Distribution of neurofilaments in myelinated axons of the optic nerve of goldfish ( Carassius auratus L.)

Abstract

Neurofilaments were counted in myelinated axons of the optic nerve of goldfish which were acclimated to 5° and 25°C. The number of neurofilaments increases markedly with increasing axonal size; axons of less than 0.1 μm 2 in area contain between 25 and 60 neurofilaments, while in the larger axons of area greater than 1.0 μm 2 there are approximately 190. The densities of the neurofilaments in the small axons are noticeably higher than in the larger ones (507 and 160, respectively). A variety of fixation procedures i.e. osmium tetroxide (OsO 4) in phosphate buffer, glutaraldehyde (4%) in phosphate buffer or in ethyleneglycol-bis-(β-aminoethyl ether)-N,N′-tetraacetic acid (EGTA) and piperazine-N-N′-bis-(2-ethanesulphonic acid) (PIPES) and post-fixed with OsO 4 had no effect on the numbers of neurofilaments relative to the size of axon. The anaesthetic MS-222 (tricaine methane-sulphonate) likewise had no effect on the numbers of neurofilaments. It is proposed that temperature acclimation alters the axon diameter concomitant with an alteration in the number of neurofilaments to fit the new diameter of the axons.