected but a significant increase in IL-1 receptor antagonist was observed. In part 2 of the study, monophosphoryl lipid A pretreatment reduced the number of volunteers who experienced one or more subjective complaints after endotoxin administration (3/6 vs. 6/6; p = .09). The febrile response and tachycardic response to endotoxin were significantly reduced by pretreatment with monophosphoryl lipid A. Monophosphoryl lipid A-pretreated volunteers demonstrated significantly reduced concentrations of TNF-alpha after endotoxin challenge, as compared with subjects treated with vehicle control (84 +/- 76 vs. 244 +/- 128 pg/mL; p < .05). IL-6 concentrations (100 +/- 91 vs. 268 +/- 171 pg/ml; p < .05) and IL-8 concentrations (136 +/- 86 vs. 632 +/- 323 pg/mL; p < .05) elicited by endotoxin challenge were also significantly reduced by monophosphoryl lipid A pretreatment. CONCLUSIONS: Data indicate that monophosphoryl lipid A, in a dose 10,000 times that of endotoxin, used in experimental pyrogenicity trials, is well tolerated in human volunteers. Pretreatment of normal human volunteers with monophosphoryl lipid A attenuated the systemic response to bacterial endotoxin. These data support further clinical testing of monophosphoryl lipid A for the prevention or amelioration of the severe sequelae of sepsis.

Adolescent↗

PubMed1995

Effect of estradiol 17 beta on pressor responses of rat mesenteric bed to norepinephrine, K+, and U-46619.

We reinvestigated the effect of estradiol 17 beta on the responses of adrenergic and nonadrenergic vasoconstrictors characterized it in terms of steroid specificity, time course, and the role of classic estrogen receptors. We evaluated the effect of estradiol 17 beta on the pressor responses of isolated perfused rat mesenteric vascular bed (McGregor's preparation). Estradiol 17 beta (7-700 nM) significantly increased the pressor response to bolus applications of norepinephrine (NE) (p < 0.05). However, estradiol 17 beta did not significantly increase the responses to endogenous NE release induced by electrical field stimulation. Other steroids, testosterone, and the 17 alpha isomer of estradiol (7 and 700 nM) were ineffective. Estradiol 17 beta (700 nM) also significantly increased the maximum pressor response of rat mesenteric preparation to both the prostaglandin endoperoxide analogue U-46619 and to K+. The potentiation by estradiol 17 beta of mesenteric vasoconstriction elicited by NE, K+, and U-46619 was rapid (2-8 min), suggesting that a nuclear receptor may not be involved. This notion received further support in that significant potentiation of the NE-induced pressor response was also observed with estradiol 17 beta conjugated to albumin (700 nM), but not when electrical field stimulation was used. The conjugate increased the effect of all NE concentrations. Its effect was also more consistent (p < 0.01) than that elicited by free estradiol 17 beta. The dose-response curve was shifted to the left, and the maximum effect was increased. These data suggest that estradiol 17 beta may possess rapid nongenomic actions unrelated to nuclear receptor binding and gene transcription.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1995

Effect of testosterone treatment on vasoconstrictor response of left anterior descending coronary artery in male and female pigs.

Androgens may be risk factors in the pathogenesis of coronary artery disease by promoting coronary vasoconstriction. We studied the effect of testosterone treatment on coronary vascular reactivity of male and female domestic pigs treated for 2 weeks with either placebo or testosterone 10 mg/kg subcutaneous (s.c.) pellets. Vascular reactivity was studied in ring segments (4-5 mm) isolated from the left anterior descending coronary artery (LAD). No significant sex difference was noted in the response of LAD segments from placebo-treated male and female animals to KCl and prostaglandin F2 alpha (PGF2 alpha). Androgen treatment increased the maximum response (Tmax) of intact vessels to KCl from 3,647 +/- 689 mg in controls to 8,939 +/- 1,284 mg in testosterone-treated males (p < 0.01) and from 3,405 +/- 669 to 10,524 +/- 1,663 mg in testosterone-treated female pigs (p < 0.01). Testosterone similarly increased the response to PGF2 alpha 10(-6) M from a mean of 2,149 +/- 1,036 to 3,163 +/- 867 mg in males (p < 0.05) and from 2,076 +/- 810 to 3,565 +/- 578 mg in female segments (p < 0.05). Endothelial denudation significantly decreased the potentiating effect of testosterone treatment in males to both KCl and PGF2 alpha (p < 0.05), but not in segments from females. Our data show that testosterone treatment potentiates contractility of porcine LAD segments to both receptor- and nonreceptor-mediated agonists. In male pigs, this effect may be mediated by an effect on endothelium.

Animals↗

PubMed1995

Pheocromocytoma and gastrointestinal bleeding.

