Intake and digestion of hill-land vegetation by the red deer and the sheep.
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Animal Husbandry↗
Biomedical subjects
A M Spence
Publications and source records attributed to A M Spence.
Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems. III. Melanin pigment and melanogenesis in experimental neurogenic tumors: a reappraisal of the histogenesis of pigmented nerve sheath tumors.
Four melanin pigment-containing intracranial tumors were found in three Long-Evans rats in the course of experimental oncogenesis by transplacental ethylnitrosourea (ENU). One of them was a leptomeningeal melanoma. Aside from the presence of scattered melanin-pigmented cells, the other three had the typical histological features of ENU-induced malignant nerve sheath tumors. Two of the three tumors were studied by electron microscopy and in tissue and organ culture systems. One of them demonstrated progressive melanogenesis in vitro; the other failed to produce more melanin and showed increasing differentiation, with a Schwannoma-like pattern by light microscopy. Melanosomes and premelanosomes were identified in both tumors by electron microscopy; the other fine structural features were those of malignant Schwannomas. These observations are relevant to the controversy on the histogenesis of pigmented nerve sheath tumors occasionally encountered in man and on the relationship of these tumors to pigmented nevi. The findings in the present study support the view of Masson that neoplastic nerve sheath cells are capable of melanogenesis.
Animals↗
Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems. II. Electron microscopy observations.
The sequential electron microscopic features of six malignant nerve sheath tumors (three cranial and three spinal) induced in rats by transplacental ethylnitrosourea and maintained in organ culture systems were compared with those of a human acoustic Schwannoma similarly cultured. After 4 weeks in vitro, the malignant tumor cells often showed progressive elongation of their processes, with the development of an interdigitating pattern resembling that seen in well-differentiated Schwannomas. This was accompanied by an increase of microtubules. Basal lamina formation, less well-developed and less complete than in the benign Schwannoma in this study, was maintained in culture. Some explants demonstrated an increase in number and width of collagen fibrils, accompanied by a relative concomitant decrease of inter-cellular basement membrane material. The malignant tumor cells also showed numerous micropinocytotic vesicles and various junctional complexes, which are characteristic of perineurial cells. Since the origin of the experimental tumors from adult Schwann cells seems well established, this apparent contradiction is best resolved by the concept that Schwann cells and perineurial fibroblasts are functional variants of the same cell type.
Animals↗
Cerebellar capillary hemangioblastoma: its histogenesis studied by organ culture and electron microscopy.
A capillary hemangioblastoma from the vermis of a 21-year-old man with von Hippel-Lindau's disease was successfully maintained in organ culture systems on Millipore filter platforms and gelatin sponge foam matrices up to 48 days. Three cell types--endothelial cells, pericytes, and stromal cells--identified by their fine structural features and their architectural relationships to vascular lumens and to the extracellular space were recognized in the original tumor. By light microscopy the explants showed, in the late stages, increased lipid droplets in the stromal cells and perivascular hyaline thickening. By electron microscopy, endothelial cells, pericytes, and stromal cells remained distinguishable as cell types. However, the stromal cells demonstrated, in addition to an increase of their normal complement of microfilaments and lipid droplets, features that were more characteristic of the two other cell types, i.e. micropinocytotic vesicles and the formation of zonula occludens junctions and hemidesmosomes. Basement membranes also became more apparent around the stromal cells. With increasing time in vitro, there was a striking increase in mature collagen fibers in the extracellular space. The roles of the different cell types in capillary hemangioblastoma and the histogenesis of the stromal cells are discussed in light of these observations. It is concluded that the capillary hemangioblastoma consists of multiple cell lines--endothelial cells, pericytes, stromal cells and, occasionally, hematopoietic cells--all of which are neoplastic and replicate in parallel with one another. Stromal cells may be regarded as an aberrant monopotential cell type which shares with the endothelial cell and pericyte a common mesenchymal, presumably angiogenic, ancestry, and may, on occasion, display morphological features, such as increased basement membrane formation and the formation of zonula occludens junctions, which recall its angiogenic lineage. However, interconvertibility between endothelial cells and stromal cells does not appear to occur in vivo or in vitro.
Adult↗
Intracisternal A-particles in transplantable murine teratomas.
Intracisternal A-particles occur in experimental transplantable murine teratomas OTT 2466 and OTT 6050 derived from embryos of the A/He and 129/Sv strains respectively. They are present in stem cells of both tumors and in the more differentiated cell types in OTT 6050, consisting of primitive endodermal cells, cells of neuroepithelial rosettes, neuroblasts, primitive glial cells and respiratory epithelial cells. Both parent strains, A/He and 129/Sv, also contain these particles.
Animals↗
An experimental mouse testicular teratoma as a model for neuroepithelial neoplasia and differentiation. II. Electron microscopy.
The electron microscopic features of the stages of divergent neuroepithelial differentiation in the solid implants of a transplantable mouse testicular teratoma (OTT-6050) are presented and compared to the sequential stages of cytogenesis that have been described in the developing avian and mammalian central nervous system. Primitive neuroepithelial tumor cells showed the features of undifferentiated multipotential matrix (or ventricular) cells of the neural tube. They formed primitive medullary rosettes, from which various transitions were traced to more differentiated, cilia-containing ependymoblastomatous rosettes; the transitional features included increased granular endoplasmic reticulum and microvilli formation. Glial differentiation was characterized by the presence of mature ependymal rosettes and of astrocytes containing glial filaments. Neuronal differentiation included the development of synapses and the presence of dense-core vesicles in nerve cell processes. No intermediate cell forms were found that suggested multiple lines of differentiation occurring within a single cell.
Animals↗
Underpigmentation of the substantia nigra in chronic disease in children.
