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Biomedical subjects

W Been

Publications and source records attributed to W Been.

9 recordsLinked to original sources
PubMed2001

Memory and DNA.

A model is presented for the storage of long-term memory. In our model consolidation takes place by specific DNA sequences. These DNA sequences are obtained by the recombination of DNA in a similar way to that during meiosis and the production of immunological antibodies. DNA has the potential of the production of large numbers of specific DNA sequences. These sequences can be attached to images of neural networks. The following considerations lead to the theory: (1)Most of the DNA is not used: approximately 3% of our DNA is used. (2)There are no cell divisions in the brain after adulthood is reached. Structural DNA arrangements will not be altered nor disrupted as a consequence of cell division and mitosis. (3)Chromosomal pairing is demonstrated in the brain, which could indicate the exchange of DNA. In addition, in our first survey experiments we found a positive reaction of components of the synaptonemal complex (SC) in the nuclei of brain cells. The SC is highly meiosis specific and plays a major role in genetic recombination.

Adult↗
PubMed1990

Hepatocytes explanted in the spleen preferentially express carbamoylphosphate synthetase rather than glutamine synthetase.

Urea cycle enzymes and glutamine synthetase are essential for NH3 detoxification and systemic pH homeostasis in mammals. Carbamoylphosphate synthetase, the first and flux-determining enzyme of the cycle, is found only in a large periportal compartment, and glutamine synthetase is found only in a small, complementary pericentral compartment. Because it is not possible to manipulate experimentally the intrahepatic distribution of carbamoylphosphate synthetase and glutamine synthetase, we looked for conditions in which explanted hepatocytes would exhibit either the carbamoylphosphate synthetase phenotype or glutamine synthetase phenotype. In the spleen hepatocytes either settle as individual cells or in small agglomerates. The dispersed cells only express the carbamoylphosphate synthetase phenotype. Within the agglomerates, sinusoids that drain on venules develop. Hepatocytes surrounding the venules stain only weakly for carbamoylphosphate synthetase but are strongly positive for glutamine synthetase. These observations were made for explanted embryonic hepatocytes (no prior expression of either carbamoylphosphate synthetase or glutamine synthetase), neonatal hepatocytes (compartments of gene expression not yet established) and adult periportal and pericentral hepatocytes.

Age Factors↗
PubMed1984

Developmental anomalies of the lower face and the hyoid cartilage due to partial elimination of the posterior mesencephalic and anterior rhombencephalic neural crest in chick embryos.

In an effort to verify the supposition that a normal development of the lower face and the hyoid apparatus is dependent on the availability of a sufficient number of cells derived from the posterior mesencephalic and anterior rhombencephalic parts of the neural crest, in a total of 52 six-somite stage chick embryos (about 26 hours of incubation) these parts of the neural crest were partially eliminated by tangential micro-laser irradiation. Among the 17 irradiated embryos sacrificed after 24 hours, several ones showed an underdevelopment of the mesenchyme in the ventral part of the first branchial arch; in 2 of these cases, additionally the second branchial arch was underdeveloped. At the age of 7-8 days, 4 out of 15 surviving embryos showed an underdevelopment of the lower beak and a reduction in size of Meckel's cartilage; in 3 of these cases, in addition, a median cleft in the lower beak and/or reduction or absence of the hyoid cartilage were observed. From these observations the conclusion is drawn that for a normal development and growth of the mandibular part of the face and the hyoid cartilage sufficient numbers of posterior mesencephalic and anterior rhombencephalic neural crest cells are indispensable, indeed.

Abnormalities, Multiple↗
PubMed1983

Cleft lip and palate due to deficiency of mesencephalic neural crest cells.

The mesencephalic crest was partially eliminated in chick embryos by means of tangential microlaser. The heads of the surviving embryos were serially sectioned and microscopically studied. A deficiency of mesenshyme in the anlage of the maxillary process was observed in 4 of the 42 embryos sacrificed after 24 hours, on the side of irradiation. Among the 99 surviving embryos sacrificed at the ages of 7 or 12 days, 26 showed a unilateral cleft lip, a wide palatal cleft or a combination of these anomalies. It is concluded that cleft lip and palate can result from insufficient growth of the mesenchyme in the maxillary process caused by partial deficiency of mesencephalic neural crest cells.

