An improved method for correlative light and electron microscopic examination of cobaltic-lysine-labelled neurons.

We describe an improved method for correlative light and electron microscopic examination of synaptic organization of neurons extracellularly labelled by the axonal transport of cobaltic-lysine (Co-lys). After filling the neurons with Co-lys and precipitating the CoS, the brain is fixed in a double-aldehyde fixative, and thick slices are cut using a Microslicer. The slices are intensified using a physical developer, postfixed in OsO4 and embedded in resin. By cutting alternating semithin and ultrathin sections, it is possible to specify sites and types of synaptic contacts on labelled neuronal profiles.