Fig. 4. Proprioceptive defects and absence of spindles. (A) Wild-type animals but not the mutants showed an abnormal hind-limb extension reflex (panels 1-3). They also had difficulties in coordinating limb movement when placed on a slippery platform (panel 4). (B) Hematoxylin/Eosin stained cross-sections of P9 soleus muscle. Two muscle spindles of a wild-type mouse are indicated by arrows. In the mutant mice no spindles could be identified. (C) Erbb2 (green) was expressed in intrafusal muscle fibers of muscle spindles. It co-localized with -bungarotoxin labeled AChR clusters in postsynaptic membranes of g-motoneuron contact sites (yellow, arrows). Scale bars: 50 µm in B; 15 µm in C.