A 46-year-old patient who presented with an abdominal mass and gastrointestinal bleeding associated with an extra-adrenal pheochromocytoma is discussed. He had no history of hypertension. An ill-defined mass was felt at the upper abdomen. CT and arteriography confirmed the presence of a large mass with calcifications in the right paravertebral region. Upper endoscopy revealed multiple varices at the third portion of the duodenum. Abdominal exploration revealed a huge tumor at the root of the small bowel mesentery with multiple arterial and venous vessels entering the third portions of the duodenum. The tumor was unresectable. Biopsy demonstrated a pheochromocytoma. The patient developed pulmonary edema in the immediate postoperative course. He recovered and was discharged home on Dibenzyline. He has been readmitted on various occasions with gastrointestinal bleeding and congestive heart failure. Presently he is working and feels relatively well 5 years after the operation. A review of the literature for gastrointestinal complications of pheochromocytomas was done. There is a scarcity of reports of gastrointestinal bleeding associated with pheochromocytomas.

Biopsy↗

PubMed1994

Evaluation of the antipyretic effect of ketorolac, acetaminophen, and placebo in endotoxin-induced fever.

The authors studied the antipyretic effect of three intramuscular doses of ketorolac (15, 30, and 60 mg), acetaminophen 650 mg PO, and placebo in healthy male volunteers using an endotoxin-induced fever model. In this double-blind, double-dummy, parallel study, subjects were assigned randomly with equal probability to one of the above treatment groups. Thirty minutes after study medication administration, a 20 unit per kilogram dose of reference standard endotoxin (RSE) was administered intravenously, and temperature was determined every 15 minutes for an 8-hour period. Compared with placebo, all active treatment groups demonstrated a statistically significant reduction in both adjusted area under the temperature-by-time curve (AAUC) and the maximum increase over baseline temperature (dTmax). Furthermore, the 30 mg intramuscular dose of ketorolac demonstrated approximately the same antipyretic activity as the 650 mg oral dose of acetaminophen, and there was a statistically significant dose response across the three ketorolac doses studied (P < .0001). The majority of side effects reported during this study were symptoms associated with fever, including chills, headache, myalgia, and dizziness, all of which are effects of RSE. The frequency of side effects tended to be less in the treatment groups with the greatest antipyretic activity.

Acetaminophen↗

PubMed1994

Inhibitory activity of 3-methylenhydroxy-5-methoxy-2,4-dihydroxy tetrahydrofurane isolated from Selaginella lepidophyla on smooth muscle of Wistar rat.

A new compound, 3-methylenhydroxy-5-methoxy-2,4-dihydroxy tetrahydrofurane, has been isolated from a methanol extract of Selaginella lepidophyla. The structure is based on 1H-NMR, 13C-NMR and MS analysis. The compound was tested on uterus (oestrus), ileum and duodenum of Wistar rats. It proved to have a slight inhibitory effect on the contraction response of the uterus, but it did not have any effect on the two other muscles.

Animals↗

PubMed1994

[Natural killer cytolytic activity in renal and prostatic cancer].

Natural killer cytolytic activity, the basis of cancer immunotherapy that uses cytolytic cells, may be impaired in cancer. The aim of this work was to study in vitro the natural killer cytolytic activity and its response to the immunomodulators interleukin-2, interferon and phytohemagglutinin stimulated lymphocyte proliferation in a group of 9 patients with renal cell cancer and 6 with prostatic cancer. The results were compared with those of 20 normal volunteers. Twelve patients were operated and were studied twice 48 h and 14 days after surgery. Natural killer cytolytic activity was significantly lower in renal cell and prostatic cancer patients than controls (3.3 +/- 1.6, 4.9 +/- 2.2 and 20.6 +/- 3.7% of specific lysis respectively). This activity was not modified in cancer patients by interleukin-2 50 UI/ml or interferon 3000 UI/ml and did not differ in the two postoperative periods. Phytohemagglutinin stimulated lymphocyte proliferation was also lower in cancer patients, compared to controls (stimulation index of 18 +/- 3 and 26.5 +/- 5 respectively). It is concluded that these patients have a low immunological level and that this study is the first step towards an immunological characterization of cancer patients that are candidate to adoptive immunotherapy.

Adult↗

PubMed1992

Order-disorder phenomena in myelinated nerve sheaths. IV. The disordering effects of high levels of local anaesthetics on rat sciatic and optic nerves.

