Nucleolar eccentricity in trigeminal ganglion neurons.

The aim of this study was to determine if measuring trigeminal ganglion neuron profiles containing nucleoli in histological sections gave a reasonable estimation of cell size. Serial sections of ferret trigeminal ganglia were prepared, and neuron profiles traced with the aid of a camera lucida. The cross sectional area of the profiles was measured. Profiles containing nucleoli formed the upper part of the size spectrum and were significantly larger than the profiles that did not contain nucleoli. When serial profiles of individual neurons were examined the largest profile contained the nucleolus in 20 of 27 cases, and the mean sizes of 'largest' and 'nucleolus-containing' profiles did not differ significantly. Computer reconstructions of individual cells show the nucleolus to be central in almost all cells viewed from almost every projection. It is concluded that the nucleolus lies at, or very near to, the centre of the neuron and at its widest dimension. Measuring the size of profiles containing nucleoli gives a satisfactory representation of cell size.