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Biomedical subjects

P Kan

Publications and source records attributed to P Kan.

11 recordsLinked to original sources
PubMed1992

The purification and comparative analysis of hemoglobin from animal bloods.

Various methods for the separation and purification of Hb from animal blood have been investigated to establish the optimal and highly reliable purification process. The Hb obtained from various sources, i.e., bovine, pig and human bloods were analyzed and compared using simple and fast analytical methods, including, electrophoresis, isoelectric focusing, and spectroscopy to study the characterization of protein structure. Further investigation along this line will enable us to realize the ultimate objectives of development for artificial RBC substitutes.

Animals↗
PubMed1992

DNA synthesis decline involved in the developmental arrest of the limb buds in the embryos of the slow worm, Anguis fragilis (L.).

The present study was carried out to try and detect the biochemical mechanism involved in the developmental arrest of the limb bud in a serpentiform Reptile. Autoradiograpy, following tritiated thymidine incorporation, in embryos of the slow-worm (Anguis fragilis, L.) reveals a strong decrease in the rate of DNA synthesis in the mesodermal cells of the limb bud, after the degeneration of the apical ectodermal ridge (AER); the curve (a function of Gompertz) visualizing this decline shows that the drop in DNA synthesis becomes accentuated just after the degeneration of the AER. This decrease precedes the reduction of the mitotic index, the cell degeneration in the mesoderm and the other regressive changes occurring in the limb bud; it thus appears as the main causative factor of the developmental arrest of the limb bud. Furthermore, these results suggest that one of the functions of the AER would be to maintain a high level of DNA synthesis in the mesoderm underlying the AER in a normal limb bud.

Animals↗
PubMed1990

Extracellular matrix: an immunological and biochemical (CAT and TOH activity) survey of in vitro differentiation of isolated amphibian neuroblasts.

After neural induction certain cells in the neuroepithelium immediately acquire the property to express certain neural phenotypes (Duprat et al., 1984, 1987). However, the activity of almost all the specific enzymes involved in the biosynthesis of neurotransmitters is considerably higher when neurectodermal cells are cultured with chordamesodermal cells than when they are cultured alone. The stimulating effects of chordamesoderm do not appear to be due to diffusible factors (Duprat et al., 1985b). The present study was designed to investigate the role of extracellular matrix components in neuronal cell differentiation. We showed that the extracellular matrix cannot replace chordamesoderm in stimulating the biochemical differentiation of neuroblasts, although fibronectin and especially laminin stimulate morphological differentiation. We suggest that interaction between neuronal and non-neuronal cells plays an important part in functional biochemical differentiation, whereas the molecules of extracellular matrix are important for morphological differentiation.

Animals↗
PubMed1990

From presumptive ectoderm to neural cells in an amphibian.

As an immediate consequence of neural induction during gastrulation, some neuroectodermal cells acquire the ability to develop a number of specific neuronal and astroglial features, without requiring subsequent chordamesodermal cues. Thus, cholinergic, dopaminergic, noradrenergic, gabaergic, somatostatinergic, enkephalinergic, etc. traits are expressed in cultures of neural plate and neural fold isolated from amphibian late gastrulae immediately after induction and cultured in a defined medium. These results strongly suggest that at the late gastrula stage, the neural precursor population does not yet constitute a homogeneous set of cells. It was of interest to know the origin of this heterogeneity. Is it a direct result of the process of neural induction itself, stochastic phenomena being involved or not at the cellular level, or does it reflect a pre-existing heterogeneity in the presumptive ectoderm? At the early gastrula state, presumptive ectoderm can be neuralized consecutively to its dissociation into single cells. Using this experimental model, we have demonstrated by means of immunological probes that neuralized presumptive ectodermal cells, without any intervention of the chordamesoderm (natural inducing tissue), can develop autonomously into glial and neuronal lineages. These data suggest the existence of diverse predispositions of presumptive ectodermal cells. Competent ectoderm seems to be a heterogeneous structure with cells presenting distinct neural predispositions that can emerge as a consequence of a permissive inductive signal without real specificity (such as a target tissue dissociation). Moreover, such a differentiated neuronal population includes neurons of the GABAergic and enkephalinergic phenotypes but not of the cholinergic, catecholaminergic, somatostatinergic, etc. phenotypes. These data show that the developmental program of ectodermal cells induced without interaction with the chordamesoderm appears restricted compared to the naturally induced ectoderm. Experiments are now under way to analyze such sequential neural events.

Amphibians↗
PubMed1989

Initial GABAergic expression in embryonic amphibian neuroblasts after neural induction.

At the late gastrula-early neurula stage some embryonic neuroblasts from neural plate and neural fold present apparently as a consequence of neural induction, the capability to develop in vitro into different neuronal subpopulations (cholinergic, dopaminergic, noradrenergic, somatostatinergic and some other peptidergic subpopulations without ongoing influences from the chordamesoderm (Duprat et al., 1987). Using the same in vitro model system, the aim of the present work was to delineate the abilities of these neuroblasts to develop GABAergic traits. The initial appearance and development of GABAergic phenotype has been quantitated by assaying the activity of glutamic acid decarboxylase (GAD). GAD activity was undetectable at the early gastrula stage (stage 8a) and was slightly measurable at the early neurula stage (stage 14- onset of the culture). It increased subsequently over the next 14 days in vitro. The temporal pattern of appearance and development of GAD activity in culture was in agreement with that observed in vivo. Immunocytochemical studies showed that GABA-like immunoreactivity was expressed in vitro in a subpopulation of neurons. Thus the developmental program for GAD expression and GABA phenotype maturation is acquired at least in some neuronal precursors. These data together with previously reported results on the expression of cholinergic, catecholaminergic and peptidergic phenotypes demonstrate that different neuronal subpopulations emerge near the end of gastrulation i.e. immediately after neural induction. The embryonic origin of this neuroblast heterogeneity remains to be determined.

