Chromatolysis

Chromatolysis is the dissolution of the Nissl bodies in the cell body of a neuron. It is an induced response of the cell usually triggered by axotomy, ischemia, toxicity to the cell, cell exhaustion, virus infections, and hibernation in lower vertebrates. Neuronal recovery through regeneration can occur after chromatolysis, but most often it is a precursor of apoptosis. The event of chromatolysis is also characterized by a prominent migration of the nucleus towards the periphery of the cell and an increase in the size of the nucleolus, nucleus, and cell body. The term "chromatolysis" was initially used in the 1940s to describe the observed form of cell death characterized by the gradual disintegration of nuclear components; a process which is now called apoptosis. Chromatolysis is still used as a term to distinguish the particular apoptotic process in the neuronal cells, where Nissl substance disintegrates.

In 1885, researcher Walther Flemming described dying cells in degenerating mammalian ovarian follicles. The cells showed variable stages of pyknotic chromatin. These stages included chromatin condensation, which Flemming described as "half-moon" shaped and appearing as "chromatin balls," or structures resembling large, smooth, and round electron-dense chromatin masses. Other stages included cell fractionation into smaller bodies. Flemming named this degenerative process "chromatolysis" to describe the gradual disintegration of nuclear components. The process he described now fits with the relatively new term, apoptosis, to describe cell death.

Around the same time of Flemming's research, chromatolysis was also studied in the lactating mammary glands and in breast cancer cells. From observing the regression of ovarian follicles in mammals, it was argued that a necessary cellular process existed to counterbalance the proliferation of cells by mitosis. At this time, chromatolysis was proposed to play a major role in this physiological process. Chromatolysis was also thought to be responsible for necessary cell elimination in various organs during development. Again, these expanded definitions of chromatolysis are consistent with what we now term apoptosis.

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