Augmentation in the infectivity of SV40 virus DNA by amphotericin B methyl ester

Summary The methyl ester of amphotericin B (100 µg/ml) enhanced the infectivity of SV40 virus DNA for CV-1 cells up to 300-fold. Amphotericin B methyl ester may prove useful for augmenting cellular penetration of macromolecules and for probing biological mechanisms.With 2 Figures     

A microperfusion investigation of bicarbonate secretion by the rat submaxillary gland

Summary Bicarbonate transport in the rat submaxillary main duct has been studied by microperfusion. Bicarbonate was concentrated in the duct lumen against an electrochemical gradient and the equilibrium concentration was estimated to be 56.5 mEq/l±3.1 (S.E.M.,n=11). The secretory mechanism could not be inhibited by 6 mMolar cyanide although such concentrations caused marked inhibition of both net sodium efflux and net potassium influx. Bicarbonate secretion in the main duct was not inhibited by acetazolamide whether applied from the duct lumen or given intravenously. Similarly, the drug was without effect on bicarbonate excretion by the intact gland even when maximum excretory rates had been induced with carbachol. It was concluded that catalytic hydration of carbon dioxide to carbonic acid was not a rate-limiting step in the bicarbonate secretory process. The data did not permit a distinction to be made between a bicarbonate secretory processper se and a process of either H⁺ reabsorption or OH^– secretion.The parasympathomimetic agent, carbachol, when given parenterally was found to increase sharply the net influx of bicarbonate into the microperfused main duct as well as to reduce net sodium efflux and net potassium influx. Previously it had been postulated that final saliva was formed in two stages. First a plasma-like primary secretion was formed at a rate depending on the degree of stimulation, and second, the primary secretion was modified in the gland duct system by reabsorptive and secretory processes whose transport rates were presumed to be independent of the degree of stimulus. It now becomes necessary to postulate that stimulation can act on electrolyte transport at both primary and secondary levels; at present, however, no data are available to show whether appreciable net water influx can ever occur at the secondary level.Preliminary reports of this study have been presented to the Australian Physiological and Pharmacological Society [28, 31].     

Energy intake during reproduction in captive common marmosets (Callithrix jacchus)

Among haplorhine primates, the highly specialized Callitrichidae (marmosets and tamarins) are expected to have comparatively high reproductive costs, a feature that might be related to the evolution of a cooperative breeding system. Costs of reproduction in captivity were investigated on the basis of changes in energy intake and body weight during pregnancy and lactation in pair-living female and male common marmosets (Callithrix jacchus). The experimental design had little effect on carrying behavior, food intake, and body weight of adults, but a negative transitory effect of offspring body weight. Increased energetic requirements during pregnancy did not result in a higher energy intake in females. During lactation, females increased their energy intake up to 100% and gradually lost weight, suggesting even higher costs. Extensive carrying behavior by males, on the other hand, did not result in an increased energy intake in males, or in changes in male body weight. It is suggested that, at least in captivity, increased energetic demands during reproduction are reduced by behavior allocations towards energetically less expensive behaviors.     

Perceptual and Motor Space Representation: An Event-Related Potential Study

The purpose of this experiment was to study the brain potentials generated during spatial tasks related to the “schema corporel” (a mental map of sensory-motor relationships). Seven right-handed subjects performed a choice reaction-time task (Experiment 1), in which the spatial position of a visual stimulus (right or left of a fixation point) was varied independently of the spatial position of the response (right or left hand). The subjects also made self-paced extensions and flexions of the right and left index fingers (Experiment 2). Experiments 1 and 2 were performed with the hands both crossed and uncrossed. Spatio-temporal maps showed that the P300 component elicited by the choice RT situation in Experiment 1 was largest ipsilateral to the hand involved in the response, whether or not the hands were crossed. The later part of the pre-movement potentials during Experiment 2 and the motor potential were significantly larger contralateral to the moving hand under all conditions. Thus this pattern of lateralization can be attributed to the superimposition of a bilateral P300 wave on the asymmetrical motor potential. This suggests that distinct neuronal populations are involved in the generation of these two components. P300 latency and RT reflected the spatial conflict: both were longer when the stimulus and response were on opposite sides than when they were on the same side, even when the hands were crossed. However, the average P300 latency was not increased when the hands were crossed, whereas the average RT was substantially increased. Since the additional time required for programming the movement in the crossed hand situation had no effect on P300 generation, we infer that the P300 does not index this motor programming. However, P300 does reflect the stimulus-response spatial matching, since its latency was delayed by spatial conflict.     

