Tarsal navicular stress fractures: radiographic evaluation

Tarsal navicular stress fractures are a potential source of disabling foot pain in physically active individuals. The diagnosis of tarsal navicular stress fracture requires a high index of clinical and radiographic suspicion because the fracture is only rarely evident on routine radiographs or standard tomograms. The radiographic diagnosis of a tarsal navicular stress fracture may require anatomic anteroposterior tomograms or a radionuclide bone scan with plantar views. Radiographic examinations of 23 fractures in 21 patients are evaluated.     

Power spectral analysis of the surface electromyogram of human jaw muscles during fatigue

Muscle fatigue in the anterior temporal and masseter muscles of 13 normal subjects was induced by maximum clench in intercuspal position. Frequency analysis using a fast Fourier transform algorithm to obtain the power-spectral density function and the power spectrum of the electromyogram signal indicated that the power spectra obtained during fatigue were statistically significantly shifted to lower frequencies and narrower than those obtained at the beginning of the clench. The shift was due to a significant increase of the power in the low-frequency range and a significant decrease of that in the high-frequency range. The power-spectrum shift to lower frequencies had an exponential time course. The most pronounced shift occurred in the first 25 per cent of the total clenching time. Decrease of the conduction velocity of the action potential along the muscle fibre seems to be the main cause of the shift.     

The helmet sign: Physiologic radioactive accumulation after 131I therapy--a case report

After 131I radioablative treatment, a 51-y-old woman underwent whole-body (131)I scanning, which revealed intense uptake along the periphery of the skull. The patient disclosed that she had not washed her hair because she had obtained a new hairstyle between the 131I treatment and the scan. The intense uptake along the periphery of the skull represented radioactive physiologic accumulation at the patient's scalp.     

Afferent modulation of dopamine neuron firing differentially regulates tonic and phasic dopamine transmission

The mesolimbic dopamine system is centrally involved in reward and goal-directed behavior, and it has been implicated in multiple psychiatric disorders. Understanding the mechanism by which dopamine participates in these activities requires comprehension of the dynamics of dopamine release. Here we report dissociable regulation of dopamine neuron discharge by two separate afferent systems in rats; inhibition of pallidal afferents selectively increased the population activity of dopamine neurons, whereas activation of pedunculopontine inputs increased burst firing. Only the increase in population activity increased ventral striatal dopamine efflux. After blockade of dopamine reuptake, however, enhanced bursting increased dopamine efflux three times more than did enhanced population activity. These results provide insight into multiple regulatory systems that modulate dopamine system function: burst firing induces massive synaptic dopamine release, which is rapidly removed by reuptake before escaping the synaptic cleft, whereas increased population activity modulates tonic extrasynaptic dopamine levels that are less influenced by reuptake.