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Biomedical subjects

R Calvert

Publications and source records attributed to R Calvert.

At least 73 records · Page 4Linked to original sources
PubMed1982

Clobazam in catamenial epilepsy. A model for evaluating anticonvulsants.

The cyclical exacerbations of epilepsy (catamenial epilepsy) were used to assess the antiepileptic effect of a benzodiazepine, clobazam. Doses of 20 mg, and in some cases 30 mg, per day were compared with placebo over predetermined ten-day periods in a double-blind cross-over study. The results were evaluated by preference in a sequential procedure. In 14 of 18 patients who received both treatments clobazam was superior to placebo, and in 4 patients no preference was established. Clobazam completely prevented seizures in most of the patients, and toxic effects were of low frequency and severity.

Acute Disease↗
PubMed1981

Effect of amniotic fluid and fetal bovine serum on the morphogenesis of mouse duodenal villi in organ culture.

When duodenal explants of 15-day mouse foetuses are cultured in Trowell T8 medium during 72 h, villi do not develop. If mouse amniotic fluid (25%) is added to the same medium, short villi appear after 12 h of culture and medium size villi are seen at 48 h. Bovine amniotic fluid and fetal bovine serum promote cell growth but morphogenesis of intestinal villi is far less stimulated.

Amniotic Fluid↗
PubMed1981

Effects of immunization with Freund's complete adjuvant and isologous spermatozoa on the seminiferous epithelium and blood-testis barrier in guinea pigs.

In order to gain insight into the earliest pathological changes underlying the development of autoimmune aspermatogenic orchitis (AIAO) the blood-testis barrier was studied by light and electron microscopy, freeze-etching, and cytochemical techniques early (from 1 to 8 days after adjuvant treatment of isoimmunization). At later times (16 to 21 days) the study was carried out by light microscopy only. Adult male guinea pigs were used either as controls or immunized with Freund's complete adjuvant alone or together with pertussis vaccine. An additional group comprised animals immunized with a suspension of isologous spermatozoa emulsified in Freund's complete adjuvant and with pertussis vaccine. Ultrastructural studies of the testes of experimental animals showed, at earlier periods, apparently normal Sertoli junctions. However, in the adluminal compartment, distended gaps were seen between the facing membranes of adjacent Sertoli cells. At later periods, a massive destruction of the germinal cells were observed. In freeze-fracture replicas, the Sertoli junctions of testes belonging to all the experimental groups were characterized by an irregular network of occasionally interrupted strands of particles associated with the P face (PF). Large concavities determined distensions between interconnecting ridges. The gap junctions were increased in number and in surface. Tracer studies using horseradish peroxidase showed that the marker permeated the myoid cells of a greater proportion of tubules than in control animals. Within the seminiferous epithelium there was only a limited passage of the marker towards the lumina of the tubules. Yet the tracer was always excluded from the adluminal compartment by the Sertoli tight junctions. Our observations suggest the possibility that the FCA causes a loosening of the Sertoli junctions. This condition could enhance exchanges between two antigenically different cellular compartments and, thus, favor occurrence of an autoimmune reaction when cytotoxic factors are experimentally induced, as in iso- or autoimmunization.

Animals↗
PubMed1981

The occluding junctions of mouse duodenal enterocytes during development. A freeze-fracture study.

The architecture of occluding junctions during the differentiation of the mouse duodenum was studied in freeze-fractured material. Irregular zonulae occludentes (ZO) (Type I) are numerous during fetal life, and are characterized by their irregular width, and by the presence of basal open-ended extensions fused with the discontinuous basal strand of the ZO. Regular ZOs (Type II), typical of the adult villous epithelium, appear after Type I junctions by day 16 of gestation. Two patterns are distinguishable: in the first, parallel strands of ridges and furrows are found without crossing branches; in the second pattern, the junction zone is organized like a network of short branches forming various types of polygons. In fetal and adult mice fasciae occludentes (FO) (Type III) are presented on the lateral cell membranes: in unfixed specimens particles are found in the furrows of the E-face and pits on the ridges of the P-face. In fixed tissues, the particles are aligned on the ridges of the P-face. These results indicate that fixation with glutaraldehyde modifies considerably the affinity of junctional particles toward the P-face during the fracture process. Moreover, the presence of numerous large FOs on the lateral cell membranes of enterocytes during late fetal life and in the adult, is possible related to cell movement along the intestinal villi.

Animals↗
PubMed1981

Establishment of regional differences in brush border enzymatic activities during the development of fetal mouse small intestine.

In order to study the establishment of regional differences in brush border enzymic activities during the development of fetal mouse small intestine we have followed (1) the differentiation of microvilli by morphometry, and (2) the developmental pattern of three brush border enzymes (lactase, glucoamylase and alkaline phosphatase). From day 16 to day 19 of gestation, the height of duodenal microvilli increases 2.4 times on the absorptive cells located near the tip of the villi. During the same period in the upper half of the duodenal villi, the number of microvilli per square micrometer rises by a factor of 2.4 and the microvillous surface area increases by a factor of 5.2. The differentiation of ileal microvilli follows a similar pattern but they are always shorter and less numerous than those of the duodenum. Lactase activity appears at 18 days of gestation; the other two brush border enzymes are first detected at 16 days of gestation. Afterwards all three enzyme activities increase rapidly and a decreasing gradient of activity is established from the proximal to the distal segment of the small intestine. Hence, the structural development of the microvilli and the appearance of brush border enzyme activities occur simultaneously and a proximo-distal gradient is already established at 16 days of gestation.

