Rate Repetitive Stimulation Research Articles

Concurrent Chronic Motor Axonal Polyneuropathy and Synaptic Impairment of Neuromuscular Junction

Polyneuropathies may exhibits clinical, electrophysiologic signs of neuromuscular junction impairment. Distal motor nerve terminals and neuromuscular junction contain pre or postsynaptically specific targets for circulating autoantibodies, if present in neuropathies. Motor nerve terminal blockade either reversible or permanent is a putative factor of muscle weakness. A 59-year-old patient exhibited oropharyngeal, facial, extremity weakness, fluctuating fatigability, and areflexia. Elecectrophysiologic studies showed purely motor axonal polyneuropathy. Thenar, facial slow rate repetitive stimulation revealed up to 47% decrement of compound muscle action potential size. Single fiber electromyography on voluntary activation confirmed increased jitter and impulse blocking in all muscles examined in one third of the fibers. Repeated testings for antibodies to gangliosides, acetylcholine, muscle tyrosine kinase receptors, voltage-gated calcium channels were negative. Oral pyridostigmine bromide improved bulbar symptoms. Pulse intravenous immunoglobulin, oral steroids, and azathioprine had steady benefit. Impairment of neuromuscular transmission if occurring in chronic axonal neuropathies highlights mechanisms and significance of neuromuscular chronic "synaptopathies."

Relief from episodic weakness with pyridostigmine in paramyotonia congenita: A family study

Pyridostigmine relieved episodic weakness in a family with paramyotonia congenita resulting from the R1448C mutation in the sodium channel gene. The transmission was autosomal dominant and the patients had paradoxical myotonia and exercise-induced weakness. On electrophysiological studies there were myotonic potentials, and there was progressive reduction of compound muscle action potential (CMAP) amplitudes after short exercise associated with clinical weakness. Pyridostigmine in doses of 60 mg three times daily abolished the drop in the postexercise CMAP amplitude and reduced the amplitude decrement to slow rate repetitive stimulation, but there continued to be a drop in amplitude on exposure to cold. The decline of the CMAP amplitude on exposure to cold was controlled by treatment with phenytoin. The clinical and electrophysiological features are discussed in relation to therapy with pyridostigmine and phenytoin.

Layer-specific short-term dynamics in network activity in the cerebral cortex

Optical imaging with a voltage-sensitive dye was conducted in frontal slices of rat auditory cortex to study spatiotemporal patterns of response to repetitive electrical stimulation. When the rate of repetitive stimulation increased to 40 Hz, the amplitude ratio of the response after the fifth stimulus to the response after the first stimulus was significantly smaller in layers II/III than in layer IV or in layers V/VI. Similar results were obtained regardless of where electrical stimulation was applied. When the rate of stimulation was at 10 Hz, no difference was observed in response ratios among layers. These results show that the manner of responding to repetitive stimulation is different among layers and that it is stimulation rate-dependent.

Effects of shifts in the rate of repetitive stimulation on sustained attention

The effects of shifts in the rate of presentation of repetitive neutral events (background event rate) were studied in a visual vigilance task. Four groups of subjects experienced either a high (21 events/min) or a low (6 events/min) event rate for 20 min and then experienced either the same or the alternate event rate for an additional 40 min. The temporal occurrence of critical target signals was identical for all groups, irrespective of event rate. The density of critical signals was 12 signals/20 min. By the end of the session, shifts in event rate were associated with changes in performance which resembled contrast effects found in other experimental situations in which shift paradigms were used. Relative to constant event rate control conditions, a shift from a low to a high event rate depressed the probability of signal detections, while a shift in the opposite direction enhanced the probability of signal detections.

A critical analysis of the contribution of the collision method to "pyramidal" identification of pericruciate neurones in the chloralosed cat.

Abstract1. In cats anaesthetized with chloralose, the identification of motor cortex neurones with axons distributed within the pyramidal tract (as assessed by their antidromic response to a bulbar pyramid shock) is critically analysed in view of the known complexity of the neuronal circuitry in this cortical area.2. The conclusions drawn from the two classical criteria of antidromic invasion – invariable latency and ability to follow high rates of repetitive stimulation — are compared with the results obtained by initiating collision between orthodromic and antidromic impulses travelling along the same axonal pathway: the principle of this method is summarized and results from 39 peri-cruciate neurones, recorded by extracellular micropipettes, are presented.3. It is shown that the collision test helps in the accurate identification of pericruciate pyramidal neurones, particularly for some neurones which do not follow the frequency criterion owing, probably, to inhibitory mechanisms in the motor cortex.4....

A study of synaptic transmission in the absence of nerve impulses.

1. The axo-axonic giant synapse in the stellate ganglion of the squid has been used to study synaptic transmission.2. When nerve impulses have been eliminated with tetrodotoxin, synaptic transfer of potential changes can still be obtained by applying brief depolarizing pulses to the presynaptic terminal.3. Suitably matched pulses are as effective as the normal presynaptic spike in evoking post-synaptic potentials. The synaptic delay and the time course of the post-synaptic potential are very similar to that in the normal preparation.4. The synaptic transfer (input/output) characteristic has been studied under different experimental conditions. With brief (1-2 msec) current pulses, post-synaptic response becomes detectable when the presynaptic depolarization exceeds about 30 mV. The post-synaptic potential increases about tenfold with 10 mV increments of presynaptic depolarization.5. Calcium increases, magnesium reduces the slope of the synaptic transfer curve. The influences on this curve of (i) duration of the pulse, (ii) preceding level of membrane potential, (iii) position of recording electrode, (iv) rate of repetitive stimulation are described.6. After loading the synaptic terminal with tetraethylammonium ions, large inside-positive potentials can be produced in the terminal and maintained for many milliseconds.7. By raising the internal potential to a sufficiently high level, synaptic transfer becomes suppressed during the pulse, and the post-synaptic response is delayed until the end of the pulse.8. This observation is in accord with a prediction of the ;calcium hypothesis', viz. that inward movement of a positively charged Ca compound, or of the calcium ion itself, constitutes one of the essential links in the ;electro-secretory' coupling process of the axon terminal.