Effects of the infraorbital nerve-transection on the formation of Ia fibers in muscle spindles of the masseter muscle in developing mice.
The effect of the transection of the infraorbital nerve on d 20 after birth on the formation of the annulospiral ending of Ia fibers of muscle spindles in the masseter muscle was investigated in developing mice. On the 20th d after the operation, there were significant differences between control and treated animals in the ratio of muscle spindles with non-coiled endings to all muscle spindles, and the ratios of muscle spindles with non-coiled endings in the masseter muscle on the operated and sham-operated sides were about equal to each other. On the 30th d after the operation, the ratio for the masseter muscle on the operated side was approximately twice that for the one on the sham-operated side. The ratio for the operated side was about equal to that for 15-d-old control mice, and about twice that for 20-d-old control animals. Thus, the present results indicate that disorder of sensory inputs following the transection of the infraorbital nerve leads to degeneration and/or inhibition of the formation of annulospiral endings in muscle spindles of the masseter muscle, and suggest that disorder of the masticatory mechanism may be caused by the degeneration and/or inhibition of the formation of the endings in many muscle spindles of the masseter muscle.
Maeda
N
N
1st Department of Oral Anatomy, School of Dentistry, Meikai University, Sakado, Japan.
Osawa
K
K
Kawasaki
T
T
Masuda
T
T
Ukai
M
M
Suwa
T
T
Watanabe
Y
Y
Yamamoto
Y
Y
Hakeda
Y
Y
Kumegawa
M
M
D000818:Animals; D000831:Animals, Newborn; D005260:Female; D008297:Male; D008406:Masseter Muscle / Q000254:growth & development* / Q000294:innervation; D008410:Masticatory Muscles / Q000254:growth & development*; D051379:Mice; D008813:Mice, Inbred ICR; D024510:Muscle Development