Fig. 6. Analysis of Ia and Ib afferent projections by parvalbumin staining. (A) Immunohistochemical analysis using an antibody against parvalbumin as a marker for Ia- and Ib afferents. At E18.5, spindles were innervated by sensory afferents in both wild-type and mutant mice (arrows). (B) Two enlarged innervated spindles in mutant mice (right) at E18.5 showing the Ia afferent spiraling around the intrafusal muscle fiber (arrows). Notice the presence of only one intrafusual fiber in mutant mice. Left panel, longitudinal; right panel, cross-section. (C) Golgi tendon organs formed and were properly innervated in wild-type and mutant animals at E18.5 (arrows). (D) At postnatal day 4, spindles in wild-type and mutant mice were innervated, but the nerve terminals in the mutants were weakly stained, appeared irregular and were less frequently found. Scale bars: 100 µm in A; 30 µm in B; 200 µm in C; 40 µm in D.