Basic study on the factors regulating the postnatal development of the masticatory organ and center

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Postnatal changes in the masticatory system and regulation factors were investigated, and following results were obtained.1.Sexual dimorphism of isozyme patterns of lactate dehydrogenase gradually appeared in the masseter muscle of developing mice. Testectomy inhibited the appearance, but not ovariectomy.2.Androgenic hormones induced the sexual differences in the masseter muscle. Cyproterone acetate which is an androgen antagonist inhibited the induction.3.Androgen receptors were certainly observed in masseter muscles of male and female mice. The receptors apppeared with maturation of male and female animals. No sexual difference was observed.4.Short-term denervation of the masseter nerve did not inhibit the appearance of sexual dimorphism in the masseter muscle.5.Sexual dimorphism in the trigeminal motor neurons innervating the mouse masseter muscle was observed. Estrogenic and androgenic hormones were involved in induction of the dimorphism.6.Less-developed periodontal ligaments in op/op mice caused the precocious atrophy of the masseter muscle, and induced the reduction in the number of motor and sensory neurons involved in the jaw-opening reflex in the mice.