RESEARCH: Neuronal dysfunction in PLS

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The following study was done by Kay Floeter, MD, PhD and her colleagues at

NIH. The only reason that this study was able to be done was that at least 25

PLSers stepped up to the plate and volunteered to be subjects in Dr. Floeter's

research. Without their help, this study would never have been done. Thanks!!!

And for all PLSers, please join the PLS Registry. Call Nailah Siddique, RN, MSN

at or email her at nsiddique@... .

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Motor neuron firing dysfunction in spastic patients with primary lateral

sclerosis.

Floeter MK, Zhai P, Saigal R, Kim Y, Statland J.

EMG section, National Institute of Neurological Disorders and Stroke, Bethesda,

MD, USA.

Patients with corticospinal tract dysfunction have slow voluntary movements with

brisk stretch reflexes and spasticity. Previous studies reported reduced firing

rates of motor units during voluntary contraction. To assess whether this firing

behavior occurs because motor neurons do not respond normally to excitatory

inputs, we studied motor units in patients with primary lateral sclerosis, a

degenerative syndrome of progressive spasticity. Firing rates were measured from

motor units in the wrist extensor muscles at varying levels of voluntary

contraction up to 10% maximal force. At each force level, the firing rate was

measured with and without added muscle vibration, a maneuver that repetitively

activates muscle spindles. In motor units from age-matched control subjects, the

firing rate increased with successively stronger contractions as well as with

the addition of vibration at each force level. In patients with primary lateral

sclerosis, motor unit firing rates remained stable,

or in some cases declined, with progressively stronger contractions or with

muscle vibration. We conclude that excitatory inputs produce a blunted response

in motor neurons in patients with primary lateral sclerosis compared to

age-matched controls. The potential explanations include abnormal activation of

voltage-activated channels that produce stable membrane plateaus at low

voltages, abnormal recruitment of the motor pool, or tonic inhibition of motor

neurons.

SOURCE: J Neurophysiol. 2005 Apr 13; [Epub ahead of print]

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=PubMed & list_uids=1\

5829597 & dopt=Abstract