Sequences of 15 minute X-ray scattering spectra were recorded with rat sciatic and optic nerves, superfused with tetracaine-containing Ringer solutions. The spectra were analysed using the algorithm advocated in this series of papers. The main results, as a function of the time of exposure to tetracaine, were: the mean value of the repeat distance increases; its variance decreases; the average number of membrane pairs per coherent domain decreases; the fraction of isolated membrane pairs increases. Eventually, the spectra were observed to give way to the continuous intensity curve of a single, isolated membrane pair. At all stages of the experiment the continuous intensity curves were found to differ from one type of nerve to the other, and to be invariant, for each type of nerve, with respect to the tetracaine treatment. The X-ray scattering study clearly identified the nature of the structural differences between the two types of myelin sheaths: in that of native sciatic nerves, packing disorder preferentially affects the cytoplasmic space of the membrane pair, and tetracaine disrupts the packing in that space; in the myelin of optic nerves it is the external space that is preferentially affected by packing disorder and disrupted by tetracaine. The time-course of the structure parameters showed that, at any stage of the experiment, tetracaine acts preferentially on the more highly disordered regions of the structure and totally disrupts them. These results corroborate earlier conclusions reported in the previous papers of this series. An electron microscope study was also performed on tetracaine-treated nerves: the results, in close agreement with those of the X-ray scattering study, neatly confirm the conclusions given above. In a more general way, the remarkable agreement between the results of the analysis of the X-ray scattering spectra and the electron microscope observations strongly supports the validity of the physical model used in this series of papers and the correctness of the mathematical treatment that we advocate. Finally, the relations between this work and the work of others are discussed. It must be stressed that the present work bears on the toxic rather than on the anaesthetic effects of tetracaine.

Action Potentials↗

PubMed1992

Cubic phases of lipid-containing systems. The structure of phase Q223 (space group Pm3n). An X-ray scattering study.

The hexagonal (H) and the cubic (Q223) phases of the systems dodecyltrimethylammonium chloride-water and palmitoyllysophosphatidy choline-water have been studied by X-ray scattering techniques. The signs of the reflections of phase H were determined by a systematic study as a function of the water content, those of phase Q223 were assessed using a pattern recognition approach based upon the axiom that the histograms of the electron density maps of phases Q223 and H, extrapolated to the same concentration and properly normalized in scale and shape, are very similar to each other. In the case of phase Q223, all the sign combinations (the phi-sets) compatible with the observed reflections were generated, and each of the corresponding histograms was compared with the histogram of the map of phase H. One novelty of this work is the use of a highly sensitive criterion to estimate the similarity of the histograms, namely the distance in the six-dimensional space of the moments [mean value of (delta rho)n]1/n, for 3 greater than or equal to n greater than or equal to 8. In the two systems, the use of this criterion has led to the unambiguous choice of one electron density map. The maps show that the structure of phase Q223 consists of disjointed micelles (of type I), belonging to two different classes: those of one class are quasi-spherical in shape and are centered at the points a, those of the other class are disc-shaped and are centred at the points c. The results of this work rule out a structure formed by a cage-like distribution of rods enclosing a set of quasi-spherical micelles and is consistent with previous proposals. This is the second example, after that of phase Q227, of a micellar cubic phases in lipid-containing systems; all the known examples of phase Q223 are of type I, those of phase Q227 of type II.

Freeze Fracturing↗

PubMed1992

Lipid polymorphism: a correction. The structure of the cubic phase of extinction symbol Fd-- consists of two types of disjointed reverse micelles embedded in a three-dimensional hydrocarbon matrix.

The X-ray scattering study of a cubic phase of extinction symbol Fd--, recently performed on a lipid extract (PFL) from Pseudomonas fluorescens [Mariani et al. (1990) Biochemistry 29, 6799-6810] has been extended to several other systems, all consisting of mixtures of water-miscible (MO, PC, PE, oleate) and of water-immiscible (FA, DG) lipids, plus water. In all of these systems the cubic phase was observed in the presence of excess water. Some inconsistencies observed between PFL and the other systems, the fact that in PFL one of the reflections of the cubic phase happened to coincide with the strongest reflection of the hexagonal phase, and the finding, in one of the original cubic samples of PFL kept in the cold for more than 3 years, that the intensity of one of the reflections had decreased dramatically all indicated that a nonnegligible amount of a hexagonal impurity was in fact present in the samples of PFL originally thought to contain a pure cubic phase. The intensities were corrected for that impurity and analyzed again using a pattern recognition approach based upon the axiom that the histogram of the electron density maps is invariant with respect to physical structure, when different phases are compared whose chemical composition is the same. The hexagonal phase provided the reference phase for the comparison. The moments mean value of (delta rho)n were used to compare the histograms.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallography↗

PubMed1992

Human liver protein map: a reference database established by microsequencing and gel comparison.

This publication establishes a reference human liver protein map obtained with immobilized pH gradients. By microsequencing, 57 spots or 42 polypeptide chains were identified. By protein map comparison and matching (liver, red blood cell and plasma sample maps), 8 additional proteins were identified. The new polypeptides and previously known proteins are listed in a table and/or labeled on the protein map, thus providing a human liver two-dimensional gel database. This reference map can be used to identify protein spots on other samples such as rectal cancer biopsies.

