Effects of s-R compatibility and task difficulty on unimaimual movement time

Using a system in which S controlled a cursor on an oscilloscope screen by moving a lever, the S-R relationship on either hand could be reversed. This system was used in two experiments designed to investigate the effect on unimanual movement time of varying S-R compatibility, and task difficulty as defined by Fitts (1954). The results indicated the necessity of specifying task difficulty in an investigation of S-R compatibility. Further, it was found that as task difficulty increased the difference in performance between the right and left hands became more marked.

Enhanced response to radiotherapy in tumours deficient in the function of hypoxia-inducible factor-1

BACKGROUND AND PURPOSE

To test the hypothesis that deficiency in expression of the transcription factor, HIF-1, renders tumours more radioresponsive than HIF-1 proficient tumours.

PATIENTS AND METHODS

Tumours comprising mouse hepatoma cells lacking HIF-1beta (and thereby HIF-1 function) were grown in nude mice and radiation-induced growth delay compared with that seen for wild-type tumours and tumours derived from HIF-1beta negative cells where HIF-1 function had been restored.

RESULTS

The xenografts that lack HIF-1 activity take longer to establish their growth and are more radioresponsive than both parental xenografts and those with restored HIF-1 function. Pre-treatment of the HIF-1 deficient xenografts with the hypoxic radiosensitizer misonidazole, had little effect on radioresponse. In contrast this treatment radiosensitized the parental xenografts. In spite of this, no difference in oxygenation status was found between the tumour types as measured by Eppendorf O(2)-electrodes and by binding of the hypoxic cell marker NITP. Admixing wild type and HIF-1 deficient cells in the same tumour at ratios of 1 in 10 and 1 in 100 restores the growth of the mixed tumours to that of a 100% HIF-1 proficient cell population. However, when comparing the effects of radiation on the mixed tumours, radioresponsiveness is maintained in those tumours containing the high proportion of HIF-1 deficient cells.

CONCLUSIONS

The differences in radioresponse do not correlate with tumour oxygenation, suggesting that the hypoxic cells within the HIF-1 deficient tumours do not contribute to the outcome of radiotherapy. Thus, hypoxia impacts on tumour radioresponsiveness not simply because of the physio-chemical mechanism of oxygen with radiation-induced radicals causing damage 'fixation', but also because hypoxia/HIF-1 promotes expression of genes that allow tumour cells to survive under these adverse conditions. Further, the results from the cell mixing experiments uncouple the growth promoting effects of HIF-1 and the underlying mechanism by which HIF-1 may increase radiation resistance in solid tumours.

A protective role for HIF-1 in response to redox manipulation and glucose deprivation: implications for tumorigenesis

We have investigated the role of HIF-1 in the cellular response to redox modulation via the inhibition of oxidative phosphorylation. We demonstrate that manipulation of redox in air, achieved by inhibiting cytochrome oxidase with cyanide, induces HIF-1 mediated transcription in wild-type CHO and HT1080 human tumour cells but not in CHO cells deficient in the oxygen responsive, HIF-1alpha sub-unit of HIF-1. Hypoglycaemia attenuates cyanide-mediated transcription in non-transformed HIF-1 wild-type CHO cells but not the human tumour derived cell line. Cells lacking either HIF-1alpha, or the second composite sub-unit of HIF-1, HIF-1beta, were markedly more sensitive to the combined stress of perturbed redox and hypoglycaemia than wild-type cells. As such conditions together with hypoxia are prevalent in tumours, these data suggest that HIF-1 may have a protective role in adaptation to the tumour micro-environment. In support of this we demonstrate that HIF-1alpha deficient cells are less tumorigenic than wild-type cells. They showed a reduced growth rate when grown as xenografts in nude mice. This was not related to vascular parameters that were identical to those found in HIF-1 wild-type tumours. The HIF-1 deficient tumours lacked focal expression of Glut-1 in hypoxic tumour regions. Compromised glucose uptake and metabolic adaptation to the tumour micro-environment may form the basis of the reduced tumorigenicity associated with these cells.

