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Biomedical subjects

U Singh

Publications and source records attributed to U Singh.

At least 109 records · Page 6Linked to original sources
PubMed1988

Thymic lymphopoiesis and cholinergic innervation.

This study was carried out to determine whether the thymic rudiments implanted into the anterior eye chambers of syngenic hosts receive cholinergic neuronal input from the host, similar to the adrenergic neuronal input into the implants, observed in previous studies. In addition, the study was also aimed at examining the effect of this (cholinergic) neuronal input on thymic lymphopoiesis. 13/14-day-old fetal thymic rudiments were implanted into the anterior eye chambers of syngenic (BALB/c) mice. They were removed at weekly intervals and examined for the presence of cholinergic nerves by localising choline-acetyltransferase (ChAT) containing nerves using an immunofluorescence method. The host animals had been subjected to surgical sympathectomy on the right side about one week prior to the implantation. The results provide evidence, for the first time, for the presence of cholinergic nerves on the basis of immunocytochemical localisation of ChAT positive nerves in a developing thymic rudiment in vivo. They also indicate that the presence of these nerves is associated with an increased thymic lymphopoiesis. The inter-relationship between the presence of cholinergic nerves and the maturation of thymocytes and their immunoreactivity is being further investigated.

Animals↗
PubMed1987

Ontogeny of cholinergic innervation of thymus in mouse.

In this study, identification of cholinergic nerves in the murine thymic rudiments during ontogenetic development, by immunonocytochemical localization of the enzyme cholin acetyltransferase (ChAT) was carried out. Fetal thymic rudiments from day 13 of gestation to the time of birth, and upto 8th post natal week were examined. Contrary to the earlier reports, the results indicate that the thymic rudiment is not innervated during early ontogenetic development and that the first ChAT positive nerve profiles were observed at around day 17/18 of gestation. Significance of cholinergic innervation in thymocyte maturation is suggested.

Animals↗
PubMed1987

Implantation of thymic epithelial grafts into the anterior chamber of the murine eye: an experimental model for analyzing T-cell ontogeny.

The object of this investigation was to establish whether the intracameral implantation of thymic epithelial grafts could be utilized as a valid in vivo experimental model for probing the possible mechanisms whereby the sympathetic innervation of the thymus influences thymocyte dynamics. Our findings suggest that deoxyguanosine-treated thymic epithelial grafts, implanted into the anterior chamber of the eye, were receptive to host lymphoid progenitor cells, capable of supporting T-lymphocyte maturational processes, and were able to export mature T cells to the secondary lymphoid organs of a previously T-cell deficient host. In addition, we verified that the number of lymphoid cells recovered from a thymic epithelial graft which had been implanted into an anterior chamber devoid of sympathetic nerve input was generally greater than the number of lymphoid cells recovered from a matched graft which had been implanted into an anterior chamber which had an intact sympathetic nerve supply. Based on the results of these studies, investigative efforts can now be directed at studying a number of important aspects associated with the relationship between T lymphocyte ontogeny and the sympathetic nervous system.

Animals↗
PubMed1987

Biochemical studies on acetate non-utilizing mutants of Aspergillus terreus IRRL 16043.

The strain Aspergillus terreus IRRL 16043 can utilize glucose as well as acetate as a sole carbon source. Thirty-nine mutants were isolated from the wild-type by treatment with a chemical mutagen, N-methyl-N'-nitro-N-nitrosoguanidine (MNTG) which could not utilize acetate as a sole carbon source, and were designated as acetate non-utilizing (acu). By complementation and biochemical analyses they were divided into three functional groups, acu A, acu B and acu C lacking isocitrate lyase, malate synthase and acetyl-CoA synthetase activity, respectively.

Acetate-CoA Ligase↗
PubMed1986

Parasympathetic innervation of the thymus: a histochemical and immunocytochemical study.

The presence of parasympathetic nerve supply to the thymus has been demonstrated by histochemical and immunocytochemical methods using antibodies against cholineacetyl transferase. Fine nerve fibres have been observed both in the thymic parenchyma and around the blood vessels. The role of the parasympathetic nerve supply to the thymus is briefly discussed.

Acetylcholinesterase↗
PubMed1985

Lymphopoiesis in the nude fetal thymus following sympathectomy.

