Kinziro Kubota

Effect of mastication on regional cerebral blood flow in humans examined by positron-emission tomography with 15O-labelled water and magnetic resonance imaging

The interaction between mastication and cerebral blood flow was studied in 12 healthy volunteers (five males and seven females) aged 18-40 years. Positron-emission tomography (PET) autoradiography was carried out after bolus injection of 1.5 GBq H₂¹⁵O (¹⁵O-labelled water) with a half life of 2 min. The PET images were superimposed on magnetic resonance images of each participant. The regional cerebral blood flow images were normalized by the global cerebral blood flow value, and subtraction images (those during gum-chewing minus those during resting) were created and recut at the magnetic resonance image slice positions. Gum specially designed for chewing training was used. Mastication increased regional cerebral blood flow in the primary sensorimotor areas by 25-28%, in the supplementary motor areas and insulae by 9-17%, and in the cerebellum and striatum by 8-11%. These increases demonstrate that chewing activates widespread regions of the brain.

Muscle Spindle Supply to the Human Jaw Muscle

Histological study of the human jaw muscle revealed that the temporal muscle displayed 342 muscle spindles, 208 in the horizontal and 134 in the vertical portion; the masseter muscle contained 114 spindles, 91 in the superficial and 23 in the profound portion; the medial pterygoid muscle had 59; and the lateral pterygoid muscle contained 6, four in the upper head and two in the lower head. These data suggest that the extensive mobility of the temporomandibular joint, and the maintenance of mandibular posture during mastication and speech are strongly influenced by proprioceptive mechanisms.

Morphological studies of the neuromuscular mechanism shifting from sucking to biting of mice

In order to give a neuroanatomical evidence to the mechanism of shifting from sucking to biting, we investigated in prenatal, newborn and postnatal mice whether there is a time difference in the neurogenesis of the neurons relative to sucking and biting or in the histogenesis of their peripheral effector organs by the HRP labeling technique and electron microscopy. The results obtained are as follows. (1) At birth the facial motoneurons exceed the trigeminal motoneurons in cell area and development. (2) After birth, the trigeminal motoneurons grow rapidly and outstrip the growth of the facial motoneurons at the age of 6 days. (3) Thereafter, the cell area of both neuron types continues to increase gradually. (4) The initial sign of the alpha motor end plates is found in the orbicularis oris muscle innervated by the facial nerve in 17-day-old fetuses, while that of the trigeminal nerve is delayed in the masseter muscle of 18-day-old fetuses. (5) The initial sign of the muscle spindle appears with the sensory terminals in the masseter muscle of 17-day-old fetuses and the fundamental structure of the muscle spindle is formed in 4-day-old youngs. (6) Myelination of the facial nerve begins in 3-day-old youngs, while that of the trigeminal nerve becomes apparent in 4- or 5-day-old youngs. From these bases, it is obvious that the facial nerve elements related to sucking are firstly developed at birth and that the differentiation of the trigeminal nerve elements related to biting is rapidly accelerated after birth.

Muscle Spindle Distribution in the Masticatory Muscle of the Japanese Shrew-Mole

This investigation was designed to obtain anatomical information about the neuromuscular mechanism of human jaw movement by a comparative study of insectivores. Study of the masticatory muscles of the Japanese shrew-mole showed that muscle spindles are concentrated in restricted areas of the inner layer of the horizontal and vertical portions of the temporal muscle, the medial portion of the medial pterygoid muscle, and the deep portion of the masseter muscle. The lateral pterygoid muscle contains no spindles.

Periodontal Sensory Innervation of the Dentition of the Japanese Shrew Mole

The neuro histological investigation of the periodontal sensory innervation in the whole dentition of the Japanese shrew mole showed that the periodontium is much more densely supplied by the free nerve endings at the apical region than at the intermediate one at a ratio of about 8:1 in the upper dentition and 5:1 in the lower dentition. The interdental gingival tissue is innervated by the nerve plexus formed by the nerve fibers deriving mostly from the gingival and a few periodontal nerve fibers. The neurohistology of the tooth is analogous to that of the vibrissa.

Muscle Spindle Distribution in the Masticatory Muscle of the Tree Shrew

Histological study of the masticatory muscles of the tree shrew showed that 140 muscle spindles are concentrated in the restricted areas of the inner lowermost layer of the horizontal and vertical portions of the temporal muscle (48 and 47 spindles, respectively), the profundus portion of the masseter muscle (42 spindles), and the zygomaticomandibular muscle (3 spindles). The medial and lateral pterygoid muscles are devoid of spindles.

