Hironori Kitamura

Immunohistochemical analysis of pulpal innervation in developing rat molars

The beginning of pulpal innervation was examined in these developing teeth. Mandibular first molars removed from newborn to 7-day-old rats were cryosectioned and nerve fibres were localized by the peroxidase-antiperoxidase technique using a neuropeptide-specific (200 kDa) antibody. Some pulps from 5- and 7-day-old rats were also examined by conventional electron microscopy. In newborn to 4-day-old rats, molars in the initial stages of the dentine deposition were innervated in the follicles but not in the pulps. In molars from 5-day-old rats, nerve fibres were found in the pulps of 11 out of 16 samples. The fibres were mainly located along the blood vessels in the basal part of the pulp, with some arborizations. In rats of 6 and 7 days old, nerve fibres were found in all the pulps examined. These had gradually extended deep into the cuspal area and were increasingly arborized with increasing age. Nerve fibres were also found along the basal laminae of blood vessels in some dental pulps from 5-day-old rats when examined by electron microscopy. At 7 days, nerve fibres were composed of bundles of axons, some of which were covered with Schwann cell processes and basal laminae. These observations indicate that the innervation of rat molar dental pulps begins after the start of the deposition of enamel, in animals of around 5 days of age, which is at the same stage as in mouse molars, as others have shown by a silver-staining method.

Actin filaments in the terminal webs of secretory ameloblasts of rats

Actin filaments decorated with heavy meromyosin in enamel-secreting ameloblasts of rat incisors were examined. Proximal and distal terminal webs contained actin filaments; some were arrayed in diverse directions to each other. Some were associated with coated and uncoated vesicles. These actin filaments may relate to the sideways movement of secreting ameloblasts, suggesting that the distal terminal web is an apparatus generating a force by which ameloblasts can slide over each other.

Three-dimensional network of microtubules in secretory ameloblasts of rat incisors

Secretory ameloblasts appear to contain isolated microtubules and microtubules arranged in bundles associated with filaments or sheets of filaments. The relation between isolated and bundled microtubules in secretory ameloblasts was investigated by serial sections. Some isolated microtubules entered microtubule bundles in adjacent sections. Microtubules which diverged from a bundle sometimes converged into another bundle in other sections. Microtubules were associated with filaments or sheets of filaments for varying distances. It is concluded that isolated microtubules frequently form bundles by joining with other microtubules, and thus, microtubules make a three-dimensional network throughout the whole cytoplasm which is probably concerned with the transport of secretion granules.

Cholinergic traits in rat mandibular processes observed by electron microscopy

SummaryCholinergic traits in rat mandibular processes were examined histochemically, under the electron microscope, scope, at early developmental stages (Stages 20 to 23, by Christies nomenclature). The histochemical reaction for detection of enzymes was performed by the thiocholine method. Nonspecific cholinesterase (EC 3.1.1.8) activity was found in ectomesenchymal cells, vascular endothelial cells, and in some epidermal cells at stages 20 and 21. The enzymatic activity was localized in the perinuclear and endoplasmic reticular cisternae. At stage 22, the number of cells with enzymatic activity decreased gradually, except in the case of the capillary endothelial cells. At stage 23, when the trigeminal nerve fiber was obvious in the mandibular processes, nonspecific cholinesterase activity was restricted to some of the endothelial cells and trigeminal ganglionic cells. In contrast, acetylcholinesterase activity was found on the membrane of trigeminal nerve fiber. Thus, the transient, nonspecific, cholinesterase activity, found in rat mandibular processes, may serve some functions in transmission, lipid metabolism or destruction of toxic cholinesters during the period that precedes organogenesis.