This study was carried out to examine the innervation of the nude fetal thymus during ontogeny and to see if lymphopoietic activity would occur within these thymic lobes in the absence of sympathetic neuronal input. Fetal thymic rudiments from nu/nu mice were removed and examined for galoxylic acid-induced histofluorescence to detect the catecholaminergic nerves. Some of these lobes were organ cultured for 5 to 7 days in the presence of deoxyguanosine to eliminate any existing lymphoid cells within the rudiments. Such "nonlymphoid" thymic rudiments were implanted into the anterior eye chambers of syngenic BALB/c mice (heterozygous) from which cervical sympathetic ganglia and part of the sympathetic chain had been surgically removed (right side) one week earlier. The left side was only sham operated. The thymic implants were allowed to grow for up to 21 days on both sides; they were then removed and examined by histofluorescence, immunofluorescence, and light microscopy. The results indicate for the first time that the nude fetal thymus is innervated by sympathetic nerves and that following sympathectomy the nude thymus is able to sustain lymphopoietic activity and generate lymphoid cells which have characteristics present on thymocytes during in vivo development in normal mice, such as binding to peanut agglutinin and expression of Thy-1 antigen. The relationship between the presence of sympathetic inhibitory influence and the thymic atrophy seen in the nude mice during ontogeny, is being investigated.

Animals↗
PubMed1984

Sympathetic innervation of fetal mouse thymus.

This study was carried out to investigate the presence of sympathetic nerve fibers in the developing thymus. Thymic rudiments from 13 days of gestation up to birth and adult thymuses were examined by histofluorescence microscopy to detect the presence of these nerve fibers during ontogeny. Sympathetic nerve fibers were first visible around day 17 of gestation and increased in density and distribution by the time of birth and in the adult thymus. The appearance of immunoreactive cells about the same time as the presence of nerve fibers in the thymic rudiments has been discussed in light of a regulatory role for the sympathetic neuronal input on the maturation of thymocytes during ontogeny.

Animals↗
PubMed1981

Changes in the surface morphologies of the cells in the bursa cloacalis (bursa of Fabricius) and thymus during ontogeny of the chick embryo.

Slices or sections through the bursa cloacalis and thymus of chick embryos at 7-21 days of incubation were observed by light and electron microscopy to determine whether major differences existed in the surface morphologies of lymphoid cells in these organs, and whether the surface morphologies of these cells changed during ontogeny. These organs were fixed concurrently and identically at each stage. The thymus was packed at all stages with spherical cells having fine structures characteristic of those of lymphoid cells. Many irregularly shaped, epithelial cell processes were present between lymphoid cells. The bursa contained many irregularly shaped stromal cells as well as spherical cells. The latter were few in number during early development, but became the predominant type of cell near the end of incubation. Spherical cells in the bursa consisted of three types based on fine structure: lymphoid cells, granulocytic cells, and cells which were probably precursors of granulocytic cells. Spherical cells in the bursa could not be classified into these three types by their surface morphologies, however, because the latter at any one stage of development were similar. At 7-8 days of incubation, spherical cells in the bursa could not be differentiated consistently from neighboring stromal cells by scanning electron microscopy alone, but by 9 days, spherical cells could be identified routinely by this method. At 9-10 days of incubation, only minor differences existed in the surface morphologies of the spherical cells in the bursa and thymus: Bursal cells displayed long, ridgelike processes, whereas thymic cells exhibited fine surface undulations and large blebs. At 11 days, the surfaces of the spherical cells in the bursa were covered by numerous short microvilli, but the surfaces of thymic cells were unchanged. Bursal cells retained their microvilli through 14 days of incubation, but between 15 and 21 days progressively lost their microvilli, becoming essentially bald near the end of this period. Likewise, thymic cells gradually lost their surface wrinkles and blebs. Near the time of hatching, both types of cells were smooth-surfaced and tightly packed, with individual cells assuming polyhedral configurations.

Animals↗
PubMed1980

In vitro lymphopoiesis in foetal thymic organ cultures: effect of various agents.

In this study 14-day-old foetal BALB/c mouse thymic lobes were removed and grown as organ culture in vitro for up to 6 days. The cultures were treated with agents which are known to alter the intracellular levels of cyclic nucleotides. The proliferative response of the lobes was judged by histological examination, 125I-UdR uptake and cell yields, of the lobes at various time intervals. The results indicate that agents which raise cyclic GMP levels stimulate the proliferative response of the lobes as judged by the various parameters used and that the response was largely restricted to the lymphoid cells. It has been suggested that most probably cyclic GMP is the positive signal for thymic lymphopoiesis perhaps not only in vitro but also in vivo.

Acetylcholine↗