study on the development, aging and the regulation factors of the maintenance of the masticatory organs

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The various factors are involved in the development, aging and maintaenance of the masticatory organs. In the present study, we investigated effects of the lack of the sensory input from the sensory endings in the periodontal ligament, resulted from tooth loss , and those of sex hormones on the trigeminal motor nucleus (Mo5) . Moreover, we studied the postnatal appearance of the oestrogen and/or androgen receptors in the masseter muscle and trigeminal motor nuerones.The lack of the sensory input from the sensory endings caused decrease in the number of Mo5 neurones that innervate the masseter muscle. In the masseter muscle of developing mice, we observed the positive immunoreactive nuclei by the 5th postnatal day in mice. No sex difference in the immunoreactivity was detected. In the Mo5, positive immunoreactivities specific for estrogen and androgen receptors were detected on the 5th and 20th postnatal days, respectively.Administration of 5a-dihydrotestosterone to female mice increased the number of motoneurones in the M05 to masculine proportions. By contrast, in male mice , treated with 17β-oestrogen, motoneurone numbers decreased to levels more typical of females. Treatment of cyproterone acetate , an androgen antagonist, significantly decreased the number of motoneurones in the Mo5 of immature male mice . Sensory neurones in the Me5 were unaffected by any of the treatment. Thus, androgenic and oestrogenic hormones are involved in the postnatal changes in motoneurone numbers of the Mo5, but not in the number of the Me5.