The central pattern generator (CPG) for masticatory movements has been located in the medial bulbar reticular formation, by using cortically induced rhythmical jaw and tongue movements as a model. To analyze how stationary input from the cortex is transformed into rhythmical output in the neuronal population comprising the CPG, rhythmical neural activities representing rhythmical food ingestive movements were experimentally induced in vitro. Bath-application of N-methyl-_D-aspartate (NMDA) induced rhythmical activities in the trigeminal (V), facial (VII) and hypoglossal (XII) nerves of in vitro brainstem-spinal cord preparations isolated from newborn rats and mice. This paper will review evidence for the notion that (1) the rhythmical XII nerve activity represents rhythmical sucking movements; (2) the population of neurons critically involved in the rhythm generation of the XII nerve is localized in the ventromedial medulla oblongata on both sides, and can induce rhythmical XII nerve activity on the same side independently of each other; (3) the rhythmical activities in the V,VII, and XII motoneurons are induced by separate CPGs, which are located segmentally at the respective level of the V motor, VII, and XII nuclei. In addition, rhythmical masticatory-like EMG activity of jaw muscles can be induced by repetitive stimulation of the pyramidal tract in the in vitro brainstem isolated from adult mice together with the oral-facial structures. We propose that the in vitro brainstem preparation is a useful tool for longitudinal analysis of postnatal development of the central pattern generation of food ingestive movements, including conversion from sucking to mastication.

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The reactions of periodontal tissues to the mechanical stimulation of teeth seem to be different in patients of different ages. Although the effects of aging on other structures of the periodontal tissues, i.e., collagen fibre, bone, and cementum, have been reported, there is very little information available concerning the effects of aging on periodontal oxytalan fibre, which is reportedly the only elastic element in the human periodontal ligament. The purpose of this research was to clarify the aging related changes in the distribution of oxytalan fibres in the periodontal ligament of mice. Histological sections of the periodontal ligament of the lower first molar of 10-week-old (control group) and 1-year-old (aged group) ICR mice were specifically stained for oxytalan fibres with aldehyde fuchsin after preoxidization, and observed by light microscopy and confocal laser scanning microscopy (CLSM). In the aged group, oxytalan fibres seemed to be more prevalent around blood vessels in comparison with the control group. Furthermore, CLSM clearly showed that oxytalan fibres in the aged group were relatively more tortuous and complex than those in the control group. This tortuosity and com­plexity might imply that the oxytalan fibres in aged mice have lost a considerable amount of their original elasticity. While further study of these changes is required, these results may help orthodontists to establish better treatment strategies and methods for adult orthodontic patients.

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Effects of ATP on the intracellular free calcium ion concentration ([Ca²⁺]_i) in the rabbit eye suprachoroid were investigated by means of fura-2 microfluorophotometry. ATP application (10 to 100 µM) elicited a dose-dependent biphasic [Ca²⁺］_i-increase: a fast phase typically peaking within 30 s and a following slow plateau phase, which lasted during the presence of ATP. The slow plateau phase was markedly diminished by removal of extracellular Ca²⁺, whereas the fast phase remained. An inhibitor of Ca²⁺ release from the sarcoplasmic reticulum (TMB-8), an endoplasmic Ca²⁺-ATPase inhibitor (thapsigargin) and a phospholipase C (PLC) inhibitor (U-73122) diminished the fast phase. A P2 receptor antagonist (Suramin) inhibited the ATP-induced [Ca²⁺］_i-response. The potency order of ATP and related substances in producing the [Ca²⁺］_i-elevation was UTP≅ATP>ATP-γ-S>ITP>ADP. β,γ-MethyleneATP, 2-methylthioATP and UDP evoked no response. This order is consistent with the P2Y₂ receptor characteristics. Cross-desensitization between ATP and UTP excludes the co-existence of the other types of receptors. In conclusion, the ATP-induced [Ca²⁺］_i-elevation in the rabbit eye suprachoroid was elicited by the Ca²⁺ release from the PLC-dependent, thapsigargin-sensitive intracellular Ca²⁺ storage sites by activating P2Y₂ nucleotide receptors.

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In mandibulectomy patients who have not undergone surgical reconstruction, the remaining mandibular segment is unstable and often deviated. Its movements have low reproducibility during mastication, deglutition and speech. The purpose of this study was to clarify three-dimensionally the differences in mandibular movements for each of these oral functions in mandibulectomy patients with and without mandibular continuity. Four mandibulectomy subjects (Group I) without mandibular continuity and three subjects (Group II) with mandibular continuity were selected. Their mandibular movements were recorded using a jaw movement tracking device with six degrees of freedom. Each movement was assessed graphically at the virtual incisor point and the rotational angles of the mandible in the frontal, sagittal and horizontal plane were analyzed. The findings were as follows ; 1. In Group I, the border movements at the virtual incisor point exhibited an irregular and asym­metric envelope deviated to the resected side in the frontal plane, whereas Group II exhibited a smooth and symmetric envelope. 2. In Group I, the rotational angles in the frontal plane during border movements and mastication, in all planes during speech, and in the frontal and horizontal plane during deglutition were significantly larger than in Group II. A comparison among border and all functional movements in mandibulectomy patients revealed characteristic movements in the rotation of the mandible in the frontal plane. It is suggested that the rotational angle of the mandible is a useful parameter for assessment of mandibular move­ments in mandibulectomy patients.

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