isolation first of nerve endings (synaptosomes), and subsequently of synaptic vesicles from mammalian brain. two competing laboratories were involved in this work, that of victor p. whittaker at the institute of animal physiology, agricultural research council, babraham, cambridge, uk and that of eduardo de robertis at the instituto de anatomía general y embriología, facultad de medicina, universidad de buenos aires, argentina. whittaker's work demonstrating acetylcholine in vesicle fractions from guinea-pig brain was first published in abstract form in 1960 and then in more detail in 1963 and 1964, and the paper of the de robertis group demonstrating an enrichment of bound acetylcholine in synaptic vesicle fractions from rat brain appeared in 1963. both groups released synaptic vesicles from isolated synaptosomes by osmotic shock. the content of acetylcholine in a vesicle was originally estimated to be 1000–2000 molecules. subsequent work identified the vesicular localization of other neurotransmitters, such as amino acids, catecholamines, serotonin, and atp. later, synaptic vesicles could also be isolated from other tissues such as the superior cervical ganglion, or the octopus brain. the isolation of highly purified fractions of cholinergic synaptic vesicles from the ray torpedo electric organ was an important step forward in the study of vesicle biochemistry and function.