The effect of colcemid on the structure and secretory activity of ameloblasts in the rat incisor as shown by radioautography after injection of3H-proline

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Abstract
Enamel secretion by ameloblasts was investigated in the incisors of 100 gm normal and colcemid‐injected male rats. Morphological studies were done on rats given a single intraperitoneal injection of 0.1 mg (1.25 mM) of colcemid and sacrificed 1 to 4 hours after injection. Protein synthesis and secretion were investigated with radioautography in normal and colcemid‐treated rats injected with 3H‐proline and sacrificed at intervals between 0.5 and 3.5 hours after injection. Colcemid was injected 0.5 hours prior to 3H‐proline in each experimental rat. Electron microscopic examination revealed several morphological alterations between 1 and 4 hours after injection of colcemid. These changes included fragmentation of the normally elongated rough endoplasmic reticulum into shorter profiles; a disorganization of thenormally tubular configuration of the Golgi apparatus into a number of separate but intact stacks of Golgi saccules; the disappearance of secretion granules and profiles of smooth endoplasmic reticulum from Tomes' processes; and the accumulation of secretion granules at the mature face ofthe Golgi stacks, as well as in the infranuclear cytoplasm where they are normally not found. Radioautography revealed that protein synthesis by the rough endoplasmic reticulum had continued in colcemid‐altered ameloblasts. Labeled secretion granules were found at the mature surface of the Golgi stacks and in the infranuclear cytoplasm, however they did not migrate into Tomes' processes. Consequently, labeled enamel matrix did not appear extracellularly at the same time as in normal controls. Quantitative radioautography in the light microscope revealed that the effect of colcemid, although reversed within 4 hours, had temporarily inhibited normal migration and exocytosis of secretion granules.