Application of stereology to the central nervous system: estimation of numerical densities of neurons and synapses or neuron number

ABSTRACT Two unbiased stereological techniques, the disector and the fractionator have been introduced. Synapse‐to‐neuron ratios were calculated from estimates of the numerical densities of neurons and synapses in the rat cerebral cortex. These estimates were made using the disector method at the light and electron microscopical levels. Neuronal nuclei were as the counting unit for neurons and paramembranous densities for synapses. The fractionator method was employed to estimate the total number of cerebellar Purkinje cells in rats. We employed a five‐stage scheme to count the nucleoli of Purkinje cells. The cerebellum was first divided into uniform random slices, which were cut, in turn, into strips. The chosen strips were cut into pieces. A systematic selection of tissues was taken, and embedded together in the same mold. Subsequently the sections sampled were examined with a light microscope. All Purkinje cell nucleoli visible in these sections were counted.