Post-activation depression in various group I spinal pathways in humans.
This investigation was designed to study the effects of post-activation depression in different spinal pathways fed by group I afferents available to investigation in human subjects. It was precipitated by a recent investigation in the cat showing that-contrary to the general assumption-post-activation depression is not a widespread phenomenon in the spinal cord. In 24 healthy subjects comparison was made between the effects of low and high-test stimulus rates on the monosynaptic Ia excitation, known to be subject to post-activation depression, and on oligosynaptic pathways fed by group I afferents. Both the amplitude of monosynaptic H reflexes and the amount of heteronymous monosynaptic Ia facilitation were significantly smaller at high than at low-test stimulus rates (1-2 s compared with 6-8 s between two consecutive stimuli). So was the amount of reciprocal Ia inhibition of tibialis anterior motoneurones. In contrast, the amount of other non-monosynaptic group I effects directed to the same motor nuclei (peroneal-induced excitation of quadriceps motoneurones, disynaptic non-reciprocal group I inhibition of flexor carpi radialis motoneurones, and D1 inhibition of flexor carpi radialis and soleus H reflexes) were enhanced at high stimulus rates. Results in humans confirm that post-activation depression depends on the type of group I afferents, and/or on the target neurones. The functional significance of the discrepancy between post-activation depression in pure Ia pathways and in other group I pathways is discussed with regard to the fusimotor-driven servo-assistance from Ia afferent discharges.
Lamy
J C
JC
U731 INSERM/UPMC, Service de Médecine Physique et Réadaptation CHU Pitié-Salpêtrière, 75651 Paris cedex 13, France.
Wargon
I
I
Baret
M
M
Ben Smail
D
D
Milani
P
P
Raoul
S
S
Pénicaud
A
A
Katz
R
R
D000328:Adult; D000842:Ankle / Q000294:innervation; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D052097:Quadriceps Muscle / Q000294:innervation; D013116:Spinal Cord / Q000502:physiology*