Journal of Cell Science, Vol 2, 573-586, Copyright © 1967 by Company of Biologists

Submitted on May 9, 1967

An Electron-Microscope Study of Subcellular Fractions of Octopus Brain

¹ Agricultural Research Council, Institute of Animal Physiology Babraham, Cambridge, Department of Anatomy, University College London, Department of Anatomy, University College London, Gower Street, London, W.C.1.

Using subcellular fractionation techniques the primary fractions (P₁; P₂ and P₃) have been prepared from homogenates of the supraoesophageal lobes (brain) of Octopus vulgaris. A morphological study of the fractions was made, particular emphasis being placed upon the synaptosomes (nerve-ending particles), and the agranular and granular vesicles they contain. The acetylcholine levels in the fractions were determined by bioassay.

Synaptosomes and isolated mitochondria are present in all the fractions examined. In addition, the remains of blood vessels are found in P₁, nuclei, vesicular structures and lamellated bodies in P₁ and P₂, and microsomes in P₃ and the final supernatant. The synaptosomes are similar to those isolated from mammalian nervous tissue. The remains of the post-synaptic endings are seen as recognizable processes around their periphery. They are more extensive than the post-synaptic membranes of mammals, and thickenings on them are seen in tissue stained with phosphotungstic acid. The number of mitochondria outside synaptosomes varies with the fixative used, being far greater with formalin than with permanganate. The agranular vesicles vary in diameter from 150 to 1200 Å; over 70 % of them are between 250 and 500 Å. In formalin-fixed preparations, the synaptosomes can be separated into two types: those containing mainly rounded vesicles, and those with many ellipsoidal vesicles. About 4 % of all the vesicles are granular; they have an average diameter of 720 Å, with few of them measuring over 1000 Å.

Acetylcholine is distributed throughout the fractions, the highest level being in P₂ with appreciable levels in the others. The total recovered for the combined fractions of the supraoesophageal lobes was 104.6 mµmole/g tissue. For the combined fractions of the optic lobes, which are also rich in synaptosomes, the total was 32.3 mµmole/g. tissue.