A quantitative electron microscopic study of mitochondria in motor neurones following axonal section

Abstract

An electron microscopic study was made of the motor neurones of the hypoglossal nuclei of a series of 10 rabbits, 10–11 days after unilateral hypoglossal neurotomy. Quantitative data obtained from the micrographs showed that on the operated side there was a significantly greater number of mitochondrial profiles per unit area of cytoplasm than on the control side. There was also a 70 per cent increase in the volume ratio of mitochondria to cytoplasm, approximately three-fifths of this being attributable to mitochondrial swelling and the remaining two-fifths to the increase in mitochondrial numbers. The findings may he interpreted as indicating that the increase in number of mitochondrial profiles on the operated side, was brought about by the formation of new mitochondria resulting in an increase in total functioning mitochondrial mass. There was a highly significant increase in the number of dense bodies (“microbodies”) per unit area of cytoplasm on the operated side, and a significant correlation was found between the average increase in the number of dense bodies and the average increase in mitochondrial numbers in the individual experiments. It has already been noted that the appearances of dense bodies in motor neurones of the rabbit were consistent with their bearing a developmental relationship to mitochondria and the present results would seem to favour the possibility that dense bodies may be concerned in mitochondrial formation. In the rat, other forms of dense body, containing areas of even greater density, were also noted.