Journal of Neurophysiology, Vol 57, Issue 4 1050-1059, Copyright © 1987 by APS
High incidence of long-chain fibers in spindles of cat superficial lumbrical muscles
L. Decorte, F. Emonet-Denand, D. W. Harker and Y. Laporte
Forty-two complete spindle poles of cat superficial lumbrical muscles were
analyzed with particular regard to the length and the diameter of
intrafusal fiber types. Poles were reconstructed from serial transverse
sections of fresh-frozen muscles. The staining module, which was repeated
throughout the whole muscle, comprised sections treated for glycogen
detection and sections treated for detecting myofibrillar ATPase activity
after preincubation at three different pH's (see METHODS). The
identification of intrafusal fiber types was essentially based on the
ATPase activity of the B region of the intrafusal fibers. Long-chain
fibers, i.e., chain fibers that have at least one pole that extends by more
than one millimeter beyond the end of the spindle capsule (6), were very
commonly observed. Of 42 spindle poles analyzed, 30 (71%) contained at
least one long-chain fiber (one in 17 spindle poles, 2 in 11 poles, and 3
in 2 poles). Of 246 poles of chain fibers, 45 (18%) were "long". In four
spindles, in which both poles could be completely examined, 10 long-chain
fibers were observed. In eight of these, only one pole was long; the
opposite pole ended either intracapsularly or at a short distance outside
the capsule. Since long-chain fiber poles, presently considered to be among
the effectors of static skeletofusimotor (beta) axons, are present in a
large proportion of muscle spindles of lumbrical muscles, it would be of
particular interest to reevaluate the beta-supply of these muscles by
physiological methods.
