An electron microscopic study of the modification by monosodium glutamate of the retinas of normal and “rodless” mice

By the use of DNA determinations and cell counts with and without previous colchicine treatment, the absolute numbers of villus epithelial cells, and of dividing and nondividing crypt epithelial cells were determined in ten successive segments of the small intestine of 17-day (weanling), 37-day (young) and 87-day old (adult) male rats. In adults, the number of villus epithelial cells per segment decreased gradually in the duodenoileal direction, while the number of dividing and nondividing crypt epithelial cells remained fairly constant. It was deduced that the turnover time of the villus epithelium gradually decreases, but that of the crypt epithelium remains constant along the small intestine. When the entire small intestine was considered, from weanling to adult age, the relative and absolute numbers of dividing and nondividing crypt epithelial cells increased; the calculated number of epithelial cells produced daily rose from 112 million to 1796 million. Meanwhile, the rate of growth of the intestinal epithelium diminished allowing more and more of the produced cells to participate in renewal: about 25, 885 and 1796 million cells daily in weanling, young and adult rats, respectively. The mean turnover time of the intestinal epithelium decreased from about 22 days in weanling rats to about 2.1 days in adult rats, indicating a tenfold increase in renewal rate.