Figure 4.

Soleus muscle stretch-evoked responses are reduced in wi/wi mutant mice. A, Experimental paradigm of Soleus (Sol) muscle nerve extracellular recordings. Top, Sequence of muscle stretches (1 mm) to which Sol muscles were subjected during a single trial. Stretch episodes (s1-s4) were alternated with intervals during which muscles were kept at resting length (r1-r4) (for details, see Materials and Methods). Middle, Recording of firing activity of wild-type Sol muscle nerve during a stretch trial. Bottom, High-resolution image of pSN firing activity during a 1 s stretch episode. B, Spontaneous (resting length) activity (SA) in wild-type, +/wi, and wi/wi mutant Sol muscle nerve is similar (mean SA^s2-s4 ± SEM in wt 11.9 ± 3.4 imp/s, +/wi 14.7 ± 2.7 imp/s, wi/wi 9.2 ± 2.8 imp/s; wt vs +/wi, p = 0.22; wt vs wi/wi, p = 0.32, Mann–Whitney rank sum test). C, Net evoked activity (NEA) in Sol muscle nerve in wild-type, +/wi, and wi/wi mutant mice. Stretch-evoked activity was significantly lower in wi/wi than in wild-type mice, whereas heterozygote wi animals showed a smaller reduction in NEA (mean NEA^s2-s4 ± SEM for wt 102.8 ± 9.3 imp/s, +/wi 77 ± 12.9 imp/s, wi/wi 51.6 ± 7.0 imp/s; wt vs +/wi, p = 0.019; wt vs wi/wi, p < 0.001, Mann–Whitney rank sum test). B, C, Tails are extended to the largest and smallest data points, which are not outliers. Black dots represent outliers. Number of Sol muscles analyzed is indicated in parentheses. *p < 0.05, **p < 0.01.