Fig. 2.

Histogram of complements of intrafusal muscle fibers in spindles of the gluteus (GL) and medial gastrocnemius (MG) muscle of mutant and wild-type (WT) mice. A,B: Note that most WT spindles contain four intrafusal fibers, whereas most Er81^−/− spindles contain two or three intrafusal fibers in both the GL and MG muscles. Also note that overexpression of NT3 in muscle has little or no effect on numbers of intrafusal fibers in spindles (myoNT3;Er81^−/− compared with Er81^−/−).