Three-dimensional structure of axonal mitochondria reflects the age of drosophila☆

This study aimed to reconstruct a three-dimensional map of axonal mitochondria using Fiji and Neurolucida software, and to observe directly the morphology and distribution of mitochondria in axons of motor neurons in dorsal longitudinal flight muscles of drosophila aged 5 days and 20 days, using electron microscopy. Results indicated that there was no difference in the total area and volume of mitochondria between 5-day-old drosophila and 20-day-old drosophila in all sections, but the ratio of mitochondrial total areas to axon total areas, as well as mitochondrial density of 20-day-old drosophila, was lower than that of 5-day-old drosophila. The number of mitochondria, whose volume was less than 1 000 000 μm(3), and between 1 000 000 μm(3) and 10 000 000 μm(3), was higher in 20-day-old drosophila than that in 5-day-old drosophila. The number of mitochondria with a volume between 1 000 000 μm(3) and 100 000 000 μm(3) was apparently higher than those with a volume less than 1 000 000 μm(3) or larger than 100 000 000 μm(3). In addition, the number of mitochondria with a volume more than 100 000 000 μm(3) was small; however, the volume was nearly 70% of the total volume in both 5-day-old and 20-day-old drosophila. In contrast, the number of mitochondria with a volume between 1 000 000 μm(3) and 10 000 000 μm(3) was large, but the volume was less than 30% of the total volume. These experimental findings suggest that changes in mitochondrial morphology and number in motor neurons from the dorsal longitudinal muscle of drosophila are present during different ages.