Activity-dependent differences in the mitochondrial density of crayfish phasic and tonic motor axons

✍ Scribed by Lnenicka, G. A.; Case, C. J.; Travis, J. L.

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 409 KB
• Volume: 280
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/(sici)1097-010x(19980101)280:1<18::aid-jez3>3.0.co;2-k

✦ Synopsis

We examined whether impulse activity influences the density of mitochondria in the motor axons innervating the crayfish claw closer muscle. Mitochondria were compared in the phasic, tonic, and chronically stimulated phasic motor axons. Tonic axons had twice the mitochondria density (total mitochondria per cross-sectional area [CSA] per axon CSA) than did phasic axons. Although individual mitochondria in phasic and tonic axons were cylindrical and similarly sized, the tonic axons had twice the number of mitochondrial per axon CSA of phasic axons. Differences in mitochondrial density included differences in transported mitochondria: the density of mitochondrial transport (total length of motile mitochondria per volume axoplasm) was approximately 50% greater in the tonic axon compared to the phasic axon. Motile mitochondria comprised a small proportion of the total axonal mitochondrial volume because the majority (60-70%) of mitochondria were stationary, and these stationary mitochondria were considerably longer than the motile ones. The differences in axonal mitochondrial density were activity-dependent. We observed a 50% increase in the density of mitochondria in phasic axons that had been electrically stimulated for 7 days. The increase in mitochondrial density appears to result from an increase in both mitochondrial length and number. These results show that tonic axons have a greater density of both transported and stationary mitochondria, and the differences in mitochondrial density are activity dependent.