Animals↗
PubMed1983

Developmental deficiencies of the upper facial skeleton due to partial elimination of mesencephalic neural crest cells in the chick embryo.

With the aim to test the hypothesis that cells derived from the mesencephalic portion of the neural crest, are involved in the process of differentiation of various upper facial bones, in 41 chick embryos of the 6-somite stage (approx. 26 hours of incubation) the anterior and middle thirds of this part of the neural crest were partially eliminated by micro-laser irradiation, either unilaterally or bilaterally. Of the 14 embryos sacrificed at the age of 12 days, a number of 6 proved to have developed harelip and/or cleft palate conditions. In these embryos, in addition a reduction or absence of the maxillary, palatal, jugale and quadrato-jugale was observed. On the contrary, other facial bones as well as the first and second branchial arch cartilages proved to have developed normally. From these results the conclusion may be drawn that (a sufficient number of) cells from the anterior and middle thirds of the mesencephalic neural crest are indispensable for a normal differentiation of the maxillary, palatal, jugale and quadrato-jugale.

Animals↗
PubMed1981

Cranial differentiation in chick embryos with experimentally induced median facio-cerebral anomalies. A preliminary note.

In an effort to answer the question whether prosencephalic neural crest cells play an essential part in the differentiation of the facial skeleton, in twenty 2- to 6-somite stage chick embryos the anteriormost part of the neural crest was eliminated. Observations on 10 of these embryos, sacrificed 2 hours after the microlaser irradiation, showed that often also some damage is done to the prosencephalic neural tissue. Among the remaining 10 embryos, 6 survived until the age of 12 days. One of these embryos showed unilateral microphthalmia, two bilateral microphthalmia, two synophthalmia and one cyclopia. In the microphthalmic embryos, the facial skeleton proved to have differentiated normally; in the other embryos, several facial bones were entirely lacking, while others only had developed rudimentarily. All affected eyes lacked a cartilaginous sclera. On the basis of these results, the question posed could not be answered. On the other hand, however, the experiments revealed that (1) prosencephalic neural crest cells are indispensable for a normal differentiation of the scleral cartilage, (2) elimination of the prosencephalic neural crest and a part of the prosencephalon does not affect the development of the mandible and the hyoid, and (3) the mesodermal mesenchyme bordering the prosencephalon, has no developmental capacities of its own. Finally, the craniofacial anomalies observed in the synophthalmic and cyclopic chick embryos, proved to be highly similar to the corresponding anomalies in man.

Abnormalities, Multiple↗
PubMed1980

Median facio-cerebral anomalies in chick embryos resulting from local destruction of the anteriormost parts of the early neural plate and neural crest.

With the aid of micro-laser irradiation, in a total of 123 chick embryos varying in age from 24-26 hours of incubation (2- to 6-somite stages), the anteriormost parts of the neural crest and the neural plate were eliminated. As a result of this treatment, 15 out of 59 embryos, studied 24 hours after irradiation, showed manifest signs of maldevelopment of the telencephalon, eyes and olfactory placodes. At the age of 7 days (6 days after irradiation), the surviving 25 embryos all proved to have developed median facio-cerebral anomalies. These anomalies included arhinencephaly, holoprosencephaly, anophthalmia, synophthalmia, microphthalmia, absence or reduction of the nasal structures, sometimes combined with the presence of a proboscis, and incidentally occurring facial cleft conditions. The 2 surviving 12 days' embryos studied showed similar facio-cerebral anomalies. These results show that median facio-cerebral deformities may devlop as a result of damage inflicted to the anteriormost parts of the early neural plate and neural crest.

Animals↗
PubMed1978

Harelip and cleft palate conditions in chick embryos following local destruction of the cephalic neural crest. A preliminary note.

With the aid of micro-laser irradiation, in a total of 156 chick embryos unilaterally (a part of) the cephalic neural crest paralleling the posterior portion of the prosencephalon and mesencephalon, was eliminated. As a result of this treatment, 2 out of 22 embryos, studied 24 hours after irradiation, showed a considerable degree of underdevelopment of the mesenchyme in the homolateral first branchial arch. At the age of 7 days (6 days after irradiation) 11 of the 44 surviving embryos proved to have developed a homolateral harelip condition. In 2 of these embryos, a wide palatal cleft was observed as well. These results demonstrate that facial clefts may develop as a result of a local deficiency of neural crest cells.

Animals↗