Animals↗
PubMed1985

Intratesticular adrenal rests diagnosed by ultrasound.

Adrenal rest tumors of the testes may occur in conditions associated with increased circulating adrenocorticotropic hormone (ACTH), including congenital adrenal hyperplasia (CAH) and Addison disease. Sonographically, these tumors appear as multiple round, hypoechoic nodules near the testicular hilus and are usually bilateral. They may undergo extensive fibrosis and become hyperechoic with acoustic shadowing. In the absence of excess ACTH or characteristic ultrasound findings, biopsy is recommended to exclude malignancy. Because malignant degeneration is very rare, close clinical and sonographic follow-up without biopsy is generally sufficient. Serial sonograms are useful to document stability or regression of tumor size during glucocorticoid replacement therapy.

Adrenal Rest Tumor↗
PubMed1985

In vitro differentiation of neuronal precursor cells from amphibian late gastrulae; morphological, immunocytochemical studies, biosynthesis, accumulation and uptake of neurotransmitters.

Neuronal differentiation has been studied in dissociated cell cultures from early neurulae of Pleurodeles waltl and Ambystoma mexicanum. Cocultures were prepared from the neural primordium and underlying chordamesoderm. NP and NF cultures were prepared from isolated neural plate and neural folds, respectively. Neuronal precursors in NP and NF cultures had distinctive aggregation properties already evident after 1-2 days in culture. After 10-15 days, mature neurones and synapses were observed by electron microscopy in the three culture types. The expression of neurofilament polypeptides and tetanus-toxin-binding sites was also present in these cultures. A small percentage of neurones contained cytochemically detectable catecholamine. Many neurones took up tritiated dopamine with a high affinity. Quantitative measurement of [3H]acetylcholine synthesis and storage from [3H]choline were negative at the early neurula stage and in 5 to 15-day-old NF cultures, and remained low in 5 to 15-day-old NP cultures. Acetylcholine production in cocultures increased linearly with time and was always much higher than in NP cultures. These results suggest that, at the early neurula stage, some neuronal precursors have acquired the capacity to express a high degree of morphological and biochemical differentiation even in the absence of further chordamesoderm influence. However, the chordamesodermal cells in the cultures increased acetylcholine synthesis.

Acetylcholine↗
PubMed1985

Neural induction: embryonic determination elicits full expression of specific neuronal traits.

In Pleurodeles waltl, the early neuronal differentiation of precursor cells from late gastrula stage has been studied by culture in vitro from either isolated neural plate (NP) or isolated neural fold (NF). The aim of this study was to delineate the information acquired by ectodermal target cells during neural induction. By culturing these cells in vitro either with or without the underlying chordamesoderm, we showed that in the absence of chordamesodermal influence such NP or NF cells exhibited a high degree of biochemical and morphological differentiation as revealed by the synthesis and the storage of neurotransmitters, the activity of specific enzymes, as well as by the expression of neuronal markers: specific changes in cell surface carbohydrates, tetanus toxin binding sites and neurofilament polypeptides. Remarkable changes in the cell adhesive properties were the first events observed in the different central (NP) and peripheral (NF) types. In cocultures the chordamesodermal cells exert a beneficial influence on this differentiation, specially increasing acetylcholine synthesis. There are some differences between central (NP) or peripheral (NF) neuroblast response to this further notochord or mesodermal influence.

Acetylcholine↗
PubMed1975

Comparative study of the activity of boric, benzene-boronic and methyl-benzene-boronic acids upon respiration, general metabolism and systemic hemodynamics of the anesthetized dog.

The authors compared the action of boric, benzene-boronic and p-methyl-benzene-boronic acids on respiration and general metabolism and on systemic hemodynamics of the anesthetized dog. They further investigated the effects on the arterial blood pressure in the rat and on the isolated rabbit heart. In the dogs, the three acids were shown to have no significant action on the systolic, diastolic and mean arterial blood pressures and a slight stimulating action on the differential arterial blood pressure. On the contrary, in the rat, all the acids were hypotensive. This action was dose dependent. In the entire animal, as well as in the isolated rabbit heart, benzene-boronic and p-methyl-benzene-boronic acids depressed the myocardial contractility. Whereas boric acid did not act on the heart contractility in situ in anesthetized dogs, it slightly stimulated the myocardial contractility of the isolated rabbit heart. The two acids seemed to be directly active on the myocardial cell. In the anesthetized dog, cardiac performances were first depressed then stimulated. Both benzene-boronic and p-methyl-benzene-boronic acids were ventilatory depressors: they reduced ventilatory output and rhythm, they first decreased then increased total O2 consumption and CO2 production.

Animals↗
PubMedDate not supplied

Neural induction.

The molecular mechanism of neural induction of embryonic cells is an important but poorly understood problem in neuroembryology. Glycoconjugates in the target cell plasma membrane and/or its structural organization play a key role in the reception of the inductive signal. It is the competent target tissue itself which probably contains the capacity and specificity for neuralization. However, the mechanism of transmission of the signal which leads to activation of the intracellular machinery involved in the process of neural determination remains to be elucidated. With respect to the information acquired by the target cells during neural induction, and the early events in differentiation, neuronal precursor cells have been shown to have acquired the potential to display a high degree of biochemical and phenotypic differentiation, even in the absence of further embryonic influences.

Animals↗