An interesting observation in this study was the consistent reflex inhibition
of the extensor carpi ulnaris (ECU) during ulnar deviation, differing greatly from co-contractions that were seen in the other wrist positions.
This reflex inhibition
helps to counteract the stretch reflex excitation (produced by spindles) from the same muscle.
On the spinal level, botulinum toxin is capable of producing reflex inhibition of the muscle spindle organ.
2) The botulinum toxin injection blocks the extrafusal and intrafusal release of acetylcholine, and effectively reduces the Ia and II afferent signal from the muscle spindle organs and the muscle tone by reflex inhibition without affecting muscle strength.
This resistance against the contraction of the agonist muscle is associated with reflex inhibition
of the antagonist muscle, that is, relaxation.
This activity-dependent potentiation (ADP) of the L30s occurs at low, behaviorally relevant activation frequencies (2 to 10 Hz), and has a time course of expression matching that of the reflex inhibition
produced by activation of the L29s (Fischer and Carew, 1993).
Since temperature may also be important in this oropharyngeal reflex inhibition
of AVP secretion, further studies are needed to determine the nature of this deficit.