Amino Acid Sequence↗

PubMed1992

In vitro effect of oestradiol on thymidine uptake in pulmonary vascular smooth muscle cell: role of the endothelium.

1. The effect of different concentrations of oestradiol-17 beta (3-300 nM) on [3H]-thymidine uptake was studied in segments from canine pulmonary artery, and cultures of rat pulmonary vascular smooth muscle cells (VSMC). 2. Incubation with oestradiol-17 beta for 24 h, potentiated in a concentration-dependent manner [3H]-thymidine uptake in VSMC cultures. 3. Oestradiol-17 beta potentiated thymidine uptake by pulmonary arterial segments but only when the endothelium had been removed. Autoradiography showed dense incorporation of radioactive thymidine in the vascular smooth muscle cells of the media. 4. The non-steroidal oestrogen, stilboestrol (300 nM), also significantly potentiated [3H]-thymidine uptake, in both VSMC cultures and pulmonary artery segments. Testosterone was ineffective at a similar concentration. 5. Pre-incubation of the pulmonary VSMC with the anti-oestrogen tamoxifen (1 microM) antagonized the potentiating effect of oestradiol-17 beta on [3H]-thymidine incorporation. The effect of tamoxifen was less pronounced in pulmonary arterial segments. 6. These data suggest that oestrogen may promote proliferation of pulmonary VSMC. Endothelial injury or dysfunction may be an important factor in the expression of the oestrogenic effect. 7. We speculate that plasma oestrogen may be a contributing factor to the proliferative lesion observed in certain forms of pulmonary vascular injury in women.

Animals↗

PubMed1992

Safety and pharmacokinetics of multiple doses of intravenous ofloxacin in healthy volunteers.

The safety and pharmacokinetics of ofloxacin in 48 healthy male volunteers were studied in a two-center, randomized, double-blind, placebo-controlled study. Ofloxacin (200 or 400 mg) or placebo was administered as 1-h infusions every 12 h for 7 days. Plasma ofloxacin concentrations were measured by high-performance liquid chromatography. Mean harmonic half-lives ranged from 4.28 to 4.98 h in the 200-mg dosing group and from 5.06 to 6.67 h in the 400-mg dosing group. Intragroup comparisons of trough plasma concentration-versus-time data from study days 2 through 7 revealed that steady state was achieved by day 2 of both multiple-dose regimens. Intergroup comparisons of mean harmonic half-lives, the areas under the concentration-time curve from 0 to 12 and 0 to 60 h, clearance, and apparent volume of distribution (area method) revealed that the pharmacokinetics of ofloxacin are dose independent. Both ofloxacin dosage regimens appeared to be reasonably well tolerated. The two dosage regimens of ofloxacin, 200 or 400 mg every 12 h, appear to be safe and provide serum drug concentrations in excess of the MICs for most susceptible pathogens over the entire dosing interval.

Adolescent↗

PubMed1991

Order-disorder phenomena in myelinated nerve sheaths. III. The structure of myelin in rat optic nerves over the course of myelinogenesis.

An X-ray scattering study was performed on optic nerves dissected from rats aged from ten days to one year. The spectra were analysed using the procedure described in the previous papers of this series. Each experiment yields the values of a variety of parameters: the average D and the variance sigma D of the repeat distance, the average number mean value of N of motifs per crystallite, the fraction alpha loose of myelin that does not belong to the compact sheaths, the sets [idiff(h/D)] and [imotif(k/2D)] that suffice to define, respectively, the spurious scattering and the continuous intensity curve of the elementary membrane pair. A surprising result is that, in the native optic, as previously found in the swollen sciatic nerves, the stacking disorder affects the external space, whereas in native sciatic nerves the disorder affects the cytoplasmic space. An analysis of the evolution of the structure parameters as a function of the age of the animal and a comparison with the results previously obtained with rat sciatic nerves led to the following conclusions: the structure of the elementary membrane pair is constant throughout myelinogenesis; mean value of N is much smaller in optic than in sciatic nerves; mean value of N and the degree of myelination increase with age in the two types of nerve; D is smaller in optic than in sciatic nerves; in optic nerves, D decreases slightly with age, but in sciatic nerves it increases; sigma D is strongly age-dependent in optic nerves, but almost age-independent in sciatic nerves. In contrast to sciatic, the structure of optic nerve myelin was found to be almost insensitive to hypertonic solutions. Finally, a pair of electron density profiles was selected, quite similar to those selected previously in sciatic nerves, one corresponding to Caspar & Kirschner's the other to Worthington & McIntosh's proposals, neither of which can be ruled out according to the criteria used in this work.

Aging↗