CHOLINERGIC NERVE ENDINGS IN OCTOPUS BRAIN

—Optic lobes of the brains of Octopus dofleini werehomogenized hasaline–sucrose medium and subjected to differential and density gradient centrifugation. The fractions and subfractions thus obtained were analysed for acetylcholine (ACh) (bioassay) and protein content and were subjected to electronmicroscopy. Bound ACh was associated with particulate fractions, and a large portion of it could be recovered in subfractions that contained predominantly nerve endings. Expressed in terms of amount of ACh per mg protein, the ACh content of the nerve ending fractions was nearly 100 times greater than that of corresponding fractions previously obtained by others from mammalian brain. Calculations show that this was the minimal amount of ACh to be expected if the isolated nerve endings were predominantly cholinergic. Octopus brain tissue is in therefore very promising for future studies on ACh metabolism and compartmentation cholinergic nerve endings.