In animals exposed to carbon monoxide, there is occasional evidence of
necrotic cells with swollen, electronlucent nuclei (Figure 9.2). These cells
show little margination of nuclear chromatin and relatively preserved
nuclear morphology. In the same animals, other neurons show early changes
of chromatin margination and convolution of the nuclear membrane as illustrated
for a pyramidal neuron (Figure 9.3) and for a possible nonpyramidal
neuron (Figure 9.4) from the cerebral cortex. At the light microscopic level,
TUNEL staining of rats exposed to sublethal carbon monoxide intoxication
suggests widespread occurrence of internucleosomal DNA cleavage.
13
These
ultrastructural nuclear changes are suggestive of an early stage of apoptosis
when considered with the cytoplasmic changes in the same cells (see below).
The interpretation of early apoptotic cells in nervous tissue is controversial.
Most likely, many intermediate forms exist and many cells may show mixed
characteristics of necrosis and apoptosis.
4,11,12
For apoptotic cell death, the late changes of significant