The central nervous system (CNS) of two mammalian species was studied autoradiographically using tritium-labeled thymidine; the rat, whose brain contains few localized mast cells (MCs) but many ubiquitous neurolipomastocytoid cells (NLMs), and the guinea pig, whose brain contains only ubiquitous NLMs. A few guinea pigs were also injected with an MC discharger compound 48/80 and the response of the NLMs, which are thought to be allied to MCs, as well as of neuroglial and vascular endothelial cells, was noted. The rats were 3 days to 6 weeks old whereas all the guinea pigs were young adults. Both MCs and NLMs took up the label, and much more so in the babies, paralleling similar uptakes in only very small immature MCs outside the CNS. Neuroglial elements, especially subependymal and oligodendroglial, as well as endothelial, perivascular, leptomeningeal and ependymal cells demonstrated some uptake. This was considerably increased upon receipt of compound 48/80, especially in the case of the subependymal glia, the NLMs and the endothelial cells; capillary neoformations were seen in the spinal cords of guinea pigs that had shown signs of paralysis. The cause of this increase is discussed in terms of mild stress induced by that compound. The subependymal response is also discussed with reference to periventricular plaques seen in multiple sclerosis and lymphoreticular and glial tumors seen in that region. It is concluded that both MCs and NLMs are capable of DNA replication and mitosis in immature animals. The NLMs can also divide upon stimulation in adult CNS.
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