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Biomedical subjects

M Horowitz

Publications and source records attributed to M Horowitz.

601 records · Page 34Linked to original sources
PubMedDate not supplied

Mechanism of heat acclimation induced bradycardia in the sand rat.

The effect of heat acclimation on chronotropic response of the heart under normothermic and hyperthermic conditions was studied in the sand rat, Psammomys obesus, a diurnal desert species. All animals were acclimated at 34 degrees C for 0, 5, 14, 30 or 60 days; heat stress was achieved by exposure at 38 degrees C. Continuous measurements of heart rate (HR) were carried out on conscious animals, using chronic subcutaneous electrodes. Atropine (0.1 mg/100 g) and propranolol (1 mg/100 g) were administered to evaluate the para-sympathetic (V) and sympathetic (S) influences on HR. Intrinsic HR (HRi) was measured following administration of both drugs simultaneously. P. obesus developed bradycardia from day 5 of the acclimation. This bradycardia was induced solely by decreased HRi, overriding partial vagal withdrawal. During hyperthermia apparent thermal insensitivity of HR was observed. This was attained by partial sympathetic withdrawal compensating for the increase in HRi due to body temperature rise. It can be concluded that in P. obesus, heat acclimation induced bradycardia is attained by intrinsic changes in the pacing cells. It also emerges that the hyperthermic response is independent of and is not affected by heat acclimation.

Acclimatization↗
PubMedDate not supplied

Primary malignant rhabdoid tumor of the central nervous system.

Since the initial description of malignant rhabdoid tumor (MRT) of the kidney by Beckwith in 1978, MRTs have been established as a distinct clinicopathologic entity lacking nephrogenic and myogenic differentiation. MRTs are highly aggressive neoplasms with characteristic histopathologic, immunocytochemical, and ultrastructural features. Many reports have appeared documenting primary extrarenal rhabdoid tumors (ERRTs) occurring at diverse sites, including infratentorial and supratentorial compartments of the central nervous system (CNS). The authors report 2 cases of primary CNS-MRT in young male children (6.5 and 7 years of age) and review the literature on CNS-MRTs. Neuroimaging studies showed an inhomogeneous parasagittal mass in the left anterior parietal region involving the motor strip and attached to the lateral aspect of the superior sagittal sinus in one case, and a right parietal parasagittal tumor with a cystic component in the other case. Metastatic workup, including abdominal CT, was negative in both cases. Histologic examination of the resected tumors showed irregular clusters and nests of cells with variable desmoplasia in both cases. Large areas of tumor necrosis and apoptotic tumor cells were present. Prominent eosinophilic cytoplasmic inclusions and eccentric, indented nuclei with conspicuous nucleoli characterized many of the tumor cells. Diffuse strong vimentin reactivity and focal strong reaction for epithelial membrane antigen (EMA) were demonstrated. Cytogenetic analyses reported a normal male karyotype in one case and an abnormal male karyotype with loss of both normal copies of chromosome 22 and gain of one structurally rearranged chromosome 22 in the other case. Ultrastructural examination displayed tumor cells with avoid to indented nuclei, marginated chromatin, and prominent nucleoli. Intercellular junctions were not found. Masses of cytoplasmic intermediate filaments in a characteristic whorled configuration were present. CNS-MRTs are consistently vimentin positive (100%) and usually EMA positive (90%). Glial fibrillary acidic protein, neuron-specific enolase, and S-100 protein are variably expressed. Markers for myogenous differentiation are invariably absent. Ultrastructural characteristics include aggregates of intermediate filaments. Monosomy 22 occurs in some CNS rhabdoid tumors, while most renal rhabdoid tumors are cytogenetically normal with only isolated cases having del(13q), del(11p), del(22)(q11), and unbalanced reciprocal translocation involving chromosomes 8 and 22. The prognosis for CNS rhabdoid tumors is dismal and almost two-thirds of patients are dead of disease shortly after diagnosis; one-third have been reported to be alive with disease, but have been followed for only short periods; and a single patient is reported to be free of disease at 5 years.

Brain Neoplasms↗
PubMedDate not supplied

Central nervous system atypical teratoid/rhabdoid tumors of infancy and childhood.

