Reliability of stereotactic biopsy. A model to test the value of diagnoses obtained from small fragments of nervous system tumors

Because of the variability of the structural features of cerebral tumors, the characteristics observed in biopsy samples may not be representative of the whole neoplasm. The reliability of cerebral stereotactic biopsy is therefore greatly debated. In order to test the value of diagnoses based on biopsy samples, the authors compared histological and cytological data obtained from a small fragment of a tumor with the definitive diagnosis obtained from surgical or necropsy specimens. An analysis of 64 cases is reported, where a correct diagnosis from the biopsy sample was achieved in 92.2% of the cases. Neuroglial tumors were more difficult to characterize than other types of intracranial tumors, with an accuracy of 81.5%.     

Effect of T3 on insulin action, insulin binding, and insulin receptor kinase activity in primary cultures of rat hepatocytes

In vivo studies have demonstrated that the liver is the main site of insulin resistance in hyperthyroidism. To further investigate the effect of thyroid hormone in the liver, we have incubated primary cultures of rat hepatocytes in the presence and absence of triiodothyronine (T3) 1 ng/ml and 5 ng/ml for 20 hr. Without affecting basal activity, T3 5 ng/ml decreased insulin-stimulated (1 x 10(-7) M) lipid synthesis but not insulin-stimulated alpha-aminoisobutyric acid uptake. These changes occur in the absence of any abnormalities in 125I-insulin binding, degradation, internalization or insulin receptors structure as determined by affinity-labeling methods. However, basal insulin receptor kinase activity using Glu4: Tyrl as phospho-acceptor was decreased by T3 without altering its insulin responsiveness. These results demonstrate the heterogeneity of T3's effects at the postinsulin binding level in the liver.     

A copy-number mutant of plasmid pSC101

Copy-number mutants of plasmid pSC101 were isolated by u.v. mutagenesis and selection for elevated expression of ampicillin resistance. Three independent mutations were identical and mapped in codon 93 of the initiation protein RepA. The mutated plasmids were maintained at a level four to five times higher than that of the wild type. For one of them, it was determined that: (i) the mRNA of the autoregulated repA gene, cloned onto a pUC19 plasmid under the control of its own promoter, was expressed at a level 1.7 times higher than that of the wild type; (ii) the RepA protein, under the same conditions, was expressed at a similarly higher level; (iii) the affinity of the mutated protein for three repeated sequences in the origin region of the plasmid was, on average, 3.4 times higher than that of the wild-type protein. We postulate that the copy-number effect is due to a combination of these two effects, i.e. higher protein concentration and increased affinity of the protein for the repeated sequences.     

Observations on the ranging behaviour and daily activity of lone silverback mountain gorillas (Gorilla gorilla beringei)

Two lone silverback mountain gorillas (Gorilla gorilla beringei) were followed during a 13-week study period in an attempt to describe the size and differential use of their respective home ranges. The ranging behaviour was compared to that of groups and possible causes of daily movement were examined. The daily activity of one individual is described. Considerable differences between silverbacks were found not only in the time spent within areas of their ranges but in the ways they ranged over their core areas. The subject that had left his parent group earlier covered his core area more vigorously, by means of circuitous routing. Lone silverback ranges overlapped their parent group ranges considerably and the group frequently entered the silverback's core area. Lone males did not move further nor more rapidly than groups. Feeding, social interactions, and location of nest sites were examined to reveal the possible causes of daily ranging behaviour and it was tentatively concluded that availability of food supply regulated the silverback's movements.     

The replication of plasmid pSC101

The origin of replication of plasmid pSC101 presents features reminiscent of those found in a number of plasmids. As for those plasmids, many details about the way it initiates its replication are beginning to be known, but the regulation of this process will not be easily understood.