Neurochemical and morphological studies of bulk isolated rat brain cells. II. Preparation of viable cerebral neurons which retain synaptic complexes

The bulk isolation from rat cerebral cortex of viable neurons retaining synaptic complexes is described. The basis of this procedure is to dissociate the neurons in situ from the surrounding glial cells. The glial structures that are normally adjacent to the neuronal cell body and to the proximal parts of the neuronal processes are largely destroyed by perfusion of the brain under special conditions. The most important of these conditions was found to be a hyperosmolar concentration of hexoses in the perfusion medium. In addition, the presence of collagenase and hyaluronidase in the perfusion medium and specific perfusate flow characteristics were required to produce the structural changes throughout the brain tissue. When the perfused brain was further dissociated into a cell suspension by mincing and sieving, isolated neurons were obtained, the majority of which retained the proximal parts of their processes. A novel feature of these neurons was the retention of synaptic boutons on the plasma membrane. Presynaptic terminals with mitochondria and vesicles as well as pre- and postsynaptic membranes and densities were observed on the isolated neurons. The neurons were fractionated to 90--95% purity using discontinuous Ficoll density gradient centrifugation with a liquid fluorocarbon as cushion. Highly purified, viable cerebral neurons retaining synaptic complexes are thus available in bulk for neurobiological studies.