Alkaline Phosphatase↗
PubMed1981

Selection of a chemically defined medium for culturing fetal mouse small intestine.

We evaluated six commercially available tissue culture media in their capacity to support villi morphogenesis and enterocyte differentiation during duodenal development of the fetal mouse in vitro: McCoy's 5A, Medium 199, Swim's S77, Trowell T8, Leibovitz L-15, and RPMI-1640. The duodenal segments were resected at 15 d gestation, before the formation of intestinal villi. In the segments cultured with the first four media, no villi differentiated even at 72 h culture. The number of epithelial cells per transverse section of the explants did not increase at 24 h and thereafter the number of epithelial cells decreased, except with McCoy's 5A. With the Leibovitz and RPMI media, rudimentary villi differentiated at 24 h of culture and they attained their longest length at 48 h. With the RPMI medium, the number of epithelial cells doubled at 24 h of culture and with Leibovitz medium it doubled at 48 h. At the fine structural level absorptive cells remained poorly differentiated with all the media studied. Goblet cells were easily identified after 24 h culture; they had a well developed rough endoplasmic reticulum and numerous mucous granules. Endocrine cells differentiated in culture and they were loaded with secretion granules. It was concluded that the small intestine of the fetal mouse can be kept in organ culture for at least 72 h. Full maturation of absorptive cells seemed to require some additional factor(s) as they remained poorly differentiated with all the media studied. Because well differentiated endocrine cells were present in all the explants, it appeared that gastrointestinal hormones do not affect villi morphogenesis and absorptive cells differentiation.

Animals↗
PubMed1981

Development of gamma-glutamyltranspeptidase activity in mouse small intestine: influence of cortisone and thyroxine.

The fetal and postnatal development of gamma-glutamyltranspeptidase (gamma-GT) activity has been examined in the different parts of the mouse small intestine. At 17 days of gestation, gamma-GT is present in all intestinal thirds and a decreasing gradient of activity from the proximal to the distal segments is already established. From 17 days of gestation up to 5 days after birth, a dramatic fall of activity is observed in all segments. gamma-GT activity reaches adult level before weaning in the proximal segment while it increases only during the 3rd postnatal week in the middle and distal intestinal segments. Daily administration of cortisone acetate (25 microgram/g b.w./day) for 3 days to 8-day-old mice elicits a premature increase of gamma-GT activity in all intestinal thirds, the maximal increase being observed in the proximal segment. On the other hand, thyroxine (1 microgram/g b.w./day) has no or little effect on the normal development of gamma-GT activity.

Aging↗
PubMed1981

The effect of epidermal growth factor (EGF) on the differentiation of the rough endoplasmic reticulum in fetal mouse small intestine in organ culture.

The differentiation of the rough endoplasmic reticulum (RER) of mouse duodenal absorptive cells located at the tip of the villi at 17 days of gestation was compared to that of absorptive cells in duodenal explants of 15-day-old mouse fetuses cultured for 72 hr 1) with Trowell T8 medium (without insulin) alone or supplemented 2) with epidermal growth factor (EGF; 100 ng/ml) or 3) with 25% bovine amniotic fluid (BAF). Glucose-6-phosphatase activity (G6Pase) was localized cytochemically to ensure a better identification of the RER. The intersections of a double lattice falling over and outside the RER were counted and the percentage of intersections over the RER was estimated. With this method, the extent of the RER is not statistically different when the absorptive cells in utero are compared to those of explants cultured with EGF. However, the extent of the RER in the absorptive cells cultured with Trowell T8 medium alone or supplemented with BAF is 50% lower than in the former two groups. It is concluded that EGF promotes the maturation of duodenal absorptive cells in organ culture.

Animals↗
PubMed1980

Properties and structural role of the subunits of human spectrin.

The subunits of spectrin from human erythrocytes were separated by ion-exchange chromatography on hydroxyapatite in the presence of urea. When renatured from the urea solution they are found to be monomeric, although the smaller subunit (band 2) is prone to aggregation. In shape, solubility and secondary structure the subunits resemble the native spectrin dimer, indicating that subunit interaction is not essential for maintaining the native conformation. When the subunits are recombined, a dimer with the sedimentation coefficient of the native species is formed. This constitutes direct evidence that native spectrin is a heterodimer, rather than a mixture containing homologous and heterologous species. The interaction of the separated subunits with the chymotryptic fragment of the spectrin-binding protein (protein 2.1, or ankyrin) of the erythrocyte membrane was studied. Only the smaller subunit has the ability to bind, and thus presumably contains the site by which the cytoskeleton is attached to the plasma membrane. On the other hand, the formation of a complex with F-actin and protein 4.1 requires the presence of both subunits. A complex of these proteins with band 2 is formed, however, when traces of an additional, as yet unidentified, protein are present.

