Journal of Neurophysiology, Vol 43, Issue 1 16-26, Copyright © 1980 by APS
Glycogen-depletion method of intrafusal distribution of gamma-axons that increase sensitivity of spindle secondary endings
L. Jami, D. Lan-Couton and J. Petit
1. The glycogen-depletion method was used in cat tenuissimus muscles to
investigate whether the action of static gamma-axons that increase the
sensitivity of spindle secondary endings to muscle length is associated
with a specific pattern of distribution of these axons to intrafusal muscle
fibers. 2. In each experiment, a single gamma-axon acting on a secondary
ending of a precisely located spindle was repetitively stimulated, and
subsequently the intrafusal muscle fibers of that spindle were examined for
glycogen depletion. 3. The gamma-axons whose repetitive stimulation
increased the length sensitivity of secondary endings depleted all the
chain fibers in one or both poles of the spindle, with the bag fibers being
inconstantly involved. The gamma-axons whose stimulation did not exert this
effect produced much more restricted patterns of glycogen depletion. 4. The
length sensitivities of two secondary endings belonging to the same spindle
were similarly affected by a single gamma-axon, whereas a gamma-axon could
increase the sensitivity of a secondary ending without altering that of the
primary ending of the same spindle. 5. The action exerted by single
gamma-axons on secondary endings appears related to their intrafusal
distribution since enhancement of the secondary endings sensitivity was
observed only when all the chain fibers of at least one spindle pole were
activated. 6. If several static gamma-axons supplying a given spindle are
firing together, an increase in the length sensitivity of the secondary
endings of that spindle can be expected since probably all chain fibers are
activated.