In 1987, a distinctive brain tumor arising in young children was first described. This tumor contained neuroepithelial, peripheral epithelial, and mesenchymal elements, but lacked divergent tissue differentiation characteristic of malignant teratomas. It was originally designated as atypical teratoid tumor, but because of the prominent rhabdoid component, the tumor designation was modified to atypical teratoid/rhabdoid tumors (AT/RT) of infancy and childhood. AT/RTs occur most commonly in infants under 2 years of age, often have central nervous system (CNS) dissemination, do not respond to therapy, and typically are fatal within 1 year. Most are located in the cerebellum (65%), but they may arise at any CNS site. Histologically, various patterns can be present within the same tumor, but they all have a population of rhabdoid cells, and 70% contain fields typical of a primitive neuroectodermal tumor (PNET/medulloblastoma). Less frequently, malignant mesenchymal tissue and/or an epithelial component are found. Necrosis and brisk mitotic activity are common. The immunocytochemical profile is complex, but germ cell markers are consistently negative. Ultrastructural features vary and depend on the site sampled, but whorled bundles of cytoplasmic intermediate filaments are a distinctive finding in cells of the rhabdoid component. The authors report 4 AT/RTs (2 males, 2 females, age range 6 months to 4 1/2 years, 3 cerebellar, 1 cerebral). All cases showed a variety of histologic patterns with necrosis. Typical rhabdoid cells, PNET areas, undifferentiated bland large cell regions, dense connective tissue, and solid clusters of epithelial cells were present. Immunocytochemistry showed strong vimentin reactivity, whereas epithelial membrane antigen, cytokeratin, glial fibrillary acidic protein, S-100 protein, desmin, and smooth muscle actin were present to a lesser extent in most cases. Germ cell markers were negative. Ultrastructurally, many cells contained aggregates of cytoplasmic intermediate filaments, and some cells had a basal lamina on one aspect. Cells with interdigitating cytoplasmic borders were seen and rare cells had microtubules. Cytogenetic studies were normal in 2 cases. Follow-up has shown that 3 children have died of disease (< 1 year after diagnosis) and 1 child is alive with disease (18 months after diagnosis). Separation of AT/RT from PNET based on histopathologic and biologic evaluation is important, because AT/RTs are aggressive tumors with a dismal prognosis and currently there is no effective treatment. Neither clinical signs and symptoms nor radiologic features will distinguish AT/RTs from PNETs.

Brain Neoplasms↗
PubMedDate not supplied

Pleomorphic ("dedifferentiated") chondrosarcoma. Report of a case initially examined by fine needle aspiration biopsy.

Fine needle aspiration (FNA) biopsy of a predominantly radiolucent, destructive lesion of the right distal femoral metaphysis of a 69-year-old man produced smears containing spindle-shaped cells with cytologic features consistent with a malignant fibrous histiocytoma. This initial diagnosis was supported by immunoperoxidase staining, which was strongly positive for vimentin and alpha-1-antichymotrypsin, focally positive for S-100 protein and negative for desmin, muscle-specific actin, keratin, carcinoembryonic antigen and epithelial membrane antigen. Subsequent surgical resection revealed a lesion with a predominance of malignant fibrous histiocytoma-type regions; however, focal microscopic areas contained a low-to-medium-grade cartilaginous component. The final diagnosis rendered was thus pleomorphic or so-called "dedifferentiated" chondrosarcoma. This rare lesion should be included in the differential diagnosis of malignant spindle-cell lesions of bone assessed by FNA biopsy.

Aged↗
PubMedDate not supplied

Herbicidal treatments for control of Cannabis sativa L.

In order to test herbicides for the destruction of illicit stands of cannabis (Cannabis sativa L.) a series of commercially available herbicides were sprayed on glasshouse-grown plants having 2 to 6 leaves. The following herbicides caused complete kill or severe injury to cannabis plants: (a) herbicides with root and foliage activity--ametryn, atrazine, metribuzin, prometryn, terbutryne, diuron, fluometuron, linuron, methabenzthiazuron, phenobenzuron, ethofumesate, karbutilate, methazole and oxadiazon; and (b) foliar-acting herbicides with brief or no soil persistence--amitrole, bentazon, 2,4-D, diquat + paraquat, glyphosate and phenmedipham. In field experiments herbicides of the latter group, and ioxynil, metribuzin, and a MSMA-cacodylate mixture, caused death or severe damage to young cannabis plants. Glyphosate, ioxynil and bentazon destroyed developed cannabis plants. In glasshouse and field experiments the following herbicides applied to young cannabis plants caused marked deformations of stems, leaves and/or inflorescences: barban, butralin, dalapon, difenzoquat, dinitramine, diphenamid, IPC, napropamide, penoxalin, triffuralin, and U-27267.

Cannabis↗
PubMedDate not supplied

Multiple familial cavernous malformations evaluated over three generations with MR.

MR imaging was used to determine the presence or absence of cavernous malformations in three generations of family members. The presenting child (proband) had sustained a symptomatic hemorrhage. Multiple malformations were identified in his father, in an older sibling, and in an asymptomatic grandfather. The father's brother had died from cavernous malformation-related intracerebral hemorrhage. Increasing numbers of malformations were found with increasing patient age, suggesting that MR-apparent lesions may grow in number as a result of repetitive small hemorrhages over time.

Adult↗