Adult↗
PubMed1980

A conformational study of human spectrin.

Urea denaturation profiles of spectrin dimer, measured by circular dichroism in the regions of the peptide and aromatic Cotton effects, reflect the existence of several independently unfolding domains, as well as the presence of flexible, non-globular structure. As shown by sedimentation velocity and cross-linking experiments, dissociation of the two subunits largely precedes unfolding. The flexible, segmentally mobile structure reveals itself further in the appearance of sharp signals in the high-resolution proton magnetic resonance spectrum. These spectra reveal that some 20% of the chain is in the segmentally mobile form, regardless of ionic strength, and that its composition is highly hydrophobic, with few polar side chains. This suggests the possibility that this part of the molecule may penetrate into the lipid bilayer. Conformational stability of the spectrin dimer, as measured by circular dichroism, is substantially unaffected by the state of phosphorylation and by the ionic strength, even though the latter is known to affect the size or shape of the molecule.

Humans↗
PubMed1979

In vitro formation of a complex between cytoskeletal proteins of the human erythrocyte.

The formation of a high-molecular weight complex between spectrin and F-actin depends on the presence of a third cytoskeletal constituent, protein 4.1. Electron microscopy shows that in this ternary complex the actin filaments are linked by bridges, which have the appearance of spectrin. The spectrin must be in the tetrameric state for such bridges to form: the dimer is evidently univalent, for it binds but forms no cross-links. G-actin also fails to form extended complexes. It is inferred that in the native cytoskeleton the spectrin is tetrameric and associated with 4.1 and probably oligomers of actin.

Actins↗
PubMed1979

Effect of clofibrate on the small intestine of fetal mice.

Pregnant Swiss ICR mice were injected with clofibrate at different dosages and time intervals, and embryos were removed either at 17 or 18 days of gestation. In embryos sacrificed at 17 days the level of intestinal catalase activity of the proximal and distal halves in the treated groups is identical in any case to that of the controls. In embryos sacrificed at 18 days, the rise in the level of catalase activity in the proximal half of the small intestine in treated groups is dose dependent up to a certain limit: with repeated injections the increase reaches a plateau. The distal halves of treated groups are much less responsive and an increase in catalase activity was noted only with repeated injections. In untreated embryos circular DAB-positive microperoxisomes (200 nm in diameter) and tubular structures (100 nm in thickness) are seen in the duodenum at 18 days of gestation. At the same stage, only circular microperoxisomes are identified in the ileum. After clofibrate treatment circular and tubular microperoxisomes are observed in the ileum also. It is concluded that clofibrate induces a rise in catalase activity in the embryo, only after 17 days of gestation. These observations are discussed in relation to the biogenesis of microperoxisome.

Animals↗
PubMed1979

Developmental pattern of glucose-6-phosphatase activity in the small intestine of the mouse fetus.

The distribution of glucose-6-phosphatase (G6Pase) activity in the epithelium of the small intestine in mouse embryos (the last 4 days of gestation) was studied by electron microscope cytochemistry and by enzymatic assays. At 16 days, the lead phosphate deposited by the cytochemical reaction is localized on the rough endoplasmic reticulum (RER) and nuclear envelope of very few cells in the duodenum and jejunum. Positive cells are more frequently seen in the upper part of the developing villi. At 17 days of gestation, a tremendous burst in RER differentiation is noticed in all parts of the small intestine and concomitantly glycogen disappears. At 18 days of gestation all the principal cells of the intestinal mucosa show a well differentiated positive RER and the enzyme is also present in the smooth endoplasmic reticulum. Biochemically, G6Pase activity is detected in the proximal 2 thirds of the small intestine at 17 days of gestation and appears at 18 days in the last third. Afterwards the activity increases up until birth. These results suggest (1) that the endoplasmic reticulum differentiates very late in the intestinal mucosa of mouse embryos (2) that the differentiation with respect to G6Pase is asynchronous between the enterocytes, (3) that for a given cell all the cisternae of RER are involved in G6Pase synthesis at the same moment and (4) that the enterocytes of the duodenum differentiate sooner and faster that those of the jejunum and ileum.

Animals↗
PubMed1978

Sequential differentiation of intestinal endocrine cells in the fetal mouse.

The duodenum and ileum of 15 to 18-day old Swiss ICR mouse embryos were studied with the electron microscope to follow the differentiation of endocrine cells. Endocrine cells were classified on purely morphological characteristics. EC cells appeared at 16 days of gestation in both segments. At the same stage G cells were seen in the duodenum and K cells in the ileum. ECL, and S cells were identified in the duodenum at 17 days. Finally, D cells were seen at 18 days of gestation in the duodenum and ileum. With the electron microscope, endocrine cells were not identified in the small intestine of the mouse before the formation of villi.

Animals↗