Microtubules in Squid Giant Axon

Cytoskeletal networks composed of microtubules (MTs), neurofilaments (NFs), and cross-bridges were well preserved in giant axons ofthe squid by adding dimethylsulfoxide (DMSO) to the glutaraldehyde solutionfor fixation. DMSO remarkably supported preservation of the otherwise labile MTs in the giant axon. Bundles of MTs, frequently associated with NFs, wereobserved in the axoplasm running parallel to the longitudinal axis of the axon. The distribution of MTs in the axon was more prominent in the peripheral axoplasm (60-80 MTs/μm2) than in the interior (20-25 MTs/μm2). At the edge of the periphery of the axoplasm, some MTs seemed to end in the axolemma, but others appeared to be cross-bridged to the axolemma by filamentous structures. In axons that had been treated with cold or had been injured, winding tubules thinner than the MT appeared in the peripheral axoplasm.