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The localization of spot 35 protein, a cerebellar Purkinje cell-specific protein, was studied in guinea pig taste buds by means of electron-microscopic immunocytochemistry. The immunoreactivity was localized in the cytoplasmic matrix of discrete bud cells. The ultrastructural features of the reactive cells indicated that they corresponded to the Type III or gustatory cells making a synaptic contact with the intragemmal nerves. All other cells specified as basal, Type I, and Type II were immunonegative for spot 35 protein. This finding indicates a method for specifically demonstrating the gustatory cells in the guinea pig taste bud and, further, gives new evidence that paraneurons may share neuron-specific substances with neurons.

Guinea pig taste buds were observed by transmission electron microscopy with special reference to cell types and innervation. The taste bud comprised four distinct cell types: basal, type I, type II, and type III cells. Basal cells, residing at the baso-lateral region of the taste bud without extending to the taste pore, were considered precursors of the other types of cells. The rest were all spindle-shaped cells reaching apically to the taste pit. Type I cells were characterized by the darkest appearance of the cytoplasm, apically possessing large, electron-dense granules and basally enveloping intragemmal nerves. This cell type, intervening between the other types of cells, was postulated to be sustentacular in nature. Type II cells, the largest and lightest cells in the taste bud, possessed a conspicuous stack of smooth endoplasmic reticulum above the nucleus. Due to their intimate and specialized relationships with nerves, the type II cells were presumed to receive an efferent innervation. Type III cells made synaptic contacts with nerves and contained dense-cored vesicles, which accumulated in the synaptic areas. This finding strongly suggests a gustatory function for the cells. The occurrence of such numerous peptidergic-type granules gathering to gustatory synapses as demonstrated in this report has not been recorded in previous papers on mammalian taste buds. The nerve terminals on the type III cell also contained synaptic vesicles, thus suggesting a reciprocal synapse here. The taste bud often included degenerating cells which were demonstrated to be phagocytosed by extrinsic cells identified as macrophages.

Histological features of the tooth plate of lungfish were investigated by light and electron microscopy and contact microradiography with primary reference to the fine structure and formation of petrodentine, one of the principal constituents of the tooth plates. Petrodentine is a highly mineralized tissue noticeably analogous to that of enameloid, and is deposited intermittently in a proximal direction by the sole participation of mesenchymal petroblasts. The petroblasts appear very likely to have prominent biphasic functions of secreting the petrodentine matrix and of eliminating the matrix by resorption. The petrodentine thus may be capable of attaining hypermineralization with the participation mesenchymal cells alone. Mineral crystals constituting the petrodentine are large, hexagonal or similar but irregularly shaped columns. Initially these crystals appeared extremely thin, with curled ones frequently noted. The petrodentine of lungfish tooth plates is considered to be structurally distinct from the pleromin (Kosmin) of holocephalian tooth plates because of the difference between their constituent crystals.

The chemosensory gustatory cells in taste buds form chemical synapses with intragemmal neurites. We investigated the ultrastructure of the guinea pig gustatory cells after stimulation with a mixture of monosodium L-glutamate and guanosine 5′-monophosphate. The gustatory cells responded to the stimulus. The dense-cored vesicles localized in the presynaptic regions discharged the contents into the synaptic cleft by means of exocytosis, which resulted in a marked decrease of their population. These findings strongly suggest that the transmitter or transmitters contained in the vesicles are released in response to the taste stimulation at the cell apex, to conduct the excitement of the cell to the nerves.

This paper describes a method for the sensitive detection of aluminium in biological tissues by real time confocal laser scanning microscopy after staining with lumogallion. The method enabled detection of aluminiumor = 9 micrograms g-1 in bone and is more sensitive than the conventional histochemical methods with aluminium and solochrome azurine, etc. Lumogallion reacts specifically with aluminium to form a fluorescent complex so that the proposed method is useful for detection and identification of aluminium in tissues.

The gross structure and microstructure of holocephalian tooth plates were initially investigated by Bargmann (1,2) and Brettnacher (3). Orvig (4,5,6) subsequently reported in the detail microstructural characteristics of both extant and fossil holocephalian tooth plates. These studies indicate the holocephalian tooth plate to consist of bony tissue and hypermineralized pleromin (4), with the hardness of pleromin comparable to that of enamel and enameloid. Ishiyama et al. (7) found the crystalline material of pleromin to be not hydroxyapatite but whitlockite by a powder X-ray diffractometry, and pleromin to be the sole sound dental tissue consisting of whitlockite in vertebrates.

Morphological observations were made of the behavior of biogenic amines in the gastric wall of rats with acetic acid-induced ulcer. In the normal rat stomach, abundant adrenergic fibers were seen in the adventitia of arteries and arterioles, with frequently distributed mast cells in their environs, in all gastric wall layers. Mast cells had a more frequent distribution in the antral region than in the corpus ventriculi while enterochromaffin-like cells (EC-like cells) were found with greater frequencies in the latter region of gastric wall. Adrenergic fibers were abundant around blood vessels in perilesional area of the gastric wall of rats with acetic acid ulcer. Mast cells, seen more frequently in the antral region as in the normal rats, showed degranulation in these rats. The population of PAS-positive mucous cells reached its peak in 10 days after injection of acetic acid and subsequently declined with healing of the ulcer, thus remarkably concordant with the ulcer index. Local administration of serotonin produced angiospasm in the greater omentum. The finding indicates a possible participation of arteriospasm by adrenergic nerve fibers in the pathogenesis of gastric ulcer. The results of the present study strongly suggest that biogenic amines have bearing as an aggressive factor upon the angiospasm theory of ulcerogenesis.

Publisher Summary This chapter discusses the carcinogenic potential of metal compounds and the mechanisms of metal carcinogenesis by referring to data obtained by mutagenicity tests in bacteria, the commonly used short-term screening procedures for carcinogenic metallic compounds, and by experimental findings in laboratory animals. The chapter discusses the findings regarding carcinogenesis of principal metallic compounds in laboratory animals and the underlying mechanisms. The chapter also discusses the results of some studies on the development of fibrosarcoma with lead acetate in the rat. Metal ions bind to constituents of the organism, especially to proteins or nucleic acids, thus giving rise to irreversible damage to the biologic function, which would lead to malignant change of affected cells. The metal ions with proven carcinogenic potential have all been shown to have mutagenic activity in bacteria. The metal ions show high degrees of affinity for proteins and nucleotide bases.

Observations were made to follow up the emergence and development of enteric plexuses in rat fetuses by histo-chemical techniques. Adrenergic neurones first appeared as faint fluorescent stains in the regions of duodenal myenteric (Auerbach’s) plexuses of 17-day fetuses, then in the submucosal (Meissner’s) plexuses and muscle layers at 18 days, the density of fluorescence increasing progressively with advancing fetal age. Cholinergic neurones also emerged in the 17-day rat fetus duodenum and showed a similar course of development. 5-Hydroxytryptamine (5-HT, serotonin) containing cells became demonstrable in the duodenal mucosa of 15-day fetuses and intensely green fluorescent stains in prevertebral sympathetic ganglions at 16 days. The amines were identified on tissue sections by spectrophotometry (MMSP), with quantitative fluorometric determination of noradrenaline (E.S.,410 nm: M.S.,480 nm), Cholinesterase activity (M.S.,480 nm), and 5-HT (E.S.,410 nm; M.S.,525 nm).