PubMed Health⌕ Search

Biomedical subjects

M Micic

Publications and source records attributed to M Micic.

10 recordsLinked to original sources
PubMed2001

Topographical characterization and surface force spectroscopy of the photochemical lignin model compound.

By combining the results from atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM), herein we investigate properties of photochemical lignin model compounds. We provide evidence that photochemical lignin forms random, probably non-functional structures. The topography of such structures is explored using ESEM. Non-functionality of such structures is proved by AFM and atomic force spectroscopy experiments wherein the photochemical lignin functionalized tip is approached to the substrate covered with photochemical lignin. There was no evidence of existence of any kind of host-guest interaction during the approach/retraction experiments. These results provide evidence for our previously stated hypothesis that photochemical lignin polymerization may be one of the degrading effects of UV radiation to the plant cell.

Dimerization↗
PubMed2000

A Comparative Study of Enzymatically and Photochemically Polymerized Artificial Lignin Supramolecular Structures Using Environmental Scanning Electron Microscopy.

Environmental scanning electron microscopy images of the self-assembled structures of enzymatically (DHP) and photochemically polymerized (PCP) artificial lignin are herein presented. Differences in the structural organization between DHP and PCP polymer at the supramolecular level were reported. Based on topological information, we proposed a hypothesis about possible new physiological roles of lignin in live plant cells and the ecological significance of possible in-vivo photochemical lignin polymerization. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Visualization of artificial lignin supramolecular structures

In this paper we are presenting the results of our environmental scanning electron microscopy (ESEM) investigation of the lignin model compound--enzymatically polymerized coniferyl alcohol, also known as dehydrogenate polymer (DHP). The goals of this study were to visualize the supramolecular organization of DHP polymer on various substrates, namely graphite, mica, and glass, and to explore the influence of substrate surface properties and associated collective phenomena on the lignin self-assembled supramolecular structure. Based on results obtained with ESEM, combined with previously published results based on scanning tunneling microscopy (STM) and electron spin resonance (ESR) technique, we looked at lignin structure ranging from a monomer on a fraction of nanometer scale to a large aggregate on a fraction of millimeter scale, therefore using six orders of magnitude range of size. Herein, we are presenting evidence that there are at least four different levels of the supramolecular structure of lignin, and that its supramolecular organization is well dependent on the substrate surface characteristics, such as hydrophobicity, delocalized orbitals, and surface-free energy.

Journal Article↗
PubMed1995

Stereological analysis of the sexually mature rat thymus after orchidectomy.

To assess the significance of gonadal function in the maintenance of thymic structure, male, sexually mature, 60 days old rats were bilaterally orchidectomized and the volumes of both the thymic compartments, total cellularity of each of them, as well as density (Nv) and mean diameter (D) of thymocytes within the specific thymic regions were stereologically analyzed 3, 7 and 15 days later. Three days after the orchidectomy a decrease in the thymic weight, and a reduction of both the cortical and medullary volumes, were observed. The reduction in cortical volume was followed by a decrease in overall number of the cortical thymocytes, suggesting an enhanced process of thymocyte death. In the same animals, the total number of the medullary thymocytes as well as D remained unchanged. Seven days after orchidectomy both volume of the cortex and total number of the cortical thymocytes reached the control values, while all the changes observed in the medulla of rats 3 days post castration, persisted. In addition, 7 days post castration, the volume of the interlobular connective tissue was increased and this persisted at day 15 post castration. The results indicate that orchidectomy can affect the thymic structure, and possibly the process of intrathymic T cell maturation; the extent of changes depending on the duration of the gonadal deprivation.

Animals↗
PubMed1992

Clinical and meiotic studies in an infertile man with Y;13 translocation.

Clinical and meiotic studies were done on an infertile man with a translocation between Yq and 13q, who was identified through the birth of his son with partial trisomy 13q. Seminal plasma transferrin showed preserved Sertoli cell function while lactate dehydrogenase C4 indicated hypospermatogenesis. A quadrivalent in diakinesis and spermatogenic arrest in the second meiotic division was detected.

Adult↗
PubMedDate not supplied

Scanning electron microscopy studies of protein-functionalized atomic force microscopy cantilever tips.

Protein-functionalized atomic force microscopy (AFM) tips have been used to investigate the interaction of individual ligand-receptor complexes. Herein we present results from scanning electron microscopy (SEM) studies of protein-functionalized AFM cantilever tips. The goals of this study were (1) to examine the surface morphology of protein-coated AFM tips and (2) to determine the stability of the coated tips. Based on SEM images, we found that bovine serum albumin (BSA) in solution spontaneously adsorbed onto the surface of silicon nitride cantilevers, forming a uniform protein layer over the surface. Additional protein layers deposited over the initial BSA-coated surface did not significantly alter the surface morphology. However, we found that avidin-functionalized tips were contaminated with debris after a series of force measurements with biotinylated agarose beads. The bound debris presumably originated from the transfer of material from the agarose bead. This observation is consistent with the observed deterioration of functional activity as measured in ligand-receptor binding force experiments.

Adsorption↗
PubMedDate not supplied

Histological and meiotic evaluation of infertile men.

A meiotic analysis in a group of 90 infertile men was carried out and also histological examination. In one third of patients there were no cells in divisions and Sertoli cells were only seen in most of them. In 30% of patients the process of spermatogenesis stopped at pachytene or between the first and second meiotic division. In 38% of patients all stages of spermatogenesis and of meiosis were present. Chromosomal translocations were detected in three patients in diakinesis. The testicular biopsy is an important tool in diagnosis and management of male infertility. The histological and meiotic investigations of the testicular tissue specimen give us the information obtainable in no other way. These both investigations are essential for prognosis and treatment of infertile men.

Humans↗
PubMedDate not supplied

Prepubertal castration alters the phenotypic profile of adult rat thymocytes.

To assess the gonadal influence on the maturation of the thymus, rats were orchidectomized at different periods critical for programming of both gonadal and immune functions, and the composition of the intrathymic thymocyte population was determined in adults by flow cytometric analysis of the surface phenotype. The relative proportion of thymocytes expressing CD4, CD8 and T cell receptor (TCR)alpha beta was measured in the adult rats castrated at 1, 7 and 30 days. Castration performed at postnatal day 1 did not significantly affect expression of these molecules. However, in rats subjected to the surgery at day 7, a significant decrease in the proportion of CD4+CD8+ double-positive cells was found, in parallel with a proportional increase in the percentage of CD4+CD8- single-positive (SP) cells. In rats castrated at age 30 days, in addition to these changes, a small but significant increase in the percentage of CD4-CD8+ SP thymocytes was measured. Castration performed at age 7 and 30 days also caused an enrichment in the thymocyte population expressing TCR alpha beta, probably related to the increase of CD4+CD8- SP cells (7 days) and both CD4+CD8- and CD4-CD8+ SP cells (30 days). The total yield of thymocytes was increased in all experimental groups. We conclude that T cell maturation sequences in the adult thymus are altered if gonadal influence is removed during certain stages of thymus development.

Age Factors↗