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Adolescent↗
Critical re-examination of the premature aging concept in progeria: a light and electron microscopic study.
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Adolescent↗
A survey of ethylnitrosourea-induced rat gliomas for the presence of tumour rejection antigens expressed in vivo.
Transplanted lines of seven F-344 (Fischer) rat malignant gliomas induced transplacentally with ethylnitrosourea (ENU) were surveyed by in vivo immunoprotection assays for the presence of tumour rejection antigens. These gliomas were representative of commonplace histological types of human primary brain tumours and were analyzed in early transplantation passages. The classical tumour ligation method of immunizing animals was attempted with five glioma lines, but was found unusable in four of these because of a high incidence of local tumour recurrences and distant metastases. In most experiments the animals were immunized by repeated inoculations of heavily-irradiated tumour cells. Two gliomas, a glioblastoma multiforms and a mixed astrocytoma-ependymoma, demonstrated weak but statistically significant tumour rejection responses. Immunization with three other tumours, a mixed oligodendroglioma-astrocytoma and two glioblastomas multiforme, led to enhanced outgrowth of the challenge cell inocula. Neither a rejection nor an enhancement response was observed in assays of the remaining two neoplasms, a glioblastoma multiforme and a mixed astrocytoma-oligodendroglioma. Immunization with a 3-methylcholanthrene-induced urinary bladder carcinoma line, used as a control in assays of six gliomas, had no effect on the outgrowth of transplanted glioma cells. These results suggest that ENU-induced malignant rat gliomas do not uniformly elicit strong tumour-rejection responses in vivo.
Animals↗
Irradiation and BCNU effects in the stroma in a rat transplanted glioma model: analysis of cerebral tumor bed effect.
F-344 rats were treated with whole-brain fractionated or unfractionated 137Cs at several time intervals up to 6 weeks before they received intracerebral grafts of an ethylnitrosourea-induced rat astrocytoma (36B-10). Rats treated with a single dose of 18 Gy at 3- and 2 week intervals prior to tumor implantation died earlier than unirradiated control tumor recipients (P less than 0.05, log rank sum test). Delivered 2 weeks prior to tumor grafting single doses of 10, 15, and 20, but not 5 Gy also reduced animal life span (P less than 0.05). Similarly, a total dose of 38 but not 28.5, 19, or 9.5 Gy, each delivered in five daily fractions 2 1/2 weeks before tumor grafting, shortened survival (P less than 0.05). Chemotherapy with 1,3-bis(2-chloroethyl)-1-nitrosourea (13.3 mg/kg) alone or in combination with a single-dose of irradiation of 18 Gy 3 weeks preceding transplantation showed no effect on animal survival. Unirradiated control tumors demonstrated sheets of densely-packed isomorphic astrocytes, perivascular brain parenchymal invasion, sparse, thin-walled vasculature, frequent mitoses, but little necrosis or hemorrhage. The tumors of rats irradiated before transplantation showed large areas of confluent necrosis associated with microvascular thrombosis, edema, and multifocal acute hemorrhages. These survival results and morphological changes indicate that the cerebral tumor bed effect involves early animal death and extensive morphological changes in the tumors; and they suggest that tumor cell death in irradiated brain tumors may, in part, result from radiation-induced vascular injury.
Animals↗
Epileptic nystagmus.
Two cases of epileptic nystagmus (EN) are described. The first patient had no history of seizures and experienced attacks of EN associated with oscillopsia and followed by horizontal diplopia and esotropia. These episodes could be triggered by certain visual stimuli and ocular pressure. The second patient had a history of generalized tonic-clonic seizures. He displayed episodes of EN that changed direction in the course of the attacks simultaneously with a shift of the EEG discharge from one occipital region to the other. Cortical blindness followed postictally. On recovery from the postictal state, both patients were neurologically normal. With standard electrodes, the EEG seizures associated with EN involved the occipital, posterotemporal, and parietal areas of the scalp contralateral to the fast phase of the nystagmus. In the first patient, use of supplementary scalp electrodes further localized the seizures to an anterior occipital site intermediate between standard occipital and posterotemporal electrodes. Thirty-six previously reported cases of EN were associated with partial seizures. Horizontal EN most commonly results from seizure activity involving the occipital cortex, although participation of adjoining portions of the parietal and temporal cortexes is possible.
Adult↗
Binding of the hypoxia tracer [3H]misonidazole in cerebral ischemia.
Radiolabelled misonidazole, a radiosensitizing drug that binds to viable hypoxic tumor cells, may be useful in identifying hypoxic cells in cerebrovascular disease. Its potential was investigated in the gerbil stroke model. Biodistribution of [3H]misonidazole was measured in normal gerbils and animals that had been subjected to right common carotid artery ligation to produce cerebral ischemia. The uptake of [3H]misonidazole in the right cerebral hemisphere and right/left hemispheral uptake ratios correlated positively with the severity of the stroke when measured 6-9 hours after carotid ligation. Histologic studies in symptomatic ligated animals showed ipsilateral widespread but patchy acute ischemic changes as well as areas that showed no morphological changes. Microscopic autoradiography in these animals showed diffuse heavy labelling only in the ipsilateral hemisphere. This was over areas that had histological damage as well as in adjacent areas that appeared intact. Studies comparing blood flow measured with [14C]iodoantipyrine and [3H]misonidazole retention in gerbils with carotid artery ligations indicated that flow is not a major determinant of retention of this hypoxia tracer. We conclude that a misonidazole congener labelled with a gamma- or positron-emitting isotope may be useful in nuclear imaging of the degree and regional distribution of hypoxic tissue in cerebrovascular disease.
Animals↗