The neuroplasmic network in Loligo and Hermissenda neurons

Abstract

Electron microscopy of the giant axon and smaller fibers of the squid Loligo pealei and of the brain system of the nudibranch Hermissenda crassicornis utilizing improved fixation methods and stereoscopic examination of relatively thick sections (0.2–1.0 μ m) has allowed demonstration of a neuroplasmic network in axons and other neural cellular extensions. The network consists primarily of longitudinally oriented neurofilaments and microfilaments, presumably actin, together with microtubules when present, linked together by a system of thin transverse filamentous bridge elements 2–3 nm in diameter, with a tendency toward a periodicity of ∼40 nm along the axonal longitudinal axis. Internal irrigation of the squid giant axon with fixative following cannulation results in dramatically improved fixation with numerous microtubules being found in the axoplasm, particularly in the subaxolemmal cortical region. The transverse bridges often appear to end at or are structurally continuous with membranous elements such as the axolemma, vesicles, endoplasmic reticulum, and mitochondria. It is thought that some or all of the neuroplasmic network components are involved in axonal transport processes.