Mathematical characterisation of the transduction chain in growth cone pathfinding.

Axon guidance by graded diffusible ligands plays an important role in the developing nervous system. Concentration gradients induce an asymmetric localisation of molecules in the axon tip, the growth cone, and the consequent internal polarised signalling pathway leads to rearrangement of the growth cone cytoskeleton and, ultimately, to motility. Here the authors provide a mathematical description of the growth cone transduction chain as a series of functional boxes characterised by input/output relations. The model relies on the assumption that the characteristic time of independent concentration measures by growth cone receptors, the characteristic time of growth cone internal reorganisation preceding motion and the characteristic time needed for a discernible axon turning belong to separated scales. The results give insight into the deterministic against stochastic regime of internal growth cone functions that are not readily accessible from experimental observations, pointing out a substantial equilibrium of the two contributions. The mathematical model predicts the decrease of the coefficient of variation of the signal moving down the functional chain leading to motion. Moreover, possible mechanisms that allow for buffering against noise are highlighted. These results have an interest also for the more experimentally minded reader, since they can be used to predict sample sizes for detecting significant differences in benchmark gradient assays.

Magnetic necklace: its therapeutic effectiveness on neck and shoulder pain.

The effect of the magnetic necklace on chronic neck and shoulder pain was studied on 101 volunteers, 46 males and 55 females. A double-blind method was applied on 4 divided groups (with pain vs without pain matched with magnetic vs nonmagnetic necklace). All the subjects wore the necklace 24 hours per day for 3 weeks. Subjective evaluation from the subjects with pain, either with magnetic or nonmagnetic treatment, was performed before and 3 weeks after the necklace treatment, and revealed a significant placebo effect in terms of decrease in intensity or frequency of pain. The objective tests with electrodiagnostic procedures were done before the treatment and at 3 weekly intervals. The proximal conduction time of the ulnar nerve was significantly reduced by magnetic treatment in the subjects without pain but was not changed in the subjects with pain. There was no significant change in the excitation threshold of the suprascapular nerve in all subjects. The possible mechanism of magnetic effects on pain and the prospect of magnetotherapy for pain relief in physical medicine are discussed.

Axillary F-loop latency of ulnar nerve in normal young adults.

F waves were studied with stimulation of the ulnar nerve in normal subjects (25 men and 15 women, with an average age of 26.5 years) using an EMG machine that permits the simultaneous display of 8 sweeps. The axillary F-loop latency (AFLL), defined at the conduction time between the axilla (25cm from the sternal notch) and the spinal cord, was 9.17 +/- 0.81msec when 8 F responses were measured but was 8.57 +/- 1.00msec when 40 F responses were used. Data from men and women showed no significant statistical difference. The mean plus 2 standard deviations were 10.8 and 10.6msec for 8 and 40 responses, respectively. On the basis of these findings, an AFLL longer than 11msec should be considered abnormal in the young adult. Four measures repeated at weekly intervals showed no significant difference from week to week, indicating that the technique can be consistently and reliably applied at different times. The average duration of the F complex was 15.78 +/- 2.55msec and was about 80% of the average duration of the M wave.