Extramedullary myeloid cell tumours localised to the mediastinum: a rare clinicopathological entity with unique karyotypic features

Extramedullary myeloid cell tumour (EMMT) localised to the mediastinum is a rare manifestation of acute myeloid leukaemia, forming less than 4% of all cases of EMMT. In contrast to other types of EMMT, cytogenetic characteristics of this rare entity are relatively unknown. This report describes a patient with EMMT who had evidence of superior vena cava syndrome and normal peripheral blood counts at diagnosis. The results from an initial biopsy specimen were consistent with a diagnosis of mediastinal large B cell lymphoma. A diagnosis of acute myeloid leukaemia was made three months after initial diagnosis by bone marrow examination. Review of the initial biopsy specimen showed strong positivity for myeloperoxidase, revealing that the patient had been initially misdiagnosed as having large B cell lymphoma. Cytogenetic studies revealed a near triploid and near tetraploid karyotype with structural abnormalities in 12 and three metaphases, respectively. Review of the literature showed that a near tetraploid or triploid karyotype is found in most of the reported cases of mediastinal EMMT. Thus, the presence of a near triploid/tetraploid karyotype and mediastinal EMMT may represent a specific subset of EMMT. The biological relevance of this observation is discussed.     

Malignant ameloblastoma,spindle cell variant

In this report, we document the histologic and clinical features of a previously undefined spindle cell variant of ameloblastoma that eventually behaved in a malignant fashion during a protracted course. The predominant histologic pattern was a well-differentiated, cellular, spindled epithelial proliferation arising in the maxilla of a 14-year-old African American girl. Over 19 years, the patient experienced numerous local recurrences, metastases to distant bones after 15 years, and finally bulky local recurrence with intracranial extension resulting in death. This ameloblastic malignancy histologically simulates a low-grade true sarcoma or an ameloblastic sarcoma, but differs in that the extensive spindle cell proliferation is epithelial, characterized by strong cytokeratin immunoreactivity and negative vimentin staining.     

Central and peripheral mediation of human force sensation following eccentric or concentric contractions

Fatigue was induced in the triceps brachii of the experimental arm by a regimen of either eccentric or concentric muscle actions. Estimates of force were assessed using a contralateral limb-matching procedure, in which target force levels (25 %, 50 % or 75 % of maximum) were defined by the unfatigued control arm. Maximum isometric force-generating capacity was reduced by 31 % immediately following eccentric contractions, and remained depressed at 24 (25 %) and 48 h (13 %) post-exercise. A less marked reduction (8.3 %) was observed immediately following concentric contractions. Those participants who performed prior eccentric contractions, consistently (at all force levels), and persistently (throughout the recovery period), overestimated the level of force applied by the experimental arm. In other words, they believed that they were generating more force than they actually achieved. When the forces applied by the experimental and the control arm, were each expressed as a proportion of the maximum force that could be attained at that time, the estimates matched extremely closely. This outcome is that which would be expected if the estimates of force were based on a sense of effort. Following eccentric exercise, the amplitude of the EMG activity recorded from the experimental arm was substantially greater than that recorded from the control arm. Cortically evoked potentials recorded from the triceps brachii (and extensor carpi radialis) of the experimental arm were also substantially larger than those elicited prior to exercise. The sense of effort was evidently not based upon a corollary of the central motor command. Rather, the relationship between the sense of effort and the motor command appears to have been altered as a result of the fatiguing eccentric contractions. It is proposed that the sense of effort is associated with activity in neural centres upstream of the motor cortex.