Biomedical subjects

D N Angelov

Publications and source records attributed to D N Angelov.

41 records · Page 3Linked to original sources

PubMed1989

Ultrastructural localization of the membrane-bound Mg-adenosine triphosphatase activity in rat meninges.

The distribution of the membrane-bound magnesium ions-dependent adenosine triphosphatase (Mg-ATPase) activity has been studied ultracytochemically in rat meninges by the method of Wachstein and Meisel (1957). A device specially constructed to avoid preparation artefacts has been used to obtain sections from the parietal region of the head. The meninges display an intense though irregularly distributed ATPase activity marked by depositions of electron-dense reaction product (RP) which is almost absent in the outer and middle dural layers. In the borderline zone between dura mater and the arachnoid the RP deposits are found at the outer surface of the inner dural cells and at the contact sites between these cells and the dural neurothelium. The intercellular cleft(s) between the neurothelium and the outer arachnoidal layer, occupied by an "electron-dense band", remains free of RP. The strongest accumulations of reactions granules are observed on the surface of the leptomeningeal cells of the arachnoidal space. In the contact region between the inner arachnoidal and the outer pial layers the distribution of the RP is similar to the one observed in the interface zone dura mater/arachnoid, while the pial cells themselves are definitely reaction-positive. In all meningeal vessels RP is found at the lumenal and abluminal aspects of the endothelium as well as at the cell membranes of the perivascular cells. These results emphasize the importance of the dural neurothelium for the functions of the blood-cerebrospinal fluid (CSF)-barrier between the dural blood vessels and the CSF.

Animals↗

PubMed1989

Embryonic development of rat diaphragm. An electron-microscopic study.

Ultrastructural aspects of white Wistar rats diaphragm during part of its embryonic development (from the 13th embryonic day till birth) have been studied. The dominating structures observed in the period of the thirteenth embryonic day (ED 13) are undifferentiated cells, their cytoplasm being poor in organelles but rich in ribosomes. The close examination of these cells reveals that some of them possess a kind of thin filaments near their Golgi zones. At ED 14-15 clusters of myoblasts are readily detected (their cytoplasm containing a lot of glycogen granules and myofibrils, some of them even with Z-line material); contact sites between their cell membranes appear, somewhere forming specialized junctions; in this period the myoblasts start to fuse giving rise to the primary generation of myotubes. At ED 16-17 the quantity of myofilaments and glycogen granules increases alongside with the initiation of a basal-lamina formation; occasionally some oval, undifferentiated cells very similar to those viewed at ED 13 are found. At ED 18-19 the cytoplasm of the myotubes contains a lot of myofibrils and a well-developed endoplasmic reticulum; at some places the adjacent membranes still form deep interdigitations. At the end of the prenatal myogenesis (ED 20-21) most of the muscle cells are close to their mature morphological appearance--the sarcomers are well-organized and some nuclei present a peripheral localization; nevertheless, in this period new generations of myotubes can be also distinguished.

Animals↗

PubMed1988

Electron microscopic study of cat meninges.

The intervascular portions of the encephalic dura mater, arachnoid membrane and pia mater were studied with special reference to their spatial relationships. The cell types were analyzed at electron microscopic level. An outer dural layer, composed of typically elongated fibroblasts and large intercellular spaces was identified. The middle dural layer was composed of collagenous connective tissue matrix together with some fibrocytes scattered in it. The inner dural layer showed epithelium-like arranged cells with light cytoplasm and long processes. The electron-dense band, measuring about 20 nm in width, located between dura mater and arachnoid was not so prominent as in the previously investigated experimental animals. The intercellular contacts among the cells of the outer arachnoid layer included maculae and zonulae adherentes and gap junctions mainly, while the tight junctions observed were quite rare. Following the arachnoid trabecular layer, an inner arachnoid layer could be hardly demonstrated. The pial cells were differentiated into 2 distinct layers, bordering the narrow and discontinuous pial space.

Animals↗

PubMedDate not supplied

Slow axonal regrowth but extreme hyperinnervation of target muscle after suture of the facial nerve in aged rats.

Unilateral transection and suture of the facial nerve was performed in 60 old rats (20 months of age). The time course of mimetic reinnervation was studied by counting all retrogradely labeled motoneurons in the facial nucleus after injection of HRP into the whiskerpad muscles for 14-112 days post operation. The comparison between these neuron counts and data for young rats yielded four conclusions. First, the qualitative equivalent of the phenomenon "misdirected reinnervation" in aged rats was the same as in young adults: HRP-labeled motoneurons were scattered throughout the facial nucleus lacking myotopic organization from 18 until 112 days post operation. Second, no age-related loss of motoneurons was detected. Third, the axonal regrowth was delayed in aged rats. Fourth, the postoperative hyperinnervation (the projection of more motoneurons into a muscle than under normal conditions, i.e., the quantitative aspect of misdirected reinnervation) was more than two times higher than in young rats. These data may provide reasonable explanations for the poor functional recovery after reconstructive surgery on the facial nerve in old patients.

Aging↗

PubMedDate not supplied

Embryonic stem-cell derived neurones express a maturation dependent pattern of voltage-gated calcium channels and calcium-binding proteins.

There are remarkable changes of calcium binding proteins and voltage dependent Ca(2+) channel subtypes during in vitro differentiation of embryonic stem cell derived neurons. To observe these maturation dependent changes neurones were studied using combined immunohistochemical, patch clamp and videomicroscopic time lapse techniques. Embryonic stem cell derived neuronal maturation proceeds from apolar to bi- and multipolar neurones, expressing all Ca(2+) channel subtypes. There is, however, a clear shift in channel contribution to whole cell current from apolar neurones with mainly N- and L-type channel contribution in favour of P/Q- and R-type participation in bi- and multipolar cells. Expression of the calcium binding protein parvalbumin could be detected in bipolar, while calretinin and calbindin was preferentially found in multipolar neurones. Our data provides new insights into fundamental neurodevelopmental mechanisms related to Ca(2+) homeostasis, and clarifies contradictory reports on the development of Ca(2+) channel expression using primary cultures of neurones already committed to certain brain compartments.

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