Nuclear medical PET-study in the causal relationship between mastication and brain function in human evolutionary and developmental processes

The principal author (Kubote 1995, 1997, 1998, 1999, 2000 a, b) has proposed that chewing food well from infancy will lead to a clear-headed and robust person, following which the same concept has been presented to the general public by the mass media. Unfortunately, however, there does not yet seem to be any direct evidence to support this claim. It is thus necessary to review mastication from the standpoint of the new concept of evidence-based medicine (EBM) and to create a new direction in medicodental research and treatment from the viewpoint of human evolution, because the causal relationship between mastication and brain function has never been clarified either in fossil science research or in the modem scientific bibliography. To confirm the human historical fossil record in regard to the causal relationship between the development of mastication and brain function in human evolutionary processes, the effect of gum chewing on brain reaction was examined in humans by means of a positron-emission tomography (PET) camera (Momose et al. 1997) after an antecubital intravenous injection of H215O. Powerful activation of the cortical cells was demonstrated in multiple cortical areas involving the marginal areas of the bilateral central sulci of the cerebral cortex (Fig. 1), and the activated areas coincided with our previous results in region of interest (ROI) analysis (Momose et al. 1887). Three-dimensionally, numerous cortical cells were shown to form nuclei on relief maps (Fig. 2). As diets and feeding habits changed in a stepwise manner from frugivorous to omnivorous via herbivorous and carnivorous over the lengthy progress of evolution, the brain concomitantly grew and the cranial capacity gradually increased in volume from 500 cm3, food from plant sources to animal sources (700 cm3), and then to both (1500 cm3), during the human evolutionary and developmental processes. Gradual increases in the cranial capacity of human fossils during the developmental stage have been demonstrated also by PET images of the human brain acquired by means of a PET camera and an antecubital intravenous injection of H215O during mastication that showed powerful activation of cortical cells in multiple areas. It could be concluded that human fossils give us concrete information on how to feed our children in the modern human life style from infancy to adulthood, so that we should bring children up by adhering to images of the principal feeding habits discovered during this research on human evolutionary and developmental processes.

Proprioceptive Innervation of the Masticatory Muscles in Pinché

This study of the masticatory muscles of the primate showed that the temporal muscle contained 107 muscle spindles, 45 in the horizontal portion and 62 in the vertical portion; the masseter muscle contained 70, 58 in the profundus portion and 12 in the superficial portion; the medial pterygoid muscle contained 15; the lateral pterygoid muscle contained 6; and the zygomaticomandibular muscle contained 9. The muscle spindles were located around the coronoid process and mandibular ramus.

Location of proprioceptive neurons innervating the muscle spindles of the snout muscles in the talpoides

Abstract Location of the primary neurons of the proprioceptive afferents from the facial musculature has been investigated by denervating the facial nerve in the Japanese shrew-mole and Japanese lesser shrew-mole. In all the cases at 5, 7 and 14 days after the operation, the muscle spindle innervation, the cells of the posterolateral group in the glossopharyngeal-vagus ganglion and the facial motor neurons on the treated side showed clearcut anterograde and retrograde changes, complete damage of the spindle nerve fibers, central chromatolysis and peripheral concentration of the Nissl granules and the excentric displacement of the nucleus in the cytoplasm of the neurons, justifying their classification as pathologically altered specimens. These findings are taken to provide experimental support for the demonstration that primary neurons of the proprioceptive afferents from the facial muscles of the talpoides exist in the posterolateral group of the glossopharyngeal-vagus ganglion. Also the presence of the thick ramus communicans between the facial nerve and the posterolateral part of the ganglion gives further information concerning the site of their somata in this part of the ganglion.

Anatomical Studies on the Salivary Gland of the Fur Seal

The present paper describes the gross anatomy and histology of the major salivary glands of the fur seals, adult, newborn and embryo. There are three pairs of salivary glands; the parotid, submandibular and sublingual. Their main ducts were found to be similar to those of other carnivores. The secretory acini of the parotid gland are monotypic, the acinar cells resembling the large sweat gland cells, “sudoriferous” cells in most of their general morphological characteristics, whose lumen is widely dilated. The yellowish-brown color of the organ may be due to abundant contents of the yellowish-brown pigment granules in the acinar cell bodies. The submandibular gland is the most developed secretory organ among the major salivary glands. The acini consist of the monotypic, secretory cells closely resembling the mucous cells in their histological characteristics. The acinar cells may be of mucous nature and they are transformed from those of the serous nature to the mucous property with increasing age. The striated ducts are greatly developed in comparison with those of other mammals. They are extremely long and highly branched and well convoluted. The duct cells are finely granular and strongly eosinophilic and possess characteristic basal striated structure. The sublingual glands possess all three kinds of ducts, but the intercalated and striated ducts are greatly reduced in comparison with those of the submandibular glands. The acini are of the mixed variety and mostly consist of mucous cells and partly of serous types. In many cases, the mucous acini open into the excretory ducts directly. Frequently, there are seen many “demilunes” in the acini.