Movement variability and bradykinesia in Parkinson's disease

When making discrete aiming movements, patients with Parkinson's disease show greater inherent variability in the endpoints of their movements than do normal subjects. Endpoint variability can be reduced, by moving more slowly, by utilizing visual guidance, and by making small amplitude movements. The greater variability of patients is not a universal finding, but depends on the conditions of movement. For small movements the performance of patients equates to that of controls. For larger movements the results indicate that if sufficient time is available, patients can use visual guidance (if available) to reduce the variability of their movements to the level of normals. Patients can generate fast and/or large amplitude arm movements if required, but they are erratic if made in the dark or over a short duration. Their difficulty lies not so much in the magnitude of muscle force available to them, but rather in an inability to produce it consistently for any given movement attempted. Bradykinesia may in part result from this inherent variability in that parkinsonian patients, in order to maintain accuracy within acceptable limits, are forced to increase the duration of their movements to a level where they can make use of visual guidance. In any event, theoretical explanations for the movement disorder in Parkinson's disease advanced in the literature need to take some account of this increased variability of movement.

Programming and execution of movement in Parkinson's disease

Programming and execution of arm movements in Parkinson's disease were investigated in choice and simple reaction time (RT) situations in which subjects made aimed movements at a target. A no-aiming condition was also studied. Reaction time was fractionated using surface EMG recording into premotor (central) and motor (peripheral) components. Premotor RT was found to be greater for parkinsonian patients than normal age-matched controls in the simple RT condition, but not in the choice condition. This effect did not depend on the parameters of the impending movement. Thus, paradoxically, parkinsonian patients were not inherently slower at initiating aiming movements from the starting position, but seemed unable to use advance information concerning motor task demands to speed up movement initiation. For both groups, low velocity movements took longer to initiate than high velocity ones. In the no-aiming condition parkinsonian RTs were markedly shorter than when aiming, but were still significantly longer than control RTs. Motor RT was constant across all conditions and was not different for patient and control subjects. In all conditions, parkinsonian movements were around 37% slower than control movements, and their movement times were more variable, the differences showing up early on in the movement, that is, during the initial ballistic phase. The within-subject variability of movement endpoints was also greater in patients. The motor dysfunction displayed in Parkinson's disease involves a number of components: (1) a basic central problem with simply initiating movements, even when minimal programming is required (no-aiming condition); (2) difficulty in maintaining computed forces for motor programs over time (simple RT condition); (3) a basic slowness of movement (bradykinesia) in all conditions; and (4) increased variability of movement in both time and space, presumably caused by inherent variability in force production.

Response Programming and Reaction Time

A feature common in the literature is that, prior to responding, subjects have been able to preview the parameters of the movement they are required to make. This introduces the possibility of programming the movement before entering the reaction time period. It is argued that this has contributed to confusion in the literature, making it difficult to detect a consistent relationship between reaction time and motor task demands. Two experiments were conducted to clarify the position. Experiment I concealed the movement parameters prior to subjects responding ("no-preview" model), and this was contrasted with a study in the typical "preview" mode (Experiment II). It was concluded that the no-preview design is more appropriate to detecting changes in reaction time dependent on task parameters, and that the observed effects on reaction time reflect programming difficulty. A third experiment supported this conclusion

Effects of S-R and R-R compatibility on bimanual movement time

Bimanual asymmetrical movements are generally found to be slower than symmetrical movements but asymmetrical movement normally involves visual separation of targets which might account for the effect. By using a system in which the subject controls two cursors on an oscilloscope screen by moving two levers the S-R relationship on either hand can be reversed, thus providing an asymmetrical movement task without visual separation of targets. Movement times for five right-handed subjects were recorded on four unimanual and six bimanual conditions varying with respect to both S-R and R-R compatibility. In the unimanual conditions, the left hand was found to be as fast as the right when the opposite S-R relationship was used. In the bimanual tasks visual separation of targets was a relatively minor factor movement time being strongly influenced by S-R compatibility and to a lesser degree by R-R compatibility. The results suggest that compatibility, rather than being a property of a single central channel, differs, as between the two cerebral hemispheres.

Hepatic Necrosis Due to Marsilid

In the patient reported here severe jaundice and death resulted from treatment with iproniazide ("marsilid") given for only three days.