Intrinsic electrical properties of spinal motoneurons vary with joint angle.
The dendrites of spinal motoneurons amplify synaptic inputs to a marked degree through persistent inward currents (PICs). Dendritic amplification is subject to neuromodulatory control from the brainstem by axons releasing the monoamines serotonin and norepinephrine; however, the monoaminergic projection to the cord is diffusely organized and does not allow independent adjustment of amplification in different motor pools. Using in vivo voltage-clamp techniques, here we show that dendritic PICs in ankle extensor motoneurons in the cat are reduced about 50% by small rotations (+/-10 degrees ) of the ankle joint. This reduction is primarily due to reciprocal inhibition, a tightly focused input shared only among strict muscle antagonists. These results demonstrate how a specific change in limb position can regulate intrinsic cellular properties set by a background of diffuse descending neuromodulation.
Hyngstrom
Allison S
AS
Department of Physiology, 303 E. Chicago Avenue, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
Johnson
Michael D
MD
Miller
Jack F
JF
Heckman
C J
CJ
D000818:Animals; D000843:Ankle Joint / Q000502:physiology*; D002415:Cats; D003655:Decerebrate State / Q000503:physiopathology; D008564:Membrane Potentials / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011187:Posture; D012044:Regression Analysis; D012371:Robotics; D013116:Spinal Cord / Q000166:cytology*