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Both the expression of amelogenin mRNA and secretion of amelogenin were investigated in rat molars by in situ hybridization and immunohistochemistry. Probes were designed by multiple-labeling of oligonucleotide probes for in situ hybridization. Amelogenin mRNA first appeared in differentiating ameloblasts of the distal region and some inner enamel epithelial cells of enamel-free area (EFA cells) of the second cusp at postnatal day 0. At the same time, amelogenin protein was detected in the extracellular matrix between dentin and differentiating ameloblasts and in some EFA cells of the second cusp. At postnatal day 1–3, amelogenin was expressed in the secretory ameloblasts, and in the matrix beneath these cells. Both amelogenin mRNA and amelogenin were detected in the EFA cells and their extracellular matrix. After postnatal day 5, amelogenin mRNA and amelogenin were detected in the secretory ameoloblasts and extracellular matrix in the enamel-forming region, respectively. At this time, amelogenin mRNA was not detected in the EFA cells, but a small amount of amelogenin was found in the matrix beneath the EFA cells. These findings suggest that EFA cells differentiate into amelogenin-secreting cells, i.e. ameloblasts, but that the secretion lasts for only a short period at the early stage of tooth development.

Antisera against nerve endings of rabbit brain cortex (RANES) and cat brain cortex (CANES) were obtained by injection into rabbits of isolated nerve endings from the corresponding species. The titres for complement fixation test varied between 1 50 – 1 130 for RANES and 1 800 – 1 1500 for CANES and a thick precipitation band was obtained in the Outcherlony test. CANES applied to the visual cortex of the cat produced epileptiform spike-dome discharges recorded in the ECG. Both CANES and RANES in the presence of complement produced lysis and disintegration of isolated nerve endings incvitro and observed under the electron microscope. The validity of these findings, in spite of the apparent lack of specificity of the seralogical and inmuno-